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The effect of TFT lithography plane inclination on lithography pattern and improvement
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摘要
薄膜晶体管光刻制程中，光刻胶光刻平面位置是决定光刻图形质量的关键因素。为了在光刻机最小分辨率条件下改善光刻图形质量，本文从光刻胶内反射光线的反射特点出发，以减小光刻胶内反射光线对非光刻区域的光刻光强及增加光刻区域的光刻胶底部光刻光强为基础，推导出光刻光线倾斜入射光刻胶平面时，光刻胶光刻平面位置调整量的计算公式，并以该公式计算出的调整量对光刻胶光刻平面进行调整。结果表明：对于最小分辨率为3.0 μm的投影光刻机，进行线间距为2.2 μm的产品光刻时，以该公式计算出的调整量对光刻胶光刻平面调整后，较未调整前，光刻图形坡度角提升了13.3%，光刻胶线宽或线间距宽度(DICD)均一性改善了14.7%，光刻图形光刻胶残留得到解决。
Abstract
In the lithography process of thin film transistor, the lithography plane position of photoresist is the key factor that determine the quality of lithography pattern. In order to improve the quality of lithography pattern under the minimum resolution of lithography machine, the reflection characteristic of the light in the photoresist is studied in this paper, based on reducing the intensity of the reflected light in the photoresist on the non-lithography region and increasing the intensity of the photoresist at the bottom on the lithography region, the computational formula for the lithography plane position adjustment of the photoresist is deduced under the oblique incidence. The adjustment amount is calculated by the formula and the lithography plane is adjusted by the adjustment. The results show that for the projection lithography machine with the minimum resolution of 3.0 μm, and for the product with the line space of 2.2 μm, after adjusting the lithography plane of photoresist with this adjustment, the slope angle of the lithography pattern is increased by 13.3%, and the uniformity of the DICD (development inspection critical dimension) is improved by 14.7%, the photoresist remain of the lithography pattern is resolved.
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Key words:
- lithography machine /
- resolution /
- oblique incidence /
- lithography plane /
- slope angle /
- lithography pattern
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Overview
Overview: In the lithography process of thin film transistor (TFT), the DICD (develop inspection critical dimension) of the TFT affects the characteristics of TFT device, which is the key factor to determine the resolution of thin film transistor liquid crystal display (TFT-LCD) and the yield of driving. With the development of TFT-LCD, people's demand for the high-resolution display is increasing, but the high-resolution display requires TFT to have the small line width and narrow line space, which also determines the DICD formed by photolithography process to become smaller and smaller, so it will make the lithography machine tend to its minimum resolution when the lithography machine carries on the lithography craft. In actual production, in order to improve the resolution of lithography machine, the way of compensating and adjusting the focusing and leveling system of lithography plane is used, which makes the lithography plane of PR tend to the focus plane of lithography system, so as to achieve the goal of minimum resolution imaging. However, in actual production, due to continuous compensation, the actual adjustment margin is small and the improvement effect is limited. The adjustment is mainly compensated by the PR plane inclining, and the lithography light is no longer incident perpendicularly to the PR plane. As a result, the lithography light is inclined to the PR plane, which will lead to the enhancement of the lithography intensity in the non-lithography region caused by the reflection of PR, and the weakness of the lithography intensity on the surface of PR bottom, which will reduce the lithography machine's ability of the fine-line lithography at minimum resolution. In order to improve the quality of lithography pattern under the minimum resolution of lithography machine, the reflection characteristics of light in the photoresist is studied in this paper, based on reducing the intensity of the reflected light in the photoresist on the non-lithography region and increasing the intensity of the photoresist at the bottom on the lithography region, the computational formula for the lithography plane position adjustment of the photoresist is deduced under the oblique incidence. The adjustment amount is calculated by the formula and the lithography plane is adjusted by the adjustment. The results show that for the projection lithography machine with the minimum resolution of 3.0 μm and the product with the line space of 2.2 μm, after adjusting the lithography plane of photoresist with this adjustment, the slope angle of the lithography pattern is increased by 13.3%, and the uniformity of the DICD is improved by 14.7%, the photoresist remain of the lithography pattern is resolved.
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图 3 PR面处于光刻焦点下方时PR内反射光线
Figure 3. The reflected light in the PR when the PR surface is under the lithography focus
图 4 PR面处于光刻焦点上方时PR内反射光线
Figure 4. The reflected light in the PR when the PR surface is above the lithography focus
图 5 任意入射光线垂直入射时PR内的反射光线
Figure 5. The reflection light in PR when incident light is vertical incidence
图 6 任意入射光线倾斜入射时PR内的反射光线
Figure 6. The reflection light in PR when incident light is oblique incidence
图 8 PR面补偿0 μm时正常产品光刻图形SEM照片
Figure 8. The SEM picture of lithography pattern of normal product after PR surface offset 0 μm
图 9 PR面补偿8.8 μm时正常产品光刻图形SEM照片
Figure 9. The SEM picture of lithography pattern of normal product after PR surface offset 8.8 μm
图 7 PR面补偿-8.8 μm时正常产品光刻图形SEM照片
Figure 7. The SEM picture of lithography pattern of normal product after PR surface offset -8.8 μm
图 10 PR面补偿18 μm时正常产品光刻图形SEM照片
Figure 10. The SEM picture of lithography pattern of normal product after PR surface offset 18 μm
图 11 PR面补偿-6.4 μm时单层光刻图形SEM照片
Figure 11. The SEM picture of lithography pattern of single layer after PR surface offset -6.4 μm
图 12 PR面补偿0 μm时单层光刻图形SEM照片
Figure 12. The SEM picture of lithography pattern of single layer after PR surface offset 0 μm
图 13 PR面补偿6.4 μm时单层光刻图形SEM照片
Figure 13. The SEM picture of lithography pattern of single layer after PR surface offset 6.4 μm
图 14 PR面补偿15 μm时单层光刻图形SEM照片
Figure 14. The SEM picture of lithography pattern of single layer after PR surface offset 15 μm
表 1 光刻条件及PR面补偿量
Table 1. The lithography conditions and the compensation of PR plane
测试产品 正性光刻胶膜厚h/μm 光刻波长λ/μm NA D/μm PR面补偿量H/μm 正常产品(Fanout线间距：2.2 μm) 1.5 0.4 0.083 1.1 8.83534 单层产品(Fanout线间距：1.6 μm) 1.5 0.4 0.083 0.8 6.425703 
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