TW201812827A - Plasma processing device for monitoring plasma process and method thereof including a plasma reaction chamber for processing substrate and a monitoring device for monitoring the substrate processing process - Google Patents

Abstract

The present invention discloses a plasma processing device for monitoring plasma process and method thereof. The plasma processing device includes a plasma reaction chamber for processing substrate and a monitoring device for monitoring the substrate processing process. The monitoring device includes an incident light source for emitting pulse incident light to the substrate surface in the reaction chamber; a spectrometer for collecting an optical signal in the reaction chamber; a data processing device for receiving the optical signal collected by the spectrometer and providing a modulation signal with a period identical to a period of the pulse incident light, wherein the modulation signal has positive and negative directions, and the modulation signal and a background optical cancel each other out after product superposition within each period. A product of a pulse reflection optical signal and the modulation signal is not zero. The data processing device is configured to calculate the end of the plasma process by using the obtained pulse reflection optical signal.

Description

Plasma processing device and method for monitoring plasma process

The invention relates to the technical field of plasma processing, and particularly to a technical field of monitoring a plasma processing process.

Plasma processing technology is widely used in semiconductor manufacturing processes. In the process of depositing or etching a semiconductor substrate, the process needs to be closely monitored to ensure that the results of the deposition process or the etching process are well controlled. One commonly used etching process control method is optical emission spectroscopy (OES). After the atoms or molecules in the plasma are excited by the electrons to the excited state, they will emit light with a specific wavelength in the process of returning to another energy state. The wavelengths of the light waves excited by different atoms or molecules are different, and the changes in the light intensity of the light waves reflect the changes in the concentration of the atoms or molecules in the plasma. OES extracts the characteristic line of the plasma (OES characteristic line) which can reflect the changes in the plasma etching process and is closely related to the chemical composition of the plasma. Provides information on the reaction conditions in the plasma etching process. The limitation of this method is that it can only monitor the state after the film is etched. Only when one of the etched target layers is etched and the plasma etched to the next target layer, The characteristic spectrum of the corresponding plasma will change significantly, so this method can only be used for the end point monitoring of the etching process.

With the increasing integration density and complexity of devices in integrated circuits, strict control of semiconductor manufacturing processes becomes more important. For the sub-deep micron polysilicon gate etching process, since the thickness of the gate oxygen layer has become very thin, how to accurately control the plasma etching process is a technical challenge faced by people. High-density plasma etching machines currently used in the semiconductor industry, such as inductively coupled plasma (ICP) sources, capacitively coupled plasma (CCP) sources, and electron spin resonance plasma (ECR) sources. The plasma produced by it has a high etching rate. If the process control is not reasonable, the over-etching that occurs can easily cause damage to the next layer of material, and then cause device failure. Therefore, some parameters in the etching process must be strictly controlled, such as the chemical gas used for etching, etching time, etching rate, and etching selection ratio. In addition, slight changes in the state of the etching machine, such as the gas flow rate, temperature, gas recirculation state in the reaction chamber, or the difference between wafers from batch to batch, will affect the control of the etching parameters. Therefore, it is necessary to monitor the change of various parameters during the etching process to ensure the consistency of the etching process. The Interference Endpoint Method (IEP) is designed for real-time monitoring of the etching process.

The Interference Endpoint Method (IEP) is the incidence of an optical signal onto the surface of a semiconductor substrate. After the incident optical signal is emitted by the semiconductor substrate, it carries information about the thickness change of the substrate film. The reflected optical signal wavelength is measured and measured according to The measurement results are analyzed and calculated, and the actual etching rate can be obtained, so that the etching process of the substrate film can be monitored in real time. However, in the process of spectrum monitoring, the specific wavelength light signal that atoms or molecules in the plasma will emit after being excited by the electrons to the excited state always exists, and the intensity is large, and sometimes the intensity of the light signal from the plasma will exceed The intensity of the incident light signal interferes with the reading of the reflected incident light signal, making it difficult to measure the incident light signal.

