JP2007123294A - Exposure apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exposure apparatus which reduces noises of signals to be detected in an exposure region, by correcting the strength of an exposure light to be emitted from a light source and keeps the exposure amounts constant between exposure regions. <P>SOLUTION: The exposure apparatus has a photodetector 1, an electric charge amplifier 2, an AD converter 3, an exposure amount data memory 5, and an exposure amount sequence controller 6. The sequence controller 6 reads a difference between an estimated voltage signal S2 between the exposure regions and a predetermined integrated amount set in advance from the data memory 5; and controls the strength of an exposure light 33 to be emitted from the light source 10 via a light source controller 8, so that the strength of the exposure light 33 to be emitted from the light source 10 is a predetermined integrated amount. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

 The present invention relates to an exposure apparatus for controlling an exposure amount on a substrate when a mask pattern is transferred onto the substrate in a lithography process for manufacturing a semiconductor device, a liquid crystal display device, an imaging device such as a CCD, a thin film magnetic head, etc. It is about.

Conventionally, in a projection exposure apparatus, in order to perform exposure amount control, a photoelectric sensor that detects an integrated exposure amount for receiving a light beam branched from exposure light during exposure of a wafer or a glass plate coated with a photosensitive material. A photodetector comprising a conversion element is arranged.
Therefore, the exposure amount on the wafer is indirectly detected through a photodetector that detects the integrated exposure amount.
In order to increase the accuracy of exposure control, a method of controlling the variation in light emission of the pulse light source for each pulse light emission is performed.
Therefore, for example, Japanese Patent Laid-Open No. 6-252022 (Patent Document 1) proposes a method of controlling the energy of each pulse illumination light and controlling the exposure amount for each pulse.
The method of controlling the energy of each pulse illumination light and controlling the exposure amount for each pulse is based on the integrated exposure amount for the region included in the slit-shaped exposure region in the scanning direction on the wafer in real time for each pulse illumination light. Measure with
Here, the slit-shaped exposure region is a region conjugate with the slit-shaped illumination region on the reticle, and the wafer is scanned relative to this region.
Further, the target energy of the next pulse illumination light is calculated individually based on the integrated exposure amount, the energy of each pulse illumination light is controlled, and the exposure amount is controlled for each pulse.
In general, the integrated exposure amount is read by receiving a part of the exposure light with a light amount sensor such as a photodiode and reading the generated charge with a charge amplifier.
The charge amplifier uses an operational amplifier to provide a capacitor for feedback, accumulates the charge generated by the light quantity sensor in the feedback capacitor, and converts it into a voltage.
There are two types of discharge of the accumulated charge, one that discharges with a resistor in the feedback and the other that resets with a transistor having a switch function.
In the case of a method in which the energy of each pulse illumination light is controlled and the exposure amount is controlled for each pulse, the exposure amount is read by charging and discharging the feedback capacitor for each pulse, and the peak voltage of the generated voltage is AD. It was digitized and read by a converter.
JP-A-6-252022

Here, in order to control the integrated exposure amount with high accuracy, it is necessary to increase the reading accuracy of a photodetector that detects the integrated exposure amount.
However, when the reading accuracy of the photodetector for detecting the integrated exposure amount is increased, noise applied to the analog signal of the charge sensor is suppressed and the S / N of the signal is not increased. There is a problem that control cannot be performed.

Along with miniaturization, a new type of exposure apparatus has been developed. The influence of noise generated in the exposure apparatus has become a problem. The problem will be described below.
With recent miniaturization, an EUV exposure apparatus using EUV light as a light source has been developed.
The EUV exposure apparatus generally uses a laser plasma (LPP) light source (LPP light source) or a discharge (DPP) light source (DPP light source) as a light source.
The LPP light source irradiates a target material such as a metal thin film, an inert gas, or a droplet supplied into the vacuum vessel with a gas jet or the like with a high-intensity pulse laser to generate high-temperature plasma.
The LPP light source uses, for example, EUV light with a wavelength of about 13 nm emitted from this plasma.
On the other hand, the DPP light source applies a high voltage between the electrodes and generates a plasma by flowing a gas such as xenon and discharging it to generate EUV light.
A high voltage is applied when generating plasma, but a large noise is generated during discharge.
A photodetector that detects the integrated exposure amount can also be used to monitor the exposure light amount of the EUV light source, but there is a problem that the correct exposure amount cannot be read due to noise generated from the apparatus on the sensor signal.
Particularly, since EUV exposure apparatus discharges at a high voltage, noise is generated during exposure, and the EUV exposure apparatus uses a high vacuum chamber.
For this reason, there is a problem that separation from a signal becomes difficult because noise generated from a pump for vacuuming and noise generated from a vacuum gauge are several KHz to several tens KHz close to the light emission period of the exposure light source. .
Accordingly, an object of the present invention is to provide an exposure apparatus that corrects the intensity of exposure light emitted from a light source, makes the exposure amount constant between exposure areas, and reduces noise in signals detected in the exposure areas. .

