CN113783101B - 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 dual-cavity excimer laser, and finding out the maximum voltage; 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 signals according to the maximum voltage value and the measured delay signals, and controlling a main oscillation discharge cavity and a power amplification discharge cavity according to the voltage and delay signals, wherein the control of the main oscillation discharge cavity comprises the following steps: and performing closed-loop control on the main oscillation discharge cavity voltage signal according to the power amplification discharge cavity voltage so as to limit the power amplification discharge cavity voltage to be in an adjustable voltage range. The invention adopts the multi-ring PI control method to control the energy output of the 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 double-cavity excimer laser, and belongs to the technical field of lithography machines.
Background
The most common excimer lasers are argon fluoride (ArF), krypton fluoride (KrF), xenon chloride (XeCl) and the like, the central wavelengths of which are 193nm, 248nm and 308nm respectively, and in the exposure process, the energy variation of the excimer laser can cause the reduction of the light-emitting stability of the photoetching machine, so that the uneven exposure lines and the reduction of the yield of chips are caused.
Because the energy of the dual-cavity laser is nonlinear change in the laser burst light emitting mode, the pulse energy stability can be obviously affected even under the same voltage due to different conditions such as gas state change, temperature change, mechanism sensitivity and the like of the laser. To meet the characteristics of controlling single input single output and to maintain 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 insufficient accuracy.
In addition, the discharge delay error of the double cavities can also have serious influence on the pulse energy of the laser, and the longer the discharge delay deviates from the optimal delay, the lower the pulse energy of the laser is, the discharge delay deviation is influenced by temperature, voltage and pulse number, and the randomness is realized. The optimal delay is the delay for enabling the light emitted by the power amplification discharge cavity and the light emitted by the main oscillation discharge cavity to reach the light emitting port of the dual-cavity excimer laser at the same time.
Therefore, how to enlarge the energy adjusting range and ensure the energy adjusting stability at the same time, so that the light output of the double-cavity laser is stable, the yield of chips is improved, and the method has great significance to the chip manufacturing industry.
Disclosure of Invention
The invention aims to provide an energy control method for a dual-cavity excimer laser.
Another technical problem to be solved by 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:
an energy control method for a dual cavity excimer laser, comprising:
detecting the energy of a light outlet of the dual-cavity excimer laser, and finding out the maximum voltage;
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 delay signal,
wherein, 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.
Wherein preferably the main oscillating discharge chamber and the power amplifying discharge chamber are controlled in dependence of the voltage and delay signals, comprising the steps of, 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,
limiting amplitude calculation is carried out on the voltage signal of the main oscillation discharge cavity according to the voltage average value of the power amplification discharge cavity, limiting voltage is output,
and calculating the error of the voltage average value and the amplitude limiting voltage of the main oscillation discharge cavity, 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 delay control signal controlled by PI.
Wherein preferably the delay control signal is PI-controlled for the error between the measured delay and the optimal delay of the plurality of pulses,
the measured delay is the delay between the power amplification discharge cavity and the main oscillation discharge cavity; the optimal delay is the delay for enabling the light emitted by the power amplification discharge cavity and the light emitted by the main oscillation discharge cavity to reach the light emitting port of the dual-cavity excimer laser at the same time.
Preferably, the final trigger delay is obtained by adding open-loop delay based on trigger delay between the power amplification discharge cavity and the main oscillation discharge cavity and closed-loop delay signals obtained based on the measured delay and the optimal delay, and is used for controlling 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 dual-cavity excimer laser and outputting an energy signal to the energy control module;
an execution/detection module 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 measured time delay signal to an energy control module,
an energy control module for calculating a voltage maximum value from the energy signal and calculating a voltage and a delay signal from the voltage maximum value and the measured delay signal to output to the execution/detection module,
wherein, 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.
