Conoscopy wafer orientation apparatus, and ion implantation apparatus including the same.

Abstract

An ion implantation apparatus comprising an ion source that generates an ion beam, a set of beamline components that guide the ion beam to a substrate along a beam axis perpendicular to a reference plane, a processing chamber that houses a substrate to receive the ion beam, and a conoscopography system. The conoscopography system may include an illumination source that guides light to a substrate position, a first polarizer assembly comprising a first polarizer element and a first pair of lenses positioned on both sides of the first polarizer element and configured to focus light to the substrate position, and a second polarizer assembly positioned to receive light after it has passed the substrate position, comprising a second polarizer element and a second pair of lenses positioned on both sides of the second polarizer element and configured to focus light to a sensor positioned on the detection surface of a detector.

Description

Technical Field

[0001]

[0001] This application claims priority to U.S. Provisional Patent Application No. 63 / 538,668, filed September 15, 2023, entitled "Conoscopic wafer orientation for ion implantation," and U.S. Non-Provisional Patent Application No. 18 / 794,728, filed August 5, 2024, entitled "Conoscopic Wafer Orientation Apparatus and Ion Implanter Including Same," the entire disclosures of which are hereby incorporated by reference.

[0002]

[0002] This embodiment relates to ion implantation, and more specifically, to substrate orientation in an ion implantation apparatus.

Background Art

[0003]

[0003] Silicon carbide has emerged as one of the most promising materials for high-voltage, high-power switching applications. SiC compounds are readily formed in many different crystal structures, each having its own crystallographic and electronic properties. The most common SiC material is the "4H" polytype. This structure has hexagonal symmetry and a pattern of hexagonal layers that repeat every four layers. ABCBABCBABC... This crystal belongs to the P63mc or C 6v 6v space group. In the hexagonal crystal, the crystal structure is characterized by a set of axes where the a-axis and b-axis have equal dimensions and extend perpendicular to the c-axis, and the c-axis has a different dimension from the a-axis and b-axis. To form a single-crystalline 4H SiC wafer, the SiC crystalline boule is typically grown at a very high temperature by vapor deposition. To maintain the polytype structure and minimize defects, the growth surface can be tilted 4° with respect to the c-axis. Due to growth, a nearly cylindrical boule is formed that is much shorter in length than the diameter of the boule, so the wafers are also cut nearly parallel to the growth surface to cut the maximum number of wafers from the SiC boule.

[0004]

[0004] The manufacture of high-voltage devices involves the creation of regions several microns thick that can withstand high voltage without depleting any charge carriers and thus without large currents. One of the best ways to achieve these regions is by deep ion implantation. For a given crystalline substrate, the depth of ion implantation is mainly determined by the energy and mass of the ions, but can be significantly altered by aligning the ion orbitals with the crystal structure of the substrate. In SiC substrates, these alignment effects have a much greater impact than in silicon substrates due to the latent energy caused by the alternation of silicon and carbon atoms in the structure and the reduction in crystal symmetry. In some cases, the ion implantation depth can vary by up to more than 100% depending on the orientation of the silicon carbide crystal. Furthermore, by aligning the ion beam with the crystal orientation, the amount of crystal damage that occurs can be significantly reduced. Therefore, knowledge of crystal orientation is very important in the processing of silicon carbide devices.

[0005]

[0005] In relation to these considerations and other considerations, this embodiment is provided. [Overview of the project]

[0006]

[0006] In one embodiment, an ion implantation apparatus is provided, comprising an ion source for generating an ion beam, a set of beamline components for guiding the ion beam to a substrate along a beam axis perpendicular to a reference plane, a processing chamber for housing the substrate to receive the ion beam, and a conoscopy system disposed within the ion implantation apparatus. The conoscopy system may include an illumination source for guiding light to a substrate position, and a first polarizer assembly disposed between the illumination source and the substrate position, comprising a first polarizing element and a first pair of lenses disposed on both sides of the first polarizing element and configured to focus light to the substrate position. The conoscopy system may also include a second polarizer assembly disposed to receive light after it has passed through the substrate position, comprising a second polarizing element and a second pair of lenses disposed on both sides of the second polarizing element and configured to focus light at a detection surface. The conoscopy system may further include a detector for detecting light after it has passed through the lenses, the detector having a sensor disposed at the detection surface.

[0007]

[0007] In further embodiments, a method for implanting into a substrate is provided. This method may include determining the offset angle of the substrate using a conoscopy system connected to an ion implanter. This method may further include generating an ion beam in the ion implanter, guiding the ion beam to the substrate along a beam trajectory, and tilting the substrate relative to the beam trajectory based on the offset angle when the ion beam is impacting the substrate.

[0008]

[0008] In another embodiment, an optical module is provided for oriented a substrate in an ion implantation apparatus. The optical module may include an illumination source for guiding light to the substrate position. The optical module may include a first polarizer assembly positioned between the illumination source and the substrate position and comprising a first polarizing element and a first pair of lenses positioned on either side of the first polarizing element and configured to focus light to the substrate position. The optical module may further include a second polarizer assembly positioned to receive light after it has passed through the substrate position, comprising a second polarizing element and a second pair of lenses positioned on either side of the second polarizing element and configured to focus light at a detection surface. The optical module may further include a detector for detecting light after it has passed through the lenses, the detector having a sensor positioned at the detection surface. [Brief explanation of the drawing]

[0009] [Figure 1] An exemplary ion implantation system according to an embodiment of this disclosure is shown. [Figure 2] An example of a conoscopy system according to an embodiment of this disclosure is shown. [Figure 3] Details of exemplary ion implantation systems according to other embodiments of this disclosure are shown. [Figure 4] An example of conoscopy imaging for determining substrate alignment is shown. [Figure 5] An example of conoscopy imaging for determining substrate alignment is shown. [Figure 6] Another example of conoscopy imaging for determining substrate alignment is shown. [Figure 7A] This is a simulated conoscopie pattern for 4H SiC irradiated with radiation at a wavelength of 550 nm. [Figure 7B] This is a simulated conoscopium pattern of 4H SiC irradiated with 380nm wavelength radiation. [Figure 7C] This is a simulated conoscopium pattern of 4H SiC irradiated with 266nm wavelength radiation. [Figure 7D] This is a simulated conoscopy pattern of 4H SiC irradiated with 550nm wavelength radiation using special optical software. [Figure 7E] Figure 7D shows a simulated conoscopy pattern for 4H SiC irradiated with 450 nm wavelength radiation using the software. [Figure 7F] Figure 7D shows a simulated conoscopy pattern for 4H SiC irradiated with 405 nm wavelength radiation using the software. [Figure 8] An example processing flow is shown. [Figure 9] This shows another exemplary processing flow. [Figure 10] Examples of conoscopy systems according to further embodiments of the present disclosure are shown. [Figure 11] Additional embodiments of the present disclosure illustrate another example of a conoscopy system. [Figure 12A] An example of an optical module according to another embodiment of this disclosure is shown. [Figure 12B] Another example of an optical module is shown according to additional embodiments of the present disclosure. [Figure 13] Alternative end-station configurations according to various embodiments of this disclosure are shown. [Figure 14] Another exemplary processing flow is shown. [Figure 15] Here is yet another example processing flow. [Modes for carrying out the invention]

