TWI559821B - method for producing steady plasma - Google Patents

Description

Method for obtaining a stable plasma source

The invention relates to the technical field of plasma surface treatment, in particular to a method for obtaining a stable plasma source.

Typically, the gas is an insulator in a closed environment of low electric field strength; however, when the electric field in the enclosed environment is enhanced to some extent by an alternating current radio frequency (RF) bias, the high electric field strength is sealed. Gases in the environment can cause discharges. In the closed environment, the released electrons have kinetic energy under the acceleration of a high electric field, and electrons having sufficient energy excite the electrons in the gas molecules in the sealed environment to dissociate the gas molecules. This phenomenon is called ionization collision. At the same time, secondary ions generated by the collision of the positive ions generated by the dissociation collision will generate secondary electrons, which will greatly increase the number of ionized gas molecules and free electrons. Eventually, during the ionization collision, the electrons may disappear due to the complex action with the gas ions, or disappear away from the electric field due to drift and diffusion; when the electron generation rate is equal to the disappearance rate, in a closed environment The plasma is in a stable state.

In recent years, with the development of Very Large-Scale Integration (VLSI) and Ultra Large-Scale Integration (ULSI), plasma surface treatment applications have become indispensable in semiconductor manufacturing. One of the main applications missing. It is conceivable that the design of the plasma source is related to the quality of the entire semiconductor process. Therefore, how to provide a stable plasma source has become a very important issue.

In view of this, Langmuir (Lanmuer, Ram) first proposed the measurement of plasma measurement in 1924, and the structure of the research is, for example, a conventional plasma measurement architecture as shown in FIG. In FIG. 1, an electrical probe 2' extends directly into a plasma reaction chamber 1'; and, in the case of turning off the RF source 3' (for example, a pulsed RF frequency generator), The current measured by the current measuring device 4' through the probe 2' is zero. If the RF source 3' is turned on and a bias voltage (for example, a negative voltage) is supplied through the capacitor 6' to the probe 2', at this time, the charged particles of the plasma 7' in the plasma reaction chamber 1' ( For example: ions) will move towards the surface of the probe 2'.

At the beginning of the electron movement, more electrons reach the surface of the probe 2' per unit time and form a negative voltage on the surface of the probe 2'; and, when the ion accumulation on the surface of the probe 2' is constant At the same time, it will have a repulsive effect on the ions and at the same time have an attracting effect on the electrons. Finally, when the electron attracting effect on the surface of the probe 2' and the ion repulsion effect are in dynamic equilibrium, the ion current measured by the probe 2' will be equal to the electron current (I+=Ie); at this time, the voltage measuring device The measured voltage value of 5' is called a floating potential.

Please refer to Figure 2 and Figure 3 for the voltage-time data curve and the current-time data curve. As shown in Fig. 2 and Fig. 3, as the supplied bias voltage increases (from a negative voltage to a zero voltage), the current measured by the probe 2' is gradually reduced, and the final probe 2' is measured. The current value is zero; such a result indicates that the internal portion of the plasma reaction chamber 1' is in a stationary state. Moreover, according to the data of FIG. 2 and FIG. 3, the engineering personnel can generate a current-voltage relationship diagram as shown in FIG. 4 by adjusting the time, thereby eliminating the time variable. In this way, by applying a nonlinear fit to the data collected during each RF burst, the relevant characteristic parameters of the plasma 7' generated in the plasma reaction chamber 1' can be determined, for example, ion saturation. Current, ion saturation slope, floating potential, plasma potential, electron temperature, electron density, and the like.

In this way, by measuring the measured plasma saturation current, ion saturation slope, floating potential, plasma potential, electron temperature, electron density, etc., the plasma characterization parameters are compared to values within a predetermined range, as long as the measured values are obtained. Each of the plasma characterization parameters falls within the predetermined range, indicating that the plasma 7' generated in the plasma reaction chamber 1' has stabilized and can serve as a stable plasma source.

In an actual RF plasma system, it is generally monitored by the following steps whether the plasma 7' of the plasma reaction chamber 1' has stabilized: Step (1): ignition of the plasma, which is monitored by monitoring Ion flux and / or electron temperature and / or floating potential to determine whether the plasma has been ignited; Step (2): Stabilize the plasma, by measuring the ion saturation current, ion saturation slope, The plasma characterization parameters such as floating potential, plasma potential, electron temperature, electron density, etc., and the measured values are compared to a reference plasma characterization parameter, as long as the measured plasma characterization parameters fall within the reference The plasma stabilization can be determined within a predetermined range of the characterization parameters of the plasma; it must be additionally noted that the aforementioned reference characterization parameters are measured from the plasma of an exemplary etch operation.

