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Photo mask etching for the 100nm technology node places new requirements on dry etching processes. As the minimum-size features on the mask, such as assist bars and optical proximity correction (OPC) patterns, shrink down to 100nm, it is necessary to produce etch CD biases of below 20nm in order to reproduce minimum resist features into chrome with good pattern fidelity. In addition, vertical profiles are necessary. In previous generations of photomask technology, footing and sidewall profile slope were tolerated, since this dry etch profile was an improvement from wet etching. However, as feature sizes shrink, it is extremely important to select etch processes which do not generate a foot, because this will affect etch linearity and also limit the smallest etched feature size. Chemically amplified resist (CAR) from TOK is patterned with a 50keV MEBES® eXara e-beam writer, allowing for patterning of small features with vertical resist profiles. This resist is developed for raster scan 50 kV e-beam systems. It has high contrast, good coating characteristics, good dry etch selectivity, and high environmental stability. Chrome etch process development has been performed using Design of Experiments to optimize parameters such as sidewall profile, etch CD bias, etch CD linearity for varying sizes of line/space patterns, etch CD linearity for varying sizes of isolated lines and spaces, loading effects, and application to contact etching. Etch processes have been developed specifically for etching small features, but these are also applicable to etching of larger feature sizes. Etch processes are capable of patterning of chrome features below 100nm with vertical sidewalls, 1μm. Excellent uniformity and reproducibility are also demonstrated. SEM micrographs illustrate processes applicable to small feature etching, along with processes that are limited to large feature etching. In this paper, we will discuss CD uniformity, sidewall profile, etching bias, loading effects, and linearity and how these relate to small-feature chrome etching.

Photomask complexity increases rapidly as semiconductor devices continue to shrink and as optical proximity correction becomes commonplace. This trend stresses the performance of mask pattern generators due to the increase in both primary and subresolution features. However, the next-generation MEBES raster scan architecture is well-suited to the challenge of maintaining throughput regardless of increases in pattern complexity. In addition, this new system provides an operating envelope that is sufficiently broad to expose all practical resist materials with a fixed number of writing passes. Write time is independent of material sensitivity, which has the benefits of allowing high-dose processes to be optimized, and also of supporting a wide selection of chemically amplified resist candidates for critical mask patterning. The new system shows the promise of being extendible to the 70 nm technology generation.

The effect of mixed PAGs on the performance of ArF photoresists based on cycloolefin/maleic anhydride (COMA) copolymers were investigated. Several different PAGs were prepared according to the size of photogenerated acid moiety and structure of light sensitive chromophore, and the impact of PAG property on lithographic performance was investigated in terms of the acid size, acid generation efficiency, and hydrophobicity of PAG. The diffusion according to the size of generated acid and hydrophobicity of PAG were found to be the most profound factors of the pattern profile and line edge roughness (LER) of developed resist pattern. Resolution capability as well as PED stability can be improved though adjustment of acid size, PAG hydrophobicity. Additionally, profile difference between dark and bright field according to mask type can be suppressed by the use of PAG with lower acid generation efficiency. However, lithographic performance, such as LER, pattern profile, and PED stability show the dissimilar trend with acid size and hydrophobicity of PAG. Thus, when PAG mixture is employed in a photoresist formulation, it is observed that both pattern profile and LER were improved simultaneously, which has been difficult to achieve for previously reported OCMA- based ArF resists.

This paper describes that attenuated phase shift masks (APSM) improve process margin compared to binary mask (BIM) in KrF and ArF lithography. We present the real problems to occur in the mask fabrication, process and mask error factor (MEF). As a result, sub-120nm cell patterns were delineated with 8% exposure latitude (EL) and ~0.6 ?m local depth of focus (LDOF) using 0.70NA KrF and APSM. The performance of ArF lithography (NA=0.63) shows the similar process margin with 10% EL and -0.6 ?m LDOF. Using APSM, we could obtain 14.4% EL and -0.6 ?m LDOF. We obtained process enhancement of 30% by using APSM. However, process instability is analyzed in a viewpoint of mask making and process issue such as mask fabrication capability, CD uniformity, and MEF. In simulation and experiment, 0.63NA ArF lithography shows resolution improvement compared to 0.70NA KrF. It is possible to obtain lOOnm pattern using ArF and APSM. Also, one of common issues is to reduce the MEF, which is decided by exposure and resist process condition. MEF is increased to about 4 or more in the sub-120nm range. This effect has influence on CD uniformity and EL margin. Reducing the MEF on the wafer, we have to optimize exposure tool, process, and mask. Shorter wavelength and APSM are one of candidates to minimize MEF. Therefore, ArF APSM is looking forward to high performance lithography.

The patterning potentialities of sub-100nm pattern for ArF lithography was evaluated with conventional alternating PSM (alt-PSM) for dense lines and spaces (L/S) and phase edge PSM (PE-PSM) for isolated lines of memory device. In dense L/S pattern,110nm pattern was defined with relatively small depth of focus(DOF) window(~ 0.2 ?m) due to phase error of mask. As pattern sizes was changed from 130nm to 200nm, critical dimension (CD) difference between two neighboring spaces was varied and it was assumed that micro loading effect was occurred in Qz etching. The linearity was guaranteed to dense L/S of 110nm and isolated line of 90nm, and Iso-Dense bias was controlled within 15nm. The 60nm and 70nm isolated lines of PE-PSM ware defined with good process windows in the case of OA_X size(X-direction size of Cr open area) of 0.5 ?m. The 55nm isolated line was also defined. The pattern shift of isolated lines was occurred with 4~7nm as phase of mask was varies within 190 ~ 200 ° . Though the alt-PSM with high numerical aperture (NA) for ArF lithography was strong candidates for sub-1 OOnm lithography of memory device, the issues of mask fabrication such as tighter phase control and minimizing etch loading effect would be big obstacles. On the contrary, there were many possibilities of sub-100nm patterning in PE-PSM with good process windows, however tighter control of pattern shift due to phase error must be studied intensively.

