JP2001105299A - Abrasive pad with window - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an abrasive pad having excellent evenness of polishing and capable of optically detecting the end of polishing, and to provide a polishing end detecting method and a polishing device using the same. SOLUTION: In an abrasive pad to be used for chemical mechanical polishing device, a polishing layer of the abrasive pad has a polishing area having bubbles and a light permeable area having bubbles, and hole ratio of the polishing area (A1) and the hole ratio of the light permeable area (A2) are set so as to satisfy the relation A1>A2>0.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polishing pad used for flattening irregularities on the surface of a wafer by chemical mechanical polishing, and more particularly to a polishing pad having a window for detecting a polishing state or the like by optical means. The present invention relates to a polishing pad, a method of detecting an end point of polishing using the same, and a polishing apparatus having the same.

[0002]

2. Description of the Related Art When a semiconductor device is manufactured, a conductive film is formed on a wafer surface, and a wiring layer is formed by photolithography, etching, or the like, or an interlayer insulating film is formed on the wiring layer. Steps for forming a film and the like are performed, and these steps cause irregularities made of a conductor or an insulator such as a metal on the wafer surface. In recent years, miniaturization of wiring and multi-layer wiring have been promoted for the purpose of increasing the density of semiconductor integrated circuits. With this, technology for flattening unevenness on the surface of a wafer has become important.

Conventionally, as a method of flattening unevenness on the surface of a wafer, chemical mechanical polishing (Chemical polishing) has been used.
Mechanical Polishing: C
MP method). In the CMP method, a surface to be polished of a wafer is pressed against a polishing surface of a polishing pad,
This is a technique for polishing using a slurry-type abrasive in which abrasive grains are dispersed (hereinafter, referred to as slurry). A polishing apparatus used in the CMP method includes, for example, as shown in FIG. 1, a polishing platen 2 supporting a polishing pad 1, a support table (polishing head) 6 supporting a workpiece (wafer) 5, and a polishing machine. An agent supply mechanism is provided. The polishing pad 1 is attached, for example, with a double-sided tape (not shown) to form a polishing platen 2.
Attached to. The polishing platen 2 and the support base 6 are arranged so that the polishing pad 1 and the workpiece 5 respectively supported are opposed to each other, and are provided with rotating shafts 8 and 9 respectively. Further, a pressure mechanism for pressing the workpiece 5 against the polishing pad 1 is provided on the support base 6 side.

In performing such a CMP process, there is a problem of determining the flatness of the wafer surface. That is, it is necessary to detect a desired surface characteristic or a point in time when the plane state is reached. Various methods are used for such detection, but a method capable of detecting a point at which a desired surface characteristic or thickness is obtained on the spot during a CMP process is desired. A typical example is an optical detecting means, specifically, detecting an end point of polishing by irradiating a wafer with a light beam through a polishing pad and monitoring an interference signal generated by its reflection. Method.

In such a method, the end point is determined by monitoring the change in the thickness of the surface layer of the wafer and knowing the approximate depth of the surface irregularities. When such a change in thickness becomes equal to the depth of the unevenness, the CMP process is terminated. Further, a method of detecting the end point of polishing by such an optical means and a polishing pad used in the method are disclosed in US Pat. No. 5,605,760 and US Pat.
No. 5,893,796 has been proposed.

US Pat. No. 5,605,760 discloses a polishing pad having at least a portion of a solid, uniform, transparent polymer sheet which transmits light of 190 to 3900 nm, and US Pat. No. 5,893,796 discloses a stepped transparent plug. Is disclosed. Both are disclosed to be used as windows for end point detection, and to suppress scattering of light by slurry during polishing,
The position (height) of the surface of the transparent sheet and the plug is configured to be substantially the same position (height) as the polished surface.

[0007]

However, in the above-mentioned polishing pad with a window, since the structure of the window and the polishing region is essentially different, the polishing performance differs between the window and the polishing region, and the uniformity of polishing is impaired. There is also a risk of being caught. Further, if the window is made of a hard material, it may cause scratches. An object of the present invention is to provide a polishing pad capable of optically detecting an end point of polishing and having good polishing uniformity, a method of detecting an end point of polishing using the same, and a polishing apparatus having the same. And

[0008]

In order to solve the above-mentioned problems, the present application provides the following inventions. (1) In a polishing pad used in a chemical mechanical polishing apparatus, a polishing layer of the polishing pad has a polishing region having bubbles and a light transmitting region having bubbles, and the porosity (A1) and light transmission of the polishing region. A polishing pad, wherein the relationship of porosity (A2) in the region is A1>A2> 0. (2) The polishing pad according to (1), wherein the polishing pad is made of a thermoplastic resin foam. (3) The relationship between the average cell diameter (B1) in the polishing area of the polishing layer and the average cell diameter (B2) in the light transmission area is B1>
The polishing pad according to (1) or (2), which is B2. (4) The polishing pad according to (1), (2) or (3), wherein the light transmission region is supported by a light transmission type support layer.

