JP3412547B2 - Laser control method, exposure system, and semiconductor device manufacturing method - Google Patents

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 discharge excitation type pulse oscillation excimer laser is used as a light source of a successive movement type reduction projection exposure apparatus (hereinafter referred to as a stepper). In the stepper,
After exposing a region on the wafer coated with the photosensitizer,
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.

For such exposure, an excimer laser is constantly oscillated continuously at a constant frequency like a g-line or i-line stepper in which a light source is always turned on, and a shutter is opened when exposure is required. However, this method is inefficient when the life of the laser light source is taken into consideration. Therefore, as an operation method of an excimer laser that is an exposure light source, a mode in which a state in which oscillation continues for a certain frequency (oscillation state) and a state in which oscillation is stopped (stop state) are repeated as shown in FIG. (Hereinafter referred to as burst mode) is used.

On the other hand, in order to manufacture a uniform semiconductor device in the stepper, it is not desirable that the amount of light integrated within the exposure time of one region, that is, the amount of exposure varies from region to region, and it is necessary to keep it as constant as possible. There is.

However, when an excimer laser excited by pulse oscillation is used as the light source, the pulse discharge itself is essentially a statistical phenomenon depending on the discharge gas and the surface state of the electrode, and therefore the laser light energy for each pulse is increased. Is difficult to keep constant. In particular, immediately after the start of oscillation such as continuous oscillation, the state of the gas and the electrode that control the discharge changes transiently, so that the laser light energy is large immediately after the start of oscillation as shown in FIG. 7 and then gradually decreases. The pattern of going (spike phenomenon) is generally seen.

Therefore, even in the burst mode,
There was an unavoidable situation in which the energy of the laser light immediately after the start of the oscillation state was large each time the oscillation state was started, and then gradually decreased and then the spike-like pattern as shown in FIG. 8 was shown. In actual exposure, this spike-shaped pattern cannot be erased by ordinary feedback control in which the discharge voltage is changed after measuring the energy of the laser light, and it can be erased for a while immediately after the start of oscillation (generally, An inefficient method is used in which the exposure is stopped (up to about 30 pulses) and the pulsed light is used for the exposure after the variation is within a certain range.

As described above, when an excimer laser whose laser light energy essentially varies from pulse to pulse is used as a light source, special consideration is required. Therefore, conventionally, this has been attempted to be solved by the following method.

One is a method of reducing the variation of 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 of 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 of the original pulse, where n is the number of integrated pulses for obtaining the same exposure amount. Decrease.

Further, the light energy for each pulse is integrated by using a stepper or an exposure meter in the laser, and when the integrated value approaches a target exposure amount, a neutral density filter or the like is placed in the laser optical path. Another method has been considered in which the energy of each pulse is corrected so that the target exposure amount is obtained.

[0010]

However, when the method of stabilizing the exposure amount by reducing the light energy of each pulse to increase the number of exposure pulses, the total number of pulses is increased, and therefore, the laser pulse is increased. Has a short life and causes problems in running cost.

Further, in recent years, with the development of a photosensitizer which reacts sensitively to light (high sensitivity) by the improvement of technology, the required exposure amount per unit area becomes smaller,
Exposure can be performed in a short time with a much smaller number of pulses than in the past, and improvement in productivity can be realized. However, the pulse train including the spike-shaped 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 that does not include the spike-shaped pattern, If the number of exposure pulses is simply reduced, there arises a problem that the variation in the exposure amount increases and exceeds the specified value.

Further, even when the exposure method for correcting the energy for each pulse so that the integrated value of light energy becomes a predetermined value as described above, the required number of pulses cannot be extremely reduced. Therefore, the conventional exposure using an excimer laser has a problem in that the characteristics of the improved high-sensitivity photosensitizer cannot be fully utilized and improvement in productivity cannot be realized.

It is an object of the present invention to solve the above problems, to obtain a laser control method and an exposure system which minimize the variation of the exposure amount and enable the exposure with a smaller number of pulses than the conventional method.