Wherein preferably the energy control module comprises:
a main oscillation discharge cavity mean value calculation module for calculating a main oscillation discharge cavity voltage mean value for the voltage signal of the power amplification discharge cavity during each burst signal period,
the limiting amplitude module is used for carrying out limiting amplitude 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 limiting voltage,
the main oscillation discharge cavity error calculation module is used 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 performing PI control on the error of the limiting voltage so as to perform closed-loop control on the voltage signal of the main oscillation discharge cavity.
Wherein preferably, the energy control module further comprises: a high-speed signal processing module for searching the maximum voltage value, 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 voltage maximum value.
Wherein preferably, the control algorithm module comprises: dose controller, mean lock controller and delay PI controller, and adder,
the dose controller generates a PI-controlled dose control signal; the average value locking controller generates a voltage average value control signal controlled by PI, the delay PI controller generates a delay control signal controlled by PI,
the adder adds the dose control signal, the voltage average 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 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 the two signals are added to obtain the final trigger delay so as to control the delay between the power amplification discharge cavity and the main oscillation discharge cavity.
The invention has the following technical effects: 1) The average value of the voltage signals of the power amplification discharge cavity is utilized to limit the amplitude of the voltage signals of the main oscillation discharge cavity, so that the adjustable range of the voltage of the power amplification discharge cavity is enlarged; 2) The multi-PI control is utilized to control the voltage signal of the power amplification discharge cavity, the voltage signal of the main oscillation discharge cavity and the trigger delay, so that the control precision and the light-emitting energy stability are improved; 3) The mode of combining the open loop control and the closed loop control on the trigger delay further improves the speed of delay control and quickens 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 flow chart of the peak finding module in FIG. 3;
fig. 5 is a flow chart of the burst signal identification module of fig. 3;
FIG. 6 is a schematic diagram of a control circuit for the power amplifying discharge chamber voltage signal of FIG. 3;
FIG. 7a is a schematic diagram of a pulse sequence within a burst in a power amplification discharge chamber voltage signal in a constant energy mode;
FIG. 7b is a voltage schematic of a plurality of burst signals;
FIG. 8 is a schematic diagram of a control circuit for the voltage signal of the main oscillating discharge chamber;
fig. 9 is a schematic diagram of a trigger delay signal control circuit.
Detailed Description
The technical contents of the present invention will be described in detail with reference to the accompanying drawings and specific examples.
As shown in fig. 1, the control system of the dual-cavity laser (hereinafter referred to as a laser) provided by the embodiment of the invention is used for controlling the dual-cavity excimer laser to emit stable laser light emitting pulses (hereinafter referred to as pulses or pulse signals). The laser control system comprises an energy control module 101, an execution/detection module 102, a main oscillating discharge chamber 104, a power amplifying discharge chamber 105, and an energy sensor 103. The energy control module 101 sends a delay command and a voltage control command to the execution/detection module 102, and the execution/detection module 102 detects the delay and sends a delay command 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 the energy signal back to the energy control module 101 to realize closed-loop control.
Referring to the burst mode light emission characteristics of the dual cavity excimer laser shown in fig. 2a and 2b, the dual cavity excimer laser typically operates in a burst mode. In burst mode, there are multiple pulse clusters 202 with burst intervals 203 between adjacent pulse clusters 202. The duration of the burst interval 203 can be set, typically to 20ms or more, but if the duration of the burst interval 203 is set to 0, then the laser is operated 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, simply 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 means that the laser light emitting frequency in the burst signal is generally between 1kHz and 6 kHz. The energy level of the pulses in the figures is schematic and does not represent the true level.
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 transmits 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, the voltage of the photodiode is small, so the voltage signal 204 has the characteristics of short time and low voltage. The energy sensor 103 has built-in amplification circuitry for amplifying the voltage signal 204 and timing circuitry for delaying the voltage signal 204 (about 20 us). The amplified and delayed energy signal 12 is transferred 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 computation control module 309, both of which may be implemented by or within two separate CPU processors.
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 finding module 303 has embedded therein a signal calculation control module 309.
