Time-depending yield degradation at microchip manufacturing
Manage the process flow to ensure the lowest dwelling time between the process end and the final test.
A special procedure of lots management was created and used as a temporary solution. Such a procedure is difficult, costly, and does not bring significant success. Rejected
Since CuF2 is water-soluble stuff, wash the wafers in water before running the final test
Washing wafers with water prior to the final test gave excellent results. The washing operation was approved and implemented as a long-term temporary solution until we got the final solution.
Eliminate the dry etch operation and replace it with the wet etch with the diluted-HF solution.
The main idea was to create the required structure using only the wet processes:
Set up process containing wet operations only.
1 operation - Cu removal with H2SO4 + H2O2 (Chem 1)
2 operation - Ti removal with diluted HF (Chem 2)
The process was completed and showed negative results - too deep an undercut is created due to interaction between HF and Ti under the Cu bumps:
Additional investigation is needed. Use 40 Inventive Principles to find a creative solution
Principle #22 - Blessing in disguise (Turn Lemons into Lemonade) seems to be very relevant
Eliminate primary harmful factors by following harmful factors.
The main idea is that we can eliminate undercut by two ways: Not to make undercut or remove overcut:
We can use Chem 1 twice to eliminate the undercut - add a makeup process:
Slightly reduce the Cu removal time with Chem 1, perform Ti removal with Chem 2, makeup - remove the overcut of Cu with Chem 1 for the ti,e remaining from the budget of the Cu removal.
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