Cascade design showerhead for transient uniformity

An apparatus for use in semiconductor processing operations to distribute process gases across a semiconductor wafer. The apparatus may include one or more annular baffles arranged in a stack of annular baffle layers within a plenum volume of the apparatus. Each annular baffle may have a mid-diameter substantially equal to and inner diameter or outer diameter of a baffle in the annular baffle layer above it. The annular baffles may be arranged in a cascading fashion.

BACKGROUND OF THE INVENTION

Semiconductor processing tools often include components designed to distribute process gases in a relatively even manner across a semiconductor substrate or wafer. Such components are commonly referred to in the industry as “showerheads.” Showerheads typically include a faceplate that fronts a plenum volume of some sort. The faceplate may include a plurality of through-holes that allow gas in the plenum volume to flow through the faceplate and into a reaction space between the substrate and the faceplate (or between a wafer support supporting the wafer and the faceplate). The through-holes are typically arranged such that the gas distribution across the wafer results in substantially uniform wafer processing.

SUMMARY OF THE INVENTION

Details of one or more implementations of the subject matter described in this specification are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages will become apparent from the description, the drawings, and the claims. Note that the relative dimensions of the following figures may not be drawn to scale unless specifically indicated as being scaled drawings.

In some implementations, an apparatus for distributing gas across a semiconductor wafer may be provided. The apparatus may include a plenum volume having a first surface and a second surface facing the first surface. The first surface and the second surface may at least partially define the plenum volume. The apparatus may also include one or more gas inlets into the plenum volume through the first surface and a first annular baffle. The first annular baffle may be substantially centered on the one or more gas inlets and may be substantially parallel to the first surface. The first annular baffle may be located between the first surface and the second surface.

In some further implementations of the apparatus, the apparatus may further include a circular baffle. The circular baffle may be substantially centered on the one or more gas inlets, substantially parallel to the first surface, and offset from the first surface by a first distance. The first annular baffle may be offset from the circular baffle by a second distance, and the circular baffle may be between the first annular baffle and the first surface.

In some further implementations of the apparatus, the circular baffle may have a diameter, the first annular baffle may have a mid-diameter, and the mid-diameter of the first annular baffle may be substantially equal to the diameter of the circular baffle. In some such implementations, the mid-diameter of the first annular baffle may be within 10% of the diameter of the circular baffle.

In some further implementations of the apparatus, the apparatus may further include one or more circumferential surfaces spanning between the first surface and the second surface. One of the one or more circumferential surfaces may have a diameter, and the first annular baffle may have an outer diameter. The diameter of the circular baffle may be substantially half the diameter of the circumferential surface and the outer diameter of the first annular baffle may be substantially equal to half of the sum of the diameters of the circumferential surface and the circular baffle.

In some further implementations of the apparatus, the apparatus may further include a second annular baffle and a third annular baffle. The second annular baffle and the third annular baffle may both be substantially centered on the one or more gas inlets, substantially parallel to the first surface, and offset from the first annular baffle by a third distance. The second annular baffle and the third annular baffle may be located between the first annular baffle and the second surface, and the first annular baffle may be between the circular baffle and the second annular baffle and between the circular baffle and the third annular baffle.

In some such implementations, the circular baffle and the first surface may be separated by a gap of approximately 0.3″, the circular baffle and the first annular baffle may be separated by a gap of approximately 0.3″, the first annular baffle and the second annular baffle may be separated by a gap of approximately 0.3″, and the first annular baffle and the third annular baffle may be separated by a gap of approximately 0.3″.

In some further implementations of the apparatus, the second annular baffle and the third annular baffle may be substantially co-planar with one another.

In some further implementations, the first annular baffle may have an inner diameter and an outer diameter and the second annular baffle and the third annular baffle may have mid-diameters. The mid-diameter of the second annular baffle may be substantially equal to the inner diameter of the first annular baffle and the mid-diameter of the third annular baffle may be substantially equal to the outer diameter of the first annular baffle.

In some such implementations, the mid-diameter of the second annular baffle may be within 10% of the inner diameter of the first annular baffle and the mid-diameter of the third annular baffle may be within 10% of the outer diameter of the first annular baffle.

In some further implementations of the apparatus, the second surface may be defined by a first side of a faceplate with a pattern of through-holes fluidly connecting the plenum volume with a second side of the faceplate opposite the first side.

In some further implementations of the apparatus, the first annular baffle, and/or other annular baffles in the apparatus (if any), may be formed by a plurality of arc-shaped baffle segments that form an annular shape when arranged in a circle. In some such implementations, the apparatus may further include a plurality of walls, each wall substantially perpendicular to the first surface and interposed between adjoining arc-shaped baffle segments of the first annular baffle. In some further such implementations, each wall may have at least one ledge that is configured to support adjoining edges of the arc-shaped baffle segments. In some such implementations, the apparatus may also include one or more circumferential surfaces spanning between the first surface and the second surface, and each wall may be a substantially radial wall substantially extending from the one or more circumferential surfaces towards the one or more gas inlets and spanning at least between the second surface and the first annular baffle.

In some further implementations of the apparatus, the apparatus may also include a backplate that provides the first surface. In such implementations, the one or more gas inlets may be arranged to distribute gas onto the first annular baffle.

