JP2000018912A - Grazing incidence interferometer - Google Patents

Abstract

(57) [Problem] To provide an interferometer that can cope with a large measurement surface at low cost by making the mechanism for switching the measurement sensitivity simple. SOLUTION: Coherent light emitted from a measurement light source is obliquely incident on a surface to be measured, and interference fringes are formed by reflected light reflected from the surface to be measured and reflected light of the coherent light reflected from a reference surface. In the oblique incidence interferometer to be obtained, a convex lens fixedly arranged to convert the coherent light emitted from the measurement light source into a substantially parallel light beam, having a reference surface facing the surface to be measured,
An optical element that passes coherent light converted into a parallel light beam by the convex lens and impinges on the surface to be measured from an oblique direction, and changes an incident angle of coherent light obliquely incident on the surface to be measured corresponding to different measurement sensitivities. Emission position changing means for changing the emission position of the coherent light emitted from the measurement light source.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a grazing incidence interferometer suitable for measuring the surface shape of an object to be measured.

[0002]

2. Description of the Related Art As an oblique incidence interferometer, there is known an oblique incidence interferometer which is used, for example, for flatness inspection of a silicon wafer in a semiconductor device manufacturing process. This oblique incidence interferometer allows light to enter the measurement surface from an oblique direction, so it can measure objects with relatively large irregularities, and can change the measurement sensitivity by changing the angle of incidence on the measurement surface. have.

Conventionally, as a configuration for changing the measurement sensitivity, for example, a configuration as shown in FIG. 5 is known. Laser light emitted from a He-Ne laser 8 as a light source is expanded into a required size by a lens 7, converted into a parallel light beam by a collimating lens 6, and incident on the prism 1 through a rotary prism 5. I do. The light reflected on the prism reference surface 2 and the light transmitted through the prism reference surface 2 and reflected on the measurement surface 3 of the measurement object cause an interference phenomenon, and the screen 4
, An interference fringe is projected. The measurement sensitivity is changed by moving the rotary prism 5 to change the incident angle of the laser beam on the prism 1.

[0004]

However, the size of semiconductor wafers in recent years has been increasing, and the diameter of semiconductor wafers is now 20 mm.
Some are 0mm. In order to cope with this, the rotary prism 5 for switching the sensitivity also needs to be approximately equal in size, but it is costly to enlarge such an optical member to maintain the required accuracy. .

Further, in the above mechanism, since the rotary prism 5 is moved and adjusted to change the measurement sensitivity, a driving device for that is required, and a mechanism for moving a large optical member becomes complicated in terms of equipment. There is a disadvantage that.

SUMMARY OF THE INVENTION In view of the above problems, it is an object of the present invention to provide an interferometer that has a simple structure for switching the measurement sensitivity and can cope with a large measurement surface at low cost.

[0007]

Means for Solving the Problems In order to solve the above problems, the present invention is characterized by having the following configuration.

(1) Coherent light emitted from a measurement light source is obliquely incident on a surface to be measured, and interferes with reflected light reflected from the measured surface and reflected light of the coherent light reflected on a reference surface. The oblique incidence interferometer for obtaining fringes has a convex lens fixedly arranged to convert the coherent light emitted from the measurement light source into a substantially parallel light beam, and a reference surface facing the surface to be measured. An optical element that allows the coherent light to pass through and enters the surface to be measured from an oblique direction, and from the measurement light source to change the incident angle of the coherent light that obliquely enters the surface to be measured corresponding to different measurement sensitivities. Emission position changing means for changing the emission position of the emitted coherent light.

(2) In the grazing incidence interferometer of (1),
A plurality of the measurement light sources are arranged at predetermined positions so as to change the incident angle of the coherent light obliquely incident on the surface to be measured in accordance with different measurement sensitivities, and the emission position variable means is any one of the plurality of measurement light sources. Is a means for selectively turning on the light.

(3) In the grazing incidence interferometer of (1),
The emission position changing means includes a moving means for moving the measurement light source.

(4) In the grazing incidence interferometer of (3),
Further, it is characterized by comprising a selection means for selecting the measurement sensitivity, and a movement control means for controlling the driving of the movement means based on a selection signal from the selection means.

(5) In the grazing incidence interferometer of (1) to (4), the measurement light source is a semiconductor laser.

