CN110998260A

CN110998260A - Spatially resolved Optical Emission Spectroscopy (OES) in plasma processing

Info

Publication number: CN110998260A
Application number: CN201880052425.3A
Authority: CN
Inventors: 孟庆玲; 霍尔格·图特耶; 陈艳; 米哈伊尔·米哈洛夫
Original assignee: Tokyo Electron Ltd
Current assignee: Tokyo Electron Ltd
Priority date: 2017-07-12
Filing date: 2018-07-11
Publication date: 2020-04-10
Anticipated expiration: 2038-07-11
Also published as: JP7266575B2; KR102600883B1; TWI794252B; WO2019014343A1; CN110998260B; TW201920917A; JP2020527705A; KR20200019258A

Abstract

Methods, systems, and apparatus for optical emission measurement are disclosed. The apparatus includes a collection system for collecting an optical emission spectrum of the plasma through an optical window disposed at a wall of the plasma processing chamber. The optical system includes: a mirror configured to scan a plurality of non-coincident rays through the plasma processing chamber; and a telecentric coupler for collecting an optical signal from the plasma and directing the optical signal to a spectrometer for measuring the optical emission spectrum of the plasma.

Description

Spatially resolved Optical Emission Spectroscopy (OES) in plasma processing

Cross Reference to Related Applications

This application claims priority from U.S. patent application No. 15/648,035 entitled "SPATIALLY RESOLVED OPTICALEMISSION SPECTROSCOPY (OES) IN PLASMA PROCESSING" (reference TTI-247), filed on 12.7.7.2017, the entire contents of which are incorporated herein by reference. Further, the present application is incorporated herein by reference to U.S. patent application No. 14/530,164 entitled "SPATIALLY RESOLVED OPTICAL EMISSIONSPECTROSCOPY (OES) IN PLASMA PROCESSING" (reference number TTI-242) filed on 31/10/2014, which is hereby incorporated herein by reference IN its entirety, and which is based on and claims the rights and priority of U.S. provisional patent application No. 61/898,975 entitled "SPATIALLY RESOLVED OPTICAL EMISSION SPECTROSCOPY (OES) IN PLASMA ETCHING" (reference number TTI-242pro v) filed on 1/11/2013.

Background

Technical Field

The present 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, the invention relates to determining a two-dimensional distribution of optical emissions of a plasma from which a two-dimensional distribution of chemical species concentrations can be determined.

Description of the Related Art

The production of semiconductor devices, displays, photovoltaic cells, etc. is carried out in a series of steps, each step having parameters optimized for maximizing device yield. In plasma processing, controlled parameters that strongly influence throughput include the chemistry of the plasma, in particular the local chemistry of the plasma, i.e., the local concentration of various chemical species in the plasma environment proximate to the substrate being processed. Certain species, particularly transient chemical species such as radicals, have a large effect on the plasma processing results and it is known that elevated local concentrations of these species can create regions of faster processing which can lead to non-uniformities in the processing steps and ultimately in the devices being produced.

The chemistry of plasma processing is controlled in a direct or indirect manner through the control of a number of process variables: for example, one or more of RF or microwave power provided to energize the plasma, the type and flow of gas provided to the plasma processing chamber, the pressure in the plasma processing chamber, the type of substrate being processed, the pumping speed delivered to the plasma processing chamber, and the like. Optical Emission Spectroscopy (OES) has proven itself as a useful tool for process development and monitoring in plasma processing. In optical emission spectroscopy, the presence and concentration of certain chemical species of particular interest, such as radicals, are deduced from the optical (i.e. light) emission spectrum of the plasma acquired, wherein the intensity of certain spectral lines and their ratios are related to the concentration of the chemical species. A detailed description of this technique can be found in, for example, selwyn, g.1993, AVS press, "Optical Diagnostic Techniques for Plasma Processing" and will not be repeated here for the sake of brevity.

While the use of optical emission spectroscopy has become relatively common, particularly in plasma process development, it is typically done by acquiring the optical emission spectroscopy from a single elongated volume in the plasma within the plasma processing chamber. The exact shape and size of the volume is determined by the optical system used to collect the optical emission from the plasma. Such collection of optical emission signals inherently results in an averaging of the optical emission spectrum of the plasma along the length of the elongated volume, also referred to as the ray, and thus all information about local variations of the optical emission spectrum of the plasma and thus also about local variations of the chemical species concentration is 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 a chemical species of interest over a substrate being processed, and therefore, changes in system design and/or process parameters can be made to minimize, for example, variations in processing results across the substrate. A further application of plasma optical emission spectroscopy techniques is in determining the endpoint of a plasma processing step by monitoring the evolution and sudden changes of the chemicals present in the plasma, the endpoint of the plasma processing step being associated with an etching step, for example, to a substrate layer of a different chemical composition, one of which is etched during the etching process. The ability to determine the endpoint of a plasma processing step over the entire surface of a substrate helps to improve device yield since the plasma processing step is not terminated prematurely.

