JP7247949B2 - Method for producing silicon single crystal - Google Patents

Description

The present invention relates to a method for manufacturing silicon single crystals.

In recent years, the improvement in performance due to miniaturization and high integration of Si transistors is approaching the limit. Expectations are high for improved performance.

The reserves of these next-generation channel materials in the earth's crust are Ge: 1.8 ppma, Ga: 18 ppma, and As: 1.5 ppma. The problem is that the

A heterostructure in which Ge, GaAs, or the like is placed on a Si substrate, which is abundant in resources, inexpensive, high-quality, and has a track record of being used in electronic devices, can be an effective solution.

However, when these heteroatom layers are formed on a Si substrate, residual stress, dislocations, and wafer warpage caused by the difference in thermal expansion coefficient between Si and the heteroatom layer pose problems.

In order to deal with this problem, it is widely known that the effect can be reduced by, for example, lowering the growth temperature, but this method has the drawback of deteriorating the crystallinity.
As another method, a Si substrate is covered with SiO ₂ or the like, and a heteroatom layer is grown on a part where the Si substrate is partially exposed (this part is called a pattern), or lateral growth is performed through the pattern. There is a way.

Although these methods can suppress the influence of the coefficient of thermal expansion, there is a problem that the influence of the difference in the coefficient of thermal expansion on the growth surface in the pattern cannot be avoided.

In addition, the introduction of strain into the channel has the beneficial aspect of increasing carrier mobility, so in order not to negate this advantage, it is preferable that the wafer itself is strong enough to suppress dislocations and wafer warpage.

In this regard, since the Si (111) plane has the highest mechanical strength as a close-packed plane compared to the generally used Si (100) plane, it is superior to other Si (111) planes in terms of suppression of dislocation and wafer warpage. It is superior to the plane orientation of

Therefore, in a heterostructure in which a high carrier mobility material is heteroepitaxially grown on a Si substrate, the Si <111> crystal is superior to Si in terms of the mechanical strength that leads to the suppression of dislocations and wafer warpage due to the difference in thermal expansion coefficient. It is superior to other plane orientations.

In recent years, Si<111> crystals have been attracting attention as applications for transistors using compound semiconductors. Among them, it is important to establish a manufacturing method for low-resistance Si<111> crystals with a resistivity of 10 mΩcm or less. It has become to.

Point defects are inevitably introduced into the Si single crystal used as the substrate of the transistor during pulling, and it is widely known that the method of introducing the point defects follows Voronkov's theory.

According to Voronkov's theory, the point defect concentration is determined depending on the ratio V/G between the growth rate V of the silicon single crystal and the temperature gradient G near the interface. In order to reduce , it is necessary to align the defect regions, and for that purpose, it is important to precisely control V/G.

In a pulling machine with a constant temperature gradient G, it is necessary to grow a single crystal with a constant pulling speed V in order to keep V/G constant.

In order to keep the pulling speed V constant, a span limit is set for the pulling speed during the production of silicon single crystals by the ordinary Czochralski method, and the deviation between the set pulling speed and the pulling speed control value is kept within a certain range. We are operating to

In the operation with the span limit on the pulling speed, the pulling speed control value is calculated by PID control by comparing the detected value of the crystal diameter and the set value, and after setting the span limit on the pulling speed control value, the pulling speed By setting an upper limit and a lower limit to the amount of change in and calculating a pull-up speed output with a limited range of fluctuation, the pull-up speed is controlled within a certain range.

However, if the pulling speed of the crystal is kept constant in a pulling machine having a constant temperature gradient G, there is a problem that the crystal diameter fluctuates greatly.

In order to solve this problem, in Patent Document 1, the heater temperature correction amount is calculated by PID control by comparing the lifting speed control value and the set lifting speed before applying the span limit to the lifting speed control value. , a method of controlling the pulling speed and the heater temperature by combining the pulling speed output and the heater temperature setting output is disclosed. We operate using the control method described in .

By the way, among the target silicon single crystals with a resistivity of 10 mΩcm or less, <100> crystals are mainly manufactured for EP-subs (wafers serving as substrates on which epitaxial layers are grown).

