JPH11265861A - Polishing and manufacture of semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable the chemical and mechanical polishing at a pH of 10 and below of a semiconductor device and to eliminate the occurrence of damage due to polishing at the high polishing rate of the semiconductor device by a method wherein a work containing a silicon oxide or containing a silicon oxide as its main component is polished using a polishing agent containing abrasive grains, which contain magnesium oxide as their main component. SOLUTION: A work containing a silicon oxide or containing a silicon oxide as its main component is polished using a polishing agent containing abrasive grains, which contain magnesium oxide as their main component. Moreover, an insulatator layer, comprising a silicon oxide layer, on the surface of a semiconductor substrate is polished using a polishing agent containing abrasive grains, which contain magnesium oxide as their main component, and after the insulator layer is flattened, the polished semiconductor substrate is cleaned using an acid selected from among a hydrochloric acid, a nitric acid and/or a sulfuric acid. As the polishing agent for the work containing the silicon oxide as its main component, such as glass and a quartz wafer, a polishing agent containing abrasive grains, which contain magnesium oxide as their main component, is used, whereby the high polishing rate of a semiconductor device can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for polishing silicon oxide or the like and a method for manufacturing a semiconductor device including the polishing method.

[0002]

2. Description of the Related Art In polishing a semiconductor substrate,
A polishing method is required that ensures a polishing rate and does not cause defects such as mechanical strain. In the conventional mechanical polishing method, by increasing the abrasive grain size and polishing load,
It is possible to secure a polishing rate. However, various defects are caused by the polishing, and it has been impossible to secure both the polishing rate and the material to be polished without defects. Therefore, chemical mechanical polishing (CMP)
A polishing method called ing) was devised. In this method, a chemical polishing action is superimposed on a mechanical polishing action so that a polishing speed can be ensured and a material to be polished has no defect. CMP is widely used in a polishing process of a silicon wafer, which needs to ensure both a high polishing rate and a defect-free material. Also, in recent years, it has become necessary to polish the surface of a wafer or a semiconductor substrate having a conductor or dielectric layer formed on the surface of the wafer at a predetermined stage of manufacturing an integrated circuit with high integration of devices. Was. The semiconductor substrate is polished to remove high bumps and planarize. Typically, this step is performed during the formation of various devices and integrated circuits on the wafer. In this polishing step, as in the polishing step of the silicon wafer, it is necessary to ensure both the polishing rate and the defect-free state. By introducing the chemical slurry, CMP is performed on the semiconductor surface to provide a higher polishing removal rate and defect-freeness. In general, a CMP process involves holding and rotating a thin, planar semiconductor material against a wet polishing surface under controlled pressure and temperature.

As typical examples of the CMP process, for example,
A polishing cloth made of a polishing slurry prepared by suspending silica particles having a particle diameter of about 300 nm in an alkaline solution such as caustic soda to a pH of about 9 to 12 and a polyurethane resin is used. At the time of polishing, the semiconductor substrate is brought into contact with the polishing cloth and rotated relatively while the chemical slurry is being spread, thereby performing the polishing.

[0004]

It is known that polishing of an insulator layer made of silicon oxide can be performed by using the above-mentioned polishing slurry containing silica particles as a polishing agent. However, the polishing rate cannot be said to be sufficient, and a long time is required for polishing, which causes an increase in cost. In addition, polishing silicon oxide with silica abrasive grains is a common rub, and the introduction of polishing flaws is a problem. In addition, since a physical method such as scrub cleaning is used as a cleaning method after polishing, it is difficult to completely remove the silica particles, and with the progress of high integration, residual silica particles have become a cause of a decrease in manufacturing yield. I have. Further, a polishing slurry containing silica particles generally contains an alkali metal such as potassium hydroxide for pH adjustment for the purpose of improving the polishing rate. However, when a material containing an alkali metal such as potassium is used in the manufacture of a semiconductor device, the semiconductor device is contaminated with the alkali metal, and its electrical characteristics deteriorate. For this reason, although there is a polishing slurry containing silica particles containing ammonia as a substitute for potassium hydroxide, the polishing rate using this slurry is 2 times that of the slurry containing potassium hydroxide.
There has been a demand for the development of an abrasive which is as slow as about / 3 and has a higher polishing rate.

