JP7266575B2 - Spatially resolved optical emission spectroscopy (OES) in plasma processing - Google Patents

Description

CROSS REFERENCE TO RELATED APPLICATIONS This application is a U.S. patent entitled "SPATIALLY RESOLVED OPTICAL EMISSION SPECTROSCOPY (OES) IN PLASMA PROCESSING," filed Jul. 12, 2017. Priority is claimed to Application Serial No. 15/648,035 (Docket No. TTI-247), the entire contents of which are incorporated herein by reference. Further, the present application is entitled "SPATIALLY RESOLVED OPTICAL EMISSION SPECTROSCOPY (OES) IN PLASMA PROCESSING" filed on October 31, 2014 (Docket No. TTI-242). US patent application Ser. No. 14/530,164 (Docket No. TTI-242) entitled " benefit of and priority to U.S. Provisional Patent Application No. 61/898,975, entitled SPATIALLY RESOLVED OPTICAL EMISSION SPECTROSCOPY (OES) IN PLASMA ETCHING, Docket No. TTI-242PROV. claim rights.

TECHNICAL FIELD This invention relates to methods, computer methods, systems, and apparatus for measuring the concentration of chemical species in semiconductor plasma processing using plasma optical emission spectroscopy (OES). In particular, this relates to identifying a two-dimensional distribution of plasma emission that can identify a two-dimensional distribution of species concentrations.

The fabrication of semiconductor devices, displays and photovoltaics proceeds in a series of steps, each step having parameters optimized for maximum device yield. In plasma processing, controlled parameters that strongly influence yield are the plasma chemistry, particularly the local plasma chemistry, i.e., the local concentration of various chemical species in the plasma environment in the vicinity of the substrate being processed. . Certain chemical species, especially transient chemical species such as radicals, have a significant effect on the results of plasma processing, and local increases in the concentration of these chemical species create areas of faster processing, which can lead to faster processing. The steps are known to eventually lead to non-uniformity in the manufactured device.

The plasma process chemistry includes one or more RF or microwave powers supplied to excite the plasma, gas flow rates and types supplied to the plasma processing chamber, pressure within the plasma processing chamber, is controlled directly or indirectly by controlling a number of process variables such as the type of substrate in the plasma, the pumping speed delivered to the plasma processing chamber, and the like. Optical emission spectroscopy (OES) has proven to be a useful tool for process development and monitoring in plasma processing. In emission spectroscopy, the presence and concentration of particular chemical species of particular interest, such as radicals, are estimated from the acquired emission (i.e., light) spectrum of the plasma, and the intensities of particular spectral lines and their ratios are Correlative to chemical species concentration. A detailed description of this technique can be found, for example, in G.J. Selwyn, "Optical Diagnostic Techniques for Plasma Processing", AVS Press, 1993 and will not be repeated here for the sake of brevity.

The use of optical emission spectroscopy has become relatively common, especially in plasma process development, and it is usually done by acquiring an emission spectrum from a single elongated volume within the plasma inside the plasma processing chamber. . The exact shape and size of this volume is determined by the optics used to collect the emission from the plasma. Collection of such emission signals essentially results in the averaging of the plasma emission spectrum along the length of the elongated volume, known as the ray, thus providing all information about the local variation of the plasma emission and thus the chemical species. Local variations in concentration are also generally lost.

In the development of plasma processes, and indeed even in the development of new and improved plasma processing systems, it is useful to know the two-dimensional distribution of chemical species of interest on the substrate being processed, thus For example, changes in system design and/or processing parameters can be made to minimize variations in processing results across substrates. A further application of plasma emission spectroscopy techniques is the evolution and abrupt changes (the to identify the endpoint of the plasma processing step by monitoring the evolution of and abrupt change. The ability to identify the endpoint of a plasma processing step across the entire surface of a substrate contributes to increased device yield. This is because premature termination of the plasma processing step is avoided.

One technique widely used in other technical fields, such as X-ray tomography, for identifying variable spatial distributions from known integral measurements along multiple rays traversing a region of interest is the Abel transform or This is fault reversal using the Radon transform. However, to be effective, this technique requires a large amount of acquired data, i.e., a large amount of light, which is transmitted through one or a few windows or optical ports built into the wall of the plasma processing chamber. is impractical in semiconductor processing tools that have limited optical access to the plasma. Tomography techniques are generally also very computationally intensive. It has also been found that local variations in species concentration are generally smooth in nature, with no sharp gradients in both radial and even circumferential (ie, azimuthal) directions. Therefore, it would be desirable to have a simple, fast, relatively low-cost plasma emission spectroscopy technique and system capable of acquiring two-dimensional distributions of plasma emission spectra without the overhead associated with tomography approaches to OES measurements. would be advantageous.

Most notably, although the circumferential variations may be small, they are not non-existent, as some prior art assumes, and ideal techniques and systems are still susceptible to these variations. would have to be able to reliably capture

Aspects of the invention include an apparatus for emission measurements having a collection system for collecting the plasma emission spectrum through an optical window located in the wall of a plasma processing chamber. The optics include a mirror configured to scan a plurality of non-coincident rays across the plasma processing chamber and a spectroscope for collecting optical signals from the plasma and measuring the plasma optical emission spectrum. and a telecentric coupler for directing the signal.

An alternative embodiment is a plasma emission measurement system comprising a plasma processing chamber, an optical window located in a wall of the plasma processing chamber, a collection system collecting the plasma emission spectrum through the optical window, and a plasma emission spectrum a spectrometer coupled to the collection system for measuring the plasma optical emission measurement system. The collection system has a mirror configured to scan the plurality of mismatched beams across the plasma processing chamber and a telecentric coupler for collecting optical signals from the plasma and directing the optical signals to the spectrograph.

