EE245 Homework 2 Due Tuesday 10 27 99 1 0 The angle between the 100 and 111 crystal planes in a silicon wafer is 54 74 degrees but a real etchant will not give perfect anisotropy Calculate the actual angle of the sidewall of a pit etched with KOH assume anisotropy 400 and EDP assume anisotropy 20 2 0 Draw a cross section of the following process flow Assume a bare 100 silicon starting substrate If I release this cantilever how will it curl 1 LPCVD PSG 2micron 2 spin negative resist expose using mask1 develop 3 timed HF etch with 50 overetch how long will this take 4 strip resist in acetone 5 LPCVD polysilicon 2 microns anneal at 900 C for 30 minutes 6 spin positive resist expose using mask 2 develop 7 plasma poly etch 50 overetch what machine should I use how long will this take 4 microns mask1 mask2 3 0 Draw a cross section of the same process as in question 2 but assume that positive resist is used for both lithography steps 4 0 Draw a cross section of the same process as in question 2 but use a plasma oxide etch and a wet silicon etch Compare the cross sections How EE245 Homework 2 September 21 1999 1 does plasma etching affect the minimum line and space that I can use in a process 5 0 Draw a cross section of the following process flow Assume a bare 100 silicon starting substrate 1 LPCVD oxide 2micron 2 LPCVD polysilicon mask1 this is short hand for spin expose develop etch and strip 3 anneal at 1000C for 30 minutes 4 10 minute HF etch 5 thermal oxidation 0 1 microns dry O2 how long will this take 6 LPCVD polysilicon mask2 6 0 A 100 wafer with a nitride mask with the following openings is etched in a KOH solution with an etch rate of 1 micron minute and a selectivity of 400 Draw the cross section after 10 minutes and 100 minutes of etching 5 microns How will the cross sections change if we use EDP instead of KOH EE245 Homework 2 September 21 1999 2
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