JPS63226937A - Foreign substance inspection system - Google Patents

Abstract

PURPOSE:To realize the good signal-to-noise ration of detection for a film- deposited wafer of various thicknesses and materials by installing a means to switch a wavelength of the light which is used to detect a foreign substance. CONSTITUTION:A means to switch a wavelength of the light to be used for detection of a foreign substance is installed at an inspection system, of the foreign substance, where the light illuminates the surface of a wafer 12 and the foreign substance on the surface of the wafer 12 is detected on the basis of a photoelectric conversion signal of the scattered light. For example, the surface of a wafer 12 is scanned in a spiral manner or in a plane manner by using a laser beam of one wavelength lambda1: the scattered light from the surface of the wafer enters a optoelectric transducer 24; when a photoelectric conversion signal exceeds a threshold level TH, a detection signal of the foreign substance is generated. If the result of the inspection of the foreign substance by using the wavelength lambda1 is abnormal, the other wavelength lambda2 is designated by an operating unit; a laser oscillator 16 of the designated wave-length is actuated; the laser beam of the wavelength ALPHA2 illuminates the surface of the wafer; the foreign substance is detected and judged on the basis of the level of the photoelectric conversion signal of the scattered light.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a foreign matter inspection device that prefers to detect foreign matter attached to the surface of a wafer, and is particularly suitable for detecting foreign matter on the surface of a wafer with a deposition film. Regarding inspection equipment.

[Prior Art] A typical foreign object inspection device that inspects wafers with deposition films for foreign objects irradiates the surface of the wafer with a laser, and detects foreign objects when the charge conversion signal of the scattered light exceeds a threshold level. There is a device that determines that it is present.

In addition, as a device that can also inspect patterned wafers for foreign substances, if the wafer is irradiated with an S-polarized laser and the photoelectric conversion signal of the P-polarized component of the scattered light exceeds a threshold level,
Alternatively, there is a method that determines that a foreign object is present when the ratio of the charging conversion signal of the P-polarized light component and the S-polarized light component of the scattered light exceeds a threshold value.

[Problems to be Solved] However, the conventional foreign matter inspection apparatus as described above has a problem in that the detection S/N ratio of foreign matter is extremely deteriorated depending on the material or thickness of the deposited film.

The reason for this is that conventional equipment uses a laser with one type of wavelength to detect and judge foreign objects, so the thickness of the deposited film takes into account the refractive index and is also related to the film quality.) When the wavelength of the irradiation laser becomes an integral multiple of approximately 172 wavelengths, interference occurs between the light reflected on the surface of the deposition film and the light that passes through the deposition film and is reflected on the wafer substrate surface. This is because the scattered light becomes extremely weak.

Therefore, an object of the present invention is to provide a foreign matter inspection device that can achieve a good detection S/N ratio for wafers with deposition films of various thicknesses and materials.

Means for Solving Problems] In order to achieve this object, the present invention provides a method for irradiating light onto the surface of a wafer, and removing the foreign matter from the surface of the wafer based on a photoelectric conversion signal of the scattered light. The inspection device is provided with means for switching the wavelength of light used for detecting foreign objects.

[How it works: In this way, the wavelength of the light used for foreign object detection can be switched, so even if interference occurs at a certain wavelength,
Since no interference occurs at other wavelengths, a good detection signal-to-noise ratio can be obtained for wafers with deposition films of various thicknesses and materials.

[Example] Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic diagram of an embodiment of the present invention.

In this embodiment, a wafer with a deposition film is inspected for foreign matter.

In the figure, reference numeral 10 denotes a moving stage, on the upper surface of which a wafer 12 is fixed by negative pressure suction or the like.

14 is a laser oscillator for irradiating the surface of the wafer 12 with a laser beam having a wavelength of λl. 156 has a wavelength of λ
This is a laser oscillator that irradiates the wafer surface with a laser beam of 2 (≠λl). Note that the irradiation angle θ of each laser beam is selected to be, for example, about 34 degrees.

18 is a laser drive control circuit that selectively drives one of the laser oscillations J14 and 18. In this example,
By selectively driving the laser oscillators 14 and 16 by this circuit, the wavelength of the light (laser) used for foreign object detection is switched to λl or λ2. Note that which wavelength the laser oscillator is to be operated is specified in advance by an operation unit (not shown).

Reference numeral 20 denotes an objective lens that receives scattered light in a substantially perpendicular direction from the wafer surface. The scattered light that passed through this objective lens 20 is
The light enters the charge conversion element 24 via the relay lens 22 .

A comparator 26 compares the output signal (photoelectric conversion signal of scattered light) of the photoelectric conversion element 24 with a threshold level TH, and sends out a foreign object detection signal when the output signal exceeds the threshold level TH.

Note that there is also a part that controls the entire apparatus, stores detected foreign object data, etc., but is not shown.