One technique that is widely used in other technical fields, such as X-ray tomography, to determine the spatial distribution of variables from known global measurements along a plurality of rays traversing a region of interest is tomographic inversion using the Abel transform or the Radon transform. However, to be effective, this technique requires a large amount of acquired data, i.e., a large number of rays, which is impractical in semiconductor processing tools that limit optical access to the plasma through one or a small number of windows or optical ports built into the plasma processing chamber wall. Tomography techniques are also generally very computationally intensive. It has also been found that the local variation of the chemical concentration is of a substantially smooth nature without any steep gradient in the radial direction and even more so in the circumferential (i.e. azimuthal) direction. It would therefore be advantageous to have a simple, fast and relatively low cost plasma optical emission spectroscopy technique and system that is capable of acquiring a two-dimensional distribution of the plasma optical emission spectrum without the overhead of tomographic methods involving OES measurements.

Most notably, although the variations in the circumferential direction may be small, as some prior art assumes, these variations are not nonexistent, and ideal techniques and systems will still have to be able to reliably capture these variations.

Disclosure of Invention

One aspect of the invention includes an apparatus for optical emission measurement that includes a collection system for collecting a plasma optical emission spectrum through an optical window disposed at a wall of a plasma processing chamber. The optical system includes: a mirror configured to scan a plurality of non-coincident rays through the plasma processing chamber; and a telecentric coupler for collecting an optical signal from the plasma and directing the optical signal to a spectrometer for measuring the optical emission spectrum of the plasma.

An alternative embodiment includes a plasma optical emission measurement system, comprising: a plasma processing chamber; an optical window disposed on a wall of the plasma processing chamber; a collection system for collecting the optical emission spectrum of the plasma through the optical window; a spectrometer coupled to the collection system for measuring the plasma optical emission spectrum. The collection system includes: a mirror configured to scan a plurality of non-coincident rays through the plasma processing chamber; and a telecentric coupler for collecting the optical signal from the plasma and directing the optical signal to the spectrometer.

Yet another embodiment of the present invention includes a method for optical emission measurement, the method comprising: placing an optical window at a wall of a plasma processing chamber; providing a collection system for collecting the optical emission spectrum of the plasma through the optical window, the collection system comprising a mirror and a telecentric coupler; scanning a plurality of non-coincident rays through the plasma processing chamber using a mirror; collecting an optical signal from the plasma via a telecentric coupler; and directing the optical signal to a spectrometer for measuring the optical emission spectrum of the plasma.

Drawings

A more complete understanding of the present invention and many of the attendant advantages thereof will become apparent by reference to the following detailed description, particularly when considered in conjunction with the accompanying drawings wherein:

fig. 1 is a side view schematic diagram of a plasma processing system equipped with an Optical Emission Spectroscopy (OES) measurement system, according to an embodiment.

FIG. 2 is a schematic top view of a plasma processing system equipped with an OES measurement system, according to an embodiment.

FIG. 3 is an exemplary plasma optical emission spectrum acquired using an OES measurement system, according to an embodiment.

Fig. 4 is a schematic diagram of an optical system for use in an OES measurement system, in accordance with an embodiment.

Fig. 5 is a schematic diagram of an optical system for use in an OES measurement system according to another embodiment.

Fig. 6 is an expanded schematic view of an embodiment of an optical system according to an embodiment.

FIG. 7 is an exemplary two-dimensional distribution of plasma optical emission measured using an OES measurement system and associated methods, according to an embodiment.

Fig. 8 is a schematic diagram of an optical system for use in an OES measurement system according to another embodiment.

FIG. 9 is an expanded schematic view of an embodiment of an optical system according to another embodiment.

Fig. 10 is a schematic top view of a plasma processing system equipped with the optical system of fig. 8.

FIG. 11 is an expanded schematic view of an embodiment of an optical system according to another embodiment.

Fig. 12 is a schematic diagram of an optical system for use in an OES measurement system according to another embodiment.

Fig. 13 is a schematic diagram showing exemplary results of a reconstruction pattern of optical emission intensity.

FIG. 14 is a flow chart illustrating a method for optical emission measurement according to one example.

Detailed Description

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

In the description that follows, the term "substrate" that refers to a workpiece being processed may be used interchangeably with terms such as semiconductor wafer, Liquid Crystal Display (LCD) panel, Light Emitting Diode (LED), Photovoltaic (PV) device panel, etc., all of which processes fall within the scope of the claimed invention.

Reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure, material, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention, but does not denote that they are 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 referring to the same embodiment of the invention. Furthermore, the particular features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments.

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

FIG. 1 shows an embodiment of a plasma processing system 10 equipped with a plasma Optical Emission Spectroscopy (OES) system 15. Plasma processing system 10 includes a plasma processing chamber 20 within which is disposed 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, wherein energetic chemicals from plasma 50 are used to perform plasma processing steps on substrate 40. Process gases are flowed into plasma processing chamber 20 (not shown) and a pumping system (not shown) is provided to maintain a vacuum in 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 kind of plasma processing.

