KR100922142B1 - Apparatus for realtime film thickness monitoring using phase difference of polarized laser and the method thereof - Google Patents

Abstract

The present invention relates to a real-time film thickness monitoring apparatus and method using a phase difference of a polarizing laser that can accurately monitor the thickness of the coating film in the Angstrom (0.1 nm) unit in the vacuum coating device in real time with the coding thickness.

As a means for realizing this, the present invention provides a laser beam generating means; A first polarization beam splitter (PBS1) for separating the laser beam generated from the laser beam generating means into two polarizations (first polarization); A first non-polarization beam splitter (NPBS1) configured to form a second polarized light by collecting each polarized light having the optical path difference reflected by injecting the first polarized light into the reference sample and the measurement sample provided in the vacuum chamber, respectively; A first phase difference plate (QWP) for converting the second polarized light into circularly polarized light; A second non-polarization beam splitter (NPBS2) which separates the circularly polarized second polarization again; A second phase difference plate (HWP) for changing the phase of any polarization of the separated second polarized light; Second and third polarization beam splitters PBS2 and PBS3 for separating the other polarization of the second polarization and the polarization transmitted through the second phase difference plate HWP, respectively; And four photodetectors PD1 to PD4 for detecting four polarizations separated from the second and third polarization beam splitters PBS2 and PBS3, respectively.

Polarizing Beam Separator, Film Thickness Measurement, Non-Polarized Beam Separator, Photodetector, Retardation Plate

Description

Apparatus for realtime film thickness monitoring using phase difference of polarized laser and the method

The present invention relates to a real-time film thickness monitoring apparatus using the phase difference of the polarizing laser, in particular a polarizing laser that can accurately monitor the coding thickness in real time with the resolution of the Angstrom (0.1nm) unit of the thickness of the film being coated in the vacuum coating device The present invention relates to a real-time film thickness monitoring apparatus using a phase difference and a method thereof.

In general, in the semiconductor process, a dielectric film, a semiconductor film, a metal film, or the like is formed on a semiconductor substrate such as a semiconductor substrate or glass. As a typical method of forming the film, physical vapor deposition (PVD) such as vacuum evaporation or sputtering, chemical vapor deposition (CVD) using a raw material such as precursor, and the like are applied.

In particular, such a film has various factors in determining the film forming process and quality, but in recent years, since the film formed on the substrate is tending to be thin and multilayered in order to increase the integration degree of the semiconductor device, it is necessary to determine the quality of the semiconductor. The specific gravity which controls the film thickness became high.

In general, the thickness measuring method of a film which is widely used can be roughly classified into a mechanical method using a probe, a method using a microscope, and an optical method.

The mechanical measurement method using the probe is a device developed to measure the thickness of the film with a step on the substrate surface. The thickness of the step is detected by detecting the pressure that is changed by the step of the film surface as the probe scratches the substrate surface. How to measure. However, this method can easily obtain the thickness of the metal film as well as the organic film because the probe is in direct contact with the sample, there are the following problems.

First of all, contact with the probe causes destruction and contamination of the sample, the thickness measurement speed is slow, and there is a concern that measurement errors may occur depending on the subjectivity of the measurer. In addition, since only the thickness of the step can be obtained, not only can the thickness of several layers be measured at a time, but there is an inconvenience in that the step must be formed in advance in the place to be measured.

As a measuring method using a microscope, there is a method of measuring with a naked eye using a general optical microscope and a method of obtaining a very high magnification image using an electron microscope and measuring the thickness thereof. This method is widely used because it can visually check the cross section of the sample, but has the following problems.

Since the sample must be cut to measure the thickness, more time is required than the mechanical measuring method described above, and a processing technique for measuring the sample is required. In particular, this method has a disadvantage in that the thickness of the film cannot be measured in real time because the cross section is measured after the film is formed.

Finally, the optical measuring method is a method of measuring the thickness of the film by using the interference phenomenon by the reflected light at the surface of the film and the reflected light at the interface below. This method is not only superior in accuracy and measurement speed compared to the two methods described above, but also has recently been described in this optical measurement method because of its many advantages, such as the ability to measure thickness by mathematical calculations for multilayer film structures. This is mainstream, but has the following problems.

