Patent Grant
8636847
The present invention relates to chemical vapor deposition methods and apparatus.
Chemical vapor deposition involves directing one or more gases containing chemical species onto a surface of a substrate, typically a flat wafer, so that the chemical species react and form a deposit on the surface. For example, compound semiconductors can be formed by epitaxial growth of the semiconductor material on a crystalline wafer. Semiconductors referred to as III-V semiconductors commonly are formed using a source of a Group III metal such as gallium, indium, aluminum, and combinations thereof and a source of a Group V element such as one or more of the hydrides or of one or more of the Group V elements such as NH3, AsH3, or PH3, or an Sb metalorganic such as tetramethyl antimony. In these processes, the gases are reacted with one another at the surface of a wafer, such as a sapphire wafer, to form a III-V compound of the general formula InXGaYAlZNAAsBPCSbD where X+Y+Z=approximately 1, and A+B+C+D=approximately 1, and each of X, Y, Z, A, B, C and D can be between 0 and 1. In some instances, bismuth may be used in place of some or all of the other Group III metals.
In certain processes, commonly referred to as a “halide” or “chloride” process, the Group III metal source is a volatile halide of the metal or metals, most commonly a chloride such as GaCl2. In another process, commonly referred to as metalorganic chemical vapor deposition or “MOCVD,” the Group III metal source is an organic compound of the Group III metal as, for example, a metal alkyl.
One form of apparatus which has been widely employed in chemical vapor deposition includes a disc-like wafer carrier mounted within the reaction chamber for rotation about a vertical axis. The wafers are held in the carrier so that surfaces of the wafers face in an upstream direction within the chamber. While the carrier is rotated about the axis, the reaction gases are introduced into the chamber from a flow inlet element upstream of the carrier. The flowing gases pass downstream toward the carrier and wafers, desirably in a laminar plug flow. As the gases approach the rotating carrier, viscous drag impels them into rotation around the axis, so that in a boundary region near the surface of the carrier, the gases flow around the axis and outwardly toward the periphery of the carrier. As the gases flow over the outer edge of the carrier, they flow downwardly toward exhaust ports disposed below the carrier. Most commonly, this process is performed with a succession of different gas compositions and, in some cases, different wafer temperatures, to deposit plural layers of semiconductor having differing compositions as required to form a desired semiconductor device. Merely by way of example, in formation of light emitting diodes (“LEDs”) and diode lasers, a multiple quantum well (“MQW”) structure can be formed by depositing layers of III-V semiconductor with different proportions of Ga and In. Each layer may be on the order of tens of Angstroms thick, i.e., a few atomic layers.
Apparatus of this type can provide a stable and orderly flow of reactive gases over the surface of the carrier and over the surface of the wafer, so that all of the wafers on the carrier, and all regions of each wafer, are exposed to substantially uniform conditions. This, in turn promotes uniform deposition of materials on the wafers. Such uniformity is important because even minor differences in the composition and thickness of the layers of material deposited on a wafer can influence the properties of the resulting devices.
Considerable effort has been devoted in the art heretofore to development of flow inlet elements for use in apparatus of this type. Commonly, the flow inlet element has inlets for the reactive gases dispersed over an active, gas-emitting area approximately equal in size to the wafer carrier. Some of these flow inlet elements carry the first reactive gas, such as a mixture of a Group V hydride, whereas others carry the second reactive gas, such as a mixture of a metal alkyl and a carrier gas. These inlets may be formed as tubes extending parallel to the axis of rotation, the inlets are distributed over the downwardly-facing or downstream surface of the flow inlet element. Considerable effort has been devoted in the art heretofore to arranging the inlets in symmetrical patterns. Typically, the first gas inlets are provided in a pattern which has radial symmetry about the axis of rotation of the wafer carrier, or which has at least two perpendicular planes of symmetry crossing one another at the axis of rotation. The second gas inlets have been provided in a similarly symmetrical pattern, interspersed with the first gas inlets. The flow inlet element commonly incorporates complex channel structures for routing the gases to the tubular inlets. Moreover, because the wafers typically are maintained at a high temperature as, for example, about 500° C. to about 1200° C., the flow inlet element must be provided with coolant channels. The coolant channels carry a circulating flow of water or other liquid and thus maintain the temperature of the flow inlet element relatively low, so as to limit or preclude premature reaction of the gases. As disclosed, for example, in U.S. Published Patent Application No. 20060021574 A1, the disclosure of which is hereby incorporated by reference herein, a flow inlet element may be provided with additional structures for discharging flows of a carrier gas devoid of reactive species.
