Patent Application
20200020512
Embodiments disclosed herein generally relate to apparatus and methods for cleaning a processing chamber, and more specifically, to methods and apparatus facilitating detection of the end point of a chamber cleaning process.
One of the steps in the fabrication of modern semiconductor devices is the formation of a thin film on a semiconductor substrate by chemical reaction of gas. Such a deposition process is referred to as chemical vapor deposition or CVD. Processes include plasma-enhanced CVD (PECVD) techniques.
The surface upon which a CVD layer is deposited may contain contaminants, such as particulate or film deposits from chamber walls or components and/or from prior processes. The presence of contaminants may affect the absorption of precursors and slow or inhibit the deposition rate of the CVD layer. Contamination within the chamber is typically controlled by periodically cleaning the chamber using cleaning gas which are excited to inductively or capacitively-coupled plasmas. Cleaning gas may bind the contaminants in order to form stable volatile products which can be exhausted from the chamber, thereby cleaning the process environment. So that all or nearly all of the contaminants in a chamber are removed, sufficient cleaning gas must be provided, and sufficient time must elapse, to allow binding reactions between the cleaning gas and all or nearly all of the contaminants.
Reactions binding cleaning gas to contaminants may generate electromagnetic radiation. The electromagnetic radiation may be in the visible light spectrum. Therefore, reactions binding cleaning gas to contaminants may be identified by a visible “glow.” Once all or nearly all of the contaminants have bound to cleaning gas (assuming sufficient cleaning gas has been provided), the end point of the chamber cleaning process may be identified by cessation of the glow. However, conventional methods (e.g., visual detection or specified-wavelength measurement) of identification of an end point may be inaccurate, imprecise, and/or inconsistent. Too short of a time period for a chamber cleaning process may result in a contaminated processing environment, while too long of a time period for a chamber cleaning process may be costly and inefficient. What is needed are methods and apparatus to more accurately, precisely, and consistently identify the end point of a chamber cleaning process.
In one or more embodiments disclosed herein, a method includes: obtaining at least one normalized baseline spectrum for a processing volume of a processing chamber; calculating a distribution value of the at least one normalized baseline spectrum; obtaining a plurality of normalized cleaning process spectrums for the processing volume over a time period during a cleaning process of the processing chamber; calculating a distribution function of the plurality of normalized cleaning process spectrums; comparing the distribution value to the distribution function over the time period; and determining an end point for the cleaning process by identifying when the distribution function approaches the distribution value.
In one or more embodiments disclosed herein, a method includes: initiating a first processing-cleaning cycle for a processing chamber, wherein: the first processing-cleaning cycle comprises a first over-cleaning period, and a first plurality of baseline spectrums for a processing volume of the processing chamber are measured during the first over-cleaning period; after the first processing-cleaning cycle, initiating a second processing-cleaning cycle for the processing chamber, wherein: the second processing-cleaning cycle comprises a second cleaning process, and a second plurality of cleaning process spectrums for the processing volume are measured during the second cleaning process; and determining a second end point for the second cleaning process by: calculating a distribution function of a second plurality of normalized cleaning process spectrums from the first plurality of baseline spectrums and the second plurality of cleaning process spectrums; calculating a distribution value of a second normalized baseline spectrum from the first plurality of baseline spectrums; comparing the distribution value of the second normalized baseline spectrum to the distribution function of the second plurality of normalized cleaning process spectrums; and identifying when the distribution function of the second plurality of normalized cleaning process spectrums approaches the distribution value of the second normalized baseline spectrum.
In one or more embodiments disclosed herein, a method includes: initiating a cleaning process in a processing chamber, the cleaning process comprising flowing a cleaning gas into a processing volume of the processing chamber; obtaining a normalized baseline spectrum for the processing volume of a processing chamber; measuring a plurality of intensity spectrums for the processing volume during the cleaning process; using the plurality of intensity spectrums to calculate a plurality of normalized cleaning process spectrums for the processing volume; comparing a distribution value of the normalized baseline spectrum to a distribution function of the plurality of normalized cleaning process spectrums; and determining an end point for the cleaning process by identifying when the distribution function of the plurality of normalized cleaning process spectrums approaches the distribution value of the normalized baseline spectrum.
So that the manner in which the above-recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this disclosure and are therefore not to be considered limiting of its scope, for the disclosure may admit to other equally effective embodiments.
To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one embodiment may be beneficially utilized on other embodiments without specific recitation.