In some further implementations of the apparatus, the apparatus may further include a second annular baffle and a third annular baffle. The second annular baffle and the third annular baffle may both be substantially centered on the one or more gas inlets, substantially parallel to the first surface, and offset from the first annular baffle by a second distance. The second annular baffle and the third annular baffle may be located between the first annular baffle and the second surface, and the first annular baffle may be between the first surface and the second annular baffle and between the first surface and the third annular baffle. In some such implementations, the second annular baffle and the third annular baffle may be substantially co-planar with one another.

In some such implementations, the first annular baffle may have an inner diameter and an outer diameter, and the second annular baffle and the third annular baffle may have mid-diameters. The mid-diameter of the second annular baffle may be substantially equal to the inner diameter of the first annular baffle and the mid-diameter of the third annular baffle may be substantially equal to the outer diameter of the first annular baffle. In some such implementations, the mid-diameter of the second annular baffle may be within 10% of the inner diameter of the first annular baffle and the mid-diameter of the third annular baffle may be within 10% of the outer diameter of the first annular baffle.

In some implementations of the apparatus, the apparatus may include one or more annular baffle layers, a first annular baffle layer of which may be formed by the first annular baffle. The annular baffle layers may be spaced apart from one another in a direction substantially normal to the annular baffle layers. Each annular baffle layer may include one or more annular baffles, and each annular baffle may be substantially centered on the one or more gas inlets. Each annular baffle layer may have twice as many annular baffles in it than the proximate annular baffle layer between that annular baffle layer and the first surface. Each annular baffle may have a mid-diameter, an outer diameter, and an inner diameter, and, for each annular baffle layer other than the first annular baffle layer, the mid-diameter of each annular baffle in that annular baffle layer may be substantially equal to a different one of the inner diameter or diameters and outer diameter or diameters of the annular baffle or annular baffles in the proximate annular baffle layer between that annular baffle layer and the first surface.

In some such implementations, for each annular baffle layer other than the first annular baffle layer, the mid-diameter of each annular baffle in that annular baffle layer may be within 10% of the different one of the inner diameter or diameters and the outer diameter or diameters of the annular baffle or annular baffles in the proximate annular baffle layer between that annular baffle layer and the first surface.

In some other implementations of the apparatus, each of the annular baffle layers may be spaced apart from any proximate annular baffle layers by at least 0.05″.

In some implementations of the apparatus, one or more of the annular baffles may be formed from a plurality of arc-shaped baffle segments arranged in a substantially annular shape. In such implementations, the apparatus may further include a plurality of walls that are positioned between adjoining arc-shaped baffle segments of the annular baffles and configured to support the arc-shaped baffle segments within the plenum volume.

In some implementations, a semiconductor processing station may include such an apparatus as described above. In some further implementations, a semiconductor processing tool may include such a semiconductor processing station. In some implementations, the semiconductor processing tool may include a stepper.

The following serve as nonlimiting examples of commercially-available semiconductor processing tools in which the implementations discussed herein may be employed: VECTOR®, ALTUS®, INOVA®, GAMMA®, G3D®, G400®, GxT®, Kiyo®, Versys®, Excelan® and Flex™ family of products available from Lam Research, Inc. (Fremont, Califorinia); Centura™, Endure™ and Producer™ family of products available from Applied Materials, Inc. (Santa Clara, Califorinia); Triase+™, Telius™, Tactras™ and UNITY™ family of products from Tokyo Electron Limited (Tokyo, Japan); and the Aspen™, SUPREMA™, Nexion™ and Alpine® family of products from Mattson Technology, Inc. (Fremont, Calif.).

DETAILED DESCRIPTION

Examples of various implementations are illustrated in the accompanying drawings and described further below. It will be understood that the discussion herein is not intended to limit the claims to the specific implementations described. On the contrary, it is intended to cover alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims. In the following description, numerous implementation-specific details are set forth in order to provide a thorough understanding of the present invention. The present invention may be practiced without some or all of these implementation-specific details. In other instances, well-known process operations have not been described in detail in order not to unnecessarily obscure the present invention.

Described herein are various implementations of showerheads featuring cascading internal baffle arrangements. Conventional showerhead designs may utilize a single, circular baffle plate positioned in front of a central gas inlet and within the showerhead plenum volume to prevent gas introduced into the showerhead plenum from jetting into the faceplate and thus producing a strong mass flow bias towards the center of the faceplate during both transient and steady-state flow.

By contrast, disclosed herein are showerheads featuring a plurality of annular baffles arranged in a multi-layered, cascading configuration within the showerhead plenum volume. Such cascade showerheads provide superior gas delivery uniformity across a wafer processed using such showerheads when compared to traditional, single-baffle showerheads, especially during transient flow conditions. For many conventional semiconductor fabrication processes, gas flow through a showerhead may occur for prolonged periods of time, and while such gas flows experience transient conditions during flow ramp-up and ramp-down, the bulk of such gas flows are at steady-state conditions. Under steady-state flow conditions, gas flow distribution out of the plenum and through the faceplate should be, and is typically, dominated primarily by the geometry of the hole pattern in the faceplate.

