Apparatus and method for fast-cycle atomic layer deposition

[0001] This application claims benefit of U.S. Provisional Patent Application Serial No. 60/337,076, entitled Apparatus and Method For Fast-Cycle Atomic Layer Deposition, filed Dec. 6, 2001, which is herein incorporated by reference.

[0002] 1. Field of the Invention

[0003] The present invention relates to the field of thin film technology for coating substrates and has particular application to atomic layer deposition.

[0004] 2. Description of the Related Art

[0005] In the field of thin film technology, requirements for thinner deposition layers, better uniformity over increasingly larger area substrates (e.g., ever increasing substrate sizes in flat panel technology as well as the move to 300 mm technology in semiconductor manufacturing), larger production yields, and higher productivity have been, and still are, the driving forces behind emerging technologies developed for coating substrates in the manufacture of various semiconductor devices. Various technologies known in the art exist for applying thin films to substrates, including sputtering or physical vapor deposition (PVD), chemical vapor deposition (CVD) and atomic layer deposition (ALD) methods.

[0006] According to the sputtering or PVD method, an inert gas such as argon (Ar), is injected into a vacuum chamber in which high voltage is applied to a target to generate Ar ions in a plasma state. Then, Ar ions are attracted onto the surface of the target such that atoms of the target become dislodged and are deposited onto the surface of the substrate. Although high purity thin films with good adhesion to the substrates can be formed by the sputtering method, it is difficult to ensure uniformity over the entire thin film.

[0007] In the CVD method, a desired layer is deposited on a substrate to a desired thickness using decomposition and reaction of gases. First, various gases are injected into a reaction chamber, and chemical reactions between the gases are induced with high energy such as heat, light, or plasma to deposit a thin film having a predetermined thickness on the substrate. The deposition rate of CVD can be increased by controlling either the amount and ratio of the gases or the reaction condition of heat, light, or plasma supplied as the reaction energy. The reactions are so rapid, however, that it is difficult to control the thermodynamic stability of atoms. Another problem is that the close proximity of the reactant and the products of reaction to the deposition surface creates a high probability of the inclusion of reaction products and other contaminants in each deposited layer.

[0008] Forming and growing thin films by ALD is based on the principle of the formation of a saturated monolayer of reactive precursor molecules by chemisorption at the deposition surface of the substrate. In ALD, appropriate reactive gaseous precursors are alternately pulsed or injected into a reaction chamber. Each pulse or injection of a reactive precursor is separated by an inert gas purge. The precursor injections react on the surface of the substrate to form a new atomic layer with each full cycle of the process. Thus, atomic layers are built up one over the other in a repetitive process to form a uniform solid layer of film. Each set of process steps performed to form an atomic layer is referred to as a cycle. The repetitive process is repeated for a number of cycles needed to form the desired film thickness.

[0009] An essential difference between ALD and other deposition methods is that film growth proceeds stepwise, atomic plane by atomic plane, resulting from a surface reaction between one component element in the gas phase with the other as surface atoms in the growing compound film. As a result, the ALD method achieves improved step coverage and allows for improved control over the thickness and composition of the grown thin film. ALD, although a slower process than CVD, demonstrates a remarkable ability to maintain ultra-uniform thin deposition layers over complex topography.

[0010] The unique mechanism of film formation provided by ALD offers several advantages over CVD and other thin film technologies. One advantage is the transparency of ALD to substrate size. For example, a 200 mm substrate will receive a uniform layer equal in thickness to one deposited on a 100 mm substrate processed in the same reactor chamber because of the self-limiting chemisorption phenomena described above. Another distinct advantage of the ALD process is the avoidance of high reactivity of precursors toward one another because chemical species are injected independently into an ALD reactor rather than together. High reactivity, while problematic in some CVD methods, is exploited to an advantage in ALD because the reaction occurs directly on the substrate surface. This high reactivity enables lower reaction temperatures and simplifies process chemistry development. Yet another distinct advantage of ALD is that surface reaction by chemisorption contributes to improved step coverage over complex topography.

