Method for measuring object plane of photoetching machine and optical system of photoetching machine

Abstract

The invention provides a photoetching machine object plane measurement method and a photoetching machine optical system, and relates to the technical field of semiconductor manufacturing. The method comprises the following steps: obtaining a plurality of motion table heights measured by a motion table z-direction interferometer according to a preset frequency, and an initial object plane height of a silicon wafer measured by a leveling and focusing system according to the preset frequency, the preset frequency being less than or equal to a preset threshold; performing error compensation on the measurement height of each light spot under each measurement round based on the height of the motion table of each measurement round to obtain the compensated height of each light spot under each measurement round; obtaining the target height of each light spot according to the compensated height of each light spot under each measurement round; and fitting all the target heights, and determining the actual surface shape information of the silicon wafer. According to the invention, through multiple times of measurement and in combination with error compensation, systematic errors and random errors caused by instability of a motion table are effectively removed, and the measurement precision of a leveling and focusing system and the authenticity of silicon wafer surface shape information are improved.

Description

Technical Field

[0001] The present application relates to the field of semiconductor manufacturing technology, and in particular to a method for measuring an object plane of a lithography machine and an optical system of a lithography machine. Background Art

[0002] In current semiconductor manufacturing processes, leveling and focusing systems are widely used to ensure that the silicon wafer surface achieves the required flatness and focus position. Existing leveling and focusing systems determine the wafer surface shape by measuring the height data of the light spots distributed on the silicon wafer surface and fitting them.

[0003] However, ambient noise and instrument vibration significantly influence low- and medium-frequency vibrations, particularly in the low-frequency range. This can lead to increased errors in the surface characteristic parameters output by the leveling and focusing system, which represent the silicon wafer's surface, thus limiting measurement accuracy. Furthermore, since the silicon wafer is placed on a motion stage, which inevitably vibrates, this vibration directly affects the measurement accuracy of the leveling and focusing system, rendering the resulting silicon wafer surface shape information less reliable and inaccurate, failing to accurately reflect the wafer's actual surface characteristics. Summary of the Invention

[0004] The purpose of this application is to provide a method for measuring the object plane of a lithography machine and a lithography machine optical system in response to the above-mentioned deficiencies in the prior art, so as to solve the problem in the prior art that the silicon wafer is placed on a moving table, and the moving table itself has inevitable vibrations. The vibration of the moving table will directly affect the measurement accuracy of the leveling and focusing system, making the final silicon wafer surface information not true and reliable enough and unable to accurately reflect the actual surface characteristics of the silicon wafer.

[0005] To achieve the above objectives, the technical solutions adopted in the embodiments of the present application are as follows: In a first aspect, an embodiment of the present application provides a method for measuring an object plane of a lithography machine, the method comprising: Acquiring multiple motion stage heights measured by a motion stage z-axis interferometer at a preset frequency, and acquiring an initial object plane height of the silicon wafer measured by a leveling and focusing system at the preset frequency, wherein the preset frequency is less than or equal to a preset threshold, and the initial object plane height includes: measured heights of multiple light spots; Based on the height of the moving stage in each measurement round, the error of the measured height of each light spot in each measurement round is compensated to obtain the compensated height of each light spot in each measurement round; According to the compensated height of each light spot in each measurement round, the target height of each light spot is obtained; Fitting processing is performed on the target heights of all light spots to determine actual surface shape information of the silicon wafer, where the actual surface shape information includes focal length information and tilt information.

[0006] As a possible implementation, performing error compensation on the measured height of each light spot in each measurement round based on the height of the moving stage in each measurement round to obtain the compensated height of each light spot in each measurement round includes: Determining a jitter height of the motion stage in the current measurement round based on the motion stage height and the stable height of the motion stage in the current measurement round, wherein the motion stage height is a measured height obtained by a z-direction interferometer of the motion stage; Based on the jitter height of the moving stage in the current measurement round, the measured height of the current light spot in the current round is error compensated to obtain the compensated height of the current light spot in the current round. The compensated height represents the stable height of the silicon wafer surface relative to the ideal focal plane of the optical system of the lithography machine.

[0007] As a possible implementation manner, determining the jitter height of the moving platform in the current measurement round based on the moving platform height and the stable height of the moving platform in the current measurement round includes: Based on the formula Calculating the shaking height of the motion platform; in, represents the measured height obtained by the z-axis interferometer of the motion stage, represents the stable height of the sports platform, Indicates the jitter height of the motion platform.

[0008] As a possible implementation manner, performing error compensation on the measured height of the current light spot in the current round based on the jitter height of the moving stage in the current measurement round to obtain the compensated height of the current light spot in the current round includes: Based on the formula Calculate the compensated height of the current light spot; in, Indicates the measured height of the current light spot, that is, the measured height of the silicon wafer surface relative to the ideal focal plane of the lithography machine optical system. Indicates the measured height of the current light spot, that is, the stable height of the silicon wafer surface relative to the ideal focal plane of the lithography machine optical system. Indicates the jitter height of the motion platform.

[0009] As a possible implementation, the target heights of all light spots are fitted to determine the actual surface shape information of the silicon wafer, where the actual surface shape information includes focal length information and tilt information, including: The target heights of the multiple light spots are fitted using the least square method to determine actual surface shape information of the silicon wafer within the light spot range of the leveling and focusing system.