Although the conventional plasma measurement architecture shown in FIG. 1 is now widely used; however, the conventional plasma measurement architecture described above still has the following major drawbacks on the practical side:

(1) Although the plasma measurement architecture can ultimately measure a stable plasma from a plasma system, the plasma measurement architecture cannot be used to assist the plasma system to "get a stable plasma." Source or "control plasma tends to be stable." More specifically, although the plasma measuring architecture can accurately measure the relevant characteristic parameters of the plasma 7' generated inside the plasma reaction chamber 1', these parameters only help the engineer to determine the plasma reaction. The plasma 7' inside the chamber 1' "is stable" does not help the engineer to quickly manufacture or obtain a stable plasma source. In addition, since the plasma 7' of the RF plasma system is excited by the RF voltage, the potential of the plasma 7' of the RF plasma system includes a DC portion and an AC RF portion; wherein the AC RF portion causes The error in the measurement of the probe results in a decrease in the accuracy of the measurement of the plasma characteristics.

(2) For RF plasma systems, different ambient temperatures and humidity may affect the ignition and stability of the plasma. As shown in the current-time data graph of Figure 5, the RF plasma system ignites the plasma at a time point of 117.5 seconds, and at 118.15 seconds, it is confirmed that the plasma 7' of the plasma reaction chamber 1' has become Stable. However, unlike FIG. 5, as shown in the current-time data graph of FIG. 6, the plasma is again ignited under different ambient temperature and humidity conditions (time point 117.5 seconds), and the probe 2' is measured. The current begins to rise at time point 121.4; that is, the plasma 7' of the plasma reaction chamber 1' must 3.9 seconds after ignition to stabilize.

(3) According to point 2 above, it is obvious that the engineer can only passively "wait" that the plasma 7' of the plasma reaction chamber 1' tends to be stable, and the engineer cannot actively control the plasma reaction chamber 1'. The concentration of the plasma 7' is stabilized.

Therefore, in view of the fact that the existing plasma measurement architecture cannot provide engineers to actively obtain a stable plasma source or control plasma from an RF plasma system, the inventors of this case tried to research and invent, and finally developed. A method of obtaining a stable plasma source of the present invention.

It is a primary object of the present invention to provide a method of obtaining a stable plasma source. Different from the conventional plasma measurement architecture, it can only be used by engineers to confirm whether the plasma in the plasma reaction chamber is stable or not, and it is impossible for engineers to quickly obtain a stable plasma when the RF plasma system is restarted. Source, the method for obtaining a stable plasma source proposed in the present invention only needs to add a probe, a power supply, an electric meter, and a regulating device to an ECR plasma system, so that the probe can be monitored through the electric meter. The specific bias voltage above and the plasma current collected by the probe effectively assist the engineer to adjust the power of the microwave generator to adjust the plasma current in the working chamber, and finally work. The plasma concentration or surface ion current in the chamber can meet the engineering personnel's needs for a particular process condition.

Therefore, in order to achieve the main object of the present invention, the inventors of the present invention have proposed a method for obtaining a stable plasma source, comprising the steps of: (1) extending a probe into the working chamber; (2) starting the pumping. And a pressure maintaining device to maintain the interior of the plasma generating chamber and the working chamber in a low pressure vacuum state; (3) activating the gas supply device to pass a working gas into the plasma generating chamber And activating the microwave generator and the magnetic system to generate a plasma in the plasma generating chamber; (4) introducing the plasma into the working chamber; (5) supplying a specific one with a power supply Biasing to the probe and determining that the plasma source in the working chamber meets a particular process condition; then recording the particular bias and the collection of the probe through an electrical meter coupled to the power supply a specific current; wherein the specific current is used as a stable plasma parameter, and the engineer can adjust and set the ECR plasma system to generate a stable plasma source to meet the specific process conditions.

