Semiconductor processing apparatus and method

Abstract: A susceptor (1) carrying semiconductor wafers (3) for process­ ing is suspended from a compliant attachment (5) at its upper end and is lowered into a reaction chamber (9) for processing. At the completion of processing the susceptor (1) is withdrawn vertically to permit a robot (11) to unload the processed wafers (3) and load unprocessed wafers. In order to fix the position of the susceptor (1), during the loading operations, a support carriage (36) is moved into position to engage the lower end of the susceptor (1). Noxious and corrosive chloride vapors are simultaneously withdrawn from the reaction chamber by a vacuum line (55) attached to the support carriages (36).

Description: The present invention relates generally to the field of silicon wafer fabrication equipment useful in the manufacture of semiconductor devices, more particularly to apparatus for depositing an epitaxial layer from a source gas by the chemical vapor deposition (CVD) method, and especially to improvements in such apparatus when used with robotic loading of wafers. Apparatus of the above type is used in the fabrication of semiconductor devices on 100 millimeter or larger wafers of silicon. Epitaxial layers are formed on the surfaces of the wafers by heating them to temperatures in the region of 1100 to 1200 °C in a bell jar containing a gaseous atmosphere consisting of a hydrogen carrier gas mixed with one or more reactive gases such as a silicon source gas or a dopant source gas. In order to provide automatic processing of a large number of wafers, a robotic loader, together with the necessary control electronics, can be used to automatically load unprocessed wafers onto the susceptor which is used to support them. The susceptor is then loaded into the reaction chamber, processing is carried out, and the susceptor is removed from the reaction chamber, whereupon the robot removes the processed wafers from the susceptor and loads unprocessed wafers. Document FR-A-2 590 879 discloses an apparatus for automatically loading and removing semiconductor substrates from a processing reaction chamber in which a susceptor is suspended from an arm like a pendulum. The known prior art is further exemplified by automated epitaxial reactor apparatus of the type represented by the Model 7010 system supplied by Applied Materials of Santa Clara, California. Such apparatus uses a robotic loader to load and unload substrates from the susceptor. The geometry and size of this apparatus permit supporting the susceptor quite rigidly from its base. When the susceptor is withdrawn from the bell jar or reaction chamber to permit operation of the robotic substrate loader, a stream of filtered air sweeps over the susceptor surface to remove corrosive vapors such as chlorides which are byproducts of the CVD process. Although these apparatuses perform well, it was desired to develop an improved automated apparatus. This object is solved by the apparatus of independent claim 1 and the process of independent claim 16. Further advantageous features are evident from the dependent claims. According to one aspect of the invention, a method for processing semiconductor wafers in a reaction chamber of the type of one of claimed in claims 1-15 having a closable opening in a wall thereof is provided comprising in the order the following steps: a. inserting a susceptor and substrate-wafers into said reaction chamber through said closable opening for processing therewithin, b. withdrawing said substrate-wafers and susceptor from said reaction chamber at the completion of said processing step, c. providing a vacuum evacuation means in a position between the susceptor and said closable opening, d. exhausting noxious process-by-product vapors from said chamber using said vacuum evacuation means. According to an embodiement of the invention, said method for processing semiconductor wafers further comprises steps for handling and supporting semiconductor wafers: a. compliantly supporting a vertically oriented susceptor from one end thereof, b. stabilizing said susceptor from the other end thereof, and c. loading or unloading substrates from said susceptor. According to a further embodiement of the invention the susceptor is supported from a single point near its upper end by a suspension mount which provides sufficient compliance to permit the susceptor to center itself below the mount through gravitational force alone. In this regard, it will be understood that the words "compliance" and "compliant", when used in this application with respect to the susceptor mounting of the present invention, denote that flexibility of the mounting which permits the susceptor to swing slightly from side to side in the same manner as if the susceptor were hung from a rope. Such a mounting causes some difficulty during the operation of the robotic loader, since the compliance of the mount