WO2020106297A1

WO2020106297A1 - Method for determining cleaning endpoint

Info

Publication number: WO2020106297A1
Application number: PCT/US2018/062306
Authority: WO
Inventors: Luc Albarede; Yassine Kabouzi; Jagadeeshwari MANNE
Original assignee: Lam Research Corp
Current assignee: Lam Research Corp
Priority date: 2018-11-21
Filing date: 2018-11-21
Publication date: 2020-05-28
Anticipated expiration: 2021-05-21

Abstract

A method for plasma cleaning a plasma processing chamber is provided. A cleaning gas is flowed into the plasma processing chamber. The cleaning gas is formed into a plasma, wherein the plasma cleans the plasma processing chamber, wherein the plasma becomes a spent gas. The spent gas is exhausted from the plasma processing chamber into a gas cell. Light absorption within the gas cell is measured. A time trace of the measured light absorption within the gas cell is generated. The time trace of the measured light absorption within the gas cell is used to determine an end point for the plasma cleaning of the plasma processing chamber.

Description

METHOD FOR DETERMINING CLEANING ENDPOINT

BACKGROUND

[0001] The present disclosure relates to methods of manufacturing of semiconductor devices. More specifically, the disclosure relates to methods for cleaning plasma processing chambers for manufacturing semiconductor devices.

[0002] During semiconductor wafer processing, plasma processing chambers for manufacturing semiconductor devices are cleaned. The plasma processing chambers may be cleaned using a plasma process between each processed wafer.

SUMMARY

[0003] To achieve the foregoing and in accordance with the purpose of the present disclosure, a method for plasma cleaning a plasma processing chamber is provided. A cleaning gas is flowed into the plasma processing chamber. The cleaning gas is formed into a plasma, wherein the plasma cleans the plasma processing chamber and wherein the plasma becomes a spent gas. The spent gas is exhausted from the plasma processing chamber into a gas cell. Light absorption within the gas cell is measured. A time trace of the measured light absorption within the gas cell is generated. The time trace of the measured light absorption within the gas cell is used to determine an end point for the plasma cleaning of the plasma processing chamber.

[0004] In another manifestation, a controller configured to control a plasma processing chamber is provided. At least one processor is provided. Computer readable media comprises computer readable code for flowing a cleaning gas into the plasma processing chamber, computer readable code for forming the cleaning gas into a plasma, wherein the plasma cleans the plasma processing chamber and wherein the plasma becomes a spent gas, wherein the spent gas is exhausted from the plasma processing chamber into a gas cell, computer readable code for measuring light absorption within the gas cell, computer readable code for generating a time trace of the measured light absorption within the gas cell, and computer readable code for using the time trace of the measured light absorption within the gas cell to determine an endpoint for the plasma cleaning of the plasma processing chamber.

[0005] These and other features of the present disclosure will be described in more detail below in the detailed description of the disclosure and in conjunction with the following figures. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] The present disclosure is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements and in which:

[0007] FIG. 1 is a high level flow chart of an embodiment.

[0008] FIG. 2A is a graph of a full time trace of a broadband signal used in an embodiment.

[0009] FIG. 2B is a graph of the difference between the full time trace of FIG.

2A and a line sputter fit.

[0010] FIG. 3 is a flow chart of another embodiment.

[0011] FIGS. 4A-H are graphs used in multispectral processes in

embodiments.

[0012] FIG. 5 are graphs illustrating a multivariate embodiment.

[0013] FIG. 6 is a schematic view of a plasma processing chamber that may be used in an embodiment.

[0014] FIG. 7 is a more detailed view of a gas cell used in an embodiment.

[0015] FIG. 8 is a computer system that may be used in an embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The present disclosure will now be described in detail with reference to a few preferred embodiments thereof as illustrated in the accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present disclosure. It will be apparent, however, to one skilled in the art, that the present disclosure may be practiced without some or all of these specific details. In other instances, well known process steps and/or structures have not been described in detail in order to not unnecessarily obscure the present disclosure.