[0010]

[0029] Next, with reference to the accompanying drawings showing some embodiments, this embodiment will be described more comprehensively. The subject matter of the present disclosure can be embodied in various different forms and should not be construed as limited to the embodiments presented herein. Instead, by providing these embodiments, this disclosure will be comprehensive and complete, fully conveying the scope of the subject matter to those skilled in the art. Throughout the figures, like numbers refer to like elements.

[0011]

[0030] The embodiments described herein relate to apparatuses and techniques for improving substrate ion implantation. The present embodiments utilize a novel ion implantation system, also referred to herein as an ion implantation apparatus, which incorporates a conoscopy system to provide accurate substrate orientation in situ. In various embodiments, the substrate orientation can be performed by aligning the crystal structure of the substrate to a so-called channeling orientation with respect to the ion beam used for implanting the substrate. In this way, the implantation profile, particularly the implantation depth of the ions of the ion beam, can be substantially increased for a given ion energy and a given substrate.

[0012]

[0031] Referring now to FIG. 1, an exemplary system according to the present disclosure is shown. Ion implantation system 100 represents a beamline ion implantation apparatus that includes, among other components, an ion source 104 for generating an ion beam 108 and a series of beamline components disposed between the ion source 104 and a substrate 132. The ion source 104 may include a chamber for receiving a gas stream or a solid target and generating ions therein. The ion source 104 may also include a power supply and an extraction electrode assembly disposed near the chamber. The beamline components may include, for example, a mass analyzer 120 and other beamline components as are known in the art. These other beamline components are represented by downstream component 124 and may include, for accelerating the ion beam 108, for decelerating the ion beam 108, for shaping the ion beam 108, for scanning the ion beam 108, acceleration stages or deceleration stages, collimators, mass resolution slits, scanners, energy filters, and / or other suitable downstream beamline components (not shown).

[0013]

[0032] The ion beam 108 may be directed toward a substrate 132 mounted to a substrate holder 130 and disposed within a processing chamber. The processing chamber may be part of an end station 134 or may be adjacent to the end station 134. As will be appreciated, the substrate may be moved using control mechanisms in one or more dimensions and types of motion (e.g., translation, rotation, and tilt).

[0014]

[0033] In various embodiments, different species may be used as source and / or additional materials. Examples of source and / or additional materials may include atomic or molecular species containing boron (B), carbon (C), nitrogen (N), oxygen (O), germanium (Ge), phosphorus (P), aluminum (Al), arsenic (As), silicon (Si), helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), gallium (Ga), magnesium (Mg), platinum (Pt), nitrogen (N), hydrogen (H), fluorine (F), and chlorine (Cl). Those skilled in the art will see that the species listed above are not limiting, and other atomic or molecular species may also be used. Depending on the application, the above species may be used as dopants or additional materials. Specifically, one species used as a dopant in one application may be used as an additional material in another application, and vice versa.

[0015]

[0034] The ion source 104 may, but is not limited, include a power generator, a plasma exciter, a plasma chamber, and the plasma itself. The plasma source may be an inductively coupled plasma (ICP) source, a toroidal coupled plasma (TCP) source, a capacitively coupled plasma (CCP) source, a helicon source, an electron cyclotron conoscograph (ECR) source, an indirectly heated cathode (IHC) source, a glow discharge power source, an electron beam generating ion source, or any other plasma source known to those skilled in the art.

[0016]

[0035] The ion source 104 can generate an ion beam 108 for injection into the substrate 132. In various embodiments, as is known in the art, the ion beam 108 (cross-section) may have a target shape such as a spot beam or a ribbon beam. In the illustrated Cartesian coordinate system, the propagation direction of the ion beam 108 may be represented as parallel to the Z-axis, although the actual trajectory of the ions having the ion beam 108 may vary. To perform injection into the substrate 132, the ion beam 108 can be accelerated to the target energy by establishing a voltage (potential) difference between the ion source 104 and the substrate 132, or by other accelerating means such as those used in linear accelerators.

[0017]

[0036] As further shown in Figure 1, the ion implantation system 100 may include a device for performing conoscopic measurements of the substrate 132, which is shown as the conoscopic system 200. In some embodiments, the conoscopic system 200 may be separated from the end station 134 and located partially or entirely within a portion of the ion implantation system 100, while in other embodiments, the conoscopic system may be at least partially integrated within the end station 134. Furthermore, the conoscopic system may be located outside the processing chamber that receives the ion beam, or at a different location within the end station 134. For example, according to some non-limiting embodiments, the conoscopic system 200 may be located within an existing load lock of the ion implantation system 100, in an orientation device that directs the substrate 132, or within a processing chamber portion of the end station 134, or in an optical system attached to a portion of the ion implantation system 100.

