JP3050095B2 - Control method of oxygen concentration in crystal - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling the oxygen concentration in a crystal, and more particularly, to pulling a Si single crystal from a Si (silicon) melt by the Czochralski method (hereinafter referred to as CZ method) or the like. The present invention relates to a method for controlling the oxygen concentration in a crystal, which is applied at the time.

[0002]

2. Description of the Related Art There are various methods for pulling a single crystal serving as a semiconductor material. One of them is a CZ method. FIG. 1 is a cross-sectional view schematically showing a crystal growth apparatus used when pulling a single crystal by the CZ method.
Reference numeral 2 denotes a container. A chamber 11 is formed by the container 12, and an upper portion of the chamber 11 is a column-shaped upper chamber 11a. A substantially cylindrical quartz crucible 13a with a bottom is disposed substantially in the center of the chamber 11, and the quartz crucible 13a is filled with a molten liquid 15 of Si. A substantially cylindrical graphite crucible 13b with a bottom is provided on the outer periphery of the quartz crucible 13a, and the crucible 13a and the graphite crucible 13b serve as a crucible.
3 are configured. The rotating shaft 1 is located below the crucible 13.
A driving device (not shown) is connected via a cable 8, and when the driving device is driven, the crucible 13 rotates and moves up and down at a predetermined speed. A heater 14 is arranged concentrically with the outside of the crucible 13, and the Si material charged into the quartz crucible 13 a is melted by the heater 14 to form a molten liquid 15. .
A pulling shaft 16 is hung on the central axis of the crucible 13,
A seed crystal 16a is attached to the tip of the pulling shaft 16, so that the pulling shaft 16 can be pulled upward. The lower portion of the container 12 is connected to a vacuum pump (not shown) through an opening 19, and the vacuum pump is driven to set the pressure in the chamber 11 (hereinafter, referred to as furnace pressure) to a predetermined pressure. It has become. A gas supply device (not shown) is connected to the upper chamber 11a. The gas supply device is driven to flow an inert gas such as Ar at a predetermined flow rate through the upper chamber 11a.
It is designed to be supplied inside. These chambers 11,
A crystal growth apparatus 20 includes a crucible 13, a heater 14, a pulling shaft 16, a driving device, a vacuum pump, a gas supply device, and the like.

When pulling a Si single crystal by the CZ method using the crystal growth apparatus 20 configured as described above, first, an Si raw material is charged into a quartz crucible 13a, and a vacuum pump is driven to evacuate the chamber 11 to a predetermined temperature. At the same time as setting the pressure, the gas supply device is driven to introduce a predetermined flow rate of the inert gas into the chamber 11. Next, a current is applied to the heater 14 to heat the crucible 13 to form a melt 15. Next, after the seed crystal 16 a at the tip of the pulling shaft 16 is brought into contact with the surface of the melt 15, the pulling shaft 16 is pulled up while rotating the crucible 13 at a predetermined speed, and the melt 15 is solidified to form the Si single crystal 17. Let it grow.

Incidentally, the pulled Si single crystal 17
One of the quality evaluation items related to the above is the oxygen concentration in the crystal. Oxygen in the crystal has a function of capturing impurities in the Si wafer (intrinsic gettering function),
Since the performance of a semiconductor element can be improved when a predetermined concentration of oxygen is dissolved in the Si single crystal 17, it is an important management item to keep the oxygen concentration in the crystal within a predetermined range. However, in the conventional CZ method, as the Si single crystal 17 is pulled up and the height of the melt 15 is reduced,
The amount of oxygen dissolved from the quartz crucible 13a into the melt 15 decreases, and the oxygen concentration in the crystal tends to decrease.
There is a problem that the oxygen concentration in the pulling direction of the single crystal 17 tends to be non-uniform. To cope with this problem, a method has been developed to control the oxygen concentration in the crystal by adjusting the rotational speed of the crucible 13, the furnace pressure, and the manipulated variable of the inert gas flow rate during the lifting (Japanese Patent Publication No. Hei 2 (1994)). 44
799, JP-A-1-160893, and JP-A-3-15986). Further, after formulating the relationship between the oxygen concentration in the crystal and the manipulated variable, a parameter fitting is performed to set the manipulated variables, and a method of controlling the oxygen concentration in the crystal based on the set manipulated variable is disclosed. (JP-A-6-172081).

