METHOD FOR DEPOSITING AN EPITAXIAL LAYER ON A FRONT SIDE OF A SEMICONDUCTOR WAFER, AND DEVICE FOR CARRYING OUT THE METHOD

Abstract

Variations in wafer thickness due to non-uniform CVD depositions at angular positions corresponding to crystallographic orientation of the wafer are reduced by providing a ring below the susceptor having inward projections at azimuthal positions which reduce radiant heat impinging upon the wafer at positions of increased deposition.

Claims

1.-9. (canceled)

10. A device for depositing an epitaxial layer on a front side of a wafer having an orientation notch, comprising a mechanism for holding and rotating a susceptor having a susceptor support shaft and susceptor support arms; and a ring positioned below the susceptor which is held by the susceptor support arms and has inwardly pointing projections; wherein the susceptor comprises a susceptor ring having a resting face for resting the wafer in the edge region of a back side of the wafer onto the susceptor ring and a stepped outer boundary of the susceptor ring that is adjacent to the resting face, the resting face having an inwardly pointing projection and the stepped outer boundary adjacent to the resting face having an inwardly pointing bulge at the same azimuthal position.

11. The device of claim 10, wherein the ring comprises quartz glass.

12. The device of claim 10, wherein a projection of the ring is made from a material which selectively reduces intensity of thermal radiation passing through it, wherein first subregions on the edge of a wafer resting on the susceptor, in which a growth rate of the epitaxial layer at uniform temperature of the wafer is greater because of the orientation of the monocrystalline material, are heated more weakly than in adjacent second subregions.

13. The device of claim 10, wherein the ring has two or four inwardly pointing projections.

14. A method for depositing an epitaxial layer on a front side of a wafer composed of monocrystalline material, comprising providing a wafer having an orientation notch; arranging the wafer on a device according to claim 10, wherein the orientation notch of the wafer has the same azimuthal position as a projection of the ring; heating the wafer to a deposition temperature by means of thermal radiation which is directed towards a front side and towards a back side of the wafer; rotating the wafer about its center; conducting a deposition gas across the front side of the wafer; and selectively reducing the intensity of a portion of the thermal radiation which is directed towards the back side of the wafer, such that first subregions on the edge of the wafer, in which a growth rate of the epitaxial layer at uniform temperature of the wafer is greater because of the orientation of the monocrystalline material, are heated more weakly than in adjacent second subregions.

15. The method of claim 14, wherein the intensity of the portion of the thermal radiation is selectively reduced by arranging material having low transmittance in the IR region of the spectrum in the beam path of the thermal radiation.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] FIG. 1 shows a wafer (101) having an orientation notch (102). The wafer (101) has a <100> orientation. The upper face of the wafer (101) is, for example, the (100) plane. The orientation notch 102 marks one of four <110> crystal directions which, distributed around the circumference of the wafer at an interval of 90°, point to corresponding planes in the region of the edge of the wafer, on which planes an epitaxial layer grows at a comparatively higher rate than on planes in the region of the edge to which four <100> crystal directions point.

[0013] FIG. 2 shows, in line with FIG. 1, a top view of a wafer (201) with <110> orientation having an orientation notch (202).

[0014] FIG. 3 illustrates one embodiment of the invention, showing the centrally rotatable susceptor and ring.

[0015] FIG. 4 illustrates a further embodiment of the invention.

[0016] FIG. 5 illustrates a top view of one embodiment of a ring for use in the invention.

[0017] FIG. 6 illustrates a top view of a further embodiment of a ring in accordance with the invention.

[0018] FIGS. 7 and 8 illustrate a susceptor ring of the invention.

[0019] FIG. 9 illustrates an inwardly pointing bulge in the wall of a wafer-receiving pocket in a susceptor.

[0020] FIG. 10 illustrates an improvement in wafer geometry which may be achieved by the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] A device (FIG. 3) according to the invention comprises not only a susceptor (301), but also a mechanism for holding and rotating the susceptor (301) having a susceptor support shaft (302) and susceptor support arms (303). Furthermore, the mechanism for holding and rotating the susceptor (301) can comprise a wafer lift shaft (304) and wafer lift pins (305). An essential feature of the device is a ring (306) which is held by the susceptor support arms (303) and is arranged under the susceptor (301) without having direct contact with the susceptor (301). The ring (306) is held by the susceptor support arms (303) such that it cannot be shifted along its circumferential direction. Preferably, susceptor support pins (307), which are inserted through holes (402, 502, 602) in the ring (306), are situated on the susceptor support arms (303). The distance between an upper face of the ring (306) and a lower face of the susceptor (301) is preferably not less than 5 mm and not more than 10 mm.

