Susceptor for epitaxial processing and epitaxial reactor including the susceptor

Abstract

A susceptor for supporting a semiconductor wafer in a heating chamber includes a body having a front surface, a rear surface, and a central plane between the front and rear surfaces. The susceptor also includes a recess extending from the front surface to a recess floor within the body, and a ledge surrounding an outer periphery of the recess floor in the recess. The ledge supports the rear surface of the semiconductor wafer in proximity to the periphery. The ledge includes a first surface forming a first acute angle with a horizontal plane extending parallel to the central plane, a second surface extending radially inward from the first surface, the second surface selectively forming a second acute angle with the horizontal plane, and a third surface extending between the second surface and the recess floor, the third surface forming a third acute angle with the horizontal plane. Each of the first surface, the second surface, and the third surface extends circumferentially along the ledge.

Description

Technical Field

[0001] Cross - Reference to Related Applications This application claims priority based on U.S. Provisional Patent Application No. 63 / 367400, filed on June 30, 2022, the disclosure of which is hereby incorporated by reference in its entirety.

[0002] The field of the present disclosure generally relates to semiconductor wafer processing, and more particularly, to susceptors for epitaxial processing.

Background Art

[0003] Epitaxial chemical vapor deposition is a process of growing a thin layer of material on a semiconductor wafer such that the lattice structure of the layer is the same as that of the wafer's lattice structure. Using this process, layers with different conductive types, dopant species, or dopant concentrations can be applied to the semiconductor wafer to obtain the required electrical properties.

[0004] Prior to epitaxial growth (or "epitaxy"), the semiconductor wafer is typically attached to a susceptor within the growth chamber of a reactor. The epitaxial growth process begins by introducing a cleaning gas to the front surface of the wafer to preheat and clean the front surface of the wafer. The cleaning gas removes native oxides from the front surface, enabling an epitaxial silicon layer to grow continuously and uniformly on the surface during subsequent growth steps. The epitaxial growth process is continued by introducing a vaporized silicon source gas to the front surface of the wafer to deposit and grow an epitaxial layer of silicon on the front surface. The back surface of the susceptor, opposite the front surface, may be simultaneously exposed to hydrogen gas. The susceptor that supports the semiconductor wafer within the growth chamber during epitaxial growth is rotated during the process so that the epitaxial layer grows uniformly.

[0005] A typical susceptor design includes a disc-shaped body having a recess with a concave or slanted ledge. The recess is defined on the upper surface of the disc-shaped body of the susceptor by sidewalls that extend downward from the periphery of the upper surface. The diameter of the recess is generally larger than the diameter of the wafer such that the sidewalls are spaced from the periphery of the wafer. The slanted ledge supports the backside of the wafer near the periphery, and the slanted ledge extends between the sidewall and the floor of the recess. The ledge may have a size and shape such that the backside of the wafer contacts the susceptor only very near the periphery of the wafer, and the floor of the recess is spaced from the backside of the wafer. As a result, damage to the polished backside is reduced. As the tilt angle of the ledge increases, damage to the polished backside may be further reduced.

[0006] Backside deposition is generally an undesirable effect of epitaxial growth, causing variations in the wafer's epitaxial delta edge roll-off (DERO), which can ultimately affect the wafer's flatness. DERO is defined as the change in the thickness profile of the wafer's periphery before and after epitaxy, i.e., the change in "edge roll-off" or ERO. During the epitaxial growth process, a small amount of silicon tends to deposit on the backside of the wafer. This backside deposition may be due to the silicon source gas flowing across the front side of the wafer leaking at the ledge between the wafer's periphery and the susceptor. The leaked source gas results in excessive growth on the backside of the wafer, which may make the area near the wafer's edge (within a few millimeters from the wafer's periphery, e.g., within 5 - 6 millimeters, within 3 - 4 millimeters, or within 1 - 2 millimeters) thicker compared to the area inside the edge. Such thickened portions may increase the DERO. Furthermore, the effect of the thickness increase due to backside deposition may be non-uniform in the area near the wafer's edge, and as a result, the DERO varies circumferentially along the wafer. Variations in the DERO may cause a mismatch between the ERO profile after epitaxy and the ERO profile before epitaxy along the area near the wafer's edge, and this mismatch affects the wafer's flatness. The flatness of the wafer may be measured by flatness parameters such as site backside ideal plane / range (SBIR), global backside ideal plane / range (GBIR), site front side least squares focus plane range (SFQR), edge site front side least squares focus plane range (ESFQR), etc.

[0007] In conventional susceptor designs, DERO variations can be a result of variations in the flatness or thickness of the susceptor (also referred to as "ledge flatness") along the circumferential extent of the ledge. In particular, the ledge flatness can vary circumferentially along the portion of the ledge that contacts the backside of the wafer. Variations in ledge flatness can lead to deviations in the deposition rate of silicon source gas near the edge of the silicon wafer, which can in turn lead to variations in DERO. For example, the amount of silicon source gas leaking between the wafer and the ledge can be non-uniform around the outer periphery of the wafer as a result of variations in ledge flatness. Variations in ledge flatness can be due to manufacturing tolerances and can only be controlled to a certain extent. Furthermore, the applicant has discovered that the inclination of the ledge in conventional susceptor designs where the ledge is inclined at a substantially single angle along the outer periphery of the ledge is insufficient to control DERO variations caused by variations in ledge flatness.

[0008] Accordingly, there is a need for a susceptor having a ledge design that facilitates minimizing or eliminating the impact of variations in ledge flatness on the flatness of the wafer during epitaxial growth processing.

[0009] This "Background" section is intended to introduce readers to various aspects of the technology that may be related to various aspects of the present disclosure described and / or claimed below. This discussion is considered useful in providing readers with background information to facilitate a better understanding of various aspects of the present disclosure. Accordingly, it should be understood that these descriptions are to be read in this light and are not an admission of prior art. SUMMARY OF THE INVENTION PROBLEM TO BE SOLVED BY THE INVENTION

[0010] In one aspect, the susceptor supports a semiconductor wafer within a heating chamber, and the susceptor includes a body having a front surface, a rear surface opposite the front surface, and a central plane extending between the front and rear surfaces. The susceptor also includes a recess extending from the front surface within the body to a recess floor. The recess receives the semiconductor wafer. The semiconductor wafer includes a front face, a rear face, and a periphery joining the front and rear faces. The susceptor includes a ledge surrounding the outer periphery of the recess floor within the recess. The ledge supports the rear surface of the semiconductor wafer in proximity to the periphery. The ledge includes a first surface forming a first acute angle with a horizontal plane extending parallel to the central plane, a second surface extending radially inward from the first surface, where the second surface selectively forms a second acute angle with the horizontal plane, and a third surface extending between the second surface and the recess floor, where the third surface forms a third acute angle with the horizontal plane. Each of the first, second, and third surfaces extends circumferentially along the ledge.

