JP5135755B2 - Polishing agent for copper and copper alloy and polishing method using the same - Google Patents

Description

  The present invention relates to a polishing agent for copper and copper alloy and a polishing method using the same, and particularly to a polishing agent for copper and copper alloy having a high polishing rate suitable for use in a chemical mechanical planarization (CMP) process and the same. The present invention relates to a polishing method using stencil.

In order to improve the performance of LSIs, the use of copper alloys as a wiring material is progressing instead of conventional aluminum alloy wiring. The copper alloy is difficult to be finely processed by the dry etching method frequently used in the formation of the conventional aluminum alloy wiring.
Therefore, a so-called damascene method is mainly employed in which a copper alloy thin film is deposited and embedded on an insulating film in which grooves have been formed in advance, and the copper alloy thin film other than the grooves is removed by CMP to form embedded wiring. (See Patent Document 1).

  The general method of metal CMP for copper alloys is to apply a polishing pad on a circular polishing platen (platen), immerse the surface of the polishing pad with a metal abrasive, and press the surface on which the metal film of the substrate is formed. Then, with a predetermined pressure (hereinafter referred to as polishing pressure) applied from the back surface, the polishing platen is rotated, and the metal film on the convex portion is removed by mechanical friction between the abrasive and the convex portion of the metal film. Is.

The metal abrasive used in CMP is generally composed of an oxidizer and abrasive grains, and a metal oxide solubilizer and a protective film forming agent are further added as necessary.
First, it is considered that the basic mechanism is to oxidize the surface of a metal film with an oxidizing agent and scrape the oxidized layer with solid abrasive grains.

  Since the oxide layer on the metal surface of the recess does not touch the polishing pad so much and does not have the effect of scraping with solid abrasive grains, the metal layer on the protrusion is removed and the substrate surface is flattened with the progress of CMP (non-patent) Reference 1).

In general, in the manufacture of LSI, an abrasive having a film thickness of about 1 μm and a polishing rate of about 0.5 μm / min is used (see Patent Document 2).
JP-A-2-278822 Journal of Electrochemical Society, Vol.138, No.11 (published in 1991) 3460-3464 JP 2003-124160 A

  In recent years, CMP processing of copper and copper alloys applied to LSIs is about to be applied to the production of high-performance and fine wiring boards such as package substrates. Since these wiring boards are thicker than the LSI, the conventional LSI polishing agent has a problem that the polishing rate is low and the productivity is lowered. For this reason, as a CMP abrasive | polishing agent for high performance wiring board manufacture, it was calculated | required that a metal film can be grind | polished at high speed compared with the conventional abrasive | polishing agent.

  It is an object of the present invention to be able to smoothly polish copper and copper alloy films at a high polishing rate of 1.5 μm / min or more, and for products that require polishing of thick metal films such as high-performance wiring boards. In production, the present invention provides a polishing agent for copper and copper alloy that can be polished in a short time and can secure sufficient productivity.

The present invention includes (1) an inorganic acid, an amino acid, a protective film-forming agent for metal surfaces, abrasive grains, an oxidizing agent and water, has a pH of 1.5 to 4, and has a neutralization titration equivalent of 0 with potassium hydroxide. It is related with the abrasive | polishing agent for copper and copper alloy which are 0.05 mol / kg or more.
The present invention also relates to (2) the abrasive for copper and copper alloys according to (1), wherein the inorganic acid is at least one of sulfuric acid and phosphoric acid.
The present invention also relates to (3) amino acids, about copper and copper alloys for abrasives logarithm of the reciprocal of the first acid dissociation constant (pK 1) _{2 to 3} amino acid (1) or (2).

The present invention also provides (4) the polishing agent for copper and copper alloys according to any one of (1) to (3), wherein the protective film forming agent for the metal surface is at least one selected from benzotriazole and derivatives thereof. About.
The present invention also relates to (5) the abrasive for copper and copper alloy according to any one of (1) to (4), wherein the abrasive grains are made of colloidal silica or colloidal alumina having an average particle diameter of 100 nm or less.
Moreover, this invention is (6) Polishing for copper and copper alloys in any one of said (1)-(5) whose oxidizing agent is at least 1 sort (s) chosen from hydrogen peroxide, persulfuric acid, and persulfate. It relates to the agent.

