Multispot optical systems and methods of using the same

Abstract

To provide optical spectroscopy systems and methods of use, regarding improvements of systems for multipoint monitoring of optical signals during semiconductor processes from within semiconductor processing equipment.SOLUTION: The disclosure provides an optical system, a semiconductor processing system, and a method for processing a semiconductor wafer. In one example, the optical system includes: a light source configured to provide source light to a source plane to form a plurality of first subbeams; optical elements configured to modify each of the first subbeams to form a plurality of interrogation spots on a wafer according to a predetermined pattern, where the optical elements are further configured to modify each of the first subbeams upon reflection from the wafer to form a plurality of second subbeams upon an image plane; and a spectrometer configured to receive collected light from the plurality of second subbeams.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] This application claims the benefit of U.S. Provisional Application No. 64 / 647,513, filed May 14, 2024 by John Corless, and U.S. Provisional Application No. 63 / 567,314, also filed March 19, 2024 by John Corless, which applications are assigned to the assignee of the present application and are incorporated herein by reference in their entireties.

[0002] The present disclosure relates generally to optical spectroscopy systems and methods of use, and more particularly to an improved system for multi-point monitoring of optical signals during semiconductor processing from within semiconductor processing equipment. [Background technology]

[0003] Optical monitoring of semiconductor processes is a well-established method for controlling processes such as etching, deposition, chemical-mechanical polishing, and implantation. Optical emission spectroscopy (OES) and interferometric endpoint detection (IEP) are two fundamental types of operational modes for data collection. In OES applications, light emitted from the process (usually from a plasma) is collected and analyzed to identify and track changes in atomic and molecular species that indicate the state or progress of the monitored process. In IEP applications, light is typically provided by an external light source, such as a flash lamp, and directed toward the workpiece. When reflected from the workpiece, the source light conveys information in the form of workpiece reflectance, which indicates the workpiece's condition. Extracting and modeling the workpiece reflectance allows for understanding film thickness and feature size / depth / width, among other properties. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] U.S. Patent No. 7,049,156 Summary of the Invention [Means for solving the problem]

[0005] In one aspect, an optical system is disclosed. In one example, the optical system includes: (1) a light source configured to provide source light to a light-emitting surface to form a plurality of first sub-beams; (2) an optical element configured to modify each of the plurality of first sub-beams to form a plurality of interrogation spots on the wafer according to a predetermined pattern, the optical element further configured to modify each of the plurality of first sub-beams upon reflection from the wafer to form a plurality of second sub-beams at an image plane; and (3) a spectrometer configured to receive light collected from the plurality of second sub-beams.

[0006] In another aspect, the present disclosure provides a semiconductor processing system. In one example, the processing system includes: (1) a processing chamber; (2) a light source configured to provide source light to a plurality of first optical fibers; (3) a spectrometer configured to receive collected light from a plurality of second optical fibers; and (4) an inspection region within the processing chamber including a plurality of inspection spots on a wafer, each of the plurality of inspection spots being defined by a pairwise arrangement of a plurality of the first optical fibers and a plurality of the second optical fibers.

[0007] In yet another aspect, a method for processing a semiconductor wafer is disclosed. In one example, the method includes: (1) illuminating a wafer in a semiconductor processing chamber with light provided by a light source through a plurality of first optical fibers, (2) collecting light reflected from the wafer through a plurality of second optical fibers, (3) processing the collected light using a plurality of input spectrometers, and (4) providing one or more control trends for controlling processing of the wafer according to the process.

[0008] Reference is now made to the following descriptions taken in conjunction with the accompanying drawings. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a block diagram of a system for monitoring and / or controlling the state of a plasma or non-plasma process within a semiconductor process tool employing OES and / or IEP. [Figure 2] FIG. 1 is a simplified diagram of the beam forming portion of a typical refractive system used in IEP. [Figure 3] 1 is a simplified diagram of a multiplexed beamforming portion of a refractive system used in an IEP according to the present disclosure. [Figure 4A] FIG. 4 is a set of plots of performance data representing a design of a system of the type described in connection with FIG. 3 in accordance with the present disclosure. [Figure 4B] FIG. 4 is a set of plots of performance data representing a design of a system of the type described in connection with FIG. 3 in accordance with the present disclosure. [Figure 4C] FIG. 4 is a set of plots of performance data representing a design of a system of the type described in connection with FIG. 3 in accordance with the present disclosure. [Figure 5A] FIG. 10 is a 3D diagram of an alternative multiplexing beamforming portion of a refractive system used in an IEP according to the present disclosure. [Figure 5B] FIG. 10 is a 3D diagram of an alternative multiplexing beamforming portion of a refractive system used in an IEP according to the present disclosure. [Figure 5C] FIG. 10 is a 3D diagram of an alternative multiplexing beamforming portion of a refractive system used in an IEP according to the present disclosure. [Figure 5D] FIG. 10 is a 3D diagram of an alternative multiplexing beamforming portion of a refractive system used in an IEP according to the present disclosure. [Figure 6A] 5A-5D according to the present disclosure. FIG. [Figure 6B] 5A-5D according to the present disclosure. FIG. [Figure 7] FIG. 1 illustrates an example of a multimode optical circulator that can be used in the multipoint optical system disclosed herein. [Figure 8] FIG. 1 shows an example of a target beam layout on a wafer. [Figure 9] 1A-1C illustrate exemplary configurations of optical fibers for separating incoming and outgoing sub-beams using fiber pairing and defocusing in accordance with the principles of the present disclosure. [Figure 10A] FIG. 10 shows an example of specific performance data and its variability using defocus over a range of wavelengths for the fiber array of FIG. 9. [Figure 10B] 10 shows an example of specific performance data and its variability with defocus over different wavelength ranges for the fiber array of FIG. 9. FIG. [Figure 11] FIG. 1 is a block diagram of several optical, electrical, and computational components of a spectrometer and an exemplary associated system in accordance with the principles of the present disclosure. [Figure 12] FIG. 1 illustrates a computing device that may be used in the processes disclosed herein, such as identifying and processing signals in spectral data. [Figure 13] 13 is a flow diagram of a method 1300 for processing a semiconductor wafer in accordance with the principles of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0010] In the following description, reference is made to the accompanying drawings, which form a part hereof, and in which is shown, by way of illustration, specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized. It is also to be understood that structural, procedural, and system changes may be made without departing from the spirit and scope of the invention. Therefore, the following description should not be construed in a limiting sense. For clarity of illustration, like features shown in the accompanying drawings will be designated with like reference numerals, and like features as shown in alternative embodiments of the drawings will be designated with like reference numerals. Other features of the invention will become apparent from the accompanying drawings and the following detailed description. It should be noted that for clarity of illustration, certain elements in the drawings may not be drawn to scale.

