JP2003297839A - Heat treatment method for silicon wafer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for heat-treating a silicon wafer using a rapid heating/quenching apparatus, particularly a heat-treatment method for a silicon wafer for obtaining a wafer exhibiting enough gettering capability in a device process. <P>SOLUTION: After first RTA treatment is performed independently in a nitrogen gas or in a mixed gas atmosphere of the nitrogen gas and an inert gas at a temperature ranging from 1,150 to 1,300°C over 1 second, a second RTA treatment is performed in an oxidative gas atmosphere or in an nonoxidative gas atmosphere at a temperature ranging from 700 to 1,100°C for 5 seconds or longer. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat treatment method for a silicon wafer for forming a semiconductor device obtained from a silicon single crystal.

[0002]

2. Description of the Related Art A silicon wafer used for a semiconductor device is manufactured by slicing a silicon single crystal ingot mainly grown by the Czochralski method (CZ method). The CZ method is a method of immersing a seed crystal in a molten silicon melt in a quartz crucible and then pulling it upward to grow a silicon single crystal at the lower end of the seed crystal. Oxygen is taken into the silicon single crystal and is sufficiently dissolved in the crystal immediately after solidification of the crystal, but the solid solubility decreases as the single crystal is cooled. Exists in a supersaturated state.

Supersaturated oxygen in a wafer taken from this single crystal is precipitated as an oxide during the subsequent heat treatment in the device manufacturing process, and the oxygen precipitate and the defects induced by the oxygen precipitate are BMD (bulk). M
It is also called "micro Defect". This BM
When D is present in the device active region, it becomes a factor that deteriorates the device characteristics, but when D is present inside the wafer, it effectively acts as a gettering source for capturing metal impurities mixed in in the device manufacturing process.

As a method for producing a silicon wafer having excellent gettering characteristics, for example, by subjecting the silicon wafer to a high temperature heat treatment at 1100 ° C. or more in a non-oxidizing atmosphere, oxygen in the surface layer of the wafer is diffused outward to diffuse the surface layer. The concentration of oxygen existing in the wafer is reduced to form a defect-free layer (Deduced Zone, hereinafter referred to as a DZ layer) on the surface of the wafer, in which there are no oxygen precipitates or defects induced by the oxygen precipitates. Then, 500-900 ° C on the silicon wafer
A method has been proposed in which oxygen precipitation nuclei are formed inside the wafer by performing low-temperature heat treatment for several hours, and then grown as oxygen precipitates inside the wafer by being subjected to heat treatment in the next device step. However, this heat treatment method requires a long time and has a problem of low productivity.

On the other hand, the wafer is rapidly heated and cooled in a short time (RT
A: Rapid Thermal Annealin
It has been proposed to control the density distribution of oxygen precipitates generated by thermal history in the subsequent manufacturing process such as a device process by performing g).

For example, in the invention of US Pat. No. 5,401,669, 1175-1 in nitrogen or an atmosphere containing nitrogen.
It has been proposed to hold the material at 275 ° C. for 3 to 60 seconds and then cool it at a cooling rate of 5 ° C./second or more. According to this method, by performing RTA treatment for a short time, oxygen precipitates are formed at high density inside the wafer in the subsequent heat treatment of the device step. There is a problem that oxygen precipitates are scarcely formed in the central portion (central portion) in the wafer thickness direction, which is limited to the vicinity of the front and back surfaces.

Further, in the invention of US Pat. No. 5,994,761, after forming an oxide film of several tens of angstroms on the surface by treatment in an oxidizing atmosphere, 1150 to 1300 ° C. in an inert gas atmosphere such as nitrogen or argon. In 1
It has been proposed to carry out a treatment of holding at ˜60 seconds and then cooling at a cooling rate of 5 to 200 ° C./second. According to this method, although oxygen precipitates are formed at a high density in the central portion (central portion) in the wafer thickness direction in the subsequent device step, the oxygen precipitates become closer to the front and back surfaces of the wafer, that is, closer to the device active region. There is a problem that the density of the precipitates decreases.

[0008]

The metal impurities mixed in the device manufacturing process are mixed from the front and back surfaces of the wafer. Therefore, in order to efficiently capture the mixed metal impurities,
It is effective to form oxygen precipitates as close to the front and back surfaces of the wafer as possible. However, since the trapping effect of metal impurities also depends on the density of oxygen precipitates formed on the entire wafer, it is desirable that oxygen precipitates are sufficiently formed inside the wafer (center portion).