Embodiments of the present invention generally relate to the fabrication of integrated circuits. More particularly, the embodiments described herein provide cleaning techniques for a plasma chamber utilized in the manufacture of integrated circuits. During manufacturing processes (e.g., plasma-enhanced chemical vapor deposition (PECVD)), material (e.g., amorphous silicon) may contaminate the chamber walls or components. During chamber cleaning processes, cleaning gas (e.g., fluorine radicals) may be used to react with and/or remove contaminants from the chamber. If insufficient cleaning gas is provided, or if insufficient time is allowed for the cleaning process, contaminants may remain, resulting in under cleaning of the chamber. However, excessive chamber cleaning may be costly and/or time consuming.
The end point of a chamber cleaning process occurs when the level of contaminates (e.g., impurities and/or dopant material) remaining in the chamber, on chamber walls, and/or on components drops below a desired amount. In general, an end point may be reached when contaminant particulate level drops, for example, to no more than about 20 to about 50 particles remaining from a single deposition process. In some embodiments, each contaminant particle is approximated about 1 nm to about 3 nm in size. In general, an end point may be reached when contamination coverage drops, for example, to cover no more than about 1% to about 5% of the total processing volume and/or chamber equipment. In some embodiments, the contamination coverage may be a film having a thickness of between about 800 Å and about 1200 Å. Embodiments disclosed herein provide methods to determine when the end point of a chamber cleaning process occurs. In some embodiments, the methods identify the end point by measuring broad-spectrum signals to provide more redundancy and/or better quality control than conventional methods. Embodiments disclosed herein, unlike conventional methods, beneficially provide methods applicable to a variety of processing materials (e.g., substrates and/or film materials, such as SiN, SiO, aSi), a variety of processing apparatus, and a variety of processing methods or formulae.
Embodiments disclosed herein may provide more accurate, more precise, and/or more consistent end point detection compared to conventional methods. For example, some conventional methods determine a cleaning process end point by measuring radiation at a few (less than 10) specified wavelengths and seeking a maximum, minimum, threshold, or value change of a specified amount. (For example, a clean spectrum for SiN typically exhibits 6 peaks, a clean spectrum for SiO typically exhibits 4 peaks, and a clean spectrum for aSi typically exhibits 2 peaks.) Determining an end point by specified-wavelength measurement may cause: (1) complications in meeting series-criteria, (2) difficulty in adjusting settings when the processing material is changed, and/or (3) difficulty in adjusting settings when the cleaning method or formula is changed. Embodiments disclosed herein utilize spectrum measurements that are not limited to peaks, maxima, or minima, and that include anywhere between 100 to 1000 different wavelength measurements. Such embodiments may beneficially provide a broad-spectrum signal to determine a cleaning process end point. Embodiments disclosed herein may simplify adjustments to setting/criteria when the processing material is changed. Embodiments disclosed herein may be applicable to different processing equipment, methods, and/or formulae.
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A window 113 is located in the sidewall 117 to provide radiation transmission between the processing volume 111 and the exterior of the chamber body 102. For example, the window 113 may be quartz or glass. In some embodiments, the window 113 may be located in sidewall 117 on the opposite side of the processing volume 111 from opening 123. In some embodiments, window 113 may be transparent to visible light radiation, for example electromagnetic radiation having wavelengths between about 300 nm and about 800 nm. In some embodiments, window 113 may be made up of a plurality of window panes, each pane extending through sidewall 117 and distinguished by varying transparencies. For example, a first pane may be transparent to electromagnetic radiation having wavelengths between about 300 nm and about 400 nm, and a second pane may be transparent to electromagnetic radiation having wavelengths between about 700 nm and about 800 nm. As another example, a third pane may be transparent to infrared radiation having wavelengths between about 700 nm and about 1 millimeter. As yet another example, a fourth pane may be 50% opaque to visible light, while a fifth pane may be 80% opaque to visible light.