[0005]

In any of the above-described methods for controlling the oxygen concentration in the crystal, no consideration is given to changes over time such as deterioration of the components that affect the oxygen concentration in the crystal, and the number of wires is increased. There was a problem in that the value of the oxygen concentration in the crystal deviated from the target. As described above, since disturbance due to a change over time occurs in the actual lifting, it is necessary to set a manipulated variable by feeding back the measured value of the oxygen concentration after the lifting. However, in providing feedback, there is a problem that it is difficult to accurately set the operation amount by a simple method because various factors are mixed in the disturbance. On the other hand, if this is done by a human, there is a problem that various know-hows are required, and it takes time to study.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and it is possible to stratify various disturbance factors, and to accurately and automatically correct and set an operation amount for each stratified disturbance factor. It is possible to suppress the occurrence of the shift of the oxygen concentration in the crystal due to the change over time due to repeated pulling,
An object of the present invention is to provide a method for controlling the oxygen concentration in a crystal, which can easily and surely keep the oxygen concentration in the crystal within a specified range, and as a result, can improve the quality and yield of the pulled single crystal. And

[0007]

According to the present invention, there is provided a method for controlling the oxygen concentration in a crystal according to the present invention, comprising the steps of: A relational expression relating to a control factor such as an oxygen concentration and a crucible rotation speed is obtained in advance, an operation amount of the control factor is determined, a crystal is pulled up based on the operation amount, and an oxygen concentration in the pulled crystal is measured. After doing
Based on the difference between the measured oxygen concentration and the oxygen concentration estimated value according to the above-mentioned relational expression, the above-mentioned relational expression is corrected for each component deterioration factor, type change factor, and other factors. The operation amount of the control factor such as the crucible rotation number is determined so that the concentration becomes a predetermined target value, and the next crystal is pulled up based on the operation amount.

The symbols used in the following description are shown in Table 1 below.
Defined as shown in

[0009]

[Table 1-1]

[0010]

[Table 1-2]

[0011]

[Table 1, 3]

The oxygen concentration estimated value [O _i ] ₀ is obtained by the following equation 1 which is a function of the pulling rate L, the crucible rotation speed R, the furnace pressure P, and the inert gas flow rate Q.

[0013]

(Equation 1)

However, the oxygen concentration in the crystal is affected by many disturbance factors in addition to the control factors such as the crucible rotation speed R and the like, and the estimated oxygen concentration [O _i ] ₀ and the measured oxygen concentration [ O _i ]. The present inventors have conducted investigations and found that errors caused by these disturbance factors include (1) an error caused by deterioration of the component i disposed in the chamber as a disturbance factor, and (2) a difference between oxygen concentration values. (Variation change factor) causes an error in the error held for each target oxygen concentration.
(3) It can be classified into errors caused by unknown disturbance factors other than the above (1) and (2), including disturbance factors that cannot be classified, such as errors between different crystal growth apparatuses. .

Then, the expected oxygen concentration [O _i ] 'at the time of the next (n + 1) crystal pull-up is the estimated oxygen concentration [O _i ].
₀ is the correction amount δ ₁ for the deterioration factor (1) of the component i,
And thus obtained by the number 2 the following formula corrected by the correction amount [delta] ₃ relative to the correction amount [delta] _2, and the unknown factor (3) with respect to the varieties change factor (2).

[0016]

(Equation 2)

Here, the correction amount δ ₂ is a value unique to each product type, and a common value is used for the correction amount δ ₃ in the same product type having the relationship of the equation (1).

The correction amount δ ₁ for the factor (1) of deterioration of the component is obtained by the following equation (3).

[0019]

(Equation 3)

Here, the deterioration correction coefficient α _i of the component _i ,
Deterioration disturbance coefficient d _i of the component i is decided to use the furnace-specific values.