Yet another embodiment of the present invention is a method for optical emission measurements comprising the steps of placing an optical window in a wall of a plasma processing chamber and a collection system collecting the plasma optical emission spectrum through the optical window. wherein the collection system has a mirror and a telecentric coupler; scanning a plurality of mismatched beams across the plasma processing chamber using the mirror; Collecting the signal and directing the optical signal to a spectroscope for measuring the plasma emission spectrum.

A more complete understanding of the invention and its attendant advantages will become readily apparent by reference to the following detailed description considered in conjunction with the accompanying drawings.
1 is a schematic side view of a plasma processing system with an optical emission spectroscopy (OES) measurement system according to an embodiment; FIG. 1 is a schematic top view of a plasma processing system with an OES measurement system according to an embodiment; FIG. FIG. 3 shows an exemplary plasma emission spectrum obtained using an OES measurement system according to an embodiment; FIG. 2 schematically illustrates an optical system used in an OES measurement system, according to an embodiment; FIG. 10 schematically illustrates an optical system used in an OES measurement system, according to another embodiment; FIG. 3 is an enlarged view schematically illustrating an embodiment of an optical system, according to an implementation; FIG. 2 illustrates an exemplary two-dimensional distribution of plasma emission measured using an OES measurement system and accompanying method, according to an embodiment; FIG. 10 schematically illustrates an optical system used in an OES measurement system, according to another embodiment; FIG. 10 is an enlarged view schematically illustrating an embodiment of an optical system, according to another implementation; 9 is a schematic top view of a plasma processing system comprising the optical system of FIG. 8; FIG. FIG. 10 is an enlarged view schematically illustrating an embodiment of an optical system, according to another implementation; FIG. 4 is a schematic diagram of an optical system used in an OES measurement system, according to another embodiment; FIG. 10 schematically illustrates exemplary results of reconstructed emission intensity patterns; 4 is a flowchart illustrating a method for luminescence measurements, according to an embodiment;

In the following description, in order to facilitate a thorough understanding of the present invention, specific details such as specific geometries of plasma optical emission spectroscopy systems and descriptions of various components and processes are set forth. described for the purposes of and not for the purposes of limitation. However, it should be understood that the invention may be practiced in other embodiments that depart from these specific details.

In the following description, the term substrate, which represents a workpiece during processing, may be used interchangeably with terms such as semiconductor wafer, liquid crystal display panel (LCD), light emitting diode (LED), photovoltaic (PV) device panel, and the like. and all such treatments are within the scope of the claims.

Throughout this specification, references to "an embodiment" or "embodiment" indicate that the particular feature, structure, material or property described in connection with the embodiment is included in at least one embodiment of the invention. implied, but not intended to be present in every embodiment. Thus, the appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment of the invention. Moreover, any of the specified features, structures, materials or properties may be combined in any suitable manner in one or more embodiments.

Various operations are described as multiple discrete operations in a manner that is most helpful for understanding the present invention. However, the order of description should not be construed to imply that these operations are necessarily order dependent. In particular, these actions need not be performed in order of presentation. Operations described may be performed in a different order than the described embodiment. Various additional operations may be performed and/or described operations may be omitted in additional embodiments.

FIG. 1 shows an embodiment of plasma processing system 10 that includes a plasma optical emission spectroscopy (OES) system 15 . Plasma processing system 10 includes a plasma processing chamber 20 within which is positioned a substrate holder 30, such as an electrostatic chuck, for receiving a substrate 40 to be processed. Radio frequency (RF) and/or microwave power is supplied to plasma processing chamber 20 (not shown) to ignite and sustain plasma 50 proximate substrate 40 . Here, energetic species from plasma 50 are used to perform plasma processing steps on substrate 40 . Process gases may flow into plasma processing chamber 20 (not shown) and a pumping system (not shown) may be provided to maintain a vacuum within plasma processing chamber 20 at a desired process pressure. Examples of plasma processing steps include plasma etching, plasma enhanced chemical vapor deposition (PECVD), plasma enhanced atomic layer deposition (PEALD), and the like. The systems and methods described herein are applicable to any type of plasma processing.

the plasma emission spectroscopy (OES) system 15 is used to acquire the plasma emission spectrum via at least one optical detector 60, the optical detector 60 communicating the acquired plasma emission spectrum to the controller 80; Controlled by controller 80 . Controller 80 may be a general purpose computer and may be located proximal to plasma processing system 10 or may be remotely located and connected to photodetector 60 via an intranet or internet connection. .

Photodetector 60 has optics configured to collect plasma emission from an elongated, generally pencil-shaped spatial volume 65 within plasma 50 . Optical access to the plasma processing chamber is provided by optical window 70 . Optical window 70 may comprise materials such as glass, quartz, fused silica, or sapphire, depending on the application and how aggressive the chemistry of plasma 50 is. Volume 65, hereinafter referred to as "ray" 65, defines the portion of space in which the plasma emission spectrum is collected from all points located along and within ray 65. represents the integral of the contribution to the plasma emission spectrum. Note that depending on the geometry and configuration of photodetector 60, the contribution of each point in beam 65 is unequal, weighted and dominated by light efficiency (discussed in more detail below). ). In a typical configuration, the light beam 65 is oriented substantially parallel to the surface of the substrate 40 and maintained at a small distance from the surface of the substrate 40 so as to reduce optical interference from the substrate surface. is maintained close enough to the substrate 40 to sample the plasma chemistry in the vicinity of the .