permits unwanted movement of the susceptor during loading, but this problem is overcome by the invention. Further, although the filtered air stream of the prior art automated system removed virtually all of the corrosive vapor and particulate contaminants, the present invention provides further improvements in this regard. The present invention provides an automated epitaxial reactor apparatus having a greater capacity than the prior art apparatus. The present invention further provides such an apparatus in which the efficiency of removal of harmful process byproducts is enhanced. The present invention also provides an apparatus with a self-centering susceptor for supporting substrates. The present invention further provides an apparatus with a means to support and fix the position of the susceptor during substrate loading operations. The present invention further provides an apparatus with a means to catch a substrate which is accidentally dropped during the operations of loading or unloading substrates, and to thereby prevent damage to the system. The present invention further provides an apparatus having a susceptor stabilization means in a form which can be extended toward the susceptor at the start of substrate loading and withdrawn at the end of substrate loading. The present invention also provides an apparatus in which susceptor stabilization and removal of harmful process byproducts is accomplished by a single movable element. To the above ends, an automated epitaxial vapor deposition apparatus according to the present invention uses an elongated, multi-sided susceptor which is suspended by a centrally located gimballed mounting at its top end. The susceptor has sufficient axial length to accommodate two or more substrates on each of its sides. The susceptor is lowered into a bell jar for processing and raised from the bell jar for loading and unloading of semiconductor substrates. Consequently, the loading of substrates is carried out while the susceptor is suspended directly over the open mouth of the bell jar. The gimballed upper support of the susceptor has considerable compliance to permit the susceptor to self-center when it is in the bell jar, such that the susceptor can be rotated during processing without significant eccentricity. However, as outlined above, the same compliance comprises a drawback during the operation of loading and unloading substrates by means of a robotic loader. The filtered air stream which is used to aid in the removal of noxious vapors has the additional and unwanted effect of causing the susceptor to swing, making loading of the substrates difficult. Accordingly, a susceptor stabilization means in the form of a carriage which is movable toward and away from the susceptor carries on its upper surface a pair of compliant contactor pads for frictionally engaging the lower end of the susceptor. When the carriage has been moved to a position near the mouth of the bell jar and beneath the susceptor, the carriage is raised slightly to cause these contactor pads to grip the lower edge of the susceptor, effectively immobilizing it during loading. The same carriage also incorporates a vacuum duct extending from an opening located on the underside of the carriage, adjacent the mouth of the bell jar, to a remotely located source of low vacuum. Consequently, when the carriage is extended into position below the susceptor, the opening on its underside draws noxious and corrosive vapors and particulate matter from the open mouth of the bell jar. At the completion of the loading operation, the carriage is withdrawn, permitting the loaded susceptor to be lowered into the bell jar. The above and other features, objects and advantages of the present invention, together with the best mode contemplated by the inventors thereof for carrying out their invention will become more apparent from reading the following description of embodiments of the invention while studying the associated drawing, the various figures of which represent: Fig. 1 is a side view, partly in elevation and partly in section, illustrating the present invention during the operations of substrate loading and unloading; Fig. 2 is a detail view, partly broken away, illustrating the gimballed susceptor mounting used in the present invention; Fig. 3 is a top view illustrating a susceptor stabilization and noxious vapor evacuation apparatus useful in the present invention; Fig. 4 is a side view of the apparatus of Fig. 3. In Fig. 1, a graphite susceptor 1 is shown as it would appear during the operation of loading and unloading semiconductor wafers 3. Susceptor 1 is, for example, an elongated, five-sided support structure having three wafers 3 retained in correspondingly-shaped recesses on each of its sides. As illustrated, susceptor 1 has a slight axial taper, such that it is larger at the bottom than at the top. Formed in this way, each of the sides of susceptor 1 slopes