[0011] A thin film having a high aspect ratio, good uniformity and good electrical and physical properties can be formed by ALD. Moreover, the films deposited by ALD have a lower impurity density than those formed by other deposition methods, and a film thickness of less than about 200 Angstroms with sufficient thickness uniformity that can be obtained with reproducibility. ALD, therefore, is a superior method for achieving uniformity, excellent step coverage, and transparency to substrate size.

[0012] While the ALD method can provide a thin film with a high aspect ratio, good uniformity, good electrical, and physical properties, it is problematic in that it has been difficult to create an acceptable commercial process (i.e., one with adequate system throughput) because of the separate deposition of each film layer and the low deposition rate of the process (e.g., typically about 100 Angstroms per minute as compared to about 1,000 Angstroms per minute for CVD). The deposition rate may be increased by increasing the number of deposition cycles per unit time. Thus, there remains a need for improved apparatus and processes for decreasing the overall time to deposit a film by ALD, thereby increasing the overall throughput of products employing layers deposited by ALD.

[0013] In certain embodiments, the present invention includes an apparatus for forming a layer on a substrate by atomic layer deposition. In order to commercialize such a process, cyclical steps are performed rapidly due to the large number of atomic layers that generally need to be deposited to achieve the desired thickness of the final product layer. The apparatus of the present invention includes a chamber and a lid that define a reaction chamber therein. A substrate support, such as a heater, supports the substrate in the reaction chamber. The top surface for the substrate support forms a dividing line that, in combination with a virtual shower curtain and walls of the chamber or liner or shadow ring, divides the reaction chamber into a first volume and a second volume or top and bottom volume.

[0014] In some embodiments, the virtual shower curtain may be established by providing at least one port through the chamber through which a vacuum may be applied, where upon application of vacuum to the at least one port, a bottom purge of the substrate support is performed and the virtual shower curtain is established between the top surface of the substrate support and the chamber wall, liner or shadow ring, to prevent flow from the top volume to the bottom volume.

[0015] In other embodiments, a high conductance showerhead may be mounted to the lid to allow closer positioning of the substrate to the showerhead, compared to use of a standard showerhead. This reduces the volume of the effective reaction chamber, further reducing step and cycle times. A high conductance showerhead described includes at least one distribution hole having a diameter of at least . Spacers may also be provided to form a gap between the high conductance showerhead and the lid upon mounting. This gap defines flow pathways for horizontally flowing a reactant and distributing it peripherally about the substrate.

[0016] In yet other embodiments, a gas valve mounted on top of the lid of the apparatus may also be designed to reduce step and cycle times. A pair of gas valves may be mounted immediately adjacent the lid to minimize dead volume in flow paths connecting the valves with the showerhead/reaction chamber. The valves may also be mounted flush against the lid, by any variety of techniques or components including welding, threading, or using other attachment methods to attach the valves to the lid or by using screws or other fastening devices to mount the valves on the lid.

[0017] In some embodiments, the valves may be ZDV valves, and may be pneumatic valves, solenoid valves or piezo valves. MEMS technology significantly reduces the valve cycle times of the valves used. MEMS is an acronym used herein to mean micro electro-mechanical system.

[0018] In other certain embodiments, an apparatus for forming a layer on a substrate by atomic layer deposition is described herein to include a chamber and a lid which define a reaction chamber therein. A high conductance showerhead is mounted to the lid and has at least one hole having a diameter of at least about for distributing gas therethrough and into the reaction chamber and allowing closer placement of the substrate with regard thereto. A substrate support is provided for supporting the substrate and, together with the formation of a virtual shower curtain, divides the reaction chamber into a first volume and a second volume, the first volume being defined above the top surface of the substrate support and the second volume being below the top surface. At least one port is provided, through which a vacuum may be applied. Upon application of the vacuum, a bottom purge of the substrate support is performed and a virtual shower curtain is established between the top surface of the substrate support and the chamber wall, liner or shadow ring to prevent flow from the first volume to the second volume.