[0005]

According to the present invention, a substance having a lower hardness than silicon oxide to be polished and having a high chemical activity with respect to silicon oxide is used as abrasive grains.
CMP at a pH of 10 or less becomes possible, and a polishing slurry which has a high polishing rate, does not cause polishing scratches, and can prevent alkali contamination can be realized. As an abrasive used for CMP of silicon oxide, the inventors have found that magnesium oxide has a lower hardness than silicon oxide, is chemically active on silicon oxide, and is useful. In addition, since magnesium oxide is easily dissolved in acids such as hydrochloric acid, nitric acid, and sulfuric acid, a polishing process with extremely good cleaning properties can be realized.

The present invention is a method for polishing silicon oxide or a workpiece mainly containing silicon oxide by using an abrasive containing abrasive grains mainly containing magnesium oxide. Further, the present invention provides a step of flattening the insulator layer made of silicon oxide on the surface of the semiconductor substrate by polishing using an abrasive containing abrasive grains mainly composed of magnesium oxide; Cleaning the polished semiconductor substrate with an acid selected from hydrochloric acid, nitric acid, and / or sulfuric acid after the step is completed.

[0007]

DETAILED DESCRIPTION OF THE INVENTION The hardness of magnesium oxide is Proc.
As shown in the eedings of the Royal Society of London. Series A, Volume 322 (1971), p. 73,
400 for various crystal planes of magnesium oxide single crystal
８００800 kg / cm ² . On the other hand, the hardness of silicon oxide is 1200 kg / cm ² with respect to the (011) plane of a quartz single crystal as shown in Journal of American Ceramics Society, Vol. 78 (1995), p. 737.
In other words, the abrasive grains mainly composed of magnesium oxide used in the present invention have lower hardness than silicon oxide as the material to be polished, and do not generate polishing scratches. Also, magnesium oxide undergoes a chemical reaction with silicon oxide to form -Si-O-Si-
Disconnect the network. Therefore, the surface layer of the silicon oxide is softened, and the surface layer of the silicon oxide is scraped off by the magnesium oxide abrasive grains. As described above, in the polishing of silicon oxide using magnesium oxide abrasive grains, a remarkable chemical mechanical polishing mechanism works, so that a higher polishing rate is realized than when using a polishing slurry containing silica particles as an abrasive. The inventor has found what can be done. Therefore, a high polishing rate can be obtained by using a polishing agent containing abrasive grains mainly containing magnesium oxide as a polishing agent for a workpiece mainly containing silicon oxide, for example, a glass or quartz wafer. it can. In addition, since the polishing rate is high, it is not necessary to set the pH to about 11 or more. Therefore, it is not necessary to use a strong base such as potassium hydroxide, and a high polishing rate can be obtained even when a base containing no alkali metal such as ammonia is used. Speed can be realized. Therefore, the problem of residual alkali metal is solved. Also, magnesium oxide readily dissolves in acids. Therefore, the use of an abrasive containing abrasive grains containing magnesium oxide as a main component can solve the problem of residual contamination of alkali metal and abrasive grains, which is often an important issue in CMP used in the manufacture of semiconductor devices. A step of polishing the insulator layer made of silicon oxide on the surface of the semiconductor substrate by using an abrasive containing abrasive grains containing magnesium oxide as a main component, thereby flattening the semiconductor device. Figure 1 shows the manufacturing method
It was shown to. The manufacture of the shallow trench isolation structure will be described as an example. FIG. 1A shows a structure in which a thermal oxide film 2 and a silicon nitride layer 3 as a polishing stopper layer are formed on a silicon substrate 1. The structure shown in FIG. 1 (b) is obtained by masking this structure and performing etching to form grooves necessary for element isolation, and oxidizing the silicon substrate. On top of this structure, a chemical vapor deposition (CVD:
Chemical Vapor Deposition
According to n), a silicon oxide insulating film 4 is formed as shown in FIG. The uppermost silicon oxide insulating film is polished by using an abrasive containing abrasives made of magnesium oxide, thereby planarizing the silicon oxide insulating film, thereby producing the shallow trench isolation structure shown in FIG. be able to. Furthermore, since magnesium oxide is easily dissolved in acids such as hydrochloric acid, nitric acid and sulfuric acid, the magnesium oxide abrasive grains are completely removed by a washing step using an acid, and a slurry containing silica abrasive grains is used. No decrease in the product yield due to the residual abrasive grains shown in FIG. In addition, by including hydrogen peroxide in the cleaning solution, the dissolution of magnesium oxide becomes faster and the cleaning time can be shortened.