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 above 1 mhz in the digital signal, 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 lookup module 303 is event triggered, such as when a rising edge of the filtered signal is detected (e.g., when the voltage of the filtered signal is detected to be greater than or equal to 0.5 v), starting a timer, which counts a preset time (e.g., 15 microseconds). And, the search for the voltage maximum value is started at the same time until the timing ends. At the end of the timing, the voltage maximum value (peak value) within the preset time is output as the energy value of the current laser pulse. Meanwhile, the primary signal calculation control module 309 is operated to perform primary control on the dual-cavity voltage and the time delay. After that, the voltage is waited for to drop (for example, the voltage is less than 0.3 v), and at this time, the processing of the current laser pulse is ended. Therefore, the laser pulse in each burst signal controls the double-cavity voltage and the time delay once, so that the control precision and the stability are improved.
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 signal 11. The voltage and delay signal 11 comprises three signals: trigger delay signal, main oscillation discharge cavity voltage signal and power amplification discharge cavity voltage signal.
Wherein the energy processing module 305 converts the voltage maximum value from the peak value 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 in millivolts from peak find module 303; y is the current laser pulse energy value, and is a unit millijoule; a. b is a linear coefficient, and needs to be determined according to practical conditions. In this embodiment, values of a and b are as follows:
| laser serial number | a | b |
| 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 |
A flow chart of the identification of the burst signal identification module 308 is shown in fig. 5. The burst identification module 308 is used to identify and pulse count the burst. Specifically, the burst signal identification module 308 first initializes when the signal calculation control module 309 is triggered. In the initialization stage, the pulse sequence number is cleared, the burst signal sequence number is cleared, and the total pulse number is cleared. After initialization is completed, the burst sequence number is incremented by 1 (e.g., from 99 to 100 in burst 100) in a burst (e.g., first burst 201) when the first pulse arrives. Then judging whether the pulse time interval is longer than a preset time length (20 milliseconds in the embodiment), if not, namely the current burst signal is not finished yet, continuing to count the pulses; if 20ms is reached, i.e., the current burst is over, the burst sequence number is returned and incremented by 1.
During the period in which the burst signal has not ended, 1 is added to the pulse sequence number and 1 is added to the total pulse number. Since the pulse sequence number is cleared after the foregoing initialization, the pulse sequence number always increases from 0, for example, from 0 to 1000, for the duration of each burst signal. The total number of pulses is only cleared during the initialization phase, but is not cleared when each burst arrives, so the total number of pulses is increasing.
The burst identification module 308 generates a pulse sequence number, a burst sequence number, and a total pulse number, and outputs the pulse sequence number, the burst sequence number, and the total pulse number to the control algorithm module 307. The sequence number of the burst (denoted i), the pulse sequence number (denoted j) and the total pulse number (denoted p) are used to control the timing implementation of the algorithm module 307.
As previously described, the inputs to the control algorithm module 307 include: the pulse sequence number, sequence number of burst signal and total pulse number from burst signal identification module 308; the 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 307 comprises a main oscillating discharge chamber voltage signal, a power amplifying discharge chamber 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 execution/detection module 102.
The power amplification discharge chamber 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 both is calculated, and output to the mean-lock controller 608 and the dose controller 607.
Error value e 63 And the measured energy value E 603 Energy target value E 604 The following equation is satisfied:
e 63 ＝E 604 -E 603
wherein e 63 A value representing the output error signal 63 of the energy error calculation module 610; e (E) 603 A value representing the measured energy signal 603; e (E) 604 Representing the value of the energy target signal 604.
