WO2000000663A1

WO2000000663A1 - Method and device for displacing wafers in a deposition reactor

Info

Publication number: WO2000000663A1
Application number: PCT/US1999/014040
Authority: WO
Inventors: Mark G. Stinson; Daniel A. Dauchess, Iii; Kenneth W. Baker; Gregory K. Chowning
Original assignee: Memc Electronic Materials, Inc.
Priority date: 1998-06-30
Filing date: 1999-06-23
Publication date: 2000-01-06
Also published as: TW417173B; WO2000000663A9

Abstract

A low pressure chemical vapor deposition reactor (10) for deposition of material on a plurality of wafers (W) in a wafer carrier (20). The wafer carrier supports the wafers in a generally upright position and each wafer is supported at a peripheral edge of the wafer. The reactor includes a reactor vessel (14) having a chamber sized for receiving the wafer carrier loaded with wafers to contain the wafers for deposition of material from vapor flowing through the chamber. An elongate beam (26) supports the wafer carrier at a first end of the beam in the reactor chamber. A mechanism displaces the elongate beam such that the wafers within the wafer carrier move relative to the wafer carrier to inhibit formation of material bridges between the wafer carrier and the wafers caused by deposition of material from vapor in the reaction chamber.

Description

METHOD AND DEVICE FOR DISPLACING WAFERS IN A DEPOSITION REACTOR

Background of the Invention

This invention relates generally to devices for use in chemical vapor deposition and more particularly to a device for reducing damage to silicon wafers processed in a deposition reactor.

It is common practice in the processing of semiconductor material (typically in the form of a wafer) to deposit a layer or film of polycrystalline semiconductor material on one face of the wafer. In the integrated circuit formed from the semiconductor wafer, the layer may provide conducting regions, electrical insulation between metals and/or protection from the environment. For example, a layer of polycrystalline silicon on a monocrystalline silicon may be used for gettering, or as the gate electrode material in MOS integrated circuit devices.

Although many methods are available for depositing a layer of material on the monocrystalline semiconductor wafer, chemical vapor deposition processes are most frequently employed. Generally, the wafer is held on a carrier in a heated reactor through which gas containing the material to be deposited in a vaporous form is circulated. The decomposition of the gas on the semiconductor wafer produces the layer. The most common process is referred to as low pressure chemical vapor deposition, or LPCVD.

As with all processing of semiconductor wafers, it is important that the wafer not be damaged during processing. However, it has been found that wafers are occasionally chipped when removed from the carrier after the LPCVD because of the breakage of solidified bridges of polycrystalline material which join the wafers to the carrier. The bridges are formed by polycrystalline material deposited from the gas onto the wafer and the carrier. If the bridges connecting the wafer to the carrier are sufficiently strong, chipping of the wafer will occur when it is removed from the carrier.

The carrier disclosed in co-assigned U.S. Patent No. 5,417,767, incorporated herein by reference, addresses the aforementioned problem in a generally satisfactory manner. The present invention represents an improvement with respect to the patented design.

Summary of the Invention

Among the several objects and features of the present invention may be noted the provision of a deposition reactor and a device therefore which inhibits formation of bridges of deposited material between a wafer carrier and the silicon wafer supported thereon; the provision of such a reactor and device which reduce the occurrence of chips along the edges of silicon wafers; and the provision of such a reactor and device which are relatively inexpensive to manufacture and is easily operated.

Briefly, apparatus of this invention is a low pressure chemical vapor deposition reactor for deposition of material on a plurality of wafers in a wafer carrier. The wafer carrier supports the wafers in a generally upright position and each wafer is supported at a peripheral edge of the wafer. The reactor includes a reactor vessel having a chamber sized for receiving the wafer carrier loaded with wafers to contain the wafers for deposition of material from vapor flowing through the chamber. An elongate beam supports the wafer carrier at a first end of the beam in the chamber. Means are included for displacing the elongate beam such that the wafers within the wafer carrier move relative to the wafer carrier to inhibit formation of material bridges between the wafer carrier and the wafers caused by deposition of material from vapor in the chamber.

A method is disclosed for depositing material on silicon wafers. Chemical vapor containing the material is circulated in a low pressure chamber of a reactor vessel containing a plurality of said wafers. The wafers are supported by a wafer carrier which is supported by an elongate beam. The improvement to the method comprises selectively displacing the wafers within the wafer carrier so that the wafers move relative to the wafer carrier during the deposition process to inhibit formation of material bridges between the wafer carrier and the wafers caused by deposition of the material. Other objects and features of the present invention will be in part apparent and in part pointed out hereinafter.

Brief Description of the Drawings

Fig. 1 is a schematic of a deposition reactor with parts broken away to show internal configuration; Fig. 2 is a vertical section taken along line

2-2 in Fig. 1;

Fig. 3 is a vertical section like Fig. 2 showing the cam and follower engaged.

