Patent Publication Number: US-10760160-B2

Title: Showerhead tilt mechanism

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation patent application of U.S. patent application Ser. No. 15/658,911, filed Jul. 25, 2017 now U.S. Pat. No. 10,190,216, the entire content of which is incorporated herein by reference. 
    
    
     FIELD OF INVENTION 
     This invention pertains to semiconductor substrate processing apparatuses used for processing semiconductor substrates, and may find particular use in performing chemical vapor depositions of thin films. 
     BACKGROUND 
     Semiconductor substrate processing apparatuses are used to process semiconductor substrates by techniques including, physical vapor deposition (PVD), chemical vapor deposition (CVD), plasma enhanced chemical vapor deposition (PECVD), atomic layer deposition (ALD), plasma enhanced atomic layer deposition (PEALD), pulsed deposition layer (PDL), molecular layer deposition (MLD), plasma enhanced pulsed deposition layer (PEPDL) processing, etching, and resist removal. One type of semiconductor substrate processing apparatus used to process semiconductor substrates includes a reaction chamber containing a showerhead module and a substrate pedestal module which supports the semiconductor substrate in the reaction chamber. The showerhead module delivers process gas into the reactor chamber so that the semiconductor substrate may be processed. In such chambers installation and removal of the showerhead module can be time consuming, and further, non-uniform film deposition (i.e. azimuthal variation) during substrate processing can occur if a lower surface of the showerhead module is not parallel to an upper surface of the substrate pedestal module. 
     SUMMARY 
     Disclosed herein is a semiconductor substrate processing apparatus for processing semiconductor substrates comprising (a) a chemical isolation chamber in which individual semiconductor substrates are processed, the chemical isolation chamber including a top plate forming an upper wall of the chemical isolation chamber, (b) a process gas source in fluid communication with the chemical isolation chamber for supplying at least one process gas into the chemical isolation chamber, (c) a showerhead module which delivers the process gas from the process gas source to a processing zone of the processing apparatus wherein the individual semiconductor substrates are processed, the showerhead module including a base attached to a lower end of a stem wherein a faceplate having gas passages therethrough forms a lower surface of the base and the stem extends through a vertically extending bore in the top plate, (d) a substrate pedestal module configured to support the semiconductor substrate in the processing zone below the faceplate during processing of the substrate, (e) a bellows assembly supporting the showerhead module, the bellows assembly including a collar, a bellows and a leveling plate, the collar having a central opening aligned with the bore in the top plate, the bellows surrounding the central opening in the collar and having a lower end attached to an upper surface of the collar and an upper end attached to a lower surface of the leveling plate, the leveling plate having a central opening aligned with the bore in the top plate, and (f) at least one showerhead tilt adjustment mechanism operable to adjust tilting of the faceplate of the showerhead module with respect to an upper surface of the substrate pedestal module adjacent the faceplate, wherein the showerhead tilt adjustment mechanism comprises a lock screw, a hollow screw, a lock plate, and a lock nut, the hollow screw having a first threaded section on an outer surface thereof and a second threaded section on the outer surface, the first threaded section having a thread pitch which is different than a thread pitch of the second threaded section, the first threaded section engaged with an internally threaded bore of the leveling plate, the second threaded section engaged with an internal thread of the locking nut, the lock screw having a lower external threaded section engaged with a threaded bore in the collar and an upper screw head engaging a shoulder of an upper socket in the hollow screw, and the lock plate movable from a first position at which the lock nut rotates with the hollow screw to a second position at which the lock nut cannot rotate, the showerhead tilt adjustment mechanism providing coarse adjustment when the lock plate is in the first position and fine adjustment when the lock plate is in the second position. 
