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一种用于微米和亚微米光刻的新对准系统己在日立公司研制成功。该系统使用了氩离子激光和电荷偶合器件(CCD)检测硅片和掩模的相对位置。在硅片分割区域线上的每一个标记都通过缩小物镜直接检测并保持对准状态直至曝光完成。利用掩模上一镀铬面作为安置在掩模下方的检测光学系统的反射器以完成对硅片的直接检测。这种结构能实现轴上TTL对准,即不需移动检测光学系统又不会阻挡曝光光线。 因为氩离子激尤能透过多层介质膜传输,因而被光刻胶覆盖的标记也能检测。硅片标记的激光摆动照明和存贮型光检测器(CCD)使表面粗糙的硅片也能获得高精度检测。 由于氩离子激光器发出的光线通过缩小投影物镜后有色差存在,硅片标记在反射后成像于模掩下方。在使用简单检测光学系统时,这种现象妨碍了硅片和掩模的相对位置检测。然而在掩模上使用双曲线光栅后,这个问题己不复存在。双曲线光栅被氩离子激光照明后在硅片标记图象面上投影出一线形图象,而这条线的位置即表示了模掩的位置。 对多次光刻过的硅片,对准系统获得了优于0.2μm的套刻精度(3σ),稳定度偏离(五天内)优于0.05μm。对准时间大约0.3秒。
A new alignment system for micrometer and submicron lithography has been successfully developed at Hitachi. The system uses argon-ion laser and charge-coupled device (CCD) to detect the relative position of the wafer and the mask. Each mark on the silicon-divided area line is detected directly by reducing the objective lens and held in alignment until exposure is complete. A mask of chromium was used as a reflector placed underneath the mask to detect the optical system to accomplish direct inspection of the wafer. This structure enables TTL on-axis alignment, ie without moving the detection optics and without blocking the exposure light. Because argon ions can be transmitted through multilayer dielectric films, the marks covered by the photoresist can also be detected. Wafer-tagged laser-swing illumination and storage-type photodetectors (CCDs) enable high-precision inspection of rough-surfaced wafers. Due to the argon ion laser light emitted by narrowing the projection objective there is a chromatic aberration, the silicon mark in the reflection after imaging under the mold cover. This phenomenon prevents the relative position of the wafer from the mask when using a simple inspection optical system. However, the use of hyperbolic gratings on masks no longer exists. A hyperbolic grating is illuminated by an argon ion laser to project a line image on the surface of the wafer marked image, and the position of the line indicates the position of the mask. For multiple photolithographically polished wafers, the alignment system achieves overprinting (3σ) of better than 0.2μm and the stability deviation (within five days) is better than 0.05μm. Alignment time about 0.3 seconds.