Abstract:
Embodiments of an apparatus for improving hot plate substrate monitoring and control in a lithography system are generally described herein. Other embodiments may be described and claimed.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to methods and heat treatment apparatus for thermally processing substrates, such as semiconductor substrates. 
       BACKGROUND OF THE INVENTION 
       [0002]    Photolithography processes for manufacturing semiconductor devices and liquid crystal displays (LCD&#39;s) generally coat a resist on a substrate, expose the resist coating to light to impart a latent image pattern, and develop the exposed resist coating to transform the latent image pattern into a final image pattern having masked and unmasked areas. Such a series of processing stages is typically carried out in a coating/developing system having discrete heating sections, such as a pre-baking unit and a post-baking unit. Each heating section of the coating/developing system may incorporate a hotplate with a built-in heater of, for example, a resistance heating type. 
         [0003]    Feature sizes of semiconductor device circuits have been scaled to less than 0.1 micron. Typically, the pattern wiring that interconnects individual device circuits is formed with sub-micron line widths. Consequently, the heat treatment temperature of the resist coating should be accurately controlled to provide reproducible and accurate feature sizes and line widths. The substrates or wafers (i.e., objects to be treated) are usually treated or processed under the same recipe (i.e., individual treatment program) in units (i.e., lots) each consisting of, for example, twenty-five substrates. Individual recipes define heat treatment conditions under which pre-baking and post-baking are performed. Substrates belonging to the same lot are heated under the same conditions. 
         [0004]    According to each of the recipes, the heat treatment temperature may be varied within such an acceptable range that the temperature will not have an effect on the final semiconductor device. In other words, a desired temperature may differ from a heat treatment temperature in practice. When the substrate is treated with heat beyond the acceptable temperature range, a desired resist coating cannot be obtained. Therefore, to obtain the desired resist coating, a temperature sensor is used for detecting the temperature of the hotplate. On the basis of the detected temperature, the power supply to the heater may be controlled with reliance on feedback from the temperature sensor. It is difficult to instantaneously determine the temperature of the hotplate using a single temperature sensor embedded within the bulk of the hotplate because the temperature of the entire hotplate is not uniform and varies with the lapsed time. 
         [0005]    The post exposure bake (PEB) process is a thermally activated process and serves multiple purposes in photoresist processing. First, the elevated temperature of the bake drives the diffusion of the photoproducts in the resist. A small amount of diffusion may be useful in minimizing the effects of standing waves, which are the periodic variations in exposure dose throughout the depth of the resist coating that result from interference of incident and reflected radiation. Another main purpose of the PEB is to drive an acid catalyzed reaction that alters polymer solubility in many chemically amplified resists. PEB also plays a role in removing solvent from the substrate surface. 
         [0006]    In addition to the intended results, numerous problems may be observed during heat treatment. For example, the light sensitive component of the resist may decompose at temperatures typically used to remove the solvent, which is a concern for a chemically amplified resist because the remaining solvent content has a strong impact on the diffusion and amplification rates. Also, heat-treating can affect the dissolution properties of the resist and, thus, have direct influence on the developed resist profile. Hotplates having uniformities within a range of a few tenths of a degree centigrade are currently available and are generally adequate for current process methods. Hotplates may be calibrated using a flat bare silicon substrate with imbedded thermal sensors. However, actual production substrates carrying deposited films on the surface of the silicon may exhibit small amounts of warpage because of the stresses induced by the deposited films. 
         [0007]    This warpage may cause the normal gap between the substrate and the hotplate (referred to as the proximity gap), to vary across the substrate from a normal value of approximately 100 μm by as much as a 100 μm deviation from the mean proximity gap. Consequently, actual production substrates may have different heating profiles than the substrate used to calibrate the hotplate. 
         [0008]    This variability in the proximity gap changes the heat transfer characteristics in the area of the varying gap. Heat transfer through gases with low thermal conductivity, such as air, in the gap can cause temperature non-uniformity across the substrate surface as the temperature of the substrate is elevated to a process temperature. This temperature nonuniformity may result in a change in critical dimension (CD) in that area of several nanometers, which can approach the entire CD variation budget for current leading edge devices, and will exceed the projected CD budget for smaller devices planned for production in the next few years. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The present invention is illustrated by way of example and not as a limitation in the accompanying figures. 
