JPS63122906A - Apparatus for measuring thickness of film - Google Patents

Abstract

PURPOSE:To accurately measure the thickness of a membrane of which the thickness is changing even when the initial thickness thereof is not known, by simultaneously projecting two measuring lights different in a wavelength to the surface having the membrane formed thereto at an incident angle larger than a Brewster angle. CONSTITUTION:A wafer 13 is placed between the electrodes 11, 12 in an etching chamber 10 to remove the membrane on the wafer 13. Further, two floodlight projectors 14, 14a oscillating laser beams 15, 15a different in wavelength respectively are arranged so that the beams 15, 15a are simultaneously incident to the membrane formed on the wafer 13 at an angle larger than a Brewster angle by a wavelength synthesizer 8. The light waves (P-component) vibrating within the incident surface of the reflected beams 16 from the membrane and the light waves (S-component) vibrating in the direction vertical to the incident surface are shifted by a predetermined value in a phase to each other. Further, a beam receiver 26 for detecting the generation of plasma in the chamber 10 is arranged. By this constitution, the reflected beams 16 being the components P, S are received by beam receivers 17, 17a and guided to a measuring operation means 22 to form an interference wave form and the absolute thickness of the membrane is measured by an operation part 25 using a predetermined formula and, further, by calculating the leading end width of a through, thickness irregularity can be measured.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) The present invention aims to minimize errors in the thickness of 8 io films formed on semiconductor substrates in order to improve yield. Because of this necessity, temporal thickness changes (hereinafter simply referred to as film thickness changes) of thin films during the etching process and thickness unevenness, which is spatial film thickness changes at specific locations, are measured. Therefore, film thickness has conventionally been measured using optical interference. In other words, monochromatic light (center wavelength λ0
), and at this time, the reflected light from the thin film is received, and the film thickness is determined from the amount of received light. Figure 12 is a diagram showing the light-receiving element with respect to the film thickness d, and this light-receiving element is calculated using the following formula (%) where n is the refractive index of the thin film, d is the film thickness, and 11 is the refraction angle inside the thin film. . In this way, the light-receiving element exhibits a sinusoidal change, and therefore, the film thickness and its temporal change can be determined from this periodicity. In addition, in FIG. 12, the amount of received light (Eri indicates the case where multiple reflections inside the thin film are not taken into account, and (more) indicates the case where multiple reflections are taken into consideration.

On the other hand, the thickness unevenness was measured using a device tK shown in FIG. That is, a laser beam (4) is outputted from a light projection device (1) consisting of a laser oscillator that oscillates a He-Ne laser beam to a thin film (3) formed on a substrate (2) at an irradiation angle θ, The reflected light (5) of the thin film (3) is received by a plurality of light receiving elements (6-1) to (6-1) arranged in parallel, and each electric signal corresponding to the amount of received light is sent through an amplifier (7) to a signal processing device ( The signal processing device (8) then determines the thickness unevenness from the difference in the amount of light received by each of the light receiving elements (6-1) to (6-11).

However, each of the above measurements has the following problems. That is, in measuring film thickness changes, the maximum or minimum value of the amount of received light is detected in order to determine the period of the amount of received light that changes sinusoidally. However, since the range of change in the signal near the maximum and minimum values is minute, if noise or the like is added, it becomes difficult to detect the maximum or minimum value.

In addition, in the measurement of thickness unevenness, multiple light receiving elements (6-1)
-(6-n) makes the entire apparatus complicated, and measurement accuracy decreases due to variations in sensitivity of each light-receiving element (6-1) to (6-fl).

Therefore, the applicant has filed an earlier application, Japanese Patent Application No. 60-1849.
No. 48 discloses an apparatus capable of detecting film thickness properties with strong noise resistance and a simple configuration.

However, this device uses optical interference to measure the film thickness, and counts the number of periods by converting one period of the detected interference signal into the film thickness. It was necessary to know the film thickness before deletion to an accuracy within one cycle.

(Problems to be Solved by the Invention) The present invention has been made based on the above-mentioned sentiment, and its purpose is to measure the thickness of a thin film whose thickness is changing without knowing the initial film thickness. An object of the present invention is to provide a highly accurate film thickness measuring device that can accurately measure film thickness.

[Structure of the invention]

(Means and effects for solving the problem) The present invention simultaneously projects two measuring beams of different wavelengths from a light projecting means onto a film surface on which a film is formed at an incident angle larger than a pre-star angle. Then, the reflected light on the film surface is received by a light receiving means and photoelectrically converted. Based on the electrical signal obtained, the phase difference between the reflected lights corresponding to each wavelength is determined, and the film thickness is detected based on this phase difference. It is a device.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a configuration diagram of a film thickness measuring device. In the same figure, the reference symbol is the etching chamber, and the electrode (lυ
, (Wafer (1al is placed between 13 and wafer 0
The top thin film is removed. (141, (14a) are projectors each consisting of a laser beam end with a wavelength of 21.1 times, and a laser oscillator that oscillates (15a), and these projectors α (14a) are also installed at a wavelength synthesizer ( 8)
At the same time, the laser beam (Is, (15a)) is incident on the thin film formed on the surface of the quefer at an angle larger than the Brister angle. A total reflection mirror (8a) that totally reflects the incident laser beam (15, l), and a beam splitter (8b) that combines the laser beam (15, l) from this total reflection mirror (8) and the laser beam (5). In other words, the second
As shown in the figure, if the refractive index in the atmosphere is nl, the refractive index of the thin film is n2, and the normal is K, then the incident angle of 50 is
- angle larger than star angle, that is, IQ = ms (n2
/nl) The above angles are, for example, 89° and 85°. Buri like this.

