JPS6118133A - Method and apparatus for detecting termination point in rie - Google Patents

Abstract

PURPOSE:To detect the termination point of reactive ion etching with high accuracy by measuring luminous intensity of plasma and determining the termination point from a value of changing rate. CONSTITUTION:An optical probe 8 is provided within a case 1 in order to detect intensity of plasma. The plasma beam enters the optical probe 8 and reaches a spectroscope 10 through an optical fiber 9. Here, two units of spectroscopes are necessary because intensities of lights of two waveformes are monitored simultaneously. The spectroscope analyzes the light transmitted through the optical fiber 9 into spectrum and sends only the light having the specified wavelength to photoelectric converters 11. The photoelectric converters 11 are provided in two units. These units generate voltage or current signals corresponding to respective intensities of light beams. Moreover, intensities of lights of two wavelengths can be obtained by amplifying such signals up to the adequate levels. A data processor 12 calculates changing rate of light intensities and judges the termination point through comparison between the absolute value of changing rate with the threshold value.

Description

Detailed Description of the Invention (7) Technical Field The present invention relates to an end point detection method and apparatus in active ion etching.

Reactive ion etching (Rmctive Io)
n arsification) is a dry etching method used in the process of manufacturing ICs.

Wet etching is a conventionally used method in which an IC substrate is immersed in an etching solution.

The dry etching method is a method of etching various films and layers on a semiconductor wafer using a gas without using a liquid.

(a) RIE method The reactive ion etching (hereinafter abbreviated as RIE) method will be explained with reference to FIG.

In the RIE method, a gas that reacts with structures on a target semiconductor wafer is made into a plasma and collides with the surface of the semiconductor wafer to selectively remove a film on the surface.

Inside the container 1, a cathode 2 and an anode 3 are provided to face each other in the vertical direction. Both have a flat plate shape, and the cathode 2 is a stand on which a wafer 5 can be placed.

Anode 3 is grounded. The cathode 2 is connected to an RF power source 4, and a high frequency high voltage is applied thereto.

In one example, this high frequency voltage has an effective value of 2800 V and a frequency of 18.56 MHz. Wafer 5 is a silicon wafer in this example.

Etchant gas is introduced into the container 1, and is constantly allowed to flow little by little until it is discharged.

For this purpose, the container 1 is provided with a gas inlet 6 and a gas exhaust lower. In this example where silicon wafers are the target, Freon CF4 is used as the gas.

The etchant gas is subjected to a high frequency electric field in the container 1 and is ionized into ions and electrons.

The container 1 is previously evacuated to a vacuum of I.times.10 Torr or less to remove unnecessary gases, and then an etchant gas is introduced to create a plasma state. The pressure at this time is
For example, it is about 8.6×10 Torr.

(1) Prior Art When dry etching a structure or film on a semiconductor wafer using the RIE method, a means for checking the end of etching is required.

If the etching time is too long, etching will proceed excessively and structures that should be left will be etched away. It is also not good if the etching time is too short.

However, the speed of etching varies depending on the gas pressure, the power of the RF power supply, and the structures provided on the wafer.

It is not possible to determine the end of etching only by measuring the length of etching time.

Therefore, the end point of etching has conventionally been detected by observing the change in the spectrum of light that occurs on the etched surface.

The light produced at the etched surface varies depending on the material being etched. FIG. 2 is a cross-sectional view showing an example of a structure on a silicon wafer.

Assume that an Aβ layer 21, a PSG (phosphorus silicate glass nitride glass) layer 23, and a resist 240 layer are present on the Si wafer 20.

In such a case, when etching the resist and
The emission spectrum when etching G is different.

The emission intensity is measured over the entire spectrum of plasma emission, and the substance currently being etched can be determined from changes in the entire spectrum.

To do this, we must use a spectrometer to measure the intensity of the light while changing the wavelength of the selected light.

However, this is not an easy task, so one or two wavelengths are selected and only the intensity of light at these wavelengths is measured to detect the end point.

The intensity of light of one wavelength is considered to be human. A threshold value C is determined in advance, and when A exceeds the value of C while monitoring the light intensity, this is determined to be the end point of RIE. In other words, the end point is detected based on the absolute value of the light intensity signal.

