JP2009206151A - Polishing composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polishing composition for polishing a tungsten film and an insulation film at a high selective rate while scarcely causing erosion. <P>SOLUTION: The polishing composition contains colloidal silicon dioxide having average primary particle size of 7-40 nm, malonic acid, hydroxide, iron nitrate and water. The malonic acid is added in the content of 10-100 g/L and the hydroxide is used for pH control. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention relates to a polishing composition used for polishing various industrial products such as semiconductors, photomasks, various memory hard disk substrates and synthetic resins or members thereof, and is particularly suitable for surface planarization processing of device wafers in the semiconductor industry and the like. The present invention relates to a polishing composition.
More particularly, the present invention relates to a polishing composition suitable for use in polishing of a tungsten plug forming step and a tungsten wiring forming step during a semiconductor manufacturing process.

  In recent years, so-called high-tech products such as computers have made remarkable progress, and components used therein, such as ULSI, are steadily increasing in integration and speed. Accordingly, the design rules of semiconductor devices are becoming finer year by year, the depth of focus in the device manufacturing process is shallower, and the flatness required for the pattern formation surface is becoming stricter.

  In addition, in order to cope with an increase in wiring resistance due to miniaturization of wiring, the wiring length is shortened by multilayering of devices, but a step on the formed pattern surface has become a problem as an obstacle to multilayering. .

  In order to perform such miniaturization and multilayering, it is necessary to flatten the desired surface in order to remove the step in the process, and so far, spin-on glass, resist etchback and other methods have been used. The flattening method was used.

  However, with these methods, partial planarization is possible, but it is difficult to achieve the global planarization (complete planarization) required for next-generation devices. Planarization by mechanochemical polishing (hereinafter referred to as “CMP”) in which physical polishing and chemical polishing are combined has been studied.

  On the other hand, CMP processing technology includes tungsten, copper, aluminum, ruthenium, platinum, gold, hafnium, cobalt and nickel as wiring materials, titanium, tantalum and their alloys as barrier films, silicon dioxide films as interlayer insulating films, Planarization of a low-K film, single crystal silicon or polycrystalline silicon serving as a substrate, formation of an element isolation structure, and other applications are being studied. In such applications, polishing compositions for polishing materials including tungsten, ruthenium, platinum, hafnium, and the like that are relatively hard and are not easily affected by chemicals, such as tungsten, have been studied.

  Patent Document 1 describes a polishing composition for tungsten containing abrasive grains, an ammonium group-containing pH adjuster, and an oxidizing agent. The characteristic of the polishing composition described in this patent document is that the content of unnecessary metal ions is very low by using an ammonium salt as a pH adjuster. However, the polishing rate for the tungsten film is not sufficient, and there is room for further improvement in order to obtain a practical polishing rate. Moreover, the erosion was also large, and the improvement was desired also from this point.

  Patent Document 2 discloses a polishing composition containing an oxidant and a catalyst having multiple oxidation sites. Specifically, this patent document illustrates a composition containing a peroxide such as hydrogen peroxide and an iron salt such as ferric nitrate. However, according to the study by the present inventors, such a polishing composition does not have a sufficiently high polishing rate with respect to the insulating film, and on the other hand, the erosion tends to increase, and improvement is necessary.

Patent Document 3 discloses a tungsten film polishing composition comprising an abrasive selected from the group consisting of silicon dioxide, aluminum oxide, cerium oxide, silicon nitride, and zirconium oxide, and water, and further comprising this composition. Disclosed is a tungsten film polishing composition comprising an iron (III) compound dissolved therein. However, agglomerates may occur during slurry storage, and there is room for improvement from the viewpoint of storage stability.
Republished 1998-054756 Japanese Patent Laid-Open No. 10-265766 JP-A-10-163142

  The present invention seeks to improve the problems in the prior art as described above. Specifically, the generation of erosion, which has been a problem in the prior art, is suppressed, and the tungsten film polishing rate is increased without deteriorating storage stability, while the insulating film polishing rate is decreased. The purpose is to do.

The polishing composition according to the present invention comprises:
1 to 20 g / L of silicon dioxide having an average primary particle size of 7 to 40 nm;
10 to 100 g / L malonic acid;
10 to 100 g / L of a hydroxide selected from the group consisting of potassium hydroxide, ammonium hydroxide, and mixtures thereof;
20 to 200 g / L of iron nitrate;
It is characterized by comprising water.