- If the incident angle is larger than the star angle, the reflected light (
Le is a light wave vibrating within the plane of incidence of the thin film as a P component, and a light wave vibrating perpendicular to this P component as an S component, and these P and S components are out of phase with each other by π. ing. a7), (17m) is a light receiver that receives each reflected wave of the P component and S component through a spectrometer (9) such as a prism or a diffraction grating, and outputs an electric signal according to the amount of received light. It is. These receivers (17), (17
An amplifier circuit a8° (181) is connected to the output terminal of 1), and a V/F conversion circuit (voltage-frequency conversion circuit) is connected to the output terminal of 1).
(11, (19), E10 conversion circuit (electrical-optical conversion circuit) (4), (20) are connected.

Therefore, the electrical signal output from the photoreceiver (1?), (17a) is converted into a frequency signal, then converted into an optical signal, propagated through the optical fiber 3υ, (21M), and measured by the calculation means (2). (2) It is now sent to rice fields. Measurement and calculation means for this
The pulse counter (to), (24a) is used to detect the light receiver (1).
7), (17) A digital signal corresponding to the amount of light received is taken in by the calculation unit (to) K.

On the other hand, on the side of the etching chamber 〇〇, there is some dirt inside a part of the etching chamber! A photoreceiver (1) is installed to detect the occurrence, and an amplifier circuit @ is installed at the output end of this photoreceiver section.
, ■/F conversion circuit (to), E10 conversion circuit and optical fiber (to) are connected to the O/E conversion circuit C11) of the measurement calculation means. And it is connected to the arithmetic unit (to) via the pulse counter (to).

Now, the calculation unit (2) obtains an interference waveform from the captured digital signal, and from this interference waveform determines either the absolute film thickness or the thickness unevenness of the portion of the thin film irradiated with the laser beam (15, (15a)). Or, it has a function to calculate and calculate both.Specifically, the absolute film thickness is calculated from the phase difference of the reflected light intensity 11.I corresponding to the wavelength λhλ, and the thickness unevenness is calculated from the width of the tip of the valley. .

Next, the operation of the apparatus configured as described above will be explained. Wavelength λ8 from the projector α. λ2 laser light QS,
(15a) is simultaneously irradiated onto the thin film of the wafer a at an angle larger than the pre-tooling angle.

Then, the reflected light (LL (16a)) has a phase shift of π between its P component and S component. Therefore, the light receiver αη, (17) is the reflected light branched at the spectrometer (9). (E!, (16Jl)) and outputs an electric signal according to the amount of received light.This electric signal is sent to the amplifier α
l, (18) is amplified to the optimal level and the next V
/F conversion circuit (Ll, (19) is converted into a frequency signal according to the voltage level and E10 conversion circuit (to), (2
0!1). Then, υ is converted into an optical signal and sent to an optical fiber.

(21j) and is input to the measurement calculation means Shie Tari. This measurement calculation means @, tH4 converts it into a voltage signal again by the O/E conversion circuit (c), (23), and further converts it into a digital signal according to the voltage level by the pulse counter (24a), and calculates it. On the other hand, the photoreceiver (e) detects the generation of plasma.In other words, in the etching chamber aQ, the etching process is performed twice on the same uniform bar (13).
During this time, gas exchange within the etching chamber 1 is performed. Therefore, the operation timing is determined by detecting plasma generation. The electrical signal output from this photoreceiver (c) is also sent to an amplifier circuit (5), a V/F conversion circuit (c), and E1.
It passes through the 0 conversion circuit Ω and the optical fiber (to) and is input to the measurement calculation means 4. The signal is then taken into the arithmetic unit (c) via the 0/E conversion circuit Gυ and the pulse counter 0.

Now, the calculation section (c) creates an interference waveform from the captured digital signal. In other words, this is the interference waveform Q shown in FIG. As described above, this interference waveform Q has a phase difference of π between the P component and the 8 components.

In other words, the P component shown in FIG. 4 and the S component shown in FIG. 5 are combined. In addition, in Figure 3, Q
o is the interference waveform of the laser beam (to) (15 m) with an incident angle of "Oo". However, in the arithmetic unit (c), the wavelength λ
1. The reflected light intensities I, , I, respectively corresponding to the λ gooses are calculated. Then, calculate the absolute film thickness using the following formula (■)
(See Figure 6).

By the way, in general, the reflected light intensity when a light beam of wavelength λ is incident on a thin film at an incident angle of 10 is expressed by the following equation (2).

