Methods for atomic-layer deposition

[0001] This application is a continuation of U.S. application Ser. No. 10/137,168 filed May 2, 2002, now U.S. Pat. No. 7,160,577, which is incorporated herein by reference.

[0002] This invention concerns methods of making integrated circuits, particularly layer formation techniques, such as chemical-vapor deposition and atomic-layer deposition.

[0003] Integrated circuits, the key components in thousands of electronic and computer products, are interconnected networks of electrical components fabricated on a common foundation, or substrate. Fabricators generally build these circuits layer by layer, using techniques, such as deposition, doping, masking, and etching, to form and interconnect thousands and even millions of microscopic transistors, resistors, and other electrical components on a silicon substrate, known as a wafer.

[0004] One common technique for forming layers in an integrated circuit is called chemical vapor deposition. Chemical vapor deposition generally entails placing a substrate in a reaction chamber, heating the substrate to prescribed temperatures, and introducing one or more gases, known as precursor gases, into the chamber to begin a deposition cycle. The precursor gases enter the chamber through a gas-distribution fixture, such as a gas ring or a showerhead, one or more centimeters above the substrate, and descend toward the heated substrate. The gases react with each other and/or the heated substrate, blanketing its surface with a layer of material. An exhaust system then pumps gaseous by-products or leftovers from the reaction out of the chamber through a separate outlet to complete the deposition cycle.

[0005] Conventional chemical-vapor-deposition (CVD) systems suffer from at least two problems. First, conventional CVD systems generally form non-uniformly thick layers that include microscopic hills and valleys, and thus generally require use of post-deposition planarization or other compensation techniques. Second, it is difficult, if not impossible, for CVD to provide uniform coverage of trench sidewalls or complete filling of holes and trenches.

[0006] To address these shortcomings, fabricators have developed atomic-layer deposition (ALD), a special form of CVD that allows highly uniform formation of ultra-thin layers having thicknesses of one molecule or several atoms of the deposited material. Though similar to CVD in terms of equipment and process flow, ALD relies on adsorption of some of the reactants into exposed surfaces, and thus provides coverage and fill of structural features that are difficult, if not impossible, using CVD.

[0007] In recent years, researchers and engineers have made strides toward making ALD commercially viable for some applications. For example, one team of researchers reportedly optimized an ALD process for depositing an aluminum oxide (AlO_x) film in thin-film heads—devices used to read and write magnetic data. See, Paranjpe et al., Atomic Layer Deposition of AlO_x for Thin Film Head Gap Applications, Journal of Electrochemical Society, 148 (9), pp. G465-G471 (2001), which is incorporated herein by reference.

[0008] However, the present inventors have recognized that the equipment and processes reported as optimal for thin-film head applications suffer from some limitations relative to use in fabricating integrated circuits. For example, the reported process deposits material at the slow rate of less than one Angstrom per cycle, suggesting that more than 50 cycles would be necessary to form a 50-Angstrom-thick layer. Moreover, the reported equipment uses a larger than desirable reaction chamber, which takes longer to fill up or pump out, and thus prolongs the duration of each deposition cycle.

[0009] Accordingly, there is a need for better systems and methods of atomic-layer deposition of aluminum oxides as well as other material compositions.

[0013] The following detailed description, which references and incorporates the above-identified figures, describes and illustrates one or more specific embodiments of the invention. These embodiments, offered not to limit but only to exemplify and teach the invention, are shown and described in sufficient detail to enable those skilled in the art to make and use the invention. Thus, where appropriate to avoid obscuring the invention, the description may omit certain information known to those of skill in the art.

[0014] One exemplary atomic-layer deposition system, well suited for aluminum-oxide depositions in integrated-circuit fabrication, includes an outer chamber, a substrate holder, and a unique gas-distribution fixture. The fixture includes a gas-distribution surface having two sets of holes and a gas-confinement member that forms a wall around the holes. In operation, one set of holes dispenses an aluminum-carrying precursor and the other dispensing an oxidizing agent gas, after the gas-confinement member engages, or otherwise cooperates with the substrate holder to form an inner chamber within the outer chamber.