The following describes the operation of the mean lock controller 608. In burst mode, the voltage of the pulses within each burst is different, even at the same energy, and thus the mean voltage of the pulses within the plurality of bursts within each burst 202 is also different. As shown in fig. 7a, where the mean line 72 is the mean scatter of the pulses in the 1000 bursts at the same pulse position, it can be observed that the pulse voltage 71 of the pulses in the bursts increases gradually with the pulse position. As shown in fig. 7b, the new burst-generated pulse voltage 71 will return to the lowest point in burst signal 701, burst signal 702, burst signal 703. The first pulse 73 of the pulses within the burst signal is the lowest point. Without mean-shift locking, a dual-cavity excimer laser requires a relatively long stabilization process. In the embodiment of the invention, the response speed is accelerated by rapidly finding the average voltage of the pulses in each burst signal. It is to be understood that burst signal identification may be implemented in hardware alone or in software.
The implementation of the method by which the average lock controller 608 achieves average locking of the average voltage of the pulses within each burst signal includes two steps: and (5) calculating a mean value and performing error closed-loop control.
The mean lock controller 608 performs the error mean calculation as follows:
wherein k is the total pulse number p, e 63(j，k) An error value representing a j-th pulse in a k-th burst signal; e, e 608(j，i) Representing the sum of errors of the first 1000 intra-burst pulses of the j-th intra-burst pulse located in the i-th burst. It will be appreciated that the error sum of the pulses in the first 1000 bursts is taken in this embodiment, but may be set to other values depending on the pulse frequency. In general, when the pulse frequency is 1kHz, 1000 is preferable.
Based on the error mean calculation result, the mean lock controller 608 performs the mean error voltage calculation according to the following formula:
v 608(j，i) ＝v 608(j，i-1) +Kp*(e 608(j，i-1) -e 608(j，i-2) )+Ki*e 608(j，i-1) j＜N
V 608(j，i) ＝v 608(j-1，i) j＞＝N
v 608 ＝v 608(j，i)
in the above equation, v 608(j，i) Is the mean voltage of the jth pulse in the ith burst signal, (v) 608 The value of the j-th pulse in the i-th burst signal, N, is typically a fixed value preselected between 30 and 500, kp, ki being the proportional and integral coefficients, respectively, of the PI control algorithm (determined experimentally). Because the average voltage is calculated based on a PI control (Proportional Integral Control) algorithm, the control accuracy is improved, and the laser light-emitting stability is improved.
The calculation 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 dose accuracy control, and its calculation steps are divided into two steps of dose error calculation and dose error closed loop.
The dose error calculation formula is as follows, and the dose error summation is obtained:
wherein, dose (j，i) For the mean value of the dose error of pulses in the j-th burst signal in the i-th burst signal, l epsilon total pulse number p, e 63(j，k) Indicating the error value of the pulses in the first burst in the ith burst, ns being the number of pulses in one dose.
Dose voltage signal v 607 The calculation method of (2) is as follows:
v 607(j-1，i) ＝v 608(j-1，i) j＜N-1
v 607(j，i-1) ＝v 607(j，i-1) j>＝N-1
v 607(j，i) ＝v 607(j-1，i) +Kp*(Dose (j-1，i) -Dose (j-2，i) )+Ki*Dose (j-1，i)
v 607 ＝v 607(j，i)
wherein: v 607(j，i) Indicated at the ithThe result of PI control algorithm based dose error control of pulses within the jth burst in the burst (i.e., v 607 The value of the j-th pulse in the i-th burst signal, kp, ki are the proportional and integral coefficients, respectively, in the PI control method (determined experimentally). The average lock-up controller 608 functions when j < N-1 such that the output v of the dose controller 607 607 Output v from the average lock controller 608 608 The same, i.e. dose controller 607, is not active. The average lock controller 608 is deactivated when j > = N-1, such that the output v of the dose controller 607 607(j，i) Is a signal subjected to PI control to improve stability. N denotes the sequence number of a pulse within a burst signal.
The delay compensation module 612 is configured to perform delay compensation. Because delay jitter can cause severe interference to the laser pulse energy, delay compensation needs to be specifically designed for the case where the delay deviates from the optimal delay. The delay compensation module 612 is comprised of delay error calculation and PI controller. The PI controller is a linear controller that forms a control deviation from a given value and an actual output value, and forms a control amount by linearly combining a proportion and an integral of the deviation to control a controlled object.