Engineering wf surprise (1+r−鴎ψ)...■ However, the phase ψ is expressed by the following formula (■).

tp = 2rr (2n cxs ih/λ-N)
...■ Here, r is the reflectance from the thin film, i is the refraction angle of the thin film, N is a positive integer, r is the visibility of interference fringes, and ln is the refractive index of the thin film. When considering the above formula 〇 as a function of film thickness, only N becomes an unknown quantity. Therefore, the wavelength λ1.
The phase difference ψ1. When calculating ψ snow, it becomes as shown in the following formula ■.

Here, the wavelength λ1. If you choose λ Snow, you can get the previous two.

Generally, the wavelength λ8. The optimal value for is ψ1-ψ, = π, where 11-I is maximum near the film thickness to be measured. By the way, Fig. 7 shows the case where the incident angle i is 89°.
8i0 on υ. It shows the relationship between g thickness and reflected light intensity. As this figure shows, when the film thickness is O, the phases are the same even if the wavelengths are different. Furthermore, as the film thickness increases, the phase difference between the two interference signals increases. This means that the phase difference or reflected light intensity 11. Using the difference of I,
This shows that the film thickness can be determined.

Next, thickness unevenness measurement will be explained. As shown in FIG. 8, when there is a thickness unevenness of ±Δd in the thin BI&(2), the phase difference for each thickness is calculated from the optical path difference of the laser beam according to the thickness unevenness d, which is the refractive index of the thin film "h", If we take the center wavelength of the laser beam as a reference, it shifts by n Δd (2) (11/λ.). Note that 11 is the refraction angle inside the thin film (c). Therefore, such reflected light When receiving the light, as shown in FIG. 9, an interference waveform with a valley tip width LS proportional to the thickness unevenness Δd·2 obtained by synthesizing the light of the phase of each thickness is obtained. Measure this valley tip width L8 to find the thickness unevenness.

Furthermore, when the thickness unevenness is continuous as shown in FIG. 10, the interference waveform becomes as shown in FIG. 11. In this case as well, the thickness unevenness can be determined by determining the valley tip @LS.

In this way, in the above-mentioned embodiment, the laser beam is irradiated onto the film surface with an incident angle equal to or greater than the Buri star angle, and the resulting reflected light α of the P component and the S component is
e is received to create an interference waveform, the absolute film thickness is measured using the previous formula (■), and the thickness unevenness is measured by finding the valley tip width LS. can be measured accurately without being affected by external noise. In particular, in this embodiment, two wavelengths λ1
．． Since the absolute film thickness is determined from the phase difference appearing in the interference waveform using λ2', there is no need to accurately determine the film thickness before thin film removal (etching).

Note that the present invention is not limited to the above-mentioned embodiment, and may be modified without departing from the spirit thereof. Although the above embodiment is applied to an etching and depositing apparatus for semiconductor manufacturing, it may also be applied to other thin film measurements.

〔Effect of the invention〕

As described in detail above, according to the present invention, it is possible to provide a highly accurate film thickness measuring device that can accurately measure film thickness with strong noise resistance and a simple configuration.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram showing an embodiment of the film/thickness measuring device according to the present invention, Fig. 2 is a diagram showing the laser beam incident angle, and Figs. 3 to 5 are P and S components of reflected light. 6 and 7 are explanatory diagrams of film thickness measurement, FIG. 8 is a diagram showing stepwise thickness unevenness, and FIG. 9 is an interference waveform of the thickness unevenness shown in FIG. 8. 10 is a diagram showing the thickness unevenness that changes continuously, FIG. 11 is a diagram showing the interference waveform of the thickness unevenness shown in FIG. 10, and FIGS. FIG. 3 is a diagram for explaining thickness unevenness measurement. αQ...Etching chamber, Housing 3...Wafer, (14), (14a)...Emitter, αη, (17a)...Receiver, bet, α8a)...
・Amplification circuit, ml, (19a)-V/F Km circuit,
U (20a) ・B10 Conversion circuit, C! υ, (2
1a)...Optical fiber, □□□...Measurement calculation means, (c), (23a)...0/E conversion circuit, (Foundation), (
24a)... Pulse counter, (c)... Arithmetic unit. Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 10

Claims (2)

[Claims] (1) A film thickness measuring device characterized by having the following configuration. (a) A light projecting means for projecting at least two measurement lights of different wavelengths onto the formed film at an incident angle larger than the Prewster's angle. (b) A light receiving means for receiving and photoelectrically converting reflected interference light of the measurement light projected onto the film for each of the wavelengths. (c) Phase difference calculating means for calculating the intensity of the reflected interference light for each of the wavelengths based on the electrical signal output from the light receiving means and calculating the intensity difference between the respective reflected interference lights. (d) Film thickness calculation means for calculating the film thickness of the film based on the intensity difference of the reflected interference light determined by the phase difference calculation means. (2) The film thickness measuring device according to claim 1, wherein the measuring light projected from the light projecting means consists of two wavelengths.