The present invention relates to the field of cleaning flat objects, in particular to wet cleaning of semiconductor wafers during production. More specifically, the invention relates to an apparatus and a method for cleaning semiconductor wafers in a wet cleaning process with the use of pulsed liquid jets.
Cleaning of surfaces of wafer substrates is one of the most important steps in the fabrication of semiconductor microelectronic devices. It is well known that the presence of chemical contaminants and particles of impurities may significantly reduce product yield and noticeably affect the performance and reliability of the produced semiconductor devices.
In view of the present trend in the semiconductor industry that goes far beyond features such as submicron sizes, the effective techniques for cleaning silicon wafers, e.g., initially and after oxidation and patterning, are now more important than ever before because of the extreme sensitivity of semiconductor surfaces to the presence of contaminants. Specifically, total metallic impurities should be far less than 1010 atoms per cm2. Presence of particles larger than 0.1 μm in size should be much less than approximately 0.1 per cm2.
In view of the fact that the above criteria are very stringent, the efficiency of the equipment and processes used for wafer cleaning should be evaluated from the point of view of satisfaction of the above requirements in the treated wafers.
There exists a plurality of various methods and processes for wafer cleaning that roughly can be subdivided into dry-physical, wet-physical, combined wet physical/chemical, vapor-phase methods, etc. Furthermore, there exists a series of apparatuses for implementing the aforementioned cleaning processes in the industry.
In a majority of cases, the cleaning processes are oriented specifically on silicon since this material is a basis for fabrication of integrated circuits.
The present invention pertains to the aforementioned wet-physical and combined wet physical/chemical processes, which are the most widely used processes for the cleaning of semiconductor wafers. The wet cleaning methods and apparatuses, in turn, have a plurality of different implementations with vertical or horizontal orientation of single or multiple wafers performing different specific movements during the cleaning cycle, the use of different cleaning media and tools, the use of different methods for drying, etc.
Attempts have been made to apply a new approach to the wafer-cleaning problem. An example of such an approach is the development of a rapid-pulse harmonic spray technology developed by the applicant and described by Mehran Janani, et al., in the article “A novel approach to metal lift-off for GaAs ICs” (see the Internet address: (http://www.compoundsemiconductor.net/articles/magazine/9/10/3/1).
The fluid droplets in each pulse interact with the wafer, which rotates slowly in a vertical orientation, to produce a hybrid of laminar and turbulent flow types. Rapid pulsing controls the fluid-mechanical interactions of jets and droplets with adsorbed contaminants. As a result, the chemical concentration gradient at the wafer/liquid interface is always positioned to favor desorption of contaminants. The moderate application of a pressurized solvent allows for a blend of mechanical and chemical energy for lift-off applications. Large particles are removed at the point of impact of the pulse spray due to the generation of turbulent flow. In the laminar flow regime, wherein the boundary layer is less than 1 μm, the solvent is responsible for dispersing and rinsing small particles and labile layer removal. Compared with other technologies that use fluids at super-critical pressures aided with co-solvents, dry CO2/liquid approaches, and jet sprays, the rapid-pulse approach manipulates all of the essential thermal, mechanical, and chemical ingredients for effective cleaning, thereby offering a simple, elegant and cost-effective solution.
Although the above-described rapid-pulse harmonic spray method and apparatus have considerably improved efficiency of cleaning, they are still insufficiently effective for removing contaminant particles having dimensions of 0.1 μm or less.
