JPH06331320A - Film thickness measuring device - Google Patents

Abstract

PURPOSE:To measure the thickness of the film on the surface of a semiconductor wafer by simply positioning the film on the pattern to be measured provided on the surface of the semiconductor wafer with high accuracy. CONSTITUTION:A silicon wafer 17 wherein an SiO2 film 23 is formed on a silicon substrate 22 is irradiated with the light from a white light source and the positioning of a part to be measured is performed on the basis of the reflected light from the silicon wafer 17. At the time, the thickness of the SiO2 film is measured on the basis of the reflected light from the silicon wafer 17.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for measuring the film thickness of a thin film on the surface of a patterned semiconductor wafer, and in particular, it can accurately and simply position it at a specific measurement position on the pattern to measure the film thickness with good accuracy. Regarding the device.

[0002]

2. Description of the Related Art Conventionally, as an example of a film thickness measuring device, an optical method such as a method utilizing light interference or a spectral reflectance measuring method is known. For example, as a method utilizing light interference, there is known a method of measuring the film thickness of a thin film with a laser beam as disclosed in Japanese Patent Laid-Open No. 57-19607. FIG. 7 shows a schematic configuration diagram of the device.

In this figure, a semiconductor laser element 45, a lens 46, and a plane mirror 47 form a self-coupling type semiconductor laser 48. The plane mirror 47 faces the light emitted from the semiconductor laser element 45 at a right angle and has an appropriate reflectance, and a dielectric film 49 is formed on the surface thereof.

The light emitted from the semiconductor laser element 45 is reflected by the plane mirror 47 and returns to the light emitting portion of the semiconductor laser element 45 again. Since the light density in the active region of the semiconductor laser element 45 changes depending on the amount of light to be returned and the terminal voltage of the semiconductor laser element 45 changes, a change in the reflectance of the plane mirror 47 is detected as a change in the terminal voltage of the semiconductor laser element 45. it can.

By the way, when there is a dielectric film having a uniform thickness on a flat surface, the reflectance and the transmittance of this surface are a cycle determined by the wavelength of incident light and the refractive index of the film substance, It changes with changes in thickness. Therefore, the film thickness can be measured by detecting the change in the reflectance or the transmittance as the change in the light intensity. This is the principle of the film thickness measuring device utilizing the interference of light.

When the thickness of the dielectric film 49 changes as the dielectric film 49 is formed, the reflectance of the plane mirror 47 changes periodically.
Therefore, by disposing the dielectric film 49 on the plane mirror 47 by vapor deposition, the film thickness of the dielectric film 49 can be easily monitored by operating only the semiconductor laser element 45.

For example, when measuring a dielectric film 49 using a SiO ₂ thin film having a refractive index of about 1.5, if a GaAs crystal having a refractive index of about 3.6 is used for the plane mirror 47, the plane mirror 4
The refractive index of No. 7 changes periodically with the change of the film thickness of SiO ₂ in the range of 32 to 35%.

In addition, a method relating to the spectral reflectance measurement method is described in Japanese Patent Application No. 5-79819, which is our prior application. Further, as a commercially available film thickness measuring apparatus of a spectral reflectance measuring method, "Lambda Ace" series by Dainippon Screen Co., Ltd. and "Nanospec" series by Nanometrics Co., Ltd. are known. No conventional device including the above-described device has a film thickness measuring device and a measuring device positioning device integrated with each other.

[0009]

SUMMARY OF THE INVENTION In a conventional film thickness measuring device using an optical method including the above-mentioned device,
The following problems will occur. That is, in the conventional techniques such as the above technique, it is necessary to irradiate the measurement object with the measurement light in advance. However, when the object to be measured is the film thickness of the thin film on the circuit pattern on the surface of the semiconductor wafer, it is necessary to perform positioning with high accuracy,
In the prior art, the positioning device had to be configured separately. In fact, even with the above commercial products, the positioning device had to be purchased separately.

Specifically, such a positioning device optically enlarges an alignment mark formed on the surface of a semiconductor wafer with a microscope or the like, images it with a camera, and processes the imaged screen with an image processing device. Typically, the position of the alignment mark is calculated and the positioning table is driven based on the position information to position the semiconductor wafer.

The positioning device as described above has a complicated mechanism and is expensive. In addition, since the apparatus itself is huge, it has been very difficult to place it in a clean room where semiconductor wafers are mainly handled or to be built in a semiconductor wafer processing apparatus.

