JPH0548612B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention includes a projection optical system that projects and images a mask pattern of a fine structure such as an IC or LSI onto a wafer surface, and an alignment optical system that adjusts the relative positional relationship between the mask pattern and the wafer. In particular, an exposure apparatus that uses a light source S ₁ whose oscillation wavelength width can be controlled in an illumination optical system that illuminates a mask pattern, and a light source that oscillates at a wavelength different from that of the light source S ₁ in an alignment optical system. It is related to.

Projection optical systems, which are traditionally used in exposure equipment to project and print minute patterns of ICs, LSIs, etc. onto wafer surfaces, are required to have extremely high resolution, primarily for microfabrication.

In general, the resolution of images projected by a projection optical system improves as the wavelength used becomes shorter.
A light source that oscillates as short a wavelength as possible is used as a light source for illuminating the mask pattern. For example, currently, ultra-high pressure mercury lamps that mainly emit light with a wavelength of 436 nm or 365 nm are often used.

Further, the exposure apparatus uses a so-called alignment optical system for detecting the relative positional relationship between the mask pattern and the wafer each time the mask pattern is printed on the wafer surface.

In order to simplify the apparatus, a so-called TTL method is often used for the alignment optical system, which utilizes part or all of the projection optical system. In many cases, the light source for illuminating the mask pattern and the light source used in the alignment optical system are different. This is because, as mentioned above, the illumination optical system must use a light source that oscillates as short a wavelength as possible, and the alignment optical system must use a light source that oscillates in a wavelength range that can be easily recognized visually for observation. be. For example, the alignment optical system uses wavelength
A He-Ne laser that oscillates at 632.8 nm is used.

In general, if chromatic aberration correction is performed in the wavelengths used by both the projection optical system and the alignment optical system in the projection optical system, each optical system can be used in common.

However, if the wavelength λ ₁ used in the projection optical system is, for example, 436 nm, and the wavelength λ ₂ used in the alignment optical system is, for example, 632.8 nm, and chromatic aberration correction is performed using two wavelengths, the chromatic aberration correction state will often be as shown in Figure 1. become.

An actual light source has a wavelength width corresponding to the oscillation wavelength, for example, a wavelength width Δλ in the figure. Therefore, at wavelength λ _1, chromatic aberration is completely corrected, but at wavelengths corresponding to the wavelength width Δλ around wavelength λ ₁ , chromatic aberration is large, and this amount of chromatic aberration greatly increases the resolving power of the projection optical system for the purpose of microfabrication. It becomes a cause of decline.

For example, the main oscillation wavelength of an ultra-high pressure mercury lamp is 436n.
When m, the wavelength width is approximately ±5 nm, so the wavelength range is 10 μ.
High resolution cannot be obtained unless chromatic aberration is almost completely corrected within the range of .

Therefore, in the past, chromatic aberration correction was performed to form a curve as shown in FIG. 2, in order to reduce the chromatic aberration over the entire wavelength range Δλ near the wavelength _λ1 . By performing such correction, it was possible to obtain high resolution even if the illumination light source had a certain wavelength width.

However, as is clear from FIG. 2, the chromatic aberration at wavelength λ ₂ for the alignment optical system cannot be completely corrected, and a considerable amount of chromatic aberration remains. For example, if the wavelength is λ ₁ -432.8 nm and the wavelength λ ₂ -632.8 nm, the amount of axial chromatic aberration at wavelength λ ₂ may be as high as about 1.3 mm.

Therefore, conventionally, during alignment, an auxiliary optical system was inserted into a part of the projection optical system to correct the chromatic aberration at wavelength λ ₁ and wavelength λ ₂ . For this reason, in the conventional exposure apparatus, the entire apparatus is complicated, and relative accuracy between the auxiliary optical system and the projection optical system is strictly required, and even a slight deviation causes a decrease in alignment accuracy.

The present invention aims to provide an exposure apparatus that does not use a conventional auxiliary optical system, simplifies the entire apparatus, and improves alignment accuracy.

The main feature of an exposure apparatus for achieving the object of the present invention is a projection exposure apparatus that illuminates a mask pattern and exposes a substrate to be exposed through the mask pattern, in which the mask pattern is imaged onto the substrate to be exposed. a projection optical system that corrects axial chromatic aberration with respect to a wavelength λ ₁ and a wavelength λ ₂ different from the wavelength ₁ ; means for illuminating the mask pattern with a laser beam of the wavelength λ ₁ ; and light of the wavelength λ ₂ . an alignment optical system that detects a positional relationship between the mask pattern and the exposed substrate using the projection optical system;
and means for narrowing the wavelength width of the laser beam.

