JP3715013B2 - Microscope and focus setting method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a microscope and its focus setting method, and more particularly to a confocal scanning laser microscope using a microscope glass layer thickness corrector and its focus setting technique.
[0002]
[Prior art]
Japanese Patent Application Laid-Open No. 7-140393 and the like describe a test for a semiconductor manufacturing mask (hereinafter referred to as a mask) using a confocal scanning laser microscope and a reduction in inspection accuracy due to a thickness deviation of a glass substrate on which the mask is formed. A technique for correcting using a glass layer thickness corrector (hereinafter simply referred to as a thickness corrector) is disclosed.
[0003]
In a confocal scanning laser microscope using such a thickness corrector, the thickness of the light transmission layer of the thickness corrector is set using the thickness measuring instrument such as a laser micrometer. By performing actual measurement, the total thickness of the light transmission layer and the glass substrate is set to a constant reference thickness. Also, the masks are classified into several types according to the thickness, and the conventional thickness setting of the light transmission layer is performed before the first mask measurement when the mask type is changed, and thereafter the same type of mask is set. Is measured with this setting. Then, in this state where the total thickness of the light transmission layer and the glass substrate becomes the reference thickness, the confocal scanning laser microscope is set so that the focal point is aligned with the lower end surface of the glass substrate.
[0004]
[Problems to be solved by the invention]
However, since the light transmission layer thickness setting method is based on physical measurement such as the thickness of the glass substrate and not on the optical thickness, it is set by changing the material of the glass substrate. There was a problem that errors were included. In addition, when the mask type changes, the thickness of the light transmission layer is set only once before the first mask measurement, and therefore the light transmission layer is caused by factors such as temperature change during the subsequent measurement of the same type of mask. Since the total thickness of the glass substrate and the glass substrate fluctuates with respect to the reference thickness, there is a problem that the focal point of the confocal scanning laser microscope is shifted.
[0005]
The present invention has been made in view of the above-described problems, and has the following objects.
(1) To provide a microscope capable of suppressing a decrease in measurement accuracy due to a difference in material of a glass layer of a measurement object.
(2) A microscope focus setting method based on the optical thickness of the glass layer of the measurement object is provided.
(3) To provide a microscope focus setting method that is stable against changes in ambient temperature.
[0006]
[Means for Solving the Problems]
In order to achieve the above-described purpose, as a first means, the measurement light is collected on the lower end surface of the glass layer by the objective lens through the light transmission layer whose thickness is set according to the thickness of the glass layer of the measurement object. In the microscope that measures the dimension of the target portion formed on the lower end surface by irradiating with light and detecting the intensity of the reflected light from the measurement object by the photodetector through the objective lens,
A focal point that is disposed oppositely on the same optical axis as the objective lens with the measurement object interposed therebetween, and the optical positional relationship with respect to the objective lens is measured in advance, and the focus setting incident light is condensed and irradiated on the lower end surface. An objective lens for setting;
A focus setting light detector for detecting the intensity of the focus setting reflected light from the lower end surface via the focus setting objective lens;
A light switching means for irradiating only the focus setting incident light to the focus setting objective lens when setting the focus of the objective lens, and irradiating only the incident light to the objective lens during measurement;
By detecting the intensity of the focus setting incident light with the photodetector and the focus setting photodetector, the thickness of the light transmission layer is adjusted to set the focus position of the objective lens.
[0007]
As a second means, in the first means, the distance between the objective lens and the focus setting objective lens when the focal point of the objective lens coincides with the focal point of the focus setting objective lens as an optical positional relationship in advance. A measure is taken.
[0008]
As a third means, in the first or second means, the thickness of the light transmission layer is set so that the intensity of the focus setting incident light detected by the photodetector and the focus setting photodetector is maximized. Is adopted.
[0009]
As a fourth means, in any one of the first to third means, the means that the incident light and the focus setting incident light are supplied from the same light source is adopted.