According to the above-described method of controlling the oxygen concentration in the crystal, many disturbance factors are classified into component deterioration factors, product change factors, and other factors, and the correction amount is reviewed for each of these factors. Therefore, the relational expression can always be accurately corrected, and the operation amount of the control factor can be automatically set based on the corrected relational expression. As a result, it is possible to reliably and easily keep the oxygen concentration in the crystal of the whole single crystal within the specified range, and to suppress the occurrence of a shift in the oxygen concentration in the crystal due to the temporal change due to repeated pulling. Thus, the quality and yield of the pulled single crystal can be improved.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a method for controlling oxygen concentration in a crystal according to the present invention will be described below with reference to the drawings.
Note that components having the same functions as those of the conventional example are denoted by the same reference numerals. FIG. 1 is a cross-sectional view schematically showing a crystal growth apparatus used for pulling a single crystal while performing the method for controlling the oxygen concentration in a crystal according to the embodiment. The driving device for the crucible 13, the vacuum pump connected to the opening 19, and the gas supply device include an adaptive feedback unit (hereinafter, simply referred to as a feedback unit) 111, an operation amount setting unit 112, and a storage unit 113 shown in FIG. Is connected to the control means 110 including the above. The storage unit 113 stores the above equation (3), the following equations (4) to (14), and oxygen concentration map data that substitutes for the equations (1) and (2). The oxygen concentration map data includes iso-oxygen line data when the crucible rotation speed is plotted on the vertical axis and the pulling rate is plotted on the horizontal axis, or the iso-oxygen data shown in FIG.
Iso-furnace pressure line data, iso-oxygen / iso-furnace internal pressure / iso-inert gas flow rate line data, etc. are recorded. The feedback unit 111 calculates an error between the oxygen concentration estimated value [O _i ] _{o (map) of} the oxygen concentration map data and the pulled oxygen concentration measurement value [O _i ] in the crystal, and calculates the error and the equation (3). The correction amount of the oxygen concentration map data is calculated based on Expressions (8) to (8). In the operation amount setting unit 112,
The number 9 expression with determining the oxygen concentration map data when pulling next calculates the correction amount [delta] ₁ to degradation factors of the component i, based on the oxygen concentration map data and the number 10 formula to several 14 formula, when pulled next Crucible rotation speed R _{n + 1 (map)} , furnace pressure P _{n + 1 (map)} , inert gas flow rate Q
An operation amount relating to a control factor such as _{n + 1 (map)} is calculated. The other configuration is the same as that of the conventional crystal growth apparatus 20, and the detailed description of the configuration is omitted here. The crystal growth apparatus 10 according to the embodiment includes the control means 110 and the like.

In the following, using the crystal growth apparatus 10 configured as described above, while controlling the oxygen concentration in the crystal,
The case where the i-single crystal is pulled will be described with reference to FIG. First, before raising the batch, the crucible rotation speed R _{n (map)} and the furnace pressure P set in the same manner as described below are set.
_The crystal is pulled up based on the manipulated variable pattern of _{n (map)} and the inert gas flow rate Qn _(map) , and the oxygen concentration [O _i ] (L _m ) at the measurement point m of the crystal is measured. Next, when the measured values [O _i ] (L _m ) and the pulling rate L _{m of} each sample are input to the control means 110 by a key, the crucible rotation speed R _{n (map)} and the furnace pressure P _{n ( map)} , the error between the oxygen concentration estimation value [O _i ] _{o (map)} and the oxygen concentration measurement value [O _i ] at the time of the inert gas flow rate Q _{n (map)} is calculated (step 1). If there is a change in the target (target) oxygen concentration from the batch (n-1), the correction amount δ ₂ for the type change factor (2) is calculated in step 2 by the following equations (4) and (5). You.

[0024]

Δ ₂ (L) = δ _2b ′ (L) + Ge ₂ (L) × (e
_{2 (L) -δ 2b '(} L))

[0025]

(Equation 5)

However, when the pulling rate L in the equation (5) is different from the oxygen concentration measuring point, this function is obtained by interpolation or extrapolation from the pulling rate at which the measured value is present, or by giving a function system passing the measured value. The value obtained based on the system is used as the measured oxygen concentration at the corresponding pulling rate.

Next, if there is no change in the target oxygen concentration and the part i has been replaced from the previous batch, a review calculation of the deterioration correction coefficient α _i of the part i is performed in step 3 by the following equation (6). .

[0028]

(Equation 6)

However, if the pulling rate L in equation (6) is different from the oxygen concentration measurement point, this function is obtained from the pulling rate with the measured value by interpolation or extrapolation, or by giving a function system passing the measured value. The value obtained based on the system is used as the measured oxygen concentration at the corresponding pulling rate.

Next, if the target oxygen concentration has not been changed or the part i has not been replaced, the correction amount δ ₃ for the unknown factor (3) is calculated in step 4 using equations (7) and (8).

