JP2010008328A - Optical inteterferometer and film thickness measuring method using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical interferometer capable of positioning by simply moving an interference optical system and measuring a film thickness quickly and accurately, and a film thickness measurement method using the same.
A light beam emitted from a light source 11 having a narrow wavelength band having a narrow wavelength spectrum enters a light beam splitting / combining unit 31 through a light beam branching unit 20, and the light beam in a reference optical path 30 is a reference mirror. The light beam reflected by 34 and incident on the light beam splitting / combining means 31 and split into the measurement optical path 50 is reflected on the surface of the test object 60 and incident on the light beam splitting / combining means 31. The luminous flux of the reference optical path 30 and the luminous flux of the measurement optical path 50 are synthesized, and the synthesized luminous flux enters the photoelectric conversion means 70 through the luminous flux branching means 20.
[Selection] Figure 1

Description

  The present invention relates to an optical interferometer that measures the thickness of a test object by detecting an optical path difference and a film thickness measuring method using the same.

  Conventionally, a first optical system for generating an optical path difference in light from a white light source, and a second optical system for detecting an optical path difference of light from the first optical system, The second optical system includes a branching unit that splits the light into two and a light detection device for detecting an interference fringe generated by the light from the branching unit, so that a moving device for the movable mirror and There are white light interferometers that do not require a displacement measuring device. (Patent Document 1).

  The case where the film thickness of a thin film etc. is measured with such a conventional white light interferometer structure will be described. As shown in FIG. 9A, the white light interferometer 100 converts the light from a low-coherence light source, for example, the white light source 101 into parallel rays by a collimator lens 102, and converts the parallel light into a first beam splitter 103. And is split into two lights by the second beam splitter 104. The object light that is the first light is collected by the objective lens 105, then reflected by the surface 106a of the sample 106, converted into parallel rays by the objective lens 105, returned to the second beam splitter 104, and the second light. The reference light is collected by an equivalent lens 107 equivalent to the objective lens 105, reflected by the mirror 108, and then returned to the second beam splitter 104. Thereafter, the first and second lights pass through the first beam splitter 103 and enter the CCD camera 109.

  Then, the stage 100a of the white light interferometer 100 is arranged so that the focal position of the object light as the first light by the objective lens 105 coincides with the surface 106a of the sample 106, and the second beam splitter 104 and the surface of the sample 106 are arranged. The mirror 108 is arranged such that the optical path length between the optical path 106a and the optical path length between the second beam splitter 104 and the mirror 108 are the same, and the focal position of the equivalent lens 107 coincides with the surface of the mirror 108. With such an arrangement, the interference fringes are detected in the CCD camera 109.

  Next, as illustrated in FIG. 9B, the stage 100 a of the white light interferometer 100 is moved by a distance A, and the focal position of the object light that is the first light is matched with the back surface 106 b of the sample 106. Then, in order to make the conditions on the optical path uniform, an optical path compensator 110 having the same refractive index as that of the sample 106 and having a known thickness is inserted between the equivalent lens 107 and the mirror 108. In this state, the mirror 108 is moved so that the distance from the second beam splitter 104 to the mirror 108 is the distance C from the distance B (see FIG. 9A), and the focal position of the equivalent lens 107 is that of the mirror 108. By arranging so as to coincide with the surface, the CCD camera 109 detects interference fringes.

Then, the thickness of the sample 106 can be obtained from the known refractive index and thickness of the optical path compensator 110 and the moving distance of the mirror 108 when the interference fringes are detected.
JP-A-8-52749

  However, in such a conventional white light interferometer 100, in order to measure the interference fringes with respect to the back surface 106b of the sample 106, (1) a structure in which the optical path compensation plate 110 can be inserted and removed after the front side measurement and (2) a mirror A structure that enables the position 108 to be moved precisely is required, and micro-vibration or the like during insertion of the optical path compensation plate 110 or movement of the mirror 108 has been a problem.