  Also, the polishing method for a plug or wiring structure according to the present invention comprises an insulator layer having holes and wiring grooves on the surface, and tungsten formed on the insulating layer so that the holes and wiring grooves are completely filled. A plug or a wiring structure including a conductive layer including the conductive layer is polished with the polishing composition.

  Furthermore, the wiring structure according to the present invention is polished once using the above polishing composition, and then polished with another polishing composition having a polishing rate for the insulating film larger than that for the tungsten film, Furthermore, good flatness can be obtained.

  According to the present invention, a polishing composition having a high polishing rate for tungsten and a low polishing rate for an insulating film is provided. Therefore, there is little loss of the insulating film at the time of polishing, and plugs and wirings can be formed at low cost. Further, since silicon dioxide used in the present invention has an appropriate hardness as compared with the case where other abrasive grains such as alumina are used, there are few scratches on the insulating film after polishing. Furthermore, problems such as corrosion of the apparatus, safety and health problems to the human body, pad life and the like can be avoided.

<Abrasive grains>
The polishing composition of the present invention comprises silicon dioxide as abrasive grains. Silicon dioxide is generally produced by a sol-gel method or the like, and various types are commercially available. In the polishing composition according to the present invention, silicon dioxide polishes the surface to be polished by mechanical action. The present invention increases the polishing rate for tungsten and reduces the polishing rate for the insulating film as much as possible, in other words, increases the so-called selection ratio obtained by dividing the polishing rate for the tungsten film by the polishing rate for the insulating film. Objective. Due to the large selection ratio, in polishing of a wiring structure having both a tungsten film and an insulating film, the tungsten film can be polished at a high speed and the polishing can be terminated when an insulating film as a stopper layer appears. This is because it becomes easy and management of the polishing operation becomes easy. In the present invention, the particle size of the silicon dioxide is preferably larger than a certain value from the viewpoint of increasing the polishing rate for tungsten. On the other hand, from the viewpoint of making the polishing rate for the insulating film as small as possible, the smaller particle size is preferable. preferable. Further, when the particle size is excessively large, erosion tends to deteriorate.

  From such a viewpoint, the size of the abrasive grains needs to be within a certain range, specifically, the average primary particle diameter measured by the BET method needs to be 7 to 40 nm, and 8 It is preferably ˜20 nm, more preferably 9 to 15 nm.

  Further, the content of the abrasive grains in the polishing composition is preferably higher from the viewpoint of increasing the polishing rate of the tungsten film, and on the other hand, it may not be excessively increased in order to reduce the polishing rate for the insulating film. preferable. Specifically, the content of the abrasive grains with respect to the polishing composition is 1 to 20 g / L, preferably 2 to 15 g / L, and more preferably 3 to 10 g / L.

  According to the present invention, the polishing rate for the tungsten film and the insulating film can be controlled by appropriately controlling the particle size and concentration of silicon dioxide as abrasive grains, and polishing is performed at a high polishing rate while maintaining a high selection ratio. In other words, a highly selective polishing composition is provided.

  In addition, the abrasive grains in the present invention do not polish the insulating film, selectively polish the tungsten film, and contain almost no metal ions, particularly sodium ions, in order to avoid contaminating the object to be polished. None is preferred. As such silicon dioxide, high purity colloidal silica synthesized using tetramethoxysilane as a raw material is preferable. Such high-purity silica is, for example, high-purity colloidal silica with a low content of impurities by dissolving tetramethoxysilane in a solvent consisting of methanol, ammonia and water and hydrolyzing it, and then substituting the solvent with water. Can be obtained. Fumed silica is also a preferred silicon dioxide with high purity. This fumed silica is produced, for example, by hydrolyzing silicon tetrachloride in an oxygen and hydrogen flame. Here, as an index indicating the metal content of silicon dioxide, the content of sodium can be used. In the present invention, the sodium content of silicon dioxide is preferably 1 ppm or less, and 0.5 ppm or less. More preferably. When 1 ppm or more of sodium is present in the colloidal silica, care should be taken because sodium may remain in an amount exceeding an allowable amount on the polished insulating film.