The carrier gas flows isolate the reactive gas flows from one another while the gases are in the vicinity of the flow inlet element. The gases do not mix with one another until they are remote from the flow inlet element. Moreover, discharging the carrier gas flows limits or prevents recirculation of the reactive gases as they exit from the flow inlet element. Thus, the reactive gases do not tend to form undesired deposits on the flow inlet element. As described, for example, in commonly assigned U.S. Published Patent Application No. 20080173735 (now U.S. Pat. No. 8,152,923), the disclosure of which is hereby incorporated by reference herein, recirculation of the discharged gases in the vicinity of the flow inlet element may be reduced by providing blade-like diffusers projecting downstream from the surface of the flow inlet element to guide the gas flows.
Typically, the inlets are constructed and arranged to provide uniform flow velocity away from the flow inlet element over the entire active region of the flow inlet element, i.e., the entire area where the inlets are arranged. In some cases, the gas inlets for a particular gas may be partitioned into two or more zones, as for example, a first zone near the axis of rotation and a second zone remote from the axis. These two zones may be provided with separate gas channels so that the flow rates of the first gas can be controlled independently in the two regions. For example, in one common arrangement, the inlets for a first gas, such as a Group V hydride, are arranged in an array covering most of the flow inlet surface, whereas the inlets for a second gas, such as a Group III alkyl, are arranged in one or more narrow strips extending generally radially with respect to the central axis. In such a system, a portion of a strip disposed remote from the axis supplies the second gas to a ring-like portion of the wafer carrier having a relatively large area, whereas a portion of the same strip near to the axis supplies the gas to a ring-like portion of the wafer carrier having a smaller area. To provide equal flux of the second gas per unit area of the wafer carrier, it has been common to zone the second gas inlets to provide unequal rates of discharge of the second gas per unit length along the strip. For example, the inlets near the axis may be supplied with a gas mixture having a relatively low concentration of the second gas, whereas the inlets remote from the axis may be supplied with a more concentrated gas mixture. Such zoning adds to the complexity of the system.
Despite all of these developments, still further improvement would be desirable.
One aspect of the invention provides a chemical vapor deposition reactor. The reactor according to this aspect of the invention desirably includes a reaction chamber having upstream and downstream directions, and also desirably includes a carrier support adapted to support a wafer carrier at a carrier location within the reaction chamber for rotation about an axis extending in the upstream and downstream directions. The reactor according to this aspect of the invention preferably has a flow inlet element mounted to the chamber upstream of the carrier location, the inlet element having a gas distribution surface extending in X and Y horizontal directions perpendicular to one another and perpendicular to the downstream direction.
The flow inlet element desirably has a plurality of elongated gas inlets for discharging gases into the chamber, the elongated gas inlets extending parallel to one another and across the gas distribution surface in the X horizontal direction. The elongated inlets desirably extend across a Y-direction medial plane of the reactor, and may extend across the major portion of the gas distribution surface. For example, the elongated inlets may cover substantially the entire gas distribution surface, or may cover an area approximately equal to the area of the wafer carrier. The elongated gas inlets preferably include a plurality of first gas inlets for discharging a first reactive gas and a plurality of second gas inlets for discharging a second reactive gas, the first gas inlets being spaced apart from one another in the Y horizontal direction, the second gas inlets being spaced apart from one another in the Y horizontal direction and interspersed with the first gas inlets.
The flow inlets may be disposed in a in a pattern which is not symmetrical about a medial plane of the reactor extending in the X horizontal direction. The pattern may be antisymmetrical about such medial plane. That is, for any first gas inlet disposed at a positive Y distance to one side of the X-direction medial plane, a second gas inlet is disposed at the corresponding negative Y distance to the opposite side of the X-direction medial plane.
Still other aspects of the invention provide methods of vapor deposition and flow inlet elements for use in a vapor deposition reactor.
A reactor according to one embodiment of the invention (
A heater 15 such as an electrical resistance heater is provided within the reactor for heating the wafer carrier and wafers. Also, an exhaust system 19 is connected to the downstream end of the reaction chamber.
The foregoing features of the apparatus may be similar to those used in reactors sold under the trademarks “TurboDisc” and “Ganzilla” by Veeco Instruments, Inc. of Plainview, N.Y.