The plasma Optical Emission Spectroscopy (OES) system 15 is used to acquire the plasma optical emission spectrum via at least one optical detector 60 that communicates the acquired plasma optical emission spectrum to the controller 80 and is controlled by the controller 80. Controller 80 may be a general purpose computer and may be located proximate to plasma processing system 10 or may be remotely located and connected to optical detector 60 via an intranet or internet connection.

The optical detector 60 has optics configured in such a way as to collect plasma optical emissions from a volume 65 of an elongated, generally pencil-shaped space within the plasma 50. Optical access to the plasma processing chamber is provided through optical window 70. Depending on the application and how aggressive the chemistry of the plasma 50 is, the optical window 70 may comprise a material such as glass, quartz, fused silica, or sapphire. The volume 65, hereinafter referred to as "ray" 65, defines the portion of space from which the optical emission spectrum of the plasma is collected, and the collected spectrum represents the integral of the contribution to the optical emission spectrum of the plasma collected from all points located along the ray 65 and within the ray 65. It should be noted that depending on the geometry and configuration of optical detector 60, the contribution of each point within ray 65 will not be equal, but rather weighted and controlled by optical efficiency (discussed in more detail later). In a typical configuration, ray 65 is oriented substantially parallel to the surface of substrate 40 and is held at a small distance from the surface of substrate 40 in order to reduce optical interference from the substrate surface, yet is held close enough to substrate 40 to sample the plasma chemistry proximate the substrate surface.

As previously mentioned, the controller 80 is used to control the plasma optical emission spectroscopy system 15, and is also used to calculate (1) a plasma optical intensity distribution from spatial position and wavelength, and to calculate (2) a spatial distribution of the chemical species of interest from the calculated plasma optical intensity distribution. This information may 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 ray 65 traversing a plasma 50 located within plasma processing chamber 20, the ray being proximate to a substrate 40 being processed. In an embodiment of the present invention, a plurality of rays 100 may be used to sample the plasma optical emission spectrum, as shown in FIG. 2, which FIG. 2 shows a top schematic view of, for example, the plasma processing system 10 of FIG. 1. In the exemplary embodiment of fig. 2, two optical detectors 60 are used to collect the plasma optical emission spectra, each from 7 rays 100. The rays 100 need to be misaligned so that the maximum amount of spatial information is obtained from the plasma 50 above the substrate 40. The number of rays 100 per optical detector 60 may vary from 2 to 9 and above 9. Furthermore, in another embodiment, a single optical detector 60 may be used with its associated fan of radiation 100, with optical access provided to plasma processing chamber 20 through only a single optical window 70. Alternatively, three or more optical detectors may be used, each having an associated ray fan. The angle of each ray 100 with respect to the centerline of its optical detector 60 is defined as

As shown in fig. 2, each point within the plasma processing chamber may be defined by its polar coordinates, i.e., (r, θ).

According to the optical detector 60, as will be described in more detail laterConfigured, all plasma optical emission spectra from the fan of associated rays 100 can be collected simultaneously. This is suitable for embodiments of the optical detector 60 having multiple optical systems and channels, allowing simultaneous collection from all rays 100. Alternatively, the plasma optical emission spectrum may be acquired sequentially along the ray 100 associated with the optical detector 60. The latter is suitable for scanning embodiments where the optical emission spectrum of the plasma follows the ray 100 from an angle

Scan to another angle and collect. It will be appreciated that the scanning and acquisition needs to occur fast enough so that rapid changes in plasma chemistry can be detected across the substrate.

FIG. 3 illustrates the use of an optical detector 60 from an angle

An exemplary optical emission spectrum of the plasma acquired from one ray 100. In this spectrum, the intensities of M wavelengths are collected, typically in the range of about 200nm to about 800 nm. The CCD of a typical spectrometer for optical emission spectroscopy has 4096 pixels across the wavelength range, but the number of pixels can vary as low as 256 and as high as 65536 depending on the desired resolution of the spectrum applied and collected.

The optical emission spectrum of the plasma collected by the optical detector 60 from the fan of its associated radiation 100 is passed to the controller 80, which is used to further process the passed data to calculate the spatial distribution of the optical emission of the plasma and hence the chemical concentration. One aspect of the present invention is an algorithm for rapidly calculating the spatial distribution of the plasma optical emission at each wavelength that allows in-situ monitoring of the plasma process for endpoint detection, fault detection, etc.