  Note that sodium silicate colloidal silica produced by treating sodium silicate with an ion exchange resin is not preferable because it contains a relatively large amount of sodium impurities and tends to increase sodium relative to the insulating film.

  In addition, the polishing composition by this invention can also contain abrasive grains other than colloidal silica. Examples of such abrasive grains include silicon dioxide other than colloidal silica, aluminum oxide, cerium oxide, silicon nitride, and zirconium oxide. However, since abrasive grains other than silicon dioxide tend to have more scratches, care must be taken in selecting the abrasive grains.

<Iron nitrate>
In the present invention, iron nitrate promotes the polishing action by a chemical action as a polishing accelerator. Especially, since it is excellent in the effect which accelerates | stimulates a grinding | polishing effect | action, ferric nitrate whose iron ion is trivalent is used suitably.

  The content of iron nitrate in the polishing composition according to the present invention is preferably large, particularly in order to increase the polishing rate for tungsten. However, if the amount added is excessive, precipitates may be generated. Specifically, the addition amount of iron nitrate is 20 to 200 g / L, preferably 40 to 150 g / L, based on the total amount of the polishing composition.

<Malonic acid>
The polishing composition according to the present invention comprises malonic acid. This malonic acid has an effect of improving the storage stability of the composition. The content of malonic acid is preferably large in order to prevent the formation of precipitates at the time of preparation, particularly when iron nitrate is added. On the other hand, precipitates are generated when the composition is at a low temperature of, for example, 5 ° C. or lower. In order to prevent this, it is preferable that the amount is not more than a certain amount.

  In the present invention, the content of malonic acid contributes to the pH of the composition described later, but is 10 to 100 g / L, preferably 20 to 70 g / L, based on the entire composition.

<Hydroxide>
The polishing composition according to the present invention comprises a hydroxide. The hydroxide is potassium hydroxide, ammonium hydroxide, or a mixture thereof. This hydroxide has the effect of adjusting the pH of the composition. That is, it is preferable that the content is large in order to maintain the stability of the abrasive grains in the composition, but a certain amount in order to suppress the generation of precipitates during the preparation of the composition, for example, when iron nitrate is added. The following is preferable. Specifically, the amount added varies depending on the content of other components, but is 10 to 100 g / L, preferably 20 to 70 g / L.

<Water>
The polishing composition according to the present invention comprises water as a solvent for dispersing or dissolving each component. From the viewpoint of suppressing the inhibition of the action of each component of the polishing composition, water is preferably water containing as little impurities as possible, specifically, after removing impurity ions with an ion exchange resin, Pure water, ultrapure water, or distilled water from which foreign substances have been removed through a filter is preferable.

<Polishing composition>
The polishing composition of the present invention is generally prepared by dispersing or dissolving the above-described components, that is, abrasive grains, iron nitrate, and inorganic acid in water. The method of dispersing or dissolving these components in water is arbitrary, and for example, they are dispersed by stirring with a blade-type stirrer or ultrasonic dispersion. Moreover, although the mixing order is arbitrary, it is preferable to add abrasive grains after dissolving malonic acid and hydroxide in water and further dissolving iron nitrate. By mixing and preparing in this order, the stability of silicon dioxide in the composition is not impaired, and precipitation of iron salts and the like can be prevented.

  In preparing the above polishing composition, various known additives may be added depending on the purpose of maintaining or stabilizing the quality of the product, the type of workpiece, processing conditions, and other polishing processing needs. An agent may be further added.

That is, suitable examples of further additives include
(A) organic acids such as succinic acid, citric acid, malic acid, glyceric acid, mandelic acid, ascorbic acid, glutamic acid, glyoxylic acid, glycolic acid, lactic acid, gluconic acid, tartaric acid, maleic acid or itaconic acid,
(B) surfactants such as anionic surfactants, nonionic surfactants, cationic surfactants,
(C) Water-soluble polymers (emulsifiers), for example, water-soluble cellulose such as polyacrylic acid, hydroxyethyl cellulose or pullulan, polyvinyl alcohol,
(D) Metal chelating agents such as ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA), etc.
Is mentioned.

  In the present invention, hydrogen peroxide and persulfate should not be used. For example, when hydrogen peroxide is added, it decomposes rapidly and generates oxygen, which may be dangerous, so care must be taken.

