1. Field of the Invention
The present invention relates to methods and apparatus for measuring and controlling the temperature of substrate holders that support substrates during processes such as semiconductor etching processes.
2. Description of the Background
Plasma or dry etching of silicon wafers to transfer a pattern of integrated circuits from photolithographic masks to the silicon wafers have become standard methods in the industry. In conventional dry etchers, the silicon wafer being etched is ordinarily held in close proximity to the wafer chuck by electrostatic force. This system is quite effective in holding the wafer securely to the chuck during processing, permitting good heat transfer and good electrical connectivity between the wafer and the other components in the etching system.
It is important to measure the temperature of the wafer chuck during the process cycle. Merely ensuring good contact between the wafer and wafer chuck is insufficient if the temperature and the temperature uniformity of the chuck is not adequately controlled.
Methods of controlling the temperature of wafer chucks include the use of thermocouples, infrared pyrometry, and liquid crystals. Thermocouples embedded in the wafer chuck are widely used for the temperature control of the wafer chuck, as are infrared emission optical pyrometry, and the use of materials such as liquid crystals that fluoresce at desired temperatures. However, these all have the shortcoming of either measuring the temperature at one point, or at most a few discrete points, around the wafer chuck.
Research publications by K. Saraswat and his group at Stanford University (for example, Mat. Res. Soc. Symp. Proc. Vol. 387, pg. 35, 1995, Materials Research Society) have disclosed the utilization of the propagation velocity of Lamb ultrasonic waves in silicon wafers to measure the temperature of the wafers. U.S. Pat. No. 6,019,000 (Stanke et al.) and U.S. Pat. No. 5,271,274 (Khuri-Yakub et al.) disclose the use of the propagation velocity of ultrasonic waves for the measurement of the thickness of films deposited on substrates such as silicon, discuss the temperature effects on the velocity of the waves in solids, and describe means for compensating for these temperature effects.
However, it is not believed that the art has recognized a way of (1) measuring a temperature at all points on a wafer chuck simultaneously, especially during processing, or (2) allowing responsive and comprehensive control of wafer chuck temperature based on the temperature measurements. It is to meet these needs, among others, that the present invention is directed.
The present invention provides for use of ultrasonic transducers together with tomographic techniques to determine the temperature of a substrate holder (e.g., a chuck or an electrotatic chuck for a substrate) at all points on the substrate holder, thereby allowing comprehensive control of the temperature of the substrate holder during processing. As used herein, “substrate” is a general term for a processed workpiece, e.g., a semiconductor wafer or liquid crystal display panel.
The invention provides an apparatus for measuring temperatures of respective portions of a substrate holder that supports a substrate on which a process is carried out. The apparatus comprises an arrangement of at least one ultrasonic transducer arranged and configured to transmit ultrasonic energy through the substrate holder, and a data processor configured to calculate, during the process, the temperatures of the respective portions of the substrate holder based on respective propagation time delays of the ultrasonic energy through the respective portions.
Similarly, the invention also provides a method for measuring temperatures of respective portions of a substrate holder that supports a substrate on which a process is carried out, the method comprising transmitting ultrasonic energy through the substrate holder using an arrangement of at least one ultrasonic transducer, and calculating, during the process, the temperatures of the respective portions of the substrate holder based on respective propagation time delays of the ultrasonic energy through the respective portions.
Moreover, the invention provides an apparatus for measuring temperatures of respective portions of a substrate holder that supports a substrate on which a process is carried out, and for controlling the temperatures of the respective portions in response to the measured temperatures. The apparatus comprises an arrangement of at least one ultrasonic transducer arranged and configured to transmit ultrasonic energy through the substrate holder, and a data processor configured to calculate, during the process, the temperatures of the respective portions of the substrate holder based on respective propagation time delays of the ultrasonic energy through the respective portions. The data processor is further configured to communicate, during the process, at least one of (1) a correction signal to a heater controller, (2) a warning signal to a display/alarm device and (3) an error signal to a process controller, if a calculated temperature exceeds a predetermined temperature limit.
