JPH0381083B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an improvement in a film thickness measuring device for measuring the thickness properties of a film such as SiO ₂ formed on a semiconductor substrate.

[Technical background of the invention]

Errors in the thickness of films such as SiO ₂ formed on the semiconductor substrate surface must be kept to a minimum in order to improve yield. ) and thickness unevenness, which is a spatial change in film thickness at a specific location, have been measured. Therefore, film thickness has conventionally been measured using optical interference. That is, the thin film is irradiated with monochromatic light (center wavelength λ ₀ ), the reflected light from the thin film is received, and the film thickness is determined from the amount of received light. FIG. 12 is a diagram showing the amount of received light I relative to the film thickness d, and this amount of received light I is expressed by the following equation.

I=sin ² {(2πnd/λ ₀ ) cos i1} (1) where n is the refractive index of the thin film, d is the film thickness, and i1 is the refraction angle inside the thin film. In this way, the amount of received light I shows a sinusoidal change, and therefore, the film thickness and its temporal change can be determined from this number of cycles. Note that in FIG. 12, the amount of received light Ia is the case where multiple reflections within the thin film are not considered, and Ib is the amount when multiple reflections are taken into consideration.

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

[Problems with background technology]

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, when measuring thickness unevenness, multiple light receiving elements 6
The use of -1 to 6-n complicates the entire device, and measurement accuracy decreases due to variations in sensitivity of the light receiving elements 6-1 to 6-n.

[Purpose of the invention]

The present invention was made based on the above circumstances, and
The purpose is to provide a highly accurate film thickness measuring device that can accurately measure film thickness characteristics with strong noise resistance and a simple configuration.

[Summary of the invention]

The present invention projects measurement light from a light projecting means onto a film surface on which a film is formed at an incident angle larger than the Brieuster angle, and receives reflected light or transmitted light on the film surface by a light receiving means to perform photoelectric conversion. This is a film thickness measurement device that detects the film thickness properties of the film surface based on the electrical signals obtained.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a configuration diagram of a film thickness measuring device. In the figure, reference numeral 10 denotes an etching chamber, in which a wafer 13 is placed between electrodes 11 and 12, and the thin film on the wafer 13 is removed. Reference numeral 14 denotes a projector made of, for example, a laser oscillator, and the projector 14 is installed at such a position that the laser beam 15 is incident on the thin film formed on the wafer 13 at an angle larger than the Brieuster angle. In other words, as shown in Figure 2, if the refractive index of the atmosphere is n1, the refractive index of the thin film is n2, and the normal is k, then the incident angle i ₀ is larger than the Brieuster angle, i.e. i ₀ = tan ^-1 (n2 /n1) Above, for example, 89° and 85°. When the incident light is incident at an angle larger than the Brieuster angle, the reflected light 16 has a P component of light waves vibrating parallel to the surface of the thin film, and an S component of light waves vibrating perpendicular to this P component. When considered as components, these P component and S component are shifted in phase from each other by π. 17
is a light receiver that receives each of the reflected waves of the P component and the S component and outputs an electric signal according to the amount of the received light. An amplifier circuit 18 is connected to the output end of the photoreceiver 17, and further a V/F conversion circuit (voltage-frequency conversion circuit) 19 and an E/O conversion circuit (electrical-optical conversion circuit) 20 are connected. Therefore, the electrical signal output from the optical receiver 17 is converted into a frequency signal, and then converted into an optical signal and transmitted through the optical fiber 2.
1 is propagated and sent to the measurement calculation means 22. In this measurement calculation means 22, O/E
A digital signal corresponding to the amount of light received by the light receiver 17 is input into a calculation section 25 by a conversion circuit (optical-electrical conversion circuit) 23 and a pulse counter 24 .

On the other hand, a photodetector 26 for detecting plasma generation within the etching chamber 10 is installed on the side surface of the etching chamber 10, and an amplifier circuit 27, a V/F conversion circuit 28,
It is connected to an O/E conversion circuit 31 of the measurement calculation means 22 via an E/O conversion circuit 29 and an optical fiber 30. The pulse counter 32 is connected to the arithmetic unit 25 via the pulse counter 32.

Now, the calculation unit 25 obtains an interference waveform from the captured digital signal, and from this interference waveform, determines the interval between valleys and the width of the tip of the valley, and determines the temporal thickness change of the thin film and the portion of the thin film irradiated with the laser beam 15. It has a function to calculate either or both of the thickness unevenness. Specifically, the film thickness change is determined from the interval between the valleys, and the thickness unevenness is determined from the width of the tip of the valley.