[0014]

In order to achieve the above object, a laser control method according to a first aspect of the present invention is a laser pulse-oscillated for exposing an object to be exposed in an exposure apparatus by adjusting a discharge voltage. In a laser control method for controlling pulse energy of light, when the exposure apparatus is not performing an exposure operation, the time after the pulse oscillation of the laser light is stopped is measured, and the measurement time is preset. Pulse of the laser light when the time exceeds
From the beginning of oscillation, the pulse energy of the laser light was
When changing the control pattern for controlling the discharge voltage so that when performing pulse oscillation of the laser light according to an oscillation command from the exposure apparatus after the measurement time exceeds the preset time, The discharge voltage is controlled using the changed control pattern.

Further, the invention of claim 2 is such that the discharge voltage is controlled for each pulse using the changed control pattern.

The exposure system of claim 4 exposes the object to be exposed by irradiating the object to be exposed in the exposure device (8) with a pulse of laser light oscillated from the laser oscillator (1). In the exposure system, a voltage supply means (5) for supplying a discharge voltage for oscillating a pulse of laser light from the laser oscillator, and a control means (4) for controlling the discharge voltage supplied from the voltage supply means. And the control means has a timer for measuring the time after the pulse oscillation of the laser light is stopped when the exposure device is not performing the exposure operation, and the measurement time by the timer is When the preset time is exceeded, the pulse of laser light is
The control pattern for controlling the discharge voltage supplied from the voltage supply means is changed so that the scanning energy is substantially constant, and the exposure time from the exposure apparatus after the time measured by the timer exceeds the preset time. When the pulse oscillation of the laser light is performed in accordance with the oscillation command, the discharge voltage supplied from the voltage supply means is controlled using the changed control pattern.

In the exposure system according to a fifth aspect of the invention, the discharge voltage is controlled for each pulse using the changed control pattern.

Further, in the exposure system according to claim 6, the control means controls the discharge voltage for each pulse using the changed control pattern so that the pulse energy of the laser light becomes substantially constant, The exposure apparatus is configured to expose the object to be exposed with the laser light from the initial stage of the pulse oscillation.

[0019]

The magnitude of the energy of the pulsed laser light emitted from the discharge excitation type excimer laser varies depending on the discharge voltage as shown in FIG. This property has been conventionally used for feedback control of the optical output of an excimer laser to maintain it constant over the long term. However, the conventional control in which the discharge voltage is changed after measuring the energy cannot remove the spike phenomenon immediately after the start of the oscillation state. This is because the gas state changed in the stopped state and the first few pulses of the oscillation state could not be controlled.

The present invention is provided with a control means for erasing the above-mentioned spike-like pattern and controlling the discharge voltage so that the energy value of each pulse in the oscillation state in the burst mode becomes substantially constant. 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 situation in which the state of the gas or the state of the electrode, which is the cause of the spike, affects the pulse energy, pulse oscillation is performed without affecting the photosensitizer.
The relationship between the pulse energy of the laser light and the discharge voltage at that time is measured, and a spike-like pattern as shown in FIG. 5A is predicted from the measured value.

In order to cancel the spike-like pattern at the time of pulse oscillation, the discharge voltage is temporally changed as shown in FIG. 5B to perform pulse oscillation. Such control means makes it possible for the first time to virtually eliminate the spike-like pulse of energy, which has been considered inevitable until now in the excimer laser operating in the burst mode.

Therefore, in the present invention, it is possible to obtain a laser beam having a substantially constant pulse energy immediately after the oscillation, and it is possible to minimize the variation in the exposure amount. Further, since the oscillation for determining the control pattern of the discharge voltage that makes 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.

Further, in the present invention, the above control is performed for approximately 30 pulses or less immediately after the pulse oscillation. This is due to the fact that in an excimer laser operating in a burst mode, a spike-shaped pattern in which the pulse energy becomes extremely large immediately after pulse oscillation does not normally extend to more than 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 down.

[0025]

EXAMPLES Examples of the present invention will be described below. Figure 1
FIG. 3 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 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 sent to the computer 4
The energy for each pulse is obtained by inputting to. Also,
The computer 4 obtains 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 the command (signal) regarding the discharge voltage to the power supply 5.

The laser power supply 5 gives a discharge voltage based on a command from the computer 4 to the laser discharge circuit. The discharge voltage is the applied voltage or the charge voltage. Further, the laser light transmitted through the beam splitter 2 is blocked by a shutter 6 capable of advancing and retracting in its optical path so as not to reach the wafer arranged in the stepper 8. Computer 4
Can also be used as an interface between the laser unit 7 and the stepper 8, and the state of the laser unit 7 including the shutter 6 can be communicated to the stepper 8.

