CN113783101A - Energy control method and device for dual-cavity excimer laser - Google Patents
Energy control method and device for dual-cavity excimer laser Download PDFInfo
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Abstract
The invention discloses an energy control method and device for a dual-cavity excimer laser. The method comprises the following steps: detecting the energy of a light outlet of the double-cavity excimer laser, and searching for the maximum voltage value; detecting the time delay between the main oscillation discharge cavity and the power amplification discharge cavity to obtain a detected time delay signal; calculating and outputting voltage and a delay signal according to the voltage maximum value and the measured delay signal, and controlling a main oscillation discharge cavity and a power amplification discharge cavity according to the voltage and the delay signal, wherein the control of the main oscillation discharge cavity comprises the following steps: and performing closed-loop control on a voltage signal of the main oscillation discharge cavity according to the voltage of the power amplification discharge cavity to limit the voltage of the power amplification discharge cavity within an adjustable voltage range. The invention adopts a multi-ring PI control method to control the energy output of two cavities of the double-cavity laser, greatly expands the energy adjusting range and ensures the stability of energy control in the energy adjusting process.
Description
Technical Field
The invention relates to an energy control method and device for a dual-cavity excimer laser, and belongs to the technical field of photoetching machines.
Background
The most common excimer lasers include argon fluoride (ArF), krypton fluoride (KrF), xenon chloride (XeCl) and the like, the central wavelengths of the excimer lasers are 193nm, 248nm and 308nm respectively, and energy changes of the excimer lasers can cause the light stability of a photoetching machine to be reduced in the exposure process, so that the exposure lines are not uniform, and the yield of chips is reduced.
Because the energy of the double-cavity laser is nonlinear change in the burst light emitting mode of the laser, the pulse energy stability can be obviously influenced even under the same voltage due to the different conditions of gas state change, temperature change, mechanism sensitivity and the like of the laser. In order to satisfy the characteristics of controlling single input and single output and maintaining energy stability, the dual-cavity laser outputs only one variable to adjust the variable of one cavity or share the variable by the dual-cavity laser. However, this method has the disadvantage of an insufficient adjustment range or an insufficient accuracy.
Moreover, the discharge delay error of the dual cavity also has a serious influence on the pulse energy of the laser, the longer the discharge delay is deviated from the optimal delay, the lower the pulse energy of the laser is, and the discharge delay deviation is influenced by the temperature, the voltage and the number of pulses, so that the laser has randomness. The optimal time delay is the time delay of leading the light emitted from the power amplification discharge cavity and the main oscillation discharge cavity to simultaneously reach the light outlet of the dual-cavity excimer laser.
Therefore, how to enlarge the energy adjustment range and ensure the energy adjustment stability simultaneously leads the light emission of the double-cavity laser to be stable so as to improve the yield of chips and has great significance to the chip manufacturing industry.
Disclosure of Invention
The invention provides an energy control method for a dual-cavity excimer laser.
Another object of the present invention is to provide an energy control device for a dual cavity excimer laser.
In order to achieve the technical purpose, the invention adopts the following technical scheme:
a method of energy control for a dual cavity excimer laser comprising:
detecting the energy of a light outlet of the double-cavity excimer laser, and searching for the maximum voltage value;
detecting the time delay between the main oscillation discharge cavity and the power amplification discharge cavity to obtain a detected time delay signal;
calculating and outputting voltage and delay signal according to the maximum voltage and the measured delay signal,
the main oscillation discharge cavity and the power amplification discharge cavity are controlled according to the voltage and the time delay signal,
wherein the control of the main oscillating discharge chamber comprises: and performing closed-loop control on the voltage signal of the main oscillation discharge cavity according to the power amplification discharge cavity voltage.
Preferably, the main oscillating discharge chamber and the power amplifying discharge chamber are controlled in accordance with the voltage and delay signals, including performing the following steps during each burst signal:
calculating the voltage average value of the power amplification discharge cavity for the voltage signal of the power amplification discharge cavity,
according to the average value of the voltage of the power amplification discharge cavity, the limiting amplitude value of the voltage signal of the main oscillation discharge cavity is calculated, and the limiting voltage is output,
and calculating the error between the mean value of the voltage of the main oscillation discharge cavity and the amplitude limiting voltage, and performing closed-loop control on the voltage signal of the main oscillation discharge cavity.
Preferably, the voltage signal of the power amplification discharge cavity is obtained by adding a dosage control signal controlled by PI, a voltage average control signal controlled by PI and a time delay control signal controlled by PI.
Wherein preferably the delay control signal is PI controlled for the error between the measured delay and the optimum delay for the plurality of pulses,
the measured time delay is the time delay between the power amplification discharge cavity and the main oscillation discharge cavity which is obtained by detection; the optimal time delay is the time delay of leading the light emitted from the power amplification discharge cavity and the main oscillation discharge cavity to simultaneously reach the light outlet of the dual-cavity excimer laser.
