WO2007076195A2 - Small volume symmetric flow single wafer ald apparatus - Google Patents

Abstract

An ALD reactor chamber contains a vertically moveable heater-susceptor having an attached annular attached flow ring conduit at its perimeter, which conduit has an external surface at its edge that isolates the outer space of the reactor above a wafer and below the wafer to the bottom of the flow ring when the heater-susceptor is in its process position. When the susceptor is in the process position, the outer edge of the flow ring is placed in proximity to an annular ring attached to a Hd of the reactor and together the ring and conduit form a tongue-in-groove (TIG) configuration. In some cases, the TIG design may have a staircase contour (SC), thereby limiting diffusion-backflow of downstream gases to the outer space of the reactor.

Description

SMALL VOLUME SYMMETRIC FLOW SINGLE WAFER ALD APPARATUS

Inventors:

Jeremie J. Dalton, 1722 Wayne Cir., San Jose, CA 95131, Citizen of USA

Martin Daulesberg, Kackertstasse 15-17 - 52072 Aachen, Germany, Citizen of Germany

Kenneth Doering, 5939 Southridge Ct., San Jose, CA 95138, Citizen of USA

M. Ziaul Karim, 2820 McAnn Ct., San Jose, CA 95121, Citizen of USA

Thomas E. Seidel, 965 E. El Camino Real #933, Sunnyvale, CA 94087, Citizen of USA

Gerhard K. Strauch, Kackertstasse 15-17 - 52072 Aachen, Germany, Citizen of Germany

Related Applications

[0001] This application is a nonprovisional of and claims priority to U.S. provisional patent application 60/820,042, filed 21 July 2006; claims priority to German patent application DE 102005056326.6, filed 22 Nov 2005; is also related to U.S. patent application 11/224,767, filed 12 Sep 2005, which is a non-provisional of, claims priority to and incorporates by reference U.S. provisional patent application 60/609,598, filed 13

Sep 2004; each of which is assigned to a common owner of the present invention and is incorporated herein by reference.

Field of the Invention

[0002] The present invention relates to a small volume symmetric-flow Atomic Layer

Deposition (ALD) apparatus that improves ALD cycle times by minimizing the reaction space volume while maintaining symmetry of gas flow related to off-axis wafer transport slot valves and/or off-axis downstream pumping conduits.

Background

[0003] ALD reactors may have a variety of design configurations. Conventional single wafer ALD reactor configurations include a cross-flow design, wherein sequential chemical precursor exposures (pulses) and removals (purges) of injected gases flow substantially horizontally across the wafer surface and are pumped out in the horizontal direction as well. Wafer transport may be carried out in the same horizontal plane, at right angles to the gas flow direction. The term "traveling wave" has been used to refer to the movement of the time-dependent precursor pulses from injection orifϊce(s) to pump orifice(s). See, e.g., T. Suntola, "Atomic Layer Epitaxy," in Handbook of Crystal Growth 3, Huerle ed., Ch. 14, pp. 601 et seq. (1994).

[0004] In so-called "pure" ALD processes, the first precursor is completely removed from the reaction space before the second precursor is introduced. See, S.M. Bedair, "Atomic layer epitaxy deposition processes," J. Vac. Sci. Tech. B12 (1), Jan / Feb, pp. 179 et seq. (1994). However, as wafers scale to larger sizes, e.g., 300 mm and 450 mm, and as cycle times are pushed to lower limits, undesirable parasitic chemical vapor deposition (CVD) takes place at the edge of the wafer in the direction of the traveling wave. The parasitic CVD is due to undesirable chemical reactions from the simultaneous co-existence, in time and space, of the remnant precursor in the dispersion trailing tail of the first precursor and the onset of the second precursor. To avoid this parasitic CVD, precursor removal is used between pulses. Often, long removal times are needed. In the horizontal single wafer architecture, to avoid this parasitic CVD the concentration of the trailing edge of the first precursor pulse must be reduced to trace levels, for example an arbitrary figure of less than approximately 1% of the first precursor's peak value. See, e.g., U.S. patent 6,015,590 to Suntola.

[0005] Since ALD is a self-limiting process, it may be argued that the direction and symmetry of flow of the precursors does not matter because if enough time is used for the precursor removal periods - commonly referred to as the "purge period" - there will be no significant CVD. However, in the pursuit of high deposition rates (thickness/unit time or low cycle times), as purge times are pushed to the lowest possible times for value in commercial manufacturing, the symmetry of the flow becomes important. [0006] Alternative single wafer designs use injected precursor gases from axi-centric and axi-symmetric vertical gas distribution modules (GDM) (e.g., using an axi-centric orifice(s) or showerhead) and in this case the dispersion tails are limited to overlap at the radius of the wafer (1/2 the value of the diameter), advantageously - in the case of high back diffusion - and allows for more rapid pumping (pumping at all azmuthal angles) and removal of unused and by-product gases.

