JP3580430B2 - Exposure system and exposure method - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to an excimer laser device used, for example, as a light source of an exposure apparatus for manufacturing a semiconductor device.
[0002]
[Prior art]
At present, a discharge excitation type pulsed excimer laser is used as a light source of a sequentially moving reduction projection exposure apparatus (hereinafter referred to as a stepper). In a stepper, a region on a wafer coated with a photosensitive agent is exposed, and then a stage on which the wafer is mounted is moved to expose another region. The entire area is exposed.
[0003]
For such exposure, a method in which an excimer laser is continuously oscillated continuously at a constant frequency and a shutter is opened when necessary for exposure, such as a g-line or i-line stepper in which a light source is always lit. However, this method is inefficient in consideration of the lifetime of the laser light source. Therefore, as an operation method of the excimer laser, which is an exposure light source, as shown in FIG. 6, a mode in which a state that continuously oscillates at a constant frequency (oscillation state) and a state that stops oscillation (stop state) are repeated. (Hereinafter referred to as burst mode) is used.
[0004]
On the other hand, in order to manufacture a homogeneous semiconductor device in a stepper, it is not desirable that the amount of light integrated within the exposure time for one area, that is, the exposure amount fluctuates depending on the area, and it is necessary to keep it as constant as possible.
[0005]
However, when an excimer laser excited by pulse oscillation is used as the light source, the pulse discharge itself is an essentially statistical phenomenon that depends on the discharge gas and the surface state of the electrode, so the laser light energy for each pulse is kept constant. It is difficult to do. In particular, immediately after the start of oscillation such as continuous oscillation, the state of the gas or electrode governing the discharge changes transiently, so that the laser beam energy is large immediately after the start of oscillation as shown in FIG. 7, and then gradually decreases. A pattern of spikes (spike phenomenon) is generally seen.
[0006]
Therefore, even in the burst mode, every time the oscillation state is started, the laser beam energy immediately after the start is large, and then it is avoided to show a spike-like pattern as shown in FIG. I was in a situation where I couldn't. In actual exposure, the spike-shaped pattern cannot be erased by normal feedback control in which the discharge voltage is changed after measuring the energy of the laser beam. The exposure is stopped (up to about 30 pulses), and an inefficient method of using pulsed light for exposure after the variation is within a certain range has been performed.
[0007]
In this way, special consideration is necessary when using an excimer laser whose laser light energy is essentially varied from pulse to pulse. Therefore, heretofore, attempts have been made to solve this by the following method.
[0008]
One is a method of reducing the variation in exposure amount by increasing the number of pulses. The frequency distribution of light energy for each pulse of the excimer laser can be approximated by a normal distribution. The variation in the exposure amount obtained by integrating the energy of the pulsed light having such a property for a certain time is 1 / √n of the variation in the original pulse, where n is the number of integrated pulses for obtaining the same exposure amount. Decrease.
[0009]
Also, the optical energy for each pulse is integrated using a stepper or an exposure meter in the laser, and when this integrated value approaches the target exposure amount, a neutral density filter or the like is inserted into the laser optical path. Then, a method of correcting the energy for each pulse so as to achieve the target exposure amount was also considered.
[0010]
[Problems to be solved by the invention]
However, when using a method that stabilizes the exposure amount by reducing the light energy of each pulse and increasing the number of exposure pulses, the total number of pulses increases, which increases the life of the laser parts and increases the running cost. Will cause problems.
[0011]
In recent years, as a photosensitive agent that reacts sensitively to light (high sensitivity) has been developed due to technological improvements, the amount of exposure required per unit area has become smaller, with a much smaller number of pulses than in the past. Exposure is possible in a short time, and productivity can be improved. However, the pulse train including the spike-like pattern of the excimer laser that is the exposure light source naturally has a large variation in the frequency distribution of the light energy for each pulse as compared with the pulse train not including the spike-like pattern. If the number of pulses for exposure is simply reduced, there arises a problem that the variation in exposure amount increases and exceeds the specified value.