[0010] As a possible implementation method, the target height of the light spot includes: coordinate, Coordinates and coordinate positions Wafer height at ; The method of fitting the target heights of the plurality of light spots using the least square method to determine the actual surface shape information of the silicon wafer within the light spot range of the leveling and focusing system includes: The light spots on the surface of the silicon wafer coordinate, Coordinates and coordinate positions Wafer height at Enter the formulas separately Perform plane fitting in and obtain the least squares solution; among them, Indicates the coordinate position The height of the silicon wafer at Represents the first parameter, Represents the second parameter, Represents the third parameter, Represents the horizontal coordinate of the light spot on the silicon wafer surface, Indicates the vertical coordinate of the light spot on the silicon wafer surface; The first parameter corresponding to the least squares solution is used as the focal length information, and the second parameter and the third parameter corresponding to the least squares solution are used as the tilt information.

[0011] As a possible implementation manner, before obtaining the initial object plane height of the silicon wafer measured by the leveling and focusing system according to the preset frequency, the method further includes: Controlling the leveling and focusing system to emit multiple light spots toward the base plate; A plane consistency test is performed on the multiple light spots emitted onto the base plate. If the plane consistency test fails, the zero plane of the leveling and focusing system is adjusted.

[0012] As a possible implementation manner, performing a plane consistency test on the multiple light spots emitted onto the base plate, and adjusting the zero plane of the leveling and focusing system if the plane consistency test fails, includes: Step A: selecting one light spot from the multiple light spots of the leveling and focusing system in sequence as an effective light spot; Step B: moving the micro-motion stage to move the center position of the preset flat area in the base plate to the effective light spot; Step C: obtaining a single point height value obtained by measuring the single point height of the effective light spot by the leveling and focusing system; Step D: Repeat steps A to C above to obtain the single point height value of each light spot; Step E: determining a height difference value of each light spot relative to a center position according to a single-point height value of each light spot; if the height difference value is greater than a preset threshold, adjusting the zero plane of the leveling and focusing system.

[0013] In a second aspect, an embodiment of the present application provides an optical system for a lithography machine, the optical system comprising at least: a motion stage z-axis interferometer, a leveling and focusing system, a motion stage, and a measuring device, the motion stage comprising at least a fine-motion stage and a wafer chuck, the wafer chuck being fixed on the fine-motion stage, and a silicon wafer being adsorbed on the wafer chuck; The motion stage z-direction interferometer, the leveling and focusing system, and the micro-motion stage are respectively connected to the measuring equipment for communication; The motion stage z-direction interferometer is used to measure the height of the motion stage under the control of the measuring device; The leveling and focusing system is used to measure the initial object plane height of the silicon wafer under the control of the measuring device; The measuring device is used to perform the steps of the lithography machine object plane measurement method described in any one of the first aspects to measure and obtain the actual surface shape information of the silicon wafer.

[0014] As a possible implementation, the lithography machine optical system further includes: a base plate; The base plate is arranged on the micro-motion stage, and the base plate includes a preset flat area.

[0015] In a third aspect, an embodiment of the present application provides a measurement device, comprising: a processor, a storage medium and a bus, wherein the storage medium stores machine-readable instructions executable by the processor. When the measurement device is running, the processor and the storage medium communicate through the bus, and the processor executes the machine-readable instructions to perform the steps of the lithography machine object surface measurement method as described in any one of the first aspects above.

[0016] In a fourth aspect, an embodiment of the present application provides a computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, the steps of the lithography machine object plane measurement method as described in any one of the above-mentioned first aspects are executed.

[0017] According to the embodiment of the present application, the lithography machine object plane measurement and lithography machine optical system obtain multiple motion stage heights measured by the motion stage z-direction interferometer at a preset frequency and the initial object plane height of the silicon wafer measured by the leveling and focusing system at a preset frequency. When the measurement error source is highly consistent, the measured height of each light spot under each measurement round is error compensated based on the motion stage height of each measurement round to obtain the compensated height of each light spot under each measurement round. According to the compensated height of each light spot under each measurement round, the target height of each light spot is obtained, and the target heights of all light spots are fitted to determine the actual surface shape information of the silicon wafer. According to the embodiment of the present application, the measurement data output by the motion stage z-direction interferometer and the leveling and focusing system are all within a preset frequency, and the preset frequency is less than or equal to the preset threshold, which limits the common effective signal range of the motion stage z-direction interferometer and the leveling and focusing system. In the presence of an irreversible low-frequency working environment, vibration errors caused by some components in the lithography machine optical system can be avoided. On this basis, error compensation is performed on the silicon wafer measurement values based on the motion stage data, thereby removing the interference components caused by the motion stage vibration and improving the authenticity of the silicon wafer surface height measurement. In addition, the data and error compensation under multiple measurement rounds are combined to effectively avoid the influence of random errors on the final results. This not only improves the measurement accuracy of the leveling and focusing system, but also makes the final silicon wafer surface shape information more real and reliable, and can accurately reflect the actual surface characteristics of the silicon wafer. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work.

