Multi zone heating and cooling ESC for plasma process chamber

An electrostatic chuck assembly including a dielectric layer with a top surface to support a workpiece. A cooling channel base disposed below the dielectric layer includes a plurality of fluid conduits disposed beneath the top surface. A chuck assembly further includes a plurality of resistive heater rods spatially distribute across the chuck assembly. In embodiments, 169 heater rods and three heat transfer fluid flow controls are independently controlled during execution of a plasma etch process.

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.

DISCUSSION OF RELATED ART

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. Plasma etching with such powers creates a greater heating of the surface of a wafer. With the increased power densities, enhanced cooling of a chuck is beneficial during processing to control the temperature of a workpiece uniformly.

Plasma etch processing of semiconductor wafers (e.g., silicon) requires uniform steady heating or cooling to achieve repeatable results. Process characteristics, such as: etch rate, selectivity, profile control and uniformity all depend upon the wafer's surface temperature. Helium gas is added between a chuck (e.g., electrostatic chuck, or “ESC”) surface and wafer as a heat transfer medium.

SUMMARY

One or more embodiments are directed to a multi zone heating and cooling electrostatic chuck (ESC) for processing operations, such as plasma processing. In one embodiment, a chuck assembly for supporting a workpiece during a manufacturing operation. The chuck assembly includes a top surface of a dielectric layer to support the workpiece. The chuck assembly includes a plurality of resistive heater rods spatially distributed over an area of an RF powered cooling channel base disposed under the dielectric layer. The chuck assembly includes a plurality of fluid conduits in the cooling channel base. Each inner fluid conduit has a separate inlet and outlet and spans separate azimuthal angles of the chuck assembly. Each of the plurality of fluid conduits is independently controlled by a separate heat transfer fluid flow control and temperature feedback control loop.

According to one embodiment, a plasma processing apparatus includes a chamber to expose a workpiece to a plasma environment and a chuck assembly with a top surface of a dielectric layer to support the workpiece within the chamber. The chuck assembly includes a plurality of resistive heater rods spatially distributed over an area of an RF powered cooling channel base disposed beneath the dielectric layer. The chuck assembly also includes a plurality of fluid conduits in the cooling channel base. Each inner fluid conduit has a separate inlet and outlet and spans separate azimuthal angles of the chuck assembly. Each of the plurality of fluid conduits is independently controlled by a separate heat transfer fluid flow control and temperature feedback control loop.

In one embodiment, a method of plasma processing includes supporting a workpiece in a plasma chamber over a top surface of a dielectric layer of a chuck assembly. The method involves exposing the workpiece to a plasma environment in the plasma chamber. The method involves independently controlling each of a plurality of resistive heater rods to heat areas of the chuck assembly based on temperature feedback. The plurality of resistive heater rods are spatially distributed over an area of an RF powered cooling channel base disposed beneath the dielectric layer. The method also involves independently controlling each of a plurality of fluid conduits by a separate heat transfer fluid flow control to cool other areas of the chuck assembly based on the temperature feedback, wherein the plurality of fluid conduits are disposed in the cooling channel base. Each inner fluid conduit has a separate inlet and outlet and spans separate azimuthal angles of the chuck assembly.

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.

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, 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 substrate fabrication process (e.g., plasma deposition systems, etc.) which 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 electrode120via a power conduit128. 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 workpiece110may 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 channel base144. A clamp electrode (not depicted) is embedded in the dielectric layer143. In particular embodiments, the chuck assembly142includes a plurality of zones, each zone independently controllable to a setpoint temperature. In the exemplary embodiment, the plurality of zones provides independent control over separate azimuthal angles relative to a center of the chuck. In the exemplary embodiment, three independent temperature zones are provided in the chuck with three-fold symmetry about a center 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, memory173, and 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 chamber105.

