Patent Application
20090101633
1. Field of the Invention
The invention generally relates to semiconductor processing equipment. More particularly, this invention relates to apparatuses for heating semiconductor substrates.
2. Description of the Related Art
In semiconductor processing, a variety of processes—including deposition, etching, and masking—involve heating of substrates. Chemical vapor deposition (CVD), for example, is a very well known process for forming thin films of materials on substrates, such as silicon wafers. In a CVD process, gaseous molecules of the material to be deposited are supplied to wafers to form a thin film of that material on the wafers by chemical reaction. Such formed thin films may be polycrystalline, amorphous or epitaxial. Typically, CVD processes are conducted at elevated temperatures to accelerate the chemical reaction and to produce high quality films. Some processes, such as epitaxial silicon deposition, are conducted at extremely high temperatures (>500° C., <1220° C.).
During a CVD process, one or more substrates are placed on a substrate support inside a reaction chamber defined within the reactor. For example, the substrate can be a wafer and the substrate support can be a susceptor. Both the substrate and often the support are heated to a desired temperature. In a typical wafer treatment step, reactant gases are passed over the heated wafer, causing chemical vapor deposition (CVD) of a thin layer of the desired material on the wafer. If the deposited layer has the same crystallographic structure as the underlying silicon wafer, it is called an epitaxial layer. This is also sometimes called a monocrystalline layer because it has only one crystal structure. Through subsequent processes, these layers are made into integrated circuits, producing from tens to thousands or even millions of integrated devices, depending on the size of the wafer and the complexity of the circuits.
Various process parameters must be carefully controlled to ensure a high quality of layers produced in semiconductor processing. One critical parameter is the temperature of the wafer during each treatment step of wafer processing. During CVD, for example, the wafer temperature dictates the rate of material deposition on the wafer because the deposition gases react at particular temperatures and deposit on the wafer. If the temperature varies across the surface of the wafer, uneven deposition of the film occurs and the physical properties will not be uniform over the wafer. Furthermore, in epitaxial deposition, even slight temperature nonuniformity can result in crystallographic slip.
In accordance with one embodiment, a semiconductor apparatus comprises a substantially circular substrate holder configured to support a semiconductor substrate during semiconductor processing, and a plurality of linear heat lamps. The entire plurality of heat lamps is positioned either above or below the substrate holder. The lamps have a plurality of different lengths, each length being shorter than a diameter of the substrate holder.
In another embodiment, a semiconductor apparatus comprises a substrate holder configured to support a semiconductor substrate during semiconductor processing, and a plurality of linear heat lamps. The plurality of heat lamps is positioned either above or below the substrate holder. Each lamp in the plurality has approximately a first, second, or third length. The second length is between 40% and 60% of the first length, and the third length is between 15% and 35% of the first length.
Another embodiment involves an array of heat lamps for providing radiant heat to a substrate being processed. The array comprises a first set of linear lamps each having approximately a first length, a second set of linear lamps each having approximately a second length that is between 40-60% of the first length, and a third set of linear lamps each having approximately a third length that is between 15-35% of the first length.
A further embodiment includes a method comprising providing a substantially circular substrate holder configured to support a semiconductor substrate during semiconductor processing, providing a plurality of linear heat lamps of a plurality of different lengths, and positioning the entire plurality of lamps either above or below the substrate holder. Each of the lengths is shorter than a diameter of the substrate holder.
In yet another embodiment, a method comprises providing a substrate holder configured to support a semiconductor substrate during semiconductor processing, providing a plurality of linear heat lamps, and positioning the plurality of lamps either above or below the substrate holder. Each lamp has approximately a first, second, or third length, the second length being less than 60% of the first length, and the third length being less than 60% of the second length.
In still another embodiment, a method comprises providing a first set of linear heat lamps each having approximately a first length. A second set of linear heat lamps is provided, each having approximately a second length that is between 40-60% of the first length. A third set of linear heat lamps is provided, each having approximately a third length that is between 15-35% of the first length. The first, second, and third sets of lamps are arranged together in an arrangement to provide radiant heat to a substrate.
For purposes of summarizing the invention and the advantages achieved over the prior art, certain objects and advantages of the invention have been described herein above. Of course, it is to be understood that not necessarily all such objects or advantages may be achieved in accordance with any particular embodiment of the invention. Thus, for example, those skilled in the art will recognize that the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein.
All of these embodiments are intended to be within the scope of the present invention herein disclosed. These and other embodiments of the present invention will become readily apparent to those skilled in the art from the following detailed description of the preferred embodiments having reference to the attached figures, the invention not being limited to any particular preferred embodiment(s) disclosed.
Reactors used in semiconductor processing, including CVD reactors, typically employ radiant heat lamps positioned around a reaction chamber to achieve the desired high temperatures in the substrate. Unfortunately, radiant energy has a tendency to create nonuniform temperature distributions, including “hot spots,” due to the use of localized radiant energy sources and consequent focusing and interference effects. The increased surface area of the substrate and the substrate holder near their outer edges also leads to convective heat loss, resulting in further temperature nonuniformities. Still other temperature nonuniformities can result from heat loss to the spider supporting the substrate, or from heat loss caused by the use of sweep gas underneath the substrate. Temperature nonuniformities result in undesirable processing nonuniformities in the wafer, such as variations in thickness of deposited films and variations in resistivity.
