Multi-zone heated ESC with independent edge zones

An electrostatic chuck (ESC) with a cooling base for plasma processing chambers, such as a plasma etch chamber. In embodiments, a plasma processing chuck includes a plurality of independent edge zones. In embodiments, the edge zones are segments spanning different azimuth angles of the chuck to permit independent edge temperature tuning, which may be used to compensate for other chamber related non-uniformities or incoming wafer non-uniformities. In embodiments, the chuck includes a center zone having a first heat transfer fluid supply and control loop, and a plurality of edge zones, together covering the remainder of the chuck area, and each having separate heat transfer fluid supply and control loops. In embodiments, the base includes a diffuser, which may have hundreds of small holes over the chuck area to provide a uniform distribution of heat transfer fluid.

TECHNICAL FIELD

Embodiments of the present invention relate to the microelectronics manufacturing industry and more particularly to temperature controlled chucks for supporting a workpiece during plasma processing.

BACKGROUND

Power density in plasma processing equipment, such as those designed to perform plasma etching of microelectronic devices and the like, is increasing with the advancement in fabrication techniques. For example, powers of 5 to 10 kilowatts are now in use for 300 mm substrates. With the increased power densities, enhanced cooling of a chuck, such as an electrostatic chuck (ESC) is beneficial during processing to control the temperature of a workpiece (wafer) uniformly.

ESC cooling bases designed for extreme thermal uniformity, specifically in the azimuthal direction that include multi-zone ESC heater control allow for the widest process window possible under various process and plasma conditions. Individual heater zones in the radial direction can compensate for minor radial non-uniformities that may be present. Such a design however does not allow for any independent azimuthal temperature control, specifically around the wafer edge. Although some processes require extreme azimuthal temperature uniformity, other processes may require more flexibility of the edge temperature as a function of azimuth angle.

SUMMARY

One or more embodiments are directed to a chuck to support a workpiece during plasma processing. According to one embodiment, the chuck includes a dielectric layer over which the workpiece is to be disposed. The chuck also includes an assembly upon which the dielectric layer is disposed. The assembly defines a plurality of independent zones through which a heat transfer fluid is to be separately circulated. The plurality of zones includes a center zone disposed proximate a center of the chuck and a plurality of edge zones disposed proximate to an outer perimeter of the chuck, surrounding the center chamber, and each spanning a different range of azimuth angles.

In one embodiment, a plasma etch system includes a vacuum chamber and a showerhead though which a source gas is supplied to the vacuum chamber. The system includes chuck with a dielectric layer over which the workpiece is to be disposed. The chuck also includes an assembly upon which the dielectric layer is disposed. The assembly defines a plurality of independent zones through which a heat transfer fluid is to be separately circulated. The plurality of zones includes a center zone disposed proximate a center of the chuck and a plurality of edge zones disposed proximate to an outer perimeter of the chuck, surrounding the center chamber, and each spanning a different range of azimuth angles. The system includes a heat transfer fluid loop fluidly coupling the zones of the chuck to a high pressure side of a heat exchanger or chiller and to a low pressure side of the heat exchanger or chiller through a manifold, the manifold including separate flow controls for two or more of the zones.

According to one embodiment, a method of plasma etching involves supporting a workpiece in a vacuum chamber over a dielectric layer of a chuck assembly. The method involves supplying a source gas to the vacuum chamber. The method involves processing the workpiece with plasma generating from the source gas. The method also involves separately circulating a heat transfer fluid though a plurality of independent zones defined in the chuck assembly. The plurality of zones includes a center zone disposed proximate a center of the chuck assembly and a plurality of edge zones disposed proximate to an outer perimeter of the chuck assembly, surrounding the center chamber, and each spanning a different range of azimuth angles.

DETAILED DESCRIPTION

The terms “over,” “under,” “between,” and “on” as used herein refer to a relative position of one component or material layer with respect to other components or layers where such physical relationships are noteworthy. For example in the context of material layers, one layer disposed over or under another layer may be directly in contact with the other layer or may have one or more intervening layers. Moreover, one layer disposed between two layers may be directly in contact with the two layers or may have one or more intervening layers. In contrast, a first layer “on” a second layer is in direct contact with that second layer. Similar distinctions are to be made in the context of component assemblies.