[0012]
Further, as described above, even when using an exposure method in which the energy for each pulse is corrected so that the integrated value of light energy becomes a predetermined value, the required number of pulses cannot be extremely reduced. Therefore, the conventional excimer laser exposure has a problem that the improved characteristics of the high-sensitivity photosensitizer cannot be fully utilized, and productivity cannot be improved.
[0013]
An object of the present invention is to provide an excimer laser device that solves the above-described problems, minimizes variations in exposure amount, and enables exposure with a smaller number of pulses than in the past.
[0014]
[Means for Solving the Problems]
In order to achieve the above object, according to the first aspect of the present invention, there is provided an exposure system for exposing an object to be exposed by irradiating the object to be exposed in the exposure apparatus with a laser beam pulse-oscillated from an excimer laser apparatus. As information on spike-like energy fluctuations of laser light that occurs immediately after starting pulse oscillation from the excimer laser device, the relationship between the energy of the laser light and the discharge voltage is the state where the laser light does not reach the object to be exposed And determining a discharge voltage pattern that does not cause spike-like energy fluctuations immediately after the start of pulse oscillation of the excimer laser device based on the relationship between the energy of the laser beam and the discharge voltage, and the determined discharge voltage It has a control device for controlling the discharge voltage to be supplied to the excimer laser device based on the pattern, the control device Therefore it was decided to exposing the object to be exposed with the laser beam from the excimer laser device based on the controlled discharge voltage.
According to a fourth aspect of the present invention, there is provided an exposure method for exposing an object to be exposed in the exposure apparatus by irradiating the object to be exposed in the exposure apparatus with laser light pulsed from the excimer laser apparatus. As information on the spike-like energy fluctuation of the laser beam that occurs immediately after the start of pulse oscillation, the relationship between the laser beam energy and the discharge voltage is obtained in a state where the laser beam does not reach the object to be exposed, and the laser Based on the relationship between the energy of light and the discharge voltage, a discharge voltage pattern that does not cause spike-like energy fluctuations immediately after the start of pulse oscillation of the excimer laser device is determined, and based on the determined discharge voltage pattern by controlling the discharge voltage applied to the excimer laser apparatus, the Ekishimare based on the controlled discharge voltage Wherein a laser beam from the device was that exposes an object.
[0019]
[Action]
The magnitude of the energy of the pulsed laser beam oscillated from the discharge excitation excimer laser varies depending on the discharge voltage as shown in FIG. This property has been used in the past in order to maintain the light output of the excimer laser constant by feedback control. However, the control by the conventional method in which the discharge voltage is changed after the energy is measured cannot remove the spike phenomenon immediately after the start of the oscillation state. This is because the gas state changed in the stop state, and the first few pulses in the oscillation state could not be controlled.
[0020]
The present invention comprises a control means for controlling the discharge voltage so as to erase the spike pattern and make the energy value for each pulse in the oscillation state in the burst mode substantially constant. On the other hand, pulse oscillation is performed in a state in which no influence is exerted, the relationship between the pulse energy and the discharge voltage at that time is obtained and stored in the storage means, and the discharge voltage is controlled based on this relationship.
[0021]
That is, in order to investigate the situation that the state of the gas and the state of the electrode, which is the cause of the spike, give to the pulse energy, the pulse oscillation is performed without affecting the photosensitive agent, and the pulse energy and discharge voltage of the laser beam at that time And a spike-like pattern as shown in FIG. 5A is predicted from the value.
[0022]
In order to cancel the spike-like pattern when the pulse is oscillated, the pulse voltage is oscillated by changing the discharge voltage with time as shown in FIG. Such a control means makes it possible for the first time to virtually eliminate spike-like pulses of energy that were previously considered inevitable in excimer lasers operating in burst mode.
[0023]
Therefore, in the present invention, it is possible to obtain laser light having a substantially constant pulse energy immediately after oscillation, and it is possible to minimize variations in exposure amount. In addition, since the oscillation for determining the discharge voltage control pattern that keeps the pulse energy constant is performed during the period when the exposure operation of the semiconductor device is not performed, the exposure time is not affected and the throughput may be reduced. Absent.
