Patent Publication Number: US-2022216039-A1

Title: Wafer processing apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based on and claims priority under 35 U.S.C. § 119 to Korean Patent Application No. 10-2021-0000987, filed on Jan. 5, 2021, in the Korean Intellectual Property Office, the disclosure of which is incorporated by reference herein in its entirety. 
     BACKGROUND 
     The inventive concept relates to a wafer processing apparatus. 
     Semiconductor devices are formed using various semiconductor manufacturing processes like a material layer deposition process, an ion implantation process, a photolithography process, and an etching process. Recently, as semiconductor devices become highly integrated, the importance of the quality of material films and patterns constituting semiconductor devices is increasing. Therefore, a semiconductor device manufacturing process using plasma is on the spotlight, and examples thereof include a plasma annealing process, a plasma polymerization process, a sputtering process, a plasma-enhanced chemical vapor deposition (PECVD) process, and a plasma etching process. Depending on plasma generation methods, pieces of plasma equipment therefor include capacitively coupled plasma equipment, inductively coupled plasma equipment, helicon plasma equipment, surface wave plasma equipment, and electron cyclotron resonance (ECR) plasma equipment. 
     SUMMARY 
     The inventive concept provides a wafer processing apparatus having improved reliability. 
     According to an aspect of the inventive concept, there is provided a wafer processing apparatus. The wafer processing apparatus includes a chamber body including a cavity region and a process region; a microwave waveguide configured to introduce a microwave into the cavity region; a first microwave window interposed between the cavity region and the process region; and a magnetic field supplying device configured to apply a magnetic field inside the chamber body, wherein a thickness of the first microwave window is constant, and the first microwave window is configured to control a beam cross-section of the microwave in the process region. 
     According to another aspect of the inventive concept, there is provided a wafer processing apparatus. The wafer processing apparatus includes a chamber body including a cavity region into which a microwave is introduced and a process region in which electron cyclotron resonance (ECR) plasma is generated; a microwave window interposed between the cavity region and the process region; and a magnetic field supplying device configured to apply a magnetic field inside the chamber body to adjust a position where the ECR plasma is generated, wherein a refractive index of the microwave window varies according to a distance from an optical axis of the microwave window. 
     According to another aspect of the inventive concept, there is provided a wafer processing apparatus. The wafer processing apparatus includes a chamber body including a cavity region into which a microwave is introduced and a process region in which plasma is generated; a microwave window interposed between the cavity region and the process region and having formed thereon a transmittance adjusting coating, wherein a top surface and a bottom surfaces of the microwave window are substantially flat surfaces; and a magnetic field supplying device configured to apply a magnetic field inside the chamber body, wherein the transmittance adjusting coating includes a first portion having a first transmittance for the microwave and a second portion having a second transmittance for the microwave that is higher than the first transmittance. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the inventive concept will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a diagram of a wafer processing apparatus according to example embodiments; 
         FIGS. 2A to 2C  are diagrams for describing an effect of a microwave window according to example embodiments; 
         FIG. 3  is a diagram of a wafer processing apparatus according to example embodiments; 
         FIG. 4A  is a plan view of a transmittance adjusting coating according to example embodiments; 
         FIG. 4B  is a plan view of a transmittance adjusting coating according to example embodiments; 
         FIG. 4C  is a plan view of a transmittance adjusting coating according to example embodiments; 
         FIG. 4D  is a plan view of a transmittance adjusting coating according to example embodiments; 
         FIG. 5  is a diagram of a wafer processing apparatus according to example embodiments; 
         FIG. 6  is a diagram of a wafer processing apparatus according to example embodiments; 
         FIG. 7  is a plan view of a microwave window included in the wafer processing apparatus of  FIG. 6 ; and 
         FIG. 8  is a diagram of a wafer processing apparatus according to example embodiments. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a diagram of a wafer processing apparatus  100  according to example embodiments. 
