JP5512137B2 - Heat treatment method for silicon wafer - Google Patents

Description

  The present invention relates to a heat treatment method applied to apply a silicon wafer obtained by slicing a silicon single crystal ingot manufactured by the Czochralski method (hereinafter referred to as CZ method) to a semiconductor device.

  Silicon wafers used as semiconductor device forming substrates (hereinafter also simply referred to as “wafers”) are heat-treated (annealed) in a predetermined environment for mirror-polished silicon wafers for the purpose of improving yield in semiconductor device processes. ) Is generally performed.

  As such a heat treatment technique, for example, a method of performing heat treatment at a temperature of 1250 to 1380 ° C. in a gas atmosphere containing 5% or more of oxygen for 1 to 20 hours (for example, Patent Document 1), nitrogen 100% or In a mixed atmosphere of oxygen 100% or oxygen and nitrogen, the maximum holding temperature is set to 1125 ° C. or higher and the melting point of silicon or lower and the heat treatment is performed for 5 seconds or longer. (For example, patent document 2) etc. which are rapidly cooled by this is known.

JP 2006-261632 A JP 2000-31150 A

However, a silicon wafer manufactured using the method described in Patent Document 1 has a problem that dislocations are likely to occur on the wafer surface during heat treatment in a semiconductor device process.
Moreover, since the silicon wafer manufactured using the method described in Patent Document 2 is subjected to rapid heating / cooling heat treatment in an atmosphere containing oxygen, the surface of the wafer after the heat treatment, that is, mirror polishing is performed. An oxide film is formed on the device forming surface, but there is a problem that the roughness of the wafer surface is deteriorated depending on the conditions.
These problems are not preferable because they cause a decrease in yield in the semiconductor device process.

  The present invention has been made to solve the above technical problem, and provides a silicon wafer heat treatment method capable of suppressing the occurrence of dislocations and the deterioration of the roughness of the wafer surface in a semiconductor device process. It is the purpose.

The heat treatment method for a silicon wafer according to the present invention is a method for heat treating a wafer obtained by slicing a silicon single crystal ingot produced by the CZ method. In an oxygen-containing atmosphere, the maximum temperature reached is 1300 ° C. or higher and the melting point of silicon or lower. The temperature is characterized by performing rapid heating / cooling heat treatment for forming an oxide film having a thickness of 3.0 nm to 9.1 nm on the wafer surface.
By performing such heat treatment, it is possible to suppress the occurrence of dislocations and the deterioration of the roughness of the wafer surface in the semiconductor device process.

The oxygen partial pressure in the oxygen-containing atmosphere is preferably 1.0% or more and 20% or less.
It is preferable to adjust the oxygen partial pressure in such a range and perform the rapid heating / cooling heat treatment to easily control the thickness of the oxide film within the above range.

  Further, the oxygen-containing atmosphere is composed of argon and oxygen from the viewpoint that it is not preferable to form other films such as nitride films or chemical reactions other than the formation of oxide films on the wafer surface. Is preferred.

  Further, from the viewpoint of improving the efficiency of the rapid heating / cooling heat treatment, it is preferable that the holding time at the maximum temperature is not less than 1 second and not more than 60 seconds.

According to the silicon wafer heat treatment method of the present invention, generation of dislocations and deterioration of the wafer surface roughness in the semiconductor device process can be suppressed.
Therefore, the silicon wafer subjected to the heat treatment according to the present invention contributes to the improvement of the yield in the device process.

It is sectional drawing which shows the outline | summary of an example of the rapid heating / cooling thermal processing apparatus used for the heat processing method of the silicon wafer which concerns on this invention. It is the schematic of the heat processing sequence in the rapid heating / cooling heat processing which concerns on this invention. In Test 1, it is the figure which showed the measuring point of the film thickness of the oxide film on the wafer surface. In Test 1, it is the graph which showed the relationship between the film thickness of the oxide film in each highest achieving temperature T1, and the wafer in-plane average value of the haze of SP1. In Test 1, it is the graph which showed the relationship between the film thickness of the oxide film in each highest attained temperature T1, and the wafer in-plane average value of the haze of SP2. In Test 2, it is the graph which showed the oxygen concentration profile of the depth direction in the wafer center. In Test 3, it is the graph which showed the relationship between the maximum oxygen concentration in a wafer surface layer, and the highest attained temperature.