(6) Coherent light emitted from the measurement light source is obliquely incident on the surface to be measured, and interferes with reflected light reflected from the measured surface and reflected light of the coherent light reflected on the reference surface. In a grazing incidence interferometer for obtaining fringes, a plurality of measurement light sources arranged at predetermined positions to change the incident angle of coherent light obliquely incident on a surface to be measured in accordance with different measurement sensitivities, and the plurality of measurement sources Selecting means for selecting the measurement sensitivity by selectively turning on one of the light sources.

(7) In the grazing incidence interferometer of (6),
The measurement light source is a semiconductor laser.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a schematic configuration of an oblique incidence interferometer according to the present invention.

Reference numeral 10 denotes a light source unit in which a laser light source for emitting coherent light is disposed. The light source unit 10 has a light source 5 so that the angle of incidence on the measurement surface 30a of the DUT 30 can be changed to switch the measurement sensitivity. Two laser light sources 11a to 11e are arranged (this arrangement will be described later). As the laser light sources 11a to 11e, semiconductor lasers (hereinafter, referred to as LDs) that emit red light having a wavelength of 655 nm are used to save the arrangement space. LD11a ~
11e is selectively turned on by the drive control of the control unit 20 by operating the sensitivity switching switch 21a of the control panel 21. Measurement sensitivity is 1 to
5 μm can be changed every 1 μm.

A laser beam emitted from one of the LDs 11a to 11e is converted into a parallel light beam by a collimating lens 12 which is fixed and then enters a prism 13. The light beam incident on the prism 13 is separated into a light beam reflected from the reference surface 13a and a light beam transmitted through the prism 13 and obliquely incident on the measurement surface 30a. The light beam reflected by the reference surface 13a and the light beam reflected by the measurement surface 30a cause an interference phenomenon, which is projected on the screen 14. The interference fringe projected on the screen 14 is captured by the television camera 16 via the field lens 15, and an output signal thereof is input to the image processing device 22. The image processing device 22 performs predetermined image processing on the input image, and measures the state of unevenness of the measurement surface 30a. Reference numeral 23 denotes a monitor on which an interference fringe image captured by the television camera 16 and a measurement result are displayed.
Reference numeral 31 denotes a mounting table for the object 30 to be measured.

Next, an LD 11 for changing the measurement sensitivity is used.
The arrangement of a to 11e will be described. In the grazing incidence interferometer, the measurement sensitivity S indicating how much one interference fringe corresponds to the height difference of the surface to be measured is determined by the normal to the prism reference surface and the prism as shown in FIG. Assuming that the angle between the emitted light and the emitted light is θ, S = λ / 2COSθ. Here, if λ = 655 nm, S = θ = 70.9 °
= 1.0 μm. Similarly, S = 2.0 μm at θ = 80.6 °,
S = 3.0 μm at θ = 83.7 °, S = 4.00 μ at θ = 85.3 °
When m and θ = 86.2 °, S = 5.0 μm.

Therefore, each of the LDs 11a to 11e may be designed and arranged so that the emitted light beam enters the measurement surface 30a via the collimating lens 12 and the prism 13 at the above-mentioned incident angle.

If the focal length of the collimating lens 12 is set short, the intervals at which the LDs are to be arranged become narrow, and the LD packages interfere with each other, making it difficult to arrange them on a line for obtaining the desired sensitivity. There are cases. In this case, the LDs 11a to 11e may be staggered as shown in FIG. 3 (FIG. 3 is a diagram of the LDs 11a to 11e viewed from the direction of the collimating lens 12).
Although the measurement sensitivity depends on the angle θ at which the light beam emitted from the prism reference surface enters the measurement surface, such an arrangement is also possible because the light beam does not need to be within the paper plane of FIG. 1 or FIG.

To change the measurement sensitivity, a desired measurement sensitivity is selected by a switch 21a on the control panel 21. The control unit 20 drives one of the LDs 11a to 11e of the light source unit 10 to light up in response to the input of the selection signal by the switch 21a. The measurement sensitivity can be changed immediately only by the electric lighting drive of the LD. In addition, since there is no mechanical movable part, there is little fear of a decrease in measurement accuracy and a failure due to an angle shift.

