JP2011171377A - Method of manufacturing silicon wafer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a silicon wafer suppressing a reduction in oxygen concentration in a device active region and greatly reducing the defect density of the device active region without performing again mirror polishing. <P>SOLUTION: The method includes the step of performing a rapid temperature rising and lowering heat treatment on a silicon wafer sliced off from a silicon monocrystalline ingot grown by Czochralski method at a highest end-point temperature which is at least 1,325°C and not more than 1,390°C in an oxidized gas atmosphere, and the step of performing a laser heat treatment on a front surface part of the device active region on the front surface side on which a semiconductor device of the heat-treated silicon wafer by irradiating it with laser light in an inert gas atmosphere at a highest end-point temperature which is at least 1,200°C and not more than 1,350°C. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for producing a silicon wafer used for a substrate for forming a semiconductor device, and in particular, to a silicon wafer sliced from a silicon single crystal ingot grown by the Czochralski method (hereinafter also simply referred to as CZ method). On the other hand, the present invention relates to a method for manufacturing a silicon wafer that can greatly reduce the defect density of the device active region on the surface side where the semiconductor device of the silicon wafer is formed by performing heat treatment.

  With the recent high integration of semiconductor devices, quality requirements for silicon wafers (hereinafter also simply referred to as “wafers”) used as substrates have become severe. In particular, there is a strong demand for reducing the defect density in the device active region of a silicon wafer.

  As a method for reducing such defect density, a technique for preventing the generation of defects in a wafer by heat-treating a silicon wafer in a temperature region of 1050 ° C. or higher in an atmosphere of hydrogen or argon or a mixture thereof (for example, is known) Patent Document 1).

  In recent years, as a technique for easily producing a silicon wafer having a very low defect in the device active region with high productivity, rapid heating / cooling heat treatment (RTP: Rapid Thermal Process, hereinafter simply referred to as RTP) Is known).

  For example, a silicon substrate manufactured by the CZ method is heat-treated at 100% nitrogen, 100% oxygen, or a mixed atmosphere of oxygen and nitrogen with a maximum holding temperature of 1125 ° C. or more and a melting point of silicon or less and a holding time of 5 seconds or more. A silicon substrate having a desired oxygen precipitation characteristic without being controlled by rapidly cooling at a cooling rate of 8 ° C./second or more from the maximum holding temperature without performing control of the oxygen concentration in the silicon substrate manufactured by the CZ method. There is known a technique capable of obtaining the above (for example, Patent Document 2).

  Also, in the pre-anneal / oxidation combined step used for RTP used in wafer processing, a predetermined defect-free region depth can be obtained by exposing the wafer to a controlled temperature, controlled pre-annealing time, and oxidizing atmosphere at atmospheric pressure. A technique capable of obtaining a predetermined target thermal oxide film corresponding to the above is known (for example, Patent Document 3).

  Further, it is cut out from a silicon single crystal ingot grown by the CZ method, and at least at 5 ° C./sec or higher in a non-oxidizing atmosphere using a rapid heating / rapid cooling heat treatment apparatus (hereinafter also referred to as RTP apparatus). Rapid heating to 1100-1300 ° C at a temperature rate, holding for 1-60 seconds, and then irradiating a laser beam to the wafer that has been rapidly cooled at a temperature decrease rate of 5 ° C / sec or more, and only the surface layer region of a predetermined depth from the surface By performing heat treatment at a temperature of 1100 ° C. or more for 0.01 msec or more and 1 sec or less, a DZ layer having no crystal defects is uniformly formed from the surface to a certain depth, and has a steep profile inside the wafer. A technique capable of ensuring and controlling oxygen precipitates with high accuracy is known (for example, Patent Document 4).

JP 2002-231726 A JP 2000-31150 A JP 2000-91259 A JP 2008-28355 A

  However, since the heat treatment technique described in Patent Document 1 has a long heat treatment time, productivity is poor, slip is likely to occur during heat treatment, and oxygen in the device active region diffuses outward during the heat treatment. There is a problem that the oxygen concentration in the device active region is lowered, the pinning force of oxygen is lowered in the heat treatment process in the subsequent semiconductor device formation step, and slip is likely to occur.