[0019] Figure 1 A schematic diagram of the architecture of an optical system of a lithography machine provided in an embodiment of the present application is shown; Figure 2 A flow chart of a method for measuring an object plane of a lithography machine provided in an embodiment of the present application is shown; Figure 3 A time domain variation diagram of a sports platform provided by an embodiment of the present application in a sampling period is shown; Figure 4 A frequency domain variation diagram of a motion platform provided by an embodiment of the present application within a sampling period is shown; Figure 5 A time domain variation diagram of a leveling and focusing system provided by an embodiment of the present application in a sampling period is shown; Figure 6A frequency domain variation diagram of a leveling and focusing system provided by an embodiment of the present application within a sampling period is shown; Figure 7 The figure shows a spectrum diagram of a motion stage z-direction interferometer and a leveling and focusing system provided in an embodiment of the present application at 0-300 Hz; Figure 8 shows a light spot distribution diagram provided by an embodiment of the present application; Figure 9 A schematic diagram of a process for determining height after compensation provided by an embodiment of the present application is shown; Figure 10 An effect diagram of a measurement data castration process provided by an embodiment of the present application is shown; Figure 11 shows an effect diagram of another measurement data castration processing provided by an embodiment of the present application; Figure 12 A structural schematic diagram of a measuring device provided in an embodiment of the present application is shown. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. It should be understood that the drawings in the present application only serve the purpose of illustration and description and are not used to limit the scope of protection of the present application. In addition, it should be understood that the schematic drawings are not drawn to scale. The flowcharts used in this application illustrate the operations implemented according to some embodiments of the present application. It should be understood that the operations of the flowcharts can be implemented out of sequence, and steps without logical context can be reversed or implemented simultaneously. In addition, those skilled in the art, under the guidance of the contents of this application, can add one or more other operations to the flowchart, or remove one or more operations from the flowchart.

[0021] In addition, the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments. The components of the embodiments of the present application generally described and shown in the drawings here can be arranged and designed in various configurations. Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the claimed application, but merely represents selected embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without making creative work are within the scope of protection of the present application.

[0022] It should be noted that the term "comprising" will be used in the embodiments of the present application to indicate the existence of the features declared thereafter, but does not exclude the addition of other features.

[0023] Figure 1FIG2 shows a schematic diagram of the optical system of a lithography machine provided by an embodiment of the present application. Figure 1 As shown, the optical system of the lithography machine includes at least a motion stage z-interferometer, a focusing and leveling system (FLS), a motion stage, and a measuring device. The motion stage includes at least a fine-motion stage, on which the silicon wafer is placed. The motion stage z-interferometer, the focusing and leveling system, and the fine-motion stage are each connected to the measuring device. The motion stage z-interferometer is used to measure the motion stage height under the control of the measuring device, and the focusing and leveling system is used to measure the initial object plane height of the silicon wafer under the control of the measuring device.

[0024] Optionally, refer to Figure 1 As shown, the lithography machine physical measurement system also includes a base plate FM, which includes a preset flat area slightly larger than the beam spot size, for example, a flat area of 2 x 2 mm. The base plate FM serves as a reference surface, and the leveling and focusing system FLS is calibrated based on the preset flat area provided by the base plate FM.

[0025] Optionally, refer to Figure 1 As shown, the optical system of the lithography machine also includes vibration dampers, a measurement frame, a base frame, a projection objective, a macro-motion stage, a suspension device (NS), marble, and air bearings. The vibration dampers, located on both sides of the measurement frame, are used to reduce the impact of external vibrations on the lithography machine optical system and ensure stability during measurement. The vibration dampers absorb and attenuate vibration energy through internal damping materials or air springs, keeping the lithography machine optical system relatively stationary during measurement. The base frame supports the bottom of the entire lithography machine optical system, providing a stable platform and ensuring that the relative positions of various components remain fixed. The projection objective is used to focus light emitted by the leveling and focusing system (FLS) onto the silicon wafer surface, forming a bright and clear light spot. The macro-motion stage, located below the micro-motion stage, is used to move the silicon wafer over a large range and bring it into the measurement area. The marble, located below the macro-motion stage, provides a stable support platform. The air bearing, located at the bottom layer, further reduces the impact of vibrations on the lithography machine optical system. The air bearings and the suspension device (NS) utilize suspension technology to suspend the entire lithography machine optical system, thereby isolating it from ground vibrations.

[0026] Based on this, the lithography machine optical system provided in the embodiments of the present application achieves high-precision measurement of silicon wafers through the collaborative operation of multiple components. Each component in the lithography machine optical system has a specific function and operating principle, which together ensure the stability and accuracy of the object plane measurement process.

[0027] The following combines the above Figure 1The contents described in the optical system of the lithography machine shown are used to provide a detailed description of the lithography machine object plane measurement method provided in the embodiment of the present application.

[0028] Figure 2 The flow chart of a method for measuring the object plane of a lithography machine provided in an embodiment of the present application is shown. The execution subject of the method is Figure 1 The measurement equipment in the optical system of the lithography machine is shown. Figure 2 As shown, the method specifically includes the following steps: S201 , obtaining a plurality of motion stage heights measured by a motion stage z-axis interferometer at a preset frequency, and obtaining an initial object plane height of a silicon wafer measured by a leveling and focusing system at a preset frequency.

[0029] Alternatively, a set of measurement data can be acquired using the maximum sampling frequency of the motion stage z-interferometer (e.g., f = 5000 Hz), and then subjected to fast Fourier transform and spectrum analysis. However, according to Nyquist's law, only signals within the range of f = fs / 2 are valid signals that are sampled. This means that the spectrum range of valid high-frequency signals that can be acquired by the motion stage z-interferometer is [0, 2500] Hz. Figure 3 The time domain variation diagram of the motion stage in one sampling period, and Figure 4 The frequency domain variation diagram of the motion stage within a sampling period is shown. By intercepting the height information of the motion stage z-axis interferometer within a sampling period (such as 0.16s) and performing detrending processing, as well as performing spectrum analysis, it can be determined that the frequencies with larger amplitudes are mainly between 0 and 300 Hz. Figure 3 The horizontal axis represents time, and the vertical axis represents the height information obtained by the z-axis interferometer of the motion stage. Figure 4 The horizontal axis represents frequency, and the vertical axis represents amplitude.

