JPH02132308A - Depth measuring instrument - Google Patents

Abstract

PURPOSE:To prevent measuring light intensity from decreasing owing to the staining of a window through which the light enters/goes out provided to a chamber where a body to be measured is mounted by separating light from a light source into two linear polarized components which differ in frequency and guiding them to 1st and 2nd optical heterodyne interferometers. CONSTITUTION:The laser light from the laser oscillator 1 is made incident on a frequency shifter 3 and separated into the P-polarized light and S-polarized light, which are made incident on a beam splitter 4 as laser light having the two orthogonal linear polarized components differing in frequency. One of the light components which are separated here illuminates a position where the groove of the body (a) to be measured in the chamber 10 is being formed through an optical heterodyne interferometer 5 and the other illuminates a part where the groove of the body (a) to be measured is not formed through an optical heterodyne interferometer 7. The output signal of the optical heterodyne interferometer 7 is used as a reference signal for the output of the optical heterodyne interferometer 5 and an arithmetic part calculates their phase difference to measure the depth of the groove without being affected by the deviation in light intensity.

Description

Detailed Description of the Invention [Object of the Invention] (Industrial Application Field) The present invention relates to a depth measuring device for measuring the depth of a deep groove in an object to be measured.

(Prior Art) Conventionally, in the manufacturing process of semiconductor devices and the like, there has been a process such as dry etching in which a wiring pattern or an element pattern is etched using a resist as a mask. In some cases, such as through-hole formation, etching is performed in two stages, and it has become necessary to monitor the end point of etching in such a process. For this purpose, a device for measuring depth is being developed.

Such a technique is basically as shown in FIG. The object to be measured is irradiated with light of a predetermined wavelength, the reflected light of the irradiated light is received, and the intensity of the light is detected. At this time, interference occurs between the light reflected from the surface of the object to be measured and the light reflected from the bottom surface of the etched groove, and as shown in the graph of Fig. 5, the light intensity of the reflected light increases at the depth of the groove. A peak is detected every time the depth becomes a positive multiple of λ/2 of the irradiated light. The depth of the groove can be detected by calculating the number of times the light intensity peaks.

Further, as another method, a method of detecting diffracted light instead of reflected light as disclosed in Japanese Patent Laid-Open No. 60-86833 has been considered. This measures the depth when the light intensity of the diffracted light from the groove portion and the diffracted light from a portion other than the groove portion become approximately the same.

(Problem to be Solved by the Invention) In the above-described means, since the object to be measured is placed in a chamber for etching, a measurement light input/output interface is provided in the chamber to take in the irradiation light. Substances generated during the etching process adhered to the windows for use, causing problems such as lowering the measurement strength.

The present invention provides a depth change measuring device that solves these problems.

[Structure of the Invention] (Means for Solving the Problems) A light source that emits monochromatic light, a frequency shifter that separates the light emitted from the light source into two mutually orthogonal linearly polarized components with different frequencies, and outputs the separated light components. A first optical heterodyne interferometer that irradiates the light whose frequency has been shifted by the frequency shifter to a predetermined part of the object to be measured where deep grooves are being formed and interferes with the reflected light flux; A second optical heterodyne interferometer that irradiates light onto a predetermined part of the measurement object that does not form a deep groove and interferes with the reflected light flux, and a first optical heterodyne interferometer that transmits the output result of this second optical heterodyne interferometer. This depth measuring device is equipped with an arithmetic unit that outputs the output result as a reference signal and measures the depth of the groove from the phase change of this output result.

(Function) When the depth measuring device is configured as described above, the output of the second optical heterodyne interferometer is used as a reference signal and the phase difference between the output of the first optical heterodyne interferometer and the output of the first optical heterodyne interferometer is calculated. A depth measuring device that is not affected by changes in light intensity can be constructed. This also occurs when the light intensity of the reflected light or the entire reflected light from the object being measured decreases, but by taking the phase difference, the light intensity decreases when detected by an optical heterodyne interferometer with only one groove. This can eliminate false detection caused by

(Example) Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a configuration diagram showing the configuration of a depth measuring device according to this embodiment. A polarizing plate (2) and a frequency shifter (3) are provided on the optical axis of laser light emitted from a laser oscillator (1). The configuration of this frequency shifter (3) is shown in FIG. The laser light incident on the frequency shifter (8) is separated by a polarizing beam splitter (3a) and sent to Bragg cells (3b), . (3c). Bragg Cell (3
The laser beams incident on b) and (3c) are shifted to different frequencies and output. These two laser beams with different frequencies are Mira (ad) and (Be), respectively.
The beams are reflected by the polarizing beam splitter (3f), where they are combined and output.

A beam splitter (4) is arranged on the optical axis of the light beam emitted from the frequency shifter (3). The laser beam transmitted through this beam splitter (4) is arranged so as to be incident on the first optical heterodyne interferometer (5), and a mirror (
6), and a second optical heterodyne interferometer (8) is provided on the optical axis deflected by this.

