JP3195695B2 - Plasma processing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma processing method, and more particularly to a method for determining an end point of a plasma processing.

[0002]

2. Description of the Related Art In a semiconductor manufacturing process, dry etching using gas plasma is an essential technique for forming a fine pattern on an object to be processed, for example, a semiconductor substrate. Such an etching process is a method in which plasma is generated using a reaction gas in a vacuum, and an etching target is removed using ions, neutral radicals, atoms, molecules, and the like in the plasma.

In such a plasma etching process,
If the etching process is continued even after the object to be etched is completely removed, the underlying material is unnecessarily shaved,
Alternatively, since the etching shape changes, it is important to accurately detect the end point of the etching in order to prevent this.

[0004] For this purpose, for example, a silicon oxide film is formed of CF.
In the case of etching with a system processing 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 of the etching is determined based on a change in the emission intensity (for example, Japanese Patent Application Laid-Open Publication No. H11-163873). See JP-A-63-81929 and JP-A-1-230236. Alternatively, a method has been proposed in which the emission intensity of the etchant is monitored together with the emission intensity of the reaction product, and the end point of etching is determined based on the difference or ratio of these emission intensities (for example, JP-A-63-91929). Gazette).

[0005]

However, in any of the conventional methods, the peak intensity (peak height) of a certain wavelength is used in monitoring the plasma emission intensity. Is weak, S
As a result, the / N ratio deteriorated, the detection sensitivity decreased, and the end point of the etching could not be determined accurately.

In particular, with the recent demand for ultra-high integration,
The region to be etched also tends to be very small, the amount of reaction products generated by etching is very small, and accurate measurement is difficult. In general, the intensity of the emission spectrum from the plasma reaction system varies slightly depending on the power supply output, the influence of the mass flow controller, the fluctuation of the processing pressure,
The fluctuations are continually caused by a rise in the substrate temperature caused by the plasma, and the fluctuations further degrade the S / N ratio, making it difficult to accurately monitor the change in the luminescence intensity of the reaction product. ing.

The present invention has been made in view of the above-mentioned problems in detecting the end point of the conventional plasma processing, and has as its object to reduce the intensity of the emission spectrum due to the plasma processing and to increase the detection sensitivity. An object of the present invention is to provide a new and improved end point determination method for a plasma etching process that can accurately determine the end point of a plasma etching process with a good S / N ratio even if the power supply falls.

[0008]

According to a first aspect of the present invention, there is provided a CF-based etching gas.
Generates plasma using silicon and etches silicon oxide film
In the method of detecting the end point of etching when
Wavelength 240 to 3 including emission spectrum of etching gas
The wavelength band selected from 50 nm and the reaction product
Wavelength 210 to 236 nm including emission spectrum of CO-based gas
Average of the emission intensities in the wavelength band selected from
Values, and calculate the ratio or difference of their sum
Detecting the end point of the plasma processing based on the
An etching end point detection method is provided.

[0009]

[0010]

Further, in the above-mentioned method for detecting the end point of etching , it is preferable that the emission band to be monitored is selected from a range excluding the emission peak value of silicon (Si).

[0012]

According to the etching end point detecting method of the present invention , the emission spectrum of the monitored plasma emission species is monitored in a spectral range having a certain fixed width. Because it is possible to detect large, even if the intensity of the emission spectrum is weak or the sensitivity of the sensor is low,
It is possible to determine the end point of the plasma processing with good S / N ratio and high accuracy. Also, the etching end point detection of the present invention
According to the method, the emission band of the observed plasma emission species is
The range that appears relatively stronger than the peak values of other luminescent species,
That is, a spectrum in which the effect of other luminescent species can be ignored.
Easy selection even with low-sensitivity sensors by selecting a range
And the S / N ratio can be further increased.
is there. Further, according to the etching end point detecting method of the present invention,
If the amount is not used after etching is completed,
Process gas active species such as C
Emission spectrum of CF-based gas such as HF ₃
No longer occurs at the end of lighting,
Emission spectrum of reaction products such as CO
That is, it shows a different change at the end of etching
Both of which are based on two luminescent species
Since the end point is determined, highly accurate determination can be easily performed.
be able to. Furthermore, the final inspection of etching of the present invention
According to the above method, the silicon oxide film is particularly treated with a CF-based processing gas.
When etching by etching,
Monitoring changes in the emission peak value of carbon oxide (CO)
At the end of etching, the silicon oxide film and CF
The amount of carbon monoxide (CO), a reaction product with gas, is rapidly increasing.
As the emission intensity decreases rapidly, the end point can be easily determined.
Can be

[0013]

[0014]

[0015]

According to the second aspect of the present invention, the emission peak value of silicon forming the base of the silicon oxide film, for example, 24
From the range excluding the wavelength band of 3 to 252 nm or 288 nm, the emission peak value or emission band to be monitored, for example, 25
By selecting a wavelength band of 5 to 287 nm, noise due to the emission spectrum of silicon can be ignored, and the end point of the plasma etching process with a higher S / N ratio can be determined.

