JP2002217099A - Excimer laser control device and exposure system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide excimer laser device which can minimize variations in the exposure by eliminating a spike-like pattern of pulse energy, and perform exposure with a less number of pulses than a conventional laser. SOLUTION: In an excimer laser device capable of performing burst-mode oscillation, the energy amount of pulses oscillated from the excimer laser device is detected, the relationship between a discharge voltage in each pulse and the amount of energy from the start of the oscillation state is obtained based on the detection result, and the discharge voltage is controlled based on the obtained relationship, so that the energy amount in each pulse during the oscillation state is almost constant.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an excimer laser device used as a light source of an exposure apparatus for manufacturing a semiconductor device, for example.

[0002]

2. Description of the Related Art At present, a pulse excitation excimer laser of a discharge excitation type is used as a light source of a successively moving reduction projection exposure apparatus (hereinafter referred to as a stepper). In the stepper,
After one area on the wafer coated with the photosensitive agent is exposed,
The stage on which the wafer is mounted is moved to expose another region, and by repeating this, the entire required region on the wafer is exposed.

[0003] In such exposure, an excimer laser is continuously oscillated at a constant frequency, such as a g-line or i-line stepper whose light source is constantly turned on, and a shutter is opened when necessary for exposure. However, this method is inefficient in consideration of the life of the laser light source. Therefore, as a method of operating an excimer laser as an exposure light source, a mode in which a state of continuously oscillating (a state of oscillation) and a state of stopping oscillation (a state of stop) as shown in FIG. (Hereinafter, referred to as a burst mode).

On the other hand, in order to manufacture a uniform semiconductor device in a stepper, it is not desirable that the amount of light integrated within a time for exposing one region, that is, the amount of exposure fluctuates depending on the region, and it is necessary to keep the amount constant as much as possible. There is. 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.
It is difficult to make the laser light energy constant for each pulse. In particular, immediately after the start of oscillation such as continuous oscillation, the state of the gas or electrode that controls the discharge changes transiently, so that the laser light energy is large immediately after the start of oscillation as shown in FIG. In general, a pattern of spikes (spike phenomenon) is observed.

Therefore, even in the burst mode,
Each time the oscillation state is started, the energy of the laser beam immediately after the start is large, and then gradually decreases, and it is inevitable that a spike-like pattern as shown in FIG. 8 is exhibited. In performing actual exposure, this spike-like pattern cannot be erased by ordinary feedback control in which the energy of the laser beam is measured and then the discharge voltage is changed. An inefficient method of stopping the exposure (up to about 30 pulses) and using the pulsed light for the exposure after the variation is within a certain range has been performed.

As described above, special consideration is required when an excimer laser having a laser beam energy that varies essentially from pulse to pulse is used as a light source. Therefore, conventionally, this has been attempted to be solved by the following method. One is a method of reducing the variation in the 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 pulse light having such a property for a certain period of time can be reduced to 1 / √n of the variation of the original pulse, where n is the number of integrated pulses for obtaining the same exposure amount. Decrease.

Further, the light energy of each pulse is integrated using a stepper or an exposure meter in a laser, and when the integrated value approaches a target exposure amount, a neutral density filter or the like is placed in the laser light path. To correct the energy of each pulse so as to obtain a target exposure amount.

[0008]

However, when using a method of stabilizing the exposure amount by increasing the number of exposure pulses by reducing the light energy of each pulse, the total number of pulses increases. The life of the parts is short, and a problem occurs in the running cost.

Further, in recent years, with the development of photosensitizers that are sensitive to light (high sensitivity) due to technological improvements, the required exposure amount per unit area has become smaller,
Exposure can be performed in a short time with a much smaller number of pulses than in the past, and the situation is such that productivity can be improved. However, a pulse train including a spike pattern of an excimer laser that is an exposure light source naturally has a large variation in the frequency distribution of light energy for each pulse, compared to a pulse train not including a spike pattern. Simply reducing the number of exposure pulses causes a problem that the variation in the exposure amount increases and exceeds a specified value.

Furthermore, as described above, even when using an exposure method for correcting the energy of each pulse so that the integrated value of the 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 characteristics of the improved high-sensitivity photosensitizer cannot be fully utilized and productivity cannot be improved.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an excimer laser apparatus which solves the above-mentioned problems, minimizes variations in the amount of exposure, and enables exposure with a smaller number of pulses than conventional ones.