Preferably, the final trigger delay is obtained by adding an open-loop delay based on the trigger delay between the power amplification discharge cavity and the main oscillation discharge cavity and a closed-loop delay signal obtained based on the measured delay and the optimal delay, and is used for controlling the delay between the power amplification discharge cavity and the main oscillation discharge cavity.
An energy control device for a dual cavity excimer laser comprising:
the energy sensor is used for detecting the energy of the light outlet of the double-cavity excimer laser and outputting an energy signal to the energy control module;
the execution/detection module is used for controlling the main oscillation discharge cavity and the power amplification discharge cavity, detecting the time delay between the main oscillation discharge cavity and the power amplification discharge cavity, outputting a detected time delay signal to the energy control module,
the energy control module is used for calculating the maximum voltage value according to the energy signal, calculating the voltage and the delay signal according to the maximum voltage value and the measured delay signal and outputting the voltage and the delay signal to the execution/detection module,
wherein the control of the main oscillating discharge chamber comprises: and performing closed-loop control on the voltage signal of the main oscillation discharge cavity according to the power amplification discharge cavity voltage.
Preferably, the energy control module comprises:
the main oscillation discharge cavity mean value calculating module is used for calculating the main oscillation discharge cavity mean value of the voltage signal of the power amplification discharge cavity in each burst signal period,
the amplitude limiting module is used for carrying out amplitude limiting calculation on the voltage signal of the main oscillation discharge cavity according to the voltage average value of the main oscillation discharge cavity and outputting amplitude limiting voltage,
the main oscillation discharge cavity error calculation module is used for calculating the error between the voltage mean value of the main oscillation discharge cavity and the amplitude limiting voltage,
and the main oscillation discharge cavity PI controller is used for carrying out PI control on the error of the amplitude limiting voltage so as to carry out closed-loop control on the voltage signal of the main oscillation discharge cavity.
Preferably, the energy control module further comprises: a high-speed signal processing module for searching the maximum value of the voltage, and a control algorithm module,
and the control algorithm module calculates and outputs the voltage and the delay signal according to the measured delay signal and the maximum voltage value.
Preferably, the control algorithm module comprises: a dose controller, a mean lock controller, and a time delay PI controller, and an adder,
the dosage controller generates a dosage control signal controlled by PI; the mean value locking controller generates a voltage mean value control signal controlled by PI, the time delay PI controller generates a time delay control signal controlled by PI,
the adder adds the dose control signal, the voltage mean value control signal and the delay control signal to obtain and output a power amplification discharge cavity voltage signal.
Preferably, the control algorithm module is based on an open-loop delay signal of trigger delay between the power amplification discharge cavity and the main oscillation discharge cavity and a closed-loop delay signal obtained based on the measured delay and the optimal delay, and the open-loop delay signal and the closed-loop delay signal are added to obtain final trigger delay so as to control delay between the power amplification discharge cavity and the main oscillation discharge cavity.
The invention has the following technical effects: 1) the voltage signal of the main oscillation discharge cavity is limited by the voltage signal average value of the power amplification discharge cavity, so that the adjustable range of the voltage of the power amplification discharge cavity is enlarged; 2) by utilizing multi-PI control, PI control is adopted for a voltage signal of the power amplification discharge cavity, a voltage signal of the main oscillation discharge cavity and trigger delay, so that the control precision and the stability of light-emitting energy are improved; 3) the method combines open-loop control and closed-loop control on the trigger delay, further improves the speed of delay control and accelerates response.
Drawings
FIG. 1 is a schematic diagram of a control structure of a dual cavity excimer laser according to an embodiment of the present invention;
FIG. 2a is a schematic diagram of burst-mode light emission characteristics of a dual-cavity excimer laser;
FIG. 2b is a schematic diagram of energy sensor signal sampling;
FIG. 3 is a schematic diagram of the energy control module of FIG. 1;
FIG. 4 is a schematic flow diagram of the peak search module of FIG. 3;
fig. 5 is a schematic flow diagram of the burst signal identification module of fig. 3;
FIG. 6 is a schematic diagram of a control circuit for the power amplified discharge chamber voltage signal of FIG. 3;
FIG. 7a is a schematic diagram of an internal burst signal pulse sequence in a power amplified discharge cavity voltage signal in a constant energy mode;
fig. 7b is a voltage diagram of a plurality of burst signals;
FIG. 8 is a schematic diagram of a voltage signal control circuit for a main oscillation discharge chamber;
fig. 9 is a schematic diagram of a trigger delay signal control circuit.
Detailed Description
The technical contents of the invention are described in detail below with reference to the accompanying drawings and specific embodiments.
