JP2001110762A - Polishing pad - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polishing pad where the optical detection of the end of polishing is possible and besides the equality of polishing is favorable, and a polishing end detection method using it, and a polisher equipped with it. SOLUTION: In a polishing pad used for a chemical/mechanical polisher, the polishing layer of that polishing pad has a polishing region which has bubbles and a light transmissive region which has bubbles, and besides relation between the number (n1) of bubbles extending in the vertical direction of the polishing region and the number (n2) of bubbles existing in the vertical direction of the light transmissive region is such that n1>n2>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 (hereinafter, referred to as slurry) in which abrasive grains are dispersed. The polishing apparatus used in the CMP method includes, for example, a polishing pad 1 as shown in FIG.
A polishing table 2, which supports a workpiece (wafer) 5; and a polishing agent supply mechanism. The polishing pad 1 is attached to the polishing platen 2 by, for example, attaching it with a double-sided tape (not shown). 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 for 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 number of bubbles existing in a direction perpendicular to the polishing region ( n1) and the number of bubbles (n2) present in the vertical direction of the light transmission region are n1>
A polishing pad, wherein n2> 0. (2) The polishing pad according to (1), wherein the light transmission region is supported by a light transmission type support layer.

(3) 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. 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 (1) or (2), wherein the relationship between n1) and the refractive index (n2) at the boundary between the sea part and the island part is n1> n2. (4) 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 (3) is used as a window for detecting the polishing end point. (5) Chemical mechanical polishing apparatus provided with the polishing pad according to any one of (1) to (3). 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. For this reason,
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. Also, if the light transmitting area is porous like the polishing area, compared to a transparent sheet window without bubbles,
The occurrence of scratches can also be suppressed.

[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 inventors have 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 number of bubbles existing in the vertical direction (thickness direction) of the light transmitting region. Even if the polishing area and the light transmitting area have the same bubble diameter, scattering of laser light by the bubbles can be suppressed if the number of bubbles existing in the vertical direction is small. In the present invention, the bubble-containing light transmission region that allows sufficient detection of the end point of polishing is defined by the number of bubbles existing in the vertical direction. In the present invention, the preferable range of the number of bubbles existing in the vertical direction of the light transmitting region is 1 to 30 pieces, more preferably 2 to 20 pieces, still more preferably 3 to 10 pieces.
Individual.

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 larger bubbles than 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, by performing a cutting process at a desired position on a back surface of the polishing pad with a desired size,
Light transmission region 7 with reduced number of bubbles existing in the vertical direction
2 can be created. In this case, on the polishing surface of the polishing pad, the polishing region 71 and the light transmitting region 72 are made of the same material,
Since the slurry is formed on the same surface without a break, the slurry does not penetrate into the back surface of the polishing pad during polishing, and thus it is possible to suppress the deterioration of the double-sided tape and the decrease in polishing uniformity. Further, since the bubble diameter in the light transmitting region is equal to that in the polishing region, the polishing uniformity can be further improved. As a specific example of the above-described cutting method, a general processing method using a lathe or a milling machine can be used.

Since a hollow portion is formed between the double-sided tape and the light transmitting region as shown in FIG. 3, if necessary, a light transmitting type material may be provided below the light transmitting region as shown in FIG. Thus, a support layer having desired compression characteristics can be formed. As an example of the material used for the light transmitting region and the polishing region of the polishing pad of the present invention, either a thermoplastic resin or a thermosetting resin can be used. In the case of a thermoplastic resin, a crosslinked body is also included. Among them, one or two selected from olefin resins, fluorine resins, polycarbonate resins, acrylic resins, nylon resins, polyurethane resins, ethylene-vinyl acetate copolymers, phenol resins, and the like.
A foam having a mixture of at least two or more species as a base material may be used.

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-tetrafluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, ethylene-tetrafluoroethylene copolymer, 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. A structure in which island portions that carry an optical transmission path are arranged, 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 amount region,
A composite material in which the relationship between the refractive index (n1) of the material of the island portion and the refractive index (n2) of the boundary portion between the sea portion and the island portion is n1> n2 can also be used.

As a specific example of such a composite material, an inorganic or plastic optical fiber can be bundled by using an adhesive or a cladding layer and then 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 area to the polishing pad, a method of fixing the bonding surface between the light transmitting area 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 transmitting area is created by cutting a part of the back surface of the pad, it is not necessary to perform a special fixing operation because the light transmitting area is integrated 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, and
To form a reflected laser beam. 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. 6 shows an example in which the position of the interferometer is changed using a beam splitter.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific examples of the present invention will be described.

[0023]

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. #
Both sides are buff-polished with a 240 belt sander, cut out to 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 having a thickness of 1.4 mm. The number of bubbles existing in the vertical direction of the polishing pad (polishing region) is 33.

(2) Creation of light transmitting region At a desired position on the back surface of the polishing pad obtained in the above (1),
A light-transmissive area is created by performing milling with a width of 5.1 cm, a length of 1.2 cm and a depth of 0.7 mm by milling. The number of bubbles existing in the vertical direction of the light transmitting region is fifteen.

(3) Wafer polishing and end point detection The polishing pad having the light transmitting region obtained in the above (2) is placed on a Mira made by Applied Materials Co., Ltd. so that the hole of the surface plate and the position of the light transmitting region match. Affix to the surface plate using double sided tape. 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. .

[0026]

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

6 is a schematic cross-sectional view of a window portion of the apparatus in FIG. 5, showing a state where 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 (5)

[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 bubbles present in a direction perpendicular to the polishing region. A polishing pad, wherein the relationship between the number (n1) and the number of bubbles (n2) existing in the vertical direction of the light transmitting region is n1>n2> 0. 2. The polishing pad according to claim 1, wherein the light transmitting region is supported by a light transmitting type support layer. 3. The light-transmitting support layer is formed of a composite sheet composed of at least two different materials, and a 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 claim 1, wherein a relationship between the refractive index (n2) of the boundary portion between the sea portion and the island portion is n1> n2. 4. A method for detecting a polishing end point in chemical mechanical polishing, comprising using a light transmitting region of the polishing pad according to claim 1 as a window for detecting a polishing end point. 5. A chemical mechanical polishing apparatus comprising the polishing pad according to claim 1.