Next, the operation of the apparatus configured as described above will be explained. Laser light from the projector 14 hits the wafer 1
The thin film No. 3 is irradiated at an angle larger than the Brilleusta angle. When the thin film of the wafer 13 is irradiated with laser light in this way, multiple reflections occur within the thin film, and reflected light 16 is generated due to multiple interference due to the multiple reflections. This reflected light 16 has a P component and an S component, but a phase shift of π occurs between the P component and the S component. Therefore,
The light receiver 17 receives the reflected light 1 of these P and S components.
6 and outputs an electrical signal according to the amount of received light. This electrical signal is amplified to an optimal level by an amplifier circuit 18, converted to a frequency signal according to the voltage level by a next V/F conversion circuit 19, and sent to an E/O conversion circuit 20. The signal is then converted into an optical signal, propagated through the optical fiber 21, and input to the measurement calculation means 22. This measurement calculation means 2
In step 2, the signal is again converted into a voltage signal by the O/E conversion circuit 23, further converted into a digital signal according to the voltage level by the pulse counter 24, and taken into the calculation section 25. On the other hand, the light receiver 26 detects plasma generation. In other words, within the etching chamber 10, the etching process is performed on the same wafer 13.
The etching process is performed twice, during which gas exchange within the etching chamber 10 is performed. Therefore, the operation timing is determined by detecting plasma generation. The electrical signal output from this photoreceiver 26 is also sent to the amplifier circuit 27, the V/F conversion circuit 28, and the E/O
The signal is inputted to the measurement calculation means 22 through the conversion circuit 29 and the optical fiber 30. The signal is then taken into the arithmetic unit 25 via the O/E conversion circuit 31 and the pulse counter 32.

Now, the calculation unit 25 creates an interference waveform from the captured digital signal. In other words, this is the interference waveform Q shown in FIG. Note that Q0 shown in the figure is an interference waveform when the incident angle of the laser beam 15 is "0°". As mentioned above, the interference waveform Q has a phase difference of π between the P component and the S component, and specifically, the P component shown in FIG. 4 and the S component shown in FIG. 5 are synthesized. Become something.

Incidentally, this interference waveform Q is due to multiple interference in the thin film, and in this multiple interference, the amplitude and waveform change depending on the reflectance of the boundary surface. Furthermore, in the case of grazing incidence greater than the Brieuster angle, the reflectance becomes extremely high and the amplitude of the signal becomes large as shown in FIG. Therefore, the interference waveform Q is completely different from the sine waveform, and the first
The amount of received light Ib shown in Figure 2, and the P component shown in Figure 4,
As shown in the S component shown in FIG. 5, the minimum portion, or valley, where the amount of received light decreases is sharp, and the area other than this minimum portion changes slowly. However, the interference waveform Q in which the P component shown in FIG. 4 and the S component shown in FIG. 5 are combined has a good contrast in which the P component and the S component clearly appear.
Therefore, the calculation unit 25 calculates and determines the interval L between the valleys, the number of valleys, and the start phase of this signal to determine the change in the thickness of the thin film. By the way, when the thickness of the thin film changes, the phase of the signal start changes in relation to the thickness. In other words, Figures 7a to 7c show cases where the film thicknesses are 4500 Å, 5000 Å, and 5500 Å, respectively, and as the film thickness increases, the number of valleys increases and the signal start phase changes. I understand. Therefore, the calculation unit 25 has the valley interval L in advance.
Information on the relationship between the number of valleys, the start phase of the signal, and the film thickness is stored, and the film thickness is determined from this information.

Next, thickness unevenness measurement will be explained. As shown in FIG. 8, if the thin film 32 has a thickness unevenness of ±Δd,
From the optical path difference of the laser beam according to these thickness unevenness Δd, the phase difference for each thickness is determined by the refractive index of the thin film as n2,
If the center wavelength of the laser beam is λ0, then n ₂ Δd cos (i1/λ0). Note that i1 is the refraction angle inside the thin film 33. Therefore, when such reflected light is received, the width of the trough tip is proportional to the thickness unevenness Δd・2, which is a combination of light of each thickness and phase, as shown in FIG.
An interference waveform with LS is obtained. Therefore, the calculation unit 25 measures the valley tip width LS to determine 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 width LS.

