JP2022181130A - Silicon wafer thermal donor behavior prediction method and silicon wafer manufacturing method - Google Patents

Abstract

Kind Code: A1 A method for predicting the amount of thermal donors produced and a method for producing the same are provided, which can be applied even when the heat treatment time is short.
A method for predicting thermal donor behavior of a silicon wafer according to the present invention uses the negative correlation between a heat treatment time and a heat treatment temperature at which the amount of thermal donors generated in the heat treatment time is maximized.
[Selection drawing] Fig. 3

Description

The present invention relates to a silicon wafer thermal donor behavior prediction method and a silicon wafer manufacturing method.

Silicon wafers are widely used as semiconductor substrates for fabricating various semiconductor devices such as RF (radio frequency) devices, MOS devices, DRAMs and NAND flash memories. 2. Description of the Related Art Various heat treatments such as oxidation treatment, nitridation treatment, plasma etching, and impurity diffusion treatment are performed in a so-called device process for manufacturing a semiconductor device using a silicon wafer.

Oxygen in a silicon wafer is normally electrically neutral. It is known that a dozen or more oxygen atoms aggregate to form an oxygen cluster in a silicon crystal. This oxygen cluster is a donor that emits electrons and is called a thermal donor. A thermal donor becomes electrically neutral when subjected to a high temperature heat treatment of about 650° C. or higher, and such high temperature heat treatment is called donor killer heat treatment (donor killer annealing).

Thermal donor generation changes the carrier concentration of the silicon wafer, and as a result, the resistivity of the silicon wafer changes before and after the low-temperature heat treatment in the device process. For example, if the silicon wafer is a p-type wafer with high resistance, it can be reversed to an n-type wafer depending on the amount of thermal donors generated.

Such changes in silicon wafer resistivity can have a significant impact on the device characteristics of semiconductor devices. So far, research has been conducted on the generation mechanism of thermal donors after low-temperature heat treatment of silicon single crystals, and various methods for accurately predicting thermal donor concentrations in silicon wafers have been investigated.

In Patent Document 1, the amount Δ[C] of carriers generated due to oxygen donors generated when a silicon single crystal is subjected to low-temperature heat treatment depends on the oxygen concentration [Oi] in the silicon single crystal and the heat treatment temperature T , the heat treatment time t, and the oxygen diffusion coefficient D(T) at the heat treatment temperature T, the following formula A is proposed.
Δ[C]=α[Oi]5×exp(−β・D(T)・[Oi]・t) (Formula A)
(In the above formula A, α and β are constants)

According to Patent Literature 1, it is said that the method is general-purpose and can evaluate the amount of carriers generated in a silicon single crystal with higher precision than conventional methods.

JP 2013-119486 A

However, until now, the prediction of the thermal donor behavior has been limited to the prediction of the thermal donor behavior when the heat treatment is performed at a low temperature of less than about 600° C. for a long time, for example, several tens of hours. Therefore, the formula (Formula A) disclosed in Patent Document 1 cannot explain the behavior of the thermal donor when the heat treatment time is short.

Accordingly, it is an object of the present invention to provide a method for predicting the amount of thermal donors produced and a manufacturing method that can be applied even when the heat treatment time is short.

When the relationship between heat treatment temperature, heat treatment time, and amount of thermal donors generated under various conditions was examined, it was found that there was a negative correlation between the heat treatment time and the heat treatment temperature at which the amount of thermal donors generated was maximized. The inventors have found. Then, it was found that the generation behavior of thermal donors can be predicted with high accuracy by using this correlation. The gist and configuration of the present invention completed based on the above findings are as follows.

<1> A method for predicting thermal donor behavior of a silicon wafer,
The relationship between the heat treatment time and the heat treatment temperature at which the thermal donor generation amount is maximized in the heat treatment time is a negative correlation.
Thermal donor behavior prediction method for silicon wafers.

