JPH0766173A - Plasma etching method - Google Patents

Abstract

PURPOSE:To determine the end of plasma etching accurately with high S/N ratio by detecting the total average value of emission intensity in the emission band for at least two plasma emission seeds and then determining the end of plasma based on the ratio or difference between two total average values. CONSTITUTION:A control section 6 comprises spectrometers 61, 62 for analyzing the light over a predetermine range of spectrum. Photoelectric converters 63, 64 convert lights of specific wavelengths from the spectrometers 61, 62 into electric signals. Amplifiers 65, 66 execute an predetermined operation on the electric signal corresponding to the light of specific wavelength. A decision section 67 determines the end of etching operation based on the operational results. The light is monitored over a predetermined wavelength band and the total average value of light is operated over the wavelength band thus determining the end of etching operation.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to plasma processing methods, and more particularly to methods for determining the end point of 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 etching treatment is a method in which plasma is generated using a reactive gas in a vacuum and the 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 base material is unnecessarily scraped,
Alternatively, since the etching shape changes, it is important to accurately detect the etching end point in order to prevent this.

Therefore, for example, a silicon oxide film is used as a CF film.
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 etching is determined based on the change in this emission intensity (for example, a special method). (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). See the bulletin).

[0005]

However, in any of the conventional methods, the peak intensity (peak height) of a certain wavelength was used in monitoring the plasma emission intensity in any case. If is weak, S
The / N ratio deteriorates, the detection sensitivity decreases, and the etching end point cannot be accurately determined, which is a problem.

In particular, with the recent demand for ultra-high integration,
The area to be etched tends to be very small, and the amount of reaction products generated by etching is very small, which makes accurate measurement difficult. Generally, the intensity of the emission spectrum from the plasma reaction system depends on a slight fluctuation of the power output, the influence of the mass flow controller, the fluctuation of the processing pressure,
It is constantly fluctuating due to the rise of the substrate temperature caused by plasma, etc. This fluctuation further deteriorates the S / N ratio, and it becomes difficult to accurately monitor the change in the emission intensity of the reaction product. ing.

The present invention has been made in view of the above problems in detecting the end point of the conventional plasma processing. The purpose of the present invention is that the emission spectrum intensity by the plasma processing is weak and the detection sensitivity is low. It is an object of the present invention to provide a new and improved method for determining the end point of a plasma etching process, which can accurately determine the end point of the plasma etching process with a good S / N ratio even if it drops.

[0008]

In order to solve the above-mentioned problems, according to a first aspect of the present invention, at least two plasma light emission is carried out when performing plasma processing on an object to be processed by converting a processing gas into plasma. Provided is a plasma processing method, which comprises detecting a sum total average value of emission intensities in a seed emission band and determining an end point of plasma processing based on a ratio or a difference of the sum average values.

Further, according to another aspect of the present invention, when the object to be processed is plasma-processed by converting the processing gas into plasma, an emission peak value of at least one plasma emission species and at least one plasma emission species. And a total average value of emission intensities in the emission band of the plasma detection method, and based on a ratio or a difference between the emission peak value and the total average value, a plasma processing end point is provided. It

In the above plasma treatment method, it is preferable to select the emission band of the plasma emission species or the emission peak value of the plasma emission species from a range in which the emission peak value appears relatively stronger than the peak values of other emission species. In addition, one of the plasma emission species of the plasma emission species for which the sum average value or emission peak value of the emission intensity is detected is selected, and the other plasma emission species for which the sum average value or emission peak value of the emission intensity is detected. It is preferable to select the product of the reaction product.

Further, in the above plasma processing method,
The emission peak value or emission band to be monitored is preferably selected from a range excluding the emission peak value of silicon (Si). Furthermore, it is preferable to select the emission peak value of carbon monoxide (CO) as the emission peak value to be monitored.