The delay error calculation block 612 has inputs of the optimal delay 601 and the measured delay signal 13 from the execution/detection block 102, and obtains the delay error 64 by the adder 62, and the delay error 64 obtains the delay voltage signal v by the PI controller 609 609 。
The delay error 64 is calculated as follows:
T e64 ＝T 602 -T 601
wherein T is e64 T is the delay error 601 The optimal delay time is preset; t (T) 602 Is the value of the measured delay signal 13 from the execution/detection module 102.
Output delay voltage signal v of delay PI controller 609 609 The calculation formula of (2) is as follows:
wherein v is 609(j，i) Is the result of the PI controller 609 at the j-th pulse of the i-th burst signal (i.e., v 609 The j-th pulse in the i-th burst signal), K p0 、K i0 The proportional and integral coefficients in PI control respectively,is the delay error of the j-1 th pulse in the i-th burst.
The outputs of the three controllers, dose controller 607, mean lock controller 608, PI controller 609, are combined together by adder 64 as power amplifier cavity voltage signal v 611 Output, which satisfies the following equation
v 611 ＝v 607 +v 608 +v 609
Wherein v is 611 For power amplifying discharge chamber voltage signal, v 607 、v 608 、v 609 A dose voltage signal output by the dose controller 607, a mean voltage signal output by the mean value lock controller 608, and a delay voltage signal output by the PI controller 609. The three are obtained by independently utilizing PI control and are used for controlling the voltage signal of the power amplification discharge cavity, so that the stability of the laser light emitting energy of the power amplification discharge cavity can be improved.
The method of controlling the voltage of the main oscillating discharge chamber is described below. The voltage regulation of the main oscillation discharge cavity 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 light-emitting energy by reducing the voltage difference.
The main oscillation discharge cavity voltage control is shown in fig. 8, and includes a power amplification discharge cavity mean value calculation module 902, a limiting amplitude module 903, a main oscillation discharge cavity error calculation module 904, and a main oscillation discharge cavity PI controller (MO PI controller) 905.
The power amplification chamber average value calculating module 902, which inputs the voltage signal 611 (shown in fig. 6) of the power amplification chamber, calculates the power amplification chamber voltage average value of 500 pulses (500 pulses in the present embodiment, or other number of pulses) according to the following formula, and outputs the calculated voltage signal to the amplitude limiting module 903:
where k is the pulse sequence number, which is the pulse sequence number based on the total number of pulses p.For the kth pulse, v in the output signal of the power amplification chamber mean computation module 902 611k Is the result of the kth time of the power amplification chamber voltage signal.
Inputs to the amplitude limiting module 903 are a main oscillating discharge chamber voltage 901 and a power amplifying discharge chamber voltage mean v 902 Which limits the amplitude of the main oscillating discharge chamber voltage 901. This is because the average voltage of the power amplification chamber 105 cannot be too close to its minimum voltage or maximum voltage so that the voltage of the power amplification chamber can be adjusted normally (adjustable range). For example, assuming that the voltage of the power amplification discharge chamber ranges from 1300V to 2000V, the voltage average value of the power amplification discharge chamber should be at least about 1400V and the voltage maximum value should be at least about 1900V. The operation mode of the amplitude limiting module 903 is:
v 903 ＝v 901 B＞v 901 ＞A
v 903 ＝A v 901 ＜A
v 903 ＝B v 901 ＞B
wherein v is 903 V to limit the output of the amplitude block 903 (limited voltage) 901 As inputs, A, B are a voltage lower limit value and a voltage upper limit value of the power amplification discharge chamber, respectively, which can be set. The amplitude limiting module 903 is used to make the voltage of the main oscillation discharging cavity in a proper range, and the voltage is not too large or too small due to the consumption of working gas and the like. Thereby facilitating the solution of the excimer laser in the discharge cavityThe gas consumption causes a problem of a decrease in light-emitting capacity (i.e., a decrease in light-emitting energy at the same voltage).