[0011] In other aspects, a susceptor for supporting a semiconductor wafer within a heating chamber includes a body having a front surface, a rear surface opposite the front surface, and a central plane extending between the front and rear surfaces. The susceptor also includes a wall extending from the front surface and defining a recess in the body. The recess has a size and shape to receive the semiconductor wafer. The susceptor includes a ledge extending between the wall and the recess floor. The ledge includes a first surface forming a first acute angle with a horizontal plane extending parallel to the central plane, a second surface forming a second angle smaller than the first angle with the horizontal plane, and a third surface forming a third acute angle with the horizontal plane. Each of the first, second, and third surfaces extends circumferentially along the ledge, and the second surface is positioned between the first and third surfaces.

[0012] In another aspect, an epitaxial growth reactor for growing a thin layer of material on a semiconductor wafer includes a reaction chamber and a susceptor for supporting the semiconductor wafer within the reaction chamber. The susceptor includes a body having a front surface, a rear surface opposite the front surface, and a central plane extending between the front surface and the rear surface. The susceptor includes a recess extending from the front surface to a recess floor within the body. The recess has a size and shape to receive the semiconductor wafer. The susceptor includes a ledge surrounding an outer periphery of the recess floor at the recess. The ledge includes a first surface forming a first acute angle with a horizontal plane extending parallel to the central plane, a second surface extending radially inward from the first surface, the second surface selectively forming a second acute angle with the horizontal plane, and a third surface extending between the second surface and the recess floor, the third surface forming a third acute angle with the horizontal plane. Each of the first surface, the second surface, and the third surface extends circumferentially along the ledge.

[0013] There are various improvements to the features described in relation to the above-described aspects. Similarly, further features may be incorporated into the above-described aspects. These improvements and additional features may exist individually or in any combination. For example, various features described hereinafter in relation to any of the illustrated embodiments may be incorporated into any of the above-described aspects, alone or in any combination.

Brief Description of the Drawings

[0014]

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[0015] Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. DETAILED DESCRIPTION OF THE INVENTION

[0016] FIG. 1 is a top view of an example of susceptor 100. FIG. 2 is a bottom view of susceptor 100. In an embodiment, susceptor 100 supports a semiconductor wafer (e.g., wafer 300 shown in FIG. 3) within a heating chamber (e.g., chemical vapor deposition reactor 200 shown in FIG. 3). Generally, and in the embodiments of the present disclosure, suitable semiconductor wafers (sometimes also referred to as "wafers" or "silicon wafers") include, for example, single crystal silicon wafers such as those obtained by slicing a silicon wafer from an ingot formed by the Czochralski method or the float zone method. Each semiconductor wafer includes a central axis, a front surface or front face, and a rear surface parallel to the front face. The front face and the rear surface are generally perpendicular to the central axis. The circumference or periphery joins the front face and the rear face. The semiconductor wafer may have any diameter suitable for use by those skilled in the art, including, for example, wafers having a diameter of 150 millimeters, 200 millimeters, 300 millimeters, 450 millimeters, etc.

[0017] The susceptor 100 includes a generally disk-shaped body 102. The body 102 includes an outer rim 104, a ledge 106, and a recess 108 formed in the front surface 110 of the body 102. The recess 108 has a size and shape for receiving a semiconductor wafer during processing, and the ledge 106 supports the semiconductor wafer disposed within the recess 108. The susceptor 100 may have other overall dimensions without departing from the scope of the present disclosure. In one embodiment, the susceptor 100 has a size and configuration such that the ledge 106 of the susceptor 100 can accommodate semiconductor wafers of any diameter, including, for example, wafers with diameters of 150 millimeters, 200 millimeters, 300 millimeters, or 450 millimeters.

[0018] Furthermore, the susceptor 100 may be made of other materials. In the embodiments shown in FIGS. 1 and 2, the susceptor 100 is composed of a conventional material such as high-purity graphite and has a silicon carbide layer covering the graphite to reduce the amount of contaminants released from the graphite into the surrounding atmosphere during high-temperature epitaxial growth processing.

[0019] The susceptor 100 also includes a plurality of holes 116 extending through the recess 108 of the body 102. Those skilled in the art will recognize that the holes 116 may be square, slots, or other shapes that allow fluid flow. The holes 116 are spaced apart on the susceptor 100 such that the cleaning gas utilized in the pre-bake step of the epitaxial growth process can substantially contact the entire back surface of the semiconductor wafer and etch it. The holes 116 are spaced apart sufficiently such that the cleaning gas can substantially contact the entire back surface of the semiconductor wafer and etch substantially all of the native oxide film from the back surface. Furthermore, in the embodiments shown in FIGS. 1 and 2, the holes 116 generally form a plurality of concentric rings. For example, the holes 116 form approximately 10 to 30 rings.

[0020] As shown in FIG. 2, susceptor 100 also includes three equally spaced racetrack-shaped holes 118 that extend into susceptor 100 from the rear surface 120 to receive the upper end of a conventional rotatable support 206 (shown in FIG. 3). These holes 118 engage support 206 so that support 206 does not slide on the susceptor when susceptor 100 rotates during processing.

[0021] The susceptor 100 described above may be used as part of a reactor for chemical vapor deposition processes such as epitaxial growth processes. Next, referring to FIG. 3, a reactor for chemical vapor deposition processes is designated generally at 200. Reactor 200 includes an epitaxial reaction chamber 202 having an internal volume or space 204. The susceptor 100 described above has a size and shape that is disposed within the internal space 204 of chamber 202, and susceptor 100 supports semiconductor wafer 300 within internal space 204. Susceptor 100 is shown schematically in FIG. 3, and not all additional features of susceptor 100 are shown in FIG. 3. Wafer 300 includes a front or front surface 302, a rear surface 304, and a circumference or periphery 306 that joins front surface 302 and rear surface 304.