Preferably, the method for stabilizing the plasma source further comprises the following steps: (6) restarting the gas supply device and the gas supply device such that the plasma generating chamber and the interior of the working chamber are maintained at a second low-pressure vacuum state; wherein the second low-pressure vacuum state is the same or similar to the first low-pressure vacuum state; (7) restarting the microwave generator and the magnetic system; (8) being connected to the power supply The meter measures an instantaneous current collected by the probe; (9) confirming whether a current difference between the instantaneous current and the specific current is zero through a regulating device connected to the meter, and if yes, performing step (11) And if not, performing step (10); (10) the regulating device instantaneously adjusts the power level of the microwave generator, and repeats the step (9); and (11) in the working chamber The plasma source has met this particular process condition.

In order to more clearly describe a method of obtaining a stable plasma source proposed by the present invention, a preferred embodiment of the present invention will be described in detail below with reference to the drawings.

The method for obtaining a stable plasma source provided by the present invention is mainly applied to an ECR (Electron Cyclotron Resonance) plasma system. As shown in FIG. 7 , an ECR plasma system 1 includes a gas supply device 10 , a microwave generator 11 , a plasma generating chamber 12 , and a magnetic system . 13. A working chamber 14 and a pumping and pressure maintaining device 15; and, in order to enable the ECR plasma system 1 to stably supply (or generate) a plasma source, the present invention further adds a probe 21, A power supply 22, an electric meter 23, and a regulating device 24 are incorporated into the ECR plasma system 1.

As shown in FIG. 7, the plasma generating chamber 12 is disposed to be connected to the working chamber 14 and communicate with the working chamber 14. Further, the working gas supply device 10 is connected to the plasma generating chamber 12 through a line for introducing a working gas such as nitrogen (N2) or argon (Ar) into the plasma generating chamber 12. In addition, the microwave generator 11 provides a microwave having a frequency range of 1 GHz to 3 GHz into the plasma generating chamber 12; thus, the working gas in the chamber 12 is dissociated freely under the excitation of the microwave. Electron, and at a specific microwave frequency and magnetic field strength, when the microwave frequency is equivalent to the cyclotron frequency of the electron in the magnetic field, electron cyclotron resonance (ECR) occurs, and the plasma concentration is greatly increased, and the plasma is further introduced into the electron. In the working chamber 14.

The technical feature of the present invention is that the plasma source of the ECR plasma system 1 is monitored and regulated by the additional probe 21, the power supply 22, the electric meter 23, and the regulating device 24, so that the ECR plasma system 1 The plasma source of a specific concentration can be correspondingly provided (produced) according to the plasma demand of the engineer under a specific process condition. The specific process conditions are, for example, an etch rate, a deposition rate, or a cutting rate.

As shown in FIG. 7, the probe 21 is a conductor electrode that penetrates the working cavity 14 from the outside. Moreover, a measuring surface of the probe 21 is located in a uniform plasma zone in the working chamber 14. Although FIG. 7 shows that the probe 21 is horizontally deep into the working cavity 14, the angle and positional relationship between the probe 21 and the working cavity 14 should not be limited. Please refer to FIG. 8 and FIG. 9 , which are a second architectural diagram and a third architectural diagram of the ECR plasma system. As shown in FIG. 8, the probe 21 can extend vertically from the bottom of the working cavity 14, and a measuring surface of the probe 21 is located in the same position as the target stage 141 in the working cavity 14. flat. Further, as shown in FIG. 9, the probe 21 extends obliquely into the working chamber 14, and the measuring surface of the probe 21 and the target stage 141 are oppositely disposed at an angle. In addition, as shown in the fourth architectural diagram of the ECR plasma system as depicted in FIG. 10, assuming that a drain electrode in the working chamber 14 is electrically connected to the power supply 22, the drain electrode can be used as The use of electrical probes.

Thus, the above-described system has completely and clearly illustrated various implementable architectures of the ECR plasma system 1. Next, a method of obtaining a stable plasma source of the present invention will be described below with the aid of a method flow chart. Referring to Figure 11, a flow chart of a first embodiment of the method of obtaining a stabilized plasma source of the present invention is shown. As shown in FIG. 11 and FIG. 7, the first embodiment of the method for obtaining a stable plasma source of the present invention mainly comprises five method steps: Step (S1): a probe 21 is inserted into the working chamber 14. Step (S2): starting the pumping and pressure maintaining device 15 to maintain the interior of the plasma generating chamber 12 and the working chamber 14 in a low pressure vacuum state; Step (S3): starting the gas supply device 10 A working gas is introduced into the plasma generating chamber 12, and the microwave generator 11 and the magnetic system 13 are activated to generate a plasma source in the plasma generating chamber 12; Step (S4): Introducing the plasma source into the working chamber 14; and step (S5): supplying a specific bias to the probe 21 by a power supply 22, and determining the plasma in the working chamber 14 The source system satisfies a particular process condition; then the particular bias voltage and a particular current collected by the probe 21 are recorded by an electricity meter 23 coupled to the power supply 22.

