Analysis of Correlation between Pad Temperature and Asperity Angle in Chemical Mechanical Planarization

Round 1

Reviewer 1 Report

The manuscript by Jeong et al. presents very interesting study on the analysis of correlation between pad temperature and asperity angle in the chemical mechanical planarization (CMP) process. The authors studied the pad temperature effect in the conditioning and polishing process. The change in asperity angle was confirmed by various characterization methods. The result showed that an increase in the asperity angle/pore formation at high temperatures would increase the polish rate and delay pad wearing. The experimental results and interpretations are sound. And thus I recommend publishing this manuscript with minor revisions. The specific comments are as follows:

1) What is the hardness and toughness value of the wafer substrate?

2) What is the within-wafer nonuniformity before and after polishing?

3) Page 7, Figure 7. The Y-axis label of 7(b) should be corrected as "asperity angle (degree)". This is indicated by Page 8, Line 180, "figure 7b that the tendency of the asperity angle at this time".

4) The material removal rate (MRR) discussed in Figure 7 and 10 is quite useful. However, the surface roughness (Ra) of the wafer is also equally important. I recommend authors to show the surface roughness of wafer before and after each polishing conditions and include a brief discussion on how the pad temperature influence the wafer surface roughness Ra and the polish quality.

5) The last data point in Figure 7 is a result of reconditioned pad, which showed much higher MRR than previous point. I recommend authors to indicate this in the Figure description.

6) In addition to MRR and surface roughness. There is also important parameters such as friction and wear coefficient. This will help provide qualitative picture of the polishing process. I would recommend authors to elaborate on those points.

Author Response

1. (1) Hardness : 18 GPa (nanoindentation at 100 uN, PECVD oxide coated Si), (2) Fracture toughness : 0.77 ± 0.15 MPa · m1/2
2. WIWNU : New unpolished wafers (0.2 %), After polishing (2.8 ~ 5.2 %)  

   Excluding excessive high temperatures (above 80 degrees), it was generally maintained at 3-5 percent.

   Since WIWNU is largely influenced by the physical properties and retaining ring of the pad itself, it is judged that it will not show much tendency in this experiment using the same pad. However, it is expected to cause a difference due to the large change in pad properties at excessive high temperatures.

3. The y-axis of figure 7b has been changed to 'Angle of asperity (degree)'.
4. Described in question 6.
5. When the removal rate of 140 nm suggested in the paper came out, the conditioning process was performed. The conditioning process was performed at normal room temperature, and after confirming that the asperity angle and removal rate were increased, the conditioning temperature effect experiment in the next section was conducted. The thesis also described it as follows. 
   'In addition, when the removal rate in the range of 140 nm was obtained for each condition, the conditioning process was performed, and it was confirmed that the removal rate and the asperity angle were recovered.
6.  It would be nice to explain it with question 4. Obviously, the consideration of surface roughness and friction is an important part and the parameters that are linked together. However, these have many tribological theories to be considered. Currently, we believe that it would be better to organize this part into a new paper on our own. We are constructing a mathematical model of the friction change caused by the asperity angle change according to the pad temperature and the scratch phenomenon on the wafer surface. Therefore, the submitted thesis will be used as an introduction paper that suggests the change of the pad asperity angle, which was not considered in the CMP study until now, and detailed elements will be composed of each paper.

Thanks for the good review and suggestions. We apologize for the fact that many of the suggested contents were related to our research curriculum and could not be significantly modified. As the current research progresses, it seems that research papers related to protrusion friction can be submitted in the near future. We would appreciate it if you could watch this part with interest.

Author Response File: Author Response.pdf

Reviewer 2 Report

This work investigates the effect of temperature on the asperity angle of the pad surface and as a result the efficiency of the CMP, material removal rate and conditioning of the worn pads. The research material has been presented coherently and clearly, however, there are some minor points shall be cosidered or corrected before publication. 

• Please retouch the abstract, avoid long sentences, correct the grammar and English language. for example line 10. write the full words before using the acronym SEM. 
• line 56, the sentence, 'when the wafer ... ', confusing, please make it more fluent. 
• line 73, confirmed or observed? Overally, please check how many times you have used verb 'confirm' in the manuscript.  Sometimes two times in a sentence or a paragraph,  please replace or apply other verbs if applicable for more fluency of the language. 
• In figure 7b, the y label is different, in the manuscript it is referred as asperity angle. 
• In figure 7a, why in the last process material removal rate increases? or asperity angle increases? Please address this in the text. 
•  

Author Response

1. Through proofreading, the overall English language was corrected.
2. When using the first SEM term, full word is written.
3. Corrected the sentence on line 56.
4. For the sake of sentence fluency, the use of the same words was avoided as much as possible (ex. confirmed)
5. The y-axis of figure 7b has been changed to 'Angle of asperity (degree)'.
6. When the removal rate of 140 nm suggested in the paper came out, the conditioning process was performed. The conditioning process was performed at normal room temperature, and after confirming that the asperity angle and removal rate were increased, the conditioning temperature effect experiment in the next section was conducted. The thesis also described it as follows. 'In addition, when the removal rate in the range of 140 nm was obtained for each condition, the conditioning process was performed, and it was confirmed that the removal rate and the asperity angle were recovered.

Please see the attachment

Author Response File: Author Response.pdf