Excimer laser dose accuracy control method and system and excimer laser

Abstract

The application discloses a kind of excimer laser dose precision control method and system.The method at least includes the following steps: S3: whether pulse position is greater than preset value n is judged, if less than or equal to, then enter S4;If greater, then enter S5;S4: single pulse energy stability control calculation is carried out, the current discharge voltage Vi of discharge cavity j is obtained, for controlling discharge cavity;Then enter S6;S5: dose precision control calculation is carried out, the current discharge voltage Vi of discharge cavity j is obtained, for controlling discharge cavity;Then enter S6;S6: based on current discharge voltage Vi j adjustment discharge voltage of discharge cavity.The application can inhibit the fluctuation caused by single pulse energy and dose, guarantee the dose precision requirement in the working process of laser.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of excimer laser dose precision control method, simultaneously relates to a kind of excimer laser dose precision control system, also relates to a corresponding excimer laser, belongs to excimer laser technical field. BACKGROUND

[0002] Due to preheating, gas degradation or renewal, and running time and other factors, excimer laser will always exist single pulse energy fluctuation and average pulse energy drift, in addition to energy overshoot phenomenon. The random fluctuation of laser output energy, in the process of working in lithography machine, it is easy to cause exposure line uneven, reduce yield, promote enterprise production cost. At the same time, limited by the life of laser internal gas, the stability of output energy will be more difficult to control with the increase of pulse number, cannot guarantee the dose precision of production requirement. Therefore, in order to improve the dose precision of excimer laser output, it is necessary to accurately and reasonably design control algorithm, so that excimer laser can work for a long time under the condition of meeting the dose precision requirement.

[0003] In the earlier application of the applicant submitted Chinese patent application (publication number: CN113783099A), a kind of excimer laser dose control method and device based on deep GRU are disclosed. The method selects in the time interval after each excimer laser emits a burst mode laser pulse energy sequence, uses deep gated recurrent network to judge whether the absolute value of the sliding average value difference of the current burst mode and the last burst mode laser pulse energy loss function is less than the threshold value;If greater, update the training parameters of deep gated recurrent network, obtain the update value of dose control parameter, apply to the dose precision control of next laser burst mode;If less, the dose control parameter used in the dose precision control of current burst mode is applied to the dose precision control of next laser burst mode. The method has strong adaptability to different target energy, repetition frequency, can well control the dose precision of excimer laser, effectively control the dose stability of laser pulse energy. SUMMARY

[0004] The primary technical problem to be solved by the present application is to provide an excimer laser dose precision control method.

[0005] Another technical problem to be solved by the present application is to provide an excimer laser dose precision control system.

[0006] Still another technical problem to be solved by the present application is to provide a corresponding excimer laser.

[0007] In order to achieve the above purpose, the present application adopts the following technical solutions:

[0008] According to a first aspect of the embodiments of the present application, a method for controlling dose accuracy of an excimer laser is provided, comprising the following steps:

[0009] S3: judging whether the pulse position is greater than a preset value n, if yes, entering step S4; if no, entering step S5;

[0010] S4: performing single pulse energy stability control calculation to obtain a current discharge voltage V ij of the discharge chamber for controlling the discharge chamber; then entering step S6;

[0011] S5: performing dose accuracy control calculation to obtain a current discharge voltage V ij of the discharge chamber for controlling the discharge chamber; then entering step S6;

[0012] S6: adjusting the discharge voltage of the discharge chamber based on the current discharge voltage V ij .

[0013] Preferably, the dose accuracy control calculation comprises a variable for increasing the discharge voltage of the discharge chamber with the increase of the burst signal, and a variable for increasing the discharge voltage of the discharge chamber with the increase of the pulse position in one burst signal.

[0014] Preferably, the dose accuracy control calculation is based on an energy fluctuation voltage variation value for suppressing energy fluctuation of the current pulse and a dose fluctuation voltage variation value for suppressing dose fluctuation of the current pulse.