<2> The negative correlation is represented by the following formula (1):
[T _m ]=−at+b (1)
(In formula (1), [T _m ] is the heat treatment temperature at which the thermal donor generation amount is maximized, t is the heat treatment time, and a and b are non-negative constants.)
The method for predicting thermal donor behavior of a silicon wafer according to any one of <1>, represented by the relational expression:

<3> The amount of thermal donor generated is expressed by the following formula (2):
[T _D ]=A×[O _i ] ^B ×t ^C ×exp{−(T−T _m ) ² /(2T ₀ ² )} (2)
(In formula (2), [T _D ] is the amount of thermal donors produced, T is the heat treatment temperature, [O _i ] is the oxygen concentration, and T ₀ , A, B, and C are constants.)
The method for predicting thermal donor behavior of a silicon wafer according to <1> or <2>, represented by the relational expression:

<4> The method for predicting thermal donor behavior of a silicon wafer according to any one of <1> to <3>, wherein the heat treatment time is 10 hours or less.

<5> Any one of <1> to <4>, wherein the silicon wafer has an oxygen concentration of 1×10 ¹⁷ atoms/cm ³ or more and 7×10 ¹⁷ atoms/cm ³ or less (ASTM F121-1979). of silicon wafer thermal donor behavior prediction method.

<6> A silicon wafer evaluation method using the silicon wafer thermal donor behavior prediction method according to any one of the above <1> to <5>,
A step of determining the amount of thermal donors generated in the silicon wafer after heat treatment;
obtaining a predicted resistivity of the silicon wafer after the heat treatment based on the thermal donor generation amount;
A method for evaluating a silicon wafer, comprising:

<7> A method for manufacturing a silicon wafer,
a step of grasping heat treatment conditions in a device process applied to the silicon wafer;
A step of obtaining a predicted resistivity of the silicon wafer after heat treatment according to the heat treatment conditions in the device process using the silicon wafer evaluation method according to <6>;
designing a target value of oxygen concentration or resistivity of the silicon wafer before being subjected to the device process based on the predicted resistivity;
A method for manufacturing a silicon wafer, comprising:

According to the present invention, it is possible to provide a method for predicting the production amount of thermal donors and a manufacturing method that can be applied even when the heat treatment time is short.

Plot of ^{thermal donor} _{concentration} and thermal 4 is a graph showing the relationship between heat treatment temperature and heat treatment time at which the amount of donors generated is maximized. A plot of the ^{thermal donor} _{concentration} and a thermal 4 is a graph showing the relationship between heat treatment temperature and heat treatment time at which the amount of donors generated is maximized. 4 is a plot showing the relationship between the heat treatment temperature and the heat treatment time at which the amount of thermal donors produced in Experiments 1 and 2 is maximized, and a graph showing the reproducibility of predicted values using calculation formula (1). 4 is a graph showing the reproducibility of the amount of thermal donors produced by the predicted value using the calculation formula (2) in Experiment 1. FIG. 10 is a graph showing the reproducibility of the amount of thermal donors produced by the predicted value using the calculation formula (2) in Experiment 2. FIG. FIG. 10 is a graph confirming the reproducibility of the amount of thermal donors produced by the predicted value using the conventional technique (formula A) in a comparative example; FIG.

Prior to the description of the embodiments, experiments conducted by the inventors leading to the present invention will be described. In order to confirm the reproducibility of the method for predicting the thermal donor behavior of silicon wafers, the present inventors confirmed experimental values of the amount of thermal donors generated when low-temperature heat treatment was performed for a short period of time. Experimental values were obtained as follows.

(Experiment 1)
An n-type silicon single crystal ingot with a diameter of 300 mm and a plane orientation (100) was grown by the CZ method. Then, after slicing the single crystal silicon ingot and processing it into silicon wafers, the oxygen concentration was measured by Fourier transform infrared spectroscopic analysis. Silicon wafers used in Experiment 1 had an oxygen concentration of 6×10 ¹⁷ atoms/cm ³ (ASTM F121-1979, hereinafter the same applies to the oxygen concentration). In order to eliminate thermal donors generated during crystal growth of the silicon wafer, a donor killer treatment was performed in advance in a nitrogen atmosphere at 650° C. for 30 minutes.

After that, low-temperature short-time heat treatment was performed in a nitrogen atmosphere at 430° C., 450° C., 470° C., 490° C., 510° C., and 530° C. for 30 minutes, 60 minutes, 120 minutes, and 300 minutes for each heat treatment temperature to obtain silicon wafers. A thermal donor was generated.