[0011] The continuous advancement of semiconductor processes toward faster processes, smaller feature sizes, more complex structures, larger wafers, and more complex process chemistries places increasing demands on process monitoring technologies. For example, higher data rates necessitate the accurate monitoring of much faster etch rates into extremely thin layers, where changes in the order of angstroms (a few atomic layers) are significant for structures such as fin field-effect transistors (FINFETs) and three-dimensional NAND (3D NAND) structures. Both OES and IEP methodologies often require wider optical bandwidths and greater signal-to-noise ratios to aid in the detection of small changes in reflectivity and / or optical emission.

[0012] Larger wafer sizes with smaller overall component feature sizes and stringent requirements for within- and between-wafer uniformity impose many constraints on the design of semiconductor processing equipment. These constraints can limit the implementation of features that support optical monitoring access. For example, typical inspection of wafers often uses signal integration over a single, relatively large spot to characterize a representative state of the wafer process. Due to the ever-increasing complexity and variety of structures, films, film stacks, and structural geometries on wafers, using a single, large spot to characterize a representative state of the wafer is becoming insufficient.

[0013] With a particular focus on monitoring and evaluating the state of a semiconductor process within a process tool, FIG. 1 illustrates a block diagram of a process system 100 for utilizing OES and / or IEP to monitor and / or control the state of a plasma or non-plasma process within a semiconductor process tool 110. The semiconductor process tool 110, or simply process tool 110, generally encloses a workpiece (represented in FIG. 1 by a wafer 120) and possibly a process plasma 130 within the typically partially evacuated volume of a processing chamber 135 that may contain various process gases. The process tool 110 may include one or more optical interfaces 140 that allow viewing into the processing chamber 135 at various locations and orientations. The interfaces 140 may include multiple types of optical elements, such as, but not limited to, optical filters, lenses, windows, apertures, mirrors, beam splitters, optical fibers, etc.

[0014] In IEP applications, a light source 150 may be connected to the interface 140 either directly or via a fiber optic cable assembly 153. As shown in this configuration, the interface 140 is oriented perpendicular to the surface of the wafer 120 and is often centered relative to the surface. Light from the light source 150 may enter the interior volume of the process chamber 135 in the form of a collimated beam 155. The beam 155 may be received again by the interface 140 upon reflection from the wafer 120. In a typical application, the interface 140 may be an optical collimator. Following reception by the interface 140, the light may be transmitted via a fiber optic cable assembly 157 to a spectrometer 160 for detection and conversion to a digital signal. The light may include source light and detection light and may include, for example, a wavelength range from deep ultraviolet (DUV) to near-infrared (NIR). The wavelength of interest may be selected from any subrange of the wavelength range.

[0015] After detection and conversion of the received optical signal by the spectrometer 160 to an analog electrical signal, the analog electrical signal is typically amplified and digitized within a subsystem of the spectrometer 160 and passed to a signal processor 170. The signal processor 170 may be, for example, an industrial PC, a PLC, or other system that employs one or more algorithms to generate an output 180, such as an analog or digital control value representing the intensity of a particular wavelength or the ratio of two wavelength bands. Alternatively, rather than being a separate device, the signal processor 170 may be integrated with the spectrometer 160. The signal processor 170 may employ OES algorithms that analyze the emission intensity signal at a predetermined wavelength and determine trend parameters related to the state of the process (e.g., endpoint detection, etch depth, etc.) that can be used to access that state. In IEP applications, the signal processor 170 may employ an algorithm that analyzes a broadband portion of the spectrum to determine film thickness. See, for example, U.S. Patent No. 7,049,156, "System and Method for In-situ Monitor and Control of Film Thickness and Trench Depth," which is incorporated herein by reference. Output 180 may be transmitted to process tool 110 via communication link 185 to monitor and / or modify the fabrication process occurring in chamber 135 of process tool 110.

[0016] The components shown and described in FIG. 1 are simplified for convenience and are commonly known. In addition to their general functionality, spectrometer 160 or signal processor 170 may also be configured to identify stationary and transient optical and non-optical signals and process these signals in accordance with the methods and / or features disclosed herein. To this end, spectrometer 160 or signal processor 170 may include algorithms, processing capabilities, and / or logic for identifying and processing optical signals and temporal trends extracted therefrom. Spectrometer 160 or signal processor 170 may also be configured to process multiple signal points (multiple collected signal points) collected in accordance with the devices, systems, and methods disclosed herein. For example, FIGS. 5A-5D and 6A-6B provide examples of gathering specific spatial information from multiple collected signal points or reflected sub-beams. Using FIGS. 5A-5D as an example, reflected sub-beams 581-587 (also referred to as multiple collected signal points) may be provided to spectrometer 160 via fiber optic cable assembly 157. Fiber optic cable assembly 157, in this example, may have seven individual fibers (one for each sub-beam). The optical signal from each individual sub-beam 581-587 may be provided to a unique input of spectrometer 160 and may be processed in a variety of ways. For example, each of sub-beams 581-587 may be processed individually (or independently), may be processed in combination with at least one other of sub-beams 581-587, or all of sub-beams 581-587 may be processed together.

[0017] The number of collected sub-beams can correspond to the number of individual optical inputs of the spectrometer 160. However, the number of sub-beams is not limited by the number of optical inputs. For example, the collected sub-beams can be multiplexed and provided to the optical inputs. Thus, the number of collected sub-beams can be greater than the number of optical inputs of the spectrometer 160 (i.e., the number of collected sub-beams can be greater than the number N of inputs). The number of collected sub-beams can also be less than the number N of optical inputs (i.e., the number of collected sub-beams can be less than the number N of inputs). The collected sub-beams can be from an IEP or OES mode of operation. The number of collected sub-beams can be, for example, 2 to 10 sub-beams.