[0012]

According to the plasma processing method of claim 1,
Since the emission spectrum of the plasma emission species to be monitored is monitored in a spectral range having a certain width, it is possible to detect a large amount of light as a whole even if the amount of individual light is small.
Alternatively, even when the sensitivity of the sensor is low, the end point of the plasma processing can be determined with a high S / N ratio and high accuracy.

According to the second aspect, on the one hand, detection is easy, that is, plasma emission species having a high emission peak value is monitored, and on the other hand, the spectrum intensity is weak and detection is difficult.
Since the emission spectrum of plasma emission species, which is important for determining the end point of the plasma processing, is monitored in a spectrum range having a certain width, the S / N ratio can be increased by appropriately selecting an object to be monitored according to the processing conditions. It is possible to detect the end point of the plasma processing with high accuracy.

According to the third aspect, the observed emission band of the plasma emission species or the range in which the emission peak value of the plasma emission species appears relatively stronger than the peak values of the other emission species, that is, the emission of the other emission species. Since it is selected in the spectral range in which the influence of is negligible, it is possible to easily detect even a sensor with low sensitivity, and it is possible to further increase the S / N ratio.

According to a fourth aspect of the present invention, when the etching is finished, the emission spectrum of a process gas active species, for example, a CF-based gas such as CHF ₃ which is not used and its amount increases and the emission intensity also increases, and when the etching ends. A reaction product that does not occur and its amount decreases and emission intensity also decreases,
For example, since the end point of the plasma etching process is determined on the basis of at least two emission species that show different changes at the end of etching, such as CO emission spectrum, more accurate determination can be easily performed.

According to the invention of claim 5, 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 the 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 having a higher S / N ratio can be determined.

According to the sixth aspect of the present invention, particularly when the silicon oxide film is etched by the CF-based processing gas, the change in the emission peak value of carbon monoxide (CO) is monitored as one reference. At the end of etching, the amount of carbon monoxide (CO), which is a reaction product of the silicon oxide film and the CF-based gas, sharply decreases and the emission intensity thereof also sharply decreases, so that the end point can be easily determined.

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

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

The vacuum chamber 3 is connected to a cassette chamber (not shown) for accommodating the object to be processed 2 via a gate valve 7 or a load lock chamber 8 if necessary, and the gate is operated during processing. It is possible to open and close the valve 7 and carry in and carry out the object 2 to be processed by a carrying mechanism (not shown). Further, 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, if necessary, an inert gas such as argon or helium, and an exhaust pipe 10 for exhausting a surplus gas or a reaction product gas are connected. , The vacuum chamber 3 in a predetermined reduced pressure atmosphere, for example, 200 mTorr.
It is possible to hold the inside.

The electrodes 4, 5 constitute a parallel plate type electrode, one of the upper electrodes 4 is grounded, and the other of the lower electrodes 5 is connected to a high frequency power source 12 via a matching capacitor 11. In addition, a high frequency voltage can be applied between both electrodes. Further, as described above, the object 2 can be mounted and fixed on the lower electrode 5 by electrostatic chuck means or the like.

Further, on the side surface of the vacuum chamber 3, there is formed a window 13 made of quartz or the like for transmitting the emitted light of the plasma generated between the electrodes 4 and 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
The light condensed at 4 is branched into two through the optical fiber 15 and sent to the control unit 6. As described above, by adopting the light detecting means including the quartz window 13, the lens 14, and the optical five 15 instead of the glass, it is possible to detect the light emission of a short wavelength up to around 200 nm.

The control section 6 spectroscopes 61 and 62 for splitting light into a spectrum of a predetermined range, and spectroscopes 61 and 62 thereof.
The photoelectric converters 63 and 64 for converting the light of the specific wavelength obtained by the above into the electric signals, the amplifiers 65 and 66, and performing a predetermined calculation on the electric signal corresponding to the light of the specific wavelength, and The determination unit 67 determines the end point of the etching process from the calculation result.