The present inventors have realized that providing a cascade baffle arrangement within a showerhead may greatly improve gas delivery uniformity across the faceplate of the showerhead during transient flow conditions. The present inventors have also realized that such improved transient-flow gas distribution may be of particular interest in processes with short cycle times, such as atomic layer deposition (ALD) processes, where gas flows through the showerhead may be pulsed for short intervals. In such pulsed flows, transient flow conditions may dominate over steady-state flow conditions or steady-state flow conditions may never be achieved.

It is to be understood that the present inventors have also realized that cascade showerheads, as discussed herein, may also be of use in longer-flow processes where steady state conditions may dominate. For example, any initial variation in mass delivery as a function of radial position that occurs during transient flow conditions may cause the deposition during subsequent steady-state flow conditions to be skewed despite substantially uniform gas delivery across the wafer during steady-state flow conditions, e.g., causing center-heavy deposition in the overall process. Another possibility is that any initial transient mass delivery non-uniformity may result in an initial film germination with substantial non-uniform features. These non-uniform features may then be propagated through the overall film thickness when subsequent material is added. Thus, even in processes with long flow times that are dominated by steady-state flow conditions, cascade showerheads may still be used to counteract non-uniformities that may be introduced during the transient-flow portions of such processes.

FIG. 1Adepicts an isometric section view of an example of an implementation of a cascade showerhead. As can be seen inFIG. 1A, a showerhead100is depicted that features a backplate164and a showerhead body166; the showerhead body166may include a faceplate124featuring a pattern of through-holes130that communicate between a first side126and a second side128of the faceplate124. A first surface104, e.g., such as provided by the backplate164, and a second surface106, e.g., such as provided by the first side126of the faceplate124, may, in conjunction with a circumferential surface or surfaces108, e.g., such as provided by an inner surface or surfaces of the showerhead body166, substantially define a plenum volume102(seeFIG. 1Bfor further indication of the plenum volume102). The plenum volume102may be supplied with a process gas, e.g., a reactant or purge gas, via a gas inlet or inlets110. The gas inlet(s)110may be substantially centered on the hole pattern of through holes130and may be connected to a process gas supply or supplies.

A number of baffle structures may be included in the plenum volume102to provide a cascading baffle arrangement. Reference also may be made below to distances and dimensions that are indicated inFIG. 1B, which depicts a side section view of the example cascade showerhead fromFIG. 1A. These baffle structures may include a circular baffle112that is positioned in front of, and substantially centered on, the gas inlet110. The circular baffle112may be offset from the first surface104by a first distance114(seeFIG. 1B). A first annular baffle118may be positioned below the circular baffle112and substantially centered on the circular baffle112; the first annular baffle118may be offset from the circular baffle112by a second distance116.

In the pictured implementation, a second annular baffle120and a third annular baffle122are also depicted. The second annular baffle120and the third annular baffle122may be co-planar with one another and offset from the first annular baffle118by a third distance117.

The circular baffle112may have a diameter140, and each annular baffle may be generally described as having an outer diameter, an inner diameter, and a mid-diameter halfway between the outer diameter and the inner diameter. Thus, for example, the first annular baffle118may have an outer diameter146, an inner diameter144, and a mid-diameter142; the second annular baffle120may have an outer diameter152, an inner diameter150, and a mid-diameter148; and the third annular baffle122may have an outer diameter158, an inner diameter156, and a mid-diameter154. Additionally, the circumferential surface108may have a diameter160; in cases where the circumferential surface has multiple actual diameters, the diameter160may refer to the outermost such diameter.

As can be seen inFIGS. 1A and 1B, each annular baffle is sized such that its mid-diameter is substantially equal to either the outer diameter or inner diameter of the annular baffle above it (or, in the case of the first annular baffle, such that the mid-diameter142is substantially equal to the diameter140). In some implementations, the mid-diameters of the annular baffles may not be exactly equal to the outer diameter, inner diameter, or diameter of the baffle above, but may be substantially equal, e.g., within 10% of such values.

With respect to the implementation shown inFIG. 1A, the diameter140may be 10″, the outer diameter146may be 14.5″, the inner diameter144may be 5.5″, the outer diameter152may be 7″, the inner diameter150may be 4″, the outer diameter158may be 18″, and the inner diameter156may be 11″. Accordingly the mid-diameter142may be 10″, the mid-diameter148may be 5.5″, and the mid-diameter154may be 14.5″. In the implementation shown, the diameter160may be 20″. Other implementations may feature annular baffles, circular baffles, and circumferential surfaces with other dimensions and aspect ratios.

The first distance114, the second distance116, and the third distance117may be sized such that flow resistance due to such distances between neighboring and overlapping baffles does not contribute significantly to overall flow resistance of the baffle stack. Such distances also may, for example, be sized to be substantially equal to one another so that any flow resistance effects that are generated due to such distances are similar in magnitude between baffle pairs. In the implementation shown, for example, the first distance114, the second distance116, and the third distance117are 0.3″. In other implementations, however, the inter-baffle spacing may be different, e.g., so as to tune the flow resistances in the baffle overlap areas. In some implementations, these distances may be limited by the plenum volume102. For example, in retrofit situations, e.g., where the showerhead must be compatible with pre-existing equipment that limits the overall thickness of the showerhead, there may be an upper limit on these distances. This upper limit may decrease depending on the number of annular baffle layers that are used. In some implementations, the inter-baffle spacing may be set to a value larger than 0.05″. In some other implementations, the inter-baffle spacing may be set to a value larger than 0.2″.