  In addition, when oxygen gas is used as the atmosphere as in the heat treatment techniques described in Patent Documents 2 and 3, oxygen in the atmosphere diffuses inward to the wafer surface, so that the concentration of dissolved oxygen in the wafer surface portion of the device active region Will increase. Therefore, since the inner wall oxide film of the void defect is difficult to be dissolved on this surface portion, the void defect may remain without disappearing. In this case, after RTP, it is necessary to perform mirror polishing or the like again in order to remove the surface portion.

  Furthermore, since the heat treatment technique described in Patent Document 4 performs RTP in a non-oxidizing atmosphere, oxygen in the device active region is diffused outward during the heat treatment, so that the oxygen concentration in the device active region decreases, In the heat treatment process in the subsequent semiconductor device formation process, there is a problem that the pinning force of oxygen is reduced and slip is likely to occur.

  The present invention has been made to solve the above technical problem, and it is not necessary to perform mirror polishing again, suppresses a decrease in oxygen concentration in the device active region, and defect density in the device active region. An object of the present invention is to provide a method for manufacturing a silicon wafer capable of greatly reducing the above.

  The method for producing a silicon wafer according to the present invention is a rapid process at a maximum temperature of 1325 ° C. to 1390 ° C. in an oxidizing gas atmosphere with respect to a silicon wafer sliced from a silicon single crystal ingot grown by the Czochralski method. In the inert gas atmosphere with respect to the surface portion of the device active region on the surface side where the semiconductor device of the silicon wafer subjected to the heat treatment is formed, and the step of performing the heating / cooling heat treatment (synonymous with rapid heating / cooling heat treatment) Irradiating a laser beam and performing a laser heat treatment at a maximum temperature not lower than 1200 ° C. and not higher than 1350 ° C.

  The wavelength of the laser beam is preferably 500 nm or more and 15 μm or less.

  The irradiation time in the laser heat treatment is preferably from 0.1 msec to 1 sec.

  According to the present invention, there is no need for mirror polishing or the like again, and there is provided a silicon wafer manufacturing method capable of suppressing a decrease in oxygen concentration in the device active region and greatly reducing the defect density in the device active region. Provided.

It is sectional drawing which shows the outline | summary of an example of the rapid heating / rapid cooling heat processing apparatus used for the manufacturing method of the silicon wafer concerning this embodiment. It is a conceptual diagram which shows the outline | summary of an example of the laser heat processing apparatus used for the manufacturing method of the silicon wafer concerning this embodiment. It is a conceptual diagram for demonstrating an example of the heat processing sequence in RTP applied to this embodiment. It is a wafer sectional view for explaining a defect density reduction mechanism in a device active region concerning this embodiment. The evaluation result figure of the LSTD density regarding the annealed wafer obtained on each condition in Test 1 is shown.

Hereinafter, a method for producing a silicon wafer according to the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a cross-sectional view showing an outline of an example of a rapid heating / cooling heat treatment apparatus used in the method for producing a silicon wafer according to the present embodiment.

  The RTP apparatus 10 shown in FIG. 1 contains a reaction tube 20 for accommodating a wafer W and performing heat treatment, a wafer holding unit 30 provided in the reaction tube 20 for holding the wafer W, and heating for heating the wafer W. Unit 40. In the state where the wafer W is held by the wafer holder 30, the first space 20a, which is a space surrounded by the inner wall of the reaction tube 20 and the surface W1 side where the semiconductor device of the wafer W is formed, and the reaction tube A second space 20b that is a space surrounded by the inner wall 20 and the back surface W2 side of the wafer W is formed.

The reaction tube 20 has a first supply port 22 for supplying the first atmospheric gas F _A into the first space 20a and a second supply port for supplying the second atmospheric gas F _B into the second space 20b. 24, a first outlet 26 for discharging the first atmosphere gas F _a which is supplied from the first space 20a, a second discharging the second ambient gas F _B which is supplied from the second space 20b And a discharge port 28. The reaction tube 20 is made of, for example, quartz.