In order to eliminate the above disadvantage of known rapid-pulse harmonic spray systems, the applicant has developed nozzles with special means for enhancing formation of medium droplets. This improved technique is disclosed in
U.S. patent application Ser. No. 299,134 filed by the applicant, R. S. Randhawa, on Dec. 12, 2005. In various embodiments of the aforementioned invention, the droplet-formation enhancement means are located inside the nozzle at the nozzle outlet end and are made in the form of a jet splitter, threaded grooves on the inner surface of the nozzle body, or in the form of a thin tube for the supply of gas into the flow of the liquid cleaning medium for the formation of gas bubbles in the medium. The method and the apparatus are based on the principle that the use of the aforementioned droplet-formation enhancement means increases the boundary surface between the liquid medium and the surrounding gaseous atmosphere and thus produces an increased amount of droplets. The efficiency of the cleaning operation is improved by combining the aforementioned controlled droplet-formation mechanism with a pulsed nature of the emitted jet. The method also takes into account such factors as mass ratio between the droplets and the contaminant particles, velocity of droplets, organization and sequence of jets that attack the surface of the wafer and flows that wash-out the separated particles, etc.
The cleaning unit of U.S. patent application Ser. No. 299,134 is intended for operation in a closed cleaning chamber located preferably in a pure and controllable environment. The unit contains a stationary nozzle array composed of a plurality of the aforementioned nozzles that may be positioned on both sides of the vertically oriented objects, e.g., a semiconductor wafer, for cleaning the front and back surfaces of the wafer simultaneously. The nozzles operate in a rapid-pulse harmonic spray mode with the formation of pulsed fluid streams of discrete droplets injected onto the wafer surface. The droplets have a specific size that matches the size and type of the contaminant particles. The jets are created by means of an electrical three-diaphragm short piston pump (not shown) and may be combined with specially selected chemistry. The apparatus may be provided with reservoirs for different cleaning media and with a heater and a cooler for heating and cooling of cleaning liquids with reference to the used chemicals and other operational conditions. Rapid-pulsed streams of chemical and cleaning liquids are fired in timed succession controlled from a central processing unit. Some embodiments provide the use of additional laminar-flow nozzles for removal of the contaminant particles separated by turbulent pulsed streams. The pulsed jet cleaning liquid and the washing liquid can be supplied at different temperatures selected with reference to specific operational requirements. However, the above-described method and apparatus are based on improvement of purely mechanical means of wafer cleaning and do not improve removal of organic components of the wafer contaminants.
On the other hand, it is known that ozone is a strong oxidizer, and systems exist that remove contaminants, especially organic contaminants and photoresist film residuals from the surfaces of semiconductor wafer substrates with the use of gaseous ozone. The contaminant removal property of ozone is based on the fact that ozone decomposes complex organic compounds into volatile and water-soluble components.
For example, the oxidizer may be H2SO4, H2O2, as well as some mixtures based on alkalized compounds depending on the type of resist. Beginning in 1988, when a patent was defended based on resist stripping by dilution of ozone with water, many “wet” processing processes were developed.
Unlike other “wet” processes, photoresist removal in aqueous solutions of ozone takes place in several stages:
1. In the beginning the ozone introduces ozonides chains into the polymer matrix on the surface of the photoresist.
2. Ozonides are then created simultaneously, resulting in destruction of polymer as indicated by the following chemical equation:
3. The final stage forms organic acids, solvents and other gaseous byproducts easily dissolved in water and then removed from the wafer surface by water flow.
The advantage of the photoresist removal method is the high degree of ecological purity of process, because polluting chemical reagents are absent.
For example, H2SO4, alkaline and H2O2 are not present. The photoresist is uniformly removed from all surfaces without stratification and without the formation of polymer strings. Such stripping technology allows removal of other surface residues, such as sulfides and other surface materials.
A disadvantage of this method is the low speed of the oxidation process, and consequently, photoresist removal. Because this is a “wet” process, one must consider how the wafers are to be rinsed and dried.
Ozone-based cleaning systems can be roughly divided into systems wherein cleaning is carried out with ozone in a gaseous form (clean air with O3) and systems wherein ozone is used in solutions, predominantly in aqueous solutions. Also known are cleaning systems wherein ozone is generated directly in oxygen or in mixtures of oxygen with rare gas (plasma methods).