In embodiments described herein, a plasma processing chuck includes a plurality of independent edge zones. In embodiments, the edge zones cover different azimuth angles of the chuck perimeter to permit independent edge temperature tuning, which may be used to compensate for other chamber related non-uniformities or incoming wafer non-uniformities. In embodiments, the chuck includes a center zone (e.g., covering 50-90% of the chuck area) having a first heat transfer fluid supply inlet and outlet and a first temperature control loop, while each of the plurality of edge zones, together covering the remainder of the chuck area, have separate heat transfer fluid supply inlets and outlets and separate temperature control loops.

FIG. 1is a schematic of a plasma etch system100including a chuck assembly142in accordance with an embodiment of the present invention. The plasma etch system100may be any type of high performance etch chamber known in the art, such as, but not limited to, Enabler™, DPS II, AdvantEdge™ G3, E-MAX®, Axiom, Orion, or Mesa CIP chambers, all of which are manufactured by Applied Materials of CA, USA. Other commercially available etch chambers may similarly utilize the chuck assemblies described herein. While the exemplary embodiments are described in the context of the plasma etch system100, the chuck assembly described herein is also adaptable to other processing systems used to perform any plasma fabrication process (e.g., plasma deposition systems, etc.) that place a heat load on the chuck.

Referring toFIG. 1, the plasma etch system100includes a grounded chamber105. Process gases are supplied from gas source(s)129through a mass flow controller149to the interior of the chamber105. Chamber105is evacuated via an exhaust valve151connected to a high capacity vacuum pump stack155. When plasma power is applied to the chamber105, a plasma is formed in a processing region over workpiece110. A plasma bias power125is coupled into the chuck assembly142to energize the plasma. The plasma bias power125typically has a low frequency between about 2 MHz to 60 MHz, and may be for example in the 13.56 MHz band. In the exemplary embodiment, the plasma etch system100includes a second plasma bias power126operating at about the 2 MHz band which is connected to the same RF match127as plasma bias power125and coupled to a lower electrode via a power conduit128. A conductor190provides DC voltage to an ESC clamp electrode disposed in the dielectric material143. A plasma source power130is coupled through a match (not depicted) to a plasma generating element135to provide high frequency source power to inductively or capacitively energize the plasma. The plasma source power130may have a higher frequency than the plasma bias power125, such as between 100 and 180 MHz, and may for example be in the 162 MHz band.

A workpiece110is loaded through an opening115and clamped to a chuck assembly142. The workpiece110, such as a semiconductor wafer, may be any conventionally employed in the plasma processing art and the present invention is not limited in this respect. The workpiece110is disposed on a top surface of a dielectric layer143disposed over a cooling base assembly210. Embedded in the dielectric layer143is a clamp electrode (not depicted). In particular embodiments, the chuck assembly142includes a center zone141and a plurality of edge zones199, each zone141,199is independently controllable to a setpoint temperature. In the exemplary embodiment, the plurality of edge zones199provides independent control over separate azimuthal angles relative to a center of the chuck. In the exemplary embodiment, nine independent temperature zones are provided with eight edge zones forming a perimeter about a center zone of the top surface area of the chuck assembly142.

The temperature controller175is to execute temperature control algorithms (e.g., temperature feedback control) and may be either software or hardware or a combination of both software and hardware. The temperature controller175may further comprise a component or module of the system controller170responsible for management of the system100through a central processing unit172, memory173and input/output interface174. The temperature controller175is to output control signals affecting the rate of heat transfer between the chuck assembly142and a heat source and/or heat sink external to the plasma chamber105for the center zone141, and separate edge zones199.