As shown in fig. 1, a dual-cavity laser (hereinafter, referred to as laser) control system according to an embodiment of the present invention is used to control a dual-cavity excimer laser to emit a stable laser output pulse (hereinafter, referred to as pulse or pulse signal). The laser control system comprises an energy control module 101, an execution/detection module 102, a main oscillation discharge chamber 104, a power amplification discharge chamber 105 and an energy sensor 103. The energy control module 101 sends a delay instruction and a voltage control instruction to the execution/detection module 102, the execution/detection module 102 detects the delay and sends the delay instruction to the energy control module 101, and sends voltage control signals to the main oscillation discharge cavity (MO cavity) 104 and the power amplification discharge cavity (PA cavity) 105, respectively. The energy sensor 103 detects an energy signal of laser emitted by the PA cavity, and feeds back the energy signal to the energy control module 101, thereby realizing closed-loop control.
Referring to the burst mode light emission characteristics of the dual cavity excimer laser shown in fig. 2a and 2b, the operating mode of the dual cavity excimer laser is generally burst mode. In burst mode, there are multiple clusters 202 with a burst interval 203 between adjacent clusters 202. The duration of the burst interval 203 can be set, typically 20ms or more, but if the duration of the burst interval 203 is set to 0, the laser operates in a continuous mode (not shown). After the burst interval comes, the laser does not emit light. Each burst signal 202 includes a plurality of laser pulses (hereinafter referred to as pulses) 201. Only the first burst signal 202a and the second burst signal 202b are schematically shown in fig. 2 a. The number of pulses and the pulse frequency of the pulses in the burst signal can be set. The pulse frequency refers to the light emitting frequency of the laser in the burst signal, which is generally between 1kHz and 6 kHz. The energy levels of the pulses in the figure are schematic and do not represent true levels.
The energy control module 101 receives the energy signal 12 from the energy sensor 103. The energy signal 12 is an analog signal. As shown in fig. 2b, the energy sensor 103 is located at the light outlet, performs laser energy detection, and sends a laser energy signal to the energy control module 101 in an analog manner. The photodiode built into the energy sensor 103 converts one laser pulse 201 into a plurality of voltage signals 204. Since the laser pulse 201 is short in time and the photodiode voltage is low, the voltage signal 204 has the characteristics of short time and low voltage. The energy sensor 103 incorporates an amplification circuit for amplifying the voltage signal 204 and a timing circuit for delaying the voltage signal 204 by about 20 us. The amplified and delayed energy signal 12 is passed to the energy control module 101.
As shown in connection with fig. 3, the energy control module 101 includes a high-speed signal processing module 304 and a signal calculation control module 309, both of which may be implemented by two separate CPU processors or located within a single CPU processor.
The high-speed signal processing module 304 includes an analog-to-digital conversion module 301, a high-frequency filtering module 302, and a peak finding module 303. In this embodiment, the peak search module 303 has a signal calculation control module 309 embedded therein.
The analog-to-digital conversion module 301 is a high-speed analog-to-digital conversion chip, and converts the input energy signal 12 into a digital signal, and outputs the digital signal to the high-frequency filtering module 302. The high-frequency filtering module 302 includes a comb filter and an infinite impulse response filter, and is configured to filter out frequency components of the digital signal that are greater than 1 mhz, and output a filtered signal to the peak searching module 303. The logic flow diagram of the peak finding module 303 is shown in fig. 4. The peak finding module 303 is triggered by an event, for example, when a rising edge of the filtered signal is detected (for example, when the voltage of the filtered signal is detected to be greater than or equal to 0.5 v), a timer is started, and a preset time (for example, 15 μ sec) is timed. And simultaneously starting to search for the maximum voltage value until the timing is finished. At the end of the timing, the maximum value (peak value) of the voltage within a preset time is output as the energy value of the current laser pulse. Meanwhile, the primary signal calculation control module 309 is operated to control the dual-cavity voltage and the time delay for one time. Thereafter, a voltage drop (e.g., a voltage less than 0.3v) is waited for, at which point the processing of the current laser pulse ends. Therefore, the laser pulse in each burst signal controls the double-cavity voltage and time delay once, so as to improve the control precision and stability.
The signal calculation control module 309 includes an energy processing module 305, a burst signal identification module 308, and a control algorithm module 307 for calculating and transmitting the voltage and delay signals 11. The voltage and delay signal 11 contains three signals: the trigger delay signal, the main oscillation discharge cavity voltage signal and the power amplification discharge cavity voltage signal.
The energy processing module 305 converts the maximum voltage value from the peak searching module 303 as a voltage signal into a current laser pulse energy value according to the following formula, and outputs the current laser pulse energy value to the control algorithm module 307:
y＝a*x+b
where x is the voltage signal from the peak lookup module 303 in millivolts; y is the current laser pulse energy value in millijoules; a. b is a linear coefficient and needs to be determined according to actual conditions. In this embodiment, values of a and b are as follows:
| laser serial number | a | |
| 1 | 0.002335 | 1.0378 |
| 2 | 0.002271 | -1.1077 |
| 3 | 0.001927 | -1.431 |
| 4 | 0.002736 | -1.377 |
| 5 | 0.002927 | 0.4122 |
Wherein the flow chart of the burst signal identification module 308 is shown in fig. 5. The burst signal identification module 308 is used to perform burst signal identification and pulse counting. Specifically, when the signal calculation control block 309 is triggered, the burst signal identification block 308 is initialized first. In the initialization stage, the pulse number is cleared, the burst signal number is cleared, and the total pulse number is cleared. After the initialization is completed, the burst number is incremented by 1 when the first pulse comes within one burst signal (e.g., the first burst signal 201) (e.g., the burst number is incremented from 99 to 100 in the 100 th burst signal), and the pulse is incremented. Then, judging whether the pulse time interval is greater than a preset time length (20 milliseconds in the embodiment), if not, namely the current burst signal is not finished, continuing to count the pulses; if 20ms is reached, i.e. the current burst signal is over, return and add 1 to the burst signal sequence number.