The main oscillation discharge chamber error calculation module 904, according to the input calculation formula, is as follows:
v 904 ＝v 902 -v 903
wherein v is 904 A voltage signal output by the main oscillation discharge cavity error calculation module 904; v 902 Voltage signal v output by power amplification discharge cavity mean value calculation module 902 903 To limit the voltage signal output by the amplitude block 903.
The calculation formula of the MO PI controller 905 is as follows:
wherein j e p is the pulse sequence number based on the total number of pulses p. K (K) p1 、K i1 Proportional and integral coefficients, v, respectively, of PI control 904(j-1) Voltage signal v of j-1 th pulse output by main oscillation discharge cavity error calculation module 904 905(j) The voltage signal of the j-th pulse output from the MO PI controller 905. Here, the MO PI controller 905 further improves the stability of the output laser energy of the main oscillation discharge chamber. It will be appreciated that the use of MO PI controller 905 for closed loop control is not limited herein, and that other closed loop control methods may be employed.
The calculation of the trigger delay in the voltage and delay signal 11 is described below. As shown in fig. 9, the final trigger delay 1008 is calculated from the delay error between the actual discharge delay (measured delay signal 13) and the optimal delay (e.g., 35 ns) between the discharges of the main oscillating discharge chamber and the power amplifying discharge chamber, and the current trigger delay 1001. The trigger delay 1001 required to achieve the optimum delay (e.g., 35 ns) can be determined experimentally by satisfying the following quadratic relationship
T(v 611 ，v 901 )＝e*v 611 2 +d*v 901 2 +c*v 611 +b*v 901 +a
Where a, b, c, d, e are all quadratic polynomial coefficients, the best delay (e.g., 35 ns) will be met when the actual trigger delay between two-chamber discharges is T. In practice the different laser parameters will be different.
The above formula is deviated due to influence of temperature and electric characteristics of the inside of the double cavity, and thus closed loop correction is required. The open-loop trigger delay and the closed-loop trigger delay are added by an adder 1007 and a final trigger delay 1008 is output. The invention can quickly eliminate delay deviation by combining open loop and closed loop.
As shown in fig. 9, the closed loop trigger delay 1006 is calculated by: the measured delay signal 13 and the optimal delay 1002 are subtracted by an adder 1004 to obtain a delay error, and the delay error is processed by a PI controller 1006 after being low-pass filtered 1005. Wherein the optimal delay signal 1002 is a value preset according to the dual-cavity electrical characteristics. Adder 1004 satisfies the following relationship:
T 1004 ＝T 13 -T 1002
wherein T is 1004 Representing the delay error of adder 1004, T 13 Representing the actual measured delay, T 1002 Indicating a preset optimal delay.
The low-pass filter 1005 satisfies the following relation:
T 1005(j) ＝(1-a)T 1005(j-1) -aT 1002
a＝1/(1+f s )
wherein f s For the frequency of the laser pulses, T 1005(j) Is the jth output of the low pass filter 1005.
The output of the PI controller 1006 satisfies the following relationship:
T 1006(j) ＝T 1005(j-1) +K p2 *(T 1005(j-1) -T 1005(j-2) )+K i2 *T 1005 (j-1)
wherein T is 1006(j) A j-th pulse representing the output signal of PI controller 1006; k (K) p2 、K i2 Proportional and integral coefficients, T, of PI control, respectively 1005(j-i) Output signal T for low pass filter 1005 1005 J-1 th pulse of (c).
The above-mentioned values are merely illustrative and can be set according to the actual laser performance. The control of the execution/detection module 102 by the energy control module 101 comprises the control of discharge delay between the two cavities and the control of voltage of the two cavities, so that the delay interference of the two-cavity excimer laser, the nonlinear relation between laser pulse energy and voltage and the energy disturbance are solved, and the stable output of energy is realized.
