JP2006270114A - Method for processing semiconductor substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for processing a semiconductor substrate, which can inhibit the generation of minute defects and oxygen deposition which cause element characteristics to deteriorate. <P>SOLUTION: In the method for processing the semiconductor substrate having a step of subjecting the semiconductor substrate, of which the surface is exposed, to a heat treatment under a gaseous atmosphere, in order to control so as to inhibit the deposition and the growth of oxygen in the semiconductor substrate by the heat treatment and the heat treatment steps before the heat treatment, a heat treatment step in an argon gas atmosphere before the heat treatment are performed under heat treating temperatures and heat treating time which are below certain limits. Thereafter, the heat treatment is performed under the argon gas atmosphere at temperatures not lower than 1,100°C. The internal minute defect concentration of the region, whose depth is 50 μm deeper than that of the surface of the semiconductor substrate, is made to be 1×10<SP>9</SP>particles/cm<SP>3</SP>or less, and the internal minute defect density of the region, whose depth is 10 μm deeper than that of the surface, is made to be 1×10<SP>7</SP>particles/cm<SP>3</SP>or less. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for processing a semiconductor substrate, and more particularly to an improvement in a method for processing a semiconductor substrate that can prevent deterioration of element characteristics.

  In recent years, large-scale integrated circuits (LSIs) formed by integrating a large number of transistors, resistors, and the like so as to achieve an electric circuit and integrating them on a single chip are often used in important parts of computers and communication devices. ing.

  The surface of a wafer used for LSI production is mirror-finished. As a mirror surface method, first, a disk-shaped wafer is cut out from a silicon crystal formed by a pulling method or a floating zone method. Next, the wafer surface is lapped, etched, and polished to obtain a wafer having a desired thickness. Finally, the wafer is cleaned with an acid or an organic solvent to obtain a wafer having a mirror-finished surface.

However, this type of method has the following problems. That is, for example, when the wafer is oxidized at a temperature of about 950 to 1100 ° C., about 10 to 100 / cm ² of oxidation induced stacking faults (OSF) are formed on the mirror surface.

As shown in FIG. 10, the generation of the OSF is caused by surface contaminants 2 on the surface of the silicon substrate 2, minute scratches 3, foreign substances 4 such as SiO ₂ and SiC, and the inside (near the surface) of the silicon substrate 1. It is thought to be caused by minute defects 5 such as swirls and oxygen precipitates. Note that the minute defect 5 occurs during crystal growth.

  When an element is formed on a wafer on which such an OSF has occurred, there is a problem in that element leakage is caused due to junction leakage, CCD (charge coupled device) image defects, and the like.

  Incidentally, a semiconductor substrate used for LSI is usually formed by a CZ (Czochralski) method. For this reason, excessive oxygen dissolves into the semiconductor substrate from the crucible or atmosphere during crystal growth. Excess oxygen in these semiconductor substrates generates precipitation nuclei inside the crystal by heat treatment, and forms internal micro defects (BMD: Bulk Micro Defect) having a size of about 0.1 to 1.0 μm around it.

  BMD will be described in more detail with reference to FIG. FIG. 11 is a diagram for explaining the precipitation of oxygen in a CMOS having a well structure. In this type of CMOS, impurities are thermally diffused on the surface of the wafer 1 at a temperature of 1100 ° C. or higher in order to form a p-well or an n-well in the initial manufacturing process. In this step, oxygen in the surface layer out of oxygen in the wafer 1 is diffused outward, so that a defect-free layer 12 called a DZ layer (Denuded Zone) is formed on the wafer 1 as shown in FIG. Formed on the surface. Next, as shown in FIG. 11B, in various processes such as formation of a nitride film by a low pressure CVD method, the wafer 1 is subjected to heat treatment at about 600 to 800 ° C. Is formed in the intermediate layer 14. Next, as shown in FIG. 11C, when the wafer 1 is subjected to a heat treatment at around 1000 ° C. in the field oxide film forming process or the like, the nuclei 13 grow precipitates around and the BMD 15 is distributed at a high concentration. .

