US20050072446A1

US20050072446A1 - Process and apparatus for treating a workpiece

Info

Publication number: US20050072446A1
Application number: US10/998,278
Authority: US
Inventors: Eric Bergman
Original assignee: Individual
Current assignee: Individual
Priority date: 1997-05-09
Filing date: 2004-11-23
Publication date: 2005-04-07
Also published as: US6701941B1; US20030205254A1; US20020050279A1; US6601594B2; US6497768B2; US20020020436A1; US20010042555A1; US6591845B1; US6267125B1; US6273108B1; US6817370B2; US6582525B2

Abstract

A novel chemistry, system and application technique reduces contamination of semiconductor wafers and similar substrates and enhances and expedites processing. A stream of liquid chemical is applied to the workpiece surface. Ozone is delivered either into the liquid process stream or into the process environment. The ozone is preferably generated by a high capacity ozone generator. The chemical stream is provided in the form of a liquid or vapor. A boundary layer of liquid or vapor forms on the workpiece surface. The thickness of the boundary layer is controlled. The chemical stream may include ammonium hydroxide for simultaneous particle and organic removal, another chemical to raise the pH of the solution, or other chemical additives designed to accomplish one or more specific cleaning steps.

Description

This Application is a Continuation of U.S. patent application Ser. No. 09/621,028, filed Jul. 21, 2000 and now pending and incorporated herein by reference, which is a Continuation-in-Part of U.S. patent application Ser. No. PCT/US99/08516, which is a Continuation-in-Part of U.S. patent application Ser. No. 09/061,318, filed Apr. 16, 1998 and now abandoned, which is a Continuation-in-Part of U.S. patent application Ser. No. 08/853,649, filed May 9, 1997, now U.S. Pat. No. 6,240,933. This Application also is a Continuation-in-Part of U.S. patent application Ser. No. 60/145,350, filed Jul. 23,1999.

FIELD OF THE INVENTION

The cleaning of semiconductor wafers is often a critical step in the fabrication processes used to manufacture integrated circuits or the like. The geometries on wafers are often on the order of fractions of a micron, while the film thicknesses may be on the order of 20 Angstroms. This renders the devices highly susceptible to performance degradation due to organic, particulates or metallic/ionic contamination.
Although wafer cleaning has a long history, the era of modern cleaning techniques is generally considered to have begun in the early 1970s when RCA developed a cleaning sequence to address the various types of contamination. Although others developed the same or similar processes in the same time frame, the general cleaning sequence in its final form is basically the same.
While this process has been effective for a number of years, it nevertheless has certain deficiencies. Such deficiencies include the high cost of chemicals, the lengthy process time required to get wafers through the various cleaning steps, high consumption of water due to the need for extensive rinsing between chemical steps, and high disposal costs. The result has been an effort to devise alternative cleaning processes that yield results as good as or better than the existing four-chemistry clean process, but which are more economically attractive.
Various chemical processes have been developed in an attempt to replace the existing cleaning process. However, such cleaning processes have failed to fully address all of the major cleaning concerns of the semiconductor processing industry. More particularly, they have failed to fully address the problem of minimizing contamination from one or more of the following contaminants: organics, particles, metals/ions, and silicon dioxide.