     Referring to  FIG. 1 , the wafer processing apparatus  100  may include a chamber body  110 , a microwave source  121 , a microwave waveguide  125 , a microwave window  130 , first to third magnetic field supplying devices  141 ,  143 , and  145 , a gas inlet  151 , a gas exhaust  155 , a shower head  160  and a wafer support  170 . 
     The wafer processing apparatus  100  may be an apparatus that generates plasma and processes a wafer W by using the plasma. The wafer processing apparatus  100  may perform a plasma process including a plasma annealing process, a plasma polymerization process, a sputtering process, a plasma-enhanced chemical vapor deposition (PECVD) process, a plasma etching process, and a plasma cleaning process on the wafer W. 
     According to example embodiments, the wafer processing apparatus  100  may be electron cyclotron resonance (ECR) equipment. The wafer processing apparatus  100  generates plasma by resonating electrons inside the chamber body  110  by simultaneously applying a magnetic field and a microwave MW into the chamber body  110 . ECR equipment may be referred to as an electrodeless plasma source, because the ECR equipment is capable of generating plasma without a current flowing to an electrode. Because an ECR plasma source is also microwave-based, plasma may be generated at a location away from a surface of a device element. 
     The chamber body  110  may provide or define an inner space for processing the wafer W. The chamber body  110  may isolate the inner space for processing the wafer W from the outside. The chamber body  110  may be clean room equipment capable of controlling a pressure and a temperature with high precision. The chamber body  110  may include a cavity region  110 C to which a microwave is introduced and a process region  110 P in which an ECR region ECRZ is formed and the wafer W is disposed. The cavity region  110 C may be a portion of the chamber body  110  between the microwave waveguide  125  and the microwave window  130 . The process region  110 P may be a portion of the chamber body  110  disposed under the shower head  160 . According to example embodiments, the cavity region  110 C and the process region  110 P may be rotationally symmetric around a Z direction, but the inventive concept is not limited thereto. The cavity region  110 C and the process region  110 P may each have a rectangular shape or a cylindrical shape. 
     The microwave source  121  may generate a microwave MW. The microwave source  121  may include a patch antenna, a dipole antenna, a monopole antenna, a microstrip antenna, a slot antenna, a Yagi-Uda antenna, etc. The microwave MW may have a frequency of, for example, 2.45 GHz or less. The microwave MW may have a frequency of, for example, 2.45 GHz. The microwave MW may travel along the microwave waveguide  125  in a transverse electric 11 (TE11) mode. The microwave MW may have a Gaussian-type spatial-intensity distribution in which the intensity of a center portion is high and the intensity of an edge portion is low on a beam cross-section. 
     The cavity region  110 C may be a region through which the microwave MW transmitted along the microwave waveguide  125  is introduced into the chamber body  110 . A stationary wave due to the microwave MW may be formed in the cavity region  110 C. According to example embodiments, a microwave coupler or waveguide launcher may be further provided between the cavity region  110 C and the microwave waveguide  125  to prevent generation of a reflected wave of the microwave MW. 
     The microwave MW may pass through the microwave window  130  and be introduced into the process region  110 P. Here, a direction perpendicular to the top surface of the microwave window  130  is defined as the Z direction, and two directions parallel to the top surface of the microwave window  130  and perpendicular to each other are defined as an X direction and a Y direction, respectively. An optical axis  130 LX of the microwave window  130  may be parallel to or coaxial with the Z direction. Hereinafter, the radius of the microwave window  130  refers to a horizontal distance (e.g., a radial distance) from the optical axis  130 LX of the microwave window  130 . 
     Here, for example, an optical axis of a particular optical element like the optical axis  130 LX of the microwave window  130  may be an axis around which the particular optical element is rotationally symmetric. An optical axis may be a straight line connecting the centers of optical surfaces included in an optical element like a lens or a mirror. Therefore, for any optical element included in an optical system, even when the optical element is rotated at an arbitrary angle around the optical axis of the optical element, the optical system may be optically identical to the optical system before rotation. 
