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Plasma processing has been a key technology for large-volume integrated circuit manufacturing for more than 30 years. In particular, various configurations of plasma reactors, along with a range of plasma chemistries, have enabled high-throughput anisotropic and selective etching of materials with attendant precision transfer of resist patterns for feature sizes from 1 μm down to 100 nm and below. This article surveys the historical developments in oxide, metal, gate, and crystalline silicon etching, along with future challenges.

Reactive interactions in plasma etching have been investigated. Simple gas-phase transport of etchants and the reaction by-products in the wafer near-surface area are discussed. A new reincidence parameter, determined with a proposed near-surface model, was used to formulate metal etch rates. The experimental results obtained from an electron cyclotron resonance microwave plasma etching system revealed that the measured etching rate agreed well with those obtained by the near-surface model. It was found that reaction by-products repeatedly arrived at the surface depending on the reincidence numbers for the metal etching. The reincidence is the result of the diffusional transport in the vicinity of the wafer and is given by the expression {(one-half of the wafer radius)/(mean-free path)}. The ratio of the by-product flux is expressed by the product of the etching-rate flux times the reincidence number. Then, the resulting ratio of the reaction products in the flux becomes very high when we compare it to th...

This paper describes short‐gas‐residence‐time electron cyclotron resonance plasma etching for high etch rates, reduced contamination, and highly anisotropic etching. The new high‐gas‐flow‐rate (high‐flow) etching system is demonstrated with effective‐pumping rate of 2500 l/s. This method produces very high etch rate while maintaining high anisotropy at very low gas pressure below 1 mTorr. The high etch rate is due to the reduction of reaction products density because of the very short gas‐residence time of 30 ms. This technique also dramatically reduces the contamination of reaction products. Etching of crystalline Si and n+ polycrystalline Si with the high‐flow etching system is demonstrated. For crystalline Si etching with Cl2, a high etch rate up to 1 μm/min is achieved at a high gas flow rate of 90 sccm at 0.5 mTorr.

Low‐temperature electron‐cyclotron‐resonance microwave plasma etching and reactive ion etching are described for ULSI device fabrication. Highly selective anisotropic etching at a high rate, which implies dry etching without tradeoffs, is performed without changing the discharge parameters. This etching is only achieved at reduced wafer temperatures. The etching mechanism and the model are discussed based on the etching yield results obtained by the mass‐selected reactive ion beam etching experiments. The new etching system and the etching properties obtained for the low‐temperature etching are reviewed comparing those obtained in the conventional reactive ion etching and electron‐cyclotron‐resonance microwave plasma etching.

A high-rate-gas-flow plasma etching technique using a very low gas pressure and very high pumping rate is described. The principle of high-flow etching is discussed. A high etch rate of 1300 nm/min at 0.5 mtorr has been obtained for the Cl/sub 2/ ECR high-flow system with a bias of -50 V. Low gas pressure discharge with high flow rate is applicable to VLSI processing. Highly directional, low-contamination etching is possible using this etching system. >

Anisotropic etching which can be performed effectively with a low-pressure and high-density plasma may sometimes produce nonuniform patterns. Such a phenomenon has been observed in Si trench etching and poly-Si etching. Although this phenomenon is thought to be based on the local electric field, the mechanism for its generation is not clear. The nonuniformity of the ion direction, which is a serious problem in the fabrication of higher-packing-density patterns of future ULSIs such as 256 M DRAMs is considered. Time-modulated (TM) etching based on a model featuring pattern-plasma interaction is also discussed. It was found that peripheral patterns are inclined by the local electric field generated by the secondary electron effect. Using TM etching with an alternately supplied bias, such nonuniformity was reduced, and quarter-micron-level anisotropic etching of dense Si patterns was achieved. >

Novel short‐gas‐residence‐time electron cyclotron resonance (ECR) plasma etching is described. Using a newly equipped high‐pumping‐rate etching system (5000 l/s), we obtained a high etch rate and high anisotropic etching of silicon at low pressure and high gas flow rate. The residence time obtained was 30 ms. The silicon etch rate with Cl2 dramatically increased up to 1 μm/min as the gas flow rate increased to 90 sccm at 0.5 mTorr. It was proven by plasma emission measurement that the reaction products were minimized by the present method. These results indicate that the short‐gas residence time produces a small amount of reaction products and a large amount of etching species.

