Off-axis alignment light source system and alignment method

Abstract

The invention provides an off-axis alignment light source system and an alignment method, and is applied to the technical field of semiconductor manufacturing. The alignment light source comprises a light source module, a light amplification module and a system control module; the system control module respectively controls the light source module and the light amplification module; the light source module outputs illumination light under the control action of the system control module; the light amplification module receives the illumination light; the light amplification module amplifies the received illumination light under the control action of the system control module; and the light amplification module outputs the amplified illumination light for illuminating the alignment mark of the silicon wafer. Light source switching is provided for processes with different illumination spectrum width requirements, light source output power control is provided for processes with different alignment imaging signal-to-noise ratio requirements, Q-switching control of the light source is achieved for processes with different alignment exposure time requirements, and the process adaptability and working efficiency of a silicon wafer alignment system are effectively improved.

Description

Technical Field

[0001] The present application relates to the field of semiconductor manufacturing technology, and in particular to an off-axis alignment light source system and an alignment method. Background Art

[0002] In the process of semiconductor integrated circuit manufacturing, the complete process of chip manufacturing usually requires dozens of lithography exposures. Except for the first lithography, the remaining layers of lithography must be accurately positioned with the graphics left by the previous layer exposure before exposure, so as to ensure that each layer of graphics has the correct relative position, that is, the overlay accuracy. The overlay accuracy directly depends on the alignment accuracy when aligning the upper and lower adjacent layers. Normally, the overlay accuracy is 1 / 3 to 1 / 5 of the resolution index of the lithography machine, while the alignment accuracy is only allowed to be within 1 / 3 of the overlay accuracy, which puts forward higher accuracy requirements on the alignment system of the lithography equipment.

[0003] In the field of projection lithography, silicon wafer alignment mostly adopts off-axis alignment. The positional relationship between the silicon wafer and the mask is indirectly obtained through the alignment mark on the workpiece stage reference plate as a transition reference, that is, the positions of the silicon wafer and the mask in the workpiece stage coordinate system are first established respectively, and then the relative positional relationship between the silicon wafer and the mask is indirectly obtained. Among them, the establishment of the position of the silicon wafer in the workpiece stage coordinate system, that is, silicon wafer alignment, is more complicated and needs to be established through reference marks. Aligning the alignment mark of the silicon wafer with the reference mark becomes the key to the problem. Off-axis alignment requires an alignment light source independent of the exposure light source. Therefore, the design of the alignment light source becomes an important research part of silicon wafer off-axis alignment.

[0004] Based on this, a new technical solution is needed. Summary of the invention

[0005] In view of this, embodiments of the present disclosure provide an off-axis alignment light source system and an alignment method.

[0006] The embodiments of this specification provide the following technical solutions:

[0007] An embodiment of the present specification provides an off-axis alignment light source system, comprising an alignment light source; the alignment light source comprises a light source module, an optical amplification module and a system control module; the system control module controls the light source module and the optical amplification module respectively; the light source module outputs illumination light under the control of the system control module; the optical amplification module receives illumination light; the optical amplification module amplifies the received illumination light under the control of the system control module; the optical amplification module outputs the amplified illumination light for illuminating an alignment mark of a silicon wafer.

[0008] Preferably, the light source module includes multiple independent light sources; and the system control module controls and determines to select one of the multiple independent light sources.

[0009] Preferably, the multiple independent light sources include a first independent light source and a second independent light source; the first independent light source includes a strongly correlated laser, a first temperature controller and a first current controller; the second independent light source includes a weakly correlated laser, a second temperature controller and a second current controller; the strongly correlated laser outputs narrow-band strongly coherent laser under the control of the first temperature controller and the first current controller; the weakly coherent laser outputs broadband weakly coherent laser under the control of the second temperature controller and the second current controller.

[0010] Preferably, the light source module also includes an optical multiplexer; the optical multiplexer receives strong coherent laser or weak coherent laser and outputs it as illumination light to the optical amplification module; the system control module includes a computing control and input-output unit; the computing control and input-output unit outputs a first control signal to control the selection to one of a first current controller and a second current controller; the computing control and input-output unit outputs a second control signal to the optical multiplexer; the computing control and input-output unit outputs a third control signal to the optical amplification module.

[0011] Preferably, the strongly correlated laser is a distributed feedback semiconductor laser; the weakly correlated laser is a superluminescent diode; the wavelength of the distributed feedback semiconductor laser includes one of 980nm, 1310nm, and 1550nm; the spectrum range of the superluminescent diode is 800nm ​​to 880nm.

[0012] Preferably, the optical amplification module includes an optical amplifier, a front optical isolator and a rear optical isolator; the front optical isolator receives the illumination light and is used to eliminate the illumination light reflected back into the light source module after being output by the light source module; the optical amplifier is used to amplify the light intensity of the illumination light processed by the front optical isolator; the rear optical isolator is used to eliminate the illumination light reflected back into the optical amplifier after being output by the optical amplifier.

