JP7485652B2 - Precursor delivery system and related methods - Patents.com - Google Patents

Description

[0001] Embodiments of the present disclosure relate generally to the field of electronic device manufacturing, and more particularly to systems and methods used to deliver a process gas having a desired diborane concentration to a process space of a process chamber.

[0002] Boron-containing (boron-doped) material layers, such as boron-doped silicon or germanium semiconductor layers, boron-doped dielectric layers, boron-doped silicon hard mask layers, or boron-doped tungsten nucleation layers, are widely used in the field of electronic device fabrication. Often, boron-doped material layers are formed using a chemical vapor deposition (CVD) process in which a boron-containing gas reacts or dissociates in the presence of one or more material precursor gases to deposit a boron-doped material layer on the surface of a substrate.

[ ₀₀₀₃ ] Diborane ( _B2H6 ) is commonly selected as the boron precursor for doping because it is relatively easy to store and transport and desirably dissociates at a relatively low temperature when compared to other boron dopant source gases. Diborane is typically stored in a pressurized gas cylinder along with a diluent gas, such as one or a combination of hydrogen ( _H2 ), argon (Ar), nitrogen ( _N2 ), or helium (He), to produce a doping gas mixture, i.e., boron doping gas. The boron doping gas is typically delivered from the pressurized gas cylinder to the process space of the CVD process chamber using a gas delivery conduit fluidly coupled therebetween. Unfortunately, over time, the diborane in the pressurized gas cylinder undesirably decomposes to produce free hydrogen and higher boranes, resulting in a decrease in the diborane concentration therein. This undesirable change in diborane concentration over time results in undesirable substrate-to-substrate variation in the boron concentration in the CVD deposited material layer formed thereon.

[0004] Thus, there is a need in the art for improved systems and related methods for monitoring and controlling diborane concentration in boron doping gases.

[0005] Embodiments of the present disclosure relate generally to the field of electronic device manufacturing, and more particularly to a processing system, diborane sensor, and method used to deliver a doping gas mixture having a desired diborane concentration to a processing space of a processing chamber.

[0006] In one embodiment, a borane concentration sensor includes a body and a plurality of windows, where individual ones of the plurality of windows are disposed at opposing ends of the body, and where the body and the plurality of windows collectively define a cell space. The borane concentration sensor further includes a radiation source disposed outside the cell space proximate a first window of the plurality of windows, and a first radiation detector disposed outside the cell space proximate a second window of the plurality of windows.

[0007] In another embodiment, a method for processing a substrate includes determining a diborane concentration in a gas sample taken from a gas conduit fluidly coupling a first gas source and a processing chamber, where determining the diborane concentration includes using an optical sensor. The method further includes mixing a boron doping gas having a desired diborane concentration by varying a flow rate of a first gas from a first gas source, a second gas from a second gas source, or both, and supplying the boron doping gas to a processing space of the processing chamber.

[0008] In another embodiment, a processing system is provided that features a computer-readable medium having stored thereon instructions for a method of processing a substrate. The method includes determining a diborane concentration in a gas sample taken from a gas conduit fluidly coupling a first gas source and a processing chamber, where determining the diborane concentration includes using an optical sensor. The method further includes mixing a boron doping gas having a desired diborane concentration by varying a flow rate of a first gas from the first gas source, a second gas from a second gas source, or both, and supplying the boron doping gas to a processing space of the processing chamber.

[0009] In order that the features of the present disclosure described above may be understood in detail, a more particular description of the present disclosure briefly summarized above may be obtained by reference to embodiments, some of which are illustrated in the accompanying drawings. It should be noted, however, that the accompanying drawings show only typical embodiments of the present disclosure, and therefore should not be considered as limiting the scope of the present disclosure, since the present disclosure may admit of other equally effective embodiments.

1 is a schematic cross-sectional view of a substrate processing system configured to perform the methods described herein, according to one embodiment. 2 is a schematic cross-sectional view of an optical sensor that may be used with the substrate processing system described in FIG. 1 according to an embodiment. 2 is a schematic cross-sectional view of an optical sensor that may be used with the substrate processing system described in FIG. 1 according to another embodiment. [0013] FIG. 1 is a graph showing a UV (ultraviolet) absorption spectrum of diborane. 1 is a graph showing an IR (infrared) absorption spectrum of diborane. 1 is a graph showing an IR (infrared) absorption spectrum of tetraborane. 1 is a graph that illustrates a schematic representation of the attenuation of radiation passing through a gas sample having various concentrations of diborane and tetraborane, according to one embodiment. 2 is a schematic cross-sectional view of an optical sensor that may be used with the substrate processing system described in FIG. 1 according to another embodiment. [0018] FIG. 2 is a schematic cross-sectional view of an optical sensor that may be used with the substrate processing system described in FIG. 1 according to another embodiment. 6 is a graph that illustrates a schematic representation of the attenuation of radiation passing through a gas sample having various concentrations of diborane and tetraborane, in accordance with another embodiment; [0020] FIG. 1 is a flow diagram illustrating a method for processing a substrate, according to one embodiment.

[0021] For ease of understanding, wherever possible, identical reference numbers have been used to designate identical elements common to the figures. It is believed that elements and features of one embodiment may be beneficially incorporated in other embodiments without further description.

