JPH05102089A - Dry etching method - Google Patents

Abstract

PURPOSE:To provide a dry etching method to detect the etching end point accurately by monitoring emission spectrum changes. CONSTITUTION:While the emission spectrum is monitored during etching, the desired spectrum intensity out of the range of 210nm-236nm in wavelength, especially any one of 219.0nm, 230.0nm, 211.2nm, 232.5nm and 224-229nm, is measured to determine the dry etching end point. Therefore, even if the system contains a large volume of additive gases such as argon gas, etc., or the object to be etched has a small etching area (low numerical aperture) per area, the changes of formation gas 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, such a wavelength range is very close to 350 to 860 nm, which is a strong emission wavelength range of argon, so that 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 entire area of the wafer, that is, the aperture ratio is 10% or less, and when the aperture ratio is smaller, it is about 2 or 3%. For this reason,
The amount of carbon monoxide gas generated is a minute amount, for example, 1/100 or less compared to the amount of argon gas introduced, and the emission intensity of carbon monoxide cannot be accurately detected, and the end point of etching can be specified. It was difficult.

Therefore, a method of monitoring the difference or the ratio between the emission intensity of the product and the emission intensity of the added gas (Japanese Patent Laid-Open No. 6-68242)
3-91929) and the like are also proposed. However, in general, the intensity of the emission spectrum from the plasma reaction system depends on the slight fluctuations in the power output, the influence of the mass flow controller,
It constantly fluctuates due to fluctuations in processing pressure, substrate temperature rises caused by plasma, etc.As a result of this fluctuation, changes in the emission intensity of the generated gas, etc. and changes in the emission intensity of the additive gas are monitored as described above. However, it was difficult to accurately determine the etching end point.

The present invention has been made to solve such conventional problems, and it is an object of the present invention to provide a dry etching method capable of accurately detecting the etching end point when dry etching a semiconductor substrate or the like. To aim.

[0009]

The dry etching method of the present invention which achieves the above object is 210 nm to 23 nm.
It controls dry etching of silicon dioxide or a silicon compound by measuring a desired spectrum intensity selected from a desired wavelength within a range of 6 nm, and is preferably 219.0 nm, 230.0 nm, 211.2 n.
m, 232.5 nm, and any of the wavelengths of 224 to 229 nm are measured to control the dry etching.

[0010]

[Function] By monitoring the emission intensity of the produced gas in a specific range of the ultraviolet region outside the strong emission wavelength range of the added gas, interference with the emission spectrum of the added gas is reduced and accurate changes in emission intensity are measured. You can
This makes it possible to accurately detect the end point of etching.

[0011]

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 to a cassette chamber (not shown) for storing the object 2 through the gate valve 7 and, if necessary, a load lock chamber (not shown), and the gate valve 7 is opened. The workpiece 2 can be transported by the transport mechanism. Further, the vacuum chamber 3 includes a gas introduction pipe 9 for introducing an etchant such as a CF-based gas such as CHF ₃ and CF ₄ and an inert gas such as argon and helium, and an exhaust pipe 10 for exhausting a surplus gas and a reaction product gas. Is connected to a predetermined vacuum degree, for example 2
The inside of the vacuum chamber 3 can be maintained at about 00 mTorr.

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 an ultraviolet light transmissive material such as quartz is formed in order to transmit the emitted light of the plasma generated between 5 to the outside. A lens 14 for condensing the light transmitted through the window 13 is installed near the window 13. This lens 1
4 is also made of an ultraviolet light transmissive material such as quartz. By using an ultraviolet light transmissive material such as quartz as the material of the window 13 and the lens 14 as described above, light in the spectral range of 250 nm or less can be condensed. The light condensed by the lens 14 passes through the optical fiber 15 made of quartz and the control unit 6
Will be sent to.

The control unit 6 disperses the light into a spectrum in a predetermined range, a spectroscope 61, a photoelectric converter 62 that converts the light of a specific wavelength obtained by the spectroscope 61 into electricity, and an amplifier 6
3 and a determination unit 64 for monitoring a change in voltage corresponding to the light of the specific wavelength. As the spectroscope 61, a spectroscope having good sensitivity to light of 300 nm or less is used. The wavelengths to be monitored are specific wavelengths selected from desired wavelengths within the range of 210 nm to 236 nm, 219.0 nm, and 230.0 n.
m, 211.2 nm, 232.5 nm and 224-22
It is preferable to use any one of 9 nm. Judgment unit 64
Is composed of, for example, an A / D converter, a CPU, and the like, and monitors the emission intensity, catches the change, performs appropriate calculation as necessary, and detects the end point of etching.

Next, the dry etching method according to the present invention in the etching apparatus 1 configured as described above will be described. First, the semiconductor substrate which is the object 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.