In order to achieve the above object, an exposure apparatus according to the present invention comprises: a light source that emits exposure light; and a light source controller that controls the light source so as to control the intensity of the exposure light emitted from the light source. An exposure apparatus that scans and exposes the object to be exposed by relatively moving the exposure light and the object to be exposed;
A photodetector that receives a part of the exposure light emitted from the light source and outputs a charge signal proportional to the intensity of the exposure light;
A charge amplifier that receives and accumulates the charge signal, converts the accumulated charge signal into an accumulated voltage signal, and outputs the voltage signal;
An AD converter that receives the accumulated voltage signal, digitizes the accumulated voltage signal, and outputs the digitized signal;
An exposure amount data memory that receives the digitized signal and stores the digitized signal; and
The difference between the integrated voltage signal between exposure areas and a predetermined integrated amount set in advance is read from the exposure amount data memory, and the intensity of the exposure light emitted from the light source is set to the predetermined predetermined amount. And an exposure amount sequence controller that controls the intensity of the exposure light emitted from the light source via the light source controller so as to be an integrated amount.

In the exposure apparatus of the present invention, the integrated voltage signal is held in the charge amplifier between the exposure regions, and the integrated charge signal held in the charge amplifier in a region other than the exposure region. The exposure amount sequence controller controls a discharge switch constituting the charge amplifier via a discharge switch control circuit so as to discharge the light.
Further, the exposure apparatus of the present invention detects the accumulated voltage signal as a noise component in a state where exposure is not performed in a region other than the exposure region in advance, and stores it in the exposure amount data memory. The noise component is read from the exposure amount data memory, and the noise component is subtracted from the integrated voltage signal between the exposure regions.

According to the exposure apparatus of the present invention, a photodetector that receives a part of the exposure light emitted from the light source and outputs a charge signal proportional to the intensity of the exposure light;
A charge amplifier that receives and accumulates the charge signal, converts the accumulated charge signal into an accumulated voltage signal, and outputs the voltage signal;
An AD converter that receives the accumulated voltage signal, digitizes the accumulated voltage signal, and outputs the digitized signal;
An exposure amount data memory that receives the digitized signal and stores the digitized signal; and
The difference between the integrated voltage signal between exposure areas and a predetermined integrated amount set in advance is read from the exposure amount data memory, and the intensity of the exposure light emitted from the light source is set to the predetermined predetermined amount. And an exposure amount sequence controller that controls the intensity of the exposure light emitted from the light source via the light source controller so that the integrated amount of the exposure light is obtained.
For this reason, the exposure amount sequence controller compares the integrated output voltage of the charge amplifier integrated for each predetermined number of light emission pulses emitted by the light source with a predetermined target voltage in real time.
Furthermore, it calculates an error with respect to the target setting of the emission intensity that has emitted a predetermined number of pulses, corrects this error amount, controls the intensity of the next emission pulse, corrects the intensity of the emission pulse emitted from the light source, The exposure amount is made constant between exposure areas.

Further, according to the present invention, the accumulated voltage signal is held in the charge amplifier between the exposure regions, and the accumulated charge signal held in the charge amplifier is discharged in a region other than the exposure region. As described above, the exposure amount sequence controller controls the discharge switch constituting the charge amplifier via the discharge switch control circuit.
For this reason, the integrated voltage output from the charge amplifier is continuously integrated between the exposure areas, and the charges accumulated in the charge amplifier are discharged outside the exposure area.
In an exposure apparatus having a noise-generating light source having a plasma light source such as EUV, the exposure areas are continuously integrated as an analog signal.
For this reason, the noise signal on the sensor signal is averaged, the noise component is removed, and the noise of the signal detected between the necessary exposure regions is effectively reduced.

Further, according to the present invention, the integrated voltage signal is detected as a noise component in a state in which exposure is not performed in a region other than the exposure region in advance, and is stored in the exposure amount data memory. The noise component is read from the exposure amount data memory, and the noise component is subtracted from the integrated voltage signal between the exposure regions.
For this reason, voltage signals previously integrated before exposure in areas other than the exposure area are detected as noise components, stored in the exposure amount data memory, and integrated exposure between the exposure areas as systematic noise components of the exposure apparatus. By subtracting from the amount, an accurate integrated exposure amount between exposure regions is obtained.

  Hereinafter, the present invention will be described with reference to the drawings based on the embodiments.