FIG. 1Cdepicts the side section view of the example cascade showerhead fromFIG. 1Bwith arrows showing nominal gas flow directions within the showerhead. As can be seen in this simplified representation, as gas flows over an edge of a baffle and onto the baffle below the edge, a portion of the gas flows radially outwards, and the remaining portion of the gas flows radially inwards. At each such transition, the gas flow is further subdivided, resulting in a more uniform gas distribution at the faceplate124, i.e., gas reaches various radial locations at the top of the faceplate at nearly equal times.

FIG. 1Ddepicts an isometric exploded view of the example cascade showerhead ofFIG. 1A. Various internal features of the showerhead100may be seen in more detail in this view. The backplate164is shown, as is a seal168that may be used to provide a hermetic seal between the backplate164and the showerhead body166. A plurality of screws or other fasteners may be used to clamp the backplate164to the showerhead body166. In other implementations, such an assembly may be replaced by a welded or bonded assembly. The backplate164and the showerhead body166may be made from a variety of materials compatible with a semiconductor processing environment, e.g., aluminum alloy, ceramics, etc. The backplate164and the showerhead body166need not be made from the same material.

Visible inFIG. 1Dis the circular baffle112which, in this implementation, is fastened to a support structure in the showerhead body166via three mounting screws. Also visible inFIG. 1Dare the first annular baffle118, the second annular baffle120, and the third annular baffle122. In this implementation, each such annular baffle is formed by arranging a plurality of arc-shaped baffle segments132in a circular pattern. The baffle segments132may be arranged such that their adjoining edges138are separated by a small gap. Each baffle segment132may be supported by ledges136in walls134that are interposed between adjoining edges138.FIG. 1Edepicts a detail view of the portion ofFIG. 1Dindicated by a dotted rectangle; the ledges136and through-holes130in the faceplate124may be more clearly visible in the detail view.

The ledges136may be provided at different heights in the walls134to allow the annular baffles to be located at different offsets from each other, if needed. The baffle segments132may be brazed, bonded, or otherwise held in place with respect to the overall assembly to prevent the baffle segments132from sliding free of the ledges136.

It is to be understood that reference to an “annular baffle” in this disclosure encompasses not only “pure” annular structures, e.g., unbroken annular shapes, but also annular structures that are built up from multiple non-annular, smaller structures, e.g., the baffle segments132. It is also to be understood that the annular baffles and circular baffles described herein may also include other features, e.g., mounting holes, that do not detract from their annularity or circularity. For example, instead of supporting each annular baffle with an array of walls134, a plurality of standoffs, screws, and through-holes in the baffles may be used to space the baffles apart from one another in a configuration similar to that discussed above.

It is to be understood that some implementations of a cascade showerhead may forgo a circular baffle within the plenum volume. For example, rather than a centrally-located gas inlet or inlets, a cascade showerhead may introduce process gas into the plenum volume via a circular pattern of gas inlets that are located in an annular zone corresponding to the mid-diameter of the first annular baffle.

FIG. 2Adepicts an isometric section view of an example of an implementation of a cascade showerhead without a circular baffle. Depicted inFIG. 2Ais a showerhead200that is similar in many respects to the showerhead100ofFIG. 1A. For example, the showerhead200includes a first annular baffle218, a second annular baffle220, and a third annular baffle222arranged in substantially the same manner as the first annular baffle118, the second annular baffle120, and the third annular baffle122ofFIG. 1A. A faceplate224with through-holes230connecting a first side226and a second side228is depicted as well. The faceplate224may form part of a showerhead body266, which may be connected with a backplate264. A seal268may be interposed between the showerhead body266and the backplate264. A plenum volume202(seeFIG. 2Bfor further indication of the plenum volume202) may be defined by a first surface204, e.g., provided by the backplate264, a second surface206, e.g., provided by the faceplate224, and a circumferential surface or surfaces208.

Notably absent inFIG. 2Ais a circular baffle, e.g., such as the circular baffle112ofFIG. 1A. Instead, the backplate264may include a recessed area capped by an end cap265. The recessed area may form a second plenum volume203that is fluidly connected with the plenum volume202via a circular pattern of gas inlets210. The second plenum volume203may be fed by a central gas feed or feeds211. Gas that is flowed into the second plenum volume203may flow from the second plenum volume203and through the gas inlets210into the plenum volume202in a substantially evenly-distributed manner due to the radial symmetry provided by the circular pattern of gas inlets210. The gas inlets210may be positioned so as to lie above the mid-diameter of the first annular baffle218. Thus, the second plenum volume203and circular pattern of gas inlets210may serve a similar function as the circular baffle112ofFIG. 1A. In effect, the portion of the backplate264that separates the second plenum volume203from the plenum volume202may act in a manner similar to a circular baffle, although instead of being located within the plenum volume, this portion acts as part of the boundary of the plenum volume202. It is to be understood that the second plenum volume and circular pattern of gas inlets may be provided using geometries other than that shown inFIGS. 2A through 2D.