[0018]

[0037] Figure 2 shows an example of a modified conoscopy system 200 according to an embodiment of the present disclosure. Figure 2 shows a configuration of the conoscopy system 200 including a lower section 140 designed to produce appropriate illumination of the substrate 132 using a focused beam of polarization, and an upper section 141 designed to produce a conoscopy image. As understood, the substrate 132 may be manipulated while in the conoscopy system 200 to perform a measurement indicating the crystal orientation of the substrate 132. As shown, the conoscopy system 200 may include an illumination source 204, which may be a visible light source or an ultraviolet (UV) light source, according to some non-limiting embodiments. The conoscopy system 200 may further include a first polarizer 208 having a first polarization axis, which for illustrative purposes may be considered to be located along the Y axis. The first polarizer 208 is positioned between the illumination source 204 and the substrate position S. Therefore, radiation (e.g., a beam of radiation) or radiation of other form, called light 206, generated from the illumination source 204, first passes through the first polarizer 208 when it is located at the substrate position S. Note that this light 206 may be collimated and first pass through a condenser lens 209 that focuses the light 206 to the substrate position S. The conoscopic system 200 may further include a second polarizer 210 having a second polarization axis. The second polarization axis is oriented, for example, along the X axis perpendicular to the Y axis and perpendicular to the first polarization axis. Note that an objective lens 211 may be provided between the substrate position S and the second polarizer to collimate the light 106. As shown in the figure, the second polarizer 210 is positioned to receive the light 206 after it has passed through the substrate position S. The conoscopic system 200 may further include a lens 212 positioned to receive the light 206 after it has passed through the second polarizer 210.

[0019]

[0038] The conoscopic system 200 may further include a two-dimensional detector, indicated as detector 214, to detect light 206 after it has passed through lens 212, and the lens images a conoscopic interference pattern onto detector 214. Detector 214 can be any suitable detector for detecting patterns of polarized and focused light, as known in the art. In some embodiments, detector 214 can form a two-dimensional image or pattern suitable for interpretation by a computer algorithm. In this conoscopic approach, the imaging lens (lens 212) is positioned such that the image sensor (see detector 214) is on the detection plane forming the back focal plane of the lens, and thus each point in the image corresponds to one propagation angle of light passing through the substrate 132. In other words, the “camera” formed by the lens and image sensor is focused to infinity such that the detected image is a conoscopic interference image of light angles in the crystal, rather than a conventional image of the sample.

[0020]

[0039] Advantageously, the conoscopy system 200 can be used to accurately determine the crystal orientation of a substrate, particularly for optically birefring single-crystal substrates. As an example, 4H polytype SiC, also referred to herein as "4H SiC," crystallizes in the P63mc space group, which represents a hexagonal crystal structure, and is strongly optically birefringent (uniaxial). Optical birefringence is caused by the reflection of light rays traveling along the c-axis of the crystal ("normal" direction) with a refractive index significantly lower than that of light rays traveling perpendicular to the c-axis ("unusual" direction) using an electric vector along the c-axis ("unusual" direction).

[0021]

[0040] For a ray with an electric vector of an intermediate angle, light incident on a 4h SiC crystal is split into two wavefronts, which then propagate through the crystal at different wavelengths and recombine when the wavefronts return to air (or vacuum). Since the two components have a phase shift when recombined, this effect rotates the plane of polarization. This rotation of polarization can be easily detected by using a condenser lens 209, an objective lens 211, and a pair of crossed polaroid filters, as embodied in the first polarizer 208 and the second polarizer 210. Thus, light with an unrotated plane of polarization passes through the second polarizer 210, and light with a rotated plane of polarization is absorbed by the second polarizer, and those parts of the image appear as black crosses (isogonal lines) in the conoscopic image. If the plane of polarization rotates by exactly 180°, or by an integral product of 180°, one other condition may occur, in which case the second polarizer again blocks the light, producing a series of concentric dark circles (isogonal circles).

[0022]

[0041] In the embodiments detailed herein, the figures and descriptions are best suited to measuring orientation in a distortion-free uniaxial crystal. In a biaxial crystal with indicatorics having three different axes, the resulting conoscillatory image is more complex. Isometric regions appear as a single dark stripe across the field of view, and the isometric regions become elliptical. In distortion-containing crystals, the image is further distorted by the piezoelectric effect. In other embodiments of this disclosure, the operation of the conoscillatory systems disclosed herein can be extended to these more complex situations by interpreting the image and matching it to a model that includes these complex effects.

[0023]

[0042] Therefore, the conoscopy system 200 can be effectively used to inspect birefringent substrates such as 4H SiC or other known birefringent materials. Note that, according to various embodiments, some components of the conoscopy system 200 may be configured similarly to known conoscopy systems and may include microscopic components to provide a moderate magnification with the objective lens focused to infinity rather than at the sample position. In this way, all positions in the image 216 formed on the detector 214 may correspond to the direction of the light 206 rather than to a position on the sample. Thus, the components of the conoscopy system 200 can be used to identify the orientation of the optical axis of the substrate 132, such as 4H SiC, relative to any suitable geometric reference system, such as a Cartesian coordinate system, used to handle and guide the substrate within the ion implantation system 100. Once the orientation of the optical axis of the substrate 132 is known, the substrate 132 can be positioned to be suitable for implantation within the end station 134, such as being positioned in an orientation that facilitates ion channeling along the c-axis of the substrate 132.

[0024]

[0043] Figure 3 shows details of an exemplary ion implantation system according to another embodiment of the present disclosure. The ion implantation system 300 may include known components of an ion implantation apparatus, such as those detailed above with respect to Figure 1. In the view of Figure 3, only the end station 134 and the conoscopy system 200 are shown.

[0025]

[0044] In the embodiment shown in Figure 3, the conoscopy system 200 is located as part of the ion implantation system, represented as chamber 222, and is separate from the processing chamber in the end station 134. However, as described above, in other embodiments, the conoscopy system 200 may be integrated, at least partially, into the processing chamber of the end station 134 that receives the implanted ion beam.

[0026]

[0045] In this embodiment, the conoscopy system 200 may further include a substrate stage 220 for holding the substrate 132 at a substrate position S. In the non-inclined configuration, shown by the dashed line, the main plane of the substrate 132 (such as the plane corresponding to the top surface of the substrate 132) may be used to define the reference plane P. For illustrative purposes, the reference plane P may correspond to the XY plane of the Cartesian coordinate system shown. The substrate stage 220 may include two adjustable angle components for inclining and rotating (also called twisting) the substrate 132 such that, in the case of inclination, the main plane m defines a non-zero angle with respect to the reference plane P. The inclination angle may be shown as θ in Figure 3, while the substrate is rotated by a twist angle φ around the normal 150 to the substrate. By inclining and twisting the substrate stage 220 to vary the value of θ, the detector 214 can be monitored to determine the orientation, also referred to herein as offset orientation. This offset orientation may correspond to the orientation of the substrate 132 that results in maximum ion channeling of the ion beam 108 when the substrate 132 is transferred to the end station 134 and ion implantation is initiated. Thus, by determining the optimal values ​​of φ and θ within the conoscopy system 200, the substrate 132 can be oriented with these same optimal values ​​of φ and θ when it is located at the end station to facilitate channeling of the ion beam 108.

