JPH05102086A - Dry etching method - Google Patents

Abstract

PURPOSE:To detect the end point of silicon dry etching accurately by determining the end point of dry etching based on the ratio of emission intensity of reaction product to active species of etching gas. CONSTITUTION:The changes of emission intensity with the change of active species and production gas of etching gas are sent as an electric signal with the corresponding magnitude from photoelectric devices 63 and 64 to a judgment section 67 through amplifiers 65 and 66. The section 67 performs arithmetic processing so as to match the gradients of change curves of both emission intensities and calculates a coefficient. Then the obtained emission intensities are computed by using the coefficient of calculate the ratio of emission intensity, and the position where the value of ratio varies by the specified range is judged as the end point of etching. Thus, even in case where there are less influences such as the fluctuation of emission intensity or the like, production gas volume is small, or the change amount at the end point is smaller than the total change amount, the end point of etching can be detected accurately.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dry etching method for semiconductor substrates and the like.

[0002]

2. Description of the Related Art In a semiconductor manufacturing process, dry etching is an indispensable technique for forming a fine pattern. This etching is a method in which plasma is generated using a reactive gas in a vacuum and an object is removed by using ions, neutral radicals, atoms, molecules and the like in the plasma.

By the way, if the etching is continued even after the object to be etched is completely removed, the underlying material is unnecessarily scraped or the etching shape is changed, and this is prevented. Therefore, it is very important to detect the etching end point accurately. Therefore, as a typical method for detecting the end point of etching in the related art, the emission intensity of a product by etching is monitored and the end point is determined based on the change in the emission intensity.
For example, when etching silicon dioxide with a CF-based etching gas, a method has been proposed in which the emission intensity of carbon monoxide, which is a reaction product, is monitored and the end point is determined based on this emission intensity change (special feature. Kaisho 63-81929,
JP-A-1-230236). That is, the reaction product exists in the reaction container during etching, but is not generated when the etching target is exhausted, so that the emission intensity of the reaction product sharply decreases. Therefore, the end point of etching can be detected by catching the decrease in the light intensity of the specific wavelength derived from the reaction product.

By the way, in performing etching,
In order to stabilize the plasma or to increase the selectivity with respect to the underlying film and the resist, a large amount of additive gas other than the etching gas is added as compared with the etching gas. For example, argon may be added to a CF-based gas in order to stabilize plasma, but the emission spectrum of the argon gas itself spreads in a band shape, and the spectrum of carbon monoxide as a reaction product is contained in this spectrum. May be overlaid and buried.

[0005] Conventionally, the emission intensity is monitored within the range of about 300 to 900 nm in order to meet the requirements of the sensitivity of a detection device such as a spectrophotometer, and particularly 482.0 nm where the peak of the carbon monoxide spectrum is recognized is preferable. It is used. However, since such a wavelength range is very close to the strong emission wavelength range of 300 to 800 nm of argon, the emission spectrum of carbon monoxide is buried in the emission spectrum of plasma itself as described above. Therefore, the emission intensity of carbon monoxide cannot be accurately detected.

Moreover, with the recent trend toward miniaturization, the area to be etched tends to be extremely small.
For example, the ratio of the area of the etching target region to the total area of the etching target, that is, the aperture ratio is 10% or less, and in some cases, about 2 or 3%. Therefore, the amount of carbon monoxide gas generated is smaller than the amount of argon gas introduced, for example, 1/100 or less, and the emission intensity of carbon monoxide cannot be accurately detected, and the etching end point is specified. Was difficult. In general, the intensity of the emission spectrum from the plasma reaction system constantly fluctuates due to slight fluctuations in the power output, effects of the mass flow controller, fluctuations in processing pressure, and rises in the substrate temperature due to plasma. Furthermore, it has been difficult to monitor changes in the emission intensity of the produced gas and the like.

On the other hand, since the etching gas is almost constant during the etching but increases with the end of the etching, the emission intensity of the etchant is monitored together with the emission intensity of the product, and the difference or ratio of these emission intensities is monitored. A method of monitoring the temperature (Japanese Patent Laid-Open No. 63-91929) has also been proposed. However, the etching gas and the generated gas are not always constant during etching, and the light amount thereof may decrease during etching depending on the type of etching apparatus. The cause of this may be the condition of the exhaust system, the temperature change, etc., but it is not clear. In this case, the etching end point cannot be accurately determined even by simply monitoring the change in the two emission intensities and the difference or ratio.

