Fh. Bell et O. Joubert, POLYSILICON GATE ETCHING IN HIGH-DENSITY PLASMAS .4. COMPARISON OF PHOTORESIST AND OXIDE MASKED POLYSILICON ETCHING-THICKNESS DETERMINATIONOF GATE OXIDE LAYERS USING X-RAY PHOTOELECTRON-SPECTROSCOPY, Journal of vacuum science & technology. B, Microelectronics and nanometer structures processing, measurement and phenomena, 14(6), 1996, pp. 3473-3482
The characteristics of oxide and photoresist masked polysilicon trench
etching has been studied by real-time HeNe laser ellipsometry and qua
si in situ x-ray photoelectron spectroscopy (XPS). Poly-Si films on Si
O2-covered Si (100) substrates were masked either with a 1-mu m-thick
photoresist or a 200-nm-thick oxide hard mask. The 200-mm-diam wafers
were etched downstream in a helicon high density plasma source using a
chlorine-based gas chemistry. When using an oxide hard mask instead o
f a photoresist mask, the selectivity of polysilicon over oxide was im
proved by a factor greater than 3. A new approach to the surface chara
cterization of semiconductor submicron structures by XPS is presented.
Photoelectron signals originating from the gate oxide him and the und
erlying silicon substrate were measured in regular arrays of trenches.
The ratio between the SiO2 peak area of the gate oxide film and the S
i 2p peak area of the silicon substrate was correlated with the thickn
ess of the SiO2 film. The thickness determined was obtained by calibra
ting peak area ratios with oxide thickness measurements using spectros
copic ellipsometry. Consequently, the gate oxide thicknesses derived f
rom the area ratios were calculated in patterned areas after etching o
f photoresist and oxide hard masked polysilicon features as a function
of the aspect ratio of the features and mask coverage on the wafer. I
f was found that the gate oxide consumption is enhanced in high aspect
ratio features masked with photoresist as well as in areas with high
photoresist coverage; the carbon coverage on the gate oxide film was f
ound to scale with the increased gate oxide etching in the small featu
res. Similar effects were not observed with the oxide masked sample. (
C) 1996 American Vacuum Society.