AVS 46th International Symposium
    Plasma Science and Technology Division Wednesday Sessions
       Session PS-WeA

Paper PS-WeA9
A Mechanism of Oxide to Nitride Selective RIE

Wednesday, October 27, 1999, 4:40 pm, Room 609

Session: Dielectric Etching
Presenter: T. Sakai, Toshiba Corporation Semiconductor Company, Japan
Authors: T. Sakai, Toshiba Corporation Semiconductor Company, Japan
T. Ohiwa, Toshiba Corporation Semiconductor Company, Japan
Correspondent: Click to Email
In highly integrated ULSIs, selective etching of oxide to nitride has been widely used for Self-Aligned Contact (SAC) etching to increase the packing factor. It is known that the CF@sub x@ polymer formed selectively on the nitride surface suppresses Si@sub 3@N@sub 4@ etching. However the origin of selective CF@sub x@ polymer formation is not understood well. We studied the mechanism of oxide to nitride selective etching with focus on selective polymer formation. In CHF@sub 3@-based chemistry, the oxide etch rate decreased slightly from 540 nm/min to 470 nm/min when the cathode temperature was increased from RT to 120 °C. On the contrary, the nitride etch rate decreased abruptly from 720 nm/min at RT to 220 nm/min at 60 °C. XPS analysis showed CF@sub x@ polymer formation on nitride at 60 °C, but no CF@sub x@ polymer at RT. Increase of temperature increases the C/F ratio of the adsorbed species on the surface, therefore CF@sub x@ polymer formation is considered to be enhanced on nitride. Following this result, the temperature in actual SAC etching using C@sub 4@F@sub 8@/CO/Ar chemistry was increased from 20 °C to 70 °C, and the selectivity at the corner of nitride increased from 10 to 18. Further surface analysis of the nitride surface etched in C@sub 4@F@sub 8@/CO/Ar chemistry at 70 °C revealed that the etched nitride surface has C-N bonds. At low temperature, the nitride etching reaction forms volatile etching products of SiF@sub 4@, CFN, C@sub 2@N@sub 2@ and etc., leading to no CF@sub x@ polymer formation similar to oxide. However, at the higher temperature, the higher C concentration of adsorbed species on the nitride surface suppresses the formation of volatile CFN, resulting in remaining of CN compounds, and forms CF@sub x@ polymer. CO, which is the etching product in oxide etching, has a much higher vapor pressure compared to CN compounds. So a difference of CF@sub x@ polymer formation arises between the oxide surface and the nitride surface, resulting in selective etching of oxide to nitride.