Substrate support ring for more uniform layer thickness

Embodiments of substrate support rings providing more uniform thickness of layers deposited or grown on a substrate are provided herein. In some embodiments, a substrate support ring includes: an inner ring with a centrally located support surface to support a substrate; and an outer ring extending radially outward from the support surface, wherein the outer ring comprises a reaction surface area disposed above and generally parallel to a support plane of the support surface, and wherein the reaction surface extends beyond the support surface by about 24 mm to about 45 mm.

FIELD

Embodiments of the present invention generally relate to semiconductor processing.

BACKGROUND

Substrates, such as semiconductor wafers, may be supported by a support apparatus, such as an edge ring, for processing within a process chamber. In some semiconductor fabrication processes, such as processes to deposit or grow an oxide layer, a combustion reaction is initiated in a process chamber to generate oxygen species to contribute to the growth of the oxide layer. However, the inventors have observed that in some processes, process non-uniformities can occur that affect the thickness uniformity of a layer on the wafer surface. In particular, varying deposition or growth rates at the substrate edge have been observed, leading to non-uniform layer formation at the edge of the substrate.

Accordingly, the inventors have provided embodiments of substrate supports that may facilitate improved process uniformity during some semiconductor fabrication processes.

SUMMARY

Embodiments of substrate support rings providing more uniform thickness of layers deposited or grown on a substrate are provided herein. In some embodiments, a substrate support ring includes: an inner ring comprising a centrally located support surface adapted to support a substrate; and an outer ring extending radially outward from the support surface, wherein the outer ring comprises a reaction surface area disposed above and generally parallel to a support plane of the support surface, and wherein the reaction surface extends beyond the support surface by about 24 mm to about 45 mm.

In some embodiments, a substrate support apparatus includes: an inner ring comprising a centrally located support surface to support a substrate; and an outer ring extending radially outward from the support surface, wherein the outer ring comprises a reaction surface area above and generally parallel to a support plane of the support surface, wherein the reaction surface extends beyond the support surface by about 24 mm to about 34 mm, and wherein the reaction surface is about 0.86 to about 0.97 mm above the support surface.

In some embodiments, a substrate processing apparatus includes a chamber body enclosing a processing volume; and a substrate support apparatus disposed and supported within the processing volume. The substrate processing apparatus includes an inner ring comprising a centrally located support surface adapted to support a substrate; and an outer ring extending radially outward from the substrate support surface wherein the outer ring comprises a reaction surface area above and generally parallel to a support plane of the support surface, the reaction surface extending beyond the support surface by about 24 mm to about 45 mm.

DETAILED DESCRIPTION

Embodiments of the present invention provide substrate support rings, or edge rings, for supporting a substrate, such as a semiconductor wafer, in a chamber for processing. The substrate support rings in accordance with embodiments of the present invention have been observed to beneficially affect process uniformity, particularly at the substrate edge. Embodiments of the disclosed support rings may beneficially affect layers deposited or grown on a substrate.

FIG. 1depicts a top view of a substrate support ring, or edge ring100, according to embodiments of the present invention. The illustrative edge ring100comprises an inner ring102having a support surface104centrally located about a center point C. The support surface104is configured to support a substrate having a given diameter (e.g., 200, 300, 450 mm semiconductor wafers, or the like) along an edge of the backside of the substrate. For example, the support surface104has an inner diameter that defines a central opening and an outer diameter defining a width of the support surface104between the inner and outer diameters.

The support surface104supports only an outer portion of the substrate, leaving the central and predominant portion of the backside of the substrate exposed. In some embodiments, the support surface104is configured to support the substrate along about 1.10 to about 1.56 percent of the diameter of the substrate. For example, for a 300 mm substrate, the support surface104may be about 3.3 to about 4.7 mm in width.

An outer ring108is disposed radially outward from the inner ring102. The outer ring108comprises an outer edge110, and inner edge112, and a reaction surface114therebetween. The inner edge112forms a radially outward limit of the support surface104(i.e., the outer diameter of the support surface104).