[0030] Alternatively, for the leveling and focusing system, the maximum sampling frequency that can be supported is 625HZ. However, since the leveling and focusing system is affected by factors such as its own measurement spot size, sampling frequency, and exposure scanning speed, the bandwidth that the leveling and focusing system can sense is limited. Therefore, by obtaining the measured height values of the five light spots of the leveling and focusing system in one sampling period (such as 0.16s) and performing demagnetization processing, refer to Figure 5 The time domain variation diagram of the leveling and focusing system in one sampling period, and Figure 6 The frequency domain variation diagram of the leveling and focusing system within a sampling period shown in the figure shows that the effective signal frequency range of the leveling and focusing system is [0, 316] Hz.

[0031] That is to say, although the sampling frequencies of the motion stage z-interferometer and the leveling and focusing system are different, spectrum analysis shows that in the measurement data of the motion stage z-interferometer, the signals with large amplitudes are concentrated in the 0~300Hz area, while the leveling and focusing system, although its maximum effective range supports up to 316Hz, mainly operates in the low frequency band of 0~300Hz. Figure 7 The frequency spectrum of the motion stage z-direction interferometer and the leveling and focusing system at 0~300Hz is shown. It is obvious that there is a certain consistency between the two in the frequency domain range of 0~300Hz. Therefore, this application limits the preset sampling frequency of the motion stage z-direction interferometer and the leveling and focusing system to the range of 0~300Hz, that is, the motion stage z-direction interferometer and the leveling and focusing system both measure the motion stage height and the initial object plane height of the silicon wafer in the common effective perception frequency region where the preset frequency is less than or equal to the preset threshold (300Hz). Among them, Figure 7 The horizontal axis represents frequency, the vertical axis represents amplitude, the red line fls represents the spectrum distribution of the leveling and focusing system in the range of 0 to 300 Hz, and the blue line ws represents the spectrum distribution of the motion stage z-direction interferometer in the range of 0 to 300 Hz.

[0032] Optionally, the initial object plane height includes: the measured heights of multiple light spots, and the distribution of the multiple light spots can refer to Figure 8 As shown in FIG. 1 , L represents half the distance between light spot 2 and light spot 3. d represents the distance between light spot 3 and light spot 1. It should be understood that the distances between light spot 2 and light spot 1, light spot 4 and light spot 1, and light spot 5 and light spot 1 are all d.

[0033] S202 , performing error compensation on the measured height of each light spot in each measurement round based on the height of the moving stage in each measurement round, to obtain a compensated height of each light spot in each measurement round.

[0034] Optionally, since the motion stage itself has vibrations that affect the measurement of the silicon wafer by the leveling and focusing system, the motion stage height measured by the motion stage z-axis interferometer is used to correct the initial object plane height of the silicon wafer measured by the leveling and focusing system to compensate for the error of the initial object plane height of the silicon wafer, and finally obtain the actual surface shape information of the silicon wafer after removing the influence of the motion stage.

[0035] Optionally, for each measurement run, the height of the motion stage measured by the motion stage z-axis interferometer during that measurement run, specifically the z-axis height of the motion stage, is used to perform error compensation on the heights of each light spot on the silicon wafer measured by the leveling and focusing system during that measurement run, thereby obtaining the compensated heights of each light spot during that measurement run. By performing multiple measurement runs, random errors in the measurement process can be eliminated.

[0036] S203 , obtaining a target height of each light spot according to the compensated height of each light spot in each measurement round.

[0037] Optionally, after error compensation, each light spot has a compensated height in different measurement rounds. The target height that best represents the position of each light spot can be determined based on the compensated height of each light spot in each measurement round. Specifically, as shown in the following formula (1), the target height of each light spot can be determined by taking the average value: (1) in, Indicates light spot, Indicates the The target height of the spot, represents the measurement round, , Indicates the The next measurement round The compensated height of a light spot represents the stable height of the silicon wafer surface relative to the ideal focal plane of the lithography machine optical system.

[0038] S204: Perform fitting processing on the target heights of all light spots to determine the actual surface shape information of the silicon wafer.

[0039] Optionally, the actual surface shape information of the silicon wafer includes focal length information and tilt information. Based on the target height of each spot, a plane fitting is performed based on the target heights of all spots to reconstruct the surface shape of the entire silicon wafer. Specifically, the plane can be fitted using the least squares method, and the actual surface shape information of the silicon wafer can be determined by solving the least squares solution of the fitted plane equation.

[0040] Based on this, according to the lithography machine object plane measurement method of the embodiment of the present application, the measurement data output by the motion stage z-direction interferometer and the leveling and focusing system are all within a preset frequency, and the preset frequency is less than or equal to the preset threshold value, which limits the common effective signal range of the motion stage z-direction interferometer and the leveling and focusing system. In the presence of an irremovable low-frequency working environment, the vibration error caused by some components in the lithography machine optical system can be avoided. On this basis, the error compensation of the silicon wafer measurement value is performed based on the motion stage data, thereby removing the interference component caused by the motion stage vibration and improving the authenticity of the silicon wafer surface height measurement. In addition, the data and error compensation under multiple measurement rounds are combined to effectively avoid the influence of random errors on the final result. This not only improves the measurement accuracy of the leveling and focusing system, but also makes the final silicon wafer surface shape information more real and reliable, and can accurately reflect the actual surface characteristics of the silicon wafer.