     The at least one showerhead tilt adjustment mechanism preferably comprises three showerhead tilt adjustment mechanisms spaced outwardly of the bellows at locations 120° apart. The lock plate can be movable in a radial direction between the first and second positions and/or the leveling plate can include an upwardly extending tubular section wherein an inner surface of the tubular section includes the threaded bore. The lock plate can include a handle at an outer end thereof extending outwardly of the collar, a wide slot at an inner end thereof which can engage the lock nut, and a narrow slot extending outward from the wide slot, and a lock plate screw extending through the narrow slot and threaded into the collar, the lock plate screw having a screw head which can be tightened against the lock plate to prevent movement of the lock plate. In a preferred embodiment, the showerhead tilt adjustment mechanism can provide a coarse gap adjustment of about 0.02 to about 0.04 inch per full rotation of the hollow screw when the lock plate is in the first position and a fine gap adjustment of about 0.002 to about 0.004 inch per full rotation of the hollow screw when the lock plate is in the second position. 
     In an embodiment, a method of controlling in-plane distortion (IPD) due to showerhead tilt in a semiconductor substrate processing apparatus comprises (a) measuring IPD changes across a wafer processed in a processing chamber of the semiconductor substrate processing apparatus, (b) adjusting tilt of a showerhead of the semiconductor substrate processing apparatus using three showerhead tilt adjustment mechanisms configured to provide coarse and fine IPD adjustments wherein each of the showerhead tilt adjustment mechanisms comprises a lock screw, a hollow screw, a lock plate and a lock nut arranged to vary a gap between a movable part attached to the showerhead and a fixed part in the processing chamber, (c) wherein the hollow screw has a first threaded section on an outer surface thereof and a second threaded section on the outer surface, the first threaded section having a thread pitch which is different than a thread pitch of the second threaded section, the first threaded section engaged with an internally threaded bore of the movable part, and the second threaded section engaged with an internal thread of the locking nut, (d) the lock screw has a lower end threaded into a bore in the fixed part and an upper screw head engaging a shoulder of an upper socket in the hollow screw; and (e) the lock plate is movable from a first position at which the lock nut rotates with the hollow screw to a second position at which the lock nut cannot rotate, the showerhead tilt adjustment mechanism providing coarse adjustment when the lock plate is in the first position and fine adjustment when the lock plate is in the second position. In making a coarse adjustment, the lock plate of one of the showerhead tilt adjustment mechanisms can be placed in the first position and the hollow screw can be rotated to a first radial position. In making a fine adjustment, the lock plate can be moved to the second position and the hollow screw can be rotated to a second radial position at which the IPD is reduced. The upper socket of the hollow screw can include a slot extending through a wall of the socket and the method can further comprise placing an indicator cap having an upper alignment mark onto the hollow screw such that a projection on the indicator cap fits within the slot, recording a pre-adjustment angle of alignment mark, removing the indicator cap and making the IPD adjustment, placing the indicator cap on the hollow screw and recording a post-adjustment angle of the alignment mark. By using first and second threaded sections having the same orientation, each of the showerhead tilt adjustment mechanisms can provide a coarse gap adjustment of about 0.02 to about 0.04 inch per full rotation of the hollow screw when the lock plate is in the first position and a fine gap adjustment of about 0.002 to about 0.004 inch per full rotation of the hollow screw when the lock plate is in the second position. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
         FIG. 1  illustrates a schematic diagram showing an overview of a chemical deposition apparatus in accordance with embodiments disclosed herein. 
         FIG. 2  illustrates a block diagram depicting various apparatus components arranged for implementing embodiments disclosed herein wherein plasma can be utilized to enhance deposition and/or surface reactions between reacting species during the generation of thin films. 
         FIG. 3A  illustrates a cross-section and  FIG. 3B  illustrates a top view of a showerhead module arranged in accordance with embodiments disclosed herein. 
         FIGS. 4A-D  illustrate gap tuning arrangements wherein  FIGS. 4A-B  show how coarse tuning is carried out with the lock plate not engaged with a lock nut and  FIGS. 4C-D  show how fine tuning is carried out with the lock plate engaged with the lock nut in accordance with embodiments disclosed herein. 
         FIG. 5  illustrates how an indicator cap fits on the hollow adjustment screw in accordance with an embodiment disclosed herein. 
