Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K10/00—Welding or cutting by means of a plasma
  • B23K10/003—Scarfing, desurfacing or deburring
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
  • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
  • H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
  • H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic Table or AIIIBV compounds with or without impurities, e.g. doping materials
  • H01L21/30—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26
  • H01L21/31—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26 to form insulating layers thereon, e.g. for masking or by using photolithographic techniques; After treatment of these layers; Selection of materials for these layers
  • H01L21/3105—After-treatment
  • H01L21/311—Etching the insulating layers by chemical or physical means
  • H01L21/31127—Etching organic layers
  • H01L21/31133—Etching organic layers by chemical means
  • H01L21/31138—Etching organic layers by chemical means by dry-etching
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K2101/00—Articles made by soldering, welding or cutting
  • B23K2101/36—Electric or electronic devices
  • B23K2101/40—Semiconductor devices

Definitions

• This invention relates to semiconductor manufacturing generally and more specifically to a step in the process of manufacturing semiconductor devices using a hot gas stream technique.
• Holes and trench like patterns with a very high depth to width aspect ratio with micron or sub-micron openings have a number of applications in the manufacture of semiconductors.
• This description uses the term high aspect ratio holes to generically describe holes and trench like patterns that have a very high depth to width ratio of greater than 10 to 1.
• Various etching methods have been developed to generate such holes in silicon. The approaches use a lithographically defined mask pattern; wet chemical etch methods that take advantage of chemical selectivity along the crystal plane; and dry, plasma etch processes, which are done at low pressure to obtain a highly directional, anisotropic etch.
• Very high aspect ratio holes have an application in semiconductor devices and in various miniature micro-machined devices (MIMMs).
• MIMMs miniature micro-machined devices
• trenches for high capacitance structures with low surface area having aspect ratios of 50:1 and higher are being investigated for advanced de- signs.
• the need for subsequent patterning after making the very high aspect ratio holes usually requires a photo- lithographically defined mask pattern be made in a photosensitive polymer such as photoresist or photosensitive polyimide. In such a step, the high aspect ratio hole is filled with the photosensitive polymer.
• the polymer mask Following the processes that use the polymer mask pattern, the polymer mask must be stripped from the device. In some applications, it may be advantageous to remove the polymer material partially, to a controlled depth to allow processing the upper, exposed section of the hole while the remaining polymer protects the lower section in the holes.
• a DRAM capacitor application that uses such a capability to increase the capacitor's area is described in "New Materials Enhance Memory Performance" a review by J. Baliga, Semiconductor International, November 1999, p 79-90, see p. 80.
• an additional requirement of the polymer removal process is that the exposed surface of the device not be subject to electrical degradation.
• Types of degradation that can occur in plasma removal processes may come from energetic species causing crystal damage or damage to a thin dielectric layer.
• Standard methods of removing photo-polymers involve a method referred to as "ashing" in which a low pressure electrical discharge generates a plasma that creates chemically reactive oxygen species that flow to the surface to strip off the polymer and convert the polymer to volatile oxide by-products (e.g., HO x , CO x ).
• ashing in which a low pressure electrical discharge generates a plasma that creates chemically reactive oxygen species that flow to the surface to strip off the polymer and convert the polymer to volatile oxide by-products (e.g., HO x , CO x ).
• the flux of active oxygen species that reaches the bottom of the hole, decreases as the aspect ratio increases, with the result that the etch rate of the polymer slows dramatically.
• HDP High Density Plasma
• This pressure is sufficiently low so that the path length between collisions of plasma generated reactive species is sufficiently long so that reactive ions can be injected into the hole by acceleration of an electric field set-up in a boundary layer "sheath" over the surface of the substrate.
• a problem with this HDP approach is that the energetic ion species can electrically degrade the device's electrical characteristics.
• the prior art has used the concept of a long path length between collisions with other gas species to enable a reactive species to reach the bottom of a very high aspect ratio hole where the species can convert the polymer to volatile by products.
• a near atmospheric pressure process that enables removal of a polymer from high aspect ratio holes, including trenches, without electrical degradation.
• These holes in substrates may have depth to width ratios greater than 10:1 including very narrow widths that can be less than 0.1 micron.
• a controlled, partial removal of the poy- mer from high aspect ratio holes can be done without electrical degradation of sensitive devices that may be on the substrate.
• the polymers may be removed at relatively high rates, > 5 microns/min.
• the polymers may be standard, photoresists or highly cross-linked polymers such as polyimide that are very difficult to remove by any standard wet or dry plasma techniques.
• the hot gas stream typically has a smaller area than the substrate so that controlled motion of the substrate through the hot gas stream is used to uniformly remove polymer from the substrate.
• the hot gas stream is a high tempera- ture arc type plasma that is generated in an inert gas such as argon.
• an object of the invention to provide a technique for the removal of a polymer from a high aspect ratio hole in a semiconductor wafer or other substrate surface.