Moreover, this invention relates to the abrasive | polishing agent for copper and copper alloys in any one of said (1)-(6) which contains water-soluble polymer other than the said component (7).
The present invention also relates to (8) the abrasive for copper and copper alloy according to (7), wherein the water-soluble polymer is any one of polyacrylic acid, a salt thereof, polymethacrylic acid and a salt thereof.
Furthermore, the present invention provides (9) a copper film, a copper alloy film, a laminated film of copper or a copper alloy and another metal using the copper and copper alloy abrasive according to any one of (1) to (8). A polishing method characterized in that a part of the metal film is removed by a step of polishing the metal film made of any of the above.

Since the polishing agent for copper and copper alloy according to the present invention is a buffer solution having a pH of 1.5 to 4 containing an inorganic acid having a strong dissolving action, the copper and copper alloy which are objects to be polished are dissolved in the polishing agent. However, it is difficult for pH fluctuation to occur, and a high polishing rate can be maintained.
Moreover, according to the polishing method of the present invention, it is possible to achieve a high polishing rate and to suppress the surface roughness on the metal film, and it is possible to achieve both improvement in productivity and improvement in product yield. For example, it is suitable for applications that require high-speed polishing of thick copper or copper alloy films such as high-performance wiring boards.

  The abrasive for copper and copper alloy of the present invention contains an inorganic acid, an amino acid, a protective film-forming agent for metal surfaces, abrasive grains, an oxidizing agent and water, and has a pH of 1.5 to 4, neutralization titration with potassium hydroxide The equivalent amount is adjusted to 0.05 mol / kg or more.

  Examples of the inorganic acid include hydrochloric acid, hydrobromic acid, hydroiodic acid, sulfuric acid, phosphoric acid, etc. Among them, sulfuric acid, phosphoric acid, or a mixture of sulfuric acid and phosphoric acid has a high polishing rate by CMP. It is preferable in that the surface roughness of the copper and copper alloy films can be reduced.

  Examples of the amino acids include glycine, alanine, valine, leucine, isoleucine, serine, threonine, cysteine, cystein, methionine, aspartic acid, glutamic acid, lysine, arginine, phenylalanine, tyrosine, histidine, tryptophan, proline, oxyproline, and the like. .

Among these, the first acid dissociation constant _{K 1} of the inverse of the logarithm (pK ₁₎ amino acids 2-3 are preferable in view of easily adjusting the pH of the polishing agent 1.5-4. Specific examples include alanine, arginine, isoleucine, glycine, glutamic acid, tryptophan, threonine, valine, methionine, lysine, and leucine, with glycine being particularly preferred.

Examples of the protective film forming agent for the metal surface include benzotriazole (BTA), BTA derivatives, triazole, quinaldic acid, anthonylic acid, salicylaldoxime and the like.
Examples of BTA derivatives include those in which one hydrogen atom of the benzene ring of BTA is substituted with a methyl group (tolyltriazole), those substituted with a carboxyl group (benzotriazole-4-carboxylic acid and benzotriazole-4-carboxylic acid). Methyl, ethyl, propyl, butyl and octyl esters). In these, BTA and its derivative (s) are preferable, and they may be individual or the mixture selected 2 or more types.

  The abrasive grains may be any of inorganic abrasive grains such as silica, alumina, zirconia, ceria, titania, silicon carbide, and organic abrasive grains such as polystyrene, polyacryl, polyvinyl chloride, etc., but are stable in the abrasive. Colloidal silica and colloidal alumina, which have good properties and have a small number of polishing scratches (scratches) generated by CMP and an average particle size of 100 nm or less, are preferred. In the present invention, the average particle diameter of the particles refers to the value of D50 (median diameter of volume distribution, cumulative median value) measured with a laser diffraction particle size distribution meter.

  Colloidal silica is known for its production by hydrolysis of silicon alkoxide or ion exchange of sodium silicate, and colloidal alumina is known for its production by hydrolysis of aluminum nitrate.

Examples of the oxidizing agent in the present invention include hydrogen sulfate (H ₂ O ₂ ), persulfates such as persulfuric acid, ammonium persulfate, and potassium persulfate, periodic acid, potassium periodate, and the like. Hydrogen, persulfuric acid and persulfate are preferred. These may be used alone or in combination of two or more.

