METHODS OF WET PROCESSING ELECTRONIC COMPONENTS USING PROCESS LIQUIDS WITH CONTROLLED LEVELS OF GASES

Abstract: The present invention is related to wet processing methods for electronic components using process liquids having controlled levels (i.e., amounts) of gases. The present invention provides methods of wet processing where at least two process liquids used during a wet processing procedure contain different levels of gases. Sonic energy may optionally be used in one or more wet process steps of a wet processing procedure to enhance results. The methods of the present invention can result in, for example, improved cleaning or reduced particle contamination during a wet processing procedure.

Description: METHODS OF WET PROCESSING ELECTRONIC COMPONENTS USING PROCESS LIQUIDS WITH CONTROLLED LEVELS OF GASES Cross-Reference to Related Applications This application claims the benefit of U.S. Provisional Application No. 60/076175, filed on February 27, 1998, the disclosure of which is hereby incorporated by reference in its entirety. Field Of The Invention The present invention is directed to wet processing methods in the manufacture of electronic components, including electronic component precursors, such as semiconductor wafers used in integrated circuits. More specifically, this invention relates to methods of wet processing electronic components using one or more process liquids where the level (i.e., amount) of gases in the process liquids is controlled. Background Of The Invention Wet processing methods are used extensively during the manufacture of integrated circuits, which typically comprise electronic components such as semiconductor wafers, flat panels, and other electronic component precursors. Wet processing methods may be used for example to prepare electronic component precursors for processing steps such as oxidation, diffusion, ion implantation, epitaxial growth, chemical vapor deposition, and hemispherical silicon grain growth, or combinations thereof. Generally, the electronic components are placed in a bath or a vessel and contacted with a series of reactive chemical process fluids and rinsing fluids. The process fluids may be used, without limitation, for etching, photoresist stripping, and prediffusion cleaning and other cleaning steps of the electronic components. See, e.g., U.S. Patent Nos. 4,577,650; 4,740,249; 4,738,272; 4,856,544; 4,633,893; 4,778,532; 4,917,123; and EPO 0 233 184, assigned to a common assignee, and Burkman et al, Wet Chemical Processes- Aqueous Cleaning Processes, pg 111-151 in Handbook of Semiconductor Wafer Cleaning Technology (edited by Werner Kern, Published by Noyes Publication Parkridge, New Jersey 1993), the disclosures of which are herein incorporated by reference in their entirety. In a typical wet processing procedure, the electronic components are treated in such equipment as a single vessel (e.g., open or enclosable to the environment), or a wet bench (system having a plurality of open baths). The electronic components are exposed to reactive chemical process fluids to, for example, remove (e.g., clean) contamination on the electronic components or to etch some part of the surface. After this chemical treatment step is performed, the chemicals may adhere to the surface or surfaces of the electronic components. The adhered chemicals are optionally then removed from the surfaces of the electronic components, before treating the electronic components with the next reactive chemical process fluid so that the chemical residue does not contaminate the next chemical treatment step. Traditionally, adhered chemicals are removed using rinsing liquids such as deionized (DI) water. After the chemical treatment steps are completed, the electronic components are generally dried. Drying of the electronic components can be done using various methods, with a goal being to ensure that there is no contamination remaining after or created during the drying process. Methods of drying include evaporation, centrifugal force in a spin-rinser-drier, direct-displace™ drying, steam or chemical drying of wafers, including the method and apparatus disclosed in, for example, U.S. Pat. Nos. 4,778,532, or 4,911 ,761. An important consideration for an effective wet processing method is that the electronic components produced by the process be ultraclean (i.e., with minimum particle contamination and minimum chemical residue). Thus, much effort has been focused on developing wet processing methods resulting in reduced particle contamination and chemical residue on the electronic components. The use of sonic energy of varying frequencies has been used to enhance the removal of particles from electronic components. For example, semiconductor wafer cleaning techniques have been supplemented with ultrasonic energy or megasonic energy. Ultrasonic energy is usually defined as sonification at frequencies that are above what is audible to humans. These frequencies are approximately 18 kHz and higher. Cleaning of electronic components using ultrasonic energy has typically been conducted at frequencies ranging from about 20 kHz to about 200 kHz and more preferably from about 40 kHz to 104kHz. Another preferred sonic energy range that has been used for cleaning electronic components is in the range of about 600 KHz to about 2 MHz. This "high frequency" ultrasonic range is commonly referred to as "megasonics." As used herein, "ultrasonic energy" will refer to sonic energy that is below the megasonic energy range of about 600 KHz to about 2 MHz, even though typically the terminology "ultrasonic energy" refers to sonification at any frequency above what is audible to humans. Typically, ultrasonic energy, including megasonic energy, is transmitted through a transducer made of piezoelectric material, which becomes electrically polarized when mechanically stressed and will mechanically deform when electrically polarized. Alternating positive and negative polarization results in alternating thickness of the material at the same frequency and ultrasonic waves are generated in the chamber. Gale et al., Experimental Study of Ultrasonic and Megasonic Particle Removal, Precision Cleaning, Vol. II, No. 4, April 1994 ("Gale Article"). It is believed that the cleaning ability of sonic energy is due to various combinations of cavitation and acoustic streaming. Acoustic streaming is the flow of liquid induced by the action of sound waves. This induced flow of liquid may enhance the removal of particles from the surfaces of electronic components. Cavitation is the formation and collapse of bubbles of either gas or vapor in a liquid subject to pressure changes. During cavitation, high intensity sound waves generate pressure fluctuations in a liquid that result in the formation of bubbles. The pressure fluctuations can also cause the formed bubbles to collapse. When the bubbles collapse, they can release energy to dislodge and disperse particles. Despite the advantages of cavitation, cavitation can also under certain conditions lead to surface damage of the electronic components. For example, the release of energy from the collapsing bubbles can also cause surface pits to be formed on the electronic components, or cause the lifting of patterns that were formed on the electronic component. Any damage to the surfaces of the electronic components is typically undesirable. The use of megasonics has become increasingly more popular to mitigate surface damage that may be