Given below are some examples of applying the ozone-based cleaning systems mentioned above in the semiconductor manufacturing industry, e.g., for resist-stripping operations where ozone is used due to its high efficiency in removing organic substances.
U.S. Pat. No. 6,851,873 issued in 2005 to H. Maruoka, et al., describes a method and an apparatus for removing an organic film, such as a resist film, from a substrate surface. The apparatus uses a treatment liquid that contains dissolved ozone and preferably is formed from liquid ethylene or propylene carbonate, or both, that is brought in contact with the substrate having an organic film. The apparatus contains a treatment liquid delivery device, a film contact device, a liquid circulation device, and an ozone dissolution device.
U.S. Pat. No. 6,863,836 issued in Mar. 8, 2005 to R. Novak, et al., discloses a method of removing photoresist from semiconductor wafers through the use of a sparger plate. According to the method, at least one semiconductor wafer is positioned in a process tank above the sparger plate. A mixture of ozone and deionized water is introduced into the process tank at a position below the sparger plate. The mixture of ozone and deionized water is then introduced across the wafer via the sparger plate at an increased flow velocity while the wafer is submerged in the mixture of deionized water and ozone. A sparger plate is a perforated plate used for spreading and distributing gas.
U.S. Pat. No. 6,701,941 issued in 2004 to Eric Bergman discloses an apparatus for supplying a mixture of a treatment liquid and ozone for treatment of the surface of a workpiece, and a corresponding method was set forth. The preferred embodiment of the apparatus comprises a liquid supply line that is used to provide fluid communication between a reservoir containing the treatment liquid and a treatment chamber housing the workpiece. A heater is disposed to heat the workpiece, either directly or indirectly. Preferably, the workpiece is heated by heating the treatment liquid that is supplied to the workpiece. One or more nozzles accepts the treatment liquid from the liquid supply line and sprays it onto the surface of the workpiece while an ozone generator provides ozone into an environment containing the workpiece.
U.S. Pat. No. 6,837,252 issued in 2005 to Eric Bergman describes a method for processing a workpiece to remove material from the first surface of the workpiece, wherein steam is introduced onto the first surface so that at least some of the steam condenses and forms a liquid boundary layer on the first surface. The condensing steam helps to maintain the first surface of the workpiece at an elevated temperature. Ozone is provided around the workpiece when the ozone diffuses through the boundary layer and reacts with the material on the first surface. The temperature of the first surface is controlled to maintain condensation of the steam.
U.S. Pat. No. 6,830,628 issued in 2004 to Eric Bergman discloses methods for cleaning surfaces of wafers or other semiconductor articles. Oxidizing is performed using an oxidation solution which is wetted onto the surface. The oxidation solution can include one or more of: water, ozone, hydrogen chloride, sulfuric acid, or hydrogen peroxide. A rinsing step removes the oxidation solution and inhibits further activity. The rinsed surface is thereafter preferably subjected to a drying step. The surface is exposed to an oxide removal vapor to remove semiconductor oxide therefrom. The oxide removal vapor can include one or more of: acids, such as a hydrogen halide, example of which is hydrogen fluoride or hydrogen chloride; water; isopropyl alcohol; or ozone. The processes can use centrifugal processing and spraying actions.
U.S. Pat. No. 6,817,370 issued in 2004 to Eric Bergman, et al., relates to an apparatus and a method for supplying a mixture of a treatment liquid and ozone for treatment of the surface of a workpiece. The preferred embodiment of the apparatus comprises a liquid supply line that is used to provide fluid communication between a reservoir containing the treatment liquid and a treatment chamber housing the workpiece. A heater is disposed to heat the workpiece, either directly or indirectly. Preferably, the workpiece is heated by heating the treatment liquid that is supplied to the workpiece. One or more nozzles accepts the treatment liquid from the liquid supply line and sprays it onto the surface of the workpiece while an ozone generator provides ozone into an environment containing the workpiece.