[0024]
Furthermore, in the present invention, the above control is performed for approximately 30 pulses or less immediately after pulse oscillation. This is in consideration of the fact that in an excimer laser operating in a burst mode, a spike-like pattern in which the pulse energy becomes extremely large immediately after pulse oscillation usually does not exceed approximately 30 pulses from the start of oscillation. . Therefore, the conventional feedback control function can be used after the spike state at the initial stage of oscillation has settled.
[0025]
【Example】
Examples of the present invention will be described below. FIG. 1 shows an exposure system when an excimer laser device according to an embodiment of the present invention is used as a light source. A part of the laser beam generated from the laser oscillator 1 is reflected by the beam splitter 2 and enters the detector 3. A photoelectric signal corresponding to the energy of the laser beam output from the detector 3 is input to the computer 4 to obtain the energy for each pulse. Further, the computer 4 obtains and stores the relationship between the discharge voltage for the laser oscillator 1 as shown in FIG. 4 and the pulse energy of the laser beam, and outputs a command (signal) relating to the discharge voltage to the power source 5. .
[0026]
The laser power source 5 supplies a discharge voltage based on a command from the computer 4 to the laser discharge circuit. The discharge voltage is an applied voltage or a charging voltage. The laser beam transmitted through the beam splitter 2 is blocked from reaching the wafer disposed in the stepper 8 by the shutter 6 which can advance and retreat in the optical path. The computer 4 can also be used as an interface between the laser unit 7 and the stepper 8, and can communicate the state of the laser unit 7 including the shutter 6 to the stepper 8.
[0027]
In a normal exposure apparatus, as disclosed in Japanese Patent Application Laid-Open No. 2-294013, cooperative control is performed on the laser side and the stepper side based on various interface signals. For example, a laser beam is emitted by outputting a trigger signal as an oscillation command from the stepper side to the laser side. Further, the shutter is controlled by outputting a signal indicating the shutter position from the laser side to the stepper side.
[0028]
Also in this embodiment, the laser unit 7 and the stepper 8 are cooperatively controlled by communicating the above interface signals between the computer 4 and the stepper 8.
In this embodiment, the beam splitter 2, the detector 3, the computer 4, and the shutter 6 are shown as being built in the laser unit 7, but these may be in the stepper 8.
[0029]
The computer 4 has, as data, a predetermined pattern of the discharge voltage with respect to the pulse oscillation time such that the pulse energy of the laser beam becomes constant. Since the energy value of the laser beam depends on the gas state, the electrode consumption state, etc., this pattern can be determined by oscillating as few pulses as possible while the burst mode is stopped, and the discharge voltage and laser beam at that time. It is preferable to determine the relationship with the energy.
[0030]
When an oscillation command from the stepper 8 is given through the computer 4, the laser unit 7 controls the power supply 5 according to the discharge voltage pattern data stored at that time, and performs pulse oscillation while changing the discharge voltage with time.
[0031]
FIG. 2 is a flowchart showing an example of an algorithm for excimer laser control based on such discharge voltage control. A specific example of control will be described below with reference to this flowchart.
The computer 4 previously stores a pattern regarding the relationship between the discharge voltage and the oscillation time as described above as initial data (step 101). The computer 4 checks whether or not there is an oscillation command from the stepper 8 (step 102), and if not, moves to the routine A for updating the pattern data.
[0032]
In routine A, first, an oscillation command from the stepper 8 is not accepted (step 201), and the shutter 6 is closed (step 202). After creating a state in which the laser beam does not reach the object to be exposed, oscillation is performed (step 203). As described above, it is desirable that this oscillation does not affect the state of the laser as much as possible, and preferably 1 to several pulses. The laser beam at this time is measured by the detector 3 (step 204), and the pulse energy of the laser beam is calculated by the computer 4 (step 205). The discharge voltage pattern data is updated according to the energy value at this time (step 206).