• Figure 1 is a schematic side plan view of an apparatus showing the concept of using a hot gas stream for the removal or controlled partial removal of a polymer in accordance with the invention from high aspect ratio holes in a semi- conductor wafer substrate surface;
• Figure 2 is a schematic side plan view of a plasma processing system that can be used to generate the needed hot gas stream
• Figure 3 is an enlarged section view of a semiconductor wafer substrate having high aspect ratio holes covered by a polymer during manufacture
• Figure 4 is an enlarged section view of a semiconductor wafer substrate as in Figure 2 with the polymer removed using the technique of our invention
• Figure 5 is an enlarged section view of a semiconductor wafer substrate as in Figure 2 but with the polymer partially removed using the technique of our invention.
• a semiconductor wafer 10 is shown mounted on a wafer holder 12.
• a hot gas stream 14 is directed onto the substrate or wafer surface.
• the wafer 10 is held in an upside down position with the ass ⁇ - tance of a negative pressure from a flow of gas such as nitrogen.
• the wafer holder 12 and technique for retaining a wafer can be as described in a C ⁇ pending provisional patent application entitled "Wafer Holder For Rotating and Translating Wafers For Processing In An Atmospheric plasma System With Control Of Wafer Holder Temperature” filed on October 12, 1999 bearing Serial No. 60/158,892 by the same inventors and owner as for this patent application and which provisional application is fully incorporated herein by reference thereto.
• an atmospheric hot gas stream 14 is generated with an apparatus 16 within a sealed chamber 13.
• the atmospheric plasma generating system 16 often referred to as a plasma jet, has previously been described, see US patent 6,040,548, by Siniaguine, entitled “Apparatus for generating and deflecting a plasma jet". Additional improvements to the apparatus de- scribed in U.S. Patent 6,040,548 for this polymer removal application are described and referenced in the description of this application.
• the apparatus 16 uses a high temperature, arc type plasma generated in an inert gas such as argon between two electrode subassemblies 18, 20 that serve as a cathode and anode for the arc discharge 22.
• an inert gas such as argon
• the arc 22 formed by the electrode configuration creates the stream 14 of hot gas to the substrate surface 28.
• the substrate or wafer 10 to be processed is moved through the treatment area formed by the hot gas stream 14 using a suitable actuator that is not shown.
• Other suitable ambient gases may be employed inside the sealed chamber 13.
• a gas injector 26 may be used to inject a gas such as oxygen or a mixture of gasses directly into the hot gas stream.
• a gas such as oxygen or a mixture of gasses directly into the hot gas stream.
• the hot gas stream is composed primarily of the inert gas from the two electrode assemblies and from the process chamber 13 ambient gas that is entrained into the hot gas stream.
• the temperature of the gas stream at the hydrodynamic gas boundary over the wafer surface 28 may typically be approximately 8,000°C. This temperature may be controlled by controlling the distance of the electrode assemblies 18 20 from the substrate 10 and the power into the arc type plasma. Typical power parameters for driving the arc plasma are approximately 150 V and 80 A.
• the size of the treatment area generally denoted as A, where the stream 14 is incident upon the substrate surface 28, is approximately 2 cm diameter, normally less than the size of the substrate 10 to be processed (e.g., a 200 mm diameter silicon wafer). Consequently, the entire substrate surface 28 is treated by multiple passes of the wafer 10 through the treatment area using a motion configuration that provides for treatment over the full wafer area.
• the relative motion of the wafer with respect to the treatment area is programmed so that uniform treatment can be obtained. Motion configurations can be by way of step and scan or by way of rotation with translation of wafer 10.
• the depth of polymer removed from a local area of a substrate as it passes through the hot gas stream depends on the time that the area spends in the hot gas stream and, consequently, on the velocity of that local area through the gas stream. For example, if a rotation and translation motion configuration is used with a constant rotational velocity, a local area of the wafer has a rotational velocity that increases with radial distance R from the center of rotation. To achieve uniform polymer removal over the full substrate, the translation velocity of the wafer through the hot gas stream must then be a function of distance from the center of rotation to account for this increase in radial velocity. To a first ap- proximation, the translation velocity will have a 1/R dependence.
• the programmed velocity may be adjusted in an iterative procedure based on a measurement after a partial polymer removal that gives a mapping of the vara- tion of the thickness of the polymer removed from uniform removal.
• the local velocities of the wafer through the hot gas stream is then adjusted to compensate for the measured thickness variation.
• a procedure for iteratively adjusting the velocity for a treating a batch of wafers using planetary motion configuration is described in the international patent WO9745856 entitled "Method for treating articles in a plasma jet," inventors Tokmouline and Siniaguine.
• the depth of polymer removed from a local area as it moves through the hot gas stream depends on the velocity of the local area through the gas stream. Velocities may be in the range of .01 to 10 meters/sec.