Similarly, the invention also provides a method for measuring temperatures of respective portions of a substrate holder that supports a substrate on which a process is carried out, and for controlling the temperatures of the respective portions in response to the measured temperatures. The method comprises transmitting ultrasonic energy through the substrate holder using an arrangement of at least one ultrasonic transducer, calculating, during the process, the temperatures of the respective portions of the substrate holder based on respective propagation time delays of the ultrasonic energy through the respective portions, and communicating, during the process, at least one of (1) a correction signal to a heater controller, (2) a warning signal to a display/alarm device and (3) an error signal to a process controller, if a calculated temperature exceeds a predetermined temperature limit.
In particular preferred embodiments, the data processor may be further configured to use tomographic techniques to construct a temperature map of the substrate holder based collectively on the calculated temperatures of the portions of the substrate holder.
In addition, the invention provides a method for measuring respective portions of a substrate holder that supports a substrate on which a process is carried out to ensure that respective elements within the substrate holder are operating correctly. The method comprises: transmitting ultrasonic energy through the substrate holder using an arrangement of at least one ultrasonic transducer; calculating, during the process, the respective propagation time delays of the ultrasonic energy through the respective portions; analyzing the respective reflection signal amplitudes; and communicating, during the process, at least one of (1) an error signal to a process controller and (2) a warning signal to a display/alarm device, if a calculated propagation time delay exceeds a predetermined limit.
Other objects, features and advantages of the present invention will be apparent to those skilled in the art upon a reading of this specification including the accompanying drawings.
The invention is better understood by reading the following Detailed Description of the Preferred Embodiments with reference to the accompanying drawing figures, in which like reference numerals refer to like elements throughout, and in which:
In describing preferred embodiments of the present invention illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the invention is not intended to be limited to the specific terminology so selected, and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner to accomplish a similar purpose.
The velocity of ultrasonic waves through material is a function of the temperature of the material. The inventors have recognized that the time for the propagation of an ultrasonic wave for a known distance may be used to interpret the temperature of the material in a substrate holder (e.g., a chuck, an electrostatic chuck or a support for holding a semiconductor wafer, a liquid crystal display panel or another material to be processed).
Tomography has become a useful instrument for generating an image or cross section of an opaque solid object. It has been widely utilized in medical applications such as CAT scans and ultrasonic mapping. However, it is not believed to have been applied to measurement and control of temperature throughout a substrate holder, especially for measurement and control during processing.
Briefly, according to the invention, ultrasonic tomography is utilized to obtain a map of the temperature of a substrate holder by applying an array of ultrasonic transducers around the periphery of the substrate holder. The length of time for the ultrasonic wave to transit the substrate holder (the propagation time) is measured and used to conclude the temperature of that slice of the substrate holder. By applying the tomographic interpretation of the temperatures of each of the transducers, a map of the temperature of the entire substrate holder is generated during the process.
In the simplified embodiment shown in
In the illustrated embodiment shown in
A transducer of the plurality of transducers 3 launches an ultrasonic wave, and at least one of the plurality of transducers 3 directly “across” the substrate from the transmitting transducer receives an ultrasonic signal. The process is then repeated for the remaining transducers 3 that have not yet transmitted. In the arrangement, shown schematically in
According to an alternate embodiment, ultrasonic waves from a plurality of transmitters are received by a plurality of receivers. This is shown schematically in
According to an alternate embodiment, a plurality of transmitters simultaneously transmit ultrasonic waves, where each wave comprises a transmitter-specific signal frequency. The ultrasonic signals that arrive at the receivers are separated into the transmitted signal frequencies using signal processing that is well known in the art.
For further details, the principles of tomography are described in The physical basis of computed tomography (Marshall et al., Warren H, Green, Inc., St. Louis, Mo.) and Process tomography (Williams & Beck, Butterworth Heinemann, 1995.), and both are incorporated herein by reference in their entirety.