[0019] In some embodiments, fast cycle valves may be mounted on top of the lid and fluidly connected with the high conductance showerhead. Each valve may be operated to a valve cycle time of less than about 400 msec. Of course, the fast cycle valves may be operated to a valve cycle time of about 400 msec or more.

[0020] In yet other certain embodiments, a method of reducing an amount of time needed to form a film on a substrate by atomic layer deposition is described to include positioning the substrate on a substrate support in a reaction chamber; establishing a virtual shower curtain between the substrate support and walls of the reaction chamber, thereby dividing the reaction chamber into an upper volume above the substrate support and the virtual shower curtain, and a lower volume, below the substrate support and the virtual shower curtain; and distributing a reactant into the upper volume, wherein the virtual shower curtain prevents the reactant from flowing into the lower volume.

[0021] In some embodiments, the distributing step may be initiated by turning on a valve connecting a source of the reactant with the reaction chamber, wherein the valve is turned on in less than about 400 msec. Of course, the valve may be turned on in about 400 msec or more.

[0022] In other embodiments, the distribution may include flowing the reactant through a showerhead having at least one distribution hole having a diameter of at least .

[0023] So that the manner in which the above recited features of the present invention are attained and can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.

[0024] FIG. 1 is a schematic cross-sectional view of one embodiment of an apparatus for performing ALD processing.

[0025] FIG. 2 is a schematic cross-sectional view of one embodiment of a top lid arrangement for ALD processing.

[0026] FIG. 3 is a schematic cross-sectional perspective view of another embodiment of a top lid and a showerhead mounted thereto.

[0027] FIG. 4 is a perspective view of another embodiment of a showerhead.

[0028] FIG. 5 is a perspective view of another embodiment of a showerhead.

[0029] FIG. 6 is a schematic view of one embodiment of valves mounted flush to the top lid.

[0030] FIG. 7 is a schematic view of the valve seats of the valves of FIG. 2.

[0031] Before the present apparatus and methods are described, it is to be understood that this inventions not limited to particular embodiments described, as such may, of course, vary. It is also to be understood that the terminology used herein is for the purpose for describing particular embodiments only, and is not intended to be limiting, since the scope of the present invention will be limited only by the appended claims.

[0032] Where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit unless the context clearly dictates otherwise, between the upper and lower limits of that range is also specifically disclosed. Each smaller range between any stated value or intervening value in a stated range and any other stated or intervening value in that stated range is encompassed within the invention. The upper and lower limits of these smaller ranges may independently be included or excluded in the range, and each range where either, neither or both limits are included in the smaller ranges is also encompassed within the invention, subject to any specifically excluded limiting the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included in the invention.

[0033] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, the preferred methods and materials are now described.

[0034] It must be noted that as used herein and in the appended claims, the singular forms a, and, the include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to a stream includes a plurality of such streams and reference to the valve includes reference to one or more valves and equivalents thereof known to those skilled in the art, and so forth.

[0035] The publications discussed herein are provided solely for their disclosure prior to the filing date of the present application. Nothing herein is to be construed as an admission that the present invention is not entitled to antedate such publication by virtue of prior invention. Further, the dates of publication provided may be different form the actual publication dates which may need to be independently confirmed.

[0036] ALD is an acronym used for atomic layer deposition

[0037] ZDV valve as used herein, is a zero dead volume valve in which valve seats are situated very close to the gland of the valve, so that very little purging is necessary.

[0038] Valve cycle time, or response time as used herein, is defined as the time it takes to reposition a valve from one to another of available settings; to turn the valve from on to off or from a setting directing a reactant to the chamber to a setting directing a purge gas to the chamber, for example.

[0039] MEMS is an acronym used herein to mean micro electro-mechanical system.