     According to example embodiments, the inner space of the chamber body  110  and the microwave window  130  may have rotational symmetry around an axis parallel to the Z direction, but the inventive concept is not limited thereto. For example, the inner space of the chamber body  110  may include a cylindrical portion, and the microwave window  130  may have a disk-like shape. 
     The top surface and the bottom surface of the microwave window  130  may be substantially flat. The thickness of the microwave window  130  in the Z direction may be substantially constant throughout the microwave window  130 , but the inventive concept is not limited thereto. 
     The microwave window  130  may include a dielectric material. The microwave window  130  may include a material transparent to the microwave MW. The microwave window  130  may include, for example, quartz. According to example embodiments, the thickness of the microwave window  130  may be less than the wavelength of the microwave MW. According to example embodiments, the thickness of the microwave window  130  may be within the range from about 10 mm to about 100 mm. According to example embodiments, the thickness of the microwave window  130  may be about 5 mm or less. 
     According to example embodiments, the microwave window  130  may have a variable refractive index. According to example embodiments, the microwave window  130  may be a gradient-index lens. According to example embodiments, the microwave window  130  may have a refractive index that varies according to a radius of the microwave window  130  from the optical axis  130 LX. According to example embodiments, the refractive index of the microwave window  130  may be determined according to Equation 1 below. 
     
       
         
           
             
               
                 
                   
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                       n 
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                         1 
                         
                           f 
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                           t 
                         
                       
                       ⁢ 
                       
                         r 
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                   [ 
                   
                     Equation 
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                     1 
                   
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     Here, n(r) denotes the refractive index of the microwave window  130  according to a radius r, f denotes a focal length, t denotes the thickness of the microwave window  130  in the Z direction, and no denotes the refractive index of the microwave window  130  along the optical axis  130 LX. 
     Equation 1 above is a thin lens equation, and, when the microwave MW has a frequency of 2.45 GHz, the wavelength thereof is about 12.24 cm. Therefore, because the thickness of the microwave window  130  is less than the wavelength of the microwave MW, Equation 1 above may be applied to the microwave window  130 . 
     According to example embodiments, the microwave window  130  may be a concave lens, and in this case, the focal length of the microwave window  130  may be from about −1000 mm to about −100 mm. According to example embodiments, the microwave window  130  may be a convex lens, and in this case, the focal length of the microwave window  130  may be from about 100 mm to about 1000 mm. 
     According to example embodiments, the microwave window  130  may adjust a space-intensity distribution of the microwave MW. According to example embodiments, the microwave window  130  may uniformly change the space-intensity distribution of the microwave MW. 
     Previously, the uniformity of a process between the center and the edge of the wafer W (e.g., a difference between etching amounts or a difference between thicknesses of deposited material films) is secured by adjusting a distance between the location of the ECR region ECRZ and the wafer W. However, when the distance between the ECR region ECRZ and the wafer is greater than certain distance such that the uniformity of a process between the center and the edge of the wafer W is equal to or greater than a certain level, a process speed for the wafer W (e.g., an etching speed or a deposition rate) is lowered. In other words, in a previous wafer processing apparatus based on ECR, the speed of a process for the wafer W and the uniformity of a process are in a trade-off relationship. 
     According to example embodiments, by providing the microwave window  130  having a variable refractive index according to a radius, the ECR region ECRZ may be formed close to the wafer W, and thus, the wafer W may be processed at a high speed and the uniformity of processing the wafer W may be improved. Therefore, the reliability and productivity of manufacturing a semiconductor device may be improved. 
     Hereinafter, the effect of the microwave window  130  according to example embodiments will be described in more detail with reference to  FIG. 2 . 
       FIGS. 2A to 2C  are diagrams for describing an effect of the microwave window  130  according to example embodiments. 