Fig. 4 shows an embodiment of optical detector 60 in which a single multi-channel spectrometer 310 is used to collect the plasma optical emission spectra from rays 305A to 305E simultaneously. For clarity, the exemplary embodiment shown here has 5 rays 305A through 305E, but the number may vary from 2 to 9 and even above 9. Optical detector 60 includes an optical system 300A through 300E for each ray 305A through 305E, all of which are positioned proximate to a wall mounted optical window 70 of plasma processing chamber 20. The rays 305A to 305E are arranged in a divergent manner so as to cover the relevant portion of the substrate 40 (not shown). The collected plasma optical emission spectra are fed from optical systems 300A-300E into multichannel spectrometer 310 via respective optical fibers 320A-320E. The optical systems 300A to 300E will be described in more detail later. Since the embodiment of fig. 4 is capable of collecting the optical emission spectrum of the plasma at the same time, it is suitable for rapid diagnosis.

Fig. 5 shows an alternative embodiment in which a single channel spectrometer 310 is used and rays 305A to 305E are formed by a scanning mirror 400 that is controllably scanned to scan the rays 305A to 305E while the plasma optical emission spectrum is acquired by the spectrometer 310 via a single optical system 300, as will be described in more detail later. This embodiment is suitable for sequential collection of plasma optical emission spectra and is therefore more suitable for diagnosis of slower evolving plasma processes. The scanning mirror 400 can be mounted on a galvanometer stage 410 and actuated by the galvanometer stage 410. Alternatively, the scan mirror 400 can be mounted on the stepper motor 410 and scanned by the stepper motor 410. The number of rays 305A to 305E is shown here as 5, but in practice this number is determined by settings in the controller software for controlling the galvanometer stage or stepper motor 410.

To ensure that an accurate volume of space is sampled, the optical systems 300A-300E of fig. 4 and the optical system 300 of fig. 5 need to be configured such that the rays 305A-305E are collimated, with divergence angles as small as can be feasibly achieved for a given target cost of the optical system.

Exemplary embodiments of optical systems 300A-300E and 300 are shown in fig. 6. The optical systems 300A to 300E, also referred to as telecentric couplers, have the following tasks: the plasma optical emission spectrum is collected from the volume of space within plasma 50 defined by rays 305A-305E and directed to end 390 of optical fibers 320A-320E or 320, whereupon the collected plasma optical emission spectrum is transmitted to spectrometer 310 of the embodiment of fig. 4 or 5. The diameter of the rays 305A-305E is defined by an optional hole 350 formed in the plate. In alternative embodiments, other optical components, such as lenses, may be used to define the diameter of rays 305A-305E. An example ray diameter is 4.5mm, but depending on the application, an example ray diameter may vary from about 1mm to 20 mm. Collected rays 305A-305E are passed through a combination of collection lenses (collection lenses)360A and 360B, which

collection lenses

360A and 360B in combination with optional apertures define rays 305A-305E. The numerical aperture of the collection system and rays 305A-305E is typically very low, e.g., about 0.005, and the resulting rays 305A-305E are substantially collimated with minimal divergence. At the other end of the optical system 300A-300E or 300 is another lens pair, coupling lenses 370A and 370B, which coupling lenses 370A and 370B are used to focus the collected optical emission spectra onto the end 390 of the optical fibers 320A-320E or 320. All lenses used in the system are preferably achromatic or even apochromatic for more demanding applications, which ensures that the focal length of each lens does not vary with wavelength, so that the optical system 300A to 300E or 300 operates satisfactorily over a large wavelength range, typically from 200 to 800nm, but in some cases as low as 150 nm. To achieve better performance in the Ultraviolet (UV) portion of the spectrum, i.e., 350nm and less than 350nm, UV grade materials are used for all optical components.

For each optical hardware configuration, it is important to know the optical efficiency w, which is a weighting factor applied to all points within rays 305A through 305E from which the plasma optical emission spectra are acquired. The optical efficiency w can be determined by simulation using optical design software, or by the following experiment: a calibration light source is used and moved across rays 305A-305E and along rays 305A-305E to determine the coupling efficiency of light from a given location within rays 305A-305E to fiber end 390. The optical efficiency w will be used in the algorithm for determining the spatial distribution of the optical emission of the plasma.

As previously mentioned, the tasks of the plasma Optical Emission Spectroscopy (OES) system 15 are as follows: a two-dimensional intensity distribution of the optical emission of the plasma is determined for each of the M measured wavelengths λ.

For each ray 100 of FIG. 2, the ray is mathematically represented by an index i, and the collected optical detector output D_iCan be defined as:

where I (r, θ) is the plasma optical emission intensity at a location (r, θ) within the ray 100 and along the ray 100, and w (r, θ) is the optical efficiency for light collected by the optical detector I from the location (r, θ). The resulting optical detector output D_iRepresenting the integral of the product of these quantities along a straight-line path from point a to point B on the circumference of the substrate (see fig. 2), the contribution from the plasma outside the circumference of substrate 40 is ignored in this model (this is a valid assumption since plasma density and hence plasma light emission is generally low in these regions).

