JP2010073782A - Method of heat-treating semiconductor wafer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of heat-treating a semiconductor wafer in which a slip of a wafer reverse surface caused in a heat treating stage is reduced and gettering effect to a thin-film device during a heat treatment can be generated. <P>SOLUTION: A silicon wafer 10 is horizontally supported on its reverse side with a support pin 12 and rapidly heated. When the heat-treatment temperature reaches 1,100 to 1,350°C, the heat-treatment temperature is always varied within a predetermined temperature range. Consequently, the wafer 10 continuously thermally expands in a wafer radial direction and the contact position of the support pin 12 on the wafer reverse surface always changes. Consequently, a slip length of the wafer 10 is suppressed and oxygen precipitate density on the device active layer side of the wafer 10 is increased to effectively generate the gettering effect to the thin film device. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a heat treatment method for a semiconductor wafer, and more particularly to a heat treatment method for a semiconductor wafer that can reduce the slip on the back surface of the wafer that occurs in the heat treatment step of the semiconductor wafer.

Intrinsic gettering (IG) and extrinsic gettering (EG) methods are known as conventional techniques for removing metal contamination in a device process from a device active layer.
As a typical example of the intrinsic gettering method, there is a method in which oxygen atoms in a silicon wafer are precipitated in the wafer, and metal contaminants are captured using distortion of the oxygen precipitates. As a typical example of the extrinsic gettering method, there is a method in which a polysilicon film is formed on the back surface of a silicon wafer and metal impurities are captured at a grain boundary of the polysilicon.

  Among these, as a method for manufacturing a silicon wafer having intrinsic gettering capability, for example, a method of performing a heat treatment at 1100 ° C. or higher for about 1 hour in an atmosphere of a non-oxidizing gas is known. As a result, a defect-free layer (DZ layer; Denuded Zone Layer) in which a COP (Crystal Originated Particle) existing in a region of 10 to 15 μm from the surface of the silicon wafer is reduced and reduced is formed, and an oxygen precipitation nucleus is present thereunder A gettering layer is formed.

  By the way, in recent years, semiconductor devices have been increasingly thinned, and accordingly, a silicon wafer in which the gettering layer described above is present in a region closer to the device active layer is required. However, in a conventional silicon wafer having intrinsic gettering capability, a DZ layer having no oxygen precipitation nuclei is formed 10 μm or more from the wafer surface. Therefore, for example, in the case of a thin film device such as an MCP (multichip package) whose final device thickness is expected to be 15 μm or less in the near future, there is a concern that the gettering capability is insufficient. Therefore, there is a demand for a wafer having an oxygen precipitate density increased on the device active layer side.

As a countermeasure, heat treatment of silicon wafers by rapid heating and rapid cooling has attracted attention. This heat treatment method uses a lamp annealing furnace, holds a silicon wafer rapidly heated to 1100 ° C. or higher in a nitrogen-containing gas atmosphere at a constant temperature of 1100 ° C. or higher for a predetermined time, and then 10 ° C./second or higher. The temperature is lowered at a speed (for example, Patent Document 1). As a result, vacancies are frozen inside the silicon wafer, and the vacancies are combined with oxygen, so that the formation of oxygen precipitates is promoted by the subsequent heat treatment.
In the rapid thermal quenching method, as described above, in order to increase the density of oxygen precipitates on the device active layer side and further increase the intrinsic gettering capability, it is necessary to further increase the rapid cooling rate and further increase the temperature. It is desired. However, if the above method is applied, there arises a problem that slip occurs frequently on the back surface of the wafer. For this reason, the above problem of increasing the gettering ability cannot be overcome. This slip is caused by stress induced by rubbing the front ends of a large number of support pins that support the silicon wafer from the back side during the heat treatment of the silicon wafer against the back side of the thermally expanded silicon wafer. Such a slip affects the reliability and yield of integrated circuit devices fabricated on a silicon wafer.