caused by sonic energy. This is because with megasonics, large cavitation bubbles, that often cause surface damage, do not usually have time to form. (See e.g., Gale Article). U.S. Patent Nos. 5,672,212; 5,383,484; 5,286,657; 5,143,103; and 5,090,432 disclose the use of megasonics during the wet processing of semiconductor wafers. Studies have also been conducted to determine the effect of particle size, sonic energy, and sonification time on particle removal during cleaning of semiconductor components with megasonics. For example, in the Gale Article, it was found that particle removal increases with increasing sonic energy, increasing sonification time, and increasing particle size. The experimental procedure in the Gale Article, however, did not consider the effect of the level of gases in a process liquids on particle removal. Although the presence of gases in process liquids used during wet processing may be desirable in certain circumstances, the presence of gases, in process liquids can in some circumstances have adverse effects. For example, it has been found that the presence of gas in a process liquid can increase the efficiency of cavitation during sonification. Despite this benefit, gas in liquids in other circumstances can promote particle deposition during wet processing. This is because particles tend to be attracted to gas-liquid interfaces, such as those surrounding bubbles, and when these bubbles contact the surfaces of the electronic components, particle contamination can occur. This contamination can be especially problematic for hydrophobic surfaces, as bubbles have the tendency to be attracted to hydrophobic surfaces. Past wet processing methods have not addressed these competing needs in a wet processing procedure. Generally, degassification equipment is either on (at one degassification level) or off during the entire wet processing procedure. This approach does not recognize the effect of the presence of gases in a process liquid in each chemical treatment step or rinsing step, or that it may even be desirable to add gases to a process liquid depending on the wet process step. It has been discovered that controlling (e.g., adjusting) the level of gases in process liquids in one or more chemical treatment steps or rinsing steps in a wet processing procedure can enhance wet processing results, such as reducing particle contamination and/or improving cleaning. The present invention provides methods of controlling the level of gases in process liquids to enhance the results obtained in wet processing procedures. The present invention also provides methods of controlling the level of gases when one or more chemical treatment or rinsing steps include the use of sonic energy. Summary Of The Invention The present invention provides, inter alia, wet processing methods for the manufacture of electronic components, including electronic component precursors, such as semiconductor wafers used in integrated circuits. More specifically, this invention relates to methods of, for example, cleaning electronic components using wet processing techniques with process liquids containing different levels of gases. It has been discovered that by selectively controlling the level of gases in process liquids used during wet processing, the results of the wet processing procedure, such as removal of particles, surface roughening, or overall process duration can be improved. The present invention provides methods of selecting an appropriate level of gases in the process liquid that is appropriate to the wet process step being performed to enhance wet processing results. In one embodiment of the present invention, the present invention includes placing the electronic components having surfaces in a reaction chamber; controlling the level of gases in at least two process liquids, where at least two of the process liquids have different levels of gases; and contacting the electronic components with each of the process liquids for a contact time. The electronic components may also optionally be exposed to sonic energy for at least a portion of the contact time or may be dried with a drying fluid. Process liquids useful in the present invention include reactive chemical liquids and rinsing liquids. In a preferred embodiment of the present invention, the level of gases in the process liquids are controlled based on the surface composition of the electronic components upon completion of the wet process step, or subsequent wet process steps to be performed, or combinations thereof In a more preferred embodiment, the methods of the present invention include using a process liquid containing high level of gases in one wet process step and using another process liquid containing low levels of gases in another wet process step of the same wet processing procedure. Through using the methods of the present invention many problems of past wet processing methodologies may be minimized. For example, the method of the present invention provides a method of contacting the electronic components with a low gas containing process liquid to prevent formation or release of bubbles where the surfaces of the electronic components are sensitive to particle deposition by bubbles (e.g., hydrophobic surfaces such as oxide-free silicon). The present invention also provides a method of contacting the electronic components with a low gas containing process liquid to ensure low oxygen levels (preferably < 20 ppb by weight, and more preferably less than 5 ppb by weight based on the total weight of the process liquid) in process liquids such as DI water when treating electronic components having surfaces that are susceptible to reaction with oxygen (e.g., surfaces having essentially oxide- free silicon). The present invention provides a method of contacting the electronic components with a high gas containing process liquid when gases in a process liquid such as DI water or a cleaning solution are useful (e.g., ultrasonic or megasonic cleaning and rinsing processes). Thus, rinsing liquids such as deionized water may have different levels of gases within one wet processing procedure depending on, for example, previous or subsequent chemical treatment steps. Brief Description of the Drawings Figure 1 is a graph of particle removal efficiency, expressed as the percentage of particles removed, versus the level of vacuum pulled in inches of Hg, gauge pressure, on a second gas-liquid contactor element of a gas adjusting unit during wet processing with an SCI solution using sonic energy. Detailed Description Of The Invention The terminology "electronic component" as used herein includes, without limitation, electronic component precursors such as semiconductor wafers, flat panels, and other components used in the manufacture of electronic components (i.e., integrated circuits). The term electronic component also includes for example CD ROM disks, hard drive memory disks, or multichip modules. The terminology "reactive process liquid," "reactive chemical process liquid," "chemical liquid," "active chemical," or "active process liquid," as used herein, refers to a liquid that performs some action on the surfaces of the electronic components. For example, the liquid may have activity in removing contamination such as particulate, metallic, or organic materials from the surfaces of the electronic components, or the liquid may have some activity in etching the surface of the electronic component, or activity in