This optical heterodyne interferometer (5). The configuration of (7) will be explained below. A polarizing beam splitter (5a
), (7a) and this polarizing beam splitter (5a
)． A mirror (5) that reflects the reference light transmitted through (7a) back to the polarizing beam splitter (5a) and (7a).
c) , (7c) and polarizing beam splitter (5a)
, (7a) and mirrors (5c), (7c).
/4 wavelength plates (5b) and (7b) are provided.

Also, a polarizing beam splitter (5a). (7a) On the optical axis of the measurement light reflected downward is a λ/4 wavelength plate (5d
)． (7d) is provided. Furthermore, a polarizing beam splitter (5a), (7a) that aligns the reference light and the measurement light on the same axis and emits them, and a polarizing plate (5e)
, (7e) Light amount detection element (5f). (7f) are sequentially provided on the optical axis.

These first and second optical heterodyne interferometers (5), (7
) is connected to an arithmetic unit (8) so as to be able to receive the detection outputs of the light quantity detection elements (5f) and (7f').

Furthermore, first and second optical heterodyne interferometers (5),
(7) At the bottom, there is a chamber (1o) of an etching device in which the object to be measured (a) is placed, and on the optical axis of the measurement light of the optical heterodyne interferometers (5) and (7) Measurement light input/output window (11-5), (11
-7) is provided.

The operation of this embodiment will be explained below.

The laser beam emitted from the laser oscillator (1) passes through the polarizing plate (2
), the predetermined polarization direction is unified, and the light is input to the frequency shifter (3).

The laser light incident on the frequency shifter (3) is separated into P polarization and S polarization by the polarization beam splitter (3a), and the laser light enters the frequency shifter (3) into P polarization and S polarization, respectively. ).

The laser beams incident on the Bragg cells (3b) and (Be) are respectively f, [fθ+f shifted by 2 minutes with respect to the original frequency fO, f. The frequency is +f2. These two laser beams with different frequencies are reflected by mirrors (3d) and (3e), respectively, and enter the polarizing beam splitter (3f), where they are combined and become two linear components of laser beam that are perpendicular to each other. is output.

The laser beam output from the frequency shifter (3) is incident on the beam splitter (4), where it is separated into two beams.

A beam splitter (one of the two separated beams)
4) is incident on the first optical heterodyne interferometer (5), and the laser beam reflected on the other beam splitter (4) is incident on the second optical heterodyne interferometer (7).

The laser beams incident on the first and second optical heterodyne interferometers (5) and (7) are polarized beam splitters (5), respectively.
a) + (7a), and the optical axis is separated into a reference phase light beam and a measurement light beam for each linearly polarized light component having a different frequency. The separated reference phase light flux is λ/
The four-wavelength plates (5b) and (7b) turn the light into circularly polarized light, which enters the mirrors (5c) and (7c).
The light reflected by (5c) and (7c) is again λ/
The light is converted into linearly polarized light by the four-wavelength plates (5b) and (7b), and re-enters the polarization beam splitters (5a) and (7a). This re-entering reference phase light flux is orthogonal to the polarization direction when it passes through the polarizing beam splitters (5a) and (7a), so the polarizing beam splitters (5a) and (7a)
a), (7a), and is reflected by the light amount detection element (5) above.
f) and (7f) via polarizing plates (5e) and (7e).

On the other hand, the measurement light beams separated by the beam splitters (5a) and (7a) are λ/4 wavelength plates (5d) and (6
d) into circularly polarized light and provided in the chamber (10) with a light beam for measurement (11-4), (11-8)
are transmitted through the chamber (10) and irradiated to predetermined positions of the object to be measured (a) in the chamber (10). The reflected light from this irradiation position is again used for measurement at the bay window (11-4), (11-6).
) and λ/4 wavelength plate (5d). (6d) and re-enters the polarizing beam splitters (5a) and (7a). The re-entering measurement light flux is polarized by the polarization beam splitter (5a), (7a) in the opposite direction to the reference phase light flux.
) and passes through the light amount detection element (5f). (H) Polarizing plate (
5e) and (7e). At this time, polarizing beam splitters (5a), (7a
) toward the light quantity detection elements (5f) and (7f), the reference phase light beam and the measurement light beam are lights having linearly polarized components orthogonal to each other, so they do not interfere with each other. Therefore, the polarization directions of the reference phase light beam and the measurement light beam are polarized in the coherent direction by passing through the polarizing plates (5e) and (7e), so that the reference phase light beam and the measurement light beam interfere with each other. The interfered light is detected by light amount detection elements (5f'), (7f)
receives light.

This light amount detection element (5f). The output result ('H') is sent as a beat signal, that is, a beat signal caused by the difference in frequency between the reference phase light beam and the measurement light beam. However, the measurement light beam of this first optical heterodyne interferometer (5) is irradiated onto the part of the object to be measured (a) where the groove is being formed, and the measurement beam of the second optical heterodyne interferometer (7) is The light beam is irradiated onto a portion of the object to be measured (a) where no groove is formed.