  The generation of BMD described above varies greatly depending not only on the thermal history of the wafer but also on the carbon concentration, the pulling conditions during crystal growth, and the like. At present, the core of BMD is considered to be minute oxygen precipitates generated during crystal pulling, and the size and the number of precipitates vary within the wafer.

  At this time, if heat treatment is performed in a non-oxidizing gas atmosphere, for example, the surface is nitrided non-uniformly in a nitrogen atmosphere, resulting in surface roughness. Further, in a rare gas atmosphere, if sufficient purity is not ensured, etching occurs unevenly on the surface, which also causes surface roughness, so that heat treatment is generally performed in an oxidizing atmosphere. For this reason, as a method of forming the DZ layer, a method of reducing the surface oxygen concentration by outward diffusion of oxygen is used. For this reason, the wafer surface is covered with a thin oxide film.

  However, since the surface oxygen concentration is reduced only to the equilibrium concentration through the oxide film in the heat treatment in an oxidizing atmosphere, the suppression of precipitates is not sufficient, and it is difficult to form a complete DZ layer. When a thin oxide film such as a gate oxide film is formed on the substrate, pinholes or the like are generated, resulting in a problem that the breakdown voltage of the oxide film is deteriorated. In addition, when oxygen is diffused for a long time in order to form a DZ layer in a deeper region, the DZ layer on the low oxygen concentration side becomes deeper, and precipitation and growth of oxygen proceed, so that the solid state in the substrate is increased. The problem is that the dissolved oxygen concentration is lowered, the substrate strength is deteriorated, and crystal defects are generated in the element active region.

  As described above, the conventional semiconductor substrate processing method has a problem that it is difficult to form a high-quality DZ layer.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for processing a semiconductor substrate capable of suppressing the generation of BMD and OSF that cause deterioration of element characteristics.

In order to achieve the above object, a semiconductor substrate processing method according to the present invention (Claim 1) is a semiconductor substrate processing method including a step of heat-treating a semiconductor substrate having an exposed surface in a gas atmosphere. The heat treatment is performed in an argon gas atmosphere of 1100 ° C. or higher with a concentration of oxygen, carbon, nitrogen, or carbon-based gas of 10 ppb or less, and the semiconductor substrate is subjected to the heat treatment in a heat process in an argon gas atmosphere before the heat treatment. The heat treatment temperature and the retention time (excluding the retention time of zero) after being inserted into the previous argon gas atmosphere are (900 ° C., 4 minutes), (800 in a plane having the heat treatment temperature and the retention time as coordinates. C., 40 minutes), (700.degree. C., 11 hours), (600.degree. C., 320 hours) included in the region below the line connecting the four points, and before the heat treatment and the heat treatment. By the thermal process, the precipitation of oxygen in the semiconductor substrate, is controlled to suppress the growth, the internal micro defect density region from the surface 50μm or more of the depth of the semiconductor substrate 1 × 10 ⁹ pieces / cm ³ Hereinafter, the density of internal micro defects in a region having a depth within 10 μm from the surface is set to 1 × 10 ⁷ pieces / cm ³ or less.

  In another semiconductor substrate processing method of the present invention, silicon is introduced between lattices in a silicon substrate, and oxygen in the silicon substrate is diffused outward, and the silicon substrate is placed in a non-oxidizing atmosphere. And a heat treatment process.

  In another semiconductor substrate processing method of the present invention, a silicon substrate is heat-treated in an oxidizing atmosphere at 1100 ° C. or higher to form an oxide film on the surface of the silicon substrate, and the oxide film is removed. And heat-treating the silicon substrate in a non-oxidizing atmosphere with the surface of the silicon substrate exposed. Here, the heat treatment in the non-oxidizing atmosphere is preferably at a temperature of 1100 ° C. or higher.

  Note that the non-oxidizing atmosphere includes not only an inert gas atmosphere such as Ar but also an atmosphere that does not cause an undesirable reaction with the substrate surface and an atmosphere that does not damage the substrate surface. For example, it may be in a hydrogen atmosphere.

Also, the semiconductor substrate of the present invention, ¹⁰⁶ in the first region from the surface within 10μm depth / cm ³ or less and becomes, and ¹⁰⁶ from the surface in the second region above a depth of 50 [mu] m / cm ^The internal crystal defect density distribution is constant in a range of ^{3 to} 5 × 10 ⁸ pieces / cm ³ and decreases toward the surface between the first region and the second region. To do.