growing an oxide layer on the surface of the electronic component. These terms may be used interchangeably. The terminology "rinsing liquid," as used herein, refers to DI water or some other liquid that is used to rinse the electronic component as compared to treating them with an active chemical or reactive chemical process liquid. A rinsing liquid may be for example DI water or a very dilute aqueous solution of an active or reactive chemical (e.g. , hydrochloric acid) to prevent, for example, metallic deposition on the surface of the electronic component. Ozone is another additive used during rinsing. The chemical concentration in such rinsing liquids is minute; generally, the concentration is not greater than about 1000 ppm by weight based on the total weight of the rinsing liquid. The primary goal of the rinsing liquid is to remove chemicals, particulates, or reaction products from the electronic component surfaces, and reaction chamber, and to inhibit redeposition of particulates. The terminology "process liquid" or "processing liquid" means any liquid that is contacted with the electronic components in a wet process step, such as a rinsing liquid or reactive chemical process liquid. The terminology "gas" or "gases," when used in the context of being "in" a process liquid, means dissolved, entrained or entrapped gas that is nonionizable in the process liquid. Examples of nonionizable gases include oxygen; nitrogen; carbon dioxide; hydrogen; noble gases, such as helium or argon; or combinations thereof. The terminology "fluid," as used herein includes liquids, gases, liquids in their vapor phases, or combinations thereof. The terminology "chemical treatment step," as used herein, refers to exposing the electronic components to a reactive chemical process liquid. The terminology "wet process step" as used herein, refers to exposing the electronic components to a process liquid , for example a rinsing liquid, or reactive chemical process liquid. The terminology "wet processing procedure" or "wet processing" as used herein, refers to exposing the electronic components to a series of process liquids to accomplish a particular purpose, for example, to clean and etch the electronic components. A wet processing procedure may include, for example, contacting the electronic components with other process fluids such as vapors or gases, and/or drying the electronic components. The terminology "reaction chamber," as used herein, refers to single vessels (enclosable or open to the atmosphere), baths, wet benches and any other reservoir suitable for wet processing electronic components. As used herein, the terminology "single vessel" refers to a wet processing system where the entire wet processing procedures is performed in one vessel. The vessel may be open or enclosable to the atmosphere. An "enclosable direct-displace vessel," refers to any wet processing system in which the electronic components are processed in a vessel capable of being closed to the atmosphere and where process fluids can be directed through the vessel sequentially so that one fluid displaces another fluid. Semiconductor fabrication, including wet processing techniques, is described generally, for example, in P. Gise et al., Semiconductor and Integrated Circuit Fabrication Techniques (Reston Publishing Co. Reston, Va. 1979), the disclosures of which are herein incorporated by reference in their entirety. The methods of the invention are generally applicable to any wet processing equipment having a reaction chamber for housing one or more electronic components, including, without limitation, single vessel systems, such as enclosable direct-displace vessel systems, wet benches, and spray cleaning systems. See, e.g., Chapter 1 : Overview and Evolution of Semiconductor Wafer Contamination and Cleaning Technology by Werner Kern and Chapter 3: Aqueous Cleaning Processes by Don C. Burkman, Donald Deal, Donald C. Grant, and Charlie A. Peterson in Handbook of Semiconductor Wafer Cleaning Technology (edited by Werner Kern, Published by Noyes Publication Parkridge, New Jersey 1993), and Wet Etch Cleaning by Hiroyuki Horiki and Takao Nakazawa in Ultraclean Technology Handbook, Volume 1, (edited by Tadahiro Ohmi published by Marcel Dekker), the disclosures of which are herein incorporated by reference in their entirety. In a preferred embodiment of the invention, the electronic components are housed in a single vessel system. Preferably, single vessels such as those disclosed in U.S. Patent Nos. 4,778,532, 4,917,123, 4,911,761, 4,795,497, 4,899,767, 4,984,597, 4,633,893, 4,917,123, 4,738,272, 4,577,650, 5,571,337 and 5,569,330, the disclosures of which are herein incorporated by reference in their entirety, are used. The most preferred type of single vessel is an enclosable direct-displace vessel such as those disclosed in U.S. Patent Nos. 4,778,532, 4,917,123, 4,911,761, 4,795,497, 4,899,767, 4,984,597, 4,633,893, 4,917,123, 4,738,272, and 4,577,650. Preferred commercially available single vessel systems are Full-Flow™ vessels such as those manufactured by CFM Technologies, Poiseidon manufactured by Steag, and 820 series models manufactured by Dainippon Screen. Such single vessel systems are preferred because they result in a more uniform treatment of the electronic components. In addition, often the chemicals utilized in the chemical treatment of electronic components are quite dangerous in that they may be strong acids, alkalis, or volatile solvents. Single vessels, especially when enclosable, minimize the hazards associated with such process fluids by avoiding atmospheric contamination and personnel exposure to the chemicals, and by making handling of the chemicals safer. Although vessels as those disclosed in the above-identified U.S. patents are preferred, any such vessels known to persons skilled in the art may be used without departing from the spirit of the invention. The reactive chemical process liquids suitable for practicing the invention include, without limitation, aqueous solutions of hydrochloric acid, ammonium hydroxide and buffers comprising the same, hydrogen peroxide, sulfuric acid, mixtures of sulfuric acid and ozone, hydrofluoric acid and buffers comprising the same, chromic acid, phosphoric acid, acetic acid and buffers comprising the same, nitric acid, ammonium fluoride buffered hydrofluoric acid, and combinations thereof The particular process liquids used, the equipment used, the exposure time (i.e., contact time), and the experimental conditions (i.e., temperature, concentration, and flow of the process liquid) will vary depending on the particular purpose of the particular wet processing procedure. Rinsing liquids useful in the present invention are any liquid that is effective in removing reactive chemical process liquids from the electronic components. In selecting a rinsing liquid such factors as the nature of the surfaces of the electronic components to be rinsed, the nature of contaminants dissolved in the reactive chemical process liquid, and the nature of reactive chemical process liquid to be rinsed should be considered. Also, the proposed rinsing liquid should be compatible (i.e., nonreactive) with the materials of construction in contact with the rinsing liquid. Rinsing liquids which may be used include for example deionized water, organic solvents, mixtures of organic solvents, ozonated water, or combinations thereof. Preferred organic solvents include those organic compounds