Patent Publication Number: US-2023140544-A1

Title: Substrate test apparatus and method for measuring dechucking force using the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority from Korean Patent Application No. 10-2021-0145982 filed on Oct. 28, 2021, in the Korean Intellectual Property Office, and all the benefits accruing therefrom under 35 U.S.C. 119, the contents of which in its entirety are herein incorporated by reference. 
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to a substrate test apparatus and a method of measuring dechucking force using the same. More particularly, the present disclosure relates to a substrate testing apparatus for evaluating the dechucking force of an electrostatic chuck and a dechucking force measuring method using the substrate testing apparatus. 
     2. Description of the Related Art 
     The plasma processing method for treating the surface of a semiconductor wafer, a flat panel display substrate, etc. is generally classified into a capacitively coupled plasma (CCP) processing method and an inductively coupled plasma (ICP) processing method that are currently in use. 
     Such substrate processing using plasma refers to a process of applying a high-frequency power to a vacuum chamber, flowing the gas supplied into the chamber in a plasma state, and thereby using the established high-energy electrons or radicals to etch and remove a thin film. To successfully perform the substrate processing using the plasma, chucking and dechucking the semiconductor substrate in the chamber is required as a significant process. 
     Existing general methods known for holding a substrate in a process chamber for manufacturing a semiconductor device include a mechanical clamp method, a method using a vacuum chuck, etc., but recent years have seen a surge in the use of electrostatic chuck (ESC) that has superior uniformity in terms of particles and processing. However, using such an electrostatic chuck on a substrate, when in the process of separating the substrate after plasma treatment from the electrostatic chuck, that is, during the dechucking process, involves sticking or other issues due to incomplete removal of the residual electric charge on the substrate surface, resulting in a broken substrate in the reaction chamber or a misplaced substrate on a substrate-holding robot&#39;s blade during unloading of the substrate from the chamber. 
     Accordingly, there are methods under study for removing the residual surface charge in the substrate during dechucking, such as applying 0 V to a dechucking-voltage applying unit or grounding the same for a predetermined time. 
     However, those conventional methods suffer from an increased capacitance of the electrostatic chuck with the increased usage of the electrostatic chuck. The resultant increase of the amount of surface charge in the substrate leads to a considerable amount of process time consuming while leaving the surface charges incompletely removed, which is problematic. 
     SUMMARY 
     There is a need for a method of evaluating the good or bad performance of the process of separating the substrate from the electrostatic chuck, that is, the dechucking process. To this end, the prior art uses a horizontal sliding method for checking whether the substrate during dechucking was well cleared of the residual surface charge. However, such a method uses a horizontal push force to the substrate to measure the dechucking force acting in the vertical direction to the substrate, which provides a dechucking force evaluation method of insufficient reliability. 
     Additionally, the prior art takes a person to manually evaluate the dechucking force, resulting in a large evaluation dispersion and a lowered evaluation efficiency. 
     Aspects of the present disclosure provide a substrate test apparatus that can measure a dechucking force with high reliability with an additional normal-force measuring unit capable of pushing or pulling a substrate in a vertical direction. 
     However, aspects of the present disclosure are not restricted to those set forth herein. The above and other aspects of the present disclosure will become more apparent to one of ordinary skill in the art to which the present disclosure pertains by referencing the detailed description of the present disclosure given below. 
     According to an aspect of the present disclosure, there is provided a substrate test apparatus including an electrostatic chuck configured to support a substrate, a normal-force measuring unit disposed on the electrostatic chuck to be capable of pushing or pulling the substrate vertically, an electrostatic-chuck power supplying unit configured to apply a driving voltage and a first ground voltage to the electrostatic chuck, and a substrate power supplying unit configured to apply a second ground voltage to the substrate, wherein the substrate test apparatus is configured to perform steps including applying the driving voltage to the electrostatic chuck, and charging the substrate by applying the second ground voltage to the substrate, subsequently discharging the substrate by applying the first ground voltage to the electrostatic chuck and by applying the second ground voltage to the substrate, and subsequently measuring a dechucking force of the substrate by pulling the substrate vertically by the normal-force measuring unit. 
