Wafer boat for supporting semiconductor wafers in furnace

Abstract

To provide a semiconductor wafer boat for supporting semiconductor wafers for use in heat treating the semiconductor wafers in a furnace.SOLUTION: In a wafer boat, each finger in a group 42 of fingers 30 includes an elongated segment 50 extending from a vertical rod and a contact protrusion 52 disposed on an elongated segment 50 toward the distal end 34 of the finger 30 and contacting and supporting a semiconductor wafer. The contact protrusion 52 is used to support any diameter of wafer including 200 mm diameter wafers, 300 mm diameter wafers and / or wafers larger than 300 mm diameter.SELECTED DRAWING: Figure 2

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Patent Application No. 63 / 044,700, filed June 26, 2020, which is incorporated by reference in its entirety. [Technical field]

[0002] The field of the disclosure relates to semiconductor wafer boats for supporting semiconductor wafers, and more particularly, to semiconductor wafer boats for use in thermal processing of semiconductor wafers in a furnace. [Background technology]

[0003] Semiconductor wafers are typically heat treated (i.e., annealed) at high temperatures to achieve certain desired properties. For example, an annealing step can be used to create a defect-free layer of silicon in the wafer. High temperature annealing processes are typically performed in vertical furnaces that expose the wafer to temperatures in excess of 1100° C. (e.g., between about 1200° C. and about 1300° C.).

[0004] Multiple semiconductor wafers may be supported in a vertical furnace by a wafer boat or "rack". A wafer boat contains one or more supports on which the semiconductor wafers rest. When exposed to high temperatures, especially temperatures above 1100 °C, the wafers become temporarily more plastic; that is, their yield strength decreases. The contact areas on the wafer where the wafers are supported can slip due to localized gravitational and thermal stresses. Slip can introduce contaminants to the wafer. Excessive slip can also lead to plastic deformation of the wafer, which can lead to production problems such as photolithography overlay defects that cause yield loss in device manufacturing.

[0005] The supports are intended to hold the semiconductor wafers while they are being thermally processed, minimizing localized gravitational and thermal stresses to prevent slippage and plastic deformation. Conventionally, wafer boats used in vertical furnaces feature three or more rods. The rods have laterally extending fingers that generally lie in a common horizontal plane. This configuration is conventional and is typically suitable for heating smaller diameter wafers, such as 200 mm or smaller. Larger diameter wafers (e.g., greater than 200 mm) are subject to greater localized gravitational and thermal stresses than smaller diameter wafers. Such larger diameter wafers are typically mounted on support rings, which provide a larger surface area for supporting the wafers. The support rings increase the time to load and unload the semiconductor wafers from the wafer boat.

[0006] What is needed is a wafer boat that includes a support structure that supports semiconductor wafers that are exposed to high temperatures during processing while reducing localized gravitational and thermal stresses to limit the occurrence of slip, and a wafer boat that has a relatively high throughput for loading and unloading wafers.

[0007] This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present disclosure, which are described and / or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. As such, it should be understood that these statements are to be read in this light, and not as admissions of prior art. Summary of the Invention

[0008] One aspect of the disclosure relates to a wafer boat for supporting a plurality of semiconductor wafers in a furnace. The wafer boat includes a vertical rod and a set of fingers extending radially inward from the vertical rod along a finger axis. Each finger of the set includes an elongated segment extending from the vertical rod. Contact protrusions are disposed on the elongated segment toward a distal end of the finger for contacting and supporting the semiconductor wafer. At least a portion of the contact protrusions are raised relative to the elongated segment. The contact protrusions have a longitudinal contact protrusion axis. The longitudinal contact protrusion axis and the finger axis are angled relative to one another.