The controller 80 controls the plasma optical emission spectroscopy system 15 as described above to (1) calculate the plasma optical intensity distribution as a function of spatial position and wavelength, and from the calculated plasma optical intensity distribution (2) the chemical species of interest is used to compute the spatial distribution of This information can then be used for process development, plasma processing tool development, in situ plasma process monitoring, plasma process fault detection, plasma process endpoint detection, and the like.

FIG. 1 shows a single ray 65 traversing plasma 50 located within plasma processing chamber 20, proximal to substrate 40 being processed. In one embodiment of the present invention, multiple light beams 100 may be used to sample the plasma emission spectrum, as shown in FIG. 2, for example, a schematic top view of the plasma processing system 10 of FIG. is. In the exemplary embodiment of FIG. 2, two photodetectors 60 are used, each capable of collecting the plasma light emission spectrum from 100 of the seven beams. Beams 100 should be mismatched so that the maximum amount of spatial information is obtained from plasma 50 on substrate 40 . The number of light beams 100 per photodetector 60 can vary from 2 to 9 and more. Also, in another embodiment where only a single optical window 70 provides optical access to the plasma processing chamber 20, a single optical detector 60 may be used with its associated beam fan 100. can be done. Alternatively, a third or more photodetectors, each having an associated fan of rays, may be used. The angle of each ray 100 is defined as θ _i with respect to the centerline of its optical detector 60 . As shown in FIG. 2, every point in the plasma processing chamber can be defined by its polar coordinates, ie (r, θ).

Depending on the configuration of the photodetector 60, all plasma emission spectra from the relevant fan of the beam 100 can be collected simultaneously, as will be described in detail below. This is suitable for embodiments of the optical detector 60 with multiple optics and channels, allowing simultaneous collection from all beams 100 . Alternatively, plasma emission spectra can be acquired continuously along the beam 100 associated with the optical detector 60 . The latter is suitable for scanning embodiments in which plasma emission spectra are collected as light beam 100 is scanned from angle θ to another angle. Of course, this scanning and collection needs to be done fast enough so that rapid changes in plasma chemistry can be detected across the substrate.

FIG. 3 shows an example of a plasma emission spectrum acquired at an angle θ from one light beam 100 using one photodetector 60 . Spectra typically collect intensity at wavelengths M in the range from about 200 nm to about 800 nm. A typical spectrometer CCD used for emission spectroscopy has 4096 pixels spanning the wavelength range, but the number of pixels varies from 256 pixels to 65536 pixels depending on the application and required resolution of the spectra collected. can change up to

The plasma emission spectrum collected by photodetector 60 from the relevant fan of light beam 100 is communicated to controller 80, which is used to further process the communicated data to calculate the spatial distribution of plasma emission. from which the spatial distribution of species concentrations can be calculated. One aspect of the present invention is an algorithm for fast computation of the spatial distribution of plasma emission for each wavelength, which enables in-situ monitoring of plasma processes for endpoint detection, fault detection, and the like.

FIG. 4 shows an embodiment of photodetector 60, where a single multi-channel spectrograph 310 is used to simultaneously collect plasma emission spectra from beams 305A-E. The exemplary embodiment shown herein has five rays 305A-E for clarity, although the number may range from 2 to 9 and even greater than 9. good. Photodetector 60 includes an optical system 300A-300E for each beam 305A-300E, all positioned proximal to optical window 70 mounted in the wall of plasma processing chamber 20. FIG. Light rays 305A-E are divergently arranged to cover relevant portions of substrate 40 (not shown). The collected plasma emission spectra are fed from optics 300A-E to multichannel spectrograph 310 via respective optical fibers 320A-E. The optical systems 300A-300E will be described later. The embodiment of FIG. 4 is suitable for fast diagnostics due to its ability to collect plasma optical emission spectra simultaneously.

FIG. 5 shows an alternative embodiment, described in more detail below, in which a single channel spectrometer 310 is used and the light beams 305A-305E are formed by a scanning mirror 400, which is controlled by Possibly scanned to sweep beams 305A-305E, during which the plasma emission spectrum is acquired by spectrometer 310 through single optical system 300. FIG. This embodiment is suitable for continuous collection of plasma emission spectra and thus more suitable for diagnosis of slower evolving plasma processes. Scanning mirror 400 may be mounted on and actuated by galvanometer stage 410 . Alternatively, scanning mirror 400 may be mounted on and scanned by a stepper motor 410 . The number of light beams 305A-E is shown here as five, but is actually determined by the controller software settings for controlling the galvanometer stage or stepper motor 410. FIG.

To ensure that the correct volume of space is sampled, optical systems 300A-300E of FIGS. 4 and 300 of FIG. It should be configured to be collimated with the smallest possible divergence angle so that it can be reached by