[0013] Preferably, the optical amplifier is an erbium-doped fiber amplifier.

[0014] Preferably, the system control module sets a periodic change in the bias current in the light source module to adjust the quality factor of the light source module. When the bias current is less than the working threshold of the light source module, the light source module enters a closed state; when the bias current is greater than the working threshold of the light source module, the light source module enters an open state.

[0015] Preferably, the off-axis alignment light source system further comprises a first beam splitter, an objective lens system, a reflector, a light receiving system, a second beam splitter, a first photodetector and a second photodetector; the illumination light output by the alignment light source passes through the first beam splitter and the objective lens system to irradiate the alignment mark on the silicon wafer, and the light irradiated on the alignment mark is diffracted to obtain diffracted light; the objective lens system partially collects the diffracted light, and the diffracted light partially collected by the objective lens system passes through the reflector and the light receiving system and is divided into a first beam of light and a second beam of light by the second beam splitter; the first photodetector detects the first beam of light to form an alignment image; the second photodetector detects the second beam of light to obtain a level value, and feeds the level value back to the system control module; the system control module determines whether the optical power of the diffracted light meets the signal-to-noise ratio requirement of the alignment image according to the level value; if the optical power of the diffracted light meets the signal-to-noise ratio requirement of the alignment image, the alignment process continues; if the optical power of the diffracted light does not meet the signal-to-noise ratio requirement of the alignment image, the system control module calculates the compensation amount for controlling the light source module or the optical amplifier module, and adjusts the output power of the illumination light output by the alignment light source.

[0016] The embodiment of the present specification also provides an off-axis alignment method, which uses the off-axis alignment light source system, including the following steps: step S1: the system control module controls the selection of an independent light source according to process requirements, and the selected independent light source outputs illumination light; step S2: the light amplification module receives the illumination light, and the system control module controls the light amplification module to amplify the received illumination light; step S3: the illumination light output by the light amplification module is irradiated with an alignment mark on a silicon wafer through a first beam splitter and an objective lens system, and the light irradiated on the alignment mark is diffracted to obtain diffracted light; step S4: the objective lens system partially collects the diffracted light, and the diffracted light collected by the objective lens system is then reflected by a reflector and a light receiving system. , divided into a first beam of light and a second beam of light by a second beam splitter; the first photodetector detects the first beam of light to form an alignment image; the second photodetector detects the second beam of light to obtain a level value; step S5: the second photodetector feeds back the level value to the system control module; the system control module determines whether the optical power of the diffracted light meets the signal-to-noise ratio requirement of the alignment image according to the level value; step S6: if the optical power of the diffracted light meets the signal-to-noise ratio requirement of the alignment image, the alignment process continues; if the optical power of the diffracted light does not meet the signal-to-noise ratio requirement of the alignment image, the system control module calculates the compensation amount for controlling the light source module or the optical amplifier module, and adjusts the output power of the illumination light output by the alignment light source.

[0017] Compared with the prior art, the at least one technical solution adopted in the embodiments of this specification can achieve the following beneficial effects:

[0018] The invention proposes to switch multiple independent light sources, such as a switchable silicon wafer off-axis alignment light source system based on a directly modulated distributed feedback semiconductor laser and a directly modulated superluminescent diode, to provide light source switching for processes with different illumination spectrum width requirements, to provide light source output power control for processes with different alignment imaging signal-to-noise ratio requirements, and to implement light source Q-switching control for processes with different alignment exposure time requirements, thereby effectively improving the process adaptability and work efficiency of the silicon wafer alignment system. In addition, the silicon wafer off-axis alignment light source system proposed by the invention reduces the complexity and development cost of the system, reduces the spatial structure size, and further opens up the development prospects of the integration of alignment light source systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0020] Figure 1 This is a schematic diagram of the structure of the alignment light source in the silicon wafer off-axis alignment light source system in this application;

[0021] Figure 2 This is a schematic diagram of the principle of aligning the light source in the silicon wafer off-axis alignment light source system in this application;

[0022] Figure 3 This is a schematic diagram of the structure of the silicon wafer off-axis alignment light source system in this application.

[0023] Figure numerals: 100, light source module; 11, distributed feedback semiconductor laser; 12, first temperature controller; 13, first current controller; 14, superluminescent diode; 15, second temperature controller; 16, second current controller; 17, optical multiplexer; 200, optical amplification module; 21, front optical isolator; 22, optical amplifier; 23, rear optical isolator; 300, system control module; 31, computing control and input-output unit; 400, alignment light source; 61, alignment mark; 62, objective lens; 63, first spectrometer; 64, reflector; 65, light receiving system; 66, second spectrometer; 67, second photodetector; 68, first photodetector. DETAILED DESCRIPTION

[0024] The embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0025] The following describes the implementation methods of the present application through specific examples, and those skilled in the art can easily understand other advantages and effects of the present application from the contents disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The present application can also be implemented or applied through other different specific implementation methods, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present application. It should be noted that, in the absence of conflict, the following embodiments and the features in the embodiments can be combined with each other. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without making creative work belong to the scope of protection of the present application.