JP 2007-290961 A

  By the way, in a heat treatment apparatus that supports a silicon wafer with a large number of support pins from the back surface side and performs rapid heating and quenching, the slip occurrence position on the back surface of the wafer after heat treatment corresponds to the position of each support pin. That is, scratches are generated in the region of the wafer back surface where the support pins are in contact, and particularly when the wafer is held at a high temperature for a certain time, the self-weight stress of the silicon wafer is constantly applied to the contact region. . For this reason, it is considered that dislocations were generated from scratches, and the dislocations were extended and observed as slips. Patent Document 1 reports a result that the slip length is shortened when the heating rate is increased. This is presumed to be because the contact time between the back surface of the wafer and the support pins becomes shorter as the temperature increase rate becomes faster.

Therefore, as a result of earnest research, the inventor has to maintain a constant temperature of 1100 ° C. or higher for 5 seconds or more in order to increase the vacancy concentration of the silicon wafer, and then reduce the slip by a rapid heat treatment, for example, 1100 A temperature region (1000 ° C. to 1200 ° C.) that is the same as the concentration of vacancies injected from the silicon surface by holding at 10 ° C. for 10 seconds should be set, and the heat treatment temperature should be constantly varied within that temperature range. I came up with it. As a result, the silicon wafer continuously expands or contracts in the wafer radial direction according to the heating temperature, and the pin contact position on the back surface of the wafer constantly changes. As a result, it has been found that the self-weight stress of the silicon wafer does not always act at a fixed position on the back surface of the wafer, and slip extension can be suppressed.
In addition, when the temperature before the start of rapid cooling is higher than the temperature maintained for a predetermined time, even higher concentration of vacancies is frozen near the surface. Therefore, it has been found that if this phenomenon is utilized, the oxygen precipitate density can be increased on the device active layer side, and the gettering effect can be effectively generated for the thin film device during heat treatment, and the present invention has been completed. It was.

  The present invention provides a method for heat treating a semiconductor wafer that can reduce the slip on the back surface of the wafer that occurs in the heat treatment process of the semiconductor wafer, and can effectively generate a gettering effect on the thin film device during the heat treatment. It is aimed.

  According to the first aspect of the present invention, three or more support pins are brought into contact with the back surface to horizontally support the semiconductor wafer, and in this state, the semiconductor wafer is rapidly heated to a heat treatment temperature of 1100 ° C. or higher. In the semiconductor wafer heat treatment method in which the temperature is maintained for a predetermined time and then rapidly cooled, while the heat treatment temperature is maintained, the temperature of the semiconductor wafer including the temperature region higher than the heat treatment temperature is constantly changed. This is a heat treatment method.

According to the first aspect of the present invention, the semiconductor wafer inserted into the furnace is supported horizontally by bringing three or more support pins into contact with the back surface of the semiconductor wafer, and the semiconductor wafer is kept at, for example, room temperature to 600 ° C. It is put into the furnace set to the extent. Thereafter, if the holding temperature is T ° C. and the holding time is t seconds as heat treatment conditions, several heat treatments can be selected.
(1) After rapidly heating the semiconductor wafer to T ° C., the semiconductor wafer is heated to a temperature higher than T ° C. (T1 ° C.) and fluctuated for t seconds in a temperature range of T ° C. to T1 ° C. In this case, since the temperature is changed on the higher temperature side than T ° C., high-density holes can be injected into the semiconductor wafer.
(2) When heated to T1 ° C., a void density equivalent to that for heating for t seconds can be obtained in a time shorter than t seconds, and productivity is increased.
(3) First, heat is rapidly heated to T0 ° C lower than T ° C, then heated to T1 ° C, and the temperature is varied between T0 ° C and T1 ° C. In consideration of the pore concentration and the diffusion constant, the heat treatment can be performed in a shorter time than t seconds.

  As a result, the semiconductor wafer continuously expands or contracts in the wafer radial direction, and the contact position of the support pins on the back surface of the wafer always changes. Therefore, the wafer self-weight stress does not act for a long time at a certain position on the back surface of the semiconductor wafer. As a result, the stress induced by the tips of the support pins coming into contact with the back surface of the silicon wafer is alleviated. Therefore, the elongation of the slip of the semiconductor wafer accompanying the support by the support pins can be suppressed.

As the semiconductor wafer, a single crystal silicon wafer, a material having a single crystal structure, a polycrystalline silicon wafer, or the like can be used.
As the support pin, a tapered rod-shaped member can be adopted. As the cross-sectional shape (cross-sectional shape orthogonal to the length direction) of the support pin, for example, a circle, an ellipse, a triangle, a polygon more than a quadrangle, and the like can be adopted. The contact surface of the support pins with the wafer back surface may be a curved surface or a flat surface.