[0041] Figure 9 FIG2 shows a flow chart of a method for determining height after compensation provided by an embodiment of the present application. Figure 9As shown, the above step S202 performs error compensation on the measured height of each light spot in each measurement round based on the height of the moving stage in each measurement round to obtain the compensated height of each light spot in each measurement round, which specifically includes the following steps: S901: Determine the jitter height of the moving platform in the current measurement round based on the height of the moving platform in the current measurement round and the stable height of the moving platform.

[0042] The height of the moving platform is the measured height obtained by the z-axis interferometer of the moving platform, and the stable height of the moving platform is the height of the moving platform in a stationary and stable state.

[0043] Alternatively, depending on the mechanical structure of the lithography machine's optical system, factors affecting unstable spot measurement data from the leveling and focusing system include: noise caused by external environmental interference, vibration caused by the mechanical resonance of the motion stage (primarily including vibration from shock absorbers and air bearings), vibration from silicon wafer adsorption, and intrinsic vibration of the charge-coupled device (CCD) sensor. Factors affecting unstable measurement data from the motion stage's z-axis interferometer include: CCD sensor noise, noise from environmental interference, and jitter caused by the mechanical resonance of the motion stage. Furthermore, even after the shock absorbers isolate these low frequencies, low-frequency vibrations of smaller amplitude may still exist.

[0044] That is to say, the height of the motion table measured by the z-axis interferometer includes the true height, the vibration caused by mechanical resonance, and other vibrations (such as air bearing vibration, shock absorber vibration, etc.), as shown in the following formulas (2) and (3): (2) in, Indicates the The vibration caused by mechanical resonance under the measurement rounds, Indicates the The vibration of the shock absorber under the measurement rounds, Indicates the Air flotation vibration under three measurement rounds.

[0045] (3) in, Indicates the The measured height obtained by the z-axis interferometer of the motion stage in each measurement round is: Indicates the The stable height of the motion platform under each measurement round, Indicates the The vibration caused by mechanical resonance under each measurement round, Indicates the The noise caused by the first additional reason under the measurement rounds.

[0046] Optionally, when the optical system of the lithography machine operates normally, the noise generated by the first additional cause is very small and can be ignored in actual calculations. On this basis, based on the above formulas (2) and (3), the following formula (4) can be obtained: (4) in, Indicates the The measured height obtained by the z-axis interferometer of the motion stage in each measurement round is: Indicates the The stable height of the motion platform under each measurement round, Indicates the The jitter height of the motion stage under each measurement round.

[0047] Specifically, for the current measurement round, based on the above formula (4), the jitter height of the motion stage in the current measurement round can be determined by using the measurement height obtained by the motion stage z-axis interferometer in the current measurement round and the stable height of the motion stage.

[0048] S902 : performing error compensation on the measured height of the current light spot in the current round based on the jitter height of the moving stage in the current measurement round to obtain a compensated height of the current light spot in the current round.

[0049] The compensated height represents the stable height of the silicon wafer surface relative to the ideal focal plane of the lithography machine optical system.

[0050] Optionally, the initial object plane height of the silicon wafer measured by the leveling and focusing system includes the true height, the vibration of the motion stage, the mechanical vibration of the leveling and focusing system itself, and the wafer adsorption vibration, as shown in the following formula (5): (5) in, Indicates the The initial object plane height (i.e. the measured height of the light spot) under each measurement round is Indicates the The stable height of the silicon wafer surface relative to the ideal focal plane of the lithography machine optical system under each measurement round, Indicates the The jitter height of the motion stage under the measurement rounds, Indicates the The mechanical vibration of the leveling and focusing system itself is adjusted during each measurement round. Indicates the Wafer adsorption vibration under each measurement round, Indicates the The noise caused by the second additional reason under the measurement round.

[0051] Furthermore, since the frequencies of the motion stage z-axis interferometer and the leveling and focusing system are limited to 0-300 Hz after spectrum analysis, in this case, the specific composition of the motion stage height measured by the motion stage z-axis interferometer and the specific composition of the initial object plane height of the silicon wafer measured by the leveling and focusing system can be referred to as shown in the following formulas (6) and (7), respectively: (6) in, Indicates the The measured height obtained by the z-axis interferometer of the motion stage in each measurement round is: Indicates the The stable height of the motion platform under each measurement round, Indicates the The vibration caused by mechanical resonance under each measurement round, Indicates the The vibration of the shock absorber under the measurement rounds, Indicates the Air flotation vibration under three measurement rounds.

[0052] (7) in, Indicates the The next measurement round The measured height of a light spot, Indicates the The next measurement round The compensated height of each spot, that is, the stable height of the silicon wafer surface relative to the ideal focal plane of the lithography machine optical system, Indicates the The jitter height of the motion stage under the measurement rounds, Indicates the Wafer adsorption vibration under three measurement runs.

[0053] Optionally, when the optical system of the lithography machine operates normally, the noise generated by the second additional reason is very small and can be ignored in actual calculations. When the wafer (silicon wafer) adsorption is stable, the wafer adsorption vibration It will approach 0 infinitely, so it can be ignored in actual calculations. Therefore, combining the above formulas (6) and (7), we can derive the following formula (8): (8) in, Indicates the The next measurement round The measured height of a light spot, Indicates the The next measurement round The compensated height of each spot, that is, the stable height of the silicon wafer surface relative to the ideal focal plane of the lithography machine optical system, Indicates the The jitter height of the motion stage under each measurement round.