In order to solve the above technical problems, the present invention discloses a plasma processing device for monitoring a process, which includes a reaction chamber for processing a substrate and a monitoring device for monitoring the processing process of the substrate. The monitoring device includes an incident light source, The substrate surface in the reaction chamber emits pulsed incident light; a spectrometer is used to collect the optical signal in the reaction chamber, and the optical signal includes the pulsed reflected light signal of the pulsed incident light on the substrate surface and the substrate Background light signal from plasma during processing; a data processing device for receiving the optical signal collected by the spectrometer and providing a modulation signal with the same period as the pulse incident light period, the modulation signal has two positive and negative Direction, and the product of the modulation signal and the background light signal is superimposed on each other to cancel each other out; the product of the pulse reflected light signal and the modulation signal is not zero; and the data processing device uses the obtained pulse The reflected light signal calculates the end of the plasma process.

Preferably, the integral area of a signal with a positive direction and the integral area of a signal with a negative direction within the period of the modulation signal are the same.

Preferably, the product of the pulse reflection light signal and the modulation signal is greater than zero.

Preferably, the modulation signal is a sine signal or a cosine signal.

Preferably, in each period, the pulse reflected light signal corresponds to a peak of the sine signal or the cosine signal.

Preferably, in each period, the pulse reflected light signal corresponds to a trough of the sine signal or the cosine signal.

Preferably, the modulation signal is a high and low level pulse period signal, the high level is greater than zero, the low level is less than zero, and the area area corresponding to the high level within the one period corresponds to the low level The area sizes are equal.

Preferably, the amplitude of the modulation signal is greater than or equal to the light intensity value of the pulse reflected light signal.

Preferably, the incident light emitted by the incident light source is full spectrum.

Preferably, the incident light source is a flash.

Preferably, the spectrometer sends a pulse trigger signal to the incident light source to control the period of the pulsed incident light emitted by the incident light source.

Further, the present invention also discloses a method for monitoring a plasma processing process. The method is performed in a plasma processing apparatus. The method includes the following steps: placing a substrate in a reaction chamber of the plasma processing apparatus. The substrate is subjected to a plasma processing process; a pulsed incident light is emitted to the substrate, and the pulsed incident light is reflected on the surface of the substrate; a spectrometer is used to collect the light signal emitted from the reaction chamber and Transmitting the optical signal to a data processing device, the optical signal includes a pulse reflection light signal reflected on the surface of the substrate and a background light signal generated by the plasma in the reaction chamber; the data processing device provides a pulse incident with the pulse The modulation signal with the same optical cycle is multiplied by the modulation signal and the optical signal collected by the spectrometer. The modulation signal is set to have a positive and negative direction and the product of the modulation signal and the background light signal cancel each other in each cycle. The position of the modulation signal and the pulse reflected light signal is such that the product of the two is not zero; the pulse reflected light signal after eliminating the background light signal is used Information for plasma treatment process of calculating the end point.

Preferably, the data processing device adjusts the positions of the modulation signal and the pulse reflected light signal so that the product of the two is greater than zero.

Preferably, the modulation signal provided by the data processing device is a sine signal or a cosine signal.

Preferably, the data processing device controls the pulsed incident light signal to correspond to a peak or trough of the sine-modulated signal or cosine-modulated signal.

Preferably, the amplitude of the modulation signal is greater than or equal to the intensity of the pulse reflected light signal.

Preferably, the incident light signal is a full-spectrum signal.

Preferably, the modulation signal is a high and low level pulse period signal, the high level is greater than zero, the low level is less than zero, and the area area corresponding to the high level within the one period corresponds to the low level The area sizes are equal.

Preferably, the spectrometer sends a pulse trigger signal to the incident light source to control the pulse period of the incident light source.

Preferably, the data processing device is a computer system.

The invention has the advantages that a modulation signal is applied to the background light signal and the pulse reflection light signal collected by the spectrometer, the period of the modulation signal is the same as the period of the pulse reflection light signal, and the modulation signal is within one period The area of signal integration with a positive direction is the same as the area of signal integration with a negative direction. Because the background light signal is relatively stable, and the change is almost zero in a period, when the product of the background light signal and the modulation signal is superimposed, the product of the background light signal and the modulation signal is the same size and has the opposite direction. Therefore, the The value is zero, thereby eliminating the interference of the background light signal. The data processing device controls the product of the pulse reflected light and the modulation signal to be non-zero. Since the reflected light signal appears only for a very short time in a modulation signal period, even within a period The superposition does not affect the reflected light signal. In particular, when the amplitude of the modulated signal is set to be greater than the light intensity of the reflected light signal, the modulated signal can also amplify the light intensity of the reflected light signal, making the data processing device It is possible to calculate the etching end point more accurately by using the reflected light signal.

