JPS63309841A - Foreign matter inspecting device - Google Patents

Abstract

PURPOSE:To realize high accuracy and high sensitivity by using at least >=two kinds of laser irradiation sources for generating laser beams which do not interfere with each other, as a laser irradiation source, so that a reflected light of at least one laser beam can always be used. CONSTITUTION:The titled device is provided with laser irradiation sources L1, L2 for irradiating a wafer on a sample base 1, and for instance, the irradiation source L1 and the irradiation source L2 are constituted so that two pieces of semiconductor lasers 3a, 3b, and two pieces of He-Ne gas lasers are radiated at an incident angle of 30 deg. onto the same vertical surface, and also, to a prescribed part, respectively. Also, the respective reflected light beams are received by a detecting part 6 through an objective lens 5, and an amplified signal 7 and a threshold level P0 are compared 8 and outputted. Moreover, even when each reflected light generates an interference by only the laser beams from one lasers 3a, 3b reflected light beams of the laser beams from the other lasers 4a, 4b can be used for detecting a foreign matter. Accordingly, the foreign matter can be detected with high accuracy and high sensitivity.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a technique that is particularly effective when applied to semiconductor manufacturing technology and wafer appearance inspection technology, such as detecting foreign matter attached to the surface of a wafer. It relates to effective techniques that can be used when

[Prior Art] Patterns of diffusion layers, wiring layers, and insulating films on wafers are becoming smaller and more dense every year, and in order to produce wafers with fine patterns at low cost and with high yield, It is necessary to perform an external appearance inspection of the wafer as early as possible, and if any foreign matter is present, it is necessary to remove it. Therefore, various foreign material inspection techniques are currently being developed.

Regarding such foreign material inspection technology, for example,
It is described in "Automation of Appearance Inspection" published by the Institute of Electrical Engineers of Japan on November 26, 2008, pages 62 to 67. The outline is as follows.

In other words, in this inspection technology, laser light is irradiated onto a predetermined part of the wafer surface, the amount of light reflected on the wafer surface is detected, and this is photoelectrically converted into an electrical signal. Foreign objects are detected by comparing the signal with a predetermined threshold after amplifying the signal.

[Problems to be Solved by the Invention] However, in the conventional foreign matter inspection technique, since light of a single wavelength is irradiated to a predetermined portion on the surface of the wafer, there is a first-order problem.

That is, in this foreign matter inspection technique, for example, Sin.

Alternatively, when inspecting the surface of a wafer for foreign matter on which a thin film such as Si3N4 is formed, depending on the thickness of the thin film, refractive index, wavelength of light, etc., the light reflected from the underlying part where no foreign matter is present and the light reflected from the foreign matter may be different. The light waves overlap each other, and the amount of light reflected from the foreign object appears to be attenuated (so-called thin film interference occurs), making it impossible to detect the optical signal from the foreign object as it is. In other words, there are drawbacks such as a substantial drop in the foreign object detection signal and a reduction in the reliability of foreign object detection.

Such a problem occurs not only when one light source that emits laser light of a single wavelength is used, but also when, for example, a plurality of light sources that emit light of the same wavelength are used to increase the amount of reflected light.

An object of the present invention is to provide a foreign matter inspection device that is capable of detecting foreign matter on an object to be inspected with high precision and sensitivity.

The above and other objects and novel features of the present invention will become apparent from the description of this specification and the accompanying drawings.

[Means for Solving the Problems] Representative inventions disclosed in this application will be summarized as follows.

That is, in the foreign matter inspection apparatus, at least two or more types of laser irradiation sources that emit laser beams that do not interfere with each other are used as laser irradiation sources.

[Operation] According to the above-mentioned means, there should be no interference between the reflected light of laser light emitted from one type of laser irradiation source and the reflected light of laser light emitted from various types of laser irradiation sources. However, even if the reflected light beams of laser beams emitted from a certain type of laser irradiation source interfere with each other and the amount of reflected light from a foreign object is attenuated, the laser beams emitted from various laser irradiation sources Since the reflected lights of the two do not interfere with each other at the same time, the reflected light of the laser light emitted from at least one of the laser irradiation sources can be used for foreign object detection at all times, thereby preventing a decrease in the amount of detected light as a whole. , the above-mentioned objective of performing foreign matter inspection with high precision and high sensitivity is achieved.

[Example〕 An embodiment of the present invention will be described below based on the drawings.

FIG. 1 shows an embodiment of a foreign matter inspection device according to the present invention.

In the figure, reference numeral 1 represents a sample stage for detachably supporting a wafer 2. As shown in FIG. This sample stage 1 is, for example,
It is moved by a driving means (not shown) in the X or Y direction in a horizontal plane and rotated about a certain vertical axis.

Further, in this foreign matter inspection apparatus, two types of laser irradiation sources L□ are capable of irradiating laser light toward a predetermined portion of the wafer 2 supported on the sample stage 1.

