Differences

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--- delayer:wet [2015/01/13 04:08] – Since a layer is rarely more than 2 um thick it should take just a minute to completely remove the layer. 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 677: / Line 698: @@
 Ingredients:
-  * 65%
+  * 65% H3PO4
 Procedure:
@@ Line 690: / Line 711: @@
   * If you are having problems completely removing it there may be a metal barrier, see "Beck barrier Ti/TiN solution" (TODO: add pictures)
-==== Phosphoric ====
+==== HCl-H2O2 ====
+Very aggressive.  Use fresh solution, degrades quickly
+Ingredients:
+  * 4 mL HCl
+  * 1 mL 35 H2O2
+  * 1 mL H2O
+[[http://ssel-sched.eecs.umich.edu/wiki/Public.HCl-based%20Aluminum%20Etchant%20Mixture.ashx|Source]].  They omitted concentrations.  I put the ones I assumed they meant / what I've been using.
+==== Nitric ====
+[[https://books.google.com/books?id=KXwgAZJBWb0C&pg=RA1-PT495&lpg=RA1-PT495&dq=nitric+acid+aluminum+maximum+corrosion&source=bl&ots=RgHSwpzs2o&sig=Y_gnaMjFzp90bGEBafZxPvtOETQ&hl=en&sa=X&ei=bZe0VJmRCYzdoATtkYFY&ved=0CEMQ6AEwBQ#v=onepage&q=nitric%20acid%20aluminum%20maximum%20corrosion&f=false|Handbook of Corrosion Data, 542]] says "At room temperature, the rate at which nitric acid attacks alloy 1100 exhibits a maximum at a concentration of 20%".  Take this as a baseline for
+Ingredients
+  * Approx 20% HNO3
+    *  1 mL 70% HNO3 : 3 mL H2O
+Procedure:
+  - Heat acid to 80C
+  - Drop die into acid
+  - Cook until done
+Notes:
+  * How long?
 ===== Au =====
@@ Line 743: / 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 ======
@@ Line 766: / Line 819: @@
   * Wikipedia: Buffered oxide etch: http://en.wikipedia.org/wiki/Buffered_oxide_etch
   * "DSP-1 emulation": http://board.zsnes.com/phpBB3/viewtopic.php?f=6&t=5868
+  * https://www.ee.washington.edu/research/microtech/cam/PROCESSES/PDF%20FILES/WetEtching.pdf