[0018] Additional processing can also be performed on the processed sub-beams. For example, the signal processor 170 can perform additional processing based on the combined information from the individually processed sub-beams, such as averaging the output values ​​from the processed sub-beams 581-587. By processing the output values ​​from the processed sub-beams 581-587, various trends and different types of data can be extracted. The obtained information can be provided to the process tool 110, for example, to control a process. Trend lines can also be determined and control signals generated based on the processing of one or more of the sub-beams. For example, seven independent trend lines can be determined based on the seven sub-beams 581-587 and sent as seven parallel control signals.

[0019] The algorithms, processing power, and / or logic may be in the form of hardware, software, firmware, or any combination thereof. The algorithms, processing power, and / or logic may be located in a single computing device or may be distributed across multiple devices, such as spectrometer 160 and signal processor 170. While this system and others described herein are based on refractive systems, it should be understood that systems based on reflective systems and / or combined refractive and reflective systems are possible and may be created and adapted from the principles and examples described and disclosed herein.

[0020] FIG. 2 shows a simplified diagram of a beamforming subsystem 200 of a typical refractive system used in an IEP. Subsystem 200 generally includes an emitter / receiver fiber optic cable subassembly 210 (an example of fiber optic cable assembly 153), which may be formed from two or more individual optical fibers arranged to provide light to subsequent components of beamforming system 200 and receive light from previous components. The enlarged inset of fiber optic cable subassembly 210 shows a random arrangement of 19 optical fibers, arranged, for example, in a close-packed or hexagonal-packed configuration. In this example, eight of the optical fibers (colored black) can be considered emitter optical fibers, and eleven of the optical fibers (colored white) can be considered receiver optical fibers. The emitter optical fiber directs light to lens 220, which refracts the light to form beam 230 (which may correspond to 155 in FIG. 1), which is directed toward wafer 240. Upon reflection from wafer 240, the light passes through lens 220 and is collected by a receiving optical fiber.

[0021] Lens 220, which may form the basis of interface 140, may typically have a diameter between 0.5 inches and 1.0 inches, with a focal length appropriate for the numerical aperture (NA) and other characteristics of the system. Instead of the singlet lens shown, lens 220 may be replaced by a doublet, triplet, or other complex lens group, or by an equivalent reflective element. For collimating systems, the spot size of the beam produced by lens 220 on wafer 240 is typically similar to the diameter of the effective aperture of lens 220. For focusing systems, the spot size of the beam on wafer 240 may be similar to the diameter of the fiber bundle in fiber optic cable subassembly 210, such as that represented by the enlarged inset, or may be modified by the design magnification of the optical system.

[0022] Generally, subsystem 200 provides measurements across a spot size that are an average of the optical response across the entire area. This large area may contain a variety of structures and / or film stacks that individually provide very different signals that, when combined in a uniform manner in this subsystem, become unclear and cannot be used for characterization and process control. It is possible to split this integrated signal into sub-portions via a beam aperture and / or by separately collecting and processing the signal from each individual receiving optical fiber. However, these methods generally do not provide specific spatial information from wafer 240 because the combined action of the optical fibers and lens 220 in fiber optic cable subassembly 210 mixes the signals both spatially and angularly.

[0023] As shown in FIG. 3, specific spatial information may be provided through multiplexing and, optionally, miniaturization of subsystem 200 of FIG. 2. Subsystem 300 includes multiple separate sets of lenses and fiber optic cables to provide multiple individual sets of spatial information. As shown enlarged for subassembly 310, fiber optic cable subassemblies 310-313 may each consist of a limited number of fibers, such as a single pair of emitter and receiver fibers. The fibers may be of a variety of commonly available core diameters, such as 50, 100, 200, 400, and 600 μm (microns). The limited number of fibers aids in miniaturization. Lenses 320-323 of subsystem 300 (which may correspond to interface 140 of FIG. 1) may be physically separate, forming what may be called a "beamlet" system (as shown), or may be physically coupled, forming what may be called a "lenslet" system. Lenses 320-323 may be single lenses or more complex lens groups. Each fiber optic cable and lens pair (e.g., 310 and 320) cooperates to form a beam (e.g., 330). Other pairs form beams 331-333. All beams may reflect from and provide information from spatially distinct regions of wafer 340. Beams 330-333 may correspond to beam 155 in FIG. 1. The emitting and receiving fibers may be radially symmetric about the axis of the optical system. For example, the emitting and receiving fiber pairs of subassembly 310 may be pairwise radially symmetric about the axis of lens 320.

[0024] Although subsystem 300 shows four combinations of fibers, lenses, and beams in a 1D linear pattern, any number of combinations may be arranged in a 2D pattern, such as a square array, a hexagonal array, or a circular pattern. The size of the individual beam spots on wafer 340 and the boundary region for the collection of lenslets or beamlet combinations may be designed to suit specific or general applications. For example, the individual beam spots may be less than 1 mm to more than 5 mm in diameter, and the entire subsystem may be bounded within a 25 mm diameter area on wafer 340. The selection of the individual beam sizes and boundary regions may be determined based on feature size, pattern density, and other characteristics of wafer 340. Alternatively or additionally, the selection of the individual beam sizes and boundary regions may be determined based on process parameters such as non-uniformity requirements and tool requirements such as available physical access.

[0025] The design and optimization of each combination takes into account design parameters such as fiber core size, the number of emitter and receiver fibers, lens focal length, NA of the entire combination, and spot size uniformity requirements over wavelength. Especially for systems based on singlet lens designs, focal length and wavelength sensitivity can lead to significant variations in coupling efficiency and spot size. Furthermore, the miniaturization of these systems, along with variations in the tolerances of lenses, fibers, and mechanical components, makes it increasingly difficult to align the fibers to the lenses and each other to the mechanical fixtures required to actually implement the system into a processing tool. Figures 4A-4C are a set of performance data plots illustrating the design of a system of the type described in connection with Figure 3.