[0010]
As a fifth means, the incident light is condensed and irradiated on the lower end surface of the glass layer by the objective lens through the light transmission layer whose thickness is set according to the thickness of the glass layer of the measurement object, and the measurement is performed. In the focus setting method of the microscope for measuring the dimension of the target portion formed on the lower end surface by detecting the intensity of the reflected light from the target object through the light transmission layer and the objective lens,
a. A step of opposingly placing a focus setting objective lens across a sample glass on the same optical axis as the objective lens;
b. The focus setting objective lens is detected by detecting the intensity of the focus setting reflected light obtained by irradiating the lower end surface of the sample glass with the focus setting incident light through the focus setting objective lens. To move the focus to the lower end surface of the sample glass,
c. The process of moving the objective lens to detect the intensity of the focus setting incident light transmitted through the sample glass through the objective lens and adjusting the focal point to the lower end surface of the sample glass;
d. In place of the sample glass, a measurement object and a light transmission layer are attached between the objective lens and the focus setting objective lens so that incident light can be focused, and the focus setting objective lens is focused on the lower end surface of the glass layer. A process of moving the position of the focus setting objective lens,
e. A step of aligning the position of the objective lens so that the lower end surface of the glass layer is focused based on the positional relationship between the focus setting objective lens and the objective lens in the steps b and c;
f. Adjusting the thickness of the light transmission layer so that the intensity of the reflected light is maximized;
A means having the following is adopted.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of a microscope and its focus setting method according to the present invention will be described with reference to FIGS.
[0012]
FIG. 1 is a configuration diagram of an optical system of a microscope in the present embodiment. In this figure, reference numeral 1 denotes a laser oscillator (light source), which outputs, for example, a single mode laser beam having a wavelength of 325 nm (nanometer) toward the reflecting mirror 2. The reflecting mirror 2 reflects the laser light toward the reflecting mirror 3. The reflecting mirror 3 reflects laser light as incident light toward the beam splitter 4.
[0013]
The beam splitter 4 reflects part of the incident light incident from the reflecting mirror 3 toward the measurement optical system A and transmits the remaining laser light to propagate to the focus setting optical system B. Here, the laser light reflected by the beam splitter 4 is guided to the measurement optical system A as incident light, and the laser light transmitted through the beam splitter 4 is guided to the focus setting optical system B as focus setting incident light.
[0014]
The measurement optical system A includes reflecting mirrors a1 to a4, shutter a5, beam splitter a6, photodetector a7, focusing lens a8, pinhole a9, 1 / 4λ phase plate a10, collimator lens a11, objective lens a12, and thickness. It comprises a corrector a13.
[0015]
The reflecting mirror a1 reflects the incident light toward the reflecting mirror a2, and the reflecting mirror a2 reflects the incident light toward the shutter a5. The shutter a5 passes or shields the incident light to turn on / off the propagation of the incident light to the beam splitter a6. The beam splitter a6 propagates incident light to the converging lens a8, and reflects reflected light obtained by reflecting the incident light propagated to the converging lens a8 to a measurement object, that is, a mask X described below, as a reflecting mirror a3. Reflect towards The converging lens a8 converges the incident light toward the hole provided in the pinhole a9, and propagates the reflected light to the beam splitter a6 as parallel light.
[0016]
The pinhole a9 is a shielding plate provided with a small-diameter hole, diffracts incident light and propagates it to the ¼λ phase plate a10, and only reflects the reflected light incident on the hole out of the reflected light. Pass toward a8. The ¼λ phase plate a10 shifts the phase of incident light by ¼ wavelength and propagates it to the collimator lens a11, and shifts reflected light by ¼ wavelength and propagates it to the pinhole a9. The collimator lens a11 converts incident light diffracted by the pinhole a9 into parallel light and propagates it to the reflecting mirror a4, and converges the reflected light toward the hole of the pinhole a9.
[0017]
The reflecting mirror a4 totally reflects the incident light and propagates it toward the objective lens a12, and totally reflects the reflected light and propagates it toward the collimator lens a11. The objective lens a12 converges the incident light and irradiates the mask X, which is a measurement object, vertically through a light transmission layer a14 described below, and converts the reflected light into parallel light toward the reflecting mirror a4. Propagate. The objective lens a12 is configured to be movable along the optical axis P1, and is provided with a position detector that detects the position of the objective lens a12 with high accuracy on the order of submicrons.