Corresponding reference characters indicate corresponding parts throughout the several views of the drawings . Detailed Description of the Preferred Embodiment

Referring now to the drawings, and in particular to Fig. 1, a low pressure chemical vapor deposition reactor, indicated generally at 10, is shown to comprise a frame 12, a reactor vessel 14 and a support assembly, indicated generally at 16. The generally cylindrical reactor vessel 14 and the support assembly 16 are mounted on the frame 12. The general construction of the reactor 10 is conventional and will not be described in detail. A suitable reactor 10 is Model No. 5200 available from Thermco Co. of Orange, California, although it is to be understood that reactors having different constructions may be used without departing from the scope of this invention. A chamber 18 of the reactor vessel 14 is sized for receiving a wafer carrier 20 loaded with silicon wafers W to contain the wafers for deposition of material (e.g., polysilicon) from vapor that flows inside the chamber. The chamber 18 receives the wafer carrier 20 through an open end 22 of the reactor vessel 14.

Preferably, the wafer carrier 20 (referred to in the industry as a "boat") holds the wafers W generally upright in slots in the wafer carrier, contacting the wafers only at their edges. A suitable wafer carrier is described in co-assigned U.S. Patent No. 5,417,767.

A rigid, elongate paddle 26 (generally, beam) supports the wafer carrier 20 at a first end of the paddle which is inside the chamber 18 during operation of the reactor 10. It is to be understood that a plurality of wafer carriers may be supported on the paddle, the wafer carriers typically extending in a single file line atop the paddle 26. The support assembly 16 includes a paddle loader 28 which receives and supports an opposite second end of the paddle 26. The paddle loader 28 is slidably mounted on a linear raceway 30 mounted on the frame 12. The linear raceway preferably includes two rails 32 (only one is shown) which mount bearings 34 of the paddle loader 28. The raceway extends a distance away from the open end 22 of the vessel 14. The paddle loader 28 is movable linearly along the raceway 30 to move the wafer carrier 20 and paddle 26 outward from said vessel 14 for loading and unloading the wafers . The linear raceway 30 is supported adjacent the vessel 14 on a support point 36 and is supported along its remaining length by brackets 38 attached to the frame 12. The raceway 30 is not fixed to the brackets 38, therefore, it may be displaced upwardly or laterally relative to the frame 12 as will be described below.

The support assembly 16 also includes a door 40 connected to the paddle loader so that as the paddle loader moves toward the reactor vessel 14, the door will engage the vessel for sealing the open end 22. Preferably, the door 40 and paddle loader 28 are connected via a flexible bellows 42 so that the door can move slightly relative to the paddle loader in order to tightly seal against the vessel 14. An O-ring seal (not shown) is provided around the door 40. The bellows 42 and the door 40 include passageways (not shown) through which the paddle 26 passes, the passageways sized and shaped to allow the paddle to move somewhat vertically and laterally relative to the door.

In a preferred embodiment of the invention, a cam 46 and a follower 48 are mounted adjacent an end of the linear raceway 30 opposite the vessel 14. The cam 46 has the shape of a cylinder and has a protrusion 50, such as a set screw, extending a relatively small distance from the periphery of the cylinder for engagement with the follower 48. The cam 46 is rotatably mounted on a motor 52 attached to a bracket 54 of the frame 12. The follower 48 has the shape of a smooth cylinder and is rotatably mounted on a block 56 attached to the linear raceway 30. The follower 48 is positioned over the cam 46 such that when the protrusion of the cam engages the follower, the block 56, the linear raceway 30 and the paddle loader 28 are displaced upward relative to the frame 12, causing the raceway to pivot about the support point 36. As shown in Fig. 1, the linear raceway 30 remains in contact with the brackets 38 of the frame 12 when the protrusion 50 of the cam 46 is not engaged with the follower 48. The motor 52 is preferably a 24V DC motor with a 728:1 ratio such as Model No. GM9413G238 available from Pittman Corp., Harleysville, PA. A conventional controller (not shown) may operate to control power to the motor 52. Preferably the motor is controlled by a controller of the reactor 10.

To operate the reactor 10, the wafers are loaded into the wafer carrier 20 which is placed on the paddle 26. The paddle loader 28 is moved into the chamber 18 of the reactor vessel 14 until the door 40 engages the reactor vessel and sealingly closes the open end 22 of the vessel. Thereafter, gas containing the material to be deposited in a vaporous form is circulated in the chamber 18. As the gas is circulated, the controller causes the motor 52 to rotate periodically a predetermined number of revolutions at a predetermined speed. For instance, the controller may be programmed so that the motor 52 turns every 15 minutes through one revolution at a speed of 4 RPM. With each revolution of the cam 46, the block 56 and the linear raceway 30 are displaced upward causing the raceway to pivot about the support point 36 and causing the first end of the paddle 26 to be displaced downward. Preferably, the displacement is only slight, e.g., the protrusion 50 of the cam 46 may be, for instance, about 3 mm, and occurs only momentarily, so that the raceway 30 moves up and down quickly. Note also that the set screw forming the protrusion 50 may be adjusted, that is screwed in or out of the cam, to change the height of the displacement.