           [0010]      FIG. 1  is a top view of a schematic diagram of a coating\developing system for use in association with the invention; 
           [0011]      FIG. 2  is a front view of the coating/developing system of  FIG. 1 ; 
           [0012]      FIG. 3  is a partially cut-away back view of the coating/developing system of  FIG. 1 ; 
           [0013]      FIG. 4  is a top view of a heat treatment apparatus for use with the coating/developing system of  FIGS. 1-3 ; 
           [0014]      FIG. 5  is a cross-sectional view of the heat treatment apparatus of  FIG. 4  generally along line  5 - 5 ; 
           [0015]      FIG. 6  is an enlarged view of a portion of  FIG. 5 ; 
           [0016]      FIG. 7  is an illustration of a flat substrate in contact with support protrusions and a lift pin configured with a temperature sensor; and 
           [0017]      FIG. 8  is an illustration of a warped substrate in contact with support protrusions and in close proximity to a lift pin configured with a temperature sensor. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    There is a general need for directly monitoring a temperature of a substrate on a hotplate and/or sensing a condition where the substrate is severely warped and/or improperly placed on the hotplate. One way to directly monitor a temperature of a substrate on a hotplate and/or sensing a warped substrate condition or a gross misalignment of the substrate is to incorporate one or more temperature sensing elements in one or more contact points of a substrate placement system. By configuring a substrate placement system with one or more temperature sensing elements, a heat treatment temperature of a substrate, comprising a thin film coating, should be accurately controlled to provide reproducible and accurate feature sizes and line widths. 
         [0019]    An embodiment of the method for thermally processing substrates utilizes a coating/developing process system  150 . The substrate, generally in the form of a substrate composed of semiconducting material, is processed by the coating/developing process system  150 . The processing is accomplished in such a way that the finished product will carry device structures on the top surface of the substrate. 
         [0020]    With reference to  FIGS. 1-3 , the coating/developing process system  150  comprises a cassette station  10 , a process station  11 , and an interface section  12 , which are contiguously formed as one unit. In the cassette station  10 , a cassette (CR)  13  storing a plurality of substrates represented by substrates (W)  14  (e.g., 25 substrates) is loaded into, and unloaded from, the system  150 . Each of the substrates  14  can be composed of a semiconductor material such as silicon, which may have the form of a single crystal material of the kind used in the art of semiconductor device manufacturing. 
         [0021]    The process station  11  includes various single-substrate processing units for applying a predetermined treatment required for a coating/developing step to individual substrates (W)  14 . These process units are arranged in predetermined positions of multiple stages, for example, within first (G 1 ), second (G 2 ), third (G 3 ), fourth (G 4 ) and fifth (G 5 ) multiple-stage process unit groups  31 ,  32 ,  33 ,  34 ,  35 . The interface section  12  delivers the substrates (W)  14  between the process station  11  and an exposure unit (not shown) that can be abutted against the process station  11 . 
         [0022]    A cassette table  20  of cassette station  10  has positioning-projections  20   a  on which a plurality of substrate cassettes (CR)  13  (for example, at most 6) is mounted. The substrate cassettes (CR)  13  are thereby aligned in line in the direction of an X-axis (the up-and-down direction of  FIG. 1 ) with a substrate inlet/outlet  17  facing the process station  11 . The cassette station  10  includes a substrate transfer carrier  21  movable in the aligning direction (X-axis) of cassettes  13  and in the aligning direction (Z-axis, vertical direction) of substrates  14  stored in the substrate cassette (CR)  13 . The substrate transfer carrier  21  gains access selectively to each of the substrate cassettes (CR)  13 . 
         [0023]    The substrate transfer carrier  21  is further designed rotatable in a θ (theta) direction, so that it can gain access to an alignment unit (ALIM)  41  and an extension unit (EXT)  42  belonging to a third multiple-stage process unit group (G 3 )  33  in the process station  11 , as described later. 
         [0024]    The process station  11  includes a main substrate transfer mechanism  22  (movable up-and-down in the vertical direction) having a substrate transfer machine  46 . All process units are arranged around the main substrate transfer mechanism  22 , as shown in  FIG. 1 . The process units may be arranged in the form of multiple stages G 1 , G 2 , G 3 , G 4  and G 5 . 