During a period in which the burst signal has not ended, 1 is added to the pulse number and 1 is added to the total number of pulses. Since the pulse number has been cleared after the aforementioned initialization, the pulse number always increases from 0, for example, from 0 to 1000, in the duration of each burst signal. The total pulse number is cleared only in the initialization stage, but is not cleared when each burst signal arrives, so the total pulse number is continuously increasing.
The burst signal identification module 308 generates a pulse number, a burst signal number and a total pulse number, and outputs the pulse number, the burst signal number and the total pulse number to the control algorithm module 307. The sequence number of the burst signal (denoted by i), the pulse sequence number (denoted by j), and the total number of pulses (denoted by p) are used to control the timing implementation of the algorithm block 307.
As previously mentioned, the inputs to the control algorithm module 307 include: the pulse number, the number of bursts, and the total number of pulses from the burst signal identification module 308; a measured delay signal 13 from the execution/detection module 102; the current laser pulse energy value from the energy processing module 305. The output signal 11 of the control algorithm module 307 contains a main oscillation discharge cavity voltage signal, a power amplification discharge cavity voltage signal and a trigger delay signal. The measured delay is the actual delay between the power amplifying discharge chamber and the main oscillating discharge chamber detected by the implementation/detection module 102.
The power amplification discharge cavity voltage signal control circuit is shown in fig. 6. The preset energy target signal 604 and the measured energy signal 603 (i.e., the current laser pulse energy value) from the energy processing module 305 are input to the adder 61, the error signal 63 of the two is calculated, and output to the mean lock controller 608 and the dose controller 607.
Error value e63And a measured energy value E603Energy target value E604The following equation is satisfied:
e63＝E604-E603
wherein e is63A value representing the output error signal 63 of the energy error calculation module 610; e603Represents the value of the measured energy signal 603; e604Representing the value of the energy target signal 604.
The operation of the mean-lock controller 608 is described below. In burst mode, the voltage of the pulses within each burst signal is different even at the same energy, and thus the average voltage of the pulses within the plurality of burst signals within each burst signal 202 is different. As shown in fig. 7a, where the mean line 72 is the mean scatter point of 1000 pulses within a burst signal at the same pulse position, it can be observed that the pulse voltage 71 of the pulses within a burst signal gradually increases with the pulse position. As shown in fig. 7b, the pulse voltage 71 returns to the lowest point after new burst signal generation among the burst signal 701, the burst signal 702, and the burst signal 703. The first pulse 73 of the pulses within the burst signal is the lowest point. If there is no mean-lock, the dual cavity excimer laser needs a relatively long stabilization process. In the embodiment of the invention, the response speed is increased by quickly finding the average voltage of the pulses in each burst signal. In addition, it is to be understood that burst signal identification may be implemented in separate hardware or may be implemented in software.
The implementation of the method for mean-locking the mean voltage of the pulses in each burst signal by mean-lock controller 608 includes two steps: mean value calculation and error closed-loop control.
The equation for the mean lock controller 608 to perform the error mean calculation is as follows:
wherein k ∈ total pulse number p, e63(j，k)To representAn error value of a jth pulse in a kth burst signal; e.g. of the type608(j，i)Which represents the error sum of the first 1000 pulses in the j-th burst signal in the i-th burst signal. It is understood that the sum of errors of the pulses in the first 1000 burst signals is taken in this embodiment, and may be set to other values according to the pulse frequency. In general, when the pulse frequency is 1kHz, 1000 is suitable.
Based on the error mean calculation, the mean lock controller 608 performs a mean error voltage calculation according to the following formula:
v608(j，i)＝v608(j，i-1)+Kp*(e608(j，i-1)-e608(j，i-2))+Ki*e608(j，i-1) j＜N
V608(j，i)＝v608(j-1，i) j＞＝N
v608＝v608(j，i)
in the above equation, v608(j，i)Is the average voltage of the jth pulse in the ith burst signal (is v608The value of the jth pulse in the ith burst), N is typically a fixed value preselected between 30 and 500, and Kp, Ki are the proportional and integral coefficients, respectively (experimentally determined) of the PI control algorithm. Since the average voltage is calculated based on a PI (Proportional Integral Control) algorithm, the Control precision is improved, and the stability of laser light emission is improved.