[0026] It should be noted that various aspects of the embodiments within the scope of the appended claims are described below. It should be apparent that the aspects described herein can be embodied in a wide variety of forms, and any specific structure and / or function described herein is merely illustrative. Based on the present application, it should be understood by those skilled in the art that an aspect described herein can be implemented independently of any other aspect, and two or more of these aspects can be combined in various ways. For example, any number and aspect described herein can be used to implement the device and / or practice the method. In addition, other structures and / or functionalities other than one or more of the aspects described herein can be used to implement this device and / or practice this method.

[0027] It should also be noted that the illustrations provided in the following embodiments are only schematic illustrations of the basic concept of the present application. The drawings only show components related to the present application rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0028] Additionally, in the following description, specific details are provided to facilitate a thorough understanding of the examples. However, it will be understood by those skilled in the art that the examples can be practiced without these specific details.

[0029] In view of this, the applicant conducted in-depth research and improvement exploration on the alignment system of the lithography equipment and the silicon wafer off-axis alignment system of the lithography equipment, and found that: the Chinese invention patent document with publication number CN101487991A discloses a silicon wafer alignment system, which uses a semiconductor laser to emit a single-wavelength laser pumped fiber laser, reducing the difficulty of designing the optical module of the silicon wafer alignment system. However, this light source has three unavoidable shortcomings. First, the fiber laser resonant cavity includes devices or equipment such as modulators and amplifiers, making the light source structure complicated. Secondly, the output of the fiber laser is a fixed 1550nm wavelength laser, and its process adaptability is single. Finally, since the resonant cavity has been fixed by the optical fiber loop, it is difficult to adjust the period of the mode-locked pulse output, and the pulse period is unstable because the optical fiber is susceptible to temperature.

[0030] The Chinese invention patent document with publication number CN104155849A discloses a silicon wafer alignment light source system for photolithography equipment. The light source of the alignment system adopts an internal amplitude modulation method to adjust the fluctuation of the light source, reduce the development cost of the silicon wafer alignment system, reduce the spatial structure size of the system, and improve the signal anti-interference and alignment repeatability. These overcome the shortcomings of fiber lasers to a certain extent. However, although the alignment laser light source in this system adopts precise electrical control, part of the output light is fed back to the control module and is only used for light beam collection, analysis and processing, resulting in a low degree of automation of the light source.

[0031] The Chinese invention patent document with publication number CN102243442A discloses a device for amplitude modulation of a light source for silicon wafer alignment. The system uses an amplitude modulation device of a light source with a feedback loop, realizes automatic optimization of power parameters, solves the inaccurate and inconvenient manual adjustment of parameters in the original device, and improves the adaptability of the light source illumination optical path to changes in the external environment, improves the device's resistance to external interference, and ensures the alignment accuracy of the silicon wafer. However, the light source amplitude modulation device only focuses on improving the stability of the light output power, and does not explore the multiple adaptability of different process layers of the silicon wafer. Its feedback loop is a self-locking loop, and does not reflect the information of the process conditions as input.

[0032] Based on this, the technical solutions provided by the embodiments of the present application are described below in conjunction with the accompanying drawings.

[0033] The embodiments of this specification provide an off-axis alignment light source system, such as Figure 1 and Figure 3As shown, the alignment light source 400 is included. The alignment light source 400 includes a light source module 100, an optical amplification module 200 and a system control module 300. The system control module 300 controls the light source module 100 and the optical amplification module 200 respectively; the light source module 100 outputs illumination light under the control of the system control module 300; the optical amplification module 200 receives illumination light; the optical amplification module 200 amplifies the received illumination light under the control of the system control module 300; the optical amplification module 200 outputs the amplified illumination light for illuminating the alignment mark 61 of the silicon wafer.

[0034] In one embodiment, the alignment light source 400 further includes an optical fiber module (not shown in the figure) and an electrical module (not shown in the figure), and the illumination light output by the light source module 100 is transmitted to the light amplification module 200 via the optical fiber module. The system control module 300 is electrically connected to the light source module 100 and the light amplification module 200 via the electrical module. The optical fiber module includes an optical fiber and an optical fiber collimator connecting the laser coupling mirror / output mirror in the light source module 100 and the light amplification module 200; the optical fiber is used as a waveguide for laser transmission, and the optical fiber collimator is used to collimate the light beam.