U.S. Pat. No. 6,869,487 issued in 2005 to Eric Bergman discloses a novel chemistry, system, and application technique for reducing contamination of semiconductor wafers and similar substrates. 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 generated preferably by a high-capacity ozone generator. The chemical stream is provided in the form of a liquid or vapor. A boundary layer 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.
U.S. Pat. No. 6,817,369 issued in 2004 to Thomas Riedel, et al., relates to a device for cleaning substrates, especially semiconductor wafers and comprises a treatment basin for receiving at least one substrate, a cover for sealing said treatment basin, a first feeding device for controllably feeding in a reactive gas, a second feeding device for controllably feeding in at least one moist fluid for promoting a reaction between the reactive gas and a deposit to be removed from the substrate, and a control device for controlling the concentration of moisture in the treatment basin. The apparatus provides a closed system and enables precise control of the concentration of moisture in the treatment tank. Moisture concentration can be adapted to the respective cleaning process, as a result of which the formation of a liquid layer on the substrates that are to be cleaned by the moisture-containing fluid can be prevented entirely or in a controlled manner. This is important in order to ensure that the reactive gas, or other reactive components, comes into contact with the contaminants or impurities. Furthermore, the ratio of the reactive gas to the fluid can be set in order to provide an optimum cleaning atmosphere and to reduce the consumption of media. The closed system furthermore prevents uncontrolled escape of the reactive gas/fluid mixture.
U.S. Pat. No. 6,848,455 issued in 2005 to Krishnan Shrinivasan, et al. discloses a method and apparatus for removing photoresist and post-etch residue from semiconductor substrates by in-situ generation of oxidizing species. Contaminants are removed from a semiconductor wafer by the in-situ generation of oxidizing species. These active species are generated by the simultaneous application of ultraviolet radiation and chemicals containing oxidants such as hydrogen peroxide and dissolved ozone. Ultrasonic or megasonic agitation is employed to facilitate removal. Radicals are generated in-situ, thus generating them close to the semiconductor substrate. The process chamber has a means of introducing both gaseous and liquid reagents, through a gas inlet, and a liquid inlet. O2, O3, and H2O vapor gases are introduced through the gas inlet. H2O and H2O2 liquids are introduced through the liquid inlet. Other liquids such as ammonium hydroxide (NH4OH), hydrochloric acid (HCl), hydrofluoric acid (HF), and the like, may be introduced to further constitute those elements of the traditional RCA cleaning. The chemicals are premixed in a desired ratio and to a predetermined level of dilution prior to being introduced into the chamber. The chamber is equipped with a megasonic or ultrasonic transducer probe placed in close proximity to the substrate as the substrate rotates with the rotating platen.
U.S. Pat. No. 6,799,583 issued in 2004 to Saraj Puri, et al. discloses a method of cleaning a surface of an article using cleaning liquids in combination with acoustic energy. Preferably, an ultradiluted concentration of a cleaning enhancement substance, such as ammonia gas, is dissolved in a liquid solvent, such as filtered deionized water, to form a cleaning liquid. The cleaning liquid is caused to contact the surface to be cleaned. Acoustic energy is applied to the liquid during such contact. Optionally, the surface to be cleaned can be oxidized, e.g., by ozonated water, prior to cleaning.
U.S. Pat. No. 6,743,301 issued in 2004 to Kousaku Matsun, et al. discloses a substrate treatment process for removing organic matter from a substrate such as a wafer, glass substrate or ceramic. The process comprises treating the substrate with ozone water and then with hydrogen water, treating the substrate with ozone-hydrogen wate, or treating the substrate with ozone water and hydrogen water at the same time.
