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Updated 08/18/2022
2

Wafer cleaning issues at the wet process

Cause and Effect Chain #

To analyze why the defects remain on the wafer while cleaning with chemistry.

The process is as follows:

  • a wafer is kept in the special chuck in 4 points
  • chemistry pores from the nozzle on the wafer
  • the wafer rotates allows removing the chemistry from the wafer together with the defects
  • parameters of the process - chemistry flow, temperature, process time, wafer rotation rate and so on can be adjusted

It seems like the process conditions are not optimal

Linear (5+ whys) analysis is needed to search for a root cause of insufficient defects removal with the chemistry and with water at rinsing

The most important point is that chemistry does not perform the process properly - improve the process is needed

Jan 14 2022 12:51:51 pm
5+ WHYS Analysis #
Causes Chain
Root Cause Analysis

Defects remain on the wafer surface after the wet cleaning process step

Why?

Try to eliminate the washing. Do we really need this?

Because the wet process does not remove the defects

Why?

To increase the density of the chemistry by temperature reduction.

Defects remain on the wafer till the very end of the process.

Why?

Ensure that the chemistry remains on the wafer as long as possible (reduce rotation of the wafer)

The chemistry is removed from the wafer before it removes the defects

Why?

Prevent evaporation of the chemistry from the wafer

Because the chemistry contaminates the wafer due to impurities or some other properties

This is the fundamental reason for the problem (FRP).

Replace the chemistry

Jan 14 2022 3:42:52 pm
Inventive principles #
Contradiction:
If
The wafer will be washed as much as needed.
Then
A big amount of chemistry or water will remain on the wafer during the cleaning process.
But
The process cost will be significantly increased.
Improving parameter
Description of what is improving:
Purity of the wafer. No defects on the wafer. No scrapped wafers anymore.
Selected improving parameter:
Volume of moving object
Worsening parameter
Description of what is worsening:
Unpredictably high cost of the process due to the usage of big amount of chemistry or water for rinsing
Selected worsening parameter:
Loss of energy
Matching principles:
  • 7
    Nesting dolls
  • 13
    The Other way around
  • 15
    Dynamism
  • 16
    Partial or excessive action
  • Jan 15 2022 10:13:14 am
    Effective Brainstorming #

    Defects remain on the wafer surface. The wet cleaning process suddenly becomes ineffective.

    Let's apply the Effective Brainstorming (EBS) tool to generate ideas and prioritize them.

    ImplementationEasyValidationEasy
    Reduce rotation rate
    3
    Apr 10 2022 11:46:04 am
    Increase the time of rinsing
    2
    Apr 10 2022 11:45:47 am
    Increase the time of cleaning
    1
    Apr 10 2022 11:45:29 am
    Increase the temperature of rinsing water
    0
    Apr 10 2022 11:45:02 am
    ImplementationEasyValidationNot Easy
    Check and adjust the pressure
    2
    Apr 10 2022 11:42:44 am
    Adjust clean air pressure
    1
    Apr 10 2022 11:43:02 am
    Replace filter
    0
    Apr 10 2022 11:43:54 am
    ImplementationNot EasyValidationEasy
    Check and adjust the flow
    Apr 10 2022 11:42:07 am
    ImplementationNot EasyValidationNot Easy
    Reduce the temperature of the chemistry
    4
    Apr 10 2022 11:44:33 am
    Replace pump
    3
    Apr 10 2022 11:44:16 am
    Replace the chemistry
    1
    Apr 10 2022 11:46:42 am
    Change spec limits
    1
    Apr 10 2022 11:47:32 am
    Add filter
    1
    Apr 10 2022 11:44:06 am
    Apr 10 2022 11:33:33 am
    Functional Modeling #

    Defects remain on the wafer surface after the wet cleaning process step.

    Single wafer wet cleaning system.

    The chemistry is pored on the rotated wafer to remove the stuff and not leave residue or particles.

    The sketch of the chamber is shown below:

    Functional rank
    Problematic rank
    Frontside Chemistry
    10
    6.7
    Stuff to remove
    5
    4.4
    Frontside nozzle
    1.7
    Pump
    1.7
    Heater
    1.7
    Chemistry Filter
    2.5
    Air
    10
    Air filter
    2.1
    Exhaust
    2.1
    Fan
    1.4

    The most problematic components are Air and Front side Chemistry:

    Do we really need an airflow? Maybe it would be better just filter without a fan. The exhaust will compensate for the pressure variations.


    Front side chemistry is also the most functional component. It means the improvement can be achieved by variation of the chemistry parameters

    All components of low functionality can be trimmed.

    The functionality of the Exhaust can be significantly improved by relocation within the chamber



    The general conclusion is to eliminate the air supply and exhaust system.

    Let air enter the chamber and convert exhaust to drain with very little under-pressure.

    This will stabilize the performance, reduce the evaporation rate of the chemistry, reduce the cost and simplify the system.

    May 7 2022 11:41:59 am
    Functional Modeling #

    Defects remain on the wafer surface after the wet cleaning process step.

    Single wafer wet cleaning system.

    The chemistry is pored on the rotated wafer to remove the stuff and not leave residue or particles.

    The sketch of the chamber is shown below:

    Functional rank
    Problematic rank
    Chuck
    10
    Front side chemistry
    6
    1.9
    Residue
    5
    0.5
    Tank with chemistry
    5
    Pump
    5
    Air
    5
    10
    Back side chemistry
    5
    Fan
    4
    Air particles
    3
    0.3
    Heater
    2
    Chemistry filter
    2
    0.8
    Air Filter
    2
    1.4
    Chemistry particles
    0.6

    The air flow is the most harmful component - prevent air flow to avoid drying and evaporation of the chemistry that results in the leaving of the residue on the wafer surface

    Jun 13 2022 8:40:11 am

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