With reference to FIGS. 1 and 2, an exposure apparatus according to Embodiment 1 of the present invention having an exposure control apparatus 50 will be described.
The exposure apparatus according to the first embodiment of the present invention is an apparatus that scans and exposes the wafer 32 that is the object to be exposed by relatively moving the exposure light 33 and the wafer 32 that is the object to be exposed.
The light source 10 is a device that irradiates the exposure light 33.
The light source controller 8 is a device that controls the light source 10 so as to control the intensity of the exposure light 33 emitted from the light source 10, that is, the intensity of the light emission pulse.
The reticle stage 20 is a device that holds the reticle 21.
The projection optical system 30 is an optical system that projects the exposure light 33 from the light source 10 reflected by the reticle 21 onto the wafer 32.
The wafer stage 31 is an apparatus that holds the wafer 32 to be exposed.
The light source controller 8 designates the light emission pulse intensity, outputs a light emission command to the light source 10, and irradiates the exposure light 33 from the light source 10.
The irradiated exposure light 33 is reflected by the reticle 21, and the exposure image of the reticle 21 is transferred to the wafer 32 on the wafer stage 31 via the projection optical system 30.
The position on the wafer 32 to be transferred is detected by the stage position detection circuit 11 including a laser interferometer and the wafer stage 31 is moved to change the exposure area.

Next, the exposure control apparatus 50 that constitutes the exposure apparatus according to the first embodiment of the present invention will be described.
The photodetector 1 is a device that receives a part 33 a of the exposure light 33 emitted from the light source 10 and outputs a charge signal S 1 proportional to the intensity of the exposure light 33.
The charge amplifier 2 is a device that receives and integrates the charge signal S1, converts the integrated charge signal S1 into an integrated voltage signal S2, and outputs the converted voltage signal S2.
The charge amplifier 2 includes an operational amplifier 2a, a capacitor 2b that stores the detected charge signal S1, and a discharge switch 2c that includes a transistor that discharges and resets the stored charge signal S1. The discharge switch 2c is controlled by the discharge switch control circuit 7.
The AD converter 3 is a device that receives the integrated voltage signal S2, inputs a numerical value to the integrated voltage signal S2, and outputs a digitalized signal S3.
The exposure data memory 5 receives the digitized signal S3 and stores the digitized signal S3.
The exposure amount data memory 5 is a memory that accumulates the signal S3 of the integrated light quantity digitized by the AD converter 3 in real time and stores the digitized data of the exposure amount between the exposure regions accumulated between the exposure regions. is there.
The exposure amount sequence controller 6 reads the difference between the integrated voltage signal S2 between the exposure regions and a predetermined integration amount set in advance from the exposure amount data memory 5, and the intensity of the exposure light 33 emitted from the light source 10 Is an apparatus that controls the intensity of the exposure light 33 emitted from the light source 10 via the light source controller 8 so that the predetermined integrated amount is set in advance.
The discharge switch control circuit 7 is a circuit that discharges charges accumulated in the capacitor 2b by controlling the discharge switch 2c formed of a transistor.

Next, the operation of the exposure amount sequence controller 6 will be described with reference to the sequence flow diagram of FIG.
The exposure amount sequence controller 6 has an exposure sequence operation in which the exposure amount in the exposure region is brought close to the target setting without being affected by noise, and the exposure amount is kept constant in the exposure range.
Step 110 is a step of performing offset measurement by the charge amplifier 2.
An offset signal obtained by integrating the noise signal received by the exposure apparatus is measured by the exposure control apparatus 50 outside the exposure area of the wafer 32.
This operation can be measured by integrating and measuring between the exposure areas without emitting exposure light between the exposure areas, and storing the obtained numerical value as an offset voltage in the exposure amount data memory 5.
At this time, the range of the signal S1 integrated in the charge amplifier 2 is set between the exposure areas, and in a range other than the exposure amount area, the discharge switch 2c including the transistor input to the feedback of the charge amplifier 2 is closed by the discharge switch control circuit 7. By performing the discharge operation, it is possible to measure the noise voltage between the exposure areas.
Alternatively, the noise voltage may be measured by integrating the charge amplifier 2 for a certain time when the exposure sequence is not performed.
It is possible to approximate the noise voltage measurement during the actual exposure operation by setting the fixed time to the time for scanning between the exposure areas.
In step 111, integrated exposure is started and an exposure sequence of the wafer 32 is performed.

FIG. 4 is a diagram showing the step operation of the exposure sequence on the wafer 32.
Point A indicates the exposure start point. At point A, the discharge switch 2c formed by the discharge transistor of the charge amplifier 2 shown in FIG. 1 is closed.
The discharge switch 2c is opened from a certain position before entering the exposure area of point B where the exposure amount is not integrated, and preparations are made to accumulate charges in the feedback capacitor 2b.
When the stage position reaches the point B that is the exposure range, the light source 10 emits pulses.