Optical lithography at resolution limit is a non-linear pattern transfer. One of the important issue is a mask critical dimension control because of nonlinear amplification of mask critical dimension error during image transferring on wafer. This amplification of mask error is called the MEF. This mask error factor has been widely used as an important parameter for indicating tighter CD control for the photomask for low-kl lithography generation.

The defect control of the attenuated-PSM is compared with that of the conventional binary intensity mask (BIM), because the fabrication process for the att-PSM tends to generate more defects than that of the BIM. To repair a defective att. PSM, a similar method used for BIM has been applied. However, this process may cause degradation of pattern fidelity with the repair pattern on the mask are transferred on the wafer, if the transmission and phase of repaired area are not well controlled. In this paper, we have investigated the effect of repairing process on the pattern fidelity to define contact holes using a KrF lithography with an att. PSM. The defects in the various distances form contact hole patterns and of various sizes were repaired. The experimental printability and simulation data from an aerial image model were compared for repaired defects. And the repair tool reliability and the simulation accuracy of the att. PSM was examined using CD-SEM. From the experimental results, repaired defects having larger size than the threshold. One or within a certain range from the pattern induced the pattern deformation. Therefore, the size of defect and the distance between the pattern and defect should be considered in repair process for the Att. PSM fabrication. Based on the experimental and simulation results, the requirements for the repair tool will be proposed.

We estimated the process margins of various cell structures and process problems for full chip process under extremeresolution limit of exposure tool. Therefore, optimizing off axis illumination (OAI) condition for various structures obtainedthe fme pattern and wider process margin using simulation and experiment. From our experiment, we should use as highernumerical aperture (NA), smaller R and smaller r as possible to reduce critical dimension (CD) difference between denseand isolated patterns. Process margins are obtained more than 8% exposure latitude (EL) and 0.5 tin depth of focus (DOF)for each cell. However, we can consider using of attenuated phase shift mask (PSM) to improve the exposure and DOFmargin. We fmd that real full chip process induces the critical problems such as isolated line (I/L) and space (L'S) patternvariation due to lens aberration, partial coherence effect, mask error effect, and optical proximity effect. These effects playa role to determine the design rule of cell and periphery structures. In spite of good lens quality, variation of I/L and USpattern for various exposure conditions is almost 4Onm or more compared to line and space (L/S) pattern. These phenomenaare becoming the critical issue to fulfill the full chip process of l3Onm lithography. By optimizing mask error effect,isolated and dense pattern bias (ID bias), and OAI, we can achieve l3Onm technology with 248nm KrF lithography.KEYWORDS : KrF, Design rule, ID bias, OAI, Full chip process, High NA, Process margin

In this paper we investigated the feasibility of printing sub-0.13 micrometers device patterns with ArF and KrF lithography by using experiment and simulation. To do this we evaluated various cell structures with different sizes from 0.26 micrometers to 0.20 micrometers pitch. In experiment 0.60NA ArF and 0.70NA KrF exposure tools, commercial and in house resists and bottom anti-reflective coating (BARC) materials are used. To predict and compare with experimental data we also used our developed simulation tool HOST base don diffused aerial iamge model. We found that ArF lithography performance is a little bit better than KrF and therefore 0.70NA KrF lithography can be used up to 0.12 micrometers design rule device and 0.60NA ArF lithography can be used up to 0.11 micrometers . But to get more than 10 percent expose latitude, 0.13 micrometers with KrF and 0.12 micrometers with ArF are the minimum design rule size. However to obtain process margin we had to use extreme off-axis illumination (OAI) which results in large isolated- dense bias and poor linearity including isolated pattern. Using higher NA can reduce ID bias and mask error factor. For contact hole it is more effective to use KrF lithography because resist thermal flow process can be used to shrink C/H size. Our developed ArF resist and BARC shows good performance and we can reduce k1 value up to 0.34. Through this study we verified again that ArF lithography can be applied for sub-0.13 micrometers device through sub-0.10 micrometers with high contrast resist and 0.75NA exposure tool.

In this study, we will introduce a new definition, as 'Degree of Patterning Performance (DOPP)' for analyzing process capability. DOPP represents the total performance, which can estimate whether it could be available to adapt any device ona certain integration process. The degree of difficulty on some projects can be represented by DOPP, which considers design rule, field size, mask error, lens aberration, illumination imperfection, resist performance, and the others. Via DOPP, one can estimate whether some project can be available on mass production or not, and machine performance is normal or not. And also, one can quantitatively analyze how effective several causes of CD variation are on total patterning performance respectively. The simple DOPP metric can be used widely on various situations, which will be introduced in detail on this paper.

Ultimate limitation of lithography has been studied by using the diffused aerial image model (DAIM). Assuming that only the 0th and 1st order diffraction beams in the off-axis illumination technique contribute to the resist patterns, aerial image is calculated for dense line and space patterns. And then DAIM is applied to achieve final image. By using this diffused aerial image, exposure latitude and mask error effect can be analyzed quantitatively. In the case of perfect image, which can be achieved from, for example, diffraction free x-ray lithography or electron beam lithography without Coulomb repulsion and back scattering effect, same approaches are possible to get the exposure latitude and mask error effect. Under the validation of DAIM, most important parameter, which characterizes dense L/S patterns, is the diffusion length of acid. In order to realize sub-o.1 micrometers pattern with enough process margins, it is required to enlarge exposure latitude and to reduce mask error effect. Therefore, reducing h acid diffusion length of chemical amplification resist (CAR) or new conceptual resist instead of CAR will be needed for sub-0.1 micrometers era.

