Page 256 - Semiconductor Manufacturing Handbook

Geng(SMH)_CH17.qxd 04/04/2005 19:57 Page 17.11

CHEMICAL MECHANICAL POLISHING

CHEMICAL MECHANICAL POLISHING 17.11

using three different chemistries. Each approximately 20 in diameter polishing platen utilizes just
one carrier for polishing. Carriers on the Mirra platform are front referencing “Titan Head” pneu-
matic bladder carriers and offer better polishing performance than the dated back referencing carri-
ers offered by many competitors. Since the platens are relatively small in diameter, the multiplaten
Mirra is also a compact CMP tool. The Mirra is called a “carousel” tool. After each process step is
completed, the cross- shaped gantry that holds the polishing heads, rotates clockwise to the next pol-
ishing platen. This allows the Mirra to complete a two chemistry polishing process and post-CMP
buffing operation on each wafer. Though slower than the Auriga, the Mirra can process odd number
CMP lots without suffering from process variability. Due to the simplicity and process flexibility of
multiplaten CMP tools, they now dominate the world’s CMP market.

17.5.4 Orbital CMP Systems

Due to increasing process flexibility and productivity requirements, IPEC Inc. developed the 676
orbital CMP. This system was developed from an orbital CMP concept originally patented by Intel.
Instead of moving the polishing platen in a rotation motion, the IPEC 676 orbits the 16 to 18 in flex-
ible polishing platen (pad backer) in a 5/8 in circular pattern at high angular velocities. Instead of the
typical 24 to 90 rpm rotational speeds of the IPEC 372/472, the 676 typically uses orbit speeds of
150 to 400 rpm to generate the required linear velocities to polish wafers with a reasonable through-
put. Polishing pressure loads are similar to rotational CMP tools. In contrast to rotational CMP tools,
carrier rotational speeds for the 676 are relatively low. In addition, to improve polishing nonunifor-
mities, the polishing pad is also dithered up to 270° back and forth at very slow rate. This dithering
is called advanced pad motion (APM).
The 676 and 776 orbital CMP tools use a perforated flexible polishing platen called the pad
backer to provide polishing loads. The pad backer provides some improvement in the polishing uni-
formity since the system uses only a simple back referencing carrier with a pneumatically controlled
wear ring for edge polish rate control. In addition, since the pad backer is perforated, slurry can be
delivered directly to the wafer surface during polishing. Fluid transport to and from the wafer for this
tool is very unique, and advantageous for abrasive-free Cu CMP. Pad conditioning on the 676 and
776 platforms is completed with a long foam-backed flexible diamond abrasive strip attached to a
rigid arm. These polishing tools had up to four individual polishing modules known as micropla-
narizers, or “MPs.” Wafer buffing, post-CMP, is completed on a smaller orbital buffing unit attached
to the back of the tool. The 676 tool is of a WIWO configuration, and the 776 has an embedded wafer
cleaner allowing for DIDO operation.
SpeedFAM and IPEC merged in the late 1990s to create Speedfam-IPEC. The combined compa-
nies revolutionized the performance of the orbital platform. The main changes made to the 776 were
stiffening the pad backer, improving the control system, and replacing the back referencing carrier
with a multizone front referencing carrier. This new hardware combination dramatically improved
the process performance of the 776 platform. This new platform is known as the Momentum tool,
and offers true 1 mm edge exclusion polishing control, dynamic polishing uniformity adjustment,
and DIDO operation. Speedfam-IPEC is now a part of Novellus Inc., who offers the tool to this day.
During the late 90s, Obsidian Inc. introduced a competitor orbital polishing tool to the 776. This
tool uses an orbiting carrier head, unlike the Momentum’s orbiting platen, to generate linear veloci-
ties required for reasonable productivity. The Obsidian tool was a web-based tool, using a flexible
fixed abrasive pad for oxide CMP. Made by 3M Inc., this “web” pad offers a superior planarization
performance to standard IC1000/SUBA IV pad polishing processes that utilize silica-based slurries.
Process development is tricky using the ceria-based 3M pad, since wafer patterns can change mate-
rial removal rates. Blanket PETEOS or steam oxide silica films are poorly polished by the 3M fixed
abrasive pad. Applied Materials purchased and absorbed Obsidian in the early 2000s.

17.5.5 Linear Drive CMP Tools

Lastly, linear CMP tools were developed to provide very high and uniform linear velocities for
CMP. These tools work analogous to a belt sander where the polishing pad is mounted to a track

Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com)
Copyright © 2004 The McGraw-Hill Companies. All rights reserved.
Any use is subject to the Terms of Use as given at the website.