The working principle of the embodiment of the present invention is described below.
As shown in fig. 2a-2b, 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 during each burst signal. As shown in fig. 3, the energy control module 101 obtains an energy signal from the energy sensor 103, finds a voltage maximum value therefrom, and outputs the voltage maximum value to the energy processing module 305. The energy processing module 305 performs a linear calculation of the voltage value as 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 by using the adder 61 based on the preset energy target value, and outputs the calculated energy error to the dose controller 607 and the average lock-out controller 608. The average lock controller 608 calculates an average voltage using PI control, resulting in an average voltage control signal.
Meanwhile, the dose controller 607 calculates a dose control signal using PI control based on the aforementioned energy error. Also, in the delay compensation module 612, a delay control signal is calculated based on the error between the actually measured delay signal 13 (measured by the execution/detection module 102) and the optimal delay signal 601 using the delay PI controller 609. The mean voltage control signal, the dose control signal, and the delay control signal are commonly input to the adder 64 to form the power amplification chamber voltage signal 611. The PI control method calculates the three components, so that the control precision can be improved, and the light-emitting stability of the power amplification discharge cavity can be further improved.
As shown in fig. 8, the amplitude of the main oscillation discharge chamber voltage signal 901 is limited based on the average value of the power amplification discharge chamber voltage signal 611, so that the power amplification discharge chamber voltage signal is limited within a preset adjustable voltage range, thereby realizing the adjustable power amplification discharge chamber voltage. This can avoid the drop of the light output energy of the excimer laser at the same voltage due to the consumption of the working gas.
Furthermore, by utilizing PI control and closed-loop control, 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 precisely controlled, so that the stability of the voltage of the main oscillation discharge cavity is improved.
As shown in fig. 9, the power amplification discharge chamber voltage signal 611 and the main oscillation discharge chamber voltage signal 901 obtained by the above calculation are used to calculate an open loop delay, and the final trigger delay 1008 is calculated based on the error between the measured delay signal 13 and the optimal delay 1002 by combining the PI control algorithm.
As shown in conjunction with fig. 1 and 3, the control algorithm 307 calculates the aforementioned power amplification chamber voltage signal 611, main oscillation chamber voltage signal 901, and final trigger delay 1008 (collectively, the three are referred to simply as voltage and delay signal 11), and sends the voltage and delay signal 11 to the execute/detect module 102. The execution/detection module amplifies the main oscillating discharge chamber voltage signal 901 in the voltage and delay signal 11 and applies an amplified high voltage to the main oscillating discharge chamber 104. Therefore, the gas in the main oscillation discharge chamber 104 is excited to generate laser after being subjected to high-voltage power generation. After a period of time (final trigger delay 1008), the execution/detection module 102 applies a high voltage to the power amplification discharge chamber 105 that amplifies the power amplification discharge chamber voltage signal 611. Accordingly, the gas in the power amplification discharge chamber 105 is excited to generate laser light after being discharged at a high voltage. By the delay control of the energy control module 101, the lasers generated by the main oscillation discharge cavity 104 and the power amplification discharge cavity 105 can be ensured to reach the light outlet at the same time (the optimal delay effect is achieved). The pulse energy of the laser can be adjusted by controlling the voltage signal of the double cavities.
In summary, the dual-cavity excimer laser according to the embodiment of the present invention has the following technical advantages:
1) The average value locking of the voltage signal of the power amplification discharge cavity, the amplitude limiting of the voltage signal of the main oscillation discharge cavity and the closed-loop adjustment of the voltage of the main oscillation discharge cavity are utilized, the adjustment range of the light-emitting energy is enlarged, and the problem of the reduction of the light-emitting capacity caused by the consumption of gas in the discharge cavity is solved;
2) The power amplification discharge cavity voltage signal, the main oscillation discharge cavity voltage signal and the trigger delay are respectively subjected to closed-loop control, so that the control precision and the light-emitting energy stability are improved;
3) The method of combining the open loop control and the closed loop control on the trigger delay further improves the speed of delay control and quickens response;
4) The combination of the mean value locking controller and the dose controller can meet the requirement of photoetching precision and can expand the energy adjusting range.
