JP2001138213A - Abrasive cloth for metal, and grinding method using thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an abrasive cloth for metal which is high in CMP speed, high in flatness, capable of reducing the dishing quantity and the erosion, high in reliability, and capable of forming the embedding pattern of a metal film, and a grinding method using the cloth. SOLUTION: In this grinding method, polished film is ground by relatively moving a turn table with a substrate while pressing the substrate having the polished film pressed against the abrasive cloth while feeding an abrasive solution for metal onto the abrasive cloth of the turn table, and the abrasive cloth for metal containing a chelate resin is used as the abrasive cloth to be used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal polishing cloth used for polishing using a metal polishing liquid in a wiring process of a semiconductor device, and a polishing method using the same.

[0002]

2. Description of the Related Art In recent years, a new fine processing technology has been developed in accordance with high integration and high performance of a semiconductor integrated circuit (hereinafter, referred to as LSI). Chemical mechanical polishing (hereinafter referred to as CMP)
The method is one of them. For example, in an LSI manufacturing process, particularly, in a multilayer wiring forming process, an interlayer insulating film is flattened, a metal plug is formed,
This is a technique frequently used in the formation of embedded wiring. This technique is disclosed, for example, in US Pat. No. 4,944,836.

Recently, use of a copper alloy as a wiring material has been attempted in order to improve the performance of an LSI. However, it is difficult to finely process a copper alloy by a dry etching method frequently used in forming a conventional aluminum alloy wiring. Therefore, a copper alloy thin film is deposited and buried on an insulating film in which a groove is formed in advance, and a copper alloy thin film other than the groove is removed by CMP to form a buried wiring.
The so-called damascene method is mainly employed. This technique is disclosed in, for example, Japanese Patent Application Laid-Open No. 2-278822.

A general method of metal CMP is to attach a polishing cloth (pad) on a circular polishing platen (platen),
The surface of the polishing pad is immersed in a polishing solution for metal, and the surface of the substrate on which the metal film is formed is pressed. The metal film on the convex portion is removed by mechanical friction with the convex portion of the metal film.

[0005] The metal polishing liquid used for CMP generally comprises an oxidizing agent and solid abrasive grains, and if necessary, a metal oxide dissolving agent and a protective film forming agent are further added. It is considered that the basic mechanism is to first oxidize the surface of the metal film by oxidation and to scrape off the oxidized layer with solid abrasive grains. Since the oxide layer on the metal surface of the concave portion does not substantially touch the polishing pad and does not have the effect of the scraping by the solid abrasive grains, the metal layer of the convex portion is removed with the progress of the CMP, and the substrate surface is flattened. See the Journal of Electrochemical Society (Journal of
Vol. 138, No. 11 (19)
1991), pages 3460-3364.

As a method of increasing the polishing rate by CMP, it is effective to add a metal oxide dissolving agent. It can be interpreted that dissolving the metal oxide particles removed by the solid abrasive grains in the polishing liquid increases the effect of the solid abrasive grains. However, when the oxide layer on the surface of the metal film in the recess is also dissolved (hereinafter referred to as etching) and the surface of the metal film is exposed, the surface of the metal film is further oxidized by the oxidizing agent. It is feared that the flattening effect is impaired. In order to prevent this, a protective film forming agent is further added. It is important to balance the effects of the metal oxide dissolving agent and the protective film forming agent. The oxide layer on the surface of the metal film in the concave portion is not etched so much, the particles of the cut oxide layer are efficiently dissolved, and polishing by CMP is performed. High speed is desirable.

As described above, by adding the metal oxide dissolving agent and the protective film forming agent to add the effect of the chemical reaction, the CMP
The speed (polishing speed by CMP) is improved and the CM
The effect of reducing the damage (damage) on the surface of the metal layer to be P is obtained.

