Patent Description:
The field of the disclosure relates to semiconductor wafer boats for supporting semiconductor wafers and, more particularly, semiconductor wafer boats for use in the heat-treatment of semiconductor wafers in a furnace.

Semiconductors wafers are commonly heat-treated at high temperatures (i.e., annealed) to achieve certain desirable characteristics. For example, annealing may be used to create a defect free layer of silicon on the wafer. The high temperature annealing process is typically carried out in a vertical furnace which subjects the wafers to temperatures above <NUM><NUM> (e.g., between about <NUM> and about <NUM>).

A plurality of semiconductor wafers may be supported in the vertical furnace by a wafer boat or "rack". The wafer boat includes one or more supports on which the semiconductor wafer rests. During exposure to the high temperatures, particularly temperatures above <NUM>, the wafers become temporarily more plastic, i.e., the yield strength of the wafers decreases. Contact areas on the wafer where the wafer is supported may undergo slip due to local gravitational and thermal stresses. Slip may introduce contaminants into the wafer. In addition, excessive slip may lead to plastic deformation of the wafers, leading to production problems, such as photolithography overlay failures causing yield losses in device manufacture.

The supports aim to hold the semiconductor wafer while minimizing local gravitational and thermal stresses to prevent slip and plastic deformation while the wafers are being heat-treated. Conventionally, a wafer boat used in a vertical furnace includes three or more rods. The rods have laterally extending fingers lying generally in a common horizontal plane. This configuration is conventional and generally adequate for heating wafers with smaller diameters such as <NUM> or less. Larger diameter wafers (e.g., greater than <NUM>) are subjected to greater local gravitational and thermal stress than smaller diameters wafers. Such larger diameter wafers are conventionally loaded onto support rings which provide a greater surface area for supporting the wafers. The support rings increase the time for loading and unloading of the semiconductor wafers onto the wafer boat.

A need exists for wafer boats that include supporting structures that reduce local gravitational and thermal stress in order to limit the incident of slip while supporting semiconductor wafers as they are subjected to high temperatures during an annealing process and for wafer boats that are capable of relatively high throughput for loading and unloading wafers.

<CIT>, <CIT>, <CIT> and <CIT> disclose wafer boats of the prior art.

This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the disclosure, which are described and/or claimed below.

One aspect of the present disclosure is directed to a wafer boat for supporting a plurality of semiconductor wafers in a furnace, as claimed in claim <NUM>.

Various refinements exist of the features noted in relation to the above-mentioned aspects of the present disclosure. Further features may also be incorporated in the above-mentioned aspects of the present disclosure as well. These refinements and additional features may exist individually or in any combination. For instance, various features discussed below in relation to any of the illustrated embodiments of the present disclosure may be incorporated into any of the above-described aspects of the present disclosure, alone or in any combination.

An example wafer boat for supporting a plurality of semiconductor wafers in a vertical furnace is indicated generally at "<NUM>" in <FIG>. The wafer boat <NUM> supports the plurality of semiconductor wafers during a high temperature heat-treatment process (also referred to herein as an "anneal"). The wafer boat <NUM> includes at least one vertical rod <NUM> (and typically three or more rods) that is coupled to a top <NUM> and a base <NUM> of the wafer boat <NUM>. The wafer boat <NUM> includes a longitudinal central axis Y<NUM> which extends from the top <NUM> to the base <NUM>. The vertical rod <NUM> is arranged a distance D<NUM> from the longitudinal central axis Y<NUM> (<FIG>).

With reference to <FIG>, the illustrated wafer boat <NUM> includes three vertical rods <NUM> and, in particular, a central rod <NUM> and two forward rods <NUM>. Each of the vertical rods <NUM> is arranged on a first circle C<NUM> (<FIG>) centered about the longitudinal central axis Y<NUM> and having a radius R<NUM>. The two forward rods <NUM> are spaced apart about the longitudinal central axis Y<NUM> by a first angle α<NUM>. The central rod <NUM> is spaced an equal circumferential distance between the two forward rods <NUM>, such that the central rod <NUM> is spaced about the longitudinal central axis Y<NUM> at a second angle α<NUM> relative to each of the two forward rods <NUM>. The two forward rods <NUM> are spaced apart by the first angle α<NUM> such that an entrance <NUM> (<FIG>) is defined between the two forward rods <NUM>. The first angle α<NUM> may be any suitable angle such that the entrance <NUM> is sized to allow a semiconductor wafer to pass through the entrance <NUM> and arranged within an interior space <NUM> of the wafer boat <NUM>. For example, the first angle α<NUM> may be <NUM>° or more and the second angle α<NUM> may be <NUM>° or less.