[0026] Figure 4A is a plot of beam spot size versus wavelength, showing strong diameter variations in the UV region, with wavelengths below approximately 0.4 μm (microns). Figure 4B is a plot of signal coupling efficiency versus wavelength, showing the wavelength dependence as the system varies spot size and the degree of focusing or collimation of light at the wafer surface for a given focal length lens's nominal fiber-to-lens distance. Figure 4C is a plot of signal coupling efficiency versus wavelength for variations in the fiber-to-lens defocus distance, highlighting the system's sensitivity to at least one mechanical tolerance. Efficiency is expressed as the IMAE efficiency, which corresponds to the IMAE operand used to perform the analysis in the optical design software ZEMAX.

[0027] 5A-5D are 3D diagrams of an alternative multiplexed beam forming portion of a refractive system 500 used for IEP. While a single interface, such as interface 140, is shown, more optical interfaces can be used to provide more beams to wafer 550. FIG. 5A shows emitting surface 510 providing light forming sub-beams 521-527 (e.g., multiple emitting signal points or simply multiple emitting points), which are directed to beam splitter 530, which then directs the light to lens 540 and thereafter to wafer 550 to form inspection spots 561-567 (e.g., multiple inspection signal points or simply multiple inspection points). Upon reflection from wafer 550, the sub-beams pass through lens 540 again, then through beam splitter 530, and reach image plane 570, where each reflected sub-beam 581-587 (e.g., multiple collection signal points or simply multiple collection points) can be independently collected by a corresponding optical fiber (not shown). The correspondence between different signal points (e.g., multiple emission points, inspection points, and collection points) can be one-to-one. The number of sub-beams can be, for example, 2 to 10.

[0028] The working F-number and magnification of system 500 may be determined based on the required working distance and magnification. For example, a system based on lens 540 with a nominal focal length of 5F and other lenses in the system (such as lenses 537 and 539 in FIG. 6B) with a nominal focal length of F provide a 5x magnification. In the illustrated example, lens 540 may have a focal length of 200 mm and a diameter of 20 mm. This lens selection results in a system with a working distance (distance from lens 540 to wafer 550) of approximately 200 mm. If a 200 μm core optical fiber is used in this system, the emission and signal sub-beams will each have a nominal diameter of 200 μm, and the inspection spot size will have a nominal diameter of 1000 μm.

[0029] Figure 5B shows an expanded view of the light-emitting surface 510 and sub-beams 521-527. While seven sub-beams are shown in this example, more or fewer sub-beams may be defined and used. The light-emitting surface 510 may be a common light-emitting surface, such as a light pipe, with a diameter large enough to encompass the emission points of all desired sub-beams. For example, for a system operating at an inspection spot size of approximately 1 mm and 5x magnification, the light pipe may be approximately 3 mm or larger in diameter to allow for an inspection area (including all individual inspection spots) of approximately 15 mm. Light pipes are typically formed of fused silica for broad-spectrum (200-800 nm) performance, but may also be made of other suitable materials. Illumination for the light pipe may be provided by a light source such as a pulsed xenon flash lamp.

[0030] The use of a light pipe to define a common light source for the light-emitting surface and sub-beams may offer advantages over the use of individual optical fibers for each sub-beam. For example, a light pipe provides a common, uniform light-emitting surface, while individual fibers may require independent focusing. Light pipes also provide a large-area light-emitting field that does not require individual lateral alignment of individual light-emitting fibers to individual signal fibers. Furthermore, the use of light pipes to achieve uniform illumination may allow the elimination of individual light-emitting fibers when illuminating a larger inspection area, with individual receiving fibers receiving any subset of the light reflected within that area. Thus, the system can be considered self-aligning, reducing the complexity required for aligning and constructing the signal-receiving optical fiber assembly. Self-alignment may include flexibility in aligning individual light-emitting fibers to the light pipe or light source and / or signal fibers to the larger illuminated inspection area provided by the light pipe. For example, an emitting light pipe can create a uniform illumination surface that continuously samples the wafer across its imaging area as it passes through the optical system. The reflected light then passes back through the optical system and is re-imaged at plane 570. Individual fibers are placed at the receiving surface to receive the returning light. Each receiving fiber collects a subset of the total beam that originates from a specific location on the light pipe, travels to the wafer, probes a specific location on the wafer, and then reflects back into the fiber. This is self-aligning in that the receiving fiber can be moved and still collect effective light from the wafer, but simply translated onto the wafer, and originating from a slightly different location on the light pipe. Compared to individual fiber optic light sources, light pipes can provide improved illumination intensity uniformity for each sub-beam.

[0031] FIG. 5C shows an expanded inspection area 555 for the intersection of wafer 550 and incident sub-beams 561-567. As mentioned above, the sub-beams provide an inspection spot approximately 1 mm to 5 mm in diameter and may be enclosed within an overall diameter of approximately 15 mm to 50 mm. FIG. 5D shows an expanded area for signal plane 570 and sub-beams 581-587. Each signal sub-beam may be spaced approximately 1 mm apart and arranged in a hexagonal pattern. This pattern may be defined according to the structure of the mating fiber optic cable assembly (not shown). This pattern may also take into account the features to be investigated on wafer 550. Engineering preferences, wafer design, and OEM requirements are some other examples of bases for pattern selection.

[0032] In cooperation with the emitting light pipe, the mating optical fiber assembly can be changed or reconfigured to provide new patterns of wafer sampling without having to modify the source of the sub-beams. Thus, the source can remain the same while the configuration of the collected sub-beams is adaptable. This pattern modification may include different spatial mapping, different inspection spot sizes (via resizing the optical fiber core), a different number of collected sub-beams, etc. The emitting and signaling functions of the system may also be reversed by illuminating the system through the signal fiber and collecting light at the emitting surface. This functionality may be used to add adjustments to the fiber layout and allow fine tuning of the measurement location (e.g., running light in the opposite direction to provide a probe beam to illuminate the wafer 500 for setup purposes).

