JPS6128810A - Observing system of mask pattern - Google Patents

Abstract

PURPOSE:To make high the precision of the inspection of a mask pattern by a system wherein a fluorescent substance emitting fluorescence by the application of an excitation light is disposed on one side of a mask and the fluorescence generated by the excitation light is detected by a detector through the mask. CONSTITUTION:A light 121 generated from a light source 102 and passing through a condenser lens 103 is made to pass through a first filter 108 so as to be turned into an excitation light 122 having a wavelength which tends to generate fluorescence. Thereafter, the direction of this light is shifted by a translucent mirror 109, and then the light is made to pass through a transparent portion of a mask 101 and irradiate a fluorescent substance 107, wherefrom fluorescence 123 is generated. Next, the fluorescence 123 is reduced to fluorescence 125 alone through the translucent mirror 109, an imaging lens 105 and a second filter 110, and the latter is imaged on a detector 106 and subjected to photoelectric transfer. Thereby the existence of a minute point (x) and a transparent minute point (y) on the mask 101 is detected, without fail, as (a) and (b) on detection signal levels. According to this system, both a minute opaque point and a transparent point can be detected.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a mask pattern observation method for observing a pattern formed on a mask such as a photomask used for manufacturing printed circuit boards and semiconductor integrated circuits.

[Background of the invention]

Conventionally, when inspecting patterns on masks, etc.

As shown in Japanese Unexamined Patent Publication No. 55-72804, a mask pattern is detected by illuminating a mask with a light source and detecting light reflected from the mask or light transmitted through the mask with a detector. I'm measuring.

FIG. 5 shows a mask inspection apparatus that observes mask patterns using such a conventional method.

In this figure, 1 is a mask to be inspected, and is illuminated from below by a light source 2 via a condenser lens 3 and a reflecting mirror 4. The light 27 that has passed through the mask 1 is imaged on the imaging surface of the detector 6 by the imaging lens 5 and converted into an electrical signal.

For example, when the pattern of the mask 1 shown in FIG. 6(a) is observed along line A-A' in FIG. 1 with such an apparatus, the detection signal waveform obtained from the detector 6 is as shown in FIG. 6(b). )
It becomes as shown in . The problem here is that the signal level Vx for the opaque minute point X existing in the transparent part of the mask 1 is -, ゛/ On the contrary, the detection signal level vy corresponding to the minute transparent point y in the opaque area does not rise to the level corresponding to the transparent area, and as a result, the minute point X.

This means that y cannot be detected. That is, the conventional method has a problem in that the S/N ratio for minute patterns is poor.

Such problems also occur when detecting light reflected from a mask.

[Purpose of the invention]

An object of the present invention is to provide a mask pattern observation method that can observe a mask pattern image with a better S/N than conventional methods.

[Summary of the invention]

In the present invention, a phosphor that generates fluorescence when irradiated with excitation light is placed on one side of a mask, the phosphor is irradiated with excitation light, the phosphor generates fluorescence, and the fluorescence is transmitted to the detector through the mask. By detecting the mask pattern, it is possible to observe the mask pattern with a better S/N ratio than before, and it is possible to inspect the mask pattern with higher precision.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic side view of a mask inspection apparatus according to an embodiment of the present invention. In this figure, 101 is a mask to be inspected, and a phosphor 107 is provided close to the underside of the mask. Reference numeral 102 denotes a light source, and light 121 generated from this light source and passed through the condenser lens 103 passes through the first filter 108 and becomes excitation light 122 having a wavelength that easily causes the phosphor 107 to generate fluorescence. This excitation light 12
2 is redirected by a semi-transparent mirror 109, and the mask 10
The phosphor 107 is irradiated through the transparent part 1.

Fluorescence 123 is generated. Mask 101 for excitation light 122
The combined light 124 of the light reflected from the surface and the excitation light 123 transmitted through the transparent part of the mask 101 passes through the semi-transparent mirror 109, the imaging lens 105 and the second filter 110, and only its fluorescent component 125 is detected. An image is formed on the imaging surface of the device 106 and photoelectrically converted.

Although various materials are possible for the phosphor 107, for example, a glass polyimide plate or a glass epoxy plate used as a base material of a printed circuit board can be used. When using a glass polyimide plate as the phosphor 107, the wavelength is 50
The amount of fluorescence generated peaks with respect to excitation light of 0 nm, and the wavelength of the fluorescence is in the range of 300 to 800 nm, centered around 600 nm. Therefore, as the first filter 108,
The transmittance peaks at 370-390nm, and at 500r
A blue filter that transmits up to a wavelength of v can be used. Further, as the second filter 110, about 500
A yellow filter that transmits light having a wavelength of nm or more and has a transmittance of 50% at a wavelength of 520 to 540 nm can be used. In this case, the light source 102 has a wavelength of 5
If a 14 or 488 nm argon laser is used, the first filter 108 can be omitted.