[0027]

[0046] It should be noted that the inclination angle θ may also be equal to the incident angle of the ion beam 108, as defined with respect to the normal 150. Therefore, when the ion beam 108 is oriented at an appropriate value θ with respect to the reference plane P, it can form a trajectory aligned along the normal to the substrate 132, so that when the substrate 132 is oriented at an appropriate value θ, the ion beam 108 collides with the surface of the substrate 132 in a trajectory defined by the same value with respect to the normal 150. Since the c-axis of the crystal forming the substrate 132 can be aligned at an angle θ with respect to the normal 150, the ion beam 108 can be incident on the substrate 132 parallel to the c-axis, and therefore along the so-called channeling direction, provided that appropriate torsional angle alignment is achieved.

[0028]

[0047] According to different embodiments of this disclosure, several operating modes are possible. For crystals with uncertain optical properties, it may be advantageous to measure the refractive index of the material and the inclination of the optical axis with respect to the surface normal by analyzing isometric and isochromatic images at different inclination angles θ at a certain position, and then observing the relative shift of the images. For crystals with known optical properties and a well-aligned optical system, it is possible to determine the inclination angle θ and the twist angle φ by positioning isometric and isometric lines on the image plane without requiring crystal movement, as shown in Figure 9, as will be described in more detail below. For crystals with significant heterogeneity or distortion, it may be advantageous to perform measurements at several different positions (x, y) to investigate possible variations in the direction of the optical axis across the entire wafer, and as a result, the average angle may be used for ion implantation. If the angular variation across the wafer is significant, it may be advantageous to change the direction of the ion beam as a function of x and y across the entire surface of the wafer (meaning the main surface of the substrate) in some systematic way to compensate for the distortion of the wafer crystal.

[0029]

[0048] In another embodiment, one operating mode that is particularly effective and can impose minimal additional delay on wafer processing is described in the following scenario. It should be noted that existing practice for wafer handling prior to a given injection procedure is to use a separate station (separate from the end station where wafer injection takes place) in a vacuum chamber to identify the twist angle of a notch or flat that the wafer manufacturer uses to indicate crystal alignment. This station already has a rotating support for the wafer and an optical sensor that generates a signal from the notch or flat on the edge of the wafer. In this new embodiment, this same station may be equipped with the conoscopy inspection system of this embodiment. The system is capable of imaging interference patterns at, for example, four rotation angles by visually inspecting through the edge of the wafer. Given knowledge of the refractive index and birefringence of the wafer material, each image may be interpreted to generate desired tilt and twist angles for injection, and the tilt / twist information is then fed forward to the injection end station controller, enabling the positioning of the wafer for injection. By using several independent positions on the wafer for inspection, accuracy checks are provided and wafers with large strains and variations in the crystal axis are made detectable.

[0030]

[0049] Alternatively, in another embodiment, conoscopy measurements can be performed at a single spot in the center of the wafer, and several (e.g., four) rotation angles can be measured for the same location. In this latter embodiment, the sampling width of the wafer may be narrower, but the advantages of this embodiment include less wafer distortion, such as warping, at the center of the wafer, and potential clearance from obstacles such as devices and masks. Measuring the same location in multiple orientations can improve measurement accuracy and compensate for small positional errors.

[0031]

[0050] Figures 4 and 5 show examples of conoscopic imaging for determining substrate alignment. Figure 4 shows a microscope image representing a possible conoscopic pattern. The image in Figure 4 can represent an image plane, where all points in the image plane correspond to the propagation angle through the crystal being measured. Dark triangular regions may represent isometric regions consisting of dark bands where only one wave propagates through the crystal. In Figure 4, the isomers do not converge at the center of the cross pattern, indicating disorder in the crystal alignment, while in Figure 5, the tips of the isomers converge at the center of the cross pattern, forming a symmetrical pattern and indicating alignment.

[0032]

[0051] Figure 6 shows another example of conoscopic imaging to determine substrate alignment. In this example, the crystal being measured is a ruby ​​crystal (corundum crystal structure), which has a hexagonal (or triangular) type crystal lattice. The isometric region is generally aligned to the center of the image, and the isometric region shows alignment with some degree of distortion, which is likely caused by twinning or distortion in the ruby ​​sample.

[0033]

[0052] Referring again to Figure 3, the advantage provided by the ion implantation system 300 is that, using an insituconoscopy system, substrates such as birefringent single-crystal substrates can be easily tilted to create a substrate surface oriented to improve channeling just before implantation begins. It should be noted that for some materials, particularly 4H SiC, the ion implantation depth is highly sensitive to substrate orientation, and even slight changes in substrate orientation can substantially alter the implantation depth. Furthermore, as mentioned above, the substrate surface (main plane) of such a 4H SiC substrate may be oriented several degrees off-axis so that the c-axis is not oriented perpendicular to the substrate surface. Therefore, when an off-cut 4H SiC substrate is placed in the implantation apparatus in a nominally horizontal orientation, with the Z-axis parallel to the ion beam and the main plane of the substrate parallel to the XY plane, the ion beam is incident on the substrate along an orbit that is not parallel to the c-axis of the 4H SiC crystal lattice. Consequently, the ion beam does not incident on the 4H SiC lattice along the channeling direction, thus reducing the potential implantation depth of the ion implantation. Furthermore, the precise offset of the substrate surface relative to the c-axis may not be known a priori. Therefore, the timely and accurate tilting of the substrate 132 to align the c-axis of the crystallographic particles with the trajectory of the ion beam 108 can be greatly utilized by the ion implantation system 300.

[0034]

[0053] To emphasize the above points, and for reference, the inventors note that the effect of the substrate offset angle on the ion depth profile for aluminum ion implantation into 4H SiC has been previously reported. Results from aluminum ion implantation showed that at 8-degree or 9-degree inclinations, ion penetration was approximately half that of ions aligned with the c-axis corresponding to the channeling orientation. Therefore, it can be expected that even a slight misalignment of the c-axis of the 4H SiC wafer can significantly reduce ion penetration into the 4H SiC wafer. Higher energies, and consequently deeper channeling implantation, require greater precision in the c-axis orientation of the 4H SiC wafer. The higher the implantation energy, the higher the required precision.