U.S. Pat. No. 6,715,944 issued in 2004 to Izumi Oya, et al. discloses an apparatus for removing a photoresist film. The apparatus includes a substrate cassette for fixing a substrate having a surface covered with a photoresist film, an ozone feed tube for supplying ozone, a liquid feed tube for supplying a liquid photoresist film removing solution, and a processing tank for recovering and processing at least the ozone or the liquid photoresist film removing solution, wherein the liquid photoresist film removing solution is supplied through the liquid feed tube as a liquid or mist, at least the ozone or the photoresist film removing solution being continuously supplied.
U.S. Pat. No. 6,616,773 issued in 2003 to Masaki Kuzumoto, et al., discloses a substrate treatment assembly for treating a work object on the surface of a substrate by supplying to the work object a wet ozone-containing gas wetted with a treatment solution. The apparatus includes a substrate heating device for maintaining a substrate at a temperature higher than room temperature, a wetting device for producing a wet ozone-containing gas by wetting an ozone-containing gas with a treatment solution, a supply device for supplying the wet ozone-containing gas to a work object on the surface of the substrate, a gas conduit connecting the wetting device to the supply device, and a heating device for heating the wet ozone-containing gas to a temperature approximately equal to or greater than the temperature of the substrate.
U.S. Pat. No. 6,632,281 issued in 2003 to Jun'ichi Kitano, et al. discloses a substrate processing apparatus and substrate processing method. On top of respective areas divided by partition plates, that is, a cassette station, a processing station, and an interface section in a coating and developing processing system, gas supply sections are provided for supplying an inert gas into the respective areas. Exhaust pipes for exhausting the atmospheres in the respective areas are provided at the bottom of the respective areas. The atmospheres in the respective areas are maintained in a clean condition by supplying the inert gas (not containing impurities such as oxygen and fine particles) from the respective gas supply sections into the respective areas and exhausting the atmospheres in the respective areas from the exhaust pipes.
U.S. Pat. No. 6,699,330 issued in 2004 to Hisashi Muraoka discloses a method of removing surface-deposited contaminants that comprises bringing an ozone-containing treating solution into contact with the surface of a target on which contaminants have been deposited. The ozone-containing treating solution comprises an organic solvent having a partition coefficient to ozone in a gas, of 0.6 or more, and ozone having been dissolved in the solvent. Contaminants having been deposited on the surfaces of various articles including substrates for electronic devices, such as semiconductor substrates and substrates for liquid crystal display devices can be safety and a good efficiently removed by room-temperature and short-time treatment.
U.S. Pat. No. 6,638,365 issued in 2003 to Jianhui Ye, et al., discloses a method of preparing a silicon surface for subsequent processing by thermal oxidation, or metal silicide formation, via the use of a novel wet chemical clean procedure. The novel wet chemical clean procedure is comprised of three specific stages, with the first stage featuring the removal of organic contaminants and the growth of a native oxide layer on the silicon surface. A second stage features removal of the native oxide layer and removal of metallic contaminants from the silicon surface, while the third stage is used to dry the silicon surface. The novel wet chemical clean procedure is performed in less time, and using fewer chemicals, and then counterpart wet chemical cleaning is also used for the preparation of silicon surfaces for subsequent processing steps.
US Patent Application Publication 2002/0033186 filed in 2002 by Srwvwn Verhaverbeke, et al., discloses a process for treating an electronic component wherein the electronic component is exposed to a heated solvent and is subsequently exposed to an ozonated process fluid. The electronic component is optionally exposed to the heated solvent by exposing the electronic component to a passing layer of a heated solvent. Also provided is an apparatus for treating electronic components with a heated solvent and an ozonated process fluid.
