Question

Design a process to deposit a 1000 A nitride layer on a silicon wafer followed by a 0.5 um polysilicon layer followed by a 1000 Å nitride layer followed by a 1.6um sacrificial oxide layer followed by a 2.0 um Poly layer.

Answer 1

Graphical representation of the process steps &- PHOTO RESTST POLYSE Nitide Silicon Substraste nitride layer poured on silicon substrate (wafer) and on top of it placed a layer of 0.5um polysilicon layer. Then coated with UV-sensitive photoresist. Patterned PHOTO RESIST SAPULYSIS 222L NITRITE The photoresist leaving behind etching Silicon Substrate in exposed areas is removed a patterned photoresist mask for polystch -Poly SI etch POLY SANE NITRILEZZ Silicon Substrate Plasma etching is used to remove the unwanted polysilicon. After the etch, the photoresist is chemically stripped in a solvent bath. Page 1

POLY SE NITRIDE Now etch Silicon Substrates placed a layer of 1000 Å nitride on layer of polysilicon. the SAC OXIDE ITRDEITZ POLY SU NITRIDES Silicon substrate} Similarly pour the photoresist after the layer of 1.6um sacrifical oxide layer. After etching of the sacrifical orcide layer Anchor fich Etch Anchor VSAÇ OXDEKK ANTIRIDE Z POLY ST NITRIDE) Silicon substrate The waters are recoated with photoresist and the fourth level (ANCHOR) is lithographically patterned. The unwanted oxide is removed in an "RIE process and the photo resist is stripped. Page 2

3 Silicon Substrate & Now placed a layer of 2.0 um poly layer. ty POLY Poly IPOU S AC OXIDE INTRANE SPY SILICONE Silicon a substrate The water is coated with photoresist and the fifen level (Poly) is lithographically patterned. The polysilicon & nitride is first etched to create a hard mask, then poly is etched by plasma etching. After the etch is completed, the photo resist and PSG hand mask are removed. Page 3