JPH06117935A - Ellipsometer - Google Patents

Abstract

(57) [Abstract] [Purpose] To downsize the ellipsometer. [Structure] A parallel polarized parallel light beam is condensed on the sample surface by a lens with a large numerical aperture, reflected light from the sample surface is converted into a parallel light beam through the lens, and detected by a two-dimensional resolution photodetector through an analyzer. To do. [Function] Since the parallel linearly polarized light flux is concentrated on the sample surface by the lens having a large numerical aperture, the irradiation angle of the irradiation light continuously changes in a wide range, and the sample reflected light is coaxial with the incident light. Since it is taken out and detected, the device becomes small.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ellipsometer.

[0002]

2. Description of the Related Art A conventional ellipsometer has a goniometer type structure as shown in FIG. That is, the light source unit A including the light source 1, the polarizer 2, and the quarter-wave plate 3, the sample stage 4 having the rotation axis orthogonal to the optical axis of the light source unit A, and the same with respect to the rotation angle of the sample The detection unit B is mounted on an arm 5 which is rotated by a double angle by an axis and has an optical axis whose optical axis intersects with the optical axis of the light source unit A on the sample surface. The detection unit B is an analyzer 6 and a photodetector. It consists of 7. Considering the sample table 4 as the center, this device has a light source section A and a detection section B protruding from both sides of the sample table, and the detection section B can be rotated around the sample table. It is necessary to secure a space, and the entire device requires a large space, and when performing measurements with different incident angles to the sample, it is necessary to repeat the measurement while rotating the sample table and detector. And the measurement efficiency is also low.

[0003]

As described above, the present invention requires a large installation space in the conventional ellipsometer,
In view of the fact that the measurement efficiency is low, the present invention intends to provide a small-sized polarization analyzer having good measurement efficiency.

[0004]

[Means for Solving the Problems] As shown in FIG.
A semitransparent mirror H is obliquely inserted on an optical axis Z perpendicular to the surface, and a straight line is formed either on the optical axis passing through the semitransparent mirror or on the optical axis Y reflected and bent by the semitransparent mirror. A polarized parallel light beam source G is placed, an analyzer P and a light-receiving element D having a two-dimensional image resolution are placed on the other side, and a lens L having a large numerical aperture is placed between the semitransparent mirror and the sample to enter the sample. The light flux was focused on the sample surface.

[0005]

[Function] The optical axis of the device is perpendicular to the sample surface, and both incident light and reflected light on the sample surface are along this optical axis. Compared with the conventional configuration in which the incident optical axis to the sample and the reflected optical axis intersect at an arbitrary angle. However, the device installation space can be made extremely small, and since the parallel light flux is focused on the sample surface by a lens with a large numerical aperture, it is the same as measuring various incident / reflected light beams at one time. Since the reflected light flux from the sample is detected by the light receiving element having a two-dimensional resolution, the light having various incident and reflected angles with respect to the sample can be measured at the same time, which is very efficient.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an outline of the device of the present invention, and FIG. 2 shows a concrete embodiment. First, the outline of the present invention will be described with reference to FIG. In the figure, G is a light source that emits a linearly polarized parallel light beam, and a laser is used. The optical axis Y of the light source G is a semitransparent mirror H
Along the optical axis X which is reflected by and is perpendicular to the surface of the sample S.
Is made incident on. The linearly polarized light, which is arranged on the front surface of the sample and has a large numerical aperture and is incident on the sample along the optical axis X, is condensed at a point 0 on the sample surface S. The lens L has NA = 0.9, the light collection angle α to the sample is 64 °, and the light incident on the sample has an incident angle in the range of 0 ° to 64 °. The reflected light from the sample has the same divergence angle 64 as the incident light.
At 0 °, it is reflected from the 0 point, becomes a parallel light flux by the lens L, travels upward along the optical axis X, travels straight through the semitransparent mirror H, and passes through the analyzer P
Then, the light enters the light receiving element D having a two-dimensional resolution capability such as a CCD cell. Therefore, a circular light spot which is a cross section of the incident light beam is projected on the CCD cell D. The illuminance in this light spot is not uniform, and when the analyzer P is rotated, the illuminance distribution changes. The polarization characteristics of the sample can be obtained by detecting and analyzing the change in the illuminance distribution with the light receiving element D.