FIG. 2Bdepicts a side section view of the example cascade showerhead fromFIG. 2A. This view may more clearly show the second plenum volume203and the plenum volume202.

FIG. 2Cdepicts an isometric exploded view of the example cascade showerhead ofFIG. 2A. As can be seen, this implementation also features a continuous first annular baffle218rather than a piecemeal first annular baffle, such as is depicted inFIG. 1D. As is perhaps more apparent fromFIG. 2D, which depicts a detail view of the portion ofFIG. 2Cindicated by a dotted rectangle, the use of a continuous first annular baffle218may allow for a different support structure configuration. For example, the first annular baffle218may rest in recessed ledges236along the top surface of walls234, whereas baffle segments232may be supported along edges238by ledges236in the sides of the walls234.

Thus, cascade arrangements of annular baffles may be used with showerheads featuring a circular baffle as well as with showerheads that do not include a circular baffle but that do provide for gas inlets arrayed in a substantially circular fashion at the mid-diameter of the first annular baffle.

As mentioned earlier in this disclosure, cascade showerheads such as those described in this disclosure may provide for greatly improved performance over conventional showerheads featuring a single, circular baffle and no cascading arrangement of annular baffles.

FIGS. 3A through 3Ddepict various graphs that demonstrate the differences in performance between cascade showerhead designs as discussed herein and more conventional showerheads, e.g., single-baffle, circular plate showerheads.FIG. 3Adepicts a graph showing reactant mass delivery rate to a wafer at various times as a function of distance from wafer center for an example showerhead with a single, circular baffle.FIG. 3Bdepicts a graph showing reactant mass delivery rate to a wafer at various times as a function of distance from wafer center for an example showerhead with a single, circular baffle that is designed for use with wafers approximately 50% larger in diameter than the wafers for which the example showerhead ofFIG. 3Ais designed.FIG. 3Cdepicts a graph showing reactant mass delivery rate to a wafer at various times as a function of distance from wafer center for an example showerhead with a cascade showerhead design.FIG. 3Ddepicts a graph showing reactant mass delivery rate to a wafer at various times as a function of distance from wafer center for the example cascade showerhead ofFIG. 3Cwith 2 times the flow rate of the flow rate ofFIG. 3C.FIGS. 3A through 3Dhave all been scaled in the Y-axis by the same amount. The gas flows represented byFIGS. 3A through 3Dall include 5 s of reactant flow followed by 5 s of purge gas flow, although the plots only show the amount of reactant mass that is delivered to the wafer. The gas flow rates represented inFIGS. 3B and 3Care approximately 2.25 times the gas flow rate represented inFIG. 3A, whereas the gas flow rate represented inFIG. 3Dis approximately twice that represented inFIG. 3C.

With reference toFIGS. 3A and 3B, it can be seen that there is considerable variation in the rate of reactant mass-delivery across the surface of a wafer by the showerheads represented inFIGS. 3A and 3B. As noted above, the showerheads represented byFIGS. 3A and 3Bboth feature a single, circular baffle plate within the plenum volume and do not include a cascade arrangement of annular baffles within the plenum volume. Furthermore, the variation in center-to-edge mass-delivery rate across the wafer increases as the showerhead ofFIG. 3Ais increased to accommodate an increase in diameter of the wafer by 50% and the flow rate is increased to 2.25× that ofFIG. 3Ato arrive at the showerhead represented inFIG. 3B. This mass-delivery rate variation is exhibited during both transient flow (t=1 s) and during more developed flow (t=9 s). It is to be understood that the decrease in reactant mass-delivery rate at t=9 s is due to the fact that the reactant flow into the showerhead is stopped at t=5 s and that the residual reactant in the plenum volume is then bled off in continuously-decreasing amounts during the subsequent purge gas flow.

By contrast, with reference toFIGS. 3C and 3D, it can be seen that utilizing a cascade showerhead, e.g., similar to the cascade showerhead ofFIG. 1A, for gas delivery may greatly reduce the variation in mass-delivery rate of the process gas to the wafer with respect to radial position. It is to be understood thatFIGS. 3B, 3C, and 3Drepresent scenarios with identical wafer sizes, i.e., 50% larger in diameter than the wafer size represented inFIG. 3A. As can be seen, the peak-to-trough variation in mass-delivery rate across the wafer at t=1 s inFIG. 3Cis less than 50% of the variation in mass-delivery rate across the wafer at t=1 s inFIG. 3B. Furthermore, such decreases in mass-delivery rate variation are exhibited by the cascade showerhead implementations ofFIGS. 3C and 3Dat all five instances in time that are plotted. Due to the increased uniformity of mass delivery rate across the wafer with the larger wafer size, cascade showerheads may be particularly well-suited for use in newer, 450 mm wafer processes, although cascade showerheads as discussed herein may, of course, also be well-suited for use with processes for other sizes of wafer, both larger and smaller than 450 mm.