[0009] There are various refinements of the features mentioned in relation to the above-mentioned aspects of the disclosure. Further features can also be incorporated into the above-mentioned aspects of the disclosure. These refinements and additional features can exist individually or in any combination. For example, the various features discussed below in relation to any of the illustrated embodiments of the disclosure can be incorporated into any of the above-mentioned aspects of the disclosure, alone or in any combination. [Brief description of the drawings]

[0010] [Figure 1] FIG. [Diagram 2] FIG. 2 is a plan view of the wafer boat showing the contact protrusions. [Diagram 3] FIG. 4 is a detailed view of the contact protrusions of the wafer boat. [Figure 4] 13A and 13B are detailed views of another embodiment of a contact protrusion. [Diagram 5] FIG. 13 is a plan view of a wafer boat having another embodiment of contact protrusions. [Figure 6] 6 is a detailed view of the contact protrusion shown in FIG. 5. [Figure 7] FIG. 13 is a detailed side view of a contact projection supported by a pin and a gimbal.

[0011] Corresponding reference characters indicate corresponding parts throughout the drawings. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] An example of a wafer boat for supporting multiple semiconductor wafers in a vertical furnace is shown generally at "10" in FIG. 1. Wafer boat 10 supports multiple semiconductor wafers during a high temperature thermal processing step (also referred to herein as "annealing"). Wafer boat 10 includes at least one vertical rod 12 (and typically three or more rods) coupled to a top 14 and a bottom 16 of wafer boat 10. Wafer boat 10 has a central longitudinal axis Y extending from top 14 to bottom 16. 10 The vertical rod 12 has a central longitudinal axis Y 10 It is located at a distance D1 from (Figure 1).

[0013] 1-3, the illustrated wafer boat 10 includes three vertical rods 12, specifically a central rod 18 and two front rods 20. Each of the vertical rods 12 extends along a central longitudinal axis Y 10 The two front rods 20 are arranged on a first circle C1 having a center at and a radius R1 (FIG. 2). 10 The central rod 18 is spaced apart from the longitudinal center axis Y by a first angle α1 with respect to each of the two front rods 20 at a second angle α2. 10 The two front rods 20 are spaced apart an equal circumferential distance between them such that the two front rods 20 are spaced apart around the inner space 26 of the wafer boat 10. The two front rods 20 are spaced apart by a first angle α1 such that an inlet 24 is defined between the two front rods 20 (FIG. 1). The first angle α1 can be any suitable angle such that the inlet 24 is sized to allow semiconductor wafers to pass through the inlet 24 and be disposed within the interior space 26 of the wafer boat 10. For example, the first angle α1 is greater than or equal to 180° and the second angle α2 is less than or equal to 90°.

[0014] The wafer boat 10 includes fingers 30 extending radially inward from the vertical rods 12 for supporting the semiconductor wafers (i.e., the boat does not include a support ring for supporting the wafers). The two front vertical rods 20 include first and second sets 36, 38 of fingers 30, respectively. The central vertical rod 18 includes a third set 40 of fingers 30. The first set 36 of fingers 30 is aligned along a first finger axis A. 36 , and the second set 38 of fingers 30 extends along a second finger axis A 38 and the third set of fingers 40 extends along a third finger axis A 40 Each finger axis A extends along the 36 , A 38 , A 40 1, the fingers 30 extend from a proximal end 32 of the fingers 30 to a distal end 34 of the fingers 30. The proximal end 32 of the fingers 30 is adjacent the vertical rod 12 and the distal end 34 of the fingers 30 is disposed in the interior space 26 of the wafer boat 10. The fingers 30 may be integrally formed with the vertical rod 12, for example, an elongated unitary structure may be cut to form the fingers 30. Alternatively, the fingers 30 may be formed separately and coupled to the vertical rod 12.

[0015] Finger axes A of the first and second sets 36, 38 of fingers 30 36 , A 38 are the chords X of the first circle C1, respectively. 36 , X 38 String X extends upwards. 36 , X 38 is the longitudinal center axis Y of the wafer boat 10 10 (i.e., the first and second sets of fingers 36, 38 are aligned such that they are aligned along the central longitudinal axis Y 10 (not centered to point at the finger axis A of the third set 40 of fingers 30) 40 is the longitudinal central axis Y 10 Chord X of the first circle C1 that intersects with 40 Extends upward.

