TWI428575B - Spectroscopic ellipsometers - Google Patents

Description

Spectral ellipsometer [Priority claim]

The present application claims priority to the provisional application of the name "Spectroscopic Ellipsometer without Moving Parts", filed on Apr. 24, 2006, which is incorporated herein by reference. The present application further claims priority to the non-transitory patent application entitled "Optical Focusing Devices", filed on Apr. 16, 2007, the disclosure of which is incorporated herein by reference. These applications are hereby incorporated by reference.

The present invention relates to detection and measurement systems, and in particular to optical detection and measurement of devices under test ("DUTs") such as semiconductor devices and/or wafers.

Spectroscopic ellipsometry is widely used in semiconductor fabrication, optical coating and material analysis for very powerful optical metrology. The ellipsometer measures the complex ratio of the reflectances Rp and Rs, where Rp is the reflectance of the electric field in the incident plane and Rs is the reflectance of the electric field whose direction is perpendicular to the incident surface. Rp and Rs are plural and they are wavelength dependent.

The ellipsometric amount is defined as: among them And Δ = δ _p - δ _s δ _p and δ _s are the phases of R _p and R _s .

In conventional ellipsometers, one of the polarization components (polarizers, analyzers, or compensators) in the system must be rotated when measuring ellipsometry, ie, Ψ and Δ. This limits the speed of the measurement. In some applications, a very small area needs to be measured (such as measuring the film thickness on a semiconductor wafer). It must focus the light to a very small area.

Therefore, it is preferable to obtain a spectral ellipsometer capable of focusing on a small focal spot. In addition, it is desirable to have an ellipsometer with minimal moving parts so that no mechanical components in the system need to be moved for measurement.

One object of the present invention is to provide a method and apparatus for an ellipsometer that can focus on small focal spots.

Another object of the present invention is to provide a method and apparatus for an ellipsometer that can simultaneously polarize, reflect, detect, and detect a plurality of rays.

Another object of the present invention is to provide a method and apparatus for ellipsometers that can simultaneously polarize, reflect, detect, and detect several rays without any mechanically movable components.

Briefly, a method for extracting information of a device under test by an ellipsometer includes the steps of: providing a plurality of incident polarized beams using a plurality of polarizers, wherein each beam is polarized at a specified polarization angle; a parabolic reflector focuses the plurality of incident polarized beams on a spot on the device under test; using a parabolic reflector to collect a plurality of beams reflected from the device under test; and using a plurality of analyzers The collected beam is biased, wherein each analyzer has a specified polarization angle relative to its respective polarizer.

One advantage of the present invention is that it provides a method and apparatus for an ellipsometer that can focus on small focal spots.

Another advantage of the present invention is that it provides a method and apparatus for an ellipsometer that can simultaneously polarize, reflect, detect, and detect several rays.

Another advantage of the present invention is that it provides a method and apparatus for ellipsometers that can simultaneously polarize, reflect, detect, and detect several rays without any mechanically movable components.

Further description of the invention is made with reference to the drawings and examples of the application thereof.

Referring to Figure 1, the basic concepts of an embodiment of the present invention are illustrated. Assuming that a parabola is placed on the y-axis and the z-axis, conceptually, the shape of the parabola can be described as a simple mathematical function, z = ay ² , where the light entering parallel to the z-axis will intersect the z-axis in it. Focus "F", where the focus is at (0, 1/4a) and "a" is a constant. The incoming ray intersects the parabolic surface and is redirected to the focus of the entrance face 112 (the plane perpendicular to the axis of symmetry and through the focus "F")

Here, as shown, the incoming incoming light 114 is parallel to the axis of symmetry. The light illuminates the parabolic surface and the parabolic reflector directs the beam to its focus due to its characteristics and intersects the z-axis at the intersection "F". After this intersection, the light illuminates the parabolic surface again, and the parabolic surface redirects the light back to its direction of incidence parallel to the axis of symmetry. Due to the unique characteristics of the paraboloid, if the incoming light is parallel to the axis of symmetry, the reflected light will always be parallel to the axis of symmetry.