[0017] In the manufacturing of semiconductor devices, plasma processing chambers may be used to etch features or deposit layers over wafers. As critical dimensions (CD) shrink, the tolerance of contaminants is reduced. Such contaminants may result from depositions on the inside of the plasma processing chambers.

Improved and more frequent cleaning of the plasma processing chambers helps to remove contaminants deposited on the inside of the plasma processing chambers. A process for cleaning a plasma processing chamber may use a plasma generated from an oxygen containing component and a halogen containing component. For such a cleaning process, if the cleaning process is too short, not enough of the contaminants are removed. If the cleaning process is too long, too much of the plasma processing chamber will be eroded by the cleaning process. A proper end point for the cleaning process would remove enough contaminants and minimize the erosion of the plasma processing chamber.

[0018] Some plasma processing chamber cleaning processes are waferless.

Such a waferless cleaning process exposes a chuck. The exposed chuck is cleaned during the waferless cleaning process. Such a waferless cleaning process may use a lower bias power to reduce erosion of the chuck. Cleaning at a lower bias power reduces the cleaning of contaminants· Some plasma processing chamber cleaning processes are performed with a cleaning wafer. Such a cleaning process covers the chuck. The covered parts of the chuck are not cleaned. A higher bias may be used during the cleaning, since the cleaning wafer protects the covered parts of the chuck from erosion. The higher bias cleans more effectively by removing more

contaminants from the plasma processing chamber.

[0019] To facilitate understanding, FIG. 1 is a high level flow chart of a process used in an embodiment. In this embodiment, a waferless clean is provided. A process wafer is removed from a plasma processing chamber. The cleaning process is performed without covering a chuck in the plasma processing chamber with a cleaning wafer. A cleaning gas is flowed into the plasma processing chamber (step 104). In this example, the cleaning gas comprises 1500-2500 standard cubic centimeters per minute (seem) of oxygen (O2) and 50-100 seem nitrogen trifluoride (NF₃). The cleaning gas is formed into a plasma (step 108). In this example, a pressure of 500-700 millitorr (mTorr) is provided. Radio frequency (RF) power at a frequency of 60 megahertz (MHz) and power of 500-700 watts is provided. In some embodiments, the cleaning gas is only O2. In other embodiments, the cleaning gas comprises O2 and NF₃ or O2 and carbon tetrafluoride (CF4) with the ratio about 2500 seem of O2 to about 100 seem of NF₃ or CF4. Spent gas from the cleaning process is vented as exhaust to a gas cell (step 112). In this example, the spent gas passes through an exhaust pump to the gas cell. Laser light absorption is measured in the gas cell (step 116). A full time trace of the laser light absorption is generated from the measured laser light absorption (step 120). [0020] FIG. 2A is a graph of a full time trace of the laser light absorption generated in an embodiment. The full time trace is used to determine the endpoint (step 124). The intensity graph 204 is a graph of the intensity of a broadband signal over time. A linear plot 208 is a line sputter fit. The line sputter fit is a linear plot 208 of a sputtering trend caused by sputtering of components of the plasma processing chamber instead of the contaminants·

[0021] FIG. 2B is a differential plot 212 of the intensity graph 204, shown in

FIG. 2A, minus the linear plot 208, shown in FIG. 2A. The endpoint 216 is indicated by the location where the differential plot 212 becomes approximately horizontal. Subtracting the linear plot 208 allows the effect of the sputtering from chamber components to be removed in order to determine the endpoint. The cleaning process is stopped when the endpoint is reached (step 128).

[0022] In this example, the measurement of laser light absorption in a gas cell after the gas has been exhausted from the plasma processing chamber provides a contaminant sensitivity of parts per trillion. The gas cell is able to provide an absolute measurement of the concentration of S1F4, SiBr , S1CI4, or other S1X4, by-products that are a direct by-product of most silicon containing etches, in the exhaust. Such a sensitivity is better than contaminant sensitivity provided by an optical emission spectroscopy system (OES). Using the full time trace of absorption allows for the removal of the change of absorption from sputtering of the plasma processing chamber to better detect when the endpoint of the waferless clean is reached.