[0022] Embodiments of the present disclosure relate generally to the field of electronic device manufacturing. In particular, embodiments herein relate to a processing system, a borane concentration sensor, and a method used to deliver a boron doping gas having a desired diborane concentration to a processing space of a processing chamber.

[0023] In a typical semiconductor device manufacturing process for depositing a boron doping material, diborane is supplied to a processing space of a processing chamber from a diborane gas source. The diborane gas source is often a pressurized cylinder containing diborane and a diluent gas, such as hydrogen ( _H2 ), argon (Ar), nitrogen ( _N2 ), or helium (He). Unfortunately, over time, the diborane in the cylinder decomposes into hydrogen and higher boranes, such as tetraborane, resulting in undesirable and uncontrollable variations in the ratio of diborane to diluent gas supplied to the processing chamber. Thus, embodiments herein compensate for variations in diborane concentration from the diborane gas source by further mixing the gas provided by the pressurized cylinder with additional diluent gas to provide a boron doping gas having a desired and known diborane concentration.

[0024] Here, the concentration of diborane in the boron doping gas is desirably controlled using in situ measurements made by one or more of the borane concentration sensors provided herein. Typically, the one or more borane concentration sensors are optical absorption-based sensors, i.e., optical spectrometers. The optical absorption-based sensors are configured to selectively measure the absorption of UV or IR radiation (emitted by a radiation source of the sensor) by borane molecules, such as diborane, tetraborane, or both, in the gas sample. The concentration of one or both of the diborane and tetraborane molecules is then determined from the measured absorption.

[0025] Figure 1 is a schematic cross-sectional view of a substrate processing system 100 configured to perform the methods described herein, according to one embodiment. Processing system 100 features a processing chamber 101 and a precursor delivery system 102. Other processing chambers that can be used in combination with precursor delivery system 102 to perform the methods described herein include processing chambers in a Producer® ETERNA CVD® system, an Ultima HDP CVD® system, or a Producer® XP Precision™ CVD system (all available from Applied Materials, Inc., Santa Clara, Calif.), as well as suitable processing chambers from other manufacturers.

[0026] The processing chamber 101 includes a chamber lid assembly 103, one or more sidewalls 104, and a chamber base 105. The chamber lid assembly 103 includes a chamber lid 106, a showerhead 107 disposed within the chamber lid 106, and an electrical insulation ring 108 interposed between the chamber lid 106 and the one or more sidewalls 104. The showerhead 107, the one or more sidewalls 104, and the chamber base 105 collectively define a processing space 109. A gas inlet 110 disposed through the chamber lid 106 is fluidly coupled to the precursor delivery system 102. The showerhead 107 has a plurality of openings 111 disposed therethrough and is used to uniformly distribute processing gases provided by the precursor delivery system 102 into the processing space 109. In some embodiments, the showerhead 107 is electrically coupled to a first power source 112, such as an RF power source, that provides power to ignite and maintain a plasma 113 of the process gas via capacitive coupling with the process gas. In other embodiments, the process chamber 101 includes an inductive plasma generator, and the plasma is generated via inductive coupling of RF power to the process gas. In some embodiments, the process chamber is not a plasma processing chamber.

[0027] Here, the processing space 109 is fluidly coupled to a vacuum source, such as one or more dedicated vacuum pumps, via a vacuum outlet 114, which maintains the processing space 109 at subatmospheric pressure and evacuates processing and other gases therefrom. A substrate support 115 disposed within the processing space 109 is disposed on a movable support shaft 116 that sealingly extends through the chamber base 105, surrounded by a bellows (not shown) in the region below the chamber base 105. Typically, the processing chamber 101 is configured to facilitate transfer of a substrate 117 to and from the substrate support 115 through an opening 118 in one of the one or more side walls 104, which is sealed with a door or valve (not shown) during substrate processing.

[0028] In some embodiments, a substrate 117 disposed on a substrate support 115 is maintained at a desired processing temperature using one or both of a heater, such as a resistive heating element 119, and one or more cooling channels 120 disposed within the substrate support 115. Typically, the one or more cooling channels 120 are fluidly coupled to a coolant source (not shown), such as a modified water source or a refrigerant source having a relatively high electrical resistance.

[0029] The precursor delivery system 102 features a diborane gas source (e.g., first gas source 121), a diluent gas source (e.g., second gas source 122), and first and second supply conduits 123a and 123b fluidly coupling the first and second gas sources 121 and 122 to a mixing point 124. The mixing point 124 is fluidly coupled to the process chamber 101 via a third supply conduit 123c. The precursor delivery system 102 further includes one or more borane concentration sensors 125, one or more flow controllers 126a-c, and one or more pressure sensors 127, each coupled to the supply conduits 123a-c, either upstream of the mixing point, downstream of the mixing point, or both.