As illustrated inFIG. 2, the reaction surface114may be generally parallel to and disposed above the support surface104by the thickness of the substrate to be processed thereon such that the upper surface of the substrate is substantially even with the reaction surface114. For example, in some embodiments, the reaction surface114is disposed above the support surface104between about 0.86 to about 0.97 mm, for example by about 0.91 mm. When a substrate is disposed on the support surface104for processing, the substrate surface S may be substantially planar with the reaction surface114in some embodiments. In other embodiments, the substrate surface S may be offset above or below the reaction surface114. For example, in some embodiments the substrate surface S is above the reaction surface114by about 0.5 mm. In other embodiments, the substrate surface S may be below the reaction surface114by about 0.5 mm. Accordingly, when supported on the support surface104for processing, the substrate surface S may be between about 0.5 mm above and about 0.5 mm below the reaction surface114. The reaction surface is substantially parallel to a support plane of the support surface104(i.e., the plane of the substrate when resting on the support surface104). The edge ring100may comprise a projection202extending downwardly from a bottom surface of the outer ring108. When disposed within a process chamber, the projection202may provide support for the ring within the chamber as discussed below with respect toFIG. 3.

The inner ring102and the outer ring108may comprise one or more process compatible materials, including non-limiting examples such as a ceramic material, for example, silicon carbide (SiC), and may be integrally formed or may be separately formed and coupled together. In some embodiments, portions of the inner ring102and the outer ring108may comprise a coating, for example a poly silicon coating. The inner ring102and the outer ring108may be concentric about axis204which passes through the center point C.

In the non-limiting embodiment illustrated inFIG. 2, the reaction surface114extends radially beyond the inner edge112a distance L. The distance L may be about 24 mm to about 45 mm, for example about 24 mm to about 34 mm. The inventors have observed that a beneficial effect may be obtained with a reaction surface114extending radially beyond the inner edge112by substantially any distance greater than about 24 mm for reasons to be discussed below. The inventors have also observed that edge rings with an L dimension greater than a certain amount, for example greater than about 34 mm, may provide suboptimal throughput, requires a larger chamber to house the edge ring, and requires additional time and energy to heat and cool.

The disclosed edge ring may be advantageously used in any process chamber configured to perform at least a rapid thermal processing process. Examples of process chambers suitable for performing the inventive method include any of the RADIANCE®, RADIANCE® PLUS, or VANTAGE® process chambers, or any other process chamber capable of performing a thermal process, for example a rapid thermal process (RTP), all available from Applied Materials, Inc., of Santa Clara, California. The disclosed edge ring may also be used in similar chambers from other manufacturers. In some embodiments, a suitable process chamber may be similar to the process chamber300described below with respect toFIG. 3.

The substrate302, which may include one or more layers344disposed thereon (such as a dielectric layer), is mounted inside the process chamber300on a substrate support304and is heated by a radiant energy source, such as lamp head310, which is disposed in a position opposing the substrate support304. The lamp head310generates radiation which is directed to a front side308of the substrate302. Alternatively, the lamp head310may be configured to heat the back side306of the substrate302, for example, such as by being disposed beneath the substrate302, or by directing the radiation to the back side306of the substrate302. In the illustrative embodiment depicted inFIG. 3, the radiation enters the process chamber300through a water-cooled quartz window assembly312. Beneath the substrate302is a reflector plate314, which is mounted on a water-cooled, stainless steel base, for example base316. The base316includes a circulation circuit318through which coolant circulates to cool the reflector plate314. In some embodiments, the reflector plate314is made of aluminum and has a highly reflective surface coating320. Water may be circulated through the base316to keep the temperature of the reflector plate314well below that of the heated substrate302. Alternatively, other coolants may be provided at the same or different temperatures. For example, antifreeze (e.g., ethylene glycol, propylene glycol, or the like) or other heat transfer fluids may be circulated through the base316and/or the base316may be coupled to a chiller (not shown). An underside or backside of the substrate302and the top of the reflector plate314form a reflecting cavity322. The reflecting cavity322enhances the effective emissivity of the substrate302.

The temperatures at localized regions of the substrate302are measured by a plurality of temperature probes324coupled to a plurality of pyrometers326. The plurality of pyrometers326is connected to a temperature controller328which controls the power supplied to the lamp head310in response to a measured temperature. The lamps may be divided into multiple zones. The zones can be individually adjusted by the controller to allow controlled radiative heating of different areas of the substrate302.

