JP4052607B2 - Polishing agent and method for polishing semiconductor substrate - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an abrasive, particularly an abrasive used when polishing the surface of a semiconductor wafer such as silicon or polishing a semiconductor substrate surface by chemical mechanical polishing (CMP). The present invention relates to a polishing method using this.
[0002]
[Prior art]
Conventionally, it is known that a silicon wafer is polished from a silicon ingot by polishing the primary, secondary, and sequentially with increasing accuracy of the abrasive grains, and finally the final polishing. In the final polishing, it is necessary to remove the unevenness and distortion on the wafer surface to the utmost limit. In recent ULSI manufacturing, the degree of contamination (purity) of wafers has become important with the progress of device miniaturization, so that high-precision polishing is possible and the purity of the wafer is not impaired. There is a need for high purity abrasives.
As such an abrasive, US Pat. No. 3,715,842 discloses an abrasive comprising an inorganic oxide such as silicon dioxide, a water-soluble cellulose derivative and an alkali. It has been shown that the above-mentioned abrasive can reduce polishing scratches on the wafer by adding a water-soluble cellulose derivative.
[0003]
A polishing apparatus (hereinafter referred to as a polishing apparatus) includes a polishing disk that is attached to a surface with a polishing cloth and rotated by a motor or the like, and a suction disk that rotatably supports the substrate and presses the rotating substrate against the polishing disk. . In order to polish a substrate using this polishing apparatus, the surface to be polished of a rotating substrate is pressed against a polishing cloth on a rotating polishing disk, and polishing is performed while supplying an abrasive (also referred to as slurry) to a processing point. It is normal. Polishing technology using this polishing apparatus is applied to the manufacture of miniaturized products such as semiconductor devices and liquid crystals.
In general, a semiconductor device such as an IC or LSI has a design process for designing an integrated circuit on a semiconductor substrate, a mask creation process for drawing an electron beam used for forming the integrated circuit, a wafer having a predetermined thickness from a single crystal ingot. Formed through various processes such as a wafer manufacturing process to be formed, a wafer processing process for forming a semiconductor element such as an integrated circuit on the wafer, an assembly process for separating and packaging the wafer into each semiconductor substrate and forming a semiconductor device, and an inspection process. Is done. Then, in the wafer processing process, metal, polysilicon, silicon oxide film (SiO 2) is formed in grooves such as trenches and contact holes.₂), Silicon nitride film (Si_ThreeN_FourAn etch back RIE (Reactive Ion Etching) method is known as a method for flattening the surface after embedding an arbitrary material such as).
[0004]
However, this etch-back RIE method has many steps such as application of etch-back resist, easy RIE damage on the wafer surface, difficult flattening, and the use of a vacuum system. There are many problems due to the complexity and the use of dangerous etching gases.
Therefore, recently, the CMP method has been studied in place of etch back RIE.
This CMP method is a method of flattening the surface of a device when manufacturing a semiconductor device, and a highly accurate abrasive is required. In particular, in the case where the object to be polished is a silicon wafer itself or a polysilicon film formed on the wafer, a polishing agent to which a water-soluble polymer is added has been proposed in order to suppress the generation of a watermark.
In other words, because the clean silicon surface is water-repellent, the silicon or polysilicon film repels water during the polishing and cleaning processes, forming a group of dust called watermarks, which reduces the cleanliness of the wafer and the device yield. There is. In order to prevent such a problem, a method of preventing the generation of the watermark by adding a water-soluble polymer to the abrasive and forming a hydrophilic film on the wafer has been adopted.
[0005]
Usually, the polishing agent used for polishing the surface of the substrate such as silicon and the film formation on the substrate as described above is abrasive particles such as silica, water as a solvent, water-soluble cellulose forming a hydrophilic film, It is comprised from pH adjusters, such as ammonia added as needed. In general, water-soluble cellulose contains a large amount of alkali metal impurities such as Na. However, if Na is present, the wafer is contaminated and a short circuit accident of wiring formed on the wafer occurs. Add to the abrasive.
Further, when polishing a substrate or the like using such an abrasive, it is usually diluted with a dispersant such as pure water or ionic water. When polishing a semiconductor wafer, it is generally diluted by 2 to 10 times, and when polishing a film (film to be polished) on a semiconductor substrate, it is generally diluted by about 20 times. In this case, the polishing agent and the dispersing agent are respectively supplied from both the polishing agent nozzle and the dispersing agent nozzle to the semiconductor wafer on the polishing board for polishing the wafer.
It is also known that polishing is performed using two types of abrasives having different compositions in combination. In this case, the abrasive is supplied from both the first abrasive nozzle and the second abrasive nozzle to the wafer on the polishing board for polishing the substrate.
[0006]
[Problems to be solved by the invention]
However, since conventional abrasives are not sufficiently managed with respect to purity, there are concerns about some problems. For example, in the polishing of silicon wafers and devices, the yield of devices may be reduced when the wafer is contaminated by an abrasive and the cleaning after polishing is insufficient. In addition, when water-soluble cellulose that is usually marketed is used, even if the amount of the alkali agent added is constant, the physical properties of the abrasive such as pH are not constant, thereby causing problems in the reproducibility of polishing. There was a case. Further, in the case of conventional abrasives, when an alkali agent having a high vapor pressure such as ammonia is used, the alkali agent is easily vaporized, and thus there are problems in the stability of the abrasive and the reproducibility of polishing. It was. Therefore, an abrasive having high purity and excellent stability and reproducibility has been demanded.
[0007]
Further, in a conventional polishing apparatus, silica particles or the like are used as abrasive particles dispersed in an abrasive, and thus may be overpolished. As a result, when the CVD oxide film embedded in the groove of the semiconductor substrate is polished, a dishing-shaped depression may be formed on the surface of the CVD oxide film in the groove. In addition to this depression, the corner portion of the groove of the semiconductor substrate 1 itself may be etched, which may cause a problem when a subsequent process is performed. For example, n⁺And p⁺Polysilicon resistance abnormality or wiring short-circuit may occur due to the generation of remaining polysilicon or metal residue. Therefore, it was necessary to reduce abrasive particles.