However, when a buried wiring is formed by CMP using a conventional metal polishing slurry containing solid abrasive grains, (1) the surface central portion of the buried metal wiring is isotropically corroded. Generation of dish-like phenomenon (hereinafter referred to as dishing), (2) generation of polishing scratches (scratch) derived from solid abrasive grains, and (3) removal of solid abrasive grains remaining on the substrate surface after polishing. The cleaning process is complicated, and (4) the cost of the solid abrasive grains itself and the cost increase due to the waste liquid treatment arise.

In order to suppress the corrosion of the copper alloy during dishing and polishing and to form a highly reliable LSI wiring, a metal oxide dissolving agent composed of aminoacetic acid or amide sulfuric acid such as glycine and BTA (benzotriazole) are used. A method using a contained metal polishing liquid has been proposed. This technique is described in, for example, Japanese Patent Application Laid-Open No. 8-83780.

In the formation of a metal buried such as the formation of a damascene wiring of copper or a copper alloy or the formation of a plug wiring of tungsten or the like, when the polishing rate of a silicon dioxide film which is an interlayer insulating film formed in a portion other than the buried portion is high, Thinning occurs in which the thickness of the wiring is thinned together with the interlayer insulating film.
As a result, variations in resistance occur due to an increase in wiring resistance, pattern density, and the like. Therefore, a characteristic in which the polishing rate of the silicon dioxide film is sufficiently low relative to the metal film to be polished is required. Therefore, a method has been proposed in which the polishing rate of the polishing liquid is made higher than pKa-0.5 by suppressing the polishing rate of silicon dioxide by anions generated by dissociation of the acid. This technique is described in, for example, Japanese Patent No. 2819196.

On the other hand, a tantalum, a tantalum alloy, a tantalum nitride, another tantalum compound, or the like is formed as a barrier layer for preventing copper from diffusing into an interlayer insulating film in a lower layer of a wiring such as copper or a copper alloy. . Therefore, it is necessary to remove the exposed barrier layer by CMP except for the wiring portion where copper or copper alloy is embedded. However, since these barrier layer conductor films have higher hardness than copper or copper alloy, a combination of polishing materials for copper or copper alloy often cannot provide a sufficient CMP rate. Therefore, a two-step polishing method including a first step of polishing copper or a copper alloy and a second step of polishing the barrier layer conductor has been studied.

In a two-step polishing method comprising a first step of polishing copper or a copper alloy and a second step of polishing a barrier layer,
Because the hardness and chemical properties of the films to be polished are different, compositions having considerably different properties are being studied for the composition of the polishing liquid such as pH, abrasive grains and additives.

[0013]

Since the above-mentioned protective effect of benzotriazole (BTA) for forming a protective film is very high, not only the etching rate but also the CMP rate is significantly reduced. Therefore, there has been a demand for a polishing method that does not lower the CMP rate even when polishing is performed using a polishing liquid whose etching rate is sufficiently lowered. Further, tantalum, tantalum alloys, tantalum nitride, and other tantalum compounds used as barrier layers are chemically stable and difficult to etch, and have high hardness, so that mechanical polishing is not as easy as copper or a copper alloy. Therefore, when the hardness of the abrasive grains is increased, polishing flaws are generated in copper or copper alloy to cause poor electrical characteristics, and when the particle concentration of the abrasive grains is increased, polishing of the silicon dioxide film is performed. There is a problem that the speed is increased and erosion occurs. The present invention provides a polishing pad for metal which expresses a high CMP rate, enables high flatness, reduces dishing and erosion, and enables formation of a highly reliable metal film buried pattern. And a polishing method.