[0023] The resulting endpoint detection allows for the detection of when the cleaning of the contaminants is complete. The improved endpoint detection removes as much contamination as possible, while minimizing erosion of the plasma processing chamber.

[0024] In another embodiment, after a process wafer is removed, a cleaning wafer is placed over the chuck to provide a clean with a cleaning wafer. A cleaning gas is flowed into the plasma processing chamber (step 104). In this example, the cleaning gas comprises 1200 seem of O and 200 seem NF3 or CF4. The cleaning gas is formed into a plasma (step 108). In this example, a chamber pressure of about 500 mTorr is provided. RF power of 2500 watts at a frequency of 60 MHz and 600 watts at a frequency of 400 (kilohertz) kHz is provided to form the cleaning gas into a plasma. Other embodiments may use a RF power with a frequency of 2 MHz and power of 500 watts and a frequency of 60 MHz at a power of 1500 watts and a chamber pressure of 500 mTorr using the same chemistry. Exhaust from the cleaning process is vented to a gas cell (step 112). In this example, the exhaust passes through an exhaust pump to the gas cell. Laser light absorption is measured in the gas cell (step 116). A full time trace of the laser light absorption is generated from the measured laser light absorption (step 120).

[0025] The cleaning with a wafer allows for a higher bias to be used, while a cleaning wafer protects the chuck from erosion. Such a cleaning with a cleaning wafer provides an improved clean of the plasma processing chamber, except for parts of the chuck covered by the cleaning wafer.

[0026] FIG. 3 is a high level flow chart of a process that may be used in an embodiment that uses both waferless cleaning and cleaning with a wafer. In this embodiment, a wafer is processed in the plasma processing chamber (step 304). The wafer is removed from the plasma processing chamber. A waferless cleaning of the plasma processing chamber is provided (step 308). In this embodiment, the waferless cleaning described above may be used. The wafer processing (step 304) and the waferless cleaning (step 308) may be repeated (step 312) for a plurality of cycles. After a number of cycles, the processing of wafers may be completed (step 316). The plurality of cycles may slowly increase undesirable deposition on the interior of the plasma processing chamber. Laser light absorption within the gas cell is used to determine chamber drift caused by the slowly increasing deposition. Because of such deposition, after a number of cycles, a cleaning with a cleaning wafer in the plasma processing chamber (step 320) is provided. The cleaning with a cleaning wafer in the plasma processing chamber (step 320) may use the process described above. The higher bias allows an improved cleaning. The cleaning wafer prevents or reduces erosion of the chuck covered by the cleaning wafer.

[0027] Using the gas cell to determine the endpoint for both a waferless clean

(step 308) and a cleaning with a cleaning wafer (step 320) provides an improved cleaning process. The improved cleaning process is able to remove more

contaminants, while simultaneously reducing erosion of the processing chamber including the chuck. The gas cell is able to measure concentrations up to parts per trillion. The improved accuracy allows for the improved cleaning process. [0028] In another embodiment, the time trace collects spectral data. The data is collected at a plurality of wavelengths or frequencies within a bandwidth. An intensity measurement may be placed in a matrix according to time and wavelength. For example, within a bandwidth from 200 nm to 900 nm, the intensity may be measured at wavelengths spaced 2 nm apart for the whole bandwidth at time intervals of about a second.

[0029] FIGS. 4A-H are graphs used in various multispectral processes. FIG.

4A is a broadband graph 404 of the intensity integrated over wavelength for a set bandwidth versus time. In FIG. 4A, four times Tl, T2, T3, and T4 are illustrated, although many more measurements are made over time, in order to obtain graph 404. In this example, Tl corresponds to 7 seconds. T2 corresponds to 22 seconds. T3 corresponds to 66 seconds. T4 corresponds to 150 seconds.

