JPH1114551A - Inspection apparatus for mask defect - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inspection apparatus, for a mask defect, by which the defect of a fine mask pattern can be detected. SOLUTION: An inspection apparatus is provided with a laser oscillation source 11 which can pulse-oscillate far-ultraviolet laser light, with a vibrating mirror 15 which reflects the laser light to be output from the laser oscillation source 11 in such a way that the space phase distribution of the laser light is changed, with a mask pattern 19 by which the laser light to be reflected by the vibrating mirror 15 is irradiated, with a light-receiving sensor 22 which receives the laser light to be passed through the mask pattern 19 and with a control circuit 10 which extracts the defect of a mask in such a way that the photographed image of the mask pattern received by the light-receiving sensor 22 is compared with the reference image of the mask pattern.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mask inspection apparatus for inspecting a mask pattern for defects using ultraviolet laser light.

[0002]

2. Description of the Related Art In recent years, the capacity of a semiconductor memory (DRAM) is about to reach 1 Gbyte or more. For this reason, the minimum line width of a semiconductor tends to become smaller and smaller. Due to this tendency, the mask pattern required for forming a semiconductor memory has been miniaturized.

For this reason, in the mask manufacturing process, it is necessary to inspect the presence or absence of a defect in the mask pattern which is substantially equal to the minimum line width of the semiconductor. As described above, when the defect size of the mask pattern becomes minute, it is necessary to shorten the wavelength of the light source of the inspection apparatus to increase the resolution of the optical system.

In a conventional mask defect inspection apparatus, a lamp such as an Hg lamp or an HgXe lamp is used as an illumination light source, and the g-line i
Inspection was performed by selecting light of a necessary short wavelength such as a line.

[0005]

The conventional mask defect inspection apparatus as described above has the following problems. When a lamp such as an Hg lamp or an HgXe lamp is used as illumination light, the amount of deep ultraviolet light is weak, and a sufficient amount of light for imaging cannot be obtained. For this reason, in the field of semiconductor exposure apparatuses, excimer lasers and YAG lasers are well known as light sources of deep ultraviolet light.

[0006] In this case, the pulse laser has spatial intensity unevenness called speckle, and it is difficult to use the pulse laser as a light source of an inspection apparatus in which illumination unevenness on a mask surface to be imaged requires 5% or less.

A method of solving the spatial illumination unevenness by the speckle has been well studied with respect to a wafer exposing apparatus using an excimer laser. First, a method of inserting a rotating phase plate in the middle of the optical path (Japanese Patent Laid-Open No. 63-17332)
No. 2) or a method of inserting a vibrating mirror before making the illumination light uniform with a fly-eye lens in the middle of the optical path (Reference: Kazuo Ushida, Optics Vol. 23 No. 10 (1994))
P602).

[0008] In each of these methods, the illumination unevenness is made uniform by changing the spatial illumination unevenness, repeating the exposure, and integrating the light amount exposed to the resist on the wafer.

In such a mask inspection apparatus, since the inspection is performed while continuously moving the mask to be inspected, there is a difficulty that means for irradiating light to the same place many times and integrating the light amount cannot be taken.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and an object of the present invention is to provide a mask defect inspection apparatus capable of detecting a defect in a miniaturized mask pattern.

[0011]

According to a first aspect of the present invention, there is provided a mask defect inspection apparatus, comprising: a laser oscillation source capable of oscillating deep ultraviolet laser light; and a laser output from the laser oscillation source. A vibration mirror that reflects the laser light so as to change the spatial phase distribution of the laser light, a mask pattern irradiated with the laser light reflected by the vibration mirror, and a light passing through the mask pattern Light-receiving sensor for receiving the laser light, and a captured image of the mask pattern and the mask pattern received by the light-receiving sensor.
Means for extracting a defect of the mask by comparing with a reference image of the mask.

The mask defect inspection apparatus according to claim 2 is
A laser oscillation source capable of oscillating deep ultraviolet laser light, and a vibration mirror for reflecting the laser light output from the laser oscillation source so as to change the spatial phase distribution of the laser light. And a mask pattern for irradiating the laser light reflected by the vibration mirror, and a CCD line sensor for receiving the laser light passing through the mask pattern. Each time is moved by .DELTA.L in the Y direction, laser light is output from the laser oscillation source, a mask pattern image captured by a CCD line sensor is stored, and the stored mask pattern image and mask pattern are stored. Means for extracting a defect of the mask by comparing with a reference image of the mask.