The present invention has been made under such circumstances, and is a high purity, excellent stability and reproducibility, an abrasive that does not damage the substrate and the polishing target film, and a semiconductor substrate coated by CMP using this abrasive. A method for planarizing a polishing film is provided.
[0008]
[Means for Solving the Problems]
The inventors of the present invention have made extensive studies to achieve the above object. As a result, when water-soluble cellulose is used, which is particularly effective for preventing watermarks, the above-mentioned problems are caused by the presence of a large amount of alkali metal elements such as sodium contained in the abrasive in the production process. I got the knowledge that it is the cause of. And by refine | purifying this water-soluble cellulose, the alkali metal was removed to the specific value and the purity of the abrasive | polishing agent was raised greatly. As a result, the use of this polishing agent not only greatly reduces contamination of silicon wafers and devices, but also significantly improves polishing stability and reproducibility by selecting specific amines as the alkaline agent to be used together. As a result, the present invention has been completed.
In the present invention, the Na content of water-soluble cellulose added to the abrasive is reduced, and the content of abrasive particles, that is, silica is 0.1 to 50% by weight (preferably 5 to 20% by weight). And, if necessary, a pH adjuster is used, an aqueous solution of a water-soluble amine having a vapor pressure of 133 Pa or less at 20 ° C. is used as the adjuster, and the concentration of the water-soluble cellulose is Cwt%. The content is adjusted so as to be 5 Cppm or less.
[0009]
The concentration of the water-soluble cellulose is 0.05 to 4 wt%, preferably 0.1 to 1 wt%, particularly preferably 0.1 to 0.5 wt%. The content of the water-soluble amine added to the abrasive is preferably 0.1 to 20 wt%. In particular, the content of the water-soluble amine is 1 to 15 wt%, preferably 3 to 10 wt%.
When CMP is performed using this abrasive, the abrasive may be diluted with a dispersing agent such as ionic water. The viscosity of the abrasive is suitably 1 to 10 centipoise (cP).
The abrasive of the present invention comprises abrasive particles such as silica, water as a solvent, water-soluble cellulose that forms a hydrophilic film, and a pH adjuster such as a water-soluble amine that is added as necessary. ing. The Na impurity contained in water-soluble cellulose is about 0.05 to 1 ppm.
Further, when polishing a substrate or the like using the abrasive of the present invention, it is usually diluted with a dispersant such as pure water or ionic water. When polishing a semiconductor wafer, it is diluted by 2 to 10 times, and when polishing a film (film to be polished) on a semiconductor substrate, it is diluted by about 20 times. Accordingly, the abrasive is used after being diluted to about 2 to 20 times. In this case, the polishing agent and the dispersing agent are respectively supplied from both the polishing agent nozzle and the dispersing agent nozzle to the semiconductor wafer on the polishing board for polishing the wafer.
[0010]
The concentration of the water-soluble cellulose when the substrate is polished by diluting the above-mentioned abrasive is preferably 0.0025 to 0.8 wt%, preferably 0.005 to 0.2 wt%, particularly preferably 0.005. 0.1 wt% is appropriate. Further, the content of the water-soluble amine added to the abrasive is preferably 0.005 to 4 wt%. In particular, 0.05 to 3 wt% is good, preferably 0.15 to 2 wt% is appropriate. At this time, the content of silica is preferably 0.005 to 10 wt%, and particularly preferably 0.25 to 4 wt%.
In the polishing method of the present invention, it is preferable to perform polishing by using the abrasive of the present invention and an abrasive having a composition different from that of the abrasive. In this case, the abrasive is supplied from both the abrasive nozzle and the other abrasive nozzle of the present invention to the semiconductor wafer on the polishing board for polishing the substrate.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, any known water-soluble cellulose can be used without particular limitation. For example, water-soluble celluloses such as methyl cellulose, methyl hydroxyethyl cellulose, methyl hydroxypropyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose and derivatives thereof can be mentioned.
The action of cellulose is mainly to reduce scratches on the wafer during polishing and to form a hydrophilic film on the wafer. From this viewpoint, among the water-soluble celluloses, hydroxyethyl cellulose is preferable because it can easily form a hydrophilic film.
The amount of cellulose added in the abrasive depends on the molecular weight of the cellulose to be used, and thus cannot be unconditionally limited, but is in the range of 0.05 to 4 wt%, preferably in the range of 0.1 to 1 wt%, more preferably A range of 0.1 to 0.5 wt% is preferred. That is, if it is less than 0.05 wt%, it may be difficult to form a uniform hydrophilic film. Further, although depending on the molecular weight of the water-soluble cellulose to be used, if it exceeds 4 wt%, the viscosity of the abrasive becomes too high and it may be difficult to handle.
[0012]
In the conventional abrasive | polishing agent using the said water-soluble polymer, there is no example which paid attention to the purity of the water-soluble polymer to be used. However, according to the confirmation of the present inventor, the water-soluble cellulose used in the present invention has many metals, particularly alkali metal impurities, which contribute to the above-described problems in polishing silicon wafers. Incidentally, water-soluble cellulose generally available from the market contains several thousand to several tens of thousands ppm of impurities such as Na. Further, since the content of the impurities varies greatly from lot to lot, there is a problem that it is difficult to produce an abrasive stably and with good reproducibility.
The reason why the water-soluble cellulose contains a lot of alkali metal elements is as follows. Water-soluble cellulose is generally obtained by producing alkali cellulose once with caustic soda using pulp or cotton as a raw material, and then reacting with ethylene oxide or the like to synthesize water-soluble cellulose. The reason is that the removal of the Na component and the like is not complete.