Ferroelectric PZT (Pb (Zr,Ti)O3) from 100 nm down to 50 nm thick was deposited on Pt/SiO2/Si substrates using MOCVD (Metal Organic Chemical Vapor Deposition) under reduced pressure at 550°C. Using Pb (DPM)2, Zr (DPM)4, and Ti(i–OC3H7)4 as precursors made it possible to control the composition of CVD films and to produce pure perovskite crystalline structure in the range of thickness less than 100 nm. Electrical measurements of the capacitors revealed that 50-nm PZT films typically had a dielectric constant of 500, resulting in the same capacitance as 0.4-nm SiO2.

The distribution of angles of incident etching ions was measured using a test sample having an overhanging mask structure. The standard deviation of ion incident angles decreased with decreasing pressure of the etching atmosphere. With conventional reactive ion etchers, standard deviations of 3 to 8° were measured at pressures from 2.6 to 101 Pa. With a microwave plasma etcher, the measured deviation at 1.3 Pa was 2°. The aspect-ratio dependence of etching with SF6 may be caused by the insufficient radical supply, which becomes the rate-determining step for etching a high-aspect-ratio trench.

Polymer deposition on Si and SiO2 surfaces has been investigated in CH2F2, CHF3, CF4, and CHClF2 gas plasmas, using a microwave plasma etching system. The dependence of the deposition rate on gas pressure, RF bias power, and substrate temperature was measured at a temperature between -120°C and 150°C. The deposition rate increased with decreasing temperature in CH2F2, CHF3, and CHClF2 plasmas. The deposition of polymers occured only below -60°C in the CF4 plasma. The obtained dependence of the deposition rate on gas pressure was examined in terms of the volume of adsorbed particles. X-ray photoelectron spectroscopy measurement showed that the number of bondings between C and F atoms in deposited polymers increases with decreasing temperature and RF power, and increasing gas pressure.

Low-temperature microwave plasma etching of crystalline silicons is described. Vertical and lateral etch rates of Si and the selectivities of Si to photoresist are measured as a function of water temperature within a range of -150 to +30° for SF6, and (3) the selectivities become high at low temperatures (e.g., >40 at -90°C and 2.3 Pa). This etching enables highly anisotropic Si etching at a high etch rate and high selectivity with fluoride gases. Less-polymerizing-type gases can provide high etch rates. An etching model of the ion-bombarded surfaces in discussed. The model implies that separate control of the side wall reaction and the horizontal surface reaction is archived by the low-temperature etching.

The effects of Cl2 addition to O2 plasma used for deep-submicron trilayer resist etching are investigated. The bottom-layer organic resist is etched using a low-temperature microwave plasma etcher. With O2+Cl2 etching gas, highly anisotropic etching is achieved at higher temperatures than with pure O2. Cl2 concentrations above 25% reduce resist selectivity relative to the SOG intermediate layer. Vertical 0.1-µm-wide resist patterns are achieved with O2+25% Cl2 at -60°C. Broadened resist patterns with tapered side walls are produced at lower temperatures and at higher Cl2 concentrations; this is thought to be caused by chlorine passivation and polymer deposition on the side walls.

Simultaneous direct recoil detection of H, C, and O and SIMS measurement of Si+ and Si+2 have been made from Si(100) exposed to 02, H2O and CH3OH. Azimuthal angular dependences of the signals have been determined showing the adsorbates to be free from shadowing and blocking effects on this surface. Matrix dependences of Si+ and Si+2 in the presence of the adsorbates are determined.