STATEMENT OF THE INVENTION

A novel chemistry, application technique, and system is used to reduce the contamination and speed up processing in the manufacturing of semiconductor wafers, memory disks, photomasks, optical media, and other substrates (collectively referred to here as “wafers”) requiring a high level of clean. Contamination may occur from organics, particles, metal/ions, and silicon dioxide. Cleaning of wafers is achieved by delivery of a chemical stream to the workpiece surface. Ozone is delivered into the process environment. The chemical stream, which may be in the form of a liquid or vapor, is applied to the wafer in a system which allows for control of the liquid boundary layer thickness.
While ozone has a limited solubility in the hot liquid solution, it is still able to diffuse through the solution and react with the surface of the wafer (whether it is silicon, photoresist, etc.) at the liquid/solid interface. Thus diffusion, rather than dissolution, is the primary mechanism used to deliver ozone to the surfaces of the wafers. Water apparently helps to hydrolyze carbon-carbon bonds or accelerate the oxidation of silicon surfaces by hydrolyzing silicon-hydrogen or silicon-hydroxyl bonds. The elevated temperature promotes the reaction kinetics and the high concentration of ozone in the gas phase promotes diffusion of the ozone through the liquid film, even though the increased temperature of the liquid film does not result in a solution having a high concentration of ozone dissolved in it.
The flow of ozone can be delivered to the process chamber through a vapor generator or the like. Such a generator is filled with water, which is temperature controlled. Thus the ozone gas stream is enriched with water vapor which maintains the boundary layer on each wafer surface at a minimal thickness so that the layer does not inhibit diffusion. At the same time, such delivery assists in preventing the wafers from drying completely during the process.
A high capacity ozone generator is preferably used to produce a mixed effluent containing a high concentration of ozone in combination with a high flow rate. A higher concentration of ozone increases the quantity of ozone provided to the surface of the wafer. A higher flow rate increases the rate at which fresh reactants are replenished, and spent or exhausted reactants are carried away from the wafer.
Purely maximizing the concentration of ozone is not optimal for process performance, as the amount of ozone then generated is then too small to create an adequate concentration within the process chamber. On the other hand, simply maximizing flow rate or volume, without sufficient concentration will result in rapid depletion of ozone in the process chamber (as a the ozone will react rapidly with organic materials in the process chamber). Thus, both high concentration and high flow rates are needed.
To further enhance the process, the temperature of the liquid supply (water supply) can be heated to generate a supply of saturated steam under pressure to the process chamber. Under such circumstances, it is possible to achieve wafer surface temperatures in excess of 100 degrees Celsius, thereby further accelerating the reaction kinetics. A steam generator may be used to pressurize the process chamber to achieve the desired temperatures. For example, saturated steam at 126 degrees Celsius may be used with a corresponding increase in the pressure of the process chamber to 240 K Pa (35 psia). The increased pressure within the processing chamber also provides for use of higher ozone concentrations, thereby generating a higher diffusion gradient across the boundary layer at the surface of each wafer. The process is applicable to various manufacturing steps that require cleaning or selective removal of contaminants from the surface of a workpiece. For example, one or more of the steps may be used to remove photoresist from the surface of a semiconductor wafer.
Novel aspects include:
1) The use of a temperature controlled liquid chemical source delivered to the wafer surface to stabilize the temperature of the wafer and, depending on the liquid utilized, provide a supply of water to support hydrolysis of the carbon-carbon bonds of contaminants at the surface of each wafer.
2) The control of the thickness of the boundary layer of liquid present on the wafer surface so that it is not of sufficient thickness to significantly inhibit the diffusion of ozone to the wafer surface. As such, the ozone is allowed to diffuse through the controlled boundary layer, where it can oxidize silicon, organics, or metals at the surface, or otherwise support any desired reaction. The boundary layer may be controlled through the control of wafer rotation rate, vapor delivery, controlled liquid spray, the use of steam, the use of surfactants or a combination of more than one of these techniques.
3) The process takes place in an enclosed processing chamber, which may or may not be used to produce a pressurized processing environment.
4) The process utilizes a mixed effluent having a higher concentration of ozone in combination with a higher flow rate for increasing the rate at which fresh reactants are supplied to the surface of the wafer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram of one embodiment of an apparatus for treating a semiconductor workpiece in which ozone is injected into a line containing a pressurized treatment liquid.
FIG. 2 is a schematic block diagram of one embodiment of an apparatus for treating a semiconductor workpiece in which the semiconductor workpiece is indirectly heated by heating a treatment liquid that is sprayed on the surface of the workpiece.
FIG. 3 is a flow diagram illustrating one embodiment of a process flow for treating a semiconductor workpiece with a treatment fluid and ozone.
