WO2020068546A2

WO2020068546A2 - Multiplexed high tcr based ampoule heaters

Info

Publication number: WO2020068546A2
Application number: PCT/US2019/051886
Authority: WO
Inventors: Ramesh Chandrasekharan
Original assignee: Lam Research Corp
Current assignee: Lam Research Corp
Priority date: 2018-09-24
Filing date: 2019-09-19
Publication date: 2020-04-02
Anticipated expiration: 2021-03-24
Also published as: KR20210053348A; WO2020068546A3; KR102813553B1; TWI815971B; TW202027195A; CN112753097B; CN112753097A

Abstract

A system for heating components of a substrate processing system includes a controller and a plurality of heaters arranged at a plurality of locations along a path of fluid flow from a source of fluid to a destination in the substrate processing system. The controller is configured to group the plurality of heaters into a plurality of groups of heaters. Each group of heaters comprises at least one of the plurality of heaters. The controller is further configured to determine a temperature gradient to be maintained across the plurality of groups of heaters. The controller is further configured to select a group of heaters from the plurality of groups of heaters and control power supplied to the selected group of heaters to maintain the temperature gradient across the plurality of groups of heaters.

Description

MULTIPLEXED HIGH TCR BASED AMPOULE HEATERS

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application No. 62/735,464, filed on September 24, 2018. The entire dislcosure of the application referenced above is incorporated herein by reference.

FIELD

[0002] The background description provided here is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.

BACKGROUND

[0003] The present disclosure relates generally to substrate processing systems and more particularly to multiplexed high temperature coefficient of resistance (TCR) based ampoule heaters for substrate processing systems.

[0004] Substrate processing systems may be used to perform etching, deposition, and/or other treatment of substrates such as semiconductor wafers. Examples of processes that may be performed on a substrate include, but are not limited to, chemical vapor deposition (CVD), plasma enhanced chemical vapor deposition (PECVD), atomic layer deposition (ALD), atomic layer etch (ALE), plasma enhanced atomic layer deposition (PEALD) and/or other etch, deposition, and cleaning processes. During processing, a substrate is arranged on a substrate support, such as a pedestal, an electrostatic chuck (ESC), etc. in a processing chamber of the substrate processing system. A process gas mixture is introduced into the processing chamber to treat the substrate. In some examples, plasma may be struck to enhance chemical reactions within the processing chamber.

[0005] Gas supply lines supply gas mixtures to the processing chamber. If the temperature of the gas mixtures in the gas supply lines is not carefully controlled, condensation of the gas mixture may occur on walls of the gas supply lines. The condensation of the gas mixture may cause defects and is often difficult to remove. SUMMARY

[0006] A system for heating components of a substrate processing system comprises a controller and a plurality of heaters arranged at a plurality of locations along a path of fluid flow from a source of fluid to a destination in the substrate processing system. The controller is configured to group the plurality of heaters into a plurality of groups of heaters. Each group of heaters comprises at least one of the plurality of heaters. The controller is further configured to determine a temperature gradient to be maintained across the plurality of groups of heaters. The controller is further configured to select a group of heaters from the plurality of groups of heaters and control power supplied to the selected group of heaters to maintain the temperature gradient across the plurality of groups of heaters.

[0007] In other features, the controller is further configured to group the plurality of heaters into the plurality of groups of heaters based on a geometry of the components in the path of fluid flow from the source of the fluid to the destination in the substrate processing system. The components include conduits and valves.

[0008] In other features, each of the plurality of heaters has a resistance that varies as a function of temperature, and the controller is further configured to measure resistances of heaters in the selected group of heaters. The controller is further configured to determine temperatures of the heaters in the selected group of heaters based on the resistances of the heaters in the selected group of heaters. The controller is further configured to control the power supplied to the selected group of heaters based on the determined temperatures of the heaters in the selected group of heaters and the temperature gradient.

[0009] In other features, each of the plurality of heaters has a resistance that varies as a function of temperature, and the controller is further configured to determine a desired temperature for heaters in the selected group of heaters based on the temperature gradient to be maintained across the plurality of groups of heaters. The controller is further configured to determine desired resistance values for the heaters in the selected group of heaters based on the desired temperature for the heaters in the selected group of heaters. The controller is further configured to measure resistances of the heaters in the selected group of heaters. The controller is further configured to control the power supplied to the selected group of heaters based on the measured resistances of the heaters in the selected group of heaters until the heaters in the selected group of heaters have the desired resistance values.

[0010] In other features, each of the plurality of heaters has a resistance that varies as a function of temperature, and the controller is further configured to determine desired temperatures for heaters in the selected group of heaters and for another group of heaters from the plurality of groups of heaters based on the temperature gradient to be maintained across the plurality of groups of heaters. The controller is further configured to determine desired resistance values for the heaters in the selected group of heaters and for heaters in the another group of heaters based on the desired temperatures for the heaters in the selected group of heaters. The controller is further configured to determine a ratio between the desired resistance values for the heaters in the selected group of heaters and for the heaters in the another group of heaters. The controller is further configured to measure resistances of the heaters in the selected group of heaters. The controller is further configured to control the power supplied to the selected group of heaters based on the measured resistances of the heaters in the selected group of heaters to maintain the ratio between the desired resistance values for the heaters in the selected group of heaters and for the heaters in the another group of heaters.

[0011] In other features, the system further comprises a temperature sensor configured to sense a temperature of the fluid in the source. The controller is further configured to stop the system when the temperature is greater than a first threshold or less than a second threshold, where the first threshold is greater than the second threshold, to ensure that the system operates when the temperature is between the first threshold and the second threshold.

[0012] In other features, the system further comprises a current sensor to sense current supplied to each of the plurality of heaters. The controller is further configured to determine resistance of each of the plurality of heaters based thereon.

[0013] In other features, the system further comprises a voltage sensor to sense voltage supplied to each of the plurality of heaters. The controller is further configured to determine resistance of each of the plurality of heaters based thereon.

[0014] In other features, the system further comprises a driver to drive the selected group of heaters based on a duty cycle and a resistance estimator to estimate resistances of the group of heaters based on the duty cycle. The controller is further configured to determine temperatures of the selected group of heaters based on the resistances.

[0015] In other features, the controller is further configured to provide a progressive heating profile across the plurality of groups of heaters from the source of the fluid to the destination. The destination includes a processing chamber to process a semiconductor substrate in the substrate processing system.

[0016] In still other features, a system for heating components of a substrate processing system comprises an oven to enclose one or more components of the substrate processing system and to maintain a predetermined temperature in the oven. The system further comprises a plurality of heaters arranged in the oven to heat the one or more components of the substrate processing system. The plurality of heaters includes uninsulated resistive heaters. The system further comprises a controller is configured to group the plurality of heaters into a plurality of groups of heaters. Each group of heaters comprises at least one of the plurality of heaters. The controller is configured to control power supplied to the plurality of groups of heaters by selecting one group of heaters from the plurality of groups of heaters at a time to maintain a temperature gradient across the plurality of groups of heaters and to maintain the predetermined temperature in localized regions in the oven.