  The wafer holding unit 30 includes a susceptor 32 that directly holds the outer peripheral portion of the back surface W2 of the wafer W in a ring shape, and a rotating body 34 that holds the susceptor 32 and rotates the susceptor 32 in the radial direction. The susceptor 32 and the rotating body 34 are made of, for example, SiC.

  The heating unit 40 is disposed outside the reaction tube 20 above the wafer holding unit 30 and heats the wafer W from the surface W1 side. The heating unit 40 is composed of, for example, a plurality of halogen lamps 50.

  FIG. 2 is a conceptual diagram showing an outline of an example of a laser heat treatment apparatus used in the method for manufacturing a silicon wafer according to the present embodiment.

  A laser heat treatment apparatus 60 shown in FIG. 2 includes a laser oscillator 62 that oscillates a laser La irradiated to a wafer W, a modulator 64 that modulates the oscillated laser La, and a reflecting mirror that reflects the modulated laser La in the wafer W direction. 66 and an irradiation lens 72 that irradiates the surface W1 of the wafer W held by the stage 70 installed in the chamber 68 with the reflected laser La. The chamber 68 includes a supply port 74 for supplying the atmospheric gas Fc and a discharge port 76 for discharging the atmospheric gas Fc. The stage 70 is connected to a moving means (not shown) that can move vertically and horizontally in the direction of the surface W1 of the wafer W, and can irradiate the entire surface W1 of the wafer W with the laser La.

  Next, the silicon wafer manufacturing method according to the present embodiment will be described more specifically.

  In the method for producing a silicon wafer according to the present embodiment, first, RTP is performed on a silicon wafer obtained by processing a slice or the like from a silicon single crystal ingot grown by the CZ method.

  The silicon single crystal ingot is grown by the CZ method by a known method.

  Specifically, the silicon single crystal ingot is grown by heating polycrystalline silicon filled in a quartz crucible to form a silicon melt, and bringing the seed crystal into contact with the liquid surface of the silicon melt. The seed crystal is pulled up while rotating and is expanded to a desired diameter to form a straight body portion, and then separated from the silicon melt.

  Next, the silicon single crystal ingot thus obtained is processed into a silicon wafer by processing such as slicing by a known method.

  Specifically, after a silicon single crystal ingot is sliced into a wafer shape with an inner peripheral blade or a wire saw, the outer peripheral portion is chamfered, lapped, etched, mirror polished, and the like.

  Next, RTP is performed on the mirror-polished silicon wafer thus obtained using an RTP apparatus 10 as shown in FIG.

  FIG. 3 is a conceptual diagram for explaining an example of a heat treatment sequence in RTP applied to the present embodiment.

The RTP applied in the present embodiment is a first space in which at least the surface W1 side of the wafer W on which the semiconductor device is formed is in contact with a mirror-polished silicon wafer using an RTP apparatus 10 as shown in FIG. an oxidizing gas is supplied as the first atmospheric gas F _a into 20a, carried out at the highest temperature of 1390 ° C. or less 1325 ° C. or higher by heat treatment sequence as shown in Figure 3.

  More specifically, a mirror-polished wafer W is placed in the reaction tube 20 held at a temperature T0 (for example, 600 ° C.), and at least the first space where the surface W1 side on which the semiconductor device of the wafer W is formed contacts. The oxidizing gas is supplied into 20a and rapidly heated from a temperature T0 (° C.) to a maximum temperature T1 (° C.) of 1325 ° C. to 1390 ° C. at a predetermined temperature increase rate ΔTu (° C./sec), A predetermined time t (second) is held at the highest temperature T1 (° C.), and then a predetermined temperature from the highest temperature T1 (° C.) to a temperature at which the wafer W is taken out of the reaction tube 20 (for example, temperature T0 (° C.)). Rapid cooling is performed at a temperature drop rate ΔTd (° C./second).

  Next, an inert gas is applied to the surface portion of the device active region on the surface W1 side on which the semiconductor device is formed, using a laser heat treatment apparatus 60 as shown in FIG. Laser heat treatment is performed in the atmosphere (preferably argon) at a maximum temperature of 1200 ° C. or higher and 1350 ° C. or lower by irradiation with laser light.

