Susceptor

Abstract

To provide a susceptor that produces uniform epitaxial films by adjusting the growth rate of epitaxial films on wafers at the periphery and center of the susceptor to be the same by tilting the crystal growth surface of the wafer in the direction of the raw material gas flow by setting an inclination in the pocket where the wafer is placed on the susceptor.SOLUTION: A susceptor 10 has a plurality of pockets 1 for placing a plurality of semiconductor wafers in the circumferential direction on the top surface of the rotating plate-shaped susceptor 10, where the inclination angle of each pocket 1 with respect to the horizontal direction is 2.5 to 3.5° and the bottom and top of the susceptor are parallel to each other.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a susceptor capable of forming a uniform semiconductor epitaxial film on a semiconductor substrate. [Background technology]

[0002] In recent years, with the miniaturization of semiconductor elements, there is a demand for reducing crystal defects on the wafer surface. To meet this demand, a technology is required to form an epitaxial film on the wafer surface or in its vicinity with highly controlled crystal defects.

[0003] The epitaxial wafer is manufactured by vapor-phase growing an epitaxial film EP on the surface of a silicon wafer W placed on a susceptor 52 using a vapor-phase epitaxial growth apparatus 50 as shown in FIG. 4. The silicon wafer W is placed on a circular recess (pocket) formed in the center of the upper surface of the susceptor. The pocket is composed of a circular bottom wall and side walls surrounding it, the bottom wall having a flat or slightly curved shape, and the side walls are formed by cutting the upper surface of the susceptor at a right angle to a predetermined depth. Then, the susceptor 52 and the silicon wafer W are rotated in a predetermined direction around a rotation axis 54, and the silicon wafer W is heated from the outside (not shown) of the chamber 51, while a reaction gas G is supplied horizontally from a reaction gas supply pipe 55 to an exhaust pipe 56. In this way, an epitaxial film EP is vapor-phase grown on the surface of the silicon wafer W.

[0004] Conventionally, various proposals have been made regarding susceptors in order to make the thickness of the epitaxial film formed on the wafer surface uniform and to reduce crystal defects.

[0005] Patent Document 1 describes a semiconductor vapor phase growth apparatus that epitaxially grows semiconductor crystals on a heated substrate by metal-organic vapor phase growth, in which multiple substrates are arranged circumferentially on a rotating, plate-like susceptor, and the center of the susceptor is bulged so that the crystal growth surfaces of the substrates are inclined at 5° with respect to the flow direction of the raw material gas (Figure 4 of Patent Document 1).

[0006] However, when the substrate is tilted by 5 degrees with respect to the flow direction of the source gas, the growth rate at the center of the susceptor becomes faster than that at the periphery of the susceptor, making it difficult to produce a uniform epitaxial film. Also, because the pocket on which the wafer is placed is tilted while the bottom surface is horizontal, the thickness of the susceptor is not constant, resulting in non-uniform thermal conduction and making it difficult to produce a uniform epitaxial film.

[0007] Furthermore, even with the technology of Patent Document 1, there was still a problem in that the region on the periphery of the epitaxial wafer could not be used for semiconductor elements due to variations in film thickness at the periphery of the epitaxial wafer caused by the crystal orientation of the wafer. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] JP 2004-207545 A Summary of the Invention [Problem to be solved by the invention]

[0009] The object of the present invention is to provide a susceptor capable of producing a uniform epitaxial film by adjusting the growth rate of the epitaxial film on the wafer at the outer periphery and center of the susceptor to be the same by providing an incline in the pocket portion of the susceptor on which the wafer is placed and tilting the crystal growth surface of the wafer relative to the flow direction of the raw material gas. [Means for solving the problem]

[0010] The susceptor of the present invention is characterized in that it has pockets for placing multiple semiconductor wafers in the circumferential direction on the top surface of a rotating plate-like susceptor, the inclination angle of each pocket with respect to the horizontal direction being 2.5 to 3.5°, and the bottom surface and top surface of the susceptor being parallel to each other. When the diameter of the susceptor is d and the thickness is t, 1≦t / d≦0.0 5 It is preferable that: Effect of the Invention

