JPH11260689A - Uniform optical system, pattern tester and pattern testing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an uniform optical system, capable of illuminating without a interference unevenness even when laser beams are used as a light source. SOLUTION: This optical system comprises an illumination optical system 32, having an integrator unit 32c comprising a plurality of lens elements 40 forming an illumination light as a uniform light and a condenser lens 32d, and an accumulated CCD line sensor 35 for measuring the intensity of lights from this illumination optical system 32. Here, an arrangement direction of the lens elements 40 of the integrator unit 32c and an arrangement direction of the accumulated CCD line sensor 35 are inclined at a predetermined angle α and arranged about an optical shaft of the illumination light. When the number of lines of the accumulated CCD line sensor 35 is (n), a line pitch is (p), a pitch of interference strips on the accumulated CCD line sensor 35 is (d), and a natural number is (m), the angle α is shown by a product of (m)and arcsin (d/np), namely α=mXarcsin (d/np).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a uniform optical system capable of performing illumination without interference unevenness even when a laser light source is used, and a pattern inspection capable of performing high-precision inspection without interference unevenness. The present invention relates to an apparatus and a pattern inspection method.

[0002]

2. Description of the Related Art A pattern inspection apparatus is used for inspecting an integrated circuit or the like. In a pattern inspection apparatus, a Koehler illumination system is used to uniformly illuminate a sample without being affected by the intensity distribution of a light source. Since a light source having a short wavelength and high intensity is required, a laser beam is used.

FIG. 3 is a diagram showing a configuration of such a pattern inspection apparatus 10. As shown in FIG. That is, the pattern inspection apparatus 10
Is a laser beam irradiator 11 for irradiating a laser beam L, and a laser beam L from the laser beam irradiator 11
Optical system 12 for irradiating a sample W and a sample W such as a semiconductor wafer
, A sample stage 13 for holding light, an objective lens 14 for converging light transmitted through the sample W, an accumulation type CCD line sensor 15 for detecting the intensity of light converged by the objective lens 14, and an accumulation type CCD line sensor 15 And an image processing unit 16 that processes the image of the sample W based on the output from

The illumination optical system 12 includes convex lenses 12a and 12b for expanding the light beam of the laser beam L, and an incident laser beam L
Unit 12c for making a uniform secondary light source, and a condenser lens 12 for illuminating the same place of the sample W with light from the integrator unit 12c.
d. In addition, the integrator lens 12c
Is an aggregate of small lens elements 20, and has a function of making the intensity distribution of light transmitted through the lens element 20 macroscopically substantially uniform as shown in FIG.

[0005] The accumulation type CCD line sensor 15 is composed of a plurality of line sensors arranged in multiple stages, and transfers and accumulates the signal of each line in synchronization with the feed of the sample stage 13. Since the signals are added for the number of lines, a bright image can be obtained even when the illumination light is weak.

[0006]

The above-described conventional pattern inspection apparatus has the following problems. That is,
Due to the good coherence of the laser beam L, the intensity unevenness shown in FIG. 4A is directly reflected on the sample W, and is regularly arranged two-dimensionally on the sample W as shown in FIG. Interference fringes appear overlapping the pattern. Therefore, the accumulation type CC
A line as shown in FIG. 4C remains in the output of the D-line sensor 15 and overlaps the original pattern on the sample W, making it impossible to inspect correctly.

On the other hand, in a conventional exposure apparatus, in order to eliminate the influence of such interference fringes, an oscillating mirror or the like is arranged on the optical axis and the interference fringes are moved regularly so that intensity unevenness is averaged. A technique was used. However,
In this case, a precise driving mechanism is required to move the interference fringes regularly.

Accordingly, the present invention provides a uniform optical system capable of performing illumination without interference unevenness even when a laser beam is used as a light source, and a pattern inspection apparatus capable of performing high-precision inspection without interference unevenness. And a pattern inspection method.

[0009]

In order to solve the above problems and achieve the object, an invention according to claim 1 is provided with a light source for generating illumination light and an optical axis of the illumination light, An integrator unit comprising a plurality of lens elements for making the illumination light uniform and an illumination optical system having a condenser lens; and a storage type CCD line sensor for detecting the intensity of light from the illumination optical system. The arrangement direction of the lens elements of the unit and the storage type C
The arrangement direction of the CD line sensors is arranged at an angle α around the optical axis of the illumination light. The angle α is n for the number of lines of the accumulation type CCD line sensor, p for the line pitch, and p for the accumulation type CCD. When the pitch of interference fringes on the line sensor is d and the natural number is m, m and arcsin
(D / np), that is, α = mXarcsin (d / np).

According to a second aspect of the present invention, in the first aspect, the angle α is arcsin
(D / np) was set within the range of ± 30%.