An exemplary embodiment of optical systems 300A-300E and 300 is shown in FIG. Optical system 300A-E, also known as a telecentric coupler, collects the plasma emission spectrum from the volume of space within plasma 50 defined by light rays 305A-E and transfers the collected plasma emission spectrum to optical fibers 320A-E or It has the task of directing to the end 390 of 320 and can therefore be transmitted to the spectrometer 310 of the embodiment of FIG. 4 or FIG. The diameters of rays 305A-305E are defined by optional apertures 350 formed in the plate. In alternate embodiments, other optical components, such as lenses, can be used to define the diameter of light beams 305A-305E. An exemplary beam diameter is 4.5 mm, but can vary from about 1 mm to 20 mm depending on the application. Collected rays 305A-E pass through a combination of collecting lenses 360A and 360B which, in combination with any aperture, define rays 305A-E. The numerical aperture of the collection system and rays 305A-E is generally very low, eg, about 0.005, and the resulting rays 305A-E have minimal divergence angles and are substantially collimated. At the other end of optical system 300A-E or 300 is another pair of lenses, coupling lenses 370A and 370B, which direct the collected emission spectrum onto end 390 of optical fiber 320A-E or 320. helps to focus on All lenses used in the system are preferably achromatic or even apochromatic for more demanding applications, which means that optical system 300A-E or 300 typically has a 200nm to 800nm to ensure that the focal length of each lens does not vary with wavelength to operate satisfactorily over a wide range of wavelengths, possibly down to 150 nm. UV grade materials are used for all optics to improve performance in the ultraviolet (UV) portion of the spectrum, ie below 350 nm.

For all optical hardware configurations, it is important to know the optical efficiency w, which is a weighting factor applied to all points within the beam 305A-E from which the plasma emission spectrum was obtained. The optical efficiency w can be determined by simulation using optical design software or by using a calibrated light source and moving them across and along the rays 305A-E to obtain a given can be determined by experimentation to determine the efficiency of the coupling of light from the position of . The optical efficiency w is used in algorithms to identify the spatial distribution of plasma emission.

As previously mentioned, the task of the plasma optical emission spectroscopy (OES) system 15 is to identify the two-dimensional intensity distribution of the plasma emission for each of the M measured wavelengths λ.

For each ray 100 in FIG. 2, mathematically denoted by index i, the collected photodetector output D _i can be defined as follows.

ここで、Ｉ（ｒ，θ）は、光線１００内及びそれに沿った位置（ｒ，θ）でのプラズマ発光強度であり、ｗ（ｒ，θ）は、光検出器ｉによる位置（ｒ，θ）からの光収集の光学効率である。結果として得られる光検出器出力Ｄ_ｉは、基板の周囲の点Ａから点Ｂへの直線経路に沿ったこれらの量の積の積分を表し（図２を参照）、基板４０の周囲の外側のプラズマからの寄与はこのモデルでは無視される（これらの領域ではプラズマ密度、したがってプラズマ発光が一般に低いため、これは有効な仮定である）。

where I(r, θ) is the plasma emission intensity at position (r, θ) in and along beam 100 and w(r, θ) is the position (r, θ ) is the optical efficiency of light collection from The resulting photodetector output D _i represents the integral of the product of these quantities along a linear path from point A to point B around the substrate (see FIG. 2), and outside around the substrate 40 The contribution from the plasma of is neglected in this model (this is a valid assumption since the plasma density and hence plasma emission is generally low in these regions).

In a plasma optical emission spectroscopy system 15 having N photodetectors and N scanning positions in the beam or beam 100, there are N collected intensities for each of the M measured wavelengths λ. Therefore, to reconstruct the spatial distribution of the plasma emission at a certain wavelength λ, a function form with N parameters must be assumed. Due to the limited number of parameters, a reasonable choice of basis functions for the plasma emission distribution must be made. The basis functions chosen should vary in both the radial coordinate r and the circumferential coordinate θ so as to adequately reproduce the circumferential variation of the plasma emission across the substrate 40 .

One class of basis functions particularly suited to this task are the Zernike polynomials

である。
ゼルニケ多項式は、半径座標ｒに依存する項と円周座標θに依存する項の積として定義される。即ち、

is.
A Zernike polynomial is defined as the product of a term dependent on the radial coordinate r and a term dependent on the circumferential coordinate θ. Namely

である。

is.

Table 1 shows the first 18th order Zernike polynomials. Here, the commonly used mathematical notation

を使用して示す。

is used to indicate

In general, for this application other basis functions can be chosen as long as they are orthogonal and the derivatives are continuous on the unit circle, as in the case of the Zernike polynomials. However, for this application, the Zernike polynomials are preferred. This is due to the property that a relatively small number of terms can be used to describe very complex variations of functions in both radial and circumferential polar coordinates.

Zernike polynomial

を、収集される検出器出力に代入すると、

to the collected detector output, we get

が得られる。
ここで、ａ_ｐは、各基底関数に関連するフィッティングパラメータ、すなわち、ゼルニケ多項式次数である。

is obtained.
where a _p is the fitting parameter associated with each basis function, ie the Zernike polynomial order.

Since the collected detector outputs D _i are defined in terms of selected basis functions, fitting parameters, and optical efficiencies, the problem of specifying the fitting parameters a _p for D _i is to minimize the following equation: That is, it solves the least-squares problem.

又は

or

ここで、Ｄ_ｉ ^{ｍｅａｓｕｒｅｄ}は、測定したプラズマ光学スペクトルの光線ｉにおける強度を表す。この最小化アルゴリズムは、Ｍ個の測定波長λごとに繰り返される必要がある。この最小二乗問題を解くための多くの方法が当技術分野で知られている。最小二乗問題の次元は比較的小さいので、プラズマ発光スペクトルが測定される時間の各瞬間に、全ての波長に対して効率的に解くことができ、さらに、かかる計算は高速で連続的に繰り返されることができ、多数のＭ個の波長に対するプラズマ発光の高速に進展する二次元分布の特定を可能にする。その後、これらのものから、終点検出、故障検出、プロセス開発（process development）、処理ツール開発（processing tool development）などに使用できる、基板４０にわたる化学種濃度の時間変化する二次元分布を特定することができる。

where D _i ^measured represents the intensity at ray i of the measured plasma optical spectrum. This minimization algorithm needs to be repeated for every M measured wavelengths λ. Many methods are known in the art for solving this least squares problem. Since the least-squares problem is of relatively small dimensionality, it can be efficiently solved for all wavelengths at each instant in time that the plasma emission spectrum is measured, and such computations are rapidly repeated continuously. , allowing identification of the fast-evolving two-dimensional distribution of the plasma emission for a large number of M wavelengths. From these, subsequently identifying time-varying two-dimensional distributions of chemical species concentrations across the substrate 40 that can be used for endpoint detection, fault detection, process development, processing tool development, etc. can be done.