[0018]
The thickness corrector a13 is disclosed in, for example, Japanese Patent Application Laid-Open No. 7-140393. The thickness corrector a13 has the same refractive index as that of a glass substrate (glass layer) X1 described below and the thickness thereof can be varied. A light transmission layer a14 is provided. The thickness of the light transmission layer a14 is set so that the thickness of the glass substrate X1 and its own thickness are always a constant reference thickness V.
[0019]
As shown in the side sectional view of FIG. 2, the mask X has a chrome pattern (target portion) X2 formed on one surface of a glass substrate X1 having a certain thickness by etching or the like. The line width L or the like is a measurement target by the microscope. In measuring the line width L, the mask X is placed on a mask holder (not shown) with the glass substrate X2 on the objective lens a12 side as shown.
[0020]
Incident light applied to the mask X is reflected by the mask X, reflected as a reflected light toward the reflecting mirror a3 by the beam splitter a6 via the thickness light transmission layer a14 and the above-described components, and a photodetector. Incident on a7. Here, since the reflected light passes through the ¼λ phase plate a10 twice, a phase shift of ½ wavelength is made, so that it is reflected by the beam splitter a6. The photodetector a7 is, for example, a photomultiplier tube, and detects the intensity of the reflected light thus entered as an electrical signal.
[0021]
On the other hand, the focus setting optical system B includes reflecting mirrors b1 to b3, shutter b4, beam splitter b5, focus setting light detector b6, focusing lens b7, pinhole b8, 1 / 4λ phase plate b9, collimator lens b10, And a focus setting objective lens b11.
[0022]
The focus setting incident light propagated from the beam splitter 4 toward the focus setting optical system B is reflected by the reflecting mirror b1 toward the shutter b4. The shutter b4 transmits / shields the focus setting incident light and propagates it to the beam splitter b5. The beam splitter b5 propagates the focus setting incident light incident from the shutter b4 to the focusing lens b7, and transmits the focus setting reflected light obtained by propagating to the focusing lens b7 and reflecting the focus setting incident light to the mask X. Reflected toward the reflecting mirror b2. The converging lens b7 converges the focus setting incident light toward a hole provided in the pinhole b8, and makes the focus setting reflected light parallel light and propagates it to the beam splitter b5.
[0023]
The pinhole b8 is, for example, a light shielding plate provided with a small-diameter hole, diffracts the focus setting incident light to pass through the ¼λ phase plate b9, and the focus incident on the hole of the focus setting reflected light. Only the set reflected light is allowed to pass toward the beam splitter b5. The quarter-wave phase plate b9 shifts the phase of the focus setting incident light by a quarter wavelength and propagates it to the collimator lens b10, and shifts the phase of the focus setting reflected light by a quarter wavelength and propagates it to the pinhole b8. Let The collimator lens b10 converts the focus setting incident light diffracted by the pinhole b8 into parallel light and propagates it to the reflecting mirror b3, and converges the focus setting reflected light toward the hole of the pinhole b8.
[0024]
The reflecting mirror b3 totally reflects the focus setting incident light and propagates it toward the focus setting objective lens b11, and propagates the focus setting reflected light toward the collimator lens b10. The focus setting objective lens b11 converges the focus setting incident light to irradiate the mask X, and makes the focus setting reflected light parallel light to propagate toward the reflecting mirror b3. The focus setting objective lens b11 is positioned so that its optical axis P2 is the same as the optical axis P1 of the objective lens a12 described above, and the positional relationship with the objective lens a12 by the procedure described below. Are optically measured in advance.
[0025]
The focus setting incident light irradiated on the mask X is reflected by the mask X, reflected by the beam splitter b5 as the focus setting reflected light through the above-described components, and further reflected by the reflecting mirror b2 for focus setting. The light enters the photodetector b6. The focus setting photodetector b6 is a photomultiplier tube similar to the photodetector a7 described above, and detects the intensity of the focus setting reflected light as an electric signal.
[0026]
Next, a method for setting the focus of the objective lens a12 performed prior to the measurement of the mask X will be described with reference to FIG.
[0027]
First, as shown in this figure, instead of the mask X, the sample glass Z is placed on the mask holder and the light transmission layer 12a is removed from the optical path. The sample glass Z is formed of the same material as the glass substrate X1 and has the reference thickness V.