In order to make the content of the present invention more clear and easy to understand, the content of the present invention is further described below with reference to the accompanying drawings. Of course, the present invention is not limited to this specific embodiment, and general substitutions well known to those skilled in the art are also covered by the protection scope of the present invention. It should be noted that the drawings are all in a very simplified form, using imprecise proportions, and are only used to facilitate and clearly achieve the purpose of assisting the description of this embodiment.

FIG. 1 is a schematic structural diagram of a plasma processing apparatus 100 provided with an interference endpoint monitoring device. In FIG. 1, a semiconductor substrate 10 is placed inside the plasma processing apparatus 100, and a reaction gas flowing in a reaction chamber of the plasma processing apparatus 100 is dissociated into a plasma 111 under the action of radio frequency power applied to the plasma processing apparatus 100. The substrate 111 is etched by the plasma 111. The method for generating the plasma 111 may be a capacitive coupling method, an inductive coupling method, or an electronic cyclotron method. Therefore, the present invention is applicable to the plasma processing apparatus 100 in various modes. The substrate 10 usually includes several layers of films to be etched, and different reaction gases and etching process parameters are required to etch different films. The reaction products of the plasma 111 during the etching of different films will emit light signals of different wavelengths. These light signals are used as background light signals, and they continue to exist during the etching process.

In the device and method for monitoring the plasma processing process by the interference endpoint method (IEP) disclosed in the present invention, an interference endpoint monitoring device is provided for endpoint monitoring of the plasma processing device 100. The interference endpoint monitoring device includes an incident light source 102 and a spectrometer 104. An optical signal entrance / exit 103 is provided on the top wall of the plasma processing device 100 to allow the optical signal emitted by the incident light source 102 to enter the plasma processing device 100 and enter the base. The sheet surface allows the reflected optical signal to enter the spectrometer 104 disposed outside the plasma processing apparatus 100. The specific working principle is that after the incident light source 102 emits an incident light signal to the surface of the etched film, the light reflected from the upper surface of the film and the light reflected by the underlying material after passing through the film interfere with each other. Because the thickness of the film determines the optical path difference between two lights that interfere with each other, different optical path differences will form interference fringes of alternating phases. Therefore, as the etching process progresses, the thin film is continuously etched and thinned. Interference enhancement can be obtained if the following formulas are satisfied:

Where Is the wavelength of the incident light signal, n is the refractive index of the thin film material, To monitor the change in film thickness, The change will show a maximum value of the light intensity on the spectrometer 104. In this way, as the thickness of the film continues to decrease, many sinusoidal signal curves will be formed. Under the premise of the wavelength and refractive index of the incident light signal, the thickness change of the monitored film can be calculated According to the sine wave signal curve received by the spectrometer 104, it is possible to obtain a period in which an interference enhancement occurs, and use this to monitor the change in film thickness And one cycle that produces the thickness change can calculate the actual etching rate in the etching process. The time required to reach the end of the etch can be calculated on the premise that the overall thickness of the etched film is known.

During the monitoring process, because the intensity of the background light signal emitted by the plasma 111 in the reaction chamber is large, sometimes it even exceeds the intensity of the light signal reflected by the incident light on the substrate film. Because both the incident light and the background light signal are full spectrum Optical signal. When the spectrometer 104 is set to collect a certain wavelength of light signal, the optical signal collected by the spectrometer 104 is the sum of the reflected light signal and the background light signal at that wavelength. The noise generated by the background light signal will make use of the reflected light signal. The calculation of the above-mentioned etching end point brings difficulties, and it is impossible to calculate the etching rate as above. In order to prevent the spectrometer 104 from being affected by the background light signal from the plasma 111 when receiving the reflected light signal from the substrate film, the spectrometer 104 can accurately read Taking the incident light signal, the present invention needs to eliminate the interference of the background light signal.

In order to eliminate the interference of the background light signal, the interference endpoint monitoring device provided by the present invention further includes a data processing device 114, and the spectrometer 104 sends the collected background light signal and the reflected light signal to the data processing device 114, The sum of the background light signal and the reflected light signal applies a modulation signal, and the modulation signal is used to eliminate the background light signal.