[0013]
Several attempts have been reported to remove impurities from water-soluble cellulose. For example, JP-A-53-102393 discloses a method in which glyoxal is bonded to hydroxyethyl cellulose, once the cellulose is made insoluble and washed, and then crosslinked to return to the original hydroxyethyl cellulose. It is difficult to completely remove impurities such as Na by such washing alone. Japanese Patent Laid-Open No. 62-32101 discloses a method for removing alkali metal content in cellulose by treating hydroxyethyl cellulose with an organic solvent containing an acidic alkyl phosphate ester or a mixed solvent of an organic solvent and water. ing. Japanese Patent Laid-Open No. 50-83427 discloses a method of purification using a cation exchange resin to remove only sodium ions in sodium acetate from hydroxyethyl cellulose containing sodium acetate as an impurity. Yes. In this example, only the cation exchange resin is used, and further, ammonium hydroxide is added, and the purpose is to prevent mold generation by the produced ammonium acetate. In the present invention, the generation method exemplified above may be used in combination.
[0014]
In the present invention, the purification of water-soluble cellulose desirably removes not only metal ions such as Na but also anions other than hydroxyl groups. The reason is that when an anion other than a hydroxyl group is present, the water-soluble cellulose aqueous solution exhibits acidity, so the amount of water-soluble amine added is not constant, and reproducibility as an abrasive is often not maintained. Because.
The method for removing the alkali metal element from the water-soluble cellulose aqueous solution is not particularly limited. As a suitable example, a method of bringing a water-soluble cellulose aqueous solution into contact with an H-type ion exchange resin and an OH-type ion exchange resin can be mentioned. By using both H-type ion exchange resin and OH-type ion exchange resin for purification, as described above, not only metal ions such as Na but also anions other than hydroxyl groups can be removed.
In the present invention, the concentration of water-soluble cellulose in the water-soluble cellulose aqueous solution to be subjected to the above treatment cannot be unconditionally determined because cellulose of various molecular weights is present in the cellulose, but generally 0.05 to 4 wt% % Range, preferably 0.1 to 1 wt%. In terms of workability of the ion exchange treatment, the water-soluble cellulose aqueous solution has a viscosity of 5 to 1000, preferably 10 to 300 cP. The aqueous solution after ion exchange can be diluted with pure water, or conversely, it can be concentrated and dried by removing water.
[0015]
In this way, the concentration of the water-soluble cellulose can be finally adjusted to an arbitrary concentration.
The contact method of the water-soluble cellulose aqueous solution and the ion exchange resin may be brought into contact with the H-type ion exchange resin and the OH-type ion exchange resin separately, or the H-type ion exchange resin and the OH-type ion exchange resin You may contact a mixture simultaneously. Such contact may be batch-wise or flow-through. A preferred embodiment is a method of supplying a water-soluble cellulose aqueous solution at a constant rate from one direction to a resin tower packed with a mixture of an H-type ion exchange resin and an OH-type ion exchange resin. In addition, fine particles can be removed from the ion-exchanged water-soluble cellulose aqueous solution by filtration or the like. The pore size of the filter to be filtered is 50 μm or less, preferably 10 μm or less, more preferably 1 μm or less. Thus, when the water-soluble cellulose filtered with the filter is used for the abrasive | polishing agent of this invention, since the dust amount on the wafer after polishing falls, it is preferable.
The water-soluble cellulose used in the abrasive of the present invention may be purified to such an extent that the specified alkali metal element content can be satisfied in the abrasive described below by the above purification treatment.
[0016]
The water-soluble amine used in the present invention is not particularly limited as long as the vapor pressure at 20 ° C. is 133 Pa or less. That is, since those having a vapor pressure higher than 133 Pa are more easily diffused in the abrasive, the action of improving the stability of the abrasive and the reproducibility of the polishing performance in cooperation with the purity of the water-soluble cellulose described later is reduced. The object of the present invention cannot be achieved.
In the abrasive of the present invention, the purpose of adding a water-soluble amine is to make the pH of the abrasive alkaline and promote the polishing action. Moreover, in the abrasive | polishing agent containing a silica, in order to prevent aggregation of a silica and water-soluble cellulose, it adds for the objective of making pH 8 or more at the time of polishing.
In the present invention, attention was paid to the stability of the abrasive and the reproducibility of the polishing, and it was found that a water-soluble amine having a vapor pressure of 20 Pa or less at 20 ° C. was particularly excellent in achieving the above properties of the abrasive. . Illustrative examples of the water-soluble amines include diethanolamine, triethanolamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, triethylenediamine, 2-aminoethanol, polyethyleneimine, aminoethylethanolamine and the like. It is done. Also, a mixture of two or more of the above amine groups, or an alkali agent other than the above in a ratio of 20 wt% or less, such as ammonia, an amine having a relatively high vapor pressure, etc. You can leave. Among the water-soluble amines exemplified above, triethanolamine is preferable because it has a very low vapor pressure and is excellent in reproducibility and stability when used in an abrasive.
[0017]
The amount of water-soluble amine added is not particularly limited as long as the performance of the abrasive can be maintained. Usually, the pH during polishing of the abrasive is appropriately selected from the range of 0.1 to 20 wt% so as to be a target value, specifically 9 to 11. In the final abrasive, the polishing rate is not considered as important, and as the water-soluble amine, the weakly basic one tends to be excellent in reproducibility and stability when used in the abrasive. In this sense, triethanolamine is preferable because it is relatively weak in basicity. When triethanolamine is used as the water-soluble amine, the blending amount is preferably relatively high, and the concentration of the abrasive is added in the range of 1 to 15 wt%, preferably in the range of 3 to 10 wt%. Is preferred.
As silica, high purity is desirable. A typical example of silica is colloidal silica produced by hydrolysis using alkoxysilane as a raw material. In the above colloidal silica, it is relatively easy to make the amount of all metal impurities other than Si 1 ppm or less. The average primary particle diameter (average particle diameter measured with an electron microscope) of the silica particles is in the range of 10 to 100 nm, preferably in the range of 30 to 60 nm. The average secondary particle diameter (average particle diameter measured with a particle size distribution meter) is in the range of 20 to 200 nm, preferably in the range of 30 to 120 nm. The particle size distribution of the silica particles may have a certain width, but it is desirable that the particle size distribution is narrow. Moreover, it is desirable not to include coarse particles of 500 nm or more, preferably 200 nm or more.
