JP2938881B2 - Lighting equipment - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to an observation / measurement illuminating device for which the amount of illumination needs to be controlled, and particularly to an observation device for observing a minute shape such as a patterned wafer. The present invention relates to a lighting device suitable for a device and a measuring device for measuring a shape such as a minute line width.

[Prior Art] In general, when observing and measuring a minute shape, it is known that a light source to be illuminated with a short wavelength and a single wavelength has higher resolution and enables more precise observation and measurement. It is also widely known that illumination light having a short wavelength and a single wavelength can be obtained by using a bandpass filter that transmits only light having a desired wavelength.

By the way, since the reflectance differs due to the difference in the material of the object to be observed / measured, etc., in order to make the device versatile,
It is necessary to obtain an appropriate brightness by adjusting the amount of illumination depending on the object. Therefore, a mechanism capable of continuously changing the illumination light amount is desired.

As a method of continuously adjusting the illumination light amount, a method of adjusting the voltage of a light source, a method using a wedge-shaped ND filter, a method using a polarizing plate, and the like are generally known. A technique for continuously changing the light amount using a polarizing plate is disclosed in JP-A-63-1259.
No. 12 discloses this.

[Problems of the prior art and problems to be solved] However, the method of continuously adjusting the amount of illumination by adjusting the voltage of the light source has poor reproducibility,
When used with low illuminance, the illuminance distribution becomes uneven, and further, the life of the lamp is shortened by increasing the voltage.

In order to make the brightness uniform within the observation range by using a wedge-shaped ND filter, it is necessary to use a pair of two, but there is a drawback that the amount of transmitted light decreases significantly if the light amount adjustment width is widened .

The polarizing plate system disclosed in Japanese Patent Application Laid-Open No. 63-125912 also has a drawback that since the light source is generally non-polarized light, it must be used as a pair, and the amount of transmitted light is reduced to 50% or less. was there.

An object of the present invention is to provide an illuminating device in which only light in a narrow wavelength range is extracted from light emitted from a light source, and the amount of light continuously changes with a minimum amount of light loss, and also has good reproducibility.

Means for Solving the Problems In order to solve the above problems, the present invention provides a lighting device for illuminating a predetermined area of an object, wherein a first light that transmits light in a narrow wavelength range between an illumination light source and the object is provided. And two second dielectric interference filters are arranged, and the first dielectric interference filter extracts light in a narrow wavelength range from the light emitted by the illumination light source,
The second dielectric interference filter is inclined with respect to the first dielectric interference filter by a driving means in a predetermined angle range,
It is characterized by obtaining a desired illumination light amount.

Further, the illumination device of the present invention is a lighting device for fluorescence observation.

[Operation] In general, a bandpass filter transmits only light in a certain wavelength range, and a single wavelength or a quasi-single wavelength can be obtained by narrowing the bandpass, but the transmittance is manufactured by a dielectric multilayer filter. In this case, it is 95% or more (Fig. 1).

Here, when the interference filter is tilted at an arbitrary angle with respect to the optical axis and passes a light beam at an oblique incidence, the peak wavelength having the highest transmittance shifts to the shorter wavelength side as shown in FIG. Therefore, focusing on the transmittance at the peak wavelength λp at normal incidence, it can be seen that the transmittance T decreases with the angle θ at which the filter is inclined as shown in FIG.

In other words, two bandpass filters are used to extract light in a narrow wavelength range from a white light source with one filter, and the other filter functions to continuously reduce the transmittance in this wavelength range. .

At this time, the loss of the light amount is 90.25 for two filters even if the transmittance of the filter is 95%, and the loss can be suppressed to about 10%.

Further, since the transmittance and the tilt angle correspond one to one, a desired transmittance can be obtained with good reproducibility by controlling the angle.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

FIG. 4 is a basic optical system layout diagram of an optical observation device using the illumination device according to the present invention. This apparatus measures a line width on the order of microns on a patterned wafer or the like.

The illumination optical system 1 is a light source for illumination, and uses an ultra-high pressure mercury lamp having a bright line spectrum with high luminance. Reference numeral 2 denotes a condenser lens for collecting light emitted from an ultra-high pressure mercury lamp.