FIG. 4 is a schematic block diagram of an alternative embodiment of the system set forth in FIG. 2 wherein the ozone and treatment fluid are provided to the semiconductor workpiece along different flow paths.
FIG. 5 is a schematic block diagram of an embodiment of an apparatus for treating a semiconductor workpiece in which pressurized steam and ozone are provided in a pressurized chamber containing a semiconductor workpiece.
FIG. 6 is a schematic block diagram of an embodiment of an apparatus for treating a semiconductor workpiece in which an ultra-violet lamp is used to enhance the kinetic reactions at the surface of the workpiece.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, the treatment system, shown generally at 10, includes a treatment chamber 15 that contains one or more workpieces 20, such as semiconductor wafer workpieces. Although the illustrated system is directed to a batch workpiece apparatus, it is readily adaptable for use in single workpiece processing as well.
The semiconductor workpieces 20 are preferably supported within the chamber 15 by one or more supports 25 extending from, for example, a rotor assembly 30. Rotor assembly 30 may seal with the housing of the treatment chamber 15 to form a sealed, closed processing environment. Further, rotor assembly 30 is provided so that the semiconductor workpieces 20 may be spun about axis 35 during or after treatment with the ozone and treatment liquid.
The chamber 15 has a volume which is minimized, and is as small as permitted by design considerations for any given capacity (i.e., the number and size of the substrates to be treated). The chamber 15 is preferably cylindrical for processing multiple wafers in a batch, or a flatter disk-shaped chamber may be used for single wafer processing. Typically, the chamber volume will range from about 5 liters, (for a single wafer) to about 50 liters (for a 50 wafer system).
One or more nozzles 40 are disposed within the treatment chamber 15 to direct a spray mixture of ozone and treatment liquid onto the surfaces of the semiconductor workpieces 20 that are to be treated. In the illustrated embodiment, the nozzles 40 direct a spray of treatment fluid to the underside of the semiconductor workpieces 20. However, the fluid spray may be directed alternatively, or in addition, to the upper surface of the semiconductor workpieces 20. The fluid may also be applied in other ways besides spraying, such as flowing, bulk deposition, immersion, etc.
Treatment liquid and ozone are preferably supplied to the nozzles 40 by system components uniquely arranged to provide a single fluid line comprising ozone mixed with the treating liquid. A reservoir 45 defines a chamber 50 in which the liquid that is to be mixed with the ozone is stored. The chamber 50 is in fluid communication with, or connected to, the input of a pump mechanism 55. The pump mechanism 55 provides the liquid under pressure along a fluid flow path, shown generally at 60, for ultimate supply to the input of the nozzles 40. The preferred treatment fluid is deionized water. Other treatment fluids, such as other aqueous or non-aqueous solutions, may also be used.
Fluid flow path 60 may include a filter 65 to filter out microscopic contaminants from the treatment fluid. The treatment fluid, still under pressure, is provided at the output of the filter 65 (if used) along fluid flow line 70. Ozone is injected along fluid flow line 70. The ozone is generated by ozone generator 75 and is supplied along fluid flow line 80 under pressure to fluid flow line 70. Optionally, the treatment liquid, now injected with ozone, is supplied to the input of a mixer 90 that mixes the ozone and the treatment liquid. The mixer 90 may be static or active. From the mixer 90, the treatment liquid and ozone are provided to be input of nozzles 40 which, in turn, spray the liquid on the surface of the semiconductor workpieces 20 that are to be treated and, further, introduce the ozone into the environment of the treatment chamber 15.
To further concentrate the ozone in the treatment liquid, an output of the ozone generator 75 may be supplied to a dispersion unit 95 disposed in the liquid chamber 50 of the reservoir 45. The dispersion unit 95 provides a dispersed flow of ozone through the treatment liquid to thereby add ozone to the fluid stream prior to injection of a further amount of ozone along the fluid path 60.
In the embodiment of the system of FIG. 1, spent liquid in chamber 15 is provided along fluid line 105 to, for example, a valve mechanism 110. The valve mechanism 110 may be operated to provide the spent liquid to either a drain output 115 or back to the liquid chamber 50 of the reservoir 45. Repeated cycling of the treatment liquid through the system and back to the reservoir 45 assists in elevating the ozone concentration in the liquid through repeated ozone injection and/or ozone dispersion.
The ozone generator 75 is preferably a high capacity ozone generator. One example of a high capacity ozone generator is the ASTeX 8403 Ozone Generator, manufactured by Applied Science and Technology, Inc., Woburn, Mass., U.S.A. The ASTeX 8403 has an ozone production rating of 160 grams per hour. At this rate a flow of approximately 12 liters/minute and having a concentration of 19% ozone, by weight, can be supported. Another example of a suitable high capacity ozone generator is the Sumitomo GR-RL Ozone Generator, manufactured by Sumitomo Precision Products Co., Ltd., Hyogo, Japan which has an ozone production rating of 180 g/hr. The ozone generator 75 preferably has a capacity of at least 90 or 100 grams per hour, or 110 or 120 grams per hour, with the capacity more preferably of at least 135 grams per hour. In terms of flow rate and concentration, the capacity should be at least 10 liters per minute at 12%, 13%, 14%, 15% ( or higher) concentration by weight. Lower flow rate applications, such as with single wafer processing, may have higher concentrations of e.g., 16-19 or greater.