[0031]

## EQU7 ## δ _{3 (n)} (L) = δ _{3 (n-1)} (L) + Ge ₃ (L) ×
(E _{3 (n)} (L) −δ _{3 (n-1)} (L))

[0032]

(Equation 8)

However, when the pulling rate L in the equation (8) is different from the oxygen concentration measuring point, this function is obtained by interpolation or extrapolation from the pulling rate at which the measured value is present, or by providing a function system passing the measured value. The value obtained based on the system is used as the measured oxygen concentration at the corresponding pulling rate.

When the correction amount is calculated as described above, the operation of the feedback unit 111 ends.

[0035] Next the operation amount setting section 112, after the correction amount [delta] ₁ to degradation factors of the parts before pulling the next batch (1) is calculated by the number 3 expression, next the number 9 the following formula (n + 1) Is determined (step 5).

[0036]

(Equation 9)

Next, in step 6, the next (n + 1) crucible rotation speed R _{(n + 1)} (L) is calculated by the following equation (10), and the manipulated variable is determined.

[0038]

R _{(n + 1)} (L) = R _b (L) + ΔR _{(n + 1)} (L) where ΔR _{(n + 1)} (L) = R _(map) (L) −R _b (L) It should be noted that R _{(n + 1)} , ΔR _{(n + 1)} and the amount of change ＲR _{(n + 1)} / ∂L of R _{(n + 1)} in the pulling rate direction have upper and lower limits, respectively. If these values are set in advance and cannot be compensated for by the crucible rotation speed because of these upper and lower limits, compensation is made by the furnace pressure in the next step 7.

Next, in step 7, the next (n + 1)
The furnace pressure _{P (n + 1) (L} ) is calculated, the operation amount is determined. There are two methods for determining the furnace pressure, a method using an oxygen concentration map and a method using an influence coefficient. In the case of using an oxygen concentration map, the following equation 11 is used.

[0040]

P _{(n + 1)} (L) = P _b (L) + ΔP _{(n + 1)} (L) where ΔP _{(n + 1)} (L) = P _(map) (L) −P _b (L) On the other hand, when it is determined by the influence coefficient, the following equation 12 is used.

[0041]

P _{(n + 1)} (L) = P _b (L) + _GP (L) × ΔP _{(n + 1)} (L) where ΔP _{(n + 1)} (L) = ∂P (L ) / ∂ [0i] ×
([O _i ] _ref (L) − [0i] _R (L)) The amount of change ∂P ₍ P _{(n + 1)} , ΔP _{(n + 1)} and P _{(n + 1)} in the pulling rate direction _{) In (n + 1)} / ∂L, upper and lower limits are set in advance, respectively. If these upper and lower limits exist and cannot be compensated by the furnace internal pressure, compensation is performed by the inert gas flow rate in the next step 8. .

Next, in step 8, the next (n + 1)
Inert gas flow rate _{Q (n + 1) (L} ) is calculated, this manipulated variable is determined. Note that there are two types of determination of the flow rate of the inert gas, a method using an oxygen map and a method using an influence coefficient. In the case of using an oxygen concentration map, the following equation (13) is used.

[0043]

(13) Q _{(n + 1)} (L) = Q (L) + ΔQ _{(n + 1)} (L) where ΔQ _{(n + 1)} (L) = Q _(map) (L) −Q (L On the other hand, when it is determined by the influence coefficient, the following Expression 14 is used.

[0044]

Equation 14] _{Q (n + 1) (L} ) = Q (L) + G Q (L) × ΔQ (n + 1) (L) _{However, ΔQ (n + 1) (} L) = ∂Q (L) / ∂ [0i] ×
([O _i ] _ref (L) − [0i] _PR (L)) Next, based on these manipulated variables, the driving device, the vacuum pump, and the gas supply device are driven, and the surface of the melt 15 in the crucible 13 is moved. Then, the seed crystal 16a at the tip of the pulling shaft 16 is brought into contact with the pulling shaft 16, and the pulling shaft 16 is pulled up.