Reference numerals 3 and 4 denote bandpass filters, each of which is constituted by a dielectric multilayer interference filter. This bandpass filter 3,4
Is the g-line (λ = 435.8 nm)
Is set to The reason why the peak wavelength is set to the g-line (λ = 435.8 nm) is that, from light emitted from an extra-high pressure mercury lamp, high-spectrum light in the short wavelength side in the visible region is aimed at.

Further, the filter 4 is set so as to be inclined up to 40 ° with respect to the optical axis. The inclination of this filter is controlled manually or electrically. In this embodiment, by changing the inclination angle from 0 ° to 40 °, the light amount ratio can be continuously changed up to 200: 1. In the present embodiment, the maximum tilt angle is set to 40 °, but may be determined as appropriate in consideration of the type of peak wavelength at normal incidence, the performance of the bandpass filter, the amount of change in the amount of light required for observation, and the like. .

In 5,7,9, it is a collector lens. 6 is an aperture stop,
It is arranged at the position where the filament image is formed. Reference numeral 8 denotes a field stop.

 Reference numeral 16 denotes a lamp light source.

The illumination optical system 100, together with the half mirror 10, the prism 11, and the objective lens 12, which constitute the shared optical system 101 shared with the observation system, constitutes a Keller illumination system as a whole.

In the above illumination optical system, only the g-line is extracted by the band-pass filter 3 disposed in front of the mercury lamp 1 and the band-pass filter (interference filter) 4 is tilted with respect to the optical axis to reduce the peak wavelength transmitted through the filter. Shifting from the g-line, the transmittance of the g-line passing through both bandpass filters 3 and 4 can be continuously changed.

Observation system The observation system includes a visual observation system 102 and a monitor observation system 103.

The visual observation system 102 includes a field stop 14 and an eyepiece 15.

The monitor observation system 103 includes a television camera 17, a camera controller 18, and a line width measuring device 19.

A television camera 17 that has imaged the surface of the DUT 13 such as a patterned wafer sends a signal to a line width measuring device 19 via a camera controller 18, and the line width measuring device 19 performs image processing to determine the line width of the pattern. Measure. The result is displayed on a monitor (not shown).

Although the above embodiment is applied to a line width measurement microscope observation apparatus, it goes without saying that it can be used regardless of the configuration of the illumination optical system or the configuration of the observation optical system.

It is also known that fluorescence observation is effective as a method for observing a resist pattern. However, this requires a high-intensity single wavelength to excite fluorescence, and an ultra-high pressure mercury lamp is used as a light source for this. Is common. However, since the ultra-high pressure mercury lamp is a discharge lamp and the voltage cannot be controlled to adjust the light quantity, the light quantity can be easily and continuously changed by using the method of the present invention.

[Effects of the Invention] According to the present invention, it is possible to efficiently obtain a light amount as compared with a conventional light amount changing method such as a wedge-shaped ND filter or a polarization method, and to reduce a change in the light amount of illumination light in a narrow wavelength range. Can be accurate and easy.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating transmission characteristics of a dielectric multilayer interference filter, FIG. 2 is a diagram illustrating transmission characteristics when the dielectric multilayer interference filter is inclined at an arbitrary angle with respect to an optical axis, and FIG. FIG. 4 is a diagram showing a change in transmittance of a peak wavelength at a vertical incidence depending on an inclination angle of a dielectric multilayer interference filter. FIG. 4 is a layout diagram of a basic optical system of an optical observation apparatus according to an embodiment of the present invention. is there. 1 ... Mercury lamp 3,4 ... Bandpass filter 12 ... Objective lens 16 ... Power supply for lamp 17 ... TV camera 18 ... Line width measuring instrument

Claims (2)

(57) [Claims] 1. An illumination device for illuminating a predetermined area of an object, wherein two first and second dielectric interference filters transmitting light in a narrow wavelength range are arranged between the illumination light source and the object. The first dielectric interference filter extracts light in a narrow wavelength range from the light emitted by the illumination light source, and the second dielectric interference filter tilts the first dielectric interference filter in a predetermined angle range by a driving unit with respect to the first dielectric interference filter. A lighting device for obtaining a desired illumination light amount. 2. An illumination device according to claim 1, wherein said illumination device is an illumination device for fluorescence observation.