In a plasmonic optical emission spectroscopy system 15 having N optical detectors and radiation, or alternatively radiation 100 having N scanning positions, there are N collected intensities for each of the M measured wavelengths λ. Therefore, in order to reconstruct the spatial distribution of the optical emission of the plasma at one wavelength λ, a functional form with N parameters must be assumed. In view of the limited number N of parameters, a judicious choice of the basis functions for the distribution of the plasma optical emission needs to be made. The basis function chosen needs to vary with both the radial coordinate r and, in addition, the circumferential coordinate θ, so that the basis function can satisfactorily reproduce the circumferential variation of the plasma emission on the substrate 40.

One class of basis functions that is particularly well suited to this task is the Zernike (Zernike) polynomial Z_p(r, θ). Zernike polynomials are defined as the product of a term dependent on the radial coordinate r and a term dependent on the circumferential coordinate θ, i.e.

Z_p(r，θ)＝R(r)G(θ)。

Table 1 lists the first 18 th order Zernike polynomials which use the common mathematical notation herein

To indicate.

TABLE 1 first 18 order Zernike polynomials

In general, other basis functions may be chosen in this application, as long as they are orthogonal and as long as their derivatives are continuous over the unit circle, as is the case with zernike polynomials. However, zernike polynomials are preferred in this application because of their following properties: a relatively small number of terms can be used to describe a fairly complex variation of the function of polar coordinates, both radial and circumferential.

A zernike polynomial Z_p(r, theta) into the collected detector output

Wherein, a_pAre the fitting parameters associated with each basis function, i.e., the zernike polynomial order.

The collected detector output D is now defined according to the selected basis functions, fitting parameters and optical efficiency_iDetermining D_iFitting parameter a of_pIs reduced to minimize the problem of solving the least squares problem

Or

Wherein the content of the first and second substances,

representing the measured optical spectral intensity of the plasma at ray i. The minimization algorithm needs to be repeated for each of the M measured wavelengths λ. A number of methods are known in the art for solving this least squares problem. Because the dimension of the least squares problem is relatively small, it can be effectively solved for all wavelengths for each instant the optical emission spectrum of the plasma is measured; and furthermore, such calculations can be repeated in rapid succession, enabling the determination of a rapidly evolving two-dimensional distribution of the plasma optical emission for a large number-M-wavelengths. From these rapidly evolving two-dimensional distributions of plasma optical emissions, a time-evolving two-dimensional distribution of chemical species concentrations on substrate 40 can then be determined, which can be used for endpoint detection, fault detection, process development, process tool development, and the like.

FIG. 7 shows an example of one such plasma optical emission intensity distribution determined using a method according to an embodiment of the present invention. Despite the relatively small number of terms, i.e., N-18, the depicted distribution clearly shows good capture of both radial and circumferential variations in the plasma optical emission intensity.

Fig. 8 shows an alternative embodiment in which a single channel spectrometer 310 is used. Rays 305A-305E are formed by scanning mirror 400 and mirror system 800 that moves the center of rotation of rays 305A-305E from the position of stepper motor 410 associated with scanning mirror 400 to optical window 70 or substantially near such optical window 70, as shown by point C in fig. 8 (i.e., point C shows the center of rotation).The optical window 70 is typically small (i.e., 1 inch in diameter) so as to sweep out the rays 305A-305E (e.g., the angle θ of the central axis of the plasma processing chamber 20) through the plasma 50_max25 deg.), rays 305A through 305E have minimal deviation at optical window 70. Thus, the center of rotation of rays 305A-305E is configured to be substantially near optical window 70 or at optical window 70. Using the configurations described herein, it is possible to use windows having dimensions of 68.5mm x 8mm or larger. The window size (i.e., upper limit) is limited by the following factors: such as contamination, chamber UV and RF leakage, and available space at the walls of plasma processing chamber 20. In one implementation, the window may have a large-sized rectangular shape in a plane corresponding to the plane of scanning of the beam. This has the advantage of minimising the size of the window whilst meeting leakage and space requirements.

Scanning mirror 400 is controllably scanned to sweep rays 305A through 305E using stepper motor 410 while the plasma optical emission spectra are acquired by spectrometer 310 via a single optical system 300.

Mirror system 800 can include a transfer mirror 802 and a fold mirror 804. Each collected ray 305A through 305E or 65 (i.e., the optical signal from the plasma with the collected ray 305) is transmitted by a transfer mirror 802 that reflects the collected ray 305 and transfers the collected ray 305 to a fold mirror 804. Fold mirror 804 reflects collected rays 305 from horizontal (azimuthal) concentricity to vertical concentricity and passes collected rays 305 to scanning mirror 400, which reflects collected rays 305 to optical system 300. The mirror system 800 and the optical system 300 are stationary. Mirror system 800, scanning mirror 400, optical system 300, and spectrometer 310 can be mounted proximate to plasma processing chamber 20.