• An example of a polymer removal process would be for a 200 mm diameter wafer with a rotation and translation motion configuration in which the time averaged polymer removal rate is 5 microns/min and the average translation velocity of a pass through the hot gas stream is 0.5 m/sec. Including the time the wafer spends out of the hot gas stream, the time of a pass through the hot gas stream would be approximately 0.5 sec. In a single pass 0.042 microns of poy- mer would be removed.
• the gas temperature is high and in thermal equilibrium in the etching gas stream; and (2) the arc generated plasma and process gas stream are highly collision dominated.
• the atomic and mdecular species are near room temperature (e.g., 100°C) while the electrons are very energetic (e.g., 5 eV, ⁇ 50,000°K).
• the atomic and molecular species are in thermal equilibrium with the electrons with the gas stream temperature being in the range of 4000 °C to 12,000 °C and preferably in the range of 7,000° to 10,000 °C.
• the mass and energy transport is described by hydrodynamic flow characteristics.
• the gas temperature may be 8,000°C while the wafer temperature may only be 100°C.
• Known hydrodynamic boundary layer characteristics applied to this appi- cation and described in the following paragraph show, that while the gas t- - perature defined by the atoms and ions drop to the substrate temperature at the surface of the substrate (e.g., 10CPC), the electrons can maintain considerably more energy at the substrate surface (e.g., 0.7eV or ⁇ 6,000°C).
• the temperature of the heavy species decrease smoothly from the temperature of the ircoming gas flow (e.g., 8000°C) down to the substrate surface temperature (e.g., 100°C).
• the boundary layer thickness, ⁇ is ⁇ 10 4 m and the boundary thickness over which the signifi- cant part of the temperature change occurs is 0.015 ⁇ 10 "6 m.
• the stream 14 of hot gas to the substrate that is generated by an atmospheric plasma consists of inert gas from the arc and process chamber ambient gas pulled or entrained into the stream and, optionally, gas injected directly into the hot gas stream by a gas injector 26.
• the stream of hot gas to the substrate can remove the polymer by two mechanisms:
• An ablation mechanism in which the flow of hot gas to the substrate surface 28 vaporizes clusters of molecules from the polymer surface which are subsequently converted to volatile by-products by reaction with the ambient oxygen in the process chamber 13 surrounding the apparatus 16.
• the ablation process is an interaction with the top monolayers of the polymer layer and it can carry away a significant amount of heat from the polymer surface 28 so that the remaining polymer layer is not thermally degraded.
• the above two mechanisms act in synergism.
• the heat flux to the surface may accelerate the ashing mechanism and the heat generated by the ashing mechanism tend to accelerate ablation.
• the atmospheric pressure approach for removal of polymers in high as- pect ratio holes is particularly effective in comparison with conventional low pressure ashing and HDP processes, as described above. It is recognized that to remove polymer from very high aspect ratio holes as illustrated at 40 in Figures 2-4 the pressure must be sufficiently low for reactive species to reach the bottom 42 of the holes 40 without being affected by collisions with other atomic or molecular species.
• the transport of the etching species into the high aspect ratio hole is by way of a flow of collision dominated gas.
• Results show that the polymer 44 can be removed from trenches or holes 40 having a 50:1 aspect ratio, with a width w of less than 0.1 micron, with little effect on the etching rate of the polymer 44 even near the bottom 42 of the hole 40. Results show no limit as to obtaining similar control of polymer removal from even higher aspect ratio holes.
• the process of this invention must uniformly remove the photoresist 44 from the holes 40 to a controlled depth S as well as maintain a high etch rate so as not to drive up the process cost.
• Obta ⁇ - ing uniform removal of photoresist is further complicated by the temperature dependence of the etch rate.
• the etch rate for photoresist and other polymers increases with temperature.
• Provisional Patent application 60/158,892 describes a wafer holder and wafer motion configuration in which a rotating wafer is trans- lated through the treatment area so that one can cause average wafer holder dependent thermal variations to be constant for a given radius. This provides axial symmetry to the temperature dependence.
• programmed motion of the center axis of a rotating wafer is used to establish uniform treatment of the wafer.
• the programmed motion of the wafer is used to compensate for thermal etch rate effects.
• the 158,892 application describes the use of a direct fluid cooled wafer holder with temperature feed-back to maintain the wafer holder at a constant temp ⁇ ature during process- ing.

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• 2000
  • 2000-09-28 WO PCT/US2000/027113 patent/WO2001023130A1/en active Application Filing
  • 2000-09-28 EP EP00967233A patent/EP1246710A4/de not_active Withdrawn
  • 2000-09-28 JP JP2001526324A patent/JP2003510824A/ja active Pending
  • 2000-09-28 AU AU77460/00A patent/AU7746000A/en not_active Abandoned
• 2007
  • 2007-02-26 JP JP2007045525A patent/JP2007235138A/ja active Pending

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