[0030] FIG. 4B are spectral graphs of intensity versus wavelength for a bandwidth between wavelengths A and B for times Tl, T2, T3, and T4. Graph 408 is the spectral graph at time Tl. Graph 412 is the spectral graph at time T2. Graph 416 is the spectral graph at time T3. Graph 420 is the spectral graph at time T4.

[0031] FIG. 4C is the spectral graph 408 at time Tl. When the intensity

(height) of the spectral graph 408 is integrated from wavelength A to wavelength B to find the area under spectral graph 408 between wavelength A and wavelength B, the value is equal to the height of Tl shown in FIG. 4 A.

[0032] FIG. 4D is the spectral graph 412 at time T2. When the intensity

(height) of the spectral graph 412 is integrated from wavelength A to wavelength B to find the area under spectral graph 412 between wavelength A and wavelength B, the value is equal to the height of T2 shown in FIG. 4A.

[0033] FIG. 4E is the spectral graph 416 at time T3. When the intensity

(height) of the spectral graph 416 is integrated from wavelength A to wavelength B to find the area under spectral graph 416 between wavelength A and wavelength B, the value is equal to the height of T3 shown in FIG. 4A.

[0034] FIG. 4F is the spectral graph 420 at time T4. When the intensity

(height) of the spectral graph 420 is integrated from wavelength A to wavelength B to find the area under spectral graph 420 between wavelength A and wavelength B, the value is equal to the height of T4 shown in FIG. 4A. [0035] When the slope of graph 404 of the broadband intensity over time is approximately equal to zero, the endpoint is reached. In an embodiment, a threshold difference may be specified. Once the slope is within the threshold distance from zero, the endpoint may be designated. In this example, the endpoint 422, shown in FIG. 4A, is a time between T3 and T4.

[0036] In another embodiment, graphs of intensity versus wavelength are examined to identify bandwidths with highest signal to noise ratios. In some embodiments, bandwidths that encompass the intensity peaks are identified as bandwidths with the highest signal to noise ratios. The identified bandwidths with the highest signal to noise ratios are used to determine the endpoint. By using bandwidths with the highest signal to noise ratio, the identification of the endpoint is improved. In this example, a weighted integral of intensity over the bandwidth is calculated for different times of the time trace. In this example, the weighting is provided by only integrating over specific bandwidths.

[0037] FIG. 4G is the spectral graph 416 at time T3. The bandwidth defined by box 424 is a bandwidth that encompasses an intensity peak region, as shown. Such a bandwidth has a high signal to noise ratio. Such a bandwidth would provide improved endpoint detection.

[0038] In another embodiment, a comparison of intensities at different times for at least two different bandwidths may be used to determine an endpoint. In some embodiments, the at least one of the bandwidths is a bandwidth with an intensity peak. In some embodiments, the comparison of intensities is a ratio of one intensity divided by another intensity. A ratio outside of a threshold may be used to determine an endpoint. FIG. 4H is the spectral graph 416 at time T3. The bandwidth defined by box 428 is a bandwidth that encompasses an intensity peak, as shown. The bandwidth defined by box 432 is a bandwidth that encompasses another intensity peak, as shown. A comparison of the peaks may be used to determine the endpoint. For example, the ratios of the heights of the peaks may be measured over time to determine the endpoint. In another embodiment, one of the boxes may encompass a bandwidth without peaks in order to provide a comparison of a peak intensity with a background intensity.

[0039] It has been found that endpoint detection is improved by comparing peaks or by using a normalization by comparing a peak intensity with a nonpeak intensity. In some embodiments, the improved endpoint detection provides more detailed endpoint detection. In other embodiments, the improved endpoint detection provides endpoint detection at different areas of the chamber. Contaminants may be completely removed from different parts or areas of a plasma processing chamber at different times. As a result, there are different endpoint times for different areas of the plasma processing chamber. By comparing different peaks, the different endpoint times can be measured.