[Action]
If the heat treatment temperature and the heat treatment time are selected as in the present invention in the heat treatment step in a non-oxidizing atmosphere, the generation of stacking faults and oxygen precipitates on the surface and inside of the semiconductor substrate can be sufficiently suppressed. Therefore, according to the semiconductor substrate processing method of the present invention (claim 1), a high-quality oxide film can be formed on the substrate surface.

  Further, according to another semiconductor substrate processing method of the present invention, silicon is preferentially introduced between the lattices in the silicon substrate, so that interstitial oxygen in the silicon substrate becomes difficult to precipitate and in the silicon substrate. Therefore, the interstitial oxygen concentration on the silicon substrate surface can be lowered without precipitation. Further, the heat treatment in a non-oxidizing atmosphere repairs micro defects and further diffuses oxygen outward. Accordingly, a silicon substrate with few substrate defects such as BMD can be obtained.

  According to another semiconductor substrate processing method of the present invention, when an oxide film is formed by heat treatment in an oxidizing atmosphere at 1100 ° C. or higher, expansion occurs on the surface of the silicon substrate and rearrangement of silicon crystals occurs. . At this time, the silicon that has not been rearranged moves into the silicon substrate, silicon is introduced between the silicon lattices, and oxygen in the silicon substrate is diffused outward, so that oxygen precipitates in the silicon substrate are formed. Less. Further, the heat treatment in a non-oxidizing atmosphere repairs micro defects and further diffuses oxygen outward. Accordingly, a silicon substrate with few substrate defects such as BMD can be obtained.

Further, according to the study by the present inventors, 10 ⁷ from the surface in the first region within a depth of 10 [mu] m / cm ³ or less and becomes, and the second region ¹⁰⁷ from the surface of the above 50μm depth Internal crystal defect density distribution that is constant in the range of not less than 1 piece / cm ^{3 and not} more than 1 × 10 ⁹ pieces / cm ³ and uniformly decreases toward the surface between the first region and the second region. It has been found that a semiconductor substrate having a can prevent deterioration of element characteristics due to a substrate defect such as BMD.

  According to the present invention, generation of minute defects and oxygen precipitates in a semiconductor substrate that cause deterioration of device characteristics can be sufficiently suppressed.

  Hereinafter, embodiments will be described with reference to the drawings.

First, the wafer is oxidized in a dry atmosphere at 780 ° C. for 3 hours and then at 1000 ° C. for 16 hours to prepare a wafer in which OSF of 2 × 10 ³ pieces / cm ² is generated. Next, this wafer is heat-treated at 1200 ° C. for about 1 to 8 hours in an inert gas atmosphere such as argon or helium.

  Next, the wafer is oxidized in a dry atmosphere at 780 ° C. for 3 hours and then at 1000 ° C. for 16 hours, and then the surface of the wafer is light-etched.

When the wafer thus obtained was observed with an optical microscope, it was found that the OSF density can be reduced at an OSF density of about 4 / cm ^{2 as} shown in FIG.

On the other hand, the OSF density was hardly generated at about 0.6 / cm ^{2 on the} wafer which had not been heat-treated at 780 ° C. for 3 hours and 1000 ° C. for 16 hours.

  The heat treatment method of this embodiment is basically performed in a state where the protective film such as an oxide film is removed from the surface of the substrate, so that oxygen, nitrogen, carbon-based gas or the like is present in an inert gas atmosphere such as argon. If mixed as impurities, the wafer surface may be roughened. For this reason, it is desirable that the impurity concentration of oxygen, carbon, nitrogen or carbon-based gas in an inert gas atmosphere such as argon is 10 ppb or less.

  Next, another embodiment of the present invention will be described.