  The polishing composition of the present invention usually exhibits acidity by the addition of its main components. Although the pH of the polishing composition varies depending on the addition of various auxiliary additives, it is preferable that the composition exhibits acidity in order to exhibit the effects of the present invention. In particular, precipitation of iron compounds derived from iron nitrate is suppressed, and in order to maintain a high polishing rate for the tungsten film, it is preferable that the pH is low. On the other hand, if the pH is excessively low, problems such as corrosion of the apparatus occur. May occur. From such a viewpoint, the pH is preferably 1.5 to 3, and more preferably 2 to 2.5. In order to achieve such a pH, the pH can be adjusted using the inorganic acid or an organic acid which is an optional component. In addition, since the polishing composition by this invention has comparatively high pH, there are few restrictions at the time of transportation and storage.

  In addition, the polishing composition of the present invention can be prepared as a stock solution having a relatively high concentration, stored or transported, and diluted and used during actual polishing. Such a method is generally advantageous from a cost standpoint. The above-mentioned preferable concentration range is described as that at the time of actual polishing, and it goes without saying that when such a method of use is used, a solution with a higher concentration is obtained in a state where it is stored or transported. .

<Polishing method>
The polishing composition according to the present invention can be applied to various objects to be polished. However, a material containing tungsten, particularly a material comprising a tungsten film and an insulating film, more specifically an insulator. It is preferably used for polishing a wiring structure comprising a support, for example, a wafer, a tungsten film for wiring applied on the support. Any tungsten may be used for forming the tungsten film as long as it is used for wiring. For example, gold, silver, platinum, copper, zinc, and others may be blended. .

  In the method for polishing a wiring structure according to the present invention, it is essential to use the above polishing composition to polish such a wiring structure. Other than that, any conventionally known polishing method can be used.

  The polishing process of the wiring structure is generally divided into two or more polishing processes. After roughly polishing at a high polishing rate, precision polishing to prepare the polishing surface or polishing target surface is performed. First, only a part of a plurality of types of structures existing in 1 is polished, and the remaining structure in another process is polished. Dividing such a polishing process into a plurality is disadvantageous in terms of cost. On the other hand, the polishing method of the present invention completes the polishing process once in order to substantially polish only the tungsten film and leave the insulating film as it is, with a high selection ratio of the polishing composition. Is possible. For this reason, the polishing method according to the present invention is preferably a one-step polishing. In other words, it can be said that the wiring structure whose surface is polished only once by the polishing composition is manufactured at a low cost and has excellent surface characteristics. However, since it is necessary to finish the surface to be polished more precisely, it is possible to perform polishing several times, and a method of polishing the insulating film with a composition not containing iron nitrate, for example, is adopted as necessary. You can also.

  According to the polishing method of the present invention, for example, a polishing rate of 200 nm / min or more for a tungsten film and 20 nm / min or less, preferably 10 m / min or less for an insulating film is achieved. The selection ratio (polishing rate for the tungsten film / polishing rate for the insulating film) is 10 or more, preferably 20 or more.

  Further, according to the polishing method of the present invention, erosion is reduced. The specific erosion amount depends on the structure of the wiring structure. For example, when the 0.25 micron plug is arranged in a space of 0.25 micron, the erosion of the plug part is generally 40 nm or less, preferably 30 nm or less, more preferably 20 nm or less.

  The present invention will be described below with reference to various examples.

表中
砥粒Ａ：テトラメトキシシランを、メタノールを含有する溶媒中でアンモニア触媒で縮合させて製造する、金属アルコキシド法により製造されたコロイダルシリカ
砥粒Ｂ：四塩化ケイ素を酸素と水素の炎中で加水分解させることにより製造されたフュームドシリカ
砥粒Ｃ：ケイ酸ナトリウムをイオン交換樹脂で処理することにより製造する、ケイ酸ソーダ法により製造されたコロイダルシリカ Preparation of Polishing Composition A polishing composition was prepared by blending silicon dioxide, malonic acid, hydroxide, and iron nitrate as abrasive grains as shown in Table 1. In addition, iron (III) nitrate prepared the composition using the 9 hydrate.