Then, the resistivity of each heat-treated silicon wafer was measured according to the resistivity measurement method by the four-probe method specified in JIS H 0602:1995. Then, based on the measurement result of this specific resistance and the measurement result of the specific resistance before the low-temperature heat treatment, the carrier concentration was obtained from the Irvin curve. Further, the difference in carrier concentration before and after the low-temperature heat treatment for generating thermal donors was defined as the amount of thermal donors generated. FIG. 1 shows the results of plotting the relationship between the heat treatment temperature and the amount of thermal donors generated for each condition. Furthermore, the plot of each heat treatment time in FIG. 1 is shown together with the point where the thermal donor generation amount is maximum and the imaginary line assumed by the present inventors.

(Experiment 2)
FIG. 2 plots the heat treatment temperature and the amount of thermal donors generated for each condition in the same manner as in Experiment 1 except that the silicon wafer was changed to a silicon wafer with an oxygen concentration of 4×10 ¹⁷ atoms/cm ³ . In addition, the plot of each heat treatment time in FIG. 2 is shown together with the point where the amount of thermal donor generation is maximum and the imaginary line assumed by the present inventors.

Conventionally, it was thought that the thermal donor generation amount was maximized by heat treatment at 450° C. regardless of the length of the heat treatment time. However, from the results of Experiments 1 and 2, the present inventors have found that there is a negative correlation between the heat treatment time and the heat treatment temperature at which the amount of thermal donor generation is maximized (that is, the peak temperature in FIG. 1 or FIG. 2). . The term "negative correlation" as used herein refers to the tendency that the shorter the heat treatment time, the higher the heat treatment temperature at which the amount of thermal donors generated in the heat treatment time becomes maximum. If the relationship between the heat treatment time and the heat treatment temperature at which the amount of thermal donors generated in the heat treatment time is maximized is known, it is possible to predict the heat treatment temperature at which the amount of thermal donors generated is maximized when the heat treatment time is changed. Then, as will be described later, it becomes possible to predict the relationship between the amount of thermal donors produced and the heat treatment temperature under arbitrary heat treatment conditions, especially the relationship in low-temperature heat treatment for a short period of time.

Next, conceived that the negative correlation is represented by a linear relationship,
[T _m ]=−at+b (1)
predicted the relational expression of In formula (1), [T _m ] is the heat treatment temperature at which the amount of thermal donors produced is maximum, t is the heat treatment time, and a and b are non-negative constants. The fact that the relationship between the heat treatment time and the heat treatment temperature at which the amount of thermal donors produced in the heat treatment time is maximized is represented by a linear function having a negative correlation is also useful in terms of simplicity of calculation. Coefficients were appropriately set so that this prediction formula matched experimental values, and the relationship shown in FIG. 3 was confirmed. In the plot showing the relationship between the heat treatment temperature and the heat treatment time at which the amount of thermal donor generation is maximized, it was confirmed that the extrapolation of the line segment represented by the above formula has good reproducibility. It was also found that this relationship can be similarly applied irrespective of the magnitude of the oxygen concentration of the silicon wafer to which the heat treatment is applied. Here, in experiments 1 and 2, the value of a was 0.11. However, the specific value of a is obtained from the above experimental results, and is determined according to the experimental results, for example, within the range of 0.05 or more and 0.15 or less. Similarly, the value of the constant b was 493 in Experiments 1 and 2, but is determined from a range of 450 or more and 550 or less, for example, according to the experimental results.