According to a third aspect of the present invention, there is provided an integrator unit and a condenser comprising a light source for generating illumination light, a plurality of lens elements arranged on an optical axis of the illumination light, and making the illumination light uniform. An illumination optical system having a lens, a storage type CCD line sensor for detecting the intensity of light from the illumination optical system, and a pattern inspection target disposed between the integrator unit and the storage type CCD line sensor. A sample stage for holding the sample, and a projection lens for projecting the illuminated pattern of the sample onto a sensor, wherein the alignment direction of the lens elements of the integrator unit and the alignment direction of the accumulation type CCD line sensor are determined by the illumination light. It is arranged at an angle α around the optical axis, and the angle α is n, the number of lines of the storage type CCD line sensor When the pitch is p, the pitch of the interference fringes on the accumulation type CCD line sensor is d, and the natural number is m, the product of m and arcsin (d / np), that is, α = mXarcsin (d / np) It was decided to be shown by.

According to a fourth aspect of the present invention, there is provided a pattern detecting method for inspecting a pattern formed on a sample.
An illumination step of irradiating the sample as uniform light with illumination light generated from a light source by an integrator unit and a condenser lens composed of a plurality of lens elements; and an arrangement direction of the lens elements and light passing through the sample and the accumulation type CC.
A light detecting step of tilting the arrangement direction of the D line sensor around the optical axis of the illumination light by an angle α and detecting the angle by the accumulation type CCD line sensor, wherein the angle α is a line of the accumulation type CCD line sensor. When the number is n, the line pitch is p, the pitch of the interference fringes on the accumulation type CCD line sensor is d, and the natural number is m, m and arcsin
(D / np), that is, α = mXarcsin (d / np).

[0013] As a result of taking the above measures, the following effects occur. That is, in the invention described in claim 1, the arrangement direction of the lens elements of the integrator unit and the arrangement direction of the storage type CCD line sensors are arranged at a predetermined angle α around the optical axis of the illumination light. The amount of appearance of interference fringes in the direction in which the accumulation type line sensors are arranged becomes uniform. Therefore, the influence of interference fringes on the output of the accumulation type line sensor can be canceled.

According to the second aspect of the present invention, if the angle α is set within a range of ± 30% of arcsin (d / np), the appearance of interference fringes can be made substantially uniform.

According to the third aspect of the present invention, the arrangement direction of the lens elements of the integrator unit and the storage type CCD
The arrangement direction of the line sensors is inclined at a predetermined angle α around the optical axis of the illumination light, so that the appearance amount of interference fringes in the arrangement direction of the accumulation type line sensors becomes uniform. Therefore, the influence of interference fringes on the output of the accumulation type line sensor can be canceled.

According to a fourth aspect of the present invention, the arrangement direction of the lens elements of the integrator unit and the storage CCD
The arrangement direction of the line sensors is inclined at a predetermined angle α around the optical axis of the illumination light, so that the appearance amount of interference fringes in the arrangement direction of the accumulation type line sensors becomes uniform. Therefore, the influence of interference fringes on the output of the accumulation type line sensor can be canceled.

[0017]

FIG. 1 is a diagram showing a configuration of a pattern inspection apparatus 30 according to one embodiment of the present invention. That is, the pattern inspection apparatus 30 includes a laser beam irradiating unit 31 that irradiates a laser beam L, and an illumination optical system 32 that irradiates a laser beam L from the laser beam irradiating unit 31 to a sample W described later.
And a sample stage 3 for holding a sample W such as a semiconductor wafer
3 and an objective lens 34 for converging light transmitted through the sample W
A storage type CCD line sensor 35 for detecting the intensity of light converged by the objective lens 34;
An image processing unit 36 that processes an image of the sample W based on an output from the D line sensor 35.

The illumination optical system 32 includes convex lenses 32a and 32b for expanding the light beam of the laser light L,
Unit 32c for making a uniform secondary light source, and a condenser lens 32 for illuminating the same place of the sample W with light from the integrator unit 32c.
d. In addition, the integrator unit 32
c is an aggregate of small lens elements 40.

The storage type CCD line sensor 35 is a line sensor 35 a formed by arranging photodetectors in the direction of arrow Y in FIG. 2 and arranged in n stages in the direction of arrow X. Synchronously, each line sensor 35a
Is transferred in the direction of arrow X and stored. This storage type C
In order to cancel the interference fringe K in the output from the CD line sensor 35, the arrangement direction of the lens elements 40 is adjusted,
The interference fringes K on the accumulation type CCD line sensor 35 are tilted around the optical axis C. That is, the arrangement direction of the lens elements 40 indicated by the arrow A in FIG. 2 is inclined by an angle α around the optical axis C of the illumination light with respect to the arrangement direction of the accumulation type CCD line sensor 35 indicated by the arrow X in FIG.