[0012]

The present invention has been made to solve the above-mentioned technical problems, and is a semiconductor wafer having a thin film and a wiring pattern forming portion on a substrate. In the film thickness measuring device for irradiating the measuring light to, and measuring the film thickness of the thin film based on the reflected light from the semiconductor wafer, calculation of data used for positioning the thin film to the measured portion, and the thin film The film thickness measuring device is characterized in that the film thickness is measured with a single optical system by using the reflected light from the semiconductor wafer.

Further, the interference light of the reflected light is dispersed, data used for positioning the thin film on the portion to be measured is calculated based on the relationship between the reflectance and the wavelength of the dispersed light, and the film thickness of the thin film is calculated. It is a film thickness measuring device characterized by measuring data.

Further, the interference light of the reflected light is spectrally divided, data used for positioning the thin film on the portion to be measured is calculated based on the relationship between the intensity and wavelength of the dispersed light, and the film thickness data of the thin film. Is a film thickness measuring device.

[0015]

The film thickness measuring apparatus of the present invention has the above-mentioned structure, and is highly accurate on the pattern to be measured on the surface of the semiconductor wafer.
It is possible to easily position and measure the film thickness on the surface of the semiconductor wafer.

[0016]

EXAMPLE A first example of the film thickness measuring apparatus of the present invention is shown in FIG.
Shown in. This film thickness measuring device includes a white light source 1, a lens 2, a lens 3, a slit 4, a lens 5, a beam splitter 6,
The objective lens 7, the lens 8, the diffraction grating 9, the one-dimensional image sensor 10, the interface 11, the xy stage 12, the base 13, the xy stage driver 14, the processing circuit 15, and the interface 16.

Here, the measurement target is a patterned wafer as shown in FIGS. 2 and 3. Figure 2
As shown in (a), elements 19 such as memories and logics, which are separated by dicing lines 18, are formed on the entire surface of a silicon wafer 17 which is a patterned wafer. As shown in FIG. 2B, the element 19 is composed of a cell 20 in which an electric circuit is formed and an Al electrode pad 21.

Further, as shown in FIG. 3, FIG.
The silicon substrate 22 and the Al electrode pad 21 are covered with the SiO ₂ film 23 when the cross section is sectioned by the line. The light beam emitted from the white light source 1 is incident on the silicon wafer 17 through the lens 2, the lens 3, the slit 4, the lens 5, the beam splitter 6, and the objective lens 7 with a beam diameter of about 30 μm. Here, it is preferable that the light beam is incident on the silicon wafer 17 in a focused state.

The silicon wafer 17 is roughly positioned on the base 13 with the patterned surface as the upper surface and its orientation flat as a mechanical reference. Here, the Al electrode pad 21 has a side of about 100.
Although the length is μm, it is very difficult to position the light beam on the Al electrode pad 21 only by performing a rough mechanical positioning.

The light beam is incident on the SiO ₂ film 23 covering the cell 20, the Al electrode pad 21 or the silicon substrate 22. As shown in FIG. 3, the incident light is SiO 2.
_The reflected light u ₁ and u ₂ are reflected by the surface of the _second film 23 and the interface between the SiO ₂ film 23 and the Al electrode pad 21 or the silicon substrate 22. FIG. 4 shows the relationship between the reflectance and the wavelength, that is, an example of the interference fringe waveform of the interference light due to u ₁ and u ₂ .

The reflected light is incident on the diffraction grating 9 through the objective lens 7, the beam splitter 6, and the lens 8 and is dispersed. The dispersed light enters the one-dimensional image sensor 10 and photoelectrically converts the intensity of light of each wavelength into an electric signal. The photoelectrically converted electric signal is input to the processing circuit 15 via the interface 11. Here, considering a certain wavelength λ ₁ , the reflectance r ₁ differs depending on where on the silicon wafer 17 the light beam is incident. That is, since the reflectance on the Al electrode pad 21 is higher than the reflectance on the silicon substrate 22, the reflectance differs depending on the relative position between the Al electrode pad 21 and the light beam.

5A and 5B, the relative position between the irradiation surface of the light beam and the Al electrode pad 21 (x, y directions).
And the reflectance r ₁ . Here, the wavelength λ ₁ is Al
The wavelength is such that the difference between the reflectance on the electrode pad 21 and the reflectance on the silicon substrate 22 is maximum.

In this embodiment, control is performed by the interface 16 based on a command from the processing circuit 15 so that the xy stage 12 is scanned by the xy stage driver 14 in the x and y directions and detected by the one-dimensional image pickup device 10. The reflectance r ₁ is obtained in the processing circuit 15 from the obtained light.

