Control method and device for improving laser wavelength stability

Abstract

The present disclosure provides a control method and device for improving the stability of laser wavelength; wherein the control method for improving the stability of laser wavelength includes: determining the current wavelength a and the target wavelength b of the laser; and controlling the operation of the motor in sections according to the current wavelength a and the target wavelength b of the laser, thereby improving the stability of the laser wavelength. The present disclosure provides a control method and device for improving the stability of laser wavelength. When the laser wavelength approaches the target wavelength, the corresponding parameters are selected in sections, thereby controlling the rotation of the motor so that the laser wavelength quickly and effectively reaches a stable state.

Description

Technical Field

[0001] The present disclosure relates to the field of laser technology, and in particular to a control method and device for improving the wavelength stability of a laser. Background Art

[0002] Excimer laser is a pulsed gas laser with a wavelength in the ultraviolet band. Its working material is composed of inert gas (neon, argon, krypton, xenon, etc.) and halogen elements (fluorine, chlorine, bromine, etc.). In the ground state, it is a mixture of two atomic gases. When it is excited to a high energy level by a short pulse current, a compound is generated. Each molecule of the compound is composed of one atom contributed by each gas, and it is in a quasi-molecular state. When electrons jump from a high energy level to a low energy level, ultraviolet lasers are radiated.

[0003] The most common excimer lasers include argon fluoride (ArF), krypton fluoride (KrF) and xenon chloride (XeCl), etc., with central wavelengths of 193nm, 248nm and 308nm respectively. They are ideal light sources for semiconductor lithography because of their high energy and short wavelength. During the exposure process, changes in the central wavelength of the excimer laser will cause changes in the position of the imaging surface of the lithography machine, causing the exposure lines to become wider and the yield of the chip to decrease. In order to obtain a stable central wavelength, an online detection module is usually provided in the excimer laser. When the detection module detects a change in the central wavelength of the laser, the change is transmitted to the laser system. The system adjusts the output wavelength of the laser according to the change to ensure that the laser outputs a beam with a stable central wavelength.

[0004] There is a method for improving the measurement accuracy and stability through the Fabry-Perot etalon (hereinafter referred to as the FP etalon) method, thereby improving the stability of the laser output wavelength. The FP etalon method is a commonly used method for measuring the center wavelength of the laser. Specifically, after the laser passes through the FP standard, interference fringes are generated, and the center wavelength of the incident laser is obtained according to the position of the peak of the interference fringes. However, the measurement accuracy of the center wavelength is easily affected by changes in environmental parameters such as temperature and pressure. When the temperature and pressure or the internal material of the FP releases gas, the spacing d of the FP etalon and the refractive index of the internal gas will change, so that the center wavelength measured by the FP etalon drifts, affecting the accuracy and stability of the laser center wavelength measurement. In order to improve the measurement accuracy of the center wavelength, CYMER has proposed two methods to improve the stability of the FP etalon: the first method is to place the FP etalon in a vacuum container, so as to avoid the influence of changes in ambient temperature and air pressure on the FP etalon. However, it is difficult to maintain a vacuum for a long time, so there will be drift in the center wavelength during long-term measurement. The second method is to place the FP standard in a constant temperature container filled with buffer gas (such as nitrogen). However, this method still cannot overcome the temperature change from cold to hot when the laser is turned on, and the constant temperature container also has a certain temperature change. Therefore, the measurement accuracy of the laser center wavelength and the wavelength stability cannot be effectively guaranteed.

[0005] In summary, the existing laser center wavelength adjustment scheme and measurement scheme cannot effectively improve the laser wavelength stability. Summary of the invention

[0006] 1. Technical issues to be resolved

[0007] In view of the above problems, the main purpose of the present disclosure is to provide a control method and device for improving the wavelength stability of a laser, so as to solve at least one of the above problems.

[0008] (II) Technical solution

[0009] In order to achieve the above object, as one aspect of the present disclosure, a control method for improving the wavelength stability of a laser is provided, comprising:

[0010] Determine the current wavelength a and the target wavelength b of the laser; and

[0011] The motor operation is controlled in sections according to the current wavelength a and the target wavelength b of the laser, thereby improving the wavelength stability of the laser.

[0012] Further, the step of controlling the motor operation in sections according to the current wavelength a of the laser and the target wavelength b includes:

[0013] If ab≥d, the motor is controlled to rotate p1 steps;

[0014] If d>ab≥e, the motor is controlled to rotate p2 steps;

[0015] Wherein, p1>p2, d is the first threshold, and e is the second threshold.

