The Slope Etching of a-Si:H Film using CF 4 + O 2 Gas
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THE SLOPE ETCHING OF a-Si:H FILM USING CF4
KANG HYUN SUNG, B.W.PARK, J.J.KIN, C.Y.KIN, J.I.CHOI, C.W.HUR. GoldStar Central Research Laboratory, Seoul, Korea.
+
02 GAS
H.K.BAE,
Y.H.PARK AND
ABSTRACT The slope etching technology of hydrogenated amorphous silicon film (a-Si:H) has been very useful for its devices; thin film transistor, contact To obtain a good image sensor and other large area electronic components. step coverage slope etching was performed by RIE using CF4 gas and optimum amount of 02 gas after modification of photoresist(PR) patterns by thermal In this experiment, primary factors were treatment. 1) thermal treatment temperature and time of PR, 2) CF4 gas flow rate, etch rate of a-Si:H film and ash rate of PR in proportion to 02 gas flow rate. As a result, the slope angle of 110 was obtained when CF4 gas flow rate was 46 SCCM, 02 gas flow rate was 7 SCCM and thermal treatment temperature 0 and time was 140 C and 30 minutes respectively.
INTRODUCTION Reactive ion etching (RIE) [1] [2] has become an important technology in the fabrication of integrated circuits because it offers a number of The most important important advantages over wet chemical etching. As the advantage of RIE is that the etching can be anisotropic [3]. minimum geometry features are reduced from the current 2-4 microns to the However, the submicron region, anisotropic etching will be essential. deposited thin film over the step performed by RIE did not show the good step coverage because of following reasons. 1) A film, deposited over isolated step, had different thickness at the vertical and the horizontal surfaces. 2) When a film was deposited over two steps close together, the deposited materials at the bottom of the step was thin and a concave or retrograde profile was formed, so deposited materials did not cover these retrograde profiles. 3) When a film was deposited over narrow space a large void which may be exposed during subsequent etching remained even if the gap was covered by Above-mentioned films had a fast-etching region along the deposition. the steps, with the vertical walls etching as much as 40% faster than the horizontal surface. This might result from different amounts of ion A fast-etching bombardment on the two surfaces during deposition [6]. region along the bottom of the steps was also observed and this might result from localized structural defects where the vertical and horizontal surfaces met.
Mat. Res. Soc. Symp. Proc. Vol. 219. 01991 Materials Research Society
812
To overcome these problems slope etching of the a-Si:H film applied in TFT, image sensor fabrication was used and this technique solved the step coverage.
EXPERIMENT First, the glass substrate was cleaned by neutral cleaner before RCA (the name of company radio corporation of America) cleaning. Ultrasonic cleaning was then perforLked using TCE (Trichloroethylene), acetone, alcohol and deionized water before compressed air blowing and baking to remove moisture. After the glass substrate was loaded in PECVD chamber, the vacuum state o
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