An object of the present invention is RTA for controlling the density distribution of oxygen precipitates in a silicon wafer.
Regarding the processing technology, in the subsequent heat treatment in the device process, oxygen precipitates, which are gettering sources, or defects induced by oxygen precipitates are formed at high density near the surface layer of the wafer near the device active region, and Another object of the present invention is to provide a method for heat treating a silicon wafer for obtaining a wafer that is formed with a high density even in a portion.

[0010]

In order to solve the above problems, the present inventors have made various studies on the effect of RTA treatment on the density distribution of oxygen precipitates.

Oxygen taken in during the growth of a single crystal is solid-soluted in a supersaturated state due to a decrease in temperature. When a substance is formed and a nucleus is formed, oxygen is preferentially aggregated therein to form an oxygen precipitate. Voids existing in the crystal are optimal as such sites, and it is considered that when a plurality of vacancies are aggregated, a precipitation nucleus that is a base of oxygen precipitates can be more easily formed. Therefore, if more vacancies can be injected into the inside of the wafer, the number of precipitation sites increases, and the oxygen precipitate density can be increased by the heat treatment in the subsequent device process. Generally, the following equation (1) is simply used as a reaction equation of oxygen precipitates in consideration of point defects.

Si + 2O + vacancy → SiO ₂ (oxygen precipitate) + interstitial silicon (1) In the interstitial silicon on the right side, volume expansion occurs due to the formation of oxygen precipitates (SiO ₂ ).

As described above, when a silicon wafer is subjected to a high temperature RTA treatment in a non-oxidizing gas atmosphere containing nitrogen, holes are positively injected into the wafer, and oxygen precipitation nuclei inside the wafer increase. Therefore, it is an effective method for improving the gettering ability of the wafer. However,
Evaluation of oxygen precipitates After heat treatment, the density distribution of oxygen precipitates formed inside the wafer is high in the vicinity of the wafer surface, and there is a problem that the density distribution becomes lower toward the center of the wafer. This is probably because the outward diffusion phenomenon of vacancies occurs during the cooling process of the wafer after the RTA treatment, and the density of oxygen precipitation nuclei in the central portion of the wafer decreases.

Therefore, as disclosed in the invention of US Pat. No. 5,401,669, it is proposed to suppress the outward diffusion of holes by increasing the cooling rate when lowering the temperature of the wafer, but The decrease in the density of oxygen precipitates in the area cannot be eliminated. This is usually a batch-type diffusion furnace that processes a plurality of wafers at once when performing a long-time heat treatment including the device manufacturing process, and, for example, in a furnace maintained at a predetermined temperature, The wafer is inserted into the furnace at a very slow speed such as 10 cm / min, and it takes several tens of minutes until the wafer is completely inserted into the furnace. It is speculated that this is happening.

The inventors of the present invention performed a high temperature RTA treatment on a silicon wafer in a non-oxidizing atmosphere, and then performed a low temperature RT treatment.
The present invention has been completed by finding that the oxygen precipitation density in the central portion of the wafer increases after the heat treatment for evaluating the oxygen precipitates by performing the A treatment, and the present invention provides the following silicon wafers. The main point is the heat treatment method.

That is, the present invention is a method for heat treating a silicon wafer made from a silicon single crystal ingot grown by the Czochralski method using a rapid heating / cooling device, in which nitrogen gas alone or nitrogen gas and an inert gas are used. 1150 to 1300 in mixed gas atmosphere with
A heat treatment method for a silicon wafer, which comprises performing a first heat treatment for 1 second or longer at 700C and then performing a second heat treatment for 5 seconds or longer at 700 to 1100C in an oxidizing gas atmosphere or a non-oxidizing gas atmosphere. is there.

In the heat treatment method of the present invention, the second heat treatment is carried out continuously in the temperature lowering process after the first heat treatment, or is performed again by raising the temperature of the silicon wafer cooled to a temperature lower than 700 ° C. It is what

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION In the first heat treatment of the present invention,
It is necessary to subject the silicon wafer to RTA treatment at 1150 to 1300 ° C. for 1 second or longer in a nitrogen gas alone or in a mixed gas atmosphere of a nitrogen gas and an inert gas.

In the first heat treatment of the present invention, a nitrogen gas alone or a mixed gas atmosphere of nitrogen gas and an inert gas is employed. This is because holes are positively injected into the wafer to form inside the wafer. This is because nitrogen gas is effective for increasing the density of oxygen precipitation nuclei. Examples of the inert gas mixed with the nitrogen gas include argon gas and hydrogen gas, and at least 50% by volume.
It is necessary to contain the above nitrogen gas.