useful as drying fluids, such as C, to C 10 alcohols, and preferably C, to C 6 alcohols. Preferably the rinsing liquid is deionized water. Rinsing liquids may optionally contain low levels of chemically reactive substances to enhance rinsing. Examples of such chemicals include, without limitation, hydrochloric acid, hydrofluoric acid, hydrogen peroxide, ozone, and surfactants. The concentration of such chemicals in a rinsing liquid is generally about 1000 ppm or less by weight based on the total weight of the rinsing liquid. The methods of the invention may be used for any wet processing procedure such as etching the surfaces of semiconductor wafers to remove any unwanted oxide layer from the silicon surface, cleaning the surfaces of semiconductor wafers to remove organic, metallic, or particulate matter, or removing photoresist from the surfaces of semiconductor wafers. The present invention may also be used in controlled oxide etching or for growing oxide layers on semiconductor wafers. Typical etchants for silicon dioxide include, without limitation, hydrofluoric acid, or ammonium fluoride buffered hydrofluoric acid. A typical processing area for treating electronic components will have storage tanks for chemical reagents, such as ammonium hydroxide (NH 4 OH) or hydrofluoric acid (HF). These reagents are typically stored in their concentrated form, which is: hydrogen peroxide (H 2 O 2 ) (31%), NH 4 OH (28%), hydrochloric acid (HC1) (37%), HF (49%), and sulfuric acid (H 2 SO 4 ) (98%>) (percentages represent weight percentages in aqueous solutions). This processing area will also include a storage tank for any vapors and/or carrier gases that may be used in performing the methods of the invention (i.e., isopropanol or nitrogen). The reaction chamber where the electronic components are being treated is in fluid communication with the storage tanks. A control valve and pump may be used as processing equipment between the storage tanks and the reaction chamber. The processing area also preferably contains one or more units for adjusting the level of gases in the process liquids ("gas adjusting unit"), which are in communication with the reaction chamber. In a preferred embodiment, the processing area includes a gas adjusting unit to adjust the level of gases in deionized water before it enters the channel (that is the fluid communications with the reaction chamber), and before it is mixed with chemical reagents that will be used in the chemical treatment step. It is also contemplated that process liquids containing chemical reagents may be passed through a gas adjusting unit. A processing control system, such as a personal computer, may be used as a means to monitor process conditions (i.e., flow rates, mix rates, exposure times, and temperature) and the proper level of gases in the process liquids. Reaction chambers suitable for practicing the invention are preferably equipped for generating sonic energy, such as ultrasonic energy and/or megasonic energy. Suitable sonic energy levels for practicing the invention include, without limitation, energy having a frequency between about 20 kHz to about 2.0 MHz, more preferably from about 40 kHz to about 1.2 MHz, and most preferably from about 400 kHz to about 1.2 MHz. The most preferred sonic energy ranges used are in the megasonic energy range, and most preferably are from about 600 kHz to about 800 kHz. In practicing a preferred embodiment of the invention, the electronic components are placed in a single vessel equipped for use with ultrasonic or megasonic energy and the process fluids, including process liquids, will be introduced into the vessel through a valve or injection port. The deionized water and chemical reagents, such as ammonium hydroxide (NH 4 OH), hydrogen peroxide (H 2 O 2 ), hydrochloric acid (HC1), and sulfuric acid (H 2 SO 4 ) (98%>) are preferably stored in tanks external to the reaction chamber. The reaction chamber where the electronic components are being treated is in fluid communication with the chemical storage tanks via a fluid line. A control valve and pump is generally used to transport the chemical reagents and deionized water from the storage area through the fluid line to the reaction chamber. A processing control system, such as a personal computer, is preferably used as a means to monitor process conditions (e.g., flow rates, mix rates, exposure times, and temperature). For example, the processing control system can be used to program the flow rates and injection levels so that the appropriate concentration of chemicals will be present in the reactive chemical process liquid (or rinsing liquid). The processing control system will also be used to program the appropriate level of gases in the deionized water or process liquid, where the desired level of gases will depend on such factors as the particular chemical treatment step that is being performed. The selection of the level (i.e., amount) of gases in the process liquids is discussed below in more detail. Typically, more than one chemical reagent is present in a reactive chemical process liquid during a single chemical treatment step. For example, the first step in a cleaning process may use a Standard Cleaning 1 solution (SCI). Typical concentrations for SCI range in parts by volume from about 5:1 :1 to about 200: 1 : 1 Water: H 2 O 2 :NH 4 OH. Each of the components of the SCI (i.e., water, H 2 O 2 , and NH 4 OH) are maintained in separate storage containers, and via a processing control system, an amount of each will be injected into a channel that is in fluid communication with the reaction chamber so that the appropriate ratio of each component is achieved. Before the deionized water is mixed with the H 2 O 2 and NH 4 OH to achieve the appropriate dilution of the particular chemical treatment step, the amount of gas in the deionized water is preferably adjusted by passing the deionized water through a gas adjusting unit. It is contemplated that the solution of SCI, or whatever liquid that is being used for the chemical treatment step, may be passed through a gas adjusting unit after each of the individual chemicals are mixed with the deionized water. The gas adjusting unit may be any type of equipment that is capable of controlling (e.g., removing, adding, replacing, or maintaining) the level of gases in a liquid. For example, the gas adjusting unit preferably is capable of removing oxygen from a liquid in a controlled amount. The gas adjusting unit is also preferably capable of adding gases, or replacing gases removed with other gases such as nitrogen or argon in a controlled amount. Additionally, the overall wet processing system may contain one or more gas adjusting units for different process liquids. Preferably, the gas adjusting unit is capable of reducing the level of dissolved, entrained, or entrapped oxygen in a process liquid to about 200 ppb or lower and more preferably to about 5 ppb or lower. The kinds of gas adjusting units preferred for practicing the method of the invention are those that have one or more gas-liquid contactor elements for separating gases in a liquid from the liquid. Preferably, the gas-liquid contactor elements are membranes made from polymeric materials, such as polypropylene, such that, gas molecules or vapor molecules, pass through the membranes, while the bulk process liquid, such as deionized water, does not. For example, a preferred gas adjusting unit for practicing the method of the