JP2005032790A - Polishing ending point detecting device for wafer polishing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polishing ending point detecting device for wafer polishing device that is simple in facility and can be improved in detection accuracy. <P>SOLUTION: The polishing ending point detecting device 12 discriminates a polishing ending point when the device 12 detects a Cu film. A filter 44 only transmits light in an a-wavelength region and another filter 46 only transmits light in a b-wavelength region. Since the intensity of reflected light changes to X and Y when a wafer W is polished and the Cu film is exposed, a computer 36 discriminates the polishing ending point based on the X and Y. Since the two information quantities of X and Y are used for discriminating the polishing ending point, the computer 36 discriminates that polishing operation does not reach the ending point and makes the polishing operation to be continued when the computer 36 detects the X, but does not detect the Y. Upon detecting both the X and Y, the computer 36 discriminates that the polishing operation reaches the ending point and causes the control section 22 of a wafer polishing device 10 to end the polishing operation by outputting a polishing ending point signal. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a polishing end point detection apparatus for a wafer polishing apparatus, which polishes a semiconductor wafer by a chemical mechanical polishing (CMP) method.
[0002]
[Prior art]
Polishing of a wafer by CMP is performed by pressing the wafer against a rotating polishing pad with a predetermined pressure while rotating the wafer, and supplying a mechanochemical abrasive (slurry) between the polishing pad and the wafer. The main purpose of this CMP is to remove steps formed on the surface of the IC circuit on the wafer, to easily achieve higher density of the IC circuit, and to remove an unnecessary layer thickness. is there.
[0003]
At this time, the film thickness of each layer forming the IC circuit is very small, and a slight film thickness may be left after the step is removed. Therefore, it is very important to detect the end point of CMP in which CMP is stopped when an unnecessary film is removed. In particular, the end point is often detected during the CMP process from the viewpoint of improving the apparatus operation rate and productivity, and various means have been proposed.
[0004]
As conventional end point detection means, there is known one that detects the polishing end point by irradiating the polishing surface of the wafer with light from a light projecting device and measuring the spectral intensity distribution of the reflected light (Patent Document 2). . That is, since the spectral intensity varies depending on the film type of the wafer, the end point is detected by detecting the change in the spectral intensity. In this case, as the light projecting device, light having a single wavelength such as laser light or light having a wide wavelength range such as white light is used.
[0005]
[Patent Document 1]
JP-A-2001-291686 [0006]
[Patent Document 2]
Japanese Patent Laid-Open No. 2000-186918
[Problems to be solved by the invention]
However, a projector that uses light of a single wavelength such as a laser beam can perform end point detection with simple equipment, but there is not enough information to obtain the spectral intensity, so high detection accuracy is achieved. There was a drawback that it could not be obtained.
[0008]
In addition, when a white light spectroscope is used as a light projecting device, the amount of information increases, so that the detection accuracy increases, but there is a disadvantage that the equipment becomes complicated.
[0009]
The present invention has been made in view of such circumstances, and an object of the present invention is to provide a wafer polishing apparatus with simple equipment and improved detection accuracy.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides light projecting means for irradiating light onto a polished surface of a wafer, and light receiving means for receiving reflected light of light emitted from the light projecting means onto the polished surface of the wafer; A light having a wavelength range corresponding to the film type of the wafer, provided for each of the plurality of optical paths divided by the means for dividing the reflected light received by the light receiving means into a plurality of optical paths and the means for separating the light A plurality of specific wavelength range light extraction means, and the light extracted by the plurality of specific wavelength range light extraction means is converted into an electrical signal corresponding to the light intensity for each wavelength range, A plurality of photoelectric conversion means for outputting as a light intensity signal, and an end point determination means for determining a polishing end point based on the light intensity signal for each wavelength region output from the plurality of photoelectric conversion means. And
[0011]
According to the present invention, the polishing surface of the wafer is irradiated with light from the light projecting means, and the reflected light is received by the light receiving means. In this case, white light having a wide wavelength range is preferable as the light projecting means. Next, the received light is divided into a plurality of optical paths according to the stage for dividing the light, and only light in a wavelength region corresponding to the film type of the wafer is obtained by a specific wavelength region light extraction means provided for each of these optical paths. Take out. The specific wavelength range light extraction means is a filter, a prism, or a diffraction grating (grating) having a different transmission wavelength range that transmits only light in a wavelength range corresponding to the film type of the wafer. The light extracted by a plurality of specific wavelength range light extraction means is converted into an electrical signal corresponding to the light intensity for each wavelength range by a plurality of photoelectric conversion means for each light, and the end point is obtained as a light intensity signal for each wavelength range Output to discrimination means. The end point determination unit determines the polishing end point based on the light intensity signal for each wavelength region output from the plurality of photoelectric conversion units. That is, since the present invention is an apparatus for determining the polishing end point based on a plurality of information amounts corresponding to the number of divided optical paths, simple equipment is required and detection accuracy is improved.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of a polishing end point detection apparatus of a wafer polishing apparatus according to the present invention will be described in detail with reference to the accompanying drawings.