In a normal 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, laser light is emitted by outputting a trigger signal from the stepper side to the laser side as an oscillation command. The shutter is controlled by outputting a signal indicating the shutter position from the laser side to the stepper side.

Also in this embodiment, the laser section 7 and the stepper 8 are cooperatively controlled by communicating the above interface signal between the computer 4 and the stepper 8. Further, in this embodiment, the beam splitter 2, the detector 3, the computer 4, and the shutter 6 are shown as incorporated in the laser unit 7, but they may be provided in the stepper 8.

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 light becomes constant. Since the energy value of laser light depends on the gas condition, electrode wear condition, etc., in order to determine such a pattern, the discharge voltage and laser light at that time are oscillated by as few pulses as possible while the burst mode is stopped. It is preferable to determine by determining the relationship with the energy of.

When the oscillation command from the stepper 8 is given through the computer 4, the laser unit 7 supplies the power supply 5 according to the data of the discharge voltage pattern stored at that time.
Pulse oscillation is performed while controlling the discharge voltage and changing the discharge voltage with time.

FIG. 2 is a flow chart showing an example of an algorithm for controlling the excimer laser by controlling the discharge voltage. A specific example of control will be described below with reference to this flowchart. Computer 4
Stores a pattern of the relation between the discharge voltage and the oscillation time as the initial data in advance (step 101). The computer 4 checks whether there is an oscillation command from the stepper 8 (step 102), and if there is no oscillation command, it proceeds to a routine A for updating the pattern data.

In routine A, the 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 light does not reach the exposed object, oscillation is performed (step 203). 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 light at this time is measured by the detector 3 (step 204), and the pulse energy of the laser light is calculated by the computer 4 (step 205). The data of the discharge voltage pattern is updated according to the energy value at this time (step 206).

As a method of updating data (step 206), for example, the following method can be considered. As shown in Fig. 5 (b), the pattern of the discharge voltage is the one in which the discharge voltage value is gradually increased and, after reaching a certain value, normal feedback control to keep the pulse energy value or control to keep the voltage constant. To do.

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

That is, the shutter 6 is closed and this routine A is executed.
When the energy value of the first few pulses when oscillating at is large, the pattern of discharge voltage change becomes steep. On the contrary, if it is not so large, the discharge voltage change pattern becomes slow.

When the pattern data is updated in this way, the stop of the oscillation acceptance performed at the beginning of routine A is released (step 207), and if there is an oscillation command from the stepper 8, the shutter 6 is opened accordingly (step 207). 10
3), oscillate the laser beam based on the data of the pattern stored or updated in the computer 4 (step 1
04). After performing exposure for a predetermined number of pulses or a predetermined exposure amount, the shutter 6 is closed (step 10).
5).

The control shown in the flow chart of FIG. 2 causes the computer 4 to recognize the stop state of the burst mode every time in order that the stepper collectively outputs the command signals of several to several tens of bursts. Instead, it is an example in which the pattern of the discharge voltage in the next pulse oscillation is determined in a state in which the pulse oscillation is stopped after the end of a plurality of collected oscillation states. Incidentally, the wafer may be replaced while the pulse oscillation is stopped.

Next, another example of laser control is shown in FIG.
This is to reset the elapsed time each time the burst mode is stopped and update the data when there is no next pulse oscillation within a predetermined time. , The gas condition of the laser changes,
It takes into account that the data up to that point 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 stopped state, the computer 4 calculates the elapsed time from the stopped state by the built-in timer (step 304). If this does not exceed the preset time T, the presence or absence of the oscillation command is checked (steps 305 and 306), and if not, the elapsed time is calculated again.

Normally, it means that it is around this loop.
However, when the elapsed time exceeds T, the presence / absence of an oscillation command is further checked (step 307), and if there is no oscillation command, the routine proceeds to routine A for updating the pattern data. In the following, the data is updated in the same process as in FIG.

When the pattern data is updated, the stop of the oscillation reception performed at the beginning of routine A is released (step 207), the elapsed time timer is reset (step 208), and the elapsed time calculation described above is performed. Return to routine.
The normal routine is repeated until the set time T elapses again. Of course, if an oscillation command is entered on the way,
At that time, the computer oscillates based on the data stored in the computer (step 308), and at the same time as the oscillation ends, the process returns to the oscillation stop state start (step 301).