If the S/N ratio cannot be improved by monitoring only the light of one wavelength, the intensity A1B of the light of two wavelengths is monitored.

An intensity variable is created from the light intensities A and B by a suitable binary operation, and the end point of RIE is detected depending on whether or not this exceeds a predetermined threshold value C.

Binary operations here include sum, difference, product, quotient, and their logarithms. However, it is desirable to choose an appropriate binary operation.

B) Problems with the Prior Art The intensity of plasma emission changes depending on the power of the RF power source and the degree of vacuum in the reaction vessel. Furthermore, the emission intensity varies depending on the area of the sample to be etched.

For this reason, the method of measuring the absolute value of the light intensity and comparing it with a fixed threshold value does not necessarily accurately detect the end point of RIE.

In order to stabilize the emission intensity, the applied power of the power supply, the degree of vacuum, etc. must be kept constant, and the number of semiconductor wafers to be processed must also be kept constant.

However, as the etching progresses, reaction gas is generated, so it is difficult to keep the pressure constant. As described above, since the luminescence intensity strongly depends on the environment inside the reaction vessel, uncertainty remains in end point detection if only the absolute value of the light intensity is measured.

Monitoring the intensity of light at two wavelengths improves this uncertainty somewhat, but it is still susceptible to environmental influences.

Furthermore, when the sample being etched becomes multilayered (eg, resist), it becomes more difficult to detect the endpoint of RIE using conventional methods.

K) Method of the present invention In the present invention, when dry etching a semiconductor wafer using an RIE apparatus as shown in FIG. 1, plasma emission intensity is measured in order to detect the end point of etching.
The end point is determined not by this absolute value but by the magnitude of the rate of change.

If the luminescence intensity A is sampled every fixed time τ, the difference between the value at a certain time t and the value τ before that value is ΔA(t) = A(t) −A(−τ)( 1). This means that τ is finite and ΔA is the difference.

Since the sampling period is τ, m is an integer, and m
The th difference is ΔAIIl=A((m+1)T)−A(mT) (
2) can also be defined.

However, it is also possible to consider the differential λ(1) by setting τ to be infinitesimal.

It is.

Here, it does not matter whether τ is finite or infinitesimal. The difference, differential, and minute are collectively called the rate of change of A,
It will be expressed by 6 people.

In the present invention, the rate of change ΔA is compared with a predetermined threshold C, and when it becomes larger than this, it is determined that this is the end point of etching.

The end point of etching is ΔA < C (4) What was ΔA≧C (5) It is detected by

The method of the present invention detects the end point of RIE by comparing the rate of change with a threshold value instead of the absolute value, and the reason for this will be explained next.

Assume that films to be etched are laminated on a wafer to be etched, in order from top to bottom: material I, material 2, . . . .

While material I is being etched, the spectrum of plasma emission should be constant. The entire spectrum becomes larger or smaller, and this is due to fluctuations in pressure and applied power.

Next, when material (1) is etched through the transition region, the spectrum of plasma emission should be constant. Spectrum (2) is of course different from spectrum (I).

Then, in the transition region where the etching layer changes from I to ■, a significant change in the plasma emission spectrum occurs.

A sudden change in the spectrum from I to ■ can be captured by the change ΔA in the light intensity A by selecting light with a characteristic wavelength.

The light intensity A of that wavelength is almost constant in spectrum I, and is also almost constant in spectrum (2). Therefore, the rate of change is approximately zero.

However, in the transition region from ■ to ■, the light intensity changes significantly, so the rate of change is large.

Therefore, when the rate of change ΔA is greater than a certain predetermined threshold value C, this means that it is in the transition region from ■ to ■.

The light intensity A for light of a certain wavelength is considered to be the sum of a part E due to the environment (gas pressure, applied power) and a part F determined by the difference in the part emitting plasma light when the environment is constant.

In the conventional method, when the equation E-4-F=C(threshold value) (6) is established, this is determined to be the end point. However, this is not always correct and does not correspond to the end point due to variations in E.

