JP6737232B2 - Method for evaluating silicon single crystal and method for manufacturing silicon single crystal - Google Patents

Description

The present invention relates to a method for evaluating a silicon single crystal and a method for manufacturing a silicon single crystal.

A silicon wafer (hereinafter sometimes referred to as “wafer”) used as a substrate of a semiconductor device is generally cut out from a silicon single crystal grown by the Czochralski method (hereinafter sometimes referred to as “CZ method”). Then, it is manufactured through processes such as polishing and heat treatment.
FIG. 1 is a vertical cross-sectional view of a pulled silicon single crystal and schematically shows an example of the relationship between defect distribution and V/G. V is the pulling rate of the silicon single crystal, and G is the temperature gradient in the growth direction of the silicon single crystal immediately after pulling. The temperature gradient G is considered to be almost constant during the pulling of the silicon single crystal due to the thermal characteristics of the hot zone structure of the CZ furnace. Therefore, V/G can be controlled by adjusting the pulling rate V.

In FIG. 1, COP (Crystal Originated Particle) is an agglomerate of vacancies lacking atoms that should form a crystal lattice during the growth of a silicon single crystal.
In the OSF (Oxidation induced Stacking Fault) region, OSF nuclei become visible as OSF when subjected to thermal oxidation treatment at a high temperature (generally 1000° C. to 1200° C.).
The P _V region and the P _I region contain neither COP nor dislocation clusters, and the P _V region contains oxygen precipitate nuclei in the as-grown state. When heat treated, oxygen precipitates (BMD) are generated. easy. As shown in FIG. 2, as V/G increases, the concentration of vacancy type point defects in the _Pv region increases.
P _I area does not include the most oxygen precipitation nuclei in as-grown state, BMD be subjected to a heat treatment hardly occurs.

A method of evaluating the number of COPs in manufacturing such a silicon single crystal is known (for example, refer to Patent Document 1).
Patent Document 1 discloses a method in which a wafer cut from a silicon single crystal is mirror-polished and then the number of COPs is evaluated.

JP, 2005-281071, A

However, in the method described in Patent Document 1, after the silicon single crystal is manufactured, the period until the COP evaluation is completed through mirror polishing is long, so that the LPD (Light Point Defect: Light Point Defect) caused by the COP is long. ), it may take some time to obtain the evaluation result.

It is an object of the present invention to provide a silicon single crystal evaluation method and a silicon single crystal manufacturing method capable of estimating the occurrence of LPD at an early stage after the production of a silicon single crystal.

A method for evaluating a silicon single crystal according to the present invention is an oxygen concentration measuring step of measuring an oxygen concentration of a silicon single crystal containing COP, and estimates a generation state of LPD of the silicon single crystal based on a measurement result of the oxygen concentration. And an LPD occurrence situation estimating step.

Measurement of the oxygen concentration of a silicon single crystal is generally performed on a sample wafer sampled at the time of block division after pulling the silicon single crystal. Therefore, the measurement result of the oxygen concentration can be obtained at an early stage as compared with the evaluation result of the mirror-polished wafer.
According to the present invention, the occurrence status of LPD can be estimated at an early stage after the production of a silicon single crystal, based on the measurement result of the oxygen concentration.

In the method for evaluating a silicon single crystal of the present invention, it is preferable that the oxygen concentration measuring step measures the oxygen concentration in a region where the solidification rate in the straight body portion is 15% or less.

According to the present invention, the occurrence state of LPD can be accurately estimated by a simple method of selecting the measurement position of oxygen concentration.
The solidification rate means the ratio of the solidified weight to the total weight of the silicon melt before pulling the silicon single crystal.

