JP2012199390A - Silicon wafer heat treatment method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a silicon wafer heat treatment method which can considerably reduce void defect of a surface layer part of a wafer, and improve oxygen concentration of the surface layer part, suppress deterioration of surface roughness of a polished surface, and improve productivity in an RTP.SOLUTION: The silicon wafer heat treatment method includes the step of terminating by hydrogen the silicon atom of a surface of a silicon wafer in which the surface having at least a semiconductor device formed thereon has been subjected to mirror polishing; the step of terminating by fluorine the silicon atom of the surface of the hydrogen-terminated silicon wafer; and the step of performing a rapid temperature increase/decrease heat treatment in which after the temperature of the hydrogen- and fluorine-terminated silicon wafer is rapidly increased and held in a temperature range of not less than 1300°C nor more than 1400°C in an inert gas atmosphere, the temperature thereof is further held by changing the inert gas atmosphere to an oxidizing gas atmosphere in the temperature range, and is then rapidly decreased.

Description

  The present invention relates to a heat treatment method for a silicon wafer in which heat treatment is performed on a silicon wafer (hereinafter also simply referred to as a wafer).

  Silicon wafers used as semiconductor device forming substrates reduce void defects such as COP (Crystal Originated Particles) and LSTD (Laser Scattering Tomography Defects) in the vicinity of the surface of the wafer that will be the device active region (hereinafter referred to as the surface layer portion). There is a need for efforts to make them defect-free.

  In recent years, as a method of manufacturing such a silicon wafer with high productivity, at least a surface on which a semiconductor device is formed is mirror-polished (hereinafter, the mirror-polished surface is also referred to as a polished surface). A technique for performing a thermal treatment (Rapid Thermal Process: hereinafter also simply referred to as RTP) is known.

  As such a technique, Patent Document 1 discloses that an oxygen-containing gas atmosphere (inert gas atmosphere as referred to in the present invention) that is mainly argon or helium at a temperature exceeding about 1175 ° C. under an oxygen partial pressure of less than about 5000 ppma, A heat treatment method is disclosed in which the wafer is heated for less than 60 seconds.

  However, since the method described in Patent Document 1 performs RTP in an inert gas atmosphere such as argon or helium, it is possible to greatly reduce void defects in the surface layer portion of the wafer. When heat treatment is performed in an atmosphere, oxygen is diffused out from the surface layer portion of the wafer, so that the oxygen concentration in the surface layer portion is lowered, and the pinning power of oxygen is reduced in the heat treatment process in the subsequent semiconductor device formation step. There is a problem that slip dislocation tends to occur. This is a problem that occurs more frequently as the temperature of the heat treatment process in the semiconductor device formation process increases.

  For such a problem, Patent Document 2 discloses that oxygen is diffused inward into the surface layer portion of the semiconductor wafer by performing a heat treatment in an oxidizing gas atmosphere, and this is cooled and solidified. A method for increasing the strength of the surface layer is disclosed in which the surface layer portion becomes a high oxygen concentration region.

However, when RTP is performed using an oxidizing gas as an atmosphere, oxygen is diffused inward into the surface layer portion of the wafer, and the oxygen concentration in the surface layer portion becomes high. Therefore, since the inner wall oxide film of the void defect existing in the surface layer portion is hardly dissolved, there is a problem that it becomes difficult to eliminate the void defect in the surface layer portion.
Furthermore, when the heat treatment is performed by supplying an oxidizing gas at a high temperature (for example, 1000 ° C. or higher), the polished surface of the wafer is etched by oxygen in the oxidizing gas, so the surface of the polished surface of the wafer There is also a problem that the roughness deteriorates.

  To deal with such a problem, Patent Document 3 discloses that in a rare gas atmosphere, the temperature is rapidly raised to a first temperature not lower than 1300 ° C. and not higher than the melting point of silicon at a first temperature rising rate, and the first temperature is maintained. Thereafter, the temperature is rapidly lowered to a second temperature of 400 ° C. or higher and 800 ° C. or lower at a first temperature drop rate, and then oxygen gas is supplied from the rare gas atmosphere to 20 vol. % Or more and 100 vol. After switching to an oxygen-containing atmosphere containing not more than 50%, the temperature is rapidly raised from the second temperature to a third temperature not lower than 1250 ° C. and not higher than the melting point of silicon at the second rate of temperature rise, and maintained at the third temperature. Then, a heat treatment method is disclosed in which the temperature is rapidly lowered from the third temperature at the second temperature drop rate.