[0007] Today many single wafer commercial ALD reactors use vertical precursor injection, with radial flow followed by vertical pumping. Figure 1 illustrates such an ALD reactor system 10 in which two precursors (A and B) are injected, via valves 12a and 12b, vertically into a reaction chamber 14. Gasses are extracted from chamber 14 by pump 16. As shown in the illustration, gas flow within the chamber 12 is initially vertical, e.g., from a showerhead or other injector 18 positioned axi-symmetically above a wafer 20, which is typically supported by a susceptor 22, and then radially outwards from the center of the wafer 20 to its edges. Gases are then pumped out of the chamber 14 in a vertical flow, giving a combined radial/vertical flow pumping. Ideally, this configuration provides symmetry of flow at the wafer's edges.

[0008] As illustrated in Figure 2, in commercial single wafer systems the wafers to be processed are introduced into the reactors by a robotic central handler 24. These wafer transport mechanisms are also commonly used in CVD apparatus serving the silicon chip making industry. The wafers 26 are introduced, typically through a rectangular slot valve 28, at a particular azimuthal angle and range (G₁ and AG₁) that is on the radius or outer surface of the reaction chamber 14 in proximity to the walls of the reactor. This slot valve 28 and its rectangular passage into the chamber 14 breaks the symmetry of radial gas flow, as shown schematically in the illustration.

[0009] Furthermore, the downstream exhaust pump 16 is commonly set at an azimuthal angle and range, θ₂ and Δθ₂, where θ₂ is in general not necessarily the same as θi. While this arrangement accommodates on-axis mechanical drive support hardware to permit movement of a susceptor in the vertical direction, together these asymmetries can lead to the formation of recirculation pockets, stagnation zones, and /or pumping azimuthal non- uniformities. For example, if the residual precursor from the first precursor's flow are pumped or swept in a non-uniform azimutal flow from the wafer, an additional mechanism is present for parasitic CVD to occur non-symmetrically or non-uniformly towards one azmuthal direction of the wafer. In this case, the onset of parasitic CVD occurs non-symmetrically and prematurely over particular azimuthal directions or angle(s) due to recirculations, stagnations and/or pumping effects. [00010] The desirability of a small reaction space volume (the space above the wafer between the wafer and the precursor injection component (e.g., a showerhead)), is known in the art. See, e.g., M. Ritala and M. Leskela, "Atomic Layer Deposition" in Handbook of Thin Film Materials, H. Nalwa, ed., vol.l, Ch. 2, pp.103 et seq. (2002). The ALD reaction space volume should be minimized for reduced precursor removal time, reduced residence time (PV/F, where P is the pressure and V the volume of the reaction space and F is the flow through same) and therefore reduced ALD cycle time. With a vertically movable susceptor design (see, e.g., U.S. Patent 5,855,675 of Doering, et. al., assigned to the assignee of the present invention and incorporated herein by reference), the distance between the wafer plane and the gas distribution orifices (showerhead) in the reactor lid may be optimized for uniformity of flow and residence time; that is, the volume of the reaction space may be minimized within the constraint of locally uniform exposures. Additionally, the reaction space may include the annulus region between the susceptor edge and the reactor's upper inner wall, which is parasitic reaction space volume.

[00011] While the broken flow symmetry due to azimuthal placement of the wafer slot valve and wafer passage was substantially restored by using a vertically movable susceptor/heater configured so that when the wafer and its heater/susceptor were in the process position the wafer was above the wafer slot valve, this approach was still limited with respect to fine control of symmetric flow. For example, downstream gases may still form stagnation regions and eddies in the pocket associated with the wafer slot valve below the wafer plane when the susceptor is in its process position. Hence, what is needed is a reactor design that provides a minimal reaction space volume and improved symmetric flow, while maintaining the ability to work with conventional wafer (slot) transport mechanisms. The current invention provides a solution to these requirements, resulting in a small, confined volume with symmetric flow resulting in a high throughput, high performance (HP) single wafer reactor. SUMMARY OF THE INVENTION

[00012] In one embodiment of the invention, a reaction chamber apparatus includes a vertically movable heater-susceptor, where the heater-susceptor is connected to an annular attached flow ring that performs as a gas conduit, with an outlet port of the flow ring extending below the bottom of a wafer transport slot valve when the susceptor is in the process (higher) position.

[00013] A further embodiment of the invention provides a reaction chamber apparatus containing a heater-susceptor connected to an annular attached flow ring conduit at the perimeter of the susceptor, the conduit having an external surface at its edge that isolates the outer space of the reactor above the wafer and below the wafer to the bottom of the flow ring from the confined reaction space when the heater-susceptor is in its process (higher) position with respect to its loading position. [00014] In still another embodiment, the present invention provides a reaction chamber apparatus containing a heater-susceptor connected to an annular attached flow ring conduit at the perimeter of the susceptor, the conduit having an external surface at its edge that isolates the outer space of the reactor above the wafer from the confined reaction space when the heater-susceptor is in its process (higher) position with respect to the loading position, the outer edge being placed in proximity with an annular ring attached to the reactor lid and together the ring and conduit outer member acting together as a tongue-in-groove (TIG) configuration. In some cases, the TIG design may have a staircase contour (SC), thereby limiting diffusion-backflow of downstream gases to the outer space of the reactor.