The calculation process of the dose controller 607 is described below. Dose accuracy is an important indicator of high repetition frequency excimer lasers for semiconductor lithography. The dose controller 607 achieves the most direct control of dose accuracy with the calculation steps divided into two steps of dose error calculation and dose error closed loop.
The dose error calculation is as follows, and the dose error sum is obtained:
therein, Dose(j，i)In the ith burstMean value of dose error of pulses in jth burst signal in the number, l ∈ total number of pulses p, e63(j，k)Represents an error value of pulses in the i-th burst signal, Ns being the number of pulses in one dose.
Dose voltage signal v607The calculation method of (2) is as follows:
v607(j-1，i)＝v608(j-1，i) j＜N-1
v607(j，i-1)＝v607(j，i-1) j>＝N-1
v607(j，i)＝v607(j-1，i)+Kp*(Dose(j-1，i)-Dose(j-2，i))+Ki*Dose(j-1，i)
v607＝v607(j，i)
wherein: v. of607(j，i)Represents the result of PI-control algorithm-based dose error control of pulses within the jth of the ith burst signals (i.e., v607The value of the jth pulse in the ith burst signal), Kp, Ki are the proportional and integral coefficients (determined experimentally) in the PI control method, respectively. The mean-value-lock controller 608 is active when j < N-1, such that the output v of the dose controller 607607Output v of and mean lock controller 608608The same, i.e. the dose controller 607 is not functioning. The mean value lock controller 608 is disabled when j > -N-1, such that the output v of the dose controller 607 is607(j，i)Is a signal subjected to PI control to improve stability. N denotes the number of a certain pulse within a burst signal.
The delay compensation module 612 is used for performing delay compensation. Since delay jitter can cause severe disturbances to the laser pulse energy, delay compensation needs to be specifically designed for cases where the delay deviates from the optimum delay. The delay compensation module 612 is composed of a delay error calculation and PI controller. The PI regulator is a linear controller that forms a control deviation from a given value and an actual output value, and linearly combines the proportion and integral of the deviation to form a control amount to control an object to be controlled.
The input to the delay error calculation module 612 isThe optimal delay 601 and the measured delay signal 13 from the execution/detection module 102 are processed by the adder 62 to obtain the delay error 64, and the delay error 64 is processed by the PI controller 609 to obtain the delay voltage signal v609。
The delay error 64 is calculated as follows:
Te64＝T602-T601
wherein, Te64For delay errors, T601The time delay is the preset optimal time delay; t is602Is the value of the measured delay signal 13 from the execution/detection module 102.
Output delay voltage signal v of delay PI controller 609609The calculation formula of (a) is as follows:
wherein v is609(j，i)Is the result of the PI controller 609 on the jth pulse of the ith burst signal (i.e., v609At the jth pulse of the ith burst signal), Kp0、Ki0Respectively a proportional coefficient and an integral coefficient in the PI control,
is the delay error at the j-1 pulse of the ith burst signal.
The outputs of the three controllers, dose 607, mean-lock 608 and PI 609, are combined together by adder 64 as the power amplified discharge chamber voltage signal v611Output in a relationship satisfying the following equation
v611＝v607+v608+v609
Wherein v is611For power amplification of the discharge-chamber voltage signal, v607、v608、v609A dose voltage signal output by the dose controller 607, a mean voltage signal output by the mean lock controller 608, and a delay voltage signal output by the PI controller 609. The three are obtained by PI control independently and used for controlling power amplifierThe voltage signal of the large discharge cavity can improve the stability of the laser light energy of the power amplification discharge cavity.
The method of controlling the voltage of the main oscillating discharge vessel is described below. The voltage regulation of the main oscillation discharge cavity of the embodiment of the invention can expand the energy regulation range, can reduce the voltage difference between the main oscillation discharge cavity and the power amplification discharge cavity, and can enhance the stability of the laser emergent light energy by reducing the voltage difference.
The voltage control of the main oscillation discharge cavity is shown in fig. 8 and comprises a power amplification discharge cavity mean value calculation module 902, a limiting amplitude value module 903, a main oscillation discharge cavity error calculation module 904 and a main oscillation discharge cavity PI controller (MO PI controller) 905.
The input of the power amplification discharge cavity mean value calculation module 902 is a voltage signal 611 (shown in fig. 6) of the power amplification discharge cavity, which calculates a power amplification discharge cavity mean value of 500 pulses (preset to 500 pulses in this embodiment, or preset to other number of pulses) according to the following formula, and outputs the mean value to the amplitude limiting module 903:
where k is the pulse train number, which is the pulse number based on the total number of pulses p.
For the k pulse, v, in the output signal of the power amplified discharge chamber mean value calculation module 902611kIs the result of the kth time of the power amplification discharge cavity voltage signal.