[0018]
Further, as the silica used in the present invention, fumed silica produced by burning silicon tetrachloride in a flame composed of oxygen and hydrogen can be highly purified depending on the production method and is preferably employed. Therefore, what is necessary is just to select and use the thing of 1 ppm or less of metals other than Si among the fumed silica generally marketed. Such fumed silica has a specific surface area of 50 to 500 m.²/ G can be manufactured, but the specific surface area is 200m for polishing silicon wafers and devices.²/ G or more is preferable. When the fumed silica is used in the abrasive of the present invention, it is desirable that the silica is finely dispersed in the abrasive.
In the abrasive of the present invention, the content of silica is preferably 0.1 to 50 wt%, particularly 5 to 20 wt%, in order to sufficiently exhibit the effect of silica.
The content of the alkali metal element in the abrasive of the present invention is controlled by controlling the content of the alkali metal element in the water-soluble cellulose, the water-soluble amine, and the purity of silica added as necessary. In order to achieve the object of the present invention, it is important to prepare the alkali metal element so that the content of the alkali metal element is 5 Cppm or less when the content is Cwt%.
[0019]
In the polishing agent of the present invention, it is more preferable to adjust the metal element other than the alkali metal element and the anion other than the OH ion to the same level as the alkali metal element. Cellulose contains metal elements other than alkali metal elements and anionic impurities simultaneously with alkali metal elements such as Na. As a result of ion chromatography, unpurified cellulose solution contains NO as an anionic impurity._Three ^-135.3 ppm, PO_Four ^-37.9 ppm was detected. The present inventors have found that such anionic impurities affect the pH value of the abrasive as well as the cationic impurities such as the alkali metal elements. That is, when a large amount of cationic impurities and anionic impurities are present, there is a problem that the variation of the pH value among the lots of abrasives becomes large, leading to the variation of the polishing rate.
In general, the cationic impurities contained in the abrasive include metal elements such as Zn, Pb, Ni, Co, Fe, Cr, Mg, Cu, Ag, Ti, Ca, and Al in addition to the alkali metal elements described above. There are ions. In addition, as anionic impurities, NO_Three ^-1, PO_Four ^-3, F^-1, Cl^-1, Br^-1, SO_Four ^-Etc.
[0020]
In the present invention, when the concentration of water-soluble cellulose is Cwt%, the content of the alkali metal element must be 5 Cppm or less. In order to prevent variation in the polishing rate of the abrasive, the alkali metal element and It is preferable that the cation impurities including other metal elements be 5 Cppm or less. Further, the content of anionic impurities is preferably 5 Cppm or less.
Thus, by adjusting the cation impurities and the anions to the above values or less, it is possible to obtain an abrasive having a small variation in pH value between lots and a small variation in polishing rate.
The application of the abrasive of the present invention is not particularly limited, and can be used for polishing used in such a composition. For example, it may be used for chemical mechanical polishing.
The abrasive of the present invention is used in the above composition at the time of polishing. However, for ease of handling, it is preferable to use a product prepared from 2 to 20 times this composition.
As for the dilution at the time of use of the above-mentioned abrasive, it is desirable to prevent contamination with alkali metal elements by using pure water.
[0021]
The polishing agent of the present invention preferably has a pH during polishing in the range of 8 to 11, preferably in the range of 9 to 10.5, and more preferably in the range of 9.5 to 10.3. When the pH is less than 8, the polishing rate is insufficient, or water-soluble cellulose and silica often cause a gelation reaction. If the pH exceeds 11, the wafer surface may be rough, which is not preferable.
EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated concretely, this invention is not restrict | limited to these Examples at all.
Example 1 A commercially available hydroxyethyl cellulose was used to prepare 100 liters of a 0.56 wt% aqueous solution (hereinafter referred to as “A solution”). The viscosity of the liquid A was 217 cP and the pH was 6.5. The viscosity was measured at 25 ° C. using a B-type viscometer and the pH was measured using a pH meter.
[0022]
Next, a mixture of H-type ion exchange resin and OH-type ion exchange resin (manufactured by Organo, Amberlite; MB-2) is packed into a 10-liter tube, and 50 liters of liquid A is added at 1 liter / liter from the bottom of the tube. Flowed at a rate of minutes. About 10 liters which came out first were discarded, and 30 liters which came out next were fractionated (henceforth B liquid). The pH of the solution B was 4.4 and dried at 100 ° C., and the solid content concentration was measured to be 0.56 wt%.
Next, 2.4 kg of triethanolamine (purity 99% or more, vapor pressure at 20 ° C. is 1.3 Pa or less) was added to 20 kg of the above B liquid and mixed uniformly (hereinafter referred to as “C liquid”). In addition, when the purity analysis of this amine was conducted, all the anions other than a metal element and OH were 0.1 ppm or less. Metal elements were analyzed by atomic absorption (Na and K) and ICP methods (metal elements other than Na and K), and anions were analyzed by ion chromatography.
4.8 kg of high purity colloidal silica (produced by hydrolysis using alkoxysilane as a raw material) and 20.8 kg of pure water were further added to the liquid C as abrasive grains, and stirred well (hereinafter referred to as E Called liquid). When the particle diameter of the colloidal silica was observed with an electron microscope, 99% or more of the particles were in the range of 35 to 65 nm. In addition, when the purity analysis of this colloidal silica was conducted, all the metal elements were 0.1 ppm or less in terms of silica.
[0023]
Further, the solution E was filtered through a 6 μm filter to produce a finished abrasive. The physical properties of this abrasive were pH 10.12, viscosity 21 cP, specific gravity 1.067 (all values at 25 ° C.). Further, when the impurities were analyzed for the above abrasive, results as shown in the characteristic diagram of FIG. 2 were obtained. As can be seen from this result, it was found that the ion-exchanged material achieved high purity of 0.1 ppm or less for alkali metal elements and other metal elements, as well as typical anions.