     The substrate test apparatus may perform a further step including setting, before the charging of the substrate, an initial charge of the substrate by applying the second ground voltage to the substrate. 
     The electrostatic-chuck power supplying unit may be responsive to the setting of the initial charge of the substrate for keeping from applying the driving voltage and the first ground voltage to the electrostatic chuck. 
     The charging of the substrate may proceed during the first operating time, and the discharging of the substrate may proceed during a second operating time different from the first operating time. 
     The substrate test apparatus may perform a further step including maintaining the substrate in a charged state, after the charging of the substrate and before the discharging of the substrate, by keeping from applying the driving voltage to the electrostatic chuck and by keeping from applying the second ground voltage to the substrate. 
     The charging of the substrate may proceed during a first operating time, the discharging of the substrate may proceed during a second operating time shorter than the first operating time, and the maintaining of the substrate in a charged state may proceed during a third operating time shorter than the second operating time. 
     The substrate test apparatus may further include a clamp disposed under the electrostatic chuck and configured to hold the electrostatic chuck in place. 
     The measuring of the dechucking force of the substrate by pulling the substrate in a vertical direction by the normal-force measuring unit may be performed while keeping from applying the second ground voltage to the substrate and keeping from applying the driving voltage and the first ground voltage to the electrostatic chuck. 
     The discharging of the substrate subsequently may leave, internally of the substrate, residual charges that generate between the substrate and the electrostatic chuck an electrostatic attraction by which the dechucking force is determined. 
     The substrate test apparatus may further include a test chamber including an interior space configured to process the substrate, and a transport unit disposed under the test chamber and configured to transport the test chamber. 
     The substrate test apparatus may further include a motor disposed on an upper surface of the test chamber and configured to provide the normal-force measuring unit with a driving force capable of pushing or pulling the substrate, the motor providing the normal-force measuring unit with the driving force through a ball screw mechanism in a direction perpendicular to the substrate. 
     Upon receiving the driving force from the motor, the normal-force measuring unit may be actuated to constantly pull the substrate at a first speed or a second speed that is different from the first speed. 
     The substrate test apparatus may further include a damper disposed between the motor and the normal-force measuring unit and configured to reduce the vibration generated when the motor provides the driving force to the normal-force measuring unit. 
     According to another aspect of the present disclosure, there is provided a method of measuring dechucking force of a substrate test apparatus including placing a substrate on an electrostatic chuck, charging the substrate by applying a driving voltage to the electrostatic chuck and applying a second ground voltage to the substrate, subsequently discharging the substrate by applying a first ground voltage to the electrostatic chuck and by applying the second ground voltage to the substrate, and subsequently measuring a dechucking force of the substrate by pulling the substrate in a vertical direction by a normal-force measuring unit that is disposed on the substrate. 
     The method may further step including, before the charging of the substrate, setting an initial charge of the substrate by applying the second ground voltage to the substrate. 
     In this case, wherein when setting the initial charge of the substrate, keeping from applying the driving voltage and the first ground voltage to the electrostatic chuck. 
     The method may further step including, after the charging of the substrate and before the discharging of the substrate, maintaining the substrate in a charged state by keeping from applying the driving voltage to the electrostatic chuck and by keeping from applying the second ground voltage to the substrate. 
     In the above-mentioned method, wherein the measuring of the dechucking force of the substrate by pulling the substrate in a vertical direction by the normal-force measuring unit is performed by keeping from applying the second ground voltage to the substrate and by keeping from applying the driving voltage and the first ground voltage to the electrostatic chuck. 
     In the above-mentioned method, wherein the discharging of the substrate subsequently leaves, internally of the substrate, residual charges that generate between the substrate and the electrostatic chuck an electrostatic attraction by which the dechucking force is determined. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects and features of the present disclosure will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings, in which: 
         FIG.  1    is a cross-sectional view for explaining a substrate test apparatus according to at least one embodiment of the present disclosure. 