invention is the Liqui-Cel® gas-liquid contactor manufactured by the Separation Products Group of Hoechst Celanese Corporation, Charlotte, NC. Preferably, the gas adjusting unit has the capacity to pull and maintain a vacuum in a controlled fashion, and can handle process liquids having various flow rates. A preferred manner of operating a gas adjusting unit useful in the present invention includes directing a process liquid, preferably deionized water, into the "liquid side" of gas-liquid contactor elements. Vacuum is preferably pulled and nitrogen is added on the "gas side" of the gas-liquid contactor elements. Gases in the process liquid, such as oxygen and nitrogen, will be controlled by adjusting the vacuum level and the amount of nitrogen added on the gas side of the membrane. For slightly soluble gases, the gas adjusting unit operates in accordance with Henry's Law (the mass of a slightly soluble gas that dissolves in a mass of liquid at a given temperature is proportional to the partial pressure of that gas). Thus, by controlling the amount of nitrogen, oxygen, or other slightly soluble gases on the gas side of the gas-liquid contactor elements, and the total pressure of the gas in contact with the liquid, the amount of gases in the process liquid may be controlled. For example, it may be desirable, such as with cleaning solutions used with megasonic energy, to increase the overall level of gases by adding gases such as nitrogen. Also, for example, it may be desirable to reduce the level of oxygen, but to add nitrogen in an amount, less than, equal to, or exceeding the amount of oxygen that was removed. In a more preferred embodiment, the gas adjusting unit contains two stages of gas- liquid contactor elements. The two stages can be operated for example by removing oxygen in the process liquid and replacing it with nitrogen in the first stage. In the second stage, the total level of nitrogen can be adjusted to a desired level. In an embodiment of a process using the Liqui-Cel® gas-liquid contactor unit, when a low level of gases is desired, the following conditions may be used: flow rate of process liquid (preferably deionized water) is about 13 gpm, vacuum is about -28 inches Hg gauge, and nitrogen sweep rate is about 0.5 scfin. After using this treatment, the level of oxygen in the deionized water is about 1 ppb and the level of nitrogen is about 770 ppb. In an embodiment of a process using the Liqui-Cel® gas-liquid contactor unit, when a high level of gas is desired the following conditions may be used: flow rate is about 13 gpm; vacuum is about -6 inches Hg gauge, and the nitrogen sweep rate is about 0.5 scfin. After using this treatment, the level of oxygen is about 4 ppb and the level of nitrogen is about 13,000 ppb. This high level of gases, in particular, nitrogen, is particularly suitable for cleaning processes because it has been found that gases can improve megasonic particle removal efficiency as described hereinafter. It will be recognized by those skilled in the art that the process conditions described above for obtaining high and low levels of gases in a process liquid are being provided as examples only and that they can be varied. For example, one skilled in the art would recognize that the process liquid flow rate, vacuum level, and nitrogen sweep can be varied to achieve the desired level of gases in a process liquid. It may also be desirable to use other gases in place of the nitrogen sweep. It has been discovered that the level of gases (i.e., nonionizable) in the process liquid is preferably adjusted depending on the particular process liquid being used to treat the electronic components, the composition of the surfaces of the electronic components, and/or subsequent wet process steps. Particularly, it has been found that the level of gases in the process liquid is preferably controlled based on the surface composition of the electronic components upon completion of a wet process step, or subsequent wet process steps to be performed, or combinations thereof For example, when the surfaces of the electronic components have a protective layer, such as an oxide layer, at the completion of a wet process step, preferably the level of gas in the process liquid is adjusted to be high ("high gas containing process liquid"). The protective layer may already be present on the surfaces of the electronic components, or be formed from the interaction of the high gas containing process liquid and surfaces of the electronic components. In a preferred embodiment, sonic energy is used when electronic components are exposed to high gas containing process liquids. When the surfaces of the electronic components are substantially free of a protective layer, such as an oxide layer, at the completion of a wet process step, preferably a process liquid with a low level of gases ("low gas containing process liquid") is used. The surfaces of the electronic components may already be substantially free of a protective layer, or a protective layer may be substantially removed from the interaction of the low gas containing process liquid and surfaces of the electronic components. Low gas containing process liquids are also preferably used when no subsequent processing steps are planned that would alter the surface composition of the electronic components to form for example a protective layer. For example, when a hydrofluoric acid etching step is performed in a wet processing procedure, preferably the hydrofluoric acid process liquid has a low level of gases. When using low gas containing process liquids, sonic energy may or may not be desired depending on the wet processing procedure. Preferably however, sonic energy is not used when contacting the electronic components with low gas containing liquids. Although in no way intending to be limited in theory, it is believed that when high gas containing process liquids are used with sonic energy, the increased the level of gases in the process liquid enhances particle removal by, for example, improving transmission of megasonic energy into the process liquid. Moreover, when a protective layer, such as oxide, is present on the electronic component, or a protective layer is formed on the surfaces of the electronic components during contact with a process liquid, the protective layer minimizes the risk of damage to the electronic component that can occur when sonic energy is used. In contrast, when the electronic component contains substantially no protective layer or a protective layer is being substantially removed, the level of gases in the process liquid is preferably low to minimize the risk of damage to the electronic components if sonification is used, and to minimize reaction (e.g., oxidation) of the surfaces of the electronic components with the gases in the process liquid. By "low gas containing process liquid" it is meant that the total level of dissolved, entrained, or entrapped nonionizable gases in the process liquid (either before or after adding chemical reagents) is preferably maintained at a level below about 90%> of the saturation level of the gases in the process liquid under the conditions (e.g., temperature and pressure) in the reaction chamber during the wet process step. This is to preferably avoid the formation of bubbles in the process liquid in the reaction chamber. Additionally, preferably, the level of oxygen is about 0.1 percent or less, and more preferably 0.01 percent or less of the level