[0030] During substrate processing, a first gas containing an unknown concentration of diborane is flowed from a first gas source 121 into a first supply conduit 123a, and a second gas containing a diluent is flowed from a second gas source 122 into a second supply conduit 123b. Typically, the second gas (e.g., _H2 ) does not react with diborane. The first and second gases mix at a mixing point 124 to produce a boron doping gas. The boron doping gas flows from the mixing point 124 through a third supply conduit 123c fluidly coupled therebetween into the process space 109. One or more borane concentration sensors 125 are used to determine the concentration of diborane in the first gas from a point upstream of the mixing point 124, to determine the concentration of diborane in the boron doping gas (a mixture of the first gas and the second gas) at a point downstream of the mixing point, or both. In some embodiments, one or more of the borane concentration sensors 125 are used to determine the concentration of tetraborane in the first gas or the boron doping gas. The diborane and/or tetraborane concentrations are communicated to a system controller 130 of the processing system 100, which adjusts the flow rate of the first gas or/and the second gas using a respective first flow controller 126a or second flow controller 126b.

[0031] The system controller 130 includes a programmable central processing unit (CPU 131) operable with memory 132 (e.g., non-volatile memory) and support circuits 133. The support circuits 133 are typically coupled to the CPU 131 and include caches, clock circuits, input/output subsystems, power supplies, and the like, and combinations thereof, coupled to the various components of the processing system 100 to facilitate their control. The CPU 131 is one of any form of general-purpose computer processor used in industrial environments, such as programmable logic controllers (PLCs), to control the various components and sub-processors of the processing system 100. The memory 132 coupled to the CPU 131 is non-transient and is typically one or more of readily available memory, such as random access memory (RAM), read-only memory (ROM), a floppy disk drive, a hard disk, or any other form of digital storage (local or remote).

[0032] Typically, memory 132 takes the form of a computer-readable storage medium (e.g., non-volatile memory) that contains instructions that, when executed by CPU 131, facilitate operation of processing system 100. The instructions in memory 132 take the form of a program product, such as a program that implements the methods of the present disclosure. The program code may conform to any one of a number of different programming languages. In one example, the present disclosure may be implemented as a program product stored on a computer-readable storage medium for use with a computer system. The program(s) of the program product define the functions of the embodiments, including the methods described herein.

[0033] Exemplary computer-readable storage media include, without limitation, (i) non-writable storage media in which information is permanently stored (e.g., a read-only memory device internal to a computer, such as a CD-ROM disk readable by a CD-ROM drive, a flash memory, a ROM chip, or any type of solid-state non-volatile semiconductor memory), and (ii) writable storage media in which substitute information is stored (e.g., a floppy disk or a hard disk drive in a diskette drive, or any type of solid-state random access semiconductor memory). Such computer-readable storage media, when carrying computer-readable instructions that direct the functions of the methods described herein, are embodiments of the present disclosure. In other embodiments, the methods described herein, or portions thereof, are performed by one or more application-specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), or other types of hardware implementations. In some other embodiments, the processes described herein are performed by a combination of software routines, ASICs, FPGAs, or other types of hardware implementations.

[0034] Here, one or more of the borane concentration sensors 125 are optical sensors configured to selectively measure the attenuation of one or more specific wavelengths of introduced radiation, i.e., one or more target wavelengths, passing through a gas sample disposed therein. The target wavelength(s) correspond to an absorption peak in the absorption spectrum of the molecular species being measured, i.e., the target molecular species, such as diborane or tetraborane. As the concentration of the target molecular species in the sample increases or decreases, the total absorption of the target wavelength(s) also increases or decreases, and thus the attenuation of the target wavelength(s) of radiation passing therethrough increases or decreases. In embodiments herein, the selective attenuation measurements are used to determine the concentration of the target molecular species in the gas sample.

[0035] Figures 2A-2B are schematic cross-sectional views of optical sensors 200a and 200b, respectively, that may be used as one or more of the borane concentration sensors 125 described in Figure 1, according to one embodiment. Figure 3 is a graph 300 illustrating a UV absorption spectrum 301 of diborane, shown here as absorption cross section ( ^cm2 /molecule) over a range of wavelengths (nm) in the UV spectrum. Figure 4A is a graph 400a illustrating an IR absorption spectrum 401 of diborane, shown here as absorbance (Au.) over a range of wavelengths (μm) in the IR spectrum. Figure 4B is a graph 400b illustrating an IR absorption spectrum 403 of tetraborane over a range of wavelengths (μm) in the IR spectrum. As shown in Figures 3 and 4A, the UV absorption spectrum 301 and IR absorption spectrum 401 of diborane include multiple UV absorption peaks 302 and IR absorption peaks 402, respectively. In Figure 4B, the IR absorption spectrum 403 of tetraborane includes multiple IR absorption peaks 404.

[0036] Here, one or a combination of optical sensors 200a and 200b are used to determine the concentration of diborane, tetraborane, or both, in a gas sample by selectively measuring the attenuation of one or more target wavelengths of radiation passing therethrough. In embodiments herein, the target wavelengths correspond to absorption peaks 302 or 402 of diborane in the UV absorption spectrum 301 or IR absorption spectrum 401, respectively, or absorption peak 404 in the IR absorption spectrum 403 of tetraborane.