The cascade showerhead represented inFIG. 3Calso demonstrates increased mass-delivery rate uniformity at higher flow rates. For example,FIG. 3Ddemonstrates the mass-delivery rate to the wafer as a function of distance from wafer center of the showerhead ofFIG. 3Cfor a gas flow that is 2 times higher than that represented inFIG. 3C. As is evident, the mass-delivery rate to the wafer remains relatively uniform across the wafer diameter for all times with the cascade showerhead, as compared with the non-cascade, single circular baffle showerhead, even at increased flow conditions.

FIG. 4Adepicts a graph showing the total reactant mass delivered to a wafer after a 5 second reactant flow for various showerhead types as a function of distance from wafer center.FIG. 4Bdepicts a graph showing the total reactant mass delivered to a wafer after a 5 second purge flow following the 5 second reactant flow ofFIG. 4Afor various showerhead types as a function of distance from wafer center. It is to be understood that whileFIG. 4B's mass-delivery values reflect the total mass delivery as a function of radial wafer position that occurs during a 5 s purge flow following a 5 s reactant flow, the total mass delivery shown forFIG. 4Bdoes not include reactant mass delivered during the 5 s reactant flow ofFIG. 4A.

WhereasFIGS. 3A through 3Drepresent instantaneous mass-delivery values as a function of wafer radial position,FIGS. 4A and 4Brepresent integrated mass-delivery values as a function of wafer radial position. Since integrated mass-delivery values may serve as a predictor of wafer feature uniformity, such plots may provide insight as to process uniformity between different types of showerheads.

InFIGS. 4A and 4B, three different data plots are shown (4-5 data points for each plot are provided, as well as a 4-th order polynomial fit for each data plot). Case A represents the integrated mass-delivery for the showerhead represented inFIG. 3Aand case B represents the integrated mass-delivery for the showerhead represented inFIG. 3B, i.e., non-cascade showerheads. Case C represents the integrated mass-delivery for the showerhead represented inFIG. 3C, i.e., a cascade showerhead. As can be seen, the cross-wafer uniformity of the integrated mass-delivery for the cascade showerhead is nearly 3 times better than that exhibited by the non-cascade showerhead ofFIG. 3Aand nearly 5 to 6 times better than that exhibited by the non-cascade showerhead ofFIG. 3B.

It is to be understood that while the examples shown inFIGS. 1A through 1Efeature planar baffles, e.g., flat disks or rings, the circular baffle and annular baffles used in a cascade showerhead according to this disclosure may have non-planar cross-sections. For example, some or all of the circular baffle (if present) and/or annular baffles may have cross-sections with sloped or curved portions. Additionally, the circular baffle (if present) and/or annular baffles may not be completely impermeable to gas flow, i.e., a pattern of through-holes may be included in a circular baffle and/or annular baffle to allow some of the gas flowing across the baffle to pass through the baffle without necessarily flowing past the inner or outer edge of the annular baffle or the outer edge of the circular baffle. The amount of such through-baffle gas flow may be modulated through regulating the size, number, and positioning of such through-holes.

FIG. 5depicts a conceptual side section view of an example of another implementation of a cascade showerhead. In this implementation, a circular baffle512is provided that has a slight conical shape. A first annular baffle518, a second annular baffle520, and a third annular baffle522are provided where each annular baffle slopes downward toward the inner diameter and the outer diameter of that annular baffle from the mid-diameter of that annular baffle. Such circular baffles and annular baffles are not “planar” since they feature non-planar cross-sections. However, such circular baffles and annular baffles may still, for convenience, be referred to as if they were planar in nature. For example, the first annular baffle518may still generally be planar since the vertical thickness of the first annular baffle518is much less than the outer diameter of the first annular baffle518. Additionally, because the annular baffles may be substantially axially symmetric, the annular baffles may be associated with reference planes that are perpendicular to the symmetry axes of the annular baffles. Thus, for example, when a non-planar baffle is said to be “parallel” to a surface, it is to be understood that such a reference may indicate that a reference plane perpendicular to a symmetry axis of the non-planar baffle is parallel to that surface.

It is to be further understood that a cascade showerhead may include more or fewer annular baffles than are shown inFIGS. 1A through 1E. For example, in some implementations, a cascade showerhead may include only one annular baffle. In some other implementations, a cascade showerhead may include six, fourteen, or more annular baffles. Generally speaking, the number N of annular baffles in a cascade showerhead correlates to a geometric series determined by the number n of annular baffle layers, where the geometric series has a sum determined by:
N=2n−1

FIG. 6depicts a conceptual side section view of an example of another implementation of a cascade showerhead. InFIG. 6, a cascade showerhead600is depicted that has four annular baffle layers662(a circular baffle612is not included in an annular baffle layer in this convention, although alternative conventions may do so with appropriate modification of the above geometric series), each of which may have one or more annular baffles670. Thus, a plenum volume602may include an annular baffle layer662A with an annular baffle670A; an annular baffle layer662B with annular baffles670B and670C; an annular baffle layer662C with annular baffles670D,670E,670F, and670G; and an annular baffle layer662D with annular baffles670H,670I,670J,670K,670L,670M,670N, and670O. The plenum volume may be bounded by a first surface604and a second surface606; the second surface606may be provided by a faceplate with a pattern of through-holes630fluidly connecting the plenum volume602with a wafer reaction space below the cascade showerhead600. A gas inlet610may supply gas to the plenum volume602.