Low-resistivity crystals for EP-subs are usually operated at a high V/G. A phenomenon of cranking occurs, and diameter variation due to cranking tends to occur.

If the width of the diameter fluctuation at this time becomes too large, there is a problem that polishing residue will be left during cylindrical grinding after crystal pulling, resulting in a significant decrease in productivity and yield. Normally, as a countermeasure against residual polishing during cylindrical grinding, operation is carried out under the condition that the crystal diameter is made thicker by several millimeters than usual.

Applying a span limit to the pulling speed under the conditions of high V/G and large diameter crystal pulling results in large melt temperature fluctuations due to heater power fluctuations, and the compositional properties described in Patent Document 2 Supercooling phenomenon is likely to occur.

Under conditions where this compositional supercooling phenomenon is likely to occur, there is a problem that troubles during operation increase. is operating in

JP 2001-316199 JP 2010-132492 JP 2018-095490 A International Publication No. WO2004/018742 Pamphlet

A single crystal having a low resistivity of 10 mΩcm or less, a diameter of 300 mm or more, and a crystal axis orientation of <111> (hereinafter, <111> crystal) ), a phenomenon occurs in which the deformed facet shown on the right side of FIG. In the single crystal shown on the left side of FIG. 2 whose crystal axis orientation is <100> (hereinafter referred to as <100> crystal), such deformed facets do not occur.

The phenomenon in which the disappearance and appearance of the deformed portion facet surface are periodically repeated will be specifically described below.

When operation is performed under conditions where no span limit is set for the pull-up speed during the straight body process, the temperature fluctuation increases due to the latent heat of solidification at the solid-liquid interface, causing the pull-up speed to fluctuate. When the set pulling speed is reached and the difference between the two becomes lower than a certain range, the deformed facet surface disappears and the crystal shape changes to a round shape.

When the facet disappears and the crystal shape changes to a round shape, the "detected value of crystal diameter" > "set value of crystal diameter". When the value is corrected so that "pulling speed control value">"set pulling speed" and the detected value of the crystal diameter approaches the set value of the crystal diameter, the facet plane appears again.

Furthermore, the facet surface appears again, and after a while, the "detected value of the crystal diameter" < the "set value of the crystal diameter". When the difference between the detected value of the crystal diameter and the set value of the crystal diameter exceeds a certain range, the deformed facet disappears again and the crystal The phenomenon that the shape changes to a round shape is repeated periodically.

Normally, when manufacturing a <111> crystal, whether dislocations are present or not is judged by looking at whether or not the deformed facet plane has disappeared. is periodically repeated, it becomes impossible to correctly determine whether or not the crystal is dislocated during operation.

For this reason, there have been frequent cases of erroneously recognizing that the crystal has been dislocated during operation, and the productivity and yield of the <111> crystal are remarkably lowered.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a manufacturing method capable of manufacturing a <111> crystal having a diameter of 300 mm or more with low resistivity with high productivity and high yield. and

In order to solve the above problems, the present invention provides a method for producing a silicon single crystal having a diameter of 300 mm or more, a resistivity of 10 mΩcm or less, and a crystal axis orientation of <111> by the Czochralski method. There is
obtaining a detection output by detecting the diameter of the silicon single crystal during the straight body process every predetermined time;
In the straight body process, the detection output is fed back to the pulling speed and heater temperature of the silicon single crystal, and the pulling speed and heater temperature of the silicon single crystal are controlled by PID control so that the diameter of the silicon single crystal reaches the target diameter. and controlling such that
In the control of the pulling speed in the straight body process, a span limit is provided only for the fluctuation width on the negative side with respect to the pulling speed set value, and the span limitation is not set for the fluctuation width on the positive side of the pulling speed set value. Provided is a method for manufacturing a silicon single crystal with

By carrying out this operation, at the time of producing a <111> crystal with a low resistivity of 10 mΩcm or less and a diameter of 300 mm or more, at least the disappearance of the deformed facet surface due to the fluctuation of the pulling speed is not observed.

Therefore, it is possible to correctly determine whether or not the crystal is dislocated during the straight body process, and the <111> crystal with a low resistivity and a large diameter of 300 mm or more can be produced with high productivity and high productivity. It becomes possible to manufacture with a high yield.

