Dispersion plate for flowing vaporizes compounds used in chemical vapor deposition of films onto semiconductor surfaces

A dispersion plate for evenly flowing at low pressure into a processing chamber vaporized material, such as a tungsten compound for deposition of metal layers onto a semiconductor, has a disc-like body with a center axis, an input face and an output face. The dispersion plate has a cup-like entrance along the center axis in its input face for receiving a stream of vaporized material and a plurality of passages for flow of vapor with each passage having a length and a diameter and extending radially from the entrance like the spokes of a wheel at inclined angles relative to the center axis from the input face to the output face. Two annular grooves are cut into the output face and intersect with the respective ends of the passages. The plate has a center hole with a flared diameter extending along the center axis from the entrance in the input face to the output face. The hole and plurality of passages are designed to have sufficiently large diameters so as to keep pressure drops low with respect to vapor flowing through the plate.

FIELD OF THE INVENTION
 This invention relates to a dispersion plate for gasses, such as vaporized
 tungsten hexacarbonyl, flowing through the plate into a reaction chamber
 to deposit by chemical vapor deposition metal films on a surface of a
 semiconductor wafer.
 BACKGROUND OF THE INVENTION
 The widespread use of semiconductors is due to their usefulness, their cost
 effectiveness and to their unique capabilities. Accompanying the growth in
 the use, and usefulness, of semiconductors is the development of new
 processes and materials for the design and manufacture of semiconductors
 together with new or improved manufacturing equipment and hardware. An
 important recent development is the use of copper (which has about twice
 the unit conductivity of more commonly used aluminum) for electrical
 interconnections, or circuit traces within very large scale integrated
 circuits (VLSIs). The use of copper has permitted faster speeds of
 operation and greater capability of the VLSI circuits but has led to the
 need to prevent atoms of copper in the copper circuits from adversely
 interacting with atoms of other materials used in the VLSIs. One way of
 preventing such interactions is to provide a "barrier" layer over and/or
 under the copper, such as a thin layer of tungsten (W).
 It is known that a layer of a material such as tungsten can be deposited by
 chemical vapor deposition (CVD) onto exposed surfaces of a semiconductor
 wafer during processing into VLSIs. Tungsten, which is a relatively heavy
 metal having an atomic weight of 183.86, has high temperature resistance
 and provides suitable protection against the reaction of copper with other
 materials during the fabrication of VLSIs. A compound of tungsten, namely
 tungsten hexacarbonyl [W(CO).sub.6 ], can be vaporized under suitable
 conditions of pressure and temperature to obtain a gaseous phase of the
 compound which can then be used in CVD processing to form a film or layer
 of metallic tungsten on a semiconductor wafer. This will be explained in
 greater detail hereinafter.
 It is desirable that a layer of metal (such as tungsten) being deposited by
 CVD on a semiconductor wafer be uniform in thickness. To achieve this, a
 chemical vapor compound of the material flowing into a reaction chamber
 where the semiconductor wafer is being processed should be controlled in
 flow direction and amplitude so that the vapor is evenly distributed and
 flows uniformly toward the wafer. This is especially true of a material
 such as tungsten hexacarbonyl vapor, the molecules of which have
 relatively high weight and inertia. In addition, because a CVD process
 step using a compound such as tungsten hexacarbonyl is typically carried
 out in a reaction chamber maintained under low pressure conditions (e.g.,
 a small fraction of a Torr), the flow of gas vapor into the chamber
 through a dispersion plate should have high-flow-conductance so that
 pressure drop across it is relatively low. The gas vapor should also be
 controlled in temperature as it passes through the plate and enters the
 chamber to prevent condensation of the vapor.
 It is desirable to have a simple and efficient dispersion plate which fills
 the above described needs.
 SUMMARY OF THE INVENTION
 In accordance with the invention in one specific embodiment thereof, there
 is provided a dispersion plate for applying vapors of materials useful in
 chemical vapor deposition in the processing of semiconductors. The
 dispersion plate comprises a body having a center axis, an outer diameter,
 an input face, an output face, and a thickness between the faces with an
 entrance along the center axis in the input face for receiving a stream of
 vaporized material. The plate defines a plurality of passages through the
 plate for flow of vapor, each passage having a length and a diameter and
 extending radially from the center axis at respective inclined angles from
 the input face to the output face. The plate further defines a hole having
 a diameter and extending along the center axis from the entrance in the
 input face to the output face. The hole and plurality of passages have
 sufficiently large diameters to result in a relatively low pressure drop
 to the vapor flowing through them and to provide dispersion of vapor
 flowing through the plate such that vapor flows evenly onto the surface of
 the semiconductor body.
