Abstract:
The invention provides an apparatus for excluding unwanted deposition at the edge of a substrate which prevents excess purge gas from flowing over the surface of the substrate at the region adjacent a notch on a substrate. Another aspect of the invention provides a wider purge gas channel that prevents excess purge gas from flowing over the surface of the substrate. Still another aspect of the present invention provides a purge gas guide that includes a notch therein to prevent excess purge gas from adversely affecting deposition at the vicinity of the substrate notch.

Description:
This application claims priority from U.S. Provisional Patent Application Ser. No. 60/067,129, filed Dec. 2, 1997. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to a chemical vapor deposition (CVD) chamber. More particularly, the present invention relates to an improved susceptor used in a CVD chamber. 
     2. Background of the Related Art 
     CVD vacuum chambers are useful for depositing thin films on semiconductor substrates. Generally, a precursor gas is flown into a vacuum chamber through a gas distribution system and reacts with a heated substrate surface to deposit a thin film thereon. The deposition gas reaction also forms volatile by-product gases which are pumped away through a chamber exhaust system. Typically, a susceptor or substrate support member is provided to secure the substrate during the deposition process as well as to heat the substrate to the required processing temperature. Furthermore, a purge gas is flown towards the backside and/or edge of the substrate during processing to prevent deposition on the backside and the edge of the substrate which tends to flake off and contaminate the chamber. Exemplary CVD chambers are disclosed in U.S. Pat. Nos. 5,516,367 and 5,476,548, both of which are hereby incorporated by reference. 
     To increase manufacturing efficiency and device capabilities, the sizes of the devices formed on a substrate have decreased while the number of devices formed on a substrate has increased. Uniform CVD deposition across the surface of the substrate has become increasingly important to form uniform devices on substrates and to maximize the number of devices that can be formed on the substrate. Moreover, reduction of particle contaminates generated in the chamber has also become increasingly important to produce functional devices. 
     FIG. 1 a  is a partial cross sectional view of a substrate  14  supported on a susceptor having a purge gas channel  30  surrounding the edge of the substrate. FIG. 1 b  is a partial top perspective view of the substrate  14  supported on the susceptor showing the purge gas channel  30  surrounding the edge of the substrate. As shown in FIG. 1 a , the substrate  14  is releaseably secured on the susceptor surface by a vacuum chuck having vacuum channels  20  which are connected to a vacuum pump (not shown), and the edge of the substrate is surrounded by a purge gas channel  30 . A purge gas feed line  22 , preferably disposed within the susceptor  10 , feeds a purge gas into the purge gas channel  30  surrounding the edge of the substrate  14 , thereby inhibiting the process gas from coming in contact with the substrate edge and depositing thereon. Preferably, a plurality of purge gas feed lines  22  supply purge gas into the purge gas channel  30  to achieve even distribution of the purge gas to the edge of the substrate. 
     Generally, the purge gas flows past the edge of the substrate  14  and outwardly away from the center of the substrate. However, because a substrate typically includes a notch  16  at the substrate edge as an identifying mark of the type and the orientation of the substrate, an excess amount of purge gas passes through the notch, diluting the processing gases adjacent to the notch and preventing formation of functional devices in the region adjacent to the notch. FIG. 1 b  shows the effects of the purge gas, as indicated by the arrows, in the region adjacent to the notch. Typically, deposition in the region adjacent to the notch  16  is non-uniform because the excess purge gas coming through the notch creates an area of exclusion on the substrate. Thus, the region adjacent the notch  16  is wasted because of improper processing. 
     A similar purging effect in the region adjacent the notch occurs in a processing system where a purge guide is used for controlling the purge gas. FIG. 2 a  is a partial cross sectional view of a purge guide  26  in combination with a substrate  14  disposed on a susceptor  10  in a processing position. FIG. 2 b  is a partial top view of a purge guide and a substrate having a notch  16 , showing the effects of the purge gas in the region adjacent the notch. As shown in FIG. 2 a , the substrate  14  is supported by the susceptor  10  and releaseably secured on the susceptor surface by a vacuum chuck having vacuum channels  20  which are connected to a vacuum pump (not shown). When the susceptor  10  is moved to a processing position, the purge guide  26  rests on the susceptor  10 , preferably on a plurality of anti-sticking grooves  21 , and a shield portion  12  of the purge guide  26  extends over the edge of the substrate  14 . The shield portion  12  of the purge guide  26  maintains a fixed gap, typically between about 2 and about 10 mils, above the substrate  14  through which the purge gas flows as the gas continues into the processing area of the CVD chamber. It is important to maintain a consistent gap around the edge of the substrate  14  to control the purge gas distribution so that a uniform center to edge deposition on the substrate can be achieved. 