For example, when the first heat treatment of the present invention is subjected to the RTA treatment in an atmosphere of argon gas alone, after the heat treatment for evaluating the oxygen precipitates, the density of oxygen precipitates in the depth direction of the wafer is high at the center of the wafer. And the distribution decreases toward the wafer surface.

On the other hand, when an oxidizing gas is used, the surface of the wafer is oxidized to form an oxide film, and when the oxide film is formed, the volume near the surface of the wafer is expanded and interstitial silicon is generated. Further, not all of the interstitial silicon atoms on the surface of the wafer contribute to the formation of an oxide film, but interstitial silicon is also generated by incomplete oxidation. If a large amount of interstitial silicon is present inside the wafer due to these phenomena, the reaction of the above-mentioned formula (1) is directed in the direction in which oxygen precipitates are difficult to form. When RTA treatment was actually performed under the same heat treatment condition in a 100% oxygen atmosphere, defects (BMD) observed as etch pits after the heat treatment for evaluation were observed.
Was not observed at all.

In the first heat treatment of the present invention, the amount of holes injected into the wafer depends on the temperature and time of the RTA treatment, so the heat treatment temperature must be controlled within the range of 1150 to 1300 ° C. At a temperature lower than 1150 ° C., it is not possible to inject a sufficient amount of vacancies into the wafer to promote the formation of oxygen precipitation nuclei, and it is not possible to form a sufficient DZ layer on the front and back surfaces of the wafer. 130
If the temperature is higher than 0 ° C., slip dislocations are generated in the wafer during heat treatment, which causes problems during device fabrication, which is not preferable.

The heat treatment time is preferably 1 second or more within the above temperature range, and if heating is performed for 10 seconds, the oxygen precipitation nuclei necessary for obtaining the density of oxygen precipitates for gettering are placed inside the wafer. It can be sufficiently formed. If the heating time is shorter than 1 second, the time required to reach the desired heat treatment reaching temperature differs in the in-plane direction and the depth direction of the wafer, which may cause a variation in quality. On the other hand, it is desirable that the upper limit of the processing time be 60 seconds or less in consideration of slip reduction and productivity.

As described above, the holes are injected into the wafer by the heat treatment for 1 second or more at the ultimate temperature. However, in order to keep the holes inside the wafer, the cooling rate when lowering the temperature of the wafer is set. It will play an important role. It is considered that the vacancies disappear when they reach the surface of the wafer, the concentration decreases near the outermost surface, and the resulting concentration difference causes outward diffusion of vacancies from the inside toward the surface. Therefore, if the cooling rate is slow, the time of staying at a high temperature becomes long, and the outward diffusion proceeds correspondingly, and the number of vacancies once injected by the high temperature RTA treatment is reduced, resulting in the formation of oxygen precipitation nuclei. It is thought that it will not be possible to secure a sufficient amount. Therefore, increasing the cooling rate can be expected to have the effect of suppressing the disappearance of pores, and the cooling rate is 5 ° C /
More than a second is required, and if the cooling rate is 30 ° C / second,
A certain degree of oxygen precipitate density can be secured in the subsequent evaluation heat treatment. In addition, it is desirable to control the temperature rising rate of the first heat treatment to 10 ° C./second or more in consideration of productivity.

However, oxygen precipitates are formed only in the vicinity of the device active region only by the above-mentioned first heat treatment,
In the central part of the wafer, the density of oxygen precipitates is not enough to obtain a sufficient gettering effect. The second heat treatment is necessary to obtain a density sufficient to obtain a sufficient gettering effect even in the central portion of the wafer.

The second heat treatment of the present invention is carried out in order to grow the oxygen precipitation nuclei formed inside the wafer by the first heat treatment to a size that does not disappear by the high temperature heat treatment in the subsequent device process. , First mentioned above
After the heat treatment, it is necessary to subject the silicon wafer to RTA treatment at 700 to 1100 ° C. for 5 seconds or more in an oxidizing gas atmosphere or a non-oxidizing gas atmosphere.

In the second heat treatment of the present invention, the temperature range is defined as 700 to 1100 ° C. The temperature of the silicon wafer is 5 seconds at RT within the predetermined temperature range.
When the A treatment is performed, the oxygen precipitate density in the central portion of the wafer is increased in the subsequent heat treatment for evaluating the oxygen precipitates.
This is because a sufficient oxygen precipitate density can be secured if the treatment is performed for 0 seconds. The upper limit of the second heat treatment time is
From the viewpoint of ensuring productivity, it is preferably within 60 seconds, and particularly when an oxidizing gas atmosphere is used, it is desirable to stay within 60 seconds from the viewpoint of suppressing interstitial silicon injection.