The angle α is represented by n for the number of lines of the storage type CCD line sensor 35, p for the line pitch,
When the pitch of the interference fringes on the D line sensor 35 is d, it is given by the following equation. That is, α = arcsin (d / np) (1) Therefore, the interference fringes K appearing on the sample W are inclined by the angle α with respect to the direction in which the elements of the line sensor are arranged. At this time, if this is imaged by the accumulation type CCD line sensor 35, the interference fringes K are smoothed and an image without unevenness is obtained.

It should be noted that the uniformity gradually decreases as the angle deviates from the angle α, but ± 30 of arcsin (d / np).
If it is within °, there is almost no problem in pattern inspection. Further, since the angle α at which the interference fringes K are smoothed exists periodically, when m is a natural number, m and arcsin
The same effect can be obtained when the product of (d / np), that is, α = m × arcsin (d / np) (2).

As described above, according to the pattern inspection apparatus 30 according to the present embodiment, even when an illumination system using the laser light L is used, a pattern image free from intensity fluctuation unevenness due to interference fringes is obtained. Can be Therefore, a highly accurate pattern inspection can be performed. In addition, since a high-precision drive mechanism or the like is not required, manufacturing can be performed at low cost.

The present invention is not limited to the above embodiment. That is, in the above-described pattern inspection apparatus, the integrator lens is inclined around the optical axis with respect to the optical axis, but the accumulation type CCD line sensor may be inclined around the optical axis. The allowable value of the angle α may be appropriately determined based on the required degree of uniformity of the image intensity. In addition, it goes without saying that various modifications can be made without departing from the spirit of the present invention.

[0024]

According to the present invention, the arrangement direction of the lens elements of the integrator unit and the arrangement direction of the accumulation type CCD line sensors are inclined at a predetermined angle α around the optical axis of the illumination light, thereby accumulating the data. The appearance amount of the interference fringes in the arrangement direction of the pattern line sensors becomes uniform. Therefore, the influence of interference fringes on the output of the accumulation type line sensor can be canceled.

[Brief description of the drawings]

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

FIG. 2 shows interference fringes and accumulation type C in the pattern inspection apparatus.
FIG. 3 is a schematic diagram showing a relationship with a CD line sensor.

FIG. 3 is a diagram showing a configuration of a conventional pattern inspection apparatus.

FIG. 4 is an explanatory view and a micrograph of interference fringes in the pattern inspection apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 30 ... Pattern inspection apparatus 31 ... Laser beam irradiation part 32 ... Illumination optical system 32c ... Integrator unit 32d ... Condenser lens 33 ... Sample stage 34 ... Objective lens 35 ... Storage type CCD line sensor 36 ... Image processing part

Claims (4)

[Claims] An illumination optical system having an integrator unit including a plurality of lens elements arranged on an optical axis of the illumination light and making the illumination light uniform, and a condenser lens; Storage type CCD that detects the intensity of light from this illumination optical system
A line sensor, wherein the arrangement direction of the lens elements of the integrator unit and the arrangement direction of the storage type CCD line sensor are arranged at an angle α around the optical axis of the illumination light, and the angle α is When the number of lines of the accumulation type CCD line sensor is n, the line pitch is p, the pitch of interference fringes on the accumulation type CCD line sensor is d, and the natural number is m, m and arcsin (d / np) , That is, α = mXarcsin (d / np). 2. The uniform optical system according to claim 1, wherein the angle α is set within a range of ± 30% of arcsin (d / np). 3. A light source for generating illumination light, an illumination optical system having an integrator unit including a plurality of lens elements arranged on the optical axis of the illumination light and making the illumination light uniform, and a condenser lens; Storage type CCD that detects the intensity of light from this illumination optical system
A line sensor, a sample stage disposed between the integrator unit and the storage type CCD line sensor, for holding a sample whose pattern is to be inspected, and a projection lens for projecting the illuminated sample pattern onto the sensor. The arrangement direction of the lens elements of the integrator unit and the arrangement direction of the accumulation type CCD line sensor are arranged at an angle α around the optical axis of the illumination light, and the angle α is the accumulation type CCD line sensor. Is the number of lines of n,
When the line pitch is p, the pitch of the interference fringes on the accumulation type CCD line sensor is d, and the natural number is m, the product of m and arcsin (d / np), that is, α = mXarcsin (d / np) A pattern inspection apparatus characterized by the following. 4. A pattern detection method for inspecting a pattern formed on a sample, comprising: an illumination step of irradiating illumination light generated from a light source to the sample as uniform light by an integrator unit including a plurality of lens elements and a condenser lens; A light detection step of detecting the light transmitted through the sample by the accumulation type CCD line sensor by inclining the arrangement direction of the lens elements and the direction of the accumulation type CCD line sensor around the optical axis of the illumination light by an angle α. Wherein the angle α is n, the line pitch of the storage CCD line sensor is p, the line pitch is p, the pitch of the interference fringes on the storage CCD line sensor is d, and the natural number is m, The product of m and arcsin (d / np), that is, a pattern characterized by α = mXarcsin (d / np)査方 method.