In theory, an ideal cascade showerhead may include an infinite number of annular baffle layers, although, in practice, constraints such as packaging space, material thickness, and other factors may impose a practical limit on the number of annular baffle layers used. For example, the number of annular baffle layers, the thicknesses of the circular baffles and the annular baffles, and the thickness of the plenum volume may result in inter-baffle gaps that are small enough that the flow resistances across the baffles in regions of the baffles that overlap as compared with the flow resistances across the regions of the baffles where there is no such overlap may vary by an amount sufficient to cause unacceptable process non-uniformity downstream.

For example, if one assumes that the annular baffle layer(s) and the circular baffle all have the same thickness (tb), that each annular or circular baffle is spaced apart from the surface above it by the same distance (toffset), that the bottom-most annular baffle layer is spaced apart from the faceplate by tbf_offset, and that the plenum has a thickness of tp, then the maximum number of annular baffle layers (L) (not including the circular baffle) that may still fit within these constraints may be easily determined by:

This relationship may, of course, be modified depending on the specific design constraints used. For example, different thicknesses of baffle, different inter-baffle spacing, and other sources of variation may require that the above relationship be modified.

As mentioned previously, a cascade showerhead may be installed in a semiconductor process chamber;FIG. 7depicts a conceptual side section view of a cascade showerhead installed in a semiconductor process chamber.

A process chamber701may include a cascade showerhead700that is mounted to the top of a chamber housing705. In some implementations, an adapter plate707may be interposed between the cascade showerhead700and the chamber housing705. A wafer support709may support a semiconductor wafer713within the process chamber701and beneath the cascade showerhead700. A microvolume may be formed between the wafer support709and the cascade showerhead700. The microvolume may serve as a wafer reaction area and may help concentrate and retain process gases in the vicinity of the semiconductor wafer713during processing. The wafer support709may be configured to move up and down to facilitate wafer load and unload operations. In other implementations, the cascade showerhead may be suspended from a lid (not shown) of the process chamber701by a stem and may not itself form part of the “lid” of the process chamber701. In such implementations, the cascade showerhead700may be configured to move up and down to facilitate wafer load/unload.

In some implementations, one or more such process chambers may be provided as process stations in a multi-station semiconductor processing tool. In some implementations, a single process chamber may include multiple processing stations, some or all of which may have their own cascade showerhead assemblies.

FIG. 8shows a schematic view of a multi-station processing tool,800, with an inbound load lock802and an outbound load lock804. A robot806, at atmospheric pressure, is configured to move wafers from a cassette loaded through a pod808into inbound load lock802via an atmospheric port810. A wafer may be placed by the robot806on a pedestal812in the inbound load lock802, the atmospheric port810may be closed, and the load lock may then be pumped down. If the inbound load lock802includes a remote plasma source, the wafer may be exposed to a remote plasma treatment in the load lock prior to being introduced into a processing chamber814. Further, the wafer also may be heated in the inbound load lock802, for example, to remove moisture and adsorbed gases. Next, a chamber transport port816to processing chamber814may be opened, and another robot (not shown) may place the wafer into the processing chamber814on a pedestal of a first station shown in the reactor for processing. While the implementation depicted inFIG. 8includes load locks, it will be appreciated that, in some implementations, direct entry of a wafer into a process station may be provided.

The depicted processing chamber814includes four process stations, numbered from 1 to 4 in the implementation shown inFIG. 8. Each station may have a heated or unheated pedestal (shown at818for station 1), and gas line inlets. It will be appreciated that in some implementations, each process station may have different or multiple purposes. For example, in some implementations, a process station may be switchable between an ALD and plasma-enhanced chemical vapor deposition (PECVD) process mode. Additionally or alternatively, in some implementations, processing chamber814may include one or more matched pairs of ALD and PECVD process stations. While the depicted processing chamber814comprises four stations, it will be understood that a processing chamber according to the present disclosure may have any suitable number of stations. For example, in some implementations, a processing chamber may have five or more stations, while in other implementations a processing chamber may have three or fewer stations.

Each station may include a separate showerhead assembly that delivers process gases to a wafer at the associated station. In some implementations, some or all of these showerheads may utilize a cascade showerhead as described herein. For example, if a station provides ALD processing, or other processing that may benefit from use of the equipment described herein, to a wafer, the showerhead for that station may be a cascade showerhead as discussed herein.

FIG. 8also depicts a wafer handling system890for transferring wafers within processing chamber814. In some implementations, wafer handling system890may transfer wafers between various process stations and/or between a process station and a load lock. It will be appreciated that any suitable wafer handling system may be employed. Non-limiting examples include wafer carousels and wafer handling robots.FIG. 8also depicts a system controller850employed to control process conditions and hardware states of process tool800. System controller850may include one or more memory devices856, one or more mass storage devices854, and one or more processors852. Processor852may include a CPU or computer, analog and/or digital input/output connections, stepper motor controller boards, etc.