Hereinafter, the present invention will be described in more detail with reference to the drawings.
In the silicon wafer heat treatment method according to the present invention, a rapid heating / cooling heat treatment is performed on a wafer obtained by slicing a silicon single crystal ingot manufactured by the CZ method. In the present invention, the rapid heating / cooling heat treatment is performed in an oxygen-containing atmosphere at a maximum temperature of 1200 ° C. or more and a melting point of silicon or less to form an oxide film having a thickness of 9.1 nm or less on the wafer surface. It is characterized by this.

The above-described dislocation occurs because stress is applied in the wafer due to trench formation or the like in the semiconductor device process, whereby dislocation is generated inside the wafer, and in the subsequent heat treatment, the dislocation extends to the wafer surface. It is considered a thing.
That is, in the heat treatment after mirror polishing, the oxygen inside the wafer is excessively diffused outwardly, the oxygen concentration in the wafer surface layer is reduced, and the pinning force of oxygen against dislocations is reduced. It is thought that it is easy to extend to the surface.

On the other hand, in the present invention, by performing the rapid heating / cooling heat treatment as described above on the silicon wafer, the solid solution limit oxygen concentration corresponding to the temperature is increased from the atmosphere to the inside of the wafer. Since it diffuses and the temperature drop time is short, the outward diffusion of oxygen in the inwardly diffused wafer can be suppressed. Therefore, it is possible to suppress an increase or decrease in the oxygen concentration on the wafer surface layer. That is, it is possible to suppress a decrease in the pinning force of oxygen with respect to dislocations, and thereby it is possible to suppress dislocations generated inside the wafer from extending to the surface.
In addition, by controlling the maximum temperature and the thickness of the oxide film within the above ranges and performing rapid heating / cooling heat treatment, deterioration of the wafer surface roughness due to the formation of the oxide film during the heat treatment is also suppressed. be able to.

In the silicon wafer heat treatment method according to the present invention, a rapid heating / cooling heat treatment is performed on a wafer obtained by slicing a silicon single crystal ingot manufactured by the CZ method.
Production of a silicon single crystal ingot by the CZ method can be performed by a known method. Specifically, the polycrystalline silicon filled in the quartz crucible is heated to form a silicon melt, the seed crystal is brought into contact with the liquid surface of the silicon melt, and the seed crystal is pulled up while rotating the seed crystal and the quartz crucible. The silicon single crystal ingot is grown by expanding to a desired diameter to form a straight body portion and then separating from the silicon melt.
Next, the silicon single crystal ingot thus obtained is processed into a silicon wafer by a known method. Specifically, after slicing a silicon single crystal ingot into a wafer shape with an inner peripheral blade or a wire saw, processing such as chamfering, lapping, etching, and mirror polishing of the outer peripheral portion is performed.

  The mirror-polished silicon wafer obtained as described above is subjected to rapid heating / rapid cooling heat treatment in an oxygen-containing atmosphere using a rapid heating / rapid cooling heat treatment apparatus (hereinafter referred to as RTP apparatus), An oxide film having a thickness of 9.1 nm or less is formed on the wafer surface.

FIG. 1 shows an outline of an example of an RTP apparatus used in the silicon wafer heat treatment method according to the present invention.
An RTP apparatus 10 shown in FIG. 1 includes a reaction tube 20 provided with an atmospheric gas inlet 20a and an atmospheric gas outlet 20b, a plurality of lamps 30 arranged on the upper portion of the reaction tube 20, and a plurality of lamps 30 inside the reaction tube 20. The reaction space 25 includes a wafer support 40 that supports the wafer W.
The wafer support 40 includes an annular susceptor 40a that directly supports the wafer W and a stage 40b that supports the susceptor 40a.
In each constituent material, for example, the reaction tube 20 and the stage 40b are made of quartz, and the susceptor 40a is made of silicon. The lamp 30 is composed of, for example, a halogen lamp.