[0014]

SUMMARY OF THE INVENTION According to the present invention, a polishing plate and a substrate are held while a substrate having a film to be polished is pressed against the polishing cloth while a metal polishing liquid is supplied onto the polishing cloth of the polishing platen. A polishing method for polishing a film to be polished by relatively moving, wherein the polishing cloth contains a chelate resin. Examples of the chelating resin used for the metal polishing cloth include a resin having an oxygen ligand, a resin having a nitrogen ligand, a resin having a sulfur ligand, a resin having a phosphorus ligand, an oxygen ligand and a nitrogen coordination. It is preferably at least one selected from a resin having a ligand and a copolymer resin obtained by combining the above ligands. Chelating resin
Polyvinyl alcohol, polyacrylic acid, polymethacrylic acid, polyacrylamide, pectic acid, agar, chitosan, polyvinylamine, polyvinylpyrrolidone, polyethyleneimine acetate, ethylenediaminetetraacetic acid (E
It is preferable to use at least one or more of a (DTA) group-containing polyamide resin and an EDTA group-containing phenol formaldehyde resin. A metal polishing cloth preferably has a metal film on a substrate having a film to be polished that contains at least one selected from copper, copper alloys and oxides thereof. The polishing method of the present invention, by supplying a polishing liquid for metal on the polishing cloth of the polishing platen, while relatively moving the polishing platen and the substrate while pressing the substrate having the film to be polished against the polishing cloth In the polishing method for polishing a film to be polished, a polishing method using one of the above-mentioned metal polishing cloths. As the metal polishing liquid, it is a preferable polishing method to use a metal polishing liquid containing no abrasive grains, or a metal polishing liquid containing less than 1% of abrasive grains even if contained.

In the present invention, by using a polishing cloth containing a chelate resin, the effects of high CMP speed, high flattening, reduction of dishing amount and reduction of erosion amount can be exhibited. Some polishing liquids for metals include those which easily form a chelate complex with copper, for example, ethylenediaminetetraacetic acid,
Although a protective film forming agent such as benzotriazole is used, this protective film forming agent has an extremely strong effect of forming a metal surface protective film. For example, when 0.5% by weight or more is contained in a metal polishing solution. The copper alloy film is no longer etched or even CMP.

On the other hand, the present inventors have found that by using a polishing cloth containing a chelate resin, a high CMP rate can be obtained even when polishing is performed using a metal polishing liquid exhibiting a sufficiently low etching rate. Was found. Moreover, it has been found that the use of such a metal polishing liquid enables polishing at a practical CMP rate without including solid abrasive grains in the polishing liquid. This is considered to be due to the fact that the scraping due to the friction of the polishing cloth was developed in contrast to the conventional effect of scraping due to the friction of the solid abrasive grains.

When a substrate having a film to be polished is brought into contact with a polishing liquid for metal, the film to be polished is dissolved and etched. However, if the value of the etching rate can be suppressed to 10 nm / min or less, a preferable flattening effect can be obtained. I understood that. As long as the decrease in the CMP rate is within an acceptable range, it is desirable that the etching rate be even lower, and 5 nm / mi.
If it can be suppressed to n or less, for example, about 50% excess CMP
(C of 1.5 times the time required for CMP removal of the metal film)
Even if MP is performed, dishing remains to the extent that no problem occurs. Further, the etching rate is 1 nm / m
As long as it can be suppressed to in or less, dishing does not pose a problem even if excess CMP of 100% or more is performed.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, a metal film containing copper or a copper alloy (such as copper / chromium) is formed and filled on a substrate having a concave portion on the surface. When the substrate is subjected to CMP using the polishing slurry for metal according to the present invention, the metal film on the convex portion of the substrate is selectively CMPed, and the metal film is left in the concave portion to obtain a desired conductor pattern. The polishing slurry for metal used in the present invention may not substantially contain solid abrasive grains, and is polished because CMP proceeds by friction with the polishing cloth of the present invention, which is much more mechanically soft than solid abrasive grains. Scratches are dramatically reduced. The metal polishing cloth of the present invention contains a chelate resin as an essential component.