2A, the optical sensor 200a features a body 202 and a number of windows (two windows 204a and 204b are shown), where individual ones of the windows 204a and 204b are disposed at opposing ends of the body 202 and collectively define a cell space 206 with the body 202. The cell space 206 is in fluid communication with a gas inlet 208 and a gas outlet 210. The optical sensor 200 further includes a radiation source 212, one or more radiation detectors 214a-b, and one or more optical filters 216a-b. In some embodiments, the optical sensor 200 or individual components thereof are disposed on and electrically coupled to a printed circuit board (PCB) 217. Typically, the radiation source 212 and the one or more radiation detectors 214a-b are disposed outside the cell space 206, at or near opposing ends of the body 202. For example, here, the radiation source 212 is disposed outside the cell volume 206 near a first window 204a at a first end of the body 202. One or more radiation detectors 214a-b are disposed at or near a second end of the body 202 in close proximity to one or more optical filters 216a-b interposed between the second window 204b and the one or more radiation detectors 214a-b.

[0038] Each of the plurality of windows 204a-b is formed from a material suitable for transmission of the broad band of UV or IR radiation emitted by the radiation source 212. Examples of suitable window materials include _MgF2 , KBr, sapphire, or combinations thereof. The broad band of UV or IR radiation emitted by the radiation source includes the target UV or IR wavelengths measured by the one or more radiation detectors 214a-b. In some embodiments, the radiation source 212 comprises one or more UV lamps or one or more UV laser sources configured to emit UV radiation including wavelengths of 132 nm or less, e.g., 115 nm or less. In other embodiments, the radiation source 212 comprises one or more IR lamps or one or more IR laser sources configured to emit IR radiation including wavelengths of 3.831 μm or greater, such as 3.968 μm or greater, 6.250 μm or greater, 8.532 μm or greater, or 10.256 μm or greater. In other embodiments, the radiation source 212 includes a UV lamp or a UV laser source configured to emit UV radiation including wavelengths of 132 nm or less, such as 115 nm or less, and an IR lamp or an IR laser source configured to emit IR radiation including wavelengths of 3.831 μm or more, such as 3.968 μm or more, 6.250 μm or more, 8.532 μm or more, or 10.256 μm or more.

[0039] Here, a gas sample including diborane molecules 218, diluent gas molecules 220, and tetraborane molecules 222 flows into the cell volume 206 through an inlet 208 and flows out of the cell volume 206 through an outlet 210. In some embodiments, the optical sensor 200 is coupled to a supply conduit, such as one of the supply conduits 123a-c described in FIG. 1. In some embodiments, both the inlet 208 and the outlet are fluidly coupled to the supply conduits 123a-c. In some embodiments, the outlet 210 is fluidly coupled to an exhaust conduit (not shown) that exhausts the gas sample from the cell volume 206. In some embodiments, the optical sensor 200 further includes a pressure sensor 224 fluidly coupled to the cell volume 206.

[0040] In some embodiments, the optical sensor 200a is configured to determine a concentration of diborane molecules 218 in a gas sample. To determine a concentration of diborane molecules 218 in a gas sample, radiation from the radiation source 213 is transmitted simultaneously along a first optical path and a second optical path. The first optical path is used to selectively measure the attenuation of a target wavelength of radiation. The target wavelength of radiation corresponds to a UV absorption peak 302 (shown in FIG. 3) or an IR absorption peak 402 (shown in FIG. 4A) of the diborane molecules 218. Here, the target wavelength corresponding to the UV absorption peak 302 is typically within about +/- 2 nm of 115 nm or 132 nm. The target wavelength corresponding to the IR absorption peak 402 is typically within about +/- 10 nm of 3.831 μm, 3.968 μm, 6.25 μm, 8.532 μm, or 10.253 μm.

[0041] In some embodiments, the optical sensor 200a is configured to determine a concentration of tetraborane molecules 222 in a gas sample. In these embodiments, the first optical path is configured to selectively measure a target wavelength of radiation that corresponds to an IR absorption peak 404 (shown in FIG. 4B) of the tetraborane molecules 222. A suitable target wavelength for determining tetraborane is within +/- 10 nm of the IR absorption peak 404 of the tetraborane IR absorption spectrum 403, for example, within about +/- 10 nm of about 4.68 μm or about 8.85 μm.

[0042] A second optical path is used to selectively measure the intensity of the radiation at a reference wavelength to provide a reference intensity measurement. Typically, the reference wavelength does not correspond to an absorption peak of a molecular species expected to be found in the gas sample. The reference intensity measurement is used to compensate for environmental, electrical, and mechanical variations that affect the first and second radiation detectors 214a-b equally, such as variations in the intensity of the radiation provided by the radiation source 212 and variations in environmental pressure and temperature.

[0043] Here, the first optical path extends from the radiation source 212 to the first radiation detector 214a and successively includes the radiation source 212, the first window 204a, the cell space 206, the second window 204b, and the first radiation detector 214a. In some embodiments, in which the radiation source 212 is an IR radiation source, the first optical path further includes a first optical filter 216a disposed between the second window 204b and the first radiation detector 214a. The first optical filter 216a selectively transmits radiation at a target wavelength corresponding to the IR absorption peak 402 (FIG. 4) of the diborane molecule 218. In some embodiments, the first optical filter 216a is an optical bandpass filter having a central transmission wavelength λ _C and a bandwidth λ _W. The central transmission wavelength λ _C of the suitable filter corresponds to the desired target wavelength, i.e., the IR absorption peak 402 of the diborane molecule 218. In some embodiments where the optical sensor 200a is configured to determine a concentration of diborane molecules, the first optical filter 216a has a central transmission wavelength λ _C that corresponds to one of the target wavelengths of 3.831 μm, 3.968 μm, 6.25 μm, 8.532 μm, or 10.253 μm. In some embodiments, the central transmission wavelength λ _C is within about +/- 250 nm, such as within about +/- 100 nm, or such as within about +/- 50 nm, of the corresponding target wavelength. In some embodiments where the optical sensor 200a is configured to determine a concentration of tetraborane molecules, the first optical filter 216a has a central transmission wavelength λ _C1 that is within about +/- 250 nm, about +/- 100 nm, or about +/- 50 nm of the IR absorption peak 404 (e.g., about 4.680 μm or about 8.850 μm). In some embodiments, the first optical filter 216a has a bandwidth λ _W of about 1 μm or less, such as about 900 nm or less, 800 nm or less, 700 nm or less, 600 nm or less, for example about 500 nm or less.

