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--- delayer:wet [2015/11/11 20:38] – mcmaster
+++ delayer:wet [2023/07/28 06:47] (current) – mcmaster
@@ Line 198: / Line 198: @@
   * Notes
     * Adding HCl may reduce insoluble oxide bi-products
+==== Pitting ====
+A common issue seems to be pitting if left in too long. As BOE itself can't etch silicon, it must be an additive. Some evidence suggests this is caused by not cleaning upper (ie metal) layers away. Possibly due to atmospheric oxygen. This also causes issues for staining and similar processes.
+Recommendation: use phosphoric acid etc to remove upper layers completely before exposing silicon. Clean die and use fresh BOE solution.
+Below example is on Generalplus GPLB52A24A
+{{mcmaster:delayer:wet:gp_overetch:dies.jpg?300}}
+Above: left 40 min etch, right 40 hour etch 130F forced air w/ BOE
+{{mcmaster:delayer:wet:gp_overetch:angle1.jpg?300}}
+Above: die at angle, left side lower than right. Right side shows deep pits in focus even though its higher than surface visible at left
+{{mcmaster:delayer:wet:gp_overetch:s2-dlyr1_01.jpg?300}}
+{{mcmaster:delayer:wet:gp_overetch:s2-dlyr1_02.jpg?300}}
+Above: deep staining shows doping much higher than substate now as evidenced by significant focus difference
@@ Line 770: / Line 791: @@
   * 1 mL 40% HF
   * 20-25 @ room temp
+Alternate:
+  * 1 mL Whink
+  * 10 mL 70% HNO3
 Notes:
-  * I haven't used this solution yet
+  * 2023-07-23: did a good job near top metal when the other solution wasn't working
 ====== References ======