According to the second aspect, the deep ultraviolet laser light output from the laser light source is controlled so that there is no interference in an illuminating section comprising, for example, a microarray lens and a rotating phase plate. Laser light without interference output from the illumination unit is reflected by a finely moving vibration mirror and is incident on a mask pattern via a condenser lens and an objective lens.

The light passing through the mask pattern is received by a light receiving sensor via a condenser lens. When an integrating CCD line sensor is used as this light receiving sensor, the line sensor moves in the stage movement direction (Y direction).
If the pitch of each line is .DELTA.L, a synchronizing signal is generated in the pulse laser and oscillated every time the movement of the stage is displaced by .DELTA.L.

The rotating phase plate is constantly rotating, and the position of the phase plate through which the light output from the pulse laser passes changes for each oscillation and the phase of the light changes. The oscillating mirror changes the position of the optical axis on the mask surface as the mirror oscillates, thereby changing the position of speckles generated on the mask surface. As a result, the position of the speckle appearing on the sensor surface every time the laser oscillates is different, and the electric charge accumulated in the element of one line is electrically integrated in the element of the next line, and the number of stages is calculated. The unevenness in the light amount is averaged by integrating the values.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing the overall configuration of a mask inspection apparatus. In FIG. 1, 11 is, for example, 1
This is a deep ultraviolet pulse laser device that oscillates a pulse laser having a wavelength of 80 to 300 nm. This pulse laser device 11 uses the fundamental wave of the YAG laser to convert it to SHG or FH.
Extract 4 times (wavelength: 266 nm) of the G crystal,
A light source is a YAG laser whose wavelength is narrowed to about ± 0.5 nm by a band narrowing element.

The pulse laser output from the deep ultraviolet pulse laser device 11 passes through the microlens array 12 and the rotating phase plate 13 and enters the lens 14. The microlens array 12 and the rotating phase plate 13 form a laser.
An illumination unit for eliminating interference of the light is configured. Where 13
a is a motor for rotating the rotary phase plate 13;

The laser light incident on the lens 14 is incident on the oscillating mirror 15 which oscillates. The swing mirror 15 is swung by a swing mechanism (not shown). This rocking mirror
The laser light reflected by the mirror surface 15 enters the condenser lens 17 through the mask plate pressure correction lens 16.
The laser light condensed via the condenser lens 17 is irradiated on a mask pattern 19 via an objective lens 18. On the mask pattern 19, a fine pattern for a semiconductor memory is formed.

The laser light having passed through the mask pattern 19 passes through a condenser lens 20 and a variable power lens 21 and is an integrated CCD line sensor 2 as a light receiving sensor.
2 is received.

The line sensor 22 is installed on a base 23. Immediately next to the line sensor 22, a confocal focus type photodetector 24 is provided. The light detector 24 is provided at the same height as the CCD line sensor 22 and in the same illumination area. With this structure, autofocus can be performed even when there are temperature and atmospheric fluctuations.

Incidentally, the mask pattern 19 is moved in a fixed direction at the XY stage. The movement of the XY stage is controlled by the control circuit 10. This control circuit 1
By observing the position of the XY stage by 0,
The position of the mask pattern is observed.

Incidentally, the integrating CCD line sensor 22
Are formed as shown in FIG. In FIG. 2, a plurality of line sensors 31 are formed continuously in accordance with the movement direction of the stage in the Y direction. The pitch for each line is defined as ΔL.

The control circuit 10 outputs a synchronizing signal to the pulse laser device 11 every time the movement of the stage is displaced by ΔL, and outputs a pulse laser synchronized with the displacement. The control circuit 10 extracts a defect of the mask pattern 19 by comparing a means for generating a reference image of the mask pattern 19 and a captured image of the mask pattern 19 integrated by the CCD line sensor 22. ing.

For example, when using a 64-row accumulation type sensor element having a size of 13 μm as the CCD line sensor 22, the stage is 10 mm / mm under the condition of 130 × optical magnification.
When the laser beam is emitted at an oscillation frequency of about 4 kHz after moving s, the same image can be superimposed eight times per line.