         FIGS.  2  and  3    are flowcharts for explaining a dechucking force evaluation method according to at least one embodiment of the present disclosure. 
         FIGS.  4  to  7    are diagrams of intermediate steps of a dechucking force evaluation method according to at least one embodiment of the present disclosure. 
         FIG.  8    is a graph for explaining voltage applications and wafer lifting in intermediate steps of the dechucking force evaluation method according to  FIG.  3   . 
         FIG.  9    is a graph for explaining the speed at which a normal-force measuring unit pulls a substrate in the intermediate steps of the dechucking force evaluation method according to  FIG.  3   . 
         FIG.  10    is a flowchart of a dechucking force evaluation method according to at least one embodiment of the present disclosure. 
         FIG.  11    is a diagram of an intermediate step for explaining a dechucking force evaluation method according to at least one embodiment of the present disclosure. 
         FIG.  12    is a graph for explaining voltage applications and wafer lifting in intermediate steps of the dechucking force evaluation method according to  FIG.  10   . 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Advantages and features of the present disclosure and methods of accomplishing the same may be understood more readily by reference to the following detailed description of exemplary embodiments and the accompanying drawings. The present disclosure may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete and will fully convey the concept of the disclosure to those skilled in the art, and the present disclosure will only be defined by the appended claims. Like reference numerals refer to like elements throughout the specification. 
     It will also be understood that when elements or layers are referred to as being present “on” another element or layer, they can be placed on the other element or layer directly as well as through another intervening layer or element. In contrast, elements or layers, which are referred to as being present “directly on” or “immediately on” another element or layer, are supposed to involve no intervening layer or element between the other element or layer. It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, components, and/or sections, these elements, components, and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, or section from another element, component, or section. Thus, a first element, first component, or first section discussed below could be termed a second element, second component, or second section without departing from the teachings of the present disclosure. 
     Terms used in the present specification, which are intended to convey the illustrative embodiments, should not be interpreted as limiting the present disclosure. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising” and the variations thereof as used herein specify the presence of the stated component, step, operation, and/or element, but do not preclude the presence or addition of one or more of other components, steps, operations, and/or elements. 
     The present disclosure relates to a substrate testing apparatus capable of measuring a dechucking force of a substrate through a normal-force measuring unit capable of pushing or pulling the substrate in a vertical direction, a substrate testing apparatus, and a dechucking force evaluation method. Hereinafter, the present disclosure will be described in detail with reference to drawings and other illustrative examples. 
       FIG.  1    is a cross-sectional view for explaining a substrate test apparatus according to at least one embodiment of the present disclosure. 
     Referring to  FIG.  1   , the substrate testing apparatus according to some embodiments may include a test chamber  10 , a substrate  100 , a substrate support unit  200 , an electrostatic-chuck power supplying unit  300 , and a substrate power supplying unit  400 , a clamp  500 , and a driving unit  600 . The substrate test apparatus may be an apparatus used for a test purpose for evaluating the dechucking force of the substrate  100 . 
     The test chamber  10  may include an internal space  13  for processing the substrate  100 . The test chamber  10  may further include a body section  11  and a frame section  12 . 
     The body section  11  may support the components of the substrate test apparatus. In particular, the body section  11  may support the substrate  100 , the substrate support  200 , and the clamp  500 . The body section  11  may be disposed under the substrate  100 , the substrate support  200 , and the clamp  500 . 
     The frame section  12  may be formed from the upper surface edge of the body section  11 . The frame section  12  may be disposed on the body section  11 . The frame section  12  may surround the inner space of the body section  11 . The test chamber  10  may secure an internal space  13  through the frame section  12 . 
     Disposed in the internal space  13  of the test chamber  10  may be the substrate  100 , substrate support unit  200 , electrostatic-chuck power supplying unit  300 , substrate power supplying unit  400 , clamp  500 , and driving unit  600 . However, this is merely exemplary, and the technical idea of the present disclosure is not limited thereto. 