The method for producing a silicon single crystal of the present invention comprises a crucible, a heater that generates a silicon melt by heating the crucible, and a pulling unit that pulls the seed crystal after contacting it with the silicon melt. A method for producing a silicon single crystal by the Czochralski method using a crystal pulling apparatus, comprising the steps of producing a first silicon single crystal containing COP and the method for evaluating a silicon single crystal described above, An evaluation step of estimating a generation state of LPD of the first silicon single crystal, and a manufacturing condition setting step of setting manufacturing conditions of the second silicon single crystal containing COP based on the estimation result in the evaluation step. It is characterized by

When the first silicon single crystal is a defective product in which a large amount of LDP is generated, all silicon single crystals manufactured thereafter are defective until the manufacturing conditions are changed.
According to the present invention, the manufacturing conditions of the second silicon single crystal are set based on the estimation result of the LPD occurrence situation obtained at an early stage after the first silicon single crystal is manufactured. Can be reduced.

Explanatory drawing which shows an example of the relationship between the defect distribution and V/G in a silicon single crystal. 6 is a graph showing the relationship between V/G and the vacancy type point defect concentration in a silicon single crystal. FIG. 1 is a schematic diagram showing a schematic configuration of a single crystal pulling apparatus used in Experiments 1 and 2 conducted to guide the present invention and one embodiment of the present invention. It is a schematic diagram which shows the schematic structure of the said single crystal pulling apparatus, and shows the state which the pulling advanced rather than the state of FIG. The graph which shows the relationship between the number of heater batches in the said experiment 1, and the moving average value of the oxygen concentration of a 1st area|region. The graph which shows the relationship between the number of heater batches in the said experiment 1, and the moving average value of LPD of the 1st area|region. 6 is a graph showing the relationship between the moving average value of oxygen concentration in the first region and the moving average value of LPD in Experiment 1. 7 is a graph showing the relationship between the moving average value of oxygen concentration in the second region and the moving average value of LPD in Experiment 2. The graph which shows the relationship between the moving average value of the oxygen concentration of the 3rd area|region in the said experiment 2, and the moving average value of LPD. The graph which shows the relationship between the moving average value of the oxygen concentration of the 4th area|region in the said experiment 2, and the moving average value of LPD. The graph which shows the relationship between the solidification rate in the said experiment 2, the moving average value of oxygen concentration, and the absolute value of the correlation coefficient of the moving average value of LPD. 3 is a flowchart showing a method for manufacturing a silicon single crystal in the one embodiment. Explanatory drawing of the effect of the said one Embodiment.

[History that led to the present invention]
[Experiment 1: Investigation of relationship between oxygen concentration of silicon single crystal and occurrence of LPD]
First, the single crystal pulling apparatus used in this experiment will be described.
As shown in FIG. 3, the single crystal pulling apparatus 1 is an apparatus used in the CZ method (Czochralski method) and includes a pulling apparatus body 2, a memory 3, and a control unit 4.
The pulling-up device main body 2 includes a chamber 21, a crucible 22 arranged in the center of the chamber 21, a heater 23 for heating the crucible 22, a pulling-up portion 24, and a heat shield 25.
A gas inlet 21</b>A for introducing an inert gas such as Ar gas into the chamber 21 is provided in the upper portion of the chamber 21. A gas exhaust port 21</b>B that exhausts the gas in the chamber 21 is provided in the lower portion of the chamber 21.
The crucible 22 melts polycrystalline silicon, which is a raw material of the wafer, to obtain a silicon melt M. The crucible 22 is supported by a support shaft 26 that can rotate and move up and down at a predetermined speed.
The heater 23 is arranged around the crucible 22 and melts the silicon in the crucible 22.
The pulling unit 24 includes a pulling cable 241 having one end to which the seed crystal SC is attached, and a pulling driving unit 242 that moves the pulling cable 241 up and down and rotates.
The heat shield 25 blocks radiant heat emitted upward from the heater 23.
The memory 3 stores various information necessary for manufacturing the silicon single crystal SM, such as the gas flow rate in the chamber 21, the furnace pressure, the electric power supplied to the heater 23, the rotation speed of the crucible 22 and the silicon single crystal SM. ..