FIG. 7 shows an example of such a plasma emission intensity distribution determined by a method according to an embodiment of the invention. The illustrated distribution clearly shows that both radial and circumferential variations in plasma emission intensity are well captured despite the relatively small number of terms, ie, N=18.

FIG. 8 shows an alternative embodiment in which a single channel spectrograph 310 is used. Light rays 305A-E are formed by scanning mirror 400 and mirror system 800, which extends from the position of stepper motor 410 relative to scanning mirror 400 to optical window 70, as indicated by point C in FIG. to or substantially near the optical window 70 (ie, point C represents the center of rotation). Optical window 70 is typically small (ie, 1 inch in diameter), and therefore, for sweeping rays 305A-E across plasma 50 (eg, angle θmax=25° of central axis of plasma processing chamber 20), ray 305A ˜E have the smallest range of motion in the optical window 70 . Accordingly, the center of rotation of light rays 305A-E is configured substantially near or at optical window 70 . By using the configuration described herein, it is possible to use windows with dimensions of 68.5 mm x 8 mm or larger. The window size (ie, upper limit) is limited by factors such as contamination, chamber UV and RF leakage, and available space in the walls of the plasma processing chamber 20 . In one embodiment, the window may have a rectangular shape with a large dimension in the plane corresponding to the scanning plane of the beam. This has the advantage of minimizing the window size while meeting leak and space requirements.

Scanning mirror 400 is controllably scanned to sweep beams 305A-E using stepper motor 410 while the plasma emission spectrum is acquired by spectrometer 310 through single optical system 300. .

Mirror system 800 may include a transfer mirror 802 and a fold mirror 804 . Each collected light ray 305A-E or 65 (ie, the optical signal from the plasma with the collected light ray 305) is transferred to reflect the collected light ray 305 and transmit the collected light ray 305 to the fold mirror 804. transmitted by mirror 802 . Fold mirror 804 reflects collected light ray 305 from horizontal (azimuth) to vertical concentricity and transmits collected light ray 305 to scanning mirror 400 which reflects the collected light ray 305 to optics 300 . Mirror system 800 and optical system 300 are stationary. Mirror system 800 , scanning mirror 400 , optics 300 , and spectroscope 310 may be mounted proximally of plasma processing chamber 20 .

As scanning mirror 400 is swept, a high spatial resolution of the spatial distribution of species concentration is obtained. For example, scanning mirror 400 can be slowly swept while the plasma emission spectrum is acquired. The acquired plasma emission spectrum is associated with any position between -θmax° and +θmax°. Therefore, very accurate spatial resolution can be obtained using the scan settings described herein.

FIG. 9 is an enlarged schematic diagram of an embodiment of the optical system 300 of FIG. 8, according to one embodiment. Optical system 300 collects the plasma emission spectrum from the volume of space within plasma 50 defined by collected light beam 305 and transmits the collected plasma emission spectrum to optical fiber 320, as previously described herein. , so that it can be transmitted to the spectrometer 310 . Optical system 300 includes a telecentric combiner with a small NA. The size of the collected scanning beam can vary from about 3-5 mm in diameter along the collection path.

Collected light rays 305 (ie, light rays reflected from scanning mirror 400 ) pass through first collecting lens 902 . The light beam can then pass through a telecentric aperture 908 having a diameter of, for example, 600 μm. Two coupling lenses 904 and 906 then function to focus the collected light emission spectrum onto end 390 of optical fiber 320 . In one example, optical fiber 320 has a diameter of 600 μm. Collection system 300 can also include an optional filter positioned between the two coupling lenses 904 and 906 .

The numerical aperture of collection system 300 is very low, eg 0.005. Lenses 902, 904 and 906 are achromatic lenses with effective focal lengths of 30 mm, 12.5 mm and 12.5 mm respectively and diameters of 12.5 mm, 6.25 mm and 6.25 mm respectively.

Referring again to FIG. 8, scanning mirror 400 can have dimensions of at least 10 mm by 10 mm. Transfer mirror 802 may be a spherical mirror. Scan mirror 400 and transfer mirror 802 have a dielectric multilayer film on top of aluminum, an aluminum coating, or a silicon monoxide (SiO) overcoat to increase reflection in certain wavelength regions (e.g., UV). be able to. The radius of the transfer mirror 802 may be between 100 mm and 120 mm. In one embodiment, the transfer mirror 802 radius is 109.411 mm. Transfer mirror 802 may be placed at a distance of 68.4 mm from the outer edge of optical window 70 . Fold mirror 804 may be placed at a distance of 71.5 mm from the plane of scan mirror 400 .

Spectrometer 310 may be an ultra-broadband (UBB) high-resolution spectrometer with a spectral resolution of 0.4 nm and a wavelength range of 200 nm to 1000 nm.