[0054] On this basis, the above step S902 specifically includes calculating the compensated height of the current light spot according to the above formula (8). Optionally, taking a light spot as an example, refer to Figure 10 As shown in the figure, the horizontal axis represents time and the vertical axis represents castration value. The castration value of the leveling and focusing system under 100 measurement rounds within a sampling period (0.16s) is taken (as shown in the figure). Figure 10 The orange curve fls in the middle) and the demagnetization value of the motion stage z-axis interferometer (as shown in Figure 10 The blue curve ws in the middle shows that the leveling and focusing data after compensation calculated by the method provided by this application is more stable. Figure 11 As shown, the horizontal axis represents time, the vertical axis represents height value, the red curve fls represents the original measurement value of the leveling and focusing system before compensation, and the blue curve fls new represents the processed value of the leveling and focusing system after compensation. The accuracy of the leveling and focusing system can be calculated by three times the standard deviation of multiple measurements. Figure 11 By calculating the two sets of data corresponding to the two curves, it can be found that the accuracy of the leveling and focusing system is reduced from 60.2nm to 46.3nm.

[0055] Based on this, for the high-precision application scenario of measuring silicon wafer surface topography in semiconductor manufacturing, the vibration of the motion stage itself introduces additional errors. This application monitors the changes in the motion stage height in real time and performs error compensation based on these changes to adjust the measurement results of the silicon wafer surface height, thereby effectively eliminating the systematic errors caused by the instability of the motion stage. Furthermore, combining multiple measurements reduces the impact of random errors on the final results.

[0056] As a possible implementation method, the above-mentioned step S204 fits the target heights of all light spots to determine the actual surface shape information of the silicon wafer, including: using the least squares method to fit the target heights of multiple light spots to determine the actual surface shape information of the silicon wafer within the light spot range of the leveling and focusing system.

[0057] Optionally, the target height of the light spot includes: coordinate, Coordinates and coordinate positions Wafer height at By using the target heights of multiple light spots, the surface morphology of the silicon wafer in the exposure field is regarded as a plane, and the plane is fitted using the least squares method. The corresponding plane equation is shown in the following formula (9): (9) in, Indicates the coordinate position The height of the silicon wafer at Represents the first parameter, Represents the second parameter, Represents the third parameter, Represents the horizontal coordinate of the light spot on the silicon wafer surface, Represents the vertical coordinate of the light spot on the silicon wafer surface.

[0058] Optionally, based on the above formula (9), the position of each light spot on the silicon wafer surface is coordinate, Coordinates and coordinate positions Wafer height at Input them into the above formula (9) for plane fitting and solve the least squares solution. Specifically, the first parameter It can be determined using the following formula (10): (10) in, Represents the first parameter, Indicates the coordinate position The height of the silicon wafer at the edge, L represents half of the distance between the two edge spots (see Figure 8 for L in the diagram).

[0059] For example, the first parameter is obtained based on the above formula (10): , the first parameter It can represent the average height of the exposure field of view and can also be used as the focal length information in the actual surface information of the silicon wafer.

[0060] Furthermore, when the leveling and focusing accuracy is Figure 8 The ratio of the maximum horizontal or vertical distance of the area formed by the five light spots shown in is greater than and hour( By taking RX or RY, where RX and RY represent the tilt information within the wafer's actual surface shape information, we can obtain RX equal to the third parameter C, and RY equal to the second parameter B. Thus, by fitting the first parameter A, the second parameter B, and the third parameter C using the least squares method, we can obtain the wafer's actual surface shape information, including the focal length information Z, the tilt information RX, and the tilt information RY.

[0061] It should be noted that in the OXYZ coordinate system, O represents the origin, the Z axis coincides with the optical axis of the projection objective, the Y axis represents the scanning direction of the lithography machine, and the X and Y planes coincide with the zero plane and focal plane of the leveling and focusing system, respectively. The entire OXYZ coordinate system conforms to the right-hand rule. Based on this, the focal length information Z represents the height from the focal plane, the tilt information RX represents the rotation angle about the X axis, and the tilt information RY represents the rotation angle about the Y axis.

[0062] Based on this, the present application compensates the measurement data of the leveling and focusing system by the jitter of the motion stage, so that the RX, RY and Z values returned by the leveling and focusing system can more realistically describe the surface of the silicon wafer.

[0063] As a possible implementation method, before obtaining the initial object plane height of the silicon wafer measured by the leveling and focusing system according to the preset frequency, the method also includes: controlling the leveling and focusing system to emit multiple light spots to the base plate, and performing plane consistency detection on the multiple light spots emitted to the base plate. If the plane consistency detection fails, adjusting the zero plane of the leveling and focusing system.

[0064] Optionally, in order to ensure the accuracy and consistency of the measurement results output by the leveling and focusing system, it is necessary to ensure that the zero plane of the leveling and focusing system itself coincides with the ideal focal plane of the lithography machine optical system, and whether the spot difference meets the standard, that is, to self-check or calibrate the leveling and focusing system to ensure that the measurement reference of the leveling and focusing system is accurate.

