JPH06221917A - Beam pattern measuring method for laser flux - Google Patents

Abstract

PURPOSE:To provide a method for measuring the spatial beam intensity distribution (beam pattern) precisely in which problems of detecting element, e.g. deterioration of sensitivity, damage, shortening of service life, are solved over a wavelength region from X-ray to ultraviolet ray. CONSTITUTION:The intensity distribution of original laser beam is measured indirectly from a surface fluorescence intensity distribution detected through a fluorescence detecting element D by focusing a fluorescent surface light source emitted from a laser through a lens L' using a fluorescent plate F having a thin fluorescent layer generating sufficient fluorescence in visible wavelength region which is linear with respect to the intensity of objective short wavelength laser beam, e.g. X-ray or UV ray. The inventive method allows the precise measurement of laser distribution on the surface of an actual sample placed in a sample moving system, a sample holder, or a vacuum chamber C. The invention also provides an absorber method for preventing measurement error due to the reflection of laser light and a damper method for enhancing measurement accuracy.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for precisely measuring the beam intensity distribution of X-rays, UV laser beams, etc.

[0002]

2. Description of the Related Art There are two conventional methods for measuring a laser beam profile: a method of directly detecting a laser beam, and a method of indirectly detecting such as burn pattern or visualization using fluorescence or phosphorescence. .

[0003]

First, as seen from FIG. 1 showing an example of measurement of a UV light beam beam pattern such as an excimer laser, a detection element (CCD
Direct detection of normal camera X-rays, UV light, etc. due to a decrease in detection sensitivity (such as a camera), damage to a detection element due to laser irradiation, deterioration, and shortened service life ((a) in FIG. 1) Will not be possible.

In applications such as laser surface modification (annealing, impurity implantation), the light intensity distribution of the laser beam irradiating the sample surface is required to have extremely high uniformity. The following problems must be solved as a precise measurement of the intensity distribution of the irradiation laser beam on the sample surface.

A sample of a laser processing object is usually placed on a processing table such as a sample holder or an XY stage or in a vacuum chamber. A conventional measuring method is used as a method for measuring a beam pattern on a processed surface by forming a conjugate surface using a bunch plate.

Since there are restrictions on the processing accuracy of the baffle plate,
The output beam from the homogenizer having a high degree of uniformity of light intensity distribution (for example, uniformity of beam intensity distribution error RMS <0.5%) is homogenized so that the diverging plate does not affect the beam uniformity. It is difficult to introduce it into the optical path between the condenser lens of the Nizer and the uniformly machined surface, and it is difficult to maintain the high-precision identity of the light intensity distribution of the bundled conjugate surface and the light intensity distribution of the sample surface. Has become. It is difficult to measure with high accuracy and reliability without measuring the luminous flux intensity distribution on the sample surface. In some cases, it may not be possible to introduce the baffle plate due to restrictions on the working distance of the processing optical system (projection lens, condenser lens of homogenizer, etc.) and the window of the vacuum chamber.

[0007]

As described above, in order to improve the accuracy and reliability of measurement, it is necessary to measure the luminous flux beam on the sample surface. In order to incorporate the optical system for directly measuring the light intensity distribution on the sample surface into the laser processing apparatus, the present invention uses a fluorescent plate in the method as shown in FIG. 1 to measure the fluorescence in the reflection direction of the incident laser light. . Since the secondary fluorescence regenerated by the reflected light of the laser light flux passing through the fluorescent plate affects the measurement result, a method of preventing the reflected light of the laser light flux is also proposed in FIG. 3 of the present invention in order to improve the measurement accuracy. is doing.

[0008]

The basic principle of the measurement of the present invention is shown in FIG. The premise of the measurement is that the fluorescent plate has a fluorescent thin film layer in which fluorescence is sufficiently generated by irradiation with the laser light flux to be measured, and the fluorescence has a linear intensity relationship with the original irradiation laser beam.

When a fluorescent plate is placed on the target position of measurement, that is, on the sample surface of the object to be processed, the thin film layer of the fluorescent substance emits fluorescence due to laser irradiation. If the thin film of the fluorescent layer becomes sufficiently thin due to the characteristics of the fluorescent plate, it becomes a fluorescent surface light source by laser irradiation. If the detection system as shown in FIG. 1 is used, it becomes easy to accurately measure the fluorescence intensity distribution of the fluorescent surface light source without distortion. Depending on the characteristics of the fluorescent plate, if the fluorescent light intensity has a linear relationship with the intensity of the laser light, the light intensity distribution on the fluorescent surface and the light intensity distribution on the processed surface of the laser light flux match.