One of the spectroscope 61 and the photoelectric converter 63
Is a wavelength band in the range of 240 to 350 nm when an etchant, for example, a CF-based gas such as CF ₃ is used,
It is possible to monitor light in the wavelength band preferably in the range 240 to 280 nm, more preferably in the wavelength band 255 to 287 nm. By selecting the range of the monitoring light from such a wavelength band, 243 to 252 nm and 288 n can be obtained.
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, the light in the wavelength band having a certain width is monitored, and the sum 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, unlike the conventional peak value detection method, an inexpensive interference filter having a relatively low resolution can be used. Especially, 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 with 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 reaction product is generated.
It can be used to monitor the light in the wavelength band of 36 nm and calculate the sum average value to determine the end point of the etching process. Also, preferably, a specific wavelength selected from the above wavelength range, for example, 219.0 nm, 23
0.0nm, 211.2nm, 232.5nm or 2
Any value between 24 and 229 nm can be monitored and its value used directly to determine the endpoint of the etching process.

In FIGS. 2 and 3, the silicon oxide film is represented by C.
200n when plasma etching is performed with HF ₃ etching gas under the conditions of high-frequency power of 800 W, processing pressure of 200 mTorr, and CHF ₃ supply of 50 sccm.
The emission spectrum at m-400 nm is shown. In the figure, a thick line shows a bare wafer on which a silicon oxide film is not formed, and a thin line shows a solid wafer on which a silicon oxide film is formed.

As is apparent 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 the wavelength band in the range of 5 to 287 nm, even if the light intensity of the peak value of each wavelength is weak, by monitoring the wavelength band of a certain width It is possible to monitor with high accuracy. Further, particularly by selecting the wavelength band in the above range, the fluctuation of the emission spectrum of the processing gas can be suppressed without being affected by the fluctuation of the emission spectrum of the silicon under the wafer having the emission peak values at 243 to 252 nm and 288 nm, respectively. Since it can be monitored, more accurate monitoring can be performed.

In FIGS. 4 and 5, the silicon oxide film is exposed to a high frequency power of 800 by CHF ₃ etching gas.
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 low pressure condition rather than m is shown. In the case of this embodiment as well,
In the figure, a thick line shows a bare wafer on which a silicon oxide film is not formed, and a thin line shows a solid wafer on which a silicon oxide film is formed.

Processing pressure 200 mT shown in FIGS. 2 and 3.
in the case of the etching process orr, in the case of low pressure process that, the recently been focused may be better understood from the comparison between the case of the etching process pressure 10mTorr shown in FIGS. 4 and 5, CHF ₃ gas The emission spectrum intensity is low, and it is difficult to detect the emission spectrum with a sensor having low sensitivity.
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 by monitoring the emission spectrum in the wavelength band of up to 280 nm. As a result, even if a sensor with low accuracy is used, highly accurate measurement can be performed, and the end point of plasma processing etching can be accurately determined.

Next, an embodiment in which the etching apparatus 1 constructed as described above is applied to a processing method constructed according to the present invention will be described. First, the object 2 to be processed, for example, a semiconductor wafer is transferred from the load lock chamber 8 by a transfer mechanism (not shown) and placed 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. Then, the gate valve 7 is closed, the inside of the vacuum chamber 3 is evacuated to a predetermined vacuum degree, for example, 200 mTorr through the exhaust pipe 10, and then a CF type gas such as CHF _{3 is used} as an etching gas from the gas introduction pipe 9. While introducing a gas at a predetermined flow rate and maintaining a predetermined gas pressure, while applying a high frequency power of a predetermined frequency, for example, 13.56 MHz, a predetermined power value, for example, several 100 W between both electrodes 4, 5. Then, plasma is generated to etch the oxide film portion on the surface of the object 2 to be processed.

