Slurry Utilization Efficiency Studies in Chemical Mechanical Planarization
- PDF / 92,490 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 27 Downloads / 219 Views
F1.4.1
Slurry Utilization Efficiency Studies in Chemical Mechanical Planarization Ara Philipossian and Erin Mitchell Department of Chemical and Environmental Engineering The University of Arizona Tucson, AZ 85721 USA ABSTRACT The residence time distribution of slurry in the pad-wafer interface was experimentally determined and used to calculate the slurry utilization efficiency (η) of the CMP process. Slurry utilization efficiency represents the percentage of slurry that actually participates in the polish by entering the region bounded between the wafer and the pad. Results show that η ranges from 2 to 22 percent, depending on operating conditions such as applied wafer pressure, relative pad wafer velocity, slurry flow rate and pad surface texture (i.e. type of pad grooving). INTRODUCTION Literature states the importance of slurry presence in the wafer-pad region [1-3], however, little has been published on the subject. For certain processes, slurry cost represents almost half of the total cost of ownership of the entire CMP operation [4], and the notion that a significant portion of this slurry may be wasted lends importance to understanding and optimizing this process parameter. Mean residence time (MRT) analysis as a function of slurry flow rate has shown that not all of the slurry introduced onto the pad actually participates in the polish process [5]. By employing classical reactor design theory and residence time distribution (RTD) techniques, this study provides insight into optimum consumables and operating parameters for maximizing slurry utilization efficiency and minimizing slurry use. APPARATUS A fully automated scaled version of a Speedfam-IPEC 472 polisher was used in this study. The polisher resides on a sliding table that measures the frictional force in the pad-slurry-wafer interface. The friction table is synchronized to the polisher such that real-time friction data – crucial for carrying out RTD experiments – can be obtained. For any given run, the coefficient of friction (COF) is determined by taking the ratio of shear force to normal force. The apparatus and the method of obtaining COF are described in detail elsewhere [5]. THEORY Slurry utilization efficiency (η) can be expressed as:
η=
q actual × 100% qtotal
In Eq. 1, qactual is the slurry flow rate beneath the wafer, and qtotal is the total flow rate of the slurry introduced onto the pad. While qtotal is a known entity for a given process, the value of qactual must be found experimentally. For a closed flow system, flow rate in the reactor is equal to the ratio of reactor volume to the mean residence time of the fluid:
Downloaded from https://www.cambridge.org/core. Columbia University - Law Library, on 02 Sep 2019 at 03:20:00, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1557/PROC-767-F1.4
(1)
F1.4.2
q actual =
V (2)
τ
In the case of CMP, the reactor volume is approximately equal to the slurry holding capacity of the pad as it contacts the wafer. The latter ca
Data Loading...
