SYSTEM AND METHODS FOR A RADIANT HEAT CAP IN A SEMICONDUCTOR WAFER REACTOR

A reaction apparatus contacts a process gas on a semiconductor wafer during a wafering process. The semiconductor wafer defines a center region. The reaction apparatus includes an upper dome, a lower dome, a shaft, and a cap. The lower dome is attached to the upper dome, and the upper dome and the lower dome define a reaction chamber. The cap is positioned on the shaft within the reaction chamber for reducing heat absorbed by the center region of the semiconductor wafer. The cap is attached to a first end of the shaft. The cap includes a tube and a disc. The tube defines a tube diameter larger than a shaft diameter of the shaft. The tube circumscribes the first end of the shaft. The disc is attached to the tube and is positioned to block radiant heat from heating the center region of the semiconductor wafer.

FIELD

The field relates generally to apparatus and methods for wafer processing, and more particularly to apparatus and methods for semiconductor wafer etching or semiconductor wafer chemical vapor deposition processes.

BACKGROUND

Epitaxial chemical vapor deposition (CVD) is a process for growing a thin layer of material on a semiconductor wafer so that the lattice structure is identical to that of the wafer. Epitaxial CVD is widely used in semiconductor wafer production to build up epitaxial layers such that devices can be fabricated directly on the epitaxial layer. The epitaxial deposition process begins by introducing a cleaning gas, such as hydrogen or a hydrogen and hydrogen chloride mixture, to a front surface of the wafer (i.e., a surface facing away from the susceptor) to pre-heat and clean the front surface of the wafer. The cleaning gas removes native oxide from the front surface, permitting the epitaxial silicon layer to grow continuously and evenly on the surface during a subsequent step of the deposition process. The epitaxial deposition process continues by introducing a vaporous silicon source gas, such as silane or a chlorinated silane, to the front surface of the wafer to deposit and grow an epitaxial layer of silicon on the front surface. A back surface opposite the front surface of the susceptor may be simultaneously subjected to hydrogen gas. The susceptor, which supports the semiconductor wafer in the deposition chamber during the epitaxial deposition, is rotated during the process to allow the epitaxial layer to grow evenly.

However, epitaxial CVD growth rates are generally not uniform across the surface of each wafer because of a non-uniform temperature profile of the semiconductor wafer. A lack of uniformity causes degradation in the flatness of the wafer and may be a result of variability or local temperature deviations within the semiconductor wafer caused by non-uniform heating of the semiconductor wafer by high intensity lamps. Accordingly, there exists a need for a practical, cost-effective apparatus to improve local temperature deviations to improve uniformity of epitaxial CVD growth rates.

SUMMARY

In one aspect, a reaction apparatus for contacting a process gas on a semiconductor wafer during a wafering process is provided. The semiconductor wafer defines a center region. The reaction apparatus includes an upper dome, a lower dome, a shaft, and a cap. The lower dome is attached to the upper dome, and the upper dome and the lower dome define a reaction chamber. The shaft supports the semiconductor wafer within the reaction chamber. The cap is positioned on the shaft within the reaction chamber for reducing heat absorbed by the center region of the semiconductor wafer. The cap is attached to a first end of the shaft. The cap includes a tube and a disc. The tube defines a tube diameter larger than a shaft diameter of the shaft. The tube circumscribes the first end of the shaft. The disc is attached to the tube and is positioned to block radiant heat from heating the center region of the semiconductor wafer.

In another aspect, a cap positioned on a shaft of a reaction apparatus for reducing heat absorbed by a center region of a semiconductor wafer during a wafering process is provided. The cap includes a tube and a disc. The tube defines a tube diameter larger than a shaft diameter of the shaft. The tube circumscribes a first end of the shaft. The disc is attached to the tube and blocks radiant heat from heating the center region of the semiconductor wafer.

In yet another aspect, a method of manufacturing a semiconductor wafer in a reaction apparatus is provided. The reaction apparatus includes an upper dome and a lower dome defining a reaction chamber and a shaft for supporting the semiconductor wafer. The reaction apparatus further includes a cap positioned on the shaft within the reaction chamber for reducing heat absorbed by a center region of the semiconductor wafer. The cap includes a tube and a disc attached to the tube. The method includes channeling a process gas into the reaction chamber. The method also includes heating the semiconductor wafer with a high intensity lamp positioned within the reaction chamber. The method further includes blocking radiant heat from the high intensity lamp from heating the center region of the semiconductor wafer with the disc. The disc generates a uniform temperature distribution on the semiconductor wafer. The method also includes depositing a layer on the semiconductor wafer with the process gas. The uniform temperature distribution forms a uniform thickness of the layer on the semiconductor wafer.