       FIG. 2A  shows, as a comparative example, propagation of the microwave MW in a free space without the microwave window  130 . In this case, the microwave MW may propagate through the free space on the wafer W, and an electric magnetic field of the TE11 mode is formed on the wafer W. Therefore, the spatial distribution of plasma formed on the wafer W becomes non-uniform in the ECR region ECRZ, thereby resulting in deterioration and/or failure of a semiconductor device. 
     Referring to  FIG. 2B , a microwave window  130 ′ of a first experimental example and propagation of the microwave MW according to the same are shown. The broken line inside represents an equivalent lens according to a change in the refractive index of the microwave window  130 ′. 
     According to example embodiments, the equivalent lens of the microwave window  130 ′ may be a concave lens having a focal length less than 0. The microwave window  130 ′ may control the beam cross-section of the microwave MW. The microwave window  130 ′ may increase the beam cross-section of the microwave MW. The microwave MW passing through the microwave window  130 ′ functioning as a concave lens may be dispersed, thereby improving the uniformity of plasma distribution formed on the wafer W. Therefore, the reliability of processing the wafer W may be improved. 
     Referring to  FIG. 2C , a microwave window  130 ″ of a second experimental example and propagation of the microwave MW according to the same are shown. The broken line inside represents an equivalent lens according to a change in the refractive index of the microwave window  130 ″. 
     According to example embodiments, the equivalent lens of the microwave window  130 ″ may be a convex lens having a focal length greater than 0. The microwave window  130 ″ may control the beam cross-section of the microwave MW. The microwave window  130 ″ may reduce the beam cross-section of the microwave MW. The microwave MW that has passed through the microwave window  130 ″ functioning as a convex lens may be focused. 
     A previous microwave window is manufactured to have a lens-like shape, but has a rough surface due to the limitation of lens processing. The roughness on a surface of the microwave window causes adverse effects like particle contamination and arc generation along with plasma, which may cause product defects. 
     According to example embodiments, by changing the refractive index according to a radius, the microwave window  130  (refer to  FIG. 1 ) including smooth surfaces may function as a lens, thereby preventing product defects due to the limitation of processing the surfaces of the microwave window  130  (refer to  FIG. 1 ) and improving the reliability of the wafer W (refer to  FIG. 1 ). 
     Referring back to  FIG. 1 , the first to third magnetic field supplying devices  141 ,  143 , and  145  may form a magnetic field inside the chamber body  110 . The first to third magnetic field supplying devices  141 ,  143 , and  145  may be arranged outside the cavity region  110 C and the process region  110 P. The magnetic field formed by the first to third magnetic field supplying devices  141 ,  143 , and  145  may apply Lorentz force to electrons inside the process region  110 P, and thus, the electrons may rotate around the Z direction. At this time, when the rotation frequency of the electrons is identical to the frequency of the microwave MW, plasma may be generated by ECR. For example, when the frequency of the microwave MW is 2.45 GHz, ECR occurs at a position where the intensity of a magnetic field is 875 Gauss (G). The ECR region ECRZ may be a region in which plasma is generated by ECR. The ECR region ECRZ may be a region having the highest plasma concentration in the chamber body  110 . 
     According to example embodiments, each of the first to third magnetic field supplying devices  141 ,  143 , and  145  may be one of a coil (i.e., an electromagnet) and a permanent magnet. According to example embodiments, some of the first to third magnetic field supplying devices  141 ,  143 , and  145  may be coils and the remaining one(s) may be permanent magnets. According to example embodiments, when at least one of the first to third magnetic field supplying devices  141 ,  143 , and  145  is a coil, a location at which ECR occurs may be controlled by adjusting a current applied to the at least one coil. 
       FIG. 1  shows an example in which three magnetic field supplying devices, for example, the first to third magnetic field supplying devices  141 ,  143 , and  145 , are provided. However, this is merely an example, and the inventive concept is not limited thereto. For example, the wafer processing apparatus  100  may include one, two, four or more magnetic field supplying devices. 