[0016] Further, p1 = k(ab);

[0017] p2=k(ab) / 2:

[0018] Wherein, k is the motor step unit coefficient corresponding to 1 unit wavelength.

[0019] Furthermore, the step of controlling the motor operation in sections according to the current wavelength a of the laser and the target wavelength b also includes:

[0020] If e>ab>c, the motor is operated according to PID control, wherein c is the third threshold value.

[0021] Furthermore, the step of controlling the motor operation in sections according to the current wavelength a of the laser and the target wavelength b also includes:

[0022] If |ab|≤c, the motor is controlled to maintain the current state.

[0023] Furthermore, when ab>c, the motor is controlled to rotate forward. If the laser wavelength approaches the target wavelength, when ab<-c, the motor is controlled to rotate reversely. Otherwise, when ab>c, the motor is controlled to rotate reversely. When ab<-c, the motor is controlled to rotate forward.

[0024] Furthermore, before controlling the motor operation in sections according to the current wavelength a and the target wavelength b of the laser, it also includes: determining whether the number of steps of the motor exceeds a step threshold, if so, controlling the motor to remain stationary, otherwise controlling the motor operation in sections according to the current wavelength a and the target wavelength b.

[0025] As another aspect of the present disclosure, a laser wavelength stability control device is provided, comprising a grating module, a spring, a lead screw, a reflector, an optical prism module group, a main control unit and an external motor; wherein the grating module, the spring, the lead screw, the reflector, and the optical prism module group are arranged in a housing, and the motor is arranged outside the housing; the reflector is connected to the spring; one end of the lead screw is connected to the housing, and the other end is connected to the reflector; the motor is used to drive the lead screw to move forward and backward; the main control unit is used to control the operation of the motor in sections according to the current wavelength a and the target wavelength b of the laser; the lead screw is driven to move by the operation of the motor to cause the reflector to move, thereby adjusting the laser wavelength.

[0026] Furthermore, the main control unit is used to control the motor to rotate k(ab) steps when ab≥d, and to control the motor to rotate k(ab) / 2 steps when d>ab≥e;

[0027] Among them, d is the first threshold, e is the second threshold, and k is the motor step unit coefficient corresponding to 1 unit wavelength.

[0028] Furthermore, the main control unit is also used to control the operation of the motor according to PID when e>ab>c, and to control the motor to maintain a current state when |ab|≤c; wherein c is a third threshold.

[0029] (III) Beneficial effects

[0030] It can be seen from the above technical solutions that the control method and device for improving the wavelength stability of laser disclosed in the present invention have at least one of the following beneficial effects:

[0031] (1) The present invention discloses a control method for improving the stability of the central wavelength of a laser (especially an excimer laser for lithography). When the laser wavelength approaches a target wavelength, corresponding parameters are selected in segments to control the rotation of a motor so that the laser wavelength reaches a stable state quickly and effectively.

[0032] (2) By adopting the control method disclosed in the present invention, when ab≥d, the motor is controlled to rotate k(ab) steps; when d>ab≥e, the motor is controlled to rotate k(ab) / 2 steps; when e>ab>c, the motor is controlled to operate according to PID; thereby, the central wavelength stability of the laser can be at least doubled compared with the existing scheme. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a flow chart of the control method disclosed in the present invention.

[0034] Figure 2 A schematic diagram of the structure of a control device for improving the wavelength stability of a laser according to an embodiment of the present disclosure.

[0035] Figure 3 This is a flow chart of the control method of the embodiment of the present disclosure.

[0036] Figure 4 This is a segmented control flow chart of an embodiment of the present disclosure.

[0037] <Description of symbols>

[0038] 1-grating module, 2-reflector fixing spring, 3-external motor driver, 4-screw, 5-reflector, 6-optical prism module group, 7-housing. DETAILED DESCRIPTION

[0039] In order to make the objectives, technical solutions and advantages of the present disclosure more clearly understood, the present disclosure is further described in detail below in combination with specific embodiments and with reference to the accompanying drawings.

[0040] The present disclosure proposes a control method for improving the wavelength stability of a laser, such as Figure 1 As shown, the control method for improving the laser wavelength stability includes:

[0041] Determine the current wavelength a and the target wavelength b of the laser; and

[0042] The motor operation is controlled in sections according to the current wavelength a of the laser and the target wavelength b, thereby improving the wavelength stability of the laser. The optical module is adjusted by the motor operation to change the laser wavelength. That is to say, the disclosed method selects corresponding parameters according to the current wavelength a of the laser and the target wavelength b to control the motor operation in sections, thereby adjusting the output wavelength of the laser, so that the output wavelength of the laser tends to the target wavelength, and improving the wavelength stability of the laser.