[0040] The terms substrate surface and surface of the substrate refer to the surface of the substrate that is exposed to the gas or vapor-phase reactant flowing into the reaction chamber. Thus, in an ALD process, the substrate surface may include one or more layers of the film currently being deposited, which were deposited in previous cycles of the current ALD process. The substrate surface may also be a film/layer previously deposited on the substrate, such as a dielectric layer, metal layer, etc.

[0041] The term valve mounted to the lid includes a valve mounted immediately adjacent the lid to minimize dead volume in flow paths connecting the valve with the showerhead/reaction chamber, and preferably includes a valve mounted flush against the lid.

[0042] FIG. 1 is a schematic cross-sectional view of one embodiment of an apparatus 10 for performing ALD. The apparatus 10 includes a vacuum or reaction chamber which is defined by the walls of the apparatus 10 as well as a lid sealing with the top of the walls. An arrangement (not shown in FIG. 1) is generally mounted on top of the apparatus 10 for supplying various gases, liquid vapors, and/or vaporized solids through a showerhead 12 to be distributed into the chamber for treatment of a substrate surface. The gas supplying arrangement is also provided to supply at least one purging gas to the reaction chamber.

[0043] A substrate support or heater 14 which includes a horizontal support (i.e. a substrate receiving surface) adapted to support a substrate 16 and a column which may or may not be integrally formed with the horizontal support is arranged for vertical movement with respect to the chamber of apparatus 10. Heater 14 may be formed of aluminum or ceramics, for example. When loading or unloading a substrate 16, heater 14 is moved downwardly with respect to the chamber so as to provide a larger space between the substrate 16 and the showerhead 12 and so as to align the substrate with a robot door (not shown). Upon aligning the substrate 16 with the robot door, the robot door opens to allow access by a robot to remove the existing substrate 16 and/or to load a new substrate 16. After loading/unloading, the robot door closes and the heater 14 moves upward to place the substrate into a processing position, as shown in FIG. 1. Alternatively, the substrate 16 may be heated using radiant heat, such as by lamps.

[0044] One embodiment of a deposition sequence making up a cycle in a ALD deposition process includes the following four steps, for example: (1) a first step comprising providing a pulse of a first reactant to the substrate 16; (2) a second step comprising providing a purge gas; (3) a third step comprising providing a pulse of a second reactant to the substrate; and (4) a fourth step comprising providing a purge gas. Reactants can be compounds, reductants, oxidizing agents, precursors, catalysts, and mixtures thereof. The second step and the fourth step may provide the same or different purge gas. Examples of purges gases that may be used N₂, Ar, He, H₂, combinations thereof, or other nonreactive or inert gas or gas combinations known and used for such purpose. Not wishing to be bound by theory, it is believed that when the first reactant is provided to the substrate, the first reactant is chemisorbed onto the surface of the substrate 16. The second reactant is provided to the substrate to react with the first reactant chemisorbed on the surface of the substrate 16 to form a thin layer of material. The purge gas between the pulse of the first reactant and the pulse of the second reactant separates the pulses of the reactants and reduces the gas phase reactions between the reactants. The purge gas may be provided as a continuous flow in which the pulses of the reactants are dosed into the continuous flow or the purge gas may be provided in pulses. These steps are repeated until the desired thickness of the film is obtained. In other words, the thickness of the film can be adjusted according to the number of repetitions of steps (1)-(4).

[0045] Since the layer to be deposited by ALD is built up one atomic layer at a time with each cycle, it is not unusual for the process to require many cycles to obtain the desired thickness in a layer being deposited. To make such a process economically feasible with regard to production throughput, it becomes critical to reduce the length of time required by each of the steps in each cycle. In reference to FIG. 1, a reduction of the processing volume V1 reduces the amount of time required to fill the space with a sufficient volume of reactant to be chemisorbed (step 1) and/or to react (step 3) with a co-reactant on the surface of the substrate. Additionally, the purge steps (steps 2 and 4) can be significantly shortened by arranging a chamber such as according to the present invention, where the reactants are confined substantially to the reaction volume (volume V1). Reaction volume is defined as the volume in which the reactant gases/purge gases occupy as the reactant gases/purge gases flow from the showerhead 12 to a vacuum port 20. In prior art arrangements, reactants pass between the substrate 16/heater 14 and the chamber walls or chamber liner walls 18, to also occupy the larger volume V2 beneath the heater 14. Not only does this require a greater volume of reactant to be distributed in each of steps 1 and 3, but even more significantly this situation requires a larger volume of purge gas and longer purge times to purge the reactants and by-products in steps 2 and 4.