     According to some embodiments, the gas inlet  151  may be provided between the microwave window  130  and the shower head  160 . The gas inlet  151  may supply process gas into the chamber body  110 . The process gas may include a material to be deposited or may be a source gas for generating reactive ions. The type and the pressure of the process gas may vary depending on the composition of a material layer to be deposited or a material layer to be etched. 
     The gas exhaust  155  may be connected to a pump like a turbo molecular pump and a dry pump and may adjust the pressure inside the chamber body  110 . Here, the turbo molecular pump is a type of vacuum pump similar to a turbo pump and may secure and maintain a vacuum. The turbo molecular pump may include, for example, a fast rotating fan rotor. The turbo molecular pump may provide a high vacuum pressure by controlling a magnitude and a direction of the momentum of gas molecules by using the fan rotor. Unlike an oil diffusion pump, the dry pump may not include oil that performs sealing and lubricating functions to maintain a vacuum formed in a process chamber. The dry pump may provide a vacuum of about 10 −2  mbar and exhibit highly clean vacuum. The dry pump may include, for example, any one of a claw pump, a multi-stage roots pump, a roots-claw combination pump, a scroll pump, a screw pump, a diaphragm pump, and a molecular drag pump. 
     The shower head  160  may be provided between the gas inlet  151  and the process region  110 P. The shower head  160  may uniformly introduce a process gas into the process region  110 P. The shower head  160  may include a plurality of fine apertures configured to diffuse the process gas. 
     The wafer support  170  may support the wafer W. The wafer support  170  may include an electrostatic chuck that fixes the wafer W by using electrostatic force. A heater for setting the temperature of the wafer W may be provided inside the wafer support  170 . 
     The wafer W may include, for example, silicon (Si). The wafer W may include a semiconductor element like germanium (Ge) or a compound semiconductor like silicon carbide (SiC), gallium arsenide (GaAs), indium arsenide (InAs), and indium phosphide (InP). According to some embodiments, the wafer W may have a silicon-on-insulator (SOI) structure. The wafer W may include a buried oxide layer. According to some embodiments, the wafer W may include a conductive region, e.g., a well doped with impurities. According to some embodiments, the wafer W may have various device isolation structures like a shallow trench isolation (STI) separating doped wells from one another. The wafer W may have a first surface, which is an active surface, and a second surface, which is an inactive surface opposite to the first surface. The wafer W may be disposed on the wafer support  170 , such that the second side thereof faces the wafer support  170 . 
       FIG. 3  is a diagram of a wafer processing apparatus according to example embodiments. 
     For convenience of explanation, descriptions identical to those already given above with reference to  FIG. 1  may be omitted, and descriptions below will focus on differences therefrom. 
     Referring to  FIG. 3 , a wafer processing apparatus  101  may include the chamber body  110 , the microwave source  121 , the microwave waveguide  125 , a microwave window  230 , the first to third magnetic field supplying devices  141 ,  143 , and  145 , the gas inlet  151 , the gas exhaust  155 , the shower head  160 , and the wafer support  170 . 
     The microwave window  230  may include a refractive index adjuster  231  and a transmittance adjusting coating  233 . The refractive index adjuster  231  may be substantially the same as the microwave window  130  of  FIG. 1 . The transmittance adjusting coating  233  may have a transmittance depending on a distance from an optical axis  231 LX of the refractive index adjuster  231 . A thickness (i.e., a length in the Z direction) of the transmittance adjusting coating  233  may be within a range from about 0.1 mm to about 50 mm. 
     Although  FIG. 3  shows that the transmittance adjusting coating  233  is formed on the top surface of the microwave window  230  (i.e., the surface facing the cavity region  110 C), the inventive concept is not limited thereto. The transmittance adjusting coating  233  may also be formed on the bottom surface of the microwave window  230  (i.e., the surface facing the process region  110 P). 
     Here, with reference to  FIG. 4A , the transmittance adjusting coating  233  will be described in more detail. 