In the case of a measuring device using a short wavelength light source, it is impossible to measure thickness when the light source does not transmit such as metal, and even if the light source is incident perpendicularly to the sample, the thickness of the film whose wavelength is λ / 4 Only when coated, the film thickness can be accurately measured, and if the thickness of the film is changed, there is a problem that the wavelength λ of the light source should be changed accordingly.

The present invention has been made in view of this point, and overcomes the technical limitation of monitoring the thickness of the film only when the interference light disappears or constructive interference in the conventional optical interference technology, and particularly in the thickness of the coated film Real-time film using the retardation of the polarization laser that can not only significantly increase the measurement resolution of the angstrom (0.1 nm), but also measure the thickness of the film even when a material such as a metal, which has not been transmitted through the conventional light source, is coated. The present invention provides a thickness monitoring apparatus and method thereof.

As a means for realizing this, the present invention,

Laser beam generating means (10);

A first polarization beam splitter (PBS1) for separating the laser beam generated from the laser beam generating means (10) into two polarizations (first polarization);

A first non-polarization beam splitter (NPBS1) configured to form a second polarized light by collecting each polarized light having the optical path difference reflected by injecting the first polarized light into the reference sample and the measurement sample provided in the vacuum chamber, respectively;

A first phase difference plate (QWP) for converting the second polarized light into circularly polarized light;

A second non-polarization beam splitter (NPBS2) for separating the circularly polarized second polarization again;

A second phase difference plate (HWP) for changing the phase of any polarization of the separated second polarized light;

Second and third polarization beam splitters PBS2 and PBS3 for separating the other polarization of the second polarization and the polarization transmitted through the second phase difference plate HWP, respectively; And

And four photodetectors PD1 to PD4 for detecting four polarizations separated from the second and third polarization beam splitters PBS2 and PBS3, respectively.

In addition, the laser beam generating means 10 is characterized in that helium-neon laser generator for generating linear polarization (linear polarization).

In addition, the laser beam generating means 10 is characterized in that for scanning the laser beam to the first polarized beam splitter (PBS1) at a linear polarization angle of 45 °.

In addition, the first polarized light separated from the first polarized beam splitter PBS1 may be polarized light having a polarization angle of 0 ° and 90 °, respectively.

In addition, the first phase difference plate is characterized in that the QWP (Quater-Wave Plate).

In addition, the second phase difference plate is characterized in that the half-wave plate (HWP).

In addition, the four photodetectors PD1 to PD4 detect light having phase differences of 0 °, 90 °, 180 °, and 270 °, respectively.

On the other hand, the real-time film thickness monitoring method using the phase difference of the polarizing laser according to the present invention,

(A) generating a polarizing laser beam (S100);

(b) projecting a polarization laser beam at a linear polarization angle of 45 ° to separate the phase into polarized light having a phase of 0 ° and 90 °, respectively, to obtain a first polarized light (S200);

(c) scanning the respective beams of the first polarized light to the reference sample 110 and the measurement sample 120, combining the reflected beams having an arbitrary polarization angle by the path difference of the beams, and circularly polarizing the combined beams. Obtaining a second polarized light (S300);

(d) changing the phase of one of the circularly polarized second polarizations to 180 ° and projecting the beam and the remaining beams to the polarization beam splitter to obtain four beams (third polarization) (S400); And,

(e) calculating a thickness of the film by detecting signal strengths having different phase differences from the third polarized light (S500).

In addition, the polarizing laser beam generation step (S100) is characterized in that for generating a polarizing laser beam by using a helium-neon (He-Ne) laser.

In addition, the third polarized light has a phase difference of 0 °, 90 °, 180 °, and 270 °, respectively.

In particular, the monitoring method according to the invention is characterized in that the polarizing laser beam generation step (S100) ~ film thickness calculation step (e) is carried out in real time.

According to a preferred embodiment of the present invention, the following effects can be obtained.

1) Even if the coating of the film is in progress, the thickness of the film can be measured by the resolution of Angstrom (0.1 nm) thickness in real time.

2) By using the phase difference of the polarizing laser, it is possible to overcome the technical limitation that the thickness of the film can be measured only by extinction or constructive interference of interference light to use the conventional optical interference.

3) Unlike conventional methods of using optical interference, it is possible to measure a film such as metal.

Hereinafter, an embodiment according to the present invention will be described.