  Moreover, it was difficult to measure a thick transparent body film thickness of 100 μm or more in the order of nm.

  The present invention has been made in view of such problems of the prior art, and its object is to move the interference optical system without requiring a structure in which an optical path compensator can be inserted and a structure for moving the position of a mirror. It is an object to provide an optical interferometer that can perform positioning and measure the film thickness quickly and accurately, and a film thickness measurement method using the same.

  The optical interferometer of the present invention solves the above-described problem, and electrically converts the light intensity of a light beam, an interference optical system movable along the optical path between the light source and the test object, and the light intensity of the light beam. Photoelectric conversion means for converting the signal and light flux branching that guides the light flux from the light source to the interference optical system side and guides the light flux from the interference optical system side to the photoelectric conversion means side in a direction different from the light source The light source comprises a narrow wavelength band light source having a narrow wavelength band with a narrow wavelength spectrum, and the interference optical system comprises a beam splitting and synthesizing means and a reference mirror, The emitted light beam enters the light beam splitting and synthesizing unit through the light beam branching unit, and is divided into a reference optical path and a measurement optical path, and the light beam in the reference optical path is reflected by the reference mirror, and is transmitted from the reference mirror side. Incident on the beam splitting and combining means, The light beam split into the measurement optical path by the bundle splitting and synthesizing unit is reflected by the surface of the test object, is incident on the light beam splitting and synthesizing unit from the test object side, and the light beam splitting and synthesizing unit performs the reference optical path. And the measurement light path are combined, and the combined light beam is incident on the photoelectric conversion means via the light beam branching means.

  Furthermore, in the film thickness measurement method using the optical interferometer of the present invention, the optical path length of the measurement optical path that reflects the interference optical system on one surface of the test object, and the reflection on the surface of the reference mirror The optical path of the measurement optical path is arranged so that the optical path length of the reference optical path matches and the photoelectric conversion means can observe interference fringes, and then the interference optical system is reflected by another surface of the test object. The optical path length of the reference optical path reflected by the surface of the reference mirror matches, and the photoelectric conversion means moves so that interference fringes can be observed, and from the moving distance from one surface of the test object It is characterized in that the film thickness up to one other surface is measured.

  According to the present invention, it is possible to quickly and accurately measure the film thickness only by moving the interference optical system without requiring a structure in which the optical path compensation plate can be inserted and removed and a structure for moving the position of the mirror. Moreover, a thick transparent body film thickness of 100 μm or more can be measured on the order of nm.

  Embodiments of an object thickness measuring apparatus according to the present invention will be described below with reference to the drawings. FIG. 1 shows an optical interferometer 1 of the present embodiment.

  The optical interferometer 1 of this embodiment has a parallel beam converting means 10 for converting a light beam from a light source 11 in a narrow wavelength band having a narrow wavelength spectrum into a parallel beam, and the parallel beam is used as an example of a beam branching unit. The light beam is reflected by the light beam splitting beam splitter 20 and is applied to the reference optical path 30 and the measurement optical path 50 by the interference optical system 2 that can move along the optical path in the optical path between the light source 11 and the sample 60 as an example of the test object. Branch. Thereafter, the branched light is reflected, passes through the light beam splitting beam splitter 20, and enters a CCD camera 70 as an example of photoelectric conversion means.

  The collimated light beam means 10 includes a light source 11, a condensing lens 12, a pinhole 13, a collimating lens 14, and a light beam limiting means 15, and the light from the light source 11 is collected by the condensing lens 12, Point light source. Thereafter, the collimating lens 14 converts the light into parallel rays, and the light ray restricting means 15 restricts the light ray frame.

  In the present embodiment, as the light source of the optical interferometer 1, as shown in FIG. 2, a light source having an isolated excitation level as shown in FIG. 3 in a narrow wavelength band having a half width of about 10 nm or less is used. .