     The substrate test apparatus according to some embodiments may further include at least one or more transport units  700 . The transport unit  700  may be disposed below the test chamber  10 . The transport unit  700  may transport the test chamber  10 . 
     The transport unit  700  is shown in the form of a wheel, but this is merely exemplary, and the technical idea of the present disclosure is not limited thereto. 
     The substrate support  200  may include a base  210 , an electrostatic chuck  220 , and an electrostatic chuck electrode  230 . The electrostatic chuck  220  may be disposed on the base  210 . 
     The electrostatic chuck  220  is adapted to support the substrate  100  seated thereon by using an electrostatic force. The electrostatic chuck  220  may be made of ceramic material. The electrostatic chuck  220  may be fixedly joined with the base  210 . 
     The base  210  may be disposed under the electrostatic chuck  220 . 
     The base  210  may be shaped with a bottom portion wider in the horizontal direction. The base  210  may have a wider diameter at the bottom. As illustrated, the base  210  may have its bottom diameter wider than its upper portion to provide a handle for the clamp  500  to hold the base  210 . Accordingly, the base  210  may be fixed by the clamp  500  as will be described below. 
     The electrostatic chuck electrode  230  may be provided in the electrostatic chuck  220 . The electrostatic chuck electrode  230  receives a direct current (DC) voltage for chucking the substrate  100  and holds by suction the substrate with an electrostatic force. Thereafter, a dechucking process is performed for separating the substrate  100  from the electrostatic chuck  220 . 
     The electrostatic-chuck power supplying unit  300  may apply a driving voltage HV and a first ground voltage GND 1  to the electrostatic chuck  220 . The electrostatic-chuck power supplying unit  300  may directly apply a voltage to the electrostatic chuck  220 . However, this is merely exemplary, and the present disclosure is not limited thereto. 
     The electrostatic-chuck power supplying unit  300  may include a driving voltage application unit  310 , a first ground voltage application unit  320 , a control unit  330 , and a switch  340 . 
     The driving voltage applying unit  310  may apply driving voltage HV to the electrostatic chuck  220 . The driving voltage applying unit  310  may use DC power. However, this is only an example, and the present disclosure is not limited thereto. 
     The first ground voltage applying unit  320  may apply the first ground voltage GND 1  to the electrostatic chuck  220 . 
     The controller  330  may be disposed between the driving voltage applying unit  310  and the first ground voltage applying unit  320 . The controller  330  may determine which one between driving voltage HV and first ground voltage GND 1  is to be applied to the electrostatic chuck  220 . 
     Additionally, the electrostatic-chuck power supplying unit  300  may stop applying a voltage through the switch  340 . For example, stopping the voltage application may be done by opening the switch  340  installed in the power line to which the voltage is applied. 
     The substrate power supplying unit  400  may apply a second ground voltage GND 2  to the substrate  100 . The substrate power supplying unit  400  may directly apply a voltage to the substrate  100 . However, this is merely exemplary, and the present disclosure is not limited thereto. 
     In the drawings, the substrate power supplying unit  400  and the electrostatic-chuck power supplying unit  300  are illustrated as using different ground voltage sources, but this is merely exemplary, and the present disclosure is not limited thereto. For example, second ground voltage GND 2  applied by the substrate power supplying unit  400  may be implemented by using the same source as the first ground voltage GND 1  applied by the electrostatic-chuck power supplying unit  300 . 
     The clamp  500  may be disposed on the upper surface of the body section  11 . The clamp  500  may be disposed peripherally of the upper surface of the body section  11 . A pair of clamp jaws may be formed into the clamp  500  on the body section  11 . However, this is merely exemplary, and the present disclosure is not limited thereto. 
     The clamp  500  may be disposed below the electrostatic chuck  220 . The clamp  500  may be disposed laterally of the substrate support  200 . The clamp  500  may hold the substrate support  200  in place. Specifically, the clamp  500  may fix the electrostatic chuck  220 . 
     For example, the clamp  500  may be integrally formed while surrounding the base  210 . 