  In a CMOS having a well structure, in order to form a p-well or an n-well in the initial manufacturing process, a heat treatment of 1100 ° C. or higher for several hours (heat treatment in a non-oxidizing atmosphere at 1100 ° C. or higher) is performed. Impurities are thermally diffused on the surface. In this step, oxygen in the surface layer out of oxygen in the wafer is diffused outward, and a defect-free layer called a predetermined DZ layer is formed on the surface of the wafer. Thereafter, in various processes such as nitride film formation by a low pressure CVD method, the wafer is subjected to a heat treatment at about 600 to 800 ° C., and nuclei of oxygen precipitates are ideally formed in an intermediate layer inside the wafer. Next, when the wafer is subjected to a heat treatment at around 1000 ° C. in a field oxide film formation process or the like, the nuclei grow precipitates around and the BMD is distributed at a high concentration. The generation of nuclei of oxygen precipitates varies greatly depending not only on the thermal history of the wafer but also on the carbon concentration, the pulling conditions during crystal growth, and the like. For this reason, the size and number of precipitates vary within the wafer.

  Before the above process, as the heat treatment of the present invention, heat treatment is performed on the wafer at 1200 ° C. for 4 hours in an argon atmosphere. In FIG. 2, the relationship between the depth from the surface of the wafer subjected to such heat treatment and the BMD density is shown by a solid line. For comparison, the relationship between the depth from the surface of a conventional wafer not subjected to the heat treatment and the BMD density is indicated by a dotted line.

From this figure, it can be seen that the BMD concentration is smaller in the present invention in the region where the depth is about 30 μm or less. Moreover, the value at 10 μm or less is sufficiently small at about 1 × 10 ⁷ (pieces / cm ³ ) or less.

  Further, in the high-temperature heat treatment in the argon atmosphere, the boat-in temperature was changed to 800 ° C. and the holding time was changed to 40 minutes or less, and it was found that oxygen precipitates on the wafer surface could be reduced as shown in FIG. . That is, when the holding time is shortened, the BMD density is generally reduced, but when the holding time is less than a certain holding time, in this case, 20 minutes or less, the BMD density is increased.

  FIG. 4 is a diagram showing regions of heat treatment time and holding time that can reduce the BMD density in this way. Of the regions divided by the solid line in the figure, the heat treatment may be performed with the heat treatment time and holding time of the hatched region (including the solid line).

  FIG. 5 is a characteristic diagram showing the relationship between the depth from the wafer surface and the BMD density. From this figure, it can be seen that the BMD of the wafer surface layer is maintained at a low density with good controllability in the heat treatment at 1100 ° C. or higher under the condition of holding time of 20 minutes.

  Further, the wafer subjected to the heat treatment of the present invention was oxidized at 950 ° C. to form an oxide film having a thickness of 20 nm, and a capacitor was prepared and evaluated.

  Capacitors made with a conventional wafer that has not been subjected to the main heat treatment have a breakdown of 20 to 60% in an electric field of 8 MV / cm or less, whereas capacitors made with a wafer that has been subjected to the main heat treatment at 1100 ° C. or higher. Only a few percent of the products had poor pressure resistance.

  In this way, by performing heat treatment at 1100 ° C. or higher in a non-oxidizing gas atmosphere such as argon, the generation of OSF can be suppressed and the generation of oxygen precipitates in the vicinity of the surface layer can be controlled without variation, so that the oxide film Effects such as prevention of breakdown voltage failure can be obtained. In addition, although the case where heat processing was performed for 4 hours was described in the said Example, the same effect will be acquired if not only this but heat processing for 1 hour or more.

  By the way, when the heat treatment time is long, the amount of oxygen precipitated in the wafer increases, so that there is a problem that the wafer is warped during the process or the stress margin for the thermal process during the process is lowered.

According to the study by the present inventors, when a quantity of oxygen exceeding 2 × 10 ¹⁷ atoms / cm ³ is precipitated inside the wafer by heat treatment in a non-oxidizing atmosphere, crystal defects are generated or device characteristics are deteriorated. I understood that. Therefore, it is necessary to select the heat treatment conditions such that the oxygen concentration on the wafer surface is 1 × 10 ¹⁷ atoms / cm ³ or less and the oxygen precipitation amount in the wafer is 2 × 10 ¹⁷ atoms / cm ³ or less. is there.

  Next, a method for treating a silicon substrate according to another embodiment of the present invention will be described.