[0015] Preferably, the dose fluctuation voltage variation value is adjusted in a non-linear amplification or reduction manner according to the dose difference value of the previous pulse position; and the energy fluctuation voltage variation value is adjusted in a non-linear amplification or reduction manner according to the energy difference value of the previous pulse position.

[0016] Preferably, the dose accuracy control calculation is further based on a pre-determined current pulse voltage, which is calculated according to the measured voltage and the output light energy of the trial discharge.

[0017] Preferably, the current pulse voltage is a preset value, and remains unchanged under the same working condition.

[0018] Preferably, the current pulse voltage is obtained by the following method under the same working condition:

[0019] a. estimating a range of estimated discharge voltage corresponding to the expected output light energy under the current gas condition;

[0020] b. Set a step length in the estimated discharge voltage range, take an incremental method, discharge at the position of each step length voltage, and average the light energy of the multiple pulses after each burst to obtain an energy average value;

[0021] c. Select the energy average value closest to the expected energy value in step b to obtain the discharge voltage corresponding to the closest expected energy value as the current pulse voltage of the next pulse under the current gas condition.

[0022] Preferably, in the single pulse energy stability control calculation, the increment of the discharge cavity discharge voltage in the same burst signal is exponential to the difference between the actual light energy and the expected light energy.

[0023] According to a second aspect of the embodiment of the present application, a dose accuracy control system of an excimer laser is provided, comprising: a high-voltage discharge assembly, a discharge cavity, a laser parameter measurement assembly, and a dose accuracy controller,

[0024] The dose accuracy controller receives a pre-set expected pulse energy, generates a discharge voltage signal of the discharge cavity according to the aforementioned excimer laser dose accuracy control method, and sends the signal to the high-voltage discharge assembly; the high-voltage discharge assembly sends an excitation voltage to the discharge cavity, the discharge cavity emits laser light, and the laser parameter measurement assembly detects the light energy value of the discharge cavity and feeds back to the dose accuracy controller.

[0025] According to a third aspect of the embodiment of the present application, an excimer laser is provided, which comprises the aforementioned excimer laser dose accuracy control system.

[0026] Compared with the prior art, the present application has the following technical effects: based on the control algorithm of the discharge output energy process, the influence of different pulse positions and gas life on the discharge light emission process is considered, the excitation voltage is calculated in a nonlinear manner by using a feedback method, the fluctuations caused by single pulse energy and dose are suppressed, the sudden change of the discharge voltage caused by the sudden change of the single pulse energy is avoided, and the dose accuracy requirement in the working process of the laser is ensured. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 A structure diagram of an excimer laser dose accuracy control system provided by the embodiment of the present application is provided;

[0028] Figure 2 An example diagram of light emission energy of a pulse sequence in a burst of an excimer laser in a constant voltage mode in the embodiment of the present application is provided;

[0029] Figure 3A A flowchart of an excimer laser dose accuracy control method provided by the embodiment of the present application is provided;

[0030] Figure 3B Schematic diagram of a logic diagram of a method for controlling the dose accuracy of an excimer laser according to an embodiment of the present invention;

[0031] Figure 4 Schematic diagram of the actual effect of the excimer laser dose accuracy control method in an embodiment of the present invention. DETAILED DESCRIPTION

[0032] The technical content of the present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0033] It should be noted that the present invention can be used in both dual-cavity lasers and single-cavity lasers. When used in a dual-cavity laser, the excimer laser dose accuracy control method provided by the embodiments of the present invention can be used to adjust the discharge voltage of the power amplifier discharge cavity. When used in a single-cavity laser, there is only one discharge cavity, so the excimer laser dose accuracy control method provided by the embodiments of the present invention adjusts the discharge voltage of the discharge cavity. The following description only describes the present invention in the scenario of applying it to a single-cavity laser, but this does not constitute any limitation on the scope of protection of the present invention.

[0034] like Figure 1 As shown, taking a single-cavity excimer laser as an example, the excimer laser dose accuracy control system provided by the embodiment of the present invention includes a high-voltage discharge component 1, a discharge cavity 2, a laser parameter measurement component 3 and a dose accuracy controller 4.