10 is a top view schematically showing a plasma processing system having the optical system of FIG. 8. FIG. Plasma processing chamber 20 may comprise the two optical systems of FIG. The optical system is called a scanning module. Each scanning module can be configured to collect X to Y ray position data. In one embodiment, each scanning module can be configured to collect data for 5-50 ray positions, providing better accuracy and being able to detect events with high spatial resolution. . In FIG. 10 one position of light ray 305 is shown. As previously described herein, the scan angle of light beam 305 may vary from -θmax°, +θmax° (eg, θmax=25° or 30°). Data from spectrograph 310 can be processed as previously described herein to obtain a two-dimensional (2D) OES intensity distribution. Each module can include a single channel spectrograph 310, or a single spectrograph with two channels can be used for the two scanning modules. Additional scanning modules can also be used to provide higher spatial resolution. The optical windows 70 (ie, the optical windows 70 of each scanning module) may be arranged perpendicular or substantially perpendicular to each other on the sidewalls of the plasma processing chamber 20 . Depending on the configuration of plasma processing chamber 20, optical window 70 may be quartz, fused silica, or sapphire, depending on the application and how aggressive the plasma chemistry is.

FIG. 11 is an enlarged schematic diagram of an embodiment of the optical system 300 of FIG. 5 or FIG. The optical system 300 has the task of directing the reflected and collected plasma emission spectrum from the scanning mirror 400 to the end 390 of the optical fiber 320 and thus to the spectrograph 310 as previously described herein. can be transmitted. Collected rays 305 pass through a collecting lens, which may be a triplet lens 1102, for example, having an effective focal length of 40 mm. The collected light beam 305 can pass through any mask aperture 1108, eg, 7 mm in diameter. Mask aperture 1108 may be positioned between scan mirror 400 and triplet lens 1102 . The collected rays 305 can then pass through an optional telecentric aperture 1110, for example with a diameter of 1.20 mm. In alternate embodiments, other optical components, such as lenses, can be used to define the diameter of light beam 305 .

Two coupling triplet lenses 1104 and 1106 function to focus the collected emission spectrum onto end 390 of optical fiber 320 . In one embodiment, combined triplet lenses 1104 and 1106 may be triplet lenses with an effective focal length of 15 mm. The effective focal length of combining triplet lenses 1104 and 1106 is a function of the type and diameter of optical fiber 320 .

All lenses used in the system are preferably achromatic or even apochromatic for more demanding applications, which means that the optical system 300A-E or 300 typically has a 200nm to 1000nm It ensures that the focal length of each lens does not vary with wavelength to operate satisfactorily over a wide range of wavelengths, possibly down to 150 nm. To improve performance in the UV portion of the spectrum, ie, below 350 nm, UV grade materials such as quartz, fused silica, calcium fluoride (CaF under 2) are used for all optical components.

Figure 12 schematically illustrates an alternative embodiment in which a single channel spectrometer 310 is used. Plasma emission spectra can be acquired sequentially using one or two modules. Each module can include a linear arc stage 1204 . Spectrograph 310 , optics 300 and folding mirror 1202 are mounted on linear arc stage 1204 . Fold mirror 1202 is positioned to receive light beam 305 collected from plasma processing chamber 20 and reflect collected light beam 305 to optical system 300 . The linear arc stage 1204 is controllably scanned to sweep the collected light beam 305 while the plasma emission spectrum is acquired by the spectrograph 310 via the single optical system 300 . Linear arc stage 1204 can be controlled via controller 80 . Point C in FIG. 12 indicates the center of rotation of linear arc stage 1204 . A single optical system 300 may be that shown and described in FIG. 9 or FIG. In one example, linear arc stage 1204 may have a scan angle of 85° and a length of 163.2 mm. The linear scanning speed can vary from 0.35m/s to 2.2m/s. Therefore, the scanning speed can be adjusted to optimize the trade-off between spatial resolution and speed depending on the application of plasma emission spectroscopy system 15 .

In further embodiments of the optical system 300 of FIGS. 6, 9 and 11, other optical components such as mirrors, prisms, lenses, spatial light modulators, digital mirror devices, etc. are used to manipulate the collected light beam 305. be able to. Although the configuration and component layout of optical system 300 of FIGS. 4-6 and 8-12 need not necessarily be as shown in FIGS. The components can be folded and manipulated to facilitate packaging the plasma emission spectroscopy system 15 into a compact package suitable for wall mounting of the plasma processing chamber 20 .

The inventors performed several experiments to reconstruct the pattern of light emission distribution and compare the reconstructed pattern with the etched pattern.

FIG. 13 schematically shows exemplary results of reconstructed emission intensity patterns. The intensity of an emission line (ie, 522.45 nm for silicon chloride) indicates the concentration of silicon chloride (SiCl) in relation to the intensity of local etching on substrate 40 . FIG. 13 shows a comparison between the actual distribution of emission collected by the plasma OES system 15 described herein at 522.5 nm and the actual etch rate. Plots 1302, 1304, and 1306 show the actual etch rates of various samples under various plasma processing conditions. Plots 1308, 1310, and 1312 show reconstructed emission distributions for the samples associated with plots 1302, 1304, and 1306, respectively.

Etch uniformity can be monitored using the apparatus and methods described herein.
For example, the apparatus can be used during process development to monitor etch uniformity for various plasma processing conditions without transferring the substrate to another apparatus. and can make various processes faster.

The results show a strong correlation between etch thickness and the reconstructed OES distribution given by species for plasma etching, including both reactants and products. OES distribution and oxide etch profile uniformity follow the same trend, eg, plot 1302 compared to plot 1308 . Substrates with better etch uniformity show a lower correlation with the OES distribution (eg, plot 1306 compared to plot 1302).