The CF-based gas, such as CHF ₃ , introduced into the vacuum chamber 3 is dissociated in plasma to generate CF _{2 and} other kinds of active species, which react with the silicon oxide film for etching. As a result, reaction products such as SiF _x , carbon monoxide, and CO ⁺ ions are generated. Among these reaction products, carbon monoxide, CO ⁺ ions, or CHF ₃ gas, which is an etching gas, emits light with their respective spectra. Therefore, the emitted light is emitted from the quartz window 13 of the vacuum chamber 3 and the lens. 1
It will be detected by the control unit 6 through the optical fiber 15 through the optical fiber 4. And the spectroscopes 61 and 6
Reference 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 band to the photoelectric converters 63 and 64. To do.

The emission spectrum obtained is a combination of the emission spectra of the reaction product and the processing gas, but the intensity of other emission species is particularly small at a certain wavelength or wavelength band. The intensity of the desired luminescent species may be relatively high. For example, the emission spectra of carbon monoxide and CO ⁺ ions almost overlap with the emission spectrum of argon gas in the wavelength band of 350 to 860 nm when argon is used as the plasma stabilizing gas, but 210 to 23.
In the wavelength band of 6 nm, since there is no emission spectrum of argon gas, it can be detected independently. Therefore, based on the present invention, it is possible to know the fluctuation of the amount of carbon monoxide in the vacuum chamber by obtaining the total average value of the emission spectra in this wavelength band and knowing the fluctuation. Regarding carbon monoxide and CO ⁺ ions, the wavelengths are particularly 219.0 nm, 230.0 nm, and 211.2 nm.
Since it has a peculiar emission spectrum in the portions of nm, 232.5 nm and 224-229 nm, it is also possible to use these wavelength peak values directly for the end point determination of plasma processing.

In order to enable such processing, for example,
The spectroscope 61 detects the emission spectrum of CF ₂ radicals produced by the 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, and more preferably 255 to 287 nm.
It is set to detect a peak wavelength of 9.0 nm.
The light transmitted from these spectroscopes 61 and 62 is controlled by the control unit 6.
In, while being converted into an electric signal corresponding to each wavelength spectrum, the sum average value is calculated for the emission spectrum of a certain wavelength band, the peak value is used as it is for the emission spectrum of a certain wavelength peak value, The determination unit 64 performs a predetermined calculation to determine the etching end point.

Next, an embodiment of the method of determining the etching end point will be briefly described. That is, in the calculation unit, the sum average value of the emission intensity of the emission spectrum of a certain wavelength band, or the calculation to match the slope of the change curve of the emission intensity of the peak wavelength of the emission spectrum of a certain wavelength, to obtain the coefficient, Then, after performing a predetermined calculation on the obtained emission intensity using this coefficient, a ratio of the 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 light (or the total average value thereof) obtained by the spectroscopes 61 and 62 changes with the progress of etching in a change curve as shown in FIG. Note that FIG. 6A shows changes in the emission intensity (or the total sum average value thereof) of the active species (output Ch ₀ of the photoelectric converter 63) and changes of the emission intensity (or the total sum average value thereof) of the produced gas (the photoelectric converter). 64 output Ch
₁ ). The determination unit 67 first (1) calculates the average value Ave ₀ of the specified section of such a change curve,
Ave ₁ is calculated, and (2) N measured values C in the specified section
The absolute value of the difference between h ₀ and 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),
Further, (3) the ratio R of the designated section averages A ₀ and A ₁ is taken. 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
The average value Ave ₀ is subtracted from this to obtain Ch ′ ₀ (curve e in FIG. 2B), and (5) this Ch ′ ₀ is divided by the ratio R to obtain Ch ″ _0.
(Curve f in FIG. 2B) is determined. As a result, the slopes of the Ch ₀ curve and the Ch ₁ curve match. Then (6) Ch '' by the Ch _"0 obtained adding the average value Ave ₁ of Ch ₁ 'Request _0. Thus coincides with the curve of the Ch _1. Then (7) Calculated Ch''' ₀ Ratio of output to Ch ₁
To calculate. Then, it is determined that the value of the ratio r has changed to be equal to or more than a predetermined threshold value set in advance, and this is set as the etching end point.