In addition, by applying the above conditions, it is possible to suppress deterioration of the inner surface of the quartz crucible due to long-term use of the quartz crucible. > It becomes possible to produce crystals.

It is preferable that the limit value of the fluctuation width of the pulling speed on the negative side is 0.01 mm/min or less.
By doing so, a large-diameter <111> crystal with a diameter of 300 mm or more with a low resistivity can be reliably prevented from disappearing of the deformed part facet surface, and can be manufactured with higher productivity and higher yield. .

In the straight-body process, the silicon single crystal has a diameter of 300 mm or more, a crystal axis orientation of <111>, and a deformed portion facet width of the as-grown silicon single crystal side surface of 80 mm or less at maximum. is preferably grown.
By doing so, it is possible to prevent a decrease in productivity and yield due to pulling a single crystal with a larger diameter.
Further, by using the silicon single crystal manufactured in this manner, it is possible to obtain a (111) silicon wafer having a diameter of 300 mm or more and a plane orientation of (111) while suppressing grinding loss.

As described above, according to the method for producing a silicon single crystal of the present invention, it is possible to produce large-diameter <111> crystals with a diameter of 300 mm or more and low resistivity with high productivity and high yield.

More specifically, the method for producing silicon single crystals of the present invention enables the production of crystals with substantially the same pulled diameter as <100> low resistivity crystals.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram showing an example of a single crystal pulling apparatus capable of implementing the method of manufacturing a silicon single crystal of the present invention; FIG. 3 is a schematic diagram for explaining the width of a deformed portion facet of a side surface of a silicon single crystal;

As described above, there has been a demand for the development of a method capable of producing large-diameter <111> crystals of 300 mm or more in diameter with low resistivity with high productivity and high yield.

As a result of intensive studies on the above problems, the present inventors have found that when manufacturing a <111> crystal with a diameter of 300 mm or more and a low resistivity of 10 mΩcm or less, the set value of the pulling speed during the straight body process in which PID control is performed By setting a span limit only on the fluctuation range on the minus side of the pull-up speed setting value and not setting a span limit on the fluctuation width on the plus side of the pull-up speed setting value, at least the disappearance of the deformed facet surface due to fluctuations in the pull-up speed can be seen. The present invention was completed after discovering that it would not be possible.

That is, the present invention is a method for producing a silicon single crystal having a diameter of 300 mm or more, a resistivity of 10 mΩcm or less, and a crystal axis orientation of <111> by the Czochralski method,
obtaining a detection output by detecting the diameter of the silicon single crystal during the straight body process every predetermined time;
In the straight body process, the detection output is fed back to the pulling speed and heater temperature of the silicon single crystal, and the pulling speed and heater temperature of the silicon single crystal are controlled by PID control so that the diameter of the silicon single crystal reaches the target diameter. and controlling such that
In the control of the pulling speed in the straight body process, a span limit is provided only for the fluctuation width on the negative side with respect to the pulling speed set value, and the span limitation is not set for the fluctuation width on the positive side of the pulling speed set value. It is a method of manufacturing a silicon single crystal to be.

In addition, Patent Document 3 specifies the range of magnetic field intensity during the straight body process, thereby reducing the width of the deformed facet surface of the crystal side surface of the <111> crystal, and manufacturing the <111> crystal with a diameter of 300 mm or more. A technique for improving the yield is disclosed. In addition, in Patent Document 4, when the amount of change in the diameter deviation between the target diameter and the measured diameter is fed back to the pulling speed of the silicon single crystal rod as a deviation, the maximum fluctuation width of the correction for the current pulling speed is not exceeded. PID control of the pull-up speed is described. However, none of these documents disclose a method of limiting the span only for fluctuations on the low speed side of pull-up speed fluctuations.

Hereinafter, the present invention will be described in detail with reference to the drawings, but the present invention is not limited thereto.

<Method for Producing Silicon Single Crystal>
First, a crystal pulling apparatus capable of implementing the method for producing a silicon single crystal of the present invention will be described.

The structure of the puller and HZ (hot zone) that can be used in the method for producing a silicon single crystal of the present invention is not particularly limited, and a general CZ silicon single crystal puller and HZ can be used. can.