It is important to note U.S. Pat. No. 5,911,837 issued in 1999 to Robert Matthews that relates to a process for treatment of semiconductor waters in fluids. The invention is aimed at the removal of organic materials from semiconductor wafers and to a process for drying the wafers by a chemical solvent. In order to obtain a sufficiently high ozone concentration in the deionized water, the bath typically is maintained at about 1 to about 15° C. Below about 1° C., ice may form in the tank. Since these semiconductor process tanks are typically made from quartz, the ice may cause the quartz to break and prohibit movement of silicon wafers into and out of the process vessel. In addition, the system will not function since the water has changed physical states from a liquid to a solid and cannot absorb gases uniformly. Above 15° C., a sufficient amount of ozone may not be absorbed into the deionized water to remove the organic material on the semiconductor wafers in a timely fashion. In a preferred embodiment, the bath is about 5° C. to about 9° C. Generally, the ozone will be diffused into the deionized water for about 1 to about 15 minutes. In a preferred embodiment, the ozone is diffused into the deionized water for about 5 to about 10 minutes.
The wafers are maintained in a stationary state in a tank that contains chilled ozonated water or are placed into a tank of deionized water, and ozone is then diffused into the tank. The amount of time needed for diffusion of the ozone into the water will depend on the nature of the organic material being removed and the amount of that material. The specific temperature of the water bath will also affect the time for diffusion of ozone since the amount of absorption of ozone into the water is dependent on the temperature, and the oxidation power of the water solution is dependent on the amount of ozone absorbed.
However, the system described in U.S. Pat. No. 5,911,837 is low efficient since the wafers are stationary and since in reality the process of dissolving ozone in deionized water may take not only 5 to 10 min., as stated in the above patent but a much longer time. Furthermore, experience has shown that rate of removing inorganic substances with ozone depends more on the concentration of ozone (O3) in liquid than on the temperature of the solution.
The use of ozone for removing inorganic components of contaminants is also known, e.g., from the article by Dae-Hong Eom, et al., entitled “Reaction of Ozone and H2O2 in MH4OH Solutions and Their Reaction with Silicon Wafers” published in Japanese Journal of Applied Physics, Vol. 43, No. 6A, 2004. It has been shown that when particles of Al2O3 were deposited on silicon wafers, the use of ozonated NH4OH in combination with the application of megatronic power could remove more than 90% of the particles from the wafer surface at room temperature.
The process is difficult to utilize in practice since, at room temperatures, the life of ozone in a solution will be very short, e.g., as mentioned in the article, the half-life of ozone at room temperature was 2 to 5 min.
Thus, the disadvantage of all above-described ozone-based substrate cleaning systems as well as other ozone-based cleaning systems known to the applicant is that they are efficient only in removing organic contaminants or films and are unsuitable for mechanical removal of inorganic contaminants such as carbon dioxide, ammonia, helium, krypton, argon, and nitrous oxide.
It is an object of the invention to provide an ozone-based method and apparatus for cleaning flat objects such as semiconductor substrates that are equally efficient in removing organic and inorganic substances from the surfaces of the flat objects. It is another object to provide the method and apparatus of the aforementioned type that combines advantages of mechanical wet pulse-jet cleaning systems for removal of inorganic substances with the advantages of the wet chemical ozone-based system for removal of organic substances. Still another object is to provide a universal and adjustable apparatus for cleaning semiconductor substrates or other flat objects from various contaminants that may accumulate on their surfaces. A further object is to provide a method and system of the aforementioned type where the efficiency of removing organic substances is further improved due to the use of a pulsed jet of a cleaning liquid that contains ozone in a pure gaseous state and in a dissolved state.