[0037] In the above operation example was to be converted by the coefficient output Ch _0, it can be converted by a factor output Ch ₁ instead. In addition, the determination unit 64
The calculation of is not limited to the above-mentioned method, and it is possible to make appropriate changes such as, for example, obtaining approximate curves of change curves of both outputs and matching the slopes of these approximate curves to obtain a ratio. is there.

Based on the judgment of the judgment unit 64, the plasma etching process is ended automatically or by a command from the operator. In addition, when overetching is required depending on the object to be processed, it is possible to terminate the etching after a predetermined overetching time has elapsed after the determination unit 64 determines the etching end point.

In the above embodiment, an example in which the emission spectrum of carbon monoxide is detected as the reaction product has been described, 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 radicals can be used to determine the endpoint of plasma etching. In that case,
The wavelength band to be monitored can be set to 430 to 450 nm. Alternatively, a specific wavelength of SiF radical, 43
Peak wavelengths such as 6.8 nm, 438.8 nm, 440.05 nm, or 443.0 nm can be used for 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 when etching a polysilicon film, an aluminum alloy film or the like. It may be applied, and the base material of the specific etching film 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 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 is also possible to apply to an etching method in which reactive gas plasma is generated in the discharge region by an electron source or the like and introduced into the etching region.

[0042]

As described above, according to the plasma processing method according to the present invention, the emission spectrum of the plasma emission species to be monitored is determined not by the emission peak value of the emission species.
Since it has a certain width and does not overlap with the emission peak value of other emission species, that is, in the spectrum range in which the influence of emission of other emission species can be ignored,
Since the total light amount can be detected even if the individual light amount is small, it is possible to increase the S / N ratio and accurately determine the end point of the plasma processing even when using a sensor with low sensitivity. You can

Further, according to still another plasma processing method constructed according to the present invention, on the one hand, the plasma emission species which is easy to detect, that is, has a high emission peak value is monitored, and on the other hand, the emission intensity is weak and the sensitivity is low. It is difficult to detect with a low sensor, but it is important to determine the end point of plasma processing by monitoring the emission spectrum of plasma emission species within a certain range and within the range that does not overlap with the emission peak value of other emission species. With a high S / N ratio, it becomes possible to select the optimum monitoring method 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 drawings]

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

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

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

FIG. 4 shows a wavelength of 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 emission intensity of an 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 emission intensity of an emission spectrum in -420 nm.

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

FIG. 7 shows a wavelength 430 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 emission intensity of the emission spectrum in -480 nm.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Etching device 2 Object to be processed 3 Vacuum chamber 4 Upper electrode 5 Lower electrode 6 Control device 13 Quartz window 14 Lens 15 Optical fiber

Claims (6)

[Claims] 1. When performing plasma processing on an object to be processed by converting a processing gas into plasma, a total average value of emission intensities in emission wavelength bands of at least two plasma emission species is detected, and a total average value of those total values is detected. A plasma processing method, wherein an end point of plasma processing is determined based on a ratio or a difference. 2. When the object is plasma-processed by converting the processing gas into plasma, the emission peak value of at least one plasma emission species and the total average value of emission intensities in the emission band of at least one plasma emission species. Is detected, and the end point of the plasma processing is determined based on the ratio or difference between the emission peak value and the total average value. 3. The emission band of the plasma emission species or the emission peak value of the plasma emission species is selected from a range in which it appears relatively stronger than the peak values of other emission species. 2. The plasma processing method described in 2. 4. The plasma emission species of one of which the total sum average value of emission intensity or the emission peak value is detected is a process gas active species, and the other plasma emission species of the emission gas intensity is detected. The plasma processing method according to claim 1, 2 or 3, wherein the plasma emission species is a reaction product. 5. The emission peak value or the emission band is selected from the range excluding at least the emission peak value of silicon (Si). Plasma treatment method. 6. The emission peak value is carbon monoxide (CO)
The emission peak value of
The plasma processing method according to any one of 2, 3, 4 and 5.