Patent Publication Number: US-2021180189-A1

Title: Apparatus for detecting or monitoring for a chemical precursor in a high temperature environment

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a Divisional of, and claims priority to and the benefit of, U.S. Utility patent application Ser. No. 16/242,852, filed on Jan. 8, 2019 and entitled “APPARATUS FOR DETECTING OR MONITORING FOR A CHEMICAL PRECURSOR IN A HIGH TEMPERATURE ENVIRONMENT,” which is a Non-provisional of, and claims priority to and the benefit of, U.S. Provisional Application No. 62/634,793, filed on Feb. 23, 2018 and entitled “APPARATUS FOR DETECTING OR MONITORING FOR A CHEMICAL PRECURSOR IN A HIGH TEMPERATURE ENVIRONMENT,” which are hereby incorporated by reference herein. 
    
    
     FIELD OF INVENTION 
     The present disclosure generally relates to an apparatus for forming a film on a semiconductor substrate. Specifically, the present disclosure relates to a chemical source for the apparatus and detecting or monitoring a concentration of a gas provided by the chemical source. 
     BACKGROUND OF THE DISCLOSURE 
     Chemical Vapor Deposition (CVD) and Atomic Layer Deposition (ALD) are both processes used to form a film on a semiconductor substrate disposed within a reaction chamber. The processes may involve flow of a first gas onto the substrate and flow of a second gas onto the substrate, such that the first gas reacts with the second gas in order to form a film having a particular chemical composition on the semiconductor substrate. 
     The chemistries used for these processes generally are kept in particular conditions in order to ensure proper film formation and to avoid any defects or clogging issues. Defects may occur due to condensation of heated chemistries along a gas pathway to the reaction chamber. The condensation of the heated chemistries may lead to a chemical reaction within the gas pathway prior to reaching the reaction chamber, leading to adverse particle formation on the film formed within the reaction chamber. 
     In addition, clogging may occur within the gas pathways due to the condensation. Clogging may result in shutting down operation of the reaction chamber in order to clear the gas pathways, as well as exacerbate the particle formation that adversely affects the film formed in the chamber. In addition, changes to process conditions may affect the deposition onto the wafer; for example, a change in temperature or pressure may lead to shifts in non-uniformities as it relates to film properties. These process shifts may lead to non-uniformities in thickness or concentration of the film, potentially resulting in scrapped wafers. 
     Prior art approaches to monitor concentrations of chemistries have been limited to temperatures less than 60-80° C. At these temperatures, condensation of gaseous precursors may occur, leading to the above described problems. An example of such a setup is described in the article entitled “Effluent Stream Monitoring of An Al2O3 Atomic Layer Deposition Process Using Optical Emission s  Spectroscopy,” by John P. Loo (available at http://www.lightwindcorp.com/uploads/6/2/8/7/62872375/ald_effluent_monitoring__.pdf). 
       FIG. 1  illustrates a prior art optical emissions spectroscopy setup  10  in an exhaust foreline. The optical emissions spectroscopy setup  10  comprises a reaction chamber  20 , an exhaust foreline  30 , a sampler  40 , an optical emission source  50 , an optical emission spectrometer  60 , an RF supply  70 , and a processor  80 . Exhaust from the reaction chamber  20  travels through the exhaust foreline  30 . The sampler  40  may take a portion of the exhaust in the exhaust foreline  30  and pass it through the optical emission source  50 , which may be an inductively coupled plasma source. The optical spectrometer  60  and the RF supply  70  are able to take readings of a spectrum generated in the optical emission source  50  and provide a reading to the processor  80 . 
     As a result, an apparatus and method to monitor concentrations of chemical precursors in a high temperature environment is desired. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
       While the specification concludes with claims particularly pointing out and distinctly claiming what are regarded as embodiments of the invention, the advantages of embodiments of the disclosure may be more readily ascertained from the description of certain examples of the embodiments of the disclosure when read in conjunction with the accompanying drawing, in which: 
         FIG. 1  illustrates a prior art optical emissions spectroscopy approach; 
         FIG. 2  illustrates an exemplary reaction chamber in accordance with at least one embodiment of the invention; 
         FIG. 3  illustrates a spectroscopy apparatus in accordance with at least one embodiment of the invention; 
         FIGS. 4A-4C  illustrate a spectroscopy apparatus in accordance with at least one embodiment of the invention; 
         FIGS. 5A-5B  illustrate an optical fiber apparatus in accordance with at least one embodiment of the invention; and 
         FIG. 6  illustrates a multiple reaction chamber setup in accordance with at least one embodiment of the invention. 
     
    
    
     It will be appreciated that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve understanding of illustrated embodiments of the present disclosure. 