[0012]

In order to achieve the above object, an excimer laser control device according to the first aspect of the present invention includes an oscillation state in which continuous pulse oscillation is maintained at a constant frequency for a predetermined time; For an excimer laser device capable of burst mode oscillation that alternately repeats a stop state in which pulse oscillation is stopped for a predetermined time, an excimer that adjusts a discharge voltage to adjust an energy amount of a pulse oscillated from the excimer laser device. In the laser control device, detecting means for detecting an energy amount of a pulse oscillated from the excimer laser device, and based on a detection result of the detecting means, the discharge voltage and the energy amount in each pulse from the start of the oscillation state. Storage means for obtaining and storing the relationship between the pulses and the energy amount of each pulse during the oscillation state. As a constant, and a control means for controlling the discharge voltage for each of the pulses on the basis of the relationship.

In the excimer laser device according to the second aspect of the present invention, an oscillation state in which continuous pulse oscillation at a constant frequency is maintained for a predetermined time and a stop state in which the pulse oscillation is stopped for a predetermined time are alternately performed. For an excimer laser device capable of burst mode oscillation that repeats, an excimer laser control device that adjusts an energy amount of a pulse oscillated from the excimer laser device by adjusting a discharge voltage; The relationship between the discharge voltage and the energy amount in a pulse,
Storage means for obtaining and storing at the time of the stop state, and control means for controlling the discharge voltage for each pulse based on the relationship so as to make the energy amount of each pulse during the oscillation state substantially constant, Equipped.

Further, in the exposure system according to the fifth aspect of the present invention, an exposure system for exposing the object to be exposed by irradiating the object to be exposed in the exposure apparatus with a laser beam pulsed from a laser device. In the laser device, a burst mode oscillation that alternately repeats an oscillation state in which continuous pulse oscillation is maintained for a predetermined period of time for a predetermined time period and a stop state in which the pulse oscillation is stopped for a predetermined time period is possible, Voltage adjusting means for adjusting a discharge voltage to the laser device, detecting means for detecting an energy amount of a pulse oscillated from the laser device, and, based on a detection result of the detecting means, for each pulse from the oscillation state start Storage means for obtaining and storing a relationship between the discharge voltage and the energy amount; and an energy amount of each pulse during the oscillation state. To a constant, and a control means for controlling said voltage adjusting means for each of the pulses on the basis of the relationship,
With.

In the exposure system according to the present invention, the object to be exposed is exposed by irradiating the object to be exposed in the exposure apparatus with a laser beam pulsed from a laser device. In the laser device, a burst mode oscillation that alternately repeats an oscillation state in which continuous pulse oscillation is maintained for a predetermined number of cycles for a predetermined time period and a stop state in which the pulse oscillation is stopped for a predetermined time period is possible, Voltage adjusting means for adjusting a discharge voltage to the laser device; storage means for obtaining and storing a relationship between the discharge voltage and the energy amount in each pulse from the start of the oscillation state during the stop state; Control means for controlling the voltage adjusting means for each pulse based on the relationship so that the energy amount of each pulse is substantially constant; I was painting.

Further, in the exposure system according to the present invention, the laser beam oscillated from the laser device is irradiated on the object in the exposure apparatus to thereby expose the object. In the laser device, a burst mode oscillation that alternately repeats an oscillation state in which continuous pulse oscillation is maintained for a predetermined number of cycles for a predetermined time period and a stop state in which the pulse oscillation is stopped for a predetermined time period is possible, Voltage adjusting means for adjusting a discharge voltage to the laser device, and a relation between the discharge voltage and the energy amount in each pulse from the start of the oscillation state is determined when the object to be exposed in the exposure apparatus is replaced. A voltage adjusting means for each pulse based on the relationship so that the energy amount of each pulse in the oscillation state is made substantially constant. And control means for controlling the means, with a.

[0017]

The magnitude of the energy of the pulsed laser light oscillated from the discharge excitation type excimer laser varies depending on the discharge voltage as shown in FIG. This property has been conventionally used to maintain the optical output of an excimer laser constant over a long period by feedback control. However, the control by the conventional method of changing the discharge voltage after measuring the energy cannot eliminate the spike phenomenon immediately after the start of the oscillation state. This is because the state of the gas changes in the stop state, and the first few pulses of the oscillation state cannot be controlled.

