AVS 51st International Symposium
    Plasma Science and Technology Monday Sessions
       Session PS1-MoM

Paper PS1-MoM7
Minimizing low-k Damage during In-situ Photoresist Strip

Monday, November 15, 2004, 10:20 am, Room 213A

Session: Low-k Dielectric Etching
Presenter: E.A. Hudson, Lam Research Corp.
Authors: E.A. Hudson, Lam Research Corp.
T. Choi, Lam Research Corp.
O. Turmel, Lam Research Corp.
L. Zheng, Lam Research Corp.
K. Takeshita, Lam Research Corp.
S. Lee, Lam Research Corp.
P. Cirigliano, Lam Research Corp.
Correspondent: Click to Email
To increase the speed of devices, microelectronics fabrication is shifting to low-k dielectric materials as insulators for interconnect layers. k values may be reduced below ~3.0 using carbon-doped materials such as organosilicate glass (OSG). k is further reduced, below ~2.5, by introducing pores in the film. Problems may arise, however, because carbon is easily removed from these materials during plasma processing, specifically during the etching of lines and vias, and the photoresist strip after etch. Carbon loss causes an increase in the dielectric constant and thus degrades device performance. This paper focuses on the damage trends for carbon-doped dielectrics arising from in-situ photoresist strip in a capacitively-coupled dielectric etch system. Microscopic test structures have been developed, which allow direct measurement of the intrinsic damage which results from the interaction of the plasma strip environment with the unprotected and unmodified sidewall of a trench. Damage trends have been evaluated as a function of pressure and frequency of RF excitation during the strip. Damage is minimized for pressures in the 10 - 50 mTorr range. Etch processes typically leave a polymer coating on the sidewall of trenches and vias. This sidewall passivation is found to greatly reduce the low-k damage induced by the strip process. Ultimately the polymer must be removed from the sidewall to allow subsequent fabrication steps, but during the strip this film acts as a protective barrier against low-k damage. Therefore an overall strategy for minimizing damage is to run a low pressure strip, under conditions which preserve sidewall passivation as long as possible.