In some embodiments, a radiation detection device 180 may be coupled to window 113 on the exterior of the chamber body 102. The radiation detection device 180 may be either permanently or removably coupled to window 113. The radiation detection device 180 may be either directly or indirectly coupled to window 113. In some embodiments, the radiation detection device 180 may be coupled to a portion of window 113 (e.g., to a subset of the panes of window 113), leaving another portion of window 113 exposed to the exterior of the chamber body 102. The radiation detection device 180 may be an optical detector, a spectrometer, a photocell, or other radiation detector. The radiation detection device 180 may be configured to detect radiation transmitted from processing volume 111 and through window 113. The radiation detection device 180 may be configured to detect and/or measure electromagnetic radiation, for example electromagnetic radiation having wavelengths between about 300 nm and about 800 nm. Radiation detection device 180 may detect radiation at a variety of wavelengths. It is currently believed that detection of infrared electromagnetic radiation by radiation detection device 180 (e.g., for the purpose of end point identification) may be subject to more noise, such as from chamber temperature variations, than visible light. In some embodiments, radiation transmitted from processing volume 111 through window 113 may follow a waveguide (e.g., optical fiber) to reach radiation detection device 180.
A gas source 122 is coupled by a conduit 134 to deliver gas (e.g., processing gas, precursor gas, purge gas, carrier gas, or cleaning gas) through the showerhead assembly 114 and into the processing volume 111. The processing system 100 also includes an exhaust system 118 configured to apply and/or maintain negative pressure to the processing volume 111. A radio frequency (RF) power source 105 is coupled to the showerhead assembly 114 to facilitate formation of a plasma in a processing region 112. The processing region 112 is generally defined between the showerhead assembly 114 and the support surface 107 of the substrate support 104.
Using a processing gas from the gas source 122, the processing system 100 may be configured to deposit a variety of materials on the large area substrate 101, including but not limited to dielectric materials (e.g., SiO2, SiOxNy, derivatives thereof or combinations thereof), semiconductive materials (e.g., Si and dopants thereof), and/or barrier materials (e.g., SiNx, SiOxNy or derivatives thereof). Specific examples of dielectric materials and semiconductive materials that are formed or deposited by the processing system 100 onto the large area substrate may include epitaxial silicon, polycrystalline silicon, amorphous silicon, microcrystalline silicon, silicon germanium, germanium, silicon dioxide, silicon oxynitride, silicon nitride, dopants thereof (e.g., B, P, or As), derivatives thereof, or combinations thereof. The processing system 100 is also configured to receive gas such as argon, hydrogen, nitrogen, helium, or combinations thereof, for use as a purge gas or a carrier gas (e.g., Ar, H2, N2, He, derivatives thereof, or combinations thereof). One example of depositing silicon thin films on the large area substrate 101 using the system 100 may be accomplished by using silane as the precursor gas in a hydrogen carrier gas. The showerhead assembly 114 is generally disposed opposing the substrate support 104 in a substantially parallel manner to facilitate plasma generation therebetween.
A temperature control device 106 may also be disposed within the substrate support 104 to control the temperature of the substrate 101 before, during, or after processing. In one aspect, the temperature control device 106 comprises a heating element to preheat the substrate 101 prior to processing. In this embodiment, the temperature control device 106 may heat the substrate support 104 to a temperature between about 200° C. and 250° C. During processing, temperatures in the processing region 112 may reach or exceed 400° C., and the temperature control device 106 may comprise one or more coolant channels to cool the substrate 101. In another aspect, the temperature control device 106 may function to cool the substrate 101 after processing. Thus, the temperature control device 106 may be coolant channels, a resistive heating element, or a combination thereof. Electrical leads for the temperature control device 106 may be routed to a power source and/or a controller through the hollow shaft 137.
During a chamber cleaning process, gas source 122 may provide cleaning gas (e.g., NF) to the processing volume 111. An energy source, such as a remote plasma source (RPS) or a radio frequency (RF) source, may be used to dissociate at least a portion of the cleaning gas molecules, thereby providing a mixture of atomic and molecular cleaning gas. The cleaning gas may react (e.g., bind) with contaminants to produce electromagnetic radiation in processing volume 111. Radiation detection device 180 may detect radiation produced by the reactions and transmitted from processing volume 111 through window 113. Radiation detection device 180 may measure the intensity of the detected radiation at various wavelengths and at various times. In some embodiments, radiation detection device 180 may measure broad-spectrum (at least about 100 to 1000 or more different wavelengths) signals of the intensity of the detected radiation.
The radiation detection device 180 and/or a data processing device 190 may utilize the intensity measurements to produce intensity spectrums. For example, the radiation detection device 180 may transmit the intensity measurements to the data processing device 190. As another example, the radiation detection device 180 may produce an intensity spectrum at a particular instant and transmit that instantaneous intensity spectrum to data processing device 190. As another example, radiation detection device 180 may transmit a plurality of instantaneous intensity spectrums to data processing device 190. In some embodiments, data processing device 190 may poll radiation detection device 180 or otherwise communicate data and/or control signals therebetween.