[0022] Wafer 300 is disposed within recess 108 of the susceptor and is supported by ledge 106. More specifically, ledge 106 supports a portion of rear surface 304 of wafer 300 proximate to periphery 306. Susceptor 100 is attached to a pair of conventional rotatable supports 206 for rotating susceptor 100 during epitaxial processing. Reaction chamber 202 also includes a heat source, such as a heating lamp array 208 disposed above and below susceptor 100, for heating wafer 300 during epitaxial growth processing. Gas can be introduced into internal space 204 of chamber 202 through upper gas inlet 210 and lower gas inlet 212.

[0023] The epitaxial reaction chamber 202 including the susceptor 100 described above may be used for both the cleaning step and the growth step of the epitaxial growth process. In an example of the epitaxial growth process, an epitaxial silicon layer grows on the front surface 302 of the semiconductor wafer 300. In this example, the silicon wafer 300 is introduced into the epitaxial growth chamber 202 at atmospheric pressure and placed at the center of the susceptor 100. A cleaning gas such as hydrogen or a mixed gas of hydrogen and hydrogen chloride is introduced into the chamber 202 from the inlet 210 to remove the native oxide layer on the front surface 302 and the back surface 304 of the semiconductor wafer 300.

[0024] When the native oxide layer is removed from both the front surface 302 and the back surface 304 of the semiconductor wafer 300, the supply of the cleaning gas is stopped, and the temperature in the reaction chamber 202 is adjusted between about 600°C and about 1200°C. A silicon-containing source gas such as silane, dichlorosilane, or trichlorosilane is introduced from the inlet 210 above the front surface 302 of the semiconductor wafer 300 at a flow rate between about 1 liter / minute and about 50 liters / minute for a sufficient time to grow an epitaxial silicon layer having a thickness between about 0.1 micrometer and about 200 micrometers on the front surface 302 of the semiconductor wafer 300. At the same time as the silicon-containing source gas is introduced into the growth chamber 202 through the inlet 210 above the front surface 302 of the semiconductor wafer 300, a gas such as nitrogen, argon, hydrogen, a mixture thereof, or a source gas is introduced through the inlet 212 below the back surface 304 of the semiconductor wafer 300 at a flow rate between about 1 liter / minute and about 80 liters / minute so that the purge gas can contact the back surface 304 of the semiconductor wafer 300 and carry the dopant atoms diffused outward from the back surface 304 toward the exhaust outlet 214. In this specification, the wafer 300 subjected to the epitaxial film formation process may be referred to as an "epitaxial wafer".

[0025] Referring to FIGS. 1 and 2, the ledge 106 of the body 102 defines the outer peripheral portion of a recess 108 that extends radially inward from the outer rim 104. As will be described in more detail herein, the ledge 106 has a shape that facilitates minimizing or eliminating the effect of variations in the flatness or thickness of the ledge 106 on the overgrowth and / or non-uniform growth of the epitaxial layer on the back surface of the wafer (e.g., the back surface 304 of the wafer 300) during growth. Excessive growth on the back surface increases the wafer's epitaxial delta edge roll-off (DERO), and non-uniform growth causes variations in the DERO. DERO is defined as the change in the thickness profile of the wafer's periphery before and after epitaxy, i.e., the change in the "edge roll-off" or ERO. An increase and / or variation in the DERO can adversely affect the flatness of the epitaxial wafer. The flatness of the wafer may be measured by flatness parameters such as, for example, site back side ideal plane / range (SBIR), global back side ideal plane / range (GBIR), site front side least squares focal plane range (SFQR), edge site front side least squares focal plane range (ESFQR), etc.

[0026] FIG. 4 is a partial cross-sectional view of the susceptor 100 of FIG. 1 taken along line 1-1 shown in FIG. 1, with the Y-axis overlapping the X-axis, and shows a cross-sectional view of the susceptor 100 taken along a line that intersects the center C of the recess 108 shown in FIG. 1. FIG. 5 is an enlarged view of portion A of the susceptor 100 shown in FIG. 4.

[0027] Referring to FIGS. 4 and 5, the ledge 106 extends between the recess wall 124 and the recess floor 126, and the ledge 106 surrounds the outer periphery of the recess floor 126. The recess wall 124 extends between the ledge 106 and the front surface 110 of the outer rim 104. The recess wall 124 is generally annular and may define the circular shape of the recess 108 (shown in FIG. 1). Alternatively, the recess wall 124 may have a non-cylindrical shape such that the ledge 106 has a radially varying length as it extends circumferentially along the outer edge of the recess 108, and the recess 108 may be asymmetric with respect to at least one of the X and Y axes (shown in FIG. 1). The X and Y axes intersect at the center C of the recess 108.

[0028] Preferably, the diameter of the recess 108 is larger than the outer diameter of the wafer 300 such that the wafer 300 can be received within the recess 108 without being damaged. Thus, when the wafer 300 is disposed within the recess 108, a space G exists between the peripheral edge 306 and the wall 124. The ledge 106 supports a portion of the rear surface 304 proximate to the peripheral edge 306. In particular, the ledge 106 contacts the rear surface 304 at the contact interface 136. As further described below, the ledge 106 generally slopes downward from the wall 124 toward the recess floor 126 such that the recess floor 126 is spaced from the rear surface 304 of the wafer 300. The recess floor 126 may be curved to account for the warp of the wafer 300 during processing. The plurality of holes 116 (shown in FIGS. 1 and 2) extending through the recess 108 may be formed such that the outer ring of the holes 116 is spaced radially inward from the ledge 106. Alternatively, a ring of one or more holes 116 may be formed in the ledge 106.

[0029] The ledge 106 includes a first surface 128, a second surface 130, and a third surface 132. Each of the first surface 128, the second surface 130, and the third surface 132 extends circumferentially along the ledge 106, which means that the first surface 128, the second surface 130, and the third surface 132 extend along the entire circumferential extent of the ledge 106 or a substantial portion of the circumferential extent of the ledge 106. As used herein, a "substantial portion" of the circumferential extent of the ledge 106 means at least about 60% (i.e., about 60% or more) of the circumferential extent of the ledge 106. For example, the surfaces 128, 130, 132 may extend along at least 60% of the circumferential extent of the ledge 106. In some examples, the surfaces 128, 130, 132 may extend along at least about 65%, at least about 70%, at least about 75%, at least about 80%, at least about 85%, at least about 90%, or at least about 95% of the circumferential extent of the ledge 106.

