Patent Publication Number: US-2023163016-A1

Title: A high precision air bearing stage with capability of parasitic error compensation

Description:
TECHNICAL FIELD 
     This disclosure relates to the field of chip processing and test, and relates to an air floating precision motion platform, in particular to a high-precision air floating motion platform and method for wafer test. 
     BACKGROUND 
     Chip is a general term for semiconductor component products and the carrier of integrated circuits. Chips are cut from wafer and are important parts of computers or other electronic equipment. In simple terms, the electronic components such as resistors and capacitors and the circuits composed of them are integrated and packaged into a small particle, which is often referred to as a chip. 
     The manufacturing process of the chip includes crystal pulling, silicon slice formation, photosensitive material coating, photolithography, etching/doping/stripping, anti-corrosion treatment, metal filling, wafer formation, wafer test, wafer cutting, wafer packaging and chip formation. The manufacturing process of the chip is extremely complex and precise. Wherein, photolithography, wafer test, wafer cutting, and wafer packaging have high requirements for the precision, speed, and displacement resolution of the motion platform, while the air floating motion platform has frictionless motion characteristic, thus it can be applied to the above four processes. 
     The existing air floating motion platforms generally include three types: a) two-axis stacking type; b) two-axis coplanar type; c) single-axis type. For example, Chinese Patent Application No. CN201710832517.0 discloses a motion platform based on an H-type air floating guide rail, which is a two-axis coplanar air floating motion platform. The motion flatness error of the two-axis coplanar air floating motion platform mainly depends on the precision of the marble base and guide rail. Based on the current level of marble processing, the surface flatness of 1 m 2  of marble can reach 2 microns, and the parallelism and perpendicularity of other surfaces can also reach micron order. Therefore, the flatness of the two-axis coplanar air floating motion platform can reach 200 nm/500 mm. Due to the current level of machining, it is difficult to further improve the vertical straightness of this type of platform. 
     The disadvantage of the two-axis stacking type is that the errors of the two axis are transmitted to each other, the precision is difficult to guarantee, and the mass of the upper axis is large, it is difficult to achieve high-speed motion. The flatness of the single-axis air floating motion platform mainly depends on the machining precision of the air floating surface, namely, the parallelism and perpendicularity between the air bearing surfaces. The flatness of the air bearing motion platform with the single-axis structure can also reach 200 nm/500 mm, but the further improvement of the vertical straightness is still limited by the finishing ability. 
     SUMMARY 
     The purpose of the present disclosure is to provide a high-precision air floating motion platform and method for wafer test, so as to solve the technical problems in the prior art that the motion platform precision is not high and the vertical straightness cannot be detected and compensated due to the inherent factors of the machining precision of the base. The technical solutions adopted by the present disclosure to solve the technical problems are as follows: 
     A high-precision air floating motion platform for wafer test, including: 
     a base used as a seat in the wafer test process; 
     a beam installed on the base; 
     a sliding table capable of sliding along a surface of the beam, and a top of the sliding table being capable of carrying a wafer; 
     a linear motor configured to drive the sliding table to slide along the beam; 
     at least three sensors distributed on sides of the sliding table, and configured to detect a vertical straightness of the wafer; 
     air bearings comprising a first air bearing, a second air bearing and a third air bearing; the first air bearing and the second air bearing being configured for a side limited suspension of the sliding table, and the third air bearing being configured for a bottom limited suspension of the sliding table; and 
     a compensation device located above the sliding table, and the compensation device being configured to compensate the vertical straightness of the wafer based on a real-time data detected by the sensors. 
     Further, the high-precision air floating motion platform further includes a high-precision plane; wherein the high-precision plane is used as a reference plane for wafer flatness, and the sensors measure a change in position of the wafer with respect to the high-precision plane, such that a detection of the vertical straightness of the wafer is realized. 
     Further, the high-precision plane is an optical flat; the optical flat is mounted on a first mounting seat, and the first mounting seat is fixed on the base; the air floating motion platform comprises two sets of the optical flat and the first mounting seat; one set of the optical flat and the first mounting seat is located on one side of the sliding table, and an other set of the optical flat and the first mounting seat is located on an other side of the sliding table. 
     Further, the high-precision air floating motion platform further includes two second mounting seats; the two second mounting seats are respectively fixed on two sides of the sliding table; and the sensors comprise a first sensor, a second sensor and a third sensor; the first sensor is installed on one second mounting seat on one side of the sliding table, and the second sensor and the third sensor are both installed on another second mounting seat on an other side of the sliding table. 