1 is a schematic diagram showing the configuration of a real-time film thickness monitoring apparatus using a phase difference of a polarizing laser according to the present invention. Here, reference numeral 100 denotes a vacuum chamber used in a production process such as a semiconductor film, 110 denotes a reference sample used as an uncoated semiconductor substrate, 120 denotes the same material as the reference sample, and the film is coated in real time. Each measurement sample which is made is shown. In addition, in Fig. 1, arrows indicated by solid lines indicate incident light and hidden arrows indicate reflected light, and other arrows indicate the flow of light, respectively.

According to the present invention, a linearly polarized laser beam is scanned on the reference sample 110 and the measurement sample 120, respectively, and the phase polarization is performed by dividing the reflected and recombined second polarized light into two, and then these reflected waves are transmitted through a polarization beam splitter. The thickness of the film was measured by calculating the intensity of the signal obtained through the photodetector.

In more detail, the present invention uses the phase difference of the reflected wave caused by the thickness of the film by scanning the laser beam on the reference sample 110 and the measurement sample 120. In the present invention, a laser beam generating means (10) is provided as a means for generating a laser beam, and the laser beam generating means (10) emits several milliwatts of visible light (632.8 nm) and uses interference in a laboratory. A helium-neon laser generator, a linear polarization laser device, is widely used for measurement, holography production, and the like.

The laser beam generated as described above is projected on the first polarization beam splitter PBS1 to enable incidence into the reference sample 110 and the measurement sample 120, respectively. The first polarized beam splitter PBS1 projects partly and partially reflects the phase according to the phase. In a preferred embodiment of the present invention, the first polarized beam splitter PBS1 is scanned by scanning a phase of the projected beam at 45 °. It is configured to transmit and reflect.

The first polarization beam splitter PBS1 separates two polarizations (first polarization) from the projected laser, and the separated first polarizations are scanned toward the reference sample 110 and the measurement sample 120, respectively. In a preferred embodiment of the present invention, the reference sample 110 and the measurement sample 120 is a vacuum chamber (100), more preferably a film (not shown) in the measurement sample 120 by a method such as current vacuum deposition, etc. It is preferable that it is the vacuum chamber 100 used at the film formation process currently being formed.

In addition, the first polarization beam splitter PBS1 includes a first mirror MR1 such that each polarization of the first polarization is scanned in a plane perpendicular to the reference sample 110 and the measurement sample 120, respectively. It is preferable.

The first polarized light having the optical path difference reflected by the reference sample 110 and the measurement sample 120 is again collected by the first polarization beam splitter PBS1, and the first polarized light at this time is an arbitrary polarization angle ( Φ). This first polarized light is projected onto the first non-polarization beam splitter NPBS1 and scanned on the first phase difference plate QWP. In this case, the first polarized light may be directly scanned on the first phase difference plate QWP, or may be scanned by being turned by MR2.

The first phase difference plate QWP forms a second polarization that is circular polarization while projecting the first polarization. In a preferred embodiment of the present invention, it is preferable that the first phase difference plate QWP uses a quater-wave plate (QWP) that changes the phase of the beam to be projected by λ / 4. That is, the first polarized light becomes a circularly polarized second polarized light with the phase change while passing through the first phase difference plate QWP.

The circularly polarized second polarization is projected onto the second non-polarization beam splitter NPBS2, and the second non-polarization beam splitter projects one of two beams from the second polarization on the second phase difference plate HWP. Here, the second phase difference plate HWP is preferably a half-wave plate (HWP) that converts the phase of the beam to be projected by λ / 2.

Therefore, one of the beams of the second polarization is converted back to the second phase difference plate HWP by λ / 2, so that the second polarization becomes a beam having phases of 0 ° and 180 °.

The second polarized light having the phase change causes each beam to be projected on the second polarized beam splitter PBS2 and the third polarized beam splitter PBS3, respectively. In a preferred embodiment of the present invention, it is preferred that the polarizing beam splitters PBS2 and PBS3 use splitting beams to have a phase difference of 90 °.

Accordingly, the second polarized light is projected onto the polarization beam splitters PBS2 and PBS3 and separated into beams having phases of 0 °, 90 °, 180 °, and 270 °. For example, a beam having a phase of 0 ° among the beams of the second polarized light is projected onto the second polarized beam splitter PBS2 and separated into beams having a phase of 0 ° and 90 °, respectively, and out of phase beams of the second polarized light. The 90 ° beam is projected onto the third polarization beam splitter PBS3 and separated into beams having phases of 90 ° and 270 °, respectively.