During processing, a first gas may be flowed from a gas panel (e.g., gas supply329) and enter the process chamber300at an inlet330(e.g., a first inlet) to at least partially fill a processing volume301. For example, in some embodiments, the gas supply329may be a remote plasma source to form a plasma from the first gas prior to providing the plasma to the process chamber. The inlet330is disposed in a side of the process chamber300and facilitates the flow of the first gas across the surface of the substrate302. The lamp head310provides sufficient energy to ignite a plasma from the first gas and maintain the plasma, or to maintain a plasma if the gas supply is a remote plasma source, in the process chamber300in the area above the substrate302. The lamp head310ignites and/or maintains the plasma in a manner sufficient to maintain an oxidation reaction at least in the processing volume301above the substrate302.

The substrate support304may be configured to be stationary or may be supported for rotation within the processing volume301to rotate the substrate302. The substrate support304includes the edge ring100which contacts the substrate302around the outer perimeter of the substrate, thereby leaving the entire underside of the substrate302exposed except for a small annular region about the outer perimeter.

In some embodiments, the projections202of the edge ring100may rest on a rotatable tubular cylinder334that is coated with silicon to render it opaque in the frequency range of the pyrometer326. The coating on the cylinder334acts as a baffle to block out radiation from the external sources that might contaminate the intensity measurements. The bottom of the cylinder334is held by an annular upper bearing336which rests on a plurality of ball bearings338that are, in turn, held within a stationary, annular, lower bearing race340. In some embodiments, the ball bearings338are made of steel and coated with silicon nitride to reduce particulate formation during operations. The upper bearing336is coupled to an actuator (not shown) which rotates the cylinder334, the edge ring100and the substrate302during processing.

The substrate support304may be coupled to a lift mechanism342capable of raising and lowering (i.e., provide vertical displacement) the substrate302with respect to the lamp head310. For example, the substrate support304may be coupled to the lift mechanism342, such that a distance between the substrate302and the reflector plate314is constant during the lifting motion.

The inventors have observed that under some process conditions, for example rapid thermal processing (RTP) at temperatures between about 700° C. and about 900° C., a layer deposited or grown on a substrate exhibits a thickness non-uniformity at the edge of the substrate. The condition exists with substrates that are not rotated during processing yielding a non-rotational profile, as well as with substrates that are rotated during processing to produce a rotational profile.FIGS. 4A and 4Bare illustrative of the observed thickness of a deposited or grown layer on a non-rotated substrate402and a rotated substrate404processed under the same chamber conditions using a conventional edge ring to support the substrate.

Each figure represents a substrate402,404supported by a conventional edge ring (not shown) with a plot403,405, respectively, above and aligned with the wafer representing the average deposited or grown layer thickness along a diameter of the respective wafer. The 0 (zero) point represents the center of the substrate402,404, and the vertical axis may be any appropriate scale or unit of measurement for grown thickness, for example angstroms (Å). In both figures, the process gas flows across the substrate from left to right as illustrated by arrow401.

As illustrated, the plot403of grown layer thickness of the non-rotated substrate402has a single peak407, or a local maximum, towards the substrate edge409first contacted by the process gas flow. Between the maximum layer thickness represented by the peak407and the minimum grown thickness408near the substrate edge409, the grown layer thickness decreases rapidly as indicated by the slope of the plot403between the peak407and the minimum grown thickness408.

The plot405of the layer thickness of the rotated substrate404has a similar peak406, or maximum, toward an edge410of the substrate. Between the maximum layer thickness represented by the peak406and the minimum grown thickness412near the substrate edge410, the grown layer thickness on the rotated substrate decreases rapidly as indicated by the slope of the plot405between the peak406and the minimum grown thickness412.

The inventors have observed that the grown layer thickness in non-rotational profiles is representative of the grown thickness of rotational profiles processed under the same chamber conditions. Although the grown thickness may not be identical in non-rotational and rotational profiles, the grown layer thickness on a rotational wafer exhibits a non-uniformity at the wafer edge that corresponds with the non-uniformity at the edge of a rotational wafer as illustrated inFIGS. 4A and 4B.

The change in the grown layer thickness between the local maximum and the outer edge of the grown layer is sometimes referred to as edge roll-off. The difference in layer thickness between a local maximum, for example the peak406or407, and the minimum grown thickness408or412, can be considered the magnitude of the edge roll-off. Because the edge roll-off effect is similar when a layer is grown on non-rotational and rotational wafers, the discussion of the edge roll-off applies to layers grown on both non-rotational and rotational wafers unless the context indicates otherwise.