[0015] The inner chamber has a smaller volume than the outer chamber and thus consumes less gas during the deposition process than would the outer chamber used alone. Also, the smaller chamber volume allows the exhaust system to pump the chamber more quickly, thus allowing shorter ALD cycles and potentially increasing rates of production.

[0016] FIG. 1 shows an exemplary atomic-layer-deposition system 100 which incorporates teachings of the present invention. In particular, system 100 includes a chamber 110, a wafer holder 120, a gas-distribution fixture (or showerhead) 130, a gas-supply system 140, and exhaust pumps 150 and 160.

[0017] More particularly, chamber 110 includes respective top and bottom plates 112 and 114 and a sidewall 116. In the exemplary embodiment, chamber 110 is a cylindrical structure formed of stainless steel or glass. However, other embodiments use different structures and materials. Bottom plate 114 includes an opening 114A. Extending through opening 114A is a stem portion 122 of wafer holder 120.

[0018] Wafer holder 120 also includes a support platform 124, one or more heating elements 126, one or more temperature sensors 128, and an RF source 129. Holder 120 (also called a chuck) raises and rotates manually or automatically via lift and rotation devices, and is coupled to a power supply and temperature control circuitry (all of which are not shown). Support platform 124 supports one or more substrates, wafers, or integrated-circuit assemblies 200. Substrate 200 has an exemplary width or diameter of about 30 centimeters and an exemplary thickness in the range of 850-1000 microns. (The term “substrate,” as used herein, encompasses a semiconductor wafer as well as structures having one or more insulative, conductive, or semiconductive layers and materials. Thus, for example, the term embraces silicon-on-insulator, silicon-on-sapphire, and other advanced structures.)

[0019] Heating elements 126 and temperature sensors 128 are used for heating substrates 200 to a desired temperature. Radio Frequency (RF) source 129, for example, a 1.25-kilowatt-13.56-megahertz RF generator, is used to generate and sustain a capacitively coupled plasma between the wafer holder and gas-distribution fixture 130. (Some embodiments use generators with smaller or larger capacities.)

[0020] Fixture 130, positioned above wafer holder 120 and substrate 200, includes a gas-distribution member 132, a surface-projection (or gas-confinement) member 134, and gas inlets 136 and 137. In the exemplary embodiment, fixture 130 has three operating positions 138A, 138B, and 138C relative support platform 124. Fixture 130 takes operating position 138A, before and after depositions and operating position 138B during depositions. Position 138C is taken during a plasma anneal to ensure stability of the plasma.

[0021] Gas-distribution member 132 includes main gas inputs 132A and 132B, gas-distribution channels 132D and 132F, and gas-distribution holes 132E and 132G. Main gas inputs 132A and 132B feed respective gas-distribution channels 132D and 132F, which in turn feed respective gas-distribution holes 132E and 132G. (Holes 132E and 132G are actually interleaved in the exemplary embodiment, though shown simply in the figure as spatially segregated groups.) Holes 132D and 132F define a gas-distribution surface 132C.

[0022] In the exemplary embodiment, holes 132D and 132F are substantially circular with a common diameter in the range of 15-20 microns; gas-distribution channels 132D and 132F have a common width in the range of 20-45 microns; and surface 132C is substantially planar and parallel to platform 124 of wafer holder 120. However, other embodiments use other surface forms as well as shapes and sizes of holes and channels.

[0023] Extending from gas-distribution surface 132C is surface-projection member (or collar) 134. Member 134 projects or extends from surface 132C toward support platform 124, defining a fixture cavity 134A. The exemplary embodiment forms surface-projection member 134 from stainless steel as a uniform annular or circular wall or collar that projects perpendicularly from surface 132C to define a right-cylindrical cavity.

[0024] However, other embodiments form member 134 to project at other angles relative surface 132C. For example, some form the projection at an acute or obtuse angle, such as 45 or 135 degrees, and others form the projection to peripherally define an oval, ellipse, triangle, square, or any desirable regular or irregular polygon. Thus, the present invention encompasses a wide variety of projection shapes and configurations, indeed any projection shape that facilitates definition of an effective cavity or gas-confinement volume in cooperation with wafer holder 120 and/or substrate 200.