[0035] Dose precision controller 4 receives the preset desired pulse energy 101 and, in accordance with the excimer laser dose precision control method provided by an embodiment of the present invention, generates a discharge voltage signal for the discharge chamber and transmits it to high-voltage discharge assembly 1. High-voltage discharge assembly 1 then transmits an excitation voltage 103 to discharge chamber 2, which emits laser light. Laser parameter measurement assembly 3 detects the output energy value of discharge chamber 2 and feeds this back to dose precision controller 4. This feedback mechanism enables precise control of the real-time output laser dose.

[0036] As we all know, the light output of excimer laser is usually in burst mode. Under a constant excitation voltage, there are multiple pulses in a burst, for example, 2000 pulse positions. The typical light output energy trend of each pulse position is as follows: Figure 2 As indicated. Figure 2 It can be seen that in the light emission sequence within a burst, the light emission energy at the front pulse position is stronger than the light emission energy at the back pulse position; and the light emission energy at the back pulse position gradually stabilizes. This shows that in burst mode, the light emission capacity of the excimer laser is related to the pulse position.

[0037] Furthermore, as previously mentioned, as the gas within the excimer laser is consumed, the output energy also changes. Therefore, to improve the stability and dose accuracy of the excimer laser's output energy, the present invention pioneers a method for controlling the dose accuracy of an excimer laser that accounts for both the output energy variations caused by varying gas conditions and the output energy variations caused by varying pulse positions.

[0038] like Figure 3A As shown, the excimer laser dose accuracy control method includes at least the following steps:

[0039] S1: count the current burst sequence;

[0040] Assuming that the current burst is the i-th burst, the burst sequence is counted so that i=i+1.

[0041] S2: count the pulse position of a single pulse;

[0042] Assume that the current burst is the jth pulse of the i-th burst, and the pulse position count of a single pulse is j=j+1. Assume that there are N pulses in a burst, then j≦N,n <N。

[0043] S3: Determine whether the pulse position is greater than a preset value n. If it is less than or equal to, proceed to step S4; if it is greater, proceed to step S5;

[0044] S4: Perform single pulse energy stability control calculation to obtain the current discharge voltage V of the discharge cavity ij , used to control the discharge of the discharge chamber; then enter step S6;

[0045] S5: Perform dose accuracy control calculation to obtain the current discharge voltage V of the discharge chamber ij , used to control the discharge of the discharge chamber; then enter step S6;

[0046] S6: Based on the current discharge voltage V ij Controlling the discharge chamber;

[0047] S7: Determine whether the pulses are in the same burst. If so, return to step S2; if not, return to step S1.

[0048] Combine Figure 3BAnd formula (1) is shown, the method for controlling dose precision of excimer laser provided by the embodiment of the application includes two parts: energy stability control of the first n pulses in one burst signal and pulse dose precision control of the subsequent pulses. Thus, based on the voltage of the pulse corresponding to the position in the previous burst, the energy stability control method of the first n pulses is used to make the light output energy at the position of the first n pulses in the current burst signal quickly stabilize to the preset expected pulse energy; the pulse dose precision control is used to consider the influence of the subsequent pulse position and gas consumption on the light output capacity, so as to amplify the voltage calculated by feedback, so that the dose precision of the excimer laser does not decrease due to gas consumption.

[0049]

[0050] The first part, the energy stability control step of the first n pulses, will be introduced first.

[0051] An independent control method is adopted for the first n pulses in each burst, which is different from the control method of the subsequent pulses. Wherein, n is selected according to the characteristics of the light output energy of the laser. In the first n pulses, the discharge cavity discharge voltage of the jth pulse in the ith+1 burst is:

[0052]

[0053] Wherein, V i+1，j is the discharge voltage of the jth (j≤n) pulse in the ith+1 burst signal; V i，j is the discharge voltage of the jth pulse in the ith burst; E i，j is the actual light output energy corresponding to the jth pulse of the ith burst; E d is the expected light output energy; k fp and c fp are preset coefficients; sign() represents the sign function.