A flow inlet element 22 is provided at the upstream end of the reaction chamber. A downstream surface 24 of the flow inlet element faces in the downstream direction, toward the wafer carrier and wafers. The flow inlet element is connected to a source of a first reactive gas 30, such as a Group V hydride, typically in admixture with a carrier gas such as N2 or H2. The flow inlet element is also connected to a source 26 of a second reactive gas, such as a metal alkyl, also typically in admixture with a carrier gas. Additionally, the flow inlet element is connected to a source 32 of a carrier gas such as N2 or H2, which is not admixed with any reactive gas, and to a coolant circulation device 33.
As best seen in
The coolant inlet and outlet sections are connected to the coolant circulation apparatus 33 (
A gas distribution plate 60 is disposed downstream from the top plate 40 so that plates 60 and 40 cooperatively define a gas distribution chamber 62 between them. The gas distribution chamber 62 communicates with the carrier gas source 32 (
As best seen in
Directions perpendicular to the axis 16, including the X and Y directions, are referred to herein as “horizontal” directions inasmuch as axis 16 normally (although not necessarily) extends vertically in the normal gravitational plane of reference. Also, planes which are perpendicular to the axis are referred to herein as horizontal planes. Thus, both top plate 40 and distribution plate 60 extend in horizontal planes. Also, the horizontal direction opposite to the +X direction is referred to herein as the −X direction, and the direction opposite to the +Y direction is referred to herein as the −Y direction, in the conventional manner of a Cartesian coordinate system. The upstream and downstream directions U and D, parallel to axis 16 constitute the third or Z direction of the Cartesian coordinate system.
Tubular elements 64 are referred to herein as first gas distribution elements. As thus seen in
An elongated diffuser 78 is mounted on the downstream wall 72 and extends lengthwise along the first gas distribution element 64. Diffuser 78 is generally in the form of a triangular prism. The diffuser is formed from two sections 80, each of which incorporates a passageway 82 extending lengthwise within the diffuser, i.e., in the X directions. Sections 80 are mounted back to back on the downstream wall 72 of the tubular element. Diffuser 80 as a whole is generally in the form of an elongated triangular prism. The width or dimension of the diffuser in the Y directions decreases with distance in the downstream direction D away from the tubular elements. A passageway or additional gas inlet 84 extends through the diffuser 78 from the tubular element to the edge of the diffuser remote from the tubular element, i.e., the downstream edge of the diffuser. The passageway or inlet 84 is in the form of an elongated slot defined by the two back-to-back triangular sections 80 of the diffuser. Passageway 84 communicates with slot 76 and hence with the interior bore 74 of the tubular element along the length of the first gas distribution element 64.
Elements 66, referred to herein as second gas distribution elements, are identical to the first gas elements 64, except that the downstream wall 86 of each second gas distribution element (
As seen in
As best seen in
As best seen in
In operation, a first reactive gas such as a mixture of ammonia or other Group V hydride in admixture with one or more carrier gases such as H2, N2 or both is supplied through the first gas section 48 of the manifold and passes into the longitudinal bores 74 (
The first and second reactive gases remain substantially separate from one another while they are in the vicinity of the flow inlet element and flow downstream from the flow inlet element in a substantially laminar, orderly flow. Several factors contribute to this action. The diffusers 90 and 76 define generally V-shaped channels between them, such channels being disposed downstream of the base inlets 104. The channels broaden gradually in the Y horizontal direction with distance downstream from the base inlets 104. This facilitates spreading of the carrier gas flows 115 in an orderly fashion, so that a substantially laminar carrier gas flow prevails at the downstream edges of diffusers 76 and 90. The first and second reactive gas flows 111 and 113 are introduced into this flow regime at the downstream edges of the diffusers and thus tend to flow in a similar orderly laminar flow. Moreover, the carrier gas flows 115 provide substantially complete isolation between the first reactive gas flows 111 and the second reactive gas flows 113. Stated another way, a path in a horizontal plane, transverse to the upstream-to-downstream axis 16, which path extends from one of the second reactive gas flows 113 to an adjacent first reactive gas flow 111 would intercept one of the carrier gas flows 115. This is true for any curve drawn in a horizontal plane, which is confined within the active area of the flow inlet element, i.e., the area where gas inlets are present. This substantially complete isolation between the first and second reactive gas flows minimizes premature reaction between the gases.