Using the single crystal pulling apparatus 1 described above, a silicon single crystal SM having a diameter of 200 mm was manufactured. Specifically, a new heater 23 was attached to the chamber 21. Then, after maintaining the inside of the chamber 21 in an inert gas atmosphere under reduced pressure and depositing the seed crystal SC on the silicon melt M, the value of V/G becomes larger than the value corresponding to A in FIG. By pulling up in this manner, a silicon single crystal SM having a neck portion SM1, a shoulder portion SM2, a straight body portion SM3, and a tail portion (not shown) and including COP in the straight body portion SM3 was manufactured. During this pulling up, the crucible 22 rotates while the distance GP (gap GP) between the liquid surface of the silicon melt M and the lower end of the heat shield 25 becomes substantially constant as shown in FIGS. 3 and 4. Rose to.
After that, a plurality of silicon single crystals SM were manufactured using the same single crystal pulling apparatus 1 without replacing the heater 23.

The oxygen concentration in the silicon single crystal SM manufactured as described above and the generation state of LPD were evaluated.
The wafer for evaluation was obtained from a region where the solidification rate in the straight body portion SM3 was 15% or less (hereinafter referred to as the first region). After performing mirror etching on this wafer, the oxygen concentration was measured by ASTM F-121 (1979) using FTIR (Fourier Transform Infrared Spectrometer). The measurement result of oxygen concentration of one wafer was used as the measurement result of one batch.
The measurement of LPD is performed by chamfering, lapping, surface grinding, etching, mirror-chamfering, primary-polishing, etc., and then mirror-polishing the wafer obtained from the region on the lower end side in the pulling direction with respect to the acquisition region of the evaluation wafer in the first region. Using a surface inspection device (SP-1 manufactured by KLA-Tencor), the number of LPDs per sheet observed on the surface was counted. The LPD having a size of 120 nm or more was measured, and the average value of the LPD measurement results on about 100 to 200 wafers was used as the measurement result for one batch.

FIG. 5 shows the relationship between the number of batches (hereinafter referred to as “heater batch number”) and the moving average value of oxygen concentration. Further, FIG. 6 shows the relationship between the number of heater batches and the moving average value of LPD.
5 and 6, the moving average value of the Nth batch means the average value of the latest four batches including the Nth batch. In addition, since the same single crystal pulling apparatus 1 was used to manufacture a silicon single crystal having a quality different from that of the object of this experiment (silicon single crystal containing COP), the moving average value is a silicon single crystal whose quality is different from that of the object of this experiment. It is an average value of the latest 4 batches containing no crystals.

As shown in FIGS. 5 and 6, when the number of heater batches reached 100, the oxygen concentration decreased and the LPD tended to increase.
The present inventor has speculated the reason for this as follows.

During the production of the silicon single crystal SM, SiO gas is generated from the silicon melt M, and this SiO gas passes between the crucible 22 and the heater 23 and is guided below the chamber 21. At this time, the SiO gas reacts with the carbon of the heater 23, and the carbon of the heater 23 is thinned. Since the SiO gas is guided from the upper side to the lower side, the above reaction occurs more remarkably in the upper part of the heater 23 than in the lower part, and the upper part of the heater 23 deteriorates more than the lower part. When the upper part of the heater 23 deteriorates, the resistivity of the upper part becomes higher than that of the lower part, the heating ratio of the upper part increases, and the heating ratio of the lower part decreases.
Further, since the main source of oxygen to the silicon melt M is the bottom of the crucible 22, if the heating ratio of the lower portion of the heater 23 decreases, the heating amount of the bottom of the crucible 22 also decreases, and the silicon melt M The supply of oxygen is also reduced. From the above, it is assumed that when the number of heater batches increases, deterioration of the upper portion of the heater 23 also progresses, and as a result, the oxygen concentration of the silicon single crystal SM decreases.

Further, when the heating ratio of the upper portion of the heater 23 increases with the increase in the number of heater batches, the cooling of the silicon single crystal SM pulled from the silicon melt M is suppressed, and compared with the case where the heating ratio of the upper portion of the heater 23 does not increase. The value of V/G also becomes large. As a result, as shown in FIG. 2, it was estimated that the concentration of vacancy type point defects was increased, the COP formed by aggregation of vacancy type point defects was increased, and the LPD was increased.