[0054] As can be seen from the above formula, during the single-pulse energy stability control calculation process, the increment of the discharge cavity discharge voltage in the two preceding and following burst signals is exponentially expressed as the difference between the actual light output energy and the expected light output energy. Therefore, when the actual light output energy of the jth pulse in the i+1th burst is less than the expected light output energy, the discharge cavity discharge voltage of the j+1th pulse in the i+2th burst calculated by formula (2) will increase; conversely, when the actual light output energy of the jth pulse in the i+1th burst is greater than the expected light output energy, the discharge cavity discharge voltage of the jth pulse in the i+2th burst calculated by formula (2) will decrease. In this way, the discharge cavity discharge voltage is feedback-controlled according to the actual light output energy of the first n pulses in different burst signals, so that the light output energy of the discharge cavity is quickly stabilized to near the expected light output energy.

[0055] This control method takes advantage of the light emission characteristics of the excimer laser: Figure 2 As shown, in a burst, the first n pulses 73 (assuming Figure 2 The light output energy of the pulse 72 is the nth pulse) is usually higher than the expected light output energy. Using formula (1) will Figure 2 The middle pulse 73) quickly stabilizes.

[0056] Next, the pulse dose accuracy control after the nth pulse is introduced.

[0057] Depend on Figure 2 It can be seen that at the nth pulse ( Figure 2 The subsequent pulses (e.g. Figure 2 The output energy of the pulse 71) is relatively stable. However, in a stable state, the energy of a single pulse remains basically around the expected output energy, but there are still fluctuations. Moreover, as the gas degrades, after the excimer laser has been emitting light for a long time, the output energy will decrease as the burst signal increases. In response to this light emission characteristic, the dose accuracy control calculation in the embodiment of the present invention includes two variables: 1) a variable that increases the discharge voltage of the discharge chamber as the burst sequence increases, and 2) a variable that increases the discharge voltage of the discharge chamber as the pulse position increases within a burst.

[0058] As shown in formula (1), the current pulse voltage V now It is the voltage that makes the light output energy of the current pulse roughly meet the expected light output energy. The so-called roughly meeting means that it is within the fluctuation range of the expected light output energy allowed in actual use. Under long-term discharge conditions, due to the deterioration of gas conditions, the pulse voltage increases with the increase in the number of bursts. In the short time after the discharge cavity starts to emit light (the first M bursts, M is a preset value), the discharge voltage of the discharge cavity can be set to the current pulse voltage V now , and the current pulse voltage Vnow Remain unchanged (in the same working condition).

[0059] In the same working condition, the current pulse voltage V now is obtained by the following method:

[0060] a. Estimate the upper and lower limits of the control voltage (discharge voltage) of the discharge chamber corresponding to the desired light output energy under the current gas condition, i.e. estimate the discharge voltage range;

[0061] b. Set a voltage interval (step size) within the estimated discharge voltage range, and take an incremental method to discharge at the position of each step voltage. Assuming X bursts (X is a preset value, for example X = 100) of discharge, take the average of the light output energy of the last Y pulses (Y is a preset value, for example Y = 200) of each burst to obtain the energy average value;

[0062] c. Select the energy average value in step b that is closest to the desired energy value, and obtain the discharge voltage corresponding to the closest desired energy value as the current pulse voltage of the next pulse under the current gas condition.

[0063] Generally, the current pulse voltage V now is obtained by trial discharge after laser debugging, and is calculated according to the measured voltage and light output energy of the trial discharge; once the current pulse voltage V now is determined, the current pulse voltage V now will not be changed if the gas condition does not change (except for natural consumption of gas due to discharge).

[0064] Since the dose accuracy is related to the single pulse energy stability, when controlling the dose accuracy of a burst signal, the single pulse (each pulse within a burst signal) energy fluctuation and dose fluctuation need to be considered. For the (j+1)th pulse in the pulse sequence of j>n within the same burst signal, the energy fluctuation voltage change value δV p，j+1 is used to suppress the voltage fluctuation caused by the energy of the (j+1)th pulse; the dose fluctuation voltage change value δV d，j+1 is used to suppress the voltage fluctuation caused by the dose of the (j+1)th pulse.