Use of a high capacity ozone generator is especially useful in connection with the methods and apparatus of the present application, because the present methods and apparatus provide for the delivery of ozone independent of the processing fluid.
In previous methods the ozone was dissolved into the aqueous solution in order to make it available for the oxidation process on the surface of the semiconductor wafer. This limited the amount of ozone, which could be delivered to the surface of the semiconductor wafer, to the amount of ozone which could be dissolved into the processing fluid. Correspondingly, there was no incentive to use higher capacity ozone generators, because any excess ozone produced would not be absorbed by the process fluid, and would eventually dissipate and be lost.
FIG. 1, (as well as the other Figures) illustrates various components and connections. While showing preferred designs, the drawings include elements which may or may not be essential to the invention. The elements essential to the invention are set forth in the claims. The drawings show both essential and non-essential elements.
A further embodiment of a system for delivering a fluid mixture for treating the surface of a semiconductor workpiece is illustrated in FIG. 2. Although the system 120 of FIG. 2 appears to be substantially similar to the system 10 of FIG. 1, there are significant differences. The system 120 of FIG. 2 is based in part on the concept that the heating of the surfaces of the semiconductor workpieces 20 with a heated liquid that is supplied along with a flow of ozone that creates an ozonated atmosphere is highly effective in photoresist stripping, ash removal, and/or cleaning processes. The system 120 therefore preferably includes one or more heaters 125 that are used to heat the treatment liquid so that it is supplied to the surfaces of the semiconductor workpieces at an elevated temperature that accelerates the surface reactions. It is also possible to directly heat the workpieces to stimulate the reactions. Such heating may take place in addition to or instead of the indirect heating of the workpieces through contact with the heated treatment liquid. For example, supports 25 may include heating elements that may be used to heat the workpieces 20. The chamber 15 may include a heater for elevating the temperature of the chamber environment and workpieces.
The preferred treatment liquid is deionized water, since it appears to be required to initiate the cleaning/removal reactions at the workpiece surface, apparently through hydrolysis of the carbon-carbon bonds of organic molecules. However, significant amounts of water can form a continuous film on the semiconductor workpiece surface. This film acts as a diffusion barrier to the ozone, thereby inhibiting reaction rates. The boundary layer thickness is controlled by controlling the rpm of the semiconductor workpiece, vapor delivery, and controlled spraying of the treatment liquid, or a combination of one or more of these techniques. By reducing the boundary layer thickness, the ozone is allowed to diffuse to the surface of the workpieces and react with the organic materials that are to be removed.
FIG. 3 illustrates one embodiment of a process that may be implemented in the system of FIG. 2 when the system 120 is used, for example, to strip photoresist from the surfaces of semiconductor workpieces. At step 200, the workpieces 20 that are to be stripped are placed in, for example, a Teflon wafer cassette. This cassette is placed in a closed environment, such as in chamber 15. Chamber 15 and its corresponding components may be constructed based on a well known spray solvent system or spray acid such as those available from Semitool, Inc., of Kalispell, Mont., U.S.A.. Alternatively, the semiconductor workpieces 20 may be disposed in chamber 15 in a carrierless manner, with an automated processing system, such as described in U.S. Pat. No. 5,784,797.
At step 205, heated deionized water is sprayed onto the surfaces of the semiconductor workpieces 20. The heated deionized water heats the surfaces of the semiconductor workpieces 20 as well as the enclosed environment of the chamber 15. When the spray is discontinued, a thin liquid film remains on the workpiece surfaces. If the surface is hydrophobic, a surfactant may be added to the deionized water to assist in creating a thin liquid boundary layer on the workpiece surfaces. The surfactant may be used in connection with hydrophilic surfaces as well. Corrosion inhibitors may also be used with the aqueous ozone, thin boundary layer process.
The surface boundary layer of deionized water is controlled at step 210 using one or more techniques. For example, the semiconductor workpieces 20 may be rotated about axis 35 by rotor 30 to thereby generate centripetal accelerations that thin the boundary layer. The flow rate of the deionized water may also be used to control the thickness of the surface boundary layer. Lowering of the flow rate results in decreased boundary layer thickness. Still further, the manner in which the deionized water is injected into the chamber 15 may be used to control the boundary layer thickness. Nozzles 40 may be designed to provide the deionized water as micro-droplets thereby resulting in a thin boundary layer.