[0028]
In this state, the shutter a5 is closed and only the focus setting incident light is irradiated onto the sample glass Z, and the focus is set so that the lower end surface Z1 (position Y0 along the optical axis P2) of the sample glass Z is in focus. The objective lens b12 is moved. At this time, the position Yb of the focus setting objective lens b11 measured by the position detector provided in the objective lens b12 is stored.
[0029]
At this time, it is detected that the intensity of the focus setting reflected light detected by the focus setting light detector b6 is the maximum, that is, the amount of the focus setting reflected light passing through the pinhole b8 is the maximum, thereby setting the focus. It is determined that the objective lens b11 is focused on the lower end surface Z1.
[0030]
When the focus of the focus setting objective lens b11 is thus focused on the lower end surface Z1, the objective lens a12 is moved to focus the objective lens a12 on the lower end surface Z1. At this time, the position Ya of the focus setting objective lens b11 is stored based on the output of the position detector provided in the focus setting objective lens b11. In this case, it is determined that the focus of the objective lens a12 is focused on the lower end surface Z1 by detecting that the output of the photodetector a7 is maximum, that is, the amount of light passing through the pinhole a9 is maximized. Is done.
[0031]
By the above procedure, the positional relationship of the objective lens a12 with respect to the position of the focus setting objective lens b11 when the focus of the objective lens a12 and the focus of the focus setting objective lens b11 coincide, that is, the objective lens a12 and the focus setting objective lens. The distance R with b11 was determined.
[0032]
Subsequently, the optical system is returned to the state shown in FIG. 1, and the focus of the objective lens a12 is adjusted to the lower end surface X3 with respect to the mask X as follows. First, the focus setting objective lens b11 is focused on the lower end surface X3 in the same manner as described above. Then, the objective lens a12 is moved to a position that satisfies the distance R. In this case, the position of the objective lens a12 is set with high accuracy based on the detection values of the position detector of the objective lens a12 and the position detector of the focus setting objective lens b11. Through the above procedure, the focal point of the objective lens a12 is optically aligned with the lower end surface X3 with high accuracy.
[0033]
In this state, the thickness of the light transmission layer a14 of the thickness corrector a13 is maximized so that the shutter b4 is closed and the shutter a5 is opened to irradiate the mask X with incident light and the output of the photodetector a7 is maximized. Is set. That is, the thickness of the thickness corrector a13 is set so that the thickness of the glass substrate X1 plus the thickness of the thickness corrector a13 becomes the thickness of the sample glass Z, that is, the reference thickness V.
[0034]
The line width L of the chrome pattern X2 is measured as follows by the microscope adjusted in focus in this way. That is, the objective lens 11 is moved along the optical axis P1 so as to be focused on the lower end surface (joint surface with the chromium pattern X2) X3 of the glass substrate X1, detected by the photodetector 13, and the intensity of the reflected light is increased. The maximum position is set. In this case, since the intensity of the reflected light varies depending on the presence or absence of the chromium pattern X2, the line width L is measured based on the intensity change.
[0035]
【The invention's effect】
As described above, the present invention has the following effects.
(1) Oppositely arranged on the same optical axis as the objective lens across the measurement object, the optical positional relationship with the objective lens is measured in advance, and the focus setting incident light is condensed and irradiated on the lower end surface. A focus setting objective lens, a focus setting photodetector for detecting the intensity of reflected light from the bottom of the glass layer through the focus setting objective lens, and a focus setting objective lens when setting the focus of the objective lens Since the optical switching means for propagating only the incident light of the focus setting and propagating only the incident light to the objective lens at the time of measurement is provided, it is possible to accurately detect the objective lens based on the optical thickness of the glass layer of the measurement object. The focal position is set.
(2) Since the focal position of the objective lens is set with high accuracy based on the optical thickness of the glass layer of the measurement object, the reduction in measurement accuracy due to the difference in the material of the glass layer of the measurement object is suppressed. Can do.
(3) The measurement object can be stably measured against changes in ambient temperature.
(4) It is not necessary to use a thickness measuring instrument that physically measures the thickness of the measurement object when measuring the measurement object.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing an embodiment of an optical system of a microscope in a microscope and its focus setting method according to the present invention.