Referring more specifically to
Transducers 3 are coupled to transducer controller 12. Transducer controller 12 determines which transducers 3 to use to as transmitters and which transducers 3 to use as receivers. Transducer controller 12 comprises multiplexer and demultiplexer elements (not shown). Transducer controller 12 also comprises frequency generating elements (not shown).
Transducer controller 12, which can be implemented as a conventional microcontroller or digital signal processor, ensures that transducers 3 are active during their respective transmit times and receive times. For example, a sequential ordering scheme can be used to ensure that ultrasonic energy from one transmitter does not interfere with the ultrasonic energy from another transmitter.
In an alternative embodiment, as shown in
Transducer controller 12 calculates information about the received waveforms, such as propagation time for a selected transducer pair, and forwards the information to a data processor 13. Data processor 13 can be implemented as a general purpose computer, for example.
In a preferred embodiment, data processor 13 performs the higher-level functions of computing velocity and temperature, based on the propagation times determined by the transducer controller. If a computed temperature measurement strays beyond an allowed parameter (determined beforehand for each particular substrate holder implementation), data processor 13 sends a message to heater controller 15, which can adjust heating elements accordingly. The heater controller can be coupled to resistive heating elements, thermoelectric devices and/or a heat exchanger in communication with fluid channels through which heated or cooled fluid can circulate.
In the event that a computed temperature violates a predetermined temperature limit at which the desired processing (e.g., etching) should not continue at all, data processor 13 sends a message on path 16 to a process controller (e.g., etch process controller, not shown), warning that the process should be interrupted. The process controller can then take appropriate action, as it may be programmed, such as halting the process. Additionally or alternatively, the data processor 13 can send a warning message to an operator via an output element 14, which can comprise a conventional display and/or audible warning (alarm) device.
For example, the received data can be in the form of a waveform of ultrasonic energy intensity as a function of time, indicated in
In
Of course, the invention can be practiced with a variety of implementations and architectures, including those in which the functions of determining propagation time, determining velocity, determining temperature, and so forth, are performed by different elements than those described above. In one such alternate embodiment, illustrated in
Step 405 indicates commencement of method 400, and step 410 indicates selection of a transducer from the set of transducers 3 to be used as a transmitter. In embodiments in which only a single transducer is used to both transmit and receive, this step indicates selection of that single transducer, but illustratively, only the embodiment using pairs of transducers is used as the basis of the following discussion. In any event, step 410 is similar to the “increment counter” step in a loop, and determines the transducer pair that is the subject of the steps in the loop that follows.
Step 420 indicates launching of the ultrasonic energy by the transducer that was selected as the transmitter during a transmit time.
Step 430 indicates the reception of ultrasonic energy by one of transducers 3 during a receive time that is later than the transmit time. The propagation time is determined by the architecture of the substrate holder and the particular “slice” (portion) of the substrate holder through which the ultrasonic energy has been transmitted. This step can include a filtering out of ultrasonic energy that arrives outside a “window” of arrival times, so that undesirable echoes from other parts of the substrate holder do not interfere with the desired signal peak. During the filtering process, the received signal can be analyzed to assure that those components, such as cooling ducts, etc., that lie within the transmission path of the ultrasonic wave are functioning properly, i.e. coolant is or is not flowing through the cooling channels. The above determination can be made by comparing the form of the received signal to a typical transmission signature when all components are functioning as expected.
Transducer controller 12 can transmit and receive signals using a single transducer by controlling the transducer to operate as a transmitter during a transmit period of time and to operate as a receiver during a receive period of time. Transducer controller 12 can transmit using a single transducer by controlling the transducer to operate as a transmitter during a transmit period of time and can receive signals from at least one other transducer by controlling the at least one other transducer to operate in a receive mode during receive periods of time. Transducer controller 12 can transmit using a number of transducers by controlling the number of transducers to operate as transmitters during transmit periods of time and can receive signals from at least one other transducer by controlling the at least one other transducer to operate in a receive mode during receive periods of time.