     A purge gas feed line  22 , preferably disposed within the susceptor  10 , feeds a purge gas into a purge gas opening  24  between the purge guide  26  and the susceptor  10 . The purge guide  26  then guides the flow of purge gas, as shown by the arrows, to the edge of the substrate  14 , thereby inhibiting the process gas from coming in contact with the substrate edge and depositing thereon. Preferably, the purge gas opening  24  completely surrounds the edge of the substrate, and a plurality of purge gas feed lines  22  supply purge gas into the purge gas opening  24  to achieve even distribution of the purge gas to the edge of the substrate. 
     However, an excess amount of purge gas passes through a notch  16  on the substrate, diluting the processing gas adjacent the notch and preventing formation of functional devices in the region adjacent the notch. FIG. 2 b  shows the effects of the purge gas, as indicated by the arrows, in the region adjacent the notch. Typically, deposition in the region adjacent the notch  16  is non-uniform because the excess purge gas coming through the notch  16  creates an area of exclusion on the substrate. Thus, the region adjacent the notch  16  is wasted because of improper processing. 
     Therefore, there remains a need for an apparatus for supporting a substrate in a processing chamber which delivers a purge gas to the edge of the substrate and prevents excess purge gas from causing non-uniform and inconsistent deposition at the region adjacent the substrate notch. 
     SUMMARY OF THE INVENTION 
     The invention provides an apparatus for supporting a substrate in a processing chamber and excluding unwanted deposition at the edge of a substrate without adversely affecting deposition on the substrate in the region adjacent the substrate notch. In one aspect of the invention, a purge gas channel is provided in a susceptor and includes a notch portion disposed outwardly of the channel to direct gases at the location of a notch on a substrate away from the upper surface of the substrates. The notched portion enables delivery of purge gas to achieve the desired edge exclusion without detrimentally affecting the deposition on the region adjacent the notch on the substrate. 
     Another aspect of the present invention provides a purge guide with a notch formed therein which guides the purge gas away from the upper surface of the substrate adjacent the notch on the substrate to achieve the desired edge exclusion without detrimentally affecting the deposition on the region adjacent the notch on the substrate. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     So that the manner in which the above recited features, advantages and objects of the present invention are attained can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof which are illustrated in the appended drawings. 
     It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
     FIG. 1 a  is a partial cross sectional view of a substrate supported on a susceptor having a purge gas channel surrounding the edge of the substrate. 
     FIG. 1 b  is a partial top perspective view of a substrate supported on a susceptor having a purge gas channel surrounding the edge of the substrate. 
     FIG. 2 a  is a partial cross sectional view of a purge guide in combination with a substrate disposed on a susceptor in a processing position. 
     FIG. 2 b  is a partial top view of a purge guide and a substrate having a notch, showing the effects of the purge gas in the region adjacent the notch. 
     FIG. 3 is a cross sectional view of a deposition chamber showing a susceptor of the invention. 
     FIG. 4 is a top perspective view of a susceptor of the invention. 
     FIG. 5 is a partial cross sectional view of the susceptor of the invention taken along the line  5 — 5 . 
     FIG. 6 is a partial top perspective view of a substrate having a notch in combination with a purge guide of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 3 is a cross sectional view of a deposition chamber  70  showing a susceptor  40  of the invention. Generally, the chamber  70  includes sidewalls  76 , a lid  78  and a bottom wall  80  which define an enclosure  82 . Process gas entering a gas inlet  84  in the lid is discharged into the chamber through a showerhead  86  which, as shown, is positioned in the upper portion of the chamber. The vertically movable susceptor  40 , also referred to as a heater or a substrate support member, is disposed through the bottom wall of the chamber and includes an upper surface  44  to support a substrate  14 . 
     The susceptor  40  is formed of an aluminum plate (although other materials may be used) supported in the chamber on a vertical shaft  41 . The susceptor  40  includes a shoulder  92  disposed around its perimeter on which a heater shield  94  is preferably disposed. The heater shield  94  is designed to prevent deposition on the susceptor  40  and to provide a surface which is easily replaced during routine maintenance. The heater shield  94  includes an inner wall  96  and an outer vertical wall  98 . The inner wall  96  of the heater shield  94  and the outer surface of the susceptor body define a purge gas channel  48 . Purge gas enters the chamber through purge gas feed lines  50  formed in the susceptor  40  where it is delivered to the edge of the substrate through the purge gas channel  48 . 