The phosphor plate shown in FIG. 3 is measured in the reflection direction of the incident laser light. It is highly possible that the laser beam emitted from the fluorescent plate (usually the absorption of the fluorescent plate is within about 10%) is reflected from the back surface of the fluorescent plate and the sample holder surface on the back side of the fluorescent plate and returns to the fluorescent plate again to regenerate fluorescence. This affects the measurement. The present invention proposes several methods for preventing reflected light as shown in FIG. 3 in order to improve the measurement accuracy.

FIG. 3A shows a method of preventing reflection due to absorption. A substance (absorption liquid, absorption glass, or the like) that absorbs the incident light wavelength and does not fluoresce may be placed on the back side of the fluorescent plate. It is also possible to prevent the reflected light by using a beam damper of the laser incident light on the back side of the fluorescent plate as shown in FIG.

[0012]

EXAMPLE FIG. 4 shows an example in which a fluorescent plate was placed in the vacuum chamber at the same position as the sample processing surface and the light intensity distribution of the laser beam was measured precisely. The incident laser irradiates the sample surface after the light beam is homogenized by using a beam homogenizer. The uniformity of the spatial intensity distribution of the light flux is ΔI = (Imax-Imin) / Imax <± 5%. The light intensity average characteristic is expected to be RMS≈1% in the uniform region. Since the homogenizer is not adjusted in order to obtain the high-intensity beam light intensity distribution, it is necessary to check the light intensity distribution of the laser beam on the sample surface. Since the sample surface is in the vacuum chamber, another measurement method is almost impossible. According to the present invention, an image forming lens is used as shown in FIG. The light intensity distribution on the sample surface of the beam was measured with high accuracy. In the fluorescent plate used in the embodiment of the present invention (FIG. 4), both the above-mentioned fluorescence intensity and fluorescence and linearity of irradiation light are recognized in the wavelength region from X-ray to 350 nm ultraviolet light. The types of lasers used for measurement are excimer lasers, Nd; YAG lasers, and most of the ultraviolet light, and the laser beam size is 120 mm x 120 m.
There are also examples up to m.

The light beam intensity distribution data from the CCD camera is sent to the beam profiler and the data is analyzed. As a result, the uniformity of the measured light beam intensity distribution is ±.
The result of the uniform light intensity distribution was also obtained in which the average characteristic of the light intensity distribution within the uniformed region was RMS ≦ 1.5% within 5%.

If the measure for preventing the reflected light as shown in FIG. 3 is not taken, noise of 10% or more is generated, which has a great adverse effect on the measurement.

[0015]

As is apparent from the above description, the present invention is directed to the irradiation laser beam on the processed sample surface, which is difficult for the ordinary measuring method due to the limitation of the vacuum chamber, the XY table, the sample holder, and the like. Highly accurate measurement of the light intensity distribution can be easily realized.

Further, the present invention proposes a measure for preventing fluorescence (noise) from reflected light, thereby improving measurement accuracy.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a measurement principle and a measurement method of a fluorescent plate method.

FIG. 2 is a projection imaging measurement of the light intensity distribution of the fluorescent surface light source in the transmission direction and the reflection direction of the fluorescent plate. (A) is an observation on the back side (transmission direction) of the fluorescent plate, and (b) is an observation on the front side (reflection direction) of the fluorescent plate.

FIG. 3 is a method for preventing reflection of laser light transmitted from a fluorescent plate. (A) is a method of absorbing the emitted laser light. A strongly absorbing and non-fluorescent liquid (for example, water for ultraviolet light) or a solid (for UV light, ordinary glass such as BK7) may be used; (b) is a method of preventing reflection by a laser beam damper.

FIG. 4 Example: Observation of laser beam profile in a vacuum chamber.

[Explanation of symbols]

○ ○ 'Optical axis of measurement system; A Position of intersection line on fluorescent screen between image plane on which detector element is placed and main plane of imaging lens. L: Condenser Lens of a
Laser Beam Homogenizer L ': Image Lens D: Detector (CCD / CID Ca
mera) C: Vaccum Chamber W: Window H: Sample Holder F: Fluorescence Plate

Claims (3)

[Claims] 1. A fluorescent thin film layer in which fluorescence is sufficiently generated by irradiation of a laser beam to be measured, and the original laser light is obtained by using a fluorescent plate having a linear intensity relationship with the original irradiation laser light. Instead of directly observing the intensity spatial distribution (beam pattern), a method of measuring the fluorescence generated from the laser irradiation by surface fluorescence. 2. A method for measuring a laser beam beam intensity distribution using fluorescence according to claim 1, wherein the fluorescence intensity in both the transmitting direction (back side of the fluorescent plate) and the reflecting direction (front side of the fluorescent plate) of the irradiation laser beam with respect to the fluorescent plate. Distribution projection measurement method. 3. A method for preventing measurement error caused by reflection of laser light and improving measurement accuracy in the method for measuring the fluorescence intensity distribution in the laser beam reflection direction with respect to the fluorescent plate according to claim 2.