As the heat treatment, various heat treatments (for example, heat treatment for forming a thin film, heat treatment for forming an oxide film, heat treatment for doping, heat treatment for donakiller, heat treatment in an annealing step, heat treatment for resist treatment, heat treatment for etching, etc. ) Can be adopted.
The type of heat treatment may be either wet heat treatment or dry heat treatment. As the furnace for heat treatment, for example, a rapid thermal processing (RTP) rapid heating furnace capable of rapid heating and rapid cooling can be employed. A lamp type rapid heating furnace is rapid heating (general specifications of commercial equipment; 1 to 100 ° C./second, maximum temperature of 1250 ° C.) by heat from a lamp heat source such as a halogen lamp, rapid cooling (general specifications of commercial equipment) 1-100 ° C./sec). In addition, a heat treatment apparatus equipped with a heater may be used.

When the heat treatment temperature (heat treatment temperature region) is lower than 1100 ° C., the concentration of vacancy injected into the semiconductor wafer is low, and therefore the density of oxygen precipitate formation in the subsequent process is low. Therefore, preferably, if it is 1100 degreeC or more, the fall of the productivity of a semiconductor wafer can be prevented. Moreover, if it exceeds 1250 degreeC, there exists an advantage which a void | hole injection | pouring density becomes high, but it cannot apply in a commercial apparatus specification. Also, if the temperature becomes too high, the occurrence of slipping from the outer periphery of the wafer is also a concern. Therefore, the preferable temperature of heat processing is 1150 degreeC-1250 degreeC. If it is this range, the void | hole density | concentration will also be a sufficiently high density | concentration, and the more suitable effect that it can respond with a commercial apparatus will be acquired.
The temperature fluctuation in the present invention includes a case where the temperature rise and the temperature fall are repeated once or a plurality of times.

The invention according to claim 2 is the method for heat treating a semiconductor wafer according to claim 1, wherein the fluctuation rate of the heat treatment temperature is 5 ° C./second or more.
If the temperature is less than 5 ° C./second, the influence of the self-weight stress of the semiconductor wafer starts to be generated, so that the extension of the dislocation length is observed.

  According to the second aspect of the present invention, since the fluctuation rate of the heat treatment temperature at 1100 ° C. or higher is set to 5 ° C./second or higher, it is possible to prevent a decrease in productivity of the semiconductor wafer.

  In the invention according to claim 3, three or more support pins are brought into contact with the back surface to horizontally support the semiconductor wafer, and in this state, the semiconductor wafer is rapidly heated to a heat treatment temperature of 1100 ° C. or higher. In the semiconductor wafer heat treatment method in which the temperature is kept for a predetermined time and then rapidly cooled, the heat treatment temperature is kept constant, and the slip caused by the wafer self-weight stress is applied to the contact portion of the support pins on the back surface of the wafer. This is a semiconductor wafer heat treatment method comprising a time during which no heat is generated and a time during which the heat treatment temperature is constantly varied including a temperature region higher than the heat treatment temperature.

According to the third aspect of the present invention, even if the heat treatment temperature is constant, a slip due to the wafer self-weight stress does not occur at the contact portion of the support pins on the back surface of the wafer for a short time. Therefore, constant temperature heat treatment is performed in a short period of time in which the above-described slip due to the weight of the wafer does not occur at least one time immediately before the time during which the heat treatment temperature is constantly varied, during the variation time, and immediately after the variation time. Accordingly, as in the case of the first aspect, the effect of suppressing the extension of the slip of the semiconductor wafer accompanying the support by the support pins can be obtained.
“The time during which the processing temperature is constant and no slip due to the wafer self-weight stress occurs at the contact portion of the support pin on the back surface of the wafer” is short enough that the slip due to the wafer self-weight stress does not occur. Say time.