In some implementations, system controller850controls all of the activities of process tool800. System controller850executes system control software858stored in mass storage device854, loaded into memory device856, and executed on processor852. System control software858may include instructions for controlling the timing, mixture of gases, chamber and/or station pressure, chamber and/or station temperature, wafer temperature, target power levels, RF power levels, substrate pedestal, chuck and/or susceptor position, and other parameters of a particular process performed by process tool800. System control software858may be configured in any suitable way. For example, various process tool component subroutines or control objects may be written to control operation of the process tool components necessary to carry out various process tool processes. System control software858may be coded in any suitable computer readable programming language.

In some implementations, system control software858may include input/output control (IOC) sequencing instructions for controlling the various parameters described above. For example, each phase of an ALD process may include one or more instructions for execution by system controller850. The instructions for setting process conditions for an ALD process phase may be included in a corresponding ALD recipe phase. In some implementations, multiple showerheads, if present, may be controlled independently to allow for separate, parallel process operations to be performed.

Other computer software and/or programs stored on mass storage device854and/or memory device856associated with system controller850may be employed in some implementations. Examples of programs or sections of programs for this purpose include a substrate positioning program, a process gas control program, a pressure control program, a heater control program, and a plasma control program.

A substrate positioning program may include program code for process tool components that are used to load the substrate onto pedestal818and to control the spacing between the substrate and other parts of process tool800.

A process gas control program may include code for controlling gas composition and flow rates and optionally for flowing gas into one or more process stations prior to deposition in order to stabilize the pressure in the process station. A pressure control program may include code for controlling the pressure in the process station by regulating, for example, a throttle valve in the exhaust system of the process station or a gas flow into the process station.

A heater control program may include code for controlling the current to a heating unit that is used to heat the substrate. Alternatively, the heater control program may control delivery of a heat transfer gas (such as helium) to the substrate.

A plasma control program may include code for setting RF power levels applied to the process electrodes in one or more process stations. The plasma control program may, in appropriate situations, include code for controlling an external plasma generator and/or valving required to supply process gas to a plasma generator or radical source volume.

In some implementations, there may be a user interface associated with system controller850. The user interface may include a display screen, graphical software displays of the apparatus and/or process conditions, and user input devices such as pointing devices, keyboards, touch screens, microphones, etc.

In some implementations, parameters adjusted by system controller850may relate to process conditions. Non-limiting examples include process gas composition and flow rates, temperature, pressure, plasma conditions (such as RF bias power levels), pressure, temperature, etc. These parameters may be provided to the user in the form of a recipe, which may be entered utilizing the user interface.

Signals for monitoring the process may be provided by analog and/or digital input connections of system controller850from various process tool sensors. The signals for controlling the process may be output on the analog and digital output connections of process tool800. Non-limiting examples of process tool sensors that may be monitored include mass flow controllers, pressure sensors (such as manometers), thermocouples, etc. Appropriately-programmed feedback and control algorithms may be used with data from these sensors to maintain process conditions.

The system controller850may provide program instructions for implementing various semiconductor fabrication processes. The program instructions may control a variety of process parameters, such as DC power level, RF bias power level, pressure, temperature, etc. The instructions may control the parameters to operate in-situ deposition of film stacks.

The system controller may typically include one or more memory devices and one or more processors configured to execute the instructions so that the apparatus will perform a method in accordance with the present invention. Machine-readable media containing instructions for controlling process operations in accordance with the present invention may be coupled to the system controller.

While the semiconductor processing tool shown inFIG. 8depicts a single, four-station process chamber, or module, other implementations of semiconductor processing tools may include multiple modules, each with a single station or multiple stations. Such modules may be interconnected with one another and/or arranged about one or more transfer chambers that may facilitate movement of wafers between the modules. One or more of the stations provided by such multi-module semiconductor processing tools may be equipped with cascade showerheads, as described herein, as needed.

Generally speaking, a cascade showerhead as described herein may be mounted in a reaction chamber above a wafer support configured to support one or more semiconductor wafers. The cascade showerhead may, for example, also serve as a lid, or part of a lid, for the reaction chamber. In other implementations, as discussed above, the cascade showerhead may be a “chandelier” type showerhead and be suspended from the lid of the reaction chamber by a stem or other support structure.

Another aspect of the invention is an apparatus configured to accomplish the methods described herein. A suitable apparatus includes hardware for accomplishing the process operations and a system controller having instructions for controlling process operations in accordance with the present invention. The system controller may be configured, for example, to control gas flows of the first process gas, the second process gas, and the precursor gas into the remote plasma source. The system controller may also control the RF output of the RF coils, and may control the flow rate and temperature of coolant circulated through any cooling channels in the system based on temperatures measured in the faceplate assembly using the temperature probes. The system controller will typically include one or more memory devices and one or more processors configured to execute the instructions so that the apparatus will perform a method in accordance with the present invention. Machine-readable media containing instructions for controlling process operations in accordance with the present invention may be communicatively coupled to the system controller.

It will be understood that unless features in any of the above-described implementations are expressly identified as incompatible with one another or the surrounding context implies that they are mutually exclusive and not readily combinable in a complementary and/or supportive sense, the totality of this disclosure contemplates and envisions that specific features of those implementations can be selectively combined to provide one or more comprehensive, but slightly different, technical solutions. It will therefore be further appreciated that the above description has been given by way of example only and that modifications in detail may be made within the scope of the disclosure.