[0033] FIGS. 6A-6B are further views of an alternative multiplexed beam forming portion of the refractive system 500 of FIGS. 5A-5D. FIG. 6A shows a cross-sectional view of the system 500 to allow for the display of the beam stop 535 and additional detail as shown in FIG. 6B. The beam stop 535 resides in the focal plane of the system 500 and controls the bilateral telecentricity performance of the system 500. The bilateral telecentricity performance is important in the system 500 because it ensures that all sub-beams of each type—emission sub-beams 521-527, inspection sub-beams 561-567, and signal sub-beams 581-587—are formed in a common plane and are orthogonally incident on the inspection and signal planes. This avoids individual longitudinal adjustments for each sub-beam on one or more of the emission plane, wafer surface, or signal plane.

[0034] FIG. 6B shows an enlarged portion of FIG. 6A, illustrating various additional features of system 500. Upon leaving the emitting surface, sub-beams 521-527 may pass through and be collimated by lens 537. Lens 537 may be a singlet, doublet, or other more complex lens group. After lens 537, the sub-beams approach and are reflected by beamsplitter 530. Beamsplitter 530 may be, for example, a broadband polka dot beamsplitter, a cube beamsplitter, or other known beamsplitter types, with or without coatings. In the illustrated design, beamsplitter 530 may be approximately 25 mm in diameter. After reflecting from beam splitter 530, the sub-beams are directed through beam stop 535, which may be, for example, 10 mm to 20 mm in diameter, depending on the system magnification, working distance, and inspection beam spot size. Beam stop 535 is positioned a focal length away from lens 537, making the system telecentric in object space. Lens 540 (FIG. 6A) is positioned a focal length away from beam stop 535, making the sub-beams telecentric at the wafer plane and therefore incident normally to the wafer plane. After reflecting from wafer 550 (more specifically, inspection area 555 of wafer 550) and passing through beam splitter 530, the sub-beams may be incident on and focused by lens 539. Lens 539 is equivalent in material composition and properties to lens 537, and may be, for example, a fused silica singlet or spaced doublet with a focal length of 40 mm and a diameter of approximately 12 mm. Lens 539 is placed its focal length away from beam stop 535 to ensure that the beam is telecentric in the signal plane to aid in efficient coupling into the signal fiber.Note that although two lenses 537 and 539 are shown, depending on focal length and NA requirements, a single lens can be used with beam splitter 530 located at the convergence region of this single lens group to perform the splitting of the outgoing and incoming sub-beams. Lens 540 and other components of FIG. 6B can correspond to interface 140 of FIG. 1.

[0035] The bilaterally telecentric systems described and illustrated in connection with FIGS. 5A-5D and 6A-6B may be modified into simpler systems by eliminating certain elements and adjusting others. These modifications to bilateral telecentricity impose certain performance tradeoffs and limitations, but may also provide certain benefits by reducing the system's complexity, cost, and size. Specifically, a simplified system based on system 500 may eliminate lenses 537 and 539, and aperture 535 may be similarly eliminated or relocated. The focal length and position of lens 540 relative to beam splitter 530 and wafer 550 may also be adjusted. The location of lens 540 may define the system aperture. Generally, beam splitter 530 is retained to separate the emission and signal sub-beams due to the double-conjugate nature of imaging in this double-pass optical system. Like system 500, this simplified system can also use a light pipe for light emission, facilitating alignment to the signal fiber and potentially facilitating configuration with changes to the signal fiber to support inspection spot size and / or location. In the simplified system, multiple light emission points do not need to be used to collect multiple signal points. Advantageously, this eliminates or at least reduces the need for alignment between multiple emission and collection points. Thus, compared to system 500, the simplified system can form a single, larger light beam on wafer 550, but can use the same effective probe pattern for wafer 550 as system 500 if the same configuration of collected sub-beams is used. Also, like system 500, the light source in the simplified system can be considered self-aligning, allowing the light source to remain the same even when the configuration of collected sub-beams is changed. Thus, the simplified system can also have an adaptable pattern of inspection spots.

[0036] Compared to a bilaterally telecentric system design, the simplified system results in a narrower, more limited field of view, resulting in inspection sub-beams, such as sub-beams 561-567 in FIG. 5C, that may not all intersect the wafer surface at right angles. Specifically, a central, on-axis sub-beam, such as sub-beam 564, may intersect wafer 550 at right angles, while peripheral sub-beams, such as sub-beams 561-563 and 565-567, may not intersect the wafer at right angles. The narrower field of view can also manifest as intensity variations among the sub-beams, with the highest intensity sub-beam being on-axis and the lower intensity sub-beams being peripheral. The field of view and intensity limit variations may be adjusted to accommodate required system performance through design changes to, at least, the lens radius, working distance, emission / signal / inspection spot size, optical fiber diameter, and overall inspection spot diameter.

[0037] One aspect to consider in a multipoint system is separating the emitting sub-beam from the signal sub-beam when the imaging design naturally returns light to the same location. For example, in system 500, emitting surface 510 and signal surface 570 are conjugate and would overlap if not spatially separated using beamsplitter 530. One option for a multipoint optical system that can help with the difficulty of separating the beams is the use of a multimode optical circulator.