The present invention is based on the applicant's finding that incorporation of ozone into a cold-water solution injected onto the surface of a treated object in a pulse-jet mode produces a synergistic effect of mechanical removal of inorganic particles and chemical removal of organic contaminants. This effect is greater than just a mere sum of separately used ozone-based cleaning and jet-pulse cleaning. The effect is greater because in a pulsed jet of liquid, ozone can be delivered to the treated object not only in a dissolved state, but it can also be decomposed under the effect of turbulent flow and thereby changed into a gaseous phase that is delivered to the treated surface, i.e., to organic contaminants, in a gaseous phase prior to oxidation. According to the invention, the ozonated pulse-jet treatment is enhanced by utilizing three different consequent cleaning pulses that are cyclically repeated during the cleaning operation. The first pulse is treating the object surface with a jet of an ozone solution, e.g., in a deionized water. Since ozone solution is ejected at a low temperature of about 5° C., and, in order to level the temperature by raising it to about 100° C. prior to the third high-temperature pulse, the second pulse consists of treating the surface with a hot inert gas, e.g., nitrogen. Since gas has a lower thermal capacity than liquid, this pulse has a longer duration than that of the jet-treatment pulse. The third pulse is treatment of the object surface with a mixture of overheated steam and water, e.g., a steam-and-water mixture, at a temperature in the range of 105° C. to 250° C., preferably about 200° C. When the hot steam-and-water mixture exits the cleaning nozzle, because of a sudden increase in volume, it is subject to adiabatic expansion. This process enhances breaking of the stream into small droplets required for efficient cleaning.
The apparatus of the invention comprises a heat-insulated casing that contains an ozone solution container connected to a water-supply source and an ozone generator. The ozone in the container is cooled by means of a cooling coil with a cooling liquid circulating through the coil. Temperature in the ozone solution container is maintained, e.g., in the range of 3° C. to 10° C., preferably, at about 5° C., with the use of a thermostat. From the container, the ozone solution is pumped by a pump with a controller to a nozzle of the cleaning mechanism which ejects the flow in a jet-pulsed mode controlled from a central processing unit onto the surface to be treated. The apparatus is also equipped with a solution heater, heater/mixer controller, etc. The apparatus is provided with three closely arranged independent systems connected to the central processing units and equipped with respective heaters, pumps with controllers, and nozzles for supplying different cleaning solutions to the nozzles of all three types.
The mechanical part of the cleaning unit of the invention may be the same in the earlier patent application of the same applicant (Ser. No. 269,250, filed on Nov. 9, 2005 and entitled “METHOD AND APPARATUS FOR CLEANING FLAT OBJECTS WITH PULSED LIQUID JET”).
An apparatus is enclosed in a sealed and filtered cabinet or enclosure that may be comprised of a class-1 self-powered ULPA-filter cabinet. The cleaning unit contains circumferentially arranged rollers, one of which is a driving roller; the remaining rollers are idler rollers. The drive roller is driven from an adjustable-speed motor. The drive roller and idler rollers are arranged in such a way that there is always a minimal radial or edge contact and no surface contact along the front or backside of the wafer W during processing/cleaning. The rapid-pulse clean unit includes the head assembly that holds the drive and idler rollers. The roller mechanism is mounted with the rollers of different diameters to hold semiconductor wafers of varying sizes from 75 mm to 300 mm and above. The upper part of the head assembly is moveable in a vertical direction on guides to provide insertion of the wafer W. The chamber also contains stationary arrays of the aforementioned ozonated solution pulse nozzles, hot gas nozzles, and overheated steam-and-water mixture nozzles positioned on both sides of the vertical wafer W diametrically across the wafer W to clean the front and back surfaces of the wafer in a simultaneous process.
The droplet formation enhancement means are located inside the ozonated solution nozzles at the nozzle outlet end and are made in the form of a jet splitter, threaded grooves on the inner surfaces of the nozzle bodies, or in the form of a thin tube for the supply of gas into the flow of the liquid cleaning medium for the formation of gas bubbles in the medium. The method also takes into account such factors as a mass ratio between the droplets and the contaminant particles, velocity of droplets, organization and sequence of jets that attack the surface of the wafer, and flows that wash-out the separated particles, etc.