       FIG. 4A  is a plan view of the transmittance adjusting coating  233  according to example embodiments. 
     Referring to  FIGS. 3 and 4A , the transmittance adjusting coating  233  may include a center portion  233 C and an edge portion  233 E. The center portion  233 C and the edge portion  233 E may be optically distinguished from each other. The center portion  233 C and the edge portion  233 E may have different transmittances for the microwave MW. 
     The center portion  223 C may be a circular region having a first radius R 1 . The edge portion  233 E may be a ring-shaped or annular region surrounding the center portion  223 C. The edge portion  233 E may have the first radius R 1  as an inner radius and a second radius R 2  greater than the first radius R 1  as an outer radius. 
     For example, a first transmittance of the center portion  233 C for the microwave MW may be lower than a second transmittance of the edge portion  233 E for the microwave MW. In this case, because the power at the center of the microwave MW may be reduced, the uniformity of a plasma density of the ECR region ECRZ may be improved. However, the inventive concept is not limited thereto, and the first transmittance of the center portion  233 C may be greater than the second transmittance of the edge portion  233 E. 
       FIG. 4B  is a plan view of a transmittance adjusting coating  233 ′ according to example embodiments. 
     For convenience of explanation, descriptions identical to those already given above with reference to  FIG. 4A  may be omitted, and descriptions below will focus on differences therefrom. 
     Referring to  FIGS. 3 and 4A , the transmittance adjusting coating  233 ′ may include a center portion  233 C and an edge portion  233 E′ and may further include an intermediate portion  233 I. The center portion  233 C, the edge portion  233 E′, and the intermediate portion  233 I may be optically distinguished from one another. The center portion  233 C, the edge portion  233 E′, and the intermediate portion  233 I may have different transmittances for the microwave MW. 
     The center portion  223 C may be a circular region having a first radius R 1 . The intermediate portion  233 I may be a ring-shaped or annular region surrounding the center portion  223 C, and the edge portion  233 E′ may be a ring-shaped or annular region surrounding the intermediate portion  233 I. The intermediate portion  233 I may have the first radius R 1  as an inner radius and a third radius R 3  greater than the first radius R 1  as an outer radius. The edge portion  233 E′ may have the third radius R 3  as the inner radius and the second radius R 2  greater than the third radius R 3  as the outer radius. 
     For example, the first transmittance of the center portion  233 C for the microwave MW may be lower than a third transmittance of the intermediate portion  233 I for the microwave MW, and the third transmittance may be lower than the second transmittance of the edge portion  233 E′ for the microwave MW. In another example, the first transmittance may be greater than the third transmittance, and the third transmittance may be greater than the second transmittance. 
       FIG. 4C  is a plan view of a transmittance adjusting coating  233 ″ according to example embodiments. 
     For convenience of explanation, descriptions identical to those already given above with reference to  FIG. 4A  may be omitted, and descriptions below will focus on differences therefrom. 
     Referring to  FIG. 4C , the transmittance adjusting coating  233 ″ may include a first portion  233 _ 1  and a second portion  233 _ 2 . The first portion  233 _ 1  and the second portion  233 _ 2  may be optically distinguished from each other. The first portion  233 _ 1  and the second portion  233 _ 2  may have different transmittances for the microwave MW. 
     According to example embodiments, the first portion  233 _ 1  and the second portion  233 _ 2  may be arbitrary geometric regions that divide the transmittance adjusting coating  233 ″. According to example embodiments, the transmittance adjusting coating  233 ″ may not have rotational symmetry. The first portion  233 _ 1  and the second portion  233 _ 2  may be determined based on equipment asymmetry of the wafer processing apparatus  101  (refer to  FIG. 3 ). 
     For example, when an optical window is not provided, a plasma density of a portion of the ECR region ECRZ overlapping the first portion  233 _ 1  in the Z direction may be greater than a plasma density of a portion of the ECR region ECRZ overlapping the second portion  233 _ 2  in the Z direction, due to the equipment asymmetry of the wafer processing apparatus  101  (refer to  FIG. 3 ). Correspondingly, the first portion  233 _ 1  may have a transmittance lower than that of the second portion  233 _ 2  for the microwave MW. 