The wafer boat <NUM> includes fingers <NUM> that extend radially inward from the vertical rods <NUM> for supporting semiconductor wafers (i.e., the boat does not include support rings for supporting wafers). The two forward vertical rods <NUM> include a first and a second set <NUM>, <NUM> of fingers <NUM>, respectively. The central vertical rod <NUM> includes a third set <NUM> of the fingers <NUM>. The first set <NUM> of fingers <NUM> extend along a first finger axis A<NUM>, the second set <NUM> of fingers <NUM> extend along a second finger axis A<NUM>, and the third set <NUM> of fingers extends along a third finger axis A<NUM>. Each finger axis A<NUM>, A<NUM>, A<NUM> extends from a proximal end <NUM> of the finger <NUM> to a distal end <NUM> of the finger <NUM>. The proximal end <NUM> of the finger <NUM> is proximate to the vertical rods <NUM> and the distal end <NUM> of the finger <NUM> is disposed in the interior space <NUM> of the wafer boat <NUM>. The fingers <NUM> may be formed integrally with the vertical rods <NUM>, e.g., cuts may be made in an elongate one-piece structure to form the fingers <NUM>. Alternatively, the fingers <NUM> may be formed separately and coupled to the vertical rods <NUM>.

The finger axes A<NUM>, A<NUM> of the first and second sets <NUM>, <NUM> of fingers <NUM>, each extends over a chord X<NUM>, X<NUM> of the first circle C<NUM>. The chords X<NUM>, X<NUM> do not intersect the longitudinal central axis Y<NUM> of the wafer boat <NUM> (i.e., the first and second sets <NUM>, <NUM> of fingers are not centered such that they point to the longitudinal central axis Y<NUM>). The finger axis A<NUM> of the third set <NUM> of fingers <NUM> extends over a chord X<NUM> of the first circle C<NUM> that intersects the longitudinal central axis Y<NUM>.

A group <NUM> of fingers <NUM> that extend from each of the vertical rods <NUM> lies in the same, generally horizontal, plane to enable the group <NUM> of fingers <NUM> to support a semiconductor wafer. The distal ends <NUM> of the fingers <NUM> in the group <NUM> lie on a second circle C<NUM>. The second circle C<NUM> has a radius R<NUM> and is centered on the longitudinal central axis Y<NUM>. The radius R<NUM> extends from the distal ends <NUM> of the fingers <NUM> to the longitudinal central axis Y<NUM> of the wafer boat <NUM>. In the illustrated embodiment, each of the distal ends <NUM> of the fingers <NUM> in the group <NUM> is arranged at an equal circumferential distance from each of the other distal ends <NUM> of the other fingers <NUM> in the group <NUM>. For example, in the illustrated embodiment including the first, second, and third sets <NUM>, <NUM>, <NUM> of fingers <NUM>, the distal ends <NUM> of each of the first, second, and third sets <NUM>, <NUM>, and <NUM> of fingers <NUM> are each spaced apart by an angle β<NUM> defined on the second circle C<NUM> centered on the longitudinal central axis Y<NUM>. In the illustrated embodiment, the angle β<NUM> is <NUM>°.

With reference to <FIG> and <FIG>, each of the fingers <NUM> includes an elongated segment <NUM> that extends from the vertical rod <NUM> and a contact protuberance <NUM> disposed on the elongated segment <NUM> towards the distal end <NUM> of the finger <NUM>. The contact protuberance <NUM> contacts and supports a semiconductor wafer. The contact protuberance <NUM> is raised with respect to the elongated segment <NUM>. The contact protuberance <NUM> has a first end <NUM>, a second end <NUM>, and a longitudinal contact protuberance axis A<NUM> that extends through the first and second ends <NUM>, <NUM> of the contact protuberance <NUM>. The contact protuberances <NUM> may be used to support any diameter of wafer including <NUM> diameter wafers, <NUM> diameter wafers and/or wafer that are greater than <NUM> in diameter.

For the first and second sets <NUM>, <NUM> of fingers <NUM>, the longitudinal contact protuberance axis A<NUM> and the respective finger axis A<NUM>, A<NUM> are angled relative to each other at an angle λ<NUM>, when viewed from above (<FIG>). The angle λ<NUM> between the longitudinal contact protuberance axis A<NUM> and the respective finger axis A<NUM>, A<NUM> is at an angle from <NUM>° to about <NUM>°; in other embodiments, it is at least <NUM>°, at least <NUM>° or at least <NUM>°. For the third set of fingers <NUM>, the longitudinal contact protuberance axis A<NUM> and the finger axis A<NUM> are angled relative to each other at an angle λ<NUM>, when viewed from above (<FIG>). The angle λ<NUM> is <NUM>° such that the longitudinal contact protuberance axis A<NUM> and the finger axis A<NUM> are perpendicular to each other. Each longitudinal contact protuberance axis A<NUM> is tangent to a third circle C<NUM> centered about the longitudinal central axis Y<NUM> of the wafer boat <NUM>, at a location where the contact protuberance <NUM> intersects the third circle C<NUM>. In this arrangement, the contact protuberance <NUM> are arranged in a rotationally symmetric pattern about the longitudinal central axis Y<NUM> (i.e., the contact protuberances are similarly spaced and angled about the central axis Y<NUM>).