     The susceptor  40  preferably includes a vacuum chuck to secure the substrate to the support member during processing. While a vacuum chuck is preferred, other types of chucks and securing devices may be used to hold the substrate on the support member. Vacuum chucks enable the substrate to be secured to the support member without contacting the purge guide. Vacuum chucks also have been shown to improve substrate temperature uniformity, improve film uniformity, generate fewer particles in the chamber and prevent bridging between the substrate and the purge guide and the substrate and the support member. 
     FIG. 4 is a top perspective view of a susceptor of the invention. FIG. 5 is a partial cross sectional view of the susceptor of the invention taken along the line  5 — 5 . The susceptor  40  generally includes a substrate receiving surface  44 , a heater (not shown) disposed in the susceptor to heat a substrate disposed on the susceptor, a plurality of substrate alignment pins  46  and a purge gas channel  48  connected to a purge gas supply  50 . 
     The susceptor  40  of the invention includes a recess  42  which is disposed correspondingly to a notch on a substrate that is placed on the susceptor  40  during processing. Preferably, the recess  42  has a height about equal to the height of the substrate, an arc length longer than the notch opening on the substrate and a width extending outwardly from the outer edge of the purge gas channel  48  to about the depth of the notch on the substrate. To direct the purge gas away from the notch, the recess  42  preferably is greater than the notch on the substrate in all dimensions (length, width and height). 
     In operation, purge gas is delivered through the support member to the annular purge gas channel  48  formed in the susceptor  40 . The purge gas is delivered through the purge gas channel  48  to the backside of the substrate  14  and across the edge of the substrate  14 . The majority of the purge gas then flows outwardly away from the edge of the substrate and does not interfere with the deposition on the substrate. 
     However, at the notch of the substrate, the purge gas tends to create a gas stream which flows inwardly toward the center of the substrate because the notch in the substrate provides a low pressure region which draws the purge gas therein. This inwardly flowing purge gas dilutes the processing gas at the region adjacent the notch and prevents fabrication of functional devices in the region adjacent the notch. By providing a recess  42 , the purge gas is drawn outwardly away from the center of the substrate. Thus, the purge gas flows past the edge of the substrate and into the recess  42 , and the processing gas at the region adjacent the notch is then able to react and deposit a film and form functional devices properly at the region adjacent the notch. 
     Although the shape of the recess is shown to approximate a rectangular box, other shapes can be utilized just as effectively to divert the purge gas away from the substrate surface adjacent the notch. These shapes include but are not limited to spherical, frustoconical, ellipsoid and triangular. Furthermore, the corners and edges of the recess  42  can be tapered to further assist purge gas flow toward the recess  42  instead of toward the notch. 
     Alternatively, the width of the purge gas channel  48  can be increased around the entire circumference of the susceptor to decrease the inwardly flowing purge gas at the region adjacent the notch on the substrate. The increase in the opening or width of the purge gas channel  48  decreases the purge gas pressure on the back side of the substrate and allows more purge gas to flow past the edge of the substrate. Thus, the purge gas is less likely to create an inwardly-flowing gas stream at the notch which would dilute the processing gas at the region adjacent the notch. Also, the purge gas channel openings can be tapered to further induce purge gas flow outwardly away from the center of the substrate to allow uniform deposition at the region adjacent the notch. 
     An other alternative embodiment provides a purge gas guide/delivery system which achieves the desired edge exclusion without detrimentally affecting the deposition on the region adjacent the notch on the substrate. FIG. 6 is a partial top perspective view of a substrate having a notch in combination with a purge guide of the invention. The purge guide  60  includes a shield portion  62  which extends over the edge of the substrate and a recess  64  on the shield portion  62  positioned correspondingly to the notch  16  on the substrate  14 . Preferably, the recess  64  on the shield portion  62  on the purge guide  60  provides at least the same size opening over the purge gas channel  24  as that provided by the substrate notch. Because of the purge gas pressure under the shield portion  62 , the purge gas tends to form a jet stream at the opening provided by the notch  16 . By providing a recess  64  on the shield portion  62  of the purge guide  60  that is comparatively larger than the notch  16 , the purge gas is diverted outwardly away from the center of the substrate. As with the recess described above for the susceptor, the recess  64  on the shield portion  62  of the purge guide  60  preferably has a rectangular shape, but can be a variety of shapes including spherical triangular and ellipsoid shapes. 
     While the foregoing is directed to the preferred embodiment of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof. The scope of the invention is determined by the claims which follow.