Abrading – Precision device or process - or with condition responsive... – Computer controlled
Reexamination Certificate
2002-06-11
2003-06-17
Hail, III, Joseph J. (Department: 3723)
Abrading
Precision device or process - or with condition responsive...
Computer controlled
C451S010000, C451S041000, C451S056000, C451S060000, C451S286000, C451S287000, C451S288000, C451S289000, C451S443000, C451S444000
Reexamination Certificate
active
06579148
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a polishing apparatus for polishing a plate-like workpiece such as a semiconductor wafer or a glass substrate.
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. Although the photolithographic process can form interconnections that are at most 0.5 &mgr;m wide, it requires that surfaces of semiconductor wafers 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 planarize the surfaces of the semiconductor wafers for photolithography. One customary way of planarizing the surfaces of the semiconductor wafers is to polish them with a polishing apparatus.
FIG. 17
of the accompanying drawings shows a main part of a conventional polishing apparatus. The polishing apparatus comprises a rotating polishing table
100
with a polishing cloth
102
made of urethane or the like attached to an upper surface thereof, a top ring (workpiece holder)
104
for holding a semiconductor wafer W which is a workpiece to be polished and pressing the semiconductor wafer W against the polishing table
100
while the top ring
104
is rotated, and a polishing liquid supply nozzle
106
for supplying a polishing liquid Q to the polishing cloth
102
. The top ring
104
is connected to a top ring shaft
110
through a spherical bearing
108
so that the top ring
104
is tiltable with respect to the top ring shaft
110
. The top ring
104
is provided with an elastic pad
112
made of polyurethane or the like on its lower surface, and the semiconductor W is held by the top ring
104
in contact with the elastic pad
112
. The top ring
104
also has a cylindrical guide ring
114
mounted on a lower outer circumferential edge thereof for retaining the semiconductor wafer W on the lower surface of the top ring
104
.
In operation, the semiconductor wafer W is held against the lower surface of the elastic pad
112
, and pressed against the polishing cloth
102
on the polishing table
100
by the top ring
104
. The polishing table
100
and the top ring
104
are rotated to move the polishing cloth
102
and the semiconductor wafer W relatively to each other. At this time, the polishing liquid Q is supplied onto the polishing cloth
102
from the polishing liquid supply nozzle
106
. The polishing liquid Q comprises a chemical solution such as an alkali solution containing abrasive particles suspended therein. The semiconductor wafer W is polished by a composite action comprising a chemical polishing action of the chemical solution and a mechanical polishing action of the abrasive particles. This polishing is called chemical mechanical polishing.
In the chemical mechanical polishing (CMP) apparatus using the polishing cloth
102
, since the polishing cloth
102
is made of material having elasticity, irregularities of a polished surface of the semiconductor wafer remain, and the surface of the semiconductor wafer cannot be sufficiently planarized. Therefore, the conventional CMP apparatus cannot cope with a demand for a higher degree of planarization of the semiconductor wafer.
To be more specific, a device pattern on the upper surface of the semiconductor wafer W has various irregularities having various dimensions and steps. When the semiconductor wafer W having step-like irregularities is planarized by the polishing cloth
102
having elasticity, not only raised regions but also depressed regions are polished, and hence irregularities of the polished surface of the semiconductor wafer are difficult to be eliminated, with the result that a high degree of flatness of the polished surface cannot be obtained.
Further, the surface of the polishing cloth
102
tends to have irregularities, and hence it is necessary to perform dressing of the surface of the polishing cloth
102
frequently for thereby removing glazing of the surface of the polishing cloth
102
.
Furthermore, a considerable proportion of the polishing liquid Q supplied to the polishing cloth
102
is discharged without reaching the surface of the semiconductor wafer to be polished. Consequently, the polishing liquid Q is required to be supplied in a large quantity, and hence an operating cost of the polishing process becomes high because the polishing liquid is expensive and the cost of a process for treating the polishing drain liquid is high.
Therefore, there has been developed a fixed abrasive type polishing apparatus and method in which polishing surface comprising an abrading plate, i.e. a fixed abrasive plate is used, in place of the polishing cloth
102
. The abrading plate comprises abrasive particles such as silica particles and a binder for binding the abrasive particles, and is formed into a flat plate.
FIG. 18
shows a main part of a conventional polishing apparatus having such abrading plate. The polishing apparatus comprises a polishing table
100
with a polishing tool
120
attached to an upper surface thereof, and liquid supply nozzles
124
connected to a liquid supply device
122
for supplying water or a chemical liquid during polishing. The polishing tool
120
attached to the upper surface of the polishing table
100
comprises a base plate
116
and an abrading plate
118
attached to the surface of the base plate
116
. Other structure of the polishing apparatus shown in
FIG. 18
is the same as that of the conventional polishing apparatus shown in FIG.
17
.
According to the above polishing process, the abrading plate (fixed abrasive) is harder than the polishing cloth and has less elastic deformation than the polishing cloth, and hence only the raised regions on the semiconductor wafer are polished and undulation of the polished surface of the semiconductor wafer is prevented from being formed. Therefore, selective polishing performance of the raised regions on the semiconductor wafer is improved, a degree of flatness of the semiconductor wafer is improved, and an expensive polishing liquid Q is not required to be used.
Further, it is confirmed by the inventors of the present application that in the polishing method using the fixed abrasive, the polished surface of the semiconductor wafer is planarized once to a certain level, and then the polishing rate is extremely lowered to show a self-stop ability of polishing because of the nature of the fixed abrasive. Therefore, the inventors of the present application have proposed to utilize such self-stop ability of polishing for detecting an endpoint of polishing or detecting a thickness of a film formed on the semiconductor wafer W in Japanese patent application Nos. 10-150546 and 10-134432.
Recently, there have been strong demands of the polishing apparatus for polishing semiconductor wafers towards improvement of productivity per an apparatus and improvement of productivity per unit installation area of the apparatus, as in other semiconductor manufacturing apparatuses. However, in the polishing apparatus having a single top ring per a polishing table, the polishing surface on the polishing table is not effectively utilized, and therefore the productivity per unit installation area of the apparatus cannot be improved.
One solution is to provide a polishing apparatus with a plurality of holders each for holding a workpiece to be polished, the holders sharing a common polishing surface. Such a polishing apparatus is referred to as a multihead polishing apparatus. The multihead polishing apparatus is advantageous in that it can simultaneously polish an increased number of workpieces per unit time. However, it is difficult for the multihead polishing apparatus to polish workpieces to a uniform finish because the simultaneously polished workpieces tend to be polished to different levels at the termination
Hirokawa Kazuto
Hiyama Hirokuni
Matsuo Hisanori
Togawa Tetsuji
Wada Yutaka
Ebara Corporation
Hail III Joseph J.
McDonald Shantese
Wenderoth , Lind & Ponack, L.L.P.
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