The sharp edges of the preferred protrusion 50 of the cam 46 are such that it causes a jerking motion of the raceway 30. However, it is contemplated that the protrusion may have smooth edges or other shapes. Moreover, the cam could include a cut-out or indentation such that the cut-out would cause the linear raceway to move downwardly. It should also be understood that it is within the scope of this invention to move the raceway 30 and the paddle 26 laterally, the wafers W being advantageously displaced by such motion.

The motion of the raceway 30 causes the first end of the paddle 26 to oscillate downward and upward until equilibrium is reached. Preferably, the displacement of the raceway 30 and the paddle 26 causes a relatively small displacement of the wafers W in the slots of the wafer carrier 20 so that the wafers move only slightly out of their original position in the slots of the carrier and so that the wafers are not damaged by the motion. The displacement must be limited so that the wafers W are not damaged by impacting the wafer carrier

20. The displacement must be great enough so that the motion prevents formation of material bridges between the wafers W and the carrier 20. Such slight displacement will inhibit the formation of strong, solidified material bridges between the wafers W and the carrier 20.

It is to be understood that other mechanisms may be substituted for the cam and follower mechanism described above for displacing the linear raceway 30 and the wafers W. For instance, a linkage mechanism may be substituted for the cam 46 and follower 48. Such a linkage has a first link rotatably connected to the motor 52 and connected to a second link connected to the block 56. Each revolution of the motor 52 causes the second link to pull the linear raceway 30 upward as described above and thus displace the wafers W. A pneumatic or hydraulic mechanism, such as a linear actuator may be used. The actuator is positioned such that its piston forces the linear raceway 30 upward upon actuation.

Preferably, the mechanism employed is capable to give a small, quick upward motion as described above.

The invention has significant advantages for deposition processes on silicon wafers, and specifically for increasing the yield of acceptable silicon wafers produced by such processes. Typically, edge chips are caused by breakage of solidified material bridges during post-deposition removal of the wafers from the wafer carrier. These edge chips may cause the wafer to be rejected. Use of this invention has been shown to reduce the formation of material bridges and decrease the number of edge chips in the wafers caused by breakage of material bridges. The invention has been found to have no deleterious effects on the wafers and thus the invention increases the yield of acceptable wafers.

Further, the invention has been found to be particularly advantageous where relatively thick layers of polysilicon are to be deposited on the wafers. Generally, increasing the thickness of the deposition increases the number and size of material bridges between the wafers and their carrier and thus increases the number and/or size of edge chips. By cyclically moving the wafers as taught by this invention, the occurrence of material bridges in thicker layer depositions has been decreased.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained. As various changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

Claims

ClaimsWHAT IS CLAIMED IS:

1. A low pressure chemical vapor deposition reactor for deposition of material on a plurality of wafers in a wafer carrier, said wafer carrier supporting the wafers in a generally upright position, each wafer being supported at a peripheral edge of the wafer, the reactor comprising: a reactor vessel having a chamber sized for receiving the wafer carrier loaded with wafers to contain the wafers for deposition of material from vapor flowing through the chamber, an elongate beam for supporting the wafer carrier at a first end of said beam in the chamber, means for displacing the elongate beam such that the wafers within the wafer carrier move relative to the wafer carrier to inhibit formation of material bridges between the wafer carrier and the wafers caused by deposition of material from vapor in the chamber.

2. A low pressure chemical vapor deposition reactor as set forth in claim 1 further comprising a support assembly and a frame, the support assembly being mounted on said frame for supporting a second end of said beam, said support assembly operable to remove the wafer carrier and beam from said chamber for loading and unloading the wafers .

3. A low pressure chemical vapor deposition reactor as set forth in claim 2 wherein said displacing means include cooperable cam and follower elements on said support assembly and on the frame of the reactor device .

4. A low pressure chemical vapor deposition reactor as set forth in claim 3 wherein said cam is rotatably mounted on the frame, and said follower is mounted on the support assembly.

5. A low pressure chemical vapor deposition reactor as set forth in claim 4 wherein said support assembly includes a linear raceway mounted on the frame such that the raceway can be moved upward relative to the frame, said follower being mounted adjacent an end of the linear raceway of the support assembly, said cam and follower operable to displace the linear raceway upward.

6. A low pressure chemical vapor deposition reactor as set forth in claim 4 further comprising a controller and a motor, the motor operable to drive said cam and the controller operable to control the motor such that the motor rotates periodically.

7. In a method of depositing material on silicon wafers of the type wherein chemical vapor containing said material is circulated in a low pressure chamber of a reactor vessel containing a plurality of said wafers, and wherein said wafers are supported by a wafer carrier which is supported by an elongate beam, the improvement comprising: selectively displacing the wafers within the wafer carrier so that the wafers move relative to the wafer carrier during the deposition process to inhibit formation of material bridges between the wafer carrier and the wafers caused by deposition of the material.

8. In a method as set forth in claim 7, the improvement wherein the wafers are displaced within the wafer carrier by displacing the elongate beam such that the beam oscillates.