Abrading – Abrading process – Glass or stone abrading
Reexamination Certificate
2001-10-19
2004-09-14
Rachuba, M (Department: 3723)
Abrading
Abrading process
Glass or stone abrading
C451S060000, C451S287000, C451S289000
Reexamination Certificate
active
06790127
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to slurry feeding apparatus and method for use in a chemical/mechanical polishing (CMP) process of a wafer.
In recent years, the surface of a semiconductor wafer is often planarized by a CMP technique to ensure sufficient uniformity for an interlevel dielectric film, for example, during the manufacturing process of transistors on the substrate. The CMP process is performed using a kind of slurry, where fumed or colloidal silica is dispersed as abrasive grains in an alkaline solution of ammonium, for example.
FIG. 8
illustrates a cross section of a known (polishing) slurry feeding apparatus F
1
as disclosed in Japanese Laid-Open Publication No. 10-15822.
As shown in
FIG. 8
, the slurry feeding apparatus F
1
includes tank
101
, delivery pipe
102
with a pump
104
, flow rate control valve
103
, feeding nozzle
110
and stirrer
106
. Polishing slurry
109
is stored in the tank
101
and delivered through the delivery pipe
102
from the tank
101
to a CMP polisher (not shown). The flow rate control valve
103
is provided in the middle of the pipe
102
downstream of the pump
104
. The feeding nozzle
110
is attached to the end of the pipe
102
for dripping the slurry
109
onto a polishing pad (not shown) of the polisher. And the stirrer
106
with a propeller is used for stirring the slurry
109
. A circulation pipe
105
is further provided as a branch from the delivery pipe
102
upstream of the valve
103
to circulate the slurry
109
by feeding the slurry
109
back to the tank
101
therethrough. A heater
107
is further provided on the bottom of the tank
101
to regulate the temperature of the slurry
109
within the tank
101
. The temperature of the heater
107
is in turn regulated by a heater temperature controller
108
. In polishing a wafer, the opening of the valve
103
is adjusted and a predetermined amount of the slurry
109
is sucked up from the tank
101
using the pump
104
and then dripped onto the polishing pad through the feeding nozzle
110
. The remainder of the slurry
109
is recovered to the tank
101
through the circulation pipe
105
. On the other hand, while the polishing process is not performed, the valve
103
is closed and all the slurry
109
is recovered to the tank
101
, thereby circulating the slurry
109
without delivering it.
As for colloidal silica, the primary grains thereof have a tiny size of 20 to 30 nm. But in the polishing slurry
109
, a certain number of primary silica grains coagulate to form secondary grains with a size of 100 to 200 nm. As for fumed silica on the other hand, the grain size thereof is 100 to 200 nm from the beginning (i.e., when they are prepared). Thus, it is generally believed that these secondary grains with a grain size of 100 to 200 nm actually contribute to the polishing process.
Nevertheless, if an excessive number of abrasive grains coagulate together to form grains with a size as large as about 500 nm or more, then micro-scratches are possibly made on the object being polished.
Thus, the conventional slurry feeding apparatus F
1
always circulates the polishing slurry
109
and stirs the slurry
109
up with the propeller, thereby suppressing the sedimentation and coagulation of the abrasive grains in the slurry
109
.
FIG. 10
illustrates a cross section of a coupling generally provided for the piping where the slurry flows in a conventional slurry feeding apparatus. By using couplings in various shapes for the corner or linear portions, piping can be formed in a complicated shape and the cross-sectional area of the piping and the overall size of the slurry feeding apparatus can be both reduced.
It is known that the excessively promoted coagulation of the abrasive grains (e.g., with a grain size of more than about 500 nm) not only causes micro-scratches on the object being polished but also decreases the polishing rate.
FIG. 9
is a graph illustrating, in comparison, respective polishing rates of Slurry
1
and
2
with mutually different concentrations of solid content (abrasive grains) in accordance with results of experiments carried out by the present inventors. As can be seen from
FIG. 9
, although the solid content concentration of Slurry
1
is only 1% lower than that of Slurry
2
, the polishing rate attained by Slurry
1
is considerably lower than that attained by Slurry
2
. Such a decrease in solid content concentration could result from the sedimentation of abrasive grains with an excessively increased size in the tank. Accordingly, it is critical to prevent the size of abrasive grains from increasing excessively in order to obtain an appropriate polishing rate.
To suppress the coagulation of abrasive grains, the conventional slurry feeding apparatus has the following draw-backs.
Firstly, the increase in size of abrasive grains in the slurry
109
cannot be suppressed sufficiently only by stirring the the slurry
109
up using the stirrer
106
with a propeller as shown in FIG.
8
.
Secondly, the slurry
109
is likely to form puddles here and there in the regions Rg of the coupling where two pipes of the piping are joined together in the slurry feeding apparatus F
1
. This is because there are many gaps and level differences between these pipes in the region Rg as shown in FIG.
10
. As a result, the excessive coagulation of the abrasive grains is possibly promoted.
Thirdly, the solidified contents of the slurry
109
are likely to deposit on the inner walls of the tank
101
as the level of the slurry solution changes in the tank
101
. And the solidified slurry
109
once deposited will collapse within the tank
101
to increase the size of the grains coagulated.
Since the size of the abrasive grains is excessively increased in this manner, the micro-scratches are made on the object being polished and the polishing rate thereof decreases or becomes inconstant.
SUMMARY OF THE INVENTION
An object of the present invention is reducing the number of micro-scratches made on the object being polished and attaining an intended polishing rate by suppressing the excessive increase in size of the abrasive grains. Exemplary measures include: improving slurry stirring and circulating methods; eliminating gaps and level differences from the inside of piping; and preventing the solidified slurry from being deposited on the inner walls of the tank.
A first exemplary slurry feeding apparatus according to the present invention is adapted to feed polishing slurry to a chemical/mechanical polisher. The apparatus includes: a container for storing the slurry therein; a first nozzle for sucking the slurry up from the container; a second nozzle for recovering the slurry back to the container; a third nozzle for dripping the slurry in the polisher; a first pipe, which is connected to the first and third nozzles for delivering the slurry to the polisher; a second pipe, which is connected to the second nozzle and the first pipe for bypassing at least part of the slurry flowing through the first pipe from the third nozzle and then recovering that part of the slurry back to the second nozzle; a control valve for regulating the flow rate of the slurry, which is now flowing through the first pipe and will be supplied to the third nozzle and the second pipe; a pump, which is provided for at least one of the first and second pipes for making the slurry flow with a pressure applied; and control means for operating the pump continuously while the polisher is operating and intermittently while the polisher is idling.
According to the first apparatus, it is possible to minimize the number of excessively large-sized abrasive grains, which usually result from their collision in the slurry due to the pressure applied from a pump.
A second exemplary slurry feeding apparatus is also adapted to feed polishing slurry to a chemical/mechanical polisher. The apparatus includes: a container for storing the slurry therein; a first nozzle for sucking the slurry up from the container; a second nozzle for recovering the slurry back to the container; a third
Hashimoto Shin
Hidaka Yoshiharu
Tanoue Akihiro
Matsushita Electric - Industrial Co., Ltd.
Nixon & Peabody LLP
Rachuba M
Studebaker Donald R.
LandOfFree
Apparatus and method for feeding slurry does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Apparatus and method for feeding slurry, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Apparatus and method for feeding slurry will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3261536