[0044] In some embodiments, for example when the radiation source 212 is a UV radiation source, the first optical path does not include the first optical filter 216a.

[0045] Here, the second optical path extends from the radiation source 212 to the second radiation detector 214b and successively includes the radiation source 212, the first window 204a, the cell space 206, the second window 204b, the second optical filter 216b, and the second radiation detector 214b. The selectivity of the second optical filter 216b transmits radiation that does not correspond to the absorption peak of diborane or the desired diluent gas. In other words, the second optical filter 216b excludes wavelengths of radiation that correspond to the absorption peak of diborane or the desired diluent gas.

[0046] Figure 2B is a schematic cross-sectional view of an optical sensor 200b configured to determine the concentration of both diborane and tetraborane in a gas sample disposed therein. Here, the optical sensor 200b is similar to the optical sensor 200a described in Figure 2a (when configured to determine the diborane concentration) and further includes a third optical path used to determine the tetraborane concentration. The third optical path extends from a radiation source 212 (here an IR radiation source) to a third radiation detector 214c. The third optical path successively includes the radiation source 212, the first window 204a, the cell space 206, the second window 204b, the third optical filter 216c, and the third radiation detector 214c. Here, the third optical filter 216c has a central transmission wavelength λ _C within about +/- 250 nm, about +/- 100 nm, or about +/- 50 nm of the IR absorption peak 404 of tetraborane (e.g., about 4.680 μm or about 8.850 μm). In some embodiments, the third optical filter 216c has a bandwidth λ _W of about 1 μm or less, such as about 900 nm or less, 800 nm or less, 700 nm or less, 600 nm or less, e.g., about 500 nm or less.

[0047] Figure 5 is a graph 500 that illustrates one or more measurements made using an optical sensor, where the optical sensor is one of the optical sensors 200a or 200b as described in Figures 2A and 2B, respectively. The graph 500 illustrates generally absorption measurements of three different gas samples 501a-c having different diborane concentrations, where radiation from the radiation source 212 is transmitted along each of the two or three optical paths as described in Figures 2A and 2B, respectively. The optical paths include at least the radiation source 212, the first window 204a, the cell space 206 in which one of the gas samples 501a-c is disposed, and the second window 204b. The first optical path further includes a first optical filter 216a and a first radiation detector 214a. Here, the first optical filter 216a has a central transmission wavelength λ _C1 and a bandwidth λ _W1 corresponding to the IR absorption peaks of diborane or tetraborane, as described above and shown in Figures 4A and 4B, respectively. The second optical path further includes a second optical filter 216b and a second radiation detector 214b. The second optical filter 216b has a central transmission wavelength λ _C2 and a bandwidth λ _W2 that do not correspond to the absorption peaks of molecular species expected to be found in the gas sample.

[0048] If used, the third optical path further includes a third optical filter 216c and a third radiation detector 214c. The third optical filter 216c has a central transmission wavelength λ _C3 corresponding to the IR absorption peak of tetraborane and a bandwidth λ _W3 . The central transmission wavelength λ _C2 of the second optical filter 216b may be greater or smaller than the central transmission wavelength λ _C1 of the first optical filter 216a or the central transmission wavelength λ _C3 of the third optical filter 216c. Similarly, the central transmission wavelength λ _C3 of the third optical filter 216c may be greater or smaller than the central transmission wavelength λ _C1 of the first optical filter 216a.

[0049] Typically, the intensity measurements obtained by the second radiation detector 214b, i.e., the reference intensity 503, are used to compensate for environmental, electrical, and mechanical variations that affect the radiation detectors 214a-c equally. As shown, the reference intensity 503 is the same for each of the three gas samples 501a-c, indicating that there is no substantial environmental, electrical, and mechanical variation between the measurements for each sample 501a-c. In some embodiments, the difference between the reference intensity 503 and the intensity for each of the samples 501a-c measured using the first radiation detector 214a, i.e., the attenuation 502a-c, is used to determine the diborane concentration therein. As shown in FIG. 5, the radiation that passed through the first gas sample 501a has the highest attenuation 502a between the radiation transmitted along the first and second optical paths, and therefore has the highest diborane concentration among the multiple samples 501a-c. The radiation that passes through the third gas sample 501c has the lowest attenuation 502c and therefore the lowest diborane concentration.