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Although certain embodiments and examples are disclosed below, it will be understood by those in the art that the invention extends beyond the specifically disclosed embodiments and/or uses of the invention and obvious modifications and equivalents thereof. Thus, it is intended that the scope of the invention disclosed should not be limited by the particular disclosed embodiments described below. 
     As used herein, the term “substrate” may refer to any underlying material or materials that may be used, or upon which, a device, a circuit or a film may be formed. 
     As used herein, the term “chemical vapor deposition” (CVD) may refer to any process wherein a substrate is exposed to one or more volatile precursors, which react and/or decompose on a substrate surface to produce a desired deposition. 
     As used herein, the term “atomic layer deposition” (ALD) may refer to a vapor deposition process in which deposition cycles, preferably a plurality of consecutive deposition cycles, are conducted in a process chamber. Typically, during each cycle the precursor is chemisorbed to a deposition surface (e.g., a substrate surface or a previously deposited underlying surface such as material from a previous ALD cycle), forming a monolayer or sub-monolayer that does not readily react with additional precursor (i.e., a self-limiting reaction). Thereafter, if necessary, a reactant (e.g., another precursor or reaction gas) may subsequently be introduced into the process chamber for use in converting the chemisorbed precursor to the desired material on the deposition surface. Typically, this reactant is capable of further reaction with the precursor. Further, purging steps may also be utilized during each cycle to remove excess precursor from the process chamber and/or remove excess reactant and/or reaction byproducts from the process chamber after conversion of the chemisorbed precursor. Further, the term “atomic layer deposition,” as used herein, is also meant to include processes designated by related terms such as, “chemical vapor atomic layer deposition”, “atomic layer epitaxy” (ALE), molecular beam epitaxy (MBE), gas source MBE, or organometallic MBE, and chemical beam epitaxy when performed with alternating pulses of precursor composition(s), reactive gas, and purge (e.g., inert carrier) gas. 
     In the specification, it will be understood that the term “on” or “over” may be used to describe a relative location relationship, another element or layer may be directly on the mentioned layer, or another layer (an intermediate layer) or element may be intervened therebetween, or a layer may be disposed on a mentioned layer but not completely cover a surface of the mentioned layer. Therefore, unless the term “directly” is separately used, the term “on” or “over” will be construed to be a relative concept. Similarly to this, it will be understood the term “under,” “underlying,” or “below” will be construed to be relative concepts. 
     Embodiments of the invention are directed to an apparatus and a method for monitoring or detecting a concentration of a chemical precursor that enters a reaction chamber. Importance of such monitoring is due to the fact that such CVD and ALD processes may require strict chemical concentrations in order to form films of a particular composition and quality. It may be necessary to verify in real-time that an appropriate amount of the chemical precursor is being delivered with each pulse or flow. By such detection or monitoring, a variation in delivery of precursor to the wafers can be detected, and potentially, this could avoid scrapping of wafers. 
     An Optical Emission Spectrometer (OES) may be used to verify the proper amount of chemical precursor. An example of an OES may include the L3 “Smart” Chemical Monitoring System manufactured by Lightwind Corporation. Other OES may include the Sensor X system manufactured by Pivotal Systems. An OES determines intensities along a wavelength spectrum of a light emanating from a specimen. In this case, the specimen may be the chemical precursor. The intensities may represent an amount of chemical precursor flowing through the OES. 
       FIG. 2  illustrates a reaction system  100  in accordance with at least one embodiment of the invention. The reaction system  100  comprises a reaction chamber  110 ; a gas source  120  for providing a gas reactant; a showerhead  130  for distributing a gas; and a substrate holder  140  for holding a substrate  150  to be processed. The reaction system  100  also includes a passageway  160  through which the gas reactant flows from the gas source  120  to the showerhead  130 . The gas source  120  may provide a plasma gas source in at least one embodiment, or may provide a gas generated by a solid source precursor. 
     Prior approaches with implementing an OES into a reaction system have not incorporated the OES directly between a solid source vessel and the reaction chamber. Embodiments in accordance with the invention may perform a real-time monitoring of a vapor delivered from a solid source vessel into a reactor. Real-time monitoring may be to monitor a gas phase emission spectrum of each wafer, preferably after a few first pulses when stability may be reached. Alternative embodiments may not measure an absolute concentration, but just detect for the presence of a particular chemistry and perform a precursor sampling. With this arrangement, an acceptable range of operation may be determined, with anything outside an error range resulting in fault detection. 