     The transmittance adjusting coating  233 ″ according to example embodiments may include portions configured as arbitrary geometric shapes based on equipment asymmetry of a wafer processing apparatus. Accordingly, the equipment asymmetry of the wafer processing apparatus may be corrected, thereby improving the reliability of manufacturing a semiconductor device. 
       FIG. 4D  is a plan view of a transmittance adjusting coating  233 ′″ according to example embodiments. 
     For convenience of explanation, descriptions identical to those already given above with reference to  FIG. 4A  may be omitted, and descriptions below will focus on differences therefrom. 
     Referring to  FIG. 4D , the transmittance adjusting coating  233 ′″ may include the center portion  233 C and the edge portion  233 E, similar to the transmittance adjusting coating  233  of  FIG. 4A . According to example embodiments, the transmittance adjusting coating  233 ′″ may further include a microwave shield  233 B that blocks the microwave MW. The microwave shield  233 B may block the microwave MW through any one of reflection and absorption. 
     The transmittance adjusting coating  233 ″ according to example embodiments may include portions configured as arbitrary geometric shapes to block the microwave MW (refer to  FIG. 3 ) at a portion with a high plasma density, based on the equipment asymmetry of the wafer processing apparatus  101  (refer to  FIG. 3 ). Accordingly, the equipment asymmetry of the wafer processing apparatus  101  (refer to  FIG. 3 ) may be corrected, thereby improving the reliability of manufacturing a semiconductor device. 
       FIG. 5  is a diagram of a wafer processing apparatus  102  according to example embodiments. 
     For convenience of explanation, descriptions identical to those already given above with reference to  FIG. 1  may be omitted, and descriptions below will focus on differences therefrom. 
     Referring to  FIG. 5 , the wafer processing apparatus  102  may include the chamber body  110 , the microwave source  121 , the microwave waveguide  125 , a first microwave window  131 , a second microwave window  133 , the first to third magnetic field supplying devices  141 ,  143 , and  145 , the gas inlet  151 , the gas exhaust  155 , the shower head  160 , and the wafer support  170 . 
     According to example embodiments, the first microwave window  131  and the second microwave window  133  may each have an overall constant thickness (i.e., a length in the Z direction). According to example embodiments, the top surfaces and the bottom surfaces of the first microwave window  131  and the second microwave window  133  may be substantially flat. According to example embodiments, each of the first microwave window  131  and the second microwave window  133  may adjust the distribution of the intensity of the microwave MW in the process region  110 P. Each of the first microwave window  131  and the second microwave window  133  may have a refractive index depending on a distance from each optical axis, similar to the microwave window  130  of  FIG. 1 . 
     According to example embodiments, the first microwave window  131  and the second microwave window  133  may form a collimating lens together. For example, the first microwave window  131  may function as a concave lens having a focal length less than 0, similar to the microwave window  130 ′ of  FIG. 2B , and the second microwave window  133  may function as a convex lens having a focal length greater than 0, similar to the microwave window  130 ″ of  FIG. 2C . In another example, the first microwave window  131  may function as a convex lens having a focal length greater than 0, similar to the microwave window  130 ″ of  FIG. 2C , and the second microwave window  133  may function as a concave lens having a focal length less than 0, similar to the microwave window  130 ′ of  FIG. 2B . 
     According to example embodiments, by providing a plurality of microwave windows, for example, the first and second microwave windows  131  and  133 , having different optical functions, the distribution of the microwave MW in the process region  110 P may be adjusted, and thus the reliability of manufacturing a semiconductor device may be improved. 
       FIG. 6  is a diagram of a wafer processing apparatus  103  according to example embodiments. 
       FIG. 7  is a plan view of a microwave window  330  included in the wafer processing apparatus  103  of  FIG. 6 . 