For example, a configuration example of a single crystal pulling apparatus capable of implementing the method of manufacturing a silicon single crystal according to the present invention will be described with reference to FIG.

A single crystal pulling apparatus 20 shown in FIG. 1 has a hollow cylindrical chamber 1, and a crucible 5 is arranged at the center thereof. This crucible has a double structure, consisting of a bottomed cylindrical quartz inner holding vessel (hereinafter simply referred to as "quartz crucible 5a") and a bottomed quartz crucible 5a adapted to hold the outside of the quartz crucible 5a. and a cylindrical graphite outer holding container (“graphite crucible 5b”).

These crucibles 5 are fixed to the upper end of a support shaft 6 so as to be able to rotate and move up and down, and a resistance heating type heater 8 is arranged generally concentrically outside the crucibles. Furthermore, a heat insulating material 9 is arranged concentrically around the outside of the heater 8 . A silicon melt 2 obtained by melting a silicon raw material is stored in the crucible by a heater 8 . Furthermore, a magnetic field applying device 13 is provided on the outer periphery of the chamber 1 .

A pull-up wire 7 rotating at a predetermined speed in the opposite direction or the same direction on the same axis as the support shaft 6 is arranged on the central axis of the crucible 5 filled with the silicon melt 2 , and the lower end of the pull-up wire 7 is arranged. A seed crystal 4 is held. A silicon single crystal 3 is formed on the lower end face of the seed crystal 4 . On the other hand, the upper end of the pulling wire 7 is connected to the pulling speed controller 10 .

Furthermore, the single crystal pulling device 20 comprises a camera 11 for measuring the diameter of the growing single crystal 3 and a diameter control device 12 for controlling the diameter of the single crystal 3 . Diameter controller 12 is electrically connected to pull speed controller 10 , camera 11 and heater 8 .

Next, a method for manufacturing a silicon single crystal according to the present invention will be described with reference to FIG. The single crystal pulling apparatus that can be used in the method for producing a silicon single crystal according to the present invention is not limited to that shown in FIG. For example, a single crystal pulling apparatus without the magnetic field applying device 13 may be used.

In the method for producing a silicon single crystal of the present invention, first, a single crystal pulling apparatus 20 as shown in FIG. 1 is used as an example, and a silicon raw material is supplied into the crucible 5 to prepare for silicon single crystal growth. . Next, the silicon raw material is heated and melted to obtain a silicon melt 2 . A silicon single crystal 3 is grown from this silicon melt 2 using a seed crystal 4 whose crystal axis orientation is <111> and whose single crystal growth axis orientation is set to <111>.

The method of manufacturing a silicon single crystal of the present invention is applied to a straight body process. The straight body process is a process of pulling up the straight body portion of the single crystal while controlling it to have a constant diameter.

Regarding the control of the crystal diameter during the straight body process, for example, by comparing the detected value of the crystal diameter by the camera 11 and the set value of the crystal diameter, the deviation is fed back to the diameter control device 12 to obtain the pulling speed control value. is calculated by PID control. At this time, before setting the span limit on the lifting speed control value, after calculating the heater temperature correction amount by PID control by comparing the lifting speed control value and the set lifting speed, the span limit is set on the lifting speed control value. It is possible to use a method in which the pulling speed is controlled by the pulling speed control device 10 by combining the output at the time of pressing and the heater temperature setting output, and the heater temperature is controlled by adjusting the power supply.

Specifically, the pulling speed is controlled by controlling the pulling speed of the silicon single crystal 3 by the pulling wire 7 with the pulling speed controller 10 . The pulling speed control device 10 controls the pulling speed based on the pulling speed control value output from the diameter control device 12 . Further, the heater temperature is specifically controlled, for example, by controlling power supply to the heater 8 . Power supply to the heater 8 is controlled by the diameter controller 12 based on the heater temperature setting output. Control of the pulling speed and heater temperature may be performed by other means.

The diameter control device 12 is provided with a CPU configured to perform the above-described computation by PID control, output of the pull-up speed control value and heater temperature setting output, and control of the heater temperature based on the heater temperature setting output.