The operation of the above-mentioned device will be described with reference to FIG. As shown in the figure, the X, Y, and Z axes are determined, the vibration direction of the electric field of the parallel light flux irradiating the sample S is set to the X direction, and such linearly polarized light is condensed on the sample surface by the lens L. Therefore, with respect to the sample incident light in the YZ plane standing on the sample surface, the vibration direction of the incident light is perpendicular to the YZ plane and parallel to the sample surface.
Light having such a relationship with the sample surface is represented by Sp.
Next, the sample incident light in the XZ plane standing on the sample surface does not have a vibration component perpendicular to the XZ plane. Light having such a relationship with the sample surface is represented by Ss. Then, the sample incident light in the plane standing upright to the sample surface in the direction of 45 ° with respect to the XY axes has the Sp component and the Ss component. Therefore, by concentrating a parallel light beam of linearly polarized light on the sample surface with a lens,
The same effect that light of various vibration directions is made incident on the sample surface, that is, the same effect as rotating the plane of linearly polarized light that is made incident on the sample with the conventional device, and the angle of incidence and reflection to the sample from 0 The same effect as changing to α is obtained at one time.

Next, assuming that the sample does not have any polarization characteristic for light reflection and the reflectance does not change depending on the incident / reflection angle, the reflected light from the sample passes through the lens and then is exactly the same as the incident light beam. It becomes a parallel light beam of polarized light, which is directed upward and is incident on the light receiving element. At this time, the illuminance distribution of the irradiation spot on the light receiving surface of the light receiving element is uniform, and the whole is brightest when the direction of the analyzer P is in the X-axis direction, and the illumination of the light receiving surface is when the direction of P is in the Y-axis direction. The spot is the lowest and highest. When the reflectance of the sample surface is the same for both Sp light and Ss light and has the same incident / reflection angle dependence, the illuminance distribution of the illumination spot on the light receiving element is the center when the direction of the analyzer P is X. It becomes a contrasting form.

Generally, the reflected light from the sample surface undergoes some change in polarization, and this change provides analytical information on the sample surface. In FIG. 3, reflected light in a plane that is oblique to the XY axes and perpendicular to the sample surface is generally rotationally polarized light, and its ellipticity and distribution in the major axis direction are symmetrical with respect to the X and Y axes. . Therefore, the illuminance distribution of the illuminated spot on the light receiving element changes when the analyzer P is rotated. As shown in FIG. 4, the point of coordinates x and y on the illumination spot is a ray whose incident / incline surface to the sample is in the direction of φ with respect to the X axis in FIG. 3 and whose incident / reflection angle α is tan α = r / F. Is the incident point on the illuminated spot of. The major axis direction of the elliptically polarized light of this light is the azimuth of the analyzer when the illuminance at the point (x, y) is maximized by rotating the analyzer P, and the ellipticity is the point (x, y) at this time. And the illuminance at the (x, y) point when the analyzer is rotated 90 ° from that direction. On the other hand, since the ratio of the Sp component and the Ss component of the incident light with the incident angle α and the incident azimuth φ is calculated in advance with reference to FIG. 3, the polarized light at various incident angles of light in various polarization directions is It is possible to quantitatively determine the state of the received modulation.