The control of the excimer laser as shown in the above embodiment may be set so as to be performed for pulse oscillation from several pulses at the beginning of pulse oscillation to about 30 pulses. This is because it is known from the experience so far that the spike phenomenon occurring immediately after the 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 about 30 pulses from the start of oscillation, and after that, so-called conventional feedback control can be used.

At this time, even if the energy of each pulse is made almost constant, it is considered that some variation remains. In that case, as the integrated exposure amount increases, the target exposure amount deviates. In order to avoid this, the energy of each pulse may be controlled so that the stack exposure amount is monitored and the target value is obtained.

[0044]

As described above, according to the present invention, it is possible to obtain a laser beam having a constant pulse energy immediately after the oscillation in the burst mode, and the variation in the exposure amount is extremely small even with a small number of pulses. It becomes possible to do. Therefore, the excellent characteristics of the latest photosensitizers can be fully utilized to realize extremely high productivity, and the total pulse number can be reduced to prolong the life of the laser and reduce the running cost. .

[Brief description of drawings]

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

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

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

FIG. 4 is a diagram illustrating a relationship between a discharge voltage of an excimer laser and pulse energy.

FIG. 5 is a diagram for explaining 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 burst mode.

[Explanation of symbols]

1: Excimer laser oscillator 2: Beam splitter 3: Detector 4: Computer 5: Laser power supply 6: Shutter 7: Laser part 8: Stepper

─────────────────────────────────────────────────── --- Continuation of the front page (56) References JP-A 1-251769 (JP, A) JP-A 2-111090 (JP, A) JP-A 5-167162 (JP, A) JP-A 4- 7883 (JP, A) JP-A-63-241925 (JP, A) Actual development Sho-57-197660 (JP, U) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01S 3/00-3 / 30 G03F 7/20 H01L 21/027 B23K 26/00-26/42

Claims (7)

(57) [Claims] 1. A laser control method for controlling pulse energy of laser light pulse-oscillated to expose an object to be exposed in an exposure apparatus by adjusting a discharge voltage, wherein the exposure operation is performed by the exposure apparatus. when not, the pulse oscillation of the laser beam measures the time from the stopped state; when exceeding the time the measurement time is set in advance, the
From the beginning of laser light pulse oscillation, pulse energy of laser light
The control pattern for controlling the discharge voltage so that the pulse voltage is substantially constant ; the pulse of the laser light is generated according to an oscillation command from the exposure apparatus after the measurement time exceeds the preset time. A laser control method comprising controlling the discharge voltage using the changed control pattern when oscillating. 2. The laser control method according to claim 1, wherein the discharge voltage is controlled for each pulse using the changed control pattern. 3. A semiconductor device manufacturing method using the laser control method according to claim 1 . 4. An exposure system which exposes an object to be exposed by irradiating the object to be exposed in an exposure apparatus with a pulse of laser light oscillated from a laser oscillator, wherein a pulse of laser light is oscillated from the laser oscillator. A voltage supply means for supplying a discharge voltage for controlling the discharge voltage, and a control means for controlling the discharge voltage supplied from the voltage supply means. wherein a pulsed laser beam is a timer for measuring the time from the stopped state, when exceeding the time time measured by the timer has been set in advance, the record to
Laser light pulse energy from the beginning of laser light pulse oscillation
Change the control pattern for controlling the discharge voltage supplied from the voltage supply means so that the voltage becomes substantially constant ,
When performing pulse oscillation of the laser light in accordance with an oscillation command from the exposure device after the time measured by the timer exceeds the preset time, the voltage supply means using the changed control pattern. An exposure system characterized in that the discharge voltage supplied from the device is controlled. 5. The exposure system according to claim 4 , wherein the control unit controls the discharge voltage for each pulse using the changed control pattern. 6. The control means after the change so that the pulse energy of the laser light is substantially constant.
5. The discharge voltage is controlled for each pulse by using a turn, and the exposure device exposes the object to be exposed with the laser light from the initial stage of the pulse oscillation.
Or the exposure system according to 5. 7. A semiconductor device manufacturing method using the exposure system according to claim 4 .