In the rapid heating / cooling heat treatment of the wafer W using the RTP apparatus 10 shown in FIG. 1, the wafer W is introduced into the reaction space 25 from a wafer introduction port (not shown) provided in the reaction tube 20 to support the wafer. This is performed by supporting the wafer W on the susceptor 40a of the unit 40, introducing atmospheric gas described later from the atmospheric gas inlet 20a, and irradiating the surface of the wafer W with the lamp 30.
The temperature in the reaction space 25 is controlled by averaging a plurality of average temperatures (for example, 9 points) in the wafer radial direction on the back surface of the wafer W by a plurality of radiation thermometers 50 embedded in the stage 40b of the wafer support 40. Based on each measured temperature, individual output control of the plurality of lamps 30 is performed by a control means (not shown).

In the rapid heating / cooling heat treatment as described above, when the thickness of the oxide film formed on the wafer surface exceeds 9.1 nm, it is difficult to suppress the deterioration of the roughness of the wafer surface.
The lower limit value of the thickness of the oxide film is preferably 3.0 nm or more. When the thickness is less than 3.0 nm, it is difficult to sufficiently increase the oxygen concentration of the wafer surface layer by inwardly diffusing oxygen in the oxygen-containing atmosphere into the wafer.

Moreover, it is preferable that the highest temperature reached in the rapid heating / cooling heat treatment is 1200 ° C. or more and the silicon melting point or less.
By setting it as such temperature conditions, the deterioration of the wafer surface roughness in rapid heating and rapid cooling heat treatment can be further suppressed. If the maximum temperature exceeds the silicon melting point, the silicon wafer subjected to the rapid heating / cooling heat treatment is melted, which is not preferable.
More preferably, the maximum temperature reached is 1300 ° C. or higher and a silicon melting point or lower.
By setting such a temperature condition, the oxygen concentration in the wafer surface layer can be made to be the same level as that of the wafer before the heat treatment, so that the occurrence of dislocations in the semiconductor device process can be further suppressed.
More preferably, the upper limit of the maximum temperature reached is 1380 ° C. or less from the viewpoint of the device life as the RTP device.

FIG. 2 schematically shows the relationship between the temperature and time of the heat treatment sequence in the rapid heating / cooling heat treatment.
As shown in FIG. 2, first, a mirror-polished silicon wafer is held at a temperature T0 (for example, 500 ° C.), and a maximum temperature T1 (° C. at a temperature rising rate ΔTu (° C./sec) in an oxygen-containing atmosphere. ) And is rapidly cooled from the maximum temperature T1 (° C.) to the temperature T0 (° C.) at a temperature drop rate ΔTd (° C./second).

The oxygen partial pressure in the oxygen-containing atmosphere is preferably 1.0% or more and 20% or less.
When the oxygen partial pressure is less than 1.0%, it is difficult to control the film thickness of the oxide film within the above range, and the amount of in-diffusion of oxygen in the atmosphere into the wafer decreases, As a result, the pinning force of oxygen is reduced, and it becomes difficult to suppress the occurrence of dislocations in the semiconductor device process.
On the other hand, when the oxygen partial pressure exceeds 20%, since the oxygen partial pressure is too high, the formed oxide film becomes thick, and it is difficult to remove this oxide film with high productivity.

The gas other than oxygen gas in the oxygen-containing atmosphere is preferably an inert gas.
When nitrogen gas is used as a gas other than the oxygen gas, a nitride film is formed on the wafer surface in the rapid heating / cooling heat treatment, and an additional etching process or the like must be added to remove the nitride film. This is not preferable because the number of steps increases.
Further, when hydrogen gas is used as a gas other than the oxygen gas, a mixed gas of oxygen and hydrogen is not preferable because there is a risk of explosion.
As the inert gas, it is particularly preferable to use argon gas. When argon gas is used, rapid heating / cooling heat treatment can be performed without formation of other films such as a nitride film, chemical reaction, or the like.

Both the temperature increase rate ΔTu and the temperature decrease rate ΔTd are preferably 10 ° C./second or more and 150 ° C./second or less.
When the temperature increase rate ΔTu or the temperature decrease rate ΔTd is less than 10 ° C./second, there is a problem that productivity is inferior.
On the other hand, when the temperature increase rate ΔTu or the temperature decrease rate ΔTd exceeds 150 ° C./second, the silicon wafer cannot withstand a temperature change that is too rapid and slip occurs.