[0017] In other features, the system further comprises a temperature sensor located remotely from the plurality of heaters to sense a temperature in the oven. The oven includes a heating element. The controller is further configured to determine an average temperature in the oven based on the sensed temperature and to control the heating element of the oven based thereon to maintain the predetermined temperature.

[0018] In another feature, the predetermined temperature is ambient temperature.

[0019] In other features, each of the plurality of heaters has a resistance that varies as a function of temperature, and the controller is further configured to measure resistances of heaters in a selected group of heaters. The controller is further configured to determine temperatures of the heaters in the selected group of heaters based on the resistances of the heaters in the selected group of heaters. The controller is further configured to control the power supplied to the selected group of heaters based on the determined temperatures of the heaters in the selected group of heaters and the temperature gradient. [0020] In other features, each of the plurality of heaters has a resistance that varies as a function of temperature, and the controller is further configured to determine a desired temperature for heaters in a selected group of heaters based on the temperature gradient to be maintained across the plurality of groups of heaters. The controller is further configured to determine desired resistance values for the heaters in the selected group of heaters based on the desired temperature for the heaters in the selected group of heaters. The controller is further configured to measure resistances of the heaters in the selected group of heaters. The controller is further configured to control the power supplied to the selected group of heaters based on the measured resistances of the heaters in the selected group of heaters until the heaters in the selected group of heaters have the desired resistance values.

[0021] In other features, each of the plurality of heaters has a resistance that varies as a function of temperature, and the controller is further configured to determine desired temperatures for heaters in a selected group of heaters and for another group of heaters from the plurality of groups of heaters based on the temperature gradient to be maintained across the plurality of groups of heaters. The controller is further configured to determine desired resistance values for the heaters in the selected group of heaters and for heaters in the another group of heaters based on the desired temperatures for the heaters in the selected group of heaters. The controller is further configured to determine a ratio between the desired resistance values for the heaters in the selected group of heaters and for the heaters in the another group of heaters. The controller is further configured to measure resistances of the heaters in the selected group of heaters. The controller is further configured to control the power supplied to the selected group of heaters based on the measured resistances of the heaters in the selected group of heaters to maintain the ratio between the desired resistance values for the heaters in the selected group of heaters and for the heaters in the another group of heaters.

[0022] In another feature, the ratio is determined at the predetermined temperature.

[0023] In another feature, the controller is further configured to adjust the ratio to provide progressive heating across the plurality of groups of heaters.

[0024] In other features, the controller is further configured to group the plurality of heaters into the plurality of groups of heaters based on a geometry of the one or more components. The components include conduits and valves in a path of fluid flow from a source of fluid to a processing chamber in the substrate processing system.

[0025] Further areas of applicability of the present disclosure will become apparent from the detailed description, the claims and the drawings. The detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein:

[0027] FIG. 1A is a functional block diagram of an example of a substrate processing system according to the present disclosure;

[0028] FIG. 1 B illustrates an example of a multi-tray vaporized precursor delivery system according to the present disclosure;

[0029] FIGS. 2A to 2D are functional block diagrams of examples of heating systems according to the present disclosure;

[0030] FIG. 3 is a graph illustrating temperature as a function of length along a gas flow path to a processing chamber;

[0031] FIG. 4 illustrates an example of a heater zone including a thermocouple;

[0032] FIGS. 5 and 6 are graphs illustrating temperature as a function of length along a gas flow path in a zone;

[0033] FIGS. 7 and 8 are flowcharts illustrating examples of methods for controlling temperature of components along a gas flow path using a plurality of heater zones heated in a multiplexed manner according to the present disclosure;

[0034] FIG. 9 is a functional block diagram of a heating system including an oven enclosing a gas flow path and uninsulated TCR heaters arranged in one or more locations; and

[0035] FIG. 10 is a flowchart of a method for operating the heating system of FIG. 9.

[0036] In the drawings, reference numbers may be reused to identify similar and/or identical elements. DETAILED DESCRIPTION

[0037] Condensation in gas lines can be mitigated using various heating schemes. For example, progressive heating may be used to overcome condensation risks in gas lines. However, the temperature measured at one location along a gas line using a thermocouple does not capture load-based changes across an entire heater zone. Pressure transitions and/or load changes due to expansions, valves, and so on can cause local temperature changes. Additionally, tubes/heaters that are designed for one application are often used for another application, and the temperature distribution can change. If a thermocouple is located at a pressure drop/expansion location, the thermocouple will sense a low temperature, and the gas line may be heated hotter than desired. If the thermocouple is located away from the pressure drop, localized cooling can occur. One solution is to increase the number of heater zones. This approach, however, adds cost and serviceability challenges due to more connections. Instead, two different heating schemes can be used to solve the above problems: progressive heating, where each heater zone is individually controlled; or multiplexed heating, where a group of heater zones are controlled at a time, and where several groups of heater zones are controlled using a multiplexed control. Each heating scheme is described below.

[0038] In progressive heating, heating systems for gas delivery systems use a heater including a heater element made of a temperature coefficient of resistance (TCR) material. In some examples, the heater element has a high TCR that is greater than 0.001 ppm/°C. For example only, molybdenum or tungsten (W) heater elements may be used. In other examples, the heater element has a lower TCR that is less than 0.001 ppm/°C. For example only, copper or nickel can be used. Throughout the present disclosure, the heater element is also called a TCR heater element, a TCR heater, or a resistive heater. A resistance of a TCR heater can be measured to provide an average temperature in a heater zone. A controller may be used to relate resistance to temperature using a lookup table or a formula. Temperature can also be monitored in each zone using a thermocouple (TC) to provide a local temperature (representing a point location in the heater zone). In some examples, the TC may be located at either a starting position or ending position of the heater zone to measure a sensed temperature at that location. A combination of primary control and secondary override/monitoring may be performed using feedback from the TCR heater and the TC in each heater zone. [0039] In a first approach, the temperature sensed by the TC can be used as a control set point for the heater zone, and an average temperature sensed by the TCR heater can be used as monitor/override. If the average temperature of the heater zone falls below or goes above a particular value, the controller can use a default duty cycle. Acceptable ranges of the average values can be assigned on a per heater zone basis to cascade progressively or to monotonically increase along a gas flow path. In some examples, the TCR heaters use high TCR elements. In other examples, the TCR heaters use low TCR elements since the average value is used as a safety check/override.

[0040] In a second approach, the average temperature sensed by the TCR heater can be used as a control variable. An entire heater zone may be heated hotter if there is a local temperature drop due to expansion related cooling in one section of the heater zone. In some examples, a local TC can be arranged close to expansion points to monitor and override if needed. If there is cooling at the location monitored by the local TC, a limit stop can be triggered, and heat can be added preemptively.