[0035]

[0054] In principle, conoscopy systems can be used to properly orient the substrate within the ion implanter and improve channeling. However, a drawback of applying conoscopy systems to measure substrates such as 4H SiC is that the accuracy of determining the ideal offset angle for orienting the substrate with c-axis alignment decreases as the substrate thickness decreases. For example, the practical thickness of substrates used in power semiconductor applications can be in the range of several hundred micrometers. At this thickness, the resulting conoscopy images may have lower accuracy in determining c-axis alignment than those provided by other techniques such as X-ray diffraction (XRD).

[0036]

[0055] To address this problem, the inventors determined that the measurement accuracy could be substantially improved by reducing the wavelength of the incident radiation used to perform the conoscopy alignment procedure outlined above. To illustrate the possible improvements by reducing the wavelength, Figure 7A shows a simulated conoscopy pattern of 4H SiC irradiated with radiation at a wavelength of 550 nm, Figure 7B shows a simulated conoscopy pattern of 4H SiC irradiated with radiation at a wavelength of 380 nm, and Figure 7C shows a simulated conoscopy pattern of 4H SiC irradiated with radiation at 266 nm. It should be noted that working at a wavelength of 266 nm can be difficult due to the significantly higher absorption of the 4H SiC material itself and additional safety and operational considerations. Specifically, each of the patterns in these figures represents a pixelated simulated image using a simple model that uses 0.1° pixels distributed over ±5°. Since a full-frame 35mm SLR camera with a 200mm lens has a field of view of ±5°, the models in these figures are within the range of practical implementations. However, in the sample shown in Figure 7A, at a wavelength of 500 nm, locating the center of pattern 710 may be difficult with the desired accuracy of at least 0.1 degrees. Conoscopy interference fringe fitting can easily provide subpixel resolution and meet the accuracy requirements for practical implementation.

[0037]

[0056] Referring to Figure 7B, at the relatively short wavelength of 380 nm, the frequency of pattern 720 increases for two reasons: the refractive index and birefringence of the SiC crystal material increase, and the number of wavelengths within the SiC wafer increases. In this example, with appropriate image processing, it may be possible to locate the center of pattern 720 within one pixel (meaning within 0.1 degrees). In addition, by fitting conoscopy interference fringes, subpixel resolution can be easily provided, meeting the accuracy requirements for practical implementation.

[0038]

[0057] Referring to Figure 7C, at 266 nm (UV wavelength), pattern 730 is detailed enough that the crystal centering and orientation can be easily achieved to less than 0.1 degrees. However, the transmittance of the SiC substrate at this wavelength may limit the use of this approach, and the cost of the required instrumentation may be too high. From the above perspective, operation at ultraviolet or near-UV wavelengths in the range of 375 nm to 450 nm may be useful for the conoscopy system of this embodiment.

[0039]

[0058] Figures 7D, 7E, and 7F show the results of conoscopy patterns simulated for wavelengths of 550 nm, 450 nm, and 405 nm, respectively, using commercially available optical software. In this example, the resolution improves as the wavelength decreases, but even at 550 nm, the resolution is sufficient to determine the crystal orientation with the accuracy required for practical implementation.

[0040]

[0059] Figure 8 shows an exemplary processing flow 800. In block 802, a single-crystal substrate is placed in the conoscograph system of the ion implanter. In one embodiment, the single-crystal substrate may be a birefringent substrate such as 4H SiC. In block 804, the single-crystal substrate is illuminated by radiation from within the conoscograph system, and the radiation is transmitted through the substrate. In some non-limiting embodiments, the wavelength of the radiation may be between 550 nm and 375 nm.

[0041]

[0060] In block 806, the single-crystal substrate is tilted around its axis, resulting in different orientations of the substrate, while the conoscopic image is received in a different orientation. This allows for the determination of an offset angle relative to the substrate that corresponds to the channeling direction of the ions injected into the substrate. In other words, the offset angle may correspond to the offcut angle of the substrate with respect to the c-axis of the substrate's crystal lattice.

[0042]

[0061] In block 808, the ion beam is guided to the substrate in the ion implanter while the substrate is positioned at an offset angle.

[0043]

[0062] Figure 9 shows another exemplary processing flow 900. In block 902, a single-crystal substrate is placed in the conoscograph system of the ion implanter. In one embodiment, the single-crystal substrate may be a birefringent substrate such as 4H SiC. In block 904, the single-crystal substrate is illuminated with light in the conoscograph system, and the light is transmitted through the substrate. In some non-limiting embodiments, the wavelength of the radiation may be between 550 nm and 375 nm.

[0044]

[0063] In block 906, based on the operations in block 904, the conosccopy image of the single-crystal substrate is interpreted and the offset angle corresponding to the channeling direction of the single-crystal substrate is determined.

[0045]

[0064] In block 908, an ion beam is guided to the single-crystal substrate in the ion implanter while the substrate is positioned at an offset angle.

[0046]

[0065] Some of the embodiments described above may be applied to measuring wafer alignment in a conoscograph system using single-wavelength light (monochromatic radiation), while other embodiments may utilize two, three, or more single-wavelength lights. In some embodiments, polychromatic radiation may be used. The use of single-wavelength, multiple single-wavelength, or polychromatic illumination, or any combination thereof, may be employed simultaneously or alternately between light sources so that each light source can be imaged separately. In some embodiments, but not limited to, optical filters may be used, including high-pass, low-pass, band-pass, band-stop, any combination thereof, or others. Filters may be used consistently, on a filter wheel, or in a similar apparatus, allowing for alternating filters and filter options between different filters.

[0047]

[0066] Figure 10 shows an embodiment of a conoscopation system according to a further embodiment of the present disclosure. In this embodiment, the conoscopation system 1000 comprises a light source 1010 that guides light through a polarizer assembly 1002. In addition to a first polarizing element (referred to as “polarizer”), the polarizer assembly 1002 may include lenses L1 and L2 that focus the light 1012 received from the light source 1010. The light 1012 may be focused onto the sample plane of the substrate S and then transmitted to an analyzer assembly 1004. Herein too, the analyzer assembly 1004 may include a second polarizing element (referred to as “analyzer”), as well as lenses L3 and L4 that focus the light 1012 with a camera 1006. In some non-limiting embodiments, the camera 1006 may be a solid-state detector such as a CMOS detector or a charge-coupled device (CCD). In some embodiments, the camera 1006 may be positioned perpendicular to the axis of the conoscopic system 1000, or at an angle other than zero relative to the perpendicular. Note that in the case of off-axis tilt, the refractive index must be considered. In some embodiments, the substrate can be placed on the stage at a set tilt angle with respect to the incident light. In some embodiments, the set tilt angle will be the center of the conoscopic image on the imaging sensor / camera. For example, in the case of SiC, the tilt angle is approximately 4 degrees, so in this example the set tilt can be set to 4 degrees + (angle of refraction of incident light passing through SiC), but this total tilt will be the center of the conoscopic image measured by the camera. Realignment of the optical axis will be corrected taking into account the substrate thickness and refractive index.