Particularly in a system in which the light emission of the etching gas gradually decreases with the progress of etching, if the amount of change is larger than the amount of change due to the etching end point, it is difficult to distinguish these changes. When the aperture ratio is small, it is more difficult because the absolute value of the latter change is small. The present invention has been made to solve such a conventional problem, and an object thereof is to provide a dry etching method capable of accurately detecting an etching end point when dry etching silicon or a silicon compound. To do. In particular, even in the case of etching with a small aperture ratio, the etching end point can be detected with certainty, and control of over-etching, etc., with a depth of 2
It is an object of the present invention to provide a dry etching method which can be applied to etching of two-layer wiring in steps.

[0009]

The dry etching method of the present invention which achieves such an object is such that when the object to be processed is dry-etched with the etching gas, the emission intensity of the active species of the etching gas and the emission of the reaction product are increased. Intensities of the active species and the luminescence intensities of the reaction products are detected, the conversion coefficient is calculated, and the obtained luminescence intensity is calculated based on this conversion coefficient. Is obtained, and the end point of dry etching is determined based on this ratio.

[0010]

The amount of active species in the etching gas and the amount of reaction products change with the progress of etching, with gradual fluctuations, and the emission intensity changes accordingly. The change in emission intensity corresponding to these active species and the reaction product is determined by monitoring the change in spectral intensity at a given wavelength. The slopes of the two emission intensity change curves differ depending on the contribution rate of the additive gas such as argon, the accuracy of the spectroscope, and other causes.

In the case where the present inventor performs an operation for matching the inclinations of the change curves of these two emission intensities, obtains a conversion coefficient for making them coincide, and thereafter obtains the ratio of the emission intensities calculated by this conversion coefficient. It has been found that the ratio shows a constant value, and after the etching is completed, it rapidly changes and then takes another constant value. Therefore, the change in the emission intensity is monitored for a certain period of time, a predetermined conversion coefficient is obtained from these change curves, and thereafter, the emission intensity is calculated based on the conversion coefficient to obtain the ratio, and the change in the ratio value is monitored. As a result, the etching end point can be reliably detected. Further, since the value of the ratio is constant even after the etching is completed, it is possible to monitor this value and control the overetching time. Also, in the case of etching a two-layer wiring with a depth of two,
Since the ratio value takes a constant value stepwise, the end point at each step can be detected.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The dry etching method of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing an etching apparatus 1 to which the dry etching method of the present invention is applied.
A vacuum chamber 3 for mainly introducing an etchant to generate plasma to etch the object 2 to be processed, for example, a semiconductor substrate, a pair of electrodes 4 and 5 installed to face the vacuum chamber 3, and the inside of the vacuum chamber 3 And a control unit 6 for monitoring the emission spectrum. Etching
The object 2 to be processed, for example, a silicon dioxide film formed on a silicon wafer is selectively etched.

The vacuum chamber 3 is connected via a gate valve 7 and, if necessary, a load lock chamber 8 to a cassette chamber (not shown) for accommodating the object 2 to be processed, and the gate valve 7 is opened. The workpiece 2 can be transported by the transport mechanism. The vacuum chamber 3 is
An etchant, for example, a gas introduction pipe 9 for introducing a CF-based gas such as CHF ₃ or CF ₄ and an inert gas such as argon or helium, and an exhaust pipe 10 for exhausting a surplus gas, a reaction product gas, etc. Vacuum degree, eg 200mTo
The inside of the vacuum chamber 3 can be maintained at about rr.

The electrodes 4 and 5 form a parallel plate electrode. One electrode, for example, the upper electrode 4 is grounded, and the other lower electrode 5 is connected to a high frequency power source 12 via a capacitor 11. Apply a high frequency voltage to. The object 2 to be processed is placed on the lower electrode 5, and a clamper or the like is provided to surely fix the object 2 to be processed.

