Slurry useful for wire-saw slicing and evaluation of slurry

Details Slurry useful for wire-saw slicing and evaluation of slurry Slurry useful for wire-saw slicing and evaluation of slurry

2000-08-11

2002-07-23

Williams, Herzon (Department: 2856)

Measuring and testing

Liquid analysis or analysis of the suspension of solids in a...

Viscosity

C073S007000, C125S021000, C083S307100

Reexamination Certificate

active

06422067

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to slurry useful for wire-saw slicing a silicon ingot, a compound semiconductor block, a quartz block or the like, and also-relates to a method of evaluating such slurry.
2. Brief Description of the Prior Art
After top and tail parts are cut off a silicon ingot produced by a pulling method or the like, the silicon ingot is processed in the steps of outer diameter grinding, orientation flat processing, etc., and then sliced to wafers of a predetermined thickness. Although a slicer equipped with an inner blade has been used so far for slicing the ingot, a wire-sawing machine using a piano wire is used for slicing a big-size ingot.
As shown in
FIG. 1
, a conventional wire-sawing machine has generally three grooved rollers
1
-
3
, one of which is coupled to a driving motor
4
. A wire
5
is pulled out of a wire reel
6
, wound several times around the grooved rollers
1
-
3
, and led to another wire reel
7
. A tension is applied to the wire
5
by a tensioner
8
, so that the wire
5
travels in a stretched state around the grooved rollers
1
-
3
.
An ingot
9
to be sliced is mounted to a holder
10
using a mounting jig located between the grooved rollers
1
and
2
. The ingot
9
is sliced to a plurality of wafers by the wire
5
. During slicing, slurry
11
is supplied to the wire
5
so as to facilitate slicing motion. The slurry
11
is fed from a slurry tank
12
through a supply pipe
13
and a nozzle
14
to the wire
5
, recovered in a pan
15
, and then returned to the slurry tank
12
. The slurry
11
is circulated between the slurry tank
12
and a heat exchanger
16
, in order to cool the slurry
11
.
Such the slurry
11
is fed to inner parts of the ingot
9
in the state that grits are uniformly dispersed in a coolant, in order to slice the ingot
9
to a plurality of wafers with the wire
5
. It is also an important factor that the grit-dispersing state is stable enough to avoid fluctuation of slicing conditions. In addition, the slurry
11
remaining on wafers cut off the ingot
9
shall be easily removed away from surfaces of the wafers.
Such slurry for wire-saw slicing is merely evaluated by viscosity, specific gravity and a pH value. The viscosity is commonly measured by a axial cylinder type viscometer
30
(Type-B viscometer) as shown in FIG.
2
. An inner cylinder
31
, which is hung from a stator
34
with a metal rod
33
, is concentrically located in a vessel
32
(an outer cylinder). Sample slurry S is poured in a space between the inner cylinder
31
and the outer cylinder
32
, and the outer cylinder
32
is rotated at a predetermined rotation speed. A force, which is corresponding to viscosity of the sample slurry S and along the rotating direction of the outer cylinder
32
, is applied to the inner cylinder
31
by the rotating motion of the outer cylinder
32
. Due to the force, a torsional moment (a torque) is applied to the metal rod
33
. A scale disc
35
provided at the metal rod
33
is rotated in proportional to the torsion value. The viscosity of the sample slurry S is judged by reading a rotation angle of the scale disc.
Specific gravity is measured by a float balance-type hydrometer. A pH value is measured by an electrode-type pH meter.
Properties measured in these ways do not accurately represent an actual state of the slurry
11
which is being used for wire-saw slicing the ingot
9
, so that slicing performance can not be forecast from those properties. Use of improper slurry sometimes causes various defects such as breakdown of the wire
5
, damage of wafers, sticking of wafers cut off the ingot
9
and accumulation of the slurry
11
in the wire-sawing machine. In this regard, the slurry is evaluated by an actual ingot-slicing test. However, the test for researching ingot-slicing conditions needs plenty of time and cost. Such the troublesome test shall be avoided accounting the tendency that the ingot
9
is bigger and bigger in diameter.
SUMMARY OF THE INVENTION
The present invention is accomplished for elimination of the aforementioned problems and aims at a slurry suitable for wire-saw slicing without necessity of an ingot-slicing test by measuring flow characteristics (rheology) of slurry effective for ingot-slicing.
According to the present invention, slurry for slicing an ingot is evaluated by measuring viscosity of the slurry under conditions different in a shear speed using a cone and plate type viscometer. Flow characteristics (rheology) of the slurry is calculated from measured viscosity values.
The viscosity of the slurry measured by the cone and plate type viscometer is useful as a value for forecasting fluidization of the slurry during wire-saw slicing an ingot. Especially, such slurry, which has viscosity adjusted to approximately 400-700 mPa·second at a shear speed of approximately 2/second and to approximately 50-300 mPa·second at a shear speed of approximately 380/second, is suitable for wire-saw slicing an ingot.


REFERENCES:
patent: 4052278 (1977-10-01), Brown et al.
patent: 4442707 (1984-04-01), Tuzson
patent: 5799643 (1998-09-01), Miyata et al.
patent: 5937844 (1999-08-01), Kiuchi et al.
patent: 6001265 (1999-12-01), Toyama et al.
patent: 6006738 (1999-12-01), Itoh et al.
patent: 6053158 (2000-04-01), Miyata et al.
patent: 6062209 (2000-05-01), Oishi
patent: 6113473 (2000-09-01), Costantini et al.
patent: 6161533 (2000-12-01), Katsumata et al.
patent: 6182729 (2001-02-01), Banzawa et al.
patent: 6221814 (2001-04-01), Kaburagi et al.

Affiliated with

Also associated with

Rating

Slurry useful for wire-saw slicing and evaluation of 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 Slurry useful for wire-saw slicing and evaluation of slurry, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Slurry useful for wire-saw slicing and evaluation of slurry will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2860134