In the present invention, it is preferable to add a water-soluble polymer to the abrasive.
As the water-soluble polymer, monomers having a carboxyl group such as polyacrylic acid, polyacrylic acid ammonium salt, polyacrylic acid sodium salt, polymethacrylic acid, polymethacrylic acid ammonium salt, polymethacrylic acid sodium salt, polyacrylamide are basically used. Examples of the polymer include a polymer having a structural unit and a monomer having a vinyl group such as a salt thereof, polyvinyl alcohol, and polyvinylpyrrolidone.

  Among these, polyacrylic acid, a salt thereof, polymethacrylic acid and a salt thereof are particularly preferable. The polishing rate can be improved by adding these water-soluble polymers.

  The pH of the polishing agent for copper and copper alloy in the present invention is in the range of pH 1.5 to pH 4 in that the polishing rate of copper and copper alloy by CMP is large and does not cause corrosion in the copper and copper alloy film, and pH 2 A range of ˜pH 3 is preferred. If the pH is less than 1.5, the surface roughness of the copper and copper alloy film becomes large. If the pH exceeds 4, the polishing rate by CMP is slow and cannot be a practical abrasive.

pH can be adjusted with the addition amount of an inorganic acid and an amino acid.
It can also be adjusted by adding alkali components such as ammonia, sodium hydroxide and tetramethylammonium hydroxide.
In the present invention, the pH of the abrasive is measured with a pH meter (for example, model number PH81 manufactured by Yokogawa Electric Corporation). After calibrating two points using a standard buffer solution (phthalate pH buffer solution pH: 4.01 (25 ° C.), neutral phosphate pH buffer solution pH 6.86 (25 ° C.)), the electrode was polished. The value after 2 minutes or more has been stabilized is adopted.

The abrasive for copper and copper alloy in the present invention is a pH buffer solution containing an inorganic acid component, and the neutralization titration equivalent with potassium hydroxide is preferably 0.05 mol / kg or more, and is 0.08 mol / kg. More preferably. .
The neutralization titration equivalent here is the number of moles of potassium hydroxide required to increase the pH value of 1 kg of the abrasive to 4. Inorganic acids are generally strong acids, and when added in a large amount, the pH drops and it is difficult to adjust the pH to the range of 1.5-4. Therefore, by adding an amino acid to the inorganic acid, the abrasive can be made into a pH buffer solution having a pH of 1.5 to 4.

  When polished, the copper and copper alloy of the film to be polished dissolve as cations in the CMP abrasive. Here, if the amount of the inorganic acid added is small, hydrogen ions are consumed by dissolution of the film to be polished, and the pH of the polishing agent increases. This reduces the polishing rate.

  On the other hand, when a polishing agent containing a sufficient amount of inorganic acid and having a pH buffering action is used, even if a large amount of metal ions such as copper ions are dissolved, an increase in pH is suppressed and stable polishing is achieved. It becomes possible. For this purpose, the amount of inorganic acid in the polishing agent is an amount equivalent to 0.05 mol / kg or more by neutralization titration with potassium hydroxide although it depends on the polishing rate and the polishing agent flow rate during polishing. For example, a disk-shaped substrate of 8 inches (20.3 cm) can be polished at a high speed with an abrasive flow rate around 200 ml / min.

  The blending amount of the protective film forming agent for the metal surface in the present invention is preferably 0.05% by mass to 1% by mass, and preferably 0.1% by mass to 0.5% by mass with respect to the total amount of the abrasive. More preferred. If it is less than 0.05% by mass, the surface roughness of the metal tends to increase, and if it exceeds 1% by mass, the polishing rate tends to decrease.

  The blending amount of the abrasive grains in the present invention is preferably 0.1% by mass to 10% by mass and more preferably 1% by mass to 5% by mass with respect to the total amount of the abrasive. If the added amount of abrasive grains is less than 0.1% by mass, the polishing rate tends to be small because the physical grinding action is small. There is no increase in speed.

  The blending amount of the oxidizing agent in the present invention is preferably 0.1 mol / kg to 5 mol / kg, and more preferably 0.5 mol / kg to 4 mol / kg with respect to the total amount of the abrasive. If the blending amount is less than 0.1 mol / kg, the polishing rate tends to be low, and if it exceeds 5 mol / kg, the polishing rate tends to decrease.

  The blending amount of the water-soluble polymer in the present invention is preferably 0.01% by mass to 2.0% by mass and more preferably 0.1% by mass to 1.0% by mass with respect to the total amount. preferable. When the blending amount is less than 0.01% by mass, the effect of improving the polishing rate is hardly recognized, and when the blending amount exceeds 2.0% by mass, the dispersion stability of the abrasive tends to be lowered.