(5) The light transmitting type support layer is formed of a composite sheet composed of at least two different materials, and the horizontal cross section of the composite sheet has a plurality of light transmissive portions in the sea. In this structure, an island portion that serves as an optical transmission path is disposed, and a boundary surface between the sea portion and the island portion is formed vertically from the lower surface of the pad to the lower surface of the light transmission region, and the refractive index of the material of the island portion ( The polishing pad according to any one of (1) to (4), wherein the relationship between n1) and the refractive index (n2) at the boundary between the sea part and the island part is n1> n2. (6) A method for detecting the polishing end point in chemical mechanical polishing, wherein the light transmitting region of the polishing pad according to any one of (1) to (5) is used as a window for detecting the polishing end point. (7) A chemical mechanical polishing apparatus comprising the polishing pad according to any one of (1) to (6).

Hereinafter, the present invention will be described in detail. The polishing pad of the present invention has a bubble-containing light transmitting region through which laser light can pass. Since the light transmitting region has bubbles like the polishing region, it has a function of holding the slurry on the surface and acting as a polishing surface. Therefore, the difference in polishing performance between the polishing region and the light transmitting region is smaller than that of a window of a transparent sheet in which no bubbles exist, and polishing uniformity is improved. In addition, if the light transmitting region is porous like the polishing region, the occurrence of scratches can be suppressed as compared with a window of a transparent sheet in which no bubbles exist.

[0011] A porous (bubble-containing) sheet originally used as a polishing layer is whitened, that is, has a higher transparency than a transparent sheet, because light scattering is caused by bubbles present therein. Usually inferior. Therefore, in the light transmitting region, the demand for uniformity of polishing and the demand for light transmittance are in conflict. However, the present inventor has found that by employing the above-described configuration of the present invention, laser light can be transmitted even when a light transmitting region having bubbles is used.

In this case, what is important is the diameter and the number of bubbles existing in the vertical direction of the light transmitting region. When the same number of bubbles are present in the vertical direction, the smaller the bubble diameter, the more the scattering of laser light is suppressed. Of course, if the bubble diameter is equal to or smaller than the wavelength of light, the light is not scattered, so that there is no problem in the transmittance of the laser light. In addition, even if the bubble diameter is the same, if the number of bubbles existing in the vertical direction is small, scattering of laser light by the bubbles can be suppressed.

In the present invention, a bubble-containing light transmitting region for sufficiently detecting the end point of polishing is defined by its porosity. The porosity is a numerical value represented by the volume occupied by the bubbles present in the foam volume, and is determined by the bubble diameter and the number of bubbles. In the present invention, the preferred range of the porosity of the bubble-containing light transmitting region is more than 0% and 80%.
%, More preferably 10% or more and 75% or less, and still more preferably 30% or more and 60% or less.

Various methods are conceivable as a method for forming the light transmitting region having bubbles used in the present invention, and specific examples will be described below. First, as shown in FIG. 2, as shown in FIG. 2, a foam having a porosity lower than that of the foam used for the polishing area 71 is bonded as the light transmitting area 72 on the same double-sided tape 74. As another specific example, as shown in FIG. 3, when the polishing pad is formed from a thermoplastic resin foam, heat and compression molding is performed at a desired position on the polishing pad in a desired size. so,
The light transmission region 72 with reduced porosity can be created. Also, in this case, the polishing area 71 and the light transmitting area 72 are formed of the same material on the polishing surface of the polishing pad and are formed on the same surface without a break, so that the slurry permeates the polishing pad back surface during polishing. However, it is possible to suppress the deterioration of the double-sided tape and the decrease in the uniformity of polishing.

[0015] Further, as shown in FIG.
When forming a hollow between the double-sided tape and the light transmission area,
If necessary, as shown in FIG. 4, a support layer having desired compression characteristics can be formed of a light-transmitting material below the light-transmitting region. Also, if the heating and compression molding in forming the light transmitting region is performed by one-side heating from the back surface of the pad, the porosity of only the back surface of the pad is reduced as shown in FIG. Therefore, the polishing uniformity can be further improved.

As an example of the material used for the light transmitting area and the polishing area of the polishing pad of the present invention, either a thermoplastic resin or a thermosetting resin can be prepared. Considering applicability, thermoplastic resins are preferred. These thermoplastic resin foams also include crosslinked products. Also, among these, olefin resins,
Fluorine resin, polycarbonate resin, acrylic resin,
Examples of the foam include a base material of one or a mixture of two or more selected from a nylon resin, a polyurethane resin, an ethylene-vinyl acetate copolymer, and the like.