DETAILED DESCRIPTION

Referring now toFIG. 1, an apparatus for etching a semiconductor wafer or for depositing an epitaxial layer on a semiconductor substrate in accordance with an embodiment of the present disclosure is generally referred to as100. The illustrated apparatus is a single wafer reactor; however, the apparatus and methods disclosed herein for providing a more uniform epitaxial layer are suitable for use in other reactor designs including, for example, multiple wafer reactors. The apparatus100includes a reaction chamber102comprising an upper dome104, a lower dome106, an upper liner108, and a lower liner110. Collectively, the upper dome104, lower dome106, upper liner108, and lower liner110define an interior space112of the reaction chamber102in which process gas contacts a semiconductor wafer114. A gas manifold116is used to direct process gas into the reaction chamber102. A perspective view of the reaction chamber102and gas manifold116is shown inFIG. 2.

The apparatus100may be used to process a wafer in a wafering process, including without limitation, depositing any type of material on a wafer performed by a chemical vapor deposition (CVD) process, such as epitaxial CVD or polycrystalline CVD. In this regard, reference herein to epitaxy and/or CVD processes should not be considered limiting as the apparatus100may also be used for other purposes such as to perform etching or smoothing processes on the wafer. Also, the wafer shown herein is generally circular in shape, though wafers of other shapes are contemplated within the scope of this disclosure.

A cross section of the apparatus100is shown inFIG. 3. Within the interior space112of the reaction chamber102is a preheat ring118for heating the process gas prior to contact with a semiconductor wafer114. The outside circumference of the preheat ring118is attached to the inner circumference of the lower liner110. For example, the preheat ring118may be supported by an annular ledge (not shown) of the lower liner110. A susceptor120(which may also be referred to herein as a “susceptor body”) traversing the space interior to the preheat ring118supports the semiconductor wafer114.

Process gas may be heated prior to contacting the semiconductor wafer114. Both the preheat ring118and the susceptor120are generally opaque to absorb radiant heating light produced by high intensity lamps122,124that may be located above and below the reaction chamber102for heating the semiconductor wafer114. Maintaining the preheat ring118and the susceptor120at a temperature above ambient allows the preheat ring118and the susceptor120to transfer heat to the process gas as the process gas passes over the preheat ring and the susceptor. Typically, the diameter of the semiconductor wafer114is less than the diameter of the susceptor120to allow the susceptor to heat the process gas before it contacts the wafer.

The preheat ring118and susceptor120may suitably be constructed of opaque graphite coated with silicon carbide, though other materials are contemplated. The upper dome104and lower dome106are typically made of a transparent material to allow radiant heating light to pass into the reaction chamber102and onto the preheat ring118and the susceptor120. The upper dome104and lower dome106may be constructed of transparent quartz. Quartz is generally transparent to infrared and visible light and is chemically stable under the reaction conditions of the deposition reaction. Equipment other than high intensity lamps122,124may be used to provide heat to the reaction chamber such as, for example, resistance heaters and inductive heaters. An infrared temperature sensor (not shown) such as a pyrometer may be mounted on the reaction chamber102to monitor the temperature of the susceptor120, preheat ring118, or semiconductor wafer114by receiving infrared radiation emitted by the susceptor, preheat ring, or wafer.

Referring now toFIGS. 3-5, wherein some components of the apparatus100are removed to better illustrate the apparatus, the apparatus100includes a shaft126that may support the susceptor120. The shaft126extends through a central column128. The shaft126includes a first end130attached to the central column128and a second end132positioned proximate a center region134of the semiconductor wafer114. The shaft126has a shaft diameter136of about 5 millimeters (mm) to about 20 mm.

The shaft126is connected to a suitable rotation mechanism (not shown) for rotation of the shaft126, susceptor120, and semiconductor wafer114about a longitudinal axis X with respect to the apparatus100. The outside edge of the susceptor120and inside edge of the preheat ring118(shown inFIG. 3) are separated by a gap138to allow rotation of the susceptor. The semiconductor wafer114is rotated to prevent an excess of material from being deposited on the wafer leading edge and provide a more uniform epitaxial layer.