At step 215, ozone is injected into the fluid flow path 60 during the water spray, or otherwise provided to the internal chamber environment of chamber 15. If the apparatus of FIG. 2 is utilized, the injection of the ozone continues after the spray has shut off. If the workpiece surface begins to dry, a brief spray is preferably activated to replenish the liquid film on the workpiece surface. This ensures that the exposed workpiece surfaces remain wetted at all times and, further, ensures that the workpiece temperature is and remains elevated at the desired reaction temperature. It has been found that a continuous spray of deionized water having a flow rate that is sufficient to maintain the workpiece surfaces at an elevated temperature, and high rotational speeds (i.e., >300 rpm, between 300 and 800 rpm, or even as high as or greater than 1500 rpm) generates a very thin boundary layer which minimizes the ozone diffusion barrier and thereby leads to an enhanced photoresist stripping rate. As such, the control of the boundary layer thickness is used to regulate the diffusion of reactive ozone to the surface of the wafer.
The surface layer thickness may range from a few molecular layers (e.g., about 1 micron ), up to 100 microns, (typically 50-100 microns), or greater.
While ozone has a limited solubility in the heated deionized water, the ozone is able to diffuse through the water and react with photoresist at the liquid/resist interface. It is believed that the presence of the deionized water itself further assists in the reactions by hydrolyzing the carbon-carbon bonds of organic deposits, such as photoresist, on the surface of the wafer. The higher temperature promotes the reaction kinetics while the high concentration of ozone in the gas phase promotes diffusion of ozone through the boundary layer film even though the high temperature of the boundary layer film does not actually have a high concentration of dissolved ozone.
Elevated or higher temperatures means temperatures above ambient or room temperature, that is temperatures above 20 or 25° and up to about 200° C.
Preferred temperature ranges are 25-150°, more preferably 55-120° or 75-115° C., and still more preferably 85-105° C. In the methods described, temperatures of 90-100° C., and preferably centering around 95° C. may be used.
After the semiconductor workpieces 20 have been processed through the reactions of the ozone and/or liquid with the materials to the removed, the workpieces are subject to a rinse at 220 and are dried at step 225. For example, the workpieces may be sprayed with a flow of deionized water during the rinse at step 220. They may then be subject to any one or more known drying techniques thereafter at step 225.
In the described processes, elevated temperatures are used to accelerate the reaction rates at the wafer surface. One manner in which the surface temperature of the wafer may be maximized is to maintain a constant delivery of heated processing liquid, such as water or steam, during the process. The heated processing liquid contacts and heats the wafer during processing. However, such a constant delivery may result in significant waste of the water or other processing liquid. In order to conserve water and achieve the thinnest possible boundary layer, a “pulsed flow” of liquid or steam may be used. In instances in which such a “pulsed flow” fails to maintain the requisite elevated wafer surface temperatures, an alternative manner of maintaining the wafer surface temperature may be needed. One such alternative is the use of a “hot wall” reactor that maintains the wafer surface and processing environment temperatures at the desired level. To this end, the process chamber may be heated by, for example, one or more embedded heated recirculating coils, a heating blanket, irradiation from a thermal source (e.g., and infrared lamp), etc.
In laboratory experiments, a 150 mm silicon wafer coated with 1 micron of photoresist was stripped in accordance with the teachings of the foregoing process. The processing chamber was pre-heated by spraying deionized water that was heated to 95 degrees Celsius into the processing chamber for 10 minutes. During the cleaning process, a pulsed flow of deionized water heated to 95 degrees Celsius was used. The pulsed flow included an “on time” of approximately five seconds followed by an “off time” of 10 seconds. The wafer was rotated at 800 rpm and the pulsed flow of deionized water was sprayed into the processing chamber through nine nozzles at a rate of 3 liters per minute. Ozone was injected into the processing chamber through a separate manifold at a rate of 8 liters per minute at a concentration of 12 percent. The resultant strip rate was 7234 Angstroms/min.
At a higher ozone flow rate, made possible by using a high capacity ozone generator for injecting ozone into. the processing chamber at a rate of 12 liters per minute and having a concentration of 19 percent, the resultant strip rates can be further increased to in excess of 8800 Angstroms/minute.
There are many benefits resulting from the use of the semiconductor cleaning processes described above. One of the most significant benefits is that the conventional 4-chem clean process may be reduced to a two-chemical step process while retaining the ability to remove organics, remove particulates, reduce metals and remove silicon dioxide. Process times, chemical consumption, water consumption and waste generation are all also significantly reduced. A further benefit of the foregoing process is its applicability to both FEOL and BEOL wafers and strip processes. Laboratory tests indicate that there is no attack on metals such as aluminum, titanium, tungsten, etc. A known exception is copper, which forms a copper oxide in the presence of ozone. This oxide is not a “hard” and uniform passivation oxide, such as the oxide that forms on metals like aluminum. As a result, the oxide can be readily removed.
A still further benefit is the higher ozone flow rates and concentrations can be used to produce higher strip rates under various processing conditions including lower wafer rotational speeds and reduced temperatures. Use of lower temperatures (between 25 and 75° C. and preferably from 25-65° C. (rather than at e.g., 95° C. as described above) may be useful where higher temperatures are undesirable.
