在电子纸行业中, 为了减少光刻次数、降低成本, 部分产品的TFT基板会采用半色调掩膜工艺, 传统的一次湿刻一次干刻(1W1D)方法要求半色调掩膜光刻胶厚度与均一性同时满足较高要求, 管控难度大, 导致曝光多次返工浪费产能; 而且, 1W1D的刻蚀均一性很差, 使玻璃四周沟道a-Si过薄, 影响良率。为了改善这两方面的问题, 我们参考了非电子纸产品的两次湿刻两次干刻(2W2D)工艺。然而非电子纸的2W2D工艺会产生较长的a-Si拖尾现象, 导致较大的寄生电容, 造成良率损失; 此外, a-Si残留和沟道特性问题也阻碍了电子纸良率的进一步提升。因此, 我们通过降低两次湿刻时间, 改善灰化条件, 减小a-Si拖尾长度; 建立a-Si处理工序, 消除a-Si残留; 调整a-Si成膜条件和钝化层成膜前处理条件, 改善沟道特性。实验结果表明: 采用改善后的2W2D工艺可以完全满足电子纸的特性要求, 并且相比于1W1D方法, 得到的沟道厚度均一性提升50%, 阵列检测良率提升4%~10%; 同时无需管控半色调掩膜光刻胶的均一性, 仅满足光刻胶厚度的管控要求即可, 使曝光返工比例降低60%。改善后的2W2D工艺有效改善了电子纸产品的沟道特性与刻蚀均一性, 提升了产品良率, 减少了产能浪费, 降低了成本, 对4次光刻电子纸产品具有重要指导意义。

In the electronic paper industry, the TFT substrates of some products use halftone mask process to reduce the number of mask. After halftone masking, the conventional single wet etching and single dry etching method (1W1D) requires both the thickness and uniformity of the halftone photoresist under control. The high requirements result in multiple rework in photo process, which leads to waste of capacity. Furthermore, the poor etching uniformity of 1W1D results in the thin channel thickness around the glass, which reduces the yield. To solve these two problems, we referred to double wet etching and double dry etching method (2W2D) for non-electronic paper. However, the 2W2D process for non-electronic paper produces a large a-Si tail, resulting in a large parasitic capacitance, which results in product yield loss. In addition, the problems of a-Si residue and channel characteristics also hinder the further improvement of the electronic paper yield. Therefore, we reduced the a-Si tail by reducing the time of both wet etching processes and optimizing the ashing conditions; eliminated a-Si residue by establishing the a-Si treatment process; improved the channel characteristics by adjusting the deposition condition of a-Si film and the pretreatment condition of passivation film. The experimental results show that the improved 2W2D method can fully meet the characteristics of electronic paper. Compared with the 1W1D method, the uniformity of channel thickness was increased by 50% and array test yield was improved by 4%~10%. Moreover, the new 2W2D etching process only needs to meet the standard thickness of photoresist, which reduced the ratio of rework in photo process by 60%. In a word, this improved 2W2D process method effectively improves the channel characteristics and etching uniformity of the electronic paper products, improves product yield, reduces productivity waste, and reduces cost, which plays an important role in 4 mask electronic paper products.