종자결정을 활용한 다결정 규소 잉곳 내의 구조적 결함 규명
Structural defects in the multicrystalline silicon ingot grown with the seed at the bottom of crucible
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초록
방향성 응고법으로 잉곳을 성장시킬 때 발생하는 온도 구배에 의해 잉곳 내에 결함이 생성되고 잔류 응력이 남게 된다. 이 결함과 잔류 응력은 잉곳의 성장 조건에 따라 달라지며, 웨이퍼의 특성에 큰 영향을 미칠 수 있다. 성장 속도의 변화에 상관 없이 대부분의 잉곳에서는 하부 영역에 비해 상부 영역에서 결정립과 쌍정경계의 크기가 작았으며, 결정립계뿐만 아니라 결정립 내에도 전위 밀도가 높았다. 이것은 상부 영역에서 성장 중에 받는 열 응력이 하부 영역보다 크다는것을 암시한다. 두 잉곳 간의 차이를 보았을 때에는 성장 속도가 느린 잉곳에서 전위 밀도가 감소하였으며, 웨이퍼의 평탄도, 뒤틀림, 휨, 절단자국이 낮게 측정되었다. 따라서 다결정 성장 공정에서는 냉각 속도가 결함이나 잔류 응력의 발생에미치는 영향이 크며, 그로 인하여 웨이퍼의 특성이 달라지는 것을 알 수 있었다.
Abstract
Because of the temperature gradient occurring during the growth of the ingot with directional solidificationmethod, defects are generated and the residual stress is produced in the ingot. Changing the growth and cooling rate duringthe crystal growth process will be helpful for us to understand the defects and residual stress generation. The defects andresidual stress can affect the properties of wafer. Generally, it was found that the size of grains and twin boundaries aresmaller at the top area than at the bottom of the ingot regardless of growth and cooling condition. In addition to that, inthe top area of silicon ingot, higher density of dislocation is observed to be present than in the bottom area of the siliconingot. This observation implies that higher stress is imposed to the top area due to the faster cooling of silicon ingot aftersolidification process. In the ingot with slower growth rate, dislocation density was reduced and the TTV (Total ThicknessVariation), saw mark, warp, and bow of wafer became lower. Therefore, optimum growth condition will help us to obtainhigh quality silicon ingot with low defect density and low residual stress.
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