  Since the silicon wafer manufacturing method according to the present invention includes the above-described means, it is not necessary to perform mirror polishing again, suppresses a decrease in oxygen concentration in the device active region, and the device active region. The defect density can be greatly reduced.

Hereinafter, this reason will be discussed with reference to the accompanying drawings.
FIG. 4 is a wafer cross-sectional view for explaining a defect density reduction mechanism in the device active region according to the present embodiment.

First, in the RTP, when an oxidizing gas is supplied to the surface W1 side of the wafer W (FIG. 4A), oxygen in the atmosphere diffuses inward into the wafer W, so that the surface W1 of the wafer W is oxidized. As the film (SiO ₂ ) is formed, the solid solution oxygen concentration of the surface portion Da of the device active region D increases. Although the inner wall oxide film of void defects existing on the surface portion Da may be dissolved depending on the depth and size thereof, the solid solution oxygen concentration at this depth (surface portion Da) is high. In many cases, it does not dissolve and remains in the void defect. On the other hand, in the surface layer portion Db of the device active region D, the solid solution oxygen concentration does not increase due to the inward diffusion of oxygen, or the oxide film disappears before the solid solution oxygen concentration increases. The inner wall oxide film of the void defect existing inside is dissolved (FIG. 4B).

  Therefore, in the surface layer portion Db, interstitial silicon (hereinafter referred to as i-Si) generated from the interface between the oxide film and the silicon fills the inside of the void defect in which the inner wall oxide film is dissolved, and thus the void defect can be eliminated. it can. On the other hand, since the inner wall oxide film remains in the void defect at the surface portion Da, the i-Si cannot enter the void defect. As a result, the void defect remains at the surface portion Da. (FIG. 4C).

  Therefore, after performing the RTP, a laser heat treatment is performed on the surface portion Da where void defects remain in an inert gas atmosphere (preferably argon) (FIG. 4D). As a result, the oxide film on the surface W1 is dissolved, and the inner wall oxide film of the void defect remaining on the surface portion Da is dissolved, whereby the shape of the void defect is changed, and i newly generated by the laser heat treatment is further generated. Since -Si fills the inside of the void defect, the void defect remaining on the surface portion Da can be eliminated (FIG. 4E). Further, since the inner wall oxide film in the void defect of the surface portion Da is reduced by RTP, the void defect can be eliminated more efficiently by this laser heat treatment. Further, since the laser heat treatment is a heat treatment for a very short time, there is almost no oxygen diffusion, and the oxygen diffused inward by the RTP can be maintained almost as it is. Further, a wide DZ layer of the order of 100 μm formed in the oxygen atmosphere RTP depends on the point defect concentration such as interstitial Si and vacancies, but the laser heat treatment according to the present invention is heating only the surface portion Da, There is an advantage that only a desired depth region where the void defect is desired to be eliminated can be heat-treated without affecting the characteristics to a region deeper than Da.

The oxidizing gas referred to in the present invention includes a mixed gas having an oxygen partial pressure of 20% or more and less than 100% in addition to 100% oxygen gas. The gas other than oxygen gas in the mixed gas is preferably an inert gas (preferably argon).
When the oxygen partial pressure is less than 20%, the amount of i-Si formed in the wafer W decreases, so it is difficult to increase the annihilation power of void defects in the surface layer portion Db of the device active region D. .

  The device active region in the present invention refers to a region from the surface W1 where the semiconductor device of the wafer W is formed to a depth of 10 μm, and the surface portion refers to a region from the surface W1 to a depth of 1 μm. That means.

When a non-oxidizing gas (for example, 100% argon gas or 100% hydrogen gas) is used in the RTP, oxygen in the device active region D diffuses outward, so that the oxygen concentration in the device active region D decreases. Therefore, it is not preferable.
Further, when an oxidizing gas is used in the laser heat treatment, an oxide film is formed on the surface W1 of the wafer W during the heat treatment, and oxygen is diffused inward into the surface portion Da. It becomes difficult for the inner wall oxide film of the void defect of the portion Da to be dissolved. Therefore, even if the laser heat treatment is performed, it is difficult to eliminate the void defects on the surface portion Da, which is not preferable.