Recently, the miniaturization of the design rule of memory devices pushes the minimum feature sizes down to sub- wavelengths of the exposure tools. The design of a memory device comprises not only the dense patterns with critical small size in the cell region but also the random patterns in the peripheral region; the latter also need sub- wavelength lithography technology as well as the former. And the optical proximity correction (OPC) has been strongly required for the random patterns in the peripheral region where the same energy is exposed as in the cell region. Therefore, the high accuracy of simulation model used in the OPC is necessary for the full chip OPC tools. However traditional aerial image simulation has a limitation to the application due to its lack of accuracy because it does not take into account a resist process. We introduced novel lithography simulation model in 1998, which describes resist process by diffusion and chemically amplification function.

The compatibility of novel organic bottom anti-reflective coatings (BARC), HEART003 and HEART004 developed by Hyundai Electronics, with various chemically amplified resists (CAR) was reported. The incompatibility between organic BARC and CARs is caused by the differences of residual activity on the surface of organic BARC after baking process and the types of dissolution inhibitors in the polymer of CAR and photo acid generators (PAG) used in their formulation. In KrF lithography, the HEART003 was much compatible with acetal type resist than annealing type resist because it's neutral acidity on the surface of BARC. The incompatibility with annealing type resist was caused by weak residual acidity on the surface of BARC, relatively. Thus we tried to adjust the feasible residual acidity on the surface of BARC and optimum thermal baking condition. The modified HEART003 has excellent compatibility not only with acetal type resist, but also with annealing type resist in the same platform. In ArF lithography, the HEART004 has also good compatibility with cycloolefin type and (meth)acrylate type ArF resist by modification of its formulation.

Photoresist using maleic anhydride/cycloolefin copolymer is a leading candidate for the 193 nm photolithography. Until recently, the efforts to improve 193 nm photoresist have been focused on resolution and dry-etch resistance. Therefore, we have synthesized some kinds of matrix resins and additives containing alicyclic group and acid labile group. The matrix resin is alternating copolymer obtained by free radical polymerization of maleic anhydride and cycloolefinic derivatives. And, the additives have a low molecular weight containing alicyclic group and acid labile group. The additives not only serve as dissolution inhibitors but also improve the pattern profile and dry-etch resistance. In this paper, we will describe the approaches to the resist materials, which are involved in our photoacid generator concept.

In our previous model, we have introduced a lot of t- butylcarboxylate group in matrix resin to achieve a high contrast and obtain a good lithographic performance. Most ArF photoresists having only t-butylcarboxylate group as a dissolution inhibitor have showed by far the inferior performance in a poor amine controlled environment. To overcome this problem, we greatly reduced the usage of t-butyl carboxylate group and increased the amount of HMEBC that contains both carboxylic acid group and alcohol group. And also, we newly introduced acid labile cross-linker for high contrast. Our novel resist exhibited an excellent lithographic performance without any protective top coating material, namely, a good PED (post exposure delay) stability, an improved CD (Critical Dimension) linearity, a proper sensitivity for process, and a good contrast. In addition, its synthetic yield is very high (>50%) and then it is cost- effective for mass production. 120 nm patterns were successfully defined at 13 mJ/cm2 by using a BIM (Binary Intensity Mask) with 2/3 annular (0.50/0.75(sigma) ).

ArF DUV ((lambda) equals 193 nm) lithography is rapidly emerging after 248 nm lithography because of the demand for further resolution improvement and wider Depth Of Focus (DOF). However, the 193 nm lithography requires innovative development in various areas, such as laser sources, resist chemistry, new PSM shifter materials, and optics materials. In this study, we evaluated TiSi-nitride based new attenuated PSM in terms of mask making process and its lithographic performance for ArF lithography. We used two kinds of TiSi- nitride based attenuated PSM blanks having 6% and 9% transmittance, respectively. Chemical durability of TiN/SiN film was evaluated. We selected optimal dry etching condition for mask making with good mask profile (side wall angle greater than or equal to 85 degrees) and Quartz (Qz) substrate roughness. The DOF margin at 9%-PSM was larger than those of others (6%-PSM and BIM) and Exposure Latitude (EL) of PSM was larger than that of BIM. Therefore, we concluded that TiSiN- based attenuated PSM was effective for ArF lithography.

Photomask is one of the most critical technologies for lithography. Optical lithography at resolution limit is a non- linear pattern transfer process. OPC (Optical Proximity Correction) technology has been used in the semiconductor industry for controlling the shape of pattern, and eliminating the line shortening and corner rounding effects for submicron feature. Therefore, OPC technology is an approach for improving lithography performance that has been received much attention recently. We investigated the lithographic performance in terms of EL (Exposure Latitude), DOF (Depth of Focus), and mask error effects for various mask fabrication. It was observed that mask error gave severe influence on the lithographic performance and the OPC simulation error also strongly depended upon the mask quality.