Further, on the side surface of the vacuum chamber 3, electrodes 4,
A window 13 made of quartz or the like is formed in order to transmit the emitted light of the plasma generated between 5 to the outside. This window 13
A lens 14 for condensing the light that has passed through the window 13 is installed close to. The light condensed by the lens 14 is branched into two through the optical fiber 15 and sent to the control unit 6. A window 13 made of quartz instead of glass, a lens 1 to detect low wavelength emission up to around 200 nm.
4 and the optical fiber 15 are used.

The control unit 6 divides the light into a spectrum of a predetermined range by the spectroscopes 61 and 62, and the photoelectric converter 6 that converts the light of the specific wavelength obtained by the spectroscopes 61 and 62 into electricity.
3, 64, amplifiers 65 and 66, and a determination unit 67 that performs a predetermined operation on the electric signal corresponding to the light of the specific wavelength and determines the etching end point from the operation result. On the other hand, the spectroscope 61 and the photoelectric converter 63 are a system for etchants such as CF ₁ and CF ₂ radicals, and a wavelength in the range of 240 to 350 nm, for example, 2 for CF ₂ radicals.
55.06 nm, 259.5 nm, 262.8 nm, 2
Monitor light such as 71.1 nm. In the emission wavelength band of CF ₂ of 240 nm to 350 nm, the emission of argon as the additive gas is particularly small. Further, since CF ₂ is an etching gas, its light emission is much stronger than that of the reaction product, so that light in this wavelength band can be separated by using an inexpensive interference filter having relatively low resolution. Particularly, the transmission center wavelength of the interference filter is set to 260 nm to 270 nm and the half width is 10 n.
If the m-thickness of 20 nm is used, photoelectric conversion can be performed with an inexpensive silicon photodiode without using a highly sensitive and expensive photomultiplier.

The other spectroscope 62 and photoelectric converter 64 are
Generated gas, for example, a system for carbon monoxide.
The wavelength may be 2.7 nm, but is preferably 210 nm to 2
Specific wavelengths selected from desired wavelengths within the range of 36 nm, more preferably 219.0 nm, 230.0 nm, 211.
Monitor 2 nm, 232.5 nm and any of 224-229 nm. The light in the range of 210 nm to 236 nm has a relatively small overlap between the emission spectrum of argon and the etchant CF _1, and does not overlap with the emission of the etchant CF ₂ , so that the light emission changes accurately even when the aperture ratio is small and the generated gas is small. Can be monitored.

FIG. 6 shows 200 nm to 400 during etching.
The emission spectrum in nm is shown. In the figure, a thick line shows a spectrum of a bare wafer, and a thin line shows a spectrum of a wafer with a full-scale silicon dioxide film etched under the conditions of high-frequency power of 600 W, 250 mTorr (mt), argon 400 SCCM, CHF ₃ 20 SCCM, and CF ₄ 20 SCCM, respectively. In addition, the dotted line uses a bare wafer, high frequency power 600 W, 250 mT
The results of performing argon plasma in the same chamber with orr (mt) and argon 400 SCCM are shown. 6 to 240n
From m to 350 nm, it can be seen that the emission of argon is on the emission peak of CF ₂ . 200 nm to 240
In nm, CF ₁ and CO from the solid wafer can be confirmed.

In order to detect the wavelength in such a range, it is preferable that the spectroscopes 61 and 62 have good sensitivity to light of 300 nm or less. The determination unit 67
For example, it is composed of an A / D converter, a CPU, and the like, and monitors the light emission intensity to catch the change and performs the calculation as described later to detect the end point of etching. Next, the dry etching method according to the present invention in the etching apparatus 1 configured as above will be described.

First, the semiconductor substrate to be processed 2 is transferred from the load lock chamber 8 by a transfer mechanism (not shown) and placed on the lower electrode 5. A mask having a predetermined pattern is formed on the silicon dioxide film of the semiconductor substrate through an exposure process. Next, the valve 7 is closed and the inside of the vacuum chamber 3 is evacuated to a predetermined degree of vacuum via the exhaust pipe 10, and then a CF type gas such as a CF ₃ gas or a CF ₄ type gas and an argon gas is used as an etching gas from the gas introducing pipe 9. An inert gas such as is introduced at a predetermined flow rate to maintain a predetermined gas pressure, and a predetermined frequency between the electrodes 4 and 5, for example, 1
While applying high frequency power of 3.56 MHz and a predetermined power value, for example, several 100 w, plasma is generated and the object to be processed 2 is processed.
The silicon dioxide film portion on the surface is etched.