The input of the limiting amplitude module 903 is a main oscillation discharge cavity voltage 901 and a power amplification discharge cavity voltage mean value v902Which amplitude limits the main oscillating discharge chamber voltage 901. This is because the average voltage of the power amplifying discharge chamber 105 cannot be too close to its minimum or maximum voltage, so that the voltage of the power amplifying discharge chamber can be normally adjusted (adjustable range). For example, assume that the voltage range of the power amplifying discharge chamber is 1300V to 2000V, the average voltage value of the power amplification discharge cavity should be about 1400V at the lowest, and the maximum voltage value should be about 1900V. The limiting amplitude module 903 operates in the following mode:
v903＝v901 B＞v901＞A
v903＝A v901＜A
v903＝B v901＞B
wherein v is903To limit the output (limiting voltage), v, of the magnitude module 903901A, B are the lower and upper voltage limits of the power amplifying discharge cavity, respectively. By using the amplitude limiting module 903, the voltage of the main oscillation discharge cavity is in a proper range and is not too large or too small due to consumption of working gas and the like. Therefore, the problem that the light emitting capability of the excimer laser is reduced (namely, the light emitting energy is reduced under the same voltage) along with the gas consumption in the discharge cavity is solved.
The main oscillation discharge cavity error calculation module 904, according to the input calculation formula, is as follows:
v904＝v902-v903
wherein v is904Is a voltage signal output by the main oscillation discharge cavity error calculation module 904; v. of902For the voltage signal, v, output by the power amplification discharge chamber mean value calculation module 902903To limit the voltage signal output by the magnitude module 903.
The calculation formula of the MO PI controller 905 is as follows:
where j ∈ p is a pulse sequence number based on the total number p of pulses. Kp1、Ki1Proportional and integral coefficients, v, of PI control, respectively904(j-1)The voltage signal of the j-1 pulse output by the main oscillation discharge cavity error calculation module 904, v905(j)The voltage signal of the jth pulse output by the MO PI controller 905. In this case, the amount of the solvent to be used,the stability of the energy of the outgoing laser of the main oscillation discharge cavity is further improved by utilizing the MO PI controller 905. It should be understood that the closed-loop control by the MO PI controller 905 is not limited thereto, and other closed-loop control methods may be adopted.
The calculation of the trigger delay in the voltage and delay signal 11 is described below. As shown in fig. 9, a final trigger delay 1008 is calculated based on a delay error between an actual discharge delay (measured delay signal 13) and an optimal delay (e.g., 35ns) between the discharges of the main oscillating discharge chamber and the power amplifying discharge chamber, and a current trigger delay 1001. The trigger delay 1001 required to achieve the optimum delay (e.g., 35ns) can be determined experimentally, and the relationship satisfies the following quadratic relationship
T(v611，v901)＝e*v611 2+d*v901 2+c*v611+b*v901+a
Where a, b, c, d, e are all quadratic polynomial coefficients, the optimum delay (e.g., 35ns) will be met when the actual trigger delay between dual chamber discharges is T. In practice the different laser parameters will be different.
Due to the influence of the temperature and electrical characteristics inside the dual chamber, the above formula is biased and therefore needs to be corrected in a closed loop. The open-loop trigger delay and the closed-loop trigger delay are added by adder 1007 and final trigger delay 1008 is output. The invention can quickly eliminate the delay deviation by a method of combining the open loop and the closed loop.
As shown in fig. 9, the closed-loop trigger delay 1006 is calculated by: the measured delay signal 13 is subtracted from the optimal delay 1002 by an adder 1004 to obtain a delay error, and the delay error is low-pass filtered 1005 and then processed by a PI controller 1006. Wherein the optimal delay signal 1002 is a predetermined value based on the dual chamber electrical characteristics. The adder 1004 satisfies the following relationship:
T1004＝T13-T1002
wherein T is1004Representing the delay error, T, of the adder 100413Representing the actual measured delay, T1002Indicating a preset optimal delay.
The low-pass filter 1005 satisfies the following relation:
T1005(j)＝(1-a)T1005(j-1)-aT1002
a＝1/(1+fs)
wherein f issAt the frequency of the laser pulses, T1005(j)Is the jth output of the low pass filter 1005.
The output of the PI controller 1006 satisfies the following relationship:
T1006(j)＝T1005(j-1)+Kp2*(T1005(j-1)-T1005(j-2))+Ki2*T1005(j-1)
wherein, T1006(j)The jth pulse representing the output signal of the PI controller 1006; kp2、Ki2Proportional and integral coefficients, T, of PI control, respectively1005(j-i)Output signal T for low pass filter 10051005The j-1 th pulse of (1).
The above-mentioned values are merely examples and can be set according to the actual laser performance. Through the control of the execution/detection module 102 by the energy control module 101, including the discharge delay control between the dual cavities and the voltage control of the dual cavities, the delay interference of the dual-cavity excimer laser and the nonlinear relation between the laser pulse energy and the voltage are solved, the energy disturbance is eliminated, and the energy stable output is realized.
The working principle of the embodiment of the present invention is described below.