         FIG. 6  illustrates an indicator cap which mounts on a hollow adjustment screw for indicating an angle of rotation after a gap adjustment. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, numerous specific embodiments are set forth in order to provide a thorough understanding of the apparatus and methods disclosed herein. However, as will be apparent to those skilled in the art, the present embodiments may be practiced without these specific details or by using alternate elements or processes. In other instances, well-known processes, procedures, and/or components have not been described in detail so as not to unnecessarily obscure aspects of embodiments disclosed herein. As used herein in connection with numerical values the term “about” refers to ±10%. 
     As indicated, present embodiments provide semiconductor substrate processing apparatuses such as deposition apparatuses (or in an alternate embodiment an etching apparatus) and associated methods for conducting a chemical vapor deposition such as a plasma enhanced chemical vapor deposition. The apparatus and methods are particularly applicable for use in conjunction with semiconductor fabrication based dielectric deposition processes or metal deposition processes which require separation of self-limiting deposition steps in a multi-step deposition process (e.g., atomic layer deposition (ALD), plasma enhanced atomic layer deposition (PEALD), plasma enhanced chemical vapor deposition (PECVD), pulsed deposition layer (PDL), molecular layer deposition (MLD), or plasma enhanced pulsed deposition layer (PEPDL) processing), however they are not so limited. Exemplary embodiments of methods of processing a semiconductor substrate can be found in commonly-assigned U.S. Published Patent Application Nos. 2013/0230987, 2013/0005140, 2013/0319329, and U.S. Pat. Nos. 8,580,697, 8,431,033, and 8,557,712, which are hereby incorporated by reference in their entirety. 
     The aforementioned processes can suffer from some drawbacks associated with non-uniform process gas delivery to an upper surface of a wafer or semiconductor substrate receiving deposited films from process gas such as a process gas precursor or reactant. For example, a non-uniform precursor distribution on the upper surface of the semiconductor substrate can form if a lower surface of a showerhead module which delivers process gas to the semiconductor substrate is not parallel to an upper surface of a substrate pedestal module which supports the semiconductor substrate. Several properties of film on wafer are impacted by the gap/leveling between showerhead and pedestal, i.e. IPD, NU %, Stress, etc. The sensitivity between these properties and the gap/leveling are different for different process. And sometimes, the normal resolution is not workable. To address this problem, an improved leveling process is described herein wherein extra fine resolution of a gap adjustment can be provided in a film deposition apparatus. 
     There are generally two main types of CVD showerhead modules: the chandelier type and the flush mount type. The chandelier showerhead modules have a stem attached to a top plate of the reaction chamber on one end and a faceplate on the other end, resembling a chandelier. A part of the stem may protrude above the top plate to enable connection of gas lines and connection to a radio frequency (“RF”) power circuit. Flush mount showerhead modules are integrated into the top of a chamber and do not have a stem. Although the examples shown herein are of a chandelier type showerhead, the showerhead module is not limited to that type of showerhead. 
     Showerhead module leveling (planarization) is typically performed after a wet clean procedure that involves cooling and venting a reaction chamber (chemical isolation chamber) of the apparatus one or multiple times. The cooling and venting may be required to access the interior of the chamber to adjust the spacing between the showerhead and the substrate pedestal module as well as the planarization of a lower surface of the showerhead with respect to an upper surface of the pedestal module. A conventional technique involves placing metallic foil balls in the chamber to measure the gap between the showerhead module and the substrate pedestal module and then adjusting a number of standoffs, usually three or more, between a backing plate of the showerhead module and the top plate of the reaction chamber based on the measurements. The standoffs can only be adjusted by opening the top plate after venting and cooling the chamber. Multiple measuring and adjusting cycles may be performed before the showerhead module is considered level. Because the showerhead cannot be leveled through external manipulation, the process can be very time-consuming, up to about 20 hours. 