Next, we conceived that the amount of thermal donors generated in the experiment was expressed by a relational expression including a Gaussian function,
[T _D ]=A×[O _i ] ^B ×t ^C ×exp{−(T−T _m ) ² /(2T ₀ ² )} (2)
predicted the relational expression of In equation (2), [T _D ] is the thermal donor production amount, T is the heat treatment temperature, [O _i ] is the oxygen concentration, and T ₀ , A, B, and C are constants. Here, T ₀ corresponds to the standard deviation in the normal distribution represented by the Gaussian function. From this equation, the _Tm obtained from the previously obtained equation (1) can be used to predict the amount of thermal donors generated in a silicon wafer with an arbitrary oxygen concentration and under heat treatment conditions. FIGS. 4 and 5 show the results of appropriately setting the coefficients so that this prediction formula matches the experimental values. It can be confirmed that the predicted value of the thermal donor production amount using the calculation formula has good reproducibility. Here, in Experiments 1 and 2, the value of constant A was 1.1×10 ⁸ . However, the value of the constant A is obtained from the above experimental results, and for example, the value of the constant A is determined from the range of 0.5×10 ⁸ to 1.5×10 ⁸ according to the experimental results. Similarly, the value of the constant B was 4 in Experiments 1 and 2, but the value of the constant B is determined from a range of 3 or more and 5 or less, for example, according to the experimental results. Similarly, the value of the constant C was 0.85 in Experiments 1 and 2, but the value of the constant C is determined according to the experimental results within the range of 0.50 to 1.30, for example. Similarly, the value of the constant T ₀ was 30 in Experiments 1 and 2, but the value of the constant T ₀ is determined from a range of 10 or more and 50 or less, for example, according to the experimental results.

In the above formulas (1) and (2), the heat treatment time is not particularly limited, but in order to obtain better reproducibility with experimental values, the heat treatment time is preferably 10 hours or less, and preferably 5 hours or less. More preferred. In the case of heat treatment for a short period of time, such as 10 hours or less, in the conventional methods for predicting thermal donor behavior, good reproducibility between predicted values and experimental values was not observed. quantity can be predicted.

In the above formulas (1) and (2), the oxygen concentration of the silicon wafer is not particularly limited, but in order to obtain better reproducibility with experimental values, the oxygen concentration of the silicon wafer is 1×10 ¹⁷ atoms/cm ^{3 .} It is preferably 7×10 ¹⁷ atoms/cm ³ or more (ASTM F121-1979), and more preferably 2×10 ¹⁷ atoms/cm ³ or more and 6×10 ¹⁷ atoms/cm ³ or less.

As the silicon wafer used in this experiment, a single crystal silicon ingot grown by the Czochralski method (CZ method) or the floating zone melting method (FZ method) sliced with a wire saw or the like can be used. Silicon wafers formed by the CZ method have a higher oxygen concentration than those by the FZ method, and are susceptible to changes in resistivity due to thermal donor generation. Therefore, it is preferable to use the prediction method according to the present embodiment for CZ wafers. Moreover, the conductivity type of the silicon wafer may be either p-type or n-type.

(Evaluation method of silicon wafer)
Silicon wafers can also be evaluated using the embodiments of the method for predicting thermal donor behavior of silicon wafers described above. First, according to the embodiment of the method for predicting thermal donor behavior of silicon wafers described above, a step of determining the amount of thermal donors produced in a silicon wafer after heat treatment under predetermined conditions is performed. As the predetermined condition, it is preferable to use the history of heat treatment that the silicon wafer undergoes in the device process. When a high-temperature heat treatment corresponding to the donor killer heat treatment is included, only the heat treatment history after the high-temperature heat treatment may be used. Then, based on the calculated amount of thermal donors produced, a step of calculating the predicted resistivity of the silicon wafer after the heat treatment under the predetermined conditions is performed. The resistivity can be obtained from the amount of generated thermal donors using an Irvin curve. With this silicon wafer evaluation method, it is possible to highly accurately evaluate whether or not the resistivity of a silicon wafer that is subjected to heat treatment under predetermined conditions satisfies a predetermined standard.

(Method for manufacturing silicon wafer)
Furthermore, it is also preferable to manufacture a silicon wafer using the evaluation method described above. First, a step of grasping the heat treatment conditions in the device process applied to the silicon wafer is performed. If high-temperature heat treatment corresponding to donor killer heat treatment is included, the presence or absence of the heat treatment and the heat treatment conditions after the high-temperature heat treatment should be ascertained. If high-temperature heat treatment is not included, all heat history should be ascertained. is preferred. Then, using the silicon wafer evaluation method described above, a step of determining the predicted resistivity of the silicon wafer after the heat treatment according to the heat treatment conditions in the device process is performed. Then, based on the obtained predicted resistivity, a step of designing a target value of oxygen concentration or resistivity of the silicon wafer before being subjected to the device process is performed, and silicon wafers are manufactured according to this design. If the silicon wafer manufactured by this silicon wafer manufacturing method is used, it becomes a silicon wafer that takes into consideration the change in resistivity of the silicon wafer after the above device process, so that the adverse effect on the device characteristics due to the generation of thermal donors can be suppressed. can.