As described above, the maximum temperature T1 is not less than 1200 ° C. and not more than the silicon melting point, preferably not less than 1300 ° C. and not more than the silicon melting point, more preferably not less than 1300 ° C. and not more than 1380 ° C.
Note that the maximum temperature T1 here is a number of points (for example, 9 points) in the wafer radial direction on the back surface of the wafer W in the case of rapid heating / cooling heat treatment using an RTP apparatus as shown in FIG. The average temperature.

The holding time t at the maximum temperature T1 is preferably not less than 1 second and not more than 60 seconds.
When the holding time t is less than 1 second, it is difficult to achieve reduction of grown-in defects, improvement of BMD density, and the like, which are the original purposes of rapid heating / cooling heat treatment.
On the other hand, when the holding time t exceeds 60 seconds, the productivity is deteriorated and the outward diffusion of oxygen inside the wafer is increased, which is not preferable.

EXAMPLES Hereinafter, although this invention is demonstrated further more concretely based on an Example, this invention is not restrict | limited by the following Example.
(Test 1) Relationship between Maximum Achievable Temperature, Oxide Film Thickness, and Surface Roughness A silicon wafer (300 mm in diameter, 775 mm in thickness, having a mirror polished surface on both sides) obtained by slicing a silicon single crystal ingot manufactured by the CZ method An oxygen concentration of 1.3 × 10 ¹⁸ atoms / cc) is introduced into an RTP apparatus as shown in FIG. 1, in a 100% oxygen atmosphere (flow rate 20 slm), temperature T0: 500 ° C., temperature increase rate ΔTu, and temperature decrease rate ΔTd: 50 ° C./second, changing the maximum temperature T1 and its holding time t, and performing rapid heating / cooling heat treatment in the heat treatment sequence as shown in FIG. An altered annealed wafer was obtained.

The thickness of the oxide film formed on the surface of each obtained annealed wafer was measured by an ellipsometry method using AutoELIII (manufactured by Rudolf Research). As shown in FIG. 3, the measurement is performed at a total of 9 points each at two positions at a wafer center O (distance 0 mm from the center) and distances 40 mm, 75 mm, 110 mm, and 145 mm from the wafer center in both directions of the circumference of the wafer. The average value was taken as the film thickness. In addition, the numerical value in FIG. 3 represents the distance from the wafer center.
Further, after removing the oxide film by cleaning with hydrofluoric acid, the average value of the surface roughness (haze) in the wafer surface was measured with a laser light scattering particle counter (SP1 and SP2; manufactured by KLA-Tencor).

  For comparison, as a conventional example, a silicon wafer similar to the above is not subjected to rapid heating / cooling heat treatment, and a well-known vertical heat treatment furnace is used, in a 100% argon atmosphere, at a temperature T0: 500. Heat treatment is performed at a temperature of 1 ° C., a temperature increase rate ΔTu and a temperature decrease rate ΔTd of 3 ° C./min, a maximum temperature T1 of 1200 ° C., and a holding time t of the maximum temperature T1 of 1 hour. In-plane average values were measured in the same manner as described above.

Table 1 shows the measurement results of the in-wafer average value of the oxide film thickness and haze at each maximum temperature T1.
FIG. 4 is a graph showing the relationship between the oxide film thickness at each maximum temperature T1 and the average value of the haze of SP1 in the wafer surface. FIG. 5 is a graph showing the oxide film thickness and SP2 at each maximum temperature T1. The graph of the relationship of the wafer in-plane average value of haze is shown. 4 and 5, the vertical axis indicates haze and the horizontal axis indicates the oxide film thickness.

  From the results shown in the graphs of FIGS. 4 and 5, the conditions satisfying the average value of the haze at the same level as in the conventional example satisfy the condition that the film thickness of the oxide film is 9.1 nm or less (Examples 1 to 10). In addition, it was confirmed that the maximum reached temperature T1 was 1200 ° C. or more and the thickness of the oxide film was 9.1 nm or less (Examples 3 to 10).

(Test 2) Relationship between Oxygen Partial Pressure and Wafer Oxygen Concentration Silicon wafer obtained by slicing a silicon single crystal ingot manufactured by the CZ method (both diameter 300 mm, thickness 775 mm, oxygen concentration 1 .3 × 10 ¹⁸ atoms / cc) is subjected to the heat treatment shown in the above conventional example, oxygen is diffused outwardly, and then introduced into an RTP apparatus as shown in FIG. 1, in an oxygen-containing atmosphere diluted with argon. (Total gas flow rate 20 slm), oxygen partial pressure is changed, maximum attainment temperature T1: 1350 ° C., retention time at maximum attainment temperature T1 t: 15 seconds, otherwise rapid heating under the same conditions as in test 1 A rapid cooling heat treatment is performed, and the oxygen concentration profile in the depth direction at the wafer center of each annealed wafer is measured with a secondary ion mass spectrometer (SIMS; Ims-6f; Ca (made by meca).