     In an embodiment, a gap adjustment is performed with screws having differential threads. In this application, a screw and two nuts are used. The screw has two threads with a different but close pitch. Each nut has one pitch that matches the screw. With two pairs of threads, the final pitch is the difference/sum of the two pitches of the two pairs of threads. When the two threads are in the same orientation, they can provide fine resolution. On the other hand, when the two threads are in opposite orientation, they can provide extra course resolution. By fixing both nuts, abnormal resolution can be obtained, and by fixing only one nut and leaving the other one free to rotate, normal resolution is available. Thus, using the differential threads, the showerhead to wafer/pedestal gap and other gaps can be adjusted with much finer/coarser resolution compared with the normal gap tuning method. And with this method, the gap can also be adjusted with the normal resolution. In this way, the gap can be tuned more precisely or faster. Thus, the showerhead to wafer/pedestal gap can be tuned more precisely, which has a large impact on IPD/NU %/etc. of film on wafers. 
     In accordance with an embodiment, differential threads are used to adjust the showerhead to wafer/pedestal gap. In this way, extra fine/coarse resolution can be provided. In the showerhead module, an extra nut can be added without changing the mounting plate and thereby provide a more retrofitable/cost saving tilt adjustment arrangement. As an example, when the two threads on the screw are in the same orientation, extra fine resolution is available, and when they are in the opposite orientations, extra coarse resolution is available. In another arrangement, final resolution can be modified by changing the resolution of the two threads. Due to space constraints in working on the tool, a tiny wrench can be used to handle the extra nut and thus avoid the need for a specially designed wrench/tool. The tiny wrench can be fixed with an available screw in the existing assembly and avoid the need to manually handle the wrench during tuning. If desired, the wrench can be movable (wrench lock the extra nut or free the extra nut), so the tuning can be changed between abnormal resolution and normal resolution. As a visual aid during tilt adjustment, a mark on the wrench can be used to indicate of its position, i.e., locking or free position. Also, a cap with compass mark can be used to mate with the screw head in a single orientation. This cap is removable and before and after each tuning, a mark can be made on the cap relative to a certain orientation. Then, the angle between the two marks before and after the tuning can be measured to determine a turned angle. In this way, no auto gapping system (“AGS”) wafer measurement is required for this application which can save a great amount of time. A discussion of AGS wafer measurements can be found in commonly-assigned U.S. Published Patent Application No. 2015/0225854, the disclosure of which is hereby incorporated by reference. 
     Disclosed herein is a showerhead module coupled to a showerhead tilt adjustment mechanism, which is designed to be leveled from outside of the reaction chamber, between process steps on the same wafer. In processes where two or more different film materials are deposited sequentially, dynamically adjusting showerhead tilt corrects for azimuthal variation without breaking vacuum. The showerhead tilt adjustment mechanism includes the differential screw tuning arrangement described above. 
     also described herein is a method of controlling in-plane distortion (IPD) due to showerhead tilt in a semiconductor substrate processing apparatus. The method includes measuring IPD changes across a wafer processed in a processing chamber of the semiconductor substrate processing apparatus and adjusting tilt of a showerhead of the semiconductor substrate processing apparatus using three showerhead tilt adjustment mechanisms having the differential screw tuning arrangement described above which provide coarse and fine IPD adjustments. 
       FIG. 1  is a schematic diagram showing an overview of a semiconductor substrate processing apparatus  201  for chemical vapor deposition in accordance with embodiments disclosed herein. A semiconductor substrate  13  such as a wafer sits on top of a movable pedestal module  223  that can be raised or lowered relative to a showerhead module  211 , which may also be moved vertically. Reactant material gases are introduced into a processing zone  318  of the chamber via gas line  203  wherein the process gas flow is controlled by a mass flow controller  229 . Note that the apparatus may be modified to have one or more gas lines, depending on the number of reactant gases used. The chamber is evacuated through vacuum lines  235  that are connected to a vacuum source  209 . The vacuum source may be a vacuum pump. 