[0065] Optionally, combined Figure 1 In the description of the optical system of the lithography machine, a fixed base plate FM is set on the micro-motion stage. The surface of the base plate FM is a film surface with high reflectivity and very flat. Multiple light spots are emitted to the base plate FM by controlling the leveling and focusing system, and a light spot is used to scan the base plate FM to find a preset flat area on the base plate FM. The preset flat area is slightly larger than the light spot size (the preset flat area is, for example, 2*2mm).

[0066] Optionally, the above-mentioned process of performing plane consistency detection on the multiple light spots emitted onto the base plate specifically includes: Step A: Select one light spot from the multiple light spots of the leveling and focusing system in sequence as an effective light spot.

[0067] For example, continue to refer to Figure 8 As shown, Figure 8 Taking the five light spots 1, 2, 3, 4 and 5 shown in FIG as an example, one of the light spots 1, 2, 3, 4 and 5 is selected in sequence as the effective light spot.

[0068] Step B: Move the micro-motion stage to move the center position of the preset flat area in the base plate to the effective light spot.

[0069] For example, taking the light spot 1 as an effective light spot, the fine-motion stage is moved to move the center position of the preset flat area to the position where the light spot 1 is located, so as to perform single-point height measurement on the light spot 1 .

[0070] Step C: Obtain a single-point height value obtained by measuring the single-point height of the effective light spot by the leveling and focusing system.

[0071] For example, based on moving the center position of the preset flat area to the effective light spot, the leveling and focusing system can measure and output the height value of the current effective light spot. Based on the communication connection between the measuring device and the leveling and focusing system, the measuring device can directly obtain the single-point height value obtained by the leveling and focusing system for measuring the single-point height of the effective light spot.

[0072] Step D: Repeat the above steps A to C to obtain the single point height value of each light spot.

[0073] For example, continue to refer to Figure 8 As shown, for Figure 8 Repeat steps A to C for each light spot shown in the figure to obtain the single-point height values of the five light spots, which are recorded as h1, h2, h3, h4, and h5 respectively.

[0074] Step E: Determine the height difference of each light spot relative to the center position according to the single-point height value of each light spot. If the height difference is greater than a preset threshold, adjust the zero plane of the leveling and focusing system.

[0075] For example, the center position is the origin position of the leveling and focusing system coordinate system, and the preset threshold is used to indicate the measurement accuracy, for example, 150nm. Figure 8 As shown in the figure, based on the single-point height values h1, h2, h3, h4, and h5 of the five light spots (Light Spot 1, Light Spot 2, Light Spot 3, Light Spot 4, and Light Spot 5), the height difference of each light spot relative to the center position is calculated. If the height difference is greater than a preset threshold, the zero plane of the leveling and focusing system is adjusted. If the measurement accuracy is still not met after adjusting the zero plane, the five linear sensors CCD of the leveling and focusing system need to be adjusted to recalibrate the leveling and focusing system.

[0076] Furthermore, after obtaining the height difference value of each light spot relative to the center position, the difference between the maximum and minimum values of the sum of the height difference values of each light spot can be further calculated. If the difference is greater than a preset threshold, the zero plane of the leveling and focusing system is also adjusted.

[0077] Based on this, the present application performs consistency detection on multiple light spots. When the detection finds that the heights of multiple light spots are inconsistent, it means that the zero plane of the leveling and focusing system is not parallel or aligned with the base plate. In this case, it is necessary to adjust the zero plane of the leveling and focusing system to recalibrate the leveling and focusing system to ensure that all height values measured by the leveling and focusing system are relative to a unified and accurate reference plane.

[0078] The present application embodiment also provides a measuring device 1200, such as Figure 12 FIG. 1 is a schematic diagram of the structure of a measurement device 1200 provided in an embodiment of the present application, comprising: a processor 1201, a memory 1202, and optionally, a bus 1203. The memory 1202 stores machine-readable instructions executable by the processor 1201. When the measurement device 1200 is running, the processor 1201 communicates with the memory 1202 via the bus 1203. When the machine-readable instructions are executed by the processor 1201, the steps of any of the above methods for measuring an object plane of a lithography machine are performed.

[0079] An embodiment of the present application further provides a computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, the steps of any of the above methods for measuring the object plane of a lithography machine are executed.

[0080] Those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific working process of the system and device described above can refer to the corresponding process in the method embodiment, and will not be repeated in this application. In the several embodiments provided in this application, it should be understood that the disclosed system, device and method can be implemented in other ways. The device embodiments described above are merely schematic. For example, the division of the modules is only a logical function division. There may be other division methods in actual implementation. For example, multiple modules or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some communication interfaces, indirect coupling or communication connection of devices or modules, which can be electrical, mechanical or other forms.

[0081] In addition, the functional units in the various embodiments of the present application can be integrated into a single processing unit, each unit can exist physically separately, or two or more units can be integrated into a single unit. If the functions are implemented in the form of software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the portion that contributes to the prior art, or a portion of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions for causing a computer device (which can be a personal computer, server, or network device, etc.) to execute all or part of the steps of the method described in the various embodiments of the present invention. The aforementioned storage medium includes various media that can store program code, such as a USB flash drive, a mobile hard drive, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, or an optical disk.

[0082] The above is only a specific implementation method of the present application, but the protection scope of the present application is not limited thereto. Any technician familiar with this technical field can easily think of changes or replacements within the technical scope disclosed in this application, which should be covered by the protection scope of the present application.