The polishing method of the present invention is characterized in that a part of the metal film is removed by the step of polishing the metal film using the copper and copper alloy polishing slurry of the present invention.
The metal film to be polished is a copper film, a copper alloy film, a laminated film of copper or a copper alloy and another metal, for example, a thick metal film in a manufacturing process of a high performance / fine wiring board such as a package substrate. Is done.

Here, a specific polishing method is to relatively move the polishing platen and the substrate while supplying the abrasive while the substrate having the surface to be polished is pressed onto the polishing cloth (pad) of the polishing platen. The method of grind | polishing a to-be-polished surface by is mentioned.
In addition, a method of bringing a metal or resin brush into contact with each other and a method of spraying an abrasive at a predetermined pressure can be mentioned.

  As an apparatus for polishing, for example, when polishing with a polishing cloth, it is common to have a surface plate to which a polishing cloth is attached and a holder that can hold the substrate to be polished, connected to a motor whose rotation speed can be changed. A simple polishing apparatus can be used. As an abrasive cloth, a general nonwoven fabric, a polyurethane foam, a porous fluororesin, etc. can be used, and there is no restriction | limiting in particular.

  The polishing conditions are not limited, but the rotation speed of the surface plate is preferably a low rotation of 200 min-1 or less so that the substrate does not jump out. The pressing pressure (polishing pressure) of the substrate having the surface to be polished to the polishing cloth is preferably 1 to 100 kPa. In order to satisfy the uniformity in the surface to be polished at the CMP rate and the flatness of the pattern, 5 More preferably, it is -50kPa. During polishing, an abrasive is continuously supplied to the polishing cloth with a pump or the like. Although there is no restriction | limiting in this supply amount, it is preferable that the surface of polishing cloth is always covered with the abrasive | polishing agent.

The substrate after polishing is preferably washed in running water and then dried after removing water droplets adhering to the substrate using spin drying or the like. In order to perform CMP with the surface state of the polishing cloth always the same, it is preferable to perform a conditioning process of the polishing cloth before polishing. For example, the polishing cloth is conditioned with a liquid containing at least water using a dresser with diamond particles.
Subsequently, it is preferable to perform a CMP polishing process according to the present invention, and further add a substrate cleaning process.
The present invention can be applied not only to polishing copper and copper alloys of wiring boards, but also to polishing copper and copper alloys of semiconductors such as LSI.

Hereinafter, the present invention will be described by way of examples. The present invention is not limited by these examples.
Example 1
(Method for producing abrasive for copper and copper alloy)
0.05 mol of sulfuric acid (5.1 g of 96% sulfuric acid) as an inorganic acid, 25 g of glycine as an amino acid, 3 g of BTA as a protective film forming agent for the metal surface, and an average particle prepared by hydrolysis of tetraethoxysilane in an ammonia solution as an abrasive In 70 g of colloidal silica having a diameter of 70 nm, it was dissolved in 646.9 g of water. What was obtained by adding 300 g of hydrogen peroxide solution (special grade, 30% aqueous solution) to this was used as an abrasive for copper and copper alloys.

The measured value of the neutralization titration equivalent was 0.09 mol / kg, and the pH was 2.6. The measurement was performed using a pH meter (PH81 manufactured by Yokogawa Electric Corporation) in a constant temperature water bath at 25 ° C.
As the substrate, a glass epoxy substrate was prepared by attaching a 18 μm thick copper foil cut out to a size of 8 inches (20.3 cm) (φ) in diameter. Using this substrate, CMP treatment was performed under the following polishing conditions while dropping the above-mentioned abrasive onto a pad attached to a surface plate of a polishing apparatus, and the following evaluation was performed.

(Polishing conditions)
Polishing equipment: Surface plate size is 600mm (φ) in diameter, rotary type Polishing pad: Polyurethane resin with closed cells Polishing pressure: 35kPa
Relative speed between substrate and polishing surface plate: 70 m / min
Abrasive flow rate: 200ml / min

(Evaluation items and evaluation methods)
Copper polishing rate by CMP: The difference in film thickness of the substrate before and after CMP was calculated from the change in sheet resistance.
Surface roughness (arithmetic average roughness Ra): The surface roughness of the copper film after polishing was measured with an AFM (atomic force microscope). The measurement was performed in a 5 μm × 5 μm area range at a location 50 mm away from the center of the substrate in the radial direction.
As a result of the evaluation, the copper polishing rate was 2.2 μm / min, and the surface roughness Ra was 2.7 nm.

