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PSG 희생층 식각시 Al 층을 보호하기 위한 새로운 HF/NH4F/Glycerine 혼합 식각액
김성운(Sung Un Kim),백승준(Seung Joon Paik),김임정(Im Jung Kim),이승기(Seung Ki Lee),조동일(Dong Il Cho) 한국센서학회 1999 센서학회지 Vol.8 No.5
The oxide sacrificial layer technology is one of the key technologies in surface micromachining. However, the commonly used aqueous HF solutions, including the NH₄F buffered HF solutions (BHF), are known to attack the Al metal layers during the oxide sacrificial etch. A mixed NH₄F/HF/glycerine aqueous solution of 4:1:2 ratio is known to have the best etch selectivity between oxide and Al, but even this sacrificial etchant has a significant etch rate for Al. This paper reports an extensive experimental study on various concentration ratios for HF, NH₄F and glycerine, and develops the optimal mixture ratio for sacrificial etching. At the NH₄F/HF/glycerine ratio of 2:1:4, the etch selectivity between PSG and Al improves by approximately 6 times over the previously known best selectivity, to a value of 7,700. At this condition, the measured etch rate of PSG film is approximately 2.1 ㎛/min, which is sufficiently fast. The developed sacrificial etchant allows the addition of a Al metal layer in surface micromachining, without the worry of Al liver erosion during sacrificial etch.
표면 미세가공에서 Al 전극 및 Al 미세 구조물 제작을 위한 습식 식각 공정
김성운(Sung Un Kim),백승준(Seung Joon Paik),이승기(Seung Kim Lee),조동일(Dong Il Cho) 한국센서학회 2000 센서학회지 Vol.9 No.3
Aluminum metal process in surface micromachining enables to fabricate Al electrodes or Al structures, which improve electrical characteristics by reducing contact- and line-resistance or makes the whole process to be simple by using oxide as sacrificial layer, However, it is not possible to use conventional sacrificial layer etching process, because HF solution attacks aluminum as well as sacrificial oxide. The mixed solution of BHF and glycerine as an alternative shows the adequate properties to meet with this end. The exact etching properties, however, are sensitively depends on the geometry of the released structure, because the most etching process of sacrificial layer proceeds to the lateral direction in narrow space. Also, the surface roughness of aluminum affects to the etching characteristics. This paper reports experimental results on the effect of microstructure and surface roughness of aluminum to the etching properties. Considering these effects, we propose the optimized etching condition, which can be used practically for the fabrication of aluminum electrodes and microstructures by using standard surface micromachining process without modification or additional process.
NH4OH - H2O2 - H2O 혼합액을 이용한 GaAs 의 습식식각 특성 연구 및 이를 이용한 부유된 시각형 단면을 가지는 GaAs 미세구조물의 제작 방법
김종팔(Jong Pal Kim),박상준(Sang Jun Park),백승준(Seung Joon Paik),김세태(Se Tae Kim),구치완(Chi Wan Koo),이승기(Seung Ki Lee),조동일(Dong Il Cho) 한국센서학회 2001 센서학회지 Vol.10 No.5
In this research, we investigate wet-etching properties of GaAs in NH₄OH-H₂O₂-H₂O, and develop the fabrication method of GaAs microstructures with rectangular cross section using (001) GaAs substrate. For obtaining wet-etching properties with respect to crystallographic orientation, the etch rates and cross-section etch profiles of (001) GaAs with 16 different compositions and the undercut rates with 5 different compositions are measured using NH₄OH-H₂O₂-H₂O mixed solutions. From these experimental data, a new GaAs micromachining method in bulk (001) GaAs is proposed, and used to fabricate a released microbridges with a rectangular cross section. The developed GaAs micromachining method can be very useful for low-less, highly-tunable capacitors for RF components and for integration with GaAs optical components.