One example where this is beneficial is the use of the process with BEOL wafers, wherein metal corrosion may occur if the metal films are exposed to high temperature de-ionized water. Correspondingly, processing at ambient temperatures may be preferred. The gain in strip rates not realized, as a result of not using higher temperatures, is offset by increases in strip rate due to the increased ozone flow rates and concentrations. The use of higher ozone concentration can offset the loss of kinetic energy from using lower temperatures.
With reference again to FIG. 3, it will be recognized that process steps 205-215 may be executed in a substantially concurrent manner. Additionally, it will be recognized that process steps 205-215 may be sequentially repeated using different processing liquids. In such instances, each of the processing liquids that are used may be specifically tailored to remove a respective set of contaminants. Preferably, however, it is desirable to use as few different processing liquids as possible. By reducing the number of different processing liquids utilized, the overall cleaning process is simplified and reducing the number of different processing liquids utilized minimizes chemical consumption.
A single processing liquid may be used to remove organic contaminants, metals, and particles in a single cycle of process steps 205-215. The processing liquid is comprised of a solution of deionized water and one or more compounds, such as HF or HCl, so as to form an acidic processing liquid solution.
The steps and parameters described above for the ozone processes apply as well to the ozone with HF and ozone process. These processes may be carried out on batches of workpieces in apparatus such as described in U.S. Pat. No. 5,544,421, or on individual workpieces in an apparatus such as described in PCT/US99/05676.
Typical chemical application times are in the range of 1:00 to 5:00 minutes. Compared to a 4-chem clean process time of around 20:00 minutes, the disclosed process with an HF and/or HCl containing processing liquid becomes very attractive. Typical H20:HF:HCl concentration ratios are on the order of 500:1:1 to 50:1:1, with and without HF and/or HC1. Higher concentrations are possible, but the economic benefits are diminished. It is important to note that gaseous HF or HCl could be injected into water to create the desired cleaning chemistry as well. Due to differences in processor configurations and desired cleaning requirements, definition of specific cleaning process parameters will vary based on these differences and requirements.
The process benefits include the following:
1. Reduction in the amount and types of chemicals used in the cleaning process.
2. Reduction in water consumption by the elimination of the numerous intermediate rinse steps required.
3. Reduction in process time.
4. Simplification of process hardware.
In the case of oxidizing and removing organic contamination, conventional aqueous ozone processes show a strip rate on photoresist (a hydrocarbon film) of around 200-700 angstroms per minute. In the boundary layer controlled system of the disclosed processes, the rate is accelerated to 2500 to 8800. angstroms per minute in a spray controlled boundary layer, or higher when the boundary layer is generated and controlled using steam at 15 psi and 126 degrees C.
With reference to FIG. 4, there is shown yet a further embodiment of the ozone treatment system 227. In the embodiment of FIG. 4, one or more nozzles 230 are disposed within the treatment chamber 15 to conduct ozone from ozone generator 75 directly into the reaction environment. The heated treatment fluid is provided to the chamber 15 through nozzles 40 that receive the treatment fluid, such as heated deionized water, through a supply line that is separate from the ozone supply line. As such, injection of ozone in fluid path 60 is optional.
Another embodiment of an ozone treatment system is shown generally at 250 in FIG. 5. In the system 250, a steam boiler 260 that supplies saturated steam under pressure to the process chamber 15 has replaced the pump mechanism. The reaction chamber 15 is preferably sealed to thereby form a pressurized atmosphere for the reactions. For example, saturated steam at 126 degrees Celsius could be generated by steam boiler 260 and supplied to reaction chamber 15 to generate a pressure of 35 psia therein during the workpiece processing. Ozone may be directly injected into the chamber 15 as shown, and/or may be injected into the path 60 for concurrent supply with the steam. Using the system architecture of this embodiment, it is thus possible to achieve semiconductor workpiece surface temperatures in excess of 100 degrees Celsius, thereby further accelerating the reaction kinetics. The steam generator in FIG. 5 may be replaced with a heater(s) as shown in FIGS. 1-4. While FIGS. 4 and 5 show the fluid and ozone delivered via separate nozzles 40, they may also be delivered from the same nozzles, using appropriate valves.
A still further enhancement that may be made to any one of the foregoing systems is illustrated in FIG. 6. In this embodiment, an ultra-violet or infrared lamp 300 is used to irradiate the surface of the semiconductor workpiece 20 during processing. Such irradiation further enhances the reaction kinetics. Although this irradiation technique is applicable to batch semiconductor workpiece processing, it is more easily and economically implemented in the illustrated single wafer processing environment where the workpiece is more easily completely exposed to the UV radiation. Megasonic or ultrasonic nozzles 40 may also be used.