According to the first and third aspects of the present invention, while the heat treatment temperature is maintained, the heat treatment temperature is constantly changed including the temperature region higher than the heat treatment temperature. The wafer thermally expands or contracts, and the contact position of the support pins on the back surface of the wafer always changes. Thereby, the wafer self-weight stress does not act on a fixed position on the back surface of the semiconductor wafer for a long time, and the stress induced by the contact of the tip of the support pin with the back surface of the silicon wafer is alleviated. As a result, the elongation of the slip of the semiconductor wafer accompanying the support by the support pins can be suppressed.
The same applies even if the constant temperature heat treatment is performed immediately before, during, and immediately after the variation time of the heat treatment temperature within a time period during which the slip due to the wafer self-weight stress does not occur. Further, the elongation of the slip of the semiconductor wafer accompanying the support by the support pins can be suppressed.

  Examples of the present invention will be described below.

The semiconductor wafer heat treatment method according to the first embodiment of the present invention will be specifically described.
First, ten silicon wafers (semiconductor wafers) 10 having a diameter of 200 mm, an initial oxygen concentration of 1.0 × 10 ¹⁸ atoms / cm ³ and a specific resistance of 10 Ω · cm grown by the CZ method are prepared.

(Comparative Examples 1-4)
As shown in FIG. 2, a part of the obtained silicon wafer 10 was placed in a horizontal state into a lamp annealing furnace 11 manufactured by AST having a furnace temperature of 600 ° C. The lamp annealing furnace is a lamp-type rapid heating furnace having a temperature rising rate of 1 to 100 ° C./second and a temperature decreasing rate of 1 to 100 ° C./second. In this furnace, the silicon wafer 10 is supported by three support pins (support members) 12 having the same length projecting from the back surface of the outer periphery of the wafer every 120 ° on the furnace bottom plate in the circumferential direction. This is simple support in which the front end abuts and the front and back surfaces of the wafer are horizontal.

  As shown in the graph of FIG. 3, the silicon wafer 10 was then heated to 1150 ° C. at a rate of temperature increase of 50 ° C./second, and then kept at 1150 ° C. for a predetermined time to heat-treat the silicon wafer 10. The predetermined time maintained at 1150 ° C. includes three types of 1.7 seconds (Comparative Example 1), 3.4 seconds (Comparative Example 2), and 8.5 seconds (Comparative Example 3). Thereafter, the temperature of the silicon wafer 10 of Comparative Examples 1 to 3 was decreased to 750 ° C. at 75 ° C./second, and the length of the slip S (slip length) on the back surface of each sample was subjected to Wright Etching for 2 minutes. Observed with a microscope. The results are shown in Table 1. The generation position of the slip S on the back surface of the wafer was only the contact position of each of the three support pins. Moreover, the slip length became longer with the extension of the holding time (FIG. 2).

(Test Example 1)
As shown in the graphs of FIGS. 1 and 4, the remaining part of the prepared silicon wafer 10 was heated to 1125 ° C. at 50 ° C./second. After the temperature of the silicon wafer 10 reached 1125 ° C., the rate of temperature increase was reduced to 5.9 ° C./second, and the temperature was increased from 1125 ° C. to 1175 ° C. for 8.5 seconds. That is, in Test Example 1, the heating temperature of the silicon wafer 10 constantly fluctuates during the heat treatment. Thereafter, the wafer heating temperature was decreased from 1175 ° C. to 750 ° C. at 75 ° C./second. The slip length of the sample of Test Example 1 obtained in this way was measured, and the results are shown in Table 1. The slip length was 258 μm, which was found to be significantly reduced compared to the slip length of 409 μm of the sample of Comparative Example 3 held for the same 8.5 seconds.

(Test Example 2)
The remaining part of the prepared silicon wafer 10 was heated to 1150 ° C. at 50 ° C./second. After the temperature of the silicon wafer 10 reached 1150 ° C., the rate of temperature increase was reduced to 10 ° C./second and the temperature was increased to 1180 ° C. for 3 seconds. Thereafter, the temperature was lowered to 1150 ° C. at 15 ° C./second for 2 seconds. After reaching 1150 ° C., the temperature was decreased to 750 ° C. at 75 ° C./second. The slip length of the obtained sample of Test Example 2 was measured, and the result is shown in Table 1. The slip length was 112 μm, and the slip was greatly reduced as compared with Comparative Example 3, and the processing time could be shortened.