In embodiments, each of the different temperature zones is coupled to a separate, independently controlled heat transfer fluid loop with flow control that is controlled based on a temperature feedback loop unique to the zone. In the exemplary embodiment having three azimuthal temperature zones, the temperature controller175is coupled to a first heat exchanger (HTX)/chiller177, a second heat exchanger/chiller178, and a third heat exchanger/chiller179with each of the HTX/chillers177,178,179fluidly coupled to one of the plurality (three) temperature zones in the chuck. The temperature controller175may acquire the temperature setpoint of the heat exchangers177,178,179and temperatures176for each of the zones of the chuck assembly142, and control heat transfer fluid flow rate through fluid conduits in the chuck assembly142. Generally, the heat exchanger177is to cool a first portion of the chuck assembly142(e.g., over a first 120° arc spanning the radius of the chuck, which may be 150 mm or 225 mm, etc.) via a plurality of first fluid conduits141. The heat exchanger178is to cool a second portion of the chuck assembly142(e.g., over a second 120° arc spanning the radius of the chuck) via a plurality of second fluid conduits140. Likewise the third heat exchanger179is coupled through a third piping to the third zone (e.g., over a first 120° arc spanning the radius of the chuck), etc.

One or more valves185,186,187(or other flow control devices) between the heat HTX/chillers177,178,179and 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 plurality of fluid conduits141,142,143. In the exemplary embodiment therefore, three 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.

In embodiments, the chuck assembly includes a plurality of independently controlled heater rods and a plurality of independent cooling fluid conduits. Each heater rod is a resistively heated element disposed within the chuck assembly to provide a heating power to the chuck assembly. Each rod is electrically coupled to a driver that may either provide pulsed power (e.g., a PWM mode) or continuous mode power. In embodiments, the heater rods are oriented with their longitudinal axis perpendicular to the top surface of the chuck assembly to maximize spatial packing density. The heater rod material may be a metal, such as stainless steel, or a ceramic.

FIG. 2illustrates a top-down plan view of the chuck assembly142without the dielectric layer143. The top transverse sectional surfaces of the heater rods209are visible. In embodiments where the diameter of the chuck, D1, is smaller than 450 mm (e.g., a chuck configured to accommodate a 300 mm workpiece), there are 169 heater rods209disposed within the chuck assembly. 169 heater rods209is advantageous in that a large array (13×13) of elements may be individually controlled as mapped over the spatial area of the chuck assembly to achieve a level of precision unobtainable by designs with fewer elements. For example, even a 12×12 array (144 elements) would lead to a significantly more discrete heating power application. This may be important when, for example, a relatively higher power must be applied to each individual heater rod209as the number of rods decreases to achieve a given heating power. This higher individual heater power would lead to hot spots spatially distributed across the chuck surface where the thermal resistance between adjacent heater rods is significant, as it may be where a thin ceramic puck serves as the dielectric143(illustrated inFIG. 1). For example, in certain embodiments, the ceramic puck thickness may only be 0.5 mm-1 mm including the bonding media, which in one embodiment is a metal for better thermal conductivity and resistance to plasma attack. However, other embodiments may include other numbers of heater rods209(e.g., fewer than or more than 169 heater rods209). In the depicted embodiment, the 169 heater rods209are spatially arranged as eight concentric rings of incrementally increasing radii (highlighted with dashed lines). For this particular heater rod layout for example, 144 rods would result in a larger arc distance between adjacent rods than for the advantageous embodiments with 169 heater rods209. In embodiments wherein the diameter D1is sufficient for a 450 mm diameter workpiece, a greater number of heater rods are present than in the depicted embodiment, for example to maintain a same spatial density of heater rod elements.

