Process dependence on two-capacitor matching properties with different etching technique

Two-capacitor matching properties for digital to analog (DA) and analog to digital (AD) converters were evaluated by using different etchers. The etching step for forming the upper layer was carried out by: (i) a barrel plasma etcher, (ii) a downstream plasma etcher, and (iii) a parallel-plate reactive ion etcher (RIE). Matching errors processed in the barrel and downstream etchers with isotropic etching characteristics were 0.38% and 0.15% in full scale, respectively. The error processed in the downstream etcher was 40% of that processed in the barrel etcher. It is estimated that the improvement in the down-stream etcher is caused by better uniformity and a smaller coefficient of lateral etching. The matching error processed in RIE was 0.096% in full scale and 62% of that processed in the downstream etcher. RIE with the anisotropic etching characteristic can minimize the lateral etching. Therefore, RIE decreases the error caused by the nonuniformity of the etching rate