Finally, the configuration of the present invention includes four photodetectors PD1 to PD4 for measuring the intensity of the signal from beams having such different phases. When the photodetectors PD1 to PD4 measure signals with respect to four beams, the results of the following cosine or sine function can be obtained.

E1 = A1cosΦ + B1

E2 = A2cos (Φ + π / 2) + B2

E3 = A3cos (Φ + π) + B3

E4 = A4cos (Φ + 2π) + B4

Here, E1 to E4 each represent the intensity of light measured by four photodetectors, A1 to A4 each represent the amplitude of the optical signal, B1 to B4 each represent the background value of the optical signal, and λ and t are each a laser. For the wavelength and the coated film thickness, Φ represents the polarization angle, respectively. In addition, the values A1 to A4 and B1 to B4 can be obtained by using a conditional expression when t = 0.

2 is a graph showing a simulation result of measuring thickness using a real-time film thickness monitoring apparatus using the phase difference of the polarizing laser according to such a configuration.

Hereinafter, a real-time film thickness monitoring method using a phase difference of a polarizing laser according to the present invention will be described with reference to FIG. 3.

The real time monitoring method according to the present invention describes an example in the process of forming a film on a substrate such as a semiconductor substrate. As a preliminary work for this purpose, the reference chamber 110 of the same material as the substrate and the measurement sample 120 for coating the film on the substrate are provided in the vacuum chamber 100 for forming the film. In particular, these samples (110, 120) is preferably installed so as to be on the same line of the virtual, it is more preferable to configure so that the coating is made only on the measurement sample 120 when coating the film.

In this state, the polarization laser beam is scanned on the reference sample 110 and the measurement sample 120. First, a step of generating a polarized laser beam is performed (S100). In this case, a He-Ne laser is used to generate a polarized laser beam.

Subsequently, the first polarized light is obtained by projecting the polarized laser beam at a polarization angle of 45 ° (S200). In this case, the polarization laser beam is projected on the first polarization beam splitter PBS1, and the two beams are separated by polarization having phases of 0 ° and 90 °, respectively.

Next, the second polarized light is obtained by scanning the first polarized light on the reference sample 110 and the measurement sample 120 (S300). In this case, the two beams of the first polarized light are respectively scanned to the reference sample 110 and the measurement sample 120, and in particular, each beam scanned using the first mirror MR1 is parallel to the reference sample 110. Scan to be incident on the measurement sample (120). The second polarized light is generated by combining the reflected light of the beam thus scanned using the first polarized beam splitter PBS1, and the first polarized light has an arbitrary polarization angle due to the optical path difference between the two beams.

The combined first polarized light is projected onto the first phase difference plate QWP to obtain a second polarized light having circular polarization having a phase difference of π / 4.

As a next step, a phase of one beam of the second polarized light is changed to 180 ° to obtain a third polarized light (S400). The beams of the second polarized light and the third polarized light are respectively projected on the second polarized light beam splitter PBS2 and the third polarized light beam splitter PBS3 to obtain four beams (third polarized light), respectively.

In this case, the polarization beam splitters PBS2 and PBS3 have a phase difference of the emitted beams to be 90 °, so that the four beams of the third polarized light have phase differences of 0 °, 90 °, 180 °, and 270 °, respectively. desirable.

Of course, each of the polarizing beam splitters PBS2 and PBS3 may change the phase difference of the emitted beam to an arbitrary angle, but it is preferable to easily determine the change trend by the phase difference of 90 °.

Finally, the thickness of the film is calculated by calculating the intensity of the signal using the four beams of the third polarized light using the respective photodetectors PD1 to PD4 (S500).

At this time, the intensity of the signal is obtained as a result of a sine function or a cosine function as shown in FIG. In addition, a voltage difference may be obtained as an output signal from the photodetectors PD1 to PD4 and the thickness may be calculated using the difference.

Although the present invention has been described in connection with the above-mentioned preferred embodiments, it is possible to make various modifications or variations without departing from the spirit and scope of the invention. Accordingly, the appended claims will cover such modifications and variations as fall within the spirit of the invention.

1 is a schematic view showing the configuration of a real-time film thickness monitoring apparatus using a phase difference of a polarizing laser according to the present invention.

Figure 2 is a graph showing the results of measuring the thickness using a real-time film thickness monitoring device using the phase difference of the polarizing laser according to the present invention.

Figure 3 is a schematic diagram for explaining a real-time film thickness monitoring method using the phase difference of the polarizing laser according to the present invention.