[0040] In another embodiment, a multivariate analysis is used to create a weighting vector. The weighting vector may be expressed as a function or matrix. In one embodiment, the weighting vector provides a greater weight to wavelengths with greater signal to noise ratios and less weight to wavelengths with smaller signal to noise ratios. In another embodiment, the multivariate analysis may be used to provide a weighting vector providing a weighting for each wavelength with respect to the endpoint instead of the signal to noise ratio. A weighted integral of intensity with respect to wavelength or frequency is calculated at different times of the time trace. A change in the integrals over time may be used to determine the endpoint.

[0041] In an example of an embodiment, FIG. 5 illustrates an embodiment that uses a weighting vector determined by multivariate analysis. In this embodiment, principal component analysis (PCA) is the multivariate method used to generate the weighted vectors. In other embodiments, other multivariate methods or time series methods may be used to create weighted vectors. Plot 504 illustrates a weighting vector derived using PCA on a broadband spectrum input. Plot 508 illustrates a weighting vector derived using PCA for a spectrum at the time of a detected endpoint. Graph 512 is the spectral graphs of intensity versus wavelength for a bandwidth between wavelengths A and B, shown in FIG 4B. The different spectrums at different times are multiplied by the different weighting vectors. Plot 516 is a graph of the spectral graphs at different times multiplied by the weighting vector from plot 504. Plot 520 is a graph of the spectral graphs at different times multiplied by the weighting vector from plot 508. The endpoint is indicated as being at a time of about 120 seconds.

[0042] FIG. 6 schematically illustrates an example of a plasma processing chamber 600, which may be used in an embodiment. The plasma processing chamber 600 includes a plasma reactor 602 having a plasma processing confinement chamber 604 therein. A plasma power supply 606, tuned by a match network 608, supplies power to a transformer coupled power (TCP) coil 610 located near a power window 612 to create a plasma 614 in the plasma processing confinement chamber 604 by providing an inductively coupled power. The TCP coil (an upper electrode) 610 may be configured to produce a uniform diffusion profile within the plasma processing confinement chamber 604. For example, the TCP coil 610 may be configured to generate a toroidal power distribution in the plasma 614. The power window 612 is provided to separate the TCP coil 610 from the plasma processing confinement chamber 604 while allowing energy to pass from the TCP coil 610 to the plasma processing confinement chamber 604. A wafer bias voltage power supply 616 tuned by a match network 618 provides power to an electrode 620 to set the bias voltage on the substrate 664. The electrode 620 is used as a chuck to support the substrate 664.

A controller 624 sets points for the plasma power supply 606, gas source/gas supply mechanism 630, and the wafer bias voltage power supply 616.

[0043] The plasma power supply 606 and the wafer bias voltage power supply

616 may be configured to operate at specific radio frequencies such as, for example, 13.56 MHz, 27 MHz, 2 MHz, 60 MHz, 200 kHz, 2.54 GHz, 400 kHz, and 1 MHz, or combinations thereof. Plasma power supply 606 and wafer bias voltage power supply 616 may be appropriately sized to supply a range of powers in order to achieve desired process performance. For example, in one embodiment, the plasma power supply 606 may supply the power in a range of 50 to 5000 Watts, and the wafer bias voltage power supply 616 may supply a bias voltage in a range of 20 to 2000 volts (V). For a bias voltage up to 4 kilovolts (kV) or 5 kV, a power of no more than 25 kilowatts (kW) is provided. In addition, the TCP coil 610 and/or the electrode 620 may be comprised of two or more sub-coils or sub-electrodes, which may be powered by a single power supply or powered by multiple power supplies.