[0030] When the surfaces 128, 130, 132 extend circumferentially along the ledge 106, the surfaces 128, 130, 132 may extend circumferentially without interruption along the entire or a substantial portion of the circumferential extent of the ledge 106. Alternatively, the circumferential extent of the surfaces 128, 130, 132 may be interrupted at regular or irregular intervals. In examples where the surfaces 128, 130, 132 are interrupted at regular or irregular intervals when extending circumferentially along the ledge 106, the individual portions of the surfaces 128, 130, 132 extend circumferentially collectively along at least a substantial portion of the circumferential extent of the ledge 106.

[0031] The cross-section of the ledge 106 along the entire circumferential range of the ledge 106, or a substantial portion of the circumferential range, includes a first surface 128, a second surface 130, and a third surface 132, as shown in FIG. 5. For example, the cross-section of the susceptor 100 shown in FIGS. 4 and 5 is along a line that overlaps the Y-axis above the X-axis (shown in FIG. 1), and the cross-section of the susceptor 100 along a line that overlaps the Y-axis below the X-axis also includes the ledge 106 having the cross-section shown in FIGS. 4 and 5. Further, the cross-section of the susceptor 100 (shown in FIG. 1) along a line that overlaps the X-axis to the right or left of the Y-axis includes the ledge 106 having the cross-section shown in FIGS. 4 and 5.

[0032] The second surface 130 extends radially inward from the first surface 128 by a length L2. The third surface 132 extends radially inward from the second surface 130 to the recess floor 126 by a length L3. The first surface 128 extends radially outward from the second surface 130 by a length L1. The first surface 128 may extend radially inward from the lower end of the wall 124. Alternatively, the ledge 106 includes a fourth surface 134 that extends between the lower end of the wall 124 and the first surface 128 by a length L4. In an example where the ledge 106 includes the fourth surface 134, the fourth surface 134 extends along the entire circumferential range of the ledge 106, or a substantial portion of the circumferential range of the ledge 106, similar to the surfaces 128, 130, 132. As will be described in more detail below, the length of L4 may vary along the circumferential range of the ledge 106.

[0033] The first surface 128 also slopes downward from the wall 124 or from the fourth surface 134 toward the second surface 130. In the example shown in FIG. 5, the first surface 128 supports a part of the rear surface 304 of the wafer 300 proximate to the periphery 306. That is, the contact interface 136 is defined between the first surface 128 of the ledge 106 and the rear surface 304 of the wafer 300. As shown, the first surface 128 is oriented at a downward angle α, as a result of which the contact line between the rear surface 302 of the wafer 300 and the surface 128 is narrowed. The angle α is an acute angle measured with respect to the plane 114 including the X-axis and the Y-axis shown in FIG. 1. The plane 114 is parallel to the central plane 138 of the susceptor 100. The central plane 138 extends between the front surface 110 and the rear surface 120 of the susceptor 100. For convenience, the plane 114 is referred to as the horizontal plane 114, and the term "horizontal plane" as used herein is not intended to limit the susceptor 100 to a particular orientation. Generally, the horizontal plane 114 extends across the front surface 110 of the outer rim 104, and the front surface 110 may be in the same plane as the horizontal plane 114.

[0034] The angle α is preferably measured with respect to the horizontal plane 114 and is, for example, between about 0.5° and about 5°, between about 0.5° and about 4.5°, between about 0.5° and about 4°, between about 0.5° and about 3.5°, between about 1° and about 5°, between about 1.5° and about 5°, between about 2° and about 5°, between about 2.5° and about 5°, between about 3° and about 5°, between about 1° and about 4.5°, between about 1° and about 4°, between about 1° and about 3.5°, between about 1.5° and about 4.5°, between about 1.5° and about 4°, between about 1.5° and about 3.5°, between about 2° and about 4.5°, between about 2° and about 4°, between about 2° and about 3.5°, between about 2.5° and about 4.5°, between about 2.5° and about 4°, between about 2.5° and about 3.5°, between about 3° and about 4.5°, between about 3° and about 4°, or between about 3° and about 3.5°. In a preferred embodiment, the angle α is measured with respect to the horizontal plane 114 and is about 3.18°. In other preferred embodiments, the angle α is any angle that allows the susceptor 100 to function as described herein.

[0035] The second surface 130 may also slope downward as the second surface 130 extends from the first surface 128 to the third surface 132, or the second surface 130 may extend substantially parallel to the horizontal plane 114 between the first surface 128 and the third surface 132. The second surface 130 forms an angle θ. In an example where the second surface 130 slopes downward, the angle θ is an acute angle measured with respect to the horizontal plane 114. In an example where the second surface 130 extends parallel to the horizontal plane 114, the angle θ is 0°.

[0036] Preferably, the angle θ is smaller than the angle α. For example, the angle θ is measured with respect to the horizontal plane 114 and is between 0° and about 3°, between 0° and about 2.5°, between 0° and about 2°, between 0° and about 1.5°, between 0° and about 1°, between 0.5° and about 3°, between about 0.5° and about 2.5°, between about 0.5° and about 1.5°, or between about 0.5° and about 1°. In a preferred embodiment, the angle θ is about 0.7° measured with respect to the horizontal plane 114. In other preferred embodiments, the angle θ is any angle that allows the susceptor 100 to function as described herein.

[0037] Preferably, the transition from the first surface 128 oriented at the angle α to the second surface 130 oriented at the angle θ, which is 0° or an acute angle smaller than the angle α, defines a space between the ledge 106 and the back surface 304 of the wafer 300 that is narrower than the space between the ledge 106 and the back surface 304 that would occur if the ledge 106 continued to extend at the angle α as the ledge 106 extends radially inward from the periphery 306 of the wafer 300. This makes it easier to limit the flow of gas that may leak out between the periphery 306 of the wafer 300 and the first surface 128 of the ledge 106 and makes it easier to minimize the growth of the epitaxial layer on the back surface 304 during deposition. Further, in some examples, the angle θ may preferably be an acute angle greater than 0° to maintain a gap between the back surface 304 and the ledge 106 and to facilitate preventing possible back surface defects caused by contact between the back surface 304 and the ledge 106.