As described above, once the engineer determines in the step (S5) that the background condition satisfies the specific process requirements, the engineer can record the specific bias voltage and the specific current. In this way, the engineer can directly apply the specific bias voltage to the probe 21 when the ECR plasma system 1 is restarted next time, and adjust the power of the microwave source until the current collected by the probe 21 reaches the specific current value. Thereafter, it can be determined that the concentration of plasma within the working chamber 14 can be used to accomplish a particular process condition (e.g., etch rate).

The above steps (S1) to (S5) belong to the method steps of manual monitoring and regulation; however, the applicability and expandability of the present invention should not be limited thereby. Referring to Figure 12, a flow diagram of a second embodiment of the method of obtaining a stabilized plasma source of the present invention is shown. As shown in FIG. 12, the method of the present invention may further comprise six steps of automatically adjusting the stable plasma source: Step (S6): restarting the gas supply device 10 and the gas supply device 10 such that the plasma generating chamber 12 and maintaining the interior of the working chamber 14 in a second low pressure vacuum state; wherein the second low pressure vacuum state is the same or similar to the first low pressure vacuum state; step (S7): restarting the microwave generator 11 and The magnetic system 13; Step (S8): when the plasma is restarted, an instantaneous current collected by the probe 21 is measured through the electric meter 23 connected to the power supply 22; Step (S9): through the connection to the electric meter 23 A regulating device 24 determines whether a current difference between the instantaneous current and the specific current is zero, and if so, performs step (11); if not, performs step (10); step (S10): the regulating device 24 The power level of the microwave generator 11 is adjusted instantaneously, and the step (8) is repeatedly performed; and the step (S11): the plasma source in the working cavity 14 has satisfied the specific process condition.

From the above description, it can be known that the specific bias value recorded in the foregoing step (S5) and the value of a specific current are stored in the regulating device 24; thus, after the engineer restarts the ECR plasma system 1, the present invention The method supplies the specific bias voltage to the probe 21 through the regulating device 24 and the power supply 22, thereby confirming whether the instantaneous current collected by the probe 21 is equivalent to the recorded specific current. It must be particularly noted that although the steps (S6) and (S7) are in the environment of the working chamber 14 of the air pressure and gas in accordance with the specific process conditions described, the microwave generator 11 and the magnetic system 13 are restarted to ignite the plasma. However, as the ambient temperature and humidity are different, the same pumping rate and pressure within the chamber may not produce the same concentration of plasma source.

Please refer to FIG. 13A to FIG. 13F , which are data curves of the voltage-instant current measured by the probe from the first height to the sixth height in the working chamber, respectively. The inventor of the present invention passes the argon gas into the plasma generating chamber 12 and the working chamber 14 through the gas supply device 10, and maintains the pressure of the working chamber 14 at 2x10-2 through the pumping and pressure maintaining device 15. Around torr. Further, the inventor repeatedly performs the above steps (S6) and (S7) repeatedly, and measures an instantaneous current collected by the probe 21 through the meter 23 connected to the power supply 22 (step ( S8)); wherein the measured instantaneous current is organized as shown in FIGS. 13A to 13F. From the data graph of the voltage-instant current of FIGS. 13A to 13F, an engineering worker familiar with the field of plasma technology should be easily found that the probe 21 is performed after each step (S6) and step (S7) are repeatedly performed. The values of the saturation currents of the collected instantaneous currents are all different. Therefore, the experimental data of Figs. 13A to 13F confirms an important phenomenon: even if the engineer applies the working gas, the chamber pressure, and the operating power of the microwave generator 11 used in the previous plasma process to the current electricity. In the slurry process, based on the plasma concentration generated in the working chamber 14, the process results of the current plasma process may not be the same as the process results of the previous plasma process.