[0065] The energy fluctuation voltage change value δV p，j+1 used to suppress the energy fluctuation of the current pulse is represented as:

[0066]

[0067] where δV p，j+1 is the energy fluctuation voltage change value used to suppress the energy fluctuation of the j+0th pulse; k p1 , k p2 , cp1 and c p2 are preset coefficients, which are used to adjust the δV p，j+1 rate of change; err pint，j is the integrated value of the single pulse energy error at the jth pulse position within the same burst, and its initial value is 0; E d is the expected energy value; E j is the single pulse energy at the jth pulse position within the same burst.

[0068] Since the laser light output mode is discrete, the integrated value err pint，j is calculated using a zero-order-hold (ZOH) discrete integration method. Therefore, the update of the integrated value of the single pulse energy error is as follows:

[0069] err pint，j+1 = err pint，j + (E d - E j ) · T (4)

[0070] where T is the sampling period of the energy sensor of the discharge cavity light output energy.

[0071] From equations (3) and (4), it can be seen that the energy fluctuation voltage change value δV p，j+1 is adjusted in a non-linearly amplified or reduced manner based on the energy difference value of the previous pulse position.

[0072] Similarly, the voltage change value δV d，j+1 for suppressing dose fluctuation is expressed as:

[0073]

[0074] where δV d，j+1 is the dose fluctuation voltage change value for suppressing the dose fluctuation of the j+1th pulse, D d is the expected dose, D j is the actual dose at the jth pulse position, k d1 , k d2 , c d1 , and c d2 are preset coefficients, and err dint，j represents the dose error integrated value at the jth pulse position, which is expressed as:

[0075] err dint，j+1 = err dint，j + (D d - D j+1 ) · T (6)

[0076] From formula (5) and (6), it can be seen that the dose fluctuation voltage change value δV d，j+1 The dose difference value according to the previous pulse position is adjusted in a non-linear amplification or reduction manner.

[0077] In the same burst, the corresponding light emission capacity of the gas is relatively weak for the pulse position being later. Similarly, for different burst sequences, the later the position is, the weaker the light emission capacity is. Considering the influence of the pulse position and the gas life, the discharge voltage of the discharge chamber corresponding to the jth pulse of the ith burst is:

[0078]

[0079] Wherein, α is a distribution coefficient (preset value) of single pulse energy stability control and dose precision control; β1(j) is a function of the internal pulse position of a burst, and β2(i) is a function of the burst sequence; for β1(j) and β2(i), the following calculation method can be selected, or other calculation methods can be used.

[0080]

[0081]

[0082] Wherein, c1 and c2 are preset coefficients, j represents the jth pulse, and i represents the ith burst signal.

[0083] In the continuous light emission process, it can be known from formula (7) and (9) that the increment of the discharge voltage of the discharge chamber is approximately exponentially increased with the increase of the burst sequence (i.e. the increase of the value of i); it can be known from formula (7) and (8) that the increment of the discharge voltage of the discharge chamber is approximately multipliedly increased with the increase of the pulse position in a burst. It can be seen that the light emission dose reduction caused by the gas degradation is quickly compensated (e.g. exponentially changed) in the present application; the compensation of the single pulse energy fluctuation and the average pulse energy drift and energy overshoot is a relatively slow compensation (e.g. multipliedly changed) compared with the former, so that the light emission energy changes caused by the two reasons are considered, so that a higher dose precision control effect can be obtained.

[0084] In order to verify the technical effect of the dose precision control method of the excimer laser provided by the embodiment of the present application, it can be obtained through simulation analysis that, under the condition that the working condition is unchanged (for example, the 248nm KrF excimer laser model works at a repetition frequency of 4KHz, and the target energy is set to 10mJ), the energy stability and the dose stability can be controlled to the best control effect by adjusting the parameters, and the energy stability and the dose stability can be controlled to the best control effect by adjusting the parameters. Figure 4 It can be known that the dose precision of each burst signal is controlled to be less than 0.3%.