of oxygen in the process liquid at saturation (also determined under the conditions in the reaction chamber during the wet process step). By "high gas containing process liquid" it is meant that the total level of dissolved, entrained, or entrapped nonionizable gases in the process liquid (either before or after adding chemical reagents) is preferably slightly below (e.g., about 90% or greater of the level of gases in the process liquid at saturation), equal to, or above the saturation level of the gases in the process liquid under the conditions present in the reaction chamber during the wet process step. Thus, with high gas containing process liquids, bubbles may or may not be present, depending on the level of gases in the process liquid. As described previously, the level of gases in the process liquid is preferably controlled based on the presence of a protective layer on the surfaces of the electronic components at the completion of a wet process step, or the formation of a protective layer in a subsequent wet process step. By "protective layer" it is meant a layer that has a surface concentration of at least one monolayer of atoms. For an oxide protective layer, the density is preferably about 10 15 oxygen atoms per cm 2 . The protective layer may already be present on the surfaces of the electronic components prior to exposure with the process liquid, or may be formed during exposure with the process liquid, or combinations thereof. For example, process liquids used for cleaning ("cleaning solutions") or process liquids used for removing photoresists ("photoresist removal solutions") tend to oxidize the surfaces of the electronic component to form, for example, a protective layer of oxides, such as silicon oxides. With such process liquids, when used in conjunction with sonic energy, it is preferred that the level of gases of the process liquid be high. Also, when the electronic component already has a protective layer formed, for example, from exposure to the atmosphere, or through a previous chemical treatment step, such as cleaning, a process liquid that does not significantly remove the protective layer (i.e., the process liquid does create a substantially unprotected surface) preferably has a high level of gases. For example, an electronic component already having a protective layer could be exposed to a high gas containing rinsing liquid in the presence of sonic energy. It is also possible that the electronic component be exposed to a high gas containing etching solution in combination with sonic energy, as long as some of the protective layer remains to provide protection during sonification (such as when lightly etching). In contrast, when the process liquid is used to remove substantially all of a protective layer such as an oxide, or the electronic component is substantially free of a protective layer, a low gas containing process liquid is preferred. By "substantially free of a protective layer" or "remove substantially all of a protective layer" it is meant that the layer on the surfaces of the electronic components is typically less than a monolayer of atoms. For example, process liquids used for etching ("etching solutions") can, under appropriate wet processing conditions, remove substantially all of a protective layer. In this case, the level of gases in a process liquid should be low. Also, when it is desired to maintain an unprotected surface of an electronic component (i.e., avoid oxidation) any process liquid that the electronic component is exposed to, preferably has a low level of gases. In practicing the method of the present invention, the electronic components may be treated with any number of process liquids as long as at least two process liquids have different levels of gases in a wet processing procedure. For example, in a preferred embodiment, the electronic components may be exposed to two process liquids where one process liquid has a high level of gases and the other process liquid has a low level of gases in one wet processing procedure. The electronic components may be exposed to the process liquid for any contact time that achieves the desired wet process step result. For example, the electronic components may be treated with cleaning solutions, photoresist removal solutions, etching solutions, rinsing liquids, or any combination thereof for any contact time. Also, for example, the electronic components, in between chemical treatment steps, may be exposed to a DI rinse or a drying vapor to remove residual chemicals from the prior treatment step, or one reactive chemical process liquid may displace the previous reactive chemical process liquid with no intervening rinse. Examples of cleaning solutions useful in the present invention are those that typically contain one or more corrosive agent such as an acid or base. Suitable acids for cleaning include for example sulfuric acid, hydrochloric acid, nitric acid, or aqua regia. Suitable bases include for example, ammonium hydroxide. The desired concentration of the corrosive agent in the cleaning solution will depend upon the particular corrosive agent chosen and the desired amount of cleaning. These corrosive agents may also be used with oxidizing agents such as ozone or hydrogen peroxide. Preferred cleaning solutions are "SCI" solutions containing water, ammonia, and hydrogen peroxide (described previously), and "SC2" solutions containing water, hydrogen peroxide, and hydrochloric acid. Typical concentrations for SCI solutions range from about 5:1:1 to about 200:1:1 parts by volume H 2 O : H 2 O 2 : NH 4 OH. Typical concentrations for SC2 solutions range from about 5:1 :1 to about 1000:0:1 parts by volume H 2 O : H 2 O 2 :HCl. Suitable etching solutions useful in the present invention contain agents that are capable of removing oxides. Common etching agents useful in the present invention are for example hydrofluoric acid, buffered hydrofluoric acid, ammonium fluoride, or other substances which generate hydrofluoric acid in solution. A hydrofluoric acid containing etching solution may contain for example from about 4: 1 to about 1000: 1 parts by volume H 2 O :HF. Photoresist removal solutions useful in the present invention include for example solutions containing sulfuric acid, and an oxidizing substance such as hydrogen peroxide, ozone or combinations thereof. One skilled in the art will recognize that there are various process liquids that can be used during wet processing. Additionally, other types of process fluids may be used during wet processing such as drying vapors. Other examples of process liquids and fluids that can be used during wet processing are disclosed in "Chemical Etching" by Werner Kern et al., in Thin Film Processes, edited by John L. Vosser et al., published by Academic Press, NY 1978, pages 401-496, which is incorporated by reference in its entirety. Using the methods of the present invention, the electronic components may be treated with any number of process fluids in any sequence. One skilled in the art will recognize that the type and sequence of wet processing will depend upon the desired treatment. It is also contemplated that the method of the present invention may include treatment with process liquids, where sonic energy is not used, and/or where the level of gases is not controlled in the process liquid, as long as the electronic components are exposed to at least two process liquids having different levels of gases in a wet processing