실리콘 카바이드 (SiC) 나노 입자 제조 및 이를 이용한 인쇄전자공정에 관한 연구

Abstract

Silicon carbide는 Si와 C의 공유결합과 부분적 이온 결합으로 이루어진 인공화합물이다. SiC는 에너지 밴드갭이 크고 열팽창계수가 낮아 고온에서도 변화가 거의 없고, 비저항의 범위가 넓고 기계적 화학적 특성이 우수하여 고전압 환경에서도 사용이 가능하여 고온 고전압 환경에서 사용되는 센서 내 히터로 사용되고 있다. SiC 히터를 만들기 위해서는 SiC를 마이크로 패터닝 하여야 하는데, 기존의 SiC 마이크로 패턴 제조 방법인 CVD법, soft lithography법, wet-etching법 등은 장치 및 공정이 복잡하고 제어가 어렵다는 단점이 있다. 이에 본 연구에서는 SiC 잉크를 제조 후 잉크젯 프린팅 공정을 이용하여 SiC 마이크로 패턴을 제조하여 낮은 공정비용으로 SiC 히터를 제작할 수 있음을 확인하였다. 3장에서는 SiC 잉크의 주재료인 SiC 나노 입자를 제조하였다. 태양전지용 단결정 실리콘 웨이퍼 제조과정에서 부산물로 나오는 실리콘 슬러지에서 SiC를 분리하였고, 분리된 SiC를 밀링 공정을 통하여 나노 크기로 분쇄하였다. 이를 통해 실리콘 슬러지 처리 시 발생하는 환경적 경제적 문제를 해결하고, 고품질의 SiC 나노 입자를 제조할 수 있었다. 본 연구에서는 다양한 밀링 공정방법 중 planetary milling 공정방법을 사용하였다. Planetary milling을 50시간 하였을 때 평균 입도 50 nm 이하의 SiC 나노입자를 제조할 수 있음을 확인하였고, 72시간 밀링 시 평균 입도 36 nm의 SiC 나노입자를 제조할 수 있음을 확인하였다. 또한 XRD pattern 분석을 통하여 SiC의 분쇄 메카니즘을 확인하였다. 밀링 초기에는 grain boundary를 따라 분쇄가 진행되고, 밀링시간이 지나면 grain이 갈라지는 형태로 밀링이 진행됨을 알 수 있었다. 또한, 밀링 시 (200)면이 다른 결정면들보다 빨리 분쇄됨을 확인할 수 있었다. 밀링 ball size에 따른 밀링 효율을 비교하고자 2.0 mm ball로 분쇄된 SiC 나노 입자의 크기와 0.1 mm ball로 분쇄된 SiC 나노 입자의 크기를 비교하였다. 비교 결과 0.1 mm ball로 분쇄된 SiC 나노 입자 크기가 더 작음을 확인하여 0.1 mm ball로 밀링을 하였을 때 더 우수한 밀링효율을 나타낸다는 것을 알 수 있었다. 4장에서는, 3장에서 제조한 SiC 나노 입자를 용질로 하여 SiC 잉크를 제조한 후, 잉크젯 프린팅 공정을 통하여 SiC 마이크로 패턴을 제조하였다. SiC 마이크로 패턴의 선폭을 미세화 하기 위하여, 표면 에너지가 다른 두 개의 기판에 잉크젯 프린팅을 하여 선폭을 비교하였다. 또한 잉크젯 장비의 piezo 소자의 V값과 t 값을 변화시켜 프린팅 시 생성되는 잉크 액적의 크기를 변화시킴을 통해 SiC 마이크로 패턴의 선폭을 변화 시켰다. 두 가지 제조 방법을 통해 SiC 잉크를 만들었다. 첫 번째 제조방법은 3장에서 제조한 SiC 나노 입자를 solvent에 분산 시키는 방법이고, 두 번째 제조방법은 밀링 공정을 통해 얻은 SiC 페이스트를 바로 solvent로 희석하는 방법이다. TGA 분석과 점도 분석을 통하여 두 잉크가 잉크젯 프린팅에 적합한 잉크임을 확인하였다. 이 후 SiC 나노입자를 solvent에 분산시켜 제조한 잉크를 alumina기판과 AlN 기판에 잉크젯 프린팅 하였고, AlN기판에서 alumina기판에서 보다 더 미세한 선폭을 가짐을 확인하였다. 접촉각 실험을 통해, AlN 기판이 alumina기판에 비해 표면에너지가 낮고 친수성 용매에 대해 낮은 wettability를 가지기 때문에 AlN 기판에서 SiC 잉크가 미세하게 프린팅 된다는 것을 알 수 있었다. 프린팅 패턴의 선폭을 미세화하기 위해 SiC paste를 희석시켜 제조한 잉크를 프린팅 할 때 잉크젯 프린팅 장비 내 압전소자의 V, t 값(jetting 변수)를 변화시켰고 그에 따른 결과를 확인하였다. 압전소자의 V 값을 줄였을 때 떨어지는 잉크의 모양이 선형에서 구형으로 변하고 이에 따라 프린팅 선폭이 얇아짐을 알 수 있었고, t 값을 줄였을 때 잉크액적의 크기가 줄어들고 이에 따라 프린팅 선폭이 얇아짐을 알 수 있었다. 이를 통해 프린팅 시 압전 소자의 V, t 값 (jetting 변수)을 조절 하여 작은 크기의 구형의 잉크액적을 형성시키면 이에 따라 작은 잉크 액적이 프린팅 됨으로 인해 프린팅 선폭이 미세해짐을 알 수 있었다.|This work relates to a study for producing a micro-pattern to be applied to the heater using a silicon carbide in silicon sludge generated in the production of single crystal wafers for solar cells. The sic raw material was pulverized to nano particles and the sic nano particles were dispersed in a solvent. And then, the ink was printed on substrate. Chapter 3, Raw material particles of silicon carbide were milled using a planetary mill to produce the silicon carbide nano particles. During milling, The particle size was initially dramatically reduced. On the other hand, the particles were slowly crushed in the second half. Also, After milling was 50 hours, The particle size was 50 nm or less. And after 72 hours, the size of the particles was 36 nm. When milling, an XRD analysis was performed in order to know how the crystalline structure of the silicon carbide changed. As a result of analysis, We could know that the particle size was reduced initially by the separation of the grain. And later, grain size was reduced because the grain was crushed. In addition, All of the crystal plane can not be crushed in the same way at the time of processing, It was found that (220) crystal plane was more quickly crushed during milling. To confirm the processing efficiency associated with the ball size, 0.1 mm ball was used instead of 2.0 mm ball during milling. The size of the milled particles with 0.1mm ball is smaller than the size of the milled particles with 2.0 mm ball. In chapter 4, We made SiC inks using the sic nano particles. Then, the inks was ink-jet printed to prepare an applicable fine pattern on a heater. To analyze the physical properties of the inks, we went a TGA analysis and viscosity measurement. And the inks was identified to be suitable for ink jet printing. Two experiments were performed to print a pattern with a thin line width. The first experiment was to compare the line width by the ink jet printing on the other of the two substrates. The ink was printed on the alumina substrate and the AlN substrate. And we confirmed that the width