[0038] The third surface 132 slopes downward from the second surface 130 toward the recess floor 126, and the third surface 132 faces at a downward angle β. The angle β is an acute angle measured with respect to the horizontal plane 114. The angle β is preferably greater than the angle θ. For example, the angle β is measured with respect to the horizontal plane 114 and is between about 2° and about 15°, between about 3° and about 15°, between about 4° and about 15°, between about 5° and about 15°, between about 6° and about 15°, between about 7° and about 15°, between about 8° and about 15°, between about 9° and about 15°, between about 10° and about 15°, between about 2° and about 14°, between about 2° and about 13°, between about 2° and about 12°, between about 2° and about 11°, between about 2° and about 10°, or between about 3° and about 10°. In a preferred embodiment, the angle β is measured with respect to the horizontal plane 114 and may be about 3°, about 5°, or about 10°. In a preferred embodiment, the angle β is measured with respect to the horizontal plane 114 and is about 3°. In another preferred embodiment, the angle β is measured with respect to the horizontal plane 114 and is about 5°. In another preferred embodiment, the angle β is measured with respect to the horizontal plane 114 and is about 10°. In other preferred embodiments, the angle β is any angle that allows the susceptor 100 to function as described herein.

[0039] The angles described above for the angles α, θ, β may be implemented in any suitable combination for the corresponding surfaces 128, 130, 132, respectively. In various examples, each of the angles α and β is greater than the angle θ, and the angle θ is an acute angle between 0° and about 1°, or 0°, measured with respect to the horizontal plane 114. In these examples, the angle β may be greater than the angle α, or the angle α may be greater than the angle β. The angle β is preferably greater than the angle α of the first surface 128 such that the angle α is between the angle θ and the angle β. A steeper angle β with respect to the angle θ allows the desired spacing between the recess floor 126 and the back surface 304 of the wafer 300 to be achieved earlier, making it possible to shorten the overall length of the ledge 106.

[0040] In one example, the first angle α is between about 3° and about 4°, the second angle θ is between 0° and about 1°, and the third angle β is between about 3° and about 10°. In another example, the first angle α is between about 3° and about 4°, the second angle θ is an acute angle greater than 0° and between about 1°, and the third angle β is between about 3° and about 10°. In another example, the first angle α is between about 3° and about 4°, the second angle θ is 0°, and the third angle β is between about 3° and about 10°. In another example, the first angle α is between about 3° and about 4°, the second angle θ is between 0° and about 1°, and the third angle β is about 3°, about 5°, or about 10°. In another example, the first angle α is about 3.18°, the second angle θ is about 0.7°, and the third angle β is about 3°, about 5°, or about 10°. In these examples, the angle β may be greater than the angle α, and unless it is clear from the context that it is not the case, the angle α may be greater than the angle β. As described above, the angles α, θ, β are measured with respect to the horizontal plane 114.

[0041] The respective radial lengths L1, L2, and L3 of the first surface 128, the second surface 130, and the third surface 132 are of appropriate lengths such that each surface can perform its intended function. For example, the radial length L1 of the first surface 128 may be selected such that the first surface 128 enables supporting the portion of the back surface 302 of the wafer 300 proximate to the periphery 306 while facilitating minimizing the contact between the back surface 304 of the wafer 300 and the ledge 106. The radial length L2 of the second surface 130 may be selected to extend along the back surface 304 of the wafer at an appropriate distance to facilitate minimizing the growth of the epitaxial layer on the back surface 304 during deposition. The radial length L3 of the third surface 132 may be selected to extend an appropriate distance to minimize the total radial length of the ledge 106.

[0042] Preferably, the radial length L2 of the second surface 130 is longer than each of the radial length L1 of the first surface 128 and the radial length L3 of the third surface 132. In some examples, the radial length L1 of the first surface 128 may be longer than the radial length L3 of the third surface 132 and shorter than the radial length L2 of the second surface 130. Alternatively, the radial length L3 of the third surface 132 may be longer than the radial length L1 of the first surface 128 and shorter than the radial length L2 of the second surface 130.

[0043] The radial length L1 of the first surface 128 is between about 0.5 millimeter (mm) and about 2 mm, between about 0.5 mm and about 1.5 mm, or between about 1 mm and about 1.5 mm. In a preferred embodiment, the radial length L1 of the first surface 128 is about 1.2 mm. In other preferred embodiments, the radial length L1 of the first surface 128 is any length that enables the susceptor 100 to function as described herein.

[0044] The radial length L2 of the second surface 130 is between about 3 mm and about 6 mm, between about 3 mm and about 5.5 mm, between about 3 mm and about 5 mm, between about 3 mm and about 4.5 mm, between about 3.5 mm and about 6 mm, between about 3.5 mm and about 5.5 mm, between about 3.5 mm and about 5 mm, between about 3.5 mm and about 4.5 mm, between about 4 mm and about 6 mm, between about 4 mm and about 5.5 mm, between about 4 mm and about 5 mm, between about 4 mm and about 4.5 mm, or between about 4.5 mm and about 5 mm. In a preferred embodiment, the radial length L2 of the second surface 130 is about 4.5 mm. In other preferred embodiments, the radial length L2 of the second surface 130 is any length that enables the susceptor 100 to function as described herein.

[0045] The radial length L3 of the third surface 132 may be from about 0.3 mm to about 1.2 mm. The radial length L3 may vary according to the angle β of the third surface 132. For example, when the angle β is 3°, the length L3 is preferably between about 1 mm and about 1.2 mm, for example about 1.16 mm. When the angle β is 5°, the length L3 is preferably between about 0.6 mm and about 0.8 mm, for example about 0.7 mm. When the angle β is 10°, the length L3 is preferably from about 0.3 mm to about 0.5 mm, for example about 0.35 mm. In other preferred embodiments, the radial length L3 of the third surface 132 is any length that enables the susceptor 100 to function as described herein.