procedure. For example, the electronic components may be treated with three process liquids, where the first process liquid is an SC 1 solution of water, hydrogen peroxide, and ammonium hydroxide (80:3: 1); the second process liquid is an SC2 solution of water, hydrogen peroxide, and hydrochloric acid (80:1 :1); and the third process liquid is an etching solution of hydrofluoric acid (about 10:1 to about 1000:1 (Water :HF)). This sequence may also be reversed. This method is particularly useful for cleaning and etching (i.e., removing oxide from the wafer surface). The SCI and SC2 would preferably have high levels of gases. The etching solution would preferably have a low level of gases, if the etching solution was being used to remove substantially all of the oxide from the surfaces of the electronic components. In other embodiments of the invention, the electronic components may be treated with a solution of concentrated sulfuric acid injected with ozone, and with a solution of hydrofluoric acid. This method is particularly useful for removing organics, such as photoresist (ashed or unashed) and particulate matter, and for leaving a hydrophobic surface. The sulfuric acid solution preferably has a concentration of approximately 98% by weight and the ozone is preferably injected at a rate of about 1.70 g/min. The hydrofluoric acid concentration range is preferably about 4:1 to about 1000:1 (Water :HF). In this example, a rinsing liquid (e.g., deionized water) used after the sulfuric acid solution and before the hydrofluoric acid solution preferably has a high level of gases. The hydrofluoric acid solution preferably has a low level of gases. Preferably, the procedure uses sonic energy during the exposure of the electronic components to the sulfuric acid/ozone and the following rinse solution. In other embodiments of the invention, the electronic components may be treated with a further series of process liquids, such as a solution of sulfuric acid saturated with ozone; followed by a solution of hydrogen peroxide and ammonium hydroxide; and then a solution of hydrogen peroxide, hydrochloric acid, and water. This method is particularly useful for the removal of organic as well as general cleaning (i.e., particle removal with minimal metal deposition) leaving a hydrophilic surface. In this example, the process liquids preferably have high levels of gases. In another embodiment of the present invention when rinsing, the level of gases in the rinsing liquid will depend upon the particular chemical treatment step that was performed just prior to the rinse. For example, if the previous chemical treatment step used an SCI solution, the level of gases in the rinsing liquid is preferably high. If the rinsing follows an etching step where a protective oxide layer was substantially removed, preferably the rinsing liquid has a low level of gases. If sonification is desired during a wet process step, the duration of sonification (i.e., sonification time) is that amount of time needed to carry out the desired effect. Preferably, the sonification is carried out for at least a portion of the contact time the electronic components are exposed to the process liquid. More preferably, the sonification is carried out for the entire contact time, except where the electronic component initially has an unprotected surface, and until a protective layer is formed during the step. In this situation, it may be desired to delay the start of sonic energy until enough time has passed for a protective layer to begin forming. After the electronic components have been treated with the last reactive chemical process fluid, the process fluid may be displaced from the surfaces of the electronic component using either a drying fluid or a rinsing liquid. Alternatively, the fluid may be drained from the chamber and the electronic components may be rinsed with one or more rinsing liquids. The electronic components are then preferably dried by any technique known to those skilled in the art. A preferred method of drying uses a drying fluid stream to directly displace the last processing solution that the electronic components are contacted with prior to drying (hereinafter referred to as "direct displacement drying"). Suitable methods and systems for direct displacement drying are disclosed in for example U.S. Patent Nos.4,778,532, 4,795,497, 4,911,761, 4,984,597, and 5,569,330. Other direct displacement dryers that can be used include Marangoni type dryers supplied by manufacturers such as Steag, Dainippon, and YieldUp. Most preferably, the system and method of U.S. Patent No. 4,7911,761 is used for drying the semiconductor substrates. After the electronic components are dried, they can be removed from the reaction chamber. In a preferred embodiment of the invention, the electronic components are maintained in a single reaction chamber and closed to the environment during the entire wet processing procedure (e.g., cleaning, rinsing, and drying). In this aspect of the invention, the electronic components are placed in a reaction chamber and the surfaces of the electronic components are contacted with one or more process liquids, having a controlled level of gas, for a contact time without removing the electronic components from the reaction chamber. The process fluids (including the process liquids) may be introduced sequentially into the reaction chamber such that one process fluid directly displaces the previous process fluid from the surface or surfaces of the electronic components, or by draining the chamber of one process fluid before exposing the electronic components to another process fluid. The last wet process step is preferably a drying step using a drying fluid. Examples The following Examples demonstrate the effectiveness of the present invention to enhance wet processing of electronic components, such as for removing particles, using controlled levels of gases in process liquids. In the following Examples particles were detected on the electronic components using a Tencor SP1 particle scanning equipment available from KLA Tencor. Example 1 The level of gases in an SC 1 solution was varied to study the effect of gases on particle removal efficiency when cleaning semiconductor wafers using sonic energy. A CFM Full-Flow™ system Model 6100 supplied by CFM Technologies was used in the following example. The CFM wet processing equipment included a vessel for holding 100 - 6" semiconductor wafers, a deionized water supply system, storage tanks for storing aqueous hydrogen peroxide and aqueous ammonium hydroxide, a Liqui-Cel® unit in flow communication with the deionized water supply system, and a sonification unit for generating sonic energy. The Liqui-Cel® unit included 2 gas-liquid contactor elements connected in series. The vessel was fully loaded with 6"diameter wafers where several wafers had known levels of particle contamination as determined by the KLA particle scanning equipment. The wafers were first contacted with 50 ° C deionized water delivered at alternating 60 second flow rate cycles of 3 gpm and 8 gpm until the deionized water exiting the vessel had a resistivity of 15 Mohm. After this target was reached, rinsing was continued in the alternating flow cycles for an additional 4 minutes. Prior to contacting the wafers, the deionized rinse water was passed through the Liqui- Cel® unit set at the following conditions: TABLE 1: Contactor Settings After wetting the wafers, an SCI solution