[0011] According to the present invention, a uniform epitaxial film can be grown on the semiconductor wafer by tilting the crystal growth surface of the wafer with respect to the flow direction of the source gas. Specifically, by tilting each pocket on the upper surface of the susceptor by 2.5 to 3.5 degrees with respect to the horizontal direction, making the thickness of the susceptor uniform, and making the bottom surface and the upper surface parallel, the growth rate of the epitaxial film on the wafer at the outer periphery of the susceptor is suppressed, and the growth rate of the epitaxial film at the outer periphery and the center of the susceptor becomes the same, and a uniform epitaxial film can be produced. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a plan view of a susceptor of the present invention. [Diagram 2] FIG. 2 is a cross-sectional view of the susceptor taken along line AA of FIG. [Diagram 3] FIG. 3 is a cross-sectional view for illustrating a process of placing a silicon wafer in the pocket portion in FIG. 2 and forming a film by chemical vapor deposition. [Figure 4] FIG. 4 is a cross-sectional view of a conventional vapor phase growth apparatus. [Diagram 5] 5 is a cross-sectional view of a susceptor having a shape in which the substrate is inclined in the opposite direction and the center of the susceptor is bulged (susceptor described in Patent Document 1). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, an embodiment of a susceptor of the present invention will be described with reference to Figures 1 to 3. Note that the drawings are schematic or conceptual, and the relationship between the thickness and width of each portion, the size ratio between portions, etc. are not accurately illustrated.

[0014] As shown in Fig. 1, the susceptor 10 of the present invention has a disk-shaped base 2 and a plurality of pockets 1 arranged concentrically near the outer periphery of the disk. The pockets 1 are arranged so that the susceptor 10 has rotational symmetry with respect to a rotation axis (not shown). In other words, the susceptor 10 of the present invention is a so-called single-wafer type susceptor having a concave pocket 1 formed on one main surface thereof for placing a semiconductor wafer W (substrate to be processed). The semiconductor wafer W is a silicon wafer or the like.

[0015] A carbon material or a carbon material whose surface is coated with silicon carbide (SiC) is used for the substrate 2 constituting the susceptor 10. The susceptor 10 is obtained by either using the disk-shaped substrate 2 as it is, in which a plurality of pockets are formed and which is inclined from the center toward both sides, or by applying a coating film of SiC to the substrate 2 by chemical vapor deposition (CVD).

[0016] The diameter d of the susceptor 10 is 600 to 850 mm, and the thickness t is 12 to 18 mm. As shown in Fig. 2, the thickness t of the susceptor is constant, and the bottom surface and the top surface are parallel to each other. When the diameter of the susceptor 10 is d and the thickness is t, 0.01≦t / d<0.05, preferably 0.02≦t / d≦0.04, and more preferably 0.02≦t / d≦0.03. That is, when the thickness t of the susceptor 10 is 0.01 to 0.05 times the diameter d, an epitaxial film having a uniform thickness and reduced crystal defects can be formed. When the thickness t is less than d×0.01 mm, the susceptor 10 is easily warped by heat during use, and a uniform epitaxial film cannot be produced. On the other hand, when the thickness t exceeds d×0.05 mm, heat is not easily transferred to the susceptor 10, and an epitaxial film cannot be produced.

[0017] The number of pockets 1 is 3 to 10, preferably 5 to 8, from the viewpoint of enabling stable rotation of the susceptor 10 and uniform supply of gas to the wafer W. The diameter d0 of the pocket 1 is formed slightly larger than the diameter of the wafer W so that the wafer W fits into the pocket. The depth of the pocket is formed to be approximately the same as the depth of the wafer W to be processed. The diameter d0 of the pocket 1 is 150 to 250 mm, preferably 175 to 225 mm. The diameter d0 of the pocket 1 is determined depending on the number of pockets 1.

[0018] The depth t0 of the pocket 1 is 70 to 100 μm, and preferably 75 to 95 μm. The depth t0 is in the range of 0.4 / 10 to 0.8 / 10 of the thickness t of the susceptor 10.

[0019] The susceptor 10 has an inclination angle (θ) of the pocket portion 1 with respect to the horizontal direction of 2.5 to 3.5°, and the bottom surface is parallel to the inclination of the upper surface and the pocket portion 1. If the inclination angle (θ) is less than 2.5°, the growth rate of the epitaxial film is faster at the outer periphery of the susceptor 10. On the other hand, if the inclination angle (θ) is more than 3.5°, the growth rate of the epitaxial film is faster at the center of the susceptor 10, making it difficult to produce a uniform epitaxial film. FIG. 2 is a front view of the susceptor 10, and the inclination angle (θ) represents the angle of inclination from the center of the susceptor 10 toward both side surfaces. When the inclination angle (θ) is within the above range, the growth rate of the epitaxial film is approximately the same at the outer periphery and center of the susceptor 10, making it possible to produce a uniform epitaxial film. It is more preferable that the inclination angle (θ) is 2.7 to 3.3°.