A plurality of fluid conduits241,242, and243are further illustrated inFIG. 2. The fluid conduits are dimensioned to pass a heat transfer fluid at a desired flow rate for pressures typical in the art (e.g., 3 PSI). The fluid conduits are routed around the heater rods209, as well as other less numerous objects in the base, such as lift pin through holes222and a central axis250dimensioned to clear a conductor to provide DC voltage to an ESC clamp electrode. As further shown, each of the fluid conduits spans an equal azimuthal angle ω for three-fold symmetry. In the exemplary embodiment each fluid conduit has an inlet (e.g.,242A), and an outlet (e.g.,242B) that is proximate the chuck center250, and more particularly between an inner most ring of heater rods209and the adjacent ring of heater rods209(i.e., the second inner more ring). Each fluid conduit is folded back on itself to form a counter current conduit pair that is separated over the length of the conduit run (from inlet to outlet) by one ring of heater rods209. As the folded conduit pair meanders radially, turns are made to run over an arc length within the azimuthal angle ω between successive rings of heater rods209. With the exemplary eight concentric rings of heater rods209, the fluid conduit makes twelve turns (corners) such that the innermost heater rods are surrounded by the lowest temperature fluid on one side (e.g., at smaller radius) and highest temperature fluid on the opposite side (e.g., at larger radius) for an average fluid temperature approximately equal to that which occurs at the outermost ring of heater rods209.

FIG. 3Ais a cross sectional view of the chuck assembly142, in accordance with an embodiment of the present invention. As visible inFIG. 3A, the chuck assembly142includes a cooling channel base344disposed over a backing plate345, which is further disposed of a base plate348. The backing plate345, the cooling channel base344, and base plate348are all RF powered and so in the exemplary embodiments are each made of electrically conductive materials (e.g., aluminum) and are in mechanical contact with one another. Disposed below the base plate348is an annular dielectric spacer ring349to electrically isolate the RF power portions of the assembly142from the portions maintained at RF ground (e.g.,351, etc.).

FIG. 3Bis an isometric sectional view of the chuck assembly inFIG. 3A, in accordance with an embodiment.FIG. 3Bis an expanded view of the top surface of the cooling channel base344, backing plate345, and base plate348. As illustrated, fluid conduits241are capped by weld covers315. A lifter pin sub-assembly362is shown as is an individual heater rod209. In embodiments, as shown inFIG. 3B, the heater rods209are disposed below a thickness of the cooling channel base344. In other words, the heater rods209are disposed within blind recesses in the cooling channel base344. In certain such embodiments, the heater rods209are configured for tip heating with a thermally conductive connection maintained between a longitudinal end of the heater rod and a top surface of the cooling channel base344. In one such embodiment, the thickness of the cooling channel base portion disposed over the heater rod209(e.g.,210inFIG. 3B) is sufficiently thick so as to reduce the amount of RF induced on each heater rod209. This reduced RF is a function of the skin effect associated with a given frequency of RF applied to the RF hot portions of the chuck assembly142. Reduced RF on the heater rods209enables RF filtering on the heater rods209to be smaller (i.e., physically smaller chokes) for reduced cost, which can be important given the potential number of heater rods209(e.g., 169, or more). Indeed, in some embodiments, no RF filters are present on the heater rod circuits. According to an embodiment, the cooling channel base344has a thickness sufficient to prevent excessive bowing resulting from vacuum pressure.

In alternative embodiments, the heater rods209may be disposed in through holes that pass completely through the entire thickness of the cooling channel base344such that the heater rods209are free to contact the overlying ceramic puck (dielectric143inFIG. 1). For certain such embodiments, the heater rods209are configured for sidewall heating and a conductive path is maintained between a sidewall of the through holes in the cooling channel base344and the heater rods209.

In embodiments, the heater rods209are coupled to a member capable of undergoing elastic strain and/or a fluidic thermal conductor to accommodate thermal expansion of the heater rods209and/or cooling channel base344. The strainable member is to maintain thermal contact between the heater rods and the surrounding bulk assembly (e.g., cooling channel base344) over a wide operating temperature range. In embodiments, the strainable member is one or more of a clip, spring, silicon pad, or elastic metal sleeve. The fluidic thermal conductor is also to maintain thermal contact between the rod and cooling base, but is a flowable thermally conductive material capable of filling voids as they form between the heater rod209and cooling channel base344and extruding as the voids disappear between the heater rod209and base344, as a function of temperature. Exemplary fluidic thermal conductor materials include the heat transfer fluid that passes through the fluid conduits241,242,243, or any conventional thermal interface material TIM (thermal paste or grease compounds, gels, and the like which may further have metallic particles, such as silver, suspended in a flowable matrix).

