JPH0546694B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention provides a method for transferring and exposing a mask pattern on which a pattern of an electronic circuit or the like is formed onto the wafer surface using an intermittent light source as a light source. The present invention relates to an exposure apparatus that can always supply an appropriate amount of exposure light to the top.

(Prior Art) Recent semiconductor manufacturing technology requires lithography technology that can form high-density circuit patterns as electronic circuits become highly integrated.

Generally, when a circuit pattern on a mask or reticle surface is transferred onto a wafer surface via a projection optical system, the resolved line width of the circuit pattern transferred onto the wafer surface is proportional to the wavelength of the light source. In addition, in the case of the so-called contact method or proximity method, in which a mask and a wafer are transferred in close contact with each other or overlaid with a distance of several to several tens of microns, the resolution is proportional to the square root of the wavelength. For this purpose, high-pressure mercury lamps, xenon mercury lamps, etc., which oscillate short wavelengths in the far ultraviolet (deep UV region) of 200 to 300 nm, are used. However, these light sources have low brightness and lack directivity, and the photoresist coated on the wafer surface has low photosensitivity, resulting in a long exposure time and a reduction in the overall output.

On the other hand, recently, an intermittent light source, for example, an excimer laser, which has an oscillation wavelength in the deep UV region, has been developed, and it is said that it is effective as a lithography technology due to its high brightness, monochromaticity, and directivity. There have been various reports.

Many excimer lasers currently on the market use a mixed gas for laser oscillation sealed in a gas chamber, circulated, and discarded after use.

As the mixed gas, for example, a highly corrosive halogen gas such as F ₂ or HCl is used. For this reason, the influence of discharge during excitation is added, and the halogen-based gas reacts with the inner wall of the laser discharge tube and the discharge electrode to form impurities, which causes the laser output to deteriorate over time. This reaction of halogen molecules always occurs even when laser light is not oscillated. For this reason, especially when the laser beam is oscillated after the laser oscillation has been stopped for a long time, the laser beam oscillates with uncertain output energy that is unrelated to the previous laser output.

Therefore, when using excimer lasers in exposure equipment for semiconductor manufacturing, it is necessary to constantly monitor changes in laser output because it is necessary to strictly control the amount of exposure to the wafer surface as circuit patterns become finer. .

(Objective of the Present Invention) The present invention was made in view of the above circumstances, and its purpose is to enable accurate exposure control and control the pattern of a mask even when an excimer laser is used as an exposure light source. An object of the present invention is to provide an exposure device that can transfer images onto a wafer with high precision.

(Means and Actions for Achieving the Object) In order to achieve the above object, the exposure apparatus of the present invention emits exposure light in a pulsed manner with an emission time on the order of nanoseconds, which is useful for transferring a mask pattern onto a wafer. an excimer laser that detects a portion of the exposure light and outputs a value proportional to the amount of light for one pulse of the exposure light; The apparatus is characterized in that it includes a control means for controlling the amount of exposure when transferring onto a wafer, and the detection means includes a silicon photodiode with a response speed on the order of microseconds.

In such an exposure apparatus of the present invention, the response speed of the detection means (silicon photodiode) is sufficiently slow compared to the emission time of the excimer laser, so that the detection means itself can absorb exposure light for one pulse of the excimer laser. This will have an integral effect on the
Therefore, it is possible to accurately detect the amount of exposure light for one pulse of the excimer laser with a simple configuration without providing an integrating circuit or the like to integrate the amount of light for each pulsed light in the detection means. In an exposure apparatus for semiconductor manufacturing using an exposure light source, highly accurate exposure control becomes possible.

Further, if the control means controls the exposure amount by using the output of a plurality of pulses of the exposure light, it becomes possible to control the exposure amount with higher precision.

(Example) FIG. 1 is a schematic diagram of an example of the exposure apparatus of the present invention.
2 is an intermittent light source, such as an excimer laser, and 2 is a switchable type whose optical density can be switched to several levels.
ND filter; 3 is a variable aperture member capable of arbitrarily changing the aperture diameter; 4 is a reflecting mirror; 5 is a detection means disposed in a part of the optical path to detect the amount of light;
For example, a photoelectric conversion element made of a general silicon photodiode is preferable. 6 is a shutter; 7 is an illumination system that illuminates the reticle and mask 8 with the light beam output from the excimer laser 1; 9 is a projection system for projecting the mask pattern on the mask 8 onto the wafer 10; 11 is the wafer 10 is mounted on an XY stage which can be driven by a drive means (not shown); 12 is a surface plate; 13 is a solenoid for driving the shutter 6; and 14 is a control means.

In this embodiment, an alignment optical system for adjusting the relative relationship between the mask 8 and the wafer 10 is provided, but it is omitted in the figure.