The illustrated contact protuberances <NUM> are rounded (e.g., each increases in height from its sides to an apex midway between the sides). The rounded contact protuberance <NUM> includes a surface that is generally cylindrical in shape. Each contact protuberance <NUM> includes a length L<NUM> (<FIG>) extending along the longitudinal contact protuberance axis A<NUM> and a width W<NUM> perpendicular to the length L<NUM>. The wafer rests on the rounded contact protuberance <NUM> generally along the longitudinal contact protuberance axis A<NUM>.

In some embodiments, the contact protuberance <NUM> has a width W<NUM> of <NUM> to <NUM> and a length L<NUM> of <NUM> to <NUM>. Alternatively or in addition, the distance from the contact protuberance <NUM> to the longitudinal central axis Y<NUM> may be <NUM> to <NUM>. In some embodiments, the contact protuberance <NUM> has a width W<NUM> of <NUM>, a length L<NUM> of <NUM>, and the distance from the contact protuberance <NUM> to the longitudinal central axis Y<NUM> is <NUM>.

In some embodiments such as the embodiment shown in <FIG>, the contact protuberance <NUM> is flat. The components shown in <FIG> that are analogous to those of <FIG> are designated by the corresponding reference number of <FIG> plus "<NUM>" (e.g., part <NUM> becomes <NUM>). The flat contact protuberance <NUM> includes a contact surface <NUM> defined by the longitudinal contact protuberance axis A<NUM> and includes a surface area that is defined by the length L<NUM> extending along the longitudinal contact protuberance axis A<NUM> and the width W<NUM>, perpendicular to the length L<NUM>. The surface <NUM>, in its entirety, is generally in contact with the semiconductor wafer resting on the flat contact protuberance <NUM>.

Alternatively, the protuberance <NUM> may be generally dome shaped with the semiconductor wafer resting on a relatively small, point-like, area.

Another embodiment of the contact protuberance <NUM> is shown in <FIG> and <FIG>. The components shown in <FIG> that are analogous to those of <FIG> are designated by the corresponding reference number of <FIG> plus "<NUM>" (e.g., part <NUM> becomes part <NUM>). The finger <NUM> includes a first contact protuberance 252a that is raised with respect to the elongated segment <NUM>. The first contact protuberance 252a has a first longitudinal contact protuberance axis A252a. The finger <NUM> also includes a second contact protuberance 252b disposed toward a distal end <NUM> of the finger <NUM>. At least a portion of the second contact protuberance 252b is raised with respect to the elongated segment <NUM>. Each of the first and second contact protuberances 252a, 252b contacts and supports a semiconductor wafer. The second contact protuberance 252b includes a first end <NUM>, a second end <NUM>, and a second longitudinal contact protuberance axis A252b extending therebetween. In the illustrated embodiment, the first longitudinal contact protuberance axis A252a and the second longitudinal contact protuberance axis A252b are general parallel to each other.

For the first and second sets <NUM>, <NUM> of fingers <NUM>, the first and second protuberances axes A252a, A252b are angled relative to the finger axis A<NUM> at an angle λ<NUM>. For the third set <NUM> of fingers <NUM>, the first and second protuberances axes A252a, A252b are generally parallel to the finger axis A<NUM>. The first and second contact protuberances 252a, 252b may be arranged at any angle λ<NUM> relative to the finger axis A<NUM> such that the contact protuberances 252a, 252b are arranged in a rotationally symmetric pattern about the longitudinal central axis Y<NUM>.

The first and second contact protuberances 252a, 252b have an elongated shape having a length of L<NUM> which extends along the first and second protuberances axes A252a, A252b. The first and second contact protuberances 252a, 252b may be separated by a distance W<NUM>. In some embodiments, W<NUM> is from <NUM> to <NUM>, <NUM> to <NUM> or, as in other embodiments, is <NUM>. The first and second contact protuberances 252a, 252b may have a variety of shapes such as a cylindrical cross-section, a rectangular cross-section (i.e., flat contact) or a trapezoidal cross-section (e.g., flattened top section).

Each group <NUM> of contact protuberances 252a, 252b that lies in a common horizontal plane is in contact with and supports a wafer. The wafer rests on top of each of the contact protuberances 252a, 252b such that the weight of the wafer is generally distributed evenly onto each of the contact protuberances <NUM>. In the illustrated embodiment, each of the six contact protuberances 252a, 252b in the group <NUM> supports <NUM>/<NUM> of the weight of the wafer.