[0085] In summary, the excimer laser dose precision control method provided by the embodiment of the present application is based on the control algorithm of the discharge output energy process, considers the influence of different pulse positions and gas life on the discharge light output process, uses feedback to perform nonlinear calculation on the excitation voltage, and simultaneously suppresses the fluctuation caused by single pulse energy and dose, avoids the sharp change of the discharge voltage caused by the mutation of the single pulse energy, and ensures the dose precision requirement in the laser working process.

[0086] The excimer laser dose precision control method and system and the excimer laser provided by the present application are described in detail above. Any obvious modification made by the general technical personnel in the field without departing from the essential content of the present application will constitute an infringement of the patent right of the present application and will bear the corresponding legal responsibility.

Claims

1. An excimer laser dose accuracy control method, characterized by The method comprises the following steps: S1: counting the current burst sequence; S2: counting the pulse position of the single pulse; S3: judging whether the pulse position is greater than a preset value n, if less than or equal to, entering step S4; if greater than, entering step S5; S4: performing single pulse energy stability control calculation to obtain the current discharge voltage Vij of the discharge cavity for controlling the discharge cavity; Then entering step S6; S5: performing dose accuracy control calculation to obtain the current discharge voltage Vij of the discharge cavity for controlling the discharge cavity; Then entering step S6; S6: adjusting the discharge voltage of the discharge cavity based on the current discharge voltage Vij; S7: judging whether it is the pulse in the same burst, if yes, returning to step S2; if not the pulse in the same burst, returning to step S1. The dose accuracy control calculation comprises a variable for increasing the discharge voltage of the discharge cavity with the increase of the burst signal, and a variable for increasing the discharge voltage of the discharge cavity with the increase of the pulse position in one burst signal.

2. The excimer laser dose accuracy control method of claim 1, wherein: The dose accuracy control calculation is calculated based on an energy fluctuation voltage change value for suppressing the energy fluctuation of the current pulse and a dose fluctuation voltage change value for suppressing the dose fluctuation of the current pulse.

3. The excimer laser dose accuracy control method of claim 2, wherein: The dose fluctuation voltage change value is adjusted in a non-linear amplification or reduction manner according to the dose difference value of the previous pulse position; the energy fluctuation voltage change value is adjusted in a non-linear amplification or reduction manner according to the energy difference value of the previous pulse position.

4. The excimer laser dose accuracy control method of claim 2, wherein: The dose accuracy control calculation is also calculated based on a predetermined current pulse voltage, which is calculated according to the measured voltage and the light output energy of the trial discharge.

5. The excimer laser dose accuracy control method of claim 4, wherein: The current pulse voltage is a preset value, and remains unchanged under the same working condition.

6. The excimer laser dose accuracy control method of claim 5, wherein: The current pulse voltage is obtained by the following method under the same working condition: a. estimating the estimated discharge voltage range corresponding to the expected light output energy under the current gas condition; b. setting a step length in the estimated discharge voltage range, and taking an incremental method to discharge at the voltage position of each step length, and taking the average of the light output energy of the multiple pulses after each burst to obtain an energy average value; c. selecting the energy average value in step b. closest to the expected energy value to obtain the discharge voltage corresponding to the closest expected energy value as the current pulse voltage of the next pulse under the current gas condition.

7. The dose accuracy control method of the excimer laser according to claim 5, wherein: In the single pulse energy stability control calculation, the increment of the discharge voltage of the discharge cavity in the same burst signal is exponential to the difference between the actual light output energy and the expected light output energy.

8. An excimer laser dose accuracy control system, characterized by The system comprises a high-voltage discharge assembly, a discharge cavity, a laser parameter measurement assembly, and a dose accuracy controller, wherein the dose accuracy controller receives a preset expected pulse energy, generates a discharge voltage signal for the discharge cavity according to the dose accuracy control method of any one of claims 1-7, and sends the discharge voltage signal to the high-voltage discharge assembly; the high-voltage discharge assembly sends an excitation voltage to the discharge cavity, the discharge cavity emits laser light, the laser parameter measurement assembly detects the light energy value of the discharge cavity, and feeds back the light energy value to the dose accuracy controller.

9. An excimer laser characterized by The system comprises the dose accuracy control system of claim 8.

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