in a sense to provide a small radially inward gravitational force component on each of wafers 3 to prevent accidental dislodging of the wafers during processing. A support hanger 5, in the form of a short stub shaft, connects susceptor 1 to a rotatable support structure 7 which can be raised to the illustrated loading position and lowered to load susceptor 1 into a reaction chamber or bell jar 9 for processing. During processing within bell jar 9, susceptor 1 and wafers 3 are subjected to temperatures in the region of 1100 to 1200 °C in a reactive gaseous environment. In order to ensure that the mixture of gases in contact with each of the wafers is uniform, susceptor 1 is rotated to agitate and stir the gaseous mixture. Such stirring action is effective at maintaining a uniform gaseous mixture only if susceptor 1 remains centered such that its axis coincides with the axis of rotation. Accordingly, support hanger 5 is supported within support structure 7 in a manner which provides considerable compliance, such that susceptor 1 will self-center by gravitational force as will become clearer from the later discussion of Fig. 2. Loading of unprocessed substrates and unloading of processed ones is carried out by a robotic loader 11 which is illustrated somewhat schematically in Fig. 1. Loader 11 is equipped with four fingers 13, only two of which are shown in Fig. 1, for gripping each substrate by its edges. Loader 11 uses a system of infrared sensors (not shown) in order to accurately map the locations of each of the three substrates on each side of susceptor 1. As each of the five sides of susceptor 1 is completed, hanger 5 is rotated to access the next side, whereupon loader 11 begins the operation of loading by storing data which determines the exact location of each of the three substrates on the side. Using this stored data, loader 11 can efficiently complete the loading of all three substrates without pausing to relocate the appropriate recesses. However, susceptor 1 must remain stationary throughout the loading of each side in order that the location data stored prior to loading remain valid throughout the loading operation. In accordance with the present invention, susceptor 1 can be maintained in a fixed position throughout the operation of loading each of its sides by the use of a susceptor stabilizer 15 which can be selectively engaged at the start of the loading operation on each side and disengaged when necessary to rotate susceptor 1. Stabilizer 15 can be simply and effectively realized in a form which engages susceptor 1 at its lower edge, as illustrated in Fig. 1. When thus engaged, susceptor 1 is supported at widely separated points located at its top and bottom, and is firmly fixed during the loading operation. Although the structure of stabilizer 15 will be fully discussed with respect to Figs. 3 and 4, it may be noted here that engagement of stabilizer 15 with susceptor 1 is accomplished simply by pressing a pair of frictional contactors 17 (only one of which is visible in Fig. 1) firmly against the lower edge of susceptor 1. For this purpose a lift arm 19, raised and lowered by a pneumatic lift cylinder which will be described later with respect to Fig. 4, is used to raise and lower stabilizer 15 during the loading of susceptor 1. In Fig. 2, details concerning the mounting of support hanger 5 within support structure 7 are clarified. Support hanger 5 is suspended from a driving shaft 21 by a mounting ring 23 and a pair of trunnion pins 25 and 27. Mounting ring 23 and trunnion pins 25 and 27 together form a gimballed joint which provides sufficient compliance to accommodate a slight misalignment between shafts 5 and 21, and to thus permit susceptor 1 to self-center through the action of gravity. Rotation of susceptor 1 both during processing and during the substrate loading operation is accomplished by rotating shaft 21, such that the rotary motion is transmitted through the gimballed joint. However, ensuring that each of the sides of susceptor 1 is correctly oriented facing the robotic loader 11 of Fig. 1 requires that the location of these sides be known in relation to the rotational position of shaft 21. Accordingly, although not shown in Fig. 2, a second pin, azimuthally displaced from pin 25 by an angle which is not 90 degrees, extends through ring 23 and shaft 21 for the purpose of ensuring that susceptor 1 can only be mounted with its sides in a preordained orientation. Fig. 3 illustrates the structure of stabilizer 15 in top view, while Fig. 4 shows the same structure from the side. A platform 29 is pivotally supported on a pair of upright posts 31 which are joined to a base 33. A stop 35 is also joined to base 33, and serves to limit the downward pivotal motion of platform 29 to the position illustrated, with platform 29 parallel to base 33. A movable shuttle or carriage 36 is supported upon a pair of traveling rods 37 which are