The embodiment shown in FIG. 2 will be described in detail. Figure 1
The same reference numerals are given to the portions corresponding to the respective portions of, and the description thereof will be omitted. Reference numeral 10 denotes a four-division photoelectric cell, which is mounted on one sliding base 11 together with the CCD cell D so that it can be moved in and out on the optical axis Z in an alternating manner. The four-division cell 10 is a light receiving element for a reference device for matching the normal line at the analysis point of the sample S with the optical axis Z, and the optical axis Z passes through the center thereof. The output of each segment of the four-division cell is fetched by the control device 12, and the control device drives the tilt motors 14X, 14Y of the sample stage 13 in the X and Y directions so that the cell outputs of the four-division cell become equal. To drive. 1
Reference numeral 5 denotes a rotary chopper which can freely move in and out on the optical axis Z, and has one slit in the radial direction, and when this slit crosses the optical axis, the length direction (that is, the radial direction of the chopper) of the four-division cell 10 is. It is made to coincide with one direction of the dividing line. Under the chopper, there is a lens 16 which is put in and out on the optical axis Z integrally with the chopper, and the chopper 15 and the lens 16 are prepared for focusing the lens L. When the lens L is at the in-focus position, the parallel light flux reflected from the sample is condensed by the lens 16 on the chopper 15. When the light flux passing through the lens 16 and the chopper 15 is incident on the four-division cell 10, the shadow of the slit of the chopper on the four-division cell surface when the lens L is above and below the in-focus position. The directions of movement of are opposite. Therefore, when the outputs of two adjacent segments of the four-division cell are combined and the four-division cell is treated as a two-division cell, whichever output pulse from the two-division cell when the slit of the chopper 15 crosses the optical axis Z The direction in which the lens L deviates from the in-focus position can be known by whether the segment outputs a pulse first. The controller 12 takes in each segment output of the 4-division cell, performs the above-mentioned data processing,
The driving means 17 of the lens L is controlled so that the phase difference between the output pulses of the two segments becomes 0 when the 4-division cell 10 is treated as a 2-division cell. After completing the above-mentioned two adjustments, both the four-division cell 10, the chopper 15, and the lens 16 are retracted from the optical axis Z, and the sample light beam passes through the two semitransparent mirrors BS1 and BS2 in the Y axis direction, The transparent mirror H moves toward the sample S along the optical axis Z. An expander lens system 18 that expands the luminous flux diameter is arranged in the middle,
The laser light beam is converted into a parallel light beam having an appropriate diameter.
The reflected light from the sample travels upward along the Z axis and is incident on the CCD cell D. The analyzer P is rotated by the motor 19, and the output of each pixel of the CCD cell D at each angular position from the azimuth 0 to 90 ° of the analyzer P is read into the controller 12, and the controller 12 analyzes the data. Is done.

A white light source 20 illuminates the sample surface, and the light reflected from the sample is reflected by the semitransparent mirror H in the Y-axis direction, and then enters the image pickup camera 21 via the semitransparent mirrors BS2 and BS1. An image of the sample surface is formed, and this image is displayed on the monitor CRT 22.
Is displayed so that the analyst can select an analysis point while looking at the image of the sample surface.

The semi-transparent mirror has a polarization characteristic, but if the polarization direction of the laser emission light (the vibration direction of the electric field) is parallel to the plane of the semi-transparent mirror H or orthogonal to it. The polarized light that illuminates the sample is linearly polarized light, and it is possible to prevent the sample irradiation light from undergoing polarization modulation. Since the reflected light from the sample transmits H,
It is polarizedly modulated by the semitransparent mirror H. Therefore, in the data processing in the control device 12, correction for this modulation is necessary. Before assembling the device, the data for this correction calculation is to make circularly polarized light incident on the semitransparent mirror H at an incident angle of 45 °, and measure the major axis direction of the elliptically polarized light of the transmitted light and the ellipticity. Obtained by

[0013]

According to the present invention, the incident light beam to the sample and the reflected light beam are coaxial with each other, and since there is no movable part for changing the incident angle to the sample, the device is compact and the device installation space is also small. It's fine. In addition, data at various incident and reflection angles can be obtained at one time, so measurement efficiency is high.

[Brief description of drawings]

FIG. 1 is a schematic explanatory diagram of the present invention.

FIG. 2 is a side view of an apparatus according to an embodiment of the present invention.

FIG. 3 is an explanatory view of the operation of the device of the present invention.

FIG. 4 is a plan view of a light receiving spot on a CCD cell.

FIG. 5 is a plan view of a conventional device.

[Explanation of symbols]

 S sample H semi-transparent mirror G linearly polarized light source (laser) P analyzer D light receiving element having two-dimensional resolution L lens

Claims (1)

[Claims] 1. A semitransparent mirror is obliquely inserted on an optical axis Z perpendicular to the sample surface, and the optical axis Y is penetrated through the semitransparent mirror or is reflected and bent by the semitransparent mirror. Place a linearly polarized parallel-beam light source on any of the above, place an analyzer and a light receiving element having a two-dimensional image resolution on the other optical axis, and place a lens between the semitransparent mirror and the sample. An ellipsometer characterized in that a parallel light beam from the above-mentioned light source which is incident on the sample surface is condensed at one point on the sample surface.