[0038] FIG. 7 illustrates an example of a multimode optical circulator 700 that can be used in the multi-point optical systems disclosed herein, such as system 500. For example, multiple multimode optical circulators 700 can be used in place of beam splitter 530, simplifying system integration and alignment of other elements, such as beam stop 535, lens 537, and lens 539. When using circulator 700, elements such as lenses 537 and 539 can be eliminated from the system in certain system configurations. Multimode optical circulator 700 is a three-port device configured so that light travels in only one direction, and light entering any port exits the next port. Thus, light entering port 1 from a light source can be provided to a wafer via port 2, and light entering port 2 from the wafer can be provided to a spectrometer via port 3. Using FIG. 5 as an example, sub-beam 524 entering port 1 is provided to wafer 550 as an inspection point via port 2 as sub-beam 564, and then sub-beam 564 reflected via port 2 is provided to the spectrometer via port 3. Specifically, through the function of circulator 700, direct optical signal communication between port 1 (light source) and port 3 (optical signal) is avoided. This is because any optical signal provided in this manner would not contain the desired information from the wafer and would therefore be considered an erroneous or background signal. The individual ports of circulator 700 may be formed from multiple individual multimode optical fibers, with a single optical fiber connected to each port. Thus, multimode optical circulator 700 may enable the use of a single optical fiber on port 2 for both the inspection sub-beam and the collection sub-beam. Multimode optical circulator 700 may be used for each of the corresponding multipoint sub-beam sets of system 500, such as sub-beams 524, 564, and 584. For example, with reference to FIGS. 5A-5D, seven circulators 700 may be used to replace beam splitter 530 and lenses 537 and 539.Each port 1 optical fiber can be coupled to a light source separately or through the use of a unified optical connection, such as through the emitting surface 510. The port 2 optical fibers can be combined into a single optical terminator, such as an SMA terminator, and spatially configured in a desired pattern to provide multiple inspection spots in the inspection region 555. Each port 3 optical fiber can be provided to a unique channel of a multichannel spectrometer, such as spectrometer 160, via fiber optic cable assembly 157. Also, the emitting and receiving fibers, such as sub-beams 524 and 584, can be paired using an optical circulator, such as multimode optical circulator 700. Multimode optical circulator 700 can be used, for example, in 400-800 nm systems or wider bandwidth systems, such as 200-800 nm. For increased robustness, BX jackets can be used on the optical fibers connected to multimode optical circulator 700. The circulator-based optical subsystem may include a suitably placed aperture stop that allows the optical system to function telecentrically to improve uniformity of light source and signal levels across multiple inspection spots within the inspection region.

[0039] FIG. 8 illustrates an example of a target beam layout 800 on a wafer, such as wafer 550, used as an example. The example target beam layout 800 includes four sub-beams 810, 820, 830, and 840, which are provided to wafer 550. Each of sub-beams 810, 820, 830, and 840 may correspond to a single beam 155 and optical interface 140, as shown in FIG. 1. In other words, target beam layout 800 may represent the layout of four optical interfaces 140 and beams 155. Each individual beam on wafer 550 is shown as a 1 mm circle that is ±2 mm from the origin in the X and Y directions. Rectangular beam layout 800 is an example of a beam layout that may be used instead of the hexagonal beam layouts shown in FIGS. 5A-5D. As an example, sub-beam 810 is shown within inspection area 555 of wafer 550 and will be used in the following discussion of Figure 9 to illustrate further fiber and optical configurations that combine features of one or more of the previously discussed configurations.

[0040] FIG. 9 illustrates an exemplary pair-wise fiber configuration 900 for separating incoming and outgoing sub-beams using defined fiber patterning (spatial mapping) and defocusing in accordance with the principles of the present disclosure. Similar to that shown in FIG. 3, optical fibers can be used in pairs, but similar to FIG. 2, optical fiber pairs may be integrated into a common bundle of multiple optical fiber pairs. Fiber configuration 900 may be used with a single lens, such as lens 220 in FIG. 2, to avoid opto-mechanical complexity such as multiple lenses, such as 320-323 in FIG. 3, or beam splitter 530 in FIG. 5. As mentioned in the discussion of FIG. 2, the use of a single lens and randomized fiber pattern results in a lack of specific spatial information, but specific spatial information can be at least partially received by using a pair-wise fiber pattern and defocusing of the optical system. In fiber layout 900, each fiber pair is labeled with a common letter, i.e., A / A for the first pair, B / B for the second pair, etc. Due to symmetry, specific receiving or emitting fibers need not be specified; they are generally interchangeable, but should be adjusted as needed by appropriate selection of light source or spectrometer. Each receiving and emitting fiber pair is radially displaced from the axis of symmetry of the optical system, which may be defined by the use of a lens, such as lens 220 in FIG. 2. Receiver and emitter fiber pair A / A may correspond to sub-beam 810 in FIG. 8, and additional fiber pairs (e.g., B / B, C / C, and D / D) correspond to sub-beams 820, 830, and 840. Fiber configuration 900 may be integrated into single or multiple lens subsystem designs, including subsystems 200 and 300.

[0041] While fiber configuration 900 illustrates a specific fiber pairing, as well as a specific arrangement and number of pairs, it should be understood that more or fewer pairs may be used, and multiple other pairwise combinations may be defined and used. Also, specific individual fibers, such as the unlabeled central fiber, may not be used within a fiber pair but simply provide the required geometry. Furthermore, while fiber pairing is used herein as an example, it should be understood that more complex groupings are possible. For example, triplet A / D / I pairs may be combined to define a larger inspection spot. Figures 10A and 10B illustrate the effect of defocus as a subsystem optimization parameter on signal efficiency (the IMAE parameter in Zemax modeling software) for a pairwise design used with a singlet lens. Figure 10A illustrates a defocus of 0.22 mm for the wavelength range of 400–800 nm, resulting in an average value of approximately 0.08. FIG. 10B shows a defocus of −3.4 mm in the wavelength range of 240 to 340 nm, with increased efficiency over a narrow range and correspondingly lower efficiency at other wavelengths.

[0042] FIG. 11 is a block diagram of an optical system 1100 including a spectrometer 1110 and specific associated systems, according to one embodiment of the present disclosure. The spectrometer 1110 can incorporate the systems, features, and methods disclosed herein to benefit from measuring, characterizing, analyzing, and processing optical signals from semiconductor processes and may be associated with the spectrometer 160 of FIG. 1 . The spectrometer 1110 may receive optical signals from an external optical system 1130, such as via fiber optic cable assembly 157 or 159, and after integration and conversion, may send data to an external system 1120, such as output 180 of FIG. 1 . This data may also be used to control the spectrometer 1110, for example, by selecting an operating mode or controlling integration timing, as defined herein. The spectrometer 1110 may include an optical interface 1140, such as a subminiature assembly (SMA) or ferrule connector (FC) optical fiber connector, or other opto-mechanical interface. Additional optical components 1145, such as slits, lenses, filters, and gratings, may function to shape, guide, and color separate received optical signals and direct these optical signals to sensor 1150 for integration and conversion. Lower-level functions of sensor 1150 may be controlled by elements such as FPGA 1160 and processor 1170. After optical-to-electrical conversion, the analog signals may be directed to an A / D converter 1180 for conversion from electrical analog signals to electrical digital signals, which may then be stored in memory 1190 for immediate or later use and transmission to external system 1120 (see signal processor 170 in FIG. 1 ). While certain interfaces and relationships are indicated by arrows, not all interactions and control relationships are shown in FIG. 11 . Multiple sub-beams may be collected as disclosed herein for processing with appropriate adaptation of optical interface 1140, e.g., to include multiple individual input capabilities for each signal sub-beam.Thus, spectrometer 1110 can be configured (i.e., designed, constructed, or programmed with the necessary logic and / or features to perform one or more tasks) to process multiple sub-beams. Spectrometer 1110 also includes a power supply 1195, which can be a conventional AC or DC power supply typically included in spectrometers.