     Further, a nano compensation motion platform is arranged on the top of the sliding table, the wafer is placed on the nano compensation motion platform, and the nano compensation motion platform is superimposed on the sliding table of the floating motion platform, the wafer is capable of moving linearly with the nano compensation motion platform. 
     Further, the high-precision air floating motion platform further includes two dampers and baffles; wherein the baffles are located on each side of the beam and is used to close the beam, and the two dampers are opposite arranged and respectively located a position close to an inner side of the baffle, and the two dampers are used to limit the motion track of the sliding table. 
     Further, the compensation device is a nano compensation table. 
     A wafer test method is further provided, the method includes: 
     S 100 : placing a wafer to be tested on a sliding table; 
     S 200 : driving, by a linear motor, the sliding table to slide along a surface of a beam; 
     S 300 : detecting, by at least three sensors, a vertical straightness of the wafer during a motion of the wafer; 
     S 400 : compensating, by a compensation device, the vertical straightness of the wafer. 
     The S 300  further includes: setting a high-precision plane, wherein a vertical runout of the air floating motion platform is measured by the sensors, such that a detection of the vertical straightness of the wafer is realized. 
     Further, the compensation process in the S 400  is: transmitting, by the sensors, a detected vertical straightness error signal of the sliding table to the compensation device; and adjusting, by the compensation device, a motion track of the sliding table to complete the compensation of the vertical straightness of the wafer. 
     According to first aspect of the technical solutions of the present disclosure, the suspension of the sliding table is realized through air bearings. The first air bearing and the second air bearing are configured for a side limited suspension of the sliding table, and the third air bearing is configured for a bottom limited suspension of the sliding table. The air floating motion platform has frictionless motion characteristics, and is rarely affected by factors inherent in base machining precision and has a higher vertical straightness. 
     According to second aspect of the technical solutions of the present disclosure, the vertical straightness of the air floating platform is detected in real time by at least three sensors. Since the three sensors can determine a plane, when the wafer moves to a different position, the three sensors can establish a real-time position map of the current wafer. By using the initial position as the initial plane, a height change map of any position can be calculated through geometric calculations; such that the vertical straightness of the wafer is detected in real time. The detection precision of the sensors in the present disclosure is on the order of nanometers, and the vertical straightness error in nanometers can be detected. 
     According to third aspect of the technical solutions of the present disclosure, the vertical straightness of the wafer is compensated by the compensation device. The compensation device is driven by piezoelectric ceramics with a resolution of 0.1 nm, and a precision of the order of nanometers. The purpose of improving the vertical straightness of the platform operation is achieved, which greatly improves the vertical straightness of the wafer in motion. 
     According to fourth aspect of the present disclosure, the motion platform of the present disclosure preferably includes a high-precision plane, such as a plane optical flat. The upper surface of the plane optical flat is detected by at least three sensors. Since the surface flatness of the plane optical flat can be 50 nm or higher, the precision of the sensor can also reach the nanometer level. The vertical straightness precision of the air floating motion platform of the present disclosure can reach 100 nm/200 nm or even higher. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a perspective view of an air floating motion platform according to an embodiment of the present disclosure; 
         FIG.  2    is a top view of the air floating platform according to an embodiment of the present disclosure; 
         FIG.  3    is a front view of the air floating platform according to an embodiment of the present disclosure; 
         FIG.  4    is a cross-sectional view of the air floating platform taken along a certain direction according to an embodiment of the present disclosure; 
         FIG.  5    is a partial enlarged view of part A in  FIG.  4   ; 
         FIG.  6    is a schematic diagram of flatness detection by using three sensors in an embodiment of the present disclosure; 
         FIG.  7    is a structural view of a compensation device of an embodiment of the present disclosure; 
         FIG.  8    is a flowchart of a method for processing and testing of chip according to an embodiment of the present disclosure. 
     
    
    
     In the figures:  1 , beam;  2 , base;  3 , high-precision plane;  4 , first mounting seat;  5 , second mounting seat;  6 , damper;  7 , linear motor;  8 , sliding table;  9 , wafer;  10 , baffle;  11 , nano compensation motion table;  12 , first sensor;  13 , second sensor;  14 , third sensor;  15 , first air bearing;  16 , second air bearing;  17 , third air bearing;  18 , vacuum preload array;  19 , compensation device. 
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     In order to make the above objectives, features and advantages of the present disclosure more obvious and understandable, the specific embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. In the following description, many specific details are explained in order to fully understand the present disclosure. However, the present disclosure can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without departing from the spirit of the present disclosure. Therefore, the present disclosure is not limited by the specific embodiments disclosed below. 