In this way, in the above embodiment, the laser beam 15 is irradiated onto the film surface with an incident angle equal to or greater than the Brieuster angle, and the resulting reflected light 16 of the P component and S component is received to form an interference waveform. The change in film thickness is measured by determining the interval between valleys, the number of valleys, and the start phase of the signal, and also the valley tip width LS
Since the thickness unevenness is measured by determining , film thickness changes and thickness unevenness can be measured with a simple configuration, and can be measured accurately without being affected by external noise.
In other words, the Grazing
This is because if the signal is incident at a certain angle (incidence), the rate of change in amplitude near the valley of the signal becomes large, making it easy to distinguish. This makes it less susceptible to optical noise caused by plasma emission. Also, the phase of the signal obtained by changing the film thickness is (2πnd/λ ₀ )×cos[sin ^-1 {(n0/n) sin i0}]...
…(2) When n0=1, n1=1.5, Grazing
The period of Incident (for example, i ₀ = 89°) is longer compared to normal incidence, but the number of valleys is 1.4 times larger due to the π phase shift of the P and S components, so as a result, compared to normal incidence, The period is approximately 0.7 times. For this reason,
The accuracy of determining film thickness is improved.

Furthermore, when measuring thickness unevenness, it is possible to measure thickness unevenness, particularly the distribution of thickness unevenness, with one light receiver without providing a plurality of light receiving elements as in the conventional method. Note that the measurement range can be arbitrarily expanded or narrowed by expanding and collimating the beam of laser light to measure the thickness unevenness. Furthermore, the measurement of film thickness changes and thickness unevenness can also be applied to multilayer films.

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. Furthermore, in the above embodiments, the troughs of the reflected light from the film surface are used to detect the film properties, but the peaks of the transmitted light from the film surface may be used for detection. In short, the extreme value portion of the electrical signal output from the light receiving means may be used to detect the film properties.

[Effects 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 properties with strong noise resistance and a simple configuration.

[Brief explanation of drawings]

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 diagrams showing the P component and S component of the reflected light. Figure 6 shows the separation state; Figure 6 shows the amplitude of the laser beam with respect to the incident angle; Figure 7 a, b, c
Figure 8 shows the periodic change in the amount of received light with respect to the film thickness.
9 shows the interference waveform of the thickness unevenness shown in FIG. 8. FIG. 10 shows the continuously changing thickness unevenness. FIG. 11 shows the thickness unevenness shown in FIG. FIGS. 12 and 13, which show interference waveforms of thickness unevenness shown in the figure, are diagrams for explaining conventional film thickness change and thickness unevenness measurement. 10... Etching chamber, 13... Wafer, 14... Emitter, 17... Light receiver, 18...
...Amplification circuit, 19...V/F conversion circuit, 20...
E/O conversion circuit, 21... optical fiber, measurement calculation means, 23... O/E conversion circuit, 24... pulse counter, 25... calculation section.

Claims (1)

[Scope of Claims] 1. Light projecting means for projecting measurement light onto a formed thin film at an incident angle larger than the Brieuster angle, and reflected light or transmitted light that is multiple-reflected on the thin film and emitted. A light-receiving means that receives and photoelectrically converts the light, and an interference waveform is created by taking in the electric signal output from this light-receiving means, and the interval between valleys of this interference waveform, the number of valleys, and the start phase of this interference waveform are determined. A film thickness measuring device comprising: a measurement processing means for determining a change in the thickness of the thin film from the width of the trough, and determining the thickness of the thin film from the width of the tip of the valley. 2. The measurement processing means includes a voltage-frequency conversion circuit that inputs the electrical signal output from the light-receiving means and performs voltage-frequency conversion, and an electrical circuit that converts the frequency signal output from the voltage-frequency conversion circuit into an optical signal.
an optical conversion circuit, an optical fiber that transmits the optical signal output from the electrical-optical conversion circuit, an optical-electrical conversion circuit that converts the optical signal transmitted by the optical fiber into a frequency signal, and a pulse counter that converts the frequency signal output from the electrical conversion circuit into a digital signal indicating the amount of light received by the light receiving means; and creating an interference waveform by inputting the digital signal output from the pulse counter; It is composed of a calculation section that calculates the change in the thickness of the thin film from the interval between the valleys of the interference waveform, the number of valleys, and the start phase of the interference waveform, and calculates the thickness of the thin film from the width of the tip of the valley. A film thickness measuring device according to claim 1.