  In Patent Document 4, a natural oxide film on a wafer surface is removed by hydrofluoric acid treatment, and then heat treatment is performed using an RTP apparatus in a mixed gas atmosphere of argon containing 100% hydrogen or 10% or more of hydrogen. Thus, a heat treatment method is disclosed in which the microroughness of the wafer surface is reduced and void defects present on the wafer surface can be removed.

JP-T-2001-509319 JP 2010-129918 A International Publication No. 2011/013280 Pamphlet JP 2000-91342 A

  However, in the method described in Patent Document 3, when switching from a rare gas atmosphere to an oxygen-containing atmosphere in order to suppress the deterioration of the surface roughness of the polished surface, the temperature is rapidly lowered from 400 ° C. to 800 ° C., and the atmosphere is switched. After that, the temperature must be further rapidly raised to 1250 ° C. or more and below the melting point of silicon, productivity is lowered, and rapid temperature rise / fall is performed twice in one RTP. There is also a problem that slip is likely to occur.

In the method described in Patent Document 4, hydrogen is terminated at silicon atoms on the wafer surface by the hydrofluoric acid treatment, so that a natural oxide film is hardly formed on the surface. Therefore, even if the RTP is performed, deterioration of the surface roughness on the wafer surface can be suppressed.
However, in order to eliminate void defects existing in the surface layer portion of the wafer by RTP, a high-temperature heat treatment of at least 1000 ° C. is required in the inert gas atmosphere. The hydrogen atoms terminated at the end are easily broken, and the silicon atoms are easily exposed on the wafer surface. The exposed silicon atoms are unstable and are easily bonded to other atoms.

Therefore, for example, when other reactive gas (such as nitrogen) is present in the atmosphere, it reacts and bonds with the exposed silicon atoms, and the bond is repeatedly etched by the atmosphere. Therefore, there is a problem that the surface shape of the wafer changes and the surface roughness deteriorates.
The above problem becomes more conspicuous as the heat treatment temperature in RTP becomes higher. On the other hand, the higher the heat treatment temperature, the higher the void defect extinction power of the surface layer portion of the wafer. .

  The present invention has been made in view of the above circumstances, and can greatly reduce void defects in the surface layer portion of the wafer, improve the oxygen concentration in the surface layer portion, and improve the surface roughness of the polished surface. It is an object of the present invention to provide a silicon wafer heat treatment method capable of suppressing deterioration and improving RTP productivity.

  The silicon wafer heat treatment method according to the present invention includes a step of terminating silicon atoms on the surface of a silicon wafer having at least a mirror-polished surface on which a semiconductor device is formed with hydrogen, and the silicon wafer terminated with hydrogen. A step of terminating silicon atoms on the surface with fluorine, and a temperature of the silicon wafer terminated with hydrogen and fluorine after being rapidly heated and maintained in a temperature range of 1300 ° C. to 1400 ° C. in an inert gas atmosphere, And a step of switching the inert gas atmosphere to an oxidizing gas atmosphere within a range and further holding and performing a rapid heating / cooling heat treatment for rapidly cooling.

  The step of terminating with hydrogen is a step of cleaning the silicon wafer with a hydrogen fluoride-based solution or a hydrogen peroxide-based solution, and the step of terminating with silicon is performed at 900 ° C. in a fluorine-based gas atmosphere. The heat treatment is preferably performed in a temperature range of 1250 ° C. or lower.

  In the silicon wafer heat treatment method according to the present invention, at least a surface on which a semiconductor device is formed is mirror-polished on a silicon wafer using a hydrogen fluoride solution or a hydrogen peroxide solution, and silicon atoms on the surface are replaced with hydrogen. And a step of rapidly raising the silicon wafer terminated with hydrogen to a first temperature range of 900 ° C. or higher and 1250 ° C. or lower in a fluorine-based gas atmosphere, and terminating silicon atoms on the surface with fluorine. In succession to the step of terminating with fluorine, the fluorine-based gas atmosphere is switched to an inert gas atmosphere in the first temperature range, and the temperature is rapidly raised to a second temperature range of 1300 ° C. to 1400 ° C. After the holding, the inert gas atmosphere is switched to the oxidizing gas atmosphere in the second temperature range and further held, and the temperature is rapidly increased. And performing heat treatment, characterized in that it comprises a.