As is clear from the above description, in the method of controlling the oxygen concentration in the crystal according to the embodiment, many disturbance factors are classified into component deterioration factors, product change factors, and other factors. Since the correction amounts δ ₁ , δ ₂ , δ ₃ are reviewed every time, the oxygen concentration map data is always accurately corrected, and based on the corrected oxygen concentration map data, the crucible rotation speed R, the furnace pressure P, the The manipulated variable of the active gas flow rate Q is automatically set. As a result, it is possible to reliably and easily bring the oxygen concentration in the crystal of the whole single crystal 17 within the specified range, and to suppress the occurrence of a shift in the oxygen concentration in the crystal due to the change over time due to repeated pulling. As a result, the quality and yield of the pulled single crystal 17 can be improved. In the method for controlling the oxygen concentration in the crystal according to the above-described embodiment, the case where the crucible rotation speed R, the furnace pressure P, and the inert gas flow rate Q are used as the manipulated variables has been described. Alternatively, any two may be used, or an operation amount other than these may be added and used.

[0046]

EXAMPLES and COMPARATIVE EXAMPLES The results of pulling up a Si single crystal 17 by performing the method for controlling the oxygen concentration in a crystal according to the embodiment will be described below. The oxygen concentration map shown in FIG. 3 was used. Table 2 shows the parameters used in the experiment. Note that only the heater was considered as the factor (1) of deterioration of the component i.

[0047]

[Table 2]

FIG. 4 is a plot diagram showing the simulation results of the oxygen control test. The graph shows the changes in the operation amounts of the crucible rotation speed, the furnace internal pressure, the inert gas flow rate, and the pulling rate 20%.
% Shows the transition of the oxygen concentration in the crystal for each pulling batch in%. As is clear from this figure, there is little variation in the oxygen concentration in the crystal between batches, all of which fall within the oxygen concentration specification values, and even when the heater parts are replaced (the number of batches is 10 times), the fluctuation of the oxygen concentration is also observed. Was extremely small. It was also confirmed that the same accuracy was obtained when the type was changed or in a simulation using another furnace.

[0049]

As described above in detail, in the method for controlling the oxygen concentration in a crystal according to the present invention, many disturbance factors are classified into component deterioration factors, product change factors, and other factors. The correction amount is reviewed for each of these factors. Therefore, the relational expression is always accurately corrected, and the manipulated variable of the control factor is automatically set based on the corrected relational expression. As a result, it is possible to reliably and easily keep the oxygen concentration in the crystal of the entire single crystal within the specified range, and to suppress the occurrence of a shift in the oxygen concentration in the crystal due to a temporal change due to repeated pulling. In addition, the quality and yield of the pulled single crystal can be improved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically showing a crystal growth apparatus used for pulling a single crystal while performing a conventional CZ method and a method for controlling oxygen concentration in a crystal according to an embodiment of the present invention. .

FIG. 2 is a flowchart schematically showing an embodiment of a method for controlling the oxygen concentration in a crystal according to the present invention.

FIG. 3 is a curve diagram schematically illustrating an example of an oxygen concentration map used for a method of controlling oxygen concentration in a crystal according to an example.

FIG. 4 is a plot showing a result of pulling a silicon single crystal by a method of controlling oxygen concentration in a crystal according to an example, showing changes in manipulated variables of a crucible rotation speed, a furnace internal pressure, and a flow rate of an inert gas; It shows changes in the oxygen concentration in the crystal for each pulling batch at a rate of 20%.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Crystal growth apparatus 13 Crucible 13a Quartz crucible 15 Melt 17 Single crystal

Continuation of the front page (56) References JP 8-259380 (JP, A) JP 5-262593 (JP, A) JP 5-279174 (JP, A) JP 6-172081 (JP) JP-A-1-160893 (JP, A) JP-A-3-15986 (JP, A) JP-A-4-209792 (JP, A) JP-B-2-44799 (JP, B2) (58) Field surveyed (Int. Cl. ⁷ , DB name) C30B 1/00-27/02

Claims (1)

(57) [Claims] In a method for controlling the oxygen concentration in a crystal when a crystal is pulled up from a melt in a quartz crucible, a relational expression relating to a control factor such as an oxygen concentration and a crucible rotation speed is obtained in advance. Determine the manipulated variable, pull up the crystal based on the manipulated variable, measure the oxygen concentration in the pulled crystal, and based on the difference between the measured oxygen concentration and the oxygen concentration estimated value by the above relational expression, The above relational expression is corrected for each of the deterioration factor, the type change factor, and other factors, and the manipulated variable of the control factor such as the crucible rotation speed is adjusted based on the corrected relational expression so that the oxygen concentration becomes a predetermined target value. Is determined, and the next crystal is pulled up based on the manipulated variable.