AVS 45th International Symposium
    Plasma Science and Technology Division Tuesday Sessions
       Session PS2-TuM

Paper PS2-TuM11
Control of Profile in High Aspect Ratio Contact and Via Etch

Tuesday, November 3, 1998, 11:40 am, Room 318/319/320

Session: Oxide Etching
Presenter: C.H. Bjorkman, Applied Materials, Inc.
Authors: C.H. Bjorkman, Applied Materials, Inc.
K. Doan, Applied Materials, Inc.
J. Wang, Applied Materials, Inc.
B. Pu, Applied Materials, Inc.
H. Shan, Applied Materials, Inc.
N. Kuo, Applied Materials, Taiwan
P. Chang, Applied Materials, Taiwan
Correspondent: Click to Email
The purpose of this study was to investigate which parameters control the profile in high aspect ratio (HAR) dielectric etch. Holes with aspect ratios in the range 6:1 - 10:1 were etched in a low-to-medium density MERIE etch chamber. A common observation among the fluorocarbon chemistries we investigated was the variation in profile angle from the top to the bottom of the hole. For example, the profile of a close to optimized single step chemistry starts off with a taper angle of 86-87°. After reaching an aspect ratio of approximately 3:1, the profile starts to straighten out. However, this trend is reversed as endpoint is approached. Typically, the taper angle at the bottom of the hole is approximately the same as what we observe at the top of the hole. This tapered bottom profile tends to decrease the CD (critical dimension) with a resulting increase in contact resistance. We divided the profiles into three components in order to quantitatively analyze our results: (1) any flaring and/or necking observed in top portion of the hole, (2) bowing or taper in the center portion and (3) excessive tapering and/or rounding of the bottom of the hole. We found that any initial tapering will remain and thus give rise to flaring at the top of hole. This can be prevented by minimizing polymer deposition on the sidewalls during the first third of the etch. We achieved this by making the chemistry leaner, raising the pressure and raising the wafer temperature. Controlling the profile during the second portion of the etch turns out to be a compromise between preventing bowing and maintaining a large bottom CD. The main parameter controlling this portion of the etch was determined to be the pressure. As for the last portion of the etch, the tendency to taper and thus reduce bottom CD was found to be controlled by the DC-bias. We obtained a straighter profile by decreasing both pressure and B-field and thus increasing the DC-bias.