     It should be understood that, in the disclosure of the present disclosure, orientations or positional relationships indicated by terms “central”, “longitudinal”, “transverse”, “width”, “thickness”, “upper”, “lower”, “front”, “rear”, “left”, “right”, “vertical”, “horizontal”, “top”, “bottom”, “inner”, “outer”, “clockwise”, “counterclockwise”, “axial”, “radial”, “circumferential” and the like are the orientations and the positional relationships illustrated on the basis of the accompanying drawings, merely used for ease of describing the present disclosure and simplifying the description, rather than indicating or implying that the stated devices or elements must have a specific orientation or must be constructed and operated in a specific orientation. Thus, those terms shall not be interpreted as any limitation to the present disclosure. 
     In the present disclosure, the term “a” or “an” as used in the claims and description shall be interpreted as “one or more”. That is, for a certain element, there may be one element in one embodiment, while there may be several elements in other embodiments. The term “a” or “an” shall not be interpreted as being unique or singular, unless the number of the element is explicitly indicated in the disclosure of the present disclosure. The term “a” or “an” shall not be interpreted as any limitation to the number. 
     In addition, the terms “first” and “second” are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features. Therefore, the features defined with “first” and “second” may explicitly or implicitly include at least one of the features. In the description of the present disclosure, “plurality” means at least two, such as two, three, etc., unless otherwise specifically defined. 
     Please refer to  FIGS.  1 - 7   , this embodiment provides a high-precision air floating motion platform for wafer test, including: a base  2 , the base  2  being used as a seat in the wafer test process; a beam  1 , installed on the base  2 ; as shown in  FIG.  1   , there are two beams  1  arranged in parallel, and the two beams  1  are substantially located in the center of an upper surface of the base  2 ; a sliding table  8 , the sliding table  8  being capable of sliding along a surface of the beam  1 , a top of the sliding table  8  being capable of carrying the wafer  9 , the wafer  9  being capable of making a reciprocating linear motion with the sliding table  8 , and a position of the wafer  9  being fed back through a grating ruler (not shown in the figures); a linear motor  7 , the linear motor  7  being located on a side of an inner wall of the beam  1 , and the linear motor  7  being used to drive the sliding table  8  to slide along the beam  1 ; at least three sensors distributed on a side of the sliding table  8 , and configured to detect a real-time position of the air floating motion platform in a detected direction, the detected direction may be the vertical direction of the air floating platform, that is, a vertical straightness; air bearings, including a first air bearing  15 , a second air bearing  16 , and a second air bearing  17 ; the first air bearing  15  and the second air bearing  16  being configured for a side limited suspension of the sliding table, and the third air bearing  17  being configured for a bottom limited suspension of the sliding table; since the first air bearing  15 , the second air bearing  16  and the third air bearing  17  are used to realize the suspension of the sliding table  8 , the air floating motion platform has frictionless motion characteristics; since the base  2  is affected by the inherent factors of the machining precision, it is difficult to further improve the vertical straightness of traditional air floating motion platforms; the air floating motion platform of this embodiment has error detection and compensation functions, and the vertical straightness can be further improved; and a compensation device  20  located above the sliding table  8 , and the compensation device  20  being configured to compensate the vertical straightness of the wafer  9  based on a real-time data detected by the sensors, for example, a distance change between capacitive sensor and an optical flat; in this embodiment, the compensation device  20  is a nano compensation table. 
     Preferably, the high-precision air floating motion platform for wafer test further includes a high-precision plane  3 ; the high-precision plane  3  is used as a reference plane of a motion error of the wafer  9  in the vertical direction; and the distance change between the capacitive sensor and the high-precision plane  3  is detected by the sensors, such that a detection of the vertical straightness of the wafer is realized. Specifically, the high-precision plane  3  is an optical flat; the optical flat is mounted on a first mounting seat  4 , and the first mounting seat  4  is fixed on the base  2 ; as shown in  FIGS.  1  and  2   , the air floating motion platform comprises two sets of the optical flat and the first mounting seat  4 ; one set of the optical flat and the first mounting seat  4  is located on one side of the sliding table  8 , and an other set of the optical flat and the first mounting seat  4  is located on an other side of the sliding table  8 . In this embodiment, the high-precision plane  3  is a plane optical flat. The plane optical flat can be used as a reference plane for detecting the vertical straightness of the wafer. The upper surface of the plane optical flat is detected by at least three sensors, and the three sensors can be used to detect the position change of the air floating motion platform relative to the high-precision plane  3 . Since the surface flatness of the plane optical flat can be 50 nm or higher, the precision of the sensor can also reach the nanometer level. The vertical straightness precision of the air motion floating platform of the present disclosure can reach 100 nm/200 nm or even higher. 