As shown in fig. 2a-2b, during each burst signal, the energy control module 101 performs the energy control of the present invention for the main oscillating discharge chamber and the power amplifying discharge chamber. As shown in fig. 3, the energy control module 101 obtains the energy signal from the energy sensor 103, finds the voltage maximum value from the energy signal, and outputs the voltage maximum value to the energy processing module 305. The energy processing module 305 performs a linear calculation on the voltage value, and outputs the linear calculation as the measured energy 603 to the energy error calculation module 610. As shown in fig. 6, the energy error calculation module 610 calculates the energy error based on the preset energy target value by using the adder 61, and outputs the energy error to the dose controller 607 and the mean value locking controller 608. The mean-value locking controller 608 calculates a mean-value voltage by PI control, and obtains a mean-value voltage control signal.
Meanwhile, the dose controller 607 calculates a dose control signal using PI control based on the aforementioned energy error. Furthermore, in the delay compensation module 612, the delay control signal is calculated based on the actually measured error between the measured delay signal 13 (measured by the execution/detection module 102) and the optimal delay signal 601 by using the delay PI controller 609. The mean voltage control signal, the dose control signal, and the delay control signal are collectively input to an adder 64 to form a power amplified discharge chamber voltage signal 611. The three are calculated by the PI control method, so that the control precision can be improved, and the light emitting stability of the power amplification discharge cavity can be improved.
As shown in fig. 8, based on the mean value of the power amplified discharge cavity voltage signal 611, the amplitude of the main oscillation discharge cavity voltage signal 901 is limited, so that the power amplified discharge cavity voltage signal is limited within a preset adjustable voltage range, thereby achieving the adjustable power amplified discharge cavity voltage. Therefore, the light output energy of the excimer laser under the same voltage can be prevented from being reduced due to the consumption of the working gas.
Furthermore, the PI control and the closed-loop control are utilized, so that the error between the voltage of the main oscillation discharge cavity and the average value of the voltage of the power amplification discharge cavity is accurately controlled, and the stability of the voltage of the main oscillation discharge cavity is improved.
As shown in fig. 9, the power amplified discharge cavity voltage signal 611 and the main oscillation discharge cavity voltage signal 901 obtained by the above calculation are used to calculate the open-loop delay, and then the final trigger delay 1008 is calculated based on the closed-loop delay obtained by using the PI control algorithm and based on the error between the measured delay signal 13 and the optimal delay 1002.
Referring to fig. 1 and fig. 3, the control algorithm module 307 calculates the power amplified discharge chamber voltage signal 611, the main oscillation discharge chamber voltage signal 901, and the final trigger delay 1008 (which are collectively referred to as the voltage and delay signal 11), and sends the voltage and delay signal 11 to the execution/detection module 102. The execution/detection module amplifies the main oscillating discharge cavity voltage signal 901 in the voltage and delay signal 11 and applies the amplified high voltage to the main oscillating discharge cavity 104. Therefore, the gas in the main oscillating discharge chamber 104 is excited to generate laser after being generated by high voltage. After a period of time (final trigger delay 1008), the execution/detection module 102 applies a high voltage to the power amplifying discharge chamber 105, which is obtained by amplifying the power amplifying discharge chamber voltage signal 611. Therefore, the gas in the power amplifying discharge cavity 105 is excited to generate laser after high-voltage discharge. Through the delay control of the energy control module 101, it can be ensured that the laser generated by the main oscillation discharge cavity 104 and the power amplification discharge cavity 105 reaches the light outlet at the same time (to achieve the optimal delay effect). The pulse energy of the laser can be adjusted by controlling the voltage signal of the dual cavity.
In summary, the dual-cavity excimer laser of the embodiment of the present invention has the following technical advantages:
1) the mean value of the voltage signal of the power amplification discharge cavity is locked, the amplitude limit is carried out on the voltage signal of the main oscillation discharge cavity, and the closed-loop adjustment of the voltage of the main oscillation discharge cavity is carried out, so that the light-emitting energy adjustment range is expanded, and the problem of light-emitting capability reduction caused by gas consumption in the discharge cavity is solved;
2) the voltage signal of the power amplification discharge cavity, the voltage signal of the main oscillation discharge cavity and the trigger time delay are respectively subjected to closed-loop control, so that the control precision and the light-emitting energy stability are improved;
3) the method combines open-loop control and closed-loop control on the trigger delay, further improves the speed of delay control and accelerates response;
4) the combination of the mean value locking controller and the dosage controller can meet the requirement of the photoetching precision and expand the energy adjusting range.
The present invention has been described in detail. It will be apparent to those skilled in the art that any obvious modifications thereof can be made without departing from the spirit of the invention, which infringes the patent right of the invention and bears the corresponding legal responsibility.