  According to the present invention, void defects in the surface layer portion of the wafer can be greatly reduced, the oxygen concentration in the surface layer portion can be improved, deterioration of the surface roughness of the polished surface can be suppressed, and production in RTP A method for heat treatment of a silicon wafer capable of improving the performance is provided.

It is a cross-sectional conceptual diagram which shows an example of the RTP apparatus applied to the heat processing method of the silicon wafer concerning this invention. It is a conceptual diagram which shows an example of the heat processing sequence in RTP applied to the heat processing method of the silicon wafer concerning this invention. It is a conceptual diagram which shows an example of the heat processing sequence in RTP for demonstrating the preferable aspect in the heat processing method of the silicon wafer which concerns on this invention. It is a conceptual diagram which shows an example of the heat processing sequence in RTP for demonstrating the more preferable aspect in the heat processing method of the silicon wafer which concerns on this invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
The silicon wafer heat treatment method according to the present invention includes a step of terminating silicon atoms on the surface of a silicon wafer having at least a mirror-polished surface on which a semiconductor device is formed with hydrogen, and the silicon wafer terminated with hydrogen. A step of terminating silicon atoms on the surface with fluorine, and a temperature of the silicon wafer terminated with hydrogen and fluorine after being rapidly heated and maintained in a temperature range of 1300 ° C. to 1400 ° C. in an inert gas atmosphere, Switching the inert gas atmosphere to an oxidizing gas atmosphere within a range and further holding the same, and performing a rapid temperature raising and lowering heat treatment for rapidly lowering the temperature.

As described above, by terminating silicon atoms on at least the polished surface of the silicon wafer on which the semiconductor device is formed with hydrogen and fluorine, the bonding force with the silicon atoms can be increased more than when only hydrogen is terminated. . Therefore, the bond is not easily broken even in a high temperature of 1300 ° C. or higher and 1400 ° C. or lower where the void defect extinction power of the surface layer portion of the wafer is high.
Therefore, even if other reactive gases (such as nitrogen) are present in the atmosphere, bonding between silicon atoms and the reactive gas can be suppressed, so that deterioration of the surface roughness of the polished surface of the wafer is suppressed. can do.

Furthermore, when switching from an inert gas atmosphere to an oxidizing gas atmosphere, as shown in Patent Document 3, even when switching is performed without rapidly lowering the temperature from 400 ° C. to 800 ° C., the surface roughness of the polished surface is increased. The deterioration of the thickness can be suppressed. Therefore, when switching to an oxidizing gas atmosphere, it is not necessary to rapidly lower the temperature to the above temperature, and switching at a high temperature of 1300 ° C. or higher and 1400 ° C. or lower is sufficient, so that productivity in RTP can be improved.
In addition, since RTP is performed in an oxidizing gas atmosphere, the oxygen concentration in the surface layer portion can also be improved.

The RTP is preferably maintained in a temperature range of 1300 ° C. or higher and 1400 ° C. or lower.
When the temperature range is less than 1300 ° C., there is a problem that the annihilation power of void defects is reduced. When the temperature range exceeds 1400 ° C., the temperature range is close to the melting point of silicon, which may unfavorably soften or melt the silicon wafer.
The temperature range is more preferably 1300 ° C. or higher and 1380 ° C. or lower from the viewpoint of the device life as an RTP device (described later) used for performing the RTP.

As the inert gas, a rare gas such as helium gas (He), argon gas (Ar), or xenon gas (Xe) is preferably used. Preferably, the inert gas is argon gas (Ar).
As the oxidizing gas, oxygen gas (O ₂ ) or a mixed gas of oxygen gas (O ₂ ) and an inert gas (preferably argon gas (Ar)) is preferably used.

The silicon wafer on which at least the surface on which the semiconductor device is formed is mirror-polished is cut out from a silicon single crystal ingot grown by the Czochralski method (hereinafter referred to as CZ method).
The silicon single crystal ingot is grown by the CZ method by a known method.
Specifically, a silicon single crystal ingot heats a silicon raw material filled in a quartz crucible to form a silicon melt, contacts the seed crystal with the liquid surface of the silicon melt, and rotates the seed crystal and the quartz crucible. The seed crystal can be pulled up to grow the neck portion, the crown portion, and the straight body portion on the seed crystal, and then separated from the silicon melt.