As described above, in the present invention, by using the light source _S1 whose wavelength width can be controlled for illuminating the mask pattern, the wavelength width is made as small as possible to achieve high resolution of the projected image. For example, if an excimer laser is used as a light source and the wavelength width is controlled by injection locking means, the present invention can be suitably applied. Regarding the control of the wavelength width, in a projection optical system which requires a high resolution with a resolution line width of about 1 to 2 .mu.m as in the present invention, it is necessary to control the wavelength width to 0.1 nm or less in the embodiments described later. In this respect, excimer lasers are preferable because when the oscillation wavelength is 248.5 nm, the wavelength width can be easily controlled to about 0.01 mm.

Next, FIG. 3 shows a schematic diagram of a part of the optical system of the exposure apparatus of the present invention. In the figure, reference numeral 1 denotes a light source for illuminating a mask 4 having an integrated circuit pattern, and the oscillation wavelength width can be controlled like an excimer laser with injection locking. 2 is an illumination optical system, 6 is a projection optical system, 7 is a wafer having a layer sensitive to the illumination light source, and 8 is a wafer mounting table that moves to align the mask 4 and the wafer 7. 3 is an optical member consisting of a microscope objective, a reflecting mirror, etc., and 9 is a light source for alignment in a wavelength range that does not expose the wafer to light, such as a laser that emits visible light. The optical member 3 and the projection optical system 6 constitute an alignment optical system, and the mask 4 and the wafer 7
The positional deviation is detected by photoelectric detectors 10, 10. In the projection optical system 6, chromatic aberration is corrected in two wavelengths: a sensitive wavelength range and a non-sensitive wavelength range.

In conventional exposure equipment, the chromatic aberration correction state of the projection optical system and alignment optical system was as shown in Figure 2.
It was necessary to correct chromatic aberration by installing an auxiliary optical system between the mask pattern 4 and the mask pattern 4 and outside the projection optical path of the pattern. In the projection optical system 6 and the alignment optical system in the present invention, as described above, the projection optical system uses the light source _S1 whose wavelength width can be controlled, and the oscillation wavelength _λ1 of the light source 1 and the alignment optical system use the light source S1. Since the chromatic aberration of the two wavelengths λ ₂ is completely corrected, there is no need to use an auxiliary optical system as in the conventional case.

FIG. 4 shows an example of the chromatic aberration correction state of the projection optical system according to the present invention. In the figure, the curve is a chromatic aberration curve corrected for two wavelengths, 632.8 nm and 436 nm, in the conventional case, and the curve is a chromatic aberration curve corrected for two wavelengths, 632.8 nm and 248.5 nm, according to the present invention.

Since the projection optical system of the present invention uses light with a short wavelength of 248.5 nm, the projection optical system is made of at least two glass materials that have good transmittance on the short wavelength side and have different dispersion, such as fused quartz, etc. It is preferably composed of calcium fluoride or the like.

As described above, according to the present invention, by using a light source whose wavelength width can be controlled in the projection optical system, it is possible to achieve an exposure apparatus with improved alignment accuracy while simplifying the entire apparatus.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram of the general chromatic aberration correction state, Figure 2
The figure is an explanatory diagram of the chromatic aberration correction state of the projection optical system used in a conventional exposure device, FIG. 3 is a schematic diagram of an embodiment of the exposure device of the present invention, and FIG. 4 is a diagram showing the chromatic aberration correction of the present invention and the conventional one. It is an explanatory diagram of a state. In the figure, 1 is an illumination light source, 2 is an illumination optical system, 3 is an optical member, 4 is a mask pattern, 6 is a projection optical system, 7 is a wafer, 8 is a wafer mounting table, and 9 is an alignment optical system.

Claims (1)

[Claims] 1. In a projection exposure apparatus that illuminates a mask pattern and exposes a substrate to be exposed through the mask pattern, a wavelength λ ₁ that forms an image of the mask pattern on the substrate to be exposed and a wavelength different from the wavelength λ ₁ a projection optical system that corrects axial chromatic aberration with respect to λ ₂ ;
means for illuminating the mask pattern with the laser beam of the wavelength λ ₁ ; and an alignment optical system for detecting the positional relationship between the mask pattern and the substrate to be exposed using the projection optical system with the light of the wavelength λ ₂ . , means for narrowing the wavelength width of the laser beam.