     The clamp  500  may have a hook shape. Accordingly, the clamp  500  may fix the base  210  of the substrate support  200  disposed thereon. 
     The shape of the clamp  500  is merely exemplary, and the present disclosure is not limited thereto. The clamp  500  may be shaped for fixing the electrostatic chuck  220  disposed thereon. 
     The clamp  500  may release the electrostatic chuck  220  for allowing the substrate test apparatus according to some embodiments to swap the electrostatic chuck  220  with another one. 
     As shown, a plate may be formed between the clamp  500  and the body section  11 . This is only an example for stability of the substrate test apparatus, and the present disclosure is not limited thereto. 
     For example, the clamp  500  may be formed on the body section  11 . The clamp  500  may be in contact with the body section  11 . 
     The driving unit  600  may be disposed on the electrostatic chuck  220 . Specifically, the driving unit  600  may be disposed on the substrate  100 . The driving unit  600  may include a normal-force measuring unit  610 , a motor  620 , and a damper  630 . 
     The normal-force measuring unit  610  may be disposed on the electrostatic chuck  220 . Specifically, the normal-force measuring unit  610  may be disposed on the substrate  100 . The normal-force measuring unit  610  may be in contact with the substrate  100 . 
     Various devices may be employed for the normal-force measuring unit  610 , such as a push-pull gauge and a load cell. However, this is merely exemplary, and the present disclosure is not limited thereto. The normal-force measuring unit  610  may be configured to measure the force in the vertical direction of the substrate  100  in measuring the electrostatic attraction of the substrate  100  by pulling thereof. 
     However, the method of measuring the force in the vertical direction of the substrate  100  by the normal-force measuring unit  610  does not limit the technical idea of the present disclosure. For example, when a load cell is employed as the normal-force measuring unit  610 , the normal force may be measured by an amount that the load cell deforms by receiving a weight. This will obviate the need for the motor unit  620  to provide a driving force to the normal-force measuring unit  610 . In the present disclosure, for convenience of description, the normal-force measuring unit  610  refers to a push-pull gauge. 
     The normal-force measuring unit  610  may push or pull the substrate  100  in a vertical direction. 
     The normal-force measuring unit  610  may be used after it is adhered to the substrate  100  to measure the dechucking force by pulling the substrate  100  in a vertical direction. A specific method of measuring the dechucking force will be described below. For example, the method of measuring dechucking force of a substrate test apparatus including placing a substrate on an electrostatic chuck, charging the substrate by applying a driving voltage to the electrostatic chuck and applying a second ground voltage to the substrate, subsequently discharging the substrate by applying a first ground voltage to the electrostatic chuck and by applying the second ground voltage to the substrate, and subsequently measuring a dechucking force of the substrate by pulling the substrate in a vertical direction by a normal-force measuring unit that is disposed on the substrate. The method may further step including, before the charging of the substrate, setting an initial charge of the substrate by applying the second ground voltage to the substrate. In this case, wherein when setting the initial charge of the substrate, keeping from applying the driving voltage and the first ground voltage to the electrostatic chuck. The method may further step including, after the charging of the substrate and before the discharging of the substrate, maintaining the substrate in a charged state by keeping from applying the driving voltage to the electrostatic chuck and by keeping from applying the second ground voltage to the substrate. In the above-mentioned method, wherein the measuring of the dechucking force of the substrate by pulling the substrate in a vertical direction by the normal-force measuring unit is performed by keeping from applying the second ground voltage to the substrate and by keeping from applying the driving voltage and the first ground voltage to the electrostatic chuck. In the above-mentioned method, wherein the discharging of the substrate subsequently leaves, internally of the substrate, residual charges that generate between the substrate and the electrostatic chuck an electrostatic attraction by which the dechucking force is determined. 
     The motor  620  may be disposed on the normal-force measuring unit  610 . The motor  620  may be disposed on an outer wall of the test chamber  10 . The motor  620  may be disposed on the upper surface of the test chamber  10 . However, this is only an example in the drawings, and the present disclosure is not limited thereto. 