     Embodiments disclosed herein can be implemented in a plasma enhanced chemical deposition apparatus (i.e. plasma-enhanced chemical vapor deposition (PECVD) apparatus, plasma-enhanced atomic layer deposition (PEALD) apparatus, or plasma-enhanced pulsed deposition layer (PEPDL) apparatus).  FIG. 2  provides a simple block diagram depicting various apparatus components arranged for implementing embodiments disclosed herein wherein plasma is utilized to enhance deposition. As shown, a processing zone  318  serves to contain the plasma generated by a capacitively coupled plasma system including a showerhead module  211  working in conjunction with a substrate pedestal module  223 , wherein the substrate pedestal module  223  is heated. RF source(s), such as at least one high-frequency (HF) RF generator  204 , connected to a matching network  206 , and an optional low-frequency (LF) RF generator  202  are connected to the showerhead module  211 . In an alternative embodiment, the HF generator  204  can be connected to the substrate pedestal module  223 . The power and frequency supplied by matching network  206  is sufficient to generate a plasma from the process gas/vapor. In an embodiment both the HF generator and the LF generator are used, and in an alternate embodiment, just the HF generator is used. In a typical process, the HF generator is operated at frequencies of about 2-100 MHz; in a preferred embodiment at 13.56 MHz or 27 MHz. The LF generator is operated at about 50 kHz to 2 MHz; in a preferred embodiment at about 350 to 600 kHz. The process parameters may be scaled based on the chamber volume, substrate size, and other factors. Similarly, the flow rates of process gas may depend on the free volume of the vacuum chamber (reaction chamber) or processing zone. 
     Within the chamber, the substrate pedestal module  223  supports a substrate  13  on which materials such as thin films may be deposited. The substrate pedestal module  223  can include a fork or lift pins to hold and transfer the substrate during and between the deposition and/or plasma treatment reactions. In an embodiment, the substrate  13  may be configured to rest on a surface of the substrate pedestal module  223 , however in alternate embodiments the substrate pedestal module  223  may include an electrostatic chuck, a mechanical chuck, or a vacuum chuck for holding the substrate  13  on the surface of the substrate pedestal module  223 . The substrate pedestal module  223  can be coupled with a heater block  220  for heating substrate  13  to a desired temperature. Substrate  13  is maintained at a temperature of about 25° C. to 500° C. or greater depending on the material to be deposited. 
     In certain embodiments, a system controller  228  is employed to control process conditions during deposition, post deposition treatments, and/or other process operations. The controller  228  will typically include one or more memory devices and one or more processors. The processor may include a CPU or computer, analog and/or digital input/output connections, stepper motor controller boards, etc. 
     In certain embodiments, the controller  228  controls all of the activities of the apparatus. The system controller  228  executes system control software including sets of instructions for controlling the timing of the processing operations, frequency and power of operations of the LF generator  202  and the HF generator  204 , flow rates and temperatures of precursors and inert gases and their relative mixing, temperature of the heater block  220  and showerhead module  211 , pressure of the chamber, tilt of the showerhead, and other parameters of a particular process. Other computer programs stored on memory devices associated with the controller may be employed in some embodiments. 
     Typically there will be a user interface associated with controller  228 . The user interface may include a display screen, graphical software displays of the apparatus and/or process conditions, and user input devices such as pointing devices, keyboards, touch screens, microphones, etc. 
     A non-transitory computer machine-readable medium can comprise program instructions for control of the apparatus. The computer program code for controlling the processing operations can be written in any conventional computer readable programming language: for example, assembly language, C, C++, Pascal, Fortran or others. Compiled object code or script is executed by the processor to perform the tasks identified in the program. 
     The controller parameters relate to process conditions such as, for example, timing of the processing steps, flow rates and temperatures of precursors and inert gases, temperature of the wafer, pressure of the chamber, tilt of the showerhead, and other parameters of a particular process. These parameters are provided to the user in the form of a recipe, and may be entered utilizing the user interface. 
     Signals for monitoring the process may be provided by analog and/or digital input connections of the system controller. The signals for controlling the process are output on the analog and digital output connections of the apparatus. 
     The system software may be designed or configured in many different ways. For example, various chamber component subroutines or control objects may be written to control operation of the chamber components necessary to carry out deposition processes. Examples of programs or sections of programs for this purpose include substrate timing of the processing steps code, flow rates and temperatures of precursors and inert gases code, and a code for pressure of the chamber. 