The apparatus100also includes a cap140positioned on the shaft126within the reaction chamber102for reducing heat absorbed by the center region134of the semiconductor wafer114. The cap140is attached to the first end130of the shaft126proximate the center region134of the semiconductor wafer114to block radiant heat from the lower high intensity lamp124from heating the center region of the semiconductor wafer. Reducing radiant heat to the center region134of the semiconductor wafer114reduces a temperature of the center region while maintaining a temperature of outer radial regions142of the semiconductor wafer114, generating a uniform temperature profile of the semiconductor wafer.

The cap140includes a tube144and a disc146attached to the tube. In the illustrated embodiment, the tube144and the disc146are integrally formed together such that the cap140has a unitary construction. In alternative embodiments, the tube144and the disc146may be formed separately and attached to each other. The tube144includes a cylindrical wall148having a first end150, a second end152, and a tube length154and defining a tube conduit156and a tube diameter158. The first end150defines a first end opening160, and the second end152defines a second end opening162. The tube diameter158is larger than the shaft diameter136such that the first end130of the shaft126is inserted into the first end opening160and the first end150circumscribes the first end of the shaft. The second end152is attached to the disc146.

The disc146includes an annular disc164defining a disc hole166, an inner diameter168, an outer diameter170, and a disc thickness172. The tube diameter158and the inner diameter168are the same, or substantially equal, such that the cylindrical wall148is substantially flush with the disc hole166and the tube conduit156and the disc hole define a cap conduit174extending through the cap140. In alternative embodiments, the tube diameter158is larger than the inner diameter168, and the tube conduit156and the disc hole166define the cap conduit174.

The annular disc164has a first side176and a second side178, and the first side of the annular disc is attached to the second end152of the tube144. The first side176of the annular disc164is oriented toward the lower high intensity lamp124, and the second side178is oriented toward the center region134of the semiconductor wafer114. The annular disc164may be attached to the tube144in any suitable manner. Additionally, the annular disc164may have other shapes, one or more recesses formed therein, and/or several openings formed therein.

The outer diameter170is larger than the tube diameter158and the inner diameter168such that the annular disc164blocks radiant heat from the lower high intensity lamp124from heating the center region of the semiconductor wafer. The annular disc164extends from the disc hole166and the cylindrical wall148such that the annular disc extends a blocking distance180from the cylindrical wall and the disc hole. The blocking distance180is configured to block a predetermined amount of radiant heat to generate the uniform temperature profile of the semiconductor wafer114.

The cap140is suitably made of an opaque material to block visible and infrared light from being transmitted to the center region134of the semiconductor wafer114. In other embodiments, rather than being opaque, the cap140may be made of a translucent material to provide local cooling to the semiconductor wafer114and decrease any local or global maximum epitaxial layer thickness, generating a uniform thickness profile of the epitaxial layer and/or the semiconductor wafer114.

Generally, the cap140corrects and/or affects the radial temperature profile of the semiconductor wafer114during processing, such as epitaxial deposition to alleviate non-uniformities. The cap140may cause the temperature of the center region134of the semiconductor wafer114above the cap to decrease (relative to when a cap is not used) thereby decreasing the amount of material (e.g., silicon) that deposits in the center region of the semiconductor wafer during epitaxial CVD processes. Accordingly, the cap140is suitably positioned a distance below the center region134of the semiconductor wafer114in which a localized or global maximum layer thickness occurs to decrease the deposition at the central region and create a more uniform radial deposition profile. Note that this maximum layer thickness may be a local or global maximum, and may generally be referred to as a non-uniformity.

The thickness profile may be determined by use of any suitable method available to those of skill in the art including, for example, use of a Fourier-Transform Infrared (FTIR) spectrometer or use of a wafer flatness tool (e.g., KLA-Tencor Wafersight or WaferSight2; Milpitas, Calif.). In some embodiments, the radial thickness profile of the substrate is determined before material deposition (e.g., before deposition of an epitaxial layer) and the thickness profile of the layered structure may then be measured. The thickness profile of the deposited layer may be determined by subtracting the substrate thickness from the layered structure thickness.