The processing circuit 15 issues a command to the interface 16 to stop the scanning of the xy stage 12 when the irradiation surface of the light beam is entirely incident on the Al electrode pad 21 and the reflectance r ₁ becomes maximum. That is, the reflectance r ₁
The silicon wafer 17 is positioned by detecting the change in The processing circuit 15 calculates the film thickness d of the SiO ₂ film 23 covering the cell 20, the Al electrode pad 21, or the silicon substrate 22 by the following formula based on the photoelectrically converted electric signal.

[0025]

[Equation 1]

Here, λ _m is the wavelength that gives the maximum or minimum of the m-th reflectance appearing in the interference fringe waveform, and λ _ml
Is a wavelength that gives the maximum or minimum of the l-th reflectance in the direction of increasing wavelength from λ _m . Further, n is the refractive index of the SiO ₂ film 23, and θ is the incident angle of the light beam on the SiO ₂ film 23.

The present invention is not limited to this first embodiment, and various changes can be made without departing from the scope of the invention. For example, FIG. 6 shows a second embodiment of the present invention in which an optical fiber is used for the light projecting / receiving system. In this film thickness measuring device, the measuring optical system 24 includes a white light source 25, a lens 26, a lens 27, a lens 28, a light projecting / receiving fiber 29, and a slit 3.
0, a reflection mirror 31, a diffraction grating 32, and a one-dimensional image sensor 33. A processing circuit 35 is provided, and the one-dimensional image pickup device 33 is connected to the processing circuit 35 via an interface 34. In addition, an xy stage driver 37 is connected via an interface 36.
Are connected.

The light projecting / receiving fiber 29 has a light projecting end 38, a light projecting / receiving end 39, and a light receiving end 40, of which the light projecting end 38 faces the white light source 25 via the lens 26. Further, the light receiving end 40 is guided to the side of the one-dimensional image pickup device 33 and faces the lens 27. The light emitting / receiving end 39 is guided via the fiber guide portion 41 onto the silicon wafer 17 on the base 44 of the xy stage 43.
The window 42 is opposed to the window 42. Here, also in this embodiment, as in the first embodiment, the SiO ₂ film 23 is adopted as a thin film.

First, the light beam emitted from the white light source 25 passes through the lens 26 to become parallel light, and the light emitting / receiving fiber 29
Is incident on the light projecting end 38 of The light beam incident on the light projecting / receiving fiber 29 is transmitted to the light projecting / receiving end 39 and is transmitted to the light projecting / receiving end 39.
The light beam emitted from the laser beam enters the silicon wafer 17 through the lens 27 and the window 42.

[0030] The light beam incident on the silicon wafer 17 and the surface and the SiO ₂ film 23 of SiO ₂ film 23 Al
Both reflected lights u ₁ , shown in FIG. 3, reflected at the interface with the electrode pad 21 or the silicon substrate 22 and shown in FIG.
u ₂ causes interference. Then, the interference light enters the light projecting / receiving end 42 and is transmitted to the light projecting end 40.

The interference light emitted from the light projecting end 40 is reflected by the lens 2
It is narrowed down to 7, passes through the slit 30, and is guided to the diffraction grating 32 by the reflection mirror 31. Then, the interference light is split by the diffraction grating 32, and the split light is incident on the one-dimensional image sensor 33.

The one-dimensional image pickup device 33 photoelectrically converts incident light and outputs a signal corresponding to the intensity of light for each wavelength. The photoelectrically converted electrical signal is input to the processing circuit 35 via the interface 34. Also in this embodiment, x is controlled by the interface 36 based on a command from the processing circuit 35,
While scanning the xy stage 43 in the x and y directions via the y stage driver 37, the processing circuit 35 obtains the reflectance r ₁ from the light detected by the one-dimensional image sensor 33.

The processing circuit 35 stops the scanning of the xy stage 43 when the irradiation surface of the light beam emitted from the light emitting / receiving end 39 is entirely incident on the Al electrode pad 21 and the reflectance r ₁ becomes maximum. The command is issued to the interface 36. That is, the silicon wafer 17 is positioned by detecting the change in the reflectance r ₁ .

Further, the output signal of the one-dimensional image pickup device 33 is sent to the processing device 35 through the interface 34, and the processing device 35 uses the input signal and the above-mentioned formula in the first embodiment to calculate the cell 20 and the Al electrode. The film thickness d of the SiO ₂ film 23 covering the pad 21 or the silicon substrate 22 is calculated.

In the above two embodiments, the diffraction is performed using the diffraction grating, but the spectroscopy is not limited to the diffraction grating, and other spectroscopic means may be used. Also, the same effect can be obtained by a method in which the diffraction grating is rotated and light is received by the photomultiplier tube without using the one-dimensional image sensor.