[0043] FIG. 12 illustrates a computing device 1200 that can be used in processes disclosed herein, such as identifying and processing signals in spectral data. The computing device 1200 can be a spectrometer or a portion of a spectrometer, such as the spectrometers 160 or 1110 disclosed herein. The computing device 1200 can include at least one interface 1232, a memory 1234, and a processor 1236. The interface 1232 includes the hardware, software, or combination thereof necessary to, for example, receive raw spectral data and transmit processed spectral data. Portions of the interface 1232 can also include the hardware, software, or combination thereof necessary to transmit analog or digital electrical signals. The interface 1232 can be a conventional interface that communicates via various communication systems, connections, buses, etc., according to a protocol, such as a standard or proprietary protocol (e.g., the interface 1232 may support I2C, USB, RS232, SPI, or MODBUS). Memory 1234 is configured to store various software and digital data aspects related to computing device 1200. Memory 1234 is also configured to store a set of operating instructions corresponding to one or more algorithms that direct the operation of processor 1236, for example, when initiating processing of a plurality of sub-beams collected as disclosed herein. Memory 1234 can be a non-transitory computer-readable medium (e.g., flash memory and / or other medium).

[0044] The processor 1236 is configured to direct the operation of the computing device 1200. To this end, the processor 1236 is in communication with the interface 1232 and the memory 1234 and includes the logic necessary to perform the functions described herein to identify and process the plurality of collected sub-beams.

[0045] 13 shows a flow diagram of a method 1300 of processing a semiconductor wafer in accordance with the principles of the present disclosure. Method 1300 can be performed using one or more of the optical systems disclosed herein, such as, for example, in FIG. 1. Method 1300 begins at step 1305.

[0046] In step 1310, a semiconductor wafer is held in a semiconductor processing chamber. The semiconductor processing chamber may be a typical chamber used to process semiconductor wafers, and the wafer may be held according to industry practices.

[0047] In step 1320, the wafer is illuminated with light provided by a light source through a plurality of first optical fibers. The first optical fibers can be luminescent optical fibers, such as those disclosed herein. The light source can be, for example, a xenon flash lamp. A light pipe can be used in conjunction with the light source.

[0048] The wafer may be illuminated at various inspection spots. The inspection spots on the wafer may follow a predetermined pattern. The pattern may be, for example, a linear pattern, a circular pattern, a hexagonal pattern, or a rectangular pattern. Other two-dimensional patterns may also be used. The pattern may be defined according to the structure of the mating fiber optic cable assembly or may take into account, for example, the features to be investigated or monitored on the wafer, engineering preferences, wafer design, or OEM requirements. A combination of considerations may be used to select the pattern. As noted herein, the pattern may be adaptive.

[0049] In step 1330, light reflected from the wafer is collected via a plurality of second optical fibers. The second optical fibers may be receiving optical fibers and may be part of a fiber optic cable assembly connected to the spectrometer. For example, the plurality of second optical fibers may be optical fibers of fiber optic cable assembly 157.

[0050] The number of the plurality of second optical fibers can correspond to, but is not determined by, the number of individual optical inputs of the spectrometer. For example, the number of the plurality of second optical fibers can be the same as, greater than, or less than the number of individual optical inputs of the multiple-input spectrometer.

[0051] In step 1340, the collected light is processed. The collected light may be processed by a plurality of input spectrometers for detection and conversion to digital signals. The collected light from each of the plurality of second optical fibers may be provided to a unique input of the plurality of input spectrometers for processing. For example, the light (or sub-beam) of each optical fiber of the plurality of second optical fibers may be processed individually (or independently), in combination with at least one other optical fiber (less than all combinations), or all together.

[0052] The processing performed by the multiple input spectrometers can be based on combined information from the individually processed sub-beams, such as averaging output values. By processing the output values ​​of the processed sub-beams, various trends and different types of data can be extracted. Trend lines, for example, can be determined for each of the sub-beams.

[0053] In step 1350, one or more control trends are provided to the processing chamber for controlling the processing of the wafer in the processing chamber according to the process. In step 1360, the wafer may then be processed using the received control trends. Method 1300 proceeds to step 1370, where it ends.

[0054] The above-described and other modifications may be made in the optical measurement systems and subsystems described herein without departing from the scope thereof. For example, while particular examples have been described in connection with semiconductor wafer processing equipment, it will be understood that the optical measurement systems described herein are applicable to other types of processing equipment, such as roll-to-roll thin film processing, solar cell manufacturing, or any application where high-precision optical measurements may be required. Furthermore, while particular examples discussed herein describe the use of a common optical analysis device, such as an imaging spectrometer, it will be understood that multiple optical analysis devices with known relative sensitivities may be utilized. Furthermore, while the term "wafer" has been used herein in describing aspects of the present invention, it will be understood that other types of workpieces, such as quartz plates, phase-shift masks, LED substrates, and other non-semiconductor process-related substrates and workpieces (including solid, gas, and liquid workpieces), may also be used.

[0055] The embodiments described herein are chosen and described in order to best explain the principles and practical applications of the present invention and to enable others skilled in the art to understand the present invention in various embodiments with various modifications as may be suitable for the particular uses contemplated. The specific embodiments described herein are not intended to limit the scope of the present invention in any way, as the present invention may be practiced in various variations and environments without departing from the scope and spirit of the present invention. Therefore, the present invention is not intended to be limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features described herein.