FIG. 14 is a flowchart illustrating a luminescence measurement method 1400 according to one embodiment. At 1402, an optical window is placed in a wall of a plasma processing chamber (eg, plasma processing chamber 20). At 1404, a collection system is provided to collect the plasma emission spectrum through the optical window. The collection system has a mirror and a telecentric coupler. A telecentric combiner can include at least one collecting lens (eg, collecting lenses 360A and 360B) and at least one combining lens (eg, combining lenses 904 and 906 of FIG. 9). At 1406, the plurality of mismatched beams are scanned across the plasma processing chamber using mirrors.
Scanning can be controlled by controller 80 . At 1408, an optical signal is collected from the plasma via a telecentric coupler. At step 1410, the optical signal is directed to a spectrometer for measuring the plasma emission spectrum.

Persons skilled in the relevant art can appreciate that many modifications and variations are possible in light of the above teachings. Those skilled in the art will recognize various equivalent combinations and permutations of the various components shown in the drawings. It is therefore intended that the scope of the invention be limited not by this detailed description, but rather by the claims appended hereto.

The above disclosure also includes the following embodiments.

(1) A method for emission measurement comprising the steps of placing an optical window in the wall of a plasma processing chamber and providing a collection system for collecting the plasma emission spectrum through the optical window, comprising: has a mirror and a telecentric coupler; scanning a plurality of mismatched beams across the plasma processing chamber with the mirror; collecting optical signals from the plasma through the telecentric coupler; plasma emission spectrum and directing the optical signal to a spectrometer for measuring the .

(2) The method of feature (1), wherein the telecentric combiner has at least one collecting lens and at least one combining lens.

(3) The method of feature (2), wherein at least one collecting lens or at least one combining lens is an achromatic lens.

(4) The method of feature (2), wherein the telecentric combiner is further positioned between the at least one collecting lens and the at least one combining lens to define diameters of the plurality of mismatched rays. have an opening.

(5) The method of any of features (1)-(4), wherein the mirror is a scanning mirror.

(6) The method of feature (5), wherein the scanning mirror is mounted on a galvanometer scanning stage and scanned by the galvanometer scanning stage.

(7) The method of feature (5), wherein the scanning mirror is mounted on a stepping motor and scanned by the stepping motor.

(8) The method of feature (5), wherein the collection system further comprises a mirror system for shifting the center of rotation of the plurality of mismatched rays to or near the optical window.

(9) The method of feature (8), wherein the mirror system includes a transfer mirror and a fold mirror, the transfer mirror configured to transfer the collected optical signal to the fold mirror. , the folding mirror is configured to transfer the collected optical signal to said mirror.

(10) The method of feature (1), wherein the telecentric coupler comprises a collecting triplet lens configured to collect the optical signal from the mirror, and an optical coupling of the collected optical signal to the spectroscope. and two coupling triplet lenses configured to focus at the ends of the fibers.

(11) The method of feature (1), further comprising collecting the plasma emission spectrum through a second optical window located in the wall of the plasma processing chamber using the second collection system. The central axis of the second optical window forms a right angle with the central axis of the optical window.

(12) The method of feature (1), wherein the collection system further comprises a linear arc stage holding the mirror, the telecentric coupler, and the spectroscope, the linear arc stage being the central axis of the optical window. and configured to scan the plurality of mismatched beams across the plasma processing chamber.

(13) The method of feature (12), wherein the mirror is a folding mirror.

(14) The method of any of features (1)-(13), wherein the plurality of mismatched beams are scanned 25° of the central axis of the optical window across the plasma processing chamber.

(15) The method of any of features (1)-(14), wherein the spectrometer is an ultra-wideband high-resolution spectrometer.

(16) The method of any of features (1)-(15), wherein the collection system has a low numerical aperture.

(17) The method of any of features (1)-(14), wherein the optical signals are collected from the 21 unmatched rays.

Claims (19)