[00015] A further embodiment of the present invention provides a reaction chamber apparatus having a vertically movable susceptor (VMS) with respect to its loading (lower) position, said susceptor being connected to an annular attached flow ring (AFR) (or deep flow ring (DFR)) conduit at the perimeter of the susceptor, said annular AFR passing reaction gas effluent to a downstream pump orifice that is off-axis with respect to the axi-centric center of the reaction chamber. In some cases a downstream baffle may be placed between the lower orifice of the annular AFR and the downstream pump to attain symmetric gas flow at the edges of the wafer in the upstream wafer plane. [00016] Still a further embodiment of the invention provides a TIG chamber configuration as described above and having a pump connected to remove gas streams from the reaction space, the AFR conduit and the lower chamber leading to the pump. A gas injection orifice that allows for by-passing the reaction space and the AFR conduit is placed such that gas injected through said orifice enters into the stream leading to the pump below the output orifice of the AFR. Hence, the orifice provides for directly injecting a gas into the pumping conduit leading directly to the input of the pump, without further restrictor(s) between the AFR output orifice and the pump input orifice, periodically during ALD cycling.

[00017] In yet another embodiment, an ALD apparatus includes a plurality of process modules, each process module having one or more reactor chambers, each reactor chamber housing a substrate holder that is moveable vertically between a process position and a load/unload position, each respective one of the substrate holders oriented within its respective reactor chamber such that when the respective substrate holder is in its process position there is formed in the respective reactor chamber a gas exhaust port, said port defined by a circumference wall of respective reactor chamber and an edge surface of the respective substrate holder. Walls of the gas exhaust port channel may be attached to and moveable with the substrate holder. An upper segment of an outer wall segment of the gas exhaust port channel is preferably located in a ring groove, which ring groove fits around a circular shield that itself fits around a gas admittance distributor of each respective reactor chamber.

[00018] Further embodiments, features and advantages of the present invention are discussed below.

BRIEF DESCRIPTION OF THE DRAWINGS

[00019] The present invention is illustrated by way of example, and not limitation, in the figures of the accompanying drawings, in which:

[00020] Figure 1 illustrates an ALD reactor with vertical precursor injection and combined radial/vertical flow pumping;

[00021] Figure 2 illustrates a slot valve and off-axis downstream pump that breaks the symmetry of radial gas flow within an ALD apparatus;

[00022] Figure 3 illustrates relative orientations of a deep flow ring (DFR), wafer slot valve position and the orifice of the DFR below the slot valve within an ALD apparatus configured in accordance with an embodiment of the present invention;

[00023] Figures 4a and 4b are detailed views of a tongue-in-groove (TIG)- configured ALD apparatus in accordance with an embodiment of the present invention showing alternative staircase designs and removal of dead zones in the corner of the reaction space by a contoured fillet that guides gases to the DFR; and

[00024] Figure 5 illustrates the use of a downstream baffle to symmetrize the flow upstream in an ALD apparatus in accordance with an embodiment of the present invention;

[00025] Figure 6 illustrates a layout top view of ALD multi-single wafer (MSW) process equipment with a total of two process modules each having four reactor chambers and a transfer chamber with associated load locks, configured in accordance with an embodiment of the present invention;

[00026] Figure 7 illustrates a cross-sectional view of the reactor chambers of the

MSW equipment shown in Figure 6; and

[00027] Figure 8 illustrates in further detail a reactor chamber of the MSW equipment shown in Figure 6 with its vertically moveable susceptor in its lower

(load/unload) position.

DETAILED DESCRIPTION

[00028] Described herein is a small volume symmetric flow (SVSF) apparatus defined for a minimal ALD reaction volume with symmetric flow with minimal chemical transport to the reactor walls. The description includes the reactor design and its functionality, as well as a discussion of the combined effects of small volume for the reaction space, generalized design for isolation of the reaction space from the reactor walls without re-circulations, the minimization of gas expansion volume below the wafer plane, and a time-phased multilevel choked downstream pump configuration suitably designed in all cases to achieve flow symmetry in the case of off-axis pumping conduits with maintainability and assembly features.

[00029] In one embodiment of the invention, a reaction chamber apparatus includes a vertically movable heater-susceptor, where the heater-susceptor is connected to an annular attached flow ring that performs as a gas conduit, with an outlet port of the flow ring extending below the bottom of a wafer transport slot valve when the susceptor is in the process (higher) position. [00030] A further embodiment of the invention provides a reaction chamber apparatus containing a heater-susceptor connected to an annular attached flow ring conduit at the perimeter of the susceptor, the conduit having an external surface at its edge that isolates the outer space of the reactor above the wafer and below the wafer to the bottom of the flow ring from the confined reaction space when the heater-susceptor is in its process (higher) position with respect to its loading position. [00031] In still another embodiment, the present invention provides a reaction chamber apparatus containing a heater-susceptor connected to an annular attached flow ring conduit at the perimeter of the susceptor, the conduit having an external surface at its edge that isolates the outer space of the reactor above the wafer from the confined reaction space when the heater-susceptor is in its process (higher) position with respect to the loading position, the outer edge being placed in proximity with an annular ring attached to the reactor lid and together the ring and conduit outer member acting together as a tongue-in-groove (TIG) configuration. In some cases, the TIG design may have a staircase contour (SC), thereby limiting diffusion-backflow of downstream gases to the outer space of the reactor.