In embodiments, each of the different temperature zones is coupled to a separate, independently controlled heat transfer fluid loop with separate flow control that is controlled based on a zone-specific temperature feedback loop. In the exemplary embodiment having a plurality of edge temperature zones199surrounding a center zone141, the temperature controller175is coupled to a first heat exchanger (HTX)/chiller177and may further be coupled to a second HTX/chiller178. The azimuthal edge temperature zones199may be plumbed to the same HTX177, as further depicted inFIG. 3, such that the temperature controller175may acquire the temperature setpoint of the heat exchanger177, as well as a center and plurality of edge temperatures176(one for each of the edge zones199), and control heat transfer fluid flow rate through fluid conduits in the chuck assembly142. Generally, the heat exchanger177is to cool both the center portion of the chuck assembly142and the annular edge temperature zones199(e.g., each spanning a 45° arc) of the chuck perimeter.

One or more valves185(or other flow control devices) between the heat exchanger/chiller177and fluid conduits in the chuck assembly142may be controlled by temperature controller175to independently control a rate of flow of the heat transfer fluid to each of the center zone141and the plurality of annular edge zones199. In the exemplary embodiment therefore, nine heat transfer fluid loops are employed, and for each loop, any heat transfer fluid known in the art may be used. For example, the heat transfer fluid may be a liquid, such as, but not limited to an ethylene glycol/water mix.

FIG. 2illustrates a plan view of the cooling base assembly210, in accordance with an embodiment. As shown, the plurality of edge zones199surround the center zone141, forming segments of an annulus. Each of the edge zones199spans a particular range of azimuth angle, ω, to permit independent tuning of the cooling base assembly210temperature as a function of azimuth angle. In the exemplary embodiment with eight edge zones199(1-8inFIG. 2), ω is ˜45°. The edge zones199are further defined by an inner edge proximate to the center zone141and an outer edge proximate to the perimeter edge of the cooling base assembly210. The radial distance between the inner and outer edges of the edge zones199may vary, but in exemplary embodiment is 15-50 mm. The center zone141may have any radius to cover the base area not occupied by the edge zones199, (e.g., 140-190 mm). In specific embodiments, the area of the cooling base assembly210occupied by the center zone141is between 50 and 90% of the total surface area of the base while edge zones199occupy the balance.

FIG. 3illustrates a schematic of a heat transfer fluid manifold399configured to supply the cooling base assembly210, in accordance with an embodiment. In the exemplary embodiment, a flow-through manifold is employed where the primary lines301forming a loop between the center zone141and the HTX177is tapped for each edge zone199. Heat transfer fluid flow to each of the edge zones199is then not isolated from the flow on the primary loop through the center zone141, and vice versa. For each edge zone, a control valve302is controlled via a feedback loop based on measurement output from a downstream flow meter303. Flow to each edge zone is thereby controlled to a setpoint determined by the temperature controller175for a desired azimuthal variation/uniformity across the edge zones. While the flow to each edge zone may only be a fraction of that in the center zone141, in alternative embodiments where flow to the edge zones199is a significant portion of the total flow on the primary loop, an isolated manifold to the edge zones may be provided, separate from the center zone141. For such embodiments, the isolated manifold is coupled to a second heat transfer fluid reservoir.

Generally, any cooling base may be utilized to implement the azimuthally independent edge zone architecture depicted inFIGS. 2 and 3. For example, in one embodiment, each cooling zone includes separate conduits passing through each region of the base in parallel (e.g., as fed by the manifold399).FIG. 4is a sectional isometric view of the cooling base inFIG. 2, in accordance with one exemplary embodiment. In this exemplary embodiment, the flow pattern of the cooling base assembly210is closer in nature to a 2-stage showerhead most often employed for gas delivery in a plasma processing chamber. However, in contrast to conventional gas delivery showerheads, where an inlet/outlet is at opposite ends of the assembly, embodiments of the cooling base assembly210have fluid inlets and outlets in a same physical plane (i.e., there is a supply and return at a first interface rather than a single-pass of fluid flow through the assembly). As shown inFIG. 4, the cooling base assembly210includes a base200over which a workpiece is to be disposed, a diffuser255over which the base200is disposed, and a reservoir plate277over which the diffuser255is disposed. In the exemplary embodiment, the diffuser255and base200is each a separate plate of a material, preferably the same material (e.g., aluminum) for the sake of matching coefficients of thermal expansion (CTE). The cooling base assembly210may be fabricated in multiple steps, with three main parts/components that are joined (e.g., permanently bonded, press fit, or removably attached by screws, etc.) during fabrication to make one complete base. Disposed over the top surface of the base200is the dielectric material143(ofFIG. 1) upon which the workpiece is to be disposed. The dielectric material143may be any known in the art and is in one advantageous embodiment a ceramic (e.g., AlN) to electrostatically clamp the workpiece during processing. Generally, the dielectric material143may be operable as any electrostatic chuck (ESC) known in the art, such as, but not limited to a Johnsen-Rahbek (JR) chuck. In one exemplary embodiment, the dielectric material143comprises a ceramic puck having at least one electrode (e.g., a mesh or grid) embedded in the ceramic to induce an electrostatic potential between a surface of the ceramic and a workpiece disposed on the surface of the ceramic when the electrode is electrified.