Next, the grown silicon single crystal ingot is cut out by a known method and processed into a silicon wafer in which at least the surface on which the semiconductor device is formed is mirror-polished.
Specifically, a straight body portion of a silicon single crystal ingot is cut into a wafer shape with an inner peripheral blade or a wire saw, and processing such as chamfering, lapping, etching, and mirror polishing of the outer peripheral portion is performed.

The step of terminating with hydrogen is a step of cleaning the silicon wafer with a hydrogen fluoride-based solution or a hydrogen peroxide-based solution, and the step of terminating with silicon is performed at 900 ° C. in a fluorine-based gas atmosphere. The heat treatment is preferably performed in a temperature range of 1250 ° C. or lower.
With such a configuration, hydrogen and fluorine can be effectively terminated to silicon atoms on the surface of the silicon wafer.

  If the temperature range of the step of terminating with fluorine is less than 900 ° C., it may be difficult to terminate fluorine on silicon atoms. When the temperature range of the said process exceeds 1250 degreeC, the grinding | polishing surface of a wafer may be etched by fluorine-type gas, and surface roughness may deteriorate.

The hydrogen fluoride-based solution mainly includes a hydrofluoric acid solution (HF) and a buffered HF solution (NH ₄ F + HF). The hydrogen peroxide-based solution mainly includes a mixed solution of hydrogen peroxide solution (H ₂ O ₂ ), hydrogen sulfide (H ₂ SO ₄ ), and hydrogen peroxide solution (H ₂ O ₂ ). The fluorine-based gas mainly includes tetrafluoromethane (CF ₄ ), sulfur hexafluoride (SF ₆ ), and nitrogen trifluoride (NF ₃ ).

FIG. 1 is a conceptual cross-sectional view showing an example of an RTP apparatus applied to a silicon wafer heat treatment method according to the present invention.
An RTP apparatus 10 shown in FIG. 1 contains a reaction chamber 20 for accommodating a wafer W and performing a heat treatment, a wafer holding unit 30 provided in the reaction chamber 20 for holding the wafer W, and heating for heating the wafer W. Unit 40. In a state where the wafer W is held by the wafer holder 30, the first space 20 a that is a space surrounded by the inner wall of the reaction chamber 20 and the surface (device formation surface) W 1 side of the wafer W, and the inner wall of the reaction chamber 20 And a second space 20b that is a space surrounded by the back surface W2 side of the wafer W facing the front surface W1 side.

The reaction chamber 20 has a supply port 22 for supplying atmospheric gas F _A (solid arrow) into the first space 20a and the second space 20b, and the supplied atmospheric gas F _A from the first space 20a and the second space 20b. And a discharge port 26 for discharging. The reaction chamber 20 is made of, for example, quartz.

  The wafer holding unit 30 includes a susceptor 32 that 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 about the center of the wafer W. The susceptor 32 and the rotating body 34 are made of, for example, SiC.

  The heating unit 40 is disposed outside the reaction chamber 20 above the front surface W1 and below the back surface W2 of the wafer W held by the wafer holding unit 30, and heats the wafer W from both sides. The heating unit 40 is composed of, for example, a plurality of halogen lamps 50.

When RTP is performed using the RTP apparatus 10 shown in FIG. 1, the wafer W is introduced into the reaction chamber 20 from a wafer introduction port (not shown) provided in the reaction chamber 20, and the outer periphery of the back surface W <b> 2 of the wafer W is introduced. part was held on the susceptor 32 of the wafer holder 30 in a ring shape, it supplies the atmospheric gas F _a, while rotating the wafer W, carried out by heating the wafer W by the heating unit 40.

FIG. 2 is a conceptual diagram showing an example of a heat treatment sequence in RTP applied to the silicon wafer heat treatment method according to the present invention.
In the heat treatment sequence used for the RTP, as shown in FIG. 2, at least a semiconductor device is formed in the reaction chamber 20 of the RTP apparatus 10 as shown in FIG. 1 held at a temperature T0 (for example, 500 ° C.). The surface W1 side is mirror-polished, and a wafer W in which silicon atoms on the surface W1 are terminated with hydrogen and fluorine is installed, and an inert gas is supplied into the first space 20a and the second space 20b.