As the above results show, by using water-soluble cellulose purified using H-type ion exchange resin and OH-type ion exchange resin and high-purity water-soluble amine and silica selected carefully, water-soluble cellulose concentration ( 0.23 wt%), it was possible to produce a finish abrasive of 1.2 ppm or less, which is the upper limit of the content of the alkali metal element calculated by the above formula.
Next, the characteristics of the abrasive produced as described above were examined.
A polishing test of a silicon wafer was performed using the above abrasive. A commercially available polishing machine was used for the polishing apparatus, and a non-woven fabric type pad was used. While supplying a solution obtained by diluting the above abrasive 5 times with pure water onto the polishing pad at a supply rate of 200 ml / min, a load of 200 g / cm²A 6-inch silicon wafer was polished under the condition that the rotation speed of the surface plate was 25 rpm.
[0024]
The result of examining the reproducibility of the polishing speed is shown in FIG. As the abrasive, about 50 liters prepared by diluting 5 times with the above-mentioned pure water were prepared, and those left in the container except when used were used.
FIG. 4 shows the result of the purity analysis of the wafer surface after cleaning the polished wafer.
The cellulose was purified in the same manner as in Example 1 except that five different lots of hydroxyethyl cellulose were used, and an abrasive was prepared. As a result, the pH value of the abrasive was extremely small in the range of 10.1 to 10.2. Also, other physical property values were almost constant. Regarding the polishing rate, it was found that there was almost no difference between the lots of cellulose. The result is shown in FIG.
(Comparative example 1) The abrasive | polishing agent similar to Example 1 was manufactured using ammonia water (vapor pressure in 20 degreeC is 483-837kPa) instead of using triethanolamine, and it tested similarly to Example 1. FIG. Table 2 shows the result of the reproducibility of the polishing rate. The physical properties of the abrasive were pH 10.2, viscosity 11.5 cP, specific gravity 1.059 (all values at 25 ° C.).
[0025]
  As can be seen from the above results, when ammonia having a high vapor pressure is used, it is clear that if the abrasive is prepared and stored for a long period of time, the reproducibility of the polishing rate is poor.
  (Comparative Example 2) An abrasive was produced in the same manner as in Example 1 except that the A solution before the ion exchange treatment was used instead of using the B solution. The abrasive was tested in the same manner as in Example 1. Figure 2 shows the results of the purity analysis of the wafer and the purity of the wafer after polishing.FIG.Shown in The physical properties of this abrasive were pH 9.95, viscosity 23 cP, specific gravity 1.065 (all values at 25 ° C.).
  In the above abrasive, the upper limit of the content of the alkali metal element calculated by the above formula from the water-soluble cellulose concentration (0.23 wt%) is 1.2 ppm. On the other hand, the abrasive used in this comparative example The content of the alkali metal element therein was 3.5 ppm.
[0026]
An abrasive was prepared in the same manner as in Comparative Example 2 except that the five different lots of hydroxyethyl cellulose used in Example 1 were used. The content of the cation impurity and the anion impurity containing the alkali metal element greatly exceeds the upper limit calculated by the above formula as shown in FIG. Further, as shown in FIG. 16, it was found that the pH value of the abrasive was largely varied in the range of 9.7 to 10.4, and the reproducibility was poor. The variation in polishing rate was also large. That is, since the cellulose used has different impurity (cation and anion) concentrations for each lot, the pH value of the abrasive varies when the cellulose is not purified, thereby varying the polishing performance (polishing rate). I understood it.
As can be seen from the above examples and comparative examples, the abrasive of the present invention is excellent in reproducibility of polishing by using a water-soluble amine having a vapor pressure of 133 Pa or less at 20 ° C., and has high purity of water-soluble cellulose. It has been found that the purity of the abrasive and the purity of the wafer after polishing can be greatly improved. It is clear that it is useful not only as a final abrasive for wafers but also as an abrasive for devices.
[0027]
FIG. 1 is a cross-sectional view of a polishing apparatus for polishing a wafer such as a silicon semiconductor or a film formed on the wafer using the abrasive of the present invention. FIG. 1 shows an outline of a polishing apparatus for performing CMP, and its mechanism will be described below.
A polishing disc receiver 23 is disposed on the stage 21 via a bearing 22. A polishing disk 24 is attached on the polishing disk receiver 23. A polishing cloth 25 for polishing the wafer is attached on the polishing board 24. In order to rotate the polishing disc receiver 23 and the polishing disc 24, a drive shaft 26 is connected to these central portions. The drive shaft 26 is rotated by a motor 27 via a rotating belt 28. On the other hand, the wafer 20 is disposed at a position facing the polishing cloth 25 and fixed to the suction cloth 30 and the template 29 attached to the suction board 31 by vacuum or water filling. The suction disk 31 is connected to the drive shaft 32. The drive shaft 32 is rotated by a motor 33 via gears 34 and 35. The drive shaft 32 is fixed to the drive base 36. The drive base 36 is attached to a cylinder 37, and the drive base 36 moves up and down as the cylinder 37 moves up and down. The abrasive of the present invention is supplied between the wafer 20 fixed to the suction disk 31 and the polishing pad 25. In this way, the wafer 20 is polished.
[0028]
Next, a method of polishing a film to be polished on a semiconductor substrate with the polishing apparatus of FIG. 1 will be described with reference to FIGS. 5 and 6 are cross-sectional views of the manufacturing process of the semiconductor device, showing an element isolation method and process for forming a groove in a silicon semiconductor substrate, filling the groove with a CVD oxide film, and flattening with a polishing apparatus. A silicon nitride film 2 is deposited on the silicon semiconductor substrate 1 to a thickness of about 70 nm to serve as a stopper film when polishing the oxide film.