  First, a silicon substrate is heat-treated in an oxidizing atmosphere (100% dry oxygen) at 1100 ° C. or higher to form a silicon oxide film on the surface of the silicon substrate. By this heat treatment, silicon atoms can be introduced between the lattices inside the silicon substrate, and oxygen can be prevented from being precipitated between the lattices inside the silicon substrate.

  Silicon atoms are introduced between the lattices when atoms are rearranged on the surface of the silicon substrate when the silicon oxide film is formed by the heat treatment at 1100 ° C. or higher. This is thought to be because surplus silicon atoms that could not contribute moved into the silicon substrate.

  Next, after removing the silicon oxide film formed on the surface of the silicon substrate, the silicon substrate is heat-treated in an inert gas atmosphere at 1200 ° C. for 4 hours. In addition, the time of this heat processing is not limited to 4 hours, Usually, it may be 1 hour or more.

  FIG. 6 is a characteristic diagram showing the relationship between the heat treatment temperature (oxidation temperature) in the oxidizing atmosphere and the amount of precipitated oxygen. As can be seen from FIG. 6, when the oxidation temperature is 1100 ° C. or higher, the amount of precipitated oxygen is smaller than that of the raw silicon substrate. Therefore, it can be seen that the oxidation temperature must be 1100 ° C. or higher.

  FIG. 7 is a characteristic diagram showing the relationship between the initial oxygen concentration and the BMD density.

  In the figure, ● represents the measurement data for the silicon substrate subjected to the heat treatment in the oxidizing atmosphere of this example.

  Specifically, it is measurement data when a silicon substrate that has been heat-treated in an oxidizing atmosphere at 1200 ° C. for 1 hour is heat-treated in an Ar gas atmosphere at 1200 ° C. for 1 hour.

  On the other hand, ◯ indicates measurement data for a silicon substrate that has not been heat-treated in an oxidizing atmosphere at 1200 ° C. That is, it is measurement data when only the heat treatment in the Ar gas atmosphere is performed.

  It can be seen from FIG. 7 that the BMD density is small regardless of the initial oxygen concentration when the heat treatment is performed in an oxidizing atmosphere at 1200 ° C.

  On the other hand, it can be seen that when the heat treatment in the oxidizing atmosphere at 1200 ° C. is not performed, the BMD density increases as the initial oxygen concentration increases.

  Therefore, it can be confirmed that the heat treatment in the oxidizing atmosphere of this example is an essential process for reducing the BMD density.

  FIG. 8 is a diagram showing the relationship between the depth from the surface of the silicon substrate and the oxygen concentration before and after the heat treatment in the inert gas atmosphere after the heat treatment in the oxidizing atmosphere. A characteristic curve before the heat treatment is shown, and a curve b shows the characteristic curve after the heat treatment.

  From this figure, it can be seen that immediately after the heat treatment in the oxidizing atmosphere, the oxygen concentration which is generally high inside the silicon substrate is lowered overall by the heat treatment in the inert gas atmosphere. The reason why the oxygen concentration is lowered is that oxygen on the surface of the silicon substrate is diffused outward by the heat treatment step in an inert gas atmosphere.

  FIG. 9 is a diagram showing the effect of the heat treatment step of the silicon substrate in the inert gas atmosphere described above, and shows the relationship between the depth from the surface of the silicon substrate and the BMD density. In the figure, curve c indicates the case where the heat treatment is performed, and curve d indicates the case where the heat treatment is not performed. It can be seen from this figure that the BMD density can be sufficiently reduced by performing the heat treatment step in the inert gas atmosphere.

  The reason why the BMD density is greatly reduced in this way is that the BMD on the silicon substrate surface disappears due to the outward diffusion of oxygen on the silicon substrate surface. At this time, the OSF also disappears.

  In addition, the inventors of the present invention oxidized the silicon substrate subjected to such a treatment at 950 ° C. to form an oxide film having a thickness of 20 nm to form a capacitor, and the BMD on the surface of the oxide film and the silicon substrate. I tried to evaluate.

  As a result, it was found that when the heat treatment temperature in the oxidizing atmosphere is 1100 ° C. or higher, the BMD on the surface of the silicon oxide film and the silicon substrate is maintained at a low density with good controllability. Further, only a few percent of the capacitors showed a breakdown voltage failure with an electric field of 8 MV / cm or less.

