氮化鎵在圖形化4H-SiC基板上的磊晶

Abstract

隨著環保意識的抬頭，全球半導體產業則聚焦在提高產品效率、降低功耗、減少材料使用等相關技術之投入，以達到 CO2 排放減量之目的；第三代半導體材料碳化矽(SiC)元件與氮化鎵(GaN)則因為具備高導熱特性，加上其材料的寬能隙特性可耐高壓、承受大電流，適合應用在高溫操作的功率元件領域而第三代半導體材料主要應用之一高功率、高亮度的LED，目前都以藍寶石(Sapphire)基板上成長GaN的方式來製作，但使用Sapphire基板確有一些缺點(晶格不匹配、熱膨脹係數)，使得成長出來的GaN磊晶品質不佳影響LED的內部量子效率(IQE)和光取出率(LEE)，需透過圖形化藍寶石基板(PSS)技術來改善磊晶品質，而在SiC基板上成長GaN相較於Sapphire基板上成長GaN是更完美的匹配，預期可以改善磊晶品質，因此本實驗將利用SiC基板並且搭配圖形化基板技術製作出圖形化碳化矽基板，分析磊晶GaN前後的表面形貌與其它性質的研究。 第一部分的圖形化碳化矽基板實驗，我們利用黃光微影技術在SiC基板上製作出圓形的點狀遮罩，再利用乾蝕刻的方式成功製作出圖形化碳化矽基板並且蝕刻出以近似等六邊形為底的小山丘和小平台兩種不同的表面形貌，將這兩種不同表面形貌的SiC基板進行磊晶GaN的實驗，利用FIB、TEM、SEM、CL等儀器觀察，發現GaN不論是在小山丘或小平台圖形都傾向於在圖形的側壁上來成長，以小山丘圖形來推測側壁為{1 ̅102}面族，並且成長出推測為{1 ̅101}面族的wurtzite結構GaN，而這種在側壁成長的現象，推測是在乾蝕刻製程中因為參數調配的關係造成過蝕刻以及離子轟擊的影響，使SiC c-plane形成蝕刻損傷層，導致GaN不易在SiC c-plane上成長而選擇在圖形側壁{1 ̅102}上成長。 第二部分的實驗，由於第一部分圖形化碳化矽基板的GaN在圖形側壁上成長的結果，我們設計另一組實驗在SiC基板上製作出圓形的SiO2點狀遮罩，預期可以使GaN在沒有SiO2點狀遮罩的區域即沒有被蝕刻損傷的SiC c-plane上來成長，而從實驗結果推測SiO2點狀遮罩確實可以抵擋住GaN成長，但是因為在製備SiO2點狀遮罩的乾蝕刻製程中，也有造成SiC c-plane輕微的損傷，使GaN會選擇在經BOE蝕刻出的無損傷SiC c-plane來成長。

Owing to the rising awareness of environment protection, the global semiconductor industry is focusing investment to improve product efficiency and reduce power consumption, reduce the use of materials and other related technologies, in order to achieve reduction of CO2 emissions; third-generation semiconductor material silicon carbide (SiC) and gallium nitride (GaN) is because with high thermal conductivity properties, with wide bandgap properties of the material can withstand high pressure, withstand high current, suitable for application in the field of high-temperature operation of the power device and the third generation of one of the main applications of semiconductor material having a high power、high-brightness LED.It currently use the way of grow the GaN on the Sapphire substrate, but using sapphire substrate do have some drawbacks(lattice mismatch、coefficient of thermal expansion), so that the GaN epitaxial growth out of the quality is not best of LED internal quantum efficiency (IQE) and light-extraction rate (LEE), required by the patterned sapphire substrate (PSS) technology to improve the quality of epitaxial, and growing GaN on SiC substrate compared to the growth of GaN on sapphire substrate is more perfect match can be expected to improve the quality of epitaxy, so this experiment will use the SiC substrate and the substrate with patterning techniques to produce patterned silicon carbide substrate, analysising the surface morphology different between before and after of epitaxial GaN and the other properties. Patterned silicon carbide substrate, the first part of the experiment, we use photolithography technique on a SiC substrate to produce a circular dot mask, and then by dry etching successful way to produce patterned silicon carbide substrate and etched to approximately equal to six polygon-based small hills and platforms of different surface morphology, which is two different surface morphology of SiC substrate epitaxial GaN experiments using FIB, TEM, SEM observation and other equipment, whether it is found that GaN in the small hills or small platform pattern tend to grow up in the sidewall of pattern, with a small hill sidewall pattern to speculate {1 ̅102}families of planes, and is presumed to be growing out of {1 ̅101} plane family of GaN, and this in sidewall growing phenomenon, presumably in the dry etching process since the parameters formulated relations caused by overetching and the effects of ion bombardment, a SiC c-plane to form an amorphous damage layer, resulting in GaN is not easy to grow on the SiC c-plane is selected in the pattern sidewall {1 ̅102} grow on. The second part of the experiment, as a result of the first part of GaN patterned silicon carbide substrate on the pattern sidewall of growth, We produce SiO2 dot mask on the SiC substrate, GaN growth is expected to be on the c-plane , and from the experimental results suggest SiO2 dot mask can indeed withstand the GaN growth, but because in the preparation of SiO2 dot mask dry etching process, there is also cause SiC c-plane minor surface damage, the GaN will choose by BOE etched SiC c-plane without damage and SiO2 dot mask gap position to grow.