FIG. 2 shows a schematic diagram of the reflected light signal, the background light signal, and the modulation signal applied by the data processing device 114 collected by the spectrometer 104. The invention chooses to set the incident light source 102 as a pulsed incident light source 102, which can emit high-energy pulsed light with a short duration into the reaction chamber at a certain frequency, such as a flash with a full spectrum, and the time that the flash emits light in each pulse period Extremely short, usually in the microsecond range, and can transmit transient optical signals at a point in time. Therefore, in the schematic diagram shown in Figure 2, the pulsed reflected optical signal generated by reflecting the pulsed incident optical signal on the surface of the substrate For a vertical line segment with a certain interval, the length of the vertical line segment indicates the intensity of the pulse reflected light signal, and the interval between the two vertical line segments indicates the period t0 of the pulsed incident light. The background light signal emitted by the plasma 111 exists throughout the plasma manufacturing process, and the range of light intensity variation is small, which is represented as a roughly horizontal smooth curve. The spectrometer 104 collects the pulse reflected light signal and the background light signal in the reaction chamber, and transmits the collected light signal to the data processing device 114. The data processing device 114 applies a modulation signal to the background light signal and the reflected light signal, and uses the modulation signal Eliminate interference from background light signals.

The modulation signal is a periodic signal with a positive and negative direction and the same frequency as the incident light signal. The key to the modulation signal's ability to eliminate the background light signal is that the areas corresponding to the positive and negative directions of the modulation signal are equal in each period. As shown by the dotted line in Figure 2, the modulation signal can be a sine signal or a cosine signal. The data processing device 114 multiplies the modulation signal with the background light signal and the pulse reflection light signal collected by the spectrometer 104. Since the intensity of the background light signal does not change much in adjacent time periods, it can be almost the same in a period. When a sine or cosine signal is applied, since the value of the sine or cosine signal in a period is greater than zero and the value is less than zero, it is equivalent to modulating the light intensity value of the background light signal to half in each period. The positive half is negative. Therefore, when the values in each period are superimposed, the light values with positive and negative values are superimposed to cancel each other, thereby eliminating the background light signal. Since the pulse reflected light signal is a high-energy pulse light with a short duration, the light intensity is not zero for only a short period of time in a lighting cycle. As long as the modulation signal and the pulse reflected light are multiplied, the modulation signal is modulated in each cycle. The position of 0 does not correspond to the reflected light signal, and the reflected light signal intensity with a certain value can be obtained. Since the background light signal has been eliminated, only the information of the reflected light signal is obtained after superimposing the multiplication structure in the data processing device 114, and the end point calculation of the etching process is performed accordingly. In order to ensure that the intensity of the reflected light signal obtained after the calculation of the modulation signal is large, so as to facilitate the calculation of the etching end point, the pulse reflected light signal corresponds to the position of the sine signal or cosine signal near the peak in each cycle. Preferably, the reflection The position of the optical signal corresponds to the peak position of the sine or cosine signal.

In addition to the sine signal and cosine signal described in the above embodiments, the modulation signal according to the present invention may have various other forms, as long as the modulation signal has a positive and negative direction and the positive and negative directions are integrated within a period, the same value can be achieved. Purpose of the invention. In the embodiment shown in FIG. 3, a pulse period signal with high and low levels is disclosed. As can be seen from the figure, the modulation signal has a positive half period and a negative half period, and the positive and negative amplitudes are the same. Therefore, the modulation signal and the When the product of the background light signal is superimposed, the superposition result in each period is zero, so as to realize the denoising of the background light signal. When performing the multiplication operation, the data processing device 114 avoids that the rising or falling edge of the modulation signal corresponds to the position of the pulse reflected light signal, and then obtains only the information of the reflected light signal, so as to calculate the etching end point accordingly.