The present invention comprises control means for controlling the discharge voltage so as to erase the above-mentioned spike-like pattern and make the energy value of each pulse during oscillation in the burst mode substantially constant. The pulse oscillation is performed without affecting the photosensitive agent, 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.

That is, in order to investigate the state of the gas state and the electrode state, which are the causes of spikes, on the pulse energy, pulse oscillation is performed without affecting the photosensitive agent.
The relationship between the pulse energy of the laser beam and the discharge voltage at that time is measured, and a spike-like pattern as shown in FIG.

In order to cancel the spike pattern at the time of pulse oscillation, pulse oscillation is performed by temporally changing the discharge voltage as shown in FIG. With such control means, it becomes possible for the first time to virtually eliminate spike-like pulses of energy which have been considered inevitable in an excimer laser operating in burst mode.

Therefore, in the present invention, a laser beam having a substantially constant pulse energy can be obtained immediately after the oscillation, and the variation in the exposure amount can be minimized. In addition, since oscillation for determining a control pattern of a discharge voltage that makes pulse energy constant is performed during a period when the semiconductor device is not performing an exposure operation, the exposure time is not affected and the throughput can be reduced. Absent.

Further, according to the present invention, the above control is performed for about 30 pulses or less immediately after the pulse oscillation. This takes into account the fact that, in an excimer laser operated in a burst mode, a spike-like pattern in which the pulse energy becomes extremely large immediately after the pulse oscillation does not usually extend over approximately 30 pulses from the start of the oscillation. . Therefore, the conventional feedback control function can be used after the spike state in the initial stage of oscillation has settled.

[0023]

Embodiments of the present invention will be described below. Figure 1
1 shows an exposure system in which an excimer laser device according to one embodiment of the present invention is used as a light source. Part of the laser light generated from the laser oscillator 1 is reflected by the beam splitter 2 and enters the detector 3. The photoelectric signal corresponding to the energy of the laser beam output from the detector 3 is transmitted to a computer 4
And the energy for each pulse is obtained. Also,
The computer 4 finds and stores the relationship between the discharge voltage for the laser oscillator 1 and the pulse energy of the laser light as shown in FIG. 4 and outputs a command (signal) regarding the discharge voltage to the power supply 5.

The laser power supply 5 supplies a discharge voltage based on a command from the computer 4 to a laser discharge circuit. The discharge voltage is an applied voltage or a charge voltage. The laser beam transmitted through the beam splitter 2 is blocked by a shutter 6 that can advance and retreat in the optical path so as not to reach a wafer disposed in the stepper 8. 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.

In a typical exposure apparatus, Japanese Patent Laid-Open No. 2-2
As disclosed in Japanese Patent No. 94013, 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. The shutter is controlled by outputting a signal indicating the shutter position from the laser side to the stepper side.

Also in the present embodiment, the laser unit 7 and the stepper 8 are coordinated by communicating the above interface signals between the computer 4 and the stepper 8. Further, in the present embodiment, the case where the beam splitter 2, the detector 3, the computer 4, and the shutter 6 are built in the laser unit 7 is shown, but these may be inside the stepper 8.

The computer 4 has, as data, a predetermined pattern of the discharge voltage with respect to the pulse oscillation time so that the pulse energy of the laser beam becomes constant. Since the energy value of the laser beam depends on the gas state, the consumption state of the electrodes, etc., such a pattern can be determined by oscillating as few pulses as possible during the stop mode of the burst mode, and then setting the discharge voltage and the laser beam It is preferable to determine the relationship with the energy.

When the oscillation command from the stepper 8 is given through the computer 4, the laser unit 7 supplies power to the power supply 5 according to the stored discharge voltage pattern data.
And pulse oscillation is performed while changing the discharge voltage with time. FIG. 2 is a flowchart illustrating an example of an algorithm for controlling the excimer laser by controlling the discharge voltage. Hereinafter, a specific example of the control will be described with reference to this flowchart.

The computer 4 previously stores a pattern about the relationship between the oscillation time and the discharge voltage as the initial data (step 101). The computer 4 checks the presence or absence of the oscillation command from the stepper 8 (step 102), and if not, proceeds to the routine A for updating the pattern data.

In the routine A, first, the oscillation command from the stepper 8 is not accepted (step 201), and the shutter 6 is closed (step 202). After a state where the laser light does not reach the object to be exposed is created, 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 one 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).