[0017]

An embodiment in which the plasma processing method according to the present invention is applied to the determination of the end point of the plasma etching processing will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a diagram schematically showing a plasma etching apparatus 1 to which the method of the present invention is applied. The etching apparatus 1 includes a vacuum chamber 3 that is configured to be airtight and can be adjusted to a desired reduced-pressure atmosphere, a pair of electrodes 4 and 5 installed in the vacuum chamber 3 so as to face each other, And a control unit 6 for monitoring the emission spectrum. An object to be processed, for example, a semiconductor wafer 2 is mounted and fixed on the lower electrode 5 by a fixing means such as an electrostatic chuck, and a processing gas can selectively etch a silicon dioxide film formed on the wafer. It is.

The vacuum chamber 3 is connected to a cassette chamber (not shown) for accommodating the object 2 through a gate valve 7 or a load lock chamber 8 as necessary. By opening the valve 7, it is possible to carry in and carry out the object 2 by a transport mechanism (not shown). The vacuum chamber 3 is
A gas introduction pipe 9 for introducing an etchant, for example, a CF-based gas such as CHF ₃ and an inert gas such as argon or helium if necessary, and an exhaust pipe 10 for exhausting surplus gas or reaction product gas are connected. The vacuum chamber 3 is set to a predetermined reduced pressure atmosphere, for example, 200 mTorr.
It is possible to hold inside.

The electrodes 4 and 5 constitute a parallel plate type electrode. One upper electrode 4 is grounded, and the other lower electrode 5 is connected to a high frequency power supply 12 via a matching capacitor 11. It is configured so that a high-frequency voltage can be applied between both electrodes. Further, as described above, the object to be processed 2 can be mounted and fixed on the lower electrode 5 by an electrostatic chuck means or the like.

Further, a window 13 made of quartz or the like is formed on a side surface of the vacuum chamber 3 for transmitting the emission of the plasma generated between the electrodes 4 and 5 to the outside. A lens 14 for condensing light transmitted through the window 13 is provided near the window 13. This lens 1
The light condensed at 4 is split into two through an optical fiber 15 and sent to the control unit 6. By employing the light detecting means including the quartz window 13, the lens 14, and the optical fiber 15 instead of the glass as described above, it is possible to detect light having a short wavelength up to around 200 nm.

The control section 6 has spectroscopes 61 and 62 for splitting light into a spectrum in a predetermined range, and the spectrometers 61 and 62.
The photoelectric converters 63 and 64 that convert the light of the specific wavelength obtained by the above into an electric signal, the amplifiers 65 and 66, and perform a predetermined operation on the electric signal corresponding to the light of the specific wavelength, A determination unit 67 that determines the end point of the etching process from the calculation result.

One spectroscope 61 and photoelectric converter 63
When using an etchant, for example, a CF-based gas such as CF _3, a wavelength range of 240 to 350 nm,
It is possible to monitor light in the wavelength band preferably in the range of 240 to 280 nm, more preferably in the wavelength band of 255 to 287 nm. By selecting the range of the monitoring light from such a wavelength band, 243 to 252 nm and 288 n
It is possible to avoid confusion between the emission spectrum of silicon having an emission peak value at m and the emission spectrum of a desired processing gas.

As described above, according to the method of the present invention, unlike the conventional method, light in a wavelength band having a certain width is monitored, and the sum total average value of the light in the wavelength band is calculated to determine the end point of the etching process. Since the determination is made, an inexpensive interference filter having a relatively low resolution can be used unlike the conventional peak value detection method. In particular, the transmission center wavelength of the interference filter is set to 24
0 to 280 nm, more preferably 255 to 287 nm
If a half-width of 10 nm to 20 nm is used as the approximate center, photoelectric conversion can be performed by an inexpensive silicon photodiode.

On the other hand, the other spectroscope 62 and the photoelectric converter 64 are, for example, 210 nm to 2 nm when a reaction product gas, for example, a carbon monoxide-based reaction product is generated.
It can be used to monitor light in a wavelength band in the range of 36 nm, calculate the sum average thereof, and determine the end point of the etching process. Also, preferably, a specific wavelength selected from within the above wavelength band range, for example, 219.0 nm, 23
0.0 nm, 211.2 nm, 232.5 nm or 2
Any one of 24-229 nm can be monitored and its value can be used to directly determine the end point of the etching process.