The present invention has been described in detail. Any obvious modifications to the present invention, without departing from the spirit thereof, would constitute an infringement of the patent rights of the invention and would take on corresponding legal liabilities.
Claims (10)
1. An energy control method for a dual-cavity excimer laser, comprising:
detecting the energy of a light outlet of the dual-cavity excimer laser, and finding out the maximum voltage;
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 voltage maximum 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 delay signal,
wherein, 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 a dual-cavity excimer laser of claim 1, wherein:
controlling the main oscillating discharge chamber and the power amplifying discharge chamber in accordance with the 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,
limiting amplitude calculation is carried out on the voltage signal of the main oscillation discharge cavity according to the voltage average value of the power amplification discharge cavity, limiting voltage is output,
and calculating the error between the voltage average value of the main oscillation discharge cavity and the limiting voltage, and performing closed-loop control on the voltage signal of the main oscillation discharge cavity.
3. The energy control method for a 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 delay control signal controlled by PI.
4. A method of energy control for a dual cavity excimer laser according to claim 3, wherein:
the delay control signal is obtained by PI control of an error between a measured delay and an optimal delay of a plurality of pulses,
wherein the measured delay is a delay between the detected power amplifying discharge chamber and the main oscillating discharge chamber; the optimal delay is the delay for enabling the light emitted from the power amplification discharge cavity and the light emitted from the main oscillation discharge cavity to reach the light emitting port of the dual-cavity excimer laser at the same time.
5. The energy control method for a dual-cavity excimer laser of claim 4, wherein:
and obtaining final trigger delay by adding open-loop delay based on trigger delay between the power amplification discharge cavity and the main oscillation discharge cavity and closed-loop delay signals obtained based on the measured delay and the optimal delay, wherein the final trigger delay is used for controlling 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 dual-cavity excimer laser and outputting an energy signal to the energy control module;
an execution/detection module 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,
an energy control module for calculating a voltage maximum value from the energy signal and calculating a voltage and a delay signal from the voltage maximum value and the measured delay signal to output to the execution/detection module,
wherein, 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. An energy control device for a dual cavity excimer laser according to claim 6, wherein:
the energy control module includes:
a main oscillation discharge cavity mean value calculation module for calculating a main oscillation discharge cavity voltage mean value for the voltage signal of the power amplification discharge cavity during each burst signal period,
the limiting amplitude module is used for calculating the limiting amplitude of the voltage signal of the main oscillation discharge cavity according to the voltage average value of the main oscillation discharge cavity and outputting 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 limiting voltage,
and the main oscillation discharge cavity PI controller is used for performing PI control on the error of the limiting voltage so as to perform closed-loop control on the voltage signal of the main oscillation discharge cavity.
8. An energy control device for a dual cavity excimer laser according to claim 7, wherein:
the energy control module further comprises: a high-speed signal processing module for searching the maximum voltage value, 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 voltage maximum value.
9. An energy control device for a dual cavity excimer laser according to claim 8, wherein:
the control algorithm module comprises: dose controller, mean lock controller and delay PI controller, and adder,
the dose controller generates a PI-controlled dose control signal; the average value locking controller generates a voltage average value control signal controlled by PI, the delay PI controller generates a delay control signal controlled by PI,
and the adder adds the dose control signal, the voltage average control signal and the delay control signal to obtain and output a power amplification discharge cavity voltage signal.
10. An energy control device for a dual cavity excimer laser according to claim 9, wherein:
the control algorithm module is used for obtaining final trigger delay based on an open-loop delay signal of 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 the two signals are added to obtain final trigger delay so as to control the delay between the power amplification discharge cavity and the main oscillation discharge cavity.
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