The base200is to function as a thermally conductive mechanical fluid barrier between the dielectric material143and the diffuser255. The base200has a bottom surface which may be exposed to a heat transfer fluid passed through the diffuser255. As heat transfer fluid is contained by the base200with no fluid passing to the top surface of the base200, the base may be considered a cap affixed to a showerhead with the diffuser255being a showerhead showering the base200with a uniform distribution of heat transfer fluid. Because the heat transfer fluid is of a controlled temperature (e.g., supplied from either of the HTX/chiller177), a uniform distribution of heat transfer fluid maintains the base200at a temperature that is highly uniform across the area of each zone (center and edge zones) in the base200, and therefore across the area of the dielectric material143, and in turn the workpiece as it undergoes processing.

The cooling base assembly210is disposed on a support plate305. The support plate305is affixed to the cooling base assembly210and includes an RF coupler600(e.g., a multi-contact fitting) disposed at a center of the chuck to receive an RF input cable for powering the chuck (e.g., the chuck assembly142ofFIG. 1). Heat transfer fluid inlet and outlet fittings to each of the edge zones199and center zone141are further provided by the support plate305as an interface for facilitating the cooling base assembly210. In the exemplary embodiment, the support plate305is of a same material as the cooling base assembly (e.g., aluminum).

In an embodiment, the diffuser255includes a plurality of supply openings330that pass through the diffuser255and place the bottom surface of the base200in fluid communication with a center zone supply reservoir310disposed between the diffuser255and the reservoir plate277. The supply openings330are to uniformly distribute heat transfer fluid to the base200across the surface area of the base200. In an advantageous embodiment, there are at least fifty supply openings330arranged with azimuthal symmetry about a circular area of the diffuser255, and in the exemplary embodiment, there are hundreds of the supply openings330. The azimuthal symmetry, large number of supply openings and wide contiguous area of the underlying supply reservoir310work together to provide concentric temperature distributions or boundary conditions within the center zone141. Annual arrangements of heater elements (e.g., resistive) can then be utilized to optimize the radial temperature distribution.

The supply openings330allow for fluid incoming from upstream below the diffuser255to build pressure and uniformly flow upward through the diffuser255. Barriers484(shown in dashed line inFIG. 4) are disposed between the center zone141and each of the edge zones199(e.g., zones1-9are demarked by dotted lines), as well as between adjacent edge zones199. The barriers484partition the supply openings330according to the separate edge and center zones. Within each zone therefore, there are a plurality of the supply openings330fed by an inlet and drained by an outlet dedicated to each zone. As such, the azimuthal symmetry of the openings ensures azimuthally symmetric heat transfer fluid flow to the base200within each zone while the independent zone-level flow control provides for the azimuth control/tunability across the base. The great number of supply openings330ensures a reasonably low pressure pump is sufficient to drive the heat transfer fluid through the coolant loop (e.g., from the HTX/chiller177, through the supply openings330, and back).

As shown, the center supply reservoir310is an in annular cavity having a width in the radial direction that spans a plurality of annular channels340. Separate edge supply reservoirs311are associated with each of the edge zones as well. Functionally, the supply reservoirs310,311are to provide a low pressure drop across contiguous area of the reservoir spanning a given zone (center zone141, or one of the edge zones199) so that openings in the diffuser255present a uniform pressure differential across the surface area of the diffuser255within the zone. As illustrated inFIG. 4, the supply reservoirs310,311are provided by a standoff at the outer perimeter of the back surface of the diffuser255, however the reservoir plate277may have a functional equivalent feature to space apart facing surfaces of the diffuser255and reservoir plate277.