FIGS. 2 and 3 show that the silicon oxide film is C
200 n when plasma etching is performed using HF ₃ etching gas under the conditions of high frequency power 800 W, processing pressure 200 mTorr, and CHF ₃ supply 50 sccm.
The emission spectrum from m to 400 nm is shown. In the drawing, the thick line indicates a bare wafer having no silicon oxide film formed thereon, and the thin line indicates a solid wafer having a silicon oxide film formed over the entire surface.

As is clear from FIGS. 2 and 3, for example, a wavelength band in the range of 240 to 350 nm, preferably 24
Wavelength band in the range of 0 to 280 nm, more preferably 25
By selecting and monitoring light in a wavelength band in the range of 5 to 287 nm, even if the light intensity of the peak value of each wavelength is weak, a wavelength band having a certain width can be monitored. It is possible to perform highly accurate monitoring. In particular, by selecting a wavelength band in the above range, the variation of the emission spectrum of the processing gas can be reduced without being affected by the variation of the emission spectrum of silicon under the wafer having emission peak values at 243 to 252 nm and 288 nm, respectively. Since monitoring can be performed, more accurate monitoring can be performed.

[0029] Figures 4 and 5 also, by a silicon oxide film CHF ₃ etching gas, high frequency power 800
W, processing pressure 10 mTorr, CHF ₃ supply 50 scc
The emission spectrum at 200 nm to 400 nm when the plasma etching process is performed under a lower pressure condition than m is shown. In the case of this embodiment, similarly,
In the drawing, a thick line indicates a bare wafer having no silicon oxide film formed thereon, and a thin line indicates a solid wafer having a silicon oxide film formed over the entire surface.

The processing pressure shown in FIGS. 2 and 3 is 200 mT.
As can be better understood by comparing the case of the etching process of orr with the case of the etching process at a processing pressure of 10 mTorr shown in FIGS. 4 and 5, in the case of the low-pressure process that has recently attracted attention, the CHF ₃ gas is used. Although the emission spectrum intensity is low and it is difficult to detect the emission spectrum with a sensor having low sensitivity, according to the method of the present invention, for example, 240
By monitoring the emission spectrum in the wavelength band of ２280 nm, even if the emission intensity at the peak wavelength of each spectrum is low, it is possible to obtain a certain level of emission intensity as a whole. As a result, even when a low-accuracy sensor is used, highly accurate measurement can be performed, and the end point of the plasma processing etching can be accurately determined.

Next, an embodiment in which the etching apparatus 1 configured as described above is applied to a processing method configured according to the present invention will be described. First, the object 2 to be processed, for example, a semiconductor wafer, is transported from the load lock chamber 8 by a transport mechanism (not shown) and is mounted and fixed on the lower electrode 5 in the processing chamber 3. A mask having a predetermined pattern is formed on the oxide film of the semiconductor wafer through an exposure process. Next, the gate valve 7 is closed, the inside of the vacuum chamber 3 is evacuated to a predetermined degree of vacuum, for example, 200 mTorr via the exhaust pipe 10, and then a CF-based gas such as CHF _{3 is used} as an etching gas from the gas introduction pipe 9. The gas is introduced at a predetermined flow rate and maintained at a predetermined gas pressure, and a high frequency power of a predetermined frequency, for example, 13.56 MHz, a predetermined power value, for example, several hundred W is applied between the electrodes 4 and 5. Then, an oxide film on the surface of the object 2 is etched by generating plasma.

The CF-based gas, for example, CHF ₃ introduced into the vacuum chamber 3 is dissociated in the plasma to generate CF _{2 and} other kinds of active species, which react with the silicon oxide film to be etched. As a result, reaction products such as SiF _x , carbon monoxide, and CO ⁺ ions are generated. Of these reaction products, carbon monoxide, CO ⁺ ions, or CHF ₃ gas as an etching gas emits light having a specific spectrum, and these lights are emitted from the quartz window 13 of the vacuum chamber 3 and the lens. 1
4 to the control unit 6 via the optical fiber 15. And the spectrometers 61 and 6
Numeral 2 disperses the light transmitted through the optical fiber 15 and displays it as a spectrum, and transmits an emission spectrum of a specific wavelength or an emission spectrum included in a specific wavelength bandwidth to the photoelectric converters 63 and 64. I do.