[00032] Importantly, in embodiments of the present invention the design and operation of the tongue and groove members are such that these members make no physical contact with each other. Touching members would be a particle source mechanism and possibly lead to metal-to-metal contact sticking (bonding of metal in vacuum) and compromise the retraction of the heater-susceptor. Moreover, a contact design would have considerable difficulty maintaining mechanical stability. For these reasons, we have designed and operated a "proximity" or "diffusion-seal" TIG mechanism.

[00033] A further embodiment of the present invention provides a reaction chamber apparatus having a vertically movable susceptor (VMS) with respect to its loading (lower) position, said susceptor being connected to an annular attached flow ring (AFR) (or deep flow ring (DFR)) conduit at the perimeter of the susceptor, said annular AFR passing reaction gas effluent to a downstream pump orifice that is off-axis with respect to the axi-centric center of the reaction chamber. In some cases a downstream baffle may be placed between the lower orifice of the annular AFR and the downstream pump to attain symmetric gas flow at the edges of the wafer in the upstream wafer plane. [00034] Still a further embodiment of the invention provides a TIG chamber configuration as described above and having a pump connected to remove gas streams from the reaction space, the AFR conduit and the lower chamber leading to the pump. A gas injection orifice that allows for by-passing the reaction space and the AFR conduit is placed such that gas injected through said orifice enters into the stream leading to the pump below the output orifice of the AFR. Hence, the orifice provides for directly injecting a gas into the pumping conduit leading directly to the input of the pump, without further restrictor(s) between the AFR output orifice and the pump input orifice, periodically during ALD cycling. In some cases the gas so injected may be injected at azmuthal points to achieve uniform exposure and uniform residence time. Also, the orifice of the AFR may have restrictors in the form of holes at the plane of its orifice, and the holes may be designed differently in different azmuthal directions to induce symmetric flow at the wafer plane. The TIG design may be such that the inner edge of the TIG lid element is curved to remove dead space in the reaction space. [00035] The HP ALD design described herein may be further utilized in a "multi- single wafer" (MSW) reactor system as described for example in the above-referenced U.S. patent application 11/224,767 and German patent application DE 102005056326.6. In that case, several (e.g., four) substantially independent HP reactors may be placed in a common vacuum housing system. In DE 102005056326.6 there is the added requirement of small gas flow (mostly back-flow by diffusion as apposed to convective flow) between the otherwise substantially independently operating reactors placed within the same master vacuum housing.

[00036] More specifically, in a multi-single wafer system a number of reactor chambers are arranged in a single process module. The substrates, which are preferably circular wafers, do not lie in a common process chamber, but instead in separate reactor chambers which are connected with respect to flow dynamics in the gas exhaust zone. The individual reactor chambers in a process module can be loaded/unloaded during a common load/unload step. To accomplish this the substrate holders are lowered from a process position into a load/unload position. In the process position the walls of the substrate holder form a gas exhaust outlet port as described herein. The individual reactor chambers are separated when the substrate holders are in the process position through diffusion barriers such that a flow of the gases form one chamber into another chamber is avoided. The individual chambers are preferably arranged on a common level, grouped around a center defined by the axis of rotation of the load/unload device. [00037] Referring now to Figure 3, an HP ALD system 30 configured in accordance with an embodiment of the present invention is illustrated and quantified with respect to the confined reaction space volume 32 (minimized and optimized), with non re-circulations, symmetric flow, and small gas reactant transport outside the HP reaction zones. The system 30 includes a reactor chamber 34 as well as a number of components similar to those described above. Housed within chamber 34 is a vertically moveable heater-susceptor 36 (e.g., configured as discussed in the above-referenced patent owned by the present assignee), on which rests a wafer 38. Heater-susceptor 36 is connected at its periphery to an annular flow ring 40 that performs as a gas conduit. Flow ring 40 has an outlet port 42 positioned below the bottom of wafer transport slot valve 28 when the susceptor 36 is in its process (higher) position.

[00038] The present ALD system may be used for a single wafer deposition, or, in some cases, a number of smaller wafers may be placed on single carrier within the chamber. Importantly, in the context of the use of this confined design as a single, stand alone wafer reactor, the reactants are beneficially shielded from deposition on the inner walls of the reactor chamber, thus providing an advance in maintenance benefits for single wafer reactors.