[0041] In both methods, the average temperature ensures progressive heating. The local temperature measurements from the local TC enable the heating system to react to local changes. The control systems described above prevent overreaction by the heating system, which may cause overheating in the heater zones. In some examples, fewer heater zones may be used to cover larger areas. In other examples, the TCs can be arranged only at expected expansion zones to address specific condensation risks while the rest of the heating area is part of a single large zone.

[0042] While the above methods recognize that the temperature distribution changes due to pressure transitions, the above approaches do not take into account the phase change that may occur, especially as fluid level changes. For example, if a temperature at a location is sensed, the sensed temperature will not indicate the phase change that may be occurring upstream or downstream from that location. Accordingly, supplying heat to that location based on the sensed temperature may result in undersupply of heat to the zone covered by that location.

[0043] The present disclosure proposes multiplexed heating, which addresses the issue that the temperature response to phase change can be poor with fewer TCs/zones. According to the multiplexed heating scheme, if phase change is detected anywhere across a zone, that is, if a zone is struggling to keep up its temperature, the temperature of that zone can be corrected independent of where the temperature is dropping in that zone. In contrast, in other heating schemes, if a TC is used to sense the temperature at a particular location, the TC might miss the location or locations in the vicinity of the TC where heat loss is occurring.

[0044] Generally, phase change occurs in a narrow region. Within a narrow region, if the temperature drops at a particular location, there is no way of detecting the temperature change at that location unless a TC is located at that location. However, installing TC’s at numerous locations can be impractical. Instead, according to the present disclosure, a zone can be constructed to cover a general area where the phase change is expected as opposed to constructing a zone at a particular location or point where the temperature is sensed. A zone constructed to cover a general area will detect phase change within that zone independent of where the phase change is occurring in that zone.

[0045] Typically, an ampoule supplying vaporized precursor is controlled using 2-4 zones (e.g., one heater zone for each of the body, lid, and valve of the ampoule; or in some cases two heater zones for the body). A typical ampoule has a region of significant heat transfer where a phase change due to evaporation from liquid or solid to vapor is typically occurring. In other vaporized precursor delivery systems (e.g., see an example of a system comprising multiple trays shown in FIG. 1 B), there can be multiple locations where phase change is occurring. As mentioned above, the temperature response to phase change, especially as fluid level changes, can be poor with few TCs/zones. Further, installing multiple TC’s/zones can become impractical from a cost and complexity perspective with conventional controls.

[0046] The present disclosure proposes using a multi-zone heater array made of high TCR elements with multiple nodes. Instead of controlling each heater independently, the present disclosure proposes multiplexing the multiple nodes. Initially, the use of high TCR materials for sensing and controlling heaters for progressive heating application is described below. Thereafter, the use of TCR based controls is extended to a multiplexed multi-zone heating system specifically applied to a fluid delivery system.

[0047] As explained below in detail, the heater zones are grouped in the form of a supposed grid like structure, with a fixed number of nodes in each row and column of the grid like structure. That is, the heater zones are not in fact arranged in a grid fashion, but are assigned to different groups, where each group is considered a row in an array. The heaters in each row are controlled together (i.e. , collectively), one row at a time, such that a temperature gradient can be established and controlled across the rows. By controlling a group of nodes in a row at a time, as opposed to controlling each node individually, the number of control points is reduced. The selection and grouping of the nodes in rows is dependent on the geometry of the heating system. The supply path from the point of exit from the ampoule to the point of entry into the process chamber can be divided into several quadrants. Each quadrant can include a plurality of nodes (i.e., TCR heaters). Each quadrant can be controlled as a row so that a temperature gradient can be established and controlled across the rows.

[0048] The temperatures of nodes in a group (e.g., in a row) can be measured by measuring the resistance values of the TCR elements installed at the nodes. Based on the measured temperatures of nodes in a group, the heat supplied to the nodes in the groups can be controlled. The groups of nodes can be controlled in a sequence or in any order so as to provide a temperature gradient across the groups. For example, the heat supplied to a group of nodes can be increased as the distance of the group of nodes increases from the ampoule. Accordingly, the control variable is essentially the temperature as calculated from the measured resistance values of the TCR elements in a group of nodes. The heating of the nodes can then be controlled by measuring the temperatures of a group of nodes and controlling the heat supplied to the group of nodes based on the measured temperatures of the nodes in the group, one group at a time. Further, based on the temperature measurements, a temperature range for a group of nodes can be determined. Based on the temperature range, the grouping of the nodes, the control (i.e., heat supply) of each group of nodes, or both can be managed. Due to the grouping of nodes and group-based heating control of the nodes in a multiplexed manner, the heating can account for the phase change that can occur at locations between the nodes.

[0049] The temperature gradient across the groups of nodes can be used to define target resistance values for the heaters in each row to be achieved through control. For example, suppose the temperature from the first to the last group of nodes can be varied (and is desired to be) between X and Y degrees, Y > X, at a temperature gradient of Z degrees per row, where Z is equal to the difference between Y and X divided by the number of rows. Based on the desired temperature or set point for each row, the target resistance values of the TCR elements in each row can be known/determined (from the temperature-resistance characteristics of the TCR elements). The heat supplied to the TCR elements in each row can then be controlled to achieve/maintain the desired resistance value (and consequently the desired temperature set point). Alternately, the temperature gradient can be used to define a ratio of resistance values of TCR elements in one row to resistance values of TCR elements in another row to be achieved through heating control. Here, for each row, the resistance values of all nodes in a row can be averaged. Again, the ratios of averaged resistance values of TCR elements between two rows can be known/determined based on the desired temperatures (i.e. , set points) for the two rows, and the heat supply to the TCR elements in the two rows can be controlled so that a desired relationship between the set points for the two rows can be achieved/maintained.

[0050] Some form of cold offset/ratio calculation can be included in the control to account for manufacturing variations of the heaters. For example, the TCR elements may be calibrated in situ to account for interface losses (e.g., due to air gaps between the TCR elements and the material of the nodes where the TCR elements are installed). In addition, a TC that is in contact with the fluid (commonly available in ampoules) can act as reference for calibration (temperature-resistance calibration) of the TCR elements. Further, the TC can also be used for setting a minimum temperature across the ampoule, which can act as an over-temperature/safety feature as well.

[0051] Accordingly, the present disclosure relates to the use of multiplexing with high TCR heaters and specifically targeting the multiplexing to set a ratio of resistances to control temperature gradient across groups of heaters. The present disclosure further relates to the use of multiplexing to control the temperature gradient for systems using multi-surface ampoules. The present disclosure further relates to the use of multiplexing to address regions of phase change and achieve progressive heating despite changing fluid levels. These and other aspects of the present disclosure are now described in detail.