As described, the ozone gas may be separately sprayed, or otherwise introduced as a gas into the process chamber, where it can diffuse through the liquid boundary layer on the workpiece. The fluid is preferably heated and sprayed or otherwise applied to the workpiece, without ozone injected into the fluid before the fluid is applied to the workpiece.
Alternatively, the ozone may be injected into the fluid, and then the ozone containing fluid applied to the workpiece. In this embodiment, if the fluid is heated, the heating preferably is performed before the ozone is injected into the fluid, to reduce the amount of ozone breakdown in the fluid during the fluid heating. Typically, due to the larger amounts of ozone desired to be injected into the fluid, and the low solubility of the ozone gas in the heated fluid, the fluid will contain some dissolved ozone, and may also contain ozone bubbles.
It is also possible to use aspects of both embodiments, that is to introduce ozone gas directly into the process chamber, and to also introduce ozone into the fluid before the fluid is delivered into the process chamber. Thus, various methods may be used for introducing ozone into the chamber.
The presently disclosed apparatus and methods may be used to treat workpieces beyond the semiconductor workpieces described above. For example, other workpieces, such as flat panel displays, hard disk media, CD glass, etc, may also have their surfaces treated using the foregoing apparatus and methods.
Although the preferred treatment liquid for the disclosed application is deionized water, other treatment liquids may also be used. For example, acidic and basic solutions may be used, depending on the particular surface to be treated and the material that is to be removed. Treatment liquids comprising sulfuric acid, hydrochloric acid, and ammonium hydroxide may be useful in various applications.
As described, one aspect of the process is the use of steam (Water vapor at temperatures exceeding 100 C) to enhance the strip rate of photoresist in the presence of an ozone environment. Preliminary testing shows that a process using hot water at 95 C produces a photoresist strip rate of around 3000-4000 angstroms per minute. Performing a similar process using steam at 120-130 C results in a strip rate of around 7000-8000 angstroms per minute. However, the resultant strip rate is not sustainable.
The high strip rate is achieved only when the steam condenses on the wafer surface. The wafer temperature rapidly approaches thermal equilibrium with the steam, and as equilibrium is achieved, there is no longer a thermal gradient to promote the formation of the condensate film. This results in the loss of the liquid boundary layer on the wafer surface. The boundary layer appears to be essential to promote the oxidation of the organic materials on the wafer surface. The absence of the liquid film results in a significant drop in the strip rate on photoresist.
Additionally, once the steam ceases to condense on the wafer surface, the reaction environment experiences the elimination of an energy source to drive the reaction kinetics. As steam condenses on the wafer surface, it must relinquish the heat of vaporization, which is approximately 540 calories per gram. This energy then becomes available to promote other reactions such as the oxidation of carbon compounds in the presence of ozone or oxygen free radicals.
In view of these experimental observations, a method for maintaining the temperature of a surface such as a semiconductor wafer surface, is provided to ensure that condensation from a steam environment continues indefinitely, thereby enabling the use of steam in applications such as photoresist strip in the presence of ozone. Thus the formation of the liquid boundary layer is assured, as well as the release of significant amounts of energy as the steam condenses.
To accomplish this, the wafer surface must be maintained at a temperature lower than that of the steam delivered to the process chamber. This may be achieved by attaching the wafer to a temperature-controlled surface or plate 350 which will act as a heat sink. This surface may then be temperature controlled either through the use of cooling coils, a solid-state heat exchanger, or other means.
In a preferred embodiment, a temperature-controlled stream of liquid is delivered to the back surface of a wafer, while steam and ozone are delivered to an enclosed process region and the steam is allowed to condense on the wafer surface. The wafer may be rotated to promote uniform distribution of the boundary layer, as well as helping to define the thickness of the boundary layer through centrifugal force. However, rotation is not an absolute requirement. The cooling stream must be at a temperature lower than the steam. If the cooling stream is water, a temperature of 75 or 85-95 C is preferably used, with steam temperatures in excess of 100 C.
In another embodiment, and one which is relatively easy to implement in a batch process, pulsed spray of cooling liquid is applied periodically to reduce the wafer temperature. Steam delivery may either be continuous or pulsed as well. The wafer may be in any orientation and additives such as hydrofluoric acid, ammonium hydroxide or some other chemical may be added to the system to promote the cleaning of the surface or the removal of specific classes of materials other than or in addition to organic materials.
This process enables the use of temperatures greater than 100 C to promote reaction kinetics in the water/ozone system for the purpose of removing organic or other materials from a surface. It helps ensure the continuous formation of a condensate film by preventing the surface from achieving thermal equilibrium with the steam. It also takes advantage of the liberated heat of vaporization in order to promote reaction rates and potentially allow the removal of more difficult materials which may require more energy than can be readily delivered in a hot water process.