[0025] FIG. 2, a plan view, shows further details of the exemplary embodiment of gas-distribution fixture 130. In particular, the plan view shows not only exemplary circular peripheries of gas-distribution member 132 and surface-projection member 134, but also an exemplary interleaved distribution pattern for holes 132E and 132G, and an exemplary orthogonal arrangement of gas-distribution channels 132D and 132F. (Holes 132E are shown darkly shaded to distinguish them from holes 132G, which are cross-hatched.)

[0026] Other embodiments use other hole distribution patterns and channel arrangements. For example, some embodiments include random or concentric hole patterns and various channel geometries, including concentric circles, rectangles, or other regular or irregular concentric polygons. Some embodiments may also dedicate various subsets of channels and corresponding holes to different gases. For example, one embodiment provides one set of holes and channels for approximately uniform distribution of a gas or vapor, such as TMA precursor and argon carrier gas mixture, and another set of holes and channels for approximately uniform distribution of a gas or vapor, such as a water-argon mixture.

[0027] Gas-distribution member 132 can be made in a number of ways. One exemplary method entails laminating several material layers, with each layer including holes and/or channels to effect distribution of the gases to the separate holes. If the layers are made of silicon, the material layers can be patterned and etched, for example, using conventional photolithographic or micro-electro-mechanical systems (MEMS) technology, to form holes and channels. Dry-etching techniques produce small openings and channels, while wet etching produces larger openings and channels. For further details, see, for example, M. Engelhardt, “Modern Application of Plasma Etching and Patterning in Silicon Process Technology,” Contrib. Plasma Physics, vol. 39, no. 5, pp. 473-478 (1999). Also see co-pending and co-assigned U.S. patent application Ser. No. 09/797,324, which was filed on Mar. 1, 2001, now U.S. Pat. No. 6,852,167, and which is incorporated herein by reference.

[0028] The processed layers can then be bonded together with the holes and channels in appropriate alignment using known wafer-bonding techniques. See, for example, G. Krauter et al., “Room Temperature Silicon Wafer Bonding with Ultra-Thin Polymer Films,” Advanced Materials, vol. 9, no. 5, pp. 417-420 (1997); C. E. Hunt et al., “Direct Bonding of Micromachined Silicon Wafers for Laser Diode Heat Exchanger Applications,” Journal of Micromechan. Microeng, vol. 1, pp. 152-156 (1991); Zucker, O. et al., “Applications of oxygen plasma processing to silicon direct bonding,” Sensors and Actuators, A. Physical, vol. 36, no. 3, pp. 227-231 (1993), which are all incorporated herein by reference. See also, co-pending and co-assigned U.S. patent application Ser. No. 09/189,276 entitled “Low Temperature Silicon Wafer Bond Process with Bulk Material Bond Strength,” which was filed Nov. 10, 1998, now U.S. Pat. No. 6,423,613, and which is also incorporated herein by reference. The resulting bonded structure is then passivated using thermal oxidation for example.

[0029] For an alternative fixture structure and manufacturing method that can be combined with those of the exemplary embodiment, see U.S. Pat. No. 5,595,606, entitled “Shower Head and Film Forming Apparatus Using Same, which is incorporated herein by reference. In particular, one embodiment based on this patent adds a projection or gas-confinement member to the reported showerhead structure.

[0030] FIG. 1 also shows that gas inlets 136 and 137, which feed respective holes 132E and 132G, are coupled to gas-supply system 140. Specifically, gas-supply system 140 includes gas lines 142 and 143, gas sources 144, 145, and 146, and manual or automated mass-flow controllers 147, 148, and 149. Gas line or conduit 142, which includes one or more flexible portions (not specifically shown), passes through an opening 116A in chamber sidewall 116 to connect with gas inlet 136. Gas sources 144 and 145 are coupled respectively via mass-flow controllers 147 and 148 to gas line 142. Gas line 143, which also includes one or more flexible portions (not specifically shown), passes through an opening 116B in chamber sidewall 116 is coupled via mass-flow controller 149 to source 146.