The emission spectrum obtained is a synthesis of the emission spectrum of each of the above reaction product and the above-mentioned processing gas. However, at a certain wavelength or wavelength band, the intensity of the other emission species is particularly small and is detected. In some cases, the intensity of the desired luminescent species is relatively strong. For example, the emission spectrum of carbon monoxide and CO ⁺ ions almost overlaps the emission spectrum of argon gas in the wavelength band of 350 to 860 nm when argon is used as a plasma stabilizing gas, for example, although it is 210 to 23.
In the wavelength band of 6 nm, since there is no emission spectrum of argon gas, it is possible to detect alone. Therefore, according to the present invention, it is possible to determine the variation in the amount of carbon monoxide in the vacuum chamber by determining the total average value of the emission spectrum in this wavelength band and knowing the variation. As for carbon monoxide and CO ⁺ ions, the wavelengths are particularly 219.0 nm, 230.0 nm, and 211.2 nm.
Since the emission spectrum has a specific emission spectrum at the wavelengths of nm, 232.5 nm and 224 to 229 nm, it is also possible to directly use these wavelength peak values for determining the end point of the plasma processing.

To enable such processing, for example,
The spectroscope 61 detects the emission spectrum of CF ₂ radicals produced by dissociation of CHF ₃ gas while avoiding noise due to the emission spectrum of silicon.
The spectroscope 62 is set to detect a wavelength in the range of 40 to 350 nm, preferably 240 to 280 nm, more preferably 255 to 287 nm.
It is set to detect a peak wavelength of 9.0 nm.
The light transmitted from these spectrometers 61 and 62 is
At the same time as being converted into an electrical signal corresponding to each wavelength spectrum, the emission spectrum of a certain wavelength band, the sum average value is calculated, for the emission spectrum of a certain wavelength peak value, the peak value is used as it is, The determination unit 64 performs a predetermined calculation to determine the etching end point.

Next, an embodiment of a method of determining the etching end point will be briefly described. That is, the calculation unit performs a calculation to match the slope of a change curve of the emission intensity of the peak wavelength of the emission spectrum of a certain wavelength, or the sum average value of the emission intensity of the emission spectrum of a certain wavelength band, and obtains a coefficient thereof. Next, a predetermined operation is performed on the obtained light emission intensity using this coefficient, a ratio of the light emission intensity is obtained, and a point where the value of the ratio changes by a predetermined amount is determined as the etching end point.

That is, the emission intensity of the light obtained by the spectroscopes 61 and 62 (or the total average value thereof) changes with the progress of the etching by drawing a change curve as shown in FIG. FIG. 6 (a) shows a change in the emission intensity (or the total average value thereof) of the active species (the output Ch ₀ of the photoelectric converter 63) and a change in the emission intensity (or the total average value of the generated gases) of the generated gas (the photoelectric converter). 64 output Ch
₁ ). The determining unit 67 firstly (1) calculates the average value Ave ₀ of the designated section of the change curve,
Ave ₁ is calculated, and (2) N measured values C in the designated section
and h _0, Ch _1, calculates the absolute value of the difference between the average value Ave _0, Ave _1, take the specified interval average A _0, A ₁ (area calculation),
(3) The ratio R of the designated section averages A ₀ and A ₁ is calculated. After calculating the designated section averages A ₀ and A ₁ and the ratio R for the designated section as described above, (4) the output Ch _{0 of the} photoelectric converter 63
Pull the average value Ave ₀ from, Ch '; ₀ seek (curve e in FIG. 6 (b)), (5 ) The Ch' divided by ₀ the ratio R, Ch '' ₀
Request (curve f of Figure 6 (b)). As a result, the slopes of the Ch ₀ curve and the Ch ₁ curve match. Then (6) determining the '' ₀ 'Ch by a ₀ is added an average value Ave ₁ of Ch _1' Ch 'obtained. This matches the curve of Ch _1. Next, (7) the ratio r between the calculated value Ch ″ ′ ₀ and the output Ch ₁
Is calculated. Then, it is determined that the value of the ratio r has changed to a predetermined threshold value or more, and this is determined as the etching end point.

In the above operation example, the output Ch ₀ is converted by a coefficient. Alternatively, the output Ch ₁ may be converted by a coefficient. Also, the judgment unit 64
Is not limited to the above-described method. For example, it is possible to apply an appropriate change such as obtaining an approximate curve of a change curve of both outputs and matching the slope of these approximate curves to obtain a ratio. is there.

Based on the above determination by the determination section 64, the plasma etching processing is terminated automatically or by an instruction from the operator. Further, when over-etching is necessary depending on the object to be processed, it is also possible to terminate the etching after a predetermined over-etching time has elapsed after the determination unit 64 determines the etching end point.