Even if the temperature of the second heat treatment of the present invention is higher or lower than the above predetermined temperature range, there is almost no increase in the oxygen precipitate density in the central portion of the wafer. This is probably because, when RTA treatment is performed at a temperature lower than 700 ° C., the heat treatment temperature is too low, so that the growth of oxygen precipitation nuclei does not easily occur, and the diffusion rate of oxygen in the crystal is slow. In combination, it is considered that the oxygen precipitation nuclei do not grow unless it takes a very long time. When RTA treatment is performed at a temperature higher than 1100 ° C., the outward diffusion of the vacancies injected in the first heat treatment is dominant. It is supposed to be.

In the second heat treatment of the present invention, the gas atmosphere used may be either an atmosphere containing oxygen or a non-oxidizing gas atmosphere such as nitrogen gas, argon gas or hydrogen gas.

That is, at a temperature of 1100 ° C. or lower, even if RTA treatment is performed in an oxidizing atmosphere, the formation of an oxide film is small, and the interstitial silicon injection amount is very small. There is no difference in oxygen precipitate density from RTA treatment in a non-oxidizing gas atmosphere.

This second heat treatment may be performed continuously after the first heat treatment in the process of cooling the wafer. Alternatively, the temperature of the wafer may be once lowered to 700 ° C. or lower and the temperature may be raised again. The same effect can be obtained by performing two heat treatments.

Both the rate of temperature rise and the rate of temperature decrease in the second heat treatment of the present invention are preferably controlled to 10 ° C./sec or more.

[0033]

EXAMPLES Examples of the present invention will be described below.

(Example 1) Oxygen concentration was 12 × 10 ¹⁷ at
725 μm in thickness and 20 in diameter taken from a silicon single crystal of oms / cm ³ (ASTM F-121,1979).
RTA treatment was performed under the following conditions using a 0 mm silicon wafer and a rapid heating / cooling device (AST-2800) using a halogen lamp light source.

As the first heat treatment, a mixed atmosphere of nitrogen and argon (volume ratio 1: 1) was set in the furnace, and after the wafer was put into the furnace kept at 600 ° C., the temperature was raised at 50 ° C./sec. After raising the temperature to 1250 ° C and holding at that temperature for 10 seconds,
The temperature was decreased to the second heat treatment temperature at a temperature decrease rate of 33 ° C./sec.

Next, after the temperature was lowered to the second heat treatment temperature, the atmosphere in the furnace was changed to 10% oxygen gas (diluted with nitrogen gas),
Second heat treatment temperature is 700 ° C, 900 ° C, 1100 ° C, 1
RTA treatment was carried out by changing to three levels of 200 ° C. In addition, a wafer that was cooled to room temperature without performing the second heat treatment was also created. Hold time is 10 for both second heat treatments
In seconds, the temperature was decreased to room temperature at a temperature decrease rate of 33 ° C./second. First
The heat patterns of the heat treatment and the second heat treatment are shown in FIG.

In order to examine the defect density distribution in the depth direction of each of the obtained wafers, the temperature was 4 ° C. at 800 ° C. in a nitrogen gas atmosphere.
After the heat treatment for 1 hour, the heat treatment for precipitation is performed at 1000 ° C. for 16 hours, and then each wafer is cleaved,
After the wafer surface was etched by immersing it in a Secco liquid (K ₂ Cr ₂ O ₇ + HF + H ₂ O) for 3 minutes, the cleaved cross section was measured for defect density in the wafer depth direction and its distribution using an optical microscope. The measurement result of the defect density distribution in the depth direction is shown in FIG.
Table 1 shows the average defect densities in the area of 400 μm) and in the vicinity of the surface layer of the wafer (area of 50 to 70 μm from the surface).
Shown in.

[0038]

[Table 1]

As is clear from these, by performing the second heat treatment in the temperature range of 700 ° C. to 1100 ° C., the defect density in the central portion of the wafer increases, and the defect density increases as the temperature of the second heat treatment decreases. It is clear that the amount of increase is about 2 as compared with the wafer not subjected to the second heat treatment.
~ 8 times, sufficient BMD even in the center of the wafer
It can be seen that the density is secured. On the other hand, the defect density in the vicinity of the wafer surface layer (in the vicinity of the device active region) hardly changes, and the increase amount is 1.1 to 1.3 times,
It can be seen that the second heat treatment greatly contributes to the increase of the defect density in the central portion of the wafer. In FIG. 1, the defect density is shown only from the front surface of the wafer to the central portion, but in contrast, the same distribution is shown from the central portion of the wafer toward the back surface.