[0052] FIG. 1A shows an example substrate processing system 20. While a processing chamber for chemical vapor deposition (CVD) or atomic layer deposition (ALD) using capacitively coupled plasma (CCP) is shown for purposes of illustration, any other type of substrate processing system can be used. The substrate processing system 20 includes a processing chamber 22 that encloses other components of the substrate processing system 20 and contains RF plasma (if used). The substrate processing system 20 includes an upper electrode 24 and a substrate support 26 such as an electrostatic chuck (ESC), pedestal, etc. During operation, a substrate 28 is arranged on the substrate support 26.

[0053] For example only, the upper electrode 24 may include a gas distribution device

29 such as a showerhead that introduces and distributes process gases. The gas distribution device 29 may include a stem portion including one end connected to a top surface of the processing chamber. A base portion is generally cylindrical and extends radially outwardly from an opposite end of the stem portion at a location that is spaced from the top surface of the processing chamber. A substrate-facing surface or faceplate of the base portion of the showerhead 29 includes a plurality of holes through which precursor, reactants, etch gases, inert gases, carrier gases, and other process gases or purge gas flow. Alternately, the upper electrode 24 may include a conducting plate and the process gases may be introduced in another manner.

[0054] The substrate support 26 includes a baseplate 30 that acts as a lower electrode. The baseplate 30 supports a heating plate 32, which may correspond to a ceramic multi-zone heating plate. A thermal resistance layer 34 may be arranged between the heating plate 32 and the baseplate 30. The baseplate 30 may include one or more channels 36 for flowing coolant through the baseplate 30.

[0055] If plasma is used, an RF generating system 40 generates and outputs an RF voltage to one of the upper electrode 24 and the lower electrode (e.g., the baseplate 30 of the substrate support 26). The other one of the upper electrode 24 and the baseplate

30 may be DC grounded, AC grounded, or floating. For example only, the RF generating system 40 may include an RF generator 42 that generates RF power that is fed by a matching and distribution network 44 to the upper electrode 24 or the baseplate 30. In other examples, the plasma may be generated inductively or remotely.

[0056] A gas delivery system 50 includes one or more gas sources 52-1 , 52-2, ... , and 52-N (collectively gas sources 52), where N is an integer greater than zero. The gas sources 52 are connected by primary valves 54-1 , 54-2, ... , and 54-N (collectively primary valves 54); MFCs 56-1 , 56-2, ... , and 56-N (collectively MFCs 56); and/or secondary valves (not shown) to a manifold 60. While a single gas delivery system 50 is shown, two or more gas delivery systems can be used.

[0057] A temperature controller 63 is connected to a plurality of resistive heaters 64 arranged in the heating plate 32. The temperature controller 63 may also be connected to one or more thermocouples 65 in the heating plate 32. The temperature controller 63 may be used to control the plurality of resistive heaters 64 to adjust and control a temperature of the substrate support 26 and the substrate 28. In some examples, a vapor delivery system 67 supplies vapor to the processing chamber.

[0058] In some examples, the temperature controller 63 and/or another controller may also communicate with a coolant assembly 66 to control coolant flow through the channels 36. For example, the coolant assembly 66 may include a coolant pump, a reservoir, and/or one or more thermocouples. In some examples, the temperature controller 63 operates the coolant assembly 66 to selectively flow the coolant through the channels 36 to cool the substrate support 26. A valve 70 and pump 72 may be used to evacuate reactants from the processing chamber 22. A system controller 80 may be used to control components of the substrate processing system 20.

[0059] FIG. 1 B shows an example of a vaporized precursor delivery system 100 that supplies vaporized precursor to a processing chamber (e.g., the processing chamber 22 of FIG. 1A) for processing substrates such as semiconductor wafers. In some examples, a flow control device 106 such as a valve, a restricted orifice, or a mass flow controller (MFC) may be used to control the supply of vaporized precursor to the process chamber 22.

[0060] The vaporized precursor delivery system 100 includes an enclosure 108 and a tray assembly 110 arranged in the enclosure 108. The tray assembly 110 includes multiple trays 112-1 , 112-2, ..., and 112-N (collectively trays 112). Each of the trays 112 may include an opening 114-1 , 114-2, ..., and 114-N (collectively openings 114) to provide a mounting location for connection to a support member 120. Alternatively, the support member 120 can be omitted, and alternative support mechanisms can be used. For example, the trays 112 may be supported by sides of the enclosure 108 (e.g., using slots or projections), or spacers between edges of the trays 112 can be used. Sides of the trays 112 are open to allow carrier gas to flow freely there between. For example, the trays 112 may have a circular, square, rectangular, uniform, non-uniform, or other shaped cross-section. The trays 112 may be arranged in a stacked, uniformly-spaced arrangement to allow carrier gas to flow freely across the liquid precursor. Each of the trays 112 defines a volume for receiving and storing liquid precursor. In some examples, the support member 120 and the trays 112 may be made of a thermally conductive material such as stainless steel, aluminum, or other material that allows heat transfer.

[0061] A liquid precursor storage tank 130 supplies liquid precursor via a valve 134 and one or more conduits 140 to the trays 112. Gravity, a pump, or an inert push gas such as helium may be used to increase line pressure. The conduit 140 may pass through openings in each of the trays 112. Openings 142-1 , 142-2, ..., and 142-N in the conduit 140 are arranged to supply the liquid precursor to each of the trays 112-1 , 112- 2, ..., and 112-N, respectively.

[0062] The liquid precursor storage tank 130 may be filled periodically by a bulk storage tank 150 using a valve 152 and conduit 154. A carrier gas 162 may be supplied by one or more valves and/or mass flow controllers (MFCs) 164 and conduit 166. The conduit 166 includes one or more restricted openings or sets of restricted openings arranged to direct carrier gas across each of the trays 112. Each of the sets of openings may include multiple openings that provide carrier gas flow in multiple directions. Openings 170-1 , 170-2, ..., and 170-N in the conduit 166 deliver carrier gas flow over the trays 112.

[0063] In some examples, a heater 180 may be used to indirectly heat the support member 120, which transfers heat to the trays 112 and the liquid precursor in the trays 112. Alternatively, a heater may be arranged inside of the support member. In some examples, one or more vibrating devices 184 may be used to impart vibration to the support member 120 (as shown) or individually to the trays 112-1 , 112-2, ..., and 112-N, respectively.

[0064] A controller 190 may be used to control one or more of the valves in the vaporized precursor delivery system 100. For example, the controller 190 may control the flow control device 106 to adjust the amount of vaporized precursor that is delivered to the process chamber 22. A pressure sensor 196 provides pressure feedback to the controller 190, which controls the flow control device 106 and the one or more valves and/or MFCs 164. The controller 190 may be connected to one or more level sensors 194 to sense a level of liquid precursor in one or more of the trays 112. Based on the sensed level of the liquid precursor in one or more of the trays 112, the controller 190 may be used to control the valve 134 to supply additional liquid precursor. The controller 190 may be used to control the one or more valves and/or MFCs 164 to adjust the flow of carrier gas across the trays 112. The controller 190 may be connected to one or more level sensors 198 to sense a level of liquid precursor in the liquid precursor storage tank 130. Based on the sensed level of the liquid precursor storage tank 130, the controller 190 may be used to control the valve 134 to supply additional liquid precursor to refill the liquid precursor storage tank 130.