We have investigated the perfomiances of positive Chemically Amplified Resist (CAR) withHigh Acceleration Voltage System on mask fabrication, widely. As we had expected, the resolutionand pattern fidelity both after development and after etching were improved dramatically, because ofits high contrast and good dry etching durability. As a result, practical resolution limitation was O.2pmand CD linearity for O.2.tm 1.O}.xm pattern range was O.034pm with Proximity Effect Correction(PEC). We obtained CD uniformity of3 l55nm, to 120X120mm2 area.Keywords : Chemically Amplified Resist (CAR), High Acceleration Voltage E-beam System,Resolution Limitation, Linearity, Uniformity, Proximity Effect Correction (PEC),Optical Proximity Correction (OPC) 1. INTRODUCTION Even though the PBS process extends its life by applying thin resist coating, it is quite difficult to define sub-micron pattern on mask because of low contrast and wet etching requirements. As dry etching resistance is not so excellent' and data sizing (over process) isindispensable, ZEP resist process is not enough to apply it to technology below O.6tm, also.The most promising candidate for sub-micron pattern is combination2 of 1) CAR process,which has already been developed and adopted in wafer process in spite of severe process

Critical issues for 150nm DUV lithography using 0.70 NA KrF and 0.60 NA ArF had been investigated. Aberration, coherence variation, mask error effect, and process margin for each case had been analyzed. Current projection lens and illumination optics are getting better and better. However, for 150nm lithography using high NA scanner, a large portion of beam should be traced on the outside of lens pupil and traced on the resist surface with a large incident angle. In such a case, lens aberration effect was observed on field edge, even though strehl ratio of projection lens and coherence variation on field edge had been improved. These effects had been investigated. One other critical issue in high NA scanner is depth of focus. The common depth of focus between dense and isolated patterns in real process using high NA scanner is mainly affected by photoresist thickness. That issue had been also investigated. Another important issue for 150nm DUV lithography is mask error effect. In the case of same design rule, lower (lambda) /NA lens is more favored than higher (lambda) /NA. Mask error issue in high NA KrF and ArF was also analyzed. Total comparisons between high NA KrF and 0.60 NA ArF have been discussed.

With KrF and off-axis illumination (OAI) technique we should set up 150nm lithography process without using phase shift mask. But isolated-dense bias (ID bias) makes 150nm lithography process difficult. We investigated ID bias trend at different OAI condition and found that it could be reduced by optimizing OAI condition. We represent OAI as quadrupole center (sigma) R and pole size radius r. With high NA, small R and small r we can reduce ID bias but cannot eliminate completely at 150nm lithography. Also we found out that ID bias of duty patterns are more severe than that of dense and isolated patterns. Using OAI at a certain space width between lines, the width of lien has its minimum. This line thinning phenomena at this weak zone depends on OAI condition such as NA, R and coherence value. We compared simulation data with experimental result and could see the same phenomena at simulation data. Therefore OPC is necessary to avoid this weak zone. By experiment and simulation with NA higher than 0.65 and Optical Proximity Correction, we could set up 150nm lithography process with below 0.20micrometers periphery pattern design rule.

In order to improve the overlay accuracy in electron beam lithography, we have investigated the optimization of alignment key that included a ratio of alignment key according to scanning beam size, an optimum key depth/width, and material's dependency. The alignment repeatability of key, has the same ratio with scanning beam size, appears good results as compared with the other ratio. Scanning beam size also correlates with an alignment key width. As a process sequence of CMOS device, the key width of under layer is changed by the thickness of deposited materials, because of the deposition on side-wall. Therefore, the scanning beam size should be optimized for each step. In each material, there exists the critical thickness not affecting on the alignment reading repeatability. The standard deviation(3 σ), which is calculated by measurement of key position with critical thickness, is less than 20nm. We have results of the critical thickness of various materials. Si02 and Si3N4 do not affect on the alignment signal, but doped WSix, Al, and doped poly-silicon are very sensitive because of back-scattering electrons. Using the optimized align key of WSix/doped poly-Si, the standard deviation (3 σ) was less than 10nm. Otherwise, non-conducting layer must be etched more than 7000A. In this case, the standard deviation(3 σ) is larger than that of conducting materials, as more than 20 nm. We have results of optimum condition of alignment key in order to enhance the overlay accuracy. The standard deviation(3 σ) of total overlay accuracy is less than 50nm which corresponds to 150nm design rules device fabrication.

A novel copolymer with alicyclic olefin moieties for an electron beam resist has been developed. In general, methacrylate copolymers widely used in the field of E-beam lithography show a low etch resistance due to their linear backbone structure. Our goal was to enhance an etch selectivity to various substrates while maintaining a high resolution. We designed alicyclic olefin copolymers with highly rigid backbone structures to improve the etch selectivity and synthesized a copolymer resin, poly(2- hydroxyethyl 5-norbornene-2-carboxylate/t-butyl 5- norbornene-2-carbolate/5-norbornene 2-carboxylic acid/maleic anhydride), which is formed with alicyclic units in their main chains. This alicyclic backbone structure of copolymer affords better etch selectivity to various substrates without sacrificing its resolution than those of other methacrylate copolymers. Etch selectivities have been studied for polysilicon, silicon dioxide, and tungsten substrates, respectively. Our resists showed the etch selectivities comparable to that of typical KrF resist for polysilicon substrate and comparable to those of typical novolac resist for silicon dioxide and tungsten substrates. The effect of photo acid generator to the electron beam lithographic performance was also investigated.

We have newly developed a novel multi-functional monomer. Application of this monomer also allows us to introduce another unit to further improve its etch resistance. Furthermore, our novel resist containing this multi- functional monomer exhibits an excellent adhesion to Si substrate, an improved CD linearity, a high sensitivity, a good contrast, and a high synthetic yield. A 110nm L/S pattern was successfully at 1:2 pitch of a strong PSM was also successfully obtained by using a 2.38wt percent TMAH aqueous solution as a developer.

