반도체 분야에서 사용되는 사파이어(sapphire)는 경도(hardness) 9에 해당하는 자연계에서 다이아몬드(diamond) 다음으로 단단한 물질이라 할 수 있다. 이러한 사파이어는 단단한 물질인 만큼 표면가공이 어렵기 때문에 웨이퍼(wafer)가 되기까지 여러 가지 공정을 거쳐야하는 실정이다. 따라서, 웨이퍼링(wafering) 공정을 단축하기 위하여 현재 많은 연구가 진행되고 있다. 본 연구에서는 새롭게 개발된 랩그라인딩(lap grinding) 공정을 사파이어 웨이퍼링 공정에 적용하고자 한다. 본 연구에서는 랩그라인딩에서 슬러리(slurry) 희석비와 압력(pressure) 조건에 따라 후속 공정인 화학기계적 연마(chemical mechanical polishing; CMP)를 진행 하였을 때 사파이어 웨이퍼 표면에 어떠한 영향을 미치는지에 대하여 연구하고자 한다. 랩그라인딩 공정에서 슬러리의 실리카(SiO2) 입자 함량 0 wt%, 10 wt%, 20 wt%, 40 wt% 조건을 변수로 택하였고, 압력 1.5 psi, 2.9 psi, 4.4 psi 조건을 변수로 택하여 실험에 적용하였다. 그리고 후속 공정인 CMP 공정에서는 일정한 조건을 실험에 적용 하였다. 실험에는 회전식 연마기인 G&P사의 POLI-500을 사용하였다. 랩그라인딩 공정에 사용된 팰렛(pellet)의 다이아몬드 고정입자 크기는 #600으로 20~30? 정도의 입자 크기를 가지고 있으며, CMP 공정에서 사용한 연마패드는 SUBA600을 사용하였다. 실험 결과 랩그라인딩 공정에서 실리카 입자 함량 20 wt% 조건을 적용한 실험이 가장 낮은 표면거칠기(surface roughness)가 나타났으며, 가장 높은 재료제거율(material removal rate; MRR)을 나타내었다. 10 wt%와 40 wt% 조건에서 20 wt%에 비해 상대적으로 높은 표면거칠기와 낮은 재료제거율을 나타내는 결과를 얻었다. 이러한 결과를 통해 랩그라인딩 공정에서 실리카 입자가 포함되어 있는 슬러리를 사용할 경우 적절한 농도의 실리카 입자가 요구된다는 것을 알 수 있었다. 압력 조건을 적용한 실험 결과에서 압력이 점차 증가함에 따라 표면거칠기는 낮아지며, 재료제거율은 높아지는 것을 확인하였다. 이러한 결과는 preston방정식이 랩그라인딩 공정에서도 적용이 된다는 것을 알 수 있었다. 랩그라인딩 공정에서 슬러리 희석비와 압력 조건을 적용한 웨이퍼를 사용하여 후속 공정인 CMP 공정을 진행한 결과 두 조건 모두 유사한 결과를 얻을 수 있었다. 위의 결과와 같이, 랩그라인딩 공정 후 재료제거율이 높게 나타난 웨이퍼를 CMP 하였을 때 재료제거율이 낮게 나타난 이유는 랩그라인딩 공정에서 멀티와이어 쏘(multi-wire saw; MWS) 공정에 의한 웨이퍼 절단된 흔적이 제거되어 CMP 공정을 진행 하였을 때 웨이퍼가 연마 패드와 닿는 실접촉면적(real contact area; RCA)이 증가하여 실접촉 압력이 증가 했기 때문인 것으로 판단된다. 본 연구를 통하여 랩그라인딩 공정에서 멀티와이어 쏘 공정에서의 웨이퍼 절단된 흔적이 대부분 제거될 수 있다면, CMP 공정에서 시간을 단축하여 사파이어 웨이퍼의 생산 효율을 높일 수 있을 것으로 판단된다.
The sapphire used in the semiconductor field is the second hardest material in the natural world, with a hardness of nine, after diamonds. Sapphire is a hard material, surface processing is difficult, so it is required to go through various processes until it becomes a wafer. A number of studies are currently underway to reduce the wafering process. Accordingly, this study intends to apply the newly developed lap grinding process to the wafering process. In this study, the effects of the sapphire wafer surface of the CMP process, which is a subsequent process after lap grinding process according to the slurry dilution ratio and pressure conditions, were investigated. In the lap grinding process, the silica(SiO2) particle concentration of the slurry(0wt%, 10wt%, 20wt%, 40wt%) conditions were selected as variables, pressure(1.5psi, 2.9psi, 4.4psi) conditions were selected as a variable was applied to the experiment. In the CMP process, which is a subsequent process, certain conditions were applied to the experiment. The equipment used in the experiment was a G&P POLI-500 machine, a rotary polishing machine. The fixed particle size of the pellet used in the lap grinding process has a particle size of about 20~30?, and the polishing pad used in the CMP process was SUBA600. The results showed that the experiment with the condition 20wt% silica particle concentration in the lap grinding process had the lowest surface roughness with a value of 154.53nm and the highest material removal rate with a value of 1.159?mi n . The results showed that the surface roughness and the material removal rate were relatively high compared to 20wt% at 10wt% and 40wt%. These results indicate that an appropriate concentration of silica particles is required when using a slurry containing silica particles in the lap grinding process. In the experimental results of applying pressure conditions, it was found that the surface roughness becomes lower and the material removal rate increases as the pressure gradually increases. These results indicate that the preston equation, except for the variable k value, can be applied to the lap grinding precess. In the lap grinding process, the wafers to which the slurry dilution ratio and the pressure conditions were applied were subjected to the CMP process, which was a subsequent process, and similar results were obtained in both conditions. The reason is that since the cut marks of the wafer are removed in the lap grinding process and the pressure is dispersed due to the increase in the actual area where the wafer touches the polishing pad, the following results are expected.
목차
Ⅰ. 서 론 ············································································································· 11.1 연구의 배경 ······························································································ 11.2 연구의 목적 및 내용 ·············································································· 51.3 논문의 구성 ······························································································ 6Ⅱ. 실험방법 및 실험조건 ············································································ 82.1 실험 장비 ·································································································· 82.2 랩그라인딩 실험조건 ············································································ 122.3 랩그라인딩 후 CMP 실험조건 ···························································· 152.4 측정 장비 및 방법 ················································································ 16Ⅲ. 실험결과 및 해석 ··················································································· 193.1 랩그라인딩 실험결과 및 고찰 ···························································· 193.1.1 랩그라인딩 재료제거 특성 ························································· 193.1.2 랩그라인딩 응력분포 해석 ························································· 243.1.3 자유입자를 이용한 하이브리드 재료제거 메커니즘 ············· 293.2 랩그라인딩 조건이 CMP 결과에 미치는 영향 ································ 393.2.1 랩그라인딩 시 압력이 CMP에 미치는 영향 ··························· 393.2.2 랩그라인딩 시 슬러리 비율이 CMP에 미치는 영향 ············· 473.2.3 사파이어의 CMP 재료제거 메커니즘 ······································· 53Ⅳ. 결론 ············································································································· 55Reference ······································································································· 57Abstract ··········································································································· 62