Examples of the chelating resin include a resin having an oxygen ligand, a resin having a nitrogen ligand, a resin having a sulfur ligand, a resin having a phosphorus ligand, an oxygen ligand and a nitrogen ligand. It is preferably at least one selected from the group consisting of a resin and a copolymer resin obtained by combining the above-mentioned ligands, and a resin selected from the following group is preferable. Polyvinyl alcohol, polymalic acid, polyacrylic acid, polymethacrylic acid, polyamic acid, polymaleic acid, polyitaconic acid, polyfumaric acid, poly (p-styrenecarboxylic acid), polyacrylamide, aminopolyacrylamide, polyacrylhydroxamic acid, poly Ammonium acrylate, sodium polyacrylate, ammonium polymethacrylate, sodium polymethacrylate, polyamic acid, ammonium polyamic acid, sodium polyamidate and polyglyoxylic acid, polyvinyl (crown ether), (crown cryptate )
Methyl polystyrene, alginic acid, pectic acid, carboxymethyl cellulose, agar, cardan, chitosan,
Resins having oxygen ligands such as heparin, hyaluronic acid, chondroitin sulfate and pullulan; polyvinylamine;
Resins having nitrogen ligands such as 3-vinylaniline copolymer, porphyrin ring-containing polymer, pyrrole ring-containing polymer, aminophenol, polyvinylpyrrolidone, etc .; Resin having a ligand; resin having a phosphorus ligand such as polyvinyl alcohol phosphate ester, phosphate ester group-containing polystyrene, etc .; poly (vinylamine vinyl alcohol), acetic acid polyethyleneimine, ED
Polyamide resin containing TA (ethylenediaminetetraacetic acid) group, phenol formaldehyde resin containing EDTA group, polyglycine, polyaspartic acid, polyglutamic acid, polylysine, glycine-phenol formaldehyde resin, tyrosine-phenol formaldehyde resin, keratin, collagen, fibroin, sericin, etc. Resins having both oxygen ligands and nitrogen ligands; and resins such as copolymers obtained by combining two or more of the above ligands. However, when the substrate to be applied is a silicon substrate for a semiconductor integrated circuit, etc., contamination by an alkali metal, an alkaline earth metal, a halide or the like is not desirable.
Acids or their ammonium salts are preferred. This is not the case when the substrate is a glass substrate or the like. Among them, polyvinyl alcohol, polyacrylic acid, polymethacrylic acid, polyacrylamide, pectic acid, agar, chitosan, polyvinylamine, polyvinylpyrrolidone, acetic acid polyethyleneimine, EDTA (ethylenediaminetetraacetic acid) group-containing polyamide resin and EDTA group-containing Phenol formaldehyde resins are preferred.

The metal film to which the present invention is applied is preferably a laminated film containing at least one selected from copper, a copper alloy, and an oxide of copper or a copper alloy (hereinafter referred to as a copper alloy).

The polishing method of the present invention is characterized in that a substrate having a film to be polished is pressed against a polishing cloth containing a chelate resin while a polishing liquid for metal is supplied onto the polishing cloth of the polishing table. This is a polishing method for polishing a film to be polished by relatively moving a substrate. As an apparatus for polishing, a general polishing apparatus having a holder for holding a semiconductor substrate and a platen on which a polishing cloth (pad) is attached (a motor or the like capable of changing the number of rotations is attached) can be used. The polishing cloth is not particularly limited as long as it contains a chelate resin. If necessary, a nonwoven fabric, a foamed polyurethane, a composite polishing cloth with a porous fluororesin or the like can be used. The polishing conditions are not limited, but the rotation speed of the platen is preferably low, such as 200 rpm or less so that the substrate does not pop out. The pressure at which the semiconductor substrate having the film to be polished is pressed against the polishing cloth is 9.8.
To 98 KPa (100 to 1000 gf / cm ² ), and in order to satisfy the uniformity of the CMP rate in the wafer surface and the flatness of the pattern, 9.8 to 49 KP is required.
a (100 to 500 gf / cm ² ). During polishing, a metal polishing liquid is continuously supplied to the polishing cloth by a pump or the like. The supply amount is not limited, but it is preferable that the surface of the polishing pad is always covered with the polishing liquid. After the polishing is completed, the semiconductor substrate is preferably washed well in running water, and then dried by spin-drying or the like to remove water droplets attached to the semiconductor substrate.

