Abstract:
Methods and apparatus for heating a substrate in a process chamber are provided herein. In some embodiments, an apparatus for heating a substrate in a process chamber includes a lamp group comprising one or more sets of lamps to provide radiant energy to heat a substrate when disposed in the process chamber, wherein each set of lamps comprises a plurality of lamps wired in series, and wherein each set of lamps is wired in parallel with respect to other sets of the one or more sets of lamps; an alternating current (AC) power source to produce an AC input waveform; and a lamp driver to power the lamp group, the lamp driver including a rectifier coupled to the AC power source to convert the AC input waveform to DC voltage; and a direct current to direct current (DC/DC) converter to reduce voltage of the DC power.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims benefit of U.S. provisional patent application Ser. No. 61/638,193, filed Apr. 25, 2012, and U.S. provisional patent application Ser. No. 61/707,488, filed Sep. 28, 2012, which are herein incorporated by reference in their entireties. 
     
    
     FIELD 
       [0002]    Embodiments of the present invention generally relate to methods and apparatus for thermal processing of substrates. 
       BACKGROUND 
       [0003]    Rapid Thermal Processing (RTP) is a semiconductor manufacturing process for heating silicon wafers at high temperatures, often 1200 degrees Celsius or greater, in a relatively short period of time, for example, in several seconds or less. During cooling in an RTP tool, wafer temperatures must be brought down evenly so as not to subject the wafer to thermal shock. This heating is often achieved using high intensity lamps, or lasers. Controlling the wafer temperature is a key challenge in rapid thermal processing. Often, this is achieved by monitoring the temperature of the wafer and using pyrometry to control, in real-time, the power and intensity of the lamps. An array of pyrometers may be used to measure the temperature of a wafer and based on that temperature, output voltage of a driver for the lamps is determined. Thus, an RTP tool for rapid thermal processing of wafers often comprises an array of lamps for heating a wafer, a chamber containing the wafer, a support for the wafer, and an array of pyrometers for measuring wafer temperature coupled to the wafer or the support for the wafer. 
         [0004]    Therefore, the inventors have provided an improved lamp driver and substrate processing tools incorporating same. 
       SUMMARY 
       [0005]    Methods and apparatus for heating a substrate in a process chamber are provided herein. In some embodiments, an apparatus for heating a substrate in a process chamber includes a lamp group comprising one or more sets of lamps to provide radiant energy to heat a substrate when disposed in the process chamber, wherein each set of lamps comprises a plurality of lamps wired in series, and wherein each set of lamps is wired in parallel with respect to other sets of the one or more sets of lamps; an alternating current (AC) power source to produce an AC input waveform; and a lamp driver to power the lamp group, the lamp driver including a rectifier coupled to the AC power source to convert the AC input waveform to DC voltage; and a direct current to direct current (DC/DC) converter to reduce voltage of the DC power. 
         [0006]    In some embodiments, a method for heating a substrate in a process chamber includes converting an alternating current (AC) power source voltage into a direct current (DC) power source voltage; powering a driver as a load using the DC voltage; and powering one or more lamp groups each comprising one or more sets of lamps to provide radiant energy to heat the substrate in the process chamber, wherein each set of lamps comprises a plurality of lamps wired in series, and wherein each set of lamps is wired in parallel with respect to other sets of the one or more sets of lamps. 
         [0007]    Other and further embodiments of the present invention are described below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    Embodiments of the present invention, briefly summarized above and discussed in greater detail below, can be understood by reference to the illustrative embodiments of the invention depicted in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
           [0009]      FIG. 1  depicts a block diagram of a substrate processing apparatus in accordance with some embodiments of the present invention. 
           [0010]      FIG. 2  depicts a circuit diagram of a substrate processing apparatus in accordance with some embodiments of the present invention. 
           [0011]      FIG. 3  depicts a circuit diagram of a substrate processing apparatus implemented with a Buck converter in accordance with some embodiments of the present invention. 
           [0012]      FIG. 4  depicts a circuit diagram of a substrate processing apparatus in accordance with some embodiments of the present invention. 
