JPS6186605A - Method and apparatus for lighting wafer - Google Patents

Abstract

PURPOSE:To obtain a reflected image, by which a specified pattern can be readily identified from other parts, by limiting the wavelength of a bright field lighting in a specified wavelength region in order to identify an aluminum wiring pattern and a layer beneath the pattern clearly. CONSTITUTION:A dark-field lighting device is composed of a dark field lamp 3 and parabolic concave mirrors 11 and 12. The light is projected to the light axis of an objective lens 2 from the slant direction. A bright-field lighting device is composed of a bright field lamp 4, a condenser lens 8, a field lens 9, a wavelength control filter 10, a half mirror 5 and a reflecting mirror 7. The light beams from both devices are applied on a wafer 1 simultaneously. The wavelength control filter 10 selects the light in the wavelength so that only the light, by which the reflectivity of patterns other than an aluminum pattern become small, can be projected on the surface of a wafer. Thus the aluminum pattern formed on the wafer 1 is identified from the other patterns clearly. Therefore, the aluminum pattern, which has been difficult to identify, can be definitely identified.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an illumination method and an illumination device for observing patterns formed on the surface of a semiconductor wafer. The present invention relates to an illumination method and device that allows a reflected image of a part to be easily distinguished.

[Background of the invention]

As a method for detecting patterns formed on a semiconductor wafer surface, for example, as shown in Japanese Patent Application No. 56-92281, bright-field illumination and dark-field illumination are applied simultaneously to detect only aluminum wiring patterns. It is known that the detection is brighter than the constituent parts of . In this method, bright-field illumination captures the flat part of the aluminum surface as a bright reflected light, while other parts are captured as effective images by dark-field illumination. Therefore, it is effective when the aluminum pattern has a higher reflection rate under bright field illumination than other components.

However, in reality, in the process of manufacturing semiconductor devices, the aluminum wiring pattern formed on the semiconductor wafer is often attached at the last step, and the attached surface has minute protrusions unique to aluminum. The influence of the lower layers cannot be ignored. In other words, there may be a high level difference in the wiring, or under conventional lighting (mercury lamp, halogen lamp, Gysenon lamp, etc.)
t, polysilicon, etc. and the aluminum surface of the wiring pattern have approximately the same reflectance as that of the aluminum surface. For this reason, the aluminum pattern could not always be detected as a brighter reflected image than the lower layer under bright field illumination.

Therefore, there is a problem in that the aluminum pattern cannot be clearly identified simply by applying bright field illumination and dark field illumination at the same time.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide an illumination method and an illumination device that can obtain a reflected image that allows a specific pattern (for example, an aluminum pattern) to be distinguished from other components.

[Summary of the invention]

The present invention focuses on the fact that the reflectance of each pattern formed on a semiconductor substrate differs depending on the wavelength of the light used for illumination, and in particular detects aluminum wiring turns. In order to clearly distinguish between the lower layer and the lower layer, the wavelength of the bright field illumination light is limited to a specific wavelength range.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to FIGS. 1 to 5. FIG. 1 is a perspective view of an example of the apparatus of the present invention configured to carry out the method of the present invention. 1 is a wafer, and 2 is an objective lens.

A lamp 3 for dark field illumination is installed on the optical axis of the objective lens 2, and a lamp 4 for bright field illumination is provided separately from the lamp 3. 5 is a mirror 7 that reflects the luminous flux 6 of the bright field illumination lamp 4.
This is a no-f mirror installed to reflect the light toward. 8 is a condensing lens for bright field illumination, and 9 is a field lens. A wavelength control filter 10 is provided in the optical path of this bright field illumination system to limit the wavelength range of light of the bright field illumination system.

On the other hand, a parabolic concave mirror 11 reflects the light from the lamp 3 for dark field illumination in parallel with the optical axis of the objective lens 2 as shown by an arrow 6'.
A parabolic concave mirror 12 is provided near the tip of the objective lens 2 to reflect the light beam 6' so that it enters the surface of the wafer 1 obliquely. 13 is a detector for detecting reflected light.