The span limitation during the straight body process is such that only the fluctuation range on the negative side is limited, and the fluctuation range on the positive side of the pulling speed is not limited. The fluctuation width on the minus side is preferably 0.01 mm/min or less, and more preferably, only the fluctuation width on the minus side is 0 mm/min. Control with span limits can also be performed by the CPU.

By carrying out this operation, at the time of producing a <111> crystal with a low resistivity of 10 mΩcm or less and a diameter of 300 mm or more, at least the disappearance of the deformed facet surface due to the fluctuation of the pulling speed is not observed.

Therefore, it is possible to correctly determine whether or not the crystal is dislocated during the straight body process, and the <111> crystal with a low resistivity and a large diameter of 300 mm or more can be produced with high productivity and high productivity. It becomes possible to manufacture with a high yield.

By applying the above conditions, the <111> crystal can be grown at a high growth rate, and the time required for single crystal growth can be shortened. As a result, it is possible to suppress the deterioration of the inner surface of the quartz crucible due to long-term use of the quartz crucible, so in this respect also, it is possible to manufacture <111> crystals with a diameter of 300 mm or more with high productivity and high yield. becomes possible.

After entering the straight body process, it is preferable to set a span limit with respect to the pull-up speed set value and perform the operation.

Moreover, it is preferable to apply a magnetic field to the silicon melt 2, and for example, it is preferable to apply a horizontal magnetic field using the magnetic field applying device 13 shown in FIG. By applying a horizontal magnetic field to the silicon melt 2, convection in the silicon melt 2 can be suppressed, and contamination of impurities such as oxygen from the quartz crucible 5a can be suppressed.

In the straight body process, the diameter is 300 mm or more, the crystal axis orientation is <111>, and the silicon single crystal is formed so that the deformed portion facet width of the side surface of the silicon single crystal in the as-grown state is 80 mm or less at the maximum. Crystal growth is preferred.

By setting the maximum value of the facet width of the deformed portion of the side surface of the silicon single crystal in the as-grown state to 80 mm or less, it is possible to avoid pulling the single crystal with a larger diameter for product extraction. Thereby, it is possible to prevent a decrease in productivity and yield.

Further, by using the silicon single crystal manufactured in this way, it is possible to obtain a (111) silicon wafer having a diameter of 300 mm or more while suppressing grinding loss.

The maximum value of the deformed portion facet surface width can be controlled, for example, by controlling the central magnetic field intensity applied to the silicon melt, which is the raw material melt. The central magnetic field strength is preferably 0.10 T or more and 0.25 T or less.

EXAMPLES The present invention will be specifically described below using Examples and Comparative Examples, but the present invention is not limited to these.
In the following examples and comparative examples, a pulling machine having the structure shown in FIG. 1 was used.

(Example 1)
360 kg of silicon raw material was placed in a quartz crucible with a diameter of 32 inches (800 mm), and the silicon raw material was melted to obtain a silicon melt. Next, a horizontal magnetic field was applied to the silicon melt, and a silicon single crystal having a crystal diameter of 310 mm and a crystal axis orientation of <111> was pulled.

The magnetic field strength applied during the straight body process was controlled so that the central magnetic field strength was 0.2T. Further, boron was added so that the resistivity was 10 mΩcm or less at all straight body positions.

Further, a camera was used to detect the diameter of the silicon single crystal during the straight body process at predetermined time intervals to obtain a detection output. Further, in this straight body process, the detected diameter of the silicon single crystal is fed back to the silicon single crystal pulling speed and heater temperature, and the silicon single crystal pulling speed and heater temperature are controlled by PID control so that the silicon single crystal diameter is the target. The diameter was controlled to be 310 mm.

Furthermore, in Example 1, the operating conditions were such that the span limit was set only for the fluctuation range on the negative side of the pull-up speed set value during the straight body process.

The pull-up speed control by PID control and span limitation, and the heater temperature control by PID control were performed in the same manner as described above.

Under these conditions, <111> crystals were pulled one by one using five different pulling apparatuses having the same configuration, and a total of five silicon single crystals were produced. The results are shown in Table 1 below.

The width of the span limitation in Example 1 was such that the width of fluctuation on the minus side was 0.01 mm/min or less, and the width of fluctuation on the plus side was not limited.