[0035] In one embodiment, the light source module 100 includes multiple independent light sources; the system control module 300 controls and determines whether to select one of the multiple independent light sources. For example, the light source module 100 may include two sets of independent light sources, each of which contains a laser, a temperature control part, and a current control part. The independent light source is selected or not under the control of the system control module 300; each independent light source outputs a laser with stable light intensity under stable and precise temperature control and current control. After being selected, the laser is amplified by the optical amplifier module 200 through the optical fiber module, and then output to the optical system of the next level for illuminating the alignment mark 61 of the silicon wafer; the system control module 300 controls the light source module 100 through the electrical module on the one hand to select the independent light source of the light source module 100 and modulate the output of the selected independent light source, and on the other hand to control the optical amplifier module 200 to automatically adjust the light intensity output by the light source system. The two independent light sources in the light source module 100 each have their own temperature control part and current control part. The output of the laser with stable light intensity by the light source module 100 depends on ensuring the stability of the laser ambient temperature and bias current.

[0036] In one embodiment, the multiple independent light sources include a first independent light source and a second independent light source; the first independent light source includes a strongly correlated laser, a first temperature controller 12, and a first current controller 13; the second independent light source includes a weakly correlated laser, a second temperature controller 15, and a second current controller 16. The first current controller 13 and the second current controller 16 are both bias current controllers. The strongly correlated laser outputs narrowband strongly coherent laser under the control of the first temperature controller 12 and the first current controller 13; the weakly coherent laser outputs broadband weakly coherent laser under the control of the second temperature controller 15 and the second current controller 16.

[0037] In one embodiment, the strongly correlated laser is a distributed feedback semiconductor laser 11 (Distributed–feedback Laser Diode, DFB-LD); the weakly correlated laser is a superluminescent diode 14 (SuperLuminescent Diode, SLD); the first temperature controller 12 and the first current controller 13 are used to control the distributed feedback semiconductor laser 11. The second temperature controller 15 and the second current controller 16 are used to control the superluminescent diode 14. The distributed feedback semiconductor laser 11 is used to output narrow-band strongly coherent laser light, and the superluminescent diode 14 is used to output broadband weakly coherent laser light. The light output by the distributed feedback semiconductor laser 11 and the superluminescent diode 14 is amplified by the optical amplifier module 200 through the optical fiber module, and then output to the optical system of the next stage for illuminating the alignment mark 61 of the silicon wafer. The wavelength of the distributed feedback semiconductor laser 11 can be one of 980nm, 1310nm, and 1550nm; the spectrum range of the superluminescent diode 14 can be 800nm ​​to 880nm.

[0038] In one embodiment, the light source module 100 further includes an optical multiplexer 17; the optical multiplexer 17 receives strong coherent laser or weak coherent laser and outputs it as illumination light to the optical amplifier module 200. That is, the optical multiplexer 17 is used to transmit the output of each independent light source to the optical amplifier module 200. The system control module 300 includes a computing control and input-output unit 31; the computing control and input-output unit 31 outputs a first control signal to control the selection to one of the first current controller 13 and the second current controller 16, and the current controller receiving the first control signal controls the corresponding laser according to the first control signal. The computing control and input-output unit 31 outputs a second control signal to the optical multiplexer 17, and the optical multiplexer 17 performs adaptive processing on the received laser according to the second control signal. The computing control and input-output unit 31 outputs a third control signal to the optical amplifier module 200, and the optical amplifier 22 in the optical amplifier module 200 controls and amplifies the illumination light processed by the optical isolator according to the third control signal. The system control module 300 receives feedback signals from the whole system in which it is located, and outputs control signals to the current control part in the light source module 100, the optical multiplexer 17 in the light source module 100, and the gain control part of the optical amplifier module 200. The gain control part of the optical amplifier module 200 is the optical fiber amplifier in the optical amplifier module 200. The system control module 300 controls the first current controller 13 and the second current controller 16 in the light source module 100 through the electrical module to directly modulate the output of the distributed feedback semiconductor laser 11 and the superluminescent diode 14 respectively, controls the optical multiplexer 17 in the light source module 100 to adapt to the selected independent light source, and controls the optical fiber amplifier in the optical amplifier module 200 to automatically adjust the optical power output by the light source system.

[0039] In one embodiment, the optical amplifier module 200 includes an optical amplifier 22, a front optical isolator 21 and a rear optical isolator 23; the front optical isolator 21 receives the illumination light and is used to eliminate the illumination light reflected back into the light source module 100 after being output by the light source module 100; the optical amplifier 22 is used to amplify the light intensity of the illumination light processed by the front optical isolator 21; the rear optical isolator 23 is used to eliminate the illumination light reflected back into the optical amplifier 22 after being output by the optical amplifier 22. The amplified illumination light processed by the rear optical isolator 23 is used to illuminate the alignment mark 61 of the silicon wafer. The front optical isolator 21 and the rear isolator can be provided one each, respectively located before and after the optical amplifier 22. The optical amplifier 22 is a fiber amplifier. A laser is used as a light source. Light intensity is light power. The front isolator before the optical amplifier 22 is used to eliminate the light reflected back into the laser resonant cavity after the laser output, so as to avoid the instability of the laser caused by externally injected light. The optical amplifier 22 is used to amplify the light intensity of the laser. The rear optical isolator 23 after the optical amplifier 22 is used to eliminate the light reflected back into the cavity of the optical amplifier 22 after the optical amplifier 22 output, so as to avoid the instability of the optical amplifier 22 caused by externally injected light.