[0065] FIG. 2A shows a heating system for a vapor delivery system (e.g., element 67 shown in FIG. 1A or element 100 shown in FIG. 1 B) according to the present disclosure. While the heating system shown in FIG. 2A includes an ampoule 200 for supplying vaporized precursor, the heating system can heat other components of a substrate processing system. A temperature sensor 214 (e.g., a thermocouple) monitors a temperature of the precursor. A heater 218 is used to heat the liquid precursor based upon the sensed temperature and a desired temperature. The controller 80 or another controller may be used to monitor the temperature sensor 214 and to control the heater 218 based on the measured temperature and the desired temperature.

[0066] Valves V214, V205 and V213 selectively supply either carrier gas or a mixture of carrier gas and the vaporized precursor to a gas flow path. Additional valves V220, V206A, V206B, V71 , V55, V79, V65, V164, and V207 are provided to allow control of gas flow along various gas flow paths. A plurality of heater zones 250-1 , 250-2, ..., 250- N (collectively heater zones 250) (where N is an integer greater than one) are used to heat gas lines, valves and/or other components along the gas flow paths.

[0067] FIG. 2B shows an example arrangement of the heater zones 250. For example, the heater zones 250 may be grouped in the form of a plurality of rows (e.g., R1 , R2, R3, and R4). For example, a first row (e.g., R1 ) may include heater zones 250 that are nearest to the ampoule 200, and a last row (e.g., R4) may include heater zones 250 that are farthest from the ampoule 100 (i.e., nearest to the processing chamber 22). Each heater zone 250 may include a TCR heater 283. Using a multiplexed control scheme implemented by a selector 286 under the control of a controller 280 (shown in FIGS. 2C and 2D and described below), the heater zones 250 can be controlled one row at a time to maintain a temperature gradient that progressively increases the temperature from the first row (e.g., R1 ) to the last row (e.g., R4).

[0068] FIG. 2C shows the controller 280 that may be used in conjunctions with the selector 286 to control the operation of the heater zones 250. A heater driver 282 may be used to supply power to a selected row of TCR heaters 283 under the control of the controller 280. Current sensors 288 may be used to sense current supplied to the TCR heaters by the heater driver 282. Voltage sensors 290 may be used to sense voltage supplied to the TCR heaters by the heater driver 282.

[0069] FIG. 2D shows that the controller 280 uses a resistance estimator 294 to monitor duty cycles of the heater zones 250 and to estimate the resistance of the heater zones 250 based on the corresponding duty cycle. In this example, it is assumed that the voltage or current is a constant value, and the duty cycle of the current or voltage is varied. In other words, the controller 280 estimates resistance based on the known voltage or current and the duty cycle for the current or voltage. Accordingly, in this example, the current sensors 288 and the voltage sensors 290 are omitted.

[0070] In FIGS. 2C and 2D, the controller 280 controls the TCR heaters 283 in the heater zones 250 as follows. The controller 280 uses the selector 286 to select a row of heater zones 250 (e.g., any row R1 , R2, and so on shown in FIG. 2B). The heater driver 282 is used to supply power to the TCR heaters 283 in the selected row of heater zones 250.

[0071] The controller 280 controls the TCR heaters 283 in the selected row collectively so that a temperature gradient can be established and controlled across the rows. By controlling the TCR heaters 283 in one selected row at a time, the number of control points is reduced. The controller 280 performs the selection and grouping of the heater zones 250 in rows depending on the geometry of the heating system. For example, the geometry may include the distance of the length of the path between the ampoule 200 and the processing chamber 22, the number of valves and the size and shape of the conduits in the path, and so on. In case of the system 100 shown in FIG. 1 B, the geometry may also include the number of trays 112, for example. Accordingly, one group (i.e. , row) of heater zones may include fewer heater zones than another group (i.e. , row). The controller 280 may dynamically reallocate a heater zone from one row to another (i.e., regroup the heater zones in the rows) to maintain a desired temperature gradient.

[0072] The controller 280 measures the temperatures of the heater zones 250 in a group (e.g., in a row) by measuring the resistance values of the TCR heaters 283. Based on the measured temperatures of the heater zones 250 in a group (e.g., in a row), the controller 280 controls the heat supplied to the heater zones 250 in the group, one group at a time. The controller 280 can control the groups of heater zones 250 in a sequence or in any other order to provide a temperature gradient across the groups. For example, in the example shown in FIG. 2B, the controller 280 may control the heater zones 250 in rows R1 to R4 in the sequence R1 then R2 then R3 then R4, or in any other order such as R1 then R3 then R2 then R4, R1 then R3 then R4 then R2, R1 then R4 then R2 then R3, or R1 then R4 then R3 then R3, and so on.

[0073] For example, the controller 280 can increase the heat supplied to a group of heater zones 250 as the distance of the group of heater zones 250 increases from the ampoule 200. Further, based on the temperature measurements, the controller 280 can determine a temperature range for a group of heater zones 250. Based on the temperature range, the controller 280 can control the grouping of the heater zones 250, the heat supply to each group of heater zones 250, or both. Due to the group-based heating of the heater zones 250 in a multiplexed manner, the heating can account for the phase change that can occur at locations between the heater zones 250.

[0074] The controller 280 can use the temperature gradient across the groups of heater zones 250 to define target resistance values for the TCR heaters 283 in each row to be achieved through control. Based on the desired temperature or set point for each row of heater zones 250, the target resistance values of the TCR heaters 283 in each row can be known/determined (from the temperature-resistance characteristics of the TCR heaters 283). The controller 280 can then control the heat supply to the TCR heaters 283 in each row to achieve/maintain the desired resistance value (and consequently the desired temperature set point).

[0075] Alternately, the controller 280 can use the temperature gradient to define a ratio of resistance values of the TCR heaters 283 in one row to resistance values of the TCR heaters 283 in another row to be achieved through heating control. For each row, the controller 280 can average the resistance values of all the TCR heaters 283 in a row. The controller 280 can determine the ratios of averaged resistance values of the TCR heaters 283 between two rows based on the desired temperatures (i.e. , set points) for the two rows. The controller 280 can then control the heat supply to the TCR heaters 283 in the two rows so that a desired relationship between the set points for the two rows can be achieved/maintained.

[0076] The controller 280 uses the TC 214 that is in contact with the fluid in the ampoule 200 as reference for calibration (temperature-resistance calibration) of the TCR heaters 283. For example, the controller 280 may calibrate TCR heaters 283 in situ to account for interface losses (e.g., due to air gaps between the TCR heaters 283 and the material of the nodes where the TCR heaters 283 are installed). Further, the controller 280 can also use the TC 214 for setting a minimum temperature across the ampoule 200, which can act as an over-temperature/safety feature.