[0043] The present invention discloses a control method for improving the stability of the central wavelength of a laser (especially an excimer laser for lithography). When the laser wavelength approaches a target wavelength, the rotation of a motor is controlled in sections so that the laser wavelength reaches a stable state quickly and effectively.

[0044] Specifically, the segmented control of the motor operation according to the current wavelength a of the laser and the target wavelength b includes: if ab≥d, controlling the motor to rotate p1 steps; if d>ab≥e, controlling the motor to rotate p2 steps; wherein p1>p2, d is the first threshold, and e is the second threshold.

[0045] Compared with the existing laser center wavelength adjustment method, the present invention adopts two different control schemes, large-range adjustment and small-range adjustment, when the gap between the current wavelength a and the target wavelength b is different, thereby achieving the set target wavelength more quickly and accurately, greatly improving the adjustment time and stability.

[0046] Preferably, p1=k(ab); p2=k(ab) / 2; thereby, the time requirement can be better met, and at the same time, back and forth oscillation after adjustment to the target position can be avoided, thereby improving stability.

[0047] Among them, k is the motor step unit coefficient corresponding to the unit wavelength, and preferably, k is the motor step unit coefficient corresponding to the wavelength of 1pm (picometer).

[0048] In addition, if e>ab>c, the motor is operated according to PID control, wherein c is a third threshold value. If |ab|≤c, the motor is controlled to maintain the current state.

[0049] Specifically, when ab>c, the motor is controlled to rotate forward. If the laser wavelength approaches the target wavelength, when ab<-c, the motor is controlled to rotate reversely. Otherwise, when ab>c, the motor is controlled to rotate reversely, and when ab<-c, the motor is controlled to rotate forward.

[0050] The present disclosure also proposes a control device for improving the wavelength stability of a laser, comprising a grating module, a spring, a motor, a lead screw, a reflector, an optical prism module group and a main control unit; wherein the grating module, the spring, the lead screw, the reflector, and the optical prism module group are arranged in a housing, the motor is arranged outside the housing, one end of the spring is connected to the housing, and the other end is connected to the reflector; one end of the lead screw is connected to the motor, and the other end is connected to the reflector; the motor is used to drive the lead screw to move forward and backward; the main control unit is used to control the operation of the motor in sections according to the current wavelength a and the target wavelength b of the laser; the lead screw is driven to move by the operation of the motor to cause the reflector to move, thereby adjusting the wavelength of the laser.

[0051] Specifically, the main control unit is used to control the motor to rotate k(ab) steps when ab≥d, and to control the motor to rotate k(ab) / 2 steps when d>ab≥e; wherein d is the first threshold, e is the second threshold, and k is the motor step unit coefficient corresponding to the wavelength of 1pm.

[0052] In addition, the main control unit is also used to control the operation of the motor according to PID when e>ab>c, and to control the motor to maintain a current state when |ab|≤c; wherein c is a third threshold value.

[0053] During the wavelength adjustment process of the laser disclosed in the present invention, the laser wavelength can be made to reach a stable state quickly and effectively.

[0054] The following is combined with Figure 2-4 The embodiments of the present disclosure are described in detail.

[0055] For ease of understanding, here we briefly introduce the control device that improves the laser wavelength stability. Figure 2As shown, the device generally includes: a grating module 1, a reflector fixing spring 2, a lead screw 4, a reflector 5, an optical prism module group 6, a main control unit (not shown) and a motor driver 3. The grating module 1, the reflector fixing spring 2, the lead screw 4, the reflector 5, and the optical prism module group 6 are arranged in a housing 7, and the motor driver 3 is arranged outside the housing 7 (i.e., an external motor), one end of the spring is connected to the housing, and the other end is connected to the reflector; one end of the lead screw is connected to the motor, and the other end is connected to the reflector; the motor is used to drive the lead screw to move forward and backward; the main control unit is used to control the operation of the motor in sections; the motor operation drives the lead screw to move so that the reflector moves, thereby adjusting the laser wavelength. Specifically, if the central wavelength of the laser is within the wavelength setting range, and the distance between the current wavelength and the target wavelength is within the set threshold range, the main control unit controls the motor to maintain the current state; if the central wavelength of the laser is not within the wavelength setting range, and the distance between the current wavelength and the target wavelength exceeds the set threshold, the main control unit controls the drive motor to rotate, and the motor rotation further drives the lead screw to move; if the lead screw moves forward, it pushes the reflector to rotate at a fulcrum; if the lead screw moves backward, the spring pulls the reflector back at the same fulcrum. In summary, the output wavelength of the laser is adjusted by controlling the operation of the motor to change the state of the optical module (including grating, reflector, prism).

