Search

Introduction: Elevated serum beta human chorionic gonadotrophin (β-hCG) in a female normally indicates pregnancy or possibly, gestational trophoblastic disease or ovarian germ cell tumours. Expression of β-hCG has been demonstrated in cervical and endometrial carcinoma and other non-germ cell tumours of the ovary, vulva, breast, prostate, lung, colon, oral/facial tissue and stomach. Case report: We report a 43-year-old premenopausal woman with p16 positive squamous cell anal cancer. Pre-treatment urinary screening was positive for β-hCG (218 IU/L), which was confirmed on serum and expressed in the tumour. Pelvic ultrasound ruled out pregnancy. Cervical cytology detected human papilloma virus p16 infection and a potential squamous intraepithelial lesion. Management and outcome: She received definitive chemoradiation (Mitomycin/5-fluorouracil) for six weeks. β-hCG, taken four weeks post completion, had returned to normal levels (<2 IU/L). Discussion: Cases of elevated serum β-hCG are documented in different cancers including breast, gastric, lung, ovarian and renal cell. In our case, the elevated β-hCG is probably ectopic excretion by the squamous cell carcinoma tumour in the anus. While this has never been reported previously in the anus, it is likely due to the documented risk of development of precancerous as well as cancerous anal and cervical lesions through human papilloma virus infection. Raised levels of β-hCG have been reported in cervical cancers. Other possible causes of β-hCG elevation were excluded. Following treatment, her β-hCG level returned to normal strengthening the hypothesis that β-hCG elevation was due to the anal carcinoma. In conclusion, unexplained ectopic secretion of β-hCG may be the first sign of a primary malignancy. [ABSTRACT FROM AUTHOR]

The primary cause of greater than unity mask error factor (MEF) is degradation of image integrity. Mathematical description of image formation reveals the gradual loss of image shape control by photomask features as the critical dimension decreases below 0.8([Lambda]/NA). The growing contribution of mask critical dimension error to line-width variation prompts generalization of the conventional two-dimensional (2-D) exposure-defocus window (ED window) to a three-dimensional (3-D) mask-exposure-defocus volume (MED volume), adding mask tolerance to exposure latitude and depth-of-focus as the important parameters of a process. The increase in MEF with feature nesting means that the relative importance of sources of line-width variation changes with pattern pitch. Mask improvement is the most effective means to reduce line-width variation for dense features, but lens quality is the most significant factor affecting line-width control for sparse patterns. The approximately 20% higher MEF of dark-field masks, low MEF of alternating phase-shifting masks, and relatively high MEF of assist features all have ramifications on lithography strategies for printing sparse lines. The MEF does not simply indicate a need for high-quality masks, it also sheds light on the critical areas in which improvements are needed for successful lithography, and the disciplines that need to cooperate for successful device fabrication. Index Terms--Lithography, mask error factor, photomask.

A general level-specific lithography optimization methodology is applied to the critical levels of a 1-Gb DRAM design at 175- and 150-nm ground rules. This three-step methodology--ruling out inapplicable approaches by physical principles, selecting promising techniques by simulation, and determining actual process window by experimentation--is based on process latitude quantification using the total window metric. The optimal lithography strategy is pattern specific, depending on the illumination configuration, pattern shape and size, mask technology, mask tone, and photoresist characteristics. These large numbers of lithography possibilities are efficiently evaluated by an accurate photoresist development bias model. Resolution enhancement techniques such as phase-shifting masks, annular illumination and optical proximity correction are essential in enlarging the inadequate process latitude of conventional lithography. Index Terms--DRAM, lithography, optimization, resolution enhancement techniques.

The next-generation beyond 7-nm node potentially requires the implementation of subresolution assist features (SRAF) with extreme ultraviolet (EUV) lithography. This paper aims at providing a clear SRAF strategy for the next-generation beyond 7-nm node designs through a series of experiments. Various factors are considered, including stochastic effects, three-dimensional (3-D) mask effects, through-slit effects, aberrations, and pixelated source mask optimization (SMO) sources. We consider process variability bands with a variety of process conditions, including focus/dose/mask bias changes and also the normalized image log-slope/image log-slope as our objective functions, to determine what the best SRAF solution is for a set of test patterns. Inverse lithography technology is implemented to optimize both the main feature (MF) mask and SRAF placement, in particular, asymmetric SRAF placement to balance the 3-D mask effects. SRAF can potentially mitigate image shift through-focus, i.e., nontelecentricity, caused by EUV 3-D shadowing effect. This shadowing effect is pattern-dependent and contributes to the overlay variation. As we approach the next-generation beyond 7-nm node, this image shift can be more significant relative to the overlay budget, hence, we further investigate the impact of SRAF placement to the image shift. Moreover, the center of focus shift due to the large 3-D mask absorber thickness can be potentially mitigated by SRAF implementation. The common process window is significantly impacted by both the center of focus shift and the individual depth of focus and is evaluated using both metal and contact layer test cases. We study the source impact to SRAF insertion by experimenting with both a symmetric source (standard source) and an asymmetric source (SMO source). Finally, we understand the importance of using full flare map and full through-slit model (including aberration variation through-slit) in the MF correction. Furthermore, we evaluate the need of using full models in SRAF insertion. This is a necessary step to determine the strategy of SRAF implementation for the next-generation beyond 7-nm node. [ABSTRACT FROM AUTHOR]