Referring to Figure 2, a presently preferred embodiment of the present invention is disclosed. Here, a side view of an optical pickup is shown, wherein the optical pickup includes a parabolic reflector 201, a polarizer 205, and an analyzer 206. The parabolic reflector can be fabricated as a paraboloid and cut in a manner such that the focus 203 is on the surface of the object 202 (device under test) to be measured or tested. The function of the parabolic reflector 201 is to focus the incoming beam 204 onto the surface of the device under test 202 on the focus 203 and collect the beam reflected from the focus 203. 3 is a front elevational view of the parabolic reflector 201 having a polarizer 205 and an analyzer 206 disposed in the opening of the parabolic reflector.

In a preferred embodiment of the invention, when performing ellipsometric measurements, the plurality of polarizers and analyzers are arranged in a manner such that the incident power of Rp and Rs and the incoming beam can be simultaneously measured. Figure 4 shows a top view of the optical pickup showing one of the above arrangements. Here, for the incoming light and the reflected light, there are eight polarizers and analyzers 405 and 406, 407 and 408, 409 and 410, and 411 and 412. Except that the axis of the analyzer 406 is perpendicular to the others, their polarization axes are parallel to each other. The four pairs of light (4a/4b, 10a/10b, 11a/11b, and 15a/15b) shown below illustrate the operation of the device. Here, the letter "a" indicates the incoming light and the letter "b" indicates the outgoing light.

Each pair of rays defines an incident surface. The light 4a passes through the polarizer 405 and becomes polarized light in the direction of the illustrated arrow. This direction is perpendicular to the entrance face 201. After the reflection leaves the parabolic reflector and the focus, the outgoing light 4b passes through another analyzer 406. This light is then received by a detector whose output is proportional to the light intensity.

The principle of operation can be further illustrated in the more rigorous mathematical formulas described below. We use the Jones representation of polarization.

Incident beam electric field: Polarizer: Parabolic reflector: sample: Coordinate rotation matrix: Polarizer: The electric field of the reflected beam: among them, and A rotation matrix of an analyzer having an angle A and a polarizer having an angle P. The angle is measured clockwise from the incident surface along the direction of propagation of the light.

The intensity on the detector is proportional to can prove Here R _p = R _p ^sample R _p ^M R _p ^M and R _s = R _s ^sample R _s ^M R _s ^M for rays 4a and 4b, A=45° and P=45° For light 10a and 10b, A=-45° and P=45° For light 11a and 11b, A = 90° and P = 90° For light 15a and 15b, A = 0° and P = 0° and so And and so, And The mirror effect can be calibrated and removed by a known number of samples.

Other reflective optical methods can also be used to achieve ellipsometric measurements, such as those depicted in Figures 5 and 6. In FIG. 5, incoming light passes through a polarizer 502, reflects away from the mirror disposed at 504 and another mirror at 506 to focus on the focus at 403 and the device under test 520. After being reflected off the device under test 520, the light reflects off the mirror at 510 and the mirror at 504 to pass through the analyzer 512. In FIG. 6, incoming ray 601 passes through polarizer 602, passes through lens 604 and is focused on focus 606 and device under test 620. The light reflects off the device under test and passes backward through lens 604 and analyzer 608. Note that a polarization analyzer can be used in which the polarization analyzer redirects the incoming light into a two orthogonal polarization direction.

Figure 7 illustrates an alternate embodiment in which the incident light is linearly polarized at P = 45° and the four analyzers are arranged at A = 45, -45, 0, and 90. The incident ray 701 passes through a polarizer 702 of P = 45°, which can be reflected by any lens or parabolic mirror away from the parabolic reflector 704 at 706 to focus on the focus 708 and reflect away from the device under test 720. The reflected light is again reflected off the parabolic reflector 704 at 710, advanced to a beam splitter 712, and directed to a first analyzer 714 of A = 45° and -45° with a = 0° and 90° Two analyzers 716.