[0050] The radiation that passed through the first gas sample 501a has the lowest attenuation 503a between the radiation transmitted along the second and third optical paths, and therefore has the lowest tetraborane concentration among the plurality of samples 501a-c. As the diborane in the pressurized gas cylinder decomposes over time to produce free hydrogen and tetraborane, the attenuation 503a-c measured using the third radiation detector 214c increases as the attenuation 502a-c decreases. Thus, the radiation that passed through the third gas sample 501c has the highest attenuation 503c, and therefore has the highest tetraborane concentration among the plurality of samples 501a-c.

6A and 6B are schematic cross-sectional views of optical sensors 600a and 600b, respectively, that may be used as one or more of the borane concentration sensors 125 described in FIG. 1 according to another embodiment. In FIG. 6A, the optical sensor 600a features a body 602, a plurality of windows 604a-b disposed at opposite ends of the body 602, and a divider 605 that collectively define a first cell space 606a and a second cell space 606b. The first cell space 606a is in fluid communication with an inlet 608 used to supply a gas sample thereto, and an outlet 610 used to exhaust the gas sample therefrom. The second cell space 606b is fluidly isolated from the first cell space 606a by the divider 605 disposed therebetween. The optical sensor 600a further includes a radiation source 612, one or more radiation detectors 614a-b, and one or more optical filters 616a-b.

[0052] In some embodiments, the optical sensor 600a or individual components thereof are disposed on and electrically coupled to a printed circuit board (PCB) 617. Typically, the radiation source 612 and one or more radiation detectors 614a-b are disposed at or near opposing ends of the body 602, outside the first and second cell spaces 606a-b. For example, here, the radiation source 612 is disposed near a first window 604a at a first end of the body 602, outside the first and second cell spaces 606a-b. The one or more radiation detectors 614a-b are disposed at or near a second end of the body 602, proximate one or more optical filters 616a-b interposed between the second window 604b and the one or more radiation detectors 614a-b.

[0053] Each of the plurality of windows 604a-b is formed from a material suitable for transmission of the broad band of UV or IR radiation emitted by the radiation source 612. Examples of suitable window materials include _MgF2 , KBr, sapphire, or combinations thereof. The broad band of UV or IR radiation emitted by the radiation source includes the target UV or IR wavelengths measured by the one or more radiation detectors 614a-b. In some embodiments, the radiation source 612 comprises one or more UV lamps or one or more UV laser sources configured to emit UV radiation including wavelengths of 132 nm or less, e.g., 115 nm or less. In other embodiments, the radiation source 612 comprises one or more IR lamps or one or more IR laser sources configured to emit IR radiation including wavelengths of 3.831 μm or greater, such as 3.968 μm or greater, 6.250 μm or greater, 8.532 μm or greater, or 10.256 μm or greater.

[0054] Typically, the gas sample, including diborane molecules 218, diluent gas molecules 220, and tetraborane molecules 222, enters the first cell volume 606a through an inlet 608 and exits the first cell volume 606a through an outlet 610. In some embodiments, the optical sensor 600 is coupled to a supply conduit, such as one of the supply conduits 123a-c depicted in FIG. 1. In these embodiments, the inlet 608 is fluidly coupled to the supply conduits 123a-c, and the outlet 610 is fluidly coupled to an exhaust conduit (not shown) that exhausts the gas sample from the first cell volume 606a.

[0055] To determine the concentration of diborane molecules 218 or tetraborane molecules 222 in the gas sample, radiation from the radiation source 612 is transmitted simultaneously along a first optical path and a second optical path. The first optical path is used to selectively measure the attenuation of a target wavelength of radiation corresponding to the UV absorption peak 302 (shown in FIG. 3) or the IR absorption peak 402 or 404 (shown in FIGS. 4A and 4B, respectively) of the diborane molecules 218 or tetraborane molecules 222. The second optical path is used to selectively measure the intensity of the radiation at a reference wavelength to provide a reference intensity measurement, where the reference wavelength may be the same as or different from the absorption peak of a molecular species expected to be present in the gas sample.

[0056] Here, the first optical path extends from the radiation source 612 to the first radiation detector 614a. In some embodiments, for example when the radiation source 612 is an IR radiation source, the first optical path successively includes the radiation source 612, the first window 604a, the first cell space 606a, the second window 604b, the first optical filter 616a, and the first radiation detector 614a. The first optical filter 616a selectively transmits radiation of a target wavelength corresponding to the IR absorption peak 402 of the diborane molecule 218 (FIG. 4A) or the IR absorption peak 404 of the tetraborane molecule 222 (FIG. 4B). In some embodiments, the first optical filter 616a is an optical bandpass filter having a central transmission wavelength λ _C and a bandwidth λ _W. In some embodiments, the first optical filter 216a has a central transmission wavelength λ _C1 corresponding to a target wavelength of diborane or tetraborane, as described above and shown in Figures 4A-4B, respectively. In some embodiments, the first optical filter 616a has a bandwidth λ _W of about 1 μm or less, such as about 900 nm or less, 800 nm or less, 700 nm or less, 600 nm or less, e.g., about 500 nm or less.

[0057] The second optical path extends from the radiation source 612 to the second radiation detector 614b. The second optical path includes, in sequence, the radiation source 612, the first window 604a, the second cell space 606b, the second window 604b, the second optical filter 616b, and the second radiation detector 614b. The second optical filter 616b may allow transmission of radiation that may or may not correspond to an absorption peak of diborane or a desired diluent gas. Typically, the second cell space 606b is maintained at reduced pressure or contains an inert gas 618.