Then, the valve 7 is closed and the inside of the vacuum chamber 3 is evacuated to a predetermined degree of vacuum through the exhaust pipe 10, and then a CF type gas such as CF ₃ gas and CF ₄ type gas is used as an etching gas from the gas introducing pipe 9. And an inert gas such as argon gas are introduced at a predetermined flow rate to maintain a predetermined gas pressure, and a predetermined frequency between both electrodes 4 and 5, for example, 13.56M.
While applying a high frequency power of Hz and a predetermined power value of, for example, several 100 w, plasma is generated to etch the silicon dioxide film portion on the surface of the target object 2.

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. The spectroscope 61 disperses the sent light and sends the light of a specific wavelength to the photoelectric converter 62. The emission spectrum obtained by the spectroscope 61 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 the most abundant argon in the range of 350 to 860 nm. It almost completely overlaps with the spectrum of gas. However, in the range of 210 nm to 236 nm, especially the wavelengths 219.0 nm, 230.0 nm, 211.2 nm,
At 232.5 nm and 224-229 nm, luminescence originating from carbon monoxide or CO ⁺ ions is observed. 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 calculates 21 of the dispersed light.
Light of a specific wavelength selected from a desired wavelength within the range of 0 nm to 236 nm is sent to the photoelectric converter 62, and the photoelectric converter 62 converts it into electricity having an intensity corresponding to the light intensity. By the way, while CO or CO ⁺ is usually etched,
It keeps a certain amount or continues to occur while gradually decreasing by drawing a specific decrease curve, but it rapidly decreases at the end point of etching. The change in the generated gas as described above is determined as the magnitude of the electric signal output from the photoelectric converter 62.
4, the determination unit 64 performs a predetermined calculation based on this electric signal to detect a sudden change in the produced gas. As the calculation performed by the determination unit 64, for example, an approximate curve of the generated gas change curve is obtained, and when there is a change of a predetermined threshold value or more from this approximate curve, this is determined. Alternatively, it is determined when the change exceeds a predetermined threshold value, and this is set as the etching end point.

Based on the judgment of the judging section 64, the etching is ended automatically or manually. If overetching is required depending on the object to be processed, the determination unit 64
Etching is terminated after a predetermined overetching time from when the end point is determined. Example 1 CHF ₃ is 20 SCCM and CF ₄ is 20 as an etching gas.
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 in which a silicon oxide film of 10,000 angstrom is formed on silicon (aperture ratio 100%, hereinafter referred to as a solid wafer). As a comparative example, the same process was performed using a bare silicon wafer (one on which no oxide film was formed). FIG. 2 shows emission spectra of a solid wafer and a bare wafer. In the figure, the thick solid line shows the emission spectrum of a bare silicon wafer, and the thin solid line shows the emission spectrum of a solid wafer with an aperture ratio of 100%.
In the bare wafer, no CO or CO ⁺ is generated due to no reaction in the etching under the above conditions, and a spectrum in which the etching gas and argon (Ar) are overlapped is seen. Further, in the case of a wafer having a silicon oxide film formed, CO
Alternatively, a change in spectrum due to CO ⁺ was observed, and this change was found to be significant in the range of 210 nm to 236 nm. Especially 211.2 nm, 219.0 nm, 23
At 0.0 nm and 232.5 nm, peaks not found on the bare wafer were observed, and at 224 to 229 nm, an increase in emission intensity was observed over that range. Therefore,
By monitoring this peak or the region where the emission intensity changes, it can be seen that the change in the produced gas can be accurately detected.

FIG. 5 shows a conventional end point detection wavelength (482 nm).
The emission spectrum in the vicinity is shown. This figure is measured under the same conditions as in FIG. According to FIG. 5, in the case of a solid wafer 40
An increase in the amount of luminescence due to CO emission of the reaction product can be confirmed in the vicinity of 0 nm to 600 nm. Further conventional 482n
The vicinity of m is the valley of the emission of Ar of the added gas, and the emission peaks of the left and right argon are 400 nm to 5 at which the emission of CO is strong.
It can be seen that the wavelength is relatively weak at 00 nm and the Ar spacing is the widest wavelength, and that it is optimum as the end point detection wavelength in the wavelength band of 400 nm or more. However, the emission intensity of CO on a solid wafer is about 1/10 of the emission intensity of nearby Ar, and the wavelength difference from Ar is 1.5 nm.
There is only a degree.