Next, the temperature was rapidly increased from the temperature T0 (° C.) to a temperature range of 1300 ° C. to 1400 ° C. (temperature T1 (° C.)) at a temperature increase rate ΔTu (° C./second) and held for a predetermined time t1 (second). Thereafter, the inert gas is switched to an oxidizing gas within a temperature T1 (° C.) range, and the oxidizing gas is supplied into the first space 20a and the second space 20b. Further, a predetermined time t2 (seconds). After the holding, for example, the temperature is rapidly decreased to a temperature T0 (° C.) at a temperature decrease rate ΔTd (° C./second).
The temperatures T0 and T1 were measured by a radiation thermometer (not shown) installed below the wafer holder 30 when the wafer W was installed in the reaction chamber 20 of the RTP apparatus 10 as shown in FIG. It is the surface temperature of the wafer W (the average temperature when a plurality of radiation thermometers are arranged in the radial direction of the wafer W).

  The step of terminating with fluorine is an apparatus other than the RTP apparatus (for example, a vertical heat treatment apparatus that performs heat treatment using a vertical boat) before the RTP, and a heat treatment sequence as shown in FIG. The system gas and the temperature T1 (° C.) may be separately performed in a temperature range of 900 ° C. to 1250 ° C. In addition, the heat treatment sequence as shown in FIG. 2 is different from or the same as the RTP apparatus (the atmosphere is a fluorine-based gas, and the temperature T1 (° C.) is a temperature range from 900 ° C. to 1250 ° C.) You may go by.

More preferably, the step of terminating with fluorine is preferably performed in the same RTP apparatus and simultaneously with the RTP (introducing a step of terminating with fluorine during the heat treatment sequence as shown in FIG. 2).
This preferred embodiment will now be described.

  In a preferred embodiment of the heat treatment method for a silicon wafer according to the present invention, a silicon wafer on which at least a surface on which a semiconductor device is formed is mirror-polished is applied to a hydrogen fluoride solution or a hydrogen peroxide solution, and silicon atoms on the surface are hydrogenated. And a step of rapidly raising the temperature of the silicon wafer terminated with hydrogen to a first temperature range of 900 ° C. or higher and 1250 ° C. or lower in a fluorine-based gas atmosphere, and terminating silicon atoms on the surface with fluorine. In succession to the step of terminating with fluorine, the fluorine-based gas atmosphere is switched to an inert gas atmosphere in the first temperature range, and the temperature is rapidly raised to a second temperature range of 1300 ° C. to 1400 ° C. Then, the inert gas atmosphere is switched to an oxidizing gas atmosphere in the second temperature range and further maintained, And performing rapid lifting thermal processing of temperature, characterized in that it comprises a.

That is, when performing the RTP, at the time of rapid temperature increase, after performing a heat treatment in a fluorine-based gas atmosphere to terminate silicon atoms with fluorine, continuously, the fluorine-based gas atmosphere is further changed to an inert gas atmosphere. Is performed by switching to an oxidizing gas atmosphere. Since other steps are the same as those described above, description thereof is omitted.
By adopting such a method, one heat treatment step for terminating the fluorine can be reduced, so that productivity can be improved and costs can be reduced.

FIG. 3 is a conceptual diagram showing an example of a heat treatment sequence in RTP for explaining a preferred embodiment in the heat treatment method for a silicon wafer according to the present invention.
In the heat treatment sequence shown in FIG. 3, at least the surface W1 side on which the semiconductor device is formed in the reaction chamber 20 of the RTP apparatus 10 shown in FIG. 1 held at the temperature T0 (for example, 500 ° C.) is mirror-polished, Then, a wafer W in which silicon atoms on the surface W1 are terminated with hydrogen is installed, and a fluorine-based gas is supplied into the first space 20a and the second space 20b.
Next, the temperature is rapidly raised from a temperature T0 (° C.) to a first temperature range of 900 ° C. or more and 1250 ° C. or less (temperature T _M (° C.)) at a rate of temperature rise ΔTu (° C./sec), whereby fluorine is removed. Terminate (fluorine termination process). Then, continuously, the fluorine-based gas atmosphere is switched to an inert gas atmosphere within the first temperature range (temperature T _M (° C.)) and supplied into the first space 20a and the second space 20b. .
Next, from the first temperature range (temperature T _M (° C.)) to a second temperature range (temperature T 1 (° C.)) of 1300 ° C. or more and 1400 ° C. or less, a rapid temperature increase rate ΔTu (° C./second). After the temperature is raised and held for a predetermined time t1 (seconds), the inert gas is switched to the oxidizing gas in the second temperature range (temperature T1 (° C.)), and the first space 20a and the second space 20b. Then, after holding for a predetermined time t2 (second), the temperature is rapidly lowered to a temperature T0 (° C.) at a temperature drop rate ΔTd (° C./second), for example.