We have investigated the effect of line edge roughness (LER) of active patterns used for shallow trench isolation to the electrical performance of MOS transistor applicable for 1 giga-bit DRAM. Three different processes for resist patterning were applied for comparative analysis to form the active pattern in MOS transistor; the first method applied a conventional single layer resist (SLR) process, the second TIPS with two step dry development, and the third another TIPS with three step dry development. The third process adopted an additional step to break-through thin silicon dioxide which may contribute to the LER. The LER data of an active pattern before and after nitride substrate etching and their profiles were investigated among these processes. The third method shows the almost same LER and CD uniformity of the active pattern as those of SLR. The electrical properties. Only, threshold voltage variation of MOS transistor by the second method shows the worse results than those of SLR. Considering the ratio of LER in isolated active pattern with channel width of 0.3 micrometers to its average CD value, we think that its ratio should be controlled well below 7 percent for TIPS to make an useful technology for real device. Based on these studies, we believed that the well-controlled TIPS process using three step dry development is a strong candidate for device production of ArF and EUV lithography, if the advantages of TIPS technology over the SLR process are considered in the respect of lithography.

Thin film imaging processes such as top surface imaging (TSI) are candidates for sub-150 nm lithography using 193 nm lithography. Single component, non-chemically amplified, positive tone TSI photoresists based on phenolic polymers demonstrate good post-etch contrast, resolution, and minimal line edge roughness, in addition to being the most straightforward thin film imaging approach. In this approach, ArF laser exposure results directly in radiation- induced crosslinking of the phenolic polymer, followed by formation of a thin etch mask at the surface of the un- exposed regions by vapor-phase silylation, followed by reactive ion etching of the non-silylated regions. However, single component resists based on poly(para-hydroxystryene) (PHS), such as MicroChem's Nano MX-P7, suffer from slow photospeed as well as low silylation contrast which can cause reproducibility and line-edge-roughness problems. We report that selected aromatic substitution of the poly(para- hydroxystryene) polymer can increase the photospeed by up to a factor of four relative to un-substituted PHS. In this paper we report the synthesis and lithographic evaluations of four experimental TSI photoresists. MX-EX-1, MX-EX-2, MX- EX-3 and MX-EX-4 are non-chemically amplified resists based on aromatic substitutions of chloro- and hydroxymethyl- groups and PHS. We report optimized lithographic processing conditions, line edge roughness, silylation contrast, and compare the results to the parent PHS photoresist.

In order to develop a new series of chemically amplified photoresists for 193-nm lithography, norbornene substituted with a steroid derivative was copolymerized with maleic anhydride by free radical polymerization. The resulting polymers have excellent transmittance at 193 nm and possess good thermal stability up to 260 degrees C. The resist formulated with the polymers showed better dry-etching resistance than the conventional poly(hydroxystyrene) resist for Cl2/O2 plasma. With the standard developer, the resists from 0.15-0.20 micrometers patterns at doses of 5-18 mJ/cm2 using an ArF excimer laser stepper.

New matrix resins containing maleic anhydride and cycloolefin units for ArF excimer laser resist have been developed. Several series of these matrix resins having good dry-etching durability were prepared by free radical polymerization using AlBN as free radical initiator. All of the resists using the matrix resins revealed good coating uniformity and adhesion to silicon wafer, and were readily soluble in a variety of resist solvents such as MMP, EEP, PGMEA and EL. In preliminary 193 nm testing a resist formulated with the matrix resins sulfonium triflate as photoacid generator afforded positive images with 0.14 micrometers L/S resolution. In this paper, we will discuss the polymerization results and lithographic properties for 193 nm exposure tool.

It is well known that TIPS(Top-surface Imaging Process by Silylation) process has a feasibility to overcome lots of problems induced from single-layer resist process. Nevertheless, chip makers have been reluctant to apply this process to giga technology with two major issues; process issues such as Line Edge Roughness (LER), residues, Critical Dimension (CD) uniformity, and rework scheme and infrastructure issues of system reliability and reproducibility. First of all, the process issues should be investigated to realize the giga device manufacturing. In this paper, we will describe the patterning results of180nm isolation structure of 1G bit DRAM on process issues. LER is a critical problem that arises from edge breakdown of thin SiOx mask generated from silylated resist during dry development. We have tried to get roughness smaller by means of the prevention of edge-breakdown of SiOx mask. Residues on the unexposed area due to unwanted silylation after dry development disappeared by using an optimized C 2 F 9 /O 2 break-through step. In this experimental, the optimum process conditions for removing of LER and residues were determined by controlling the condition of dry development. The results are compared to those obtained using two-step and three-step dry development. We achieved excellent 3sigma values of 17nm and 20nm for CD uniformity within a chip and a wafer, respectively. We have also developed rework procedures to remove the resist pattern formed after dry development by using BOE and clean-D (mixture of H 2 SO 4 and H 2 O 2 ) solutions. From these studies, it was confirmed that TIPS process using a cluster-tool silylation system incorporating a LRC TCP TM 9400SE dry development module was verified as a production-worthy process for 180nm isolation pattern formation.

Optical proximity correction technique has been studied. The occurrence of proximity effect in the optical lithography is composed of an element caused by diffraction of light, which can be explained by aerial image simulation, and an element caused by resist process, in which acid diffusion is a major factor causing non-linearity. In the case of very thin resist, absorbed energy that generates the acid can be described by two-dimensional instead of three-dimensional distribution. Under this simple assumption, acid diffusion by post exposure bake is equivalent to the diffusion of aerial image, and chemical amplification can be analytically described also. Modified aerial image including diffusion and chemical amplification, we call it diffused aerial image, can give the information for patterning status directly. Therefore, diffused aerial image model can explain experimental results very well compared to the expectation by using aerial image only without loss of simplicity and calculation speed.

