Optimal Design of High-Frequency Induction Heating Apparatus for Wafer Cleaning Equipment Using Superheated Steam
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energies Article Optimal Design of High-Frequency Induction Heating Apparatus for Wafer Cleaning Equipment Using Superheated Steam Sang Min Park 1 , Eunsu Jang 2, Joon Sung Park 1 , Jin-Hong Kim 1, Jun-Hyuk Choi 1 and Byoung Kuk Lee 2,* 1 Intelligent Mechatronics Research Center, Korea Electronics Technology Institute (KETI), Bucheon 14502, Korea; [email protected] (S.M.P.); [email protected] (J.S.P.); [email protected] (J.-H.K.); [email protected] (J.-H.C.) 2 Department of Electrical and Computer Engineering, Sungkyunkwan University (SKKU), Suwon 16419, Korea; [email protected] * Correspondence: [email protected]; Tel.: +82-31-299-4581 Received: 19 October 2020; Accepted: 22 November 2020; Published: 25 November 2020 Abstract: In this study, wafer cleaning equipment was designed and fabricated using the induction heating (IH) method and a short-time superheated steam (SHS) generation process. To prevent problems arising from the presence of particulate matter in the fluid flow region, pure grade 2 titanium (Ti) R50400 was used in the wafer cleaning equipment for heating objects via induction. The Ti load was designed and manufactured with a specific shape, along with the resonant network, to efficiently generate high-temperature steam by increasing the residence time of the fluid in the heating object. The IH performance of various shapes of heating objects made of Ti was analyzed and the results were compared. In addition, the heat capacity required to generate SHS was mathematically calculated and analyzed. The SHS heating performance was verified by conducting experiments using the designed 2.2 kW wafer cleaning equipment. The performance of the proposed pure Ti-based SHS generation system was found to be satisfactory, and SHS with a temperature higher than 200 ◦C was generated within 10 s using this system. Keywords: induction heating (IH); superheated steam (SHS); LCL resonant network; cleaning equipment; titanium (Ti); high frequency; wafer cleaning 1. Introduction The cleaning process is the most important task in improving the yield and reliability of the manufacturing process. With advancements in the fabrication technology of liquid crystal displays (LCDs), the size of the mother glass (MG) is continually being increased, and the cleaning processes employed during fabrication are becoming increasingly vital. In particular, the process of depositing a transistor layer on an MG substrate that is employed to fabricate thin film transistors (TFTs) requires a cleaning process for the MG substrate, as shown in Figure1. Contaminants such as residual organic materials and particulates are present on the surface of work pieces such as semiconductor wafers and the MG of LCDs [1,2]. Cleaning processes for removing such organic materials and particles are indispensable because these substances can generate defects in manufactured products; various cleaning methods have been proposed in this regard [3–5]. A wet cleaning method, known as vapor phase cleaning (VPC), is widely used because it is inexpensive and has proven technology. However, wet cleaning methods that involve the use of strong acids are regulated due to environmental pollution and safety issues [6,7]. A dry cleaning method has been developed to compensate for the disadvantages Energies 2020, 13, 6196; doi:10.3390/en13236196 www.mdpi.com/journal/energies Energies 2020, 13, 6196 2 of 16 Energies 2020, 13, x FOR PEER REVIEW 2 of 16 of the wet cleaning methods. This dry cleaning method includes processes such as ultrasonic cleaning, excimerultrasonic ultraviolet cleaning, (EUV) excimer cleaning, ultraviolet and plasma (EUV) cleaning cleaning, [8– 10and]. However,plasma clea thening disadvantage [8–10]. However, of dry cleaningthe disadvantage equipment of dry is that cleaning it is di equipmentfficult to construct is that it and is difficult is large to in construct size [9,11 and]. is large in size [9,11]. Cleaning Deposition Cleaning PR Coating PR Strip Etch Develop Exposure Figure 1.1. OverviewOverview of of the the thin thin film film transistor transistor (TFT)–liquid (TFT)–liquid crystal crystal display displa (LCD)y manufacturing(LCD) manufacturing process. process. Recently, cleaning equipment that is eco-friendly and has excellent washing capability has been developedRecently, using cleaning superheated equipment steam that (SHS) is eco-friendly at a high temperature and has excellent and pressure washing [12 ].capability The SHS has cleaning been equipmentdeveloped using uses asuperheated heater to heat steam water (SHS) contained at a high in temperature a tank to generate and pressure SHS at[12]. temperatures The SHS cleaning above 200equipment◦C; then, uses the a SHS