 A better understanding of the invention together with a fuller appreciation
 of its many advantages will best be gained from a study of the following
 description given in conjunction with the accompanying drawings and
 claims.

DETAILED DESCRIPTION OF THE DRAWINGS
 Referring now to FIG. 1, there is shown in cross-section and partially
 broken away, an apparatus 10 useful in chemical vapor deposition (CVD) of
 materials onto semiconductor wafers. The apparatus 10 comprises a
 processing chamber 12 (of which only a part is shown), a susceptor or
 platform 14, a semiconductor wafer (body) 16 positioned on the platform 14
 for CVD processing, a manifold 18, and a dispersion plate 20 embodying
 features of the invention for controlling and directing the flow of
 vaporized (gaseous) material into the chamber 12 so that it flows
 uniformly down toward the wafer 16. The chamber 12, is hermetically
 sealable and can be maintained at sub-atmospheric pressure. The wafer 16,
 after being inserted into the chamber 12, is lowered onto the platform 14
 to the position shown by pins 21 (only one of which is shown). The pins 21
 are vertically movable up and down on command on insertion or removal of
 the wafer 16. The platform 14 may be movable vertically as well. The
 platform 14 is heated (by means not shown) and in turn heats the wafer 16
 to an elevated temperature (e.g., about 400.degree. C.) At such
 temperature vaporized material flowing into the chamber 12 upon reaching
 and touching the surface of the wafer 16 will break down into its
 constituents and a tungsten film is deposited onto a top surface of the
 wafer 16. Unwanted residues and gas are exhausted from the chamber 12 via
 an exit port (not shown).
 The manifold 18 supplies vaporized material to the dispersion plate 20 and
 is attached by bolts 22 to the plate 20 at a cup-shaped entrance 24 in the
 dispersion plate 20. The manifold 18 (well known in the art) may if deemed
 desirable apply heat and ultrasonic energy to material (indicated by an
 arrow 26) flowing to it from a source (not shown) to ensure that vaporized
 material flowing into the entrance 24 is entirely vaporized and free of
 droplets or particles.
 The dispersion plate 20, in the specific embodiment illustrated herein, has
 in accordance with one feature of the invention high-flow-conductance,
 that is, low pressure drop across the plate of the vapor flowing through
 it. This enables the plate 20 to function well in CVD processing using
 materials such as tungsten hexacarbonyl [W(CO).sub.6 ] where the pressure
 within the chamber 12 must be maintained at a low value (e.g., about 50
 milli-Torr). In accordance with another feature of the invention, the
 plate 20 is configured to control and direct the flow of a relatively
 heavy vapor, such as tungsten hexacarbonyl, so that the vapor flows from
 the plate 20 uniformly onto the wafer 16. This helps ensure that a film
 (e.g., of tungsten) being deposited onto the wafer 16 has improved
 uniformity across the wafer 16. The dispersion plate 20 is advantageously
 made from a disc-like solid block of a metal such as aluminum having high
 heat conductivity and ease of machining. The plate 20 is attached to an
 upper wall 25 of the processing chamber 12 by a plurality of bolts 26,
 (only two of which are shown) and together with the wall 25 forms a top
 seal for the chamber 12.
 As will be explained in greater detail hereinafter, the dispersion plate 20
 has a center axis 28 and has drilled through it a number of radially
 extending passages 30 and 32 and a center hole 33. Vaporized material from
 the manifold 18 flowing into the entrance 24 flows through the plate 20
 along the passages 30, 32, and hole 33 as indicated by the respective
 arrows 34, 36, and 37. The plate 20 has an output face, generally
 indicated at 40, which has cut into it an annular groove, near the outer
 diameter of the plate 20 and indicated by brackets 42, a smaller diameter
 annular groove, indicated by brackets 44, and a flared opening or funnel
 46 beneath the center hole 33.
 The passages 30 in the plate 20 extend radially from the center axis 28
 like the individual spokes of a wheel. The passages 30 are each inclined
 at a uniform downward angle relative to the axis 28 and each has a
 diameter larger than that of the passages 32. The latter similarly extend
 like the spokes of a wheel and are inclined downward at an angle smaller
 than the inclined angle of the passages 30. The diameter of the center
 hole 33 is smaller than that of the passages 32. The particular shapes and
 configurations of the center hole 33, funnel 46, the passages 30 and 32,
 and of the grooves 42 and 44 in the output face 40 of the dispersion plate
 20, in the specific embodiment of the invention illustrated herein, ensure
 that a vaporized material, such as tungsten hexacarbonyl, flowing into the
 chamber 12 will flow evenly down toward the wafer 16. An important result
 of this is that a thin layer of material (e.g., tungsten metal less than a
 micron thick) can be deposited with improved uniformity across the surface
 of the wafer 16.