     For example, the motor  620  may well be disposed in the inner space  13  of the test chamber  10 . 
     The motor  620  may provide the normal-force measuring unit  610  with a driving force for pushing or pulling the substrate  100 . The motor  620  may provide the normal-force measuring unit  610  with a driving force in a direction perpendicular to the substrate  100 . The motor  620  may provide a driving force to the normal-force measuring unit  610  through, for example, a ball screw mechanism. However, the power transmission method of the motor  620  is merely exemplary, and the present disclosure is not limited thereto. 
     The damper  630  may be disposed between the vertical force measurement unit  610  and the motor  620 . The damper  630  may dampen the vibration generated while the motor  620  provides the driving force to the normal-force measuring unit  610 . 
       FIGS.  2  and  3    are flowcharts for explaining a dechucking force evaluation method according to at least one embodiment of the present disclosure.  FIGS.  4  to  7    are diagrams of intermediate steps for explaining a dechucking force evaluation method according to at least one embodiment of the present disclosure.  FIG.  8    is a graph for explaining a voltage application state and a lifting state of a wafer in intermediate steps of the dechucking force evaluation method according to  FIG.  3   .  FIG.  9    is a graph for explaining the speed at which the normal-force measuring unit  610  pulls the substrate  100  in the intermediate steps of the dechucking force evaluation method according to  FIG.  3   . 
     For reference,  FIGS.  2  and  3    show a sequence of a dechucking force evaluation method using a substrate test apparatus according to some embodiments. 
     Referring to  FIG.  2   , Step S 100  may turn on the substrate test apparatus. The substrate test device is an electronic device that evaluates the dechucking force by providing voltage and driving force, so an electric power supply may be required. 
     Next, an initial set-up may be performed with respect to the substrate  100  (S 200 ). The initial set-up may mean evaluating an initial position, an initial voltage, etc. to evaluate a dechucking force for the substrate  100 . 
     As an example, the substrate  100  may be positioned on the electrostatic chuck  220 . The substrate  100  may be disposed between the electrostatic chuck  220  and the normal-force measuring unit  610 . 
     As another example, referring to  FIGS.  2  and  4   , second ground voltage GND 2  may be applied to the substrate  100 . The application of second ground voltage GND 2  to the substrate  100  may be to remove residual charges remaining in the substrate  100 . Accordingly, before charging the substrate  100 , the initial charge of the substrate  100  may be set. 
     When setting the initial charge of the substrate  100 , the electrostatic-chuck power supplying unit  300  may not apply the driving voltage HV and first ground voltage GND 1  to the electrostatic chuck  220 . 
     Referring to  FIGS.  2 ,  3 , and  5  to  7   , after the initial set-up of the substrate  100 , the substrate test apparatus may perform the dechucking evaluation of the electrostatic chuck  220  (S 300 ). 
     First, the substrate  100  may be charged (S 310 ). To charge the substrate  100 , a driving voltage HV may be applied to the electrostatic chuck  220 . A second ground voltage GND 2  may be applied to the substrate  100 . 
     The driving voltage HV to the electrostatic chuck  220  may be about 2.73 kV. As the driving voltage HV is applied to the electrostatic chuck  220 , the substrate  100  may be charged. First residual charges C 10  may be collected toward the lower surface of the substrate  100  adjacent to the electrostatic chuck  220 . 
     Charging the substrate  100  (S 310 ) may simulate a process of chucking the substrate  100  on the electrostatic chuck  220  as carried out in a semiconductor processing process. 
     Second, the substrate  100  may be discharged (S 320 ). To discharge the substrate  100 , first ground voltage GND 1  may be applied to the electrostatic chuck  220 . Second ground voltage GND 2  may be applied to the substrate  100 . 