[0048]

[0067] Figure 11 shows another example of a conoscopy system according to an additional embodiment of the present disclosure. Conoscopy system 1020 may be configured similarly to conoscopy system 1000, and similar components are labeled as such. Conoscopy system 1020 may further include a laser light source 1022 and a detector 1024, the laser light source 1022 guiding an incident laser beam that acts as a probe beam reflected from the surface of the substrate S to be received by the detector 1024. Conoscopy system 1020 may also include additional components, including but not limited to lenses and spatial filters. The laser light source 1022 and detector 1024 may be used to determine whether the location on the substrate S to which the light 1012 strikes is locally flat. This type of local curvature information is useful because the crystalline alignment determined by the conoscopy measurement is determined over a relatively small area of ​​the substrate S. Therefore, the local substrate curvature in the region P where the light 1012 is focused on the substrate S may affect the conoscopy measurement. In other words, if the substrate in region P does not extend parallel to the expected substrate plane, this misalignment can affect conoscopic optical measurements and introduce an incorrect offset angle to the substrate. For example, if the curvature of the measurement region P is tilted by 0.1 degrees in a particular direction, this curvature is added to the intrinsic crystal orientation measured using conoscopic imaging. Therefore, if curvature is not considered, the systematic error in the estimated tilt angle will be 0.1 degrees, and this error may exceed the accuracy required for practical implementation. By taking these local curvature effects into account, the offset angle of a given single-crystal substrate can be determined with an accuracy of 0.1 degrees or better.

[0049]

[0068] Specifically, the conoscopic system 1020 measures the flatness of the substrate at the conoscopic illumination spot in region P, with respect to the optical axis of the optical conoscopic imaging subsystem. In some embodiments, as shown in Figure 11, the flatness can be measured directly using the laser reflected from the substrate and the reflected beam measured by a detector on the opposite side (such as a camera). The deviation of the angle theta between the laser and the substrate from the flatness results in a deviation of twice the theta recorded by the detector. Given that the substrate can deviate in two different oscillation directions, the detector itself can be two-dimensional and capable of considering both angles, or two laser detectors and two linear detectors, or two-dimensional laser detectors can be used perpendicular to each other. The flatness information can then be registered and incorporated into the analysis of the conoscopic imaging system to compensate for any lack of flatness of the substrate at the measurement spot.

[0050]

[0069] Figure 12A shows an example of an optical module 1040 including a further conoscopy system 1050 according to another embodiment of the present disclosure. The conoscopy system 1050 may be located in any suitable chamber of an ion implantation system according to several non-limiting embodiments. In one embodiment, the conoscopy system is part of a pre-positioning module connected to the processing chamber of an ion implantation apparatus. The optical module 1040 includes a substrate stage 1054 which may include rotating and tilting components to manipulate the substrate S, tilt the substrate S, and rotate the substrate S around an axis 1060. The conoscopy system 1050 further includes a polarizer assembly 1002, an analyzer assembly 1004, for example, the components described above. The conoscopy system 1050 further includes a laser, laser diode, LED, or other light source 1056 connected to an optical fiber to guide radiation through the polarizer assembly 1002. The conoscopy system further includes an inclined mirror positioned to receive light after it has passed through the polarizer assembly 1002, and to reflect the light through the substrate S and the analyzer assembly 1004 for reception by the camera 1006. Thus, the conoscopy system 1050 can provide a suitable approach for manipulating the substrate S and easily determining the offset angle within the substrate S before loading it into the final implantation station for ion implantation.

[0051]

[0070] The substrate stage 1054 may include a mechanical stage equipped with substrate handling and high-precision marking determination optics. The mechanical stage includes rotation and translation of the substrate. Mechanical precision can accommodate the overall measurement accuracy required, including accuracy and repeatability of up to 1 micrometer. Mechanical substrate handling includes mechanical clamping of the substrate by various techniques, including but not limited to vacuum suction, mechanical clamping, electrostatic chucks, or others, depending on the module's position and other considerations. Mechanical substrate handling should allow a portion of the substrate to be exposed and freely suspended, enabling a measurement spot for optical conoscopic imaging. The pedestal 1058 shown in Figure 12A should be smaller than the diameter of the substrate S, including but not limited to one-third or one-third of the substrate diameter, half of the substrate diameter, or other. Mechanical substrate handling can also flatten the substrate, thereby improving optical measurements for both conoscopic and marking determination optical measurements. A high-precision marking determination optical system 1064 is provided for measuring torsional orientation markings on a substrate, such as flat markings, notches, or other markings.

[0052]

[0071] The marking determination accuracy can accommodate the overall measurement accuracy required, including accuracy and repeatability of up to 0.001 degrees. To achieve high parallel positioning accuracy of the substrate, the substrate handling can use a marking determination optical system to position the substrate on a mechanical stage and measure the substrate position. If there is a deviation from the optimal alignment, the substrate can be repositioned based on the measurement to achieve the required positioning accuracy. In some embodiments, the tilt of the substrate stage 1054 may be controlled to a tilt accuracy of 0.05 degrees or better, and the rotation of the substrate stage may be controlled to a torsional accuracy of 0.5 degrees or better.

[0053]

[0072] As mentioned above, determining the appropriate substrate orientation for channeling injection involves both determining the appropriate tilt angle for tilting the substrate for proper channeling and determining the appropriate torsion angle. For substrates such as semiconductor wafers containing 4H SiC, the nominal torsion angle may be close to 90 degrees. Due to the three-dimensional shape dimensions of the semiconductor wafer's crystal lattice, the sensitivity to torsion angle misalignment is about 14 times lower than the sensitivity to tilt angle misalignment; therefore, determining an appropriate torsion angle of 1 degree or less may be sufficient to properly align the substrate.