           [0013]      FIG. 5  depicts a circuit diagram of a substrate processing apparatus in accordance with some embodiments of the present invention. 
           [0014]      FIG. 6  depicts a flow diagram of a method for powering an array of lamps for processing a substrate in accordance with some embodiments of the present invention. 
       
    
    
       [0015]    To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. The figures are not drawn to scale and may be simplified for clarity. It is contemplated that elements and features of some embodiments may be beneficially incorporated in other embodiments without further recitation. 
       DETAILED DESCRIPTION 
       [0016]    Embodiments of the present invention are directed to methods and apparatus for powering an array of lamps to heat a substrate in various thermal processes, such as rapid thermal processing (RTP), chemical vapor deposition (e.g., epitaxial deposition), or other substrate processes that use lamps for heating. The substrate processing tool used for the thermal processing is powered by an AC power source, which is, in some embodiments, 480V. A rectifier is used to convert the AC power source to a direct current (DC) power source. A DC to DC converter is used to step down the voltage to power an array of lamps and lamp groups. 
         [0017]    High power lamp heaters used on new generation of semiconductor equipment will require prohibitive amount of current if supplied by 208VAC. Examples of lamps include incandescent lamps, such as halogen or tungsten halogen incandescent lamps, or the like. The configuration of the lamp driver can vary dependent upon the type of lamp used. For example, typically, 100V halogen lamps are used in lamp heaters for semiconductor equipment. Two lamps disposed in series allow the use of a phase angle control based lamp driver and a 208V AC power line. However, use of a higher voltage power line, for example 480V AC, is not feasible for the same type of halogen lamps for at least two reasons. First, a configuration with two lamps connected in series yields low accuracy of phase angle control and poor power factor of the system which is unacceptable be due to low duty cycle of the phase angle controlled driver. In addition, connecting more than two lamps in series to increase the phase angle control accuracy and improve power factor is not feasible because it decreases the granularity of the heating pattern, disables functionality of the lamp fuse by limiting fuse current, and increases risk of arcing in a low pressure atmosphere. 
         [0018]    However, a problem exists that in this design an output voltage of 200V cannot be exceeded, such that only two about 80-120V, or about 100V, lamps can be connected in series. Another problem is that there are limitations on the current that may be provided to the semiconductor equipment, such as a Rapid Thermal Processing (RTP) tool or other thermal processing tool that uses or can use lamps similar to as described herein. In this scheme, adding more lamps to the lamp array for thermal processing is not feasible, as current limits will be exceeded. For example, the power source for an RTP tool is often a multiple phase alternating current (NC) power source. However, transformer losses, excessive harmonics, and the like are generated when the current across the three phases is imbalanced. 
         [0019]      FIG. 1  depicts a block diagram of a substrate processing apparatus  100  in accordance with embodiments of the present invention. Although the specific configuration of the substrate processing apparatus  100  shown in  FIG. 1  is suitable for RTP, it is contemplated that the substrate processing apparatus  100  may be configured for epitaxial deposition or other thermal substrate processes. As depicted in  FIG. 1 , the substrate processing apparatus  100  comprises a chamber  102 , a support  104  for a substrate  106 , support systems  110 , lamp array  112 , lamp driver  114 , controller  116 , an AC power source  118  and, optionally, a polarity switch  119 . The substrate  106  is, for example, a semiconductor wafer. The support  104  holds the substrate  106  so that it may be thermally processed in the chamber  102 . The support systems  110  control the support and allow for adjustment of the support  104  position, and in turn, the position of the substrate  106 . 
         [0020]    The AC power source  118  delivers AC power to the lamp driver  114 . The AC power may have one or more phases, and in some embodiments, has three phases. In some embodiments, the AC power source delivers 480V to the lamp driver  114 . The controller  116  controls the operation of the lamp driver  114 . The lamp driver  114  transforms the AC power to DC power and steps down the DC power voltage. The lamp driver  114  distributes the stepped-down power to the lamp array  112 . In turn, the lamp array  112  produces heat to thermally process the substrate  106  within the chamber  102 . In some embodiments, the lamp array  112  comprises several about 80V to about 120V, such as about 100V, lamps, such as halogen lamps, and the stepped-down voltage is 200V. In other embodiments, other types of lamps with different power constraints may be used, such as incandescent lamps having other voltage ratings, or the like. 