As the scan mirror 400 is swept, a high spatial resolution spatial distribution of chemical concentration is obtained. For example, the scanning mirror 400 can be slowly swept while acquiring the optical emission spectrum of the plasma. Acquired optical emission spectrum of plasma and-theta_maxFrom DEG to + theta_maxAny position relationship between. Thus, using the scanning device described herein, one can obtainVery accurate spatial resolution.

Fig. 9 is an expanded schematic view of an embodiment of the optical system 300 of fig. 8, according to an embodiment. The optical system 300 has the following tasks: the plasma optical emission spectrum is collected from the volume of space within the plasma 50 defined by the collected rays 305 and directed to the end 390 of the optical fiber 320, so that the plasma optical emission spectrum can be transmitted to the spectrometer 310 as previously described herein. The optical system 300 includes a telecentric coupler having a small NA. The size of the collected scanning rays may vary in diameter from about 3mm to 5mm along the collection path.

The collected rays 305 (i.e., rays reflected from the scan mirror 400) are passed through a first collection lens 902. The rays may then be passed through a telecentric aperture 908, for example, having a diameter of 600 μm. Two

coupling lenses

904 and 906 are then used to focus the collected optical emission spectrum onto the end 390 of the optical fiber 320. In one example, the optical fiber 320 has a diameter of 600 μm. The collection system 300 may also include an optional filter positioned between the two

coupling lenses

904 and 906.

The numerical aperture of collection system 300 is very low, e.g., 0.005.

Lenses

902, 904, 906 are achromatic lenses having effective focal lengths of 30mm, 12.5mm, and 12.5mm, respectively, and having diameters of 12.5mm, 6.25mm, and 6.25mm, respectively.

Referring back to FIG. 8, the scan mirror 400 can have dimensions of at least 10mm by 10 mm. The transfer mirror 802 may be a spherical mirror. The scanning mirror 400 and the transfer mirror 802 can have an aluminum coating, a multi-layer dielectric film on top of the aluminum, or a silicon monoxide (SiO) overcoat to increase the reflectivity of a particular wavelength region (e.g., UV). The radius of the transfer mirror 802 may be between 100mm and 120 mm. In one implementation, the radius of the transfer mirror 802 is 109.411 mm. The transfer mirror 802 may be located at a distance of 68.4mm from the outer edge of the optical window 70. The fold mirror 804 can be located at a distance of 71.5mm from the plane of the scan mirror 400.

The spectrometer 310 may be an ultra-wideband (UBB) high resolution spectrometer having a spectral resolution of 0.4nm and having a wavelength range between 200nm and 1000 nm.

Fig. 10 is a schematic top view of a plasma processing system equipped with the optical system of fig. 8. The plasma processing chamber 20 can be equipped with two optical systems of fig. 8. This optical system is called a scanning module. Each scan module may be configured to collect data from X to Y ray positions. In one implementation, each scan module may be configured to collect data from 5 to 50 ray positions that provide better accuracy to detect events with high spatial resolution. In fig. 10, one location of ray 305 is shown. As previously described herein, the scan angle of ray 305 may be from- θ_maxChange to + theta_maxDEG (e.g. theta)_max25 ° or 30 °). Data from spectrometer 310 is processed as previously described herein to obtain a two-dimensional (2D) OES intensity distribution. Each module may include a single channel spectrometer 310, or alternatively, a single spectrometer with two channels may be used for both scanning modules. Additional scanning modules may also be used to provide higher spatial resolution. The optical windows 70 (i.e., the optical windows 70 of each scan module) can be located on the sidewalls of the plasma processing chamber 20 perpendicular or substantially perpendicular to each other. Depending on the configuration of the plasma processing chamber 20, the optical window 70 may be quartz, fused silica, or sapphire depending on the application and how aggressive the chemistry of the plasma is.

Fig. 11 is an expanded schematic view of an embodiment of the optical system 300 of fig. 5 or 8. The optical system 300 has the following tasks: the reflected collected plasma optical emission spectrum is directed from the scanning mirror 400 to the end 390 of the optical fiber 320 so that the reflected collected plasma optical emission spectrum can be transmitted to the spectrometer 310 as previously described herein. The collected rays 305 are passed through a collection lens, which may be, for example, a triplet lens 1102 having an effective focal length of 40 mm. The collected rays 305 may be passed through an optional mask aperture 1108, for example, having a diameter of 7 mm. The mask aperture 1108 may be located between the scan mirror 400 and the triplet 1102. The collected rays 305 may then be passed through an optional telecentric aperture 1110, for example, having a diameter of 1.20 mm. In alternative embodiments, other optical components, such as lenses, may be used to define the diameter of the ray 305.

Two

coupling triplet lenses

1104 and 1106 are used to focus the collected optical emission spectrum onto the end 390 of the optical fiber 320. In one implementation,

coupling triplet lenses

1104 and 1106 may be triplet lenses having an effective focal length of 15 mm. The effective focal length of the

coupling triplet

1104 and 1106 is a function of the type and diameter of the fiber 320.