[0077] FIG. 3 shows a graph that illustrates ideal temperature as a function of length along a gas flow path to a processing chamber (e.g., from the ampoule 200 to the processing chamber 22). In some applications, it is desirable for the temperature of the gas flow path to monotonically increase as the gas traverses the plurality of heater zones 250. If the temperature decreases, condensation can occur. In FIG. 3, an ideal temperature characteristic is shown as a straight line having a positive slope. In practice, however, the temperature of the gas flowing through the gas flow path is less ideal due to localized cooling or heating. For example, gas cools as it flows through pressure drop/expansion locations.

[0078] FIG. 4 illustrates an example of a heater zone 400. The heater zone 400 includes a first gas line 410 that is connected to a second gas line 420 at a node 430 located adjacent to a bend/fitting 434. An insulated heater 440 includes an insulating material 442 and a heater element 444. The heater zones 250 according to the present disclosure do not use thermocouples. Flowever, to appreciate the improvements provided by the multiplexed heating scheme of the present disclosure, it is instructive to note that when used, thermocouples can monitor a temperature of each of the heater zones. For example, a thermocouple TC can be arranged in a first position TC_Pi or a second position TC_P2. Flowever, different temperature control characteristics will occur depending upon the selected location of the thermocouple TC.

[0079] FIGS. 5 and 6 show graphs illustrating temperature as a function of length along a gas flow path in a zone. In FIG. 5, a target temperature profile monotonically increases from one end of a zone to another. Flowever, in FIG. 6, the temperature may decrease due to pressure drop/expansion locations. Flow the temperature is controlled will vary depending upon where the thermocouple is located. Controlling heat when the thermocouple is located after the pressure drop/expansion locations (such as TC_P2) will cause a higher overall temperature and may lead to temperature drops in other zones that follow. Controlling heat when the thermocouple is located before the pressure drop/expansion locations (such as TC_Pi) will cause a lower overall temperature and may lead to temperature drops in the heater zone. [0080] FIG. 7 is a flowchart of a method 700 for controlling temperature of a gas flow path between an ampoule (e.g., ampoule 200) and a processing chamber (e.g., processing chamber 22). The method 700 uses a plurality of TCR heaters (e.g., TCR heaters 283) arranged in heating zones (e.g., heater zones 250) along the gas flow path. The method 700 is performed by a controller (e.g., controller 280). The method 700 heats groups of heater zones in a multiplexed manner as follows.

[0081] At 702, the method 700 forms groups of heater zones, where the grouping of the heater zones is based on the geometry of the heating system. At 704, based on a desired temperature range for the heating system (i.e. , for the path from the ampoule to the processing chamber) and the number of groups of heater zones, the method 700 determines temperature set points for each group of heater zones in order to maintain a desired temperature gradient across the groups of heater zones. At 706, the method 700 measures resistances of heaters in a group of heater zones. At 708, based on the resistance measurements, the method 700 determines temperatures of the heater zones in the group.

[0082] At 710, the method 700 determines whether the average temperature of the heater zones in the group is less than or equal to the set point for the group of heater zones. Alternatively, the method 700 determines whether the temperature of at least one heater zone in the group is less than or equal to the set point for the group of heater zones. The method 700 returns to 706 if the temperature of at least one heater zone or the average temperature of the heater zones in the group is greater than the set point for the group of heater zones.

[0083] At 712, if the temperature of at least one heater zone or the average temperature of the heater zones in the group is less than or equal to the set point for the group of heater zones, the method 700 supplies power to the group of heater zones to increase the temperature of the group of heater zones. At 714, the method 700 determines whether the temperature of the heater zones in the group is equal to the set point temperature for the group. The method 700 returns to 706 if the temperature of the heater zones in the group is equal to the set point for the group. The method 700 returns to 712 if the temperature of the heater zones in the group is not equal to the set point temperature for the group.

[0084] FIG. 8 is a flowchart of another method 800 for controlling temperature of a gas flow path between an ampoule (e.g., ampoule 200) and a processing chamber (e.g., processing chamber 22). The method 700 uses a plurality of TCR heaters (e.g., TCR heaters 283) arranged in heating zones (e.g., heater zones 250) along the gas flow path. The method 800 is performed by a controller (e.g., controller 280). The method 800 heats groups of heater zones in a multiplexed manner as follows.

[0085] At 802, the method 800 forms groups of heater zones, where the grouping of the heater zones is based on the geometry of the heating system. At 804, based on a desired temperature range for the heating system (i.e. , for the path from the ampoule to the processing chamber) and the number of groups of heater zones, the method 800 determines temperature set points for each group of heater zones in order to maintain a desired temperature gradient across the groups of heater zones.

[0086] At 806, based on the set points, the method 800 defines target ratios of resistance values of heaters in a first group relative to resistance values of heaters in the second group. To determine the target ratios, the method uses the average resistance values of heaters in each group. At 808, the method 800 measures resistances of heaters in each of the first and second groups of heater zones and calculates average values of the resistances of heaters in each group of heater zones.

[0087] At 810, the method 800 determines whether the ratio of the average measured resistance values of heaters in the first and second groups is equal to the target ratio for the first and second groups. The method returns to 808 if the ratio of the average measured resistance values of heaters in the first and second groups is equal to the target ratio for the first and second groups. At 812, if the ratio of the average measured resistance values is not equal to the target ratio, the method 800 supplies power to the heaters in that group where the resistances of heaters changed and caused the ratio of the average measured resistance values to deviate from the target ratio. The power supplied heats the heaters in that group until the average measured resistance values becomes equal to the target ratio, which is when the method 800 stops supplying power to the heaters in that group.

[0088] FIG. 9 shows a heating system 900 for a gas delivery system including an oven 910 enclosing one or more components of a substrate processing system. In some examples, the components include components of a gas delivery system and/or a gas flow path. A thermocouple 920 and one or more oven heating elements 922 may be arranged in the oven 910 and are used to maintain an average temperature inside of the oven 910. [0089] As described above, local cooling and/or heating of components within the substrate processing system may occur. For example, gas lines may experience local cooling due to factors such as gas expansion through fittings, valves, etc., and additionally due to phase changes. While the oven maintains the average temperature in the oven, TCR heaters 940-1 , 940-2, ..., and 940-R (collectively TCR heaters 940) (where R is an integer greater than one) are arranged in groups at locations (such as on portions of the components) along the gas lines where temperature variations (such as cooling) and phase change are likely to occur as shown. When the localized cooling and phase change occur, the TCR heaters 940, controlled in multiplexed groups as described above, provide heat to attempt to maintain the temperature at the predetermined temperature despite the localized cooling and phase change. Examples of locations may include pressure drop/expansion locations or other locations where localized heating variations and phase change may occur.

