(Digital Presentation) Research on Single Wafer RCA Clean in High Aspect Ratio Trenches
Authors: Chen Fuping , Zhang David Wei , Wei Xiongfei , Zhang Xiaoyan , Liu Feng , Henry Sally Ann , Hu Haibo , Yao Liang , Chen Wei , Shou Xiaodong , Cui Yao 
Published: July 2022

I
ntroduction.

High aspect ratio (AR) processes are widely used in front end of line (FEOL) IC manufacturing. Figure 1 depicts high (AR) trench cleaning process. Polymerization residues produced during the dry etch process will cause many problems such as STI voids in the follow-up process if the residues are not removed. This can lead to lower yield and reduction of chip life[1]. It is difficult to completely clean the residue inside trench with aspect ratio greater than 10.
As shown in Figure.2, poor wetting of the liquid in the high AR trench, prevents the cleaning of the whole trench. Typically, the wafer surface can be easily cleaned, however residues remain inside of the trench. The cleaning of polymerization residues inside the trench and eliminating watermarks are the main issues in high (AR) cleaning processes. In this paper, we design an infiltration experiment, polymerization residues cleaning experiment and drying experiment to verify single wafer RCA clean performance on high (AR) trench processes. The verification of the single wafer RCA wafer clean is through yield data.

Experimental.

In the infiltration experiment, a layer of 500A SiO2 was grown on the high aspect ratios trench wafer. As shown in Table I, This was followed by treating the wafers with different process conditions on ACM single wafer tool. The remaining oxide thickness inside trench was measured by transmission electron microscope (TEM). Figure 3 shows experimental steps.
In the polymerization residue cleaning experiment, 7 wafers with trenches after dry etching were treated with different chemical and process mode shown in Table II on ACM single wafer tool. The defect count was measured by the inline defect detection equipment and the scanning electron microscope.(SEM)
In the drying experiment, high AR wafers were processed on an ACM single wafer tool, under different drying conditions. The trench wafer were then transferred into a vacuum bag and the air was evacuated. If there is no watermark on wafer surface within 15 minutes, we consider that the wafer has been dried in the macro level.
Wafers were split between being cleaned by single wafer RCA clean and by bench RCA clean. The wafers are scanned for defect count on the wafer surface after the cleaning process for both the base line (bench) and the single wafer tool. Finally, we review yield on device completion to check results of single wafer and bench clean.

Results.

Table I shows the result of dHF infiltration experiment. When the pre rinse DIW time exceeds 30 seconds, the whole trench is soaked by DIW, allowing the dHF to permeate the whole trench, with oxide loss being similar from the top to the bottom of the trench.
Table II shows the result of cleaning experiment. ACM Single wafer dHF+SC1 (mega) process can effectively clean the whole trench. Figure 4 and 5 shows defect map and SEM picture after single DHF+SC1(mega).
Figure 6 shows the effect of chuck rotation speed and N2 flow rate on wafer drying. Figure 10 shows particle performance under different drying process conditions. Figure 7 shows the inline defect map and SEM after dry process.
Figure 8 & 9 show the particle performance after the clean process. No special particle map appears with the single wafer clean process. Fig 10 shows the yield performance after all of the processes are completed. Average yield of single clean process is better than the baseline bench clean process. Table 3 shows detailed yield data from the wafer splits .

Conclusion.

Infiltration and cleaning experiment result shows that single wafer RCA clean can effectively clean the polymerization residues inside of high aspect ratio trenches. Dry experiment result shows that single wafer process can reduce watermark and particles in the dry step. Inline particle performance and final yield performance shows that single wafer RCA clean is better than baseline bench. Single wafer clean has lower standard deviation than bench clean and SW RCA clean in high (AR) trench process is feasible and effective.

References.

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JiHoon Cha, ChangSup Mun, etal. Low Si recess on cleaning process by dilute HF/SC-1 with megasonic[J]. Solid State Phenomena, 2008, 134:209-212.

H Wang, Yue Ma, Fuping.Chen, etal. Removal of Fine Particle using SAPS Technology and Functional Water[J]. Solid State Phenomena, 2013, 195:185-190.

Dae-Hong EOM, Geun-Bae LIM, etal. Reaction of Ozone and H2O2 in NH4OH Solutionsand Their Reaction with Silicon Wafers[J]. Japanese Journal of Applied Physics, 2004, 43:3335-3339.

Figure 1