As a method of updating the data (step 206), for example, the following method can be considered. The pattern of the discharge voltage is usually a normal feedback control for gradually increasing the discharge voltage value and maintaining the pulse energy value after reaching a constant value, or a control for keeping the voltage constant, as shown in FIG. 5 (b). Is what you do.

If it is considered that a spike-like pattern of laser light energy generated when the laser beam oscillates at a constant discharge voltage as shown in FIG. 5A, the change in the discharge voltage stored in the computer 4 as described above is considered. Pattern (Fig. 5
b) becomes steeper and the initial discharge voltage value should be smaller. Conversely, if the spike-like pattern is expected to appear weak, the pattern of the discharge voltage change stored in the computer should be slow.

That is, the shutter 6 is closed and this routine A
When the energy value of the first few pulses at the time of oscillation is large, the discharge voltage change pattern becomes steep. Conversely, if not so large, the pattern of the discharge voltage change becomes slow. When the pattern data is updated in this manner, the suspension of the oscillation reception performed at the beginning of the routine A is released (step 207), and if there is an oscillation command from the stepper 8, the shutter 6 is opened according to the instruction (step 103). A laser beam is oscillated based on the data of the pattern stored or updated in the computer 4 (step 104). After exposure is performed for a predetermined number of pulses or a predetermined exposure amount, the shutter 6 is closed (step 105).

In the control shown in the flow chart of FIG. 2, the computer 4 recognizes the stop state of the burst mode each time so that the stepper outputs command signals of several to several tens of bursts at once. In this example, after a plurality of oscillation states have been completed, the pattern of the discharge voltage in the next pulse oscillation is determined in a state where the pulse oscillation is stopped. The wafer may be replaced while the pulse oscillation is stopped.

Next, another example of laser control is shown in FIG.
In this method, the elapsed time is reset each time the burst mode is stopped, and data is updated when there is no next pulse oscillation within a predetermined time. Changes the gas state of the laser,
This is due to the fact that the previous data lacks accuracy.

First, the laser is stopped (step 301) and the timer is reset (step 3).
02). 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.

Normally, this loop is being performed.
However, when the elapsed time exceeds T, it is further checked whether or not there is an oscillation instruction (step 307). If not, the routine proceeds to a routine A for updating pattern data. Thereafter, data is updated in the same process as in FIG.

When the pattern data is updated, the suspension of the reception of the oscillation performed at the beginning of the routine A is canceled (step 207), the elapsed time timer is reset (step 208), and the calculation of the elapsed time is performed. Return to routine.
Until the set time T elapses again, the normal routine is performed. Of course, if an oscillation command is input on the way,
At that time, the computer oscillates based on the data stored in the computer (step 308), and returns to the oscillation stop state start (step 301) at the same time when the oscillation is completed.

The control of the excimer laser as described in the above embodiment may be set so as to be performed for the pulse oscillation from several pulses at the beginning of the pulse oscillation to about 30 pulses. This is because the experience shows that the spike phenomenon that occurs immediately after pulse oscillation is from the first few pulses to about 30 pulses, and does not extend beyond that. Therefore, the predetermined discharge voltage pattern may be up to about 30 pulses from the start of oscillation, after which so-called conventional feedback control can be used.

At this time, even if the energy of each pulse is made substantially constant, a slight variation may be considered. In this case, as the integrated exposure increases, the target exposure is deviated. In order to avoid this, the energy of each pulse may be controlled so as to reach the target value by monitoring the lamination exposure amount.

[0041]

As described above, in the present invention, a laser beam having a constant pulse energy can be obtained immediately after the oscillation in the burst mode, and even if the number of pulses is small, the variation in the exposure amount is extremely small. It is possible to do. Therefore, it is possible to realize extremely high productivity by fully extracting the excellent features of the latest photosensitizers, and to reduce the total number of pulses, thereby extending the life of the laser and reducing running costs. .

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an exposure apparatus using an excimer laser device according to one embodiment of the present invention.

FIG. 2 is a flowchart illustrating a procedure of excimer laser control according to one embodiment of the present invention.

FIG. 3 is a flowchart illustrating a procedure of excimer laser control according to one embodiment of the present invention.