[0056] like Figure 3 As shown, the laser wavelength adjustment process of this embodiment is as follows: collect the current wavelength a of the laser and obtain the target wavelength b of the laser; if the current wavelength of the laser is within the wavelength setting range and the distance between the current wavelength and the target wavelength is within the set threshold range (a is between bc and b+c), that is, |ab|≤c, then control the motor to maintain the current state; otherwise, start adjustment and control the motor to start running. In the above formula, c is a set threshold (the size of the threshold c affects the wavelength stability and can be selected as appropriate according to the equipment index requirements. If the threshold c is too small, the adjustment time will be sacrificed accordingly). If ab>c, the motor is controlled to rotate forward (the direction of motor rotation is related to the actual wavelength change. If the motor rotates forward and the laser wavelength approaches the target wavelength, the forward rotation is set to the set direction. If the motor reverses and the laser wavelength approaches the target wavelength, the reverse rotation is set to the set direction. Here, it is assumed that the forward rotation is the set direction). According to k, the number of steps (ab)×k can be obtained. If the number of steps of the motor does not exceed the step threshold (mainly for protection, the step threshold can be reasonably set), the main control unit is as follows Figure 4 The control process shown controls the motor driver to execute the rotation steps until the motor stops rotating. The control cycle is completed and continues to the next cycle; if ab<-c, the motor reverses. The specific process is consistent with the principle of motor forward rotation. After multiple control cycles, the collected wavelength is consistent with the target wavelength.

[0057] As mentioned above, if the main control unit calculates and determines that the number of forward rotation steps of the motor is within the threshold range, the main control unit performs the following steps: Figure 4 The control method shown controls the number of rotation steps performed by the motor driver as follows (the principle of motor reverse rotation is similar to that of forward rotation):

[0058] Entering the control loop, the main control unit determines ab≥d, where d is the large-scale adjustment threshold. If this formula is true, the main control unit controls the motor to rotate k(ab) steps; if this formula is false, ab≥e is determined at the same time, where e is the small-scale adjustment threshold. If this formula is true, the main control unit controls the motor to rotate k(ab) / 2 steps, k is the motor step unit coefficient corresponding to the unit wavelength, if this formula is false, the main control unit controls the motor output according to the PID module (the PID module here is a special module provided by LabVIEW, and the P, I, D parameters can be selected according to the specific debugging situation), and the control loop ends. After several cycles, the current wavelength can be stably adjusted to the target wavelength. k is the motor step unit coefficient corresponding to the unit wavelength; preferably, k is the motor step unit coefficient corresponding to the 1pm wavelength.

[0059] Among them, the thresholds c, d, and e can be set according to the actual adjustment accuracy, stability, and adjustment time.

[0060] The present invention discloses a control method for improving the stability of the central wavelength of a laser (especially an excimer laser for lithography). When the laser wavelength approaches the target wavelength, the corresponding parameters are selected in sections, thereby controlling the rotation of the motor so that the laser wavelength reaches a stable state quickly and effectively. The control method disclosed in the present invention can improve the stability of the central wavelength of the laser by at least twice compared with the existing method.

[0061] In addition, the above definitions of the various elements and methods are not limited to the various specific structures, shapes or methods mentioned in the embodiments, and those skilled in the art can simply change or replace them.

[0062] It should be noted that the directional terms mentioned in the embodiments, such as "upper", "lower", "front", "back", "left", "right", etc., are only reference directions of the drawings and are not intended to limit the scope of protection of the present disclosure. Throughout the drawings, the same elements are represented by the same or similar reference numerals. Conventional structures or constructions will be omitted when they may cause confusion in the understanding of the present disclosure. And the shapes and sizes of the components in the figures do not reflect the actual size and proportion, but only illustrate the contents of the embodiments of the present disclosure. In addition, in the claims, any reference symbols between brackets should not be constructed as limitations on the claims.

[0063] Furthermore, the word "comprising" or "including" does not exclude the presence of elements or steps not listed in a claim. The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements.