FIG. 4 is a conceptual diagram showing an example of a heat treatment sequence in RTP for explaining a more preferable aspect in the silicon wafer heat treatment method according to the present invention.
As shown in FIG. 4, switching from the fluorine-based gas atmosphere to the inert gas atmosphere is preferably performed in a state of being kept constant in the first temperature range (temperature T _M (° C.)).
That is, a temperature rise rate ΔTu1 (° C.) of a silicon wafer in which silicon atoms on the surface W1 are terminated with hydrogen to a first temperature range (temperature T _M (° C.)) of 900 ° C. to 1250 ° C. in a fluorine-based gas atmosphere. The temperature is rapidly raised at 1 second / second) and kept constant for a predetermined time (t _M1 (second)) within the first temperature range (temperature T _M (° C.)), and then the first temperature range (temperature T _M ( )), The fluorine-based gas atmosphere is switched to an inert gas atmosphere, and is kept constant for a predetermined time (t _M2 (second)). Thereafter, the temperature rise rate ΔTu2 (° C./second) is 1300 ° C. or higher and 1400 ° C. It is preferable to perform the RTP by rapidly raising the temperature to a second temperature range (temperature T1 (° C.)) of less than or equal to ° C.

  By adopting such a method, although productivity is slightly reduced, it becomes possible to reliably terminate fluorine in a fluorine-based gas atmosphere. Further, when the gas is switched, the fluorine-based gas is removed from the reaction chamber 20. It becomes easy to discharge completely. Therefore, since the risk of exposing the polished surface of the wafer to the fluorine-based gas at a high temperature exceeding 1250 ° C. is reduced, deterioration of the surface roughness on the polished surface can be suppressed.

The holding time (t _M1 (second)) for holding the first temperature range (temperature T _M (° C.)) in the fluorine-based gas atmosphere is 1 second or more and 5 seconds or less, and after the switching, In the active gas atmosphere, the holding time (t _M2 (second)) for holding the first temperature range (temperature T _M (° C.)) is preferably 1 second or more and 5 seconds or less.
By setting it as such holding time, while suppressing the fall of productivity, it can terminate a fluorine reliably and can also suppress the deterioration of the surface roughness by fluorine-type gas.

The temperature rising rates ΔTu, ΔTu1, and ΔTu2 in the RTP are preferably 10 ° C./second or more and 150 ° C./second or less.
By setting such temperature increase rates ΔTu, ΔTu1, and ΔTu2, in the RTP, it is possible to suppress the occurrence of contact marks and slips due to a rapid temperature change at the time of rapid temperature increase while suppressing the productivity from being lowered. be able to.

The temperature drop rate ΔTd in the RTP is preferably 10 ° C./second or more and 150 ° C./second or less.
By setting such a temperature decrease rate ΔTd, it is possible to suppress the occurrence of contact traces and slips due to a rapid temperature change at the time of rapid temperature decrease, while suppressing a decrease in productivity in the RTP.

FIG first temperature range in the heat treatment sequence 4 (temperature T _{M (°} C.)) to the Atsushi Nobori rate ΔTu1 (℃ / sec) and after the switching, from the first temperature range (temperature T _{M (°} C.)) The temperature increase rate ΔTu2 (° C./second) up to the second temperature range (temperature T1 (° C.)) may be the same temperature increase rate as long as it is 10 ° C./second or more and 150 ° C./second or less. It may be a temperature rate.

The holding time t1 in the inert gas atmosphere in the second temperature range (temperature T1 (° C.)) is preferably 1 second or longer and 15 seconds or shorter.
By setting the holding time t1 as described above, it is possible to efficiently eliminate void defects while suppressing a decrease in productivity.

The holding time t2 in the oxidizing gas atmosphere in the second temperature range (temperature T1 (° C.)) is preferably 1 second or more and 15 seconds or less.
By setting it as such holding time t2, oxygen can be efficiently diffused inward to the surface layer part of a wafer, suppressing productivity falling.

