Problem 3: Alkali Etching (( LOOK AT THE PIC PLEASE, PIC SAME AS QUESTION BUT MO

Question

Problem 3: Alkali Etching (( LOOK AT THE PIC PLEASE, PIC SAME AS QUESTION BUT MORE CLEAR AND HAVE GRAPH))
The Damage Etch Engineering Team is working on developing a new process for a new type of wafers, called
“Diamond Wire Sawn Wafers”. These wafers have less surface damage, and therefore the process recipe needs to be
redesigned. In this problem, you will be determining appropriate recipe settings for the new type of wafer based on
available data.
The graph below shows the process characteristic “Silicon Etch Rate (microns/hour) versus NaOH Concentration” for
the process.

Problem 3: Alkali Etching The Damage Etch Engineering Team is working on developing a new process for a new type of wafers, called Diamond Wire Sawn Wafers". These wafers have less surface damage, and therefore the process recipe needs to be redesigned. In this problem you will be determining appropriate recipe settings for the new type of wafer based on available data. The graph below shows the process characteristic "Silicon Etch Rate (microns/hour) versus NaOH Concentration" for the process. Silicon Etch Rate (microns/hour) 60 50 E 40 30 20 10 Etch Rate (micron/hour) 10 20 30 NaOH Concentration (%) 40 The current process recipe has a NaOH concentration of 30% and an etch time of 30 minutes. a For the curent process recipe, how uch silicon is etched from each side of the wafer? If the wafer stating thiclness is 200 microns, what is the wafer thiclness after the etching process. NOTE: both sides will be etching during the etch process. b. The new Diamond Wire Sawn Wafers require 20 microns of silicon to be etched from each side of the wafer. c. Predict the etch time that would be required for these waters, if NaOH concentration was kept fixed at 30%? d. Predict the smallest NaOH concentration that would be required for these wafers, if time was kept fixed at 30 minutes? e. Management wants the process to run faster. Predict the NaOH concentration that would be required for these wafers, if a process time of 15 minutes was required. f Part e presents an interesting situation Make one suggestion about what other things the engineering team might do to change the alkali etching process recipe in order to address this interesting situation.

Explanation / Answer

Given, current recipe has a NaOH concentration of 30% and etch time of 30 minutes.

a) At NaOH concentration of 30%, we have Silicon etching rate of approx 50 microns/hour/side

In 1 hour (60 min) total Silicon etched = 50microns per side

Therefore, total silicon etched out from each side in 30 min = 30 x (50/60) = 25 microns per side.

b) If the starting wafer thickness= 200 microns, we have etching from both the sides.

So, total etching=25 x 2 = 50 microns in 30 min.

Therefore, wafer thickness after the etching process = 150 microns.

(c) Given, diamond wire sawn wafers require 20 microns of silicon etching for 30% NaOH concentraion.

We have, 50 microns etching time per side = 60 min

Therefore, 20 microns eching time per side = 20 x (60/50) = 24 min.

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