     As the first ground voltage GND 1  is applied to the electrostatic chuck  220 , the substrate  100  may be discharged. Specifically, the first residual charges C 10 , which are collected on the lower surface of the substrate  100  adjacent to the electrostatic chuck  220 , may be dispersed. Accordingly, on the lower surface of the substrate  100 , an amount of second residual charges C 20  may be collected, which is smaller than first residual charges C 10  that keep the substrate  100  in the charged state. 
     Discharging the substrate  100  (S 320 ) may simulate a process of discharging the substrate  100  as carried out in the semiconductor processing process to dechuck the substrate  100  from the electrostatic chuck  220 . 
     Third, the substrate  100  may be dechucked (S 330 ). To dechuck the substrate  100 , driving voltage HV and first ground voltage GND 1  may be kept from being applied to the electrostatic chuck  220 . Second ground voltage GND 2  may be kept from being applied to the substrate  100 . 
     Thereafter, the normal-force measuring unit  610  may pull the substrate  100  in a vertical direction. Accordingly, the substrate  100  may be dechucked to be spaced apart from the electrostatic chuck  220 . 
     After the substrate  100  is discharged, the second residual charge C 20  may remain inside the substrate  100 . The second residual charge C 20  may cause an electrostatic attraction to be generated between the substrate  100  and the electrostatic chuck  220 . With no voltage applied to the electrostatic chuck  220  and the substrate  100 , an electrostatic attraction may stay with the electrostatic chuck  220  due to the second residual charge C 20  remaining in the substrate  100 . 
     At this time, the normal-force measuring unit  610  may pull the substrate  100  and thereby measure the electrostatic attraction. The electrostatic attraction may correspond to a dechucking force F. In other words, dechucking force F may be determined by the electrostatic attraction. 
     Referring to  FIGS.  3  and  8   , Step S 310  of charging the substrate  100  may proceed until a first time t 1 . 
     For reference, the horizontal axis in  FIG.  8    is an axis for describing time. The vertical axis indicates whether driving voltage HV and first ground voltage GND 1  are applied to the electrostatic chuck  220 , whether second ground voltage GND 2  is applied to the substrate  100 , and whether the normal-force measuring unit  610  pulls or lifts up the substrate  100 . 
     Up to the first time t 1 , driving voltage HV is applied to the electrostatic chuck  220 . First ground voltage GND 1  is not applied to the electrostatic chuck  220 . Second ground voltage GND 2  is applied to the substrate  100 . 
     The discharging of the substrate  100  (S 320 ) may proceed from the first time t 1  to a second time t 2 . 
     Driving voltage HV is not applied to the electrostatic chuck  220  from first time t 1  to second time t 2 . First ground voltage GND 1  is applied to the electrostatic chuck  220 . Second ground voltage GND 2  is applied to the substrate  100 . 
     The time taken for the substrate  100  to be charged until the first time t 1  may be referred to as a first operating time 0 to t 1 . The time taken for the substrate  100  to be charged from the first time t 1  to the second time t 2  may be referred to as a second operating time t 1  to t 2 . The first operating time 0 to t 1  may be different from the second operating time t 1  to t 2 . Specifically, the first operating time 0 to t 1  may be longer than the second operating time t 1  to t 2 . 
     After discharging the substrate  100 , from the second time t 2 , the substrate  100  may be lifted by the normal-force measuring unit  610 . At this time, the driving voltage HV is not applied to the electrostatic chuck  220 . First ground voltage GND 1  is not applied to the electrostatic chuck  220 . Second ground voltage GND 2  is not applied to the substrate  100 . 
     Referring to  FIGS.  3  and  9   , Step S 330  of dechucking the substrate  100  may be performed after the second time t 2 . 
     For reference, in  FIG.  9   , the horizontal axis is an axis for describing time, and the vertical axis is an axis for describing speed. Additionally,  FIG.  9    is a graph for explaining various speeds of the normal-force measuring unit  610  when lifting up the substrate  100 . 
     Upon receiving a driving force from the motor  620 , the normal-force measuring unit  610  can constantly pull the substrate  100  at a first speed v 1  or a second speed v 2 . First speed v 1  may be different from second speed v 2 . 