[0058] In some embodiments, such as those in which the radiation source is a UV radiation source, one or both of the first or second optical paths do not include the respective first or second optical filters 616a-b.

[0059] In some embodiments, the optical sensor 600a further includes a pressure sensor 622 fluidly coupled to the first cell volume 606a that is used to monitor the pressure of a gas sample disposed therein. In some embodiments, the optical sensor further includes one or more mirrors 624 that are used to direct radiation from the radiation source 612 through the first and second cell volumes 606a-b.

[0060] FIG. 6B is a schematic cross-sectional view of an optical sensor 600b configured to determine the concentration of both diborane and tetraborane in a gas sample disposed therein. Here, the optical sensor 600b is similar to the optical sensor 600a described in FIG. 6a (when configured to determine the diborane concentration) and further includes a third optical path used to determine the tetraborane concentration. The third optical path extends from a radiation source 612 (here an IR radiation source) to a third radiation detector 614c. The third optical path successively includes the radiation source 612, the first window 604a, the cell space 606a, the second window 604b, the third optical filter 616c, and the third radiation detector 614c. The third optical filter 616c selectively transmits radiation at a target wavelength corresponding to the IR absorption peak 404 (FIG. 4B) of the tetraborane molecule 222 as described above with respect to the third optical filter 216c of FIG. 2B.

[0061] In some embodiments, the optical sensor described herein is calibrated before being installed in a processing system. Typically, the optical sensor is calibrated using a low toxicity (relative to diborane) proxy gas that has a UV or IR absorption peak similar to that of diborane. Examples of suitable proxy gases include _NH3 , methanethiol, ethanethiol, or combinations thereof.

[0062] Figure 7 is a graph 700 showing measurements taken using an optical sensor (here optical sensor 600b as shown in Figure 6B) of three gas samples 701a-c, each having different diborane and tetraborane concentrations, where radiation from a radiation source 612 is transmitted along an optical path as shown in Figure 6B. The first optical path includes the radiation source 612, a first window 604a, a first cell volume 606a having one of the gas samples 701a-c disposed therein, a second window 604b, a first optical filter 616a, and a first radiation detector 614a. The first optical filter 616a has a central transmission wavelength λ _C1 and a bandwidth λ _W1 that correspond to the above-mentioned IR absorption peak of diborane shown in Figure 4A.

[0063] The second optical path includes a radiation source 612, a first window 604a, a second cell space 606b having an inert gas 618 disposed therein, a second window 604b, a second optical filter 616b, and a second radiation detector 614b. The second optical filter 616b has a central transmission wavelength λ _C2 and a bandwidth λ _W2 that may or may not correspond to an absorption peak of a molecular species expected to be found in the gas sample. The third optical path includes a radiation source 612, a first window 604a, a first cell space 606a having one of the gas samples 701a-c disposed therein, a second window 604b, a third optical filter 616c, and a third radiation detector 614c. The third optical filter 616c has a central transmission wavelength λ _C3 and a bandwidth λ _W3 that correspond to the IR absorption peak of tetraborane described above and shown in FIG. 4B. Here, the central transmission wavelength λ _C2 of the second optical filter 616b may be greater than, less than, or equal to the central transmission wavelength λ _C1 of the first optical filter 616a, and the central transmission wavelength λ _C3 of the third optical filter 616c may be greater than or less than the central transmission wavelength λ _C1 of the first optical filter 616a or the central transmission wavelength λ _C2 of the second optical filter 616b.

[0064] Typically, the intensity measurement obtained by the second radiation detector 614b, i.e., the reference intensity 703, is used to compensate for environmental, electrical, and mechanical variations that affect the first and second radiation detectors 614a-b equally. The difference between the reference intensity 703 and the intensity for each of the samples 701a-c transmitted along the first optical path, i.e., the attenuation 702a-c, is then used to identify the diborane concentration in each sample. The attenuation 703a-c between the reference intensity 703 and the intensity for each of the samples 701a-c transmitted along the third optical path is used to identify the tetraborane concentration in each sample. As shown in FIG. 7, among the three samples 701a-c, the radiation that passed through the first gas sample 701a has the highest attenuation 702a, and therefore the highest diborane concentration, and the lowest attenuation 703a, and therefore the lowest tetraborane concentration. Of the three samples 701a-c, the radiation passing through the third gas sample 701c has the lowest attenuation 702c and the highest attenuation 703c, and therefore the lowest diborane concentration and the highest tetraborane concentration.

[0065] FIG. 8 is a flow diagram illustrating a method of processing a substrate, according to one embodiment. In operation 801, the method 800 includes determining a diborane concentration in a gas sample taken from a gas conduit fluidly coupling a first gas source and a processing chamber, where determining the diborane concentration includes using an optical sensor, such as one of the optical sensors 200a-b or 600a-b illustrated in FIGS. 2A-2B or 6A-6B, respectively. In operation 802, the method 800 includes mixing a boron doping gas having a desired diborane concentration by varying a flow rate of a first gas from a first gas source, a second gas from a second gas source, or both. In operation 803, the method includes supplying the boron doping gas to a processing space of the processing chamber.