Claims (10)
1. A method of energy control for a dual cavity excimer laser comprising:
detecting the energy of a light outlet of the double-cavity excimer laser, and searching for the maximum voltage value;
detecting the time delay between the main oscillation discharge cavity and the power amplification discharge cavity to obtain a detected time delay signal;
calculating and outputting a voltage and a delay signal according to the maximum voltage value and the measured delay signal,
the main oscillation discharge cavity and the power amplification discharge cavity are controlled according to the voltage and the time delay signal,
wherein the control of the main oscillating discharge chamber comprises: and performing closed-loop control on the voltage signal of the main oscillation discharge cavity according to the voltage of the power amplification discharge cavity.
2. The energy control method for the dual cavity excimer laser of claim 1, wherein:
controlling the main oscillating discharge chamber and the power amplifying discharge chamber in accordance with said voltage and delay signals, comprising performing the following steps during each burst signal:
calculating the voltage average value of the power amplification discharge cavity for the voltage signal of the power amplification discharge cavity,
according to the voltage average value of the power amplification discharge cavity, the limiting amplitude value of the voltage signal of the main oscillation discharge cavity is calculated, and the limiting voltage is output,
and calculating the error between the mean value of the voltage of the main oscillation discharge cavity and the amplitude limiting voltage, and performing closed-loop control on the voltage signal of the main oscillation discharge cavity.
3. The energy control method for the dual cavity excimer laser of claim 2, wherein:
the voltage signal of the power amplification discharge cavity is obtained by adding a dosage control signal controlled by PI, a voltage average control signal controlled by PI and a time delay control signal controlled by PI.
4. The energy control method for the dual cavity excimer laser of claim 3, wherein:
the delay control signal is obtained by performing PI control on an error between the measured delay and the optimal delay of the plurality of pulses,
wherein the measured delay is the detected delay between the power amplifying discharge cavity and the main oscillation discharge cavity; the optimal time delay is the time delay for leading the light emitted from the power amplification discharge cavity and the main oscillation discharge cavity to simultaneously reach the light outlet of the double-cavity excimer laser.
5. The energy control method for the dual cavity excimer laser of claim 4, wherein:
and adding the open-loop delay based on the trigger delay between the power amplification discharge cavity and the main oscillation discharge cavity and the closed-loop delay signal based on the measured delay and the optimal delay to obtain a final trigger delay for controlling the delay between the power amplification discharge cavity and the main oscillation discharge cavity.
6. An energy control device for a dual cavity excimer laser, comprising
The energy sensor is used for detecting the energy of the light outlet of the double-cavity excimer laser and outputting an energy signal to the energy control module;
the execution/detection module is used for controlling the main oscillation discharge cavity and the power amplification discharge cavity, detecting the time delay between the main oscillation discharge cavity and the power amplification discharge cavity and outputting a detected time delay signal to the energy control module,
an energy control module for calculating a voltage maximum value according to the energy signal, and calculating a voltage and a delay signal according to the voltage maximum value and the measured delay signal to output to the execution/detection module,
wherein the control of the main oscillating discharge chamber comprises: and performing closed-loop control on the voltage signal of the main oscillation discharge cavity according to the voltage of the power amplification discharge cavity.
7. The energy control device for a dual cavity excimer laser of claim 6, wherein:
the energy control module includes:
the main oscillation discharge cavity mean value calculating module is used for calculating the main oscillation discharge cavity mean value of the voltage signal of the power amplification discharge cavity in each burst signal period,
the amplitude limiting module is used for carrying out amplitude limiting calculation on the voltage signal of the main oscillation discharge cavity according to the voltage average value of the main oscillation discharge cavity and outputting amplitude limiting voltage,
a main oscillation discharge cavity error calculation module for calculating the error between the voltage average value of the main oscillation discharge cavity and the amplitude limiting voltage,
and the main oscillation discharge cavity PI controller is used for carrying out PI control on the error of the amplitude limiting voltage so as to carry out closed-loop control on the voltage signal of the main oscillation discharge cavity.
8. The energy control device for a dual cavity excimer laser of claim 7, wherein:
the energy control module further comprises: a high-speed signal processing module for searching the maximum value of the voltage, and a control algorithm module,
and the control algorithm module calculates and outputs the voltage and the delay signal according to the measured delay signal and the maximum voltage value.
9. The energy control device for a dual cavity excimer laser of claim 8, wherein:
the control algorithm module comprises: a dose controller, a mean lock controller, and a time delay PI controller, and an adder,
the dose controller generates a PI controlled dose control signal; the mean value locking controller generates a voltage mean value control signal controlled by PI, the time delay PI controller generates a time delay control signal controlled by PI,
and the adder adds the dose control signal, the voltage mean value control signal and the delay control signal to obtain and output a power amplification discharge cavity voltage signal.
10. The energy control device for a dual cavity excimer laser of claim 9, wherein:
the control algorithm module is used for obtaining final trigger delay by adding an open-loop delay signal based on the trigger delay between the power amplification discharge cavity and the main oscillation discharge cavity and a closed-loop delay signal based on the measured delay and the optimal delay so as to control the delay between the power amplification discharge cavity and the main oscillation discharge cavity.
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