[0044] The gas source/gas supply mechanism 630 is in fluid connection with plasma processing confinement chamber 604 through a gas inlet, such as a shower head 640. The gas inlet may be located in any advantageous location in the plasma processing confinement chamber 604, and may take any form for injecting gas. Preferably, however, the gas inlet may be configured to produce a“tunable” gas injection profile, which allows independent adjustment of the respective flow of the gases to multiple zones in the plasma process confinement chamber 604. The process gases and by-products are removed from the plasma process confinement chamber 604 via a pressure control valve 642 and a pump 644, which also serve to maintain a particular pressure within the plasma processing confinement chamber 604. A Kiyo® tool made by Lam Research Corp. of Fremont, CA, may be used to practice an embodiment. In other examples, a Flex™ tool made by Lam Research Corp. of Fremont, CA, may be used to practice an embodiment.

[0045] In this embodiment, connected to an exhaust pipe 646 after the pump

644, a gas cell 632 is provided. The exhaust pipe 646 exhausts gas flows. An infrared (IR) light source 634 is positioned adjacent to a window in the gas cell 632, so that an IR beam 760 from the IR light source 634 is directed into the gas cell 632. The IR beam 760 can travel through the gas cell 632 multiple times (typically with a pathlength > 1 meter) to achieve ppt detection limits, so that the gas cell 632 is a multi-pass gas cell. The IR light is absorbed by the gas as it travels inside the gas cell 632. An IR detector 636 is positioned adjacent to another window in the gas cell 632 to measure the light absorption level.

[0046] FIG. 7 is a more detailed schematic view of the gas cell 632 of the embodiment, shown in FIG. 6. The exhaust pipe 646 extends from the output of pump 644. The gas cell 632 comprises a gas chamber 704, a first mirror 708, and a second mirror 712. The gas chamber 704, the first mirror 708, and the second mirror 712 define an optical cavity 716. The exhaust pipe 646 causes exhaust to flow into the optical cavity 716 in the gas chamber 704 and then out of the optical cavity 716 through an output port 720. In this embodiment, the flow of the exhaust into and out of the optical cavity 716 is along a linear path. An IR light source 634 in this embodiment is a quantum cascade laser (QCL) IR light source. The IR light source 634 is provided adjacent to a window 728 in the first mirror 708. An output fiber 732 is optically connected between an IR detector 636 and the optical cavity 716 through the second mirror 712. The light can be coupled directly into the gas cell 632 or through optical fibers. Heaters 736 are placed adjacent to the first mirror 708 and the second mirror 712. One or more of the heaters 736 may have heat sensors. The heaters 736 may be electrically connected to and controlled by the controller 624. The heaters 736 may provide temperature data to the controller 624. A first purge ring 740 with a first purge ring channel 742 and a second purge ring 744 with a second purge ring channel 746 are provided and surround the gas chamber 704. The first purge ring 740 is adjacent to the first mirror 708 and has a first purge gas input 748. The second purge ring 744 is adjacent to the second mirror 712 and has a second purge gas input 752. The first purge ring 740 and the second purge ring 744 are in fluid communication with the gas cell 632 and optical cavity 716 through a plurality of purge gas nozzles 756.

[0047] FIG. 8 is a high level block diagram showing a computer system 800, which is suitable for implementing a controller 624 used in embodiments. The computer system may have many physical forms ranging from an integrated circuit, a printed circuit board, and a small handheld device, up to a huge super computer. The computer system 800 includes one or more processors 802, and further can include an electronic display device 804 (for displaying graphics, text, and other data), a main memory 806 (e.g., random access memory (RAM)), storage device 808 (e.g., hard disk drive), removable storage device 810 (e.g., optical disk drive), user interface devices 812 (e.g., keyboards, touch screens, keypads, mice or other pointing devices, etc.), and a communication interface 814 (e.g., wireless network interface). The communication interface 814 allows software and data to be transferred between the computer system 800 and external devices via a link. The system may also include a communications infrastructure 816 (e.g., a communications bus, cross-over bar, or network) to which the aforementioned devices/modules are connected.