With the above configuration, from the dark field lamp 3 and the parabolic concave mirror 11 and 12, and with respect to the optical axis of the objective lens 20,
Dark-field illumination light illuminated from an oblique direction and a bright-field illumination lamp4. Condensing lens 8. Field lens9. Bright field illumination light consisting of the wavelength control filter 10, half mirror 52 and reflecting mirror 7 can be irradiated onto the wafer 1 at the same time.

Here, in order to clearly distinguish between the aluminum pattern formed on the wafer 1 and other patterns, the wavelength control filter 10 only transmits light in a wavelength range so that the reflection of patterns other than the aluminum pattern is smaller. This is a filter that allows selective irradiation onto the wafer surface. As a specific example, we investigated a MOS memory element in which there is about 1100 (StO2) of 1 as a layer under the aluminum pattern, and a 1 μm thick aluminum pattern layer is formed thereon.

FIG. 2 shows a schematic video signal of the pattern shown in FIG. 14 is aluminum pattern part 1 on α ray
5 is the signal level, 16 is the signal level of the lower layer part 17 on the same line, and generally the level of the luminous pattern part is high. FIG. 4 shows the reflectance of the lower layer when the wavelength range of the wavelength control filter 10 in FIG. 4 is changed and the aluminum pattern portion is set to 1. As can be seen from FIG. 4, the reflectance of the lower layer increases rapidly at wavelengths of 560 wn and above. Therefore, in the case of this element, it can be seen that a filter having the characteristics shown in FIG. 5, which can sharply cut off wavelengths of 56 Qnm or more, is effective as a wavelength control filter. As mentioned above,
υ, bright field illumination by arbitrarily changing the wavelength range of bright field illumination light.

Aluminum patterns that could not be clearly identified even with dark field illumination can now be clearly identified.

In this embodiment, a configuration is described in which a wavelength control filter is provided in the bright field illumination optical path, but even if a similar filter is provided in front of the detector 13, it will not be possible to control the wavelength range of the bright field illumination light. It can be seen that they are the same.

〔Effect of the invention〕

As described in detail above, according to the illumination method of the present invention, a reflected image can be obtained so that a specific pattern formed on the wafer surface can be easily identified from other constituent parts. Moreover, according to the apparatus of the present invention, the above-described method of the present invention can be easily carried out.

[Brief explanation of drawings]

FIG. 1 is a perspective view of an embodiment of the wafer illumination device of the present invention, the second blade is a schematic diagram of the aluminum pattern part and the underlying video signal of FIG. 6, and FIG. A diagram showing the aluminum pattern, Figure 4 is a diagram showing the brightness ratio of the aluminum pattern part and the lower layer when changing the wavelength range of the wavelength control filter, and Figure 5 is the wavelength control when applied to MOS memory. This is an example of filter characteristics. 1... Wafer 2... Objective lens 3...
・Darkfield illumination lamp 4...Brightfield illumination lamp 10・
... Wavelength control filter 11.12 ... Parabolic concave mirror 1
3...Detector 14...Signal level of the aluminum pattern part 16...Signal level of the lower layer 7Me patent attorney Akio Takahashi'- Yan? Figure 3

Claims (1)

[Claims] 1. Among the reflected light from a wafer having a wiring pattern on its surface, the wavelength of the reflected light is set so that the difference in the amount of reflected light between the wiring pattern and the underlying layer is equal to or greater than the detection limit of the detector. A wafer illumination method characterized by limiting the area. 2. The wafer illumination method according to claim 1, wherein the wiring pattern is made of Al formed on a SiO_2 film and uses reflected light having a wavelength shorter than 560 nm. lighting method. 3. a light source that emits white light, a filter that transmits a portion of the light from the light source, a half mirror that reflects the light that has passed through the filter, and an optical system that guides the light from the half mirror onto the wafer; A wafer illumination device including a detector that receives light from the optical system after passing through the half mirror. 4. The wafer illumination device according to claim 3, wherein the wiring pattern is made of Al formed on a SiO_2 film, and the filter is a filter that transmits wavelengths shorter than 560 nm. Wafer illumination device.