[0090] In some examples, the TCR heaters 940 are uninsulated. In other words, when the TCR heaters 940 are not being operated, the location of the TCR heater 940 will be heated by the oven. In some examples, the TCR heaters 940 are controlled in groups based on ratios of resistances of the TCR heaters in one group to another. The resistance ratios can be maintained between the groups of the TCR heaters 940. The resistance ratios can be determined when all of the TCR heaters 940 are at the same reference temperature (such as ambient temperature or another temperature). In some examples, the TCR heaters 940 are made using the same material for the resistive element of the TCR heater 940. Therefore, the resistance ratios should remain relatively constant at other temperatures since all of the TCR heaters 940 should have approximately the same slope (temperature as a function of resistance).

[0091] In other words, the resistance ratios are determined at a predetermined temperature where all of the TCR heaters 940 are at the same temperature. In some examples, the predetermined temperature for determining the resistance ratios is ambient temperature. During operation, the resistances of each of the TCR heaters 940 in a group are measured and the predetermined ratios between the groups are maintained by a controller that varies output power to each group of the TCR heaters 940. In some examples, a plurality of TCR heater zones may be arranged along a gas flow path from the source of the gas to the outlet of the oven and/or to the processing chamber (for example, similar to the heater zones shown in FIG. 2A and 2B). Additional details relating to controlling resistive ratios of TCR heaters can be found in commonly- assigned U.S. Provisional Patent Application Serial No. 62/694, 171 filed on July 5, 2018, which is hereby incorporated by reference in its entirety.

[0092] Control can be performed using a control system similar to those shown in FIGS. 2C and 2D. In this example, the TC 920 monitors the average temperature in the oven 910. The controller 280 stores the resistance ratios of the groups of TCR heaters and controls the power output to each group of the TCR heaters based thereon. In some examples, the resistance ratios across the groups of the TCR heaters are maintained by the controller 280 to maintain uniform temperature in each group of the heater zones and to maintain a desired temperature gradient across the groups of the TCR heaters. In other examples, the controller 280 further adjusts the resistance ratios of the TCRs depending on position. For example, the controller 280 adds incremental values to the resistance ratios of the groups of TCR heaters to adjust the resistance ratios incrementally across the groups. This approach can be used to achieve a progressively increasing temperature of the gas lines in a direction from the source towards the processing chamber.

[0093] Referring now to FIG. 10, a method 1000 for operating the heating system 900 of FIG. 9 is shown. At 1010, a temperature of the oven is monitored using the thermocouple. At 1020, a predetermined temperature is maintained in the oven based upon the measured temperature and a desired temperature. At 1030, resistances of the TCR heaters in each group are measured. At 1040, predetermined resistance ratios are maintained between the groups of TCR heaters by varying power supplied to each group of heater zones in a multiplexed manner as described above.

[0094] The foregoing description is merely illustrative in nature and is not intended to limit the disclosure, its application, or uses. The broad teachings of the disclosure can be implemented in a variety of forms. Therefore, while this disclosure includes particular examples, the true scope of the disclosure should not be so limited since other modifications will become apparent upon a study of the drawings, the specification, and the following claims. It should be understood that one or more steps within a method may be executed in different order (or concurrently) without altering the principles of the present disclosure. Further, although each of the embodiments is described above as having certain features, any one or more of those features described with respect to any embodiment of the disclosure can be implemented in and/or combined with features of any of the other embodiments, even if that combination is not explicitly described. In other words, the described embodiments are not mutually exclusive, and permutations of one or more embodiments with one another remain within the scope of this disclosure.

[0095] Spatial and functional relationships between elements (for example, between modules, circuit elements, semiconductor layers, etc.) are described using various terms, including“connected,”“engaged,”“coupled,”“adjacent,”“next to,”“on top of,” “above,”“below,” and“disposed.” Unless explicitly described as being“direct,” when a relationship between first and second elements is described in the above disclosure, that relationship can be a direct relationship where no other intervening elements are present between the first and second elements, but can also be an indirect relationship where one or more intervening elements are present (either spatially or functionally) between the first and second elements. As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A OR B OR C), using a non-exclusive logical OR, and should not be construed to mean“at least one of A, at least one of B, and at least one of C.”

[0096] In some implementations, a controller is part of a system, which may be part of the above-described examples. Such systems can comprise semiconductor processing equipment, including a processing tool or tools, chamber or chambers, a platform or platforms for processing, and/or specific processing components (a wafer substrate support, a gas flow system, etc.). These systems may be integrated with electronics for controlling their operation before, during, and after processing of a semiconductor wafer or substrate. The electronics may be referred to as the“controller,” which may control various components or subparts of the system or systems. The controller, depending on the processing requirements and/or the type of system, may be programmed to control any of the processes disclosed herein, including the delivery of processing gases, temperature settings (e.g., heating and/or cooling), pressure settings, vacuum settings, power settings, radio frequency (RF) generator settings, RF matching circuit settings, frequency settings, flow rate settings, fluid delivery settings, positional and operation settings, wafer transfers into and out of a tool and other transfer tools and/or load locks connected to or interfaced with a specific system.

[0097] Broadly speaking, the controller may be defined as electronics having various integrated circuits, logic, memory, and/or software that receive instructions, issue instructions, control operation, enable cleaning operations, enable endpoint measurements, and the like. The integrated circuits may include chips in the form of firmware that store program instructions, digital signal processors (DSPs), chips defined as application specific integrated circuits (ASICs), and/or one or more microprocessors, or microcontrollers that execute program instructions (e.g., software). Program instructions may be instructions communicated to the controller in the form of various individual settings (or program files), defining operational parameters for carrying out a particular process on or for a semiconductor wafer or to a system. The operational parameters may, in some embodiments, be part of a recipe defined by process engineers to accomplish one or more processing steps during the fabrication of one or more layers, materials, metals, oxides, silicon, silicon dioxide, surfaces, circuits, and/or dies of a wafer.

[0098] The controller, in some implementations, may be a part of or coupled to a computer that is integrated with the system, coupled to the system, otherwise networked to the system, or a combination thereof. For example, the controller may be in the“cloud” or all or a part of a fab host computer system, which can allow for remote access of the wafer processing. The computer may enable remote access to the system to monitor current progress of fabrication operations, examine a history of past fabrication operations, examine trends or performance metrics from a plurality of fabrication operations, to change parameters of current processing, to set processing steps to follow a current processing, or to start a new process. In some examples, a remote computer (e.g. a server) can provide process recipes to a system over a network, which may include a local network or the Internet. The remote computer may include a user interface that enables entry or programming of parameters and/or settings, which are then communicated to the system from the remote computer. In some examples, the controller receives instructions in the form of data, which specify parameters for each of the processing steps to be performed during one or more operations. It should be understood that the parameters may be specific to the type of process to be performed and the type of tool that the controller is configured to interface with or control. Thus as described above, the controller may be distributed, such as by comprising one or more discrete controllers that are networked together and working towards a common purpose, such as the processes and controls described herein. An example of a distributed controller for such purposes would be one or more integrated circuits on a chamber in communication with one or more integrated circuits located remotely (such as at the platform level or as part of a remote computer) that combine to control a process on the chamber.