     The showerhead module  211  is preferably temperature controlled and the pedestal is preferably RF powered. An exemplary embodiment of a temperature controlled RF powered showerhead module can be found in commonly-assigned U.S. Published Patent Application No. 2013/0316094 which is hereby incorporated by reference in its entirety. 
     According to embodiments disclosed herein, the showerhead module preferably includes a showerhead tilt adjustment mechanism for manually adjusting tilt, angle, gap and planarization of the showerhead module. As illustrated in  FIGS. 3A and 3B , a showerhead module  211  preferably includes a stem  305 , a base  315  which includes a backing plate  317  and a faceplate  316  as well as the showerhead tilt adjustment mechanism  400  for adjusting the planarization of the showerhead module  211 . The planarization of the showerhead module  211  can also be coarsely adjusted by tightening or loosening three adjustment screws  405  located 120° apart. Adjustment screws  405  comprise a coarse thread and a fine thread that can be used to manually adjust the showerhead module  211  in tilt and in axial position. The adjustment screws  405  mate with lock nuts and threaded bores in a leveling plate as explained in more detail below. 
     In one embodiment, planarization of the faceplate  316  of the showerhead module  211  can be adjusted using three tilt adjustment mechanisms as part of a showerhead adjustment mechanism to manually provide three degrees of freedom: an axial translation and two directions of tilt. With reference to  FIGS. 3A and 3B , the showerhead module  211  is supported by a bellows assembly  500  which includes a collar  502 , bellows  504  and leveling plate  506 . A cooling plate  508  can be attached to the leveling plate  506 . 
     As illustrated in  FIG. 3A , the showerhead module  211  is preferably supported in a top plate  330  of the chemical isolation chamber (i.e. reaction chamber). The top plate  330  preferably supports the collar  502  in a stepped bore. A horizontal upper surface of the top plate  330  preferably has openings, such as threaded openings, wherein corresponding openings, for receiving fasteners  512 , in the collar  502  include at least three fasteners  512  which attach the collar  502  to the top plate  330 . The collar  502  supports the remainder of showerhead tilt adjustment mechanism  400  in the top plate  330 . The showerhead tilt adjustment mechanism  400  is electrically grounded by the top plate  330 . 
     An O-ring  514  forms an airtight seal (i.e. a hermetic seal) between the leveling plate  506  and the cooling plate  508  supported above the collar  502  by three adjustment screws  405  wherein the three adjustment screws  405  are also operable to coarsely adjust the planarization of the cooling plate  508  with respect to the collar  502 . As explained in more detail below, an upper end of each adjustment screw  405  is threaded into a threaded bore of the leveling plate  506  and a lower end of each respective adjustment screw  405  is threaded into a lock nut  516  which is free to rotate with the adjustment screw  405  when not engaged with lock plate  518  or the lock nut  516  can be locked by engagement with the lock plate  518  so as not to rotate when the adjustment screw  405  is rotated. The showerhead stem  305  extends through a central opening in the collar  502 , the bellows  504 , and the leveling plate  506  and an upper end of the stem  305  is attached to the leveling plate  506  so that the faceplate  316  can be tilted to a desired angle by rotation of the adjustment screws  405 . 
     The bellows  504  preferably forms an airtight expandable and flexible vacuum seal between the collar  502  and the leveling plate  506  wherein the stem  305  extends through the airtight expandable vacuum seal such that the planarization of the showerhead module  211  can be adjusted without breaking the airtight expandable vacuum seal. The bellows  504  is preferably welded at an upper end to the leveling plate  506  and at a lower end to the collar  502 . 
     The showerhead tilt adjustment mechanism  400  may be attached to the top plate  330  of a chemical isolation chamber via three or more fasteners  512 . The showerhead tilt adjustment mechanism preferably includes three differential screw assemblies wherein each differential screw assembly provides one degree of motion. Three differential screw assemblies would give three degrees of motion: two tilts and axial position. 