[00039] The annular flow ring conduit 40 attached at the perimeter of the susceptor 36 has an external surface 44 at its edge that isolates the outer space of the reactor above the wafer and below the wafer to the bottom of the flow ring from the confined reaction space when the heater-susceptor is in its process (higher) position with respect to its loading position. This outer edge 44 is in proximity with an annular ring 46 attached to the reactor lid 48 and together the ring 46 and conduit outer member 44 act as a tongue-in-groove (TIG) configuration. That is, as shown in the figure, the outer edge of the flow ring fits within a groove in the annular ring attached to the reactor lid. In some cases, the TIG design may have a staircase contour (SC), thereby limiting diffusion-backfiow of downstream gases to the outer space of the reactor. The annular flow ring passes reaction gas effluent to a downstream pump 16 that is off-axis with respect to the axi-centric center of the reaction chamber. [00040] A consideration for the design of the small volume symmetric flow ALD reactor is the requirement to deliver gas precursors rapidly and substantially uniformally across the semiconductor wafer or wafers, or work piece or work pieces, with high topology features. To achieve minimal exposure times and efficient precursor use, we desire chemical precursors to be brought to high, aspect features in the center and the edge of the wafer in nearly the same timeframe, with nearly the same concentration. [00041] The benefit of same time exposure is to achieve efficient conformal coatings over the wafer area. The within-wafer non-uniformity of high topology features will be optimally small, while simultaneously using a minimal amount of precursor. To understand this, we refer to the theory for coating "holes" with high aspect ratios. R. Gordon, et al., "A Kinetic Model for Step Coverage by Atomic layer Deposition in Narrow Holes or Trenches," Chem. Vap. Deposition, 9, No.2, pp. 73 et seq. (2003). The exposure of a single ALD precursor proceeds by gas diffusion transport from the top down to the bottom of the hole. Holes placed near the location on the wafer having the first precursor arrival will coat first near the top and later coat at the bottom of the hole with a single pulse of suitably sufficient dosage. Holes farther away from the position of first precursor arrival to the wafer will coat to saturation at the bottom of their features at a later time. Reactors with distributed vertical injection are better suited to meet this condition efficiently, while reactors with horizontal injection perform poorly in this regard. In order to achieve an efficient coating, it is desirable to use a suitably designed showerhead or gas distribution manifold (GDM), where the gases are dispensed as simultaneously as possible over the entire wafer surface.

[00042] An optimal ALD system includes consideration of a rapid and efficient chemical precursor delivery into the GDM₅ and a GDM that, in turn, provides rapid precursor flow into the reaction space (see, e.g., U.S. patent application 11/278,700 of Dalton et al., filed 5 Apr 2006, assigned to the assignee of the present invention and incorporated herein by reference). The detailed design of showerheads of uniform injection and low residence times (as well as chemical precursor source vaporizers of high partial pressure) are separate considerations from the design of the reactor itself, but must be optimized and integrated with best practices to obtain a fully competitive system. [00043] In summary, a high performance system configured in accordance with the present invention includes a chemical precursor source capable of rapidly delivering high partial pressures of precursor vapors by way of the GDM and optimized reactor chamber design. For the purposes of this disclosure, we consider the chemical source/delivery, GDM and reactor as modular with respect to each other and separately optimized. However, as mentioned above, for efficient uniform coatings of high topology features, one advantageously uses axisymmetric exposure at the center and edge of the wafer at nearly the same time and a reactor design that is axisymmetric with respect to flow at the edge of the wafer.

[00044] In considering the merits of axi-symmetric flow, we discuss the benefits of the symmetric flow during the exposure as well as the removal of the reactants and byproducts. The importance of removing precursors with azmithual symmetry is related to the minimization of the onset of parasitic CVD at all azmuthal points around the edge of the wafer. Additionally, whether having azmuthal symmetry or not, if the design permits flows to re-circulate in the pocket regions associated with the wafer slot valve, or stagnate in unnecessary corners, then eddies can result and precursor remnants may exist in the precursor removal/purge periods and give rise to parasitic CVD [00045] Thus, the starting constraints of design are: a. The injection flow favors a GDM of axi-symmetric geometry with respect to the target work piece. For example, this may be a circular GDM with its center aligning (at least when in the processing position) with the center of a circular wafer (or other work piece) or a group of circular wafers (or work pieces) upon which depositions will take place. b. The wafers are placed on the heater-susceptor using horizontal motion by robotic handling through a rectangular slot valve. c. The pumping port leading to the downstream pump may be off-axis with respect to the central wafer axis. d. The reaction space (the volume between the showerhead and the wafer surface) is to be minimized. e. The downstream volumes are to be minimized, minimizing gas expansion that would lead to long purge times, and the use of (unnecessary) downstream constrictions eliminated, maximizing the conductance from the reaction space to the downstream pump. f . A multilevel flow may be implemented without the use of limiting constriction on the downstream side of the point of introduction of a gas inlet to modify the effective pumping speed of the downstream pump to improve the ALD reaction efficiency on the wafer.

[00046] The ALD cycle time (CT) consists of exposure of a first precursor, followed by removal (or "purge") of unused portions of the first precursor and first precursor's reaction by-products, followed by exposure of a second precursor and removal of the unused portions of the second precursor and second precursor's reaction by-products. The sum of these four cycle time elements are the ALD CT. [00047] In our approach, to minimize the reaction space volume, a confined flow path is defined by attaching a guiding pumping conduit to the edge of the heater- susceptor. This design places the flow path as close to the wafer as possible and takes the form of a flow ring that is mechanically attached to the heater-susceptor. Removal periods are greatly reduced and CT is improved by using an annular conduit flow ring that is attached to a movable vertical susceptor.