Causes of intra field critical dimension variation using KrF scanner for 0.18 micrometer lithography have been investigated. Scanner is different from traditional stepper system. Scanner might have synchronization error, which results in degrading contrast over full intra field. Aberration of illumination optics brings about coherence difference between field center and edge. In a scanner system, vertical patterns (cross scan direction) are geometrically tangential, and horizontal patterns are sagittal. Such a H/V different ray tracing results in horizontal pattern having better contrast than vertical one under diffraction limited design rule patterning. Mask error can be a very critical issue in 4X system. Focus drift and exposure dose change during scan exposing result in intra field CD variation, and some stray light is a cause of intra field CD variation also.

Recently reported ArF positive photoresists can be classified into three groups: derivative methacrylate copolymers (methacrylate resist), methacrylate copolymers functionalized with pendant alicyclic moieties (alicyclic resist), and cycloolefin-maleic anhydride copolymers (cycloolefin resist). Each system has its own advantages and drawbacks from the viewpoint of lithographic properties. Methacrylate resist has been used for the assessment of ArF lens performance. However, it is hard to apply them in real device process because of its low plasma-etch resistance. Previous studies have reported that alicyclic resists possess adequate etch resistance with the help of cyclic carbon units, however these resists show poor adhesion and seldom dissolve in 2.38% TMAH developer. The cycloolefin resists will be good candidate for addressing the trade-off between etch resistance and requisite material properties for lithographic performance because these resists, unlike methacrylate-based resists, contain large quantities of alicyclic structures directly in the polymer backbone and such properties as dissolution, adhesion can be readily controlled by incorporation of -COOH and -OH functional groups into cycloolefin structures. We have synthesized poly(2-hydroxylethyl 5-norbornene-2-carboxylate/t-butyl 5- norbornene-2-carboxylate/5-norbornene-2-carboxylic acid/maleic anhydride; HNC/BNC/NC/MA) resists with a variety of functional groups and obtained lithographic performance using ArF stepper (0.6 NA). In this paper, we will describe the basic idea for designing of the novel olefin resist and demonstrate lithographic capabilities, especially in terms of process window for 130 nm feature. We believe that both off-axis illumination and bottom anti-reflective technologies should be applied in order to obtain wider process window.

The most critical issues for lithographers, resolution, depth of focus, exposure latitude and proximity effect, have been frequently discussed. In addition to those issues, lens aberration effects such as astigmatism, coma, field curvature and distortion have been emphasized in view of process stabilization. Deep UV lenses have undergone improvements in the field curvature, distortion, and other aberrations to the point that they can be implemented for near quarter micron patterning. KrF excimer laser stepper and scanner have made Deep UV technology as a practical choice for lithographers to develop their own DRAM processes. In order to adopt process development beyond the region of ultimate resolution limit, precise lens aberration analyses are necessary. KrF excimer laser stepper (NA equals 0.55), used for 0.18 micrometers design rule patterning, is examined. Several types of real device pattern, such as word and bit line, active, storage node, contact hole patterns, are tested under various illumination conditions (conventional, various partial coherence, off-axis illumination). These results are compared with simulation results.

Top-surface imaging process by silylation (TIPS) has been suggested as an attractive solution to cope not only with limitation of resolution and process latitudes but also with line width variations due to reflections over steps. However this technique has not received a wide acceptance as a production worthy process until now, because of the stringent requirements on suitable silylation and dry development equipment that have good uniformity and good reproducibility. In a parametric study of TIPS dry development steps, we found the most important factors in the first step and the second step respectively. The optimized process demonstrated good etch rate uniformity and excellent 0.17 micrometer dense and isolated pattern of gate and islands pattern of capacitor in 1 G bit DRAM device. Their profiles were vertical and uniform within a wafer, while the proximity effect between dense and isolated pattern of gate remained 0.01 micrometer. In islands pattern, wider process margins of both local depth of focus (LDOF) and exposure latitude (EL) could be obtained and excellent 3(sigma) value of critical dimension (CD) uniformity within a wafer confirmed better applicability to 1 G bit DRAM and beyond. When silylated resist patten was transferred into substrate layer CD bias and uniformity could be controlled less than 0.02 micrometer. There were also no residues after both photoresist strip and induced polymer removal step. From these studies. TIPS process using cluster tool of silylation system made by LRC and TCP TM 9400 TM SE etcher for dry development was demonstrated a production worth process for the sub-0.20 micrometer lithography in terms of obtaining finer pattern without pattern problems and a reliable process for 1 G bit DRAM and beyond.

Modified illumination scheme such as off-axis illumination or low partial coherence illumination in combination with phase shift mask is very reliable technique even to the manufacturing stage. In spite of its benefit of drastic improvements in resolution and depth of focus, it has several well known drawbacks. Those are pattern structure dependency, increased proximity effect and significant degradation of illumination power. Furthermore, several studies are reported about the distortion-like registration error between each illumination aperture while various apertures are mix-used. However, the origin of this distortion-like overlay errors is still uncertain and just considered as having some relationship with lens aberration probably, coma. In this study, we investigated the nonlinear character of the registration errors and try to find out the implicit relations of its to the lens aberration character through experiments and simulations.