(Example)
It was confirmed that the above equations (1) and (2) can well reproduce the plot values of the oxygen concentration in the experimental results described above (see FIGS. 3 to 5). The constants in the formulas (1) and (2) were subjected to regression analysis, and the following values were adopted as the constants in the formulas (1) and (2).
a = 0.11
b = 493
_T0 = 30
A = 1.1 x ¹⁰⁸
B=4
C=0.85

(Comparative example)
The experimental values described above with reference to FIG. 1 were compared with the calculation results of the following formula A disclosed in Patent Document 1 (Japanese Patent Application Laid-Open No. 2013-119486).
Δ[C]=α[Oi]5×exp(−β・D(T)・[Oi]・t) (Formula A)
(In the above formula A, α and β are constants)
The results are shown in FIG. The values of constants α and β were set to α=1×10 ⁻⁷⁶ and β=1×10 ⁻⁵ respectively. From the comparison between the experimental values and the calculated values, it was found that the behavior of thermal donor generation cannot be reproduced by the calculation method of Patent Document 1 in such extremely short-time low-temperature heat treatment.

The following facts were found from the examples and comparative examples. That is, in Experiments 1 and 2, the relationship between the heat treatment time and the heat treatment temperature at which the amount of thermal donor generation is maximized in the heat treatment time is grasped, and by obtaining the formula (1), the amount of thermal donor generated in short-time low-temperature heat treatment It became possible to predict the heat treatment temperature at which The present inventors confirmed that the prediction of the amount of thermal donors produced using formula (2) including formula (1) can accurately reproduce the amount of thermal donors produced even under the conditions of low-temperature heat treatment for an extremely short period of time.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for predicting the amount of thermal donors to be generated and a manufacturing method that can be applied even when the heat treatment time is short.

Claims (7)

A method for predicting thermal donor behavior of a silicon wafer,
The relationship between the heat treatment time and the heat treatment temperature at which the thermal donor generation amount is maximized in the heat treatment time is a negative correlation.
Thermal donor behavior prediction method for silicon wafers. The negative correlation is represented by the following formula (1):
[T _m ]=−at+b (1)
(In formula (1), [T _m ] is the heat treatment temperature at which the thermal donor generation amount is maximized, t is the heat treatment time, and a and b are non-negative constants.)
2. The method for predicting thermal donor behavior of a silicon wafer according to claim 1, wherein the relational expression is: The thermal donor generation amount is given by the following formula (2):
[T _D ]=A×[O _i ] ^B ×t ^C ×exp{−(T−T _m ) ² /(2T ₀ ² )} (2)
(In formula (2), [T _D ] is the amount of thermal donors produced, T is the heat treatment temperature, [O _i ] is the oxygen concentration, and T ₀ , A, B, and C are constants.)
3. The method for predicting thermal donor behavior of a silicon wafer according to claim 1, wherein the relational expression is: 4. The method for predicting thermal donor behavior of a silicon wafer according to claim 1, wherein said heat treatment time is 10 hours or less. The silicon wafer according to any one of claims 1 to 4, wherein the silicon wafer has an oxygen concentration of 1 × 10 ¹⁷ atoms/cm ³ or more and 7 × 10 ¹⁷ atoms/cm ³ or less (ASTM F121-1979). thermal donor behavior prediction method. A silicon wafer evaluation method using the silicon wafer thermal donor behavior prediction method according to any one of claims 1 to 5,
A step of determining the amount of thermal donors generated in the silicon wafer after heat treatment;
obtaining a predicted resistivity of the silicon wafer after the heat treatment based on the thermal donor generation amount;
A method for evaluating a silicon wafer, comprising: A method for manufacturing a silicon wafer,
a step of grasping heat treatment conditions in a device process applied to the silicon wafer;
obtaining a predicted resistivity of the silicon wafer after heat treatment according to the heat treatment conditions in the device process, using the silicon wafer evaluation method according to claim 6;
designing a target value of oxygen concentration or resistivity of the silicon wafer before being subjected to the device process based on the predicted resistivity;
A method for manufacturing a silicon wafer, comprising:

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