         [0021]    The polarity switch  119 , when present, is coupled to the lamp driver  114  and the lamp array  112 , and allows for toggling the polarity of the circuit. According to some embodiments, the polarity switch  119  reverses the polarity of the substrate processing apparatus  100  for every n wafers transferred into the chamber  102 , where n=1 to a about 100 wafers. For example, the polarity may be reversed after every wafer, or after a number of wafers in a single cassette (for example about 25), or greater numbers, such as after processing about 100 wafers. Switching the polarity of the circuit may facilitate mitigating DC notching, or faceting, of the filament of the lamp, which would lead to failure of the lamp. 
         [0022]      FIG. 2  depicts a circuit diagram of a substrate processing apparatus  200  in accordance with embodiments of the present invention. The substrate processing apparatus  200  comprises an AC power source  202 , a rectifier  204 , a capacitor  206 , a DC to DC converter  208  and two lamps  210  and  212 . The AC power source  202  delivers AC power to the rectifier  204 . The rectifier  204  converts the AC voltage from the AC power source  202  to DC voltage, i.e., it “rectifies” the AC voltage to DC voltage. In some embodiments, the AC power source is a 480V power source and the rectifier  204  rectifies the AC 480V to DC 700V. Together, the rectifier  204 , the capacitor  206  and the DC to DC converter  208  form the lamp driver  114  shown in  FIG. 1 . As mentioned above, in some embodiments, the lamps  210  and  212  may be halogen lamps, such as tungsten-halogen incandescent lamps. In addition, the lamps are coupled in series in this embodiment. 
         [0023]      FIG. 3  depicts a circuit diagram of a substrate processing apparatus  300  using a Buck Converter in accordance with embodiments of the present invention. The substrate processing apparatus  300  comprises an AC voltage source  301 , a rectifier  302 , a controller  303 , a Buck converter  306 , a capacitor  307  and lamps  312  and  313 . The rectifier  302  converts the AC voltage from the AC power source  202  to DC voltage, i.e., it “rectifies” the AC voltage to DC voltage. The rectifier  302  produces a DC signal According to some embodiments, the capacitor  311  acts as a filter capacitor for filtering the rectified voltage from the AC voltage source  301 . In this embodiment, the DC to DC converter  208  is a buck converter, which is a step-down DC to DC converter. Buck converters have high efficiency and efficiently convert the 700V DC to 200V DC required by the lamps  210  and  212 . 
         [0024]    The Buck converter  306  consists of a switch  308 , an inductor  310 , a diode  309 , and a capacitor  311 . The controller  303  receives a set point signal  304  which the controller  303  compares with an actual output voltage  305  to form the control signal to the Buck converter  306 . By changing the ratio between T on  and T off  time according to the timing diagram  314 , the controller  303  controls the output voltage on the output of the Buck converter  306 . When the switch  308  is closed (on state), the voltage across the inductor  310  is equal to the difference between the voltage from  301  and the voltage across lams  312  and  313 . The current through the inductor  310  rises linearly. As the diode  309  is reverse-biased by the voltage source  301 , no current flows through it. When the switch  308  is opened (off state), the diode  309  is forward biased. The voltage across the inductor is equal to the negative of the voltage across the lamps  312  and  313  (neglecting diode drop). The current across the inductor  310  decreases. 
         [0025]      FIG. 4  depicts a circuit diagram of a substrate processing apparatus  400  in accordance with some embodiments of the present invention. In contrast to  FIG. 2 , substrate processing apparatus  400  comprises a plurality of lamp drivers  402   1  to  402   n  to drive a plurality of lamp groups (e.g., having multiple channels). A single AC power source  401  is coupled to each lamp driver. The lamp driver  402   1  comprises a rectifier  404   1  which converts AC power into DC power, as described above with regard to rectifier  204 . In the embodiment shown, the rectifier  404   1  is a three-phase rectifier for converting AC power to DC power. In the embodiment shown, the rectifier  404   1  comprises diodes  405   1  to  405   6  coupled together. Diode  405   1  and diode  405   4  are connected in series with each other, diodes  405   2  and  405   5  are connected in series with each other and diodes  405   3  and  405   6  are connected in series with each other, respectively. The serially connected diode pairs are then coupled in parallel with respect to each other pair and with a capacitor  406  for filtering the DC voltage rectified by the rectifier  404   1 . 