     For example, first speed v 1  may be lower than second speed v 2 . 
     Although the normal-force measuring unit  610  has been described as lifting or pulling the substrate  100  at two speeds, which is merely exemplary, the present disclosure is not limited thereto. For example, the normal-force measuring unit  610  may constantly pull the substrate  100  at two or more speeds. 
     After the dechucking evaluation of the electrostatic chuck  220  is performed (S 300 ), the measured dechucking force F is checked (S 400 ). 
     The higher dechucking force F is measured, the larger amount of electrostatic attraction remains between the substrate  100  and the electrostatic chuck  220 . It may mean that dechucking of the substrate  100  is incompletely performed due to a large amount of charge remaining on the substrate  100 . 
     The evaluation of the dechucking force is then completed (S 500 ). 
       FIG.  10    is a flowchart of a dechucking force evaluation method according to at least one embodiment of the present disclosure.  FIG.  11    is an intermediate step diagram for explaining a dechucking force evaluation method according to at least one embodiment of the present disclosure.  FIG.  12    is a graph for explaining voltage applications and wafer lifting in intermediate steps of the dechucking force evaluation method according to  FIG.  10   . For the convenience of description, redundant descriptions of those described with reference to  FIGS.  2  to  8    will be simplified or omitted. 
     For reference,  FIG.  10    illustrates a detailed sequence of Step S 300  in a dechucking force evaluation method using a substrate test apparatus according to some embodiments. 
     Referring to  FIGS.  10  and  11   , the dechucking force evaluation method may further include, after charging the substrate  100  (S 310 ) and before discharging the substrate  100  (S 320 ), Step S 315  of idling the substrate  100 . 
     While idling the substrate  100  (S 315 ), driving voltage HV and first ground voltage GND 1  may not be applied to the electrostatic chuck  220 . Second ground voltage GND 2  may not be applied to the substrate  100 . 
     With no voltage applied to the electrostatic chuck  220  and the substrate  100 , the substrate  100  may be maintained in a charged state. Therefore, first residual charges C 10  may remain collected on the lower surface of the substrate  100  adjacent to the electrostatic chuck  220 . 
     The idling of the substrate  100  (S 315 ) may definitely distinguish between the charging of the substrate  100  (S 310 ) and the discharging of the substrate  100  (S 320 ) to well define the proceeding of the steps. 
     Referring to  FIG.  12   , between the step of charging the substrate  100  and the step of discharging the substrate  100 , the step of idling the substrate  100  may be included. 
     The step of idling for the substrate  100  may proceed from the first time t 1  to the third time t 3  after the substrate  100  is charged. 
     The driving voltage HV and the first ground voltage GND 1  are not applied to the electrostatic chuck  220  from first time t 1  to third time t 3 . The second ground voltage GND 2  is not applied to the substrate  100 . 
     The discharging of the substrate  100  (S 320 ) may proceed from the third time t 3  to the second time t 2 . 
     The driving voltage HV is not applied to the electrostatic chuck  220  from the third time t 3  to the second time t 2 . First ground voltage GND 1  is applied to the electrostatic chuck  220 . Second ground voltage GND 2  is applied to the substrate  100 . 
     The time taken for the substrate  100  to be charged until the first time t 1  may be defined as the first operating time 0 to t 1 . The time taken for the substrate  100  to be discharged from third time t 3  to second time t 2  may be defined as the second operating time t 3  to t 2 . The first operating time 0 to t 1  may be different from the second operating time t 3  to t 2 . Specifically, the first operating time 0 to t 1  may be longer than the second operating time t 3  to t 2 . 
     The time taken from the first time t 1  to the third time t 3  for maintaining the substrate  100  in a charged state may be defined as the third operating time t 1  to t 3 . The third operating time t 1  to t 3  may be shorter than the first operating time 0 to t 1  and the second operating time t 3  to t 2 . 
     While some embodiments of the present disclosure have been particularly shown and described with reference to the accompanying drawings, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the technical idea and scope of the present disclosure as defined by the following claims.