[0031] In the exemplary embodiment, which is tailored for aluminum oxide deposition, source 144 provides a vapor-drawn aluminum precursor, such as trimethylaluminum (TMA) with a vapor pressure of 11 Torr at room temperature; source 145 provides a carrier gas, such as argon; and source 146 provides an oxidant, such as a water-argon mixture. The water-argon mixture can be implemented by bubbling an argon carrier through a water reservoir. Other embodiments use other aluminum precursors, such as triisobutylaluminum (TIBA), dimethylaluminum hydride (DMAH), AlC₃, and other halogenated precursors and organometallic precursors. Other types of oxidants include H₂O₂, O₂, O₃, N₂O. Thus, the present invention is not limited to specific aluminum precursors or oxidants.

[0032] System 100 also includes vacuum pumps 150 and 160. Vacuum pump 150 is coupled to gas-distribution fixture 130 via a mass-flow controller 152 and gas line 142. And, vacuum pump 160 is coupled to the interior of chamber 110 via a line 162 and an opening 114B in chamber bottom plate 114.

[0033] In general operation, system 100 functions, via manual or automatic control, to move gas-distribution fixture 130 from operating position 138A to position 138B, to introduce reactant gases from sources 145, 146, and 147 through holes 132E and 132G in gas-distribution fixture 130 onto substrate 200, and to deposit desired matter, such as an aluminum oxide, onto a substrate.

[0034] More particularly, FIG. 3 shows a flowchart 300 which illustrates an exemplary method of operating system 100. Flowchart 300 includes process blocks 302-320.

[0035] The exemplary method begins at block 302 with insertion of substrate 200 onto wafer holder 120. Execution then proceeds to block 304.

[0036] In block 304, the system forms or closes an inner chamber around substrate 200, or at least a portion of substrate 200 targeted for deposition. In the exemplary embodiment, this entails using a lever or other actuation mechanism (not shown) to move gas-distribution fixture 130 from position 138A to position 138B or to move wafer holder 120 from position 138B to 138A. In either case, this movement places gas-distribution surface 132C 10-20 millimeters from an upper most surface of substrate 200. In this exemplary position, a lower-most surface of surface-projection member 134 contacts the upper surface of support platform 124, with the inner chamber bounded by gas-distribution surface 132C, surface-projection member 134, and the upper surface of support platform 124.

[0037] Other embodiments define the inner chamber in other ways. For example, some embodiments include a surface-projection member on support platform 124 of wafer holder 120 to define a cavity analogous in structure and/or function to cavity 134A. In these embodiments, the surface-projection member takes the form of a vertical or slanted or curved wall, that extends from support platform 124 and completely around substrate 200, and the gas-distribution fixture omits a surface-projection member. However, some embodiments include one or more surface-projection members on the gas-distribution fixture and the on the support platform, with the projection members on the fixture mating, engaging, or otherwise cooperating with those on the support platform to define a substantially or effectively closed chamber. In other words, the inner chamber need not be completely closed, but only sufficiently closed to facilitate a desired deposition.

[0038] In block 306, after forming the inner chamber, the exemplary method continues by establishing desired ambient conditions for the desired deposition. This entails setting temperature and pressure conditions within chamber 110, including cavity 134A. To this end, the exemplary embodiment operates heating element 126 to heat substrate 200 to a desired temperature, such as 150-200° C., and operating vacuum pump 150 and/or pump 160 to establish a desired ambient pressure, such as 3.0 Torr. Gas-distribution fixture 130 is held at a temperature 30-50° C. warmer than its surroundings. (However, other embodiments can maintain the fixture at other relative operating temperatures.) After establishing the desired ambient conditions, execution continues at block 308.

[0039] Block 308 entails hydroxylating the surface of substrate 200 by introducing an oxidant into the separate chamber. To this end, the exemplary embodiment shuts mass-flow controllers 147 and 148 and operates mass-flow controller 149 to transfer an oxidant, such as a water in an argon carrier, from source 146 through gas line 143 and holes 132G into cavity 134A for a period, such as two seconds.