 Referring now to FIG. 2, there is shown a perspective view, partially
 broken away of the dispersion plate 20 of FIG. 1, showing its output face
 40. As seen in FIG. 2, the face 40 has the annular grooves 42 and 44 and
 the funnel 46. The groove 42 is somewhat V-shaped and along its bottom
 intersects the output ends of the multiple passages 30 (only three of
 which are visible in this view). Similarly, the groove 44 is somewhat
 V-shaped and along its bottom intersects the output ends of the passages
 36 (only some of which are visible). The funnel 46 provides a flared
 output for the center hole 33. The passages 30, 32, and the hole 33
 originate in the entrance 24. The grooves 42, 44, and the funnel 46 blend
 or mix the individual vapor streams from the passages 30, 32 and the hole
 33 into a uniform flow of gas vapor from the plate 20 toward the wafer 16
 (see FIG. 1). The grooves 42, 44, and the funnel 46 also eliminate much of
 the flat part of the surface of the face 40. This, as will be explained in
 greater detail hereinafter, helps reduce unwanted deposition of solid
 material on the face 40 instead of on the wafer 16.
 Referring now to FIG. 3 there is shown a cross-section of the dispersion
 plate 20. The spoke-like outer passages 30 are inclined relative to the
 center axis 28 by an angle indicated by an arc 52. Each passage 30 extends
 radially from the entrance 24 to the bottom of the groove 42. The
 spoke-like inner passages 32 are inclined relative to the center axis 28
 by an angle indicated by an arc 54, and each passage 32 extends radially
 from the entrance 24 to the bottom of the groove 44. The hole 33 and its
 funnel 46 are aligned along the axis 28.
 Referring now to FIG. 4, there is shown an enlarged cross-section view of
 the dispersion plate 20 showing further details of the entrance 24, other
 portions of the plate being broken away. The bottom of the entrance 24 has
 a flat center surface 56, which is pierced by the center hole 33. The
 bottom of the entrance 24 has an outer, annular shoulder indicated at 58
 comprising a downward-sloping surface 60 and a vertical cylindrical wall
 62 into which are formed the passages 30 (see also FIGS. 1 and 3). As was
 explained previously, these passages 30 extend radially and individually
 like the spokes of a wheel from the center axis 28. They extend downward
 at an angle (indicated by the arc 52) into the groove 42 (see also FIG.
 2). Similarly, the bottom of the entrance 24 in the plate 20 has an
 intermediate annular shoulder indicated at 64 into which are formed the
 passages 32. Like the passages 30, the respective passages 32 also extend
 radially individually from the center axis 28 and extend downward at an
 angle, indicated by the arc 54, into their respective groove 44. The
 provision of the shoulders 58 and 64 in the entrance 24 facilitates the
 accurate placement and forming of the multiple passages 30 and 32 through
 the dispersion plate 20.
 Referring now to FIG. 5, there is shown a graph 70 illustrating the
 relationship of vapor phase to solid phase of a material such as tungsten
 carbonyl as a function of temperature versus pressure. The horizontal axis
 of the graph 70 indicates temperature in degrees Centigrade (.degree. C.),
 and the vertical axis indicates pressure in Torr. The axes are not
 necessarily linear. The graph 70 shows a line 72 along which the material
 is in vapor phase. When the temperature or pressure moves sufficiently to
 the left or up in the graph 70 away from the line 72, the material returns
 to solid (or liquid) state. For a given material (e.g., tungsten
 hexacarbonyl), when being used in CVD processing there are conveniently
 employed a range of temperatures, indicated in the graph 70 by a bracket
 74, and a range of pressures indicated by a bracket 76 with a nominal
 operating value of temperature at a point A and of pressure at a point B.
 In the case of tungsten hexacarbonyl, the temperature range 74 may be
 80.degree. C. to 100.degree. C. with a nominal operating value at the
 point A of about 90.degree. C. The pressure range 76 may be a few
 milli-Torr with an operating value at the point B of about 50 milli-Torr.