         [0025]    The main substrate transfer mechanism  22  has a substrate transfer machine  46  that is movable up and down in the vertical direction (Z-direction) within a hollow cylindrical supporter  49 , as shown in  FIG. 3 . The hollow cylindrical supporter  49  is connected to a rotational shaft of a motor (not shown). The cylindrical supporter  49  can be rotated about the shaft synchronously with the substrate transfer machine  46  by the driving force of the motor rotation. Thus, the substrate transfer machine  46  is rotatable in the θ direction. Note that the hollow cylindrical supporter  49  may be connected to another rotational axis (not shown), which is rotated by a motor. 
         [0026]    The substrate transfer machine  46  has a plurality of holding members  48  which are movable back and forth on a table carrier  47 . The substrate (W)  14  is delivered between the process units by the holding members  48 . 
         [0027]    In the process unit station  11  of this embodiment, five process unit groups G 1 , G 2 , G 3 , G 4 , and G 5  may be sufficiently arranged. For example, first (G 1 ) and second (G 2 ) multiple-stage process unit groups  31 ,  32  are arranged in the front portion  151  (in the forehead in  FIG. 1 ) of the system  150 . A third multiple-stage process unit group (G 3 )  33  is abutted against the cassette station  10 . A fourth multiple-stage process unit group (G 4 ) is abutted against the interface section  12 . A fifth multiple-stage process unit group (G 5 ) can be optionally arranged in a back portion  152  of system  150 . 
         [0028]    As shown in  FIG. 2 , in the first process unit group (G 1 )  31 , two spinner-type process units, for example, a resist coating unit (COT)  36  and a developing unit (DEV)  37 , are stacked in the order mentioned from the bottom. The spinner-type process unit used herein refers to a process unit in which a predetermined treatment is applied to the substrate (W)  14  mounted on a spin chuck (not shown) placed in a cup (CP)  38 . Also, in the second process unit group (G 2 )  32 , two spinner process units such as a resist coating unit (COT)  36  and a developing unit (DEV)  37 , are stacked in the order mentioned from the bottom. It is preferable that the resist coating unit (COT)  36  be positioned in a lower stage from a structural point of view and to reduce maintenance time associated with the resist-solution discharge. However, if necessary, the coating unit (COT)  36  may be positioned in the upper stage. 
         [0029]    As shown in  FIG. 3 , in the third process unit group (G 3 )  33 , open-type process units, for example, a cooling unit (COL)  39  for applying a cooling treatment, an alignment unit (ALIM)  41  for performing alignment, an extension unit (EXT)  42 , an adhesion unit (AD)  40  for applying an adhesion treatment to increase the deposition properties of the resist, two pre-baking units (PREBAKE)  43  for heating a substrate  14  before light-exposure, and two postbaking units (POBAKE)  44  for heating a substrate  14  after light exposure, are stacked in eight stages in the order mentioned from the bottom. The open type process unit used herein refers to a process unit in which a predetermined treatment is applied to a substrate  14  mounted on a support platform within one of the processing units. Similarly, in the fourth process unit group (G 4 )  34 , open type process units, for example, a cooling unit (COL)  39 , an extension/cooling unit (EXTCOL)  45 , an extension unit (EXT)  42 , another cooling unit (COL), two pre-baking units (PREBAKE)  43  and two post-baking units (POBAKE)  44  are stacked in eight stages in the order mentioned from the bottom. 
         [0030]    Because the process units for low-temperature treatments, such as the cooling unit (COL)  39  and the extension/cooling unit (EXTCOL)  45 , are arranged in the lower stages and the process units for higher-temperature treatments, such as the pre-baking units (PREBAKE)  43  and the post-baking units (POBAKE)  44  and the adhesion unit (AD)  40  are arranged in the upper stages in the aforementioned unit groups, thermal interference between units can be reduced. Alternatively, these process units may be arranged differently. 
         [0031]    The interface section  12  has the same size as that of the process station  11  in the X direction but shorter in the width direction. A movable pickup cassette (PCR)  15  and an unmovable buffer cassette (BR)  16  are stacked in two stages in the front portion of the interface section  12 , an optical edge bead remover  23  is arranged in the back portion, and a substrate carrier  24  is arranged in the center portion. The substrate transfer carrier  24  moves in the X- and Z-directions to gain access to both cassettes (PCR)  15  and (BR)  16  and the optical edge bead remover  23 . The substrate carrier  24  is also designed rotatable in the θ direction; so that it can gain access to the extension unit (EXT)  42  located in the fourth multiple-stage process unit group (G 4 )  34  in the process station  11  and to a substrate deliver stage (not shown) abutted against the exposure unit (not shown). 