Thereafter, a CVD oxide film serving as a groove forming mask is deposited on the silicon nitride film 2. In order to pattern the mask and the stopper film, a photoresist (not shown) is applied to the entire surface of the CVD oxide film. Next, this photoresist is patterned, and using this as a mask, a CVD oxide film and a silicon nitride film 2 as a stopper film thereunder are opened by RIE or the like. Next, a groove 5 is formed in the silicon semiconductor substrate 1 by the RIE method using the opened CVD oxide film and silicon nitride film 2 as a mask (FIG. 5A). After the formation of the groove 5, the CVD oxide film, the reaction product during RIE processing, and the damaged layer are removed by wet processing. Then, a CVD oxide film 6 or a BPSG film is deposited on the silicon nitride film 2 and in the groove 5 (FIG. 5B). The CVD oxide film 6 is polished as a film to be polished using the polishing apparatus shown in FIG.
[0029]
In this polishing apparatus, the abrasive of the present invention is used. In order to uniformly disperse in the abrasive, the silicon nitride particles are dispersed in a colloidal state. The viscosity of the abrasive is suitably 1 to 10 cP. This is because if the viscosity is low, it is difficult to uniformly disperse the abrasive particles, and if the viscosity is high, the mechanical polish becomes strong, and the warpage of the wafer and the uniformity of the film thickness greatly affect the uniformity after CMP. become. Therefore, it becomes difficult to obtain uniformity.
The polishing temperature is suitably 20 to 70 ° C., and the chemical action is particularly strong at high temperature treatment. Polishing by this polishing apparatus is performed, for example, by being pressed against the polishing cloth 25 on the polishing board 24 rotating at about 100 rpm. The rotational speed of the polishing board 24 at that time is 20 to 200 rpm, and the pressing pressure is 50 to 500 g / cm.²It is.
FIG. 6A shows a state after the CVD oxide film 6 is planarized by this polishing apparatus. After polishing, the silicon nitride film 2 which is a stopper film is removed by etching (FIG. 6B). Thereafter, finishing polishing is performed to finish the surface of the semiconductor substrate and the surface of the CVD oxide film 6 into a uniform surface (FIG. 6C). By this polishing, it was possible to obtain a good processed shape in which the silicon semiconductor substrate 1 and the embedded CVD oxide film 6 were not dished.
[0030]
Next, a process of embedding polysilicon in the groove formed in the semiconductor substrate will be described with reference to cross-sectional views showing the polishing process of FIGS.
The main surface of the silicon substrate 1 is thermally oxidized to a thickness of about 10 to 50 nm to obtain a buffer oxide film (SiO₂) 8 is formed. Thereafter, a silicon nitride film 2 used as a stopper film when polishing the second polysilicon film and used as a mask for protecting the element region is deposited on the buffer oxide film 8 to a thickness of about 70 nm. Thereafter, a CVD oxide film 3 serving as a groove forming mask is deposited on the silicon nitride film 2. In order to pattern the mask and the silicon nitride film, a photoresist is applied to the entire surface of the CVD oxide film 3 and patterned. Using this photoresist as a mask, the CVD oxide film 3 and the silicon nitride film 2 serving as a stopper film are simultaneously opened by the RIE method or the like. A groove portion is formed in the semiconductor substrate 1, and then a reaction product and a damage layer at the time of RIE processing are removed by wet processing, and then the inner surface of the groove portion is thermally oxidized to form an oxide film 11. Next, a polysilicon film 12 is deposited inside the trench and on the CVD oxide film 3 by low pressure CVD or the like (FIG. 7A).
Next, the first polishing is performed using the polishing apparatus shown in FIG. 1 using the polysilicon film 12 as a film to be polished. A CVD oxide film 3 is used as a stopper film in the first polishing. FIG. 7B shows a state after the polysilicon film 12 is planarized by this polishing apparatus.
[0031]
After the first polishing, the CVD oxide film 3 is etched with an etchant containing HF (FIG. 8A). As a result of removing the CVD oxide film 3, the polysilicon film 12 protrudes from the semiconductor substrate 1.
Next, a second polishing is performed using the protruding polysilicon film 12 as a film to be polished using the polishing apparatus shown in FIG. The polishing agent used in this polishing apparatus is the same as that in the first polishing. FIG. 8B shows a state after the polysilicon film 12 is planarized by this polishing apparatus. The trench is filled with the polysilicon film 12 without being dished by this planarization. Since a part of the silicon nitride film 2 is used as it is as a mask for LOCOS, a photoresist 13 is formed on the part through a photolithography process (FIG. 9A). Then, after removing the region of the silicon nitride film 2 excluding the region covered with the photoresist 13 by RIE or the like, the photoresist is peeled off (FIG. 9B). Then, the surface of the semiconductor substrate 1 is covered with the LOCOS oxide film 14 by heat treatment (FIG. 9C). The LOCOS mask has a thin peripheral part due to over-polishing and can form a bird's beak. However, since this is formed smaller than the conventional one, the area area is not affected so much that the device characteristics are greatly affected.
[0032]
In the present invention, an excellent flat shape as shown in FIG. 8B can be obtained by using an abrasive having a novel structure, and as a result, a LOCOS pattern conversion difference as shown in FIG. A good processed shape can be obtained.
Next, a process of forming embedded Cu wiring on the semiconductor substrate using the polishing apparatus of FIG. 1 will be described with reference to FIG.
SiO on the semiconductor substrate 1₂CVD oxide film 3 made of, etc. and SiO formed by plasma CVD₂An oxide film (hereinafter referred to as a plasma oxide film) 15 is continuously formed. Next, the plasma oxide film 15 is patterned to form a groove at a predetermined location of the semiconductor substrate 1. A Cu film 16 is deposited in the groove and on the entire surface of the plasma oxide film 15 (FIG. 10A). Next, the Cu film 16 is polished with the plasma oxide film 15 as a stopper film by the polishing apparatus of FIG. Polishing of the Cu film 16 is terminated when the plasma oxide film 15 is exposed. By this process, the Cu film is embedded only in the groove, and the embedded wiring 16 of the Cu film is formed (FIG. 10B). By this polishing, the surface of the semiconductor substrate 1 is flattened without dishing. The second plasma oxide film (SiO2)₂) 18 can be easily formed (FIG. 10C). The planarization by the CMP method facilitates the formation of second and third electrode wirings (not shown).