Examples of the olefin resin include polyethylene such as high-density polyethylene, low-density polyethylene, and linear low-density polyethylene, ethylene-propylene copolymer, polypropylene, poly-4-methyl-pentene, and ionomer resin. No. Examples of the fluororesin include polyvinyl fluoride, polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer, and tetrafluoroethylene. Ethylene-hexafluoropropylene copolymer, tetrafluoroethylene-perfluoromethyl-perfluorovinyl ether copolymer, tetrafluoroethylene-perfluoroethyl-perfluorovinyl ether copolymer, tetrafluoroethylene-perfluoropropyl-perfluorovinyl ether And copolymers.

Of these, it is preferable to use a fluororesin foam from the viewpoint of polishing performance and durability. As a support layer used as a lower layer of the above-mentioned light transmission region, a transparent sheet capable of suppressing scattering of laser light is used.
As these materials, both inorganic and organic materials can be used as long as they do not affect the scattering of laser light. For inorganic materials, quartz or glass can be used.For organic resin materials, in addition to the material used for the foam in the polishing area and light transmission area, transparent rubber with appropriate elasticity in consideration of polishing uniformity As the sheet, for example, fluorine rubber, silicone rubber, polyurethane elastomer or the like can be used.

The light-transmitting support layer is formed of a composite sheet composed of at least two different materials, and the horizontal cross section of the composite sheet has a plurality of light-transmitting portions in the sea. , An island portion serving as an optical transmission line is arranged, the boundary surface between the sea portion and the island portion is formed vertically from the lower surface of the pad to the light transmission amount region, and the refractive index of the material of the island portion (n1 ) And a composite material in which the relationship between the refractive index (n2) of the boundary portion between the sea portion and the island portion is n1> n2.

As a specific example of such a composite material, an inorganic or plastic optical fiber may be bundled by using an adhesive or a cladding layer and sliced. In this case, the use of a multi-core plastic optical fiber is one of the preferred embodiments of the present invention. Further, as a support layer, a bubble in the porous body, a transparent porous sheet filled with a liquid having the same refractive index, for example, a cellulose acetate porous membrane impregnated with glycerin, or very fine bubbles. It is also possible to use a transparent porous sheet having the same.

As a method of fixing the light transmitting region to the polishing pad, a method of fixing the bonding surface between the light transmitting region and the polishing pad with an adhesive, a method of using a double-sided tape for attaching the polishing pad to a surface plate, Specifically, a method of sticking the light transmission area on the double-sided tape opposite to the opening provided in the polishing pad, or forming an opening smaller than the polishing pad opening on the double-sided tape and fixing the sheet to that part There is a method to make it. Of course, when a light transmission area is created by heating and compression molding a part of the pad, it is not necessary to perform a special fixing operation because it is integral with the polishing area.

Next, a method of detecting the end point of polishing using the polishing pad of the present invention will be described with reference to FIGS. FIG.
1 is a schematic side view showing an example of a CMP polishing apparatus having an end point detection device according to the present invention. The light transmitting area 72 is set at a position facing the hole of the surface plate, and is positioned so that the wafer 5 can be seen during polishing regardless of the translational movement of the polishing head 6. The laser interferometer 3 is installed below the window of the surface plate, and the laser light 4 oscillated from the laser interferometer 3
Passes through the holes of the platen and the light transmitting region 72 and hits the surface of the wafer 5 via slurry (not shown). For example, when the wafer has an oxide layer formed on a silicon substrate, a part of the laser light hitting the surface of the wafer 5 is reflected on the surface of the oxide layer to form a first reflected laser light. I do.

Part of the incident light passes through the oxide layer and is reflected at the interface between the oxide layer and the silicon substrate, forming a second reflected laser beam. When the first and second reflected lights are combined, the phase relationship is expressed as a function of the thickness of the oxide layer. This interference light enters the interferometer 3 and the polishing state can be analyzed. FIG. 7 shows an example in which the position of the interferometer is changed using a beam splitter.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific examples of the present invention will be described. (1) Measurement method of porosity Porosity (%) = (ρp−ρf) / ρp × 100 calculated from the density (ρf) of the foam and the resin density (ρp) obtained by the submersion method.