In step 440 the propagation time is determined. In the illustrated embodiment, the calculation of the propagation time is based on a subtraction of the launching time from the reception time. Alternatively, the propagation time can be calculated using multiple launch times and/or multiple reception times. In the exemplary embodiment shown in
In step 450, the velocity of the ultrasonic energy is determined. For example, the formula (velocity=distance/time) can be used. In the exemplary embodiment of
If the computed temperature is within allowed parameters, then control returns to step 410 for selection of the next transducer pair, and method 400 continues as shown in
If step 470 determines that there is a moderate temperature variation that does not require halting of the process, control passes to block 480. In step 480, the temperature of the substrate holder is adjusted. For example, data processor 13 can send a message to heater controller 15 indicating that it should correct the temperature in the portion of the substrate holder that corresponds to the portion through which the ultrasonic energy traveled.
If step 470 determines that an extreme temperature limit was exceeded, control passes to block 490 in which the process is halted. For example, data processor 13 can send a message indicating that the process should be halted altogether, either by a message on
It will be appreciated that
However, after block 460 determines a temperature for a selected transducer pair, decision block 461 determines whether there are any more transducer pairs to process. If there are more transducer pairs to process, control returns to block 410 in which a next transducer pair is selected for processing. An exemplary set of transducer pairs can include pairs wherein a transmitting transducer is selected from the plurality of transducers 3 and the receiving transducer is multi-plexed through all of the transducers in contact with substrate holder 1. This process can be repeated where each transducer is selected as the transmitting transducer. When all the transducer pairs have been processed, control passes to block 465, which indicates data processor 13's construction of a spatial temperature map of the substrate holder in accordance with a suitable tomographic technique. Alternately, multiple transducers can be selected during a particular receive time.
Decision block 471 indicates the data processor's decision of whether the spatial temperature map lies within allowed parameters. For example, the variance or root-mean-square of spatial deviations of the measured temperature map from the expected temperature map (determined empirically and stored in a look-up table) can be computed and employed for the above decision.
If data processor 13 determines that the spatial temperature map lies within allowed parameters, control returns to block 405 where method 401 continues as shown in
If data processor 13 determines that the map deviates moderately from ideal but does not require halting of the etching process, control passes to block 481. In block 481 the temperature is adjusted. For example, data processor 13 can send a message to heater controller 15 indicating that it should correct the temperature throughout the portions of the substrate holder that caused the deviation from ideal temperature.
If data processor 13 determines that an extreme deviation from the ideal temperature map has occurred, control passes to block 491 in which method 401 ends. For example, data processor 13 can send a message indicating that the process should be halted altogether, either by a message on
Those skilled in the art will appreciate that
As stated above, the system includes at least one computer readable medium. Examples of computer readable media are compact discs 119, hard disks 112, floppy disks, tape, magneto-optical disks, PROMs (EPROM, EEPROM, Flash EPROM), DRAM, SRAM, SDRAM, etc. Stored on any one or on a combination of computer readable media, the present invention includes software for controlling both the hardware of the computer 100 and for enabling the computer 100 to interact with a human user. Such software may include, but is not limited to, device drivers, operating systems and user applications, such as development tools. Such computer readable media further includes the computer program product of the present invention for tracking temperature and tomographic information. The computer code devices of the present invention can be any interpreted or executable code mechanism, including but not limited to scripts, interpreters, dynamic link libraries, Java classes, and complete executable programs.
Modifications and variations of the above-described embodiments of the present invention are possible, as appreciated by those skilled in the art in light of the above teachings. For example, the number, arrangement, and composition of the transducers may be varied while remaining within the scope of the present invention. Further, the invention contemplates that a wide variety of implementations of hardware architecture and software processing techniques may be employed to achieve the functions and advantages described herein. It is therefore to be understood that, within the scope of the appended claims and their equivalents, the invention may be practiced otherwise than as specifically described.
This application claims priority to U.S. Provisional Application Ser. No. 60/301,433, filed on Jun. 29, 2001, the entire contents of which are incorporated herein by reference.
Number | Date | Country | |
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60301433 | Jun 2001 | US |
Number | Date | Country | |
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Parent | 10183360 | Jun 2002 | US |
Child | 10994312 | Nov 2004 | US |