         [0032]    In the coating/developing process system  150 , the fifth multiple-stage process unit group (G 5 , indicated by a broken line)  35  is designed to be optionally arranged in the back portion  152  at the backside of the main substrate transfer mechanism  22 , as described above. The fifth multiple-stage process unit group (G 5 )  35  is designed to be shifted sideward along a guide rail  25  as viewed from the main substrate transfer mechanism  22 . Hence, when the fifth multiple-stage process unit group (G 5 )  35  is positioned as shown in  FIG. 1 , a sufficient space is obtained by sliding the fifth process unit group (G 5 )  35  along the guide rail  25 . As a result, a maintenance operation to the main substrate transfer mechanism  22  can be easily carried out from the backside. To maintain the space for maintenance operation to the main substrate transfer mechanism  22 , the fifth process unit group (G 5 )  35  may be not only slid linearly along the guide rail  25  but also shifted rotatably outward in the system. 
         [0033]    The baking process performed by the adhesion unit (AD)  40  is not as sensitive to warpage of the substrate  14  as are the pre- and post-bake processes performed by the prebaking units (PREBAKE)  43  and the post-baking units (POBAKE)  44 . Therefore, the adhesion unit (AD)  40  may continue to utilize a hotplate in the heat treatment apparatus. 
         [0034]    With reference to  FIGS. 4 and 5 , the pre-baking unit (PREBAKE)  43  or the postbaking unit (POBAKE)  44  may comprise a heat treatment apparatus  100  in which substrates  14  are heated to temperatures above room temperature. Each heat treatment apparatus  100  includes a processing chamber  50 , a substrate support in the representative form of a hotplate  58 , and a heating element  59  contained in the hotplate  58 . The substrate  14  includes a front surface  14   a  (also referred to herein as the “front side”) and a rear surface  14   b  (also referred to herein as the “backside”). 
         [0035]    The heating element  59  of the hotplate  58  may comprise, for example, a resistance-heating element. A temperature-sensing element  88 , such as a thermistor, a thermocouple, a resistance temperature detector (RTD), or an optical fiber fluorescence decay temperature sensor may be thermally coupled with the hotplate  58 . The temperature-sensing element  88 , embedded in the hotplate  58  is electrically coupled with a temperature controller  90 . The temperature controller  90  is also electrically coupled with the heating element  59  and powers the heating element  59  to generate heat energy used to elevate the temperature of the hotplate  58 . The temperature-sensing element  88  may provide a feedback, either independently or in combination with feedback from additional temperature sensing elements, to a temperature controller  90  for optimizing the temperature setting or the uniformity of the temperature distribution across the substrate  14  supported by the hotplate  58 , which may include different temperature zones. 
         [0036]    As the heating element  59  elevates the temperature of the hotplate  58 , heat energy from the hotplate  58  is conducted through the gap G, which then heats the substrate  14 . The temperature of the substrate  14  may be inferred from the measured hotplate temperature or may be measured directly using a temperature sensor  92  such as, for example, a pyrometer. The temperature sensor  92 , which is also electrically coupled with the temperature controller  90 , may sample the temperature on a front-side  14   a  of the substrate  14 . 
         [0037]    The hotplate  58  has a plurality of passageways  60  and a plurality of lift pins  62  projecting into the passageways  60 . The lift pins  62  are moveable between a first position, or lowered position, where the pins are flush or below the upper support surface  58   a  of hotplate  58  to a second position, or lifted position, where the lift pins project above the upper support surface  58   a  of hotplate  58 . When the lift pins  62  are in the first position, they may be in contact or in close proximity to the backside  14   b  of the substrate  14 . The lift pins  62  are connected to and supported by an arm  80  which is further connected to, and supported by, a rod  84   a  of a vertical cylinder  84 . When the rod  84   a  is actuated by the vertical cylinder  84  to protrude from the vertical cylinder  84 , the lift pins  62  are moved from the first position to the second position, contacting the backside  14   b  of the substrate  14  and thereby lifting the substrate  14 . 