<Explanation of symbols for the main parts of the drawings>

10: laser beam generating means

100: vacuum chamber

110: reference sample

120: measurement sample

HWP: Half-Wave Plate

MR1: first mirror

NPBS1: Non-Polarized Beam Splitter

NPBS2: second non-polarization beam splitter

PBS1: Polarized Beam Splitter

PBS2: second polarization beam splitter

PBS3: third polarization beam splitter

PD1 to PD4: First to fourth photodetectors

QWP: Quarter-Wave Plate

Claims (11)

Laser beam generating means (10); A first polarization beam splitter (PBS1) for separating the laser beam generated from the laser beam generating means (10) into two polarizations (first polarization); A first non-polarization beam splitter (NPBS1) configured to form a second polarized light by condensing each polarized light having an optical path difference reflected by incident the first polarized light into a reference sample and a measurement sample provided in the vacuum chamber; A first phase difference plate (QWP) for converting the second polarized light into circularly polarized light; A second non-polarization beam splitter (NPBS2) for separating the circularly polarized second polarization again; A second phase difference plate (HWP) for changing the phase of any polarization of the separated second polarized light; Second and third polarization beam splitters (PBS2, PBS3) for separating the other polarization of the second polarization and the polarization transmitted through the second phase difference plate (HWP), respectively; And Real-time film thickness using the phase difference of the polarizing laser, characterized in that it comprises four photodetectors (PD1 ~ PD4) for detecting four polarized light separated from the second and third polarized beam splitter (PBS2, PBS3), respectively. Monitoring device. The method of claim 1, The laser beam generating means 10 is a real-time film thickness monitoring apparatus using the phase difference of the polarizing laser, characterized in that the helium-neon laser generation to generate linearly polarized light. The method according to claim 1 or 2, The laser beam generating means 10 is a real-time film thickness monitoring apparatus using the phase difference of the polarizing laser, characterized in that for scanning the laser beam to the first polarization beam splitter (PBS1) at a linear polarization angle of 45 °. The method of claim 1, The first polarized light separated from the first polarized beam splitter (PBS1) is a real-time film thickness monitoring device using the phase difference of the polarizing laser, characterized in that the polarization having a polarization angle of 0 ° and 90 °, respectively. The method of claim 1, The first phase difference plate is a QWP (Quater-Wave Plate) characterized in that the real-time film thickness monitoring device using the phase difference of the polarizing laser. The method of claim 1, The second phase difference plate is a real-time film thickness monitoring device using a phase difference of the polarizing laser, characterized in that the half-wave plate (HWP). The method of claim 1, The four photo detectors (PD1 ~ PD4) is a real-time film thickness monitoring device using the phase difference of the polarizing laser, characterized in that for detecting the light having a phase difference of 0 °, 90 °, 180 °, 270 °, respectively. (A) generating a polarizing laser beam (S100); (b) projecting the polarization laser beam at a linear polarization angle of 45 ° to separate the phase into polarization having a phase of 0 ° and 90 °, respectively, to obtain a first polarized light (S200); (c) scanning the respective beams of the first polarized light to the reference sample 110 and the measurement sample 120, and combining the reflected beams with an arbitrary polarization angle by the path difference of the beams, and circularly polarizing the combined beams. To obtain a second polarized light (S300); (d) changing a phase of one beam among the circularly polarized second polarizations to 180 °, and projecting the beams and the remaining beams to a polarization beam splitter to obtain four beams (third polarizations) (S400); And, (e) detecting a signal intensity having a different phase difference from the third polarized light and calculating a thickness of the film (S500); and real-time film thickness monitoring method using the phase difference of the polarizing laser, comprising: a. The method of claim 8, The polarizing laser beam generation step (S100) is a real-time film thickness monitoring method using the phase difference of the polarizing laser, characterized in that for generating a polarizing laser beam using a helium-neon laser. The method of claim 8, wherein in the third polarization generation step (S400), The third polarization is a real-time film thickness monitoring method using the phase difference of the polarizing laser, characterized in that the phase difference is respectively 0 °, 90 °, 180 °, 270 °. The method according to any one of claims 8 to 10, The monitoring method is a real-time film thickness monitoring method using the phase difference of the polarizing laser, characterized in that to repeat the polarizing laser beam generation step (S100) ~ film thickness calculation step (S500) in real time.

Images