Abrasive grain A in the table: produced by condensing tetramethoxysilane with an ammonia catalyst in a solvent containing methanol, colloidal silica abrasive grain B produced by a metal alkoxide method: silicon tetrachloride in a flame of oxygen and hydrogen Fumed silica abrasive grains C produced by hydrolysis: colloidal silica produced by a sodium silicate method, produced by treating sodium silicate with an ion exchange resin

  Each polishing composition obtained was evaluated by the following methods.

Measurement of Polishing Rate A tungsten blanket wafer having a diameter of 200 mm was prepared as a sample for measuring the tungsten film polishing rate, and a TEOS blanket wafer was prepared as a sample for measuring the polishing rate of the insulating film. These wafers were polished under the following polishing conditions 1.
<Polishing condition 1>
Polishing machine: Polishing machine for single-sided CMP (Applied Mirra Mesa CMP system (trade name); manufactured by Applied Materials (USA))
Polishing pad: Laminated polishing pad made of polyurethane (IC-1000 / SubaIV; manufactured by Rohm and Haas (USA))
Polishing pressure: 4 psi (= about 28 kPa)
Plate rotation speed: 68 [rpm]
Supply rate of polishing composition: 150 [ml / min]
Carrier rotation speed: 72 [rpm]

  The polishing rate is determined by measuring the thickness of an object to be polished before and after polishing using a sheet resistance measuring instrument (VR-120 (trade name), manufactured by Kokusai Electric System Service Co., Ltd.). Was the polishing rate. The selection ratio was obtained by dividing the polishing rate for the tungsten film by the polishing rate for the TEOS film.

As an object to be measured for erosion , a tungsten pattern wafer (manufactured by Advantech Co., Ltd., DDTEG mask pattern, tungsten film thickness 4000 mm, initial recess 4000 mm) was prepared. This wafer has a portion in which 0.25 micron plugs are arranged in a 0.25 micron space, and a wiring portion in which 0.25 micron tungsten wires (lines) are arranged in a 0.25 micron space. It is what has.

  This polishing object is polished using the polishing composition of each example until the insulating film is cut by 20 nm under the polishing condition 1, and the erosion amount in the plug portion and line portion of the polished tungsten pattern wafer surface is contacted. It was measured using a profila (HRP340 (trade name); manufactured by KLA-Tencor Corporation) which is a surface measuring device of the formula.

Evaluation of Stability of Polishing Composition 1 l of the prepared polishing composition is filled in each 1 liter-sized polybin, which is then allowed to stand still in an environment of 0 ° C, 25 ° C, 40 ° C, 60 ° C and 80 ° C. Then, the stability was evaluated by observing the occurrence of gelation or precipitates. The evaluation criteria are as follows.
○: No gelation for 1 week or more at all temperature conditions, or no precipitation occurred ×: Gelation or precipitation occurred within 1 week at at least one temperature condition

Evaluation of the amount of sodium remaining on the wafer after polishing Evaluation of the amount of sodium remaining on the wafer after polishing was performed by polishing the TEOS film for 1 minute using each polishing composition and washing with pure water. Metal impurities on the wafer surface were dissolved and recovered with an aqueous HF solution, and the amount of sodium in the recovered solution was quantitatively analyzed by inductively coupled plasma mass spectrometry (ICP-MS). The evaluation criteria are as follows.
○: Residual amount of sodium is very small and good. △: Residual amount of sodium is recognized, but practically usable. ×: Sodium remains at a level that is not practical.

Claims (5)

1 to 20 g / L of silicon dioxide having an average primary particle size of 7 to 40 nm;
10 to 100 g / L malonic acid;
10 to 100 g / L of a hydroxide selected from the group consisting of potassium hydroxide, ammonium hydroxide, and mixtures thereof;
20 to 200 g / L of iron nitrate;
A polishing composition comprising water.   The polishing composition according to claim 1, wherein the silicon dioxide is produced by hydrolyzing tetramethoxysilane.   Polishing composition of Claim 1 or 2 whose sodium content of the said silicon dioxide is 1 ppm or less.   The polishing composition according to any one of claims 1 to 3, wherein the polishing composition has a pH of 1.5 to 3.   A wiring structure comprising: an insulating layer having a wiring groove on a surface; and a conductor layer containing tungsten formed on the insulating layer so as to completely fill the wiring groove. A method for polishing a wiring structure, comprising polishing the body with the polishing composition according to any one of claims 1 to 4.