FIG. 4 is a diagram illustrating a relationship between 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 illustrating 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 device 6: shutter 7: laser unit 8: stepper

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01S 3/223 E

Claims (9)

[Claims] An excimer laser device capable of performing burst mode oscillation in which an oscillation state in which continuous pulse oscillation is maintained at a constant frequency for a predetermined time and a stop state in which the pulse oscillation is stopped for a predetermined time are alternately performed. An excimer laser control device that adjusts an energy amount of a pulse oscillated from the excimer laser device by adjusting a discharge voltage; detecting means for detecting an energy amount of a pulse oscillated from the excimer laser device; Storage means for obtaining and storing the relationship between the discharge voltage and the energy amount in each pulse from the start of the oscillation state based on the detection result of the means; and making the energy amount of each pulse in the oscillation state substantially constant. Control means for controlling the discharge voltage for each pulse based on the relationship. And an excimer laser control device. 2. An excimer laser device capable of burst mode oscillation in which an oscillation state in which continuous pulse oscillation at a constant frequency is maintained for a predetermined time and a stop state in which the pulse oscillation is stopped for a predetermined time are alternately repeated. In an excimer laser control device that adjusts the energy amount of a pulse oscillated from the excimer laser device by adjusting a discharge voltage, the relationship between the discharge voltage and the energy amount in each pulse from the start of the oscillation state is Storage means for obtaining and storing at the time of the stop state, and control means for controlling the discharge voltage for each pulse based on the relationship so that the energy amount of each pulse during the oscillation state is substantially constant. An excimer laser control device. 3. The storage device according to claim 1, wherein the storage means obtains and stores a relationship between the discharge voltage and the energy amount after a lapse of a predetermined time or more in the stop state.
Or the excimer laser control device according to 2. 4. The excimer laser control device according to claim 1, wherein said control means controls an output from immediately after oscillation of said pulse to approximately 30 pulses. 5. An exposure system for exposing an object to be exposed by irradiating the object to be exposed in the exposure apparatus with a pulsed laser beam from a laser device, wherein the laser device is continuously arranged at a constant cycle number. An oscillation state for maintaining a constant pulse oscillation for a predetermined time, and a burst mode oscillation that alternately repeats a stop state for stopping the pulse oscillation for a predetermined time, voltage adjustment means for adjusting a discharge voltage to the laser device, Detecting means for detecting an energy amount of a pulse oscillated from the laser device, and obtaining a relationship between the discharge voltage and the energy amount in each pulse from the start of the oscillation state based on a detection result of the detecting means. Storage means for storing, for each pulse based on the relationship, so that the energy amount of each pulse in the oscillation state is substantially constant Exposure system characterized by and a control means for controlling the serial voltage regulator. 6. An exposure system for exposing an object to be exposed by irradiating an object to be exposed in the exposure apparatus with a laser beam pulsed from the laser apparatus, wherein the laser apparatus continuously emits light at a constant cycle number. An oscillation state for maintaining a constant pulse oscillation for a predetermined time, and a burst mode oscillation that alternately repeats a stop state for stopping the pulse oscillation for a predetermined time, voltage adjustment means for adjusting a discharge voltage to the laser device, A storage unit that obtains and stores the relationship between the discharge voltage and the energy amount in each pulse from the start of the oscillation state during the stop state, so that the energy amount of each pulse in the oscillation state is substantially constant. An exposure system, comprising: control means for controlling the voltage adjustment means for each pulse based on the relationship. 7. The storage device according to claim 5, wherein the storage means obtains and stores a relationship between the discharge voltage and the energy amount after the stop state has elapsed for a predetermined time or more.
Or the exposure system according to 6. 8. An exposure system for exposing an object to be exposed by irradiating an object to be exposed in the exposure apparatus with laser light pulsed from the laser apparatus, wherein the laser apparatus continuously emits light at a constant cycle number. An oscillation state for maintaining a constant pulse oscillation for a predetermined time, and a burst mode oscillation that alternately repeats a stop state for stopping the pulse oscillation for a predetermined time, voltage adjustment means for adjusting a discharge voltage to the laser device, Storage means for obtaining and storing the relationship between the discharge voltage and the energy amount in each pulse from the start of the oscillation state when the object to be exposed in the exposure apparatus is exchanged; and Control means for controlling the voltage adjusting means for each pulse based on the relationship so as to make the energy amount of the pulse substantially constant. Exposure system. 9. The exposure system according to claim 5, wherein the control unit controls an output from immediately after the oscillation of the pulse to about 30 pulses.