In the present invention, in addition to eliminating the background light signal, the modulation signal can amplify the intensity value of the reflected light signal required for calculation. By setting the amplitude value of the modulation signal to be greater than the intensity value of the reflected light signal, and setting the reflected light signal and The peak position of the modulation signal corresponds. As shown in Figure 4, when the data processing device 114 multiplies the optical signal collected by the spectrometer 104 and the modulation signal, the background light signal is eliminated and the intensity of the reflected light signal is amplified by A. Times (A is the amplitude of the modulation signal). The magnified value of the reflected light signal intensity can make up for problems such as the weak intensity of the incident light emitted by the incident light source 102 and the inaccurate prediction of the etching end point caused by the inconspicuous reflected light signal. The present invention utilizes a data processing device 114 to conveniently generate modulation signals of various amplitudes, and to flexibly adjust according to the incident light intensity of the incident light source 102 and the reflected light intensity required for calculation.

The periodicity of the incident light signal emitted by the pulsed incident light source 102 according to the present invention can be set in a variety of ways. For example, the flash light used in the present invention can periodically emit the incident light signal. In order to adjust the periodicity of the incident light signal more flexibly, As shown in FIG. 5, the spectrometer 104 sends a pulse signal to trigger the emission period of the incident light source 102. Using the method shown in FIG. 5 to trigger the incident light source 102 can effectively control the periodic synchronization of the reflected light signal and the modulation signal, and can adjust the positional relationship between the reflected light signal and the modulation signal. During the calculation process of the data processing device 114, Optimized reflected light signal information.

Compared with the conventional technology, by setting the incident light source 102 to be turned on and off periodically so that the spectrometer 104 can acquire pulsed reflected light signals, the present invention uses a flash lamp that continuously emits pulsed light signals as the incident light source 102 to avoid frequent incident light sources 102. Mechanically switch the incident light source 102 to reduce the mechanical damage of the incident light source 102. At the same time, because the time of emitting the incident light in each pulse period of the flash is shorter than the time of the incident light source 102 emitting the incident light in one period controlled by the mechanical switch , The effective light emitting time of the incident light source 102 can be extended, and the service life of the incident light source 102 can be improved. In addition, the present invention uses a flash lamp as the incident light source 102, which can provide a full spectrum of incident light, so that the user of the plasma processing apparatus 100 has more choices in the wavelength range. At the same time, the flash can emit a high-energy light signal with a short duration in accordance with a certain period, which can ensure that the intensity of the reflected light signal received by the spectrometer 104 is large enough, and at the same time, the continuous light emission time of the incident light source 102 can extend the life of the light source. The optical signals collected by the spectrometer 104 can be processed in real time, improving accuracy and efficiency.

In the present invention, a modulation signal is applied to the optical signal collected by the spectrometer 104, and the interference of the background light signal is removed by using the positive and negative amplitudes of the modulation signal being the same as the frequency of the incident light signal. In addition, the modulation signal can amplify the reflection The value of the optical signal intensity improves the accuracy of calculating the end point of the etching. Thus, the progress of the etching process of the thin film of the substrate 10 is accurately monitored. The data processing device 114 may be a computer system.

In addition to the etching process, the IEP described in the present invention can also monitor the process of the deposition process. Unlike the etching process, the deposition process is a process in which the thickness of the film is continuously increasing, by projecting an incident light into the deposition reaction chamber. According to the optical signal, the deposition rate of the deposition process can be calculated according to the above description. When the accurate deposition rate and the thickness of the film to be deposited can be accurately determined, the end point of the deposition process can be accurately known.

Although the present invention is disclosed in the preferred embodiment as above, it is not intended to limit the present invention. Any person skilled in the art can make possible changes and modifications without departing from the spirit and scope of the present invention. Therefore, the present invention The scope of protection shall be determined by the scope defined by the claims of the present invention.

10‧‧‧ substrate

100‧‧‧ Plasma treatment device

102‧‧‧incident light source

103‧‧‧Optical signal entrance

104‧‧‧Spectrometer

111‧‧‧ Plasma

114‧‧‧data processing device

Other features, objects, and advantages of the present invention will become more apparent by reading the detailed description of the non-limiting embodiments with reference to the following drawings.

FIG. 1 is a schematic structural diagram of a plasma processing device provided with an interference endpoint monitoring device.

FIG. 2 shows a schematic diagram of a reflected light signal, a background light signal, and a modulation signal.

FIG. 3 is a schematic diagram of a reflected light signal, a background light signal, and a modulation signal according to another embodiment.

FIG. 4 shows a schematic diagram of a modulation signal, a reflected light signal, and a background light signal having an amplification factor.

FIG. 5 is a schematic structural diagram of another plasma processing device provided with an interference endpoint monitoring device.