 It is apparent from the graph 70, that a material such as tungsten
 hexacarbonyl, when employed in CVD processing in the apparatus 10 requires
 a low chamber pressure (e.g., about 50 milli-Torr). Such material at
 normal atmospheric temperature and pressure is a solid but it can be made
 to sublime into vapor. It is delivered, as indicated by the arrow 26, to
 the manifold 18 (FIG. 1) It is desirable therefore to prevent the vapor
 from returning to solid (or liquid) phase in passing from the manifold 18
 into and through the dispersion plate 20 that such vapor not be
 significantly impeded in its flow. Accordingly, the plate 20 should have
 high-flow-conductance, meaning that the pressure drop across or through it
 be low (e.g., a few milli-Torr). The plate 20 should also maintain the
 vapor at a desired temperature (e.g., the temperature value at the point A
 in the graph 70) as the vapor passes within and through the plate 20. The
 plate 20 advantageously is made of a metal, such as aluminum, which meets
 these needs well.
 As is shown in FIG. 1, the front face 40 of the plate 20 is positioned at a
 relatively close distance (e.g., a faction of an inch) from the wafer 16
 and its platform 14. During operation of the apparatus 10 the wafer 16 is
 heated by contact with the platform 14 to an elevated temperature (e.g.,
 390.degree. C). Heat from the wafer 16 is radiated to the plate face 40,
 and some of this radiant heat is absorbed by the dispersion plate 20 which
 raises its temperature. The extent to which the temperature of the plate
 20 is raised depends on, among other things, the surface-reflectivity of
 the face 40. The higher the reflectivity, the lower the absorption of
 radiated heat and hence lower temperature rise for the plate 20. Where
 deposition of solid material, such as a thin layer of a tungsten compound,
 occurs on the face 40 its reflectivity increases substantially. But the
 presence of the grooves 42 and 44, and the funnel 46 cut into the face 40
 of the plate 20 minimizes the deposition of solid material on the face 40.
 Thus it is possible during CVD processing with a vaporized material such
 as tungsten hexacarbonyl, to operate the apparatus 10 with the plate 20 at
 a desired temperature (e.g., 90.degree. C.) maintained at a substantially
 constant value by radiant heat alone and not affected by changes in
 surface reflectivity. There is no need under these conditions for an
 additional heat source for the plate 20. Also, because the passages 30 and
 32 and center hole 33 through the plate 20 are relatively large,
 plasma-excited gas can pass through the plate 20. This makes it possible
 to place a source for plasma excitation above the entrance 24 in the plate
 20 and outside of the chamber 12.
 In the specific embodiment of the invention illustrated herein, the
 diameter of the outer passages 30 in the dispersion plate 20 is about 0.25
 inch; the diameter of the inner passages 32 is about 0.15 inch; and the
 diameter of the center hole 33 is about 0.060 inch. There are twenty-four
 outer passages 30, twelve inner passages 32 and one center hole 33 for a
 total of thirty-seven openings for vapor flow through the plate 20
 downward and outward from the entrance 24. The inside diameter of the
 entrance 24 is about two inches and depth about half an inch. The diameter
 of the dispersion plate 20 between opposite bolts 26 is about 9 inches.
 The thickness of the plate 20 from the bottom of the entrance 24 to the
 front face 40 is about an inch. The angle 52 (FIG. 3) is about 70.degree.
 and the angle 54, about 50.degree.. If the dispersion plate 20 is imagined
 as the face of a clock, the group of twenty-four passages 30 point
 respectively to each hour and half-hour (e.g., 12, 12:30, 1, 1:30, etc.)
 around the clock. The twelve passages 32 point respectively to fifteen
 minutes after each hour (e.g., 12:15, 1:15, 2:15 etc.) around the clock.
 Thus, the passages 30 are offset around the center axis 28 by a small
 angle relative to the passages 32. During CVD processing a flow of
 vaporized tungsten hexacarbonyl in the range from about 2 to 10 standard
 cubic centimeters per minute (SCCM) mixed with about 100 SCCM of argon was
 passed through the plate 20 (maintained at about 90.degree. C.) into the
 chamber 12 where the pressure was about 50 milli-Torr. The temperature of
 the wafer 16 was about 390.degree. C. and it was positioned about one-half
 inch from the face 40 of the plate 20. The processing cycle lasted several
 minutes.
 The above description is intended in illustration and not in limitation of
 the invention. Various changes or modifications in the dispersion plate 20
 embodying features of the invention may occur to those skilled in the art
 and can be made without departing from the spirit or scope of the
 invention as set forth herein and as defined by the accompanying claims.
 For example, the invention is not limited to use with only vaporized
 tungsten hexacarbonyl but is useful with other vaporized materials. Still
 further, it is not limited to a particular set of dimensions or diameter
 of a dispersion plate, or to the particular numbers, sizes and angles of
 the passages 30 and 32, or the center hole 33, as described above, or to a
 particular material or method of manufacture for a dispersion plate or to
 a particular size, shape and number of annular grooves and center funnel
 in the face of the plate.