Here, the outgoing ray 718 for A=45° and P=45° For outgoing light 720 with A=-45° and P=45° For outgoing light 724 with A = 90° and P = 45° And the outgoing ray 722 for A=0° and P=45°

and so, And

and so, And

Figure 8 illustrates another alternate embodiment in which the incident light is linearly polarized at P = 45° and the four analyzers are arranged at A = 45, -45, 0, and 90. The incident ray 801 passes through a P=45° polarizer 802, which can be reflected by any lens or parabolic mirror away from the parabolic reflector 804 at 806 to focus on the focus 808 and reflect away from the device under test 820. The reflected light is again reflected off the parabolic reflector 804 at 810, proceeds to the first beam splitter 812, and is directed to the second beam splitter 814 and the third beam splitter 816. From the second beam splitter, the light is advanced to an A=45° analyzer 822 and an A=-45° analyzer 824; and from the third beam splitter 816, the light is advanced to an A=0° analyzer 818 And an A=90° analyzer 820.

Although the invention has been described with reference to certain preferred embodiments, it is understood that the invention is not limited to the specific embodiments. Rather, the inventors claim that the present invention is to be understood and construed in the broadest scope of the scope of the invention. Accordingly, the scope of the invention is to be understood as not limited by the description

4a, 4b, 10a, 10b, 11a, 11b, 15a, 15b, 114, 601, 701, 801. . . Light

112. . . Incident surface

201, 704, 804. . . Parabolic reflector

202, 520, 620, 720, 820. . . Device under test (DUT)

203, 606, 708, 808. . . focus

204. . . beam

205, 405, 407, 409, 411, 502, 602, 702, 802. . . Polarizer

206, 406, 408, 410, 412, 512, 608, 714, 716, 818, 820, 822, 824. . . Polarizer

604. . . lens

712, 812, 814, 816. . . Splitter

1 is a two-dimensional conceptual diagram of the technology of the present invention; FIG. 2 is a side view of a preferred embodiment of the present invention using a parabolic reflector, a polarizer, and a polarization analyzer; FIG. 3 is a parabolic reflector, An angled upper view of a preferred embodiment of the present invention, and a polarizer and a plurality of polarizers and analyzers, Figure 5 is a side elevational view of an alternate embodiment of the present invention using different reflectors; Figure 6 is a side view of another alternative embodiment of the present invention using different reflectors; Figure 7 is a splitter Another embodiment of the present invention that is used to direct light to different analyzers; and Figure 8 is another embodiment of the present invention in which the beamsplitter is used to direct light to different analyzers.

201. . . Parabolic reflector

202. . . Device under test (DUT)

203. . . focus

204. . . beam

205. . . Polarizer

206. . . Polarizer

Claims (5)

A method for extracting information of a device under test, comprising the steps of: providing a plurality of incident polarized beams; focusing the plurality of incident polarized beams on a spot on a device to be tested; collecting a plurality of light beams reflected by the device under test; and detecting the collected light beam, wherein the step of providing a plurality of incident polarized light beams is performed by a plurality of polarizers having the same first Polarization angle, the step of detecting is implemented by a plurality of analyzers, one of the plurality of analyzers having a polarization angle perpendicular to the first polarization angle, and the other of the plurality of analyzers having a parallel The polarization angle of the first polarization angle. The method of claim 1, wherein the focusing step is performed using a parabolic reflector. The method of claim 1, wherein the collecting step is performed using a parabolic reflector. The method of claim 1, wherein the focusing step, the collecting step, and the detecting step are performed simultaneously. A method for extracting information of a device under test, comprising the steps of: providing a plurality of incoming polarized beams using a plurality of polarizers, wherein each beam is polarized at a specified first polarization angle; using a paraboloid The reflector uses the plurality of incident polarized beams as phases The same incident angle is focused on a spot on the device to be tested; a parabolic reflector is used to collect the plurality of beams reflected from the device under test; and the collected beam is analyzed using a plurality of analyzers, wherein One of the plurality of analyzers has a polarization angle perpendicular to the first polarization angle with respect to its corresponding polarizer, and the other of the plurality of analyzers has a parallel first with respect to its corresponding polarizer The polarization angle of the polarization angle.