Abrading – Abrading process – Glass or stone abrading
Reexamination Certificate
2001-08-31
2003-10-28
Rachuba, M. (Department: 3723)
Abrading
Abrading process
Glass or stone abrading
C451S036000, C451S037000, C451S057000, C134S003000
Reexamination Certificate
active
06638145
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present inventions pertain to semiconductor fabrication processing. More particularly, the present inventions relate to a system for reducing defectivity during semiconductor processing by maintaining a constant pH during the planarization process.
2. Description of the Prior Art
Referring now to
FIGS. 1 and 2
, there is shown a block diagram of a prior art CMP machine
100
and a side partial perspective view of a wafer
105
(FIG.
2
). The CMP machine
100
is fed wafers to be polished by an arm
101
and places them onto a rotating polishing pad
102
. The polishing pad
102
is made of a resilient material and is textured, often with a plurality of predetermined grooves, to aid the polishing process. A conditioning arm
103
conditions the polishing pad.
The polishing pad
102
rotates on a platen
104
, a turntable located beneath the polishing pad
102
, at a predetermined speed. A wafer is held in place on the polishing pad
102
and the arm
101
by a carrier ring and a carrier film not shown. The lower surface of the wafer
105
rests against the polishing pad
102
. The upper surface of the wafer
105
is against the lower surface of the carrier film of the arm
101
. As the polishing pad
102
rotates, the arm
101
rotates the wafer
105
at a predetermined rate. The arm
101
forces the wafer
105
into the polishing pad
102
with a predetermined amount of down force. The CMP machine
100
also includes a slurry dispense tube
107
, extending across the radius of the polishing pad
102
. The slurry dispense tube
107
dispenses a flow of slurry
106
onto the polishing pad
102
from the slurry source
112
. The slurry
106
is a mixture of deionized water and polishing agents designed to aid chemically the smooth and predictable planarization of the wafer. In a system using silica slurry the pH of the slurry is very high, typically having a pH of around 10 or 11.
The rotating action of both the polishing pad
102
and the wafer
105
, in conjunction with the polishing action of the slurry, combine to planarize, or polish, the wafer
105
at some nominal rate. The polishing action of the slurry is comprised of an abrasive frictional component and a chemical component. The abrasive frictional component is due to the friction between the surface of the polishing pad, the surface of the wafer, and abrasive particles suspended in the slurry. The chemical component is due to the presence in the slurry of polishing agents which chemically interact with the material of the dielectric or metal layer of the wafer. The chemical component of the slurry is used to soften the surface of the dielectric layer to be polished, while the frictional component removes material from the surface of the wafer.
Slurry dispense termination is accomplished by turning off a pump, which will stop the flow of slurry onto the pad. After the slurry dispense process is terminated, deionized water having a pH of about 6 is dispensed from the deionized water source
110
via the water dispense tube
108
onto the pad. The wafer substrate is then rid of the slurry, and the pH at the surface of the wafer is lowered to a pH of about 6.
A typical chemical mechanical polish cycle includes two or more linear or rotary tables that do the planarizing and then a third table that does a water buff on a softer pad. During the chemical mechanical planarization (CMP) process, a wafer undergoes many pH changes. Slurry is used to first polish the wafer and then dionized water is used to clean the wafer afterwards. The pH is raised during the polish steps, then lowered by deionized water whenever the wafer is to be kept wet. At post-CMP cleans, the pH is also raised for cleaning then lowered as the wafer is rinsed and dried. This amounts to many fluctuations between a pH of approximately 11 and a pH of approximately 6.
Referring now to
FIG. 3
, there is shown a block diagram of one example of a prior art typical CMP process
200
. To prevent slurry from drying on the wafer, the wafer surface is kept wet through-out the clean-up process. A wet transfer input station mechanism
210
is used to load and unload the wafers while keeping the surface of the wafer wet with deionized water. The wafer
105
is then transferred to polishing platen
220
, where a high pH slurry polish is followed by an automatic rinse of deionized water, once the polish is complete. The wafer is then transferred to secondary polishing platen
230
, where a second high pH slurry polish is again followed by a deionized water rinse, when the secondary polish is complete. Typically, the wafer is transferred to a third, softer platen
240
, where the wafer is buffed on the pad while deionized water is sprayed on the pad. Typically, the above three platens,
220
,
230
and
240
are included on the same multiple platen CMP machine
205
.
The wafer
105
is then unloaded and kept wet using the input station mechanism
210
. Then, optionally, the wafer
105
may be transferred to brush stations
250
and
255
, where the wafer is brushed with a scrub solution spray having a pH similar to that of the slurry, such as dilute ammonia, or NH
4
OH. Finally, the wafer
105
is transferred to the drying station
260
, where it is rinsed with deionized water and dryed.
FIG. 4
is a table showing the pH level of the wafer surface at the end of each polishing step of the system
200
of FIG.
3
. Note that the pH at the surface of the wafer fluctuates numerous times between a pH of approximately 11 and a pH of approximately 6, during the CMP process.
All particulate matter develops an electrically charged thin layer when suspended in a liquid solution. This charge is known as the zeta potential and can be either negative or positive. The zeta potential appears at the outer surface of the particle such that the particle is surrounded by a small charge field. Silica particles in a basic aqueous solution having a pH of about 10 or more results in a negative zeta potential on the silica particles. In addition, the zeta potential of any other particles present, as well as that of the surfaces contacted by the solution, is negative at such a high pH. The silica particles are thus electrostatically repelled from the semiconductor wafer facilitating the removal of the slurry residue from the wafer surface. When the pH at the surface of the wafer is lowered in the presence of silica particles, colloids form and silica agglomeration occurs on the surface of the wafer. As such, any time the pH of the wafer surface is lowered, a higher defectivity environment exists in the presence of microscopic particles. Defects generated include scratches on the wafer by slurry abrasive agglomerates and slurry abrasive (or any other particle) attaching to the wafer surface.
What is needed is a method for providing a constant, high pH through the entire CMP polish and clean process to minimize slurry abrasive agglomeration and fluctuations of pH.
This object, and others, is satisfied by Applicant's present inventions disclosed herebelow.
SUMMARY OF THE INVENTIONS
The present inventions are directed a system and method for chemical mechanical planarization with reduced defects. A high pH is maintained at the wafer surface through the entire polish process and only lowered when necessary in a controlled fashion after CMP and during the post-polish clean. The system includes a wafer input/output area including a wet transfer mechanism for transferring a first wafer to a first polishing platen and to a second polishing platen while keeping the wafer wetted with a high pH solution. A first polishing platen including a first high pH slurry source and a first high pH solution rinse source is used to polish and rinse the wafer surface. A second polishing platen performs a second polish on the wafer using a second high pH slurry source and a second high pH solution rinse source. The number of defects at the surface of the wafer is reduced as the pH at the wafer surface is maintained substantially constant during processing and,
Black Andrew J.
Hall Stacy W.
Koninklijke Philips Electronics , N.V.
Rachuba M.
Zawilski Peter
LandOfFree
Constant pH polish and scrub does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Constant pH polish and scrub, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Constant pH polish and scrub will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3160527