Abrading – Machine – Sandblast
Reexamination Certificate
2000-03-24
2002-01-15
Banks, Derris H. (Department: 3723)
Abrading
Machine
Sandblast
C451S099000
Reexamination Certificate
active
06338671
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus for supplying a polishing liquid used for polishing a surface of a semiconductor substrate, and more particularly to an apparatus for supplying a polishing liquid containing uniformly dispersed abrasive particles therein to a polishing surface of a polishing unit in a stable condition.
2. Description of the Related Art
Recent rapid progress in semiconductor device integration demands smaller and smaller wiring patterns or interconnections and also narrower spaces between interconnections which connect active areas. One of the processes available for forming such interconnection is photolithography. Though the photolithographic process can form interconnections that are at most 0.5 &mgr;m wide, it requires that surfaces on which pattern images are to be focused by a stepper be as flat as possible because the depth of focus of the optical system is relatively small.
It is therefore necessary to make the surfaces of semiconductor wafers flat for photolithography. One customary way of flattening the surfaces of semiconductor wafers is to polish them with a polishing apparatus having a polishing unit (or section).
Conventionally, a polishing unit has a turntable and a top ring which rotate at respective individual speeds. A polishing cloth constituting a polishing surface is attached to the upper surface of the turntable. A semiconductor substrate to be polished is placed on the polishing cloth and clamped between the top ring and the turntable. An abrasive liquid containing abrasive particles is supplied onto the polishing cloth and retained on the polishing cloth. During operation, the top ring exerts a certain pressure on the turntable, and the surface of the semiconductor substrate held against the polishing cloth is therefore polished by a combination of chemical polishing and mechanical polishing to a flat mirror finish while the top ring and the turntable are rotated.
FIG. 7
is a schematic view showing the essential parts in an example of a polishing unit. The polishing unit comprises a turntable
142
having an upper surface to which a polishing cloth
140
is attached, a top ring
144
for holding a semiconductor wafer W as a polishing object and pressing the semiconductor wafer W against the polishing cloth
140
while rotating the semiconductor wafer W, and a polishing liquid supply nozzle
146
for supplying a polishing liquid Q to the polishing cloth
140
. The polishing cloth
140
constitutes a polishing surface. The top ring
144
is coupled to a top ring shaft
148
, and is vertically movably supported by an air cylinder (not shown).
The top ring
144
has an elastic pad
150
made of polyurethane or the like on its lower surface, and the semiconductor wafer W is held in such a manner that the semiconductor wafer W is closely brought in contact with the elastic pad
150
. The top ring
144
is further provided with a cylindrical guide ring
152
on its outer periphery so that the semiconductor wafer W is not dislodged from the lower surface of the top ring
144
. The guide ring
152
is fixed to the top ring
144
, and the lower end of the guide ring
152
projects from the holding surface of the top ring
144
so that the semiconductor wafer W is retained in a recess defined by the holding surface of the top ring
144
and the guide ring
152
.
In the polishing unit having the above structure, the semiconductor wafer W is held by the lower surface of the elastic pad
150
of the top ring
144
, and pressed against the polishing cloth
140
on the turntable
142
by the top ring
144
, and the turntable
142
and the top ring
144
are rotated so as to cause a relative sliding motion between the polishing cloth
140
and the semiconductor wafer W. At this time, a polishing liquid Q is supplied from the polishing liquid supply nozzle
146
to the polishing cloth
140
. The polishing liquid comprises abrasive particles such as silica particles suspended in a chemical solution such as an alkali solution, and the semiconductor wafer W is polished by a combination of chemical polishing with alkali and mechanical polishing with the abrasive particles.
In order to perform a high quality polishing in the above polishing unit, it is necessary to supply a polishing liquid having a constant concentration at a constant flow rate to the polishing surface of the polishing unit. A polishing liquid supply system may comprise a storage tank for storing a condensate comprising a mixture of, for example, alkali such as KOH or NH
4
OH and silica particles, an adjusting tank for adjusting the condensate to a desired concentration by diluting the condensate with a liquid such as pure water or chemical solution, a supply tank for storing temporarily a polishing liquid adjusted in the adjusting tank, and a polishing liquid supply pipe for delivering the polishing liquid to a nozzle from the supply tank. The polishing liquid supply system further comprises pipes for connecting the tanks.
It is known that a polishing rate and a polishing quality in a polishing process depend on the concentration of the polishing liquid used for polishing semiconductor wafers. On the other hand, for reducing equipment cost and operating cost, a common polishing liquid supply source is required to be used for a plurality of polishing units. For this reason, the polishing liquid having a given concentration is temporarily stored in the adjusting tank or the supply tank, and is then delivered to the respective polishing units. As a result, the quality of the polishing liquid stored in the adjusting tank or the supply tank is degraded with an elapse of time, and hence the abrasive particles tend to aggregate for thereby making the effective size of particles larger. Thus, an undesirable polishing liquid containing excessively large abrasive particles may be delivered to the polishing units to cause a polished surface of the semiconductor substrate to be scratched or to decrease a polishing rate.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an apparatus for supplying a polishing liquid which can continuously supply a polishing liquid having stable properties to a polishing section to perform a high quality polishing at all times.
In order to achieve the above object, according to a first aspect of the present invention, there is provided an apparatus for supplying a polishing liquid to a polishing section, comprising: a supply tank for storing a polishing liquid having given properties; a supply pipe for supplying the polishing liquid to the polishing section; a sensing device for detecting properties of the polishing liquid flowing through the supply pipe; and a stabilization device for maintaining properties of the polishing liquid stored in the supply tank or flowing through the supply pipe within an allowable range on the basis of an output signal from the sensing device.
According to the present invention, the properties of the polishing liquid supplied to the polishing section are continuously monitored, and when the polishing liquid has been degraded up to a condition that scratches are likely to be formed on a polished surface of the substrate by aggregated abrasive particles, various remedial procedures can be taken to stabilize the properties of the polishing liquid. Thus, the polishing liquid having stable properties is continuously supplied to the polishing section to provide a high quality polishing at all times. If it is found that the polishing liquid has been degraded to a large degree, then the operation of the polishing apparatus may be stopped to prevent inferior products from being produced.
In a preferred embodiment, the sensing device may measure at least one of particle size distribution, the number of coarse particles, oxidation-reduction potential, and solid material concentration in the polishing liquid.
According to the present invention, degradation of abrasive particles in the polishing liquid may be detected in real time directly or indirectl
Kawashima Kiyotaka
Komatsu Mitsunori
Tanikawa Mutsumi
Toyomasu Fujihiko
Banks Derris H.
Ebara Corporation
Wenderoth , Lind & Ponack, L.L.P.
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