JP2013045805A - Silicon epitaxial wafer manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of effectively manufacturing a silicon epitaxial wafer having a uniform resistance distribution by inhibiting auto-doping.SOLUTION: A silicon epitaxial wafer manufacturing method of epitaxially growing a silicon single crystal on a silicon single crystal substrate to laminate an epitaxial layer, comprises: growing on the silicon single crystal substrate doped with boron having resistivity of not less than 0.5 mΩ cm and not more than 20.0 mΩ cm, an epitaxial layer having resistivity of not less than 0.5 Ω cm and not more than 2000 Ω cm and grown at a growth rate of not less than 5 μm/min. and not more than 15 μm/min.

Description

  The present invention relates to a method of manufacturing a silicon epitaxial wafer by growing an epitaxial layer on a boron-doped low-resistance substrate.

  A silicon epitaxial wafer (hereinafter simply referred to as “epitaxial wafer”) is manufactured, for example, as follows.

A silicon single crystal substrate (hereinafter simply referred to as “substrate”) is placed on a susceptor in a reaction vessel of a vapor phase growth apparatus, and the temperature in the reaction vessel is raised to 1100 ° C. to 1200 ° C. with hydrogen gas flowing. (Temperature raising step). When the temperature in the reaction vessel reaches 1100 ° C. or higher, a natural oxide film (SiO ₂ : Silicon Dioxide) formed on the substrate surface is removed. In this state, a hydrogen source gas such as trichlorosilane (SiHCl ₃ : Trichlorosilane) and a dopant gas such as diborane (B ₂ H ₆ : Diborane), phosphine (PH ₃ : Phosphine), arsine (AsH ₃ : Arsine) are hydrogenated. The gas is supplied into the reaction vessel together with the gas. In this way, a silicon single crystal thin film (hereinafter referred to as “epitaxial layer” or simply “thin film”) is epitaxially grown on the main surface of the substrate (film formation step). After the thin film is epitaxially grown to a desired thickness in this manner, the supply of the silicon source gas and the dopant gas is stopped, and the temperature in the reaction vessel is lowered while maintaining the hydrogen atmosphere (cooling step). An epitaxial wafer can be manufactured by the process as described above.
Such a method for manufacturing an epitaxial wafer is described in, for example, Patent Document 1.

  Regarding the quality of the epitaxial wafer, the device manufacturer is required to improve the uniformity of the film thickness and resistivity of the epitaxial layer within the wafer surface (hereinafter referred to as “film thickness distribution” and “resistance distribution”). Among these, there is a strong demand for tightening the resistance distribution.

  By the way, in the process of manufacturing an epitaxial wafer as described above, in the film forming process, three elements of (i) film forming temperature, (ii) silicon source gas supply amount, and (iii) reaction pressure are important. Can be changed intentionally (adjustment). If these three elements are uniform in the plane of the substrate, the film thickness distribution and resistance distribution of the epitaxial layer are the best. However, as an important factor that cannot be changed intentionally in addition to the above, (iv) outgas generated from the substrate. The relationship between resistance distribution and outgas will be described below.

  In the film formation process, the substrate is annealed at the film formation temperature, and thus an outgas containing a dopant is generated from the substrate. Outgas is generated particularly from the back surface of the substrate and goes around to the front surface side. At this time, since vapor phase growth is performed on the surface, outgas greatly affects the vicinity of the wafer edge (periphery). Epitaxial growth on the surface is performed by a process gas. At this time, outgas is mixed and taken into the growing epitaxial layer. Hereinafter, this phenomenon is referred to as “auto-doping”.

Japanese Patent Laid-Open No. 08-139027

The above-mentioned auto-doping causes a difference in the amount of incorporated dopant between the central portion and the edge portion of the epitaxial wafer. In particular, a low-resistance substrate doped with boron (20.0 mΩ · cm or less, particularly 0.8 mΩ · cm In the following, the outgas increases and the effect becomes remarkable. This deteriorates the resistance distribution of the manufactured epitaxial wafer.
There is also a method of suppressing such auto-doping by providing a hole in the susceptor of the vapor phase growth apparatus, but the effect of auto-doping suppression is not sufficient, and the nanotopography (hereinafter, referred to as the backside of the wafer) due to the influence of the hole Another problem arises that it deteriorates the nanotopo).

  The present invention has been made in view of the above problems, and an object thereof is to provide a method capable of efficiently and stably producing a silicon epitaxial wafer having a uniform resistance distribution by suppressing autodoping. To do.

  In order to achieve the above object, according to the present invention, in a method for manufacturing a silicon epitaxial wafer in which a silicon single crystal is epitaxially grown on a silicon single crystal substrate and an epitaxial layer is laminated, the resistivity is 0.5 mΩ · cm or more. On the silicon single crystal substrate doped with boron at 0 mΩ · cm or less, the growth rate is 5 μm / min or more and 15 μm / min or less, and the resistivity is 0.5 Ω · cm or more and 2000 Ω · cm or less. A method for producing a silicon epitaxial wafer, characterized by growing a layer.