[0046] The present invention provides a bottom purge feature which is preferably operative during the process sequence of steps 1, 2, 3, and 4, so that when reactants are being distributed from the showerhead 12 to the surface of the substrate 16, a virtual shower curtain is established to effectively prevent the reactants from passing between the heater 14 and liner 18 (or chamber wall if no liner is used). This effectively constrains the volume that the reactant is contained in to volume V1, which reduces the time for performing each of steps 1-4. Not only does the virtual shower curtain reduce the volume of reactants, by-products, etc. to be purged in steps 2 and 4, but the virtual shower curtain also substantially prevents reactions from occurring in the chamber volume V2 below the heater, thereby facilitating decontaminate during the purging steps. Also, the virtual shower curtain reduces the times for purges performed (steps 2 and 4) since the purge gas from the showerhead 12 is contained in volume V1. The purging of the entire chamber is performed with a bottom purge, during which a vacuum is drawn through the port(s) 20 to evacuate the chamber.

[0047] While delivering reactants to the substrate during steps 1 and 3, the virtual shower curtain may be established by drawing a vacuum through port(s) 20, for example. The heater 16 may be provided with one or more channels through both the horizontal support and the vertical support so that vacuum flow proceeds as indicated by the arrows in FIG. 1. The relatively high velocity flow (for example, flow rates of about 100 to 500 sccm in a TanOx Xz chamber, although these numbers will vary with according to variations in the volume of the chamber being used) of an inert purging gas (e.g., nitrogen and/or argon) through the gap between the heater/substrate 14, 16 and the liner 18 or shadow ring (which may be formed with the liner 18) or chamber wall, cause a venturi effect that prevents flow of reactants into volume V2 while keeping them in the volume V1, with some small amount of purging of the same via port(s) 20.

[0048] Another way of shortening the cycle times for ALD is to reduce the reaction volume V1, in which the processing steps are carried out. Preferably, the reaction volume V1 between the showerhead 12 and the substrate support 14 is less than about 1.0 L, more preferably less than about 0.6 L, for a substrate support 14 adapted to support a 200 mm diameter substrate and is less than about 2.25 L, more preferably less than about 1.35 L, for a substrate support 14 adapted to support a 300 mm diameter substrate. By reducing the size of volume V1, this also reduces the amount of time required, at any given flow rate, to fill the volume with a reactant for carrying out a processing step. Further, as noted above with regard to volume V2, a reduction in the volume V1 also reduces the amounts of purging gas that are required during a purging step to purge a reactant from the volume V1 prior to going forward with another processing/reaction step. Thus, for any given flow rate of purge gas, a reduction in the volume V1 reduces the amount of time required to purge that volume of reactants/by-products. Additionally, by maximizing rates of conductance in all flow paths for reactants as well as purging gases used in the process, this will reduce the amount of time needed to complete each step since the purging gas or reactant can be delivered in a sufficient amount in less time relative to a set up with slower conductance pathways.

[0049] One critical area for improving conductance pathways is in the showerhead 12. Conductance forms an inverse relationship with resistance, so an objective is to reduce the resistance build up within the showerhead. To achieve a reduction in resistance a reduction in surface contact between the reactant or purging gas and the surfaces of the showerhead needs to be achieved. For a pipeline (e.g. a conductance pathway in a showerhead), conductance increases to the fourth power as a function of increase in diameter of the pipeline, i.e., C%d⁴. Therefore, by increasing the size or diameter of the cross-sections of the flow pathways in the showerhead, increased conductance can be achieved. However, a countervailing consideration is the concern for controlling how fast the gas expands in the showerhead, and the distribution of the reactant over the surface of the substrate 16 as it exits the showerhead. It is noted that the desire to minimize volume V1 by moving the substrate surface 16 as close as possible to the showerhead 12, in some configurations, may also countervail against even distribution of the reactant by the showerhead 12 over the surface of the substrate 16.