  When the maximum temperature reached in the RTP is less than 1325 ° C., it is difficult to greatly reduce the defect density, and when the temperature exceeds 1390 ° C., there is a problem in durability as an RTP device. As a result, the deterioration of the device characteristics of the heat-treated silicon wafer is deteriorated.

  When the maximum temperature reached in the laser heat treatment is less than 1200 ° C., it is difficult to greatly reduce the defect density. When the temperature exceeds 1350 ° C., the temperature of the surface portion Da heated in the laser heat treatment is Near melting point. Further, since the surface layer portion Db is not heated, the surface portion Da grows solidly along the surface layer portion Db. At this time, dislocations such as stacking faults may occur at the interface between the two layers.

  When the RTP apparatus 10 as shown in FIG. 1 is used, the above-described temperature is measured by a laser heat treatment as shown in FIG. 2 by a radiation thermometer (not shown) installed below the wafer holder 30. When the apparatus 60 is used, each can be measured by a known method using a radiation thermometer (not shown) installed above the surface W1 of the wafer W. In addition, when measuring several point temperature to the radial direction of the wafer W with the said radiation thermometer, it can also be set as the average temperature.

In the RTP, when using the RTP apparatus 10 as shown in FIG. 1, the second atmosphere gas supplied to the second space 20b of the rear surface W2 side of the wafer W is in contact F _B may be an oxidizing gas, an inert gas However, it may not be supplied.

In the RTP, the holding time (t) at the maximum temperature T1 (° C.) is preferably 1 second or longer and 60 seconds or shorter from the viewpoint of productivity.
When the holding time (t) is less than 1 second, the holding time (t) is short, so that the defect density may not be reduced in the device active region, which is not preferable.

  The temperature increase rate ΔTu (° C./second) is preferably 10 ° C./second or more and 150 ° C./second or less from the viewpoint of productivity and prevention of occurrence of slip dislocation. Further, the temperature drop rate ΔTd (° C./second) is preferably 10 ° C./second or more and 150 ° C./second or less from the same viewpoint.

  The wavelength of the laser beam is appropriately selected according to the depth to be heated. However, when the wavelength is long and the penetration depth into the wafer is large, it is difficult to efficiently heat the surface portion of the wafer. From the above viewpoint, the wavelength of the laser beam is preferably 500 nm or more and 15 μm or less.

The irradiation time in the laser heat treatment is preferably from 0.1 msec to 1 sec.
When the irradiation time is less than 0.1 msec, since the irradiation time is short, the defect density may not be reduced in the device active region, which is not preferable. When the irradiation time exceeds 1 sec, the stress on the wafer increases and causes slip dislocation, which is not preferable.

EXAMPLES Hereinafter, although this invention is demonstrated further more concretely based on an Example, this invention is not limitedly interpreted by the following Example.
(Test 1)
A silicon single crystal ingot having a region in which vacancy-type point defects exist dominantly by controlling v / G (v: pulling speed, G: temperature gradient in the pulling axis direction in the single crystal) by the CZ method. A wafer having a mirror polished surface (diameter 300 mm, thickness 775 mm, oxygen concentration 1.1 × 10 ¹⁸ atoms / cm) obtained by growing and then slicing from a region where vacancy-type point defects exist predominantly ³ (old-ASTM terms, the same applies hereinafter)), and by using the RTP apparatus 10 as shown in FIG. 1, a first atmospheric gas _{F a,} second atmospheric gas _{F B} together, a 100% oxygen gas The holding time t (second) is 15 seconds, the temperature T0 is 600 ° C., the temperature increase rate ΔTu is 75 ° C./second, the temperature decrease rate ΔTd is 25 ° C./second, and the maximum temperature T1 is 1300 ° C., 1325 ° C. Varies with 1350 ° C and 1390 ° C RTP was performed for each.

  For each wafer obtained under the above conditions, a laser heat treatment apparatus 60 as shown in FIG. 2 is used for each condition, a laser wavelength of 532 nm (laser penetration length: about 1 μm), a moving speed of 150 mm / sec, Processing time: At about 0.7 msec, the laser output is changed, and the maximum temperature reached is 1100 ° C., 1200 ° C., 1250 ° C., 1300 ° C., 1350 ° C., 1390 ° C. Produced.