         [0038]    With continued reference to  FIGS. 4 and 5 , the processing chamber  50  includes a sidewall  52 , a lid  68 , and a horizontal shielding plate  55  that defines a base with which the lid  68  is engaged. When engaged with the shielding plate  55 , the lid  68  defines a process space  67  filled by a gaseous environment when lid  68  is united with the horizontal shielding plate  55 . Gaps  50   a,    50   b  are formed at a front surface side (aisle side of the main substrate transfer mechanism  22 ) and a rear surface side of the processing chamber  50 , respectively. The substrate  14  is loaded into and unloaded from the processing chamber  50  through the gaps  50   a,    50   b.  A circular opening  56  is formed at the center of the horizontal shielding plate  55 . The hotplate  58  is housed in the opening  56 . The hotplate  58  is supported by the horizontal shielding plate  55  with the aid of a supporting plate  76 . The supporting plate  76 , shutter arm  78 , lift pin arm  80 , and liftable cylinders  82 ,  84  are arranged in a compartment  74 . The compartment  74  is defined by the shielding plate  55 , two sidewalls  53 , and a bottom plate  72 . 
         [0039]    A ring-form shutter (not shown) may be attached to the outer periphery of the hotplate  58 . Injection openings (not shown) are formed along the periphery of the shutter at constant or varying intervals of central angles. The injection openings communicate with a cooling gas supply source (not shown). The shutter may be liftably supported by a cylinder  82  via a shutter arm  78 . When the shutter is raised, a cooling gas, such as nitrogen gas or air, is exhausted from the injection openings, which is used to drop the temperature of the substrate  14  below the reaction temperature quickly while the substrate  14  is waiting to be picked up and moved to the next stage of processing. In an alternative embodiment, a cooling arm may be attached to a cooling plate that moves in when the substrate  14  is finished processing. The substrate  14  then sits on the cooling plate until it&#39;s ready to be picked up. The cooling plate may be cooled by chilled water. 
         [0040]    The substrates  14  each carry a layer  94  of processable material, such as resist. The layer  94  may contain a substance that is volatized and released at the process temperature. The resist coating unit (COT)  36  may be used to apply the layer  94  that is thermally processed in a subsequent process step by a heat treatment apparatus  100  at the process temperature. This volatile substance evaporates off of the substrate  14  when the layer  94  is exposed to the heat energy produced by the hotplate  58  at a temperature sufficient to heat the substrate  14  and layer  94  to the process temperature. An exhaust port  68   a  at the center of the lid  68  communicates with an exhaust pipe  70 . One or more waste products generated from the front-side  14   a  of the substrate  14  at the process temperature are exhausted through the exhaust port  68   a  and vented from the processing chamber  50  via exhaust pipe  70  to a vacuum pump  71 , or other evacuation unit, that can be throttled to regulate the exhaust rate. 
         [0041]    With reference to  FIG. 4 , projections  86  are arranged as alignment pins on the upper support surface  58   a  of the hotplate  58  and are used for accurately and reproducibly positioning the substrate  14  on hotplate  58 . Support protrusions  66  define proximity pins that project from the upper support surface  58   a  of the hotplate  58 . The support protrusions  66  bear all or a portion of the mass or weight of the substrate  14  so as to support substrate  14  during thermal processing. When the substrate  14  is mounted on the hotplate  58 , top portions of the support protrusions  66  have a contacting relationship with the backside  14   b  of substrate  14 , which is in a spaced relationship with the confronting support surface  58   a  on the hotplate  58 . When supported on the support protrusions  66 , the lift pins  62  have a contacting relationship or are in close proximity to the backside  14   b.  In one embodiment, the substrate  14  is flat and the backside  14   b  is in contact with all lift pins  62  and support protrusions  66 . In another embodiment, the substrate  14  is warped and the backside  14   b  is in contact with one or more lift pins  62  and support protrusions  66 , and in close proximity to at least one lift pin  62 . In a further embodiment, the substrate  14  is misaligned relative to the hotplate  58 . In this embodiment, the backside  14   b  may be in contact with or in close proximity to at least one lift pin  62  and support protrusions  66 . 
         [0042]    A narrow heat exchange gap G is formed between the backside  14   b  of the substrate  14  and the upper support surface  58   a  of the hotplate  58 . The width of the gap G may be approximately equal to the height H 2  of the support protrusions  66 . The gap G prevents the backside  14   b  of the substrate  14  from being strained and damaged by contact with the support surface  58   a  on the hot plate  58 . 
