湿法刻蚀条件对TFT中Cu电极坡度角和均一性的影响及工艺参数优化

Effect of Wet Etching Conditions on Profile and Uniformity of Cu Electrode in TFT and Optimization of Process Parameters

目的 在高世代薄膜晶体管(Thin Film Transistor,TFT)产线的栅极刻蚀制程,明确大气压等离子体(Atmosphere Pressure Plasma,APP)清洗功率、清洗时间及刻蚀时间对刻蚀性能(关键尺寸偏差、均一性、坡度角)的影响规律,并获得最佳工艺条件,进而提升良率。方法 以APP清洗功率、清洗时间和刻蚀时间为影响因素,以关键尺寸偏差(CD Bias)、均一性、坡度角作为因变量,开展正交试验,明确因素影响重要性顺序;然后,对Cu电极坡度角的形成和刻蚀均一性变化进行分析;最后,采用回归分析获得刻蚀性能与刻蚀时间的函数关系式。结果 结果表明:刻蚀时间对刻蚀性能的影响最大,对APP清洁时间和功率的影响较小。刻蚀时间延长,关键尺寸偏差(CD Bias)增加、均一性变差、坡度角变大。为改善均一性和平缓坡度角,应缩短刻蚀时间。最佳工艺组合为:刻蚀时间85 s,APP电压9 kV,APP传输速度5 400 r/min。结论 刻蚀时间延长,未被光刻胶覆盖的Cu膜层被完全刻蚀,形成台阶,该台阶使刻蚀液形成回流路径。沿着回流路径,刻蚀液浓度、温度逐渐下降,刻蚀均一性由此恶化,坡度角因此增加。采用回归分析得到的刻蚀性能与刻蚀时间的函数关系式,为预测刻蚀效果和优选刻蚀时间提供了依据。

In the gate etching process of high generation thin film transistor(TFT) production line,the effect of cleaning power,cleaning time and etching time of atmosphere pressure plasma(APP) on etching performance(critical dimensional Bias,etching uniformity,profile angle) should be identified and the optimal process conditions should be obtained to improve the yield.With APP cleaning power(7,9,11 kV),cleaning time(5 400,5 700,6 000 r/min) and etching time(85,95,105 s) as the affecting factors(i.e.,independent variables) and critical dimensional deviation(CD Bias),etching uniformity,and profile angle as dependent variables,a three-factor with three-level orthogonal experiment was conducted by an L_9(3~4)-type orthogonal table( a total of nine experiments) to clarify the order of importance of factor effects.Then,the formation of profile angle and etching uniformity change of Cu electrode were analyzed in conjunction with the wet etching process,and the hypothesis that the formation of reflux flow path of Cu etchant affected the profile angle and etching uniformity was proposed.Meanwhile,different etching time experiments(75,85,95 s) were set up to verify the proposed ideas.Finally,regression analysis was performed on the orthogonal experimental results to obtain the etching performance(CD Bias,profile angle,etching uniformity)as a function of etching time.The results show that the etching time has the greatest effect on the etching performance,and the APP cleaning time and power have less effect.With the increase of etching time,the critical dimension Bias(CD Bias) increases,the uniformity becomes worse,and the profile angle becomes larger.Therefore,the etching time should be shortened to improve the etching uniformity and smooth the profile angle.The recommended optimal process combination is:etching time of 85 s,APP voltage of 9 k V,and APP transfer speed of 5 400 r/min.Validation experiments with different etching times show that the degree of etching increases simultaneously with increasing etching time,but the degree of etching at the bottom of the electrode is higher than that at the top,so profile angle of the electrode increases.The hypothesis of Cu etchant reflux path is confirmed.A scheme to improve etching uniformity and smooth the profile angle by increasing the exposure dose and development time while decreasing the etching time is proposed.CD Bias and etching uniformity all maintain a quadratic function with etching time,and the profile angle and etching time then remain linear functions.As the etching time increases,the Cu film layer not covered by photoresist is completely etched in the thickness direction,forming a step,which makes the Cu etchant form a reflux path.Along the reflux path,the etchant concentration and temperature gradually decrease,so the etching uniformity deteriorates.In addition,along the reflux path,the etchant contacts the bottom and top of the electrode in turn,and the bottom etching degree is large,so the profile angle increases.The equation of etching performance as a function of etching time obtained by regression analysis provides a basis for predicting etching effect and optimizing etching time.The results of this research can provide a reference for the optimization of production line parameters and yield improvement.