was formed by injecting the appropriate volumes of aqueous hydrogen peroxide (31 wt% concentration hydrogen peroxide) and aqueous ammonium hydroxide (28 wt% concentration ammonium hydroxide) held in the storage tanks into a stream of deionized water flowing at a rate of 3 gpm to form an SCI solution having a temperature of 50 °C and concentration in parts by volume of 40:3:1 water: hydrogen peroxide: ammonium hydroxide. The gas in the deionized water was adjusted using the Liqui-Cel® unit operated at the same parameters as in Table I. The SCI solution having a controlled level of gases was directed into the vessel at a flow rate of 3 gpm to fill the vessel for a fill time of 60 seconds . After filling the vessel, the wafers were soaked with the SCI solution for a soak time of 5 minutes. One minute after beginning the soak, the SCI solution was exposed to sonic energy for a sonification time of 4 minutes in the megasonic energy range. Following soaking, the SC 1 solution was displaced with deionized water delivered into the vessel at alternating flow rate cycles of 5 gpm and 10 gpm and alternating temperatures of 50 °C and 40 °C respectively until the deionized water exiting the vessel had a resistivity of 2 Mohm. After this target was reached, rinsing was continued in the alternating flow cycles for an additional 3 minutes (each flow rate cycle being about 60 seconds in time). During rinsing, the deionized water was passed through the Liqui-Cel® unit at the conditions shown in Table I, and sonification was used during the entire rinsing cycle in the megasonic energy range. Following rinsing, the wafers were dried with a drying vapor of isopropanol directed into the vessel at a pressure of 1.5 psig for 8 minutes. The wafers were removed from the vessel following drying. Several more batches of wafers were processed in the manner described above, except the level of vacuum on the second contactor was adjusted to 0, -7, -12, -4, and -15 for a total of 5 more runs to vary the level of gases in the deionized water used to wet, rinse and form the SC 1 solution. Two wafers from each batch of wafers were then analyzed for particle contamination for particles ranging in size from 0.16 μm to 1.0 μm using the KLA particle scanning equipment. A particle removal efficiency (%) was calculated by dividing the number of particles removed by the starting number of particles on a wafer and multiplying by 100. The results are shown in Figure 1. Figure 1 is a graph of the particle removal efficiency (in percent) versus the level of vacuum pulled on the second contactor in inches of Hg gauge pressure. The results show that the particle removal efficiency for an SCI Solution is surprisingly improved as the vacuum pressure was increased from about -18 in Hg gauge pressure to about 0 inches Hg gauge pressure. This SCI cleaning protocol could be used in a wet processing procedure where another wet process step uses a low gas containing process liquid (such as in an etching chemical treatment step). Although the present invention has been described above with respect to particular preferred embodiments, it will be apparent to those skilled in the art that numerous modifications and variations can be made to those designs. The descriptions provided are for illustrative purposes and are not intended to limit the invention.

Claims: What is claimed is: 1. A method for wet processing electronic components comprising: a) placing the electronic components having surfaces in a reaction chamber; b) controlling the level of gases in at least two process liquids, wherein at least two of the process liquids have different levels of gases; and c) contacting the electronic components with each of the process liquids for a contact time. 2. The method of claim 1 wherein the electronic components are contacted with a high gas containing process liquid in a wet process step and are contacted with a low gas containing process liquid in another wet process step. 3. The method of claim 1 wherein the level of gases in the process liquids are controlled based on the surface composition of the electronic components upon completion of the wet process step, or subsequent wet process step to be performed, or combinations thereof. 4. The method of claim 1 wherein the electronic components are contacted with a high gas containing process liquid in a wet process step and the surfaces of the electronic components have a protective layer at the completion of the wet process step. 5. The method of claim 4 wherein the high gas containing process liquid in the reaction chamber comprises gases in a total amount slightly below saturation, equal to saturation, or greater than saturation. 6. The method of claim 4 wherein the high gas containing process liquid is a cleaning solution. 7. The method of claim 6 wherein the cleaning solution is an SCI solution or an SC2 solution. 8. The method of claim 4 wherein the high gas containing process liquid is a rinsing liquid. 9. The method of claim 8 wherein the rinsing liquid is deionized water. 10. The method of claim 4 wherein the high gas containing process liquid is a photoresist removal solution. 11. The method of claim 10 wherein the photoresist removal solution comprises sulfuric acid. 12. The method of claim 4 further comprising the step of exposing the electronic components to sonic energy for at least a portion of the contact time that the electronic components are contacted with the high gas containing process liquid. 13. The method of claim 1 wherein the electronic components are contacted with a low gas containing process liquid in a wet process step, and the surfaces of the electronic components are substantially free of a protective layer at the completion of the wet process step. 14. The method of claim 13 wherein the low gas containing process liquid in the reaction chamber comprises gases at a level below the saturation level of the gases in the process liquid and comprises oxygen in an amount of less than 0.1 percent of the level of oxygen at saturation in the process liquid 15. The method of claim 13 wherein the low gas containing process liquid is an etching solution. 16. The method of claim 15 wherein the etching solution comprises hydrofluoric acid or buffered hydrofluoric acid. 17. The method of claim 13 wherein the low gas containing process liquid is a rinsing liquid that directly follows an etching chemical treatment step. 18. The method of claim 17 wherein the rinsing liquid is deionized water. 19. The method of claim 1 wherein the electronic components are contacted with a high gas containing process liquid in a wet process step and the high gas containing process liquid comprises aqueous solutions of hydrochloric acid, ammonium hydroxide or buffers comprising the same, hydrogen peroxide, sulfuric acid, mixtures of sulfuric acid and ozone, chromic acid, phosphoric acid, acetic acid or buffers comprising the same, nitric acid, or combinations thereof. 20. The method of claim 1 further comprising the step of exposing the electronic components to sonic energy for at least a portion of the contact time that the electronic components are contacted with at least one of the process liquids.

Inventors: BAY STEVEN T, DURR KEVIN R, MCCONNELL CHRISTOPHER F, VERHAVERBEKE STEVEN, BAY, STEVEN, T., DURR, KEVIN, R., MCCONNELL, CHRISTOPHER, F., VERHAVERBEKE, STEVEN
Applicants: CFMT INC, CFMT, INC.
Application year: 1999
Main classification: B08B3
IPC codes: B08B3, H01L21