The apparatus consists of three main sub-systems, which will be considered separately in sequence, i.e., an ozonated cleaning solution sub-system 20 shown in block-diagram form in
As shown in
In order to intensify ozonation of the cleaning liquid, the ozonated solution container 28 is connected to an ozonated oxygen/air pump 40 that is used for bubbling of the cleaning liquid simultaneously with the supply of gaseous ozone (O3). The ozone solution container 28 is cooled by means of a cooler 42 with a pump 43, a thermostat 45, and cooling coil 44 wound around the outer periphery of the container 28. The ozonated cleaning liquid in the container 28 is maintained at a level such that at the exit from the nozzle, the temperature of the solution is maintained in the range of 3° C. to 10° C., preferably, at about 5° C. Since cleaning efficiency to a great extent depends on the concentration of ozone in the cleaning liquid, the sub-system 20 is equipped with an ozone-concentration sensor 46 immersed into the ozonated solution of the container 28. The ozonated solution container 28 is connected to a jet-pulse nozzle 48 via a pump 50 with a controller 52 that is connected to a central processing unit (CPU). Connected to the CPU is a user interface 53. The liquid is emitted from the nozzle 48 in a pulsed mode.
Since release of ozone wastes to the atmosphere is restricted, the sub-system 20 can be equipped with an ozone killer 54 connected to the container 28 via a safety valve 56. The ozone killer changes the detrimental ozone gas into oxygen through a catalyst, such as active charcoal, or the like.
The steam-and-water cleaning sub-system 22 shown in
The optional deionized-water sub-system 25, which is shown in
The hot-gas sub-system 24 shown in
The apparatus of the invention makes it possible to combine types of cleaning pulses and their sequences. For example,
Combinations and sequences of pulses are not limited by the above examples and other combinations are possible, e.g., 1) cold ozonated solution→hot gas→overheated; steam; 2) cold ozonated solution→dionized water→overheated steam; etc.
The pulses may have different shapes, e.g., as shown in
A three-dimensional view of the nozzle unit 132 of the apparatus is shown in
The apparatus also contains stationary nozzle arrays 152 and 154 positioned on both sides of the vertical wafer W diametrically across the wafer W to clean the front and back surfaces of the wafer in a simultaneous process. The arrangement of the stationary nozzle arrays 152 and 154 is shown in
As shown in
The nozzles operate in so-called rapid-pulse harmonic spray modes of the type shown in
Similarly, the hot-gas nozzles 152a2, 152b2, 152c2, and 152d2 emit onto the surface of the treated object W jets of hot gas at a temperature of about 100° C., while nozzles 152a3, 152b3, 152c3, and 152d3 impinge the surface of the object with jets of a steam-and-water mixture at a temperature of about 200° C.
Thus, it has been shown that the invention provides an ozone-based method and apparatus for cleaning flat objects such as semiconductor substrates that are equally efficient in removing organic and inorganic substances from the surfaces of the flat objects, that combine the advantages of mechanical wet pulse-jet cleaning systems for removal of inorganic substances with the advantages of the wet chemical ozone-based system for removal of organic substances. The invention provides a universal and adjustable apparatus for cleaning semiconductor substrates or other flat objects from various contaminants that may accumulate on their surfaces. Efficiency of removal of organic substances is further improved due to the use of a pulsed jet of a cleaning liquid that contains ozone in a pure gaseous state and in a dissolved state.
Although the invention has been shown and described with reference to specific embodiments, it is understood that these embodiments should not be construed as limiting the areas of application of the invention and that any changes and modifications are possible, provided these changes and modifications do not depart from the scope of the attached patent claims. For example, pulses may have a substantially rectangular shape, sinusoidal shape, trapezoidal shape, etc. Ozone may be dissolved not only in a deionized water but also in ultrapure water. The nozzles may have arrangements different from those shown in
The present patent application is related to U.S. patent application Ser. No. 269,250 filed by R. S. Randhawa on Nov. 9, 2005, entitled “Apparatus and Method for Cleaning Flat Objects in a Vertical Orientation with Pulsed Liquid Jet” and to U.S. patent application Ser. No. 299,134 filed by R. S. Randhawa on Dec. 12, 2005 entitled “Method and Apparatus for Cleaning Flat Objects with Pulsed Liquid Jet”.