For each annealed wafer obtained in the above test, the LSTD of the device active region was measured, and the defect density was calculated (hereinafter referred to as LSTD density). The measurement of this LSTD is performed using the LSTD (Laser
Using a Scattering Tomography Defect scanner (MO-601 manufactured by Raytex Co., Ltd.), evaluation was performed at a wavelength of 680 nm (penetration length: 5 μm).

FIG. 5 shows the evaluation results of the LSTD density of the annealed wafer obtained in this test.
As shown in FIG. 5, when the maximum temperature reached in RTP is 1325 ° C. or higher and 1390 ° C. or lower and the maximum temperature reached in laser heat treatment is 1200 ° C. or higher and 1350 ° C. or lower, the LSTD density tends to be greatly reduced. Admitted. Note that the large deterioration of the LSTD density at 1390 ° C. in the laser heat treatment is considered to be due to the detection of stacking faults and the like that occurred at the interface between the laser penetration length range of 1 μm depth and its lower layer.

(Test 2)
The ambient gas in the test 1 of the RTP first atmospheric gas _{F A,} second atmospheric gas _{F B} together, as an argon gas, also, 1350 ° C. The maximum temperature RTP, the maximum temperature of the laser heat treatment as 1300 ° C. Other than that, an annealed wafer was produced under the same conditions as in Test 1.

(Test 3)
Annealed wafer under the same conditions as in Test 1 except that the atmosphere gas in the laser heat treatment of Test 1 is 100% oxygen gas, the maximum temperature of RTP is 1350 ° C., the maximum temperature of laser heat treatment is 1300 ° C. Was made.

With respect to each of the annealed wafers obtained in Tests 2 and 3 above, LSTD measurement was performed in the same manner as in Test 1, and the LSTD density was calculated.
Furthermore, the annealed wafer obtained in Tests 2 and 3 and the annealed wafer of Test 1 obtained under the same heat treatment conditions as in Tests 2 and 3 (the highest ultimate temperature of RTP 1350 ° C. and the highest ultimate temperature of laser heat treatment 1300 ° C.) The average oxygen concentration in the range of 1 μm depth from the surface was measured by Secondary Ion Mass Spectrometry (SIMS).
Table 1 shows the measurement results of the LSTD density and the oxygen concentration of the surface W1 of the device active region D in this test.

  As shown in Table 1, it is recognized that the annealed wafer (Test 2) in which RTP is performed in an argon atmosphere has a low effect of reducing the LSTD density, and the oxygen concentration of the surface W1 of the device active region D is greatly reduced. It was. In addition, in the annealed wafer (Test 3) performed in an oxidizing atmosphere in the laser heat treatment, it was confirmed that the effect of reducing the LSTD density was low.

  DESCRIPTION OF SYMBOLS 10 RTP apparatus 20 Reaction tube 30 Wafer holding part 32 Susceptor 34 Rotating body 40 Heating part 50 Halogen lamp 60 Laser heat treatment apparatus 62 Laser oscillator 64 Modulator 66 Reflection mirror 68 Chamber 70 Stage 72 Irradiation lens 74 Supply port 76 Ejection port La Laser light

Claims (3)

A step of performing a rapid heating / cooling heat treatment on a silicon wafer sliced from a silicon single crystal ingot grown by the Czochralski method in an oxidizing gas atmosphere at a maximum temperature of 1325 ° C. or higher and 1390 ° C. or lower;
The surface temperature of the device active region on the surface side where the semiconductor device of the silicon wafer subjected to the heat treatment is formed is irradiated with laser light in an inert gas atmosphere, and the highest temperature reached from 1200 ° C. to 1350 ° C. Performing a laser heat treatment at
A method for producing a silicon wafer, comprising:   2. The method for producing a silicon wafer according to claim 1, wherein the wavelength of the laser beam is 500 nm or more and 15 [mu] m or less. The method for producing a silicon wafer according to claim 1 or 2, wherein an irradiation time in the laser heat treatment is 0.1 msec or more and 1 sec or less.

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