[0048] Information transferred via communications interface 814 may be in the form of signals such as electronic, electromagnetic, optical, or other signals capable of being received by communications interface 814, via a communication link that carries signals and may be implemented using wire or cable, fiber optics, a phone line, a cellular phone link, a radio frequency link, and/or other communication channels. With such a communications interface, it is contemplated that the one or more processors 802 might receive information from a network, or might output information to the network in the course of performing the above-described method steps. Furthermore, method embodiments may execute solely upon the processors or may execute over a network such as the Internet in conjunction with remote processors that shares a portion of the processing.

[0049] The term“non-transient computer readable medium” is used generally to refer to media such as main memory, secondary memory, removable storage, and storage devices, such as hard disks, flash memory, disk drive memory, CD-ROM, and other forms of persistent memory and shall not be construed to cover transitory subject matter, such as carrier waves or signals. Examples of computer code include machine code, such as produced by a compiler, and files containing higher level code that are executed by a computer using an interpreter. Computer readable media may also be computer code transmitted by a computer data signal embodied in a carrier wave and representing a sequence of instructions that are executable by a processor.

[0050] It has been unexpectedly found that such methods are successful when concentrations can be measured with an accuracy of parts per billion (ppb) and more preferably parts per trillion (ppt). For low pressure plasma processing systems, it has been found that a post exhaust gas cell with a light path of greater than 1 meter provides the required accuracy. Advantages of placing the gas cell after the exhaust pump are that the gas is denser after the exhaust pump than the gas in the processing chamber. In addition, reflective surfaces are not exposed to the plasma in the processing chamber, so that reflective surfaces would not be degraded by plasma radicals or ions. In other embodiments, visible light or ultra violet (UV) light may be used instead of IR light.

[0051] In various embodiments, the processing the wafer (step 304) may be a plasma process used for etching memory devices such as dynamic random access memory (DRAM) and three dimensional not and (3D-NAND) devices. In various embodiments, the plasma process is an etch process of a silicon containing layer or a low-k dielectric layer. In various embodiments, the RF power may be inductively coupled or capacitively coupled. A Flex™ tool made by Lam Research Corp. of Fremont, CA, may be used to practice an embodiment with capacitive coupling to etch DRAM and 3D NAND structures. In other embodiments, other types of plasma power coupling may be used. In other embodiments, alternating layers of silicon oxide and polysilicon (OPOP) may be etched.

[0052] During cleaning process, the concentration of the at least one gas by product is measured over time by measuring laser light absorption in the gas cell 632 (step 116). In this embodiment, exhaust from the pump 644 flows to the gas cell 632. The IR light source 634 provides the IR beam 760 of IR laser light into the gas cell 632. The first mirror 708 and the second mirror 712 reflect the IR beam 760 a plurality of times before the IR beam 760 is directed to the IR detector 636. The IR detector 636 measures the intensity of the IR beam 760. In an embodiment, during the cleaning process, purge gas is not flowed through the first purge ring channel 742 and the second purge ring 744. In such an embodiment, not flowing the purge gas would prevent the purge gas from lowering the concentration of the at least one gas by product. The optical path length of the IR beam 760 can reach few meters to few hundreds of meters, thus allowing for the ppt detection limit. In an embodiment, the optical path is at least one meter. Data from the IR detector 636 is sent to the controller 624. The controller 624 uses the data to determine the concentration of contaminants·

[0053] While this disclosure has been described in terms of several preferred embodiments, there are alterations, permutations, modifications, and various substitute equivalents, which fall within the scope of this disclosure. It should also be noted that there are many alternative ways of implementing the methods and apparatuses of the present disclosure. It is therefore intended that the following appended claims be interpreted as including all such alterations, permutations, and various substitute equivalents as fall within the true spirit and scope of the present disclosure.