[0046] The above-described radial lengths L1, L2, and L3 may be implemented in any suitable combination for the corresponding surfaces 128, 130, and 132, respectively. In various examples, the radial length L2 may be longer than each of the radial lengths L1 and L3, and the radial length L1 may be longer or shorter than the radial length L3. In one example, the radial length L1 is between about 0.5 mm and about 1.5 mm, the radial length L2 is between about 4 mm and about 5 mm, and the radial length L3 is between about 0.3 mm and about 1.2 mm. In another example, the radial length L1 is between about 0.5 mm and about 1.5 mm, the radial length L2 is between about 4 mm and about 5 mm, and the radial length L3 is between about 1 mm and about 1.2 mm, between about 0.6 mm and about 0.8 mm, or between about 0.3 mm and about 0.5 mm. In another example, the radial length L1 is about 1.2 mm, the radial length L2 is about 4.5 mm, and the radial length L3 is about 1.16 mm, about 0.7 mm, or about 0.35 mm.

[0047] Preferably, the radial lengths L1, L2, and L3 of each of the first surface 128, the second surface 130, and the third surface 132 are constant along the entire circumferential range of the ledge 106, or along a substantial portion of the circumferential range of the ledge 106. Thus, in an example where the ledge 106 is composed of the first surface 128, the second surface 130, and the third surface 132, the total radial length of the ledge 106 is the sum of the radial lengths L1, L2, and L3, and the total radial length of the ledge 106 is constant along the entire circumferential range of the ledge 106, or along a substantial portion of the circumferential range. When the ledge 106 transitions between adjacent surfaces having different orientations (e.g., between the first surface 128 and the second surface 130, between the second surface 130 and the third surface 132, or between the third surface 132 and the recess floor 126), the ledge 106 may have an acute angle at the intersection of the adjacent surfaces, or the ledge 106 may have a small radius of curvature between the adjacent surfaces to smooth the transition at the intersection of the adjacent surfaces.

[0048] The ledge 106 may also include a fourth surface 134 extending with a radial length L4 between the wall 124 and the first surface 128. The fourth surface 134 may be substantially flat, i.e., the fourth surface 134 extends substantially parallel to the horizontal plane 114 for a length L4. The wall 124 may extend substantially perpendicular to the horizontal plane 114 such that the fourth surface 134 and the wall 124 are orthogonal to each other. The fourth surface 134 is located radially outside the first surface 128, and as a result, is located radially outside the periphery 306 of the wafer 300. As a result, the fourth surface 134 increases the radial distance of the space G between the periphery 306 of the wafer 300 and the wall 124. The ledge 106 may have an acute angle at the intersection between the adjacent first surface 128 and the fourth surface 134, and / or at the intersection between the adjacent fourth surface 134 and the wall 124, or the ledge 106 may have a small radius of curvature between the adjacent first surface 128 and the fourth surface 134, and / or between the adjacent fourth surface 134 and the wall 124 to smooth the transition at the intersection of the adjacent surfaces.

[0049] The extent of the space G between the periphery 306 of the wafer 300 and the wall 124 may affect the flatness of the epitaxial layer growing on the front surface 302 of the semiconductor wafer 300. For example, if the space G between the periphery 306 of the wafer 300 and the wall 124 is too large, more material may be deposited on the periphery 306 and / or the front surface 302 close to the periphery 306, and the DERO of the wafer may undesirably increase. The radial length L4 of the fourth surface 134 is selected to facilitate preventing the space G between the periphery 306 and the wall 124 from adversely affecting the flatness of the epitaxial wafer. For example, the radial length L4 may be between 0 mm and about 2 mm, such as between 0 mm and about 1.1 mm. The radial length L4 of the fourth surface 134 may be implemented in any suitable combination with any of the radial lengths L1, L2, L3 described for the respective surfaces 128, 130, 132.

[0050] The wall 124 defines the overall shape of the recess 108. In one example of the susceptor 100, the wall 124 has a generally annular shape and defines a circular recess 108. In this example, the fourth surface 134, if present, has a constant radial length L4 along the circumferential extent of the ledge 106. Alternatively, the wall 124 may have a non-annular shape such that the radial length of the entire length of the ledge 106 varies along the circumferential extent of the ledge 106, in which case the radial length L4 of the fourth surface 134 may be required to vary along the circumferential extent of the ledge 106. That is, when the recess floor 126 has a constant diameter and the first surface 128, the second surface 130, and the third surface 132 each have a constant radial length L1, L2, L3 along the circumferential extent of the ledge 106, the variation in the radial length of the entire length of the ledge 106 along the circumferential extent of the ledge 106 is brought about by the variation in the radial length L4 of the fourth surface 134. For example, the radial length L4 of the fourth surface 134 may vary between 0 mm and 2 mm, such as between 0 mm and 1.1 mm, along the circumferential extent of the ledge 106.

[0051] In an example where the susceptor includes the non-circular concave wall 124, the recess 108 has a non-circular shape, and the radius of the recess 108 varies as the wall 124 extends circumferentially along the outer rim 104. Thus, the recess 108 may be asymmetric with respect to at least one of the X-axis and the Y-axis (shown in FIG. 1). For example, the recess 108 may be asymmetric with respect to the X-axis and symmetric with respect to the Y-axis. In other examples, the recess 108 may be symmetric with respect to the X-axis and asymmetric with respect to the Y-axis. In other examples, the recess 108 may be asymmetric with respect to each of the X-axis and the Y-axis.

[0052] In some examples, the front surface 110 may be substantially flat such that the height of the wall 124, measured as the extent of the wall 124 between the ledge 106 and the front surface 110 of the outer rim 104, is substantially constant along the circumferential extent of the wall 124. In these examples, the front surface 110 of the outer rim 104 is substantially in the same plane as the horizontal plane 114 along the circumferential extent of the outer rim 104, and the height of the front surface 110, measured as the distance between the front surface 110 and the central plane 138, is substantially constant along the circumferential extent of the outer rim 104.

[0053] Alternatively, the front surface 110 of the outer rim 104 may have a "wavy" shape. The wavy shape of the front surface 110 may complement the non-circular shape of the recess 108 and may be implemented with a circular-shaped recess 108. To provide the wavy shape of the front surface 110 of the outer rim 104, the height of the wall 124 may vary along the circumferential extent of the wall 124. In an example including the wavy shape of the front surface 110, the height of the front surface 110 varies along the circumferential extent of the outer rim 104. The rear surface 120 may be substantially flat such that the overall height of the rear surface 120, measured as the distance between the rear surface 120 and the central plane 138, is constant. In examples where the front surface 110 and / or the rear surface 120 are substantially flat, there may be slight variations in the height of the front surface 110 and / or the rear surface 120, for example, due to manufacturing tolerances.