[0050] A showerhead used in a CVD process will typically contain 1000 or more distribution holes of about 0.008 to 0.032 diameter for example. Such a design, while providing good distribution patterns for CVD, also provides a considerable amount of resistance to flow therethrough, and pump down times to reach operating pressures and flows is not insignificant for purposes of ALD cycling. The present invention substantially reduces the resistance in the showerheads used to greatly reduce the pump down time, as well as the time to deliver reactants and/or purge gas from the showerhead 12, while also allowing a reduction in the processing volume V1.

[0051] FIG. 2 is a schematic cross-sectional view of one embodiment of a top lid arrangement 30 for ALD processing. As mentioned above, a top lid 30 seals with the chamber 10 to provide the processing environment therein. The showerhead 12 mounts to the underside of the top lid 30 and receives reactants as well as one or more purge gases that are conveyed through the flow paths 32a, 34a in the top lid 30 when one or both of valves 32, 34 are opened.

[0052] FIG. 3 is a schematic cross-sectional perspective view of another embodiment of a top lid 30 and a showerhead 12 mounted thereto. Showerhead 12 employs a high conductance design in which a fewer number of holes 13 are employed, but each having a significantly greater diameter than the prior art holes described above. For example, holes 13 may have a diameter ranging from about to about . Holes 13 generally all have the same diameter, although this is not necessary. Additionally, spacers 15 (see also FIG. 4) are provided on showerhead 12 to prevent a fluid-tight seal of the showerhead against the top lid 30, thereby forming a gap 17 of up to about 200 mils, more preferably about 100 to 200 mils, through which reactant/purge gas can flow. Thus, not only does the gas flow through holes 13 to be distributed on the substrate surface 16, but it also flows radially, in the directions of arrows 17a in FIG. 3, and also in all radial directions outwardly to the circumference of the showerhead 12 which aids in the distribution of reactants at the peripheral regions of the substrate surface 16. Gap 17 not only reduces the resistance to flow of the reactant or purge gas into volume V1, but it also allows a reduction in the volume V1 as the substrate 16 can be moved relatively closer (e.g., to leave a spacing of about 200 to 400 mils) to the showerhead 12 while the showerhead still maintains the ability to adequately distribute reactant over the entire surface of the substrate 16, since the gap 17 broadens the effective range of distribution area at close distance, compared to a showerhead having no such pathways defined by a gap. Additionally, by directing some of the flow horizontally, gap 17 reduces vertical velocity of the gas being delivered to reduce the likelihood of blowing off reactants chemisorbed on the surface of the substrate 16.

[0053] FIG. 5 is a schematic perspective view of another embodiment of a showerhead 12 having a single, large open bore or hole 13, which, when mounted to the top lid 30 aligns with delivery bore 36 (FIG. 3). As shown in FIG. 5, bore 13 has a somewhat smaller diameter than bore 36 and is provided with a taper 13a where the two meet. However, the bore 13 may be made as large as the bore 36. Bore 13 is typically made to have a diameter of about 2 to 6 inches. This showerhead provides a very direct, high conductance throughput of reactant/purge gas, although distribution of reactants to the periphery of the substrate surface 16 may not be as uniform as with the showerhead shown in FIG. 4, particularly for extremely large substrates.