heater is sprayedto heat water onto thecontained MG and in wafer a tank to to clean generate them. SHS The at conventionaltemperatures equipment above 200 utilized°C; then, for the generating SHS is sprayed SHS heats onto water the MG directly and using wafer a heatingto clean wire.them. In The this conventional method, the powerequipment used toutilized generate for generating SHS is significant SHS heats and water the processdirectly isusing time a consuming.heating wire. Furthermore,In this method, in the such power methods, used theto generate preparation SHS timeis significant for the cleaning and the process is ti longme consuming. and the precise Furthermore, temperature in such control methods, capability the requiredpreparation for cleaningtime for maythe cleaning be lacking. process is long and the precise temperature control capability requiredIn this for study, cleaning considering may be lacking. the need for a short-time SHS generation process, cleaning equipment that canIn this uniformly study, considering heat the heating the need object for with a short- hightime efficiency SHS generation was designed proc byess, applying cleaning the equipment induction heatingthat can(IH) uniformly method. heat Common the heating metals, object such with as cast high iron, efficiency cannot bewas used designed as heating by objectsapplying in the TFT–LCDinduction cleaningheating (IH) process method. because Common of particle metals, problems such as in thecast fluid iron, flow cannot area be [13 used,14]. as Thus, heating pure objects grade 2in titanium the TFT–LCD (Ti) R50400 cleaning was usedprocess as thebecause heating of objectparticle for problems IH cleaning in andthe fluid IH joule flow heating area [13,14]. of the Ti Thus, load. Additionally,pure grade 2 titanium the Ti load (Ti) was R50400 designed was used and manufacturedas the heating inobject a specific for IH shape, cleaning along and with IH joule the resonant heating network,of the Ti load. to effi cientlyAdditionally, generate the high-temperature Ti load was designed steam byand increasing manufactured the residence in a specific time ofshape, the fluid along in thewith heating the resonant object. network, Moreover, to efficiently several heating generate objects high-temperature were designed steam and by manufactured increasing the using residence pure Ti,time and of thethe IH fluid performances in the heating of the object. heating Moreover, objects with several respect heating to the objects shape werewere experimentallydesigned and compared.manufactured The using SHS heating pure Ti, performance and the IH performances of the proposed of cleaningthe heating system objects was with verified respect via experimentsto the shape usingwere experimentally the designed 2.2 compared. kW wafer The cleaning SHS heating equipment. performance of the proposed cleaning system was verified via experiments using the designed 2.2 kW wafer cleaning equipment. 2. Analysis of Specific Enthalpy Steam and Titanium Characterization 2. AnalysisIn this of section, Specific the Enthalpy heat capacity Steam forand generating Titanium Characterization SHS is mathematically calculated, and the characteristicsIn this section, of the non-magneticthe heat capacity Ti load for are genera analyzed.ting TheSHS power is mathematically capacity of the calculated, cleaning equipment and the wascharacteristics selected based of the on thenon-magnetic results of this Ti analysis; load are in addition,analyzed. the The cleaning power equipment capacity isof manufacturedthe cleaning byequipment new power was plasma selected (NPP) based Corporation on the results in Korea.of this analysis; in addition, the cleaning equipment is manufactured by new power plasma (NPP) Corporation in Korea. 2.1. Calculation of Steam Heat Capacity 2.1. CalculationSHS is high-temperature of Steam Heat Capacity steam that is further heated using saturated steam generated from boilingSHS water, is high-temperature as shown in Figure steam2. Because that is SHSfurthe isr a heated gas in ausing low-oxygen saturated state steam in which generated only water from (Hboiling2O) molecules water, as shown exist, oxidation in Figure of 2. the Because heated SHS object is a doesgas in not a low-oxygen occur, and the state risk in of which fire or only explosion water is reduced [15,16]. Furthermore, SHS has a strong drying ability because it possesses high thermal (H2O) molecules exist, oxidation of the heated object does not occur, and the risk of fire or explosion conductivity.is reduced [15,16]. However, Furthermore, as the specific SHS has heat a strong capacity drying of water ability is relatively because it higher possesses than high that ofthermal other substances,conductivity. the However, temperature as the change specific is heat slow, capacity as shown of inwater Figure is 2relativelya [ 17–19