[0025]

Example 1 (1) Preparation of Pad Polyvinylidene fluoride (melting point 168 ° C., MFR 2.9)
(230 ° C., 12.5 kg)) by heating and extruding to form a 1.1 mm thick sheet. The sheet is irradiated with an electron beam at 15 Mrad using an electron beam irradiation machine of 500 KV to crosslink. The crosslinked sheet is placed in a pressure vessel, and tetrafluoroethane is injected as a foaming agent and kept at 70 ° C. for 30 hours. The sheet impregnated with the foaming agent is held in a heating furnace equipped with a far-infrared heater at a temperature of 200 ° C. to foam the sheet. The foam sheet has a porosity of 75% and an average cell diameter of 80 microns. The foamed sheet is buff-polished on both sides with a # 240 belt sander, cut into a desired size, and concentric grooves (groove width 0.2 mm, groove depth 0.5 mm, groove pitch 1.5 mm) are formed on the polishing pad. ) To form a grooved polishing pad by cutting.

(2) Creation of light transmitting region The polishing pad obtained in the above (1) is heated to 220 ° C. at a desired position by heating a mold having a width of 5.1 cm and a length of 1.2 cm to 220 ° C.
Compression molding to create a light transmitting area. The thickness of the light transmitting region is 0.5 mm, and the porosity is 41%. Then, a double-sided tape is attached to the polishing pad. (3) Wafer polishing and end point detection The double-sided tape of the polishing pad having the light transmitting region obtained in the above (2) is placed on a mirra manufactured by Applied Materials Co., Ltd. so that the hole of the surface plate and the light transmitting region are aligned. Paste on the surface plate using. When a wafer having a TEOS (tetraethylorthosilicate) film on the outermost surface is polished using the ILD-1200 manufactured by Rodale as the slurry, the film thickness can be measured during the polishing, and thereby the end point can be detected. .

[0027]

When CMP polishing is performed using the polishing pad of the present invention, the end point can be detected, and the wafer can be polished while holding the slurry on the surface even in the light transmitting region. Therefore, there is an effect that uniformity of polishing is sufficiently maintained. Further, the use of the polishing pad of the present invention can also suppress the occurrence of scratches.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an example of a conventional polishing apparatus used in CMP polishing.

FIG. 2 is a schematic cross-sectional view showing an example of a light transmitting region having bubbles according to the present invention.

FIG. 3 is a schematic cross-sectional view showing an example of a light transmitting region having bubbles according to the present invention.

FIG. 4 is a schematic cross-sectional view showing an example of a light transmitting region having bubbles according to the present invention.

FIG. 5 is a schematic cross-sectional view showing an example of a light transmitting region having bubbles according to the present invention.

FIG. 6 is a schematic side view showing an example of a CMP polishing apparatus having an end point detection device of the present invention.

7 is a schematic cross-sectional view of a window portion of the apparatus of FIG. 6, showing a state in which a laser interferometer irradiates a laser beam and detects a reflected interference beam.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Polishing pad 2 Surface plate 3 Laser interferometer 4 Laser beam 5 Material to be polished (wafer) 6 Material to be polished (wafer) support base [polishing head] 71 Polishing area 72 Light transmission area 73 Bubbles 74 Double-sided tape 75 Support layer 8, Reference Signs 9 Rotating shaft 10 Detector 11 Abrasive (slurry) 12 Beam splitter

Claims (7)

[Claims] 1. A polishing pad used in a chemical mechanical polishing apparatus, wherein a polishing layer of the polishing pad has a polishing region having bubbles and a light transmitting region having bubbles, and a porosity (A1) of the polishing region. A polishing pad, wherein the relationship of the porosity (A2) of the light transmitting region is A1>A2> 0. 2. The polishing pad according to claim 1, wherein the polishing pad is made of a thermoplastic resin foam. 3. The polishing method according to claim 1, wherein the relationship between the average cell diameter (B1) in the polishing region of the polishing layer and the average cell diameter (B2) in the light transmitting region is B1> B2. pad. 4. The polishing pad according to claim 1, wherein the light transmitting region is supported by a light transmitting type support layer. 5. The light-transmitting support layer is formed of a composite sheet composed of at least two different materials, and the horizontal section of the composite sheet has a plurality of light-transmitting portions in the sea. , An island portion serving as an optical transmission path is arranged, the boundary surface between the sea portion and the island portion is formed vertically from the lower surface of the pad to the lower surface of the light transmission region, and the refractive index of the material of the island portion (n1 The polishing pad according to any one of claims 1 to 4, wherein a relationship between (i) and a refractive index (n2) of a boundary portion between the sea portion and the island portion is n1> n2. 6. A method for detecting a polishing end point in chemical mechanical polishing, wherein a light transmitting region of the polishing pad according to claim 1 is used as a window for detecting a polishing end point. 7. A chemical mechanical polishing apparatus comprising the polishing pad according to claim 1.