In this paper we report here on lithographic performance of high resolution, environmentally stable and aqueous base developable positive tone resist for DUV lithography. There have been a lot of efforts to prevent the resist from suffering from the deactivation of acid during the delay time between exposure and post exposure bake (PEB). The new design of matrix resin containing amide functional group has advantages over current lithographic techniques. The effects of amide functional group as a basic additive in a chemically amplified resist was investigated. A new class of matrix resin containing amide functional group, poly(hydroxystyrene-co-t- butyl acrylate-co-3-(t-butoxycarbonyl)-1-vinyl-2-caprolactam), was developed. It showed 0.20 micrometer lines/spaces patterns of this resist using KrF excimer stepper (NA 0.55, partial coherence factor 0.55) with an exposure dose of 25 mJ/cm2. This resist showed no change of pattern profile after 2 hours post exposure delay in which ammonia concentration is 5 ppb. 3-(t-butoxycarbonyl)-1-vinyl-2-caprolatam (BCVC) unit as a basic additive can not only solve amine contamination effectively, but also improve the resolution of the resist. BCVC unit reduces the diffusion of acid and it results in sharp contrast at the interface between the exposed and unexposed areas. Therefore, adding BCVC unit in matrix resin leads to the stabilization of the pattern profile and higher resolution.

In this study, we investigated the effects of the addition of CF4, Cl2, and N2 gases to oxygen electron cyclotron resonance (ECR) plasma on the reactive ion etching (RIE) properties of RuO2 film such as etch rate, selectivity, and etched profile. The concentration of the etching species in the plasma was analyzed with an optical emission spectroscopy (OES) and a quadrupole mass spectrometer (QMS). The etch product was also examined with QMS.The addition of a small amount of CF4, Cl2, or N2 to the O2 plasma increases the concentration of oxygen radicals and accordingly increases the etch rate of the RUO2 films appreciably. The etch rate of the RuO2 film was enhanced more with the addition of a small amount of CF4 and CI2 than with the addition of N2. On the contrary, the etched profile obtained in O2/N2 plasma was superior, without any damaged layer at the sidewall, to O2/CF4 and O2/Cl2 plasma. The selectivity of RuO2 to Si)2 mask was over 20:1 for each of the additive gas proportion at which the etch rate was maximum for each plasma system.

In order to develop 1 G bit DRAM of 0.18 micrometers design rule, it is required to generate 0.2 micrometers contact hole patterns with local DOF over 1.0 micrometers . One of good candidates is DUV attenuated phase shift mask (PSM), which improves the lithographic process margin such as depth of focus (DOF), especially in contact hole patterns due to edge enhancement effect. In the case of DUV attenuated PSM, the optimum condition for contact hole patterns near 0.2 micrometers has been investigated by simulations and experiments using chromium- based attenuated PSM with the transmittance of 6% at 248 nm wavelength. We obtained local DOF of 1.2 micrometers for 0.2 micrometers contact hole of 1 G bit DRAM with printing bias of -0.046 micrometers using KrF laser system (0.31 (sigma) , 0.55 NA). We evaluated the characteristics of contact hole with various duty ratios and defect printability using programmed defects.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

In the case of silicon nitride films acid pretreatment can eliminate resist scum so that we can get clean resist profiles. The acid used, called Clean D treatment for photoresist strip, normally consists of a mixture of sulfuric acid (80% water) and hydrogen peroxide (80% water). ESCA (electron spectroscopy by chemical analysis) was used to examine the surface of the films after cleaning with acid and to monitor the changes in atomic percents of the films with time. Considering all the analytical data, this acid treatment to silicon nitride makes the film surface oxide-rich resulting in forming barrier layer between substrates and protons from PAG (photo acid generator). For BPSG boro-phosphorous silicate glass) films the mechanism of the formation of resist foot is quite different from that of silicon nitride. Improved resist profiles on BPSG were obtained by the dehydration bake. Therefore it could be speculated that the formation of resist scums on silicon nitride films are due to the nitrogen in films and on the BPSG moisture. O2 plasma surface pretreatment was also reviewed. It is quite certain that these two methods, acid and O2 plasma treatments are very effective, economical and simple process. However, there are delay time effects after pretreating films unlike other conventional oxide capping layers. This problem is also discussed in detail.

An alternating phase shift mask is very effective to memory devices which have highly repeated patterns. In order to apply the alternating phase shift mask to real device, we have investigated the design problems such as proximity effect, phase contradiction, phase transition, and linewidth variation. We also design various hard defects in order to check defect printability on wafer. Using i-line lithography with an alternating phase shift mask, we obtain useful focus latitude of 1.2micrometers for bit line of 256M DRAM. Deep UV alternating phase shift mask is used for isolation patterns with design rule of 0.16micrometers . The experimental and simulation results for phase-induced problems and defect printability on wafer are described in detail.

The lithography technology for sub 0.25 micron requires new technology to cope with the resolution limit and line width variations due to interference effects and reflections over topography as well as precise overlay accuracy. The high density deices such as 256M DRAM and 1G DRAM require still tighter overlay accuracy. At the same time, the number of overlay measurement steps are even more increased. For example, in the case of 256M DRAM, there are more than 30 overlay measurement marks and 20 making steps. In this paper, new overlay measurement marks (NOMM) are suggested, because this will result in improving not only the overlay process and yield, but also the simplicity of the measurement steps. The function of NOMM is very useful in measuring overlap accuracy among the three circuit patterns simultaneously. Finally, the NOMM implements performance in terms of high speed data analysis and economy of space on the scribe lines. In addition, NOMM can achieve superior execution in the overlay process with still higher accuracy by utilizing optimized overlay mark type.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Alternating phase shift mask (PSM) is very effective to memory devices which have highly repeated patterns. In order to apply the alternating PSM to a real device, we have investigated the design problems such as proximity effect, phase contradiction, phase transition, and linewidth variation. We also designed various hard defects to check defect printability on a wafer. Using i-line lithography (0.50 NA, 0.46 sigma) with alternating PSM, we obtained a useful DOF of 1.2 micrometer for a bit line of 256 M DRAM. The experimental and simulation results for phase-induced problems and defect printability on wafer are described in detail.