     In addition, embodiments may measure or detect concentrations of particular chemistries at the solid source vessel or on a foreline of gas going towards the reaction chamber. Particular embodiments may allow for obtaining better signals and readings compared to other embodiments of the invention. A better signal may be obtained, but via an apparatus setup that may reduce the amount of precursor that enters into the reaction chamber, resulting in a higher cost to operate the reaction chamber. 
     Additional benefits obtained by embodiments of the invention may include an ability to match processes within more than one reaction chamber. An OES may be used to ensure that each reaction chamber is receiving an acceptably matching dose of chemistry. The OES may also determine if certain chemicals used in the film formation are present in an acceptable and repeatable amount for given process conditions. 
       FIG. 3  illustrates the gas source  120  in accordance with at least one embodiment of the invention. The gas source  120  may be configured to perform a real-time concentration monitoring. The gas source  120  comprises a heated vacuum enclosure  200 , an RF source  220 , an optical emissions spectrometer  230 , an exhaust pump  240 , a flow restrictor  250 , a valve  260 A, a gas line  270 A, a plurality of heaters  280 A- 280 B, and an optical fiber  300 . The heated vacuum enclosure  200  comprises a solid source vessel  210 , a plurality of valves  260 B- 260 C, and a gas line  270 B. 
     The solid source vessel  210  may hold a solid precursor and convert it into a gaseous precursor. The solid source vessel  210  may be a vessel described in U.S. patent application Ser. No. 15/283,120, entitled “Reactant Vaporizer and Related Systems and Methods” and filed on Sep. 30, 2016, or in U.S. patent application Ser. No. 15/585,540, entitled “Reactant Vaporizer and Related Systems and Methods” and filed on May 3, 2017, both of which are incorporated by reference. 
     The gaseous precursor then travels from the solid source vessel  210  through a valve  260 C, and then can either go along a gas line  270 B to the passageway  160  or to the RF source  220  via a valve  260 B. The majority of the gaseous precursor goes to the passageway  160  and subsequently the reaction chamber  110 , where it will reach the surface of the wafer  150 . 
     Of the gas that does not go to the reaction chamber  110 , the RF source  220  takes the draw of gaseous precursor and ionizes it. The RF source may be an inductively coupled plasma source, a capacitively coupled plasma source, a microwave source, or a hot filament gas ionizer; an example of such an RF source may include an ICP, manufactured by Lightwind, for example. The optical emissions spectrometer  230  is able to obtain a light spectrum of the ionized gaseous precursor in the RF source  220  through the optical fiber  300 . The optical emissions spectrometer  230  may then monitor desired wavelengths in order to determine whether there is an acceptable amount of gaseous precursor. The ionized gaseous precursor in the RF source  220  then passes through the flow restrictor  250  and a valve  260 A to the exhaust pump  240  along a gas line  270 A. 
     In addition, the flow restrictor  250  may prevent an excess of gaseous precursor from being sent to the exhaust pump  240 , and thus, result in more efficient use of the gaseous precursor. The flow restrictor  250  may comprise a control orifice, a needle valve, or a fixed or variable restrictor, for example. The heaters  280 A- 280 B would provide heat to a gaseous precursor diverted from the solid source vessel  210  to the RF source  220 , as well as the precursor traveling along the gas line  270 B. The heating of the gaseous precursor primarily avoids condensation of the gaseous precursor. 
       FIG. 4A  illustrates a gas source  120  in accordance with at least one embodiment of the invention. The embodiment of the invention allows for flow of gas through the RF source  220  rather than diffusion of gas into the RF source; this may result in a stronger spectrometer reading. The gas source  120  may detect a presence of a chemical in a setup allowing for precursor sampling. The gas source  120  comprises a heated vacuum enclosure  200 . The heated vacuum enclosure  200  comprises a solid source vessel  210 , a plurality of valves  260 B- 260 F, a gas line  270 B, a flow restrictor  290 , and an inert gas source  310 . Gas from the inert gas source  310  travels in the gas line  270 B through the valve  260 B into the solid source vessel  210 , where it carries a gaseous precursor formed from a solid precursor. The resulting gaseous precursor travels through the valves  260 D- 260 E and may either go to the reaction chamber  160  or be sampled by going through valve  260 F and the flow restrictor  290 . The valve  260 C serves as a bypass valve in isolating the solid source vessel  210 . 
     The gas source  120  also comprises an RF source  220 , an optical emissions spectrometer  230 , an exhaust pump  240 , a flow restrictor  250 , a valve  260 A, a plurality of heaters  280 A- 280 B, a gas line  270 A, and an optical fiber  300 . The heater  280 A heats exhaust gas within the gas line  270 A, while the heater  280 B heats the portion of the gas line disposed between the vacuum enclosure  200  and the RF source. 