In the growth of an epitaxial layer on a low-resistance substrate where resistance distribution deterioration due to auto-doping is likely to occur, by adjusting the growth rate of the epitaxial layer within the above range, the auto-doping is effectively suppressed and stabilized. Can be epitaxially grown. In addition, since the epitaxial layer can be grown while suppressing auto-doping without using a special apparatus or the like, the productivity is good, and deterioration of nanotopo on the back surface of the wafer does not occur.
As described above, according to the present invention, a high-quality silicon epitaxial wafer having a uniform resistance distribution can be manufactured with high productivity.

At this time, the resistivity of the epitaxial layer is preferably 1 Ω · cm or more and 500 Ω · cm or less.
In the case where an epitaxial layer having the above-described resistivity is grown on a low-resistance substrate, the present invention is suitable because the resistivity is likely to be uneven due to auto-doping.

  As described above, according to the present invention, a high-quality silicon epitaxial wafer having a uniform resistance distribution and high productivity can be stably manufactured.

It is a flowchart which shows an example of the epitaxial growth process in the manufacturing method of the silicon epitaxial wafer of this invention. It is a graph which shows the result of having investigated the correlation of a growth rate and dopant concentration distribution in an Example and a comparative example.

  Conventionally, during epitaxial growth on a boron-doped low-resistance substrate, there has been a problem that the resistance distribution by auto-doping becomes non-uniform. On the other hand, in the conventional method, the autodoping suppression effect is insufficient, or the nanotopo on the back surface of the wafer is deteriorated by the perforated susceptor for autodoping suppression.

  On the other hand, as a result of intensive studies by the present inventors, it has been found that the amount of autodoping can be reduced by increasing the growth rate of epitaxial growth, which is normally performed at a growth rate of about 3.6 μm / min or less. When an epitaxial layer having a resistivity of 0.5 to 2000 Ω · cm is grown on a low resistance substrate having a resistivity of 0.5 to 20.0 mΩ · cm by doping boron, the growth rate is set to 5 μm / cm 2. The present invention has been completed by finding that a silicon epitaxial wafer having a uniform resistance distribution can be stably produced by controlling the autodoping sufficiently by setting the speed to 15 μm / min or more.

Hereinafter, the present invention will be described in detail as an example of an embodiment with reference to the drawings, but the present invention is not limited thereto.
In the present invention, first, as a substrate for epitaxial growth, a P-type silicon single crystal substrate having a resistivity of 0.5 mΩ · cm to 20.0 mΩ · cm and highly doped with boron is prepared.

  Low resistance substrate doped with boron and having a resistivity of 0.5mΩ · cm or more and 20.0mΩ · cm or less reduces the resistance component of switching operation when manufacturing epitaxial wafers for power devices such as MOSFETs. can do. However, since the substrate having the above-described resistivity is doped with boron at a high concentration, autodoping is particularly likely to occur during epitaxial growth, and the resistance distribution of the epitaxial layer to be grown tends to deteriorate. Even in such a low resistance substrate, autodoping can be effectively suppressed by the production method of the present invention.

As a silicon single crystal substrate to be prepared, for example, a substrate produced by slicing a silicon single crystal ingot grown by CZ (Czochralski) method or FZ (floating zone) method and lapping, grinding, polishing, etching, etc. It can be. In the case of the CZ method, a substrate having the above resistivity doped with boron can be produced by growing a silicon single crystal ingot from a raw material melt to which boron is added. In the case of the FZ method, boron can be doped by gas doping or the like using a gas containing diborane or the like.
Further, after the substrate is manufactured, for example, boron can be doped by ion implantation or the like to obtain the above resistivity.

Next, an epitaxial layer having a resistivity of 0.5 Ω · cm to 2000 Ω · cm is grown on the above-described silicon single crystal substrate at a growth rate of 5 μm / min to 15 μm / min.
Thus, if the growth rate is 5 μm / min or more, particularly 6 μm / min or more, the above-described low-resistance boron-doped substrate has a resistance of 0.5 Ω · cm to 2000 Ω · cm, particularly 1 Ω · cm to 500 Ω · cm. Even if an epitaxial layer having the following resistivity is formed, the resistance distribution can be made sufficiently uniform. Further, if the growth rate is 15 μm / min or less, it is possible to suppress generation of HCl gas that inhibits epitaxial growth due to the reaction between the silicon source gas and hydrogen gas, and stable epitaxial growth can be achieved.

  In addition, it is preferable to obtain an optimum growth rate within the above range based on the correlation between the growth rate and the autodoping amount obtained in advance.

