Abrading – Precision device or process - or with condition responsive... – By optical sensor
Reexamination Certificate
2001-08-27
2004-01-20
Hail, III, Joseph J. (Department: 3723)
Abrading
Precision device or process - or with condition responsive...
By optical sensor
C451S041000, C451S067000
Reexamination Certificate
active
06679756
ABSTRACT:
This application is filed under 35 U.S.C. §371 from International Application PCT/JP00/08993, with an international filing date of Dec. 19, 2000, which claims the benefit of priority to Japanese Application No. 11-371820, filed Dec. 27, 1999, which are incorporated by reference in their entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a polishing state monitoring method, polishing state monitoring device and polishing apparatus suitable for use in the planarization of semiconductor devices in a process in which semiconductor devices (such as ULSI devices, etc.) are manufactured, as well as a process wafer used in this polishing apparatus, a semiconductor device manufacturing method using this polishing apparatus, and a semiconductor device manufactured by this method.
2. Discussion of the Related Art
As semiconductor integrated circuits have become more highly integrated and smaller in size, processes required for the manufacture of such semiconductor integrated circuits have become more numerous and complicated. As a result, the surfaces of semiconductor devices are no longer always flat. The presence of step differences on the surfaces of semiconductor devices leads to wiring interruptions and local increases in resistance, etc., and thus causes circuit breaks and a drop in electrical capacitance. Furthermore, this also leads to deterioration of the withstand voltage and the occurrence of leakage in insulating films.
Meanwhile, as semiconductor integrated circuits have become more highly integrated and smaller in size, the light source wavelengths of semiconductor exposure apparatuses used in photolithography have become shorter, and the numerical apertures, or so-called NA, of the projection lenses of such semiconductor exposure apparatuses have become larger. As a result, the focal depths of the projection lenses of semiconductor exposure apparatuses have become substantially shallower. In order to handle such increased shallowness of the focal depth, it is necessary to flatten the surfaces of semiconductor devices to a greater degree than has previously been accomplished.
To describe this in concrete terms, a flattening technique such as that shown in FIGS.
11
A
1
,
11
A
2
,
11
B
1
, and
11
B
2
has become essential in semiconductor processes. Here, a semiconductor device
24
, an inter-layer insulating film
22
consisting of SiO
2
and a metal film
23
consisting of A
1
are formed on the surface of a silicon wafer
21
. FIGS.
11
A
1
and
11
A
2
show examples in which the inter-layer insulating film
22
on the surface of the semiconductor device is flattened. FIGS.
11
B
1
and
11
B
2
show examples in which the metal film
23
on the surface of the semiconductor device is polished, so that a so-called “damascene” is formed. Chemical mechanical polishing or chemical mechanical-planarization (hereafter referred to as “CMP”) has attracted attention as a method for the flattening of such semiconductor device surfaces.
CMP is a process in which irregularities in the surface of the wafer are removed by combining a chemical action (elution by means of a polishing agent or solution) with physical polishing; this process is an influential candidate for a global flattening technique. In concrete terms, a polishing agent called a “slurry” is used in which polishing particles (generally silica, alumina or cerium oxide, etc.) are dispersed in a medium such as an acid or alkali, etc., in which the object of polishing is soluble; polishing is caused to proceed by applying pressure to the wafer surface with a suitable polishing cloth, and grinding the surface by means of relative motion. Uniform polishing within the plane [of the surface] can be accomplished by making the application of pressure and speed of relative motion uniform over the entire surface of the wafer.
This process still suffers from many problems in terms of matching with conventional semiconductor processes, etc.; generally, a major problem that remains to be solved is monitoring of the polishing state (detection of the amount of polishing or polishing endpoint, etc.) while the polishing process is being performed (i.e., in-situ monitoring of the polishing state). There is a great demand for this in terms of improving the process efficiency as well.
In CMP, variations in the polishing rate occur as a result of local differences in the temperature distribution on the surface of the polishing pad and differences in the conditions of slurry supply, as well as differences in the pressure distribution. Furthermore, there are also differences in the polishing rate caused by variations in the surface conditions of the pad due to dressing, a drop in the polishing rate according to the number of wafers treated (deterioration caused by use) and individual differences in the pads used, etc. As a result of such problems, it is difficult to determine the endpoint of a specified amount of polishing by polishing time control.
Accordingly, methods have been proposed in which the endpoint is determined while measuring the motor torque or vibration, etc., in situ instead of determining the endpoint by time control. Such methods are somewhat effective in the case of CMP in which the material that is the object of polishing varies (e.g., CMP of wiring materials or CMP in which stopper layers are present). However, in the case of silicon wafers with complicated patterns, there is little variation in the material that is the object of polishing; accordingly, there may be instances in which determination of the endpoint is difficult. Furthermore, in the case of CMP of inter-layer insulating films, it is necessary to control the inter-wiring capacitance; accordingly, control of the residual film thickness is required rather than control of the polishing endpoint. It is difficult to measure the film thickness using methods that determine the endpoint by in-situ measurement of motor torque or vibration, etc.
Recently, therefore, monitoring of the polishing state (in-situ endpoint determination and in-situ film thickness measurement, etc.) by optical measurements, and specifically by the measurement of spectroscopic reflection, as described (for example) in Japanese Patent Application Kokai No. H11-33901, has been considered effective. In the case of such monitoring of the polishing state by the measurement of spectroscopic reflection, the wafer that is the object of polishing is irradiated with a probe light during CMP, and the amount of polishing or polishing endpoint is detected during polishing according to variations in the spectroscopic reflectivity of the light reflected from the wafer.
Light reflected from the polished surface of a wafer on which a semiconductor element is formed may be viewed as a superimposition of light waves from various layers and various parts of the device (laminated thin films); the waveform of the spectroscopic reflectivity varies according to the thickness of the layer that is being polished (i.e., the uppermost layer). This variation is stable (reproducible), and tends not to be affected by the interposed slurry, non-uniformity of the film thickness, or recesses and indentations in the surface or interfaces, etc. Accordingly, if the polishing state ascertained by measurement of the above-mentioned spectroscopic reflection is monitored, the wafer thickness, amount of polishing or polishing endpoint can be detected accurately in spite of the above-mentioned noise factors. Furthermore, the amount of polishing can be indirectly measured from the initial thickness of the wafer and the measured thickness of the wafer.
In the above-mentioned conventional monitoring of the polishing state by measurement of spectroscopic reflection, the measured spectrum which is the spectrum (intensity at various wavelengths) of the light reflected by the wafer indicates the spectroscopic reflectivity; accordingly, it would appear that the film thickness, etc., could be immediately determined from the measured spectrum.
In this case, however, the following problem
Ishikawa Akira
Ushio Yoshijiro
Hail III Joseph J.
Morgan & Lewis & Bockius, LLP
Ojini Anthony
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