in turn supported within four ball slides 39 mounted on platform 29. Carriage 36 is shown extended to the left in Figs. 1, 3, and 4 as it would be when in use to stabilize susceptor 1. However, carriage 36 is movable to the right as indicated by the phantom outline 41 in Fig. 4, such that its full range of motion is as indicated by arrow 43. A pneumatic cylinder 45 is used to drive carriage 36 either to the left or right in the drawing by applying air pressure to either of a pair of air pressure lines 47a or 47b. Similarly, the entire stabilizer assembly consisting of platform 29, carriage 36, rods 37, slides 39 and cylinder 45 can be raised and lowered by a pneumatic lift cylinder 49 to cause contactor pads 17 to press against the lower edge of susceptor 1. These horizontal and vertical movements are controlled by automatically actuated air pressure valves (not shown) controlled by a computer (not shown) which also sequences the operation of the robotic loader 11. Data concerning the horizontal position of carriage 36 is provided by a horizontal position switch 51 which is indicated schematically in Fig. 3. Similarly, data concerning the vertical position of the mechanism is provided by a vertical position switch 53 which is indicated schematically in Fig. 4. Each of switches 51 and 53 is shown coupled to carriage 36 by a dotted line. Whenever carriage 36 is lowered away from susceptor 1, the contacts of switch 53 are closed. Similarly, whenever carriage 36 is withdrawn from the region of susceptor 1 (i.e., moved all the way to the right in the figures), the contacts of switch 51 are closed. Accordingly, by sensing the states of switches 51 and 53, the computer can determine when susceptor 1 can safely be rotated to permit accessing a different side thereof. In order to extract corrosive vapors from the open mouth of bell jar 9 when carriage 36 is in its illustrated left position, a remotely located vacuum system ( not shown) is coupled via a vacuum duct 55 to the underside of carriage 36. Carriage 36 is formed as a hollow member, having a lower wall identical to the upper wall illustrated in Fig. 3 with the exception that the leftmost edge of the lower wall, as indicated by dotted line 57, is undercut to form a downwardly oriented vacuum opening. Accordingly, carriage 36 serves as a portion of the vacuum duct. During the loading cycle, corrosive vapors and particulate matter within bell jar 9 are drawn into carriage 36, through duct 55, and are collected by the remote vacuum system.

Claims: A semiconductor-processing apparatus of the type employing a reaction chamber (9) for confining a reactive gaseous atmosphere in contact with a substrate (3), comprising: a susceptor (1) for supporting said substrate (3), susceptor mounting means (5, 7) for supporting said susceptor (1) within said apparatus; a reaction chamber (9) having a closable opening through which said susceptor (1) can be inserted and removed from said chamber (9), the closable opening being preferably situated at the upper side of said chamber (9); chamber loading means for causing relative motion between said chamber (9) and susceptor (1) along a chamber loading axis between a closed position in which said susceptor is confined within said chamber during substrate processing, and an open position in which said susceptor is withdrawn from said chamber through said chamber opening to permit removal of a processed substrate and loading of an unprocessed substrate, and chamber exhaust means (55) for producing a vacuum in a region adjacent said chamber opening for withdrawing noxious process-by-product vapors from said chamber (9) when said closable opening is open. The apparatus of claim 1, further comprising: substrate loading means (11) selectively operable to: (a) load a substrate onto said susceptor (1) for processing within said apparatus, and (b) remove a substrate from said susceptor (1) at the completion of said processing; and susceptor stabilization means (15) mounted on said apparatus and selectively operable to (a) provide supporting engagement of said susceptor for fixing the position of said susceptor during the operations of loading and removing a substrate, and (b) withdraw said supporting engagement from said susceptor. The apparatus of one of the preceding claims, wherein: said susceptor mounting means (5, 7) suspends said susceptor (1) within said apparatus at an upper support point on said susceptor (1); and/or said susceptor stabilization means selectively provides said supporting engagement at a point on said susceptor (1) removed from upper support point. The apparatus of one of the preceding claims in which the susceptor mounting means (5, 7) is arranged such as to suspend the susceptor (1) above the reaction chamber (9). The apparatus of one of the preceding claims in which the susceptor mounting means (5, 7) provides for raising and lowering the susceptor (1) vertically