[00048] The flow ring 40 has a conduit with an input orifice 50 at nominally the same height as the susceptor 36. The lower orifice 42 of the flow ring 40 is below or substantially below the lower edge of the slot valve 28 when the wafer (i.e., the susceptor) is in the processing position. This constraint provides excellent convective flow isolation from the slot valve and improves flow symmetry at the edge of the wafer and just downstream of the wafer surface. The deep flow ring (DFR) then is suitably defined. The outer edge of the DFR is placed close to the inside of the downstream reactor chamber wall 51, minimizing diffusive back flow to the slot valve and upper outer reactor wall surfaces. [00049] When the vertically movable susceptor 36 with the flow ring 40 is elevated into its "up" or processing position, the outer surface element 44 of the DFR is placed in close proximity and overlapped with respect to a bottom of a second surface element of a "lid-ring" 46 that is attached to inside of the lid 48 of the reactor. The inner surface of the lid ring element and the outer surface of the flow ring define the confining surfaces for the reactant flows and provide confinement of the reaction space. [00050] By iterative simulation, it has been found that (still) some small amount of reactants back-diffuse upstream within the conduit of the flow ring and reach the intended isolated region 55 outside of the lid ring. This results in unwanted deposits on the reactor wall 57 and, in the case of the multi-single- wafer reactor, results in excessive diffusive cross-talk between intended independent reactors.

[00051] Hence, in one embodiment of the invention the lid ring 46 is configured with a recess that permits insertion of the outer surface 44 of the flow ring into the recess when positioned "up" for processing. The result is a "tongue in groove" (TIG) design, as illustrated in Figure 4a. By simulation, this design produces a 100-fold level of reduction in the steady state deposition rate on the outer reactor wall relative to the wafer deposition rate.

[00052] Still further reduction of diffusive back-flow can be obtained by using a

TIG with matched staircase surface contours on the flow ring 40 and lid ring 46. This configuration is shown in Figure 4b. In this configuration, the outer surface of the flow ring 40 is split into two portions 44a and 44b, with an inner portion 44a overlapping a portion of the groove 52 formed between inner and outer portions of the lid ring 46, and an outer portion 44b extending into the groove 52. Together, the inner and outer portions 44a and 44b of the flow ring resemble a staircase-like structure that overlaps and extends into groove 52 in the lid ring 46.

[00053] Supporting simulations for the back-diffusion for the staircase TIG design of Figure 4b indicate up to a 10,000-fold reduction in back-diffusion relative to the steady state wafer deposition rate, depending on the spacing(s) in the staircase. The staircase design also addresses mechanical thermal expansion issues that may otherwise make the tolerances required in a TIG design difficult to maintain. Not shown (although contemplated within the scope of the invention) are multiple-level staircase designs (e.g., which include multiple portions such as 44a and 44b, each overlapping and extending successive distances within groove 52, that can reduce the diffusive transport to the reactor walls even further. Thus, there is a hierarchy of performance for attached flow ring designs that can lead to a "generalized staircase" design, using multiple steps. [00054] Alternatively, if a single fin element (rather than a double ring) were attached to the inner surface of the reactor lid and the DFR were placed into an overlap position with respect to the susceptor's outer ring during the process position, an alternate embodiment is realized. However, in this case, the reaction space would be confined but the reactant diffusion to the outer walls of the reactor at the same vertical levels as the wafer would not be well isolated. Similarly, if the DFR were not defined as extending deeper than the slot valve, then the re-circulations and isolation with respect to the slot valve would be poor. These poor alternatives imply a certain preference for the attached extended depth annular DFR combined with a staircase TIG design. The TIG design may be such that the inner edge of the TIG lid element is curved to remove dead space in the reaction space. For example, a curved or countered fillet 54 such as that illustrated in Figure 4 may be used.

[00055] Simulations indicate that the design as shown in Figure 3 has a non- symmetric flow of approximately 10% due to the off-axis pump. This off-axis pump location can be engineered by placing an azmuthal baffle 56 covering an azmuthal angle of approximately 10 to 150 degrees, centered to balance the azmuthal flows. Such a configuration is shown in Figure 5.

[00056] The above-described ALD system can be operated using a multilevel flow design, such as that described in U.S. patent application 10/791,030 of Liu et al., assigned to the assignee of the present invention and incorporated herein by reference (which application also discusses a bi-level flow system proposed by Sneh in WO 03/062490), wherein there is no downstream restrictor. Hence, embodiments of the invention may provide a TIG chamber configuration as described above and having a pump connected to remove gas streams from the reaction space, the AFR conduit and the lower chamber leading to the pump. A gas injection orifice that allows for by-passing the reaction space and the AFR conduit is placed such that gas injected through said orifice enters into the stream leading to the pump below the output orifice of the AFR. The orifice thus provides for directly injecting a gas into the pumping conduit leading directly to the input of the pump, without further restrictor(s) between the AFR output orifice and the pump input orifice, periodically during ALD cycling. In some cases the gas so injected may be injected at azmuthal points to achieve uniform exposure and uniform residence time. The TIG design may be such that the inner edge of the TIG lid element is curved to remove dead space in the reaction space, for example, a curved or countered fillet 54 such as that illustrated in Figure 4 may be used.