All lenses used in the system are preferably achromatic or even apochromatic for more demanding applications, which ensures that the focal length of each lens does not vary with wavelength, so that the optical system 300A to 300E or 300 operates satisfactorily over a large wavelength range, typically from 200 to 1000nm, but in some cases as low as 150 nm. To obtain better performance in the UV portion of the spectrum, i.e. 350nm and less than 350nm, UV grade materials such as quartz, fused silica, calcium fluoride (CaF2) are used for all optical components.

Fig. 12 is a schematic diagram of an alternative embodiment in which a single channel spectrometer 310 is used. One or both modules may be used to sequentially acquire the optical emission spectrum of the plasma. Each module may include a linear arc stage 1204. Spectrometer 310, optical system 300, and fold mirror 1202 are mounted on linear arc stage 1204. Fold mirror 1202 is positioned to receive collected radiation 305 from plasma processing chamber 20 and reflect collected radiation 305 to optical system 300. The linear arc stage 1204 is controllably scanned to sweep out the collected rays 305 while the plasma optical emission spectra are acquired by the spectrometer 310 via the single optical system 300. The linear arc stage 1204 may be controlled via the controller 80. Point C in fig. 12 represents the center of rotation of the linear arc stage 1204. The single optical system 300 may be the optical system shown and described in fig. 9 or fig. 11. In one implementation, the linear arc stage 1204 may have a scan angle of 85 ° and a length of 163.2 mm. The linear scan speed may vary from 0.35m/s to 2.2 m/s. Accordingly, the scan speed may be adjusted to optimize the trade-off between spatial resolution and speed depending on the application of the plasmonic optical emission spectroscopy system 15.

In other embodiments of the optical system 300 of fig. 6, 9, and 11, other optical components, such as mirrors, prisms, lenses, spatial light modulators, digital micromirror devices, and the like, may be used to manipulate the collected light 305. The configuration and component layout of the optical system 300 of fig. 4-6 and 8-12 need not be exactly as shown in fig. 4-6 and 8-12, but the collected radiation 305 may be folded and manipulated by way of additional optical components in order to package the plasma optical emission spectroscopy system 15 into a compact package suitable for mounting on the walls of the plasma processing chamber 20.

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

Fig. 13 is a schematic diagram showing exemplary results of a reconstruction pattern of optical emission intensity. The intensity of the emission line (i.e., 522.45nm for silicon chloride) represents the concentration of silicon chloride (SiCl), which in turn correlates to the intensity of the localized etch on substrate 40. Fig. 13 shows a comparison between the actual distribution of optical emission at 522.5nm and the actual etch rate obtained by plasma OES system 15 described herein. Plot 1302, plot 1304, and plot 1306 show the actual etch rates of the respective samples under various plasma processing conditions. Block 1308, block 1310, and block 1312 show the reconstructed optical emission distributions of the samples associated with block 1302, block 1304, and block 1306, respectively.

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

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

Fig. 14 is a flow chart illustrating a method 1400 for optical emission measurement according to one example. At 1402, an optical window is placed at a wall of a plasma processing chamber (e.g., plasma processing chamber 20). At 1404, a collection system for collecting a plasma optical emission spectrum through an optical window is provided. The collection system may include a mirror and a telecentric coupler. The telecentric coupler can include at least one collection lens (e.g.,

collection lenses

360A and 360B) and at least one coupling lens (e.g.,

coupling lenses

904 and 906 of fig. 9). At 1406, a plurality of non-coincident rays are scanned through the plasma processing chamber using a mirror. The scanning may be controlled by a controller 80. At 1408, an optical signal is collected from the plasma via the telecentric coupler. At step 1410, the optical signal is directed to a spectrometer for measuring the optical emission spectrum of the plasma.

One skilled in the relevant art will appreciate that many modifications and variations are possible in light of the above teaching. Those skilled in the art will recognize various equivalent combinations and substitutions for various components shown in the figures. 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 embodiments listed below.

(1) A method for optical emission measurement, comprising: placing an optical window at a wall of a plasma processing chamber; providing a collection system for collecting the optical emission spectrum of the plasma through the optical window, the collection system comprising a mirror and a telecentric coupler; scanning a plurality of non-coincident rays through the plasma processing chamber using the mirror; collecting an optical signal from the plasma via the telecentric coupler; and directing the optical signal to a spectrometer for measuring the plasma optical emission spectrum.

(2) The method of feature (1), wherein the telecentric coupler comprises: at least one collecting lens; and at least one coupling lens.

(3) The method of feature (2), wherein the at least one collection lens or the at least one coupling lens is an achromatic lens.

(4) The method of feature (2), wherein the telecentric coupler further comprises: an aperture disposed between the at least one collection lens and the at least one coupling lens for defining a diameter of the plurality of non-coincident rays.