Claims

1. A method for processing a workpiece, comprising:

placing the workpiece into a chamber;

pressurizing the chamber to an above ambient pressure;

directly or indirectly heating the workpiece,

providing water vapor into the chamber, with the water vapor exceeding about 100 C; and

providing ozone gas into the chamber.

2. The method of claim 1 wherein the workpiece is coated with photoresist, and with the steam and ozone chemically reacting with and removing the photoresist.

3. The method of claim 1 wherein the water vapor forms a layer on the wafer surface, with the layer having a thickness of from about 1-100 microns.

4. The method of claim 1 wherein the water vapor forms a layer a few molecular layers thick.

5. The method of claim 2 wherein the photoresist is hydrolyzed.

6. The method of claim 1 wherein the water vapor is at about 120-130 C.

7. The method of claim 1 wherein the chamber is flat and disk-shaped.

8. The method of claim 1 wherein the ozone is provided at a concentration of at least 12% by weight.

9. The method of claim 1 wherein the ozone and water vapor are provided into the chamber for about 1-5 minutes.

10. The method of claim 1 further including heating the workpiece via contact heaters in the chamber.

11. The method of claim 1 with the ozone provided at a flow rate of at least 10 liters/minute, and at a concentration of at least 12% by weight.

12. A method for removing photoresist from a wafer, comprising:

placing the wafer into a chamber;

directly or indirectly heating the wafer with one or more heaters in or on the chamber,

providing steam in the chamber;

providing ozone gas into the chamber;

pressurizing the chamber;

contacting the wafer with steam and ozone, with the steam and ozone chemically reacting with the photoresist; and

rinsing the wafer.

13. The method of claim 12 with the steam forming a molecular layer on a surface of the workpiece.

14. The method of claim 13 with the workpiece surface having a temperature exceeding 100 C.

15. The method of claim 12 with the photoresist having carbon-carbon bonds hydrolyzed in the presence of the steam and ozone.

16. A method for cleaning a workpiece, comprising:

placing the workpiece into a chamber;

directly or indirectly heating the workpiece with one or more heaters,

providing heated water vapor in the chamber;

providing ozone gas into the chamber;

pressurizing the chamber to an above ambient pressure;

contacting the workpiece with heated and ozone, with the steam and ozone chemically reacting, in the presence of hydroxyl radicals, to clean the workpiece; and

rinsing the workpiece.

17. The method of claim 16 with the heated water vapor forming a layer on the workpiece, and with the ozone gas diffusing through the layer.

18. The method of claim 16 including providing the ozone gas at a concentration of at least 12% and a flow rate of at least 10 liters/minute.

19. A system for cleaning a workpiece, comprising:

a pressurizable chamber;

a heated water vapor supply associated with the chamber;

an ozone gas supply connecting into the chamber;

a workpiece support in the chamber for supporting the workpiece; and

a workpiece heater in the chamber on or in the wafer support for directly heating the wafer.

20. The system of claim 19 with the chamber is disk-shaped.

21. The system of claim 19 with the ozone gas supply providing at least 90 grams/hour of ozone.