[0054]

[0073] Figure 12B shows another example of the optical module 1040B, including a further conoscopy system 1050, according to another embodiment of the present disclosure. In this embodiment, the substrate stage 1054B includes a pedestal 1058B configured differently from the pedestal 1058. The conoscopy measurement is performed at the center of the substrate S, and a hollow bore at the center of the pedestal 1058B allows the optical path and components to access the center of the substrate S. Measurements at the center of the substrate S often result in less curvature distortion, with or without further planarization of the substrate S, which enables multiple conoscopy imaging measurements at the same location, resulting in improved accuracy and other advantages. The integration of the marking determination optical system and the mechanical clamp is similar to the features described for the embodiment in Figure 12A.

[0055]

[0074] Figure 13 shows an exemplary architecture of end station 1070 illustrating various alternative configurations for providing a location for an optical measurement module based on a conosccopy system. In this example, several suitable locations are shown that are located inside end station 1070 but outside the processing chamber 1072, which may be “external locations”. Note that in this embodiment, end station 1070 can communicate directly or indirectly with the processing chamber 1072, but is considered to constitute components and chambers that do not include the processing chamber 1072. External locations may be, but are not limited to, the inside of the EFEM module, the inside of the robot represented as “location L1” near the robot, the outside represented as “location L2” of the load port, or the side of the EFEM with access to the EFEM represented as “location L3”. Other features such as conosccopy imaging implementation, optical determination of substrate markings, and flatness measurement can also be implemented inside and around the orienter in a vacuum environment. Since operating in a vacuum environment does not allow the use of vacuum suction clamps on wafers, other clamping techniques may be used. The optical windows at the top and bottom of the orienta module are used as access points for optical elements, and also allow for the normal operation of the orienta and miniaturization of optical components to fit within the vacuum chamber in an appropriate form factor to enable optical conoscopist measurements.

[0056]

[0075] In some embodiments, optical conoscopic measurements must be calibrated to maintain alignment and compensate for mechanical drift and imperfections. A calibration substrate may be used. The calibration substrate can be any material with uniaxial birefringence, such as quartz, sapphire, calcite, SiC, or other materials. The crystal orientation of the calibration material can be verified based on XRD measurements of the crystal orientation. Another calibration procedure involves conoscopic measurements of the calibration substrate at 0 degrees relative to the optical axis, including some errors in crystal cutting, and the calibration substrate at various twist angles to compensate for any small miscut deviations from true 0 degrees. This procedure provides true zeros for the conoscopic system.

[0057]

[0076] In some embodiments, optical conosccopy measurements may be further calibrated to compensate for deviations that may occur even with true zero calibration. These deviations include nonlinearity in the conosccopy image recorded by the sensor and the actual crystal orientation. One direct method for calibrating these deviations is to measure several substrates using XRD measurements of crystal orientation as a reference and cross-reference the results with optical conosccopy measurements of the same substrates. The number of substrates measured will be determined by the scale of the nonlinear deviation and the precision required to determine the tilt and twist angles.

[0058]

[0077] In some embodiments, the optical measurement module may be used in a standalone measurement tool. Similar to a standalone XRD crystal orientation measurement tool, a standalone optical measurement tool may include a load port for a substrate batch or FOUP (Front Aperture Unified Pod), mechanical handling of the substrates to the optical measurement module, return to the load port, data analysis, storage, and communication of the crystal orientation of each measured substrate to an external connection (such as an injection device or a centralized software management platform for the manufacturing facility).

[0059]

[0078] Figure 14 shows another exemplary processing flow 1400. In block 1402, light is guided from an illumination source to a first polarizer assembly, which comprises a first lens pair. The wavelength of the light may be in the range of 550 nm to 375 nm, according to various non-limiting embodiments. In block 1404, the light is focused to a substrate position. In block 1406, the light passes through a second polarizer assembly having a second lens pair. In block 1408, the light passing through the second polarizer assembly is focused to a detection plane. In block 1410, a sensor of a detector positioned on the detection plane forms a conoscopic image of the substrate. In block 1412, the offset angle of the substrate is determined by tilting and rotating the substrate through a series of orientations and recording the conoscopic images determined by blocks 1402 to 1410 for the series of orientations of the substrate. In block 1414, the ion beam is guided to the substrate while the substrate is oriented at an offset angle with respect to the ion beam trajectory.

[0060]

[0079] Figure 15 shows yet another exemplary processing flow 1500. In block 102, an apparent offset angle is determined relative to a first region of the substrate using a conoscopy system connected to the ion implanter. In block 1504, the local curvature of the substrate is measured in the first region. In block 1506, the offset angle of the substrate is determined based on the local curvature and apparent offset angle of the substrate. In block 1508, an ion beam is guided to the substrate within the ion implanter when the substrate is positioned at the offset angle.

[0061]

[0080] As a first advantage, this embodiment provides an optical module that can measure the crystal orientation of materials having birefringence and appropriate transparency, such as 4H-SiC and other materials, at low cost and with high accuracy. Several embodiments provide a flexible module including different optical setups and configurations for conoscopic imaging, including cases where the substrate is tilted and cases where it is not; illumination with a single wavelength; illumination with multiple single wavelengths; multicolor illumination or a combination thereof; measurement at different spots on the substrate; measurement at the center of the substrate; or a combination thereof. Another advantage of this embodiment is the analysis of one or more conoscopic interference images to obtain subpixel accuracy. This embodiment further provides a complementary subsystem that enables high-precision marking determination optics, high-precision substrate translational positioning procedures, optical curvature measurement at the conoscopic measurement spot to avoid system errors in crystal orientation measurement, and substrate handling and clamping with or without additional planarization of the substrate. A further advantage provided by this embodiment is the increased applicability for the integration of optical modules in ion implantation equipment at various locations. In addition, this embodiment provides a standalone full system based on a conoscopic imaging approach, as well as complementary subsystems that can operate independently of the injection device.

[0062]

[0081] This disclosure should not be limited in scope by the specific embodiments described herein. In fact, from the foregoing description and accompanying drawings, various other embodiments and modifications of this disclosure, in addition to those described herein, will be obvious to those skilled in the art. Thus, such other embodiments and modifications are also intended to be included within the scope of this disclosure. Furthermore, although this disclosure has been described in the context of a specific implementation in a specific environment for a specific purpose, those skilled in the art will recognize that its usefulness is not limited thereto, and that this disclosure can be usefully implemented in any number of environments for any number of purposes. Thus, the claims described below should be interpreted in light of the entire scope and essence of this disclosure as described herein.