         [0043]    After the substrate  14  is mounted on the hotplate  58 , the gap G primarily contains a first gas, which may be a mixture of gaseous elements, such as air, or predominantly a single element, such as nitrogen. A second gas, such as hydrogen or helium, with a higher thermal conductivity than the first gas may be introduced into the gap G between the substrate  14  and the hotplate  58 , to increase the thermal conductance in the gap G. Thermal conductance is the quantity of heat transmitted per unit time from a unit of surface of material to an opposite unit of surface material under a unit temperature differential between the surfaces. As the high thermal conductivity gas is introduced into the gap G, it displaces the first gas causing the first gas to flow out of the gap G. A loose seal may be formed between a sealing member  102 , such as an o-ring ( FIG. 6 ), and the rear surface  14   b  of the substrate  14 . The sealing member  102  assists in keeping the high thermal conductivity gas contained in the gap G and inhibits any reentry of the first gas back into the gap G. 
         [0044]    Heat energy from the hotplate  58  is conducted through the high thermal conductivity gas in the gap G to the substrate  14 . The thermal conductivity represents a measure of material to conduct heat. The thermal conductivity of the material forming the substrate  14  is sufficient to transfer heat from the backside  14   b  to the front-side  14   a  of the substrate  14 . The higher thermal conductivity of the gas makes the system less sensitive to warpage in the substrate  14  by compensating for variations in flatness that modulate the width of gap G. For example, a system with air in the gap G between the substrate  14  and the hotplate  58  may produce about a 1° C. temperature gradient in different parts of the substrate  14  due to warpage. The temperature gradient may be reduced to about 0.17° C. (about 0.31 degree Fahrenheit) by replacing the air, or other low conductivity gas, in the gap G with the high thermal conductivity gas such as helium, which has a thermal conductivity of almost six times greater than the thermal conductivity of air. 
         [0045]    The hotplate  58  further includes a groove  101  in the hotplate  58  and a sealing member  102 , such as an o-ring, placed in the groove  101 , as best shown in  FIG. 6 . The substrate  14  is delivered to the processing chamber  50 , as discussed above, and lift pins  62  lower the substrate  14  as shown diagrammatically by arrow  64  ( FIG. 5 ). The substrate  14  is guided into position by projections  86  in proximity to the sealing member  102  and is supported above the hotplate  58  on support protrusions  66  where the backside  14   b  of the substrate  14  contacts a top of the support protrusions  66 . The height H 1  of the sealing member  102  relative to the upper support surface  58   a  of hotplate  58  may be slightly shorter than the height H 2  of the support protrusions  66  to assist the high thermal conductivity gas in displacing the air, or other low thermal conductivity gas, in the gap G. The difference in height H 1  and height H 2  results in a loose seal or dam being formed between an outer perimeter of the substrate  14  and the sealing member  102  as best seen in  FIG. 6 . The loose seal allows gases from the gap G between the substrate  14  and the hotplate  58  to escape from beneath the substrate  14  by passing between the sealing member  102  and the substrate  14 , while inhibiting gases from the processing chamber  50  from moving back into the gap G. 
         [0046]    The high thermal conductivity gas is introduced into gap G through delivery passageways  104  in the hotplate  58 . The delivery passageways  104  communicate with a high thermal conductivity gas supply  106 . The air, or other low thermal conductivity gas, in the gap G is displaced as the high thermal conductivity gas from the gas supply  106  is delivered into the gap G. The resulting gaseous environment in the gap G between the backside  14   b  of the substrate  14  and upper support surface  58   a  of the hotplate  58  is primarily composed of the high thermal conductivity gas, which increases the thermal conductance in the gap G. The high thermal conductivity gas need not displace all of the air in the gap G. However, a gaseous environment in the gap G containing higher concentrations of the high thermal conductivity gas than air, or other low thermal conductivity gas, will promote greater heat transfer and thermal conductance between the hotplate  58  and the substrate  14 . In alternate embodiments, the delivery passageways  104  may supply a continuous flow of high thermal conductivity gas to displace the air in the gap G. The continuous flow of the high thermal conductivity gas prevents air, or other low thermal conductivity gas, from re-entering and filling the gap G. 