A low energy mass-separated ion beam deposition system was developed. Ge+ ions of 100 μA were obtained at an acceleration energy of 100 eV with a beam spot size of 5 mm o at 5 × 10−8 Torr. Material buildup has been observed at the range of ion energy where the self-sputtering yield is below unity. The incident ion energy dependence of the reactions of the F+ and CFx+ ions with a silicon substrate has been measured, as well as the physical phenomena conventionally observed between impinging ions and a substrate material. Epitaxial growth of Ge films on Ge and Si single crystal substrates has been observed at 300°C with a Ge+ ion energy of 100 eV. Deposited Ge crystal properties were evaluated.

A new low‐temperature reactive ion etching and microwave plasma etching method is described. Highly anisotropic silicon etching with extremely small width shifts has been performed with high selectivities of 30 for organic resist films. High etch rates of 500 and 1000 nm/min by reactive ion etching and microwave plasma etching, respectively, were achieved with a SF6 gas plasma at low wafer temperatures from −130 to −100 °C. It is concluded that lower temperatures during plasma treatment yield lower side etching and increase the dry etch resistance of organic masks.

Chemical and physical sputtering yields of silicon by fluorocarbon ions such as F+, CF+, CF2 +, CF3 + and C+ were investigated as a function of incident ion energy. Yield measurements over the 100–3000 eV incident ion energy range were performed through the use of mass-selected single species ion beam etching and in situ quartz crystal oscillator in an ultrahigh vacuum atmosphere. It was found that Si surface was fully covered with carboneous polymer and carbon in the cases of CF+ and C+ irradiation in the energy ranges of 100–700 eV and 100–2500 eV, respectively. Small quantity of carbon accumulation was also observed in the CF2 + ion beam irradiation of silicon in the 100–200 eV region, on the other hand, no carbon accumulation took place for F+ and CF3 + ion beam cases. In conventional Si dry etching by a CF4 gas plasma, since low energy (less than 1000 eV) fluorocarbon ions impinge the etched surface, it can be concluded that suppression of silicon etch rates mainly arises from the incidence of C+ and CF+ ion species.

Silicon etching was performed by a mass-selected, low-energy, F+ ion beam in an ultrahigh vacuum and the amount of etched Si was measured by the “in situ” quartz crystal oscillator microbalance technique. Through this method, it was possible to derive separate chemical and physical sputtering yields for Si over the incident ion energy range of 100 eV∼3000 eV. The chemical sputtering yield was found to be larger than the physical one when the incident ion energy became less than 200 eV.

Chemical sputtering yields of silicon resulting from the incidence of isotopically pure 19F+, 35Cl+, and 81Br+ ion beams were measured in the 100–3000 eV energy range. It is found for these cases that the chemical sputtering yields saturate in the high energy range of more than 600 eV. The saturated yields (atoms/ion) are 0.18 for F+/Si, 0.45 for Cl+/Si, and 0.23 for Br+/Si. The yields increased with increasing ion energy in the 100–500 eV region with different slopes. The steepest slope is observed for the case of Br+/Si, and the smallest is the F+/Si case. This difference in the slope indicates that the chemical reaction between Br+ and Si cannot be activated without high acceleration of Br+, and the same occurs for Cl+/Si. On the other hand the F+ ion is assumed to react with Si with a relatively high probability even when the energy is low. On the basis of these results, a reactive spot model is proposed for the ion‐assisted chemical etching process. A generalized method to get anisotropic profiles is...

Electrical properties of 16 keV, focused-ion-beam (FIB) (beam diameter: 1 µm, current density: 50 mA/cm2) boron-implanted silicon layers have been investigated as a function of beam scan speed and ion dose, and compared with those obtained by conventional implantation (current density: 0.4 µA/cm2). High electrical activation of the FIB implanted layers is obtained by annealing below 800°C as a result of the increase in amorphous zones created in the implanted layers. Amorphous zone overlapping is assumed to occur at FIB implantation doses of 3–4×1015 ions/cm2 from the results of electrical activation and the carrier profile of implanted regions annealed at low temperature, if beam scan speed is lowered to about 10-2 cm/s.