In addition, the oxygen concentration profile in the depth direction at the wafer center of each annealed wafer was also evaluated when a rapid heating / cooling heat treatment was performed by changing the oxygen flow rate in an oxygen 100% atmosphere.
Furthermore, the oxygen concentration profile of the annealed wafer obtained in the conventional example of Test 1 was also evaluated under the same conditions.

  FIG. 6 shows a graph of these evaluation results. The oxygen concentration is a value converted to old-ASTM. In FIG. 6, “AT” is a wafer that has been annealed only in the conventional example, and “PW” is an oxygen concentration profile of the mirror-polished wafer that has not been annealed at all.

From the results shown in the graph of FIG. 6, the wafer subjected to the rapid heating / cooling heat treatment in the atmosphere of oxygen partial pressure of 1% diluted with argon gas is also compared with the wafer under other oxygen atmosphere conditions. It was confirmed that oxygen was sufficiently diffused in the surface layer.
However, when the oxygen partial pressure was 0.4%, a sufficient oxygen concentration was not obtained (not shown).
Further, as shown in FIG. 6, the wafer (AT) subjected only to the conventional annealing has a much lower oxygen concentration on the surface of the wafer than the annealed wafer further subjected to rapid heating / cooling heat treatment in an oxygen-containing atmosphere. It was recognized that

(Test 3) Relationship between Maximum Achieving Temperature / Holding Time and Oxygen Concentration of Wafer Silicon Wafer Mirrored on Both Sides Obtained by Slicing Silicon Single Crystal Ingot Manufactured by CZ Method (Diameter 300mm, Thickness 775mm, Introducing an oxygen concentration of 1.3 × 10 ¹⁸ atoms / cc into an RTP apparatus as shown in FIG. 1 and rapid heating by changing the maximum temperature and its holding time in an oxygen 100% atmosphere (flow rate 20 slm)・ Rapid cooling heat treatment was performed, and the oxygen concentration profile in the depth direction at the wafer center of each annealed wafer was evaluated with a secondary ion mass spectrometer (SIMS; Ims-6f; manufactured by Cameca). The maximum oxygen concentration at 1-2 μm) was determined.
FIG. 7 shows a graph of the relationship between the maximum oxygen concentration in the wafer surface layer and the maximum temperature reached.

From the results shown in the graph of FIG. 7, it was confirmed that the maximum oxygen concentration in the surface layer of the annealed wafer was determined at the maximum temperature reached without depending on the processing time.
In particular, when the temperature is 1300 ° C. or higher, the maximum oxygen concentration exceeds the polishing substrate (PW), so it is estimated that the dislocation suppression effect is comparable.
Therefore, from the above results, it is preferable that the maximum temperature reached in the rapid heating / cooling thermal treatment is 1300 ° C. or higher from the viewpoint of suppressing the decrease in oxygen concentration.

10 RTP device 20 Reaction tube 30 Lamp 40 Wafer support 50 Radiation thermometer

Claims (4)

In a method for heat-treating a wafer obtained by slicing a silicon single crystal ingot produced by the Czochralski method, the surface temperature is increased to 1300 ° C. or higher and below the melting point of silicon in an oxygen-containing atmosphere. A heat treatment method for a silicon wafer, characterized by performing a rapid heating / cooling heat treatment to form an oxide film having a thickness of 3.0 nm to 9.1 nm . 2. The method for heat-treating a silicon wafer according to claim 1 , wherein an oxygen partial pressure is set to 1.0% or more and 20% or less in the oxygen-containing atmosphere. Said oxygen-containing atmosphere, the heat treatment method of a silicon wafer according to claim 1 or 2, characterized in that it consists of argon and oxygen. The heat treatment method for a silicon wafer according to any one of claims 1 to 3 , wherein a holding time at the maximum temperature is not less than 1 second and not more than 60 seconds.

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