FIG. 2 is a configuration diagram of an optical system during focus adjustment of an objective lens in the microscope and the focus setting method according to the present invention.
FIG. 3 is a side sectional view showing a configuration of a mask to be measured in the microscope and the focus setting method according to the present invention.
[Explanation of symbols]
1 laser oscillator 2, a5, b4 shutter 3, a1 to a4, b1 to b3 reflecting mirror 4, a6, b5 beam splitter A measuring optical system B focus setting optical system a7 photodetectors a8, b7 focusing lenses a9, b8 pins Hall a10, b9 1 / 4λ phase plate a11, b10 Collimator lens a12 Objective lens a13 Thickness corrector a14 Light transmission layer b6 Focus setting photodetector b11 Focus setting objective lens L Chrome pattern line width P1 Objective lens light Axis P2 Optical axis R of focus setting objective lens R Distance between objective lens and focus setting objective lens X Mask X1 Glass substrate X2 Chrome pattern X3 Bottom edge surface Y0 Position of sample glass bottom edge along optical axis Ya Optical axis Position of objective lens along Yb Position of objective lens for focus setting along optical axis Z Sample glass Z1 Lower end surface of sample glass

Claims (5)

The measurement light is focused and irradiated on the lower end surface of the glass layer by the objective lens through the light transmission layer whose thickness is set according to the thickness of the glass layer of the measurement object, and the reflected light from the measurement object In the microscope that measures the size of the target part formed on the lower end surface by detecting the intensity of the light by the photodetector through the objective lens,
A focal point that is disposed oppositely on the same optical axis as the objective lens with the measurement object interposed therebetween, and the optical positional relationship with respect to the objective lens is measured in advance, and the focus setting incident light is condensed and irradiated on the lower end surface. An objective lens for setting;
A focus setting light detector for detecting the intensity of the focus setting reflected light from the lower end surface via the focus setting objective lens;
A light switching means for irradiating only the focus setting incident light to the focus setting objective lens when setting the focus of the objective lens, and irradiating only the incident light to the objective lens during measurement;
A microscope characterized in that the focus position of an objective lens is set by adjusting the thickness of a light transmission layer by detecting the intensity of focus setting incident light with the photodetector and the focus setting photodetector. 2. The distance between the objective lens and the focus setting objective lens when the focal point of the objective lens coincides with the focus of the focus setting objective lens is measured in advance as the optical positional relationship. Microscope. 3. The microscope according to claim 1, wherein the thickness of the light transmission layer is set so that the intensity of the focus setting incident light detected by the photodetector and the focus setting photodetector is maximized. 4. The microscope according to claim 1, wherein the incident light and the focus setting incident light are supplied from the same light source. The incident light is focused and irradiated on the lower end surface of the glass layer by the objective lens through the light transmission layer whose thickness is set according to the thickness of the glass layer of the measurement object, and the reflected light from the measurement object. A focus setting method for a microscope that measures the size of the target portion formed on the lower end surface by detecting the intensity of the light through the light transmission layer and the objective lens,
a. A step of opposingly placing a focus setting objective lens across a sample glass on the same optical axis as the objective lens;
b. The focus setting objective lens is detected by detecting the intensity of the focus setting reflected light obtained by irradiating the lower end surface of the sample glass with the focus setting incident light through the focus setting objective lens. To move the focus to the lower end surface of the sample glass,
c. The process of moving the objective lens to detect the intensity of the focus setting incident light transmitted through the sample glass through the objective lens and adjusting the focal point to the lower end surface of the sample glass;
d. In place of the sample glass, a measurement object and a light transmission layer are attached between the objective lens and the focus setting objective lens so that incident light can be focused, and the focus setting objective lens is focused on the lower end surface of the glass layer. A process of moving the position of the focus setting objective lens,
e. A step of aligning the position of the objective lens so that the lower end surface of the glass layer is focused based on the positional relationship between the focus setting objective lens and the objective lens in the steps b and c;
f. Adjusting the thickness of the light transmission layer so that the intensity of the reflected light is maximized;
A method for setting a focus of a microscope.

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