       FIG. 4B  illustrates a gas source  120  in accordance with at least one embodiment of the invention. The gas source  120  is similar to that illustrated in  FIG. 4A  as it also is capable of performing a periodic detection of a chemical concentration. A gas line  270   c  is split from a gas line  270   b,  while a heater  280  heats the gas line outside of a vacuum enclosure  200  up to an RF source  220  and a valve  260   a.    
     An optical fiber  300  may obtain a light spectrum signal from the RF source  220  and provide it to an optical emissions spectrometer  230 . The arrangement of the RF source  220  and the optical fiber  300  may avoid deposition of a film on a window attached to the optical fiber  300 . In addition, build-up of a precursor may be avoided within a vacuum exhaust that travels through the valve  260   a  and a pump  240  along the gas line  270   c.    
       FIG. 4C  illustrates a gas source  120  in accordance with at least one embodiment of the invention. The gas source  120  is similar to that illustrated in  FIG. 4A , with the main difference in that a valve  260 F is disposed between a gas line having a valve  260 D and a valve  260 E, while in  FIG. 4A , the valve  260 F is disposed in the gas line after the valve  260 E. In other words, the valve  260 F is upstream of the valve  260 E in  FIG. 4C , while it is disposed downstream of the valve  260 E in  FIG. 4A . The embodiment illustrated in  FIG. 4C  may sample the gaseous precursor between processing of wafers or front opening unified pods (FOUPs) rather than real time monitoring. 
       FIGS. 5A-5B  illustrate an optical fiber  300  in accordance with at least one embodiment of the invention.  FIG. 5A  illustrates an end view of the optical fiber  300 , while 
       FIG. 5B  illustrates a cross-sectional view of the optical fiber  300 . The optical fiber  300  comprises a light transmission section  307 , a purge gas channel  320 , and a high-temperature outer sheath  330 . The optical fiber  300  also comprises a wide view fiber optic  340  attached to the light transmission section  307  and a purge nozzle  350  attached to the high-temperature outer sheath  330 . The purge nozzle  350 , along with a purge gas traveling through the purge gas channel  320 , may allow for reducing or minimizing build-up of a film formed on the wide view fiber optic  340 . The optical fiber  300  may be useful for monitoring within a foreline disposed proximate to a gas source. 
       FIG. 6  illustrates a multiple reaction chamber setup  400  in accordance with at least one embodiment of the invention. The multiple reaction chamber setup  400  allows for a matching of the process in multiple chambers, and comprises: a first reaction chamber  410 A, a second reaction chamber  410 B, a first gas source  420 A, a second gas source  420 B, a first sampling port  430 A, a second sampling port  430 B, a first valve  440 A, a second valve  440 B, a first gas line  450 A, a second gas line  450 B, a RF source/OES device  460 , an exhaust line  470 , and an exhaust pump  480 . 
     The first gas source  420 A and the second gas source  420 B may be configured to provide a same gaseous precursor to the first reaction chamber  410 A and the second reaction chamber  410 B. The first sampling port  430 A may be configured to sample a gas within the first reaction chamber  410 A. In an alternative embodiment, the first sampling port  430 A may be configured to be between the first gas source  420 A and the first reaction chamber  410 A. Similarly, the second sampling port  430 B may be configured to sample a gas within the second reaction chamber  410 B. In an alternative embodiment, the second sampling port  430 B may be configured to be between the second gas source  420 B and the second reaction chamber  410 B. 
     The first valve  440 A and the second valve  440 B may be configured to restrict the amount of gas that leaves the first reaction chamber  410 A and the second reaction chamber  410 B and into the first gas line  450 A and the second gas line  450 B, respectively. The first valve  440 A and the second valve  440 B may comprise a needle valve, a fixed flow restrictor, or a variable flow restrictor, for example. The first gas line  450 A and the second gas line  450 B may feed into the RF source/OES  460 ; in an alternative embodiment, there may be separate RF source/OES setups for each of the first gas line  450 A and the second gas line  450 B. The RF source/OES  460  may perform a gas ionization and a spectrometry reading in a manner described previously on the gaseous precursor, before sending the gas to the exhaust pump  480  via the exhaust line  470 . 
     The example embodiments of the disclosure described above do not limit the scope of the invention, since these embodiments are merely examples of the embodiments of the invention, which is defined by the appended claims and their legal equivalents. Any equivalent embodiments are intended to be within the scope of this invention. Indeed, various modifications of the disclosure, in addition to those shown and described herein, such as alternative useful combination of the elements described, may become apparent to those skilled in the art from the description. Such modifications and embodiments are also intended to fall within the scope of the appended claims.