     Please refer to  FIGS.  1 - 3   , the air floating motion platform of this embodiment further includes two second mounting seats  5 ; the two second mounting seats  5  are respectively fixed on two sides of the sliding table  8 ; and the sensors comprise a first sensor  12 , a second sensor  13  and a third sensor  14 ; the first sensor  12  is installed on one second mounting seat  5  on one side of the sliding table  8 , and the second sensor  13  and the third sensor  14  are both installed on another second mounting seat  5  on an other side of the sliding table  8 . As shown in  FIG.  6   , the principle of flatness detection by the three sensors is roughly as follows: first, a plane M is determined by the first sensor  12 , the second sensor  13  and the third sensor  14 ; the plane M can be used as an initial plane; when the wafer  9  moves to a different position, for example, the detection points of the first sensor  12 , the second sensor  13  and the third sensor  14  can move up and down in the direction indicated by arrows shown in  FIG.  6   , or move arbitrarily in other directions; at this time, the three sensors can establish a current real-time position map of the wafer  9 ; then, by using the initial position of the plane M as the initial plane, a height change map of any position on the plane M can be calculated through geometric calculations; for example, a dynamic spatial position change map of the wafer  9  plane can be calculated by the detection algorithm; and then the error of different points is established through the error separation algorithm and a certain geometric relationship mapping, so as to detect the vertical straightness of the wafer  9  in real time. The sensors in the present disclosure can be, for example, capacitive sensors, optical sensors or an inductance sensors, etc., the detection precision of the capacitive sensor is on the order of nanometers, and the capacitive sensor can detect the vertical straightness in nanometers. The number of sensors can also be 4, 5 or more, as long as the plane M can be determined by at least three of the sensors. 
     A nano compensation motion platform  11  is arranged on the top of the sliding table  8 , the wafer  9  is placed on the nano compensation motion platform  11 , and the nano compensation motion platform  11  is superimposed on the sliding table  8  of the floating motion platform, the wafer  9  is capable of moving linearly with the nano compensation motion platform  11 . The nano compensation motion table is driven by piezoelectric ceramics. This driving manner has high bandwidth and high resolution characteristics. The air floating motion platform of this embodiment further includes dampers  6  and baffles  10 , as shown in  FIG.  1   , there are two baffles  10 , which are located on each side of the beam  1 . The two baffles  10  are used to close the beam  1 . There are two dampers  6  arranged opposite to each other and located close to an inner side of the baffles  10  respectively. The dampers  6  are used to limit the motion track of the sliding table  8  and prevent the sliding table  8  and the wafers  9  from falling off the beam  1 . 
     As shown in  FIGS.  4  and  5   , the sliding table  8  is suspended by air bearings. The air bearings include a first air bearing  15 , a second air bearing  16  and a third air bearing  17 . Specifically, the first air bearing  15  is located on a lower left side of the sliding table  8  and can make the sliding table  8  suspend to the left. The second air bearing  16  is located on a lower right of the sliding table  8  and can make the sliding table  8  suspend to the right. The bearing surfaces of the first air bearing  15  and the second air bearing  16  are the side surface of the beam  1 . The first air bearing  15  and the second air bearing  16  are symmetrically preloaded on both sides, and the third air bearing  17  and a vacuum preload array  18  together form a bottom air floating module. The bearing surface of the bottom air floating module is the upper surface of the base  2 . The bottom air floating module can make the sliding table  8  float upward. The vertical straightness of the motion of the wafer  9  depends on the machining precision of the air floating surface of the base  2 . In this embodiment, the base  2  is a marble base. 
     Due to the machining inprecision of the base  2 , the vibration of the air film caused by the external force, or the low-frequency vortex breaking in the air film, etc., the vertical motion error of the air floating motion platform will occur in motion. The low-frequency vortex breaking in the air film is one of the reasons for the error. In order to overcome this technical problem, the present disclosure provides a vacuum preload array recovery air type air bearing (not shown in the figures), including a rectangular vacuum seal tank, a cross-shaped vacuum tank located inside the vacuum seal tank, four porous media air bearings, and four vacuum chambers. The four porous media air bearings are located at the intersection of the vacuum seal tank and the vacuum tank. The four vacuum chambers are located at about the center of the four sides of the vacuum tank respectively. The four porous media air bearings increase a positive pressure, and the four vacuum chambers provide a preload force, and the cross-shaped vacuum tank prevents the intersection of four porous throttling flow fields, thereby greatly reducing the possibility of vortexes intersection generated by the flow field. The vacuum seal tank can recover the air generated in the positive pressure zone of the porous media air bearings, thereby reducing the noise and airflow disturbance caused by the airflow entering the environment. The method of error detection and error compensation can greatly improve the measurement precision of the wafer. 