[0016] The groups 42 of fingers 30 extending from each of the vertical rods 12 are in the same, generally horizontal plane so that the groups 42 of fingers 30 can support a semiconductor wafer. The distal ends 34 of the fingers 30 of the group 42 lie on a second circle C2. The second circle C2 has a radius R2 and is aligned about a central longitudinal axis Y. 10 The radius R2 is the distance from the distal end 34 of the finger 30 to the longitudinal center axis Y of the wafer boat 10. 10 In the illustrated embodiment, each of the distal ends 34 of the fingers 30 in the group 42 is disposed an equal circumferential distance from each of the other distal ends 34 of the other fingers 30 in the group 42. For example, in the illustrated embodiment including first, second, and third sets 36, 38, 40 of fingers 30, the distal ends 34 of each of the first, second, and third sets 36, 38, 40 of fingers 30, respectively, are spaced apart from each other along the central longitudinal axis Y 10 The first and second circles C2 are spaced apart by an angle β1 defined on a second circle C2 centered at . In the illustrated embodiment, the angle β1 is 120°.

[0017] 2 and 3, each of the fingers 30 includes an elongated segment 50 extending from the vertical rod 12 and a contact protrusion 52 disposed on the elongated segment 50 toward the distal end 34 of the finger 30. The contact protrusion 52 contacts and supports a semiconductor wafer. The contact protrusion 52 is elevated relative to the elongated segment 50. The contact protrusion 52 has a first end 54, a second end 56, and a longitudinal contact protrusion axis A that extends through the first and second ends 54, 56 of the contact protrusion 52. 52 The contact protrusions 52 may be used to support any diameter of wafer, including 200 mm diameter wafers, 300 mm diameter wafers, and / or wafers greater than 300 mm diameter.

[0018] For the first and second sets 36, 38 of fingers 30, the longitudinal contact projection axis A 52 and each finger axis A 36 , A 38are angled relative to each other by an angle λ1 when viewed from above (Figure 2). 52 and each finger axis A 36 , A 38 The angle λ1 between the longitudinal contact projection axis A and the longitudinal contact projection axis B is at least 5°, or in other embodiments, at least 10°, at least 15°, at least 20°, 5° to about 90°, or 5° to about 75°. 52 and finger axis A 40 are angled relative to each other by an angle λ2. The angle λ2 is 52 and finger axis A 30 The longitudinal contact projection axis A is perpendicular to each other. 52 is the position where the contact protrusion 52 intersects with the third circle C3, and is aligned with the longitudinal center axis Y 10 In this configuration, the contact protrusion 52 is tangent to a third circle C3 having a center at the longitudinal center axis Y 10 (i.e., the contact protrusions are arranged in a rotationally symmetric pattern about the central axis Y 10 similarly spaced and angled around the

[0019] The illustrated contact protrusions 52 are rounded (e.g., increase in height from each side to an apex midway between the sides). A round contact protrusion 52 includes a surface that is generally cylindrical in shape. Each contact protrusion 52 is aligned along a longitudinal contact protrusion axis A. 52 The wafer includes a length L1 (FIG. 3) extending along the longitudinal axis A of the contact protrusion, and a width W1 perpendicular to the length L1. 52 4. The contact rests on a rounded contact projection 52 approximately along the length of the contact.

[0020] In some embodiments, the contact protrusion 52 has a width W1 of 10 mm to 25 mm and a length L1 of 20 mm to 40 mm. 10In some embodiments, the contact protrusion 52 has a width W1 of 8 mm, a length L1 of 30 mm, and a distance from the contact protrusion 52 to the central longitudinal axis Y 10 The distance to is 100 mm.