[0056] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the present invention. As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms unless the context clearly indicates otherwise. Furthermore, it will be understood that the terms "comprises" and / or "comprising," as used herein, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0057] Those skilled in the art will appreciate that portions disclosed herein may be embodied as a method, system, or computer program product. Accordingly, the disclosed portions may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, microcode, etc.), or an embodiment combining software and hardware aspects, collectively referred to herein as a "circuit" or "module." Each of the example independent claims in this Summary may include one or more of the following elements in combination:

[0058] Element 1: The optical system further includes a light pipe proximate the light-emitting surface. Element 2: The predetermined pattern of the inspection spots is adaptable. Element 3: The plurality of first sub-beams includes 2 to 10 sub-beams. Element 4: Each of the plurality of second sub-beams is collected and processed independently. Element 5: The optical element includes at least one of a lens, a beam splitter, a beam stop, and an optical circulator. Element 6: The pattern of the inspection spots is one of a linear pattern, a circular pattern, a hexagonal pattern, or a rectangular pattern. Element 7: The light source provides source light to the light-emitting surface by fiber optic technology, and each of the plurality of first sub-beams is defined by an individual optical fiber. Element 8: The spectrometer is configured to receive light collected from the image plane by fiber optic technology, and each of the plurality of second sub-beams is defined by an individual optical fiber. Element 9: The individual optical fibers defining the plurality of first sub-beams and the individual optical fibers defining the plurality of second sub-beams are pairwise radially symmetric about an axis of the optical system. Element 10: The pairwise arrangement of the plurality of first optical fibers and the plurality of second optical fibers is configured as a plurality of optical circulators. Element 11: The optical system further includes a light source and a light pipe proximal to the plurality of first optical fibers. Element 12: The plurality of inspection spots includes 2 to 10 inspection spots. Element 13: The spectrometer individually processes the light collected from the plurality of second optical fibers. Element 14: The pattern of the inspection spots is one of a linear pattern, a circular pattern, a hexagonal pattern, or a rectangular pattern. Element 15: The optical system further includes defining the plurality of inspection spots on the semiconductor wafer according to a predetermined pattern. Element 16: The predetermined pattern is selected according to a feature to be monitored on the semiconductor wafer. Element 17: Processing the collected light to provide one or more control trends for controlling processing of the wafer includes combining the light collected from multiple of the multiple second optical fibers.

Claims

1. a light source configured to provide source light to the light emitting surface to form a plurality of first sub-beams; an optical element configured to modify each of the plurality of first sub-beams to form a plurality of inspection spots on the wafer according to a predetermined pattern, the optical element being further configured to modify each of the plurality of first sub-beams upon reflection from the wafer to form a plurality of second sub-beams at an image plane; a spectrometer configured to receive collected light from the plurality of second sub-beams; and An optical system comprising:

2. The optical system of claim 1 , further comprising a light pipe proximate the light emitting surface.

3. The optical system of claim 2 , wherein the predetermined pattern of the inspection spots is adaptive.

4. The optical system of claim 1 , wherein the plurality of first sub-beams comprises between 2 and 10 sub-beams.

5. The optical system of claim 1 , wherein each of the plurality of second sub-beams is collected and processed independently.

6. The optical system of claim 1 , wherein the optical element comprises at least one of a lens, a beam splitter, a beam stop, and an optical circulator.

7. The optical system of claim 1 , wherein the pattern of the inspection spots is one of a linear pattern, a circular pattern, a hexagonal pattern, or a rectangular pattern.

8. The optical system of claim 1 , wherein the light source provides the source light to the light-emitting surface by fiber optic technology, and each of the plurality of first sub-beams is defined by a respective optical fiber.

9. 9. The optical system of claim 8, wherein the spectrometer is configured to receive the collected light from the image plane by fiber optic technology, and wherein each of the plurality of second sub-beams is defined by a respective optical fiber.

10. 10. The optical system of claim 9, wherein the individual optical fibers defining the plurality of first sub-beams and the individual optical fibers defining the plurality of second sub-beams are pair-wise radially symmetric about an axis of the optical system.

11. a processing chamber; a light source configured to provide source light to a plurality of first optical fibers; a spectrometer configured to receive collected light from the plurality of second optical fibers; an inspection region within the processing chamber including a plurality of inspection spots on a wafer, each of the plurality of inspection spots being defined by a pairwise arrangement of the plurality of first optical fibers and the plurality of second optical fibers; 1. A semiconductor processing system comprising:

12. 12. The semiconductor processing system of claim 11, wherein said pairwise arrangement of said plurality of first optical fibers and said plurality of second optical fibers is configured as a plurality of optical circulators.

13. 12. The semiconductor processing system of claim 11, further comprising a light pipe proximate said light source and said plurality of first optical fibers.

14. 12. The semiconductor processing system of claim 11, wherein the plurality of test spots comprises between 2 and 10 test spots.

15. 12. The semiconductor processing system of claim 11, wherein the spectrometer processes the collected light from the plurality of second optical fibers individually.

16. 12. The semiconductor processing system of claim 11, wherein the pattern of the test spots is one of a linear pattern, a circular pattern, a hexagonal pattern, or a rectangular pattern.

17. illuminating a wafer in a semiconductor processing chamber via a plurality of first optical fibers with light provided by a light source; collecting the light reflected from the wafer via a plurality of second optical fibers; processing the collected light using a plurality of input spectrometers; providing one or more control trends for controlling processing of the wafer according to the process; 1. A method for processing a semiconductor wafer, comprising:

18. 20. The method of processing a semiconductor wafer of claim 17, further comprising defining a plurality of inspection spots on the semiconductor wafer according to a predetermined pattern.

19. 20. The method of processing a semiconductor wafer of claim 18, wherein the predetermined pattern is selected according to a feature to be monitored on the semiconductor wafer.

20. 20. The method of processing a semiconductor wafer of claim 17, wherein processing the collected light to provide one or more control trends for controlling processing of the wafer comprises combining light collected from multiple of the multiple second optical fibers.

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