On the other hand, in the method of the present invention, both E and F have a rate of change ΔE
Assuming that 1ΔF can be defined, the end point is detected by ΔE + Δp'=C (threshold) (7).

ΔE is a change in pressure and power, and is not dependent on the progress of etching. ΔF is zero during etching of substance I or substance 11, and becomes a large value during the transition from ■ to ■. Although ΔE cannot be reduced to 0, it can be made smaller than ΔF in the transition region.

Therefore, the transition region can be detected correctly within an error on the order of ΔF/ΔE.

Although the above description assumes that the rate of change ΔA is positive, it may be negative. The point where the absolute value of ΔA is greater than C is the end point.

The light to be monitored does not have to be of one wavelength.

The intensity of light of two wavelengths is monitored, this is set as AB, and D is calculated by an appropriate binary operation. When the absolute value of the rate of change IΔD1 becomes larger than the threshold value C, the end point of RIE is detected. , etc.

Binary operations are D=A+B', <8) D=AB (9)-Person D -/B (10) D ==
A-B (11) D = Aiog
A/B(12) is arbitrary.

Using the sample shown in FIG. 2, an RIE experiment was conducted using the apparatus shown in FIG. The wavelength of light to be monitored is 246
nm and 451 nm. The intensity of this light A,
Absolute value of the difference between B D D = l A (24enm), -B (45xnm
) l (ta) is shown in FIG. The horizontal axis is etching time (minutes). The vertical axis is IA-Bl, which is expressed as the voltage (v) of the detector.

From 0 to 60 minutes, the resist 24 is etched. The absolute value of the difference IA-Bl is stable and almost constant.
.

For 60 to 80 minutes, the interface between the resist 24 and the PSG 23 is etched. The value of IA-Bl changes significantly here. The slope of the graph increases.

After 80 minutes, psc 23 etching is supported. The value of IA-Bl becomes a substantially constant value again.

Although not shown, if etching is continued further,
At the boundary between PSG and Si, this power decreases rapidly. In other words, the rate of change in IA-J takes a large negative value.

Thus, at the boundary, the rate of change of D-IA-81 increases. This allows boundaries to be detected.

Since the end point of etching is always the boundary between materials, this allows the end point to be accurately recognized.

(Form) Apparatus of the Invention The reactive ion etching apparatus shown in FIG. 1 is used, but the configuration of the data processing section 12 is slightly different. In FIG. 1, the RIE apparatus consists of a container 1, a cathode 2 and an anode 3 provided vertically opposite each other in the container 1, an RF power source 4, and the like.

The cathode 2 and anode 3 are horizontal flat plates. A large number of semiconductor wafers 5 can be placed on the cathode 2.

The side wall of the container 1 is provided with a gas inlet 6 and a gas exhaust lower.

Anode 3 is grounded. A high frequency voltage of 2800V of 18.6 MH2, for example, is applied to the cathode 2 by an RF power source.

A suitable etchant gas is introduced from the gas inlet 6,
The gas is exhausted from the gas exhaust port γ. When a high frequency electric field is applied while maintaining an appropriate degree of vacuum, the gas becomes a plasma and collides with the wafer 5.

The constituent elements of the wafer and the gas cause a chemical reaction, and the constituents on the wafer are gradually removed.

On the other hand, the generated plasma emits light, and in order to detect the intensity of the light, an optical probe 8 is placed inside the container 1.
will be established. This includes appropriate focusing optical systems such as lenses and mirrors. Light generated by the plasma emission enters the optical probe 8, passes through the optical fiber 9, and reaches the spectrometer 1o.

The number of spectrometers 10 required is equal to the number of wavelengths of light to be monitored. Here, the intensity of light of two wavelengths is monitored simultaneously, so two spectrometers are required.

The spectrometer decomposes the light transmitted through the optical fiber 9 into spectra and supplies only light with a certain wavelength to the photoelectric conversion unit 11 . - Two photoelectric conversion units 11 are also provided. A voltage or current signal corresponding to the intensity of each light is generated. Furthermore, this is amplified to an appropriate level.

In this way, the intensities A and B of the light having the wavelengths 27) are obtained.