[0040] In one embodiment, the optical amplifier 22 may be an erbium-doped fiber amplifier.

[0041] In one embodiment, if Figure 1 and Figure 2 As shown, the system control module 300 sets the bias current in the light source module 100 to change periodically, and adjusts the quality factor of the light source module 100. When the bias current is less than the working threshold of the light source module 100, the light source module 100 enters the off state; when the bias current is greater than the working threshold of the light source module 100, the light source module 100 enters the on state. After turning on the light source module 100, the selected independent light source is set, and the bias current of the laser in the light source module 100 is set to change periodically, and the laser is Q-switched, and Q represents the quality factor of the laser resonant cavity. When the bias current is less than the working threshold of the laser in the light source module 100, the laser enters the OFF state, and the output optical power is 0, and the OFF state represents the off state. When the bias current is greater than the working threshold of the laser, the laser enters the ON state, and the output optical power is a stable constant, and the ON state represents the on state. In this way, the laser switches periodically between the OFF and ON states, and the time of the state ON is determined by the system control module 300, so as to realize the controllability of the alignment exposure time. Regardless of whether the distributed feedback semiconductor laser 11 or the superluminescent diode 14 is selected as the alignment light source 400, the linearity of the outputs of both can meet the above-mentioned operation requirements. Figure 2 The figure shows the principle of the implementation method of the present invention using the off-axis alignment light source system of the silicon wafer. The left side shows the output power-bias current (LI) curve of the distributed feedback laser 11 or the superluminescent diode 14, showing the inherent nonlinearity of the two. The right side shows the relationship between output power and time. When the bias current (such as a low level) is less than the threshold, the output light intensity is 0 and is in the OFF state; when the bias current (such as a high level) is greater than the threshold and is stable, the output light intensity is a stable constant and is in the ON state. When performing field-by-field exposure lithography, the lithography equipment will be in a working mode of "alignment-lithography-moving to the next exposure field position-alignment-lithography". The light source control module 200 is set to make the bias current of the independent light source in the light source module 100 change periodically. Alignment and lithography are performed alternately. Fine control of the alignment exposure time will greatly improve the performance of the whole machine, ensure the accuracy of overlay and improve the yield.

[0042] In one embodiment, if Figure 1 and Figure 3As shown, the off-axis alignment light source system further includes a first beam splitter 63, an objective lens system, a reflector 64, a light receiving system 65, a second beam splitter 66, a first photodetector, and a second photodetector; the illumination light output by the alignment light source 400 passes through the first beam splitter 63 and the objective lens system to irradiate the alignment mark 61 on the silicon wafer, and the light irradiated on the alignment mark 61 is diffracted to obtain diffracted light; the objective lens system partially collects the diffracted light, and the diffracted light collected by the objective lens system passes through the reflector 64 and the light receiving system 65, and is then divided into a first beam of light and a second beam of light by the second beam splitter 66; the first photodetector 68 detects An alignment image is formed after the first beam of light; the second photodetector 67 obtains a level value after detecting the second beam of light, and feeds the level value back to the system control module 300; the system control module 300 determines whether the optical power of the diffracted light meets the signal-to-noise ratio requirement of the alignment image according to the level value; if the optical power of the diffracted light meets the signal-to-noise ratio requirement of the alignment image, the alignment process continues; if the optical power of the diffracted light does not meet the signal-to-noise ratio requirement of the alignment image, the system control module 300 calculates the compensation amount for controlling the light source module 100 or the optical amplifier module 200, and adjusts the output power of the illumination light output by the alignment light source 400.

[0043] Specifically, the silicon wafer off-axis alignment light source system is used for alignment, and the alignment light source 400 is aligned at Figure 33 main parts are shown in FIG: a light source module 100, an optical amplifier module 200 and a system control module 300. The output of the alignment light source 400 passes through a first beam splitter 63 and an objective lens 62 to illuminate an alignment mark 61 on a silicon wafer. The light is diffracted on the alignment mark 61, and the diffracted light is partially collected by the objective lens 62. The diffracted light collected by the objective lens 62 passes through a reflector 64 and a light receiving system 65, and is then divided into two beams by a second beam splitter 66, which are detected by photoelectric detection devices respectively. The first beam of light passes through a first photodetector 68 to form an alignment image for alignment analysis, and the second beam of light passes through a second photodetector 67 to obtain a certain level value, which is fed back to the system control module 300 in the alignment light source 400. For a calibrated system, the level value output by the second photodetector 67 directly reflects the optical power of the diffracted light. The system control module 300 determines whether the optical power provides a sufficiently good signal-to-noise ratio for the alignment image based on the information in the system calibration. If the optical power of the diffracted light provides a sufficiently good signal-to-noise ratio for the alignment image, the alignment process continues. Otherwise, the system control module 300 will calculate the compensation amount for the control of the light source module 100 or the optical amplifier module 200 through an algorithm, and automatically adjust the output power of the alignment light source 400. Among them, a good signal-to-noise ratio (SNR) means that during the silicon wafer alignment process, the diffracted light signal is strong and stable enough to clearly and accurately reflect the information of the silicon wafer alignment mark, and the noise is relatively low, which will not cause significant interference to the alignment image and related measurements, thereby ensuring the high precision and reliability of the alignment system. When the optical power of the diffracted light reflected by the level value detected by the second photodetector 67 is high enough, the first photodetector 68 can form a clear and accurate alignment image. This means that the signal strength must be higher than a certain threshold so that the features of the alignment mark can be accurately identified and located.