Next, the operation will be explained. When the wafer 12 is set on the moving stage 10, the moving stage 10 is moved to the chisel position. In addition, the laser drive control circuit 18 allows
One of the laser oscillators 14 (or 1
6) is driven, and a laser beam of wavelength λl (or λ2) is irradiated onto the wafer surface.

Then, the moving stage IO rotates or moves, and the surface of the wafer 12 is scanned in a spiral or in a plane by a laser beam of wavelength λl (or λ2). Scattered light from the wafer surface enters the photoelectric conversion element 24. Then, when the photoelectric conversion signal exceeds the threshold level TH, a foreign object detection signal is generated.

That is, it is determined that there is a foreign object at the laser irradiation position at that time. The results of this foreign object detection are stored in a not-shown portion, but since this is not the gist of the present invention, a description thereof will be omitted.

In this way, if the result of the foreign substance inspection using the wavelength λl (or λ2) is abnormal, the other wavelength λ2 (or λ1) is specified using an operation unit (not shown). In that case,
Only the laser oscillator 16 (or 14) with the designated wavelength is driven by the laser drive control circuit 18, and the laser beam with the designated wavelength is irradiated onto the wafer. A detection judgment is made.

In this manner, in this embodiment, by selectively irradiating the wafer with laser beams of two different wavelengths, the wavelength used for foreign matter detection can be switched.

Therefore, in the case of a wafer where interference occurs at one wavelength, it is possible to switch to the other wavelength to prevent interference and obtain a good detection S/N ratio.

FIG. 2 is a schematic diagram of another embodiment of the invention. In this figure, parts equivalent to those in FIG. 1 are given the same reference numerals.

In this embodiment, laser oscillation nt4. t6 are both constantly driven, and the surface of the wafer 12 is simultaneously irradiated with a laser beam of wavelength λl and a laser beam of wavelength λ2.

The scattered light that has passed through the objective lens 20 and the relay lens 22 enters the dichroic mirror 28 for wavelength separation, and the component with the wavelength λl enters one charging conversion element 24a, and the component with the wavelength λ2 enters the other photoelectric conversion element. 24b.

30 is the output signal of the photoelectric conversion elements 24a and 24b,
This is a signal selection circuit that selects one No. 45 designated by an operation section (not shown) and inputs it to the comparator 2nd.

As is clear from the above description, in this embodiment, the signal selection circuit 30 selects the photoelectric conversion element 24a for scattered light of wavelength λ1 or the charging conversion element 24b for scattered light of wavelength λ2. This switches the wavelength of the laser used to detect foreign objects. Therefore, a good Ill S/N ratio can be obtained for wafers with deposition films of various materials and thicknesses.

In each of the above embodiments, one laser oscillator for each wavelength is shown, but two or more of each laser oscillator may be provided. The irradiation angle may also be changed as necessary. The irradiating laser beam may be unpolarized or polarized.

Furthermore, when a multi-pixel charging conversion element such as a pin photodiode array is used for photoelectric conversion of scattered light, individual I+! A comparator may be provided for each pixel or for each predetermined number of pixels to compare the charge conversion signal with a threshold level (FA object detection determination).

Furthermore, since the photoelectric conversion signal of scattered light is almost proportional to the size of the foreign object, the photoelectric conversion signal may be compared with two or more different threshold levels to discriminate and detect foreign objects by size. .

In addition, the present invention can be modified and implemented in various ways without departing from the spirit thereof.

[Effects of the Invention] As is clear from the above description, the present invention allows the wavelength of light used to detect foreign objects to be switched, so even if interference occurs at one wavelength, it will not occur at another wavelength. Since no interference occurs, it is possible to achieve the effect of obtaining a good detection S/N ratio for wafers with deposition films of various thicknesses and materials.

[Brief explanation of the drawing]

FIG. 1 is a W1 diagram of an embodiment of the present invention, and FIG.
FIG. 6 is an mi diagram of another embodiment of the present invention. 12... wafer, 14. te...laser oscillator, 1
8... Laser drive control circuit, 20... Objective lens,
22...Relay lens, 24.24a, 24b...
・Photoelectric conversion element, 28... Dichroic mirror, 2
6...Comparison.

Claims (3)

[Claims] (1) In a foreign matter inspection device that irradiates light onto the wafer surface and detects foreign matter on the wafer surface based on the photoelectric conversion signal of the scattered light, a means for switching the wavelength of the light used for foreign matter detection is provided. A foreign matter inspection device comprising: (2) Foreign matter inspection according to claim 1, wherein the means for switching the wavelength of light used for foreign matter detection is a means for switching the wavelength of light irradiated onto the surface of the wafer. Device. (3) The scope of claims characterized in that the means for switching the wavelength of light used for detecting foreign matter is a means for switching the wavelength component of light scattered from the surface of the wafer used for determining the detection of foreign matter. The foreign matter inspection device according to item 1.