[0021] In some embodiments, such as the embodiment shown in Figure 4, the contact protrusion 52 is flat. Components shown in Figure 4 that are similar to components in Figures 1-3 are designated by the corresponding reference numbers in Figures 1-3 with the addition of "100" (e.g., part 52 becomes part 152). The flat contact protrusion 152 is aligned along the longitudinal contact protrusion axis A. 152 and a contact surface 153 defined by a longitudinal contact projection axis A 152 and a width W1 perpendicular to length L1. Contact surface 153 generally is in substantial contact with a semiconductor wafer resting on planar contact bump 152.

[0022] Alternatively, the protrusion 52 may be generally dome-shaped, with the semiconductor wafer resting on a relatively small point-like area.

[0023] Another embodiment of the contact protrusion 52 is shown in Figures 5 and 6. Components shown in Figures 5 and 6 that are similar to components in Figures 1-3 are designated by the corresponding reference numbers in Figures 1-3 with the addition of "200" (e.g., part 52 becomes part 252). The finger 230 includes a first contact protrusion 252a that is elevated relative to the elongated segment 250. The first contact protrusion 252a is aligned along a first longitudinal contact protrusion axis A. 252aThe finger 230 also includes a second contact protrusion 252b disposed toward the distal end 234 of the finger 230. At least a portion of the second contact protrusion 252b is raised relative to the elongated segment 250. Each of the first and second contact protrusions 252a, 252b contacts and supports a semiconductor wafer. The second contact protrusion 252b has a first end 254, a second end 256, and a second longitudinal contact protrusion axis A extending therebetween. 252b In the illustrated embodiment, the first longitudinal contact projection axis A 252a and a second longitudinal contact projection axis A 252b are approximately parallel to each other.

[0024] For the first and second sets 236, 238 of fingers 230, the first and second lug axes A 252a , A 252b is finger axis A 230 With respect to the angle λ 201 In the third set 240 of fingers 230, the first and second prong axes A 252a , A 252b is finger axis A 230 The first and second contact protrusions 252a, 252b are substantially parallel to the longitudinal center axis Y. 210 The fingers are arranged in a rotationally symmetric pattern around the finger axis A. 230 Any angle λ 201 It can be arranged in.

[0025] The first and second contact protrusions 252a, 252b are aligned along the first and second protrusion axes A. 252a , A 252bThe first and second contact protrusions 252a, 252b have an elongated shape with a length L2 extending along the length of the contact protrusions 252a, 252b. The first and second contact protrusions 252a, 252b can be separated by a distance W2. In some embodiments, W2 is 10 mm to 40 mm, 15 mm to 30 mm, or 24 mm in other embodiments. The first and second contact protrusions 252a, 252b can have a variety of shapes, such as a cylindrical cross-section, a rectangular cross-section (i.e., flat contacts), or a trapezoidal cross-section (e.g., flat top).

[0026] Each group 242 of contact protrusions 252a, 252b in a common horizontal plane contacts and supports a wafer. The wafer is placed on each of the contact protrusions 252a, 252b such that the weight of the wafer is approximately evenly distributed across each of the contact protrusions 252. In the illustrated embodiment, each of the six contact protrusions 252a, 252b in a group 242 supports 1 / 6 of the weight of the wafer.

[0027] Another embodiment of the contact protrusion 352 is shown in FIG. 7. Components shown in FIG. 7 that are similar to components in FIGS. 1-3 are designated by the corresponding reference numbers in FIGS. 1-3 with the addition of "300" (e.g., part 10 becomes part 310). Referring to FIG. 7, each of the fingers 330 includes an elongated segment 350 extending from a vertical rod 312. The fingers 330 include a platform 360 that supports first and second contact protrusions 352a, 352b. The platform 360 is coupled to the elongated segment 350 by a pin 362, which is pivotally connected to the elongated segment 350 by a cylindrical joint or gimbal 364. Thus, the pin 362 and gimbal 364 allow the platform 360 to pivot relative to the elongated segment 350. The platform 360 supports first and second contact protrusions 352a, 352b, each of which contacts and supports a semiconductor wafer.