out and into said reaction chamber (9). The apparatus of one of the preceding claims in which the susceptor mounting means (7) provides a sufficient compliance to permit self-centering of the susceptor (1) when it is in the reaction chamber (9). The apparatus of one of the preceding claims in which the susceptor mounting means (5, 7) provides a rotability for the susceptor (1) and/or the susceptor mounting means (7) provides a gimballed upper support for the susceptor (1). The apparataus of one of the preceding claims wherein said susceptor stabilization means (15) includes means (17) to frictionally engage the lower end of said susceptor (1). The apparatus of one of the preceding claims further comprising indicator means (51, 53), coupled to said susceptor stabilization means (15) for supplying an indication of withdrawal of said supporting engagement of said susceptor stabilization means (15) and said susceptor (1). The apparatus of one of the preceding claims wherein said susceptor stabilization means (15) comprises: a contactor means (17) to engage said susceptor (1) when brought into contact therewith; a transport means for selectively moving said contactor means (a) toward and into engagement with, said susceptor, and (b) away from said susceptor (1). The apparatus of claim 10 wherein said transport means comprises: first transport means (37, 39, 45) for moving said contactor (17) toward or away from said susceptor (1) along a first path of motion (43) lying generally in a first plane; a second transport means (19) for moving said contactor (17) toward or away from said susceptor along a second path of motion lying generally in a second plane which intersects said first plane; said first and second transport means being selectively operatable (a) to move said contactor means (17) toward said susceptor (1) along said first and second paths of motion to a contact position in which said contactor (17) engages said susceptor (1) and (b) to move said contactor means (17) away from said susceptor (1) along said first and second paths of motion to a rest position in which said susceptor stabilization means (15) is removed from said susceptor (1). The apparatus of one of the preceding claims wherein said exhaust means comprises: a carriage (36) selectively movable along a path (43) of motion generally transverse to said chamber loading axis, said path of motion extending from a position adjacent said chamber opening to a position remote from said chamber opening; a vacuum duct (55) coupled to said carriage (36) for movement therewith along said path of motion, said vacuum duct (55) having an opening adjacent a portion of said carriage facing said chamber loading axis, and extending therefrom to a location remote from said chamber axis for connection to a source of vacuum. The apparatus of claim 12 in which said carriage (36) is integrated into the transport means (15) for moving the susceptor stabilization means. The apparatus of claim 12 or 13 said carriage (36) being further selectively movable along a second path of motion extending generally along said loading axis from said chamber opening to said open position of said susceptor (1), and, contactor means (17) positioned on said carriage (36) surface facing said susceptor (1) for engaging and fixedly supporting said susceptor (1) when brought into contact therewith. The apparatus of claim 14 further comprising indicator means (51, 53) coupled to said carriage (36) for supplying an indication of withdrawal of said supporting engagement of said susceptor stabilization means (15) and said susceptor (1). A method for processing semiconductor wafers in a reaction chamber of the type of one of the preceding claim 1-15 having a closable opening in a wall thereof, comprising in the order of the following steps: a. inserting a susceptor and substrate-wafers into said reaction chamber through said closable opening for processing therewithin, b. withdrawing said substrate-wafers and susceptor from said reaction chamber at the completion of said processing step, and c. providing a vacuum evacuation means in a position between the susceptor and said closable opening, d. exhausting noxious process-byproduct vapors from said chamber using said vacuum evacuation means. A method for processing semiconductor wafers in a reaction chamber of the type having a closable opening in a wall thereof especially according to claim 16, comprising the following steps: a. compliantly supporting a vertically oriented susceptor from one end thereof, b. stabilizing said susceptor from the other end thereof, and c. loading or unloading substrates onto said susceptor.

Inventors: CARLSON DAVID K, LINDSTROM PAUL R, SEVERNS DAVID W, TOMPSON BRIAN, CARLSON, DAVID K., LINDSTROM, PAUL R., SEVERNS, DAVID W., TOMPSON, BRIAN
Applicants: APPLIED MATERIALS INC, APPLIED MATERIALS, INC.
Application year: 1990
Main classification: C23C16
IPC codes: H01L21