JPS63190333A - Device for regulating quantity of light - Google Patents

Abstract

PURPOSE:To obtain the required quantity of light excellently and in a short time, by making the quantity of light required for an object to be compared with a boundary value and next varying the quantity of light for respective pulses and the number of pulses. CONSTITUTION:In consideration of the allowable quantity of light per pulse and the number of required minimum pulses, a boundary value of the integral quantity of light is set up, and the quantity of light required for an object is compared with this boundary value by a comparison means BD. In succession, when the quantity of light required for the object is smaller than the boundary value in a condition setting-up means BE, conditions for obtaining the quantity of light required for the object can be determined by setting up the quantity of light pulses into the minimum pulse number and varying the quantity of light for respective pulses. On the other hand, the quantity of light required for the object is larger than the boundary value, the conditions for obtaining the quantity of light required for the object can be determined by setting up the quantity of light for light pulses into the allowable quantity of light in an optical system and varying the number of pulses. Next, the conditions related with the quantity of light are outputted to a controlling means for the quantity of light BB, and the conditions related with the number of pulses are outputted to a controlling means for the number of pulses BF. Thus, the quantity of light and the number of pulses can be controlled.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a light amount adjustment device for a light source that emits pulsed light, and for example, uses an excimer laser to project a mask pattern onto a photosensitive material on a semiconductor wafer. The present invention relates to a light amount adjustment device suitable for an exposure apparatus that performs.

[Prior Art] Conventionally, a reduction projection type exposure apparatus, a so-called stepper, used in one step of lithography for manufacturing integrated circuits uses an ultra-high pressure mercury lamp as an exposure light source.

This ultra-high-pressure mercury lamp outputs light with multiple wavelengths, but as the resolution required for lithography improves, the wavelength of the light used also becomes shorter, and now it is not only possible to output light with a wavelength of 436 nm (365 nm). light has also come to be used.

However, at wavelengths below this, the amount of energy becomes small1, and only lithography with extremely low throughput can be realized.

Recently, excimer lasers have been attracting attention as a solution to these problems.

When using an excimer laser, the wavelength is 308 nm, 249 nm.
It is possible to obtain strong light at wavelengths such as nm and 193 nm. This laser has the property of being oscillated and output in a pulsed manner with a time width of 10 to 20 SeC.

The amount of exposure light required by the photosensitive material is adjusted by appropriately setting the number of pulses and the amount of energy of each pulse.

In such a pulsed laser light source, there are generally variations in the energy value between each of the plurality of pulses.

Therefore, in order to adjust the exposure amount with good reproducibility using a pulsed laser light source in the above-mentioned exposure apparatus, it is necessary to integrate multiple pulses to statistically reduce the relative amount of variation, or to integrate multiple pulses to statistically reduce the relative amount of variation. It is necessary to control the energy and reduce the amount of variation.

However, these methods require a certain number of pulses or more in order to obtain a predetermined stable amount of exposure energy.

[Problems to be Solved by the Invention] In the above-described exposure apparatus, the photosensitivity of the resist film, which is the photosensitive material to be exposed, varies greatly depending on the type of the resist film. The change is, for example, 102 to 1
It reaches as high as 0.03.

In this way, sensitivity varies considerably depending on the subject to be exposed, so
In setting conditions such as the intensity of the pulse output from the light source, the following inconvenience occurs.

First, if the number of pulses is set to an appropriate number (for example, the small number of pulses necessary to obtain a stable exposure amount) centered on a highly sensitive photosensitive material, the energy per pulse will be relatively low. becomes.

If you set a light source under these conditions and apply it to a photosensitive material with low sensitivity and adjust the number of pulses, the number of pulses to obtain the required exposure amount will be very large, and the exposure will take a lot of time. There is an inconvenience that it takes time.

Furthermore, in this case, if the number of pulses is fixed and the amount of energy per pulse is adjusted, there is a problem that underexposure may occur even if it is the maximum value that can be adjusted.

On the other hand, if the number of pulses is set to an appropriate number centered on a photosensitive material with low sensitivity, the energy per pulse will be relatively high.

If we set the light source under these conditions and apply it to a highly sensitive photosensitive material to adjust the number of pulses, then 1
Since the energy per pulse is very high, there is a risk of overexposure or of the power or energy density incident on the optical element being too high and destroying the optical element. Particularly in the case of light having an oscillation spectrum in the ultraviolet region, such as excimer laser light, a large amount of light is absorbed by the elements of the optical system, and this becomes heat and is accumulated within the element.

Furthermore, in this case, if the number of pulses is fixed and the amount of energy per pulse is adjusted, there is a disadvantage that it is necessary to significantly attenuate the amount of energy per pulse.

The present invention has been made in view of this point, and even if the required energy or light amount changes greatly depending on the irradiation target, it can be used without causing any danger such as damage to the optical system.
It is an object of the present invention to provide a light amount adjusting device that can satisfactorily apply the required amount of energy to an irradiation target in a short period of time.

