Wafer boat for supporting semiconductor wafers in a furnace

Abstract

A wafer boat for supporting a plurality of semiconductor wafers in a furnace, the wafer boat including a set of fingers each having contact protrusions for contacting and supporting the semiconductor wafers.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Patent Application No. 63 / 044,698, filed June 26, 2020, which is incorporated herein 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 wafers to temperatures above 1100°C (e.g., between about 1200°C and about 1300°C).

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

[0005] The supports are intended to hold semiconductor wafers while minimizing localized gravitational and thermal stresses to prevent slippage and plastic deformation during thermal processing. Traditionally, wafer boats used in vertical furnaces have 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 those 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. These larger diameter wafers are typically mounted on support rings, which provide a larger surface area for supporting the wafers. Support rings increase the time required to load and unload 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 slippage, 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. Accordingly, 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 present 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. 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 wafers. At least a portion of the contact protrusions are raised relative to the elongated segment.

[0009] Various refinements of the features mentioned in connection with the above-described aspects of the present disclosure exist. Additional features may also be incorporated into the above-described aspects of the present disclosure. These refinements and additional features may exist individually or in any combination. For example, the various features discussed below in connection with any of the illustrated embodiments of the present disclosure may be incorporated into any of the above-described aspects of the present disclosure, either alone or in any combination. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. [Figure 2] FIG. 10 is a plan view of the wafer boat showing the contact protrusions. [Figure 3] FIG. 3 is a detailed view of the contact protrusion shown in FIG. 2. [Figure 4] 10 is a detailed view of another embodiment of a contact protrusion. FIG. [Figure 5] 10 is a probability plot of slip length versus first and second lengths of the contact protrusion.

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

[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 treatment process (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] 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 by a first angle α1 about the longitudinal center axis Y 10 The two front rods 20 are spaced an equal circumferential distance apart such that they are spaced a second angle α2 about the front rod 20. The two front rods 20 are spaced a first angle α1 such that an inlet 24 ( FIG. 1 ) is defined between the two front rods 20. The first angle α1 can be any suitable angle such that the inlet 24 is sized such that semiconductor wafers can 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 180° or greater, and the second angle α2 is 90° or less.

[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 36 , A 38 , A 40 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 to 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, by cutting an elongated unitary structure 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 upward. 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 parallel to 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, substantially 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 groups 42 lie on a second circle C2. The second circle C2 has a radius R2 and a central longitudinal axis Y 10 The radius R2 is measured from the distal end 34 of the finger 30 to the longitudinal center axis Y of the wafer boat 10. 10In 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 the central longitudinal axis Y 10 The first and second electrodes are spaced apart by an angle β defined on a second circle C2 centered at . In the illustrated embodiment, the angle β is 120°.

[0017] 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 the semiconductor wafer. The contact protrusion 52 is raised 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 extending 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] The illustrated contact protrusions 52 are rounded (e.g., extending from each side to the axis A 36 (These contact protrusions increase in height to a vertex extending along a longitudinal contact protrusion axis A.) The rounded contact protrusions 52 include a surface that is generally cylindrical in shape. Each contact protrusion 52 extends along a longitudinal contact protrusion axis A. 52 and a width W1 perpendicular to the length L1. 52 The contact rests on a rounded contact protrusion 52 that extends approximately along the length of the contact.

[0019] In some embodiments, the contact protrusions 52 have a width W1 of 3 mm to 20 mm and a length L1 of 10 mm to 50 mm, and the distance from the contact protrusions 52 to the longitudinal center axis Y of the wafer boat is 10 In some embodiments, the contact protrusions 52 have a width W1 of 8 mm and a length L1 of 30 mm, and the distance from the contact protrusions 52 to the longitudinal center axis Y of the wafer boat 10 is 75 mm to 125 mm. 10 The distance to the

[0020] In some embodiments, such as the embodiment shown in Figure 4, 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 numerals in Figures 1-3 with "100" added (e.g., part 52 becomes part 152). Flat contact protrusion 152 is aligned along the longitudinal contact protrusion axis A. 152 and a width W1 perpendicular to length L2. The contact surface generally is in substantial contact with a semiconductor wafer resting on the planar contact protrusion 152.