[0054] As shown in FIG. 4, the ledge 106 has a height or thickness T (hereinafter referred to as thickness T) at the contact interface 136 between the ledge 106 and the back surface 304 of the wafer 300. Referring additionally to FIG. 5, in the exemplary susceptor 100, the thickness T is defined as the distance between the center plane 138 and the first surface 128 at the contact interface 136. The thickness T may vary along the circumferential extent of the ledge 106. More generally, the distance between the surface of the ledge 106 (e.g., the first surface 128, the second surface 130, or the third surface 132) and the center plane 138, i.e., the height or thickness of the ledge 106 at the surface, may vary along the circumferential extent of the ledge 106 at a constant radial distance from the center C of the recess 108 (shown in FIG. 1).

[0055] Variations in the height of the ledge 106 along the circumferential extent of the ledge 106 result in variations in the flatness of the ledge 106 along the circumferential extent of the ledge 106. Thus, variations in the thickness T imply variations in the flatness of the ledge 106. Further, variations in the flatness of the ledge 106, and the accompanying variations in the thickness T, may be due to manufacturing tolerances and can only be controlled to a certain extent.

[0056] During deposition, the silicon source gas may leak through a small gap (not shown) along the contact interface 136 between the ledge 106 and the back surface 304. The small gap may be more pronounced at certain positions along the contact interface 136 due to variations in the thickness T of the ledge 106. If there is a more pronounced gap at a position along the contact interface 136, more silicon source gas will leak through that position along the contact interface 136. As a result, excessive and / or non-uniform leakage of the silicon source gas through the contact interface 136 may occur due to variations in the thickness T.

[0057] The ledge 106 is designed to facilitate minimizing or eliminating excessive and / or non-uniform epitaxial growth due to leakage of silicon source gas through the contact interface 136, thereby facilitating minimizing or eliminating the impact of variations in thickness T on variations in DERO. More specifically, as described above, the first surface 128 is oriented at an angle α and has a radial length L1, the second surface 130 is oriented at an angle θ and has a radial length L2, and the third surface 132 is oriented at an angle β and has a radial length L3. The angles and lengths of each of the surfaces 128, 130, 132 are selected to enable the ledge 106 to function as described herein. The susceptor 100 may include additional features that further facilitate minimizing or eliminating the impact of variations in thickness T on variations in DERO. For example, the ledge 106 may also include a fourth surface 134 that extends radially outward from the first surface 128, and the radial length L4 may be selected to facilitate minimizing variations in DERO during deposition. Additionally, the susceptor 100 may include, as described above, a non-circular recess 108 and / or a wavy outer rim 104, and the shapes of the recess 108 and the outer rim 104 may be complementary to each other to further facilitate minimizing variations in DERO during deposition.

[0058] For further illustration, FIGS. 6-9 compare the impact of variations in the thickness or flatness of the ledge (the "ledge flatness") of a conventional prior art susceptor on the DERO of an epitaxial wafer supported by the prior art susceptor, and the impact of variations in the ledge flatness of a susceptor of an embodiment that includes a ledge having three surfaces that are each oriented at a different acute angle and extend circumferentially along the ledge on the DERO of an epitaxial wafer supported by the susceptor of the embodiment during epitaxial growth.

[0059] FIG. 6 shows a plot of the ledge flatness profile of a conventional prior art susceptor that includes a ledge tilted at a single angle. FIG. 8 shows a plot of the ledge flatness profile of the susceptor of the example. The ledge flatness profiles in FIGS. 6 and 8 are characterized by the normalized flatness measured along the circumferential (360-degree) extent of the ledge. In particular, the normalized flatness is measured at various points along the ledge at a constant radius, and each point is positioned at a location on the ledge corresponding to the contact interface between the ledge and the wafer supported by the ledge. The normalized flatness is the thickness (or height) of the ledge measured as the distance between the surface of the ledge and the central plane of the susceptor at each point normalized with respect to a reference plane R1. The reference plane R1 is the least squares calculation of the thickness of all the measured ledges. Each normalized flatness measurement is quantified in arbitrary units. The ledge flatness profile may vary between susceptors (as shown in FIGS. 6 and 8), for example, due to manufacturing tolerances.

[0060] As shown in FIG. 6, the prior art susceptor has a "valley" in the flatness of the ledge at the 290-degree position. As shown in FIG. 8, the susceptor of the example has valleys in the ledge flatness at the 135-degree and 270-degree positions. The DERO of the epitaxial wafer can be particularly affected at locations along the vicinity of the edge of the wafer adjacent to the position of the valley in the ledge flatness of the susceptor ledge that supports the wafer during deposition.

[0061] FIG. 7 shows the DERO profile of an epitaxial wafer supported by a prior art susceptor having the ledge flatness profile of FIG. 6. FIG. 9 shows the DERO profile of an epitaxial wafer supported by a susceptor of an embodiment having the ledge flatness profile of FIG. 8. The DERO profiles in FIGS. 7 and 9 are characterized by the normalized DERO measured along the circumferential (360 degrees) range of the portion near the edge of the wafer. In particular, the normalized DERO is measured at various points along the wafer at a constant radius, and each of those points is located at a position on the wafer corresponding to the contact interface between the wafer and the susceptor supporting the wafer. The normalized DERO is quantified in any unit and plotted against a reference plane R2.

[0062] As shown in FIG. 7, the epitaxial wafer supported by the prior art susceptor had an abnormal DERO at the 290-degree position corresponding to the position on the prior art susceptor where a valley in the ledge flatness was observed. As shown in FIG. 9, the epitaxial wafer supported by the susceptor of the embodiment did not exhibit abnormal DERO at the 135-degree position and the 260-degree position corresponding to the positions on the susceptor of the embodiment where valleys in the ledge flatness were observed. Thus, in the prior art susceptor, the significant variation in ledge flatness characterized by the position of the valley in the ledge flatness resulted in an abnormal variation in the DERO of the epitaxial wafer supported by the prior art susceptor, whereas in the susceptor of the embodiment, the significant variation in ledge flatness did not result in an abnormal variation in the DERO of the epitaxial wafer supported by the susceptor of the embodiment. Therefore, the ledge design of the susceptor of the present embodiment facilitates better control of the variation in DERO in the epitaxial wafer by minimizing the influence of the variation in the ledge flatness of the susceptor.