[0044] The embodiment of this specification also proposes an off-axis alignment method, which uses an off-axis alignment light source system, including the following steps:

[0045] Step S1: The system control module 300 controls and selects an independent light source according to the process requirements, and the selected independent light source outputs illumination light. Specifically, the light source module 100 is turned on, and an independent light source is selected according to the process requirements. For example, when the surface of the current process layer is rough, a broadband light source can be used, or when the depth of the alignment mark 61 of the current process layer becomes shallow, a narrowband light source can be used. Then, the bias current of the laser in the light source module 100 is made greater than the working threshold, so that the light source module 100 enters the working state of outputting continuous waves, and stably outputs the illumination light for alignment.

[0046] Step S2: The optical amplifier module 200 receives the illumination light, and the system control module 300 controls the optical amplifier module 200 to amplify the received illumination light, that is, the illumination light passes through the optical amplifier module 200 so that the output optical power reaches a value corresponding to the optimal signal-to-noise ratio.

[0047] Step S3: The amplified illumination light output by the optical amplification module 200 passes through the first beam splitter 63 and the objective lens system to illuminate the alignment mark 61 on the silicon wafer, and the light irradiated on the alignment mark 61 is diffracted to obtain diffracted light. That is, the light output by the optical amplification module 200 passes through the first beam splitter 63 and the objective lens 62 of the objective lens system to illuminate the alignment mark 61 on the silicon wafer, and the light is diffracted on the alignment mark 61, and the diffracted light is partially collected by the objective lens system.

[0048] Step S4: The objective lens system partially collects the diffracted light, and the diffracted light collected by the objective lens system passes through the reflector 64 and the light receiving system 65, and is then divided into a first beam and a second beam by the second beam splitter 66; the first photodetector 68 detects the first beam to form an alignment image. The second photodetector 67 detects the second beam to obtain a level value. Specifically, the diffracted light collected by the objective lens system passes through the reflector 64 and the light receiving system 65, and is then divided into two beams by the second beam splitter 66, which are detected by the photoelectric detection device respectively, wherein the first beam forms an alignment image after passing through the first photodetector, which is used for alignment analysis, and the second beam obtains a certain level value after passing through the second photodetector. For a calibrated system, the level value directly reflects the optical power of the diffracted light.

[0049] Step S5: The second photodetector 67 feeds back the level value to the system control module 300; the system control module 300 determines whether the optical power of the diffracted light meets the signal-to-noise ratio requirement of the alignment image based on the level value. Specifically, the level value generated by the second beam of light after passing through the photodetector feeds back the information of the optical power of the diffracted light to the system control module 300 in the alignment light source 400 through electrical connection, and the system control module 300 determines whether the optical power provides a sufficiently good signal-to-noise ratio for the alignment image based on the information in the system calibration.

[0050] Step S6: If the optical power of the diffracted light meets the signal-to-noise ratio requirement of the alignment image, the alignment process continues; if the optical power of the diffracted light does not meet the signal-to-noise ratio requirement of the alignment image, the system control module 300 calculates the compensation amount for controlling the light source module 100 or the optical amplifier module 200, and adjusts the output power of the illumination light output by the alignment light source 400. Specifically, if the optical power of the diffracted light provides a sufficiently good signal-to-noise ratio for the alignment image, the alignment process continues; otherwise, the system control module 300 calculates the compensation amount for controlling the light source module 100 or the optical amplifier module 200 through an algorithm, and automatically adjusts the output power of the alignment light source 400.

[0051] The present invention embodies the advantage of process adaptability of silicon wafer alignment light source 400. Compared with the prior art using fiber laser or visible light as silicon wafer alignment light source 400, the control of the light source in the alignment light source 400 proposed by the present invention is more flexible, and the controllable degree of freedom of the light source is higher. First, the present invention provides two light source options, narrowband and broadband, which have better adaptability to process layers with different parameters such as thickness and material, and the narrowband light source can be expanded and increased to achieve narrowband wavelength switching; second, the Q-switching method proposed by the present invention is used to modulate the light source module 100, which can achieve periodic switching or more complex switching, thereby achieving flexible control of the alignment exposure time, and relying on the good linearity of the laser LI curve, when modulating the laser, the laser output light power can be flexibly and stably controlled within a certain range by controlling the laser bias current; third, in the alignment method proposed by the present invention, part of the diffracted light from the alignment mark 61 is fed back to the system control module 300 for generating a control signal to adjust the light output power, which can achieve automatic adjustment of the light output power for different process layers. These three technical effects clearly demonstrate the good process adaptability of the alignment light source 400 in the present invention.

