Wafer grinder and method of detecting grinding amount

Details Wafer grinder and method of detecting grinding amount Wafer grinder and method of detecting grinding amount

2000-06-15

2002-06-11

Eley, Timothy V. (Department: 3723)

Abrading

Precision device or process - or with condition responsive...

Computer controlled

C451S007000, C451S009000, C451S010000, C451S041000, C451S053000, C451S059000, C451S288000

Reexamination Certificate

active

06402589

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a wafer polishing apparatus and a wafer polishing quantity detection method or, in particular, to a wafer polishing apparatus and a wafer polishing quantity detection method based on the chemical mechanical polishing (CMP) process used for flattening the surface of a wafer during the process of forming an IC pattern thereon.
In recent years, the IC has been further miniaturized and IC patterns have been formed over a multiplicity of layers. Some unevenness unavoidably occurs in the surface of a layer formed with a pattern. In the prior art, the next pattern is formed directly on such an uneven surface. With the increase in the number of layers, however, the reduced size of line widths makes it difficult to form a superior pattern, often leading to a defect. In view of this, a practice prevails in that the surface formed with a pattern is polished to a flat surface followed by forming the pattern of the next layer. Also, a metal layer for connecting the layers is formed by forming a hole and then plating, and the metal layer on the surface is removed by polishing while leaving intact the portion of the metal layer corresponding to the hole. For polishing the wafer during the process of forming the IC pattern in this way, a wafer polishing apparatus (CMP apparatus) based on the CMP method is used.
BACKGROUND ART
FIGS. 1A and 1B
are diagrams for explaining the machining process using the CMP method in the fabrication of an IC.
FIG. 1A
shows the process of flattening by polishing the surface of a layer insulating film, and
FIG. 1B
shows the process of polishing the surface so that only the metal layer corresponding to the hole portion is left intact. In the case where the layer insulating film
3
is formed after forming a pattern
2
of a metal layer on a substrate
1
, the portion of the pattern
2
is higher than the other portions, thereby causing an unevenness in the surface. In view of this, the surface is polished with the CMP apparatus into the state, as shown on the right side, and then the next pattern is formed. Also, when forming a metal layer for connecting the layers, a connecting hole is formed on the pattern
2
of the lower layer as shown in
FIG. 1B
, after which the metal layer
4
is formed over the entire surface by plating or the like. After that, the surface is polished until the metal layer
4
on the surface is entirely removed by the CMP apparatus.
FIG. 2
is a diagram schematically showing a basic configuration of the CMP apparatus. As shown in
FIG. 2
, the CMP apparatus includes a polishing stool
11
and a wafer holding head
20
. An elastic polishing cloth
14
is attached on the surface of the polishing stool
11
. The polishing stool
11
is coupled to a motor
13
through a spindle
12
and adapted to rotate in the direction of arrow. A slurry providing an abrasive is supplied on the polishing cloth
14
of the rotating polishing stool
11
from a nozzle not shown. The polishing cloth
14
may be formed with a groove for facilitating the supply of the slurry to the contact surface with the wafer. The wafer holding head
20
holds the wafer to be polished, and rotates while pressing the wafer against the polishing cloth
14
under a predetermined pressure. As a result, the surface of the wafer held is polished. Although
FIG. 2
shows the case in which only one wafer holding head
20
is provided, a plurality of wafer holding heads
20
may be provided on a single polishing stool.
Various types of wafer holding mechanisms are available for the wafer holding head
20
. For example, Japanese Unexamined Patent Publications (Kokai) No. 6-79618, No. 8-229808 and No. 10-175161 disclose a wafer polishing apparatus in which a wafer is held by being closely attached to a carrier by adsorption or the like means and the carrier is pushed thereby to press the wafer against the polishing cloth. On the other hand, Japanese Unexamined Patent Publication (Kokai) No. 51-90095 discloses a lapping apparatus, not a CMP apparatus, in which a wafer is held by being attached to a carrier with an adhesive or two-side tape or the like and the carrier is pushed to press the wafer against the polishing cloth. Such apparatuses can securely hold the wafer being polished, but in the presence of dust or the like foreign matter between the carrier and the back of the wafer, the pressure of the carrier cannot be uniformly transmitted over the entire wafer surface, thereby making it difficult to polish the whole wafer surface uniformly. In order to solve this problem, Japanese Unexamined Patent Publication (Kokai) No. 1-188265 discloses a lapping apparatus in which a carrier includes an air outlet for applying an air pressure from the back of the wafer and by thus pressing the wafer against the stool, the surface is polished while at the same time keeping the carrier and the wafer out of contact with each other. Also, the present applicant has disclosed in Japanese Patent Publication (Kokai) No. 9-138925 corresponding published application JP-A-11-347918 and U.S. application Ser. No. 09/053,062, a wafer polishing apparatus comprising an air bag for pressing the carrier with an air outlet thereby to facilitate the adjustment of the pressure of the wafer against the polishing cloth in contactless manner.
In the CMP apparatus, the surface of the IC pattern is required to be polished accurately by a predetermined quantity. Various methods have been proposed for controlling the polishing quantity accurately. A method capable of most accurately controlling the polishing quantity is a process control method in which the polishing work is conducted little by little while measuring the polishing quantity. According to this method, in order to secure the required film thickness, the remaining film thickness is measured after every polishing session of several seconds, and if there is any shortage of the polishing quantity, the polishing is repeated. This method, however, is very low in productivity and encounters the problem of difficulty of application to mass production. Another method of controlling the polishing quantity is by controlling the time while stabilizing the polishing process. Due to the variations of the polishing process, however, it is difficult to control the polishing quantity with high accuracy. Also, the use of a dummy wafer for monitoring the relation between the polishing time and the polishing quantity poses the problem of a reduced throughput. Other methods that have thus far been proposed include a method for detecting the capacity with the metal wiring layer under an oxide film and a method in which the torque change is detected taking advantage of the fact that the torque required for polishing varies with the type of the layer. Under the circumstances, however, these methods fail to be satisfactory solutions as the scope of application is limited and the detection accuracy is not sufficiently high.
It is therefore desirable to directly measure the thickness of the wafer being polished and to calculate and control the polishing quantity based on the change in the thickness. Nevertheless, it is difficult to measure the wafer thickness during the polishing operation. Various methods have thus been proposed for measuring the quantity corresponding to the change in the wafer thickness. The patent publication No. 51-90095 described above, for example, discloses a lapping apparatus in which one of the parts constituting a detector such as an electric micrometer is mounted in a sample holder arranged on a lapping stool and the other parts are mounted in a sample holding frame with the work attached thereto thereby to detect the change in the thickness of the work. The sample holder, like the work, is in contact with the lapping stool, and the polishing quantity can be detected by detecting the displacement of the sample holding frame. In this lapping apparatus, however, the sample holding frame is urged by the sample holder in such a manner as to be pressed against the lapping stool, and therefore the force is devel

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