Abrading – Abrading process – Utilizing fluent abradant
Reexamination Certificate
2001-08-31
2003-07-01
Eley, Timothy V. (Department: 3723)
Abrading
Abrading process
Utilizing fluent abradant
C451S053000, C451S057000, C451S059000
Reexamination Certificate
active
06585567
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 and method for reducing defects during short polishes of semiconductor wafers by raising the pH of the wafer surface in the presence of abrasives.
2. Description of the Prior Art
Currently semiconductor wafers are reworked on a regular basis. Wafers are reworked when the final thickness of the wafer after the polish is too thick to send on to the next step in the line. The causes of a wafer being underpolished are tool interruptions, incorrect process recipes, improper tool setup and bad consumables.
Wafer rework recipes are typically shortened wafer polishing product recipes. Rework recipes, like polish recipes, typically include two or more linear or rotary tables that do the planarizing and a third table that does a water buff on a softer pad.
Referring now to
FIGS. 1 and 2
, there is shown a block diagram of a CMP machine
100
including a rotary process table 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. A wafer is held in place on the polishing pad
102
by the arm
101
with a predetermined amount of down force.
During polishing, the lower surface of the wafer
105
rests against the polishing pad
102
. As the polishing pad
102
rotates, the arm
101
rotates the wafer
105
at a predetermined rate. 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
. Typically, the polishing pad
102
is primed with slurry
106
for about 8 seconds. The slurry
106
is a mixture of deionized water and polishing agents designed to aid chemically the smooth and predictable planarization of the wafer. 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. In current systems using silica slurry the pH of the slurry is very high, typically having a pH of around 10 or 11.
After the slurry dispense process is terminated, deionized water 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.
Referring now to
FIG. 3
, there is shown a block diagram of one example of a CMP process
200
which is typically used to rework wafers having a final thickness too thick to send on to the next step in the line. Input/output station mechanism
210
is used to load and unload the wafers and to transfer the wafer 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. The wafer is then transferred to a third, softer pad, where it is buffed with deionized water. The above three platens are included on the same multiple platen CMP machine
205
. The processing that occurs on the platens defined by CMP machine
205
is referred to herein collectively as the “CMP polish processing”.
The wafer
105
may then be then unloaded manually or may be unloaded using the input station mechanism
210
. The wafer then undergoes post CMP cleaning. If desired, the wafer
105
may be transferred to brush stations
250
and/or
255
where the wafer is brushed with a scrub solution spray which, typically, has a high pH. Finally, the wafer
105
is transferred to the spin rinse and dry station
260
, where the wafer is rinsed with deionized water and then dried. The processing that occurs at the brush stations and the drying station
260
is referred to herein collectively as the “post-CMP polish processing”.
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 a small charge field surrounds the particle. 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. If the pH of the liquid in contact with the wafer surface is not maintained at a high pH, the combination of downforce and abrasive particles will lead to high defects.
Three conditions are theoretically necessary to leave behind slurry residues, pits, and scratches on the wafer surfaces. First, there must be colloidal particles present on the wafer surface. These particles are the source of residual particles on the wafer surface, they are the same particles that can agglomerate and cause microscratches and oxide pit defects. Second, high downforce is necessary to overcome the energy barrier between a colloid (abrasive particle) and the wafer surface. Both electrical repulsion and Van der Waals attraction combine to create the net energy barrier between the wafer surface and the colloid. Third, in a silica based slurry system low pH reduces the electrical repulsion between the colloidal particles and makes the possibility of overcoming the energy barrier between the wafer surface and the colloidal particles more likely. Once the energy barrier is overcome, three types of destructive phenomenon can theoretically occur. First, colloidal particles begin to agglomerate. Second, colloidal particles and/or agglomerates of colloidal particles attach to the wafer surface. Third, larger agglomerates of colloidal particles scratch or pit the wafer surface, but do not adhere to the wafer surface.
Currently used short polish methods do not add defects when the polish time on each platen is greater then twenty seconds. However, when the planarization or oxide removal time on each platen decreases to less than about 15 seconds per platen, defects, especially slurry residues, become an issue. This minimum amount of total polish time forces a minimum film removal allowed for a short polish or rework. This minimum film removal is sometimes more than the final thickness specifications allow. The limitations of short polishes then, create a tradeoff between correct final wafer thickness and low post-CMP defectivity.
Referring now to
FIG. 4
, there is shown a first polishing platen
220
and a second polishing platen
230
, such as those of FIG.
3
. Once the slurry polish is completed on platen
220
, the wafer
410
is kept wet with deionized water until the wafer
415
on platen
230
is finished being processed. Deionized water on platen
220
is carried on the surface of wafer
410
to platen
230
. After the end-of-polish clean of wafer
415
is completed on platen
230
, the platen
230
is primed with slurry, typically for abou
Black Andrew J.
Deen Allison
Grant Alvin J
Zawilski Peter
LandOfFree
Short CMP polish method does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Short CMP polish method, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Short CMP polish method will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3023913