FIG. 3 is a diagram showing the number of light emission pulses and the voltage output of the charge amplifier 2.
The voltage increases stepwise for each emission pulse.
Assuming that the output voltage with the pulse number Pn is Vn and the pulse number Pn + m after the constant value m is Vn + m, the mth integrated light quantity voltage is Vn + m, and m is, for example, 4, from the first pulse emission to the fourth. Is expressed by V4-V1.
Assuming that the intensity of one pulse is the ideal state V ₀ , the pulse P ₅ operates so as to correct the voltage difference from the exposure amount at (V 4 −V 1 −4 V ₀ ) / 4.

The operation is shown in FIG.
In the section C in Fig. 4 where the actual integrated light intensity is read every 4 sections in one pulse step and the pulse emission intensity is sequentially corrected to keep the exposure area constant, the integrated light intensity is added in real time in this manner. The exposure is corrected every time.
In the correction, the light quantity of the light source 10 is controlled by outputting an error amount with respect to the data from the ideal light emission pulse intensity for each predetermined pulse section obtained by the exposure sequence controller 6 to the light source controller 8.
The target exposure amount can be determined in advance by managing the test exposure.
When reaching D in FIG. 4, which is a region past the exposure region, the discharge switch control circuit 7 closes the discharge switch 2 c of the charge amplifier 2 to discharge the accumulated exposure amount of charge.
In step 112 shown in FIG. 5, it is checked whether it is within the exposure range.
Whether it is within the exposure range is determined by obtaining the position data of the wafer 32 by the stage position detection circuit 11 shown in FIG.
If it is within the exposure range, the exposure amount is controlled in step 113.
In step 115, scanning of all exposure ranges is completed.
If it is determined in step 115 that scanning of the entire exposure range is not completed, it is confirmed again in step 112 whether the exposure area is reached.
If the exposure range is exceeded, in step 114, the discharge switch control circuit 7 closes the discharge switch 2c of the charge amplifier 2 to discharge the accumulated charge, thereby bringing the exposure range close to the target value and keeping the exposure amount constant. To control.

It is a block diagram of the exposure apparatus of Example 1 of this invention. It is a block diagram of the exposure apparatus of Example 1 of this invention. It is explanatory drawing of measuring the exposure amount in the exposure area | region in the exposure apparatus of Example 1 of this invention, and controlling the light emission pulse for every light emission pulse. It is explanatory drawing of the sequence of exposure control in the exposure range on the wafer in the exposure apparatus of Example 1 of this invention. It is a flowchart for demonstrating the sequence of the exposure control in the exposure range on the wafer in the exposure apparatus of Example 1 of this invention. It is explanatory drawing of the light emission pulse relationship controlled with respect to the light emission pulse in the exposure range in the exposure apparatus of Example 1 of this invention.

Explanation of symbols

1: Photodetector 2: Charge amplifier
2a: operational amplifier 2b: capacitor 2c: discharge switch
3: AD converter 5: Exposure amount data memory 6: Controller 7: Discharge switch control circuit 8: Light source controller 10: Light source 11: Stage position detection circuit 20: Reticle stage 21: Reticle 30: Projection optical system 31: Wafer stage 32 : Wafer 33: Exposure light 33a: Part 50: Exposure control device

Claims (3)

A light source that emits exposure light; and a light source controller that controls the light source so as to control the intensity of the exposure light emitted from the light source, and relatively moves the exposure light and the object to be exposed. In an exposure apparatus that scans and exposes the object to be exposed,
A photodetector that receives a part of the exposure light emitted from the light source and outputs a charge signal proportional to the intensity of the exposure light;
A charge amplifier that receives and accumulates the charge signal, converts the accumulated charge signal into an accumulated voltage signal, and outputs the voltage signal;
An AD converter that receives the accumulated voltage signal, digitizes the accumulated voltage signal, and outputs the digitized signal;
An exposure amount data memory that receives the digitized signal and stores the digitized signal; and
The difference between the integrated voltage signal between exposure areas and a predetermined integrated amount set in advance is read from the exposure amount data memory, and the intensity of the exposure light emitted from the light source is set to the predetermined predetermined amount. An exposure apparatus comprising: an exposure control device having an exposure amount sequence controller for controlling the intensity of the exposure light emitted from the light source via the light source controller so as to obtain an integrated amount of.   The accumulated voltage signal is held in the charge amplifier between the exposure areas, and the exposure amount sequence is discharged so that the accumulated charge signal held in the charge amplifier is discharged in an area other than the exposure area. 2. The exposure apparatus according to claim 1, wherein the controller controls a discharge switch constituting the charge amplifier via a discharge switch control circuit.   The integrated voltage signal is detected as a noise component in a state where exposure is not performed in a region other than the exposure region in advance, and is stored in the exposure amount data memory. The exposure amount sequence controller is configured to detect the noise component from the exposure amount data memory. The exposure apparatus according to claim 2, wherein the noise component is subtracted from the integrated voltage signal between the exposure regions.

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