According to the present invention, unlike metal polishing cloths made using only thermoplastic polyurethane, the present invention does not rely on strong mechanical friction caused by solid abrasive grains, but rather by friction with a much softer polishing cloth. A metal polishing cloth capable of CMP flattening can be provided. It is presumed that the inclusion of the chelate resin in the metal polishing cloth expresses a new metal film removing function instead of solid abrasive grains, that is, a metal ion capturing function, and the CMP proceeds. Generally, in CMP, the degree of occurrence of polishing scratches depends on the grain size, grain size distribution, and shape of solid abrasive grains, and a decrease in film thickness (hereinafter referred to as "erosion") due to abrasion of an insulating film and a deterioration in a planarization effect are caused. Again, depending on the particle size of the solid abrasive grains and the physical properties of the polishing pad, when benzotriazole (BTA) is applied to the metal film, especially the copper film surface, dishing of the metal film depends on the hardness of the polishing cloth and the chemical properties of the polishing liquid. It is thought to depend on the nature. That is, although hard solid abrasive grains are necessary for the progress of CMP, the flattening effect and the CMP
It is not desirable to improve the surface integrity (no damage such as polishing scratches). It can be seen that the flattening effect actually depends on the characteristics of the polishing cloth softer than the solid abrasive grains. From this, in the present invention, even if there is no solid abrasive, C
It can be seen that in terms of realizing the progress of MP, it is extremely desirable for CMP of a copper alloy and, consequently, formation of a buried pattern using the same. Among the protective film forming agents, BT
Taking A as an example, when the surface of the copper alloy film is exposed to a solution containing BTA, Cu (I) BTA or Cu (II) BTA is formed by the reaction between copper (Cu) or its oxide and BTA.
It is considered that a polymer-like complex compound film having the structure of (1) as a main skeleton is formed. This film is quite strong, and when a metal polishing solution containing 1% by weight of BTA is used, even if the polishing solution contains solid abrasive grains, it is generally hardly polished. It has been conventionally known that different types of protective films are formed in accordance with the type of the protective film forming agent as described above. With the combination, both a high CMP rate and a low etching rate can be achieved, and strong friction caused by solid abrasive grains is not required.

[0023]

The present invention will be described below in detail with reference to examples. The present invention is not limited by these examples. (Preparation of Metal Polishing Cloth) A thermoplastic polyurethane was kneaded with a chelating resin, wet-solidified, and then dried by heating at 130 ° C. to obtain a metal polishing cloth.

In Examples 1-3 and Comparative Examples 1-2, Table 1
The above-mentioned various chelating resins were subjected to CMP under the following polishing conditions using the above-mentioned metal polishing cloth. (Preparation of polishing liquid) 0.15 parts by weight of DL-malic acid (special grade reagent) and water 7
0 parts by weight were added and dissolved, and a solution of 0.2 parts by weight of benzotriazole in 0.8 parts by weight of methanol was added thereto.
Finally, hydrogen peroxide solution (special grade reagent, 30% by weight aqueous solution) 3
What was obtained by adding 3.2 parts by weight was used as a metal polishing liquid. When using abrasive grains, γ-alumina having a particle size of 300 nm was added. (Polishing conditions) Substrate: Silicon substrate on which a copper film having a thickness of 1 μm was formed Polishing pressure: 20.6 KPa (210 g / cm ² ) Relative speed between substrate and polishing platen: 36 m / min (Evaluation of polished product) CMP speed : The difference in film thickness of the copper film before and after CMP was calculated from the electrical resistance value. Etching rate: The difference in the thickness of the copper layer before and after immersion in a stirred metal polishing liquid (25 ° C., stirring 100 rpm) was calculated from the electrical resistance value. Further, in order to evaluate actual CMP characteristics, CMP was performed using a silicon substrate in which a groove having a depth of 0.5 μm was formed in an insulating layer, a copper film was formed by a known sputtering method, and embedded by a known heat treatment. went. Erosion is observed by visual inspection, optical microscope observation, and electron microscope observation of the substrate after CMP.
The presence or absence of John and polishing scratches was confirmed. As a result, no erosion or polishing scratches were found.