An attenuated phase shift mask (PSM) is the most promising candidate for the high volume production lithography process among the various PSM types. It has been shown that attenuated PSM improves the lithographic performance such as depth of focus, especially in contact window by its edge enhancement. In this paper, the side lobe effect that restricts the lithographic performance of attenuated PSM and the light intensity distribution have been examined on changing the pattern density and the transmittance by experimental and simulation. The side lobe effect caused by proximity effect is very severe when pitch sizes are in the range of 0.7-0.9 micrometers for 0.35-0.45 micrometers contact hole on mask and it is enlarged by defocus exposure condition. The side lobe effect in this range of pitch size may forms the additional pattern in wafer, which restricts the application of attenuated PSM. The side lobe effect can be removed by additional pattern positioning at the center of four contact hole patterns, but simulation result of Exposure-Defocus tree (E-D tree) shows that lithographic performance of attenuated PSM is decreased by an auxiliary pattern. In the application of attenuated PSM in dense pattern, the relation between performance and side lobe effect is mutually contradictory.

The optical lithography is extending its life by combining high numerical aperture (NA) optics and shorter wavelength. The shorter wavelength lithography has required the new developments of related technologies. In particular, DUV resists require an entirely different resist chemistry. Much progress has been demonstrated in the field of transparent chemically amplified resists with high sensitivity. However, this DUV lithography ((lambda) equals 248 nm) has been delayed for mass production due to their limitations, such as (i) delay time effects, (ii) high cost ownership due to expensive resist materials and laser maintenance, and (iii) critical dimension (CD) variation over topography caused by multireflection of topographic features. On the other hand, i- line lithography ((lambda) equals 365 nm) has apparently been applied to 64M DRAM of 0.35 micrometers design rule, and attempted to 0.30 micrometers technology which corresponds to 2nd generation 64M DRAM or 1st generation 256 M DRAM. It might be achieved by combination of off-axis illumination (OAI), phase shift mask (PMS) and advanced resist process technique of i-line lithography. Therefore, i-line lithography can be more practical method rather than DUV lithography for the mass production. In this paper, we have optimized the i-line lithographic techniques for the various pattern shape and density for 0.30 micrometers design rule. Optimum duty ratio was tried to find for line and space, contact hole patterns. The basic rule is to keep the minimum Cr width over 0.30 micrometers mask. OAI have been applied to get higher contrast of line and space, and even contact hole patterns, and achieve good pattern fidelities of island patterns. By the implementation of OAI, process latitudes were greatly improved compared to that of conventional techniques. In order to optimize the process over the actual topography, optimum numerical aperture (NA) and aperture of the OAI were selected. In conclusion, 0.30 micrometers design rule device was successfully fabricated by optimizing the advanced i-line lithographic techniques.

The global proximity effects of densed line, semi-isolated line are studied for conventional illumination, off-axis illumination, and finally off-axis illumination in combination with attenuated phase shift masks which have transmittance of 4% and 8%, respectively, by experiments and simulations. To analyze the behavior of proximity effects, the lithographic performances of the super resolution technique are investigated comparing the cross-sectional view of resist pattern profile, useful depth of focus, and the curves of linewidth vs. defocus for 0.30 micrometers , 0.35 micrometers , and 0.40 micrometers pattern size, respectively. The global proximity effect is quantitatively analyzed by fitting the curve for densed line and isolated line to 2nd order polynomials. Off- axis illumination with attenuated phase shift mask is very effective to minimize the proximity effects for the pattern size less than 0.40 micrometers , and have useful depth of focus of 1.0 micrometers for 0.30 micrometers patterns.

Comparative analysis of the total overlay accuracy on aluminum (Al) and chemical vapor deposition tungsten (CVD-W) was carried out as a function of the available alignment techniques over the various process conditions. In the case of Al films, they were prepared at the various sputtering temperatures, thicknesses, and step heights. The total accuracy was also examined associated with standard and off-axis illumination (OAl). The effect of the sputtering temperature of single and dual Al deposition has been especially investigated in a view of surface roughness, which significantly affects total overlay accuracy. It was observed that CVD-W film can be an alternative of Al film. As the Al film deposition temperature decreases, it was found out that random requisition error with a large distribution was improved by implementing an off-axis alignment (OAA) technique with a visual broadband light source. Meanwhile, Al thickness was not so much critical to overlay accuracy comparing with Al sputtering temperature. And also scaling error determined by asymmetric alignment mark shape was minimized according to the optimization of exposure data file. Minimum detectable step height of alignment mark was down to 300 angstrom using a sensitive alignment techniques over the Al film.

New developments in the field of embedded shifter materials look very promising for defect free phase shifting mask (PSM) manufacturing. Nevertheless, a good control of the shifter parameters (phase shift and absorber transmittance) remains of utmost importance. In this paper, a lithography sensitivity analysis to shifter deviations has been carried out. It was found that dark field masks require different tolerances than light fields. Because of a growing need for an accurate measurement method of the phase shift, an optical technique, based on measurement of the zero diffraction order of diffraction gratings, is investigated. Using this technique, an attenuated PSM manufacturing process has been optimized for deep-UV, in order to demonstrate the possibilities of quarter micron PSM lithography. As a result, 0.3 micrometers contact windows could be printed with sufficient process latitudes. Using modified illumination techniques in combination with the attenuated PSM, considerable gain in process latitudes was found for quarter micron gates as well, although proximity effects are still a concern.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.