[0052] The present invention embodies the advantages of the silicon chip alignment light source 400 structure. Compared with the prior art using fiber lasers or visible light as the silicon chip alignment light source 400, the alignment light source 400 proposed by the present invention uses a distributed feedback semiconductor laser 11 and a superluminescent diode 14, and has a more compact and simple structure, occupies less space, and has lower power consumption. The distributed feedback semiconductor laser 11 and the superluminescent diode 14 used in the present invention are also easy to integrate with other optoelectronic devices, retaining the potential for further multifunctionalization and miniaturization of the alignment light source 400. For example, a mode-locked pulse operating mode can be achieved by integrating a saturated absorber in the resonant cavity.

[0053] The present invention embodies the advantages of the cooperation between the silicon wafer alignment system and other subsystems of the photolithography equipment. Compared with the silicon wafer alignment light source system in the prior art, the silicon wafer alignment light source system proposed in the present invention can work in cooperation with other subsystems in several cases to improve the automation level of the photolithography equipment. First, the control signal of the light source module 100 for the alignment exposure time can be set to a signal from the outside of the alignment light source 400, which electrifies the process of controlling the alignment exposure time, replaces the mechanical shutter used in the prior art or cooperates with the mechanical shutter used in the prior art to more finely control the alignment exposure time. Under the strategy of field-by-field alignment, the photolithography equipment will be in a working mode of "alignment-lithography-move to the next exposure field position-alignment-lithography", and alignment and lithography are performed alternately. Fine control of the alignment exposure time will greatly improve the performance of the whole machine, ensure the accuracy of overlay and improve the yield. Secondly, the control signal of the bias current of the light source module 100 and the gain control signal of the system control module 300 to the optical amplifier module 200 can be set as a signal from the outside of the alignment light source 400, so as to electrify the control of the optical power output by the alignment light source 400 and precisely control the optical power output by the alignment light source 400. When aligning different process layers, different materials show different refractive indices to the wavelength of the alignment light source 400, which causes the intensity of the diffracted light collected during the alignment process to change, and then causes the signal-to-noise ratio of the alignment image to change. The present invention can use a spectrometer and a photoelectric detection device to monitor the diffracted light power of the alignment mark 61 after illumination in real time, and feed back the electrical signal corresponding to the optical power to the system control module 300 in the alignment light source 400, so that it can compensate for the bias current of the light source module 100 and the gain of the optical amplifier module 200, automatically adjust the optical power output by the alignment light source 400, optimize the signal-to-noise ratio of the alignment image, and effectively improve the alignment accuracy.

[0054] The switchable silicon wafer off-axis alignment light source system based on the directly modulated distributed feedback semiconductor laser 11 and the directly modulated superluminescent diode 14 proposed in the present invention provides light source switching for processes with different illumination spectrum width requirements, provides light source output power control for processes with different alignment imaging signal-to-noise ratio requirements, and realizes Q-switching control of the light source for processes with different alignment exposure time requirements, effectively improving the process adaptability and work efficiency of the silicon wafer alignment system. In addition, compared with the prior art, the silicon wafer off-axis alignment light source system proposed in the present invention reduces the complexity and development cost of the system, reduces the spatial structure size, and further opens up the development prospect of the integration of the alignment light source 400.

[0055] In this specification, the same or similar parts between the various embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the embodiments described later, the description is relatively simple, and the relevant parts can be referred to the partial description of the previous embodiments.

[0056] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application shall be based on the protection scope of the claims.

Claims

1. An off-axis alignment light source system, characterized in that: including an alignment light source (400); The alignment light source (400) comprises a light source module (100), a light amplification module (200) and a system control module (300); The system control module (300) controls the light source module (100) and the light amplification module (200) respectively; The light source module (100) outputs illumination light under the control of the system control module (300); The light amplification module (200) receives illumination light; The light amplification module (200) amplifies the received illumination light under the control of the system control module (300); The light amplification module (200) outputs amplified illumination light for illuminating an alignment mark (61) on a silicon wafer.

2. The off-axis alignment light source system according to claim 1, characterized in that: The light source module (100) comprises a plurality of independent light sources; The system control module (300) controls and determines the selection of one of a plurality of independent light sources.

3. The off-axis alignment light source system according to claim 2, characterized in that: The plurality of independent light sources include a first independent light source and a second independent light source; The first independent light source comprises a strongly correlated laser, a first temperature controller (12) and a first current controller (13); The second independent light source comprises a weakly correlated laser, a second temperature controller (15) and a second current controller (16); The strongly correlated laser outputs narrow-band strongly coherent laser under the control of the first temperature controller (12) and the first current controller (13); The weak coherent laser outputs broadband weak coherent laser under the control of the second temperature controller (15) and the second current controller (16).