Claims

1. An ion implantation device, An ion source that generates an ion beam, A set of beamline components that guide the ion beam to the substrate along a beam axis perpendicular to the reference plane, A processing chamber for housing the substrate so as to receive the ion beam, The conoscopy system arranged within the ion implantation apparatus, The conoscopy system is equipped with, An illumination source that guides light to the substrate position, A first polarizer assembly disposed between the irradiation source and the substrate position, comprising a first polarizing element and a first lens pair disposed on both sides of the first polarizing element, wherein the first lens pair is configured to focus the light to the substrate position, A second polarizer assembly, positioned to receive the light after it has passed through the substrate position, comprising a second polarizing element and a second pair of lenses positioned on both sides of the second polarizing element, wherein the second pair of lenses is configured to focus the light onto a detection surface, A detector for detecting the light after it has passed through the lens, comprising a detector having a sensor disposed on the detection surface, Ion implantation device.

2. The ion implantation apparatus according to claim 1, wherein the conoscopy system further comprises a substrate stage that holds the substrate at the substrate position, and the conoscopy system is configured to determine the offset angle of the substrate according to the detected image of the light formed by the detector.

3. The ion implantation apparatus according to claim 2, wherein when the substrate is tilted at the offset angle, the light forms a symmetrical pattern in the detector and the c-axis of the substrate is aligned with the beam axis.

4. The ion implantation apparatus according to claim 2, wherein the conoscopy system is configured to determine the value of the offset angle to within 0.1 degrees, the tilt of the substrate stage is controlled to a tilt accuracy of 0.05 degrees or better, and the rotation of the substrate stage is controlled to a torsion accuracy of 0.5 degrees or better.

5. The light is focused into a first region of the substrate, and the conoscopy system is The system further comprises a measurement system for measuring the local curvature of the substrate in the first region, The ion implantation apparatus according to claim 2, wherein the inclination of the substrate is based on the offset angle and the local curvature.

6. The curvature measurement system, A laser source that guides the incident laser beam to the first region, A detector that receives the laser beam after it has been reflected from the first region and The ion implantation apparatus according to claim 5, comprising:

7. The ion implantation apparatus according to claim 1, wherein the conoscopy system is located in an end station at a position outside the processing chamber, and the conoscopy system further comprises a mirror, the mirror being arranged to receive light from the first polarizer and reflect the light through the substrate to the second polarizer.

8. The aforementioned conoscopy system is located outside the processing chamber within the end station. The ion implantation apparatus according to claim 2, wherein the substrate stage includes a tilting component for tilting the substrate within the end station, and when the substrate is tilted with respect to the ion beam at the offset angle, it is in the channeling direction with respect to the ion beam.

9. A method for injecting into a substrate, The offset angle of the substrate is determined using a conoscopy system connected to an ion implantation apparatus, The ion beam is generated within the ion implantation apparatus, The ion beam is guided to the substrate along the beam trajectory, When the ion beam is colliding with the substrate, the substrate is tilted relative to the beam trajectory based on the offset angle. Methods that include...

10. The aforementioned conoscopy system, An illumination source that guides light to the substrate, A first polarizer assembly disposed between the irradiation source and the substrate position, comprising a first polarizing element and a first lens pair disposed on both sides of the first polarizing element, wherein the first lens pair is configured to focus the light to the substrate position, A second polarizer assembly, arranged to receive the light after it has passed through the substrate, comprising a second polarizing element and a second pair of lenses arranged on both sides of the second polarizing element, wherein the second pair of lenses is configured to focus the light onto a detection surface, A detector for detecting the light after it has passed through the lens, the detector having a sensor disposed on the detection surface, The method according to claim 9, comprising:

11. The method according to claim 10, wherein when the substrate is tilted at the offset angle, the light forms a symmetrical pattern in the detector, and the c-axis of the substrate is aligned along the trajectory of the light on the substrate.

12. The method according to claim 9, wherein when the substrate is tilted at the offset angle, the substrate is channeled with respect to the ion beam.

13. The method according to claim 9, wherein the conoscopy system further comprises a rotating component that provides rotation of the substrate through a twist angle, the conoscopy system is configured to determine the value of the offset angle to be within 0.1 degrees, the inclination is controlled to an inclination accuracy of 0.05 degrees or better, and the rotation is controlled to a twist accuracy of 0.5 degrees or better.

14. The ion beam collides with the substrate within the processing chamber, the conoscopy system is located outside the processing chamber, and the method is Transferring the substrate from the conoscopy system to the substrate holder within the processing chamber, The method further includes tilting and rotating the substrate on the substrate holder so that the substrate is tilted at the offset angle, The method according to claim 9, wherein the ion beam collides with the substrate along a beam trajectory that defines the offset angle with respect to the beam trajectory.

15. The light is focused within the first region of the substrate, and the method is The method further includes measuring the local curvature of the substrate in the first region, The method according to claim 13, wherein the tilt and rotation of the substrate are based on the offset angle and the local curvature.

16. Measuring the aforementioned local curvature The laser beam is guided to the first region as an incident laser beam, The method according to claim 15, comprising detecting the laser beam after it has been reflected from the first region.

17. The method according to claim 9, wherein the substrate is 4H-SiC.

18. The method according to claim 9, wherein the light includes radiation having wavelengths between 375 nm and 550 nm.

19. An optical module for aligning a substrate in an ion implantation apparatus, An illumination source that guides light to the substrate position, A first polarizer assembly disposed between the irradiation source and the substrate position, comprising a first polarizing element and a first lens pair disposed on both sides of the first polarizing element and configured to focus the light to the substrate position, A second polarizer assembly, arranged to receive the light after it has passed through the substrate position, comprising a second polarizing element and a second lens pair arranged on both sides of the second polarizing element and configured to focus the light onto a detection surface, A detector for detecting the light after it has passed through the lens, the detector having a sensor disposed on the detection surface, An optical module equipped with the following features.

20. The optical module according to claim 19, further comprising a substrate stage for supporting the substrate, wherein the optical module is located within the ion implantation apparatus, outside the processing chamber of the ion implantation apparatus.

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