For some applications, the edge roll-off as illustrated inFIGS. 4A and 4Bis undesirable, and may be unacceptable in some applications. The inventors have observed that an edge ring100having an outer diameter within a specific range larger than the substrate diameter provides a practical mechanism for improving the uniformity of the grown layer on the substrate302under some process conditions.

The graph500inFIG. 5depicts exemplary layer thickness grown at different temperatures, while maintaining the other process parameters (e.g., pressure and process gas flow rates) essentially the same. The layer thicknesses represented inFIG. 5may represent layers grown on a substrate. In the figure, curve502is illustrative of a layer thickness grown during a process at T1. Similarly, curves504and506are each illustrative of a layer thickness grown during a process at T2and T3, respectively, where T1<T2<T3, for example, T1may be 800° C., T2may be 900° C., and T3may be 1000° C. The origin of the horizontal axis represents the edge of the grown layer and corresponds with the outer edge of the effective combustion reaction taking place in the chamber above the substrate (for example, the outer edge110of the edge ring100). The region within the outer edge of the effective combustion reaction region grows an acceptably uniform layer thickness, while areas outside the outer edge grow an insufficient layer thickness. The origin may also correspond with the edge of the wafer or the outer edge of the edge ring. The increasing horizontal scale represents a horizontal distance (in meters) in the direction of the process gas flow. The vertical axis may be any appropriate scale or unit of measurement for grown thickness, for example angstroms (Å).

The inventors observed that the magnitude of the edge roll-off decreases as the distance increases from the edge of the grown layer in the direction of process gas flow. For example, at a distance of about 0.05 m (50 mm) or greater, curves502,504, and506exhibit very little, if any, roll-off. As illustrated, at about 50 mm, curves504and506are in a generally upwardly sloped, linear portion of the respective curves. At 50 mm, curve504is at the approximate maximum (corresponding to406or407inFIGS. 4A and 4B). The inventors have observed that when the grown layer thickness is measured at a distance of about 10 mm to about 50 mm, for example from about 10 mm to 30 mm, from the edge of the grown layer, the magnitude of the roll-off is within an acceptable range for some processes.

The inventors discovered that it is advantageous to process a substrate such that the peripheral edge of the wafer is positioned at about 10 mm to about 50 mm, or at about 10 m to about 30 mm, with respect to the outer edge of the effective combustion reaction taking place in the chamber. For example, such processing may advantageously yield enhanced layer growth because of reduced edge roll-off occurring on the substrate. A substrate processed such that the peripheral edge of the substrate was positioned more than 0.05 m from the edge of the effective combustion reaction would exhibit similar desirable characteristics, but for reasons discussed below, such processing conditions may be suboptimal.

The inventors succeeded in advantageously manipulating the position of the outer edge of the effective combustion reaction region to be about 10 mm to about 50 mm, or about 10 mm to about 30 mm, beyond the substrate edge by providing an edge ring100with an outer diameter between about 24 mm and about 45 mm, for example between about 24 mm and 34 mm, larger than the diameter of the substrate302.

As discussed above with reference toFIGS. 1 and 2, the edge ring100comprises an outer ring108having an outer edge110and inner edge112which forms an outer limit of the support surface104. Between the inner edge112and the outer edge110is a reaction surface114. The reaction surface114is an annular ring concentric with the support surface104and extending radially beyond the support surface104and a substrate302supported thereon by between about 24 mm and about 45 mm, or between about 24 mm and 34 mm. The reaction surface114of the edge ring100contributes to the enhanced performance of the edge ring.

The inventors have observed that edge rings100with reaction surfaces114which extend beyond the support surface104by more than about 45 mm increase production and operation costs. For example, a larger reaction surface requires additional material to fabricate, requiring a larger process chamber, and provides a greater area to support a combustion reaction, consuming additional process gases and energy. Although larger reaction surfaces may produce a reduced edge roll-off, the cost of achieving the reduction exceeds the benefit.

The inventors have also observed that edge rings100with reaction surfaces which extend beyond the support surface by less than about 24 mm do not adequately manipulate the outer edge of the effective combustion reaction region to reduce the edge roll-off an amount sufficient to yield the desired result.