When the relationship between the moving average value of oxygen concentration and the moving average value of LPD obtained from the results of FIGS. 5 and 6 was examined, it was found that there was a correlation between the two, as shown in FIG. 7.
The formula of the approximate straight line LA1 based on the data of FIG. 7 is as follows when the moving average value of oxygen concentration is X (×10 ¹⁷ atoms/cm ³ ) and the moving average value of LPD is Y (pieces/sheet). It is represented by (1).
Y=−103.72×X+1680.3 (1)

From the relationship shown in FIG. 7, in the single crystal pulling apparatus 1 used in this experiment, when the oxygen concentration of the silicon single crystal SM was 13.4×10 ¹⁷ atoms/cm ³ or less, When the number of LPDs per wafer is 300 or more and exceeds 13.4×10 ¹⁷ atoms/cm ³ , it can be estimated that the number of LPDs is less than 300.
Therefore, based on the measurement result of the oxygen concentration, it was confirmed that the generation state of LPD can be estimated at an early stage after the production of the silicon single crystal SM. When the silicon single crystal SM used for measuring the oxygen concentration is the first silicon single crystal, the second silicon single crystal produced after the first silicon single crystal is measured based on the measurement result of the oxygen concentration. The number of defective products can be reduced by setting the manufacturing conditions, specifically, by slowing the pulling speed.

[Experiment 2: Investigation of Relationship between Solidification Rate of Straight Body and Correlation of Oxygen Concentration and LPD Occurrence State]
A region where the solidification rate in the silicon single crystal SM of Experiment 1 exceeds 15% and 30% or less (hereinafter referred to as the second region), a region where the solidification rate exceeds 30% and 50% or less (hereinafter referred to as the third region), and 50% are set. A wafer was obtained from a region exceeding the region (hereinafter referred to as the fourth region). Then, the relationship between the number of heater batches and the moving average value of oxygen concentration and the relationship between the number of heater batches and the moving average value of LPD in these wafers are obtained, and the moving average value of oxygen concentration and the moving average of LPD are calculated from these relationships. The relationship with the value was investigated.
FIG. 8 shows the relationship between the second regions, FIG. 9 shows the relationship between the third regions, and FIG. 10 shows the relationship between the fourth regions.
As shown in FIGS. 8 to 10, referring to the approximate straight lines LA2 to LA4 based on the data in each figure, in the second to fourth regions, as in the first region, the moving average value of the oxygen concentration becomes large. It was confirmed that the moving average value of LPD was small.

In addition, the absolute value of the correlation coefficient between the moving average value of oxygen concentration and the moving average value of LPD in the first to fourth regions was calculated. The result is shown in FIG.
As shown in FIG. 11, the correlation in the first region was higher than that in the other regions.
The present inventor has speculated the reason for this as follows.

The lower the solidification rate, the larger the amount of the silicon melt M. Since the gap GP is substantially constant during the pulling of the silicon single crystal SM, the lower the solidification rate, the lower the position of the crucible 22, and the shorter the distance between the bottom of the crucible 22 and the lower portion of the heater 23. For this reason, the influence when the heating ratio of the lower part of the heater 23 decreases and the heating amount of the bottom part of the crucible 22 decreases with the deterioration of the upper part of the heater 23 increases as the solidification rate decreases. From the above, it was speculated that by measuring the oxygen concentration in the region where the solidification rate is 15% or less, the occurrence state of LPD can be estimated more accurately than in the case of measuring in other regions.

The results of Experiments 1 and 2 shown in FIGS. 5 to 11 differ depending on the size and the arrangement position of each constituent member of the single crystal pulling apparatus, but the correlation between the oxygen concentration and the LPD generation state is different for each constituent member. It is considered to be the same as the results of Experiments 1 and 2 regardless of the size and the arrangement position.