[0066] In some embodiments, method 800 further includes determining a tetraborane concentration in a gas sample taken from a gas conduit fluidly coupling the first gas source and the process chamber. In some embodiments, determining the tetraborane concentration includes using the same optical sensor used to determine the diborane concentration, or using a different optical sensor, such as using one or a combination of optical sensors 200a-b and 600a-b described herein.

[0067] The systems and methods provided herein advantageously enable in situ monitoring and control of diborane concentration in the boron doping gas, reducing undesirable variations in boron doping from substrate to substrate.

[0068] While the foregoing is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof, the scope of which is defined by the following claims.

Claims (18)

Main unit,
a plurality of windows, each of the plurality of windows being disposed at an opposing end of the body, the body and the plurality of windows defining a cell space;
a radiation source disposed outside the cell volume and adjacent a first window of the plurality of windows ;
a first radiation detector disposed outside the cell volume and adjacent a second window of the plurality of windows ;
a first optical filter interposed between the first radiation detector and the second window; and
a second radiation detector, and a second optical filter disposed between the radiation source and the second radiation detector.
Equipped with
A borane concentration sensor, wherein the first optical filter has a central transmission wavelength λ _C within about +/- 250 nm of an IR absorption peak of diborane , and the second optical filter has a central transmission wavelength within about +/- 250 nm of an IR absorption peak of tetraborane . 2. The borane concentration sensor of claim 1, wherein one or both of the first window and the second window are formed from _MgF2 , KBr, sapphire, or combinations thereof. 2. The borane concentration sensor of claim 1 , wherein the first optical filter has a central transmission wavelength λ _C within about +/- 250 nm of an IR absorption peak of diborane or within about +/- 250 nm of an IR absorption peak of tetraborane. 1. A method for processing a substrate, comprising:
determining a diborane concentration in a gas sample taken from a gas conduit fluidly connecting the first gas source and the process chamber using an optical sensor;
mixing a boron doping gas having a desired diborane concentration by varying a flow rate of a first gas from the first gas source, a second gas from a second gas source, or both based on the determined diborane concentration ; and supplying the boron doping gas to a process space of the process chamber. The optical sensor comprises:
Main unit,
a plurality of windows, each of the plurality of windows being disposed at an opposing end of the body, the body and the plurality of windows defining a cell space;
5. The method of claim 4, further comprising: a radiation source disposed outside the cell space and adjacent to a first window of the plurality of windows; and a first radiation detector disposed outside the cell space and adjacent to a second window of the plurality of windows. 6. The method of claim 5 , wherein one or both of the first window and the second window are formed from _MgF2 , KBr, sapphire, or combinations thereof. The method of claim 5 , wherein the optical sensor further comprises a second radiation detector. The method of claim 5 , wherein the optical sensor further comprises a first optical filter interposed between the first radiation detector and the second window. 9. The method of claim 8 , wherein the first optical filter has a central transmission wavelength λ _C within about +/- 250 nm of an IR absorption peak of diborane or within about +/- 250 nm of an IR absorption peak of tetraborane. 9. The method of claim 8, wherein the optical sensor further comprises a second radiation detector and a second optical filter disposed between the radiation source and the second radiation detector, the first optical filter having a central transmission wavelength λ _C within about +/- 250 nm of an IR absorption peak of diborane and the second optical filter having a central transmission wavelength within about +/- 250 nm of an IR absorption peak of tetraborane. 1. A processing system comprising a computer readable medium having stored thereon instructions for a method of processing a substrate, the method comprising:
determining a diborane concentration in a gas sample taken from a gas conduit fluidly connecting the first gas source and the process chamber using an optical sensor;
mixing a boron doping gas having a desired diborane concentration by varying a flow rate of a first gas from the first gas source, a second gas from a second gas source, or both based on the determined diborane concentration ; and supplying the boron doping gas to a process space of the process chamber. The optical sensor comprises:
Main unit,
a plurality of windows, each of the plurality of windows being disposed at an opposing end of the body, the body and the plurality of windows defining a cell space;
12. The processing system of claim 11, comprising: a radiation source positioned outside the cell space and adjacent to a first window of the plurality of windows; and a first radiation detector positioned outside the cell space and adjacent to a second window of the plurality of windows. 13. The processing system of claim 12 , wherein one or both of the first window and the second window of the optical sensor are formed from _MgF2 , KBr, sapphire, or combinations thereof. 13. The processing system of claim 12 , wherein the optical sensor further comprises a first optical filter interposed between the first radiation detector and the second window. 15. The processing system of claim 14 , wherein said first optical filter has a central transmission wavelength λ _C within about +/- 250 nm of an IR absorption peak of diborane or within about +/- 250 nm of an IR absorption peak of tetraborane. 15. The processing system of claim 14, wherein the optical sensor further comprises a second radiation detector and a second optical filter disposed between the radiation source and the second radiation detector, the first optical filter having a central transmission wavelength λ _C within about +/- 250 nm of an IR absorption peak of diborane and the second optical filter having a central transmission wavelength within about +/- 250 nm of an IR absorption peak of tetraborane. The processing system of claim 16 , further comprising the processing chamber. 20. The processing system of claim 16 , wherein the method further comprises determining a concentration of tetraborane in the gas sample using an optical sensor.

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