[0013]
FIG. 1 is a block diagram illustrating a configuration of a wafer polishing apparatus 10 and a polishing end point detection apparatus 12 according to an embodiment.
[0014]
The wafer polishing apparatus 10 is driven by a motor (not shown) and rotates horizontally, a polishing pad 16 adhered to the surface of the platen 14, a wafer W held by the polishing pad 16 at a predetermined pressure. A wafer holding head 18 to be pressed, a slurry supply nozzle 20 for supplying slurry to the surface of the polishing pad 16, and a control unit 22 for controlling overall driving of the apparatus.
[0015]
The platen 14 is formed in a disk shape, and an observation hole 24 is opened at a predetermined position. The observation hole 24 is formed through the platen 14, and a transparent observation window 26 is attached to the polishing pad 16 corresponding to the upper end opening.
[0016]
The wafer holding head 18 presses the wafer W against the polishing pad 16 at a position eccentric from the rotation center of the platen 14 and is driven horizontally by a motor (not shown) to rotate. Further, the wafer holding head 18 moves up and down vertically with respect to the polishing pad 16 by being driven by a lifting means (not shown).
[0017]
The polishing of the wafer W is performed by pressing the wafer W held by the wafer holding head 18 against the polishing pad 16 with a predetermined pressure, and rotating the polishing pad 16 and the wafer W while slurry is applied to the polishing pad 16 from the slurry supply nozzle 20. This is done by supplying.
[0018]
The polishing end point detection device 12 is mainly composed of an irradiation / light reception optical system 28, a two-branch light guide 30, a light source unit 32, an optical splitter 34, and a computer 36.
[0019]
The irradiation / light reception optical system 28 is supported by a bracket (not shown) and is installed at a position below the observation hole 24. The irradiation / light-receiving optical system 28 includes a lens barrel 38 and a condenser lens 40 installed in the lens barrel 38 as shown in FIG.
[0020]
The two-branch light guide 30 in FIG. 1 is configured by bundling a large number of optical fibers, and is branched into two in the middle. The first branched light guide 30A is connected to the light source unit 32 as an irradiation side light guide, and the second light guide 30B is connected to the optical splitter 34 as a light receiving side light guide. The bundling end 31 of the two-branch light guide 30 is connected to the irradiation / light reception optical system 28 as shown in FIG.
[0021]
The light source unit 32 shown in FIG. 1 incorporates a halogen lamp, and white light from the halogen lamp is guided to the irradiation / light reception optical system 28 through the irradiation side light guide 30A. Then, the white light emitted from the two-branch light guide 30 is condensed by the condenser lens 40 of the irradiation / light-receiving optical system 28 and then polished through the observation window 26 from the observation hole 24 formed in the platen 14. The polishing surface (lower surface) of the wafer W on the pad 16 is irradiated. Then, the reflected light is condensed by the condenser lens 40 of the irradiation / light-receiving optical system 28 and guided to the two-branch light guide 30 and then guided to the optical splitter 34 via the light-receiving side light guide 30B.
[0022]
The optical splitter 34 divides the reflected light guided by the light-receiving side light guide 30B into a plurality of optical paths, and acquires the light in two wavelength ranges by passing the divided light through a predetermined filter. Then, the acquired light in the two wavelength ranges is converted into an electrical signal corresponding to the light intensity for each wavelength range, and output to the computer 36 as a light intensity signal for each wavelength range.
[0023]
As shown in FIG. 3, the optical splitter 34 includes a beam splitter (means for separating light) 42, filters (specific wavelength region light extraction means) 44 and 46, array light receiving elements 48 and 50, and the like. The reflected light guided to the optical splitter 34 by the light receiving side light guide 30B is divided into two optical paths A and B by the beam splitter 42. The light in the optical path A is filtered to the filter 44, and the light in the optical path B is filtered 46. Each led to
[0024]
The polishing end point detection device 12 of the embodiment is a device that determines the polishing end point when a Cu film is detected. In this case, the Cu film in FIG. 4 is known to have X value intensity when the wavelength of the reflected light is in the a wavelength range, and the wavelength of the reflected light is in the b wavelength range. It is known to have a Y value intensity.