[0040] Notably, the inner chamber is smaller in volume than chamber 100 and thus requires less gas and less fill time to achieve desired chemical concentrations (assuming all other factors equal.) More precisely, the exemplary embodiment provides an inner chamber with an empty volume in the range of 70 to 350 cubic centimeters, based on a 1-to-5 millimeter inner-chamber height and a fixture with a 30-centimeter diameter. Additionally, the number and arrangement of holes in the fixture as well as the placement of the holes close to the substrate, for example within five millimeters of the substrate, promote normal gas incidence and uniform distribution of gases over the targeted portion of substrate 200.

[0041] Block 310 entails purging or evacuating the inner chamber to reduce water concentration in the gas-distribution fixture and inner chamber to trace levels. To this end, the exemplary method initially drives a high flow of argon gas from source 145 through fixture 130 into the inner chamber and then draws the gas out of the inner chamber through the fixture via vacuum pump 150, defining a purge cycle of less than five seconds, for example three-four seconds. The present invention, however, is not believed to be limited to any particular purge-cycle duration.

[0042] Next, as block 312 shows, the exemplary method introduces an aluminum precursor into the inner chamber through gas-distribution fixture 130. This entail operating mass-flow controllers 147 and 148 to respectively allow the flow of TMA and an argon carrier into fixture 130 via line 142 for a period of time such as 0.5-2.0 seconds. During this period, the argon carries the TMA to the hydroxylated surface of the substrate, causing formation of an approximately 0.8 Angstrom (Å) monolayer of aluminum oxide (AlO_x).

[0043] Block 314 entails purging or evacuating the inner chamber to reduce precursor concentration in the gas-distribution fixture and inner chamber to trace levels. To this end, the exemplary method initially drives a flow of argon gas from source 145 through fixture 130 into the inner chamber and then draws the gas out of the inner chamber through the fixture via vacuum pump 150. Again, this purge cycle is expected to consume less than five seconds.

[0044] At this point, as represented by a return path 315 back to block 304, blocks 304-314 can be repeated as many times as desired to achieve an aluminum-oxide layer within roughly one Angstrom of virtually any desired thickness from 5-10 Angstroms upwards. For semiconductor applications, such as forming gate dielectrics, thicknesses in the range of 50-80 Angstroms could be used.

[0045] Block 316 entails annealing the substrate and deposited aluminum-oxide layer to enhance the dielectric breakdown voltage of the layer. In the exemplary embodiment, this entails moving fixture 130 to operating position 138C (which establishes a substrate-to-fixture separation in the range of 30-50 millimeters) and using RF source 129 to generate a 250 Watt capacitively coupled plasma at 0.12 Torr in an argon-oxygen atmosphere (10 atom percent O₂) between the wafer holder. Some embodiments anneal after every monolayer to maximize dielectric breakdown strength, and some anneal after each 25-50 Angstroms of deposited material thickness. Though various anneal times are feasible, the exemplary embodiment anneals for 10-15 seconds in high-temperature environment. A return path 317 back to block 304 indicates that blocks 304-316 can be repeated as many times as desired.

[0046] In block 318, the system opens the separate chamber. In the exemplary embodiment, this entails automatically or manually moving gas-distribution fixture 130 to position 138A. Other embodiments, however, move the wafer holder or both the fixture and the wafer holder. Still other embodiments may use multipart collar or gas-confinement members which are moved laterally relative the wafer holder or gas-distribution fixture to open and close an inner chamber.

[0047] In block 320, substrate 200 is unloaded from chamber 110. Some embodiments remove the substrate manually, and others remove it using an automated wafer transport system.

[0048] In furtherance of the art, the inventors have presented new systems, methods, and apparatuses for atomic-layer deposition. One exemplary system includes an outer chamber, a substrate holder, and a unique gas-distribution fixture. The fixture engages, or otherwise cooperates with the substrate holder to form an inner chamber within the outer chamber. Notably, the inner chamber not only consumes less gas during deposition to reduce deposition waste and cost, but also facilitates rapid filling and purging to reduce deposition cycle times (with all other factors being equal.)

[0049] The embodiments described above are intended only to illustrate and teach one or more ways of practicing or implementing the present invention, not to restrict its breadth or scope. The actual scope of the invention, which embraces all ways of practicing or implementing the invention, is defined only by the following claims and their equivalents.