  Specifically, a phosphor, a sodium lamp, a mercury lamp, or the like may be applied as the light source. In particular, as the phosphor as an example of the light source, trivalent europium is preferable. As shown in FIG. 4, trivalent europium has a center wavelength: about 612 mm, a half-value width: about 4 nm, and a coherence length: about 70 μm. Furthermore, spatial coherence may be adjusted using a lens or the like.

  Next, the light from the collimating means 10 is reflected by the light beam splitting beam splitter 20 and enters the interference optical system 2. The light beam in the interference optical system 2 is divided into a first reference optical path 30 and a measurement optical path 50.

  The first reference optical path 30 includes a beam splitter 31, an objective lens 33, and a reference mirror 34 as an example of a beam splitting / combining unit. Further, the measurement optical path 50 has a measurement objective lens 51.

  The objective lens 33 preferably has the same configuration as the measurement objective lens 51. The objective lens 33 and the measurement objective lens 51 may not be particularly used.

  The light beam incident on the interference optical system 2 is first split into two light beams of the reference optical path 30 and the measurement optical path 50 by the beam splitter 31.

  The light beam in the measurement light path 50 and the light beam in the reference light path 30 divided by the beam splitter 31 are incident on the objective lens 33, collected, and reflected by the surface of the reference mirror 34. After reflection, the light is incident on the objective lens 33 to be converted into parallel light, and is incident on the CCD camera 70 through the optical path compensation beam splitter 32, the beam splitter 31, and the beam splitting beam splitter 20.

  The light beam in the measurement optical path 50 is collected by the measurement objective lens 51 and reflected by the front surface 60a as the first surface or the back surface 60b as the second surface of the sample 60. After reflection, the light beam in the measurement optical path 50 is incident on the CCD camera 70 through the measurement objective lens 51, the beam splitter 31, and the light beam branching beam splitter 20.

  Accordingly, each light beam is combined in the beam splitter 31 with the light beam in the reference optical path 30 and the light beam in the measurement optical path 50, and enters the CCD camera 70 through the light beam splitting beam splitter 20.

  The operation of the phosphor interferometer 1 will be described.

  First, in the interference optical system 2, the optical path length of the measurement optical path 50 reflected from the surface 60a of the sample 60 and the optical path length of the reference optical path 30 reflected from the surface of the reference mirror 34 coincide, and interference fringes are observed by the CCD camera 70. Move along the light path as you can.

  Next, as shown in FIG. 5, in the interference optical system 2, the optical path length of the measurement optical path 50 reflected by the back surface 60b of the sample 60 and the optical path length of the reference optical path 30 reflected by the surface of the reference mirror 34 match. The CCD camera 70 is moved along the optical path so that interference fringes can be observed.

  At this time, the thickness d of the sample 60 can be calculated from the moving distance L of the interference optical system 2 and measured by the following equation (1). Here, n is a refractive index.

d = nL (1)
In addition, you may obtain | require by the table etc. which put together the relationship between a refractive index and a movement distance, and the thickness of the sample 60 previously, without calculating.

  Thus, the optical interferometer 1 of the present embodiment does not require a structure for moving the mirror position and a structure for moving the mirror position so that the optical path compensation plate can be inserted and removed, and only moves the interference optical system 2. Thus, the thickness of the sample 60 can be measured quickly and accurately.

  FIG. 6 shows a case where a second sample 80 having two layers having different refractive indexes is applied as the sample of the optical interferometer 1 of the present embodiment.

  Also in this case, first, in the interference optical system 2, the optical path length of the measurement optical path 50 reflected by the surface 80a of the sample 80 and the optical path length of the reference optical path 30 reflected by the surface of the reference mirror 34 coincide with each other. At 70, the light is moved along the optical path so that the interference fringes can be observed.

  Next, as shown in FIG. 7, in the interference optical system 2, the optical path length of the measurement optical path 50 reflected by the back surface 80b of the sample 80 matches the optical path length of the reference optical path 30 reflected by the surface of the reference mirror 34. The CCD camera 70 is moved along the optical path so that the interference fringes can be observed.