  For comparison, when a capacitor formed on a conventional silicon substrate not subjected to a heat treatment in an oxidizing atmosphere was examined, 20 to 60% of the capacitors exhibiting a breakdown voltage with an electric field of 8 MV / cm or less.

  As described above, according to the present embodiment, the silicon substrate is subjected to heat treatment in an oxidizing atmosphere at 1100 ° C., and then subjected to heat treatment in an inert gas atmosphere at 1200 ° C., thereby reducing the strength of the silicon substrate. Without causing it, it is possible to suppress the occurrence of BMD and OSF that cause the device characteristics to deteriorate.

  Next, a method for treating a silicon substrate according to another embodiment of the present invention will be described.

  First, an oxide film is formed on a silicon substrate. This oxide film is formed using a film forming method such as a thermal oxidation method or a CVD method.

  Next, the silicon substrate is heat-treated in a non-oxidizing gas atmosphere such as nitrogen at 1100 ° C. or higher.

  Next, after removing the oxide film formed on the silicon substrate, heat treatment is performed in an inert gas atmosphere such as argon.

  Even in the method described above, silicon is introduced between lattices in the silicon substrate by heat treatment in a non-oxidizing gas atmosphere such as nitrogen at 1100 ° C. or higher, and oxygen in the silicon substrate is diffused outward. Further, the amount of oxygen precipitates generated can be made sufficiently small, and the same effect as in the previous examples can be expected.

  In addition, this invention is not limited to the Example mentioned above. For example, in the above embodiment, an argon gas atmosphere is used as the non-oxidizing atmosphere, but the same effect can be obtained by using an atmosphere of other rare gas or a hydrogen atmosphere. In addition, various modifications can be made without departing from the scope of the present invention.

The characteristic view which shows the relationship between heat processing time and OSF density. The characteristic view which shows the relationship between depth and BMD density. The characteristic view which shows the relationship between holding time and BMD density in case heat processing temperature is 800 degreeC. The figure which shows the area | region of the heat processing temperature and heat processing time from which a low defect density is obtained. The characteristic view which shows the relationship between BMD density, depth, and heat processing temperature. The characteristic view which shows the relationship between oxidation temperature and the amount of oxygen precipitation. The characteristic view which shows the relationship between initial stage oxygen concentration and BMD density. The figure which shows the relationship between the depth from the surface of a silicon substrate, and oxygen concentration. The figure which shows the relationship between the depth from the surface of a silicon substrate, and BMD density. The wafer sectional view for explaining the conventional problem. The figure for demonstrating the precipitation behavior of oxygen.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Silicon substrate, 2 ... Surface contaminant, 3 ... Fine flaw, 4 ... Foreign material, 5 ... Micro defect, 12 ... Defect-free layer, 13 ... Core, 14 ... Intermediate layer, 15 ... BMD.

Claims (2)

In a semiconductor substrate processing method including a step of heat-treating a semiconductor substrate having an exposed surface in a gas atmosphere,
The heat treatment is performed in an argon gas atmosphere of 1100 ° C. or higher with a concentration of oxygen, carbon, nitrogen, or a carbon-based gas of 10 ppb or less, and the semiconductor substrate is subjected to the heat treatment in an argon gas atmosphere before the heat treatment. The heat treatment temperature and holding time (excluding the holding time of zero) after insertion into the argon gas atmosphere before the heat treatment are (900 ° C., 4 minutes) in a plane with the heat treatment temperature and the holding time as coordinates (900 ° C., 4 minutes), ( 800 ° C., 40 minutes), (700 ° C., 11 hours), (600 ° C., 320 hours) included in the region below the line connecting the four points, and by the heat treatment and the heat step before the heat treatment, the precipitation of oxygen in the semiconductor substrate, is controlled to suppress the growth, the internal micro defect density region from the surface 50μm or more of the depth of the semiconductor substrate 1 × 10 ⁹ pieces / cm ³ or less Method of treating a semiconductor substrate, which comprises an internal micro defect density in the depth of the region within 10μm from the surface below 1 × 10 ⁷ cells / cm ^3. The method for processing a semiconductor substrate according to claim 1, wherein the semiconductor substrate is a silicon substrate.

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