As this epitaxial growth, for example, as shown in the flow chart of FIG. 1, first, a silicon single crystal substrate is placed on a susceptor provided in a reaction vessel of a vapor phase growth apparatus using a transfer device ((a) preparation Process).
The susceptor of the vapor phase growth apparatus used at this time is not particularly limited. However, if a susceptor not provided with an outgas discharge hole is used, it is possible to prevent deterioration of nanotopo on the back surface of the wafer. In the present invention, autodoping can be sufficiently reduced by increasing the growth rate without providing such holes. In addition, a vapor phase growth apparatus is not specifically limited, A single wafer type or a batch type apparatus can be used.

  Next, with the hydrogen gas flowing in the reaction vessel, the temperature in the reaction vessel is raised to a film formation temperature for vapor phase growth of the epitaxial layer ((b) temperature raising step). The film forming temperature is set to 1000 ° C. or higher at which the natural oxide film on the substrate surface can be removed with hydrogen.

Next, while maintaining the inside of the reaction vessel at the film formation temperature, silicon source gas such as trichlorosilane (SiHCl ₃ ), diborane (B ₂ H ₆ ), phosphine (PH ₃ ), arsine (AsH) together with hydrogen gas. ₃ ) A dopant gas such as ₁ ) is supplied at a predetermined flow rate, and an epitaxial layer is grown until a predetermined film thickness is obtained ((c) film forming step).
When performing high-speed growth of 5 to 15 μm / min according to the present invention, although depending on the film formation temperature, the silicon source gas is increased approximately 1.5 to 4.0 times compared to the case of performing at a normal growth rate. . For example, when growing an epitaxial layer having a desired resistivity while increasing the growth rate, the flow rate of the silicon source gas is changed as described above. Change (increase) from flow rate.

  Next, the temperature in the reaction vessel is lowered to cool the epitaxial wafer to the extraction temperature ((d) cooling step). In this cooling step, the hydrogen atmosphere is switched to the nitrogen atmosphere between about 800 ° C. and 400 ° C. Then, when the extraction temperature is reached in the nitrogen atmosphere, the epitaxial wafer is taken out from the vapor phase growth apparatus ((e) taking-out step).

  Next, the extracted epitaxial wafer can be appropriately cleaned such as RCA cleaning ((f) cleaning step). As a cleaning method in this cleaning step, in addition to a typical RCA cleaning, a method in which the concentration and type of a chemical solution are changed within a normal range can be used.

  Then, particles on the surface of the epitaxial wafer are measured by a particle counter ((g) particle counter measurement), and an epitaxial wafer to be a product is selected ((h) selection).

  With the manufacturing method of the present invention as described above, a high-quality silicon epitaxial wafer having a uniform resistivity within the surface can be manufactured with high productivity.

EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated more concretely, this invention is not limited to these.
(Examples and comparative examples)
An epitaxial layer having a resistivity of 13.0 Ω · cm was formed on a boron-doped silicon substrate having a resistivity of 2.0 mΩ · cm at a growth rate of 1 μm / min to 9 μm / min to manufacture an epitaxial wafer.

FIG. 2 shows the result of measuring the dopant concentration in the center portion and the edge portion of the epitaxial layer in the manufactured epitaxial wafer.
As shown in FIG. 2, when an epitaxial wafer having the above resistance condition is epitaxially grown at a normal growth rate (about 1 to 3 μm / min), the dopant concentration of the epitaxial layer becomes large at the edge portion, and the resistivity tends to decrease. . When a device is manufactured using such an epitaxial wafer, the characteristics of the device fluctuate between the central portion and the edge portion of the wafer, causing a characteristic defect at the edge portion. However, as is apparent from FIG. 2, the dopant concentration at the edge portion begins to decrease at a growth rate of 2 μm / min or more, decreases significantly at 5 μm / min, and is almost the same as the value at the center at 6 μm / min or more. I found out. Therefore, it can be said that a growth rate of 5 μm / min or more is necessary in order not to affect the device characteristics. Furthermore, it can be seen that if the growth rate is 6 μm / min or more, the dopant concentration is approximately the same at the center portion and the edge portion, which is more preferable.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has substantially the same configuration as the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.

Claims (2)

  In a method of manufacturing a silicon epitaxial wafer by epitaxially growing a silicon single crystal on a silicon single crystal substrate and laminating an epitaxial layer, the resistivity is 0.5 mΩ · cm or more and 20.0 mΩ · cm or less, and boron is doped. A silicon epitaxial wafer characterized by growing the epitaxial layer having a resistivity of 0.5 Ω · cm to 2000 Ω · cm on the silicon single crystal substrate at a growth rate of 5 μm / min to 15 μm / min. Manufacturing method.   2. The method for producing a silicon epitaxial wafer according to claim 1, wherein the resistivity of the epitaxial layer is 1 Ω · cm or more and 500 Ω · cm or less.

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