Example 2 In order to investigate the influence of the gas atmosphere used in the second heat treatment, the second heat treatment temperature was set to 1000 ° C.
Then, the gas atmosphere to be used was changed to three levels of oxygen gas, nitrogen gas and argon gas, and RTA treatment was performed respectively. The other conditions are the same as in Example 1. The results of evaluation heat treatment and defect density measurement under the same conditions as in Example 1 for each of the obtained wafers are shown in FIG. 2 and Table 2.

[0041]

[Table 2]

As is clear from these, even if the gas atmosphere used in the second heat treatment is changed to an oxidizing gas or a non-oxidizing gas, the defect density does not change. It can be seen that it is effective in increasing

Example 3 As in Example 1, the oxygen concentration was 12 × 10 ¹⁷ atoms / cm ³ (ASTMF-12).
1, 1979) thickness 72 taken from a silicon single crystal
Rapid heating / cooling device (AS) using a halogen lamp light source with a silicon wafer of 5 μm and a diameter of 200 mm
T-2800) was used to perform RTA treatment under the following conditions.

First, as the first heat treatment, a mixed atmosphere of nitrogen and argon (volume ratio 1: 1) was set in the furnace, and after the wafer was put into the furnace kept at 600 ° C., the temperature was raised to 50 ° C./sec. The temperature was raised up to 1200 ° C., the temperature was maintained for 30 seconds, the temperature was lowered down to room temperature at a temperature lowering rate of 33 ° C./second, and then the wafer was taken out of the furnace.

Next, the wafer whose temperature has been lowered to room temperature is charged again into the furnace kept at 600 ° C.
A second heat treatment was performed in which the temperature was raised to 1000 ° C. at a heating rate of / sec, the temperature was held for 10 seconds, and then the temperature was lowered to room temperature at a cooling rate of 33 ° C./sec. The gas atmosphere used in the second heat treatment was changed to four levels of oxygen gas, nitrogen gas, argon gas and mixed gas atmosphere of nitrogen gas and argon gas (volume ratio 1: 1), and the RTA-treated wafer and the second A wafer that was not subjected to heat treatment was created. FIG. 5 shows heat patterns of the first heat treatment and the second heat treatment.

The results of the evaluation heat treatment and the defect density measurement under the same conditions as in Example 1 are shown in FIG. 3 and Table 3 for each of the four levels of wafers and the wafer not subjected to the second heat treatment.

[0047]

[Table 3]

As is apparent from these, even if the wafer is once cooled to room temperature after the first heat treatment and taken out from the furnace, if the second heat treatment is performed again, the gas atmosphere of the second heat treatment is obtained. Irrespective of, the defect density inside the wafer can be increased as in the case where the first heat treatment is continuously performed.

[0049]

As described above, according to the present invention, it is possible to manufacture a wafer in which sufficient oxygen precipitates are formed not only in the vicinity of the surface layer of the wafer but also in the center of the wafer. In this way, it is possible to manufacture a wafer that exhibits a sufficient gettering ability.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the defect density and the distance (depth) from the wafer surface when the temperature of the second heat treatment is changed.

FIG. 2 is a graph showing the relationship between the distance (depth) from the wafer surface and the defect density when the gas atmosphere of the second heat treatment is changed.

FIG. 3 is a graph showing the relationship between the distance (depth) from the wafer surface and the defect density when the gas atmosphere of the second heat treatment is changed.

FIG. 4 is a graph showing heat patterns of first heat treatment and second heat treatment in Example 1 and Example 2.

5 is a graph showing heat patterns of a first heat treatment and a second heat treatment in Example 3. FIG.

Claims (3)

[Claims] 1. A method of heat-treating a silicon wafer made from a silicon single crystal ingot grown by the Czochralski method using a rapid heating / cooling device, nitrogen gas alone or a mixed gas of nitrogen gas and an inert gas. 1st over 1 second at 1150 ~ 1300 ℃ in atmosphere
A heat treatment method for a silicon wafer, comprising performing a second heat treatment at 700 to 1100 ° C. for 5 seconds or more in an oxidizing gas atmosphere or a non-oxidizing gas atmosphere after the heat treatment. 2. The second heat treatment is continuously performed in a temperature decreasing process after the first heat treatment.
A method for heat treatment of the described silicon wafer. 3. The heat treatment method for a silicon wafer according to claim 1, wherein the second heat treatment is performed by raising the temperature of the silicon wafer cooled to a temperature lower than 700 ° C. again.