To promote uniform temperature of the substrate during processing, some reactors include lamps which are grouped in separately controllable heating zones, allowing differing levels of power to be supplied to each individual zone. Other reactors include segmented lamps having differing filament winding densities along the length of the lamp, such that power output along the length of each lamp differs. Such zoned heating apparatuses are described in further detail in U.S. Pat. No. 6,465,761.
In order to correct a temperature nonuniformity in a particular region of the substrate, however, these and other conventional systems require the power to an entire lamp to be adjusted. As conventional systems use long lamps which span at least the diameter of the substrate, this leads to nonuniform temperature in other parts of the substrate. The resulting nonuniformities must then be compensated for by adjusting power to other lamps, making it very difficult to create uniform temperature throughout the substrate.
Thus, embodiments of the present invention desirably provide a lamp system allowing for localized control of radiant heat output in a semiconductor reactor.
The reactor 10 is shown with a conventional arrangement of heating lamps 14 (described in further detail below in connection with
Without localized control of power output to the heat lamps 14, these temperature nonuniformities are either undercompensated or overcompensated. Consequently, the conventional lamp design normally results in some degree of processing nonuniformities in the processed wafer, which can render some portions of the wafer unusable. For example, the area near the outer radial edge 8 of the substrate 16 is commonly referred to as an “exclusion zone,” because this area cannot be used to fabricate satisfactory chips.
Referring once again to
With reference now to
Although the lamps 14 are disposed in a uniform pattern, temperature nonuniformities still occur in the substrate, as discussed above in connection with
Against this background, aspects and advantages of the present invention will now be described with reference to the drawings of several preferred embodiments, which embodiments are intended to illustrate and not to limit the invention.
Referring now to
As illustrated in
With reference now to
As will be understood by one of skill in the art, providing more, shorter lamps desirably allows for control of incident power over smaller portions of a substrate, allowing temperature adjustment over a smaller area without affecting temperature over an adjoining area. In advantageous embodiments of the invention, shorter lamps can be strategically placed to cover certain areas of the substrate where temperature nonuniformity issues need to be resolved.
Another advantage of these and other embodiments including more, shorter lamps is that the desired high temperatures in the substrate can be achieved by operating most of the lamps in a lower power output range than with the conventional arrangement of long lamps. Providing more, shorter lamps thus avoids unnecessary stress on the lamps, thereby prolonging lamp life and reducing the risk of lamp failures due to overheating. Yet another advantage of providing more, shorter lamps instead of fewer, longer lamps is that filaments of shorter lamps are less susceptible to sag. Thus, these and other embodiments desirably reduce lamp failures.
Accordingly, these and other inventive lamp arrangements can be used in an advantageous method to provide improved temperature uniformity across a substrate during processing. The method can involve arranging a plurality of heat lamps above and/or below a substrate holder to allow for localized control of heat output in a reactor. A plurality of linear heat lamps of a plurality of different lengths may be provided, each of the lengths being shorter than a diameter of the substrate holder. Lamps of the same wattage or of differing wattages can be used. The lamps may be positioned above and/or below the substrate holder in locations where temperature nonuniformities may occur or where localized control of temperature is otherwise desirable. The lamps may be arranged, for example and without limitation, in a direction generally parallel to one another, generally perpendicular to one another, generally radially with respect to the substrate holder, or in any combination of the above. The power to each set of lamps, or to each individual lamp, may be varied in order to achieve a substantially uniform temperature throughout a substrate during processing.
A bank of lamps may be disposed above the substrate, and/or a bank of lamps may be disposed below the substrate. Optionally, each bank of lamps may be oriented substantially within a single plane that is either generally parallel with respect to the substrate and/or substrate holder, or at an angle with respect to the substrate and/or substrate holder. Additionally, some lamps may be arranged closer to the substrate holder than others, in one or more planes. Some lamps may be disposed at varying angles with respect to the substrate and/or substrate holder. Some lamps may also be arranged closer together than others, to allow for finer temperature control in particular areas. The lamps may further be arranged in any other configuration suitable for addressing temperature nonuniformities that may occur during substrate processing, such as those discussed above in connection with
Skilled artisans will appreciate that the claimed embodiments are not limited to use within the particular reactor 10 disclosed herein. In particular, one of skill in the art can find application for the lamp arrangements described herein for other semiconductor processing equipment, wherein a substrate is desirably heated to a uniform temperature, particularly where the support is subject to edge losses near the substrate edge. Moreover, while illustrated in the context of standard silicon wafers, the lamp arrangements described herein can be used to provide localized heat control in a variety of other applications.
It will also be understood by those of skill in the art that numerous and various modifications can be made without departing from the spirit of the present invention. Therefore, it should be clearly understood that the forms of the invention described herein are illustrative only and are not intended to limit the scope of the invention.
