Mr. Beliakou

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)

Eliminate the dry etch operation and replace it with the wet etch with the diluted-HF solution.

Since CuF2 is water-soluble stuff, wash the wafers in water before running the final test

Manage the process flow to ensure the lowest dwelling time between the process end and the final test.

The project was dedicated to production yield improvement in microchip manufacturing.
The bumps are created on the top of a wafer and used for the final test of all dies. 
Only good dies are taken for the packaging. All dies that fail the test will be scrapped. The process yield depends on the amount of "good" and "bad" dies.
It was revealed that in some cases, the time between the end of the process and the final test impacts the yield. 
The longer the dwelling, the more dies fail the final test. 
If the dwelling exceeds hundreds of hours, the amount of failed dies becomes dramatically high, which results in the scrapping of the whole wafer.
The problem was analyzed and solved.

Time-depending yield degradation at microchip manufacturing

Projects related to innovations and problem solving in the microchip manufacturing

Object Affected Harmful Factors - This parameter is designed as a catch-all for any form of action or phenomenon in or around a system that manifests itself as a harmful effect on something in the system.

External harm affects the object

The Other way around

Blessing in disguise (Turn Lemons into Lemonade)

Intermediary

Parameter changes

The number of useful (value-adding) functions or operations performed by a system per unit time.  The time per unit function or operation.  Useful output per unit of time.  Cost per unit output, or amount of useful output.  (See 'Speed' –  #14 – which is more focused on issues of dynamics rather than the output of product.)

Productivity

The dry etch operation is performed with the fluorine compound

The dry etch process contaminates the bump with fluorine that converts slowly to the CuF2 that covers the surface of the bump

Previous process affected the bump surface that results in the formation of dielectric stuff on the surface of the bump.

Some stuff that has high resistivity is formed on the surface of the bump.

The resistivity of the bumps increases during the dwelling

Dwelling time before the final electrical test results in the dies failing

Manage the process flow to achieve the lowest dwelling time

Eliminate the dry etch operation. Replace it with the relevant wet etch process.

The best way to eliminate high resistivity on the surface of a bump is to use a chemical etching process.

One way to eliminate this dielectric stuff on the surface of the bump is to clean the bump surface with a solvent or chemical solution. This will help to remove any residue or contaminants that may have been left behind from the previous process. Additionally, it is important to ensure that the surface of the bump is dry before any further processing takes place. If necessary, the bump can also be polished to remove any remaining dielectric material.

One way to eliminate this contamination is to use a wet etch process instead of a dry etch process. Wet etching is a chemical process that uses an aqueous solution to remove material from the surface of a substrate. This process does not involve fluorine, so it will not cause the formation of CuF2 on the surface of the bump. Additionally, wet etching can be more precise and can produce better results than dry etching.
As a temporary solution - wash the wafers with water prior to the final test.

The best way to eliminate the use of fluorine compounds is in a dry etch operation. Eliminate the dry etch operation at all.

The operation aims to remove Cu from the surface of the wafer. The process - Wet etch with H2SO4 + H2O2 solution that dissolves Cu and does not dissolve TiProduct - Dissolved Cu

1. Cu removal with H2SO4+H2O2

The operation aims to remove Ti on the open area between the bumps.The process - Dry etch (plasma) with NF3 gas. Fluorine generated from NF3 in plasma interacts with Ti and converts it to TiF4 with low melting and boiling points. At the process conditions, TiF4 presents in the form of gas that is removed by the exhaust of the dry etch chamber. Product - TiF4 - gas

2. Ti removal between bumps with NF3 plasma

The operation aims to remove the residue of Ti remains between the bumps after the dry (plasma) etch operation.The process is performed by wet cleaning using diluted HF solution (Chem 2). HF solution dissolves rare refractory metals including Ti. HF converts the Ti to soluble acid H2TiF6. Dissolved Ti is removed from the wafer with liquids Product - Dissolved Ti

Time-depending yield degradation at microchip manufacturing

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