Next, the operation of the embodiment of the present invention configured as described above will be described. The control circuit 10
Every time the movement amount of the XY stage in the Y direction is displaced by ΔL, the pulse laser device 11 outputs a synchronization signal to the pulse laser device 11. In response to this synchronization signal, the pulse laser device 11
The G laser is output.

This YAG laser is laid through a microlens array 12 and a rotating phase plate 13 which is always rotating.
Processing for eliminating interference of the light is performed. In other words, the rotating phase plate 13 is always rotating, and the position of the phase plate through which the light output from the pulse laser passes changes for each oscillation and the phase of the light changes.

The laser light incident on the lens 14 is incident on the oscillating mirror 15 which oscillates. The swing mirror 15 is swung by a swing mechanism (not shown). This rocking mirror
The laser light reflected by the mirror surface 15 enters the condenser lens 17 through the mask plate pressure correction lens 16.
The laser light condensed via the condenser lens 17 is irradiated on a mask pattern 19 via an objective lens 18. On the mask pattern 19, a fine pattern for a semiconductor memory is formed.

The laser light having passed through the mask pattern 19 passes through a condenser lens 20 and a variable power lens 21 so that the integrating CCD line sensor 2 as a light receiving sensor can be used.
2 is received.

The oscillating mirror changes the position of the optical axis on the mask surface as the mirror oscillates, thereby changing the position of speckles generated on the mask surface. As a result, each time the laser oscillates, the position of the speckle appearing on the sensor surface differs,
The electric charge accumulated in the elements of the line is electrically integrated in the elements of the next one line, and the accumulated light is integrated in multiple stages, thereby averaging the unevenness in the light amount.

In the control circuit 10, the mask pattern 1
The defect of the mask pattern 19 is extracted by comparing the reference image 9 and the captured image of the mask pattern 19 integrated by the CCD line sensor 22.

By doing so, when inspecting for defects in the mask pattern using deep ultraviolet laser light, it is possible to eliminate unevenness in the amount of light. -Defects can be detected.

Although the microlens array 12 is used in the above embodiment, a fly-eye lens can be used. In the present invention, a continuous oscillation laser oscillation source such as an Ar laser may be used instead of a laser oscillation source capable of pulse oscillation.

[0033]

According to the first to third aspects of the present invention, even when deep ultraviolet laser light is used, unevenness in the amount of light can be eliminated, so that a mask pattern with a fine order of 0.1 μm is used. Defects can be detected.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a mask inspection apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of a line sensor according to the embodiment.

[Explanation of symbols]

11: pulse laser device, 12: micro lens array, 13: rotating phase plate, 14: lens, 15: oscillating mirror, 16: mask plate pressure correcting lens, 17: condenser lens, 18: objective lens, 19 ... Mask pattern, 20
... condenser lens, 21 ... variable power lens, 22 ... line sensor, 23 ... base, 24 ... light detector.

Claims (3)

[Claims] 1. A laser oscillation source capable of oscillating deep ultraviolet laser light, and a laser light output from the laser oscillation source is used to change a spatial phase distribution of the laser light. Vibration mirror reflecting on
A mask pattern irradiated with the laser light reflected by the vibration mirror; a light receiving sensor receiving the laser light passing through the mask pattern; and a mask pattern received by the light receiving sensor. Means for extracting a mask defect by comparing a captured image of the mask with a reference image of the mask pattern. 2. A laser oscillation source capable of oscillating deep ultraviolet laser light, and a laser light output from the laser oscillation source is used to change a spatial phase distribution of the laser light. Vibration mirror reflecting on
A mask pattern to be irradiated with laser light reflected by the vibration mirror; and a CC to receive laser light passing through the mask pattern.
A laser line is output from the laser oscillation source each time the mask pattern is moved by .DELTA.L in the Y direction, and a mask pattern image captured by the CCD line sensor is stored. Means for extracting a mask defect by comparing the stored mask pattern image with a reference image of the mask pattern. 3. The laser beam has a wavelength of 180 to 300 n.
3. The mask defect inspection apparatus according to claim 1, wherein m is a number.