[0028] The pivoting of the platform 360, enabled by the pins 362 and gimbal 364, counters uneven load distribution caused by machining inaccuracies and allows the platform 360 to pivot in response to uneven loading on the contact prongs 352a, 352b. The platform 360 can pivot to more evenly distribute the weight of the wafers on each of the contact prongs 352a, 352b. After the wafer boat 310 is placed in the vertical furnace and exposed to oxidation, the pins 362 and gimbal 364 are secured to prevent the platform 360 from further pivoting during the annealing process.

[0029] The wafer boat of the present disclosure has several advantages over conventional wafer boats. In embodiments where the wafer boat includes one or more contact protrusions arranged in a rotationally symmetric pattern, localized gravitational and thermal stresses of semiconductor wafers loaded on the wafer boat are reduced during annealing, reducing slippage. In embodiments where the wafer boat includes pins and gimbals supporting a platform with two or more contact protrusions, the platform can pivot to accommodate uneven loading of the contact protrusions caused by machining inaccuracies.

[0030] example The processes of the present disclosure are further illustrated by the following examples, which should not be construed in a limiting sense.

[0031] Example 1: Peak stress in wafers for various boat designs The peak stresses of the wafers were measured for various boat designs with different finger arrangements using finite element modeling. One wafer boat contained fingers with flat contact protrusions where the contact protrusions of the fingers extending from the front rods were not angled with respect to the finger axis (i.e., the contact protrusion axis and the finger axis were parallel and the contact protrusions were not rotationally symmetric). The second wafer boat was similar to the first, but the contact protrusions were cylindrical. The third wafer boat contained cylindrically shaped contacts arranged as shown in Figure 2 (i.e., fingers extending from two front rods with contact protrusions angled with respect to the finger axis and fingers extending from a central rod perpendicular to the central axis such that the contact protrusions were rotationally symmetric). The fourth boat contained two contact protrusions on each finger that were rotationally symmetric as shown in Figures 5 and 6. The peak stresses for each boat are shown in Table 1 below.

[0032] TIFF2025041837000002.tif36144 Table 1: Peak stress on wafer for various boat designs with different contact bump arrangements

[0033] As shown in Table 1, the wafer boats with rotationally symmetric contact protrusions (Boats 3 and 4) had reduced peak stresses which reduced slippage of semiconductor wafers annealed in the wafer boats.

[0034] As used herein, the terms "about," "substantially," "essentially," and "approximately," when used in conjunction with a range of a dimension, concentration, 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 property or range of properties, including, for example, variations due to rounding, measurement method, or other statistical variations.

[0035] When introducing elements of this disclosure or embodiments thereof, the articles "a," "an," "the," and "said" are intended to mean that there are one or more elements. The terms "comprising," "including," "containing," and "having" are intended to be inclusive and mean that there may be additional elements other than the listed elements. Use of specific directional terms (such as "top," "bottom," "side," etc.) is for convenience of description and does not require a particular orientation of the items being described.

[0036] Because various changes may be made in the structures and methods described above without departing from the scope of the present disclosure, it is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not limiting.

Claims

1. 1. A wafer boat for supporting a plurality of semiconductor wafers in a furnace, comprising: A vertical rod; a set of fingers extending radially inward from the vertical rod along a finger axis; Each finger in the set is an elongated segment extending from the vertical rod; and contact projections disposed on elongated segments toward distal ends of the fingers for contacting and supporting a semiconductor wafer, at least a portion of the contact projections being raised relative to the elongated segments, the contact projections having longitudinal contact projection axes, the contact projection axis and the finger axis being angled relative to one another.