[00057] Maintenance features are also favorable. ALD deposits on the inside walls of the deep flow ring will ultimately require maintenance. This is carried out by a maintenance procedure using lid-access to the heater-susceptor, followed by manual removal and replacement of the used DFR component. The used deep flow ring may be cleaned and reused.

[00058] The simulation methodologies and results, along with supporting data were set forth in Appendix A to the above-cited provisional patent application, incorporated herein by reference.

[00059] Turning now to Figure 6, a multi-single wafer ALD process device similar to that discussed above and which may include individual reactor chambers configured with the TIG-fitted rings discussed above is shown. An exemplary apparatus includes a total of two process modules 58, each having four individual chambers 60. With the help of a robot arm, which is not shown here, of a transfer chamber 62, substrates can be transferred from the two load locks 64 into the process modules 58 where they are coated in the reactor chambers 60. The atmospheric wafer transfer module 68 and the two adjacent load locks provide wafer transfer for loading and unloading to and from the vacuum transfer chamber. A cooling station 66 is also provided.

[00060] As shown in Figure 7, each of the reactor chambers includes a substrate holder 70 for the support of a substrate 72. The substrate 72 rests on the substrate holder

70, covering most of its area. Merely the outer perimeter zone of the chamber 60, which is defined by a shield 74 surrounding the process chamber, is not covered by the substrate holder 70. This configuration leads to a circular gas exhaust port 76. [00061] The lid or ceiling of every chamber 60 contains a gas admittance orifice

(like GDM) component 78, which is enveloped by the circular shield 74. A gas inlet 80 for the process gases and a carrier gas join together into the gas admittance orifice. The gas inlet 80 feeds into a gas volume which extends over nearly the whole level of the gases admittance orifice 78. The gas admittance orifice 78 features on its underside, pointing towards the chamber 60, a multiple number of sieve-like gas outlet openings (not shown in this view). Through these gas outlet openings the process gas and the carrier gas can flow into the chamber 60.

[00062] In particular, in this embodiment the gasses flow horizontally (after vertical injection) through the chamber in a radial direction towards the perimeter area where they are diverted vertically downwards by the shield 74. The gasses then flow though the circular gas exhaust channel 76, which is defined by an inner channel wall 82 and an outer channel wall 84. The gas flowing from the gas exhaust channel 76 flows into a common gas outlet conduit 86 which surrounds the center axis of the process module 98. A fore line and vacuum pump may be connected to this common gas outlet conduit 86.

[00063] The channel inside wall 82 is also the outer wall of the substrate holder 70.

The substrate holder 70 forms, all together, a body shaped like an inverted pot. The flat outer wall (or "bottom") of the pot forms the support surface for the substrate 72. The outer wall of the cylindrical pot wall 82 forms the inner wall of the gas exhaust outlet port 76. The channel outer wall 84, which is separated from the channel inner wall 82 by a gap, is firmly connected with channel inner wall 82, and therefore the also substrate holder 70. For this firm connection, ribs or struts may be used (not shown). [00064] An upper segment 90 of the channel outer wall 84 (the "riser" of the staircase design) fits into a ring groove of a sealing ring 92, which is located radially outside with respect to the shield when the substrate holder 70 is in its process position. In this upper segment 90 the material thickness of the outer channel wall 84 is decreased according to designed-in step. The sealing ring 92 forms a ring groove, open at the bottom, into which the segment 90 of the outer channel wall 84 can enter. A gas sealing is thereby created between the chamber 60 and the gap space 94. The outer channel wall channel (of the deep flow ring) also forms a (gas diffusion flow) sealing surface against the inner wall 96 of the gas outlet conduit 86. Therefore the gases that flow through the gas outlet conduit 86 cannot reach into the gap space 94. If the substrate holder 70 is lowered from the process position into the load position, the outer surface of the pipe- shaped outer channel wall 84 moves (with small spacing) along the inner wall 96 of the gas outlet conduit 86.

[00065] As shown, the ALD apparatus may be symmetrical with respect to a central axis 98. Lifting pins 100 (which operate through openings 102 in the substrate holder 70) may also be provided. Substrate holder 70 is supported by a pedestal 104 and the chamber may have a top 106.

[00066] When starting from the position shown in Figure 7, the lift pins 100 are in a retracted state so that the substrate 72 comes to rest on the contact points 108, 110. Figure 8 shows the substrate holder in its lower (loading/unloading) position within reactor 60. In order to transfer a substrate 72 into/out of the reactor, the substrate may be raised using lift pins 100 which are driven by a drive mechanism (not shown) from a retracted position as shown in Figure 7 into a substrate supporting position, supported by the lift pins at a position which is above the level at which a loading and unloading transfer may take place. In this manner substrates can be successively loaded/unloaded to/from the reactor chamber.