(Test Example 3)
Further, it was found from Comparative Examples 1 and 2 that even if the heat treatment temperature was not constantly changed, slip extension did not occur when the holding time was 3.4 seconds or less. This is presumably because it takes time for dislocations generated from scratches to start moving and be observed as slips even when the wafer's own weight stress is applied.
The following test was implemented for the confirmation. The remaining part of the prepared silicon wafer 10 was heated to 1150 ° C. at 50 ° C./second. After the temperature of the silicon wafer 10 reached 1150 ° C., this temperature was maintained for 3 seconds, the temperature increase rate was 25 ° C./second, and the temperature was increased to 1175 ° C. for 1 second. When the temperature reached 1175 ° C., the temperature was decreased to 750 ° C. at 75 ° C./second. The slip length of the sample of Test Example 3 thus obtained was measured, and the result is shown in Table 1. Compared with Comparative Example 3, slip was significantly reduced and the processing time could be shortened.

  From the above, in the samples of Test Examples 1 and 2, the silicon wafer 10 is continuously thermally expanded in the wafer radial direction, and the contact position of the support pins 12 on the back surface of the wafer constantly changes. In this case, as shown in FIG. 2, it was found that the wafer self-weight stress does not act for a long time at a certain position on the back surface of the silicon wafer 10. As a result, the stress induced by the tip of the support pin 12 coming into contact with the back surface of the silicon wafer 10 is relieved, and the slip S of the silicon wafer 10 is extended due to the support by the support pin 12, as shown in FIG. It was found to be suppressed.

Thereafter, the 8.5 second holding sample of Comparative Example 3 and the samples of Test Examples 1 to 3 were heat-treated at 800 ° C. for 4 hours and further kept at 1000 ° C. for 16 hours. Went. Both the obtained samples were cleaved and then subjected to Wright etching, and the oxygen precipitate density was measured based on observation under a microscope. The results are shown in Table 1.
As is clear from Table 1, the oxygen precipitate density of both samples was the same as about 5 × 10 ⁵ atoms / cm ² or more. That is, by applying the present invention, the oxygen precipitate density equivalent to the conventional one was obtained. As a result, during the heat treatment of the thin film device obtained from the silicon wafer 10 of Example 1, a gettering effect can be effectively generated for the thin film device, and the slip at the pin support position on the back surface of the wafer can be achieved. It was found that can be reduced.
In addition, this Example is an example and the combination is free.

It is a principal part expanded sectional view which shows the wafer heat processing state by the heat processing method of the semiconductor wafer which concerns on Example 1 of this invention. It is a principal part expanded sectional view which shows the wafer heat processing state by the heat processing method of the semiconductor wafer which concerns on the conventional means. It is a graph which shows the temperature sequence in the heat processing of the semiconductor wafer which concerns on the conventional means. It is a graph which shows the temperature sequence during the heat processing of the semiconductor wafer which concerns on Example 1 of this invention.

Explanation of symbols

10 Silicon wafer (semiconductor wafer),
11 Lamp annealing furnace (lamp type rapid heating furnace),
12 Support pin (support member).

Claims (3)

Three or more support pins are brought into contact with the back surface to horizontally support the semiconductor wafer, and in this state, the semiconductor wafer is rapidly heated to a heat treatment temperature of 1100 ° C. or higher and held for a predetermined time, and then rapidly cooled. In the semiconductor wafer heat treatment method,
A semiconductor wafer heat treatment method in which the heat treatment temperature is constantly varied including the temperature region higher than the heat treatment temperature while the heat treatment temperature is maintained.   The method for heat treatment of a semiconductor wafer according to claim 1, wherein a fluctuation rate of the heat treatment temperature is 5 ° C./second or more. Three or more support pins are brought into contact with the back surface to horizontally support the semiconductor wafer, and in this state, the semiconductor wafer is rapidly heated to a heat treatment temperature of 1100 ° C. or higher and held for a predetermined time, and then rapidly cooled. In the semiconductor wafer heat treatment method,
The holding time of the heat treatment temperature is
The time during which the heat treatment temperature is constant and slip does not occur due to the wafer self-weight stress at the contact portion of the support pin on the back surface of the wafer,
A method for heat-treating a semiconductor wafer, comprising a time during which the heat-treatment temperature is constantly varied including a temperature region on a higher temperature side than the heat-treatment temperature.

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