[0054] Referring again to FIG. 2, valves 32 and 34 are mounted to the top lid 30. In one embodiment, the valves 32 and 34 are mounted to the top lid 30 leaving enough space to allow sufficient travel for nuts 32b, 34b to be unthreaded off of the respective valves for servicing/replacement of the valves. Whether the valves 32 and 34 are mounted immediately adjacent the top lid 30 or mounted flush to the top lid 30, the distance between the valves and the volume V1 is minimized and the volume of gas left in either flow path 32a or 34a is reduced. Therefore, the amount of purging gas that needs to be flowed though the flow paths during a purging step is reduced, thereby making it possible to reduce the time of those steps. The shortened distances also make it possible to fill the volume V1 with a reactant in less time during the reaction process steps. Thus, the pulses times of the reactants (for example, steps 1 and 2) and/or purge times (for example, steps 3 and 4) may be minimized. FIG. 6 shows an arrangement in which valves 32 and 34 are mounted flush to the top lid 30, which still further decreases the dead space or dead volume in the flow paths 32a and 34a between the vales 32 and 34 and the volume V1, respectively.

[0055] In either case, the valves are arranged to introduce the reactants into the reaction volume V1 to carry out the ALD process. For example, valve 32 may be connected with a source of a first reactant A and valve 34 may be connected with a source of a second reactant B. As described above, a first step of the cycle is carried out by flowing the reactant A into the volume V1 where it is saturatively chemisorbed at the surface of the substrate 16. Thus, for carrying out the first step, valve 32 is opened to allow flow of reactant A to volume V1 though pathway 32a and through the showerhead 12. At the same time, as also described above, a vacuum is applied through port/ports 20 to perform a bottom purge forming the virtual shower curtain to contain the reactant A in volume V1. The reactant used as reactant A may vary as the process may be used to deposit various types of layers by ALD. For example, a high k dielectric layer such as Ta₂O₅ may be deposited in which case reactant A may be TAETO (tantalum pentaethoxide) or TBTDET (tertiarybutylamino tris(diethylamino) (tantalum), or other known precursors for the formation of tantalum pentoxide, for example. Other high k dielectric layers may be formed by the process according to the present invention, including, but not limited to zirconium oxides (e.g., ZrO₂), hafnium oxides (HfOx), lanthanum oxides (LaOx), barium strontium titanates (BST), strontium bismuth tantalates (SBT) and lead zirconium titanates (PZT); using precursors known for forming such layer. Still further, other layers such as Al₂O₃ or composite layers including Al₂O₃ and tantalum pentoxide, for example may be formed using the present apparatus and processes. For the formation of an Al₂O₃ layer, a good non-pyrophoric reactant A was found to be di-methyl aluminum hydroxide-ligand (DMAH-L) although other known precursors may be used for reactant A in forming an Al₂O₃ layer. For the formation of a Ta₂O₅ layer or a Al₂O₃, reactant B may be ozone, for example, or other reactive oxygen containing species such as atomic oxygen from a plasma from ozone gas (O₃), oxygen gas (O₂), water vapor (H₂O), other suitable gases and combinations thereof.

[0056] It is noted that each of valves 32 and 34 may be operated in a number positions which may be better understood by reference to FIG. 7 which shows a schematic arrangement of valves 32 and 34. Valve 32 may have a valve seat 32r for controlling the flow of a reactant gas A and may have a valve seat 32p for controlling the flow of a purge gas. Valve 34 may have a valve seat 34r for controlling the flow of a reactant gas B and may have a valve seat 34p for controlling the flow of a purge gas. Valve seat 32r may be opened and closed to provide pulses of the reactant gas A. Valve seat 34r may be opened and closed to provide pulses of the reactant gas B. Valve seat 32p and/or valve seat 34p may be opened and closed to provide a purge gas into the chamber. In one aspect, the valve seat 32p and/or valve seat 34p may be opened and closed to provide pulses of the purge gas.