FIGS. 3C, 3D, and 3Eillustrate schematics of various elements and techniques to maintain thermal contact between a heater rod and a surrounding chuck assembly, in accordance with embodiments.FIG. 3Cillustrates a heater rod209disposed within a blind hole in the cooling channel base344with a clip378maintaining a spring force between opposing sidewalls of the heater rod209and cooling channel base344. Such an embodiment may be utilized, for example, where the heater rod209is configured for sidewall heating.

FIG. 3Dillustrates a heater rod209disposed within a blind hole in the cooling channel base344with a fluidic thermal conductor material, or compressible thermal conductor material379. In one embodiment, the compressible thermal conductor material379comprises a silver or mercury-based amalgam. For fluidic thermal conductor embodiments, an non-compressible thermally conductive fluid flows into and out of regions of variable volume between the heater rod209and cooling channel base344(as denoted by the dashed arrows). A pressurized reservoir, for example common to all heater rods, may maintain an appropriate volume of the fluidic thermal conductor material. Alternatively, a small portion of the heat transfer fluid passed through the conduits241,242,243may surround all heater rods as maintained by the heat transfer fluid loop. For compressible thermal conductor embodiments, such as a silicone pad, or like material, rather than flow, internal elastic strain accommodates thermal expansion.

FIG. 3Eillustrates a heater rod209disposed within a blind hole in the cooling channel base344with a spring-loaded heater rod209. Such an embodiment, with a rod end spring380compressed between a rod end and a reference surface (e.g., base plate348), may be utilized where the heater rod209is configured for tip heating, for example.

FIGS. 4A and 4Bare isometric views of an underside of the chuck assembly142, in accordance with an embodiment. As shown inFIG. 4A, the base plate348and backing plate345are annular with a center opening to accommodate the heat transfer fluid plumbing to the three separate inlet/outlet fittings410, and to further accommodate a heater rod wire harness supporting the plurality of heater rods (e.g., 169 two conductor wires with a pair to each rod for fully isolated heater rod embodiments advantageous where RF filtering is needed, or 170 single conductor wires where a common heater ground is employed). As shown inFIG. 4B, pairs of fluid conduit lines411, each fluidly coupled to one of the fluid conduits141,142,143(FIG. 2) through the fittings410, drop down through the chamber bottom to the remote HTX177,178, and179(FIG. 1).

FIG. 5is a flow diagram of a method500of plasma processing, in accordance with an embodiment. The method500begins at operation502with supporting a workpiece in a plasma chamber over a top surface of a dielectric layer of a chuck assembly. The chuck assembly includes a plurality of resistive heater rods and fluid conduits, and may be the same or similar to any of the workpieces and chuck assemblies described above with respect toFIGS. 1-4B. According to one embodiment, the plurality of resistive heater rods are spatially distributed over an area of an RF powered cooling channel base disposed beneath the dielectric layer. The plurality of fluid conduits are disposed in the cooling channel base. In one embodiment, each inner fluid conduit has a separate inlet and outlet and spans separate azimuthal angles of the chuck assembly (e.g., such as the fluid conduits241,242, and243ofFIG. 2).

The workpiece supported over the chuck assembly is exposed to a plasma environment in the plasma chamber, at operation504. During plasma processing, the temperature of different zones of the chuck assembly can then be tuned by independently controlling each of a plurality of resistive heater rods to heat areas of the chuck assembly, and the plurality of fluid conduits to cool areas of the chuck assembly, based on temperature feedback at operations506and508.

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.