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

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

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

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

(9) The method according to feature (8), wherein the mirror system comprises: a transfer mirror; a folding mirror; and wherein the transfer mirror is configured to transfer the collected signal to the fold mirror, and the fold mirror is configured to transfer the collected signal to the mirror.

(10) The method of feature (1), wherein the telecentric coupler comprises: a collection triplet configured to collect the optical signal from the mirror; and two coupling triplet lenses configured to focus the collected signals into the end of an optical fiber coupled to the spectrometer.

(11) The method of feature (1), further comprising collecting the plasma optical emission spectrum via a second optical window disposed at the wall of the plasma processing chamber using a second collection system. The central axis of the second optical window is perpendicular to 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 spectrometer, the linear arc stage configured to move radially relative to a central axis of the optical window such that the plurality of misaligned rays are scanned through the plasma processing chamber.

(13) The method according to feature (12), wherein the mirror is a fold mirror.

(14) The method of any of features (1) through (13), wherein the plurality of non-coincident rays are scanned through the plasma processing chamber at 25 ° of a central axis of the optical window.

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

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

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

Claims

1. An apparatus for optical emission measurement, the apparatus comprising:

a collection system for collecting a plasma optical emission spectrum through an optical window disposed at a wall of a plasma processing chamber, the optical system comprising:

a mirror configured to scan a plurality of non-coincident rays through the plasma processing chamber; and

a telecentric coupler for collecting an optical signal from the plasma and directing the optical signal to a spectrometer for measuring the optical emission spectrum of the plasma.

2. The apparatus of claim 1, wherein the telecentric coupler comprises:

at least one collecting lens; and

at least one coupling lens.

3. The apparatus of claim 2, wherein the at least one collection lens or the at least one coupling lens is an achromatic lens.

4. The apparatus of claim 2, wherein the telecentric coupler further comprises:

an aperture disposed between the at least one collection lens and the at least one coupling lens for defining a diameter of the plurality of non-coincident rays.

5. The apparatus of claim 1, wherein the mirror is a scanning mirror.

6. The apparatus of claim 5, wherein the scanning mirror is mounted on and scanned by a galvanometer scanning stage.

7. The apparatus of claim 5, wherein the scan mirror is mounted on and scanned by a stepper motor.

8. The apparatus of claim 5, wherein the collection system further comprises:

a mirror system for shifting a center of rotation of the plurality of non-coincident rays to or near the optical window.

9. The apparatus of claim 8, wherein the mirror system comprises:

a transfer mirror;

a folding mirror; and

wherein the transfer mirror is configured to transfer the collected signals to the fold mirror, and the fold mirror is configured to transfer the collected signals to the mirror.

10. The apparatus of claim 1, wherein the telecentric coupler comprises:

a collection triplet configured to collect the optical signal from the mirror; and

two coupling triplet lenses configured to focus the collected signals into an end of an optical fiber coupled to the spectrometer.

11. The apparatus of claim 1, further comprising:

a second collection system for collecting the plasma optical emission spectrum through a second optical window disposed at a wall of the plasma processing chamber, the second optical window having a central axis perpendicular to a central axis of the optical window.

12. The apparatus of claim 1, wherein the collection system further comprises:

a linear arc stage holding the mirror, the telecentric coupler, and the spectrometer, the linear arc stage configured to move radially relative to a central axis of the optical window such that the plurality of misaligned rays are scanned through the plasma processing chamber.

13. The apparatus of claim 12, wherein the mirror is a fold mirror.

14. The apparatus of claim 1, wherein the plurality of non-coincident rays are scanned through the plasma processing chamber at 25 ° of a central axis of the optical window.

15. The apparatus of claim 1, wherein the spectrometer is an ultra-wideband high resolution spectrometer.

16. The apparatus of claim 1, wherein the collection system has a low numerical aperture.

17. The apparatus of claim 1, wherein the optical signals are collected from 21 non-coincident rays.

18. A system for plasma processing, comprising:

a plasma processing chamber;

an optical window disposed on a wall of the plasma processing chamber;

a collection system for collecting a plasma optical emission spectrum through the optical window;

a spectrometer coupled to the collection system for measuring the plasma optical emission spectrum; and

wherein the collection system comprises:

a telecentric coupler for collecting an optical signal from the plasma and directing the optical signal to the spectrometer.

19. A method for optical emission measurement, comprising:

placing an optical window at a wall of a plasma processing chamber;

providing a collection system for collecting the optical emission spectrum of the plasma through the optical window, the collection system comprising a mirror and a telecentric coupler;

scanning a plurality of non-coincident rays through the plasma processing chamber using the mirror;

collecting an optical signal from the plasma via the telecentric coupler; and

directing the optical signal to a spectrometer for measuring the optical emission spectrum of the plasma.

20. The method of claim 19, further comprising:

shifting a center of rotation of the plurality of non-coincident rays to or near the optical window using a mirror system, the mirror system comprising at least a transfer mirror and a fold mirror.