Example 2
A polishing agent for copper and a copper compound was prepared in the same manner as in Example 1 except that 0.02 M phosphoric acid (2.3 g of 85% phosphoric acid) was added and the amount of water added was reduced to 644.6 g. The measured value of neutralization titration equivalent was 0.11 mol / kg and pH was 2.5. A CMP process was performed in the same manner as in Example 1 using the above abrasive, and evaluation was performed.
As a result of the evaluation, the polishing rate of the copper film was 2.7 μm / min, the surface roughness was 1.3 nm in Ra, the polishing rate was increased, and the surface roughness was improved.

Example 3
A polishing agent for copper and a copper compound was prepared in the same manner as in Example 2 except that 5 g of polyacrylic acid having a molecular weight of 20,000 was added as a water-soluble polymer and water was reduced to 639.6 g. The measured value of the neutralization titration equivalent was 0.12 mol / kg, and the pH was 2.5. A CMP process was performed in the same manner as in Example 1 using the above abrasive, and evaluation was performed.
As a result of the evaluation, the polishing rate of the copper film was 2.9 μm / min, the surface roughness was 1.1 nm in Ra, the polishing rate was increased, and the surface roughness was improved.

Comparative Example 1
A polishing agent for copper and copper alloy films was prepared in the same manner as in Example 1 except that glycine as an amino acid was not added and water was increased to 664.6 g. The measured value of the neutralization titration equivalent was 0.09 mol / kg, and the pH was 1.2. A CMP process was performed in the same manner as in Example 1 using the above abrasive, and evaluation was performed.
As a result of the evaluation, the polishing rate of the copper film was 2.1 μm / min, the surface roughness was 35.6 nm in Ra, and no significant change in the polishing rate was observed, but the surface roughness was reduced.

Comparative Example 2
A polishing agent for copper and copper alloy films was prepared in the same manner as in Example 1 except that the inorganic acid was reduced to 0.01 mol of sulfuric acid (96% sulfuric acid 1.02 g). The measured value of the neutralization titration equivalent was 0.018 mol / kg, and the pH was 3.3. A CMP process was performed in the same manner as in Example 1 using the above abrasive, and evaluation was performed.
As a result of the evaluation, the polishing rate of the copper film was 0.8 μm / min, the surface roughness was 2.1 nm in Ra, and the polishing rate was greatly reduced.

Claims (9)

Inorganic acid, amino acid, protective film forming agent for metal surface, abrasive grains, oxidizing agent and water,
pH is 1.5 to 3,
The first-stage acid dissociation index of the amino acid at 25 ° C. is 2 or more and 3 or less,
A polishing agent for copper and copper alloys , wherein a neutralization titration equivalent with potassium hydroxide is 0.05 mol / kg or more.   The abrasive for copper and copper alloy according to claim 1, wherein the inorganic acid is at least one of sulfuric acid and phosphoric acid. The polishing agent for copper and copper alloy according to claim 1 or 2, wherein the amino acid is selected from the group consisting of alanine, arginine, isoleucine, glycine, glutamic acid, tryptophan, threonine, valine, methionine, lysine, and leucine .
  The abrasive | polishing agent for copper and copper alloys in any one of Claims 1-3 which the protective film formation agent with respect to a metal surface consists of 1 or more types chosen from the benzotriazole and its derivative (s).   The abrasive | polishing agent for copper and copper alloys in any one of Claims 1-4 in which an abrasive grain consists of colloidal silica or colloidal alumina with an average particle diameter of 100 nm or less.   The polishing agent for copper and copper alloy according to any one of claims 1 to 5, wherein the oxidizing agent is at least one selected from hydrogen peroxide, persulfuric acid and persulfate.   Furthermore, the abrasive | polishing agent for copper and copper alloys in any one of Claims 1-6 formed by containing water-soluble polymer.   The abrasive for copper and copper alloy according to claim 7, wherein the water-soluble polymer is any one of polyacrylic acid, a salt thereof, polymethacrylic acid and a salt thereof.   A metal film comprising any one of a copper film, a copper alloy film, a laminated film of copper or a copper alloy and another metal is polished using the abrasive for copper and copper alloy according to claim 1. A polishing method, wherein a part of the metal film is removed by a process.