       FIGS. 4A-4D  show further details of the showerhead tilt adjustment mechanism and how the showerhead tilt mechanism can provide coarse and fine gap adjustments. The adjustment screw  405  includes a first externally threaded section  405   a  engaged with an internally threaded section  506   a  in an upwardly extending tubular projection  506   b  on the leveling plate  506  and a second externally threaded section  405   b  engaged with internal threads of the lock screw  516 . The first threaded section  405   a  and the second threaded section  405   b  preferably have different thread pitches oriented in the same direction. The upper end of the adjustment screw  405  includes a socket  405   c  which can engage a tool such as a hexagonal screw driver (not shown) and a slot  405   d  in an upper portion of the socket  405   c  is adapted to receive a projection of an indicator cap. A fastener  520  such as a bolt is located inside the adjustment screw  405  with a lower end  520   a  threaded into a threaded hole in the collar  502  and an enlarged head  520   b  at the upper end received inside the socket  405   c . the head  520   b  fills a lower portion of the socket  405   c  so that a tool such as a hexagonal screw driver can engage the remainder of the socket  405   c  to rotate the adjustment screw  405  during a gap/tilt adjustment. 
     The lock plate  518  includes a handle  518   a  at one end, a wide slot  518   b  at the opposite end, and a narrow slot  518   c  extending from the wide slot  518   b . The shaft of fastener  512  extends through the narrow slot  518   c  and allows the lock plate  518  to slide radially inwardly to engage the lock nut  516 . As shown in  FIGS. 4A-4B , when the lock plate  518  is not engaged with the lock nut  516 , the lock nut  516  rotates with the adjustment screw  405  to provide a coarse gap adjustment. As shown in  FIGS. 4C-4D , when the lock plate  518  is engaged with the lock nut  516 , the lock nut  516  is prevented from rotating with the adjustment screw  405  to provide a fine gap adjustment. The lock plate  518  includes a reference mark  518   d  which provides a visual indication of when the lock plate  518  is not engaged with the lock nut  516  (reference mark  518   d  is outside the outer periphery of leveling plate  506  as shown in  FIGS. 4A-4B ) and when the lock plate  518  is engaged with the lock nut  516  (reference mark  518   d  is inside the outer periphery of the leveling plate  506  as shown in  FIGS. 4C-4D ). 
       FIG. 5  shows details of an indicator cap  522  fitted in the socket  405   c  of the adjustment screw  405 . The indicator cap  522  includes a projection  522   a  which fits in the slot  405   d  of the adjustment screw  405 . In making a gap/tilt adjustment, the indicator cap  522  can be placed on the adjustment screw  405  and its angular position can be recorded. Then, the indicator cap is removed and a gap/tilt adjustment is performed by rotating the adjustment screw  405  with the lock nut  516  not engaged with the lock plate  518  or with the lock nut  516  engaged with the lock plate  518 . When the gap/tilt adjustment is completed, the indicator cap is placed on the adjustment screw  405  and its angular position is recorded. 
     As shown in  FIG. 6 , the indicator cap can include a pointer  522   b  extending upwardly from a circular dial  522   c  having indicator circumferentially spaced marks  522   d  which provide a visual indication of the angular position of the pointer before and after a gap/tilt adjustment. 
     The adjustment screw  405  may also be used for coarse and fine adjustment of the showerhead module  211  position. Depending on the choice of thread pitches, coarse adjustments in the range of about 0.02 to about 0.04 inch and fine adjustments in the range of about 0.002 to 0.004 inch per full rotation of the adjustment screw  405  can be achieved. For example, the coarse adjustment can be 0.03125 inch per full rotation of the adjustment screw and the fine adjustment can be 0.0035 inch per full rotation of the adjustment screw. 
     While the semiconductor substrate processing apparatus including the baffle arrangement has been described in detail with reference to specific embodiments thereof, it will be apparent to those skilled in the art that various changes and modifications can be made, and equivalents employed, without departing from the scope of the appended claims.