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention provides an optical system through which light pulses of a predetermined period are transmitted, an allowable amount of light per pulse for an object, and a stable cumulative amount of light. Considering the minimum number of pulses required for
For example, a value corresponding to the product of the above-mentioned allowable light amount and the minimum number of pulses) is set, and a comparison means for comparing this boundary value with the required light amount of the object, and a comparison means that compares the required light amount of the object with the boundary value. If the number of light pulses is smaller than the above-mentioned minimum pulse number, the light intensity of each pulse is changed while the number of light pulses is set to the above-mentioned minimum pulse number. Technically, it is provided with a condition setting means for changing the number of pulses while setting the permissible light amount of the optical system, and a control means for controlling the light pulses irradiated to the object based on the set light amount and number. This is the main point.

An example of the basic configuration of this invention is shown in FIG. In this figure, the light pulses output from the pulse light source BA are controlled by a light amount control means BB such as a variable attenuator.
The light passes through and enters the object BC.

On the other hand, the output side of the comparison means BD for comparing the required light amount of the object BC with the boundary value is connected to the condition setting means BE, and the output side of the condition setting means BE is connected to the light amount control means B.
E and pulse number control means BF, respectively.

[Function] In the present invention, an optical system through which a light pulse of a predetermined period passes and an allowable amount of light per pulse for an object,
The boundary value of the integrated light amount is set by considering the minimum number of pulses required to obtain a stable integrated light amount. and,
This boundary value and the required amount of light for the object are compared by, for example, the comparing means BD in FIG.

This comparison result is manually input to the condition setting means BE. Here, if the required light amount of the object is smaller than the boundary value, the number of light pulses is set to the minimum pulse number, and the light amount of each pulse is changed by 1 to reduce the required light amount of the object. The conditions for obtaining it are set.

On the other hand, if the required light amount of the object is larger than the boundary value, the light amount of the optical pulse is set to the allowable light amount of the optical system, and the number of pulses is changed to obtain the required light amount of the object. conditions are set.

Next, among the conditions set as described above, the condition regarding the light amount is sent from the condition setting means BE to the light amount control means BB.
The conditions regarding the number of pulses are output to the condition setting means B.
E is output to the pulse number control means BF.

The light amount control means BB controls the amount of pulsed light based on manually entered conditions. The pulse number control means BF controls the number of pulses output from the pulse light source BA based on the input conditions.

[Embodiments] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 2 shows one embodiment of the invention. In this figure, a laser light source 10 is a light source that emits pulsed light, such as an excimer laser. The output pulse of this laser light source 10 is made to enter a variable attenuator 12 that can control the amount of incident light.

Next, the pulsed light transmitted through the variable attenuator 12 is caused to enter an exposure target 16 such as a semiconductor wafer by the action of an appropriate optical system 14.

Next, an exposure control section 18 is connected to each of the laser light source 10 and variable attenuator 12 described above. The exposure control unit 18 receives an exposure dose signal S d from an external host computer (not shown) that instructs the exposure energy (appropriate exposure dose) E dose required for the object 16 .
ose and the exposure start signal Sexp are manually input.

This exposure control section 18 receives a manually input exposure amount signal S do
It has a function of outputting a pulse number signal Sn to the laser light source 1o and outputting an energy amount signal Sa to the variable attenuator 12 based on se and the exposure start signal Sexp.

Among these signals, the pulse number signal Sn instructs the number of pulses to be output to the variable attenuator 12, and the laser light source 1o outputs the designated number of pulses at approximately constant intervals. Output.

Further, the energy amount signal Se indicates the energy amount of the pulse outputted to the optical system 4, and the variable attenuator 12 adjusts the energy amount of the incident pulse to the value specified by this. Control.

Next, a detailed procedure for determining the number of pulses and the amount of energy thereof in the above embodiment will be explained.

Among the above-mentioned components, the maximum value of the energy of the pulse output from the laser light source 10 and irradiated onto the exposure target (maximum amount of light per pulse) is limited by the ability of the laser light source 10, but other , the optical system 14 or the exposure target 16 are not damaged.

FIG. 1 shows a graph of such basic operation.

This figure shows the relationship between the average energy e per pulse and the total exposure energy E dose.

In this figure, eth is the optical system 14 with one pulse of light emission.
It is a value of energy that may cause damage to the exposed object 16 (hereinafter simply referred to as "damage value"), and e
max is an energy value that is less than the damage value eth and can be set practically (hereinafter simply referred to as "practical maximum value J").

In this embodiment, in consideration of safety in the event of a malfunction, the maximum output of the laser light source 10 is set so as not to exceed the above-mentioned practical maximum value e max even when the pulse passage rate of the variable attenuator 12 is at its maximum. Value is set.

Therefore, the energy of each pulse is set to be equal to or less than the practical maximum value e max, regardless of the value of the energy required by the exposure target 16.

Next, the total number of pulses must be greater than or equal to the minimum number of pulses nm1n sufficient to reduce fluctuations in energy between each pulse.

Here, the number of pulses is fixed to n min, and the exposed object 1
Let E be the total exposure energy irradiated to 6, and increase the average energy e of each pulse from zero, E=nmin −e・・・・・・・・・・・・・・・
...(1), and the graph GA in FIG. 3 is obtained.

