Investigation of a Macromolecular Additive on the Decrease of the Aluminum Horizontal Etching Rate in the Wet Etching Process

Round 1

Reviewer 1 Report

The specific comments are listed below.

It will be much better if the author can provide more details about the advantages or disadvantages of your method compared with the others.

Line 87 The thickness of Al films was measured in a four-point resistance probe. Can you explain the method?

• It is not clear in the Experimental section that the additive is 1% and also why Polyethylene-polypropylene glycol was choose? Please explain all the mixtures tested.
• I would suggest presenting the structure/chemical characterization (XRD, EDX) of the samples at every of the additive concentrations;
• Many figures are not adequately visible. Please improve and enlarge Fig. 2.
• May the authors provide a chemical reactions during the etching process?
• Provide the limitations to this study and the future directions in the conclusion section;
• There is missing the parameters of the reproducibility.

Finally, the language is in general correct, but some parts require a revision.

Author Response

A point-by-point response to the reviewer-1’s comments was given.  Please see the attachment. 

Author Response File: Author Response.pdf

Reviewer 2 Report

Overall, the manuscript is quite well written and clear. However, at many places the authors should be more precise in their formulation, extend their discussion and interpretation of the data. Please mention repeatability and accuracy of the determined values (e.g., etch rate). Therefore, in the present form I would recommend to reject the work for publication. 

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Line 29

[bias] > What is that exactly about ? Unclear 

Line 37-38

[when etching times is longer than 20 minutes] > Please carefully check English formulation. 

Line 39

[basin] > What is that about ? Unclear. 

Line 58

[level in outer bath is lower than that in inner’s.] >[level in the outer bath is lower than that in the inner bath.]

Line 64

[ According to manufacturer] > [ According to the manufacturer]

Line 67

[Then, a kind of macromolecule additive (BASF, Taiwan) was added]. This is quite a vague formulation ! What exactly is the product name / product number ? In line 68 it is mentioned what the main component is, however, if there are other components in the commercial product, that should be mentioned ! Therefore, carefully rewrite line 67. 

Line 76-77

[Then, three concentrations of 0.2, 1, and 5% were also studied on the dissolution and distributions.] > [Then, the impact of three concentrations (0.2, 1, and 5%) and particle size distribution on aluminum dissolution was studied.]

Distribution of what ? Unclear. 

Line 80

[physics ] > Check for correct name of PVD

Line 99-106 / Figure 2

The authors should be more precise in formulating how the experiment was exactly performed. The impact of pump flow on the particle size distribution is shown in Figure 2(d). How was the experiment exactly performed ? Is it important to measure the distribution IMMEDIATELY after taking a sample ? Does the PSD change over time, after taking a sample from the bath ? How important is fast analysis and does is have an impact on the observed PSD ? Did the authors monitor the PSD as a function of time after taking a sample from the bath ? Are the observations being ascribed to liquid cavitation ?

Line 149

[are around 700 nm/min by measuring the remaining thickness on bare Al wafers] > How many times did the authors perform the experiment ? How reproducible are their 'vertical etch rate' measurements ? Can the authors indicate the standard deviation in the results for EACH additive concentration that was tested and indicate how many times the experiment was performed ? To make strong statements that should be properly mentioned. Especially because in Table 1 the RHV is calculated, taking the 700 nm/min value for the horizontal ER. 

Line 158

[Obviously, it is observed] > Please rephrase.

Figure 4B + 4C

Please indicate the PR, oxide layer, and Al layer (consistent with the style used in Figure 4D).

Line 208

[with different thickness is different] Avoid using the same word twice in the same sentence.

Line 224

[four-point probes] > Where are these results discussed in the manuscript ? The technique is mentioned on line 87 and I didn't see any more details in the manuscript. Did the authors perform a 4PP measurement for a wide range of Al thicknesses ? Did the authors cross-check the thickness values with other methods, such a cross-section SEM or RBS ? How goed is their 'calibration' of thickness and sheet resistance, i.e. how accurate is the 4PP method in yielding the Al thickness value ? Is there an impact of surface roughness on the 4PP value ? To determine an etch rate, a post-etching 4PP measurement will be done, the 4PP calibration curve used for extracting the remaining Al film thickness and then it is UNavoidable that surface roughness of the surface AFTER etching is different. How representative is their 4PP thickness-sheet resistance calibration curve ?  

Line 232

[novel method] > Where is the novel aspect ? Using additives to impact ER should not be considered 'novel', has been done numerous times in the literature for many material/metal - etchant systems !

Author Response

A point-by-point response to the reviewer 2’s comments was given. Please see the attachment. 

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The answers are correct and complete. 

Author Response

Thanks for your great help.

Reviewer 2 Report

This reviewer would like to thank the authors to take into consideration the questions and remarks from the previous round. Therefore, the work can be accepted after the following comments are addressed:

Line 96-97: [due to the square resistance was linearly related to the thickness] > Are the authors referring to the sheet resistance here ? Is it true that sheet resistance is linearly related to the thickness ? Really ?

Line 251: [provided] > [provides]

Line 253: [studied] > [ studies]

Author Response

Dear Referee, thanks very much for your suggestion.  The replies to your comments were given below， 

1) Comments: Line 96-97: [due to the square resistance was linearly related to the thickness] > Are the authors referring to the sheet resistance here ? Is it true that sheet resistance is linearly related to the thickness ? Really ?

Reply: Thank you for pointing this question. It was a big mistake. Here the square resistance just refers to the sheet resistance.  To be more professional，it was changed to be "sheet resistance“. Moreover, the sheet resistance is inversely proportional to the thickness. Then the corresponding sentence was corrected.

2) Comments: Line 251: [provided] > [provides]

Reply: Thanks, the word was corrected.

3) Comments: Line 253: [studied] > [ studies]

Reply: Thanks, the word was corrected.