[0022] FIG. 4 shows a top view of a ring (401) which, in the embodiment shown, has holes (402) and four inwardly pointing projections (403) which are arranged so as to be distributed across the circumference at an interval of 90°. This embodiment is suitable for use in a device as per FIG. 3 for depositing therein, according to the invention, an epitaxial layer on the front side of a wafer having a <100> orientation. Preferably, the ring (401) consists of quartz glass and the projections (403) consist of a material having low transmittance in the IR region of the spectrum. In this region, the transmittance of the projections (403) is preferably not more than 20% and particularly preferably not more than 5%, based on a material thickness of 10 mm. The projections (403) preferably consist of opaque quartz glass.

[0023] FIG. 5 shows a top view of a ring (501) which, in the embodiment shown, has holes (502) and two inwardly pointing projections (503) which are arranged so as to be distributed across the circumference at an interval of 180°. This embodiment is suitable for use in a device as per FIG. 3 for depositing therein, according to the invention, an epitaxial layer on the front side of a wafer having a <110> orientation.

[0024] Preferably, an inner edge (404, 504) of the projection (403, 503) of the ring (401, 501) is situated at a radial position, the distance of which in relation to a centre Z of the ring (401, 501) is not less than 140 mm, preferably not less than 145 mm and particularly preferably 148 mm to 150 mm.

[0025] FIG. 6 shows a top view of a ring (601) which, in the embodiment shown, has holes 602 and four inwardly pointing projections (603) which are arranged so as to be distributed across the circumference at an interval of 90°. This embodiment is suitable for use in a device as per FIG. 3 for depositing therein, according to the invention, an epitaxial layer on the front side of a wafer having a <100> orientation. In the embodiment depicted, the projections (603) are T-shaped and each comprise a web (604) and a ring segment (605). The ring segment (605) has a radial length and a width in the circumferential direction. The radial length is preferably not less than 3 mm and not more than 8 mm. Expressed as opening angle α, the width is preferably not less than 15° and not more than 25° and most preferably 20°. Preferably, the ring (601) and/or the webs (604) consist of quartz glass and the ring segments consist of a material having low transmittance in the IR region of the spectrum. In this region, the transmittance of the ring segment (605) is preferably not more than 20% and particularly preferably not more than 5%, based on a material thickness of 10 mm. The ring segments (605) preferably consist of opaque quartz glass.

[0026] FIGS. 7 and 8 show a susceptor ring (701, 801) having a resting face (703, 805) and the adjacent stepped boundary (702, 806). One embodiment of a susceptor ring (701, 801) according to the invention envisages that the resting face has an inwardly pointing projection. This means that the radial width W.sub.1 of the resting face (703, 805) of the susceptor ring (701, 801) at an azimuthal position is greater than the radial width W.sub.2 at the opposite position.

[0027] In addition, a wafer (704, 804) can preferably be positioned in the susceptor ring (701, 801) such that the position with the greatest width of the resting face W.sub.1 (802) coincides with the position of the orientation notch (803).

[0028] In addition, the stepped boundary (FIG. 9, 901) adjacent to the rest can preferably be realized such that it has an inwardly pointing bulge (FIG. 9, 902).

[0029] Preferably, the azimuthal position of an inwardly pointing bulge of the stepped boundary (902) adjacent to the rest is identical to the azimuthal position of the inwardly pointing projection of the resting face (403, 503).

[0030] To deposit an epitaxial layer on a front side of a wafer composed of monocrystalline material, the wafer is preferably arranged in the described device such that the orientation notch of the wafer has the same azimuthal position as a projection of the ring. Thereafter, the wafer is brought to a deposition temperature by means of thermal radiation which is directed towards a front side and towards a back side of the wafer and deposition gases are conducted across the front side of the wafer.

[0031] Said deposition gases preferably contain silanes, chlorosilanes or mixtures thereof, diluted in a carrier gas (preferably hydrogen).

[0032] What is understood by said deposition temperature is the temperature at which a layer is deposited on the wafer under the given boundary conditions.

[0033] The means of the described device ensure the selective reduction of the intensity of a portion of the thermal radiation which is directed towards the back side of the wafer, the result being that first subregions on the edge of the wafer, in which a growth rate of the epitaxial layer at uniform temperature of the wafer is greater because of the orientation of the monocrystalline material, are heated more weakly than in adjacent second subregions.

[0034] The above description of exemplary embodiments is to be understood exemplarily. The disclosure made thereby firstly enables a person skilled in the art to understand the present invention and the associated advantages and secondly encompasses alterations and modifications to the described structures and methods that are also obvious in the understanding of a person skilled in the art. Therefore, all such alterations and modifications and also equivalents are to be covered by the scope of protection of the claims.

[0035] FIG. 10 illustrates the effect achieved by use of the method according to the invention in epitaxy. Here, the azimuthal coordinates in degrees [° ] are plotted on the x-axis D.sub.x. The y-axis D.sub.y shows layer thickness in dimensionless coordinates, which are measured along a perimeter of the wafer. Dashed line A represents the height curve which can be achieved using prior-art methods. Solid line B is achieved by use of the method according to the invention. The orientation notch was situated at position 0°, or 360°.