     For convenience of explanation, descriptions identical to those already given above with reference to  FIG. 1  may be omitted, and descriptions below will focus on differences therefrom. 
     Referring to  FIGS. 6 and 7 , the wafer processing apparatus  103  may include the chamber body  110 , the microwave source  121 , the microwave waveguide  125 , the microwave window  330 , the first to third magnetic field supplying devices  141 ,  143 , and  145 , the gas inlet  151 , the gas exhaust  155 , the shower head  160 , and the wafer support  170 . 
     According to example embodiments, the microwave window  330  may be a substantially flat lens including a nano structure for focusing a beam, e.g., a meta lens. For example, when the microwave window  330  is a meta lens, patterns  330 P for configuring the meta lens may be formed on the top surface or the bottom surface of the microwave window  330 . In some cases, the patterns  330 P for configuring a meta lens may be formed on both the top surface and the bottom surface of the microwave window  330 . The patterns  330 P include the same material as the microwave window  330  and may be integrally formed with the microwave window  330 . However, the inventive concept is not limited thereto, and the patterns  330 P may include a material different from that constituting the microwave window  330 . According to example embodiments, the patterns  330 P may include TiO 2  or Au. 
     According to example embodiments, the patterns  330 P may be arranged in the X direction and the Y direction to form a matrix. The microwave window  330  may be divided into a plurality of unit cells  330 C having edges parallel to or along the X direction and the Y direction, and the patterns  330 P may be formed inside the unit cells  330 C, respectively. Lengths of each of the unit cells  330 C in the X direction and the Y direction may be within a range from about 1/10 to about 1/100 of the wavelength of the microwave MW. 
     Although  FIG. 7  shows that the patterns  330 P have a substantially rectangular and planar shape, this is merely for convenience of explanation and the inventive concept is not limited thereto. The patterns  330 P may have various shapes like a circular shape, a ring shape, an oval shape, an arbitrary polygonal shape, a cross shape, a straight shape, and a star shape. 
     According to example embodiments, the height of the patterns  330 P in the Z direction may be within a range from about 1/1000 to 1/100 of the wavelength of the microwave MW. Therefore, variations in the height of a concavo-convex portion of the microwave window  330  due to the patterns  330 P is about 1% or less of the total thickness of the microwave window  330 , and the microwave window  330  may be considered to have a substantially constant thickness. 
       FIG. 8  is a diagram of a wafer processing apparatus  104  according to example embodiments. 
     For convenience of explanation, descriptions identical to those already given above with reference to  FIG. 1  may be omitted, and descriptions below will focus on differences therefrom. 
     Referring to  FIG. 8 , the wafer processing apparatus  104  may include the chamber body  110 , the microwave source  121 , the microwave waveguide  125 , a microwave window  132 , a lens  134 , the first to third magnetic field supplying devices  141 ,  143 , and  145 , the gas inlet  151 , the gas exhaust  155 , the shower head  160 , and the wafer support  170 . 
     According to some embodiments, the microwave window  132  may be substantially the same as the microwave window  130  of  FIG. 1 . In addition to the microwave window  132 , the wafer processing apparatus  104  further includes the lens  134  for adjusting the distribution of the intensity of the microwave MW in the process region  110 P, and the precision of adjusting the distribution of the intensity of the microwave MW in the process region  110 P may be improved. Therefore, the reliability of the wafer processing apparatus  104  may be improved. Also, because no plasma is formed in the cavity region  110 C, particle contamination and an arc may not be generated even when the lens  134  including a curved surface is provided in the cavity region  110 C. 
     According to some other embodiments, the microwave window  132  may have an overall uniform refractive index. In this case, only the lens  134  including a curved surface may control the distribution of the intensity of the microwave MW. 
     While the inventive concept has been particularly shown and described with reference to embodiments thereof, it will be understood that various changes in form and details may be made therein without departing from the scope of the following claims.