In this graph, the total exposure energy corresponding to the practical maximum value e max is defined as El (hereinafter simply referred to as "boundary energy").

This boundary energy E1 is the maximum amount of energy that can be irradiated with the minimum number of pulses n min (emax x nm1
n), below which the number of pulses cannot be reduced, and above which the pulse energy value cannot be increased.

Therefore, the energy required by the exposure target 16 is
dose, [A] E dose < E, (7) then Niha, (
1) The number of pulses n is n min......1...
・・・・・・・・・・・・(2)(2) The average energy e of each pulse is e = E dose/n min...
・・・Phase・・・・・・・・・(3)

[B] In the case of Edose≧E1, (1) The average energy e of each pulse is e == e
max・・・φ・・・・・・・・・・・・・・・・・・
・・・・・・・・・・・・(4)(2) The number of pulses n is n=E dose/e max・・・・・・・・・
......φ(5).

In either case, the required energy E dos
Depending on the value of e, it may be necessary to perform delicate amount control of less than the amount of energy for one pulse.

In such a case, for example, the average energy e is decreased, the number of pulses n is increased, and some of the pulses are attenuated to adjust the overall energy amount.

The condition setting as described above is shown in Fig. 3. First, if E dose < El, the conditions are set along the area LA of the graph GA, and E dose≧
In the case of E1, conditions are set along area LB of graph GB where e = e max.

Next, the number of pulses n when the conditions are set as above
The relationship between this and the exposure time T per wafer W will be explained with reference to FIG.

In FIG. 4, a graph GC shows the relationship between the number of pulses n and the exposure time T. This graph is a straight line whose slope is the pulse period. The exposure time corresponding to the minimum number of pulses n min is indicated by Tm1n. In this figure, if [A] E dose < E +, the number of pulses is n = n min, so the exposure time is T =
T min and is represented by point Q.

[If B/E dose≧E1, the number of pulses or n>
Since n min, the exposure time is T)Tmin, which is expressed as area LC of graph GC.

Next, the overall operation of the above embodiment will be explained with reference to the flowchart of FIG.

First, an exposure amount signal S dos is sent from an external device (not shown).
e and an exposure start signal S exp are input to the exposure control section 18 (see step SA in FIG. 5).

Next, in the exposure control section 18, the manually inputted exposure amount signal S
Required energy indicated by doSe E do
It is determined whether se is less than or equal to the boundary energy E1 (see step SC).

As a result, if E dose<E 1, the conditions are set using equations (2) and (3) as described above (see step SC).

On the other hand, in the case of EdO8e≧E1, as mentioned above,
Conditions are set using equations (4) and (5) (see step SC).

After the pulse number and energy amount are set as described above, the pulse number is instructed (set) to the laser light source 10 by the pulse number signal Sn (see step SC), and then, An attenuation instruction is given to the variable attenuator 12 to set the energy amount to the energy amount signal Se (see step SC).

After such an instruction, a pulse is output, and the exposed object 1 is
Exposure for 6 is started (see Step SG).

When the output of all pulses is completed (see step SC), the exposure is completed.

It should be noted that the present invention is not limited to the above-mentioned embodiments; for example, a Norse light source other than an excimer laser may be used, and it is also applicable to devices other than exposure devices.

Further, in the above embodiments, the light amount was controlled using a variable attenuator, but depending on the case, the output pulse optical distortion may be controlled by the light source itself.

[Effects of the Invention] As explained above, according to the present invention, even if the amount of energy required by the illumination target changes greatly, the required minimum range can be maintained without causing any risk of optical damage to the optical system. This has the effect of being able to always provide the optimum irradiation energy at a given time.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing a basic configuration example of the present invention;
The figure is a block diagram showing an embodiment of the present invention, FIG. 3 is a diagram showing the relationship between the average energy of each pulse and exposure energy, and FIG. 4 is a diagram showing the relationship between the number of pulses and exposure time.
FIG. 5 is a flowchart showing the operation of the above embodiment. [Explanation of symbols of main parts 10...Laser light source, 12...Variable attenuator, 14...Optical system, 16...Exposure object, 18...
- Exposure control section.

Claims (1)

[Scope of Claims] A light amount adjustment device that adjusts the integrated light amount of a plurality of light pulses that are irradiated onto an object through an optical system at a predetermined period by changing the light amount or quantity of each pulse, comprising: The boundary value of the integrated light amount is set in consideration of the permissible light amount per pulse for the system and the target object, and the minimum number of pulses necessary to obtain a stable integrated light amount, and the boundary value of the integrated light amount is set, and this boundary value and the target object a comparison means for comparing the amount of light required for the object, and when the amount of light required for the object is smaller than the boundary value, the number of light pulses is set approximately to the minimum number of pulses, and the light amount of each pulse is changed. condition setting means for changing the number of pulses by setting the light intensity of the light pulse to approximately the allowable light intensity for the optical system or the object when the required light amount of the object is larger than the boundary value; A light amount adjusting device comprising: a control means for controlling a light pulse irradiated onto a target object based on the light amount and quantity.