     In one embodiment, a wafer test method is further provided. As shown in  FIG.  8   , the test method includes: S 100 : placing a wafer  9  to be tested on a sliding table  8 ; S 200 : driving, by a linear motor  7 , the sliding table  8  to slide along a surface of a beam  1 ; S 300 : detecting, by at least three sensors, a vertical straightness of the wafer  9  during a motion of the wafer  9 ; S 400 : compensating, by a compensation device  20 , the vertical straightness of the wafer  9 . 
     The S 300  further comprises: setting a high-precision plane  3 , wherein the flatness of the high-precision plane  3  is detected by at least three sensors to realize the detection of the vertical straightness of the wafer  9 . The high-precision plane  3  may be, for example, a plane optical flat, which is used to detect the vertical straightness of the wafer  9 . The plane optical flat is used as the reference plane of the vertical straightness of the wafer  9 , such that the vertical straightness of the wafer  9  is obtained by measuring the flatness of the high-precision plane  3  by the sensors. On the other hand, the surface flatness of the plane optical flat can reach 50 nm or even higher, and the precision of the sensor can also reach the nanometer level, the vertical straightness of the air floating motion platform can reach 100 nm/200 mm or even higher by adopting the active compensation method of the present disclosure. 
     The compensating step in S 400  includes passive error compensation and active error compensation. The process of active error compensation includes: placing three piezoelectric ceramic drivers above the three capacitive sensors; and the three piezoelectric ceramic drivers and three capacitive sensors correspond to each other; such that a closed-loop control is formed; directly outputting the runout error of the air bearings measured by the capacitive sensors in motion of the air bearing motion platform to the controller as a control command to drive the corresponding piezoelectric ceramic driver for error compensation and maintain the vertical straightness of the air bearing motion platform; for example, in actual detection applications, the measured flatness error data is directly used to correct the measurement results of the detection head of the sensor (not shown in the figure). The method of correcting the vertical straightness of the motion platform through the algorithm is the passive error compensation. The active error compensation means that the detected vertical straightness errors are transmitted to the nano compensation table or detection head by at least three sensors, and the errors are eliminated through the motion of the nano compensation table. In this embodiment, an active error compensation method is adopted, that is, the compensation process in step S 400  is specifically: transmitting, by the sensors, the detected vertical straightness error signal of the sliding table  8  to the compensation device  20 ; and adjusting, by the compensation device  20 , the motion track of the sliding table  8  to complete the compensation of the vertical straightness of wafer  9 . The detection can also be carried out through a combination of passive error compensation and active error compensation. The nano compensation table is driven by piezoelectric ceramics with a resolution of 0.1 nm and a nanometer level precision. The flatness precision of the air floating motion platform detected by the method of the present application can be improved to 100 nm/200 mm or even higher. The air floating motion platform and method for wafer test of the present disclosure can be applied to the XY two-axis air floating motion platform. 
     The implementation process of passive error compensation includes: 1) recording the measured values of the three capacitance sensors in real time; extracting the fluctuation values of the measured values of the three capacitance sensors after measurement, and converting into the vertical runout error and pitch/roll runout error of the air floating motion platform; calculating the wafer measurement error caused by the runout error of the air floating motion platform according to the corresponding position of the measured point of the wafer, and correcting the measurement error. The present disclosure is not limited to the error measurement and compensation in the vertical straightness direction. The layout of the capacitance sensors can be changed to apply in horizontal straightness error detection and compensation. 
     At least three sensors are used to online detect the vertical straightness of the air floating motion platform, and nanometer level flatness errors can be detected. By actively or passively compensating the detected flatness errors, the precision of the air floating motion platform is further improved. The purpose of improving the straightness of the platform operation is achieved, and the compensation of the slight runout in the vertical direction of the platform operation is realized, which greatly improves the vertical straightness of the wafer in motion. 
     The above examples only describe several embodiments of the present disclosure, and the descriptions are relatively specific and detailed, but they cannot be understood to limit the protection scope of the present disclosure. It should be pointed out that for those of ordinary skill in the art, without departing from the spirit of the present disclosure, several modifications and improvements can be made, and these all fall within the protection scope of the present disclosure. Therefore, the protection scope of the present disclosure should be subject to the appended claims.