[0021] In some embodiments, the contact protrusions 152 have a width W1 of 3 mm to 20 mm and a length L1 of 10 mm to 50 mm, and the distance from the contact protrusions 152 to the longitudinal center axis Y of the wafer boat 10 is 10 Alternatively or additionally, the contact protrusion 152 has a width W1 of 8 mm and a length L1 of 25 mm, and the distance from the contact protrusion 152 to the longitudinal center axis Y of the wafer boat is 75 mm to 125 mm. 110 The distance to the wafer is 100 mm. The wafer rests on the flat contact bumps 152 so that the wafer is in contact with the entire surface area.

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

[0023] The wafer boat of the present disclosure has several advantages over conventional wafer boats. The contact protrusions reduce the contact area between the wafer boat and the wafer, reducing slippage. The equally spaced circumferential contact protrusions promote uniform distribution of the wafer weight to each contact protrusion. As known to those skilled in the art, peak stresses in wafers are sensitive to machining inaccuracies in the contact protrusions that can cause uneven loading. In embodiments in which the contact protrusions are rounded, the dimensions and shape of the rounded contact protrusions minimize the effect of potential machining inaccuracies and limit uneven loading of the wafer weight.

[0024] example The processes of the present disclosure are further illustrated by the following examples, which should not be construed in a limiting sense.

[0025] Example 1: Probability plot of slip length One set of silicon wafers was annealed using a wafer boat containing 10 mm long round contact protrusions, and another set was annealed in a wafer boat containing 20 mm long round contact protrusions. The probability slip length at a 95% confidence interval was determined for wafer boats with cylindrical contact protrusions with contact protrusion lengths of 10 mm and 20 mm, respectively (Figure 5). As shown in Figure 5, the 20 mm long contact protrusions exhibited a reduced slip length compared to the 10 mm long contact protrusions.

[0026] As used herein, the terms "about," "substantially," "essentially," and "approximately," when used in conjunction with a range of dimensions, concentrations, temperatures, or other physical or chemical properties or characteristics, 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 methods, or other statistical variations.

[0027] 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. The use of specific directional terms (such as "top," "bottom," and "side") is for convenience of description and does not require a particular orientation of the items being described.

[0028] Because various changes can 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 first vertical rod; a first set of fingers extending radially inward from the first vertical rod along a first finger axis, the first finger axis extending on a chord of a circle centered about the central longitudinal axis of the wafer boat, the chord not intersecting the central longitudinal axis of the wafer boat; Each finger of the first set of fingers an elongated segment extending from the first vertical rod; contact projections disposed on the elongated segments toward the distal ends of the fingers for contacting and supporting the semiconductor wafer, at least a portion of the contact projections being raised relative to the elongated segments; The wafer boat further comprises: 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 chord of a circle, the chord not intersecting the central longitudinal axis of the wafer boat; Each finger of the second set of fingers an elongated segment extending from the second vertical rod; 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 wafer boat further comprises: a third vertical rod; and 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 chord of a circle, the chord intersecting a central longitudinal axis of the wafer boat; Each finger of the third set of fingers an elongated segment extending from the third vertical rod; 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 protrusions of the first, second, and third sets of fingers are arranged at 120° intervals around the circumference of the wafer boat, each contact protrusion being rounded by increasing in height from a side of the contact protrusion to an apex extending along the finger axis, each contact protrusion having a longitudinal contact protrusion axis, a length extending along the longitudinal contact protrusion axis, and a width perpendicular to the length, the width of each contact protrusion being 3 mm to 20 mm, the length of each contact protrusion being 10 mm to 50 mm, and the distance from the contact protrusion to the longitudinal central axis of the wafer boat being 75 mm to 125 mm; and a wafer boat for placing semiconductor wafers on the rounded contact protrusions along the longitudinal contact protrusion axis.

2. 2. The wafer boat according to claim 1, wherein the contact protrusions have a width of 8 mm and a length of 30 mm, and the distance from the contact protrusions to the longitudinal center axis of the wafer boat is 100 mm.

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