On the other hand, from FIG. 2, it is understood that near 219 nm, the emission intensity of CF ₁ (223.8 nm) in the vicinity and the emission intensity of 219 nm, which is the emission of the reaction product from the solid wafer, are almost equal. Furthermore, the wavelength difference is 4.8 nm,
Even an inexpensive low-resolution spectroscope can sufficiently disperse CO emission. On the contrary, there is a merit that the amount of spectrum that can lower the resolution can be increased to make it stronger against noise. From the comparison of these emission spectra, it can be seen that the new detection wavelength of 219 nm is more excellent as the end point detection wavelength. Example 2 shows a change in light amount during actual etching. Example 2 Silicon oxide having an aperture ratio of 10% was etched under the same conditions as in Example 1, and the change in the emission intensity at 219.0 nm (thick solid line) and the rate of change in the emission intensity at 482.0 nm (fine change) with the progress of etching. The results of monitoring the solid line) with two spectroscopes at the same time are shown in FIG. As is clear from FIG. 3, the emission intensity gradually decreases from the start of etching,
It decreased rapidly after about 150 seconds and became flat after about 170 seconds. That is, it is understood that the etching is completed at this point. Approximate curve of decrease curve 1
The value (rate of change) obtained by converting the difference between the emission intensity when extended to 70 seconds and the actual emission intensity with the emission intensity at 100 seconds being 100 was 3.4%. On the other hand, the rate of change (thin solid line) of the emission intensity at the conventional measurement wavelength of 482.0 nm is 1.8%, which shows that the method of the present invention has a large rate of change and is excellent.

FIG. 6 shows a solid wafer (aperture ratio of 10
(0%) shows the change in the amount of light during etching. It can be seen from FIG. 6 that even in the case of a solid wafer, the rate of change is almost twice as large and excellent in the method of the present invention. Example 3 Etching was performed under the same conditions as in Example 1 except that the degree of vacuum was changed to 1.7 Torr (t) and etching was performed to obtain the rate of change when the aperture ratio was 10%. The rate of change at each wavelength in this case is shown in FIG. The rate of change in the case of 250 mTorr (mt) is also shown. In the figure, the thick solid line is the spectrum of the bare wafer in the case of 250 mTorr (mt), and the dotted line is the same as 250 mTorr (mt).
Shows the spectrum of the solid wafer in the case of, and the thin solid line is 1.
The spectrum of a bare wafer in the case of 7 Torr (t) is shown.
For reference, a spectrum (500 mTorr) when only argon gas was introduced is shown. As is clear from FIG. 4, the rate of change was 5% or more at the wavelength of 219.0 nm, and about 2% at the wavelengths of 211.2 nm, 230.0 nm and 232.5 nm.

From the above embodiment, the wavelengths of 210 to 236
Range, preferably 219.0 nm, 230.0 nm, 21
1.2 nm, 232.5 nm and 224-229 nm
End point of etching gas by monitoring emission intensity
It is clear that can be accurately detected. In addition, etch
In order to detect the end point of the ring gas, the product gas (CO or C
O ⁺) Change may be monitored, but the change in product gas
End point detection method such as taking the ratio of the etching gas to the etching gas change
It goes without saying that it may be combined with.

Further, in the above-mentioned embodiments, an example in which CF-based gas is used as an etching gas and argon is used as an additive gas has been explained, but the dry etching method of the present invention is a dry etching which produces a generated gas having an emission peak in the ultraviolet region. The method can also be applied to a dry etching method using an etchant having an emission peak in the ultraviolet region.

Furthermore, the present invention is not limited to the case of etching a silicon dioxide film, but may be applied to the case of etching a polysilicon film, an aluminum alloy film, or the like, and may be applied to the base of the film to be etched. The certain material may be a material other than single crystal silicon, such as polysilicon or an oxide film. The present invention can be applied to both a cathode coupling type etching apparatus in which the object to be processed is placed on the cathode side and an anode coupling type etching apparatus in which the object to be processed is placed on the anode side. It can also be applied to an etching method in which a reactive gas plasma is generated in the discharge chamber and is guided to the etching region.

[0028]

As is apparent from the above description, according to the dry etching method of the present invention, the emission intensity at the specific wavelength of 210 nm to 236 nm in the ultraviolet region is monitored during etching. Accurately tracking changes in the amount of generated gas even when the amount of generated gas to be detected is small and when the etching gas contains a large amount of inert gas resulting in a low concentration of generated gas. Therefore, the etching end point can be accurately detected. As a result, it is possible to prevent excessive etching such as unnecessary removal of the base material or change in etching shape.

[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 showing an emission spectrum at the time of dry etching at wavelengths of 210 nm to 236 nm.

FIG. 3 is a wavelength 2 obtained by etching a wafer having an aperture ratio of 10%.
The figure which shows the change of the light emission intensity in 19.0 nm and 482.0 nm.

FIG. 4 is a diagram showing an emission spectrum and a rate of change during dry etching.

FIG. 5 is a diagram showing an emission spectrum at the time of dry etching at a conventional end point detection wavelength of 482 nm.

FIG. 6 is a diagram showing changes in emission intensity at wavelengths 219.0 nm and 482.0 nm obtained by etching a wafer having an aperture ratio of 100%.

[Explanation of symbols]

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

Claims (2)

[Claims] 1. An end point of dry etching is determined by measuring a desired spectrum intensity selected from a desired wavelength within a range of 210 nm to 236 nm when dry etching an object to be processed with an etching gas. Dry etching method. 2. The etching gas is a CF-based gas,
The wavelengths are 219.0 nm, 230.0 nm, 21
The dry etching method according to claim 1, wherein the dry etching method is any one of 1.2 nm, 232.5 nm and 224 to 229 nm.