When the LD is turned on, an interference fringe having a desired measurement sensitivity is projected on the screen 14 by the light beam reflected by the reference surface 13a and the light beam reflected by the measurement surface 30a.
The interference fringes are captured by the television camera 16 and input to the image processing device 22. The image processing device 22 performs a predetermined image analysis on the captured image data. Further, since the information on the measurement sensitivity selected by the switch 21a is input to the image processing device 22 via the control unit 20, the measurement surface 30 is determined based on the result of the image analysis and the information on the measurement sensitivity.
The measurement result of the flatness a is calculated.

In the embodiment described above, a plurality of light sources are provided. However, as shown in FIG. 4 (the same elements as those in the previous embodiment are denoted by the same reference numerals), one LD 11 is used. Then, by moving the position by the moving device 40, the emission position of the laser light emitted from the LD 11 may be changed, and the incident angle of the laser light obliquely incident on the measurement surface 30a may be changed. The control unit 20 drives the moving device 40 according to a sensitivity change signal from the control panel 21, and moves the LD 11 to a position corresponding to the sensitivity. In this case, the measurement sensitivity can be continuously varied.

In this embodiment, the movable mechanism for changing the measurement sensitivity only needs to move the light source, and the use of a small LD as the light source does not require the mechanism to be large, so that a large measurement can be performed. It can be configured inexpensively for the surface.

[0025]

As described above, according to the present invention,
The mechanism for switching the measurement sensitivity can be simplified and a large measurement surface can be inexpensively handled.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of an oblique incidence interferometer according to the present invention.

FIG. 2 is a diagram illustrating an incident angle of light obliquely incident on a surface to be measured in accordance with measurement sensitivity.

FIG. 3 is a diagram illustrating an example of an arrangement in a case where an interval at which light sources are to be arranged is small.

FIG. 4 is a diagram showing a modification of the present invention.

FIG. 5 is a diagram showing a mechanism for switching measurement sensitivity in a conventional grazing incidence interferometer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Light source part 11a-11b Laser light source 12 Collimating lens 13 Prism 13a Reference surface 14 Screen 15 Field lens 20 Control part 30 Object under test 30a Measurement surface

Claims (7)

[Claims] 1. A coherent light emitted from a measurement light source is obliquely incident on a surface to be measured, and interference fringes are formed by reflected light reflected from the surface to be measured and reflected light of the coherent light reflected from a reference surface. In a grazing incidence interferometer, a convex lens fixedly arranged to convert the coherent light emitted from the measurement light source into a substantially parallel light beam, and having a reference surface facing the surface to be measured,
An optical element that passes coherent light converted into a parallel light beam by the convex lens and impinges on the surface to be measured from an oblique direction, and changes an incident angle of coherent light obliquely incident on the surface to be measured in accordance with different measurement sensitivities. An oblique-incidence interferometer, comprising: an emission-position changing unit that changes an emission position of the coherent light emitted from the measurement light source. 2. A grazing incidence interferometer according to claim 1, wherein a plurality of said measuring light sources are arranged at predetermined positions so as to correspond to different measuring sensitivities and to change an incident angle of coherent light obliquely incident on a surface to be measured. The oblique incidence interferometer is characterized in that the emission position changing means selectively turns on any one of a plurality of measurement light sources. 3. The grazing incidence interferometer according to claim 1, wherein said emission position changing means includes a moving means for moving said measuring light source. 4. The grazing incidence interferometer according to claim 3, further comprising a selection unit for selecting a measurement sensitivity, and a movement control unit for controlling the driving of the movement unit based on a selection signal from the selection unit. A grazing incidence interferometer, characterized in that 5. The grazing incidence interferometer according to claim 1, wherein
The grazing incidence interferometer, wherein the measurement light source is a semiconductor laser. 6. Coherent light emitted from a measurement light source is obliquely incident on a surface to be measured, and interference fringes are formed by reflected light reflected from the surface to be measured and reflected light of the coherent light reflected from a reference surface. In a grazing incidence interferometer, a plurality of measurement light sources arranged at predetermined positions to change the incident angle of coherent light obliquely incident on the surface to be measured in accordance with different measurement sensitivities,
Selecting means for selecting measurement sensitivity by selectively turning on one of the plurality of measurement light sources. 7. The grazing incidence interferometer according to claim 6, wherein the measurement light source is a semiconductor laser.