If the particle size of the abrasive particles containing magnesium oxide as a main component is larger than 10 μm, sedimentation is likely to occur, and the supply pipe of the slurry is clogged.
The following is preferred. In order to utilize the chemical activity, it is effective to use fine particles and increase the specific surface area, and the particle size of the abrasive grains mainly composed of magnesium oxide is 2 to 500 nm.
Is particularly preferred. If the content of magnesium oxide abrasive grains in the slurry is less than 0.1 wt%, the polishing effect is low, and if the content is 30 wt% or more, the polishing rate is almost constant. Therefore, the range of 0.1 to 30 wt% is desirable.

[0009]

EXAMPLES The object to be polished, by using the CVD method, about 700nm to TEOS-SiO ₂ film on a silicon wafer
A wafer deposited to a thickness was prepared. The polishing slurry used was a slurry containing 5 wt% of magnesium oxide having an average particle diameter of 200 nm and having a pH of 10 using ammonia. On the other hand, for comparison, as a conventional silica slurry,
SEMI-SRERS commercially available from Cabot
E12 (fumed silica 1 having an average secondary particle size of 150 nm)
2.5 wt% content, pH = 11) based on KOH. As the polishing pad, a two-layer pad of IC1000 / SUBA400 commercially available from Rodale Nitta was used. The polishing pressure was 400 g / cm ² , and each wafer was polished for 2 minutes. The film thickness of the SiO ₂ film was measured using Nanospec manufactured by Nanometrics.
After the polishing, the wafer polished with the magnesium oxide-containing slurry of the present invention was washed with a hydrochloric acid solution, and the wafer polished using SEMI-SLERSE12 of Comparative Example was SC- After one washing, brush scrub washing was performed. After the rinsed wafer is rinsed with pure water, the number of residual particles having a size of 0.17 μm or more on the polished surface is evaluated with a Hitachi DECO particle counter, and the amount of residual potassium on the polished surface is determined by ICP.
It was evaluated by analysis. The lower limit of quantification of potassium in ICP analysis is 1 × 10 ¹⁰ atoms / cm ² . Figure 2 shows the results.
Is shown in Table 1.

As a result, the magnesium oxide slurry of the present invention has a significantly higher polishing rate than the conventional silica slurry. Also, the number of remaining particles was significantly reduced. In the particle counter, 52 foreign particles / wafer surface foreign matter were also observed in the example, and the foreign matter was mainly caused by pits (COP: Crystal O) caused by crystals.
It is thought to be due to surface defects, such as a registered particle. For confirmation, ICP analysis was performed on magnesium. The amount of residual magnesium was less than the lower limit of quantification (= 1 × 10 ⁹ atoms / cm ² ), and the magnesium oxide abrasive of the present invention was easily dissolved by washing with an acid solution. Make sure you do. In the present invention, since no alkali metal was added to the polishing agent, the amount of residual potassium was less than the lower limit of quantification (= 1 × 10 ¹⁰ atoms / cm ² ) of ICP analysis, and the residual amount of silica slurry of the comparative example was It is significantly less than the amount of potassium. From the above, it was confirmed that the abrasive of the present invention has a remarkable effect on improving the polishing rate and reducing residual contamination of abrasive grains and alkali metal.

The present invention is not limited to the above-described embodiment, and various modifications can be made within the scope of the invention.

[0012]

According to the polishing method and the method for manufacturing a semiconductor device of the present invention, a high polishing rate can be achieved in polishing a silicon oxide insulator layer on a semiconductor substrate, the throughput is improved, and the abrasive grains and An improvement in the production yield due to a reduction in the residual contamination of the alkali metal is realized, and the semiconductor device can be manufactured at low cost.

[Brief description of the drawings]

FIGS. 1A to 1D are diagrams illustrating a manufacturing process of a semiconductor device.

FIG. 2 is a table showing experimental results.

[Explanation of symbols]

 Reference Signs List 1 silicon substrate 2 silicon oxide film 3 silicon nitride film 4 silicon oxide insulating film

Claims (2)

[Claims] 1. A polishing method for polishing a silicon oxide or a workpiece mainly composed of silicon oxide, comprising using an abrasive containing abrasive grains mainly composed of magnesium oxide. . 2. A step of flattening an insulator layer made of silicon oxide on the surface of a semiconductor substrate by polishing using an abrasive containing abrasive grains mainly composed of magnesium oxide, and a step of flattening. Cleaning the polished semiconductor substrate with an acid selected from hydrochloric acid, nitric acid and / or sulfuric acid after completion.