[0063] When introducing elements of the present disclosure or embodiments of the present disclosure, the articles "a", "an", "the", and "said" are intended to mean that there is one or more of the elements. The terms "comprising", "including", and "having" are intended to be inclusive and mean that additional elements other than the recited elements may exist. Also, terms indicating a particular orientation (e.g., "top" and "bottom", "front" and "rear", "above" and "below", "vertical" and "horizontal", and other variations of these terms and directions) are for convenience only and do not require a particular orientation of the components.

[0064] The terms "about", "substantially", "essentially", and "approximately", when used in connection with a range of dimensions, density, temperature, or other physical or chemical property or characteristic, are meant to encompass variations that may exist at the upper and / or lower limits of the range of the property or characteristic. Such variations include, for example, variations resulting from rounding, measurement methods, or other statistical variations.

[0065] Without departing from the scope of the present disclosure, various changes are possible in the above-described structures and methods, and thus all matters included in the above description and shown in the accompanying drawings are intended to be interpreted as illustrative rather than in a limiting sense.

Claims

1. A susceptor for supporting a semiconductor wafer in a heating chamber, wherein the semiconductor wafer has a front surface, a rear surface, and a periphery joining the front surface and the rear surface, and the susceptor comprises: a main body having a front surface, a rear surface opposite to the front surface, and a central plane extending between the front surface and the rear surface; a recess extending from the front surface to a recess floor within the main body, the recess receiving the semiconductor wafer, the recess; a ledge surrounding an outer periphery of the recess floor in the recess, the ledge supporting the rear surface of the semiconductor wafer in proximity to the periphery, the ledge; comprising; the ledge; a first surface forming a first acute angle with a horizontal plane extending parallel to the central plane; a second surface extending radially inward from the first surface, the second surface selectively forming a second acute angle with the horizontal plane, the second surface; a third surface extending between the second surface and the recess floor, the third surface forming a third acute angle with the horizontal plane, the third surface; comprising; each of the first surface, the second surface, and the third surface extends circumferentially along the ledge, a susceptor.

2. The susceptor according to claim 1, wherein the first surface has a first length and the second surface has a second length longer than the first length.

3. The susceptor according to claim 2, wherein the third surface has a third length shorter than the second length.

4. The susceptor according to claim 3, wherein the first length and the second length are each longer than the third length.

5. The susceptor according to claim 1, further comprising a recess wall extending between the front surface and the ledge, the ledge extending between the recess wall and the first surface and having a fourth surface parallel to the horizontal plane.

6. The susceptor according to claim 1, wherein the second surface faces the second acute angle, and the first angle and the third angle are each larger than the second angle.

7. The susceptor according to claim 6, wherein the third angle is larger than the first angle.

8. The susceptor according to claim 6, wherein the second angle is between 0° and 3°.

9. The susceptor according to claim 1, wherein the third angle is between 3° and 10°.

10. The susceptor according to claim 1, wherein the third angle is 10°.

11. The susceptor according to claim 10, wherein the length of the third surface is between 0.3 mm and 0.5 mm.

12. The susceptor according to claim 1, wherein the second surface faces at the second angle, the first angle is between 3° and 4°, the second angle is between 0° and 1°, and the third angle is between 3° and 10°.

13. The susceptor according to claim 12, wherein the first length of the first surface is between 0.5 mm and 2 mm, the second length of the second surface is between 3 mm and 6 mm, and the third length of the third surface is between 0.3 mm and 1.2 mm.

14. A susceptor for supporting a semiconductor wafer in a heating chamber, the susceptor comprising: a main body having a front surface, a rear surface, and a central plane extending between the front surface and the rear surface; a wall extending from the front surface and defining a recess in the main body, the recess having a size and shape for receiving the semiconductor wafer; a ledge extending between the wall and the recess floor; and comprising: The ledge: a first surface forming a first acute angle with a horizontal plane extending parallel to the central plane; a second surface forming a second angle smaller than the first angle with the horizontal plane; a third surface forming a third acute angle with the horizontal plane; and comprising: Each of the first surface, the second surface, and the third surface extends circumferentially along the ledge, and the second surface is located between the first surface and the third surface.

15. The susceptor according to claim 14, wherein the ledge extends between the wall and the first surface and comprises a fourth surface parallel to the horizontal plane.

16. The susceptor according to claim 14, wherein the first surface has a first length, the second surface has a second length, the third surface has a third length, and the second length is longer than each of the first length and the third length.

17. The susceptor according to claim 14, wherein the third angle is 10°, and the length of the third surface is between 0.3 mm and 0.5 mm.

18. An epitaxial growth reactor for growing a thin layer of material on a semiconductor wafer, the reactor comprising: a reaction chamber; a susceptor for supporting the semiconductor wafer in the reaction chamber; and comprising: The susceptor: a main body having a front surface, a rear surface opposite the front surface, and a central plane extending between the front surface and the rear surface; A recess that extends from the front surface to the recess floor within the body, the recess having a size and shape for receiving the semiconductor wafer, the recess; A ledge that surrounds the outer periphery of the recess floor in the recess; Comprising; The ledge is; A first surface that forms a first acute angle with respect to a horizontal plane extending parallel to the central plane; A second surface that extends radially inward from the first surface, the second surface selectively forming a second acute angle with respect to the horizontal plane, the second surface; A third surface that extends between the second surface and the recess floor, the third surface forming a third acute angle with respect to the horizontal plane, the third surface; Comprising; Each of the first surface, the second surface, and the third surface extends circumferentially along the ledge, an epitaxial growth reactor.

19. The second surface faces at the second angle, the second angle being smaller than each of the first angle and the third angle, and a first length of the first surface and a third length of the third surface are each shorter than a second length of the second surface, the reactor according to claim 18.

20. The susceptor includes a recess wall that extends between the front surface and the ledge, the ledge extends between the recess wall and the first surface, and includes a fourth surface parallel to the horizontal plane, the reactor according to claim 18.

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