4. The off-axis alignment light source system according to claim 3, characterized in that: The light source module (100) further comprises a light multiplexer (17); The optical multiplexer (17) receives strong coherent laser light or weak coherent laser light and outputs it to the optical amplification module (200) as illumination light; The system control module (300) includes a computing control and input-output unit (31); The calculation control and input-output unit (31) outputs a first control signal to control the selection to one of the first current controller (13) and the second current controller (16); The computing control and input-output unit (31) outputs a second control signal to the optical multiplexer (17); The calculation control and input-output unit (31) outputs a third control signal to the optical amplification module (200).

5. The off-axis alignment light source system according to claim 3, characterized in that: The strongly correlated laser is a distributed feedback semiconductor laser (11); The weakly correlated laser is a superluminescent diode (14); The wavelength of the distributed feedback semiconductor laser (11) includes one of 980nm, 1310nm and 1550nm; The spectrum range of the superluminescent diode (14) is 800nm-880nm.

6. The off-axis alignment light source system according to claim 1, characterized in that: The optical amplification module (200) comprises an optical amplifier (22), a front optical isolator (21) and a rear optical isolator (23); The front light isolator (21) receives illumination light and is used to eliminate illumination light reflected back into the light source module (100) after being output by the light source module (100); The optical amplifier (22) is used to amplify the light intensity of the illumination light processed by the front optical isolator (21); The rear optical isolator (23) is used to eliminate the illumination light reflected back into the optical amplifier (22) after being output by the optical amplifier (22).

7. The off-axis alignment light source system according to claim 6, characterized in that: The optical amplifier (22) is an erbium-doped optical fiber amplifier.

8. The off-axis alignment light source system according to claim 1, characterized in that: The system control module (300) sets a bias current in the light source module (100) to change periodically, and adjusts the quality factor of the light source module (100); when the bias current is less than a working threshold of the light source module (100), the light source module (100) enters a closed state; when the bias current is greater than the working threshold of the light source module (100), the light source module (100) enters an open state.

9. The off-axis alignment light source system according to claim 2, characterized in that: The off-axis alignment light source system also includes a first beam splitter (63), an objective lens system, a reflector (64), a light receiving system (65), a second beam splitter (66), a first photodetector, and a second photodetector; The illumination light output by the alignment light source (400) passes through a first beam splitter (63) and an objective lens system to illuminate an alignment mark (61) on a silicon wafer, and the light irradiated on the alignment mark (61) is diffracted to obtain diffracted light; The objective lens system part collects the diffracted light, and the diffracted light collected by the objective lens system part passes through a reflector (64) and a light receiving system (65), and is then divided into a first beam of light and a second beam of light by a second beam splitter (66); The first photodetector (68) forms an alignment image after detecting the first beam of light; The second photoelectric detector (67) detects the second beam of light to obtain a level value, and feeds the level value back to the system control module (300); The system control module (300) determines whether the optical power of the diffracted light meets the signal-to-noise ratio requirement of the alignment image according to the level value; if the optical power of the diffracted light meets the signal-to-noise ratio requirement of the alignment image, the alignment process continues; if the optical power of the diffracted light does not meet the signal-to-noise ratio requirement of the alignment image, the system control module (300) calculates a compensation amount for controlling the light source module (100) or the light amplification module (200), and adjusts the output power of the illumination light output by the alignment light source (400).

10. An off-axis alignment method, characterized in that: The off-axis alignment light source system according to claim 9 comprises the following steps: Step S1: the system control module (300) controls and selects an independent light source according to process requirements, and the selected independent light source outputs illumination light; Step S2: the optical amplification module (200) receives illumination light, and the system control module (300) controls the optical amplification module (200) to amplify the received illumination light; Step S3: the amplified illumination light output by the optical amplification module (200) passes through the first beam splitter (63) and the objective lens system to illuminate the alignment mark (61) on the silicon wafer, and the light irradiated on the alignment mark (61) is diffracted to obtain diffracted light; Step S4: the objective lens system part collects the diffracted light, and the diffracted light collected by the objective lens system part passes through the reflector (64) and the light receiving system (65), and is then divided into a first beam of light and a second beam of light by a second beam splitter (66); the first photodetector (68) detects the first beam of light to form an alignment image; the second photodetector (67) detects the second beam of light to obtain a level value; Step S5: the second photodetector (67) feeds back the level value to the system control module (300); the system control module (300) determines whether the optical power of the diffracted light meets the signal-to-noise ratio requirement of the alignment image according to the level value; Step S6: If the optical power of the diffracted light meets the signal-to-noise ratio requirement of the alignment image, the alignment process continues; if the optical power of the diffracted light does not meet the signal-to-noise ratio requirement of the alignment image, the system control module (300) calculates the compensation amount for controlling the light source module (100) or the light amplification module (200), and adjusts the output power of the illumination light output by the alignment light source (400).

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