[0099] Without limitation, example systems may include a plasma etch chamber or module, a deposition chamber or module, a spin-rinse chamber or module, a metal plating chamber or module, a clean chamber or module, a bevel edge etch chamber or module, a physical vapor deposition (PVD) chamber or module, a chemical vapor deposition (CVD) chamber or module, an atomic layer deposition (ALD) chamber or module, an atomic layer etch (ALE) chamber or module, an ion implantation chamber or module, a track chamber or module, and any other semiconductor processing systems that may be associated or used in the fabrication and/or manufacturing of semiconductor wafers.

[00100] As noted above, depending on the process step or steps to be performed by the tool, the controller might communicate with one or more of other tool circuits or modules, other tool components, cluster tools, other tool interfaces, adjacent tools, neighboring tools, tools located throughout a factory, a main computer, another controller, or tools used in material transport that bring containers of wafers to and from tool locations and/or load ports in a semiconductor manufacturing factory.

Claims

1. A system for heating components of a substrate processing system comprising: a plurality of heaters arranged at a plurality of locations along a path of fluid flow from a source of fluid to a destination in the substrate processing system; and

a controller configured to:

group the plurality of heaters into a plurality of groups of heaters, each group of heaters comprising at least one of the plurality of heaters;

determine a temperature gradient to be maintained across the plurality of groups of heaters;

select a group of heaters from the plurality of groups of heaters; and control power supplied to the selected group of heaters to maintain the temperature gradient across the plurality of groups of heaters.

2. The system of claim 1 wherein the controller is configured to group the plurality of heaters into the plurality of groups of heaters based on a geometry of the components in the path of fluid flow from the source of the fluid to the destination in the substrate processing system and wherein the components include conduits and valves.

3. The system of claim 1 wherein each of the plurality of heaters has a resistance that varies as a function of temperature and wherein the controller is configured to: measure resistances of heaters in the selected group of heaters;

determine temperatures of the heaters in the selected group of heaters based on the resistances of the heaters in the selected group of heaters; and

control the power supplied to the selected group of heaters based on the determined temperatures of the heaters in the selected group of heaters and the temperature gradient.

4. The system of claim 1 wherein each of the plurality of heaters has a resistance that varies as a function of temperature and wherein the controller is configured to: determine a desired temperature for heaters in the selected group of heaters based on the temperature gradient to be maintained across the plurality of groups of heaters; determine desired resistance values for the heaters in the selected group of heaters based on the desired temperature for the heaters in the selected group of heaters;

measure resistances of the heaters in the selected group of heaters; and control the power supplied to the selected group of heaters based on the measured resistances of the heaters in the selected group of heaters until the heaters in the selected group of heaters have the desired resistance values.

5. The system of claim 1 wherein each of the plurality of heaters has a resistance that varies as a function of temperature and wherein the controller is configured to: determine desired temperatures for heaters in the selected group of heaters and for another group of heaters from the plurality of groups of heaters based on the temperature gradient to be maintained across the plurality of groups of heaters;

determine desired resistance values for the heaters in the selected group of heaters and for heaters in the another group of heaters based on the desired temperatures for the heaters in the selected group of heaters;

determine a ratio between the desired resistance values for the heaters in the selected group of heaters and for the heaters in the another group of heaters;

measure resistances of the heaters in the selected group of heaters; and control the power supplied to the selected group of heaters based on the measured resistances of the heaters in the selected group of heaters to maintain the ratio between the desired resistance values for the heaters in the selected group of heaters and for the heaters in the another group of heaters.

6. The system of claim 1 further comprising:

a temperature sensor configured to sense a temperature of the fluid in the source,

wherein the controller is configured to stop the system when the temperature is greater than a first threshold or less than a second threshold, where the first threshold is greater than the second threshold, to ensure that the system operates when the temperature is between the first threshold and the second threshold.

7. The system of claim 1 further comprising:

a current sensor to sense current supplied to each of the plurality of heaters, wherein the controller is configured to determine resistance of each of the plurality of heaters based thereon.

8. The system of claim 1 further comprising:

a voltage sensor to sense voltage supplied to each of the plurality of heaters, wherein the controller is configured to determine resistance of each of the plurality of heaters based thereon.

9. The system of claim 1 further comprising:

a driver to drive the selected group of heaters based on a duty cycle; and a resistance estimator to estimate resistances of the group of heaters based on the duty cycle,

wherein the controller is configured to determine temperatures of the selected group of heaters based on the resistances.

10. The system of claim 1 wherein the controller is configured to provide a progressive heating profile across the plurality of groups of heaters from the source of the fluid to the destination and wherein the destination includes a processing chamber to process a semiconductor substrate in the substrate processing system.

11. A system for heating components of a substrate processing system comprising: an oven to enclose one or more components of the substrate processing system and to maintain a predetermined temperature in the oven;

a plurality of heaters arranged in the oven to heat the one or more components of the substrate processing system wherein the plurality of heaters includes uninsulated resistive heaters; and

a controller configured to:

group the plurality of heaters into a plurality of groups of heaters, each group of heaters comprising at least one of the plurality of heaters; and

control power supplied to the plurality of groups of heaters by selecting one group of heaters from the plurality of groups of heaters at a time to maintain a temperature gradient across the plurality of groups of heaters and to maintain the predetermined temperature in localized regions in the oven.

12. The system of claim 11 further comprising:

a temperature sensor located remotely from the plurality of heaters to sense a temperature in the oven,

wherein the oven includes a heating element, and

the controller is configured to determine an average temperature in the oven based on the sensed temperature and to control the heating element of the oven based thereon to maintain the predetermined temperature.

13. The system of claim 11 wherein the predetermined temperature is ambient temperature.

14. The system of claim 11 wherein each of the plurality of heaters has a resistance that varies as a function of temperature and wherein the controller is configured to: measure resistances of heaters in a selected group of heaters;

15. The system of claim 11 wherein each of the plurality of heaters has a resistance that varies as a function of temperature and wherein the controller is configured to: determine a desired temperature for heaters in a selected group of heaters based on the temperature gradient to be maintained across the plurality of groups of heaters;

determine desired resistance values for the heaters in the selected group of heaters based on the desired temperature for the heaters in the selected group of heaters;

16. The system of claim 11 wherein each of the plurality of heaters has a resistance that varies as a function of temperature and wherein the controller is configured to: determine desired temperatures for heaters in a selected group of heaters and for another group of heaters from the plurality of groups of heaters based on the temperature gradient to be maintained across the plurality of groups of heaters;

17. The system of claim 16 wherein the ratio is determined at the predetermined temperature.

18. The system of claim 16 wherein the controller is configured to adjust the ratio to provide progressive heating across the plurality of groups of heaters.

19. The system of claim 11 wherein the controller is configured to group the plurality of heaters into the plurality of groups of heaters based on a geometry of the one or more components and wherein the components include conduits and valves in a path of fluid flow from a source of fluid to a processing chamber in the substrate processing system.