[0064] The ordinal numbers used in the specification and claims, such as "first", "second", "third", etc., to modify the corresponding elements, do not themselves mean that the elements have any ordinal numbers, nor do they represent the order of one element and another element, or the order in the manufacturing method. The use of these ordinal numbers is only used to clearly distinguish a component with a certain name from another component with the same name.

[0065] Similarly, it should be understood that in order to streamline the present disclosure and aid in understanding one or more of the various disclosed aspects, in the above description of the exemplary embodiments of the present disclosure, the various features of the present disclosure are sometimes grouped together into a single embodiment, figure, or description thereof. However, this disclosed method should not be interpreted as reflecting the following intention: the claimed disclosure requires more features than the features explicitly recited in each claim. More specifically, as reflected in the claims below, the disclosed aspects are less than all the features of the single embodiment disclosed above. Therefore, the claims that follow the specific embodiment are hereby expressly incorporated into the specific embodiment, with each claim itself serving as a separate embodiment of the present disclosure.

[0066] The specific embodiments described above further illustrate the purpose, technical solutions and beneficial effects of the present disclosure. It should be understood that the above description is only a specific embodiment of the present disclosure and is not intended to limit the present disclosure. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present disclosure should be included in the protection scope of the present disclosure.

Claims

1. A control method for improving the wavelength stability of a laser, characterized in that: include: Determine the current wavelength a and the target wavelength b of the laser; as well as The motor operation is controlled in sections according to the current wavelength a and the target wavelength b of the laser, so as to improve the wavelength stability of the laser; the laser comprises a grating module, a spring, a lead screw, a reflector, an optical prism module group and a motor; wherein the grating module, the spring, the lead screw, the reflector, and the optical prism module group are arranged in a housing, and the motor is arranged outside the housing; the reflector is connected to the spring; one end of the lead screw is connected to the housing, and the other end is connected to the reflector; the motor is used to drive the lead screw to move forward and backward to move the reflector, so as to adjust the wavelength of the laser; like , then control the motor to rotate p1 steps; like , then control the motor to rotate p2 steps; and like , then the motor runs according to PID control; in, , d is the first threshold, e is the second threshold, and c is the third threshold; The method further comprises: exist When the motor is controlled to rotate forward, if the wavelength of the laser approaches the target wavelength, When the motor is controlled to reverse; otherwise, When the motor is controlled to reverse, When , the motor is controlled to rotate forward.

2. The control method for improving the wavelength stability of a laser according to claim 1, characterized in that: ； ； in, It is the motor step unit coefficient corresponding to 1 unit wavelength.

3. The control method for improving the wavelength stability of a laser according to claim 1, characterized in that: The step of controlling the motor operation in sections according to the current wavelength a and the target wavelength b of the laser further comprises: like , the motor is controlled to maintain the current state.

4. The control method for improving the wavelength stability of a laser according to claim 1, characterized in that: Before controlling the motor operation in sections according to the current wavelength a and the target wavelength b of the laser, it also includes: determining whether the number of steps of the motor exceeds a step number threshold, if so, controlling the motor to remain stationary, otherwise controlling the motor operation in sections according to the current wavelength a and the target wavelength b.

5. A control device for improving the wavelength stability of a laser, characterized in that: The laser comprises a grating module, a spring, a lead screw, a reflector, an optical prism module group and a motor; wherein the grating module, the spring, the lead screw, the reflector, and the optical prism module group are arranged in a housing, and the motor is arranged outside the housing; the reflector is connected to the spring; one end of the lead screw is connected to the housing, and the other end is connected to the reflector; the motor is used to drive the lead screw to move forward and backward; The control device includes a main control unit, which is used to control the operation of the motor in sections according to the current wavelength a and the target wavelength b of the laser; the motor is used to drive the lead screw to move so as to move the reflector, thereby adjusting the wavelength of the laser; if , then control the motor to rotate p1 steps; if , then control the motor to rotate p2 steps; if , then the motor runs according to PID control; wherein, , d is the first threshold, e is the second threshold, and c is the third threshold; The control device also includes: exist When the motor is controlled to rotate forward, if the wavelength of the laser approaches the target wavelength, When the motor is controlled to reverse; otherwise, When the motor is controlled to reverse, When , the motor is controlled to rotate forward.

6. The device according to claim 5, characterized in that The main control unit is used to When controlling the motor to rotate Step, in When controlling the motor to rotate step; Where d is the first threshold, e is the second threshold, The unit wavelength corresponds to the motor step unit coefficient.

7. The device according to claim 6, characterized in that The main control unit is also used to The motor runs according to PID control. , the motor is controlled to maintain the current state; wherein c is the third threshold value.

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