Specifically, in the illustrated embodiment, the tube length154is about 10 mm to about 30 mm; the tube diameter158is about 5 mm to about 20 mm; the inner diameter168is about 5 mm to about 20 mm; the outer diameter170is about 10 mm to about 40 mm; the disc thickness172is about 3 mm to about 10 mm; and the blocking distance180is about 5 mm to about 35 mm. In alternative embodiments, the shaft diameter136, the tube length154, the tube diameter158, the inner diameter168, the outer diameter170, the disc thickness172, and the blocking distance180may be any distance that enables the cap140to operate as described herein. More specifically, the shaft diameter136, the tube length154, the tube diameter158, the inner diameter168, the outer diameter170, the disc thickness172, and the blocking distance180are suitably chosen depending on a location and size of a local or global epitaxial layer thickness minimum or maximum.

A distance182between the cap140and the susceptor120that is less than about 40 mm, less than about 20 mm, or even less than about 1 mm. Decreasing the distance182between the cap140and the susceptor120generally results in deposition of more material on the wafer in portions of the wafer above the ring and increasing the distance generally results in less deposition. Therefore, the amount of material deposited on portions of the wafer above the cap140may be adjusted by varying this distance.

The ranges recited above for the shaft diameter136, the tube length154, the tube diameter158, the inner diameter168, the outer diameter170, the disc thickness172, the blocking distance180, the distance182, and the like are exemplary and values outside of the stated ranges may be used without limitation. As shown inFIG. 8, the disc146has a substantially uniform circular shape. In other embodiments, the disc146may be shaped to include various projections and/or notches or recesses. The disc146may also be beveled or rounded. Such non-uniform shapes may enable the disc146to block radiant heat from the lower high intensity lamp124from heating regions out the center region134of the semiconductor wafer114. For example, analysis of the temperature profile of the semiconductor wafer114may identify regions outside of the center region134that have elevated temperatures such that the deposition of material in those areas is non-uniform. The shape of the disc146may be adjusted to block radiant heat from the lower high intensity lamp124from heating those regions to decrease material deposition within those regions.

FIG. 11is a flow diagram of a method200of manufacturing a semiconductor wafer in a reaction apparatus. The method200includes channeling202a process gas into the reaction chamber. The method200also includes heating204the semiconductor wafer with a high intensity lamp positioned within the reaction chamber. The method200further includes blocking206radiant heat from the high intensity lamp from heating the center region of the semiconductor wafer with the disc. The disc generates a uniform temperature distribution on the semiconductor wafer. The method200also includes depositing208a layer on the semiconductor wafer with the process gas. The uniform temperature distribution forms a uniform thickness of the layer on the semiconductor wafer.

EXAMPLES

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

Example 1: Determining the Effect of Using a Cap on the Radial Temperature Profile of the Semiconductor Wafer

An opaque cap as described herein was tested in a single wafer epitaxy reactor to determine their effect on the epitaxial wafer temperature profile. The epitaxial wafers were prepared by exposing single crystal silicon wafer produced by the Czochralski method to a process gas at a wafer temperature between 1050° C. to 1150° C. The disc of the cap had an outer diameter of 10 mm.

A control run was performed in which a cap was not used.FIG. 12is a graph300of epitaxial wafer radial temperature as a function of wafer radial distance. As can be seen fromFIG. 12, the control resulted in a non-uniform epitaxial wafer radial temperature profile302, and the cap resulted in a uniform epitaxial wafer radial temperature profile304. The uniform epitaxial wafer radial temperature profile304is more uniform because the local temperature maximums at the ends of the profile are less than the local temperature maximums at the ends of the non-uniform epitaxial wafer radial temperature profile302. Accordingly, the cap generated a uniform temperature profile of the epitaxial wafer.

Compared to conventional methods for producing silicon wafers, the systems and methods of the present disclosure have several advantages. For example, reactors that include caps as described facilitate cost-effective manufacture of semiconductor wafers with a uniform temperature profile during deposition. The uniform temperature profile generates a more uniform deposition thickness profile. Thus, the caps enable production of a semiconductor wafer with a uniform thickness profile. An example cap has a disc in or around a center region of the wafer and blocks radiant heat from heating the center region of the wafer. The temperature of the center region is thereby reduced, generating a uniform temperature profile and a uniform thickness profile. Accordingly, the example caps eliminate or reduce local temperature deviations, as compared to the prior art, to improve the uniformity of epitaxial CVD growth on a wafer. Additionally, use of the above examples can improve the production rate of the epitaxial CVD system, and can lower operational costs by reducing waste.