In Examples 1 to 4 and Comparative Examples 1 to 3,
Table 1 shows the evaluation results of the CMP rate, the etching rate, and the dishing amount.

[0026]

[Table 1]

As shown in Comparative Example 1, when a polishing cloth containing no chelating resin is used, the CMP speed (polishing speed)
Decrease. Also, as shown in Comparative Examples 2 and 3, when a polishing cloth containing no chelating resin and a metal polishing liquid containing abrasive grains are used, the etching rate increases, and as a result, the dishing amount increases. On the other hand, as shown in Examples 1 to 4, when a metal polishing cloth containing a chelate resin is used, the CMP rate is low despite the low etching rate.
The speed can be increased and the polishing time can be reduced. In addition, the dishing amount is small and high flatness can be achieved.

[0028]

The metal polishing cloth of the present invention can exhibit a high CMP rate by forming a chelating resin and can form a highly reliable embedded pattern.

 ──────────────────────────────────────────────────の Continued on front page (72) Inventor Yasushi Kurata 48 Wadai, Tsukuba, Ibaraki Prefecture Within Hitachi Chemical Co., Ltd. (72) Inventor Hiroki Terasaki 48 Wadai, Tsukuba, Ibaraki Prefecture Hitachi Chemical Co., Ltd. In-house (72) Inventor Akiko Igarashi 48 Wadai, Tsukuba-shi, Ibaraki F-term in Hitachi Chemical Co., Ltd. Research Laboratory 3C058 AA07 AA09 CA01 CB03 DA02 DA12

Claims (7)

[Claims] 1. A substrate to be polished by relatively moving a polishing platen and a substrate while a substrate having a film to be polished is pressed against the polishing cloth while supplying a polishing liquid for metal onto the polishing cloth of the polishing platen. A polishing cloth for metal, wherein the polishing cloth contains a chelate resin. 2. The chelating resin is a resin having an oxygen ligand, a resin having a nitrogen ligand, a resin having a sulfur ligand, a resin having a phosphorus ligand, an oxygen ligand and a nitrogen ligand. 2. The metal polishing cloth according to claim 1, wherein the polishing pad is at least one selected from a resin having the following and a copolymer resin obtained by combining the ligands. 3. 3. The method according to claim 1, wherein the chelating resin is polyvinyl alcohol.
, Polyacrylic acid, polymethacrylic acid, polyacrylamide, pectic acid, agar, chitosan, polyvinylamine, polyvinylpyrrolidone, acetated polyethyleneimine, polyamide resin containing ethylenediaminetetraacetic acid (EDTA) group, and phenol formaldehyde resin containing EDTA group 2. The method according to claim 1, wherein at least one kind is used.
Alternatively, the metal polishing cloth according to claim 2. 4. The method according to claim 1, wherein the metal film of the substrate having the film to be polished contains at least one selected from copper, copper alloys and oxides thereof. Polishing cloth for metal. 5. A substrate to be polished by relatively moving a polishing platen and a substrate while a substrate having a film to be polished is pressed against the polishing cloth while supplying a polishing liquid for metal onto the polishing cloth of the polishing platen. A polishing method for polishing a film, wherein the polishing is performed by using the metal polishing cloth according to claim 1. 6. The polishing method according to claim 5, wherein the metal polishing liquid contains no abrasive grains. 7. The polishing method according to claim 5, wherein a polishing liquid for metal containing less than 1% of abrasive grains is used.