In this embodiment, when projecting and exposing a mask pattern onto a wafer surface, the shutter 6 is first closed and one or several pulsed lights are output from the excimer laser 1, and the output energy of the pulsed light at that time is detected by the detection means 5. Detect with. This makes it possible to know the degree of deterioration of the mixed gas sealed in the excimer laser 1. The mask 8 is then controlled by the control means 14 based on the output signal from the detection means 5.
Controls the amount of light irradiated onto the surface. Control at this time is performed by using a voltage adjusting means (not shown) that varies the discharge voltage of the excimer laser 1, by changing the optical density by using the switching type ND filter 2, by changing the aperture diameter of the variable aperture member 3, or by changing each of these elements. This is performed by an exposure amount control means that performs the following operations in duplicate. When the detection means 5 detects a predetermined amount of light, the detection means 5 is moved out of the optical path and the second
As shown in the figure, the shutter 6 is opened by the solenoid 13, the mask pattern is irradiated with pulsed light from the excimer laser 1, and the mask pattern is projected and exposed onto the surface of the wafer 10 by a projection system with an appropriate exposure amount.

In this embodiment, the switchable ND filter 2,
The object of the present invention can be achieved even if the detection means 5, shutter 6, etc. are placed at any position in the optical path from the excimer laser 1 to the wafer 10. Further, the object of the present invention can be achieved even if the variable aperture member 3 is placed at any position as long as it is at the pupil position of the wafer or at its optical conjugate surface. Further, the detection means 5 may be arranged at the position 5' by using 4 as a half mirror. At this time, it can be monitored even during exposure.

In this embodiment, the shutter 6 does not need to be provided. However, in this case, excimer laser 1
When outputting the image, it is necessary to remove the wafer 10 from the XY stage.

When using an excimer laser as a light source as in this embodiment and performing repeated exposure using the so-called step-and-repeat method, the XY stage can be Transfer exposure can be performed while continuously feeding without stopping.
In such cases, high throughput can be easily achieved by performing one exposure with one pulse of light. In such a case, the present invention accurately controls one pulse-like output for exposure, so that accurate exposure can be performed.

The present invention can also be applied to a so-called contact method in which a mask and a wafer are brought into close contact with each other, or a proximity method in which a mask and a wafer are placed apart from each other by a small space of several to several tens of microns.

FIG. 2 is a timing chart for explaining the operation of FIG. 1. In the case of Example A, the power is turned on after a long period of stoppage, and a plurality of output laser pulses, for example four, are used for exposure detection. During these four pulse output periods, the shutter 6 is closed, and the computer in the control means 14 calculates the average value of the four pulses, adjusts the laser output as described above, and starts from the fifth output. Start exposure.

Example B shows a case where the number of this monitoring pulse is one. As a specific example of the detection means 5, a silicon photodiode is preferably used as described above. because
If the element has a fast response speed, such as a PIN (Positive Intrinsic Negative) photodiode, the output current will be almost the same as the excimer laser pulse in FIG. 3A, as shown in FIG. 3C. Here, if the waveform shape of laser pulse A is always constant, the peak value of C is approximately proportional to the area of A, so the peak value of C can be regarded as the energy of A.
However, in the case of an excimer laser, its output waveform is generally unstable, so an integrating circuit is required to detect a value proportional to the area of A. However, as shown as B in Figure 3, silicon photodiodes have a slow response speed of several microseconds (on the order of microseconds), so they themselves have an integral effect, and therefore, this peak value S is as shown in Figure 3. It is proportional to the area of the excimer laser output waveform of A, and by detecting this S, the laser output energy can be measured without using an integrating circuit. FIG. 4 shows an example in which the laser is output only in each exposure area C1, C2, . . . on the wafer, and the wafer is exposed while continuously moving.

That is, first, the first exposure area C1 is exposed with a laser beam. Next, the second exposure area C2
Move to position C1 and perform the second exposure. During this movement, the output of the laser 1 is of course stopped.

Furthermore, during the second exposure, the wafer 10 is not stopped but is exposed while it is moving. Thereafter, the wafer 10 is continuously moved to the exposure area C5, and exposures of C3, C4, and C5 are performed. When this is completed, the wafer 10 is moved upward by one line, and exposure is performed while continuously moving C6 to C12 of the next line.

The following processing is performed in the same manner. Since the wafer is exposed continuously in this way, the throughput is improved.

(Effects) As described in detail above, according to the present invention, it is possible to accurately detect the amount of exposure light for one pulse of an excimer laser, so it is possible to accurately detect the amount of exposure light for one pulse of an excimer laser. In the device,
Highly accurate exposure control is possible. Furthermore, such exposure amount control can be implemented with a simple configuration.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of an example of the present invention, Figures 2 to 4
The figure is a timing chart for explaining the operation. 1...excimer laser source, 5...silicon photodiode.

Claims (1)

[Scope of Claims] 1. An excimer laser that emits exposure light useful for transferring a mask pattern onto a wafer in a pulsed manner with an emission time on the order of nanoseconds; a detection means for outputting a value proportional to the amount of light for one pulse of the detection means; and a control means for controlling the exposure amount when transferring the pattern of the mask onto the wafer using the output of the detection means; An exposure apparatus characterized in that the means includes a silicon photodiode whose response speed is on the order of microseconds. 2. The exposure apparatus according to claim 1, wherein the control means controls the exposure amount using the output of a plurality of pulses of the exposure light.