Claims

CLAIMS What is claimed is:

1. A method for plasma cleaning a plasma processing chamber, comprising: flowing a cleaning gas into the plasma processing chamber;

forming the cleaning gas into a plasma, wherein the plasma cleans the plasma processing chamber and wherein the plasma becomes a spent gas;

exhausting the spent gas from the plasma processing chamber into a gas cell; measuring light absorption within the gas cell;

generating a time trace of the measured light absorption within the gas cell; and

using the time trace of the measured light absorption within the gas cell to determine an endpoint for the plasma cleaning of the plasma processing chamber.

2. The method, as recited in claim 1 , wherein the gas cell is a multi-pass gas cell.

3. The method, as recited in claim 2, wherein the gas cell provides an optical path for light, wherein the optical path has a length of greater than 10 meters.

4. The method, as recited in claim 1 , wherein the flowing a cleaning gas into the plasma processing chamber is performed when the plasma processing chamber is waferless.

5. The method, as recited in claim 1, wherein the measuring light absorption within the gas cell measures light intensity at a plurality of wavelengths or frequencies within a bandwidth.

6. The method, as recited in claim 5, wherein the generating a time trace of the measured light absorption within the gas cell generates a plurality of graphs of intensity versus wavelength or frequency at a plurality of times.

7. The method, as recited in claim 5, wherein the using the time trace of the measured light absorption within the gas cell to determine an endpoint for the plasma cleaning of the plasma processing chamber comprises determining weighted integrals of intensity with respect to wavelength or frequency at different times.

8. The method, as recited in claim 7, wherein the weighted integrals of intensity versus wavelength are generated using a weighting vector.

9. The method, as recited in claim 8, further comprising using a multivariate analysis to generate the weighting vector.

10. The method, as recited in claim 7, wherein the weighted integrals are weighted by only integrating over bandwidths of intensity peak regions.

11. The method, as recited in claim 5, further comprising comparing an intensity at a first bandwidth with an intensity at a second bandwidth.

12. The method, as recited in claim 1, wherein the measuring light absorption within the gas cell measures and stores time, intensity, and wavelength or frequency at a plurality of times and wavelengths or frequencies.

13. The method, as recited in claim 1, further comprising using the light absorption within the gas cell to determine chamber drift.

14. The method, as recited in claim 1, wherein the using the time trace of the measured light absorption within the gas cell to determine the endpoint for the plasma cleaning of the plasma processing chamber comprises removing a sputtering trend from the time trace.

15. The method, as recited in claim 1, further comprising placing a cleaning wafer in the plasma processing chamber before flowing the cleaning gas into the plasma processing chamber, wherein the plasma cleans the plasma processing chamber while the cleaning wafer is in the plasma processing chamber.

16. A controller configured to control a plasma processing chamber, comprising: at least one processor; and

computer readable media, comprising:

computer readable code for flowing a cleaning gas into the plasma processing chamber;

computer readable code for forming the cleaning gas into a plasma, wherein the plasma cleans the plasma processing chamber and wherein the plasma becomes a spent gas, wherein the spent gas is exhausted from the plasma processing chamber into a gas cell;

computer readable code for measuring light absorption within the gas cell;

computer readable code for generating a time trace of the measured light absorption within the gas cell; and

computer readable code for using the time trace of the measured light absorption within the gas cell to determine an endpoint for the plasma cleaning of the plasma processing chamber.

17. The controller as recited in claim 16, wherein the computer readable code for generating a time trace of the measured light absorption within the gas cell comprises computer readable code for generating a plurality of graphs of intensity versus wavelength or frequency at a plurality of times.

18. The controller, as recited in claim 16, wherein the computer readable code for using the time trace of the measured light absorption within the gas cell to determine an endpoint for the plasma cleaning of the plasma processing chamber comprises computer readable code for determining weighted integrals of intensity with respect to wavelength or frequency at different times.

19. The controller, as recited in claim 16, wherein the computer readable code for measuring light absorption within the gas cell, comprises computer readable code for measuring and storing time, intensity, and wavelength or frequency at a plurality of times and wavelengths or frequencies.