L2 is provided. One of these laser source L
1 is two semiconductor lasers (for example, wavelength λ = 780 nm)
3a and 3b, which are disposed on the same vertical plane, and can irradiate a predetermined portion of the wafer 2 at an incident angle of, for example, 30''.In addition, another laser irradiation source L2 is composed of two He-Ne gas lasers (for example, wavelength λ=633 nm) 4a and 4b, which are arranged in the same vertical plane and have an incident angle of, for example, 30'' toward a predetermined part of the wafer 2. It is now possible to irradiate it. Here, the wavelengths of the laser beams irradiated from the gas lasers 4a and 4b include the semiconductor laser 3a,
A wavelength is selected that does not interfere with the laser beam irradiated from 3b. Specifically speaking, semiconductor lasers 3a, 3
The wavelength of the laser beam irradiated from 4b is the same as that of the gas laser 4a.
, 4b are selected so that the wavelength is not an integral multiple of the wavelength of the laser beam irradiated. In addition, in this example,
The reason why each of the laser irradiation sources is composed of two lasers is to increase the amount of reflected light and increase the detection sensitivity of foreign matter.

Further, an objective lens 5 is provided on the sample stage 1 to converge the reflected light from the wafer 2, and the light converged by the objective lens 2 is made to enter a detector 6 disposed above the objective lens 5. It has become. The detector 6 then performs photoelectric conversion, and the electrical signal passes through an amplifier 7 to a comparator 8.
It is now sent to The comparator 8 also has a threshold value P for distinguishing noise from the detector 6 and amplifier 7 and for determining the particle size of the detected foreign object.

is set, and when the electric signal supplied thereto exceeds a threshold value P, a high level signal (foreign object detection signal) is emitted, for example.

Next, the operation of the foreign object detection device configured as described above will be explained as follows.

First, two semiconductor lasers 3a and 3b and two He-N
The same part of the wafer 2 supported on the sample stage 1 is irradiated with the e-gas lasers 4a and 4b at the same time.

Then, the reflected light from the wafer 2 is received by the detector 6 through the objective lens 5, where it is converted into an electrical signal corresponding to the amount of light. Next, the electrical signal is amplified by an amplifier 7, and a comparator 8 combines the amplified signal with a threshold value P. are compared.

If the object is equal to or greater than the threshold value 20, it is determined that it is a foreign object, and the comparator 8 issues a foreign object detection signal. Such operations are performed on the entire surface of the wafer 2.

At that time, for example, if only the laser light irradiated from the semiconductor lasers 3a and 3b is used, the light waves reflected from the underlying portion where no foreign matter is present and the light waves reflected from the foreign matter overlap each other, and the amount of light reflected from the foreign matter appears to be Even if the gas laser 4a is attenuated.

The reflected lights of the laser beams irradiated from 4b are received by the detector 6 without causing interference with each other. Also,
In the opposite case, ie gas laser 4a.

If only the laser beam irradiated from the semiconductor laser 4b is used, the light waves reflected from the underlying portion where no foreign matter is present and the light waves reflected from the foreign matter overlap each other, and even if the amount of light reflected from the foreign matter appears to be attenuated, the semiconductor laser 3a , 3b are received by the detector 6 without interference.

According to the foreign matter inspection apparatus configured in this way, the following effects can be obtained.

That is, since there are two types of laser irradiation sources that emit laser beams that do not cause interference with each other, the reflected light of the laser beam emitted from one laser irradiation source and the reflected light from the other laser irradiation source are separated. Not only will there be no interference between the reflected laser beams emitted from one laser irradiation source, but even if the reflected beams of laser beams emitted from one laser irradiation source interfere with each other, they will not interfere with each other. Since the reflected lights of the laser beams emitted from the sources do not interfere with each other at the same time, the reflected light of the laser beams emitted from at least one of the laser irradiation sources can be used at all times for foreign object detection. Highly sensitive foreign body inspection becomes possible.

Although the invention made by the present inventor has been specifically explained above based on Examples, it goes without saying that the present invention is not limited to the above-mentioned Examples, and can be modified in various ways without departing from the gist thereof. Nor.

For example, although two types of laser irradiation sources are used in the above embodiment, three or more types of laser irradiation sources may be used.

The above explanation has mainly been about the application of the invention made by the present inventor to wafer visual inspection technology, which is the field of application behind the invention, but it is not limited to this, and only applies to certain types of laser light. It can be applied to anything that cannot be inspected due to interference.

[Effects of the Invention] The effects obtained by typical inventions disclosed in this application are briefly explained below.

In other words, since a variety of laser irradiation sources that emit laser beams that do not cause mutual interference are used, at least a portion of their reflected light can be used to detect foreign objects, and as a result, highly accurate and sensitive foreign object inspection is possible. Become.

[Brief explanation of drawings]

FIG. 1 is an illustrative perspective view of a foreign matter inspection device that is an embodiment of the present invention. 2... Wafer, 3a, 3b... Semiconductor laser,
4a, 4b...Gas laser, Ll, L2...
Laser irradiation source. Figure 1 b

Claims (1)

[Claims] 1. Foreign matter that is attached to the object to be inspected is detected by irradiating a laser beam from a laser irradiation source to a predetermined part of the surface of the object to be inspected and detecting the amount of reflected light. A foreign matter inspection device characterized in that the laser irradiation source is at least two types of laser irradiation sources that emit laser beams that do not interfere with each other. 2. Claim 1, wherein the laser irradiation source is composed of a semiconductor laser and a gas laser.
Foreign matter inspection device as described in section.