[Embodiment]
Next, as an embodiment of the present invention, a method for manufacturing a silicon single crystal SM containing COP will be described with reference to the drawings.
The present embodiment exemplifies a case where a p-type silicon single crystal SM having a resistivity of 8 Ω·cm or more and 12 Ω·cm or less and a diameter of the straight body portion SM3 after grinding the outer periphery of 200 mm is manufactured. Further, a case will be exemplified in which the single crystal pulling apparatus 1 is used so that the relationship between the oxygen concentration and the LPD generation state in the first region of the silicon single crystal SM has the relationship shown in FIG. 7. Further, the memory 3 stores LPD occurrence status estimation information indicating the relationship shown in FIG. 7.
The diameter of the straight body portion SM3 after grinding the outer periphery may be another size such as 300 mm or 450 mm.

First, the control unit 4 of the single crystal pulling apparatus 1 sets the manufacturing conditions of the silicon single crystal SM, such as heater power, Ar flow rate, furnace pressure, rotation speed of the crucible 22 and the silicon single crystal SM.
Next, the control unit 4 heats the crucible 22 to melt the polysilicon material (silicon raw material) and the dopant in the crucible 22 to generate the silicon melt M. Thereafter, as shown in FIG. 12, the control unit 4 maintains the inside of the chamber 21 in an inert atmosphere under reduced pressure, rotates the crucible 22 and raises the gap GP to be substantially constant while rotating the straight body. A first silicon single crystal SM containing COP is manufactured in the portion SM3 (step S1: manufacturing process).

Next, the worker measures the oxygen concentration of the straight body portion SM3 of the first silicon single crystal SM (step S2: oxygen concentration measuring step (evaluation step)). In this step S2, the operator acquires a wafer for evaluation from the straight body portion SM3 of the first silicon single crystal. The evaluation wafer is preferably obtained from a region where the solidification rate in the straight body portion SM3 is 15% or less. Then, as in Experiment 1, the worker measures the oxygen concentration of the evaluation wafer after mirror etching by FTIR. The worker may measure the resistivity and the carbon concentration in addition to the oxygen concentration.

Thereafter, when the operator inputs the oxygen concentration, the control unit 4 estimates the LPD occurrence status based on the oxygen concentration and the LPD occurrence status estimation information of the memory 3 as shown in FIG. 7. (Step S3: LPD occurrence situation estimation step (evaluation step)).
In step S3, the control unit 4 estimates that the LPD per wafer is equal to or higher than the quality reference value when the oxygen concentration is equal to or lower than the determination threshold value, and estimates that the LPD per wafer is lower than the quality reference value when lower than the determination threshold value. To do. In this embodiment, the determination threshold value is 13.4×10 ¹⁷ atoms/cm ³ and the quality reference value is 300 pieces.

When the control unit 4 estimates that the LPD is equal to or higher than the quality reference value, it changes the manufacturing condition (step S4: manufacturing condition setting step), and the straight body portion SM3 includes the COP under the changed manufacturing condition. A second silicon single crystal SM is manufactured (step S5). In step S4, the control unit 4 slows down the pulling rate in order to reduce the number of LPDs generated in the second silicon single crystal SM. In this case, the relationship between the COP concentration and the pulling rate may be obtained in advance, and the pulling rate corresponding to the number of LPDs to be reduced may be obtained based on this relationship.
Here, when the silicon single crystal SM is manufactured during the process of step S3, the manufacturing condition change in step S4 is not performed for the silicon single crystal SM, but for the second silicon of the next batch. This is performed for the single crystal SM. In addition, when the silicon single crystal SM is not manufactured during the process of step S3, the second batch of the second silicon single crystal SM is performed.

On the other hand, when the control unit 4 estimates that the LPD is less than the quality reference value, the control unit 4 maintains the manufacturing condition (step S6: manufacturing condition setting step), and the second manufacturing condition is the same as that of the first silicon single crystal SM. A silicon single crystal SM is manufactured (step S5).