As a result of the operation under the above conditions, as shown in Table 1 below, there was no loss of deformed facets due to fluctuations in the pulling speed during the straight body process, and the yield of the product was as high as 98%. was gotten.

In other words, it was confirmed that the disappearance of deformed facets caused by fluctuations in the pulling speed eliminated the misidentification of the crystal as having dislocations during operation.

That is, according to Example 1, a silicon single crystal having a low resistivity, a diameter of 300 mm or more, and a crystal axis orientation of <111> could be produced with high productivity and high yield.

(Comparative Examples 1 and 2)
Based on the operating conditions of Example 1, the conditions were changed without the span limit of the pull-up speed setting value during the straight body process in Comparative Example 1, the plus side and minus side of the pull-up speed setting value during the straight body process. A <111> crystal with a crystal diameter of 310 mm was pulled under the conditions of Comparative Example 2 in which both fluctuation widths were changed to 0.01 mm/min or less.

In Comparative Example 1 and Comparative Example 2, each <111> crystal was pulled under the above conditions by five different pulling apparatuses having the same configuration, and a total of five silicon single crystals were pulled. manufactured. The results are shown in Table 2 below.

First, as a result of the operation under the conditions of Comparative Example 1, as shown in Table 2 above, the deformed part facets disappeared due to fluctuations in the pulling speed in all five operations, and as a result, crystals were formed. It was determined that dislocation had occurred, and the crystal was cut off during the straight body process.
Therefore, in Comparative Example 1, the product yield was 60%, resulting in a significant drop in yield.

From this result, it can be seen that if <111> crystals are pulled under conditions that are not limited to the span limit of the pulling speed in the conventional straight body process, the productivity and yield are significantly reduced.

On the other hand, as a result of the operation under the conditions of Comparative Example 2, as shown in Table 2 above, although the facets of the deformed portion due to fluctuations in the pulling speed did not disappear, the yield of the product was 82%. It can be seen that the yield is lower than in Example 1.

In Comparative Example 2, the span limit is set not only on the minus side of the pull-up speed set value but also on the plus side. Although no facet disappearance was observed in the part, the diameter fluctuation increased due to the effect of the temperature pattern accompanying the span limitation on both sides of the pull-up speed during the straight body process, and dislocations occurred during the straight body process. Product yield decreased compared to Example 1.

It should be noted that the present invention is not limited to the above embodiments. The above-described embodiment is an example, and any device having substantially the same configuration as the technical idea described in the claims of the present invention and exhibiting the same effect is the present invention. included in the technical scope of

DESCRIPTION OF SYMBOLS 1... Chamber 2... Silicon melt 3... Silicon single crystal 4... Seed crystal 5... Crucible 5a... Quartz crucible 5b... Graphite crucible 6... Support shaft 7... Pulling wire 8... Heater 9 Heat insulating material 10 Pulling speed control device 11 Camera 12 Diameter control device 13 Magnetic field applying device 20 Single crystal pulling device.

Claims (3)

A method for producing a silicon single crystal having a diameter of 300 mm or more, a resistivity of 10 mΩcm or less, and a crystal axis orientation of <111> by the Czochralski method,
obtaining a detection output by detecting the diameter of the silicon single crystal during the straight body process every predetermined time;
In the straight body process, the detection output is fed back to the pulling speed and heater temperature of the silicon single crystal, and the pulling speed and heater temperature of the silicon single crystal are controlled by PID control so that the diameter of the silicon single crystal reaches the target diameter. and controlling such that
In the control of the pulling speed in the straight body process, a span limit is provided only for the fluctuation width on the negative side with respect to the pulling speed set value, and the span limitation is not set for the fluctuation width on the positive side of the pulling speed set value. A method of manufacturing a silicon single crystal to 2. The method for producing a silicon single crystal according to claim 1, wherein the limiting value of the fluctuation width of the minus side of the pulling speed is 0.01 mm/min or less. In the straight-body process, the silicon single crystal has a diameter of 300 mm or more, a crystal axis orientation of <111>, and a deformed portion facet width of the as-grown silicon single crystal side surface of 80 mm or less at maximum. 3. The method for producing a silicon single crystal according to claim 1 or 2, wherein the growth of the silicon single crystal is performed.

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