In the above embodiment, an example was described in which the emission spectrum of carbon monoxide was detected as a reaction product, but the method of the present invention is not limited to this example. For example, when low-pressure processing is performed, SiF as shown in FIG.
The emission spectrum of the radical can be used to determine the end point of the plasma etching. In that case,
The wavelength band to be monitored can be set to 430 to 450 nm. Alternatively, the specific wavelength of the SiF radical, 43
Peak wavelengths such as 6.8 nm, 438.8 nm, 440.05 nm, or 443.0 nm can be used for the determination.

Further, in the above embodiment, the case where the silicon oxide film is etched has been described. However, the method of the present invention is not limited to such etching, and the method of the present invention is not limited to the case where the polysilicon film or the aluminum alloy film is etched. A material other than single crystal silicon, for example, polysilicon or the like may be used as a base material of the specific etching film.

The present invention can be applied to any of a cathode coupling type etching apparatus in which an object to be processed is mounted on the cathode side and an anode coupling type in which an object to be processed is mounted on the anode side. The present invention can also be applied to an etching method in which a reactive gas plasma is generated in a discharge region by an electron source or the like and is introduced into an etching region.

[0042]

As described above, according to the present invention, error in accordance with the present invention
According to the switching end point detection method , the emission spectrum of the plasma emission species to be monitored is not the emission peak value of the emission species, but a spectrum range having a certain width and not overlapping with the emission peak values of other emission species, that is, Since monitoring is performed in a spectral range where the influence of light emission of other light-emitting species can be ignored, even if the light amount of each individual is small, it is possible to detect the light amount of the whole as a whole, so even when a low-sensitivity sensor is used, It is possible to increase the S / N ratio and determine the end point of the plasma processing with high accuracy.

Further, according to another etching end point detecting method constituted based on the present invention, detection is easy, that is, the plasma emission species having a high emission peak value is monitored on the one hand, and the emission intensity is weak and the sensitivity is low on the other hand. Although it is difficult to detect with a low-temperature sensor, it is important to monitor the emission spectrum of the important plasma emission species within a certain width and not overlapping with the emission peak values of other emission species when determining the end point of plasma processing. Accordingly, it is possible to select an optimum monitoring method at a high S / N ratio according to the processing gas and the processing environment of the object to be processed, and it is possible to detect the end point of the plasma processing with higher accuracy.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing an embodiment of an etching apparatus to which a processing method configured according to the present invention can be applied.

FIG. 2 shows a wavelength 20 when a silicon oxide film is etched with a CHF ₃ gas at a processing pressure of 200 mTorr.
It is a figure which shows the distribution of the light emission intensity of the light emission spectrum in 0-310 nm.

FIG. 3 shows a wavelength 31 when a silicon oxide film is etched with a CHF ₃ gas at a processing pressure of 200 mTorr.
It is a figure which shows the distribution of the light emission intensity of the light emission spectrum in 0-420 nm.

FIG. 4 shows a wavelength 200 when a silicon oxide film is etched by CHF ₃ gas at a processing pressure of 10 mTorr.
It is a figure which shows the distribution of the light emission intensity of the light emission spectrum in 310 nm.

FIG. 5 shows a wavelength 310 when a silicon oxide film is etched by CHF ₃ gas at a processing pressure of 10 mTorr.
It is a figure which shows the distribution of the light emission intensity of the light emission spectrum in -420 nm.

FIG. 6 is a diagram illustrating an example of a calculation in the dry etching method of the present invention.

FIG. 7 shows a wavelength 430 when a silicon oxide film is etched with a CHF ₃ gas at a processing pressure of 10 mTorr.
It is a figure which shows the distribution of the light emission intensity of the light emission spectrum in -480 nm.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Etching apparatus 2 Object 3 Vacuum chamber 4 Upper electrode 5 Lower electrode 6 Controller 13 Quartz window 14 Lens 15 Optical fiber

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 21/3065 C23C 16/509

Claims (2)

(57) [Claims] A plasma is generated using a CF-based etching gas.
Etching when generating and etching silicon oxide film
In the method of detecting the end point of the laser beam, the wavelength 2 including the emission spectrum of the CF etching gas
A wavelength band selected from 40 to 350 nm and a reaction product
Wavelength 210 including the emission spectrum of CO-based gas as
Emission intensity in the wavelength band selected from 236 nm
Detects the sum total average value and calculates the ratio of those sum average values.
Or to detect the end point of the plasma processing based on the difference.
Characteristic etching end point detection method. 2. The method according to claim 2, wherein the emission band is at least silicon (S).
2. The method according to claim 1, wherein the method is selected from a range excluding the emission peak value of i).