The CF type gas introduced into the vacuum chamber 3 is dissociated in plasma to generate various kinds of active species, which participate in the etching reaction. For example, C as an active species
Taking F ₂ gas as an example, the reaction by this CF ₂ radical proceeds as follows, and products such as 2CF ₂ + SiO ₂ → SiF ₄ + 2CO carbon monoxide, CO ⁺ ions, hydrogen radicals, and fluorine radicals are generated. To do.

Carbon monoxide and CO ⁺ which are these generated gases
Ions, and argon gas, which is a plasma stabilizing gas,
The CF gas, which is an etching gas, emits light with a unique spectrum, and the emitted light is sent to the control unit 6 through the optical fiber 15 through the window 13 and the lens 14 of the vacuum chamber 3 and detected there. Spectrometer 61, 6
Reference numeral 2 disperses the sent light, displays it as a spectrum, and sends the light of a specific wavelength to the photoelectric converters 63 and 64, respectively. By the way, the emission spectrum obtained is a combination of the emission spectra of the above-mentioned plurality of gases, and the emission spectra of carbon monoxide and CO ⁺ ions are 35.
In the range of 0 to 860 nm, the spectrum of the most abundant argon gas almost completely overlaps. However, in the range of 210 nm to 236 nm, the wavelength 219.
0 nm, 230.0 nm, 211.2 nm, 232.5
nm and 224 to 229 nm, emission originating from carbon monoxide or CO ⁺ ions is observed. On the other hand, CF ₂ gas, which is an active species, has emission peaks at wavelengths such as 255 nm and 259.5 nm which are out of the spectral range of argon gas. Therefore, by tracking the light emission at any of these wavelengths, it is possible to detect the fluctuation of the generated gas at the etching end point.

That is, the spectroscope 61 has, for example, a wavelength of 255 nm.
Further, the spectroscope 62 is set to a specific wavelength selected from a desired wavelength within the range of 210 nm to 236 nm, and the photoelectric converters 63 and 64 correspond the light from these spectroscopes 61 and 62 to their light intensity. Convert it to the strength of electricity. The change in the emission intensity due to the change in the active species of the etching gas and the generated gas is sent to the determination unit 64 via the amplifiers 65 and 66 as the magnitude of the electric signal output from the photoelectric converters 63 and 64, and the determination is performed. The unit 64 performs a predetermined calculation based on this electric signal to determine the etching end point. That is, the calculation is performed to match the slopes of the change curves of the emission intensity of both, and the coefficient is obtained. Then, after performing a predetermined calculation on the obtained emission intensity using this coefficient, the ratio of the emission intensity is obtained, and the point where the value of the ratio changes by a predetermined amount is determined as the etching end point.

An example of the calculation performed by the determination unit 64 will be described below. The emission intensity of light obtained by the spectroscopes 61 and 62 gradually changes with the progress of etching in a change curve as shown in FIG. FIG. 2A shows changes in emission intensity related to active species (output Ch ₀ of photoelectric converter 63) and changes in emission intensity related to generated gas (output C of photoelectric converter 64).
h ₁ ) is shown. The determination unit 67 first (1) averages Ave ₀ , Ave in the designated section of such a change curve.
ve ₁ is calculated, and (2) N measured values Ch ₀ in the specified section,
The absolute value of the difference between Ch ₁ and the average values Ave ₀ and Ave ₁ is calculated and the specified section averages A ₀ and A ₁ are taken (area calculation).

A ₀ = Σ | Ch ₀ −Ave ₀ | / NA ₁ = Σ | Ch ₁ −Ave ₁ | / N (3) The ratio R of the designated section averages A ₀ and A ₁ is calculated. R = A ₀ / A ₁ After calculating the average values Ave ₀ , Ave ₁ and the ratio R for the designated section as described above, the photoelectric converter 63 is calculated based on these coefficients.
The following calculation is performed on the output Ch ₀ of the above, and the ratio between the calculated value obtained and the output Ch ₁ of the photoelectric converter 64 is calculated. (4) Subtract the average value Ave ₀ from the measured value Ch ₀ .

Ch ' ₀ = Ch ₀ -Ave ₀ Ch' ₀ is shown by the curve e in FIG. 2 (b). (5) Divide Ch ′ ₀ by the ratio R. This gives the Ch ₀ curve and Ch
The slopes of the curves of ₁ match. Ch ″ ₀ = Ch ′ ₀ / R Ch ″ ₀ is shown by the curve f in FIG. (6) Add the average value Ave ₁ of Ch ₁ to Ch ″ ₀ . This agrees with the curve of Ch ₁ .

Ch ″ ′ ₀ = Ch ″ ₀ + Ave ₁ (7) The ratio r between the calculated value Ch ′ ″ ₀ and the output Ch ₁ is calculated. Then, it is determined when the ratio value has changed to a preset threshold value or more, and this is set as the etching end point. Although the output Ch ₀ is converted by the coefficient in this calculation example, it goes without saying that the output Ch ₁ may be converted. Further, the calculation of the determination unit 64 is not limited to the above-described method, and an appropriate change is made, for example, by obtaining approximate curves of change curves of both outputs and obtaining a ratio by matching the inclinations of the approximate curves. be able to.

Based on the judgment of the judgment unit 64, the etching is finished automatically or manually. Further, when overetching is required depending on the object to be processed, the determination unit 6
Etching is terminated after a predetermined overetching time from when the end point 4 is determined. Example 1 CHF ₃ is 60 SCCM and CF ₄ is 60 as etching gases.
SCCM and argon gas were introduced into the vacuum chamber at 800 SCCM, 750 mTorr (mt), RF 13.56 MHz,
Plasma etching was performed at 600 W and a wafer temperature of -25 ° C. The object to be processed is a wafer (aperture ratio of 10% and 2.5%) in which a silicon oxide film of 10,000 angstrom is formed on silicon.

255 nm or 2 with etching progress
The change in emission intensity at 71 nm and the rate of change in emission intensity at 219 nm were monitored. Further, the average value of these emission intensities and the ratio R were obtained in the section from the etching progress of 60 seconds to 100 seconds, and a predetermined calculation was performed on the measured values based on the coefficients obtained thereafter to obtain the emission intensity ratio r. The results are shown in FIG. In the figure, the solid line a is the emission intensity at 255 nm, the solid line b is the emission intensity at 219 nm, and the solid line c.
Indicates the ratio r of both after the calculation. As is clear from FIG. 3, the emission intensity at both wavelengths gradually decreases from the start of etching, the emission intensity at 219 nm decreases rapidly after about 120 seconds, and the emission intensity at 255 nm decreases gradually. .. Fluctuations are seen on these curves, making it difficult to capture changes. On the other hand, the one obtained by performing the predetermined calculation and taking the ratio of both (solid line c) is almost constant until about 120 seconds, but after this time, it rises sharply and then becomes constant again. Recognize. The values of the light intensity and the ratio in the figure are values standardized with the value at 100 seconds as 100.

FIG. 4 shows the change in the ratio r of the two emission intensities after the predetermined calculation, and shows the change rate when the value in the designated section from 60 seconds to 100 seconds is 100. As can be seen from the figure, in the case of monitoring the change of the emission intensity at 271 nm with respect to CF ₂ , 5.2% (solid line b) when the aperture ratio is 10%, and 1. 2 when the aperture ratio is 2.5%.
A change of 2% (solid line d) was obtained. In addition, in the case of monitoring the change in emission intensity at 255 nm with respect to CF ₂ , a change of 5.9% (solid line a) when the aperture ratio is 10% and 1.7% (solid line c) when the aperture ratio is 2.5%. was gotten. All of these values were changes that could stably determine the end point. The variation of the ratio r in the designated section was within 0.13%. Example 2 CHF ₃ was 20 SCCM and CF ₄ was 20 as etching gases.
SCCM and argon gas are introduced into the vacuum chamber at 400 SCCM, 250 mTorr (mt), RF 13.56 MHz,
Plasma etching was performed at 600 W and a wafer temperature of -25 ° C. The object to be processed is a wafer (aperture ratio 2.5%) in which a silicon oxide film of 10,000 angstrom is formed on silicon.

The change in the emission intensity at 255 nm and the rate of change of the emission intensity at 219 nm with the progress of etching were monitored, and the progress of etching was changed from 60 seconds to 10 seconds.
The average value of these emission intensities and the ratio R were obtained for the section of 0 second, and a predetermined calculation was performed on the measured values based on the coefficients obtained thereafter to obtain the emission intensity ratio r. The results are shown in FIG. In the figure, the solid line a is the emission intensity at 255 nm, and the solid line b is 2.
The emission intensity at 19 nm and the solid line c indicate the ratio r of both after the calculation. As is apparent from FIG. 5, the ratio of the two calculated by performing the predetermined calculation as in the first embodiment (solid line c) is almost constant up to about 140 seconds, but beyond this point. It can be seen that it rises sharply and becomes constant after 150 seconds. The values of light intensity and ratio in the figure are 1
The value normalized by setting the value at 20 seconds as 100 is shown.

As is clear from the above embodiment, the end point of etching is extremely clear as compared with the case where one emission intensity is monitored by calculating the ratio of the two emission intensities after the predetermined calculation. Can be detected. Further, since the ratio value is constant even after the etching end point, the over-etching time can be controlled, and even in the case of etching a two-layer wiring having a depth of two, the end point is set at each step. It is possible to detect.

In the above embodiments, the case where the silicon dioxide film is etched has been described, but the present invention is not limited to these etchings and is applied to the case where a polysilicon film or an aluminum alloy film is etched. Alternatively, the material forming the base of the film to be etched may be a material other than single crystal silicon, such as polysilicon.

Further, the present invention can be applied to both a cathode coupling type etching apparatus in which an object to be processed is placed on the cathode side and an anode coupling type etching apparatus in which an object to be processed is placed on the anode side. It is also applicable to an etching method in which reactive gas plasma is generated in the discharge chamber by the above method and is guided to the etching region.

[0035]

As is apparent from the above description, according to the dry etching method of the present invention, changes in two emission intensities corresponding to an etching gas and a product are monitored during etching, and predetermined changes are made to these. Since the ratio is calculated by performing the above calculation, the amount of change at the end point is not affected by fluctuations in the emission intensity, even when the aperture ratio is small and the amount of generated gas to be detected is small. Even if the change is smaller than the total change of the above, the end point of etching can be detected extremely accurately. As a result, it is possible to prevent excessive etching such as unnecessary removal of the base material or change in etching shape. In addition, overetching can be controlled if necessary.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of an etching apparatus to which a dry etching method of the present invention is applied.

FIG. 2 is a diagram illustrating an example of calculation in the dry etching method of the present invention.

FIG. 3 is a diagram showing changes in emission intensity at wavelengths of 255 nm and 219 nm and a ratio of these emission intensities after a predetermined calculation.

FIG. 4 is a diagram showing a rate of change of a ratio of emission intensity after a predetermined calculation.

FIG. 5 is a diagram showing changes in emission intensity at wavelengths of 255 nm and 219 nm and a ratio of these emission intensities after a predetermined calculation.

FIG. 6 shows the emission intensity in the wavelength range of 200 nm to 400 nm when a bare wafer (thick line), a wafer with a full-scale silicon dioxide film (thin line) is measured during treatment with Ar, CHF ₃ , and CF ₄ , and the bare wafer (dotted line) alone. The figure which shows the comparison about the case where it measures during the process.

[Explanation of symbols]

 1 ··· Etching device 2 ·· To-be-processed object 3 ··· Vacuum chamber 6 ··· Control device

Claims (1)

[Claims] 1. When dry etching an object to be processed with an etching gas, the emission intensity of the active species of the etching gas and the emission intensity of the reaction product are respectively detected to detect the emission intensity of the active species and the reaction product. A dry etching method characterized in that after a predetermined calculation of emission intensity, a ratio of two emission intensities is obtained, and the end point of dry etching is determined based on this ratio.