The data processing section does not directly compare the light intensity with a threshold value as in the past, but first calculates the rate of change.

This can be obtained by sampling at fixed time intervals τ and determining the change in intensity during τ.

When there is only one type of light to be monitored, simply compare the absolute value of the rate of change with the threshold value C, and know that the end point is reached when 1ΔAt>C(14). Stop etching here.

If there are two types of light to be monitored, a binary operation is performed to calculate the function. D is illustrated in (8) to (12). The absolute value of the rate of change of D is compared with the threshold value C, and when it becomes 1ΔDl)C(15), this is determined to be the end point.

In the example of FIG. 1, an optical probe 8 and a spectrometer 10
are coupled by the optical fiber 9, but the invention is not limited thereto. It is also possible to combine the two using a lens system. Alternatively, the spectrometer 10 may be directly coupled to the container 1.

(g) Effects (1) Instead of monitoring only the plasma emission intensity and comparing it with a threshold value as in the past, the rate of change in the emission intensity is monitored and compared with the threshold value to determine the end point of RIE. I'm trying to detect it.

The end point of RIE can be stably monitored even if the environment inside the reaction vessel, such as the degree of vacuum or the power of the power supply, changes and therefore the luminescence intensity changes somewhat.

(2) For the same reason, even if the number of semiconductor wafers to be etched changes, the end point of RIE can be stably monitored.

[Brief explanation of the drawing]

FIG. 1 is an overall configuration diagram of the RIE device and end point detection device. FIG. 2 is a sectional view showing an example of a structure on a silicon wafer. Figure 3 shows 246 nm and 451 nm when reactive ion etching was performed on a silicon wafer with the cross section shown in Figure 2.
3 is a graph plotting the absolute value of the difference in intensity of light having a wavelength of nm over the course of etching time. Each curve corresponds to each wafer processed simultaneously. 1... Container 2...
・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・
- Code 4...RF power supply 5... Semiconductor wafer 6...
...... Gas inlet γ ...... Gas exhaust port 8 ...... Optical probe 9 ・
...... Optical fiber 10 ...... Spectrometer 11 ...... Photoelectric conversion section 12 ...
... Data processing section inventor Hori
Minori 1) Next Tadashi Nomura

Claims (2)

[Claims] (1) Consists of a container 1, a cathode 2 and an anode 3 provided in the container 1, and an RF power source 4. A semiconductor wafer 5 is placed on the cathode 2, and a high frequency voltage is applied between the cathode 2 and the anode 3. In RIE etching, in which a reactive gas is flowed into the container 1 and made into a plasma state to etch the structure of the semiconductor wafer 5, the intensity A of light of one or two wavelengths among the light generated by the reactive gas plasma is , or A and B are measured, and the absolute value of the rate of change ΔA of the intensity A of single wavelength light |ΔA|, or the change in value D obtained from the intensity A and B of light of two wavelengths by binary operation An end point detection method in RIE, characterized in that the end point of etching is detected by comparing the absolute value |ΔD| of the rate ΔD with a predetermined threshold value C. (2) Consisting of a container 1, a cathode 2 and an anode 3 provided in the container 1, and an RF power source 4, a semiconductor wafer 5 is placed on the cathode 2, and a high frequency voltage is applied between the cathode 2 and the anode 3. In an RIE etching apparatus that flows a reactive gas into a container 1 and turns it into a plasma state to etch a structure on a semiconductor wafer 5, an optical probe 8 that makes light generated from the reactive gas plasma enter an optical system, and an optical probe are used. 1 or 2 spectrometers 10 that select light of one or two wavelengths from the light incident on 8; and 1 that converts the intensity of the selected one or two wavelengths of light into an electrical signal. One or two photoelectric conversion units 11 and the rate of change ΔA of the light intensity A of one wavelength converted into an electrical signal, or the change in the value D obtained from the light intensity A and B of two wavelengths by binary operation. a data processing unit 12 that calculates the rate ΔD, compares the absolute values of the rate of change |ΔA|, |ΔD| with a predetermined threshold C, and detects the end point of RIE when the absolute value of the rate of change exceeds the threshold; RI characterized by consisting of
End point detection device at E.