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随着设计尺寸的缩小,改进曝光场内套准精度变得十分重要。通过跟踪研究每个工艺步骤(即隔离层蚀刻和多晶硅淀积),发现硅局部氧化(LOCOS) 工艺对曝光场放大有相当大的影响。对400 ～1 000 nm 范围的LOCOS 氧化厚度,曝光场放大率约为3-8 ～4-2 ×10 - 6 。在这一厚度范围,放大率与氧化厚度成正比。在20 m m 边长的曝光场,放大值(4 ×10- 6) 等于0-08 μm 。曝光场四角处的套准精度等于0-04 μm 。对0-25 μm设计尺寸,0-04 μm 的套准误差是不可忽略的。为改进由于LOCOS氧化工艺导致场放大的套准精度,研究隔离层缩小投影倍率表明,投影倍率缩小3 ×10 - 6 ,套准精度提高0-065μm ,如同3σ值一样,套准精度提高到未缩小投影倍率时的0-5 倍
As design dimensions shrink, it becomes important to improve the registration accuracy within the exposure field. By tracking each process step (ie, isolation etch and polysilicon deposition), it has been found that the LOCOS process has a considerable impact on the exposure field magnification. For LOCOS oxidation thickness in the range of 400-1000 nm, the exposure field magnification is about 3-8-4-2 × 10-6. In this thickness range, the magnification is proportional to the thickness of the oxidation. At a field length of 20 m m, the magnification (4 × 10 -6) is equal to 0-08 μm. The registration accuracy at the four corners of the exposure field is equal to 0-04 μm. For 0-25 μm design sizes, registration errors of 0-04 μm are not negligible. In order to improve the registration accuracy of the field amplification caused by the LOCOS oxidation process, the study on the reduction of the projection magnification of the isolation layer shows that the projection magnification is reduced by 3 × 10 -6 and the registration accuracy is improved by 0-065 μm. As with the 3σ value, the registration precision is increased to not Reduce the projection magnification 0-5 times