[0033]
In this embodiment of the present invention, plasma CVD SiO is used as a base oxide film or a wiring metal material.₂If a film, Cu film, etc. are used, but satisfy their respective insulation performance and performance as metal wiring, plasma CVDSi_ThreeN_FourOther materials such as a film, Al, Au, W, and other alloys may be used, and the depth of the wiring groove formed in the base oxide film and the thickness of the deposited metal material for wiring can be appropriately selected.
The polishing agent used in the polishing method of the present invention supplies the polishing agent to the processing point of the semiconductor substrate and polishes the dispersing agent (ionic water) when polishing the semiconductor substrate mounted on the polishing apparatus during the CMP process. To supply.
[0034]
Next, the polishing method of the present invention will be described with reference to FIG.
FIG. 1 is a schematic perspective view and a cross-sectional view of a polishing processing portion including a polishing disk and a suction disk of the polishing apparatus shown in FIG. Here, it is characterized in that ionic water is used as a dispersant during polishing. The usefulness of pure water and ultrapure water is recognized in the manufacturing technology of semiconductor devices. Pure water is high-purity water having a resistivity of about 5 to 18 MΩcm from which impurities such as ions, fine particles, and microbial organic substances are almost removed. Ultrapure water is extremely high-purity water having a higher purity than the suspended water, dissolved substances and pure water removed with high efficiency by ultrapure water production equipment. Expressed in terms of electrical conductivity, the pure water conductivity ρ is less than 10 μScm, and the ultrapure water conductivity ρ is less than 0.055 μScm. By electrolyzing these waters, highly oxidative acidic ionic water and highly reducible alkaline ionic water used in the manufacture of semiconductor devices are produced.
[0035]
Here, in a polishing apparatus used in a semiconductor manufacturing apparatus, a pipe for injecting an abrasive at a processing point of an abrasive cloth and another pipe for injecting ion water are provided. That is, the abrasive is supplied after being diluted at the processing point of the semiconductor substrate on which the polishing target film is formed.
The polishing apparatus shown in FIG. 11 includes a polishing board 24. A driving shaft (not shown) is connected to the center of the polishing disk 24 via a polishing disk receiver (not shown). A polishing cloth 25 for polishing a substrate such as a semiconductor wafer is attached on the polishing board 24. The polishing cloth 25 is made of polyurethane foam, polyurethane nonwoven fabric, or the like. The drive shaft is rotated by a motor to rotate the polishing disc receiver and the polishing disc 24. The semiconductor wafer is adsorbed by an adsorbing plate 31 provided with an adsorbing cloth (not shown) (not shown) by vacuum or the like so as to come to a position facing the polishing cloth 25. The suction disk 31 is connected to the drive shaft 32, and the semiconductor wafer held by the suction disk 31 is pressed against or separated from the polishing cloth 25 by the movement of the drive shaft 32.
[0036]
When polishing a semiconductor wafer, the abrasive of the present invention is supplied from the abrasive tank 40 to the polishing cloth 25 via the abrasive supply pipe 38 and the ionic water generated in the electrolytic bath 41 is supplied from the ionic water supply pipe 39. While doing. Therefore, the abrasive supply pipe 38 and the ionic water supply pipe 39 are arranged in the vicinity of the suction plate 31 in which the nozzles at the tips thereof hold the semiconductor wafer above the polishing cloth 25.
Then, the polishing agent supplied from these supply pipes 38 and 39 and ion water are injected into a processing point on the semiconductor wafer placed on the polishing cloth 25 and mixed together. The supply pipes 38 and 39 are movable to arbitrary positions on the polishing pad 25. Unnecessary ionic water generated in the electrolytic bath 41 is discharged to the outside through the drain pipe 42.
There are two types of ionized water: alkaline ionized water and acidic ionized water. A solid electrolyte is placed in an electrolytic cell, and the electrolyte, that is, pure water containing no metal impurities or ultrapure water is electrolyzed at a low voltage, and any ion water is used. pH ionic water is produced. In the case of alkaline ionized water, when the polishing rate fluctuates during polishing, stable polishing is possible by controlling the pH to be more alkaline to increase the rate and to the neutral to decrease the rate. Also, in the case of acidic ionized water, if the polishing rate fluctuates during polishing, stable polishing is possible by controlling the pH to be more acidic to increase the rate and to the neutral side to decrease the rate. .
[0037]
Next, silica particles contained in the abrasive will be described with reference to FIGS. FIG. 12 is a cross-sectional view of a semiconductor substrate subjected to CMP, and FIGS. 13 to 14 are characteristic diagrams showing changes in polishing characteristics when the content of abrasive particles (silica) in the abrasive is changed. 13 shows the polishing rate (nm / min) and the uniformity of the film to be polished (1σ%), FIG. 14 shows the dishing amount (nm), and FIG. 15 shows the thinning amount (nm).
FIG. 12 shows a process of forming a groove (trench) in the semiconductor substrate and embedding polysilicon in the groove. Silicon nitride (Si) is applied to the silicon semiconductor substrate 1._ThreeN_Four) After the film 2 is deposited, an opening is formed in the silicon nitride film 2 in a predetermined size at a predetermined position. Grooves 5 are formed in the semiconductor substrate 1 using this opening as a mask. Next, a polysilicon film 12 is deposited on the silicon nitride film 2 and the inside of the groove 5. The polysilicon film 12 is polished by CMP. The silicon nitride film 2 is used as a stopper for this CMP, the silicon nitride film 2 is exposed to the semiconductor substrate 1 by polishing, and the polysilicon film 12 is embedded in the groove 5.