The flows of first and second gases are not symmetrical about the medial plane 108 extending in the X direction. If the wafer carrier and wafers were static, this would result in nonuniform exposure of the wafer carrier and wafers to the first and second reactive gases. For example, as schematically depicted in
In this arrangement, each unit length along one of the elongated first gas distribution elements 64 (
It should be appreciated that the impact patterns shown in
The structure and method of operation discussed above can be utilized in reaction chambers of essentially any size. The structure can be scaled up to relatively large sizes as, for example, reactors having a wafer carrier of about 600 mm or more and having a flow inlet element with an active, gas-emitting region of approximately the same diameter or more. Moreover, the flow inlet element can be fabricated readily.
Numerous variations and combinations of the structures discussed above can be employed. In a variant of the arrangement discussed above, the first gas distribution elements 64 may be used to supply flows of carrier gas, whereas the base inlets 104 may be used to supply flows of a reactive first gas and the second gas distribution elements may be used to supply a reactive second gas. In still other variants, more than two reactive gasses may be used. For example, the gas distribution elements may include first, second and third gas distribution elements extending generally parallel to one another.
In a further variant shown in
In another embodiment (
In yet another variant, the diffusers mounted on the downstream surface of the gas distribution plate may be omitted. In a still further variant, a porous screen may be provided over the downstream surface of the composite plate except at the inlets. In yet another arrangement (
In the embodiments discussed above, the gas distribution plate is formed from separate elongated gas distribution elements joined to one another. However, the gas distribution plate also can be formed from one or more unitary plates defining elongated inlets similar to those discussed above.
In the embodiments discussed above, the elongated gas inlets are straight. However, this is not essential. For example, in the embodiment of
In the embodiments discussed above, each elongated gas inlet provides the same mass flow rate of a reactive gas per unit length along its entire length. In a variant, the mass flow rate of the reactive gas per unit length may vary progressively along the length of the elongated gas inlet. This may occur, for example, where a particular elongated gas distribution element receives a gas mixture at only one end, and has appreciable resistance to flow along its length.
In the embodiments discussed above, the first and second gas inlets are provided in equal number and arranged in 1:1 alternating order in the Y direction. However, this is not essential. For example, 2, 3 or more elongated first gas inlets may be provided between each pair of second gas inlets.
Also, it is not essential to place the elongated gas inlets in exact anti-symmetrical arrangement about the medial plane extending in the X direction. Deviations from this arrangement, up to and including a symmetrical arrangement, can be used. Also, in the embodiments discussed above, the plate defining the elongated gas inlets includes elongated tubular gas distribution elements. However, elongated gas inlets may be provided by other structures as, for example a one or more unitary plates having appropriate gas distribution channels or chambers communicating with the inlets.
A chemical vapor deposition apparatus according to a further embodiment of the invention (
The first gas inlets extend only within a region of the gas distribution surface having a first radius R1 from the central axis 716. Stated another way, the first gas outlets extend to a first radius R1 from the central axis. The second gas outlets extend to a second radius R2 from the central axis, which in this embodiment is equal to the first radius R1. The third gas inlets extend to a radius R3 which is greater than the first and second radii, and hence greater than R1 and R2. In the particular example depicted, the radius R3 is equal to, or just slightly less than, the interior radius of the reaction chamber at the gas distribution surface. The first and second radii R1 and R2 may be approximately equal to the radius of the wafer carrier.
In operation, the gasses issuing from the first and second gas inlets will pass downstream (in the direction along axis 716 toward the viewer in
Moreover, omission of the first and second inlets in the gap region G reduces the required total flow of the first and second reactant gases to maintain a given flux of reactants toward the wafer carrier. Stated another way, if first and second reactive gasses were provided in the gap region G, they would simply pass around the outside of the wafer carrier, without ever impinging on the wafers. Avoiding this waste reduces the cost of reactant gases used in the process, and also reduces discharge of waste reactant gases.
The arrangement shown in
As these and other variations and combinations of the features discussed above can be utilized without departing from the present invention, the foregoing description of the preferred embodiments should be taken only by way of illustration and not by way of limitation of the present invention.
The present invention can be applied, for example, in manufacture of semiconductor devices.
This application is a divisional of U.S. patent application Ser. No. 12/631,079, filed Dec. 4, 2009, which application claims the benefit of the filing date of U.S. Provisional Patent Application No. 61/201,074 filed Dec. 4, 2008, the disclosure of which is hereby incorporated herein by reference.
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| Child | 13606130 | US |