Here, to explain the above-mentioned operation in detail once again, the light beam having two mutually orthogonal linearly polarized components with different frequencies outputted from the frequency shifter (3) is divided into two, and the first and second optical heterodyne interference is performed. This leads to totals (5) and (7). At this time, as shown in Figure 3, the object to be measured (a)
The complex amplitude of the light reflected from the surface of the groove is U1, the complex amplitude of the light reflected from the bottom of the groove is U2, and the mirror (
5c), the complex amplitude of the light reflected from (7c) is U3, A1, A1, A3 is the amplitude of each luminous flux, Φ1
, Φ2, Φ3 are the same phase, d is the depth of the groove, k==2π
/λ, t is time, U2, U2, U3 are respectively U + − A Iexp(2 π(fo + f2
)t+δ1), U2−A2exp(2yr
(f'o +f2)t+(δ, +2kd)), U
s = A3exp (2 yt (f'o + l', )
t+δ3). Here, since the light received by the light amount detection element (7f) is the reflected light from the surface of the object to be measured (a) and the reflected light from the mirror (7c), the output result of the light amount detection element (7r) is is, 1+ =lU+ +Ua l2 =A, 2 +Al2 + 2 AH A3 cos(2 yr (r2
+f1)t+Φ1)...(1) It can be expressed by the following equation. (However, Φ1-δ1-δ3) This (1
) is shown in the graph of FIG. 3(a) with time on the horizontal axis and light intensity on the vertical axis.

Next, the light received by the light amount detection element (5f) is composed of the reflected light from the surface of the object to be measured (a) and the groove bottom, and the reflected light from the mirror (5f).
c), so the light amount detection element (5f)
The output result is 12 − l Ul +U2 +LJ3 12==A
, '2 +A2 2 +A9 2+2 AH A2
cos (Φ2) + 2 AIA3 cos (2 yr (f2 + f1
)t10Φ1)+2 A2 A3 cos(2π(
h + [1)t10Φ3)...(2). (However, Φ2-2kd, Φ3-δ1-δ3+
It is 2kd. ) The arithmetic unit (8) receives this output result. The depth d of the groove to be determined here can be calculated by determining the phase Φ3, since the phase Φ3 can be expressed as δ1-δ3+2kd. Therefore, take the difference between equation (2) and equation (1).

I, -I2 = A1 2+2AI A2 cos(Φ2)+2 A
2 A3 cos(2 yr (f2 +('+)t
+Φ3)...(3) This equation (3) is shown in FIG. 3(b) similarly to equation (1).

Since Φ3-Φ, +2kd from equation (2), the depth d can be calculated by finding (Φ3-ΦI) with a phase meter.

The depth at a certain moment can be calculated using the above method. In order to measure the change in depth that changes moment by moment due to etching, it can be calculated by determining the change in phase at any time as shown in FIG. 3(e). Here, the phase 2π is a change in wavelength λ/2, and by calculating the number of phases, the change in depth can be easily determined.

[Effects of the invention] By configuring the depth measuring device as described above, even if there are fluctuations in A and A2 in equation (3) due to dirt on the measurement light input/output window of the chamber, only the phase component can be calculated. As a result, stable measurements can be made without affecting the depth measurement.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the depth measuring device of the present invention, FIG. 2 is a block diagram of a frequency shifter, and FIG.
The figure is also a graph for explaining the depth measurement principle of the present invention, FIG. 4 is an explanatory diagram for showing the depth measurement principle of the prior art, and FIG. 5 is a graph. 1... Laser oscillator, 2... Polarizing plate, 3...
Frequency shifter, 3a...Polarizing beam splitter, 3b, 3c...
... Bragg cell, ad, Be... Mirror 3f... Polarizing beam splitter, 4... Beam splitter, 6... Mirror 5... First optical heterodyne interferometer, 7... Third No. 2 optical heterodyne interferometer, 5a, 7a...Polarizing beam splitter, 5c, 7
c...Mirrors 5b, 7b...λ/4 wavelength plate, 5d, 7d...λ/4 wavelength plate, 5e. 7e... Polarizing plate, 5f, 7f... Light amount detection element, 8... Arithmetic unit.

Claims (1)

[Claims] In a depth measuring device that measures the depth of deep grooves in an object being formed, a light source emits monochromatic light and the light emitted from this light source is divided into two mutually orthogonal linearly polarized lights with different frequencies. A frequency shifter that separates and outputs the components; and a first optical heterodyne interferometer that irradiates the light whose frequency has been shifted by the frequency shifter to a predetermined part of the object to be measured where a deep groove is being formed and causes the reflected light flux to interfere with each other. and a second optical heterodyne interferometer that irradiates light whose frequency has been shifted by the frequency shifter to a predetermined part of the object to be measured that does not form a deep groove and interferes with the reflected light beam, and this second optical heterodyne interference. a calculation section that outputs the output result of the meter as a reference signal for the output result of the first optical heterodyne interferometer, and measures the depth of the groove from the phase change of this output result. measuring device.