  Thereby, the thickness d of the sample 80 can be calculated from the moving distance of the interference optical system 2 and measured.

  Further, as shown in FIG. 8, the optical path length of the measurement optical path 50 reflected from the boundary surface 80 c of the sample 80 is matched with the optical path length of the reference optical path 30 reflected from the surface of the reference mirror 34. By moving along the optical path so that the interference fringes can be observed with the CCD camera 70, the movement distance of the interference optical system 2 from the time of measuring the front surface 80a of the sample 80 and the interference optical system from the time of measuring the back surface 80b of the sample 80. From the moving distance of 2, the thickness d1 of the first layer and the thickness d2 of the second layer of the sample 80 can be calculated and measured.

  In addition, the sample is not limited to two layers, and it is possible to measure even more layers.

It is a figure which shows the time of the surface measurement of the sample by the object thickness measuring apparatus of this embodiment. It is a figure which shows the relationship between the wavelength of the light source of this embodiment, and light intensity. It is a figure which shows the energy level of the light source of this embodiment. It is a figure which shows the relationship between the wavelength of trivalent europium as an example of a light source, and light intensity. It is a figure which shows the time of the back surface measurement of the sample by the object thickness measuring apparatus of this embodiment. It is a figure which shows the time of the surface measurement of the two-layer sample by the object thickness measuring apparatus of this embodiment. It is a figure which shows the time of the back surface measurement of the two-layer sample by the object thickness measuring apparatus of this embodiment. It is a figure which shows the time of the interface measurement of the two-layer sample by the object thickness measuring apparatus of this embodiment. It is a figure which shows the prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Optical interferometer 2 ... Interference optical system 10 ... Parallel beam-forming means 11 ... Light source (narrow wavelength band light source)
DESCRIPTION OF SYMBOLS 12 ... Condensing lens 13 ... Pinhole 14 ... Collimating lens 15 ... Light beam limiting means 20 ... Beam splitting beam splitter (beam splitting means)
30: Reference optical path 31 ... Beam splitter (Flux splitting and combining means)
33 ... Objective lens 34 ... Reference mirror 50 ... Measurement optical path 51 ... Measurement objective lens 60, 80 ... Sample (test object)
70: CCD camera (photoelectric conversion means)

Claims (2)

A light source, an interference optical system movable along the optical path between the light source and the test object, photoelectric conversion means for converting the light intensity of the light beam into an electrical signal, and the light beam from the light source as the interference optical In an optical interferometer comprising: a light beam branching unit that guides the light beam from the interference optical system side to the photoelectric conversion unit side in a direction different from the light source,
The light source comprises a narrow wavelength band light source having a narrow wavelength band with a narrow wavelength spectrum,
The interference optical system includes a beam splitting and combining unit and a reference mirror,
The light beam emitted from the light source is incident on the light beam splitting and synthesizing unit through the light beam branching unit, and is divided into a reference optical path and a measurement optical path. The light beam in the reference optical path is reflected by the reference mirror, Incident on the beam splitting and combining means from the side,
The light beam divided into the measurement optical path by the light beam splitting and synthesizing means is
Reflected by the surface of the test object, incident on the beam splitting and combining means from the test object side,
The light beam splitting and combining unit combines the light beam of the reference optical path and the light beam of the measurement optical path,
The combined light beam is incident on the photoelectric conversion means through the light beam branching means. The optical path length of the measurement optical path that reflects the interference optical system on one surface of the test object coincides with the optical path length of the reference optical path that reflects on the surface of the reference mirror. Arranged so that can be observed,
Thereafter, the optical path length of the measurement optical path that reflects the interference optical system on the other surface of the test object matches the optical path length of the reference optical path that reflects on the surface of the reference mirror, and the photoelectric conversion Move so that interference fringes can be observed by means,
2. The film thickness measurement method using an optical interferometer according to claim 1, wherein a film thickness from one surface of the test object to another surface is measured from the moving distance.

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