The data processing device 190 may receive, analyze, and/or store intensity measurements and intensity spectrums from radiation detection device 180. Based on the received, analyzed, and/or stored information, the data processing device 190 may communicate with gas source 122. For example, data processing device 190 may identify the end point of a cleaning process. In some embodiments, in response to identification of the end point of a cleaning process, data processing device 190 may send control signals to gas source 122 to reduce or cease flow of cleaning gas to processing volume 111. In some embodiments, data processing device 190 may communicate data and/or control signals with various other components of processing system 100 (e.g., temperature control device 106).
Cleaning process 200 continues at box 220 wherein the baseline spectrum(s) obtained at box 210 are averaged. For example, the time-series of baseline spectrums may be averaged to produce an average baseline spectrum. It should be understood that radiation noise may vary depending on targeted cleaning conditions, equipment type, equipment age and usage characteristics, ambient temperature or pressure, etc. Averaging baseline spectrums may provide a more stable estimate of background radiation than would be available from a single baseline spectrum.
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At box 260, the distribution value of the normalized baseline spectrum(s) is compared with the distribution function of the normalized cleaning process spectrum(s). It should be appreciated that the end point EP of the cleaning process 200 may be reached when, near the end of the cleaning process 200, the noise level of the background is substantially similar to or equal to the reaction radiation detected at a particular instant. For example, the end point EP may be reached when, for a given point in time, the distribution value of the normalized baseline spectrum(s) is substantially similar or equal to the value of the distribution function of the normalized cleaning process spectrum(s) at that point in time. In some embodiments, a spectrum ratio R may be utilized to indicate when the distribution value of the normalized baseline spectrum(s) is substantially similar to or equal to the value of the distribution function of the normalized cleaning process spectrum(s). For example, the spectrum ratio R may be, at a given point in time, a ratio of the distribution value of the normalized baseline spectrum(s) to the value of the distribution function of the normalized cleaning process spectrum(s) at that point in time. The spectrum ratio R may be computed for each normalized cleaning process spectrum(s) and tracked over time as a spectrum ratio function R(t).
Before binding reactions begin, near the beginning of the cleaning process 200, the value of the distribution function of the normalized cleaning process spectrum should be similar to the distribution value of the normalized baseline spectrum, and the spectrum ratio R should be near 1. As binding reactions begin, during cleaning process 200, the radiation detected and measured by the normalized cleaning process spectrum increases, and the spectrum ratio R drops below 1. As contaminants are depleted from the processing volume, near the end of cleaning process 200, the rate of binding reactions drops, and the spectrum ratio R again approaches 1. Once binding reactions cease due to depletion of contaminants, the value of the distribution function of the normalized cleaning process spectrum should be substantially similar to or equal to the distribution value of the normalized baseline spectrum, and the spectrum ratio R should stabilize at or near 1. The end point EP of the cleaning process 200 may be deemed to be reached when the spectrum ratio function R(t) stabilizes at or near 1.
It should be appreciated that some operational conditions may be more sensitive to contamination, and such processes may benefit from more extensive cleaning. Alternatively, other operational conditions may be more sensitive to time and/or cost factors, and such alternative processes may benefit from less extensive cleaning. Therefore, at box 270, a clean threshold may be optionally input to identify the acceptable contamination level following cleaning process 200. For example, a low clean threshold may be set so that the end point EP will be identified when the spectrum ratio R (near the end of a cleaning process) exceeds 0.60. As another example, a high clean threshold may be set so that the end point EP will be identified when the spectrum ratio R (near the end of a cleaning process) exceeds 0.95.
A person of ordinary skill in the art with the benefit of this disclosure should understand that the comparison at box 260 (i.e., comparing the distribution value of the normalized baseline spectrum(s) to the distribution function of the normalized cleaning process spectrum(s)) may be analyzed and/or computed according to a variety of mathematical constructs. As illustrated in
In some embodiments, processing system 100 (from
In some embodiments, during a series of processing-cleaning cycles, conventional means (e.g., visual detection or single-wavelength measurement) may be utilized to determine the end point of the first cleaning process. The first cleaning process may conclude with an over-cleaning period. For example, the gas source 122 (from
It should be understood that the background radiation spectrum of processing system 100 (from
While the foregoing is directed to embodiments of the disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof.