A device for luminescence measurements, said device comprising:
a collection system for collecting the plasma emission spectrum through an optical window located in the wall of the plasma processing chamber;
The optical system is
a mirror configured to scan a plurality of mismatched beams across the plasma processing chamber;
a telecentric coupler for collecting an optical signal from a plasma and directing the optical signal to a spectroscope for measuring the plasma emission spectrum;
said mirror is a scanning mirror that rotates to sweep said plurality of mismatched beams ;
The collection system further comprises a mirror system for shifting the center of rotation of the plurality of mismatched rays by the scanning mirror from the scanning mirror to or near the optical window;
the mirror system comprises a transfer mirror and a fold mirror positioned between the scanning mirror and the optical window ;
the transfer mirror is configured to transfer the collected optical signal to the fold mirror;
The apparatus of claim 1, wherein the folding mirror is configured to transfer the collected optical signal to the scanning mirror. A device for luminescence measurements, said device comprising:
a collection system for collecting the plasma emission spectrum through an optical window located in the wall of the plasma processing chamber;
The optical system is
a mirror configured to scan a plurality of mismatched beams across the plasma processing chamber;
a telecentric coupler for collecting an optical signal from a plasma and directing the optical signal to a spectroscope for measuring the plasma emission spectrum;
the collection system further comprises a linear arc stage holding the mirror, the telecentric coupler, and the spectrograph;
The linear arc stage is
having a scan angle and a linear scan length,
configured to move the mirror, the telecentric coupler, and the spectrograph along an arcuate path about a center of rotation to scan the plurality of mismatched beams across the plasma processing chamber; the center is located at or near the optical window and along the central axis of the optical window ;
Device. the telecentric combiner has at least one collecting lens and at least one coupling lens;
3. Apparatus according to claim 1 or 2. said at least one collecting lens or said at least one combining lens is an achromatic lens;
4. Apparatus according to claim 3. the telecentric combiner further having an aperture positioned between the at least one collecting lens and the at least one combining lens for defining diameters of the plurality of mismatched rays;
4. Apparatus according to claim 3. said mirror is a scanning mirror,
Apparatus according to claim 1 . the scanning mirror is mounted on and scanned by the galvanometer scanning stage;
7. Apparatus according to claim 6. the scanning mirror is mounted on a stepping motor and scanned by the stepping motor;
7. Apparatus according to claim 6 . The telecentric coupler is
a collecting triplet lens configured to collect the optical signal from the mirror;
and two coupling triplet lenses configured to focus the collected optical signal onto the end of an optical fiber coupled to the spectrograph.
3. Apparatus according to claim 1 or 2. the apparatus further comprises a second collection system for collecting the plasma emission spectrum through a second optical window located in the wall of the plasma processing chamber;
the second optical window has a central axis perpendicular to the central axis of the optical window;
3. Apparatus according to claim 1 or 2. the plurality of mismatched beams are scanned 25° of the central axis of the optical window across the plasma processing chamber;
3. Apparatus according to claim 1 or 2. The spectroscope is an ultra-broadband high-resolution spectroscope,
3. Apparatus according to claim 1 or 2. the collection system has a low numerical aperture,
3. Apparatus according to claim 1 or 2. the optical signal is collected from 21 mismatched rays;
3. Apparatus according to claim 1 or 2. A plasma processing system comprising:
a plasma processing chamber;
an optical window positioned in a wall of the plasma processing chamber;
a collection system for collecting the plasma emission spectrum through the optical window;
a spectrometer coupled to the collection system for measuring the plasma emission spectrum;
with
The collection system includes:
a mirror configured to scan a plurality of mismatched beams across the plasma processing chamber;
a telecentric coupler for collecting an optical signal from the plasma and directing said optical signal to said spectrograph;
has
said mirror is a scanning mirror that rotates to sweep said plurality of mismatched beams ;
The collection system further comprises a mirror system for shifting the center of rotation of the plurality of mismatched rays by the scanning mirror from the scanning mirror to or near the optical window;
the mirror system comprises a transfer mirror and a fold mirror positioned between the scanning mirror and the optical window ;
the transfer mirror is configured to transfer the collected optical signal to the fold mirror;
the folding mirror is configured to transfer the collected optical signal to the scanning mirror;
system. A plasma processing system comprising:
a plasma processing chamber;
an optical window positioned in a wall of the plasma processing chamber;
a collection system for collecting the plasma emission spectrum through the optical window;
a spectrometer coupled to the collection system for measuring the plasma emission spectrum;
with
The collection system includes:
a mirror configured to scan a plurality of mismatched beams across the plasma processing chamber;
a telecentric coupler for collecting an optical signal from the plasma and directing said optical signal to said spectrograph;
has
the collection system further comprises a linear arc stage holding the mirror, the telecentric coupler, and the spectrograph;
The linear arc stage is
having a scan angle and a linear scan length,
configured to move the mirror, the telecentric coupler, and the spectrograph along an arcuate path about a center of rotation to scan the plurality of mismatched beams across the plasma processing chamber ; the center is located at or near the optical window and along the central axis of the optical window ;
system . A method for luminescence measurements, comprising:
placing an optical window in the wall of the plasma processing chamber;
providing a collection system for collecting the plasma emission spectrum through the optical window, the collection system comprising a mirror and a telecentric coupler;
scanning a plurality of mismatched beams across the plasma processing chamber using the mirror;
collecting an optical signal from the plasma through the telecentric coupler;
directing an optical signal to a spectrometer for measuring the plasma emission spectrum;
including
said mirror is a scanning mirror that rotates to sweep said plurality of mismatched beams ;
The collection system further comprises a mirror system for shifting the center of rotation of the plurality of mismatched rays by the scanning mirror from the scanning mirror to or near the optical window;
the mirror system comprises a transfer mirror and a fold mirror positioned between the scanning mirror and the optical window ;
the transfer mirror is configured to transfer the collected optical signal to the fold mirror;
The method, wherein the folding mirror is configured to transfer the collected optical signal to the scanning mirror. A method for luminescence measurements, comprising:
placing an optical window in the wall of the plasma processing chamber;
providing a collection system for collecting the plasma emission spectrum through the optical window, the collection system comprising a mirror and a telecentric coupler;
scanning a plurality of mismatched beams across the plasma processing chamber using the mirror;
collecting an optical signal from the plasma through the telecentric coupler;
directing an optical signal to a spectrometer for measuring the plasma emission spectrum;
including
the collection system further comprises a linear arc stage holding the mirror, the telecentric coupler, and the spectrograph;
The linear arc stage is
having a scan angle and a linear scan length,
configured to move the mirror, the telecentric coupler, and the spectrograph along an arcuate path about a center of rotation to scan the plurality of mismatched beams across the plasma processing chamber ; the center is located at or near the optical window and along the central axis of the optical window ;
Method. The method further comprises:
shifting the center of rotation of a plurality of mismatched rays to or near the optical window using a mirror system, the mirror system comprising at least a transfer mirror and a fold mirror;
19. A method according to claim 17 or 18 .

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