[00067] Also shown in Figure 8 is an expanded view of the sealing interface in which the segment 90 of the outer channel wall 84 is inserted into the ring groove 114 of the sealing ring 92.

[00068] Hence, when the substrate holder is in the process position an upper segment of a channel wall, which is firmly connected with the substrate holder, inserts itself into a groove of a circular sealing ring which is covered by a shield. The circular shield 74 and the sealing ring 92 may be combined into a single piece-part. The circular shield 74 forms the circumferential wall of the process chamber and extends in vertical direction from the gas admittance orifice downwards to the gas exhaust channel which is bounded by the inner 82 and outer 84 walls of the gas exhaust channel 76, where the inner wall is firmly connected with the substrate holder 70. If the substrate holder is lowered from the abovementioned process position in which the layer growth on the surface of the substrate occurs, to a load/unload position, the gap space between the individual process chambers is opened. In this load and unload position the substrate holder lies below the gap space. The substrate holder features openings for the penetration of lift pins. The lift pins are raised by the lift mechanism and lift the substrate from underneath, to separate them from the substrate holder. To accomplish load and unload operations, the reactor chamber features a lateral slot opening through which a robot arm can reach into the reactor chamber. The substrate holders are carried by a lift shaft, which can shift the substrate holders vertically, as described above. [00069] Accordingly, a small volume symmetric flow (SVSF) apparatus defined for a minimal ALD reaction volume with symmetric flow with minimal chemical transport to the reactor walls has been described. Although discussed with respect to certain illustrated embodiments, the present invention is not meant to be limited thereby and should only be measured in terms of the claims, which follow.

Claims

CLAIMSWhat is claimed is:

1. A reaction chamber apparatus comprising a vertically movable heater-susceptor coupled to an annular attached flow ring configured as a gas conduit and having an outlet port extending below a bottom of a wafer transport slot valve of the reaction chamber apparatus when the heater-susceptor is in a processing position.

2. A reaction chamber apparatus comprising a heater-susceptor coupled to an annular attached flow ring conduit at a perimeter of the heater-susceptor, the flow ring conduit having an external surface at its edge that isolates an outer space of the reactor above a wafer position and below the position wafer to a bottom of the flow ring when the heater- susceptor is in a processing position.

3. A reaction chamber apparatus comprising a heater-susceptor connected to an annular attached flow ring conduit at a perimeter of the heater-susceptor, the conduit having an external surface at its edge that isolates an outer space of the reaction chamber above a wafer position from a confined reaction space of the reaction chamber when the heater- susceptor is in a processing position, the edge being in proximity with an annular ring attached to a lid of the reactor such that the annular ring and an outer member of the conduit form a tongue-in-groove (TIG) configuration.

4. The reaction chamber apparatus of claim 3, wherein the TIG configuration comprises a staircase contour, operable to limit diffusion-backflow of downstream gases to an outer space of the apparatus.

5. A reaction chamber apparatus comprising a vertically movable susceptor coupled to an annular attached flow ring conduit at a perimeter of the susceptor, said annular attached flow ring configured to pass reaction gas effluent to a downstream pump orifice that is located off-axis with respect to an axi-centric center of the reaction chamber.

6. The reaction chamber apparatus of claim 5, further comprising a downstream baffle located between a lower orifice of the annular attached flow ring and a downstream pump.

7. The reaction chamber apparatus of claim 3, further comprising a pump coupled to remove gas streams from the reaction chamber, the flow ring conduit and a lower chamber leading to the pump.

8. The reaction chamber apparatus of claim 7, further comprising a gas injection orifice coupled to permit by-passing of the reaction chamber and the flow ring conduit such that gas injected through said orifice enters into a stream leading to the pump below an output orifice of the flow ring.

9. The reaction chamber apparatus of claim 8, wherein the gas injection orfice is configured such that gas is injected at azmuthal points.

10. The reaction chamber apparatus of claims 8, wherein the flow ring orifice includes restrictors in the form of holes at a plane of the orifice.

11. The reaction chamber apparatus of claim 10, wherein the holes are configured differently in different azmuthal directions.

12. The reaction chamber apparatus of claim 3, wherein an inner edge of the lid is curved.

13. An ALD apparatus, comprising a plurality of process modules, each process module having one or more reactor chambers, each reactor chamber housing a substrate holder that is moveable vertically between a process position and a load/unload position, each respective one of the substrate holders oriented within its respective reactor chamber such that when the respective substrate holder is in its process position there is formed in the respective reactor chamber a gas exhaust port, said port defined by a circumference wall of respective reactor chamber and an edge surface of the respective substrate holder.

14. An apparatus according to claim 13, wherein walls of the gas exhaust port channel are attached to and moveable with the substrate holder.

15. An apparatus according to claim 13, wherein an upper segment of an outer wall segment of the gas exhaust port channel is located in a ring groove.

16. An apparatus according to claim 15, wherein the ring groove fits around a circular shield, which fits around a gas admittance distributor of each respective reactor chamber.