The method of scanning the xy stage 43 is not limited to the method of scanning the entire optical system or the method of scanning the light beam with a mirror or the like. 1 in the above two examples
Although the reflectance was measured for one measurement wavelength and the positioning was performed, the reflectance can be measured for a specific wavelength band and the positioning can be performed based on the integrated value. Alternatively, it is also possible to obtain the difference between the reflectance on the Al electrode pad 21 and the reflectance on the silicon substrate 22 using a plurality of wavelengths, and perform positioning based on the maximum value of the difference in the reflectance.

In addition, the film thickness measuring apparatus of the present invention is not limited to the measurement in the atmosphere, but can be measured by using the optical system having the optical parameter corresponding to water even when the silicon wafer 17 is submerged in water. Is. Further, also in the measurement in unclean water containing the polishing material and the measurement in the state where the polishing material is adhered to the surface of the silicon wafer 17, the positioning can be performed by selecting the wavelength of the measurement light so as to pass through the polishing material. Then, the film thickness can be obtained.

In the embodiment, the SiO ₂ film 23 is used as the thin film to be measured and the Al electrode pad 21 is used as the pattern to be measured, but the object to be measured is not limited to these. Also Al
The reflectance on the electrode pad 21 and the reflectance on the silicon substrate 22 are compared with each other. However, if the parameters are such that the two can be compared, the intensity may be compared by using the intensity of light obtained by dispersing the reflected light instead of the reflectance. . Actually, it can be easily realized by changing the configurations of the processing circuits 15 and 35.

[0039]

According to the present invention, in the apparatus for measuring the film thickness of the thin film on the surface of the patterned semiconductor wafer, particularly, the film thickness is accurately and simply positioned at a specific measurement position on the pattern and at the same time, the film thickness is accurately measured. A device can be provided. In this way, since it is not necessary to connect a complicated device for positioning at a specific measurement position on the pattern, it is possible to downsize the entire measuring device and manufacture the entire measuring device at low cost.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing a first embodiment of the present invention.

FIG. 2A is a configuration diagram of a silicon wafer. (B) is an enlarged view of (a).

FIG. 3 is a cross-sectional view taken along the line AA ′ of FIG.

FIG. 4 is a diagram showing the relationship between the reflectance and the wavelength of interference light.

FIG. 5A is a relationship diagram of a relative position between a light beam irradiation surface and an Al electrode pad. (B) is the relative position and the reflectance r
Relationship diagram with ₁ .

FIG. 6 is a schematic configuration diagram showing a second embodiment of the present invention.

FIG. 7 is a schematic configuration diagram showing a conventional example.

[Explanation of symbols]

1.25 ... White light source 2/3/5/8/26/27/28/46 ... Lens 4/30 ... Slit 6 ... Beam splitter 7 ... Objective lens 9.32 ... Diffraction grating 10.33 ... One-dimensional image sensor 11.16.34.36 ... Interface 12.43 ... XY stage 13.44 ... Base 14.37 ... XY stage driver 15.35 ... Processing circuit 17 ... Silicon wafer 19 ... Element 20 ... Cell 21 ... Al electrode pad 22 Silicon substrate 23 SiO ₂ film 24 Measurement optical system 29 Light emitting / receiving fiber 31 Reflecting mirror 38 Light emitting end 39 Light emitting / receiving end 40 Light receiving end 41 Fiber guide portion 42 Window 45 Semiconductor laser device 47 ... Plane mirror 48 ... Self-coupling type semiconductor laser 49 ... Dielectric film

Claims (3)

[Claims] 1. A film for irradiating a semiconductor wafer having a thin film and a wiring pattern forming portion on a substrate with measuring light, and measuring the film thickness of the thin film based on the reflected light from the semiconductor wafer. In the thickness measuring device, it is possible to detect the data used for positioning the thin film on the portion to be measured and to measure the film thickness data of the thin film with a single optical system using the reflected light from the semiconductor wafer. Characteristic film thickness measuring device. 2. The interference light of the reflected light is spectrally separated, and the data used for positioning the thin film on the portion to be measured is detected based on the relationship between the reflectance and the wavelength of the dispersed light, and the film of the thin film. The film thickness measuring device according to claim 1, which measures thickness data. 3. Interfering light of the reflected light is separated, and data used to position the thin film on a portion to be measured is detected based on the relationship between the intensity and wavelength of the separated light, and the film thickness of the thin film. The measurement of data is performed, The film thickness measuring device of Claim 1 characterized by the above-mentioned.