         [0047]    Each of the passageways  60  includes a ring-shaped groove  107  in a sidewall surrounding each passageway  60  and a seal member  108  in the groove  61  that creates a pressure seal between one of the lift pins  62  and its respective passageway  60  at least when the lift pins  62  are retracted into the hotplate  58  to the first position. The seal members  108  prevent or significantly restrict the flow of the high thermal conductivity gas through the passageways  60  and out of the gap G. Likewise, sealing the passageways  60  inhibits the flow of air back into the gap G. Alternatively, each of the lift pins  62  may carry a seal member (not shown) that provides a seal with the corresponding passageway  60  as a substitute for seal members  108 . 
         [0048]      FIG. 7  is an illustration of a flat substrate  160  in contact at a temperature sensor contact point  63  with support protrusions  66  and a lift pin  62  configured with a temperature sensor  163 . In another embodiment (not shown), a plurality of lift pins  62  each configured with a temperature sensor  163 , are used to measure a temperature at various contact points  63  across the surface of the flat substrate  160 . Each temperature sensor  163  may be a thermocouple, a thermistor, a resistance temperature detector, a fiber optic fluorescence decay temperature sensor, or another temperature sensing device configured to measure a contact temperature, or surface temperature of the substrate measured through conduction. 
         [0049]    The lift pin  62  configured with a temperature sensor  163  may support at least a portion of the flat substrate  160  when the flat substrate  160  is disposed on support protrusions  66 . A temperature controller  90  controls a temperature of the heating element based, at least in part on a temperature measured by each temperature sensor  163 . The temperature controller  90  may determine that a substrate  14  is flat and properly placed on the hotplate  58  when all lift pins  62  configured with temperature sensors  163  sense a temperature within an expected range. For example, when all temperature sensors  163  measure a process temperature ranging from about 90° C. to about 130° C., it may indicate that the substrate  14  is flat and properly placed on the hotplate  58 . 
         [0050]      FIG. 8  is an illustration of a warped substrate  170  in contact with support protrusions  66  and in close proximity to a lift pin  62  configured with a temperature sensor  163 . In this embodiment, the lift pin  62  configured with a temperature sensor  163  does not support, in whole or in part, the flat substrate  160  when the warped substrate  170  substrate  160  is disposed on support protrusions  66 . The temperature controller  90  may determine that a substrate  14  is warped and/or improperly placed on the hotplate  58  when all lift pins  62  configured with temperature sensors  163  do not sense a temperature within an expected range. For example, when all temperature sensors  163  do not measure a process temperature ranging from about 90° C. to about 130° C., it may indicate that the substrate  14  is warped and/or improperly placed on the hotplate  58 . 
         [0051]    A plurality of embodiments for forming very thin layers on surfaces resulting in a film with a consistent or desired thickness profile has been described. The foregoing description of the embodiments of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. This description and the claims following include terms, such as left, right, top, bottom, over, under, upper, lower, first, second, etc. that are used for descriptive purposes only and are not to be construed as limiting. For example, terms designating relative vertical position refer to a situation where a device side (or active surface) of a substrate or upper layer is the “top” surface of that substrate; the substrate may actually be in any orientation so that a “top” side of a substrate may be lower than the “bottom” side in a standard terrestrial frame of reference and still fall within the meaning of the term “top.” 
         [0052]    The term “on” as used herein (including in the claims) does not indicate that a first layer “on” a second layer is directly on and in immediate contact with the second layer unless such is specifically stated; there may be a third layer or other structure between the first layer and the second layer on the first layer. The embodiments of a device or article described herein can be manufactured, used, or shipped in a number of positions and orientations. 
         [0053]    Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, material, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention, but do not denote that they are present in every embodiment. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily referring to the same embodiment of the invention. Furthermore, the particular features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments. Various additional layers and/or structures may be included and/or described features may be omitted in other embodiments. 
         [0054]    Various operations will be described as multiple discrete operations in turn, in a manner that is most helpful in understanding the invention. However, the order of description should not be construed as to imply that these operations are necessarily order dependent. In particular, these operations need not be performed in the order of presentation. Operations described may be performed in a different order than the described embodiment. Various additional operations may be performed and/or described operations may be omitted in additional embodiments. 
         [0055]    Persons skilled in the relevant art can appreciate that many modifications and variations are possible in light of the above teaching. Persons skilled in the art will recognize various equivalent combinations and substitutions for various components shown in the Figures. It is therefore intended that the scope of the invention be limited not by this detailed description, but rather by the claims appended hereto.