         [0026]    The rectified DC voltage is stepped down to the requisite level of DC voltage by the DC to DC converter  408 . The stepped down DC voltage powers the coupled lamp group  410 , which, in the embodiment shown, comprises two lamps coupled in series. In other configurations, the lamp group can include multiple pairs of lamps, each pair connected in series, and the multiple pairs connected in parallel to each other, as in lamp driver  402   n . In lamp group  402   n , there is an increased load requirement due to the increased number of lamps in the lamp group, yet the current across the phases remains balanced. Therefore, in this configuration, current remains balanced regardless of lamp driver lines having different loads and the voltage is adjusted as required. 
         [0027]    In some embodiments, each lamp driver  402   1  . . .  402   n  may share certain components, such as the rectifier, and the filter capacitor. Each channel retains support of a similar or varying load of lamp groups. Each channel of the plurality of channels retains control with independent voltage outputs to the lamp groups. 
         [0028]    For example,  FIG. 5  depicts a circuit diagram of a substrate processing apparatus  500  with lamp driver channels having shared components in accordance with embodiments of the present invention. The substrate processing apparatus  500  comprises a power source  501 , a rectifier  502 , a filter capacitor  503 , a first DC/DC converter  504   a  and a second DC/DC converter  504   b,  and lamps  505   a,    505   b,    506   a  and  506   c.  In this embodiment, source  501  provides a three phase (A/B/C in  FIG. 5 ) voltage to distinct portions of the rectifier  502 . The rectifier  502  and filter  503  are coupled to independently controlled lamp groups, where the first lamp group includes lamps  505   a  and  506   a,  and the second lamp group includes  505   b  and  506   b.  Therefore, in this embodiment, one rectifier  502  and one filter capacitor  503  is shared amongst several lamp groups. In other embodiments, more than two lamp groups are supported. 
         [0029]      FIG. 6  depicts a flow diagram of a method  600  for powering an array of lamps for use in substrate processing in accordance with embodiments of the present invention. The method begins at  602  and proceeds to  604 . At  604 , the circuit receives AC power from the AC power source (e.g., AC power source  401  as shown in  FIG. 4 ). As discussed above, the AC power source, in some embodiments, is a 480V source. 
         [0030]    At  606 , the AC power is converted into DC power. For example, the rectifier  404   1  of  FIG. 4  converts the AC power into DC power. For example, the aforementioned 480V power may be converted to 650V DC. At  608 , the DC power may be conditioned, or smoothed, so that there are no voltage spikes, or hiccups in power delivery to the lamp groups. For example, the filter capacitor  406  may smooth the DC power. 
         [0031]    At  610 , a DC to DC converter steps down the voltage to a voltage required for the lamp group. For example, the voltage may be stepped down to the 200V powering lamp group  410  as shown in  FIG. 4 . The step-down converter is, in some embodiments, a buck converter, as described above. At  612 , the stepped down voltage is delivered to power the lamps. The lamps may be several lamp groups, such as lamp group  410  with various configurations of lamps and various voltage requirements. At  614 , the heat from the lamps heats the substrate, for example, a semiconductor wafer. 
         [0032]    Optionally, the method  600  may iterate one or more times during processing to control the energy provided by the lamps to achieve a desired process result. For example, the method  600  may iterate between  610  and  614  to step down the voltage to a desired or setpoint voltage, to deliver the desired or setpoint voltage to power the lamps, and to heat the substrate with the energy provided by the lamps. This iteration may continue one or more times to achieve a desired process result. The method  600  generally ends at  616 . 
         [0033]    While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof.