Calculate the flow rate of the etching solution

Click For Summary

Discussion Overview

The discussion revolves around calculating the flow rate of an etching solution used in semiconductor manufacturing, specifically for the etching of silicon wafers. Participants explore the stoichiometry involved in the chemical reaction and the necessary calculations to determine the flow rate in kilograms per hour, as well as identifying the limiting reagent in the process.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Technical explanation

Main Points Raised

  • One participant notes the need to calculate how much silicon will be etched and the time frame for the etching process, suggesting that stoichiometry will guide the solution.
  • Another participant assumes that silicon is the limiting reagent and provides a stoichiometric breakdown of the reactants and products based on a hypothetical scenario of using 100 moles of acetic acid.
  • A question is raised about the role of specific gravities in the calculations and whether they should be incorporated into the volume calculations for the etching solution.
  • One participant expresses uncertainty about the concept of a limiting reagent and suggests that silicon should not be considered limiting since some will remain after the reaction.
  • Participants discuss the need to compare the stoichiometric ratios of the acids used in the etching solution with the introduced amounts to determine the limiting reagent accurately.

Areas of Agreement / Disagreement

There is no consensus on the limiting reagent, with some participants asserting that silicon is limiting while others question this assumption. The discussion remains unresolved regarding the specific calculations and the role of specific gravities.

Contextual Notes

Participants express uncertainty about the initial steps in solving the problem, the application of stoichiometry, and the implications of specific gravities in the calculations. There are also unresolved questions about the volume of silicon to be removed and its mass.

Pr0x1mo
Messages
21
Reaction score
0

Homework Statement


In the semiconductor industry, integrated circuit (IC) production begins with the mechanical
slicing of silicon rods into wafers. Once the wafers are sliced, the surfaces are lapped and
polished to uniform flat surfaces. Contaminants and microscopic defects (work damage) are then removed chemically by etching. A tradition etching solution consists of a 4:1:3 volumetric ratio of 49% hydrofluoric (HF), 70% nitric (HNO3), and 100% acetic (CH3CO2H) acids, respectively.

Although work damage is usually 10 μm deep, overetching to 20 μm per side is common. The
reaction for dissolving the silicon surface is:

3 Si + 4 HNO3 + 18 HF -> 3 H2SiF6 + 4 NO + 8 H2O

Calculate the flow rate of the etching solution in kilograms per hour if 20μm per side is to be
etched for 6000 wafers per hour of 150 mm diameter. What is the limiting reagent?

Si – 2.33 g/cm3 M.W. 28.09g/mol
Sp gr 49% HF is 1.198 M.W. 20.01g/mol
Sp gr 70% HNO3 is 1.4134 M.W. 63.01g/mol
Sp gr 100% CH3CO2H is 1.0492 M.W. 60.05g/mol




Ok, this is a question that i have for my chemical engineering class, its one out of 10 questions (its not due, or has to be done). But looking at it, i want to know how to solve this. I've tried looking up in my textbook for a way to calculate this but i couldn't find anything on it. Maybe my teacher pulled this question from another book.

I don't even know the first step into solving this. Can someone get me on the right track?
 
Physics news on Phys.org
I think it is a simple stoichiometry. How much silicon is to be etched? In what time? Make sure stoichiometric amount of etching solution is introduced in this time and you should be done.

--
 
Well, Si is the limiting reagent I'm assuming.

and If CH3CO2H is 100% i can set that to CH3CO2H 100 mols and using the stoichemetric ratios, i get:

CH3CO2H 100 mols
Si 52.5 mols
HNO3 70 mols
HF 49 mols
H2SiF6 52.5 mol
NO 70 mol
H2O 140 mol

From here, where does the specific gravity's come into play? Do i have to add each one of their sp's and multiply it by 20μm*20μm times 150mm diameter times 6000 wafers for one hour?
 
What volume of silicon is going to be removed? What is its mass? Number of moles?

Actually I am not sure what is a limiting reagent - but as after the reaction ends a lot of silicon should stay in, silicon is not.

There is a stoichiometric ratio of acids and introduced ratio of acids - compare them.
 
Last edited:

Similar threads

Can Teflon Tape Withstand the Attack of Etching Solutions?
  • · Replies 9 ·
Replies
9
Views
2K