[Operation and effect of the embodiment]
According to the above embodiment, the following operational effects can be obtained.
Conventionally, as shown in FIG. 13, the manufacturing condition setting based on the occurrence state of LPD is performed after performing steps S1 and S2 of the present embodiment, and then, from the slice to the mirror surface with respect to the remaining portion of the straight body portion SM3. The steps up to polishing are performed (step S11). Then, the LPD of the wafer after mirror polishing was measured (step S12), and the manufacturing conditions were changed or maintained based on whether or not the LPD was equal to or higher than the quality reference value (step S13). In such a method, the process of step S11 particularly requires time. Therefore, when the next batch of the manufacturing batch of the first silicon single crystal SM is the first batch, for example, the LPD measurement result is only in the middle of the seventh batch. Cannot be obtained, and the manufacturing conditions can be set only from the eighth batch. In this case, the first to seventh batches of silicon single crystals SM may become defective products.
On the other hand, in the present embodiment, the occurrence state of LPD is estimated based on the oxygen concentration measurement result of the evaluation wafer without performing the steps S11 and S12 (step S3), and the manufacturing is performed based on this estimation result. The conditions are changed or maintained (steps S4 and S6). Since the process of step S11 that requires time is not performed in this way, for example, the estimation result of LPD can be obtained in the middle of the second batch. Further, the manufacturing conditions for the third batch (second silicon single crystal SM) can be set based on the LPD estimation result. Therefore, even if the silicon single crystal SM of the first batch is a defective product, the silicon single crystals SM of the second and subsequent batches can be made good products, and the number of defective products can be reduced.

[Modification]
The present invention is not limited to the above-described embodiment, and various improvements and design changes can be made without departing from the spirit of the present invention.
For example, the judgment threshold value and the quality reference value are not limited to the above values, and may be other values according to needs.
In addition to the first area, or instead of the first area, the LPD occurrence status estimation information of at least one of the second to fourth areas may be stored in the memory 3. In this case, when the operator inputs the oxygen concentration and the acquisition region of the evaluation wafer, the control unit 4 generates LPD on the basis of the LPD occurrence state estimation information corresponding to the acquisition region and the oxygen concentration. The situation may be estimated.
An operator may perform the processing of steps S3 to S6.
Although the relationship between the oxygen concentration and the LPD generation state was obtained based on the oxygen concentration and the moving average value of LPD, the data of each batch may be used as it is.

DESCRIPTION OF SYMBOLS 1... Single-crystal pulling apparatus, 22... Crucible, 23... Heater, 24... Pulling part, SM... Silicon single crystal, SM3... Straight body part.

Claims (4)

An oxygen concentration measuring step for measuring the oxygen concentration of the evaluation wafer obtained from the straight body of the silicon single crystal containing COP;
In the measurement result in the oxygen concentration measurement step, a LPD occurrence state estimation step of estimating the LPD occurrence state of the silicon single crystal when the oxygen concentration tends to decrease occurs. Single crystal evaluation method. The method for evaluating a silicon single crystal according to claim 1,
The method for measuring a silicon single crystal, wherein the oxygen concentration measuring step measures an oxygen concentration in a region where the solidification rate in the straight body portion is 15% or less. The silicon single crystal evaluation method according to claim 1, wherein the evaluation wafer is a sample wafer sampled when the silicon single crystal is divided into blocks. With a crucible,
A heater that generates a silicon melt by heating the crucible,
A method for producing a silicon single crystal by the Czochralski method using a single crystal pulling apparatus having a pulling unit that pulls a seed crystal after bringing it into contact with the silicon melt,
A manufacturing process for manufacturing a first silicon single crystal containing COP;
An evaluation step of estimating the occurrence state of LPD of the first silicon single crystal using the method for evaluating a silicon single crystal according to claim 1 .
And a manufacturing condition setting step of setting manufacturing conditions of the second silicon single crystal containing COP based on the estimation result in the evaluation step.

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