[0038]
If this CMP is not successful, the polysilicon film 12 and the silicon nitride film 2 are overpolished, and the surface of the polysilicon film 12 and the surface of the silicon nitride film 2 around the groove 5 are etched deeper than the original surface. That is, dishing-like depressions 7 are formed in the shaved portions. The amount by which the silicon nitride film is shaved the most is called the thinning amount (t), and the amount by which the polysilicon film is shaved the most is called the dishing amount (d). The positions where these are weighed are substantially at the center of the edge portion (t) of the groove portion 5 of the silicon nitride film 2 and the groove portion 5 of the polysilicon film 12. As shown in FIGS. 13 to 15, the polishing rate increases as the silica concentration (wt%) increases, and reaches a peak at approximately 7.5 wt%. The uniformity is uniform up to about 5 wt% but gradually decreases (improves uniformity) and peaks at 7.5 wt%. However, the amount of dishing and the amount of thinning increase as the silica concentration increases, increasing the size of the depression and making it impossible to perform precise polishing. Considering such contradictory characteristics, the concentration of silica contained in the abrasive of the present invention is suitably 7.5 wt% or less, more preferably 5 wt% or less, particularly 5 wt%.
[0039]
In the polishing method of the present invention, polishing can be performed using the abrasive of the present invention and an abrasive having a composition different from that of the abrasive. In this case, the abrasive is supplied from both the abrasive nozzle and the other abrasive nozzle of the present invention to the semiconductor wafer on the polishing board for polishing the substrate. For example, a slurry obtained by adding silica particles as silica particles and water as a solvent to which piperazine is added from a first abrasive nozzle is supplied to a semiconductor substrate, and the slurry of the present invention is supplied from a second abrasive nozzle.
[0040]
【The invention's effect】
As described above, the water-soluble cellulose of the polishing agent of the present invention does not deteriorate the purity of the wafer after polishing because the content of the alkali metal element is adjusted to a low purity. Further, the abrasive of the present invention is not only able to obtain an abrasive with good reproducibility in combination with the use of the above water-soluble cellulose, but also has excellent reproducibility of physical properties of the abrasive, particularly pH value, and lots of abrasives. Variation in polishing performance during the period can be suppressed.
The polishing agent of the present invention is optimal for finish polishing of a wafer such as a silicon semiconductor, and polishing using this polishing agent without forming dishing-like depressions in the polishing target film on the wafer becomes possible.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a polishing apparatus using an abrasive of the present invention.
FIG. 2 is a characteristic diagram showing the amount of impurities of the present invention and a conventional abrasive.
FIG. 3 is a characteristic diagram showing reproducibility of polishing rate by the present invention and a conventional abrasive.
FIG. 4 is a characteristic diagram showing a state of a wafer surface polished by the present invention and a conventional abrasive.
FIG. 5 is a cross-sectional view showing a manufacturing process of a semiconductor device using the abrasive of the present invention.
FIG. 6 is a cross-sectional view showing a manufacturing process of a semiconductor device using the abrasive of the present invention.
7 is a cross-sectional view showing a manufacturing process of a semiconductor device using the abrasive of the present invention. FIG.
FIG. 8 is a cross-sectional view showing a manufacturing process of a semiconductor device using the abrasive of the present invention.
FIG. 9 is a cross-sectional view showing a manufacturing process of a semiconductor device using the abrasive of the present invention.
FIG. 10 is a cross-sectional view showing a manufacturing process of a semiconductor device using the abrasive of the present invention.
FIGS. 11A and 11B are a perspective view and a cross-sectional view of a polishing apparatus using the abrasive of the present invention. FIGS.
FIG. 12 is a cross-sectional view of a semiconductor substrate polished by the polishing method of the present invention.
FIG. 13 is a characteristic diagram showing the silica concentration dependence of the polishing rate and the uniformity of the film to be polished by the polishing method of the present invention.
FIG. 14 is a characteristic diagram showing the silica concentration dependence of the dishing amount by the polishing method of the present invention.
FIG. 15 is a characteristic diagram showing the silica concentration dependence of the amount of thinning by the polishing method of the present invention.
FIG. 16 is a characteristic diagram showing the stability of the pH and polishing rate of the abrasive of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Semiconductor substrate, 2 ... Silicon nitride film, 5 ... Groove part,
6 ... CVD oxide film, 7 ... depression, 8 ... buffer oxide film,
11 ... oxide film, 12 ... polysilicon film,
13 ... photoresist, 14 ... LOCOS oxide film,
15, 18 ... plasma oxide film, 16 ... Cu film, embedded Cu wiring,
20 ... wafer, 21 ... stage, 22 ... bearing,
23 ... Polishing board receiver, 24 ... Polishing board, 25 ... Polishing cloth,
26 ... Drive shaft, 27, 33 ... Motor,
28 ... rotating belt, 29 ... template,
30 ... Adsorption cloth, 31 ... Adsorption board, 32 ... Drive shaft,
34, 35 ... gear, 36 ... drive base, 37 ... cylinder,
38 ... Abrasive supply pipe, 39 ... Ionized water supply pipe,
40 ... Abrasive tank, 41 ... Electrolysis tank,
42 ... Drain pipe.

Claims (10)

It has abrasive particles mainly composed of silica particles, a solvent composed of water, and water-soluble cellulose, and when the concentration of the water-soluble cellulose is C wt%, the content of alkali metal impurities is 5 Cppm or less. An abrasive characterized by being. The abrasive | polishing agent of Claim 1 whose density | concentration (C) of the said water-soluble cellulose is 0.05 to 4 weight%. The abrasive according to claim 1 or 2, wherein the content of the silica particles is 0.1 to 50% by weight or less. The abrasive according to any one of claims 1 to 3, further comprising a pH adjusting agent. The abrasive according to claim 4, wherein the pH adjuster is a water-soluble amine. The abrasive according to any one of claims 1 to 5, wherein the pH is 8-11. Polishing, wherein the polishing agent according to claim 1 is polished while being supplied to a polishing surface of a semiconductor wafer sliced from an ingot that is polished a plurality of times and is finally polished. Method. 7. A polishing method comprising performing chemical mechanical polishing while supplying the polishing agent according to claim 1 to a polishing target film formed on a semiconductor substrate. The polishing method according to claim 8, wherein a dispersing agent is supplied to the polishing target film together with the polishing agent. The polishing method according to claim 9, wherein the dispersant is ionic water or pure water.

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