[0033]
As a data update (step 206) method, for example, the following can be considered. As shown in FIG. 5 (b), the discharge voltage pattern is usually a normal feedback control that gradually increases the discharge voltage value and maintains the pulse energy value after reaching a certain value, or a control that keeps the voltage constant. To do.
[0034]
If it is considered that a spike pattern of laser light energy generated when oscillating at a constant discharge voltage as shown in FIG. 5A appears strongly, the discharge voltage change pattern stored in the computer 4 as described above (see FIG. 5). 5b) becomes steep and the initial discharge voltage value should be made smaller. Conversely, if the spike pattern is expected to appear weak, the discharge voltage change pattern stored in the computer should be slow.
[0035]
That is, when the energy value of the first few pulses when the shutter 6 is closed and oscillates in this routine A is large, the discharge voltage change pattern becomes steep. Conversely, the discharge voltage change pattern becomes slow unless it is so large.
[0036]
When the pattern data is updated in this way, the stop of the oscillation reception performed at the beginning of the routine A is canceled (step 207), and if there is an oscillation command from the stepper 8, the shutter 6 is opened accordingly (step 103). Laser light is oscillated based on the pattern data stored or updated in the computer 4 (step 104). After performing exposure for a predetermined number of pulses or a predetermined exposure amount, the shutter 6 is closed (step 105).
[0037]
The control shown in the flowchart of FIG. 2 does not allow the computer 4 to recognize the stop state of the burst mode every time because the stepper collectively outputs a command signal of several to several tens of bursts. This is an example of determining the discharge voltage pattern in the next pulse oscillation in a state in which the pulse oscillation is stopped after the grouped oscillation state ends. Incidentally, the wafer may be replaced while the pulse oscillation is stopped.
[0038]
Next, another example of laser control is shown in FIG. This is to reset the elapsed time every time the burst mode is stopped, and to update the data when there is no next pulse oscillation within a predetermined time. When there is no pulse oscillation for a predetermined time or more, This takes into account the fact that the gas state of the laser changes and the data so far lacks accuracy.
[0039]
First, the laser is stopped (step 301) and the timer is reset (step 302). At this time, a certain pattern is given as data in advance. Simultaneously with the start of the stop state, the computer 4 calculates the elapsed time from the stop state by a built-in timer (step 304). If this does not exceed the preset time T, the presence or absence of an oscillation command is checked (steps 305 and 306), and if not, the elapsed time is calculated again.
[0040]
Normally you will be going around this loop. However, when the elapsed time exceeds T, the presence / absence of an oscillation command is further checked (step 307), and if not, the routine moves to a routine A for updating pattern data. In the following, data is updated in the same process as in FIG.
[0041]
When the pattern data is updated, the suspension of oscillation reception performed at the beginning of routine A is canceled (step 207), the elapsed time timer is reset (step 208), and the process returns to the previous elapsed time calculation routine. . Until the set time T elapses again, the normal routine is performed. Of course, if an oscillation command is input midway, oscillation is performed according to the instruction and based on the data stored in the computer at that time (step 308), and at the same time the oscillation is terminated, the oscillation stop state start (step 301) is resumed. It will be a thing.
[0042]
The control of the excimer laser as shown in the above embodiments may be set so as to be performed for pulse oscillation from several pulses at the initial stage of pulse oscillation to about 30 pulses. This is because, from experience so far, it is understood that the spike phenomenon that occurs immediately after the pulse oscillation is from the first few pulses to almost 30 pulses and does not extend beyond that. Accordingly, the predetermined discharge voltage pattern may be about 30 pulses from the start of oscillation, and so-called conventional feedback control can be used thereafter.
[0043]
At this time, even if the energy for each pulse is made substantially constant, some variation may remain. In that case, the target exposure amount will deviate as the integrated exposure amount increases. In order to avoid this, the energy of each pulse may be controlled so that the laminated exposure amount is monitored and becomes a target value.