[0020] To form an epitaxial film on the upper surface of the wafer W using the susceptor 10, the wafer W is placed in a pocket 1 of the susceptor 10 in a chamber (not shown) as shown in FIG. 3. Then, while rotating the susceptor 10 and the wafer W in a predetermined direction at a predetermined speed (see FIG. 4), the wafer W is heated by a heater (not shown) provided outside the chamber. Then, the wafer W is brought into contact with a reaction gas G introduced horizontally into the chamber, and an epitaxial film is grown on the wafer W by chemical vapor deposition.

[0021] Since the susceptor 10 is inclined from the center toward both sides, when an epitaxial film is formed on the wafer W held in the pocket portion 1, the reaction gas G supplied horizontally flows along the shape of the susceptor as shown in Fig. 3. This allows the reaction gas G to flow uniformly over the entire wafer W, reducing the variation in thickness of the epitaxial film being formed.

[0022] The thickness t of the susceptor 10 is constant. That is, the surface on which the pocket portion 1 is formed is parallel to the opposite surface. By making the thickness t constant, the thermal conduction of the entire susceptor 10 becomes uniform, and a uniform epitaxial film can be manufactured. In addition, as shown in FIG. 3, the reaction gas G flows along the upper surface of the susceptor, so that the reaction gas G hits the entire upper surface of the susceptor 10, which contributes to the uniformity of the thickness of the epitaxial film formed on the wafer W. EXAMPLES

[0023] The present invention will now be described in more detail with reference to examples, but the present invention is not limited to the following examples.

[0024] The susceptor used had eight pockets 1 arranged concentrically around the outer periphery of a carbon substrate with a diameter d of 63 cm. The inner peripheral end of the pockets was located at a radius R of 127.5 mm from the center of the susceptor, and the outer peripheral end of the pockets was located at a radius R of 282.5 mm from the center of the susceptor. The diameter d0 of each pocket 1 was 155 mm, and the depth t0 was 0.8 mm.

[0025] The inclination angle (θ) from the center of the susceptor toward both sides was set to the conditions of Examples 1 to 6 and Comparative Examples 1 to 3. In each example, an epitaxial film was formed on a silicon wafer using the prepared susceptor, and the state of the film was evaluated. The conditions and evaluation results of other examples are shown in Table 1. In Table 1, the difference between the maximum and minimum thicknesses of the epitaxial film within the wafer surface was marked with ◯ when it was 5 μm or less, with × when it was over 10 μm, and with △ when it was over 5 μm and 10 μm or less.

[0026] [Table 1]

[0027] As shown in Examples 1 to 6, when the inclination angle (θ) from the center of the susceptor toward both side surfaces was in the range of 2.5 to 3.5°, the film formation results on the silicon wafer were good. When the ratio (t / d) of the susceptor thickness t to the susceptor diameter d is 0.01≦t / d≦0.05 (Examples 1 to 6), the difference between the maximum and minimum thicknesses of the epitaxial film in the wafer surface is 10 μm or less, and when it is 0.02≦t / d≦0.04 (Examples 1, 2, and 45), the difference between the maximum and minimum thicknesses of the epitaxial film in the wafer surface is 5 μm or less, which shows good film formation results. On the other hand, when the inclination angle θ is 2.3° (Comparative Example 1) and when the inclination angle θ is 3.7° (Comparative Example 2), the heat from the bottom surface of the susceptor is not uniformly transferred, and the film becomes non-uniform. In Comparative Example 3 using the susceptor shown in FIG. 5, the bottom surface and the top surface of the susceptor are not parallel, so the growth rate of the epitaxial film is not uniform between the outer periphery and the center of the susceptor, and a uniform epitaxial film cannot be obtained. [Explanation of symbols]

[0028] 1 Pocket 2 Base 10 Susceptor 50 Epitaxial growth equipment 51 Chamber 52 Susceptor 53 Pocket 54 Rotational Axis 55 Reaction gas supply pipe 56 Exhaust pipe W: Semiconductor wafer (substrate to be processed) EP epitaxial film G Reactive gas

Claims

1. A disk-shaped susceptor having a plurality of pockets on an upper surface for placing semiconductor wafers therein, a bottom surface of the susceptor is parallel to the top surface and the pocket portion; The upper surface is inclined downward from the center to the outer periphery, The inclination angle of the pocket portion with respect to the horizontal direction is 2.5 to 3.5 degrees, A susceptor, characterized in that, when the diameter of the susceptor is d and the thickness of the susceptor is t, 0.01≦t / d≦0.

05.

2. A susceptor as described in claim 1, wherein a raw material gas is supplied from the horizontal direction and is used to flow along the upper surface of the susceptor.

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