Another embodiment of the contact protuberance <NUM> is shown in <FIG>. The components shown in <FIG> that are analogous to those of <FIG> are designated by the corresponding reference number of <FIG> plus "<NUM>" (e.g., part <NUM> becomes part <NUM>). In reference to <FIG>, each of the fingers <NUM> includes an elongated segment <NUM> that extends from a vertical rod <NUM>. The fingers <NUM> include a platform <NUM> that supports a first and second contact protuberance 352a, 352b. The platform <NUM> is coupled to the elongated segment <NUM> by a pin <NUM> which is pivotally connected to the elongated segment <NUM> by a cylindrical joint or a gimbal <NUM>. Accordingly, the pin <NUM> and gimbal <NUM> allow the platform <NUM> to pivot relative to the elongated segment <NUM>. The platform <NUM> supports the first and the second contact protuberances 352a, 352b each of which contacts and supports a semiconductor wafer.

The pivoting of the platform <NUM> enabled by the pin <NUM> and gimbal <NUM>, counter acts uneven load distribution caused by machining inaccuracies and allows the platform <NUM> to pivot in response to the uneven loading on the contact protuberances 352a, 352b. The platform <NUM> may pivot to more evenly distribute the wafer weight on each of the contact protuberance 352a, 352b. After the wafer boat <NUM> is placed in the vertical furnace and exposed to oxidization, the pin <NUM> and the gimbal <NUM> will become fixed, preventing further pivoting of the platform <NUM>, for the duration of the annealing process.

The wafer boats of the present disclosure have several advantages compared to conventional wafer boats. In embodiments wherein the wafer boat includes one or more contact protuberances arranged in a rotationally symmetric pattern, the local gravitational and thermal stress in semiconductor wafers loaded onto the wafer boat are reduced during annealing which reduced slip. In embodiments wherein the wafer boat includes a pin and gimbal which supports a platform having two or more contact protuberances, the platform may pivot to adjust for uneven loading of the contact protuberances caused by machining inaccuracies.

The processes of the present disclosure are further illustrated by the following Examples. These Examples should not be viewed in a limiting sense.

Peak stress in wafers was measured for different boat designs having different finger arrangements using a finite element model. One wafer boat included fingers having flat contact protuberances with the contact protuberances of the fingers extending from the forward rods not being angled with respect to the finger axis (i.e., the contact protuberance axis and finger axis were parallel causing the contact protuberances to not be rotationally symmetric). A second wafer boat was similar to the first but the contact protuberances were cylindrical. A third wafer boat included cylindrical contacts arranged as shown in <FIG> (i.e., the fingers extending from the two forward rods having contact protuberances angled with respect to the finger axis and the fingers extending from the central rod being perpendicular to the central axis such that the contact protuberances were rotationally symmetric). A fourth boat included two contact protuberances on each finger that were rotationally symmetric as shown in <FIG>. The peak stresses for each boat are shown in Table <NUM> below:.

As shown in Table <NUM>, the wafer boats in which the contact protuberances were rotationally symmetric (Boats <NUM> and <NUM>) had reduced peak stresses which reduced slip in semiconductor wafers annealed in the wafer boats.

As used herein, the terms "about," "substantially," "essentially" and "approximately" when used in conjunction with ranges of dimensions, concentrations, temperatures or other physical or chemical properties or characteristics is meant to cover variations that may exist in the upper and/or lower limits of the ranges of the properties or characteristics, including, for example, variations resulting from rounding, measurement methodology or other statistical variation.

When introducing elements of the present disclosure or the embodiment(s) thereof, the articles "a," "an," "the," and "said" are intended to mean that there are one or more of the 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 terms indicating a particular orientation (e.g., "top," "bottom," "side," etc.) is for convenience of description and does not require any particular orientation of the item described.

Claim 1:
A wafer boat (<NUM>) for supporting a plurality of semiconductor wafers in a furnace comprising:
a vertical rod (<NUM>);
a set of fingers (<NUM>) that extend radially inward from the vertical rod along a finger axis (A<NUM>), each finger of the set comprising:
an elongated segment (<NUM>) that extends from the vertical rod; and
a contact protuberance (<NUM>) disposed on the elongated segment toward a distal end of the finger for contacting and supporting a semiconductor wafer, at least a portion of the contact protuberance being raised with respect to the elongated segment, the contact protuberance having a longitudinal contact protuberance axis (A<NUM>), the longitudinal contact protuberance axis and the finger axis being angled relative to each other at an angle (λ<NUM>) from <NUM>° to about <NUM>°, wherein the longitudinal contact protuberance axis is tangent to a circle (C<NUM>) centered about a longitudinal central axis of the wafer boat, at a location where the contact protuberance intersects the circle.