Now, in this apparatus, the mask 1 shown in FIG. 2(a)
When observing the pattern on the line A-A' for 01, a detection signal as shown in FIG. 2(b) is detected by the detector 10.
It is output from 6. As can be seen, the mask 101
The detection signal level Vx for the opaque minute point X existing in the transparent part of is lowered to the signal level corresponding to the opaque part (shaded part).

Conversely, the detection signal level vy for the transparent minute point y in the opaque area increases to the detection signal level corresponding to the transparent area. Therefore, the presence of the minute point Xl'3/ can be reliably detected from the detection signal level, and the mask pattern can be observed and inspected more accurately than before.

FIG. 3 shows and describes a mask inspection apparatus according to another embodiment of the present invention. In this embodiment, a light source 102, a condenser lens 103, a first filter 108, and a reflecting mirror 1 are used to irradiate the back surface of the phosphor 107 with excitation light.
04 is placed.

Further, a filter corresponding to the second filter 110 in FIG. 1 is omitted. Fluorescence 1 generated from phosphor 107
The amount transmitted through the transparent part of the mask 101 of No. 23 and the phosphor 1
07 and the excitation light 12 transmitted through the transparent part of the mask 101
The combined light 126 with 2 is imaged on the imaging surface of the detector 106 by the imaging lens 105 and photoelectrically converted.

In the case of this embodiment, since the mask pattern is detected by the combined light 126 of fluorescence and excitation light, the detection signal level can be increased compared to the above embodiment, and the S/N
can be further improved.

A mask inspection apparatus according to another embodiment of the present invention is shown in FIG. In this embodiment, a phosphor 123 is placed above the mask 101, and the excitation light 122 is irradiated onto the phosphor 123 through the transparent portion of the mask 101. mask 101
The combined light 124 of the fluorescent light 123 that has passed through the transparent part of the mask 101 and the excitation light 122 reflected by the mask 101 is changed in direction by the reflecting mirror 104, passes through the imaging lens 105 and the filter 110, and is sent to the detector 106 as the fluorescent light 125. The image is formed on the imaging plane.

Here, since the excitation light 122 is irradiated to the mask 101 from an oblique direction, its specularly reflected light component is reflected from the reflector]04
Only the diffusely reflected light component enters the reflecting mirror 10/l side. Since the surface of the mask 101 is smooth, the diffusely reflected light component can be almost ignored.

Therefore, the combined light 124 that enters the reflecting mirror 104 can be regarded as the fluorescence 123 that has mostly passed through the transparent portion of the mask 101. Therefore, mask pattern observation with good S/N ratio is possible as in each of the embodiments described above.

Further, in this embodiment, since the phosphor 123 is arranged above the mask 101, it is possible to prevent dust from falling and adhering to the mask 101.

〔Effect of the invention〕

As the present invention has been described above, it is possible to reliably detect minute opaque or transparent points on a mask, which were difficult to detect in the past, and it is possible to observe and inspect mask patterns with higher precision. becomes.

[Brief explanation of drawings]

FIG. 1 is a schematic side view showing a mask inspection apparatus according to an embodiment of the present invention, FIG. 2(a) is a plan view showing an example of a mask, and FIG. 2. A waveform diagram of the pattern detection signal corresponding to the line A-A' in FIG. 2(a). FIG.
y A schematic side view of an inspection device. i FIG. 4 is a schematic side view of a mask inspection device according to another embodiment of the present invention.
FIG. 5 is a schematic side view showing a conventional mask inspection device, and FIG. 6(a) is a plan view showing an example of a mask.
FIG. 6(b) shows A of FIG. 6(b) in the above conventional device.
FIG. 3 is a waveform diagram of a pattern detection signal obtained for the -A' line. 101...Mask, 102...Light source, 103...
...Condenser lens, 104...Reflector. 105...Imaging lens, 106...Detector. 107...phosphor, 108,110...filter. 109...Semi-transparent mirror, ]22...Excitation light. 123...Fluorescence. Figure 1 Figure 2 Body, lx Figure 3 Z1 Figure 4 Figure 5 Figure 6 I I

Claims (1)

[Claims] (1) A phosphor that generates fluorescence when irradiated with excitation light is placed on one side of the mask, and the phosphor is irradiated with excitation light,
A mask pattern observation method characterized in that a pattern of the mask is observed by detecting fluorescence emitted from the phosphor with a detector through the mask.