Claims (20)

A plasma processing device for a monitoring process includes a reaction chamber for processing a substrate and a monitoring device for monitoring the substrate processing process, wherein the monitoring device includes: an incident light source for feeding the substrate in the reaction chamber. A pulsed incident light is emitted from the surface; a spectrometer is used to collect an optical signal in the reaction chamber, the optical signal includes a pulsed reflected light signal of the pulsed incident light on the surface of the substrate and a plasma during the processing of the substrate A background light signal sent out; a data processing device for receiving the optical signal collected by the spectrometer and providing a modulation signal with the same period as a pulse incident light period, the modulation signal has two directions of plus and minus, and each cycle The product of the modulation signal and the background light signal is superimposed to cancel each other out; the product of the pulse reflection light signal and the modulation signal is not zero; and the data processing device uses the obtained pulse reflection light signal to calculate a plasma process The end. The device according to item 1 of the scope of the patent application, wherein the integral area of the signal whose modulation direction is positive in one period is the same as the integral area of the signal whose direction is negative. The device according to item 1 of the scope of patent application, wherein the product of the pulse reflected light signal and the modulation signal is greater than zero. The device according to item 1 of the patent application scope, wherein the modulation signal is a sine signal or a cosine signal. The device according to item 4 of the scope of patent application, wherein in each period, the pulse reflected light signal corresponds to the peak of a sine signal or a cosine signal. The device according to item 4 of the scope of patent application, wherein in each period, the pulse reflected light signal corresponds to the trough of the sine signal or the cosine signal. The device according to item 1 of the scope of patent application, wherein the modulation signal is a high-low pulse period signal, the high level is greater than zero, and the low level is less than zero. The corresponding areas have the same size. The device according to item 4 or item 7 of the scope of patent application, wherein the amplitude of the modulation signal is greater than or equal to the light intensity value of the pulse reflection light signal. The device according to item 1 of the scope of patent application, wherein the incident light emitted by the incident light source is full spectrum. The device according to item 1 of the scope of patent application, wherein the incident light source is a flash lamp. The device according to item 1 of the scope of patent application, wherein the spectrometer sends a pulse trigger signal to the incident light source to control the period of the incident light source emitting the pulsed incident light. A method for monitoring a plasma processing process is performed in a plasma processing apparatus, wherein the method includes the following steps: a substrate is placed in a reaction chamber of the plasma processing apparatus, and the substrate is electrically charged. Processing of the pulp process; emitting a pulse of incident light to the substrate, and the pulse of incident light is reflected on the surface of the substrate; using a spectrometer to collect a light signal emitted from the reaction chamber, and transmitting the light signal to a data processing Device, the optical signal includes a pulse reflection light signal reflected on the surface of the substrate and a background light signal generated by the plasma in the reaction chamber; the data processing device provides a modulation signal having the same period as the pulse incident light, and The modulation signal and the light signal collected by the spectrometer are multiplied; the modulation signal is set to have a positive and negative direction and the product of the background light signal cancels each other in each cycle; the position of the modulation signal and the pulse reflected light signal is set, So that the product of the two is not zero; and plasma processing using a pulse reflected light signal information after eliminating the background light signal End of calculation. The method according to item 12 of the patent application scope, wherein the data processing device adjusts the positions of the modulation signal and the pulse reflected light signal so that a product of the two is greater than zero. The method according to item 12 of the scope of patent application, wherein the modulation signal provided by the data processing device is a sine signal or a cosine signal. The method according to item 12 of the scope of patent application, wherein the data processing device controls the pulsed incident light signal to correspond to the peak or trough of the sine-modulated signal or the cosine-modulated signal. The method according to item 12 of the scope of patent application, wherein the amplitude of the modulated signal is greater than or equal to the intensity of the pulsed reflected light signal. The method according to item 12 of the patent application scope, wherein the incident light signal is a full spectrum signal. The method according to item 12 of the scope of patent application, wherein the modulation signal is a high-low pulse period signal, the high level is greater than zero, and the low level is less than zero. The corresponding areas have the same size. The method according to item 12 of the scope of patent application, wherein the spectrometer sends a pulse trigger signal to the incident light source to control the pulse period of the incident light source. The method according to item 12 of the patent application scope, wherein the data processing device is a computer system.