[0044]
【The invention's effect】
As described above, in the present invention, it is possible to obtain laser light having a constant pulse energy immediately after burst mode oscillation, and it is possible to extremely reduce the variation in exposure amount even with a small number of pulses. Become. Therefore, the excellent features of the latest photosensitizers can be fully utilized to achieve extremely high productivity, and the total number of pulses can be reduced, resulting in longer laser life and lower running costs. .
[Brief description of the drawings]
FIG. 1 is a schematic block diagram of an exposure apparatus using an excimer laser apparatus according to an embodiment of the present invention.
FIG. 2 is a flowchart illustrating a procedure for excimer laser control according to an embodiment of the present invention.
FIG. 3 is a flowchart illustrating the procedure of excimer laser control according to an embodiment of the present invention.
FIG. 4 is a diagram illustrating the relationship between the discharge voltage and pulse energy of an excimer laser.
FIG. 5 is a diagram illustrating the operation of the present invention.
FIG. 6 is a diagram illustrating a burst mode in a stepper.
FIG. 7 is a diagram showing the magnitude of energy for each pulse of excimer laser light.
FIG. 8 is a diagram showing the magnitude of energy for each pulse of excimer laser light in a burst mode.
[Explanation of symbols]
1: Excimer laser oscillator 2: Beam splitter 3: Detector 4: Computer 5: Laser power supply 6: Shutter 7: Laser unit 8: Stepper

Claims (6)

In an exposure system that exposes an object to be exposed in the exposure apparatus by irradiating the object to be exposed in the exposure apparatus with a laser beam pulsed from an excimer laser apparatus,
As information on the spike-like energy fluctuation of the laser beam that occurs immediately after the start of pulse oscillation from the excimer laser device, the relationship between the energy of the laser beam and the discharge voltage is shown in a state where the laser beam does not reach the object to be exposed. And determining a discharge voltage pattern that does not cause spike-like energy fluctuations immediately after the start of pulse oscillation of the excimer laser device based on the relationship between the energy of the laser beam and the discharge voltage, and the determined discharge voltage pattern wherein it has a control device for controlling the discharge voltage to be applied to excimer laser device, exposing the object to be exposed with the laser beam from the excimer laser device based on the discharge voltage that is controlled by the control device on the basis of the Exposure system. A shutter for blocking the optical path of the laser beam;
2. The exposure system according to claim 1, wherein the control device obtains information on energy fluctuation of the laser beam in a state where the optical path of the laser beam is blocked by the shutter. The control device controls a discharge voltage applied to the excimer laser device for each pulse based on the determined discharge voltage pattern so that the energy of the laser beam becomes substantially constant, and the exposure device performs the pulse oscillation. 3. The exposure system according to claim 1, wherein the object to be exposed is exposed from the initial stage with the laser beam. In an exposure method for exposing an object to be exposed in the exposure apparatus by irradiating the object to be exposed in the exposure apparatus with laser light pulsed from an excimer laser device,
As information on the spike-like energy fluctuation of the laser beam that occurs immediately after the start of pulse oscillation from the excimer laser device, the relationship between the laser beam energy and the discharge voltage is shown under the condition that the laser beam does not reach the object to be exposed. And determining a discharge voltage pattern that does not cause spike-like energy fluctuations immediately after the start of pulse oscillation of the excimer laser device based on the relationship between the energy of the laser beam and the discharge voltage, and the determined discharge voltage An exposure method comprising: controlling a discharge voltage applied to the excimer laser device based on a pattern, and exposing the object to be exposed with laser light from the excimer laser device based on the controlled discharge voltage . A part of the laser beam pulse-oscillated from the excimer laser device is incident, the energy of the incident laser beam is detected, and the excimer laser device is used as information on the energy fluctuation of the laser beam based on the detection result 5. The exposure method according to claim 4, wherein the relationship between the energy of the laser beam immediately after the start of pulse oscillation from and the discharge voltage is obtained. The discharge voltage applied to the excimer laser device is controlled for each pulse based on the relationship between the laser beam energy and the discharge voltage so that the laser beam energy is substantially constant. 6. The exposure method according to claim 4, wherein the exposure object is exposed by the laser beam.

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