EXAMPLES Hereinafter, although this invention is demonstrated further more concretely based on an Example, this invention is not limitedly interpreted by the following Example.
Example 1
Controlling v / G (v: pulling speed, G: temperature gradient in the pulling axis direction in the single crystal) by the CZ method to produce a silicon single crystal ingot having a region in which vacant point defects exist, With respect to a silicon wafer (diameter 300 mm, thickness 775 μm, oxygen concentration 1.2-1.3 × 10 ¹⁸ atoms / cm ³ ) obtained by cutting out from the region, both surfaces are mirror-polished. The whole wafer was immersed in a hydrofluoric acid solution and washed for 5 minutes (hydrogen termination treatment), and then the wafer was washed with pure water and dried by spin drying.

Next, using the RTP apparatus 10 as shown in FIG. 1 for the dried wafer, RTP was performed in a heat treatment sequence as shown in FIG. 3 to produce an annealed wafer.
Specifically, the dried wafer is put into a reaction chamber held at 500 ° C., and an atmosphere is supplied with tetrafluoromethane gas (CF ₄ ), and the temperature rise rate is 75 ° C./sec. The temperature is rapidly raised to the first temperature range), and then the atmosphere is switched from tetrafluoromethane gas (CF ₄ ) to argon gas (Ar) at 1000 ° C., and then 1300 ° C. (first temperature at 75 ° C./second). 2) and after holding at 1300 ° C. for 15 seconds, at 1300 ° C., switching from argon gas (Ar) to oxygen gas (O ₂ ), further holding for 15 seconds, then The temperature was rapidly decreased to 500 ° C. at a temperature decrease rate of 90 ° C./second.

(Example 2)
An annealed wafer was fabricated under the same conditions as in Example 1 except that the second temperature range in the RTP was 1350 ° C.

(Example 3)
An annealed wafer was fabricated under the same conditions as in Example 1 except that RTP was performed using a heat treatment sequence as shown in FIG.
Specifically, the dried wafer is put into a reaction chamber held at 500 ° C., and an atmosphere is supplied with tetrafluoromethane gas (CF ₄ ), and the temperature rise rate is 75 ° C./sec. The temperature is rapidly raised to the first temperature range), and then kept constant at 1000 ° C. for 5 seconds, and then the atmosphere is switched from tetrafluoromethane gas (CF ₄ ) to argon gas (Ar). The temperature is kept constant for 5 seconds, and then rapidly raised to 1300 ° C. (second temperature range) at a heating rate of 75 ° C./second, held at 1300 ° C. for 15 seconds, and then argon gas (Ar ) Was switched to oxygen gas (O ₂ ) and maintained for 15 seconds, and then rapidly cooled to 500 ° C. at a temperature decrease rate of 90 ° C./second.

Example 4
An annealed wafer was fabricated under the same conditions as in Example 3 except that the second temperature range in the RTP was 1350 ° C.

(Comparative Example 1)
An annealed wafer was fabricated under the same conditions as in Example 1 except that RTP was performed on the wafer that had been subjected to the hydrogen termination without performing the fluorine termination.

(Comparative Example 2)
An annealed wafer was fabricated under the same conditions as in Example 1 except that the second temperature range in the RTP was 1200 ° C.

(Comparative Example 3)
In Example 1, after maintaining at 1300 ° C. for 15 seconds in an inert gas atmosphere, the temperature was rapidly decreased to 800 ° C. at a temperature decrease rate of 90 ° C./second, and the argon gas was switched to oxygen gas at 800 ° C. An annealed wafer was fabricated under the same conditions as in Example 1 except that the temperature was rapidly raised to 1300 ° C. at 75 ° C./second, and further maintained at 1300 ° C. for 15 seconds.

RMS (measurement range: 3 μm × 3 μm) of surface roughness of the annealed wafer obtained in Examples 1 to 4 and Comparative Examples 1 to 3 on the semiconductor device forming surface was evaluated using an AFM (Atomic Force Microscope). did.
Further, the appearance of concave pits on the semiconductor device forming surface was evaluated by visual inspection.
Furthermore, regarding the defect density in the surface layer part from the wafer surface to a depth of 5 μm, an LSTD scanner (Laser Scattering Topology Defect)
(Scanner) at a wavelength of 680 nm.
As a reference example, the surface roughness RMS (measurement range: 3 μm × 3 μm) on the semiconductor device forming surface of the wafer after fluorine termination and before RTP was also evaluated using AFM.
The evaluation results in this test are shown in Table 1.