of line on AlN substrate were more thinner than the width of line on alumina substrate. To find out the cause, the contact angle was measured on an alumina substrate and AlN substrate. As a result, We found that the AlN substrate has a low wettability to hydrophilic solvent. The width of printed patten on AlN was thinner than the width of printed pattern on Alumina because SiC ink used in this experiment is composed of a hydrophilic solvent. Furthermore, it was demonstrated that it is possible to produce a 50 um fine pattern when sic ink is printed on AlN substrate throughout the experiment. The second experiment was to confirm the change in the line width when the jetting parameters changed. We prepared three different jetting parameters consist of voltage and time, and confirmed the droplet size and the line width of the jetting parameters. As the voltage and time of jetting parameters was reduced, size of the droplets is decreased. and width of the line was also decreased. Therefore, in order to draw a thin line width, it is important to make a small droplet by setting the appropriate jetting parameter.; This work relates to a study for producing a micro-pattern to be applied to the heater using a silicon carbide in silicon sludge generated in the production of single crystal wafers for solar cells. The sic raw material was pulverized to nano particles and the sic nano particles were dispersed in a solvent. And then, the ink was printed on substrate. Chapter 3, Raw material particles of silicon carbide were milled using a planetary mill to produce the silicon carbide nano particles. During milling, The particle size was initially dramatically reduced. On the other hand, the particles were slowly crushed in the second half. Also, After milling was 50 hours, The particle size was 50 nm or less. And after 72 hours, the size of the particles was 36 nm. When milling, an XRD analysis was performed in order to know how the crystalline structure of the silicon carbide changed. As a result of analysis, We could know that the particle size was reduced initially by the separation of the grain. And later, grain size was reduced because the grain was crushed. In addition, All of the crystal plane can not be crushed in the same way at the time of processing, It was found that (220) crystal plane was more quickly crushed during milling. To confirm the processing efficiency associated with the ball size, 0.1 mm ball was used instead of 2.0 mm ball during milling. The size of the milled particles with 0.1mm ball is smaller than the size of the milled particles with 2.0 mm ball. In chapter 4, We made SiC inks using the sic nano particles. Then, the inks was ink-jet printed to prepare an applicable fine pattern on a heater. To analyze the physical properties of the inks, we went a TGA analysis and viscosity measurement. And the inks was identified to be suitable for ink jet printing. Two experiments were performed to print a pattern with a thin line width. The first experiment was to compare the line width by the ink jet printing on the other of the two substrates. The ink was printed on the alumina substrate and the AlN substrate. And we confirmed that the width of line on AlN substrate were more thinner than the width of line on alumina substrate. To find out the cause, the contact angle was measured on an alumina substrate and AlN substrate. As a result, We found that the AlN substrate has a low wettability to hydrophilic solvent. The width of printed patten on AlN was thinner than the width of printed pattern on Alumina because SiC ink used in this experiment is composed of a hydrophilic solvent. Furthermore, it was demonstrated that it is possible to produce a 50 um fine pattern when sic ink is printed on AlN substrate throughout the experiment. The second experiment was to confirm the change in the line width when the jetting parameters changed. We prepared three different jetting parameters consist of voltage and time, and confirmed the droplet size and the line width of the jetting parameters. As the voltage and time of jetting parameters was reduced, size of the droplets is decreased. and width of the line was also decreased. Therefore, in order to draw a thin line width, it is important to make a small droplet by setting the appropriate jetting parameter.