Claims

1. A method for measuring an object plane of a lithography machine, characterized in that: include: Acquiring multiple motion stage heights measured by a motion stage z-axis interferometer at a preset frequency, and acquiring an initial object plane height of the silicon wafer measured by a leveling and focusing system at the preset frequency, wherein the preset frequency is less than or equal to a preset threshold, and the initial object plane height includes: measured heights of multiple light spots; Based on the height of the moving stage in each measurement round, the error of the measured height of each light spot in each measurement round is compensated to obtain the compensated height of each light spot in each measurement round; According to the compensated height of each light spot in each measurement round, the target height of each light spot is obtained; The target heights of all light spots are fitted to determine actual surface shape information of the silicon wafer, where the actual surface shape information includes focal length information and tilt information.

2. The method according to claim 1, characterized in that The error compensation of the measured height of each light spot in each measurement round based on the height of the moving stage in each measurement round to obtain the compensated height of each light spot in each measurement round includes: Determining a jitter height of the motion stage in the current measurement round based on the motion stage height and the stable height of the motion stage in the current measurement round, wherein the motion stage height is a measured height obtained by a z-direction interferometer of the motion stage; Based on the jitter height of the moving stage in the current measurement round, the measured height of the current light spot in the current round is error compensated to obtain the compensated height of the current light spot in the current round. The compensated height represents the stable height of the silicon wafer surface relative to the ideal focal plane of the optical system of the lithography machine.

3. The method according to claim 2, characterized in that The determining the jitter height of the moving platform in the current measurement round based on the moving platform height and the stable height of the moving platform in the current measurement round includes: Based on the formula Calculating the shaking height of the motion platform; in, represents the measured height obtained by the z-axis interferometer of the motion stage, represents the stable height of the motion platform, Indicates the jitter height of the motion platform.

4. The method according to claim 2, characterized in that The error compensation for the measured height of the current light spot in the current round based on the jitter height of the moving stage in the current measurement round to obtain the compensated height of the current light spot in the current round includes: Based on the formula Calculate the compensated height of the current light spot; in, Indicates the measured height of the current light spot, that is, the measured height of the silicon wafer surface relative to the ideal focal plane of the lithography machine optical system. Indicates the compensated height of the current light spot, that is, the stable height of the silicon wafer surface relative to the ideal focal plane of the lithography machine optical system. Indicates the jitter height of the motion platform.

5. The method according to claim 1, wherein The fitting process for the target heights of all light spots to determine the actual surface shape information of the silicon wafer includes: The target heights of the multiple light spots are fitted using the least square method to determine actual surface shape information of the silicon wafer within the light spot range of the leveling and focusing system.

6. The method according to claim 5, characterized in that The target height of the light spot includes: coordinate, Coordinates and coordinate positions Wafer height at ; The method of fitting the target heights of the plurality of light spots using the least square method to determine the actual surface shape information of the silicon wafer within the light spot range of the leveling and focusing system includes: The light spots on the surface of the silicon wafer coordinate, Coordinates and coordinate positions Wafer height at Enter the formulas separately Perform plane fitting in and obtain the least squares solution; among them, Indicates the coordinate position The height of the silicon wafer at Represents the first parameter, Represents the second parameter, Represents the third parameter, Represents the horizontal coordinate of the light spot on the silicon wafer surface, Indicates the vertical coordinate of the light spot on the silicon wafer surface; The first parameter corresponding to the least squares solution is used as the focal length information, and the second parameter and the third parameter corresponding to the least squares solution are used as the tilt information.

7. The method according to claim 1, characterized in that Before obtaining the initial object plane height of the silicon wafer measured by the leveling and focusing system according to the preset frequency, the method further includes: Controlling the leveling and focusing system to emit multiple light spots toward the base plate; A plane consistency test is performed on the multiple light spots emitted onto the base plate. If the plane consistency test fails, the zero plane of the leveling and focusing system is adjusted.

8. The method according to claim 7, characterized in that The performing plane consistency detection on the multiple light spots emitted onto the base plate, and adjusting the zero plane of the leveling and focusing system if the plane consistency detection fails, comprises: Step A: selecting one light spot from the multiple light spots of the leveling and focusing system in sequence as an effective light spot; Step B: moving the micro-motion stage to move the center position of the preset flat area in the base plate to the effective light spot; Step C: obtaining a single point height value obtained by measuring the single point height of the effective light spot by the leveling and focusing system; Step D: Repeat steps A to C above to obtain the single point height value of each light spot; Step E: determining a height difference value of each light spot relative to a center position according to a single-point height value of each light spot; if the height difference value is greater than a preset threshold, adjusting the zero plane of the leveling and focusing system.

9. A lithography optical system, characterized in that: The optical system of the lithography machine includes at least: a motion stage z-axis interferometer, a leveling and focusing system, a motion stage, and a measuring device. The motion stage includes at least a fine-motion stage and a wafer chuck. The wafer chuck is fixed on the fine-motion stage, and the silicon wafer is adsorbed on the wafer chuck. The motion stage z-direction interferometer, the leveling and focusing system, and the micro-motion stage are respectively connected to the measuring equipment for communication; The motion stage z-direction interferometer is used to measure the height of the motion stage under the control of the measuring device; The leveling and focusing system is used to measure the initial object plane height of the silicon wafer under the control of the measuring device; The measuring device is used to perform the steps of the lithography machine object plane measurement method according to any one of claims 1 to 8 to measure and obtain the actual surface shape information of the silicon wafer.

10. The system according to claim 9, characterized in that The optical system of the photolithography machine further includes: a base plate; The base plate is arranged on the micro-motion stage, and the base plate includes a preset flat area.

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