As shown in Table 1, with respect to Comparative Example 1 in which the fluorine termination treatment is not performed, the surface roughness tends to be worse than that of the reference example. Further, it is recognized that the defect density extinction power is low with respect to Comparative Example 2 in which the second temperature range of RTP is 1200 ° C. Furthermore, regarding Examples 1 to 4 subjected to the fluorine termination treatment, the tendency that the surface roughness is improved as compared with the comparative example and the reference example is recognized. In addition, with respect to Examples 3 and 4 performed by the heat treatment sequence of FIG. 4, it is recognized that the surface roughness tends to be improved compared to the heat treatment sequence (Examples 1 and 2) shown in FIG.
In addition, it is recognized that Examples 1 to 4 have the same level of surface roughness and defect density as Comparative Example 3 in which the temperature is rapidly lowered to 800 ° C. and switched.

(Temperature change test 1: Examples 5 to 11)
An annealed wafer was fabricated under the same conditions as in Example 1 except that the first temperature range in the fluorine termination treatment was changed.
The surface roughness (RMS) on the semiconductor device formation surface of the obtained annealed wafer and the occurrence of concave pits were evaluated in the same manner as in Example 1.
Table 2 shows test conditions and evaluation results in this test.

  As shown in Table 2, when the first temperature range is set to 900 ° C. or more and 1250 ° C. or less, the surface roughness: RMS (nm) tends to be improved.

(Temperature change test 2: Examples 12 to 17)
An annealed wafer was fabricated under the same conditions as in the temperature change test 1 except that the second temperature range in the RTP was 1350 ° C.
The surface roughness (RMS) on the semiconductor device formation surface of the obtained annealed wafer and the occurrence of concave pits were evaluated in the same manner as in Example 1.
Table 3 shows test conditions and evaluation results in this test.

  Also in this test, as shown in Table 3, the same tendency as in the temperature change test 1 (surface roughness: RMS (nm) is improved by setting the first temperature range to 900 ° C. or more and 1250 ° C. or less. It is recognized that there is a tendency).

10 RTP apparatus 20 Reaction chamber 30 Wafer holding part 40 Heating part

Claims (3)

Terminating at least the silicon atoms on the surface of the silicon wafer on which the surface on which the semiconductor device is formed is mirror-polished with hydrogen;
Terminating the silicon atoms on the surface of the silicon wafer terminated with hydrogen with fluorine;
The silicon wafer terminated with hydrogen and fluorine is rapidly heated and held in a temperature range of 1300 ° C. to 1400 ° C. in an inert gas atmosphere, and then the inert gas atmosphere is oxidized gas atmosphere in the temperature range. And a step of performing a rapid temperature raising and lowering heat treatment for further holding and switching to the temperature, and performing a heat treatment method for a silicon wafer. The step of terminating with hydrogen is a step of washing the silicon wafer with a hydrogen fluoride solution or a hydrogen peroxide solution,
The silicon wafer heat treatment method according to claim 1, wherein the step of terminating with fluorine is a step of heat treating the silicon wafer in a temperature range of 900 ° C. to 1250 ° C. in a fluorine-based gas atmosphere. A step of terminating a silicon atom on the surface with hydrogen by a hydrogen fluoride-based solution or a hydrogen peroxide-based solution at least on a silicon wafer having a mirror-polished surface on which a semiconductor device is formed;
Rapidly heating the silicon-terminated silicon wafer to a first temperature range of 900 ° C. or higher and 1250 ° C. or lower in a fluorine-based gas atmosphere, and terminating silicon atoms on the surface with fluorine;
Continuing from the step of terminating with fluorine, the fluorine-based gas atmosphere is switched to an inert gas atmosphere in the first temperature range, and the temperature is rapidly raised to a second temperature range of 1300 ° C. to 1400 ° C. and held. Then, a process of switching the inert gas atmosphere to an oxidizing gas atmosphere in the second temperature range and further holding it, and performing a rapid temperature raising and lowering heat treatment for rapidly lowering the temperature, is provided. Method.

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