In an embodiment, the diffuser255includes at least one return opening350for each zone through which heat transfer fluid is returned through the reservoir plate277. As shown in the cross-section, the return openings pass through the diffuser255. Aligned with the return opening350, the diffuser255forms a male fitting that seats into a return opening in the reservoir plate277. The male fitting forms a return conduit that passes though the supply reservoirs310,311.

In an embodiment, at least a first of the base200and the diffuser255have a plurality of bosses320in physical contact with a second of the base200and the diffuser255. Either a bottom surface of the base200or a top surface of the diffuser255, facing the bottom surface of the base200, may be machined to have the bosses320. In the exemplary embodiment, the bosses320are machined into the diffuser255. As shown inFIG. 4, a top surface of a boss320is in direct physical contact with a bottom surface of the base200. The annular channels340place the plurality of supply openings330in fluid communication with at least one return opening350for each one of the center zone141, or edge zones199. Because the bosses320are discontinuous along the azimuth angle, the plurality of bosses320further define a plurality of radial channels fluidly coupling adjacent annular channels340. The supply opening330is disposed within a boss320with each boss320further including a boss channel fluidly coupling the supply opening330with an annular channel340. In embodiments, the return openings350are disposed in one or more of the annular channels340, and/or radial channels. In the exemplary embodiment, the return openings350are disposed in an annular channel340. As illustrated byFIG. 4, a plurality of return openings350are disposed at a same radial distance as one of the annular channels340and at different azimuthal angles (e.g., about every 18° in the depicted embodiment).

In embodiments, resistive heaters are embedded in at least one of the dielectric material143, the base200, the diffuser255, the reservoir plate277, or the support plate305. In one advantageous embodiment, resistive heaters are embedded in the dielectric material143. In the exemplary embodiment, a plurality of individual heater zones in the radial direction (e.g., an inner diameter and an outer annulus surrounding the inner diameter) is to compensate for minor radial non-uniformities in temperature that may be present.

FIG. 5is a flow diagram of a method500of plasma processing, in accordance with an embodiment.

The method500begins with supporting a workpiece in a vacuum chamber over a dielectric layer of a chuck assembly, at operation502. For example, the workpiece may be supported over a dielectric layer of a chuck assembly such as the chuck assembly142ofFIG. 1. The method involves supplying a source gas to the vacuum chamber and processing the workpiece with plasma generated from the source gas, at operations504and506.

While processing the workpiece, the method500involves separately circulating a heat transfer fluid though a plurality of independent zones defined in the chuck assembly, at operation508.FIG. 2illustrates one example of a plurality of nine independent zones. The plurality of zones includes a center zone (e.g., the center zone141ofFIG. 2) disposed proximate a center of the chuck assembly and a plurality of edge zones (e.g., the edge zones199ofFIG. 2) disposed proximate to an outer perimeter of the chuck assembly, surrounding the center chamber, and each spanning a different range of azimuth angles. In one embodiment, separately circulating the heat transfer fluid involves circulating the heat transfer fluid through a loop fluidly coupling the zones of the chuck to a high pressure side of a heat exchanger or chiller and to a low pressure side of the heat exchanger or chiller through a manifold. In one such embodiment, the manifold includes separate flow controls for two or more of the zones. Thus, according to embodiments, independent zone-level flow control may provide for independent temperature tunability across the base.

It is to be understood that the above description is intended to be illustrative, and not restrictive. For example, while flow diagrams in the figures show a particular order of operations performed by certain embodiments of the invention, it should be understood that such order is not required (e.g., alternative embodiments may perform the operations in a different order, combine certain operations, overlap certain operations, etc.). Furthermore, many other embodiments will be apparent to those of skill in the art upon reading and understanding the above description. Although the present invention has been described with reference to specific exemplary embodiments, it will be recognized that the invention is not limited to the embodiments described, but can be practiced with modification and alteration within the spirit and scope of the appended claims. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.