[0025]
Therefore, a filter that transmits only light in the a wavelength region is used as the filter 44, and a filter that transmits only light in the b wavelength region is used as the filter 46. The light in the a and b wavelength ranges that has passed through the filters 44 and 46 is imaged on the array light receiving elements 48 and 50. The light imaged on the array light receiving elements 48 and 50 is converted into an electrical signal corresponding to the light intensity for each wavelength range by the array light receiving elements 48 and 50 and output to the computer 36 as a light intensity signal for each wavelength range. Is done.
[0026]
The computer 36 determines the polishing end point based on the light intensity signal for each wavelength range of the reflected light output from the optical splitter 34. That is, when the wafer W is polished and the Cu film is exposed, the light intensity of the reflected light changes to X and Y, so the computer 36 determines the polishing end point based on this. At this time, since the information amount for determining the end point has two information amounts of X and Y, for example, when X is detected but Y cannot be detected, the end point is not reached. Judged to continue polishing. When both X and Y are detected, it is determined that the end point has been reached, a polishing end point signal is output to the control unit 22 of the wafer polishing apparatus 10, and the polishing process is terminated.
[0027]
As described above, the polishing end point detection device 12 according to the embodiment determines the polishing end point based on the two information amounts corresponding to the number of the optical paths A and B of the divided light. Accuracy is improved.
[0028]
The number of divided optical paths is not limited to two, and the light projecting means is not limited to a halogen lamp. The present invention can also be applied to a laser light irradiation device that irradiates light in a plurality of wavelength regions and an LED device that irradiates light in a plurality of wavelength regions.
[0029]
In the embodiments, the filters 44 and 46 having different transmission wavelength ranges that transmit only light in the wavelength range corresponding to the film type of the wafer have been described as the specific wavelength range light extraction means. However, the present invention is not limited to this. Instead, a prism or a diffraction grating (grating) can be applied instead of the filters 44 and 46.
[0030]
When a prism is applied, the same effect can be obtained if a photoelectric conversion element such as an LED or the like receives only light in a wavelength region corresponding to the film type of the wafer out of the light dispersed for each wavelength region by the prism. be able to.
[0031]
In addition, when a diffraction grating is applied, the diffraction grating is also an optical element that disperses white light into light in each wavelength range, so that, as in the case of the prism, out of the light dispersed in each wavelength range, the film on the wafer Only light in the wavelength region corresponding to the seeds may be received by a photoelectric conversion element such as an LED.
[0032]
【The invention's effect】
As described above, according to the polishing end point detection device of the wafer polishing apparatus according to the present invention, since the polishing end point is determined based on a plurality of information amounts corresponding to the number of divided optical paths, simple equipment is sufficient, and Detection accuracy is improved.
[Brief description of the drawings]
1 is an overall configuration diagram of a wafer polishing apparatus and a polishing end point detection apparatus according to an embodiment. FIG. 2 is a cross-sectional view of a polishing pad and an irradiation / light-receiving optical system of the wafer polishing apparatus shown in FIG. Fig. 4 is a block diagram showing the configuration of the optical splitter shown in Fig. 4. Fig. 4 is a graph showing the relationship between the wavelength and intensity of the reflected light in the Cu film.
DESCRIPTION OF SYMBOLS 10 ... Wafer polisher, 12 ... Polishing end point detector, 14 ... Platen, 16 ... Polishing pad, 18 ... Wafer holding head, 20 ... Slurry supply nozzle, 22 ... Control part, 24 ... Observation hole, 26 ... Observation window, 28 Irradiating / receiving optical system, 30 ... two-branch light guide, 32 ... light source unit, 34 ... optical splitter, 36 ... computer, 38 ... lens barrel, 42 ... beam splitter, 44, 46 ... filter, 48, 50 ... Array photo detector

Claims (2)

A light projecting means for irradiating light onto the polished surface of the wafer;
A light receiving means for receiving reflected light of light irradiated on the polished surface of the wafer from the light projecting means;
Means for dividing the reflected light received by the light receiving means into a plurality of optical paths;
A plurality of specific wavelength range light extraction means that are provided for each of the plurality of optical paths divided by the means for dividing the light and extract only light in a wavelength range corresponding to the film type of the wafer;
A plurality of photoelectric conversion means for converting the light extracted by the plurality of specific wavelength range light extraction means into an electrical signal corresponding to the light intensity for each wavelength range, and outputting as a light intensity signal for each wavelength range;
End point determination means for determining a polishing end point based on a light intensity signal for each wavelength region output from the plurality of photoelectric conversion means;
A polishing end point detection apparatus for a wafer polishing apparatus, comprising: The specific wavelength range light extraction means is a plurality of filters, prisms, or diffraction gratings having different transmission wavelength ranges that transmit only light in a wavelength range corresponding to the film type of the wafer. 2. A polishing end point detection apparatus for a wafer polishing apparatus according to 1.

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