[0057] For example, during the first step of the cycle, valve seat 32r is opened to introduce a pulse of reactant A. After a predetermined time to allow saturative chemisorption of reactant A on the surface of substrate 16, the time for which varies depending upon the type of reactant being distributed and the volume V1, valve seat 32r is closed thereby preventing any further flow of reactant A into flowpath 32a. Then, in a second step, valve seat 32p and/or valve seat 34p is opened to introduce a purge gas from flowpath 38 to flow pathways 32a and/or 34a. Flowpath 38 provides a common purge gas source to valves 32 and 34. A common purge gas source instead of two separate purge sources to the valves simplifies the gas delivery apparatus. A bottom purge may be conducted simultaneously while valve 32 and/or valve 34 is being purged (i.e. the top purge). Purge gases used in performing the top and bottom purges are evacuated through port(s) 20. Preferably, both valve seat 32p and valve seat 34p are open to purge their associated flowpaths during the second step since there is a potential for backflow of reactant A into flowpath 34a. Further, without flow of the purging gas through flowpath 34a during this purging step, it would also be possible for some of the reactant A being purged to be driven into the flowpath 34a. Examples of purges gases that may be used N₂, Ar, He, H₂, combinations thereof, or other nonreactive or inert gas or gas combinations known and used for such purpose. The purging of the second step is generally conducted for about 10-100 msec.

[0058] After completion of the second step, in a third step, valve seat 34r is opened to introduce a pulse of reactant B. At the termination of the third step, in a fourth step, valve seat 34r is closed and valve seat 34p and/or valve seat 32p is opened to purge the flow pathways 34a and/or 32a. Preferably both valve seat 34p and valve seat 32p are open to purge their associated flow paths. The time for carrying out the fourth step may not be the same as that for carrying out the second step due to the existence of different species/by-products to be removed after completion of step three. Upon completion of the purge during the fourth step, valve seat 32r is opened to start the first step of the next cycle. As noted above, the cycle is repeated until a sufficient number of layers have been deposited to achieve the desired thickness of the layer being deposited.

[0059] Valves 32 and 34 may be operated in other positions. For example, valve seat 32p and/or valve seat 34p may remain open to provide a continuous flow of a purge gas into the chamber in which pulses of the reactant gas A and reactant gas B are dosed into the stream of the purge gas.

[0060] In addition to mounting the valves 32 and 34 to the lid 30 so as to minimize the amount of dead volume remaining in the flow paths of the chamber lid area (e.g., the length of pathways 32a and 34a) it is also desirable to provide valves with a minimum of dead volume within the valve mechanisms themselves (i.e., between the inputs of reactants and purge gases and the output that directs these gases to the chamber lid 30). Such valves are known as ZDV valves or zero dead volume valves and further reduce the amounts of gases needed to be flowed through the system for reacting as well as for purging. A zero dead volume valve is a valve in which valve seats are situated very close to the gland of the valve, so that very little purging is necessary. For example, the valve seat 32p and/or valve seat 34p is position in close proximity to the valve seat 32r and/or valve seat 32r to reduce the amount of Dead Volume in the line to be purged. A zero dead volume valve has negligible dead volume (i.e. not necessary zero dead volume.)

[0061] The zero dead volume aspect of these valves decreases processing times by decreasing the amount or volume of a gas that must be pumped in any given step. To further decrease processing times, valves are chosen to have a fast response time or valve cycle time, where a response time or valve cycle time is defined as the time it takes to reposition a valve from one to another of the above-described three positions.

[0062] Currently, pneumatic valves having a valve cycle time of about 1-2 seconds (such as those available from Variflo in Richmond, Calif.) may be used. Alternatively solenoid driven valves such as those available from Swagelok (Sunnyvale, Calif.) may be used. With the use of MEMS technology (i.e., micro electro-mechanical system), available from Redwood Microsystems, Inc. (Menlo Park, Calif.), the valve cycle times of these valves can be reduced to about 200-300 msec or less. To further speed up the valve cycle time piezo driven valves, such as those supplied by Horiba/Stec or Fujikin (Fujikin of America, Inc., Santa Clara, Calif.) may be used. Used with MEMS technology control, these valves exhibit valve cycle times of about 100 msec or less.

[0063] While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.