2. 2. The wafer boat of claim 1, wherein the contact protrusions are rounded.

3. 3. The wafer boat according to claim 2, wherein the contact protrusions have a width of 10 mm to 25 mm and a length of 20 mm to 40 mm, and the distance from the contact protrusions to the longitudinal center axis of the wafer boat is 75 mm to 125 mm.

4. 3. The wafer boat according to claim 2, wherein the contact protrusions have a width of 16 mm, a length of 30 mm, and a distance from the contact protrusions to a longitudinal center axis of the wafer boat is 100 mm.

5. 2. The wafer boat of claim 1, wherein the contact protrusions are flat.

6. 6. The wafer boat of claim 1, wherein the angle between the longitudinal contact projection axis and the finger axis is at least 5°, at least 10°, at least 15°, at least 20°, or from 5° to about 90°, or from 5° to about 75°.

7. 7. The wafer boat according to claim 1, wherein the longitudinal contact protrusion axis is tangent to a circle centered on the longitudinal central axis of the wafer boat at a position where the contact protrusion intersects the circle.

8. 7. The wafer boat of claim 1, wherein the contact protrusions are first contact protrusions, the longitudinal contact protrusion axis is a longitudinal first contact protrusion axis, the fingers include second contact protrusions toward distal ends of the fingers for contacting and supporting the semiconductor wafer, at least a portion of the second contact protrusions being raised relative to the elongated segment, the second contact protrusions having a longitudinal second contact protrusion axis, and the longitudinal second contact protrusion axis and the finger axis being angled relative to each other.

9. 9. The wafer boat of claim 8, wherein the second longitudinal contact protrusion axis is parallel to the first longitudinal contact protrusion axis.

10. 10. The wafer boat of claim 8 or 9, wherein the first and second contact projections are supported by a platform, the platform mounted on a pin pivotable about a gimbal mounted to the distal end of the elongated segment.

11. 11. The wafer boat according to claim 1, wherein the finger axis extends on a chord of a circle centered on the longitudinal central axis of the wafer boat, and the chord does not intersect with the longitudinal central axis of the wafer boat.

12. the vertical rod is a first rod, the set of fingers is a first set of fingers, the chord is a first chord, and the wafer boat is A second vertical rod; a second set of fingers extending radially inward from the second vertical rod along a second finger axis, the second finger axis extending on a second chord of a circle, the second chord not intersecting a central longitudinal axis of the wafer boat; Each finger of the second set an elongated segment extending from the second vertical rod; 12. The wafer boat of claim 11, comprising: a contact protrusion disposed on the elongated segment toward a distal end of the finger for contacting and supporting the semiconductor wafer, at least a portion of the contact protrusion being raised relative to the elongated segment, the contact protrusion having a longitudinal contact protrusion axis, the longitudinal contact protrusion axis and the second finger axis being angled relative to one another.

13. A third rod; a third set of fingers extending radially inward from the third vertical rod along a third finger axis, the third finger axis extending on a third chord of a circle, the third chord intersecting a central longitudinal axis of the wafer boat; Each finger of the third set has an elongated segment extending from the third vertical rod; 13. The wafer boat of claim 12, further comprising: a contact protrusion disposed on the elongated segment toward a distal end of the finger for contacting and supporting the semiconductor wafer, at least a portion of the contact protrusion being raised relative to the elongated segment, the contact protrusion having a longitudinal contact protrusion axis, the contact protrusion axis and the third finger axis being orthogonal.

14. 14. The wafer boat of claim 13, wherein the distal ends of each finger are spaced approximately 120 degrees apart around the wafer boat.

15. 14. The wafer boat of claim 13, wherein the first set, the second set, and the third set of contact protrusions are spaced 120 degrees apart around the wafer boat.

16. 16. The wafer boat of claim 13, wherein the first set, the second set, and the third set of contact protrusions are arranged in a rotationally symmetrical pattern with respect to each other.

Images