Even so, the inventors of the present invention have found through a number of experiments that the working chamber 14 can be operated as long as the power of the microwave generator 11 is appropriately fine-tuned so that the instantaneous current collected by the probe 21 is equivalent to the recorded specific current. The parameters such as the plasma source concentration and the surface ion current are adjusted to specific values to facilitate the engineer to use the plasma source to achieve a specific process (for example, an etching process). Please refer to Figure 14 for a graph of the voltage-average instantaneous current measured by the probe in the working chamber. It can be found from the experimental data of FIG. 14 that the probe 21 is placed at the first height, the second height, and the fourth height in the working chamber 14, and the above steps (S6) to (S11) are repeated to obtain an average instant. After the current, the probe 21 approaches the same value of the saturation current of the plasma measured at the first height, the second height, and the fourth height, which means that the plasma concentration in the working chamber 14 may approach the same. . It must be particularly noted that the plasma current measured by the probe 21 at the fifth height and the sixth height is significantly lower than the plasma current measured by the probe 21 at the first height, the second height, and the fourth height. The reason is that the fifth height and the sixth height have been separated from the uniform plasma zone of the plasma.

Thus, the above description completely and clearly illustrates the detailed steps and technical features of the method for obtaining a stable plasma source of the present invention; and, as described above, the present invention has the following advantages:

(1) As shown in Figure 1, the conventional plasma measurement architecture can only be used to assist the engineering staff to confirm whether the plasma in the plasma reaction chamber is stable or not, and cannot help the engineer to restart the RF. The plasma system quickly manufactures or obtains a stable plasma source. However, the method for obtaining a stable plasma source proposed in the present invention only needs to add a probe 21, a power supply 22, an electric meter 23, and a regulating device 24 to an ECR plasma system 1 to pass through the electric meter. The manner of monitoring the specific bias voltage applied to the probe 21 and the plasma current collected by the probe 21 effectively assists the engineer in regulating the working chamber 14 by adjusting the power level of the microwave generator 11. The magnitude of the surface plasma current within the chamber ultimately allows the plasma concentration in the working chamber 14 to meet the plasma concentration requirements of the engineer on a particular process condition.

(2) In addition, the method of this case does not need to measure and calculate the relevant characteristic parameters of the plasma, such as: ion saturation current, ion saturation slope, floating potential, plasma potential, electron temperature, electron density, etc.; otherwise, this case only needs Measuring the current at the plasma boundary (such as the boundary saturation current) is very easy to import directly into existing ECR plasma systems.

(3) In the traditional ECR plasma application, there are usually strict environmental requirements, such as temperature, humidity, pressure, etc., which need to be strictly controlled to maintain the consistency of plasma parameters every time the plasma source is restarted. This indirectly limits the popularity and use of ECR plasma. The invention is successfully tested in a laboratory without constant temperature and humidity and without lateral pressure control, and can control the error of surface ion current and demand value within 1% under manual adjustment. Therefore, after the application of the present invention, a stable ECR plasma source can be used in a factory or a research unit with poor conditions, and the popularity of the ECR process can be increased.

It is to be understood that the foregoing detailed description of the embodiments of the present invention is not intended to Both should be included in the scope of the patent in this case.

<present invention>
1‧‧‧ECR plasma system
10‧‧‧ gas supply unit
11‧‧‧Microwave generator
12‧‧‧ Plasma generating chamber
13‧‧‧Magnetic system
14‧‧‧Working chamber
15‧‧‧Exhaust and pressure maintenance devices
21‧‧‧ probe
22‧‧‧Power supply
23‧‧‧Electric meter
24‧‧‧Control device
141‧‧‧ Target stage
S1~S5‧‧‧ method steps
S6~S11‧‧‧ method steps

<知知>
1'‧‧‧ Plasma Reaction Chamber
2'‧‧‧ probe
3'‧‧‧RF source
4'‧‧‧ Current measuring device
6'‧‧‧ capacitor
7'‧‧‧ Plasma
5'‧‧‧Voltage measuring device

1 is a conventional plasma measurement architecture diagram; FIG. 2 is a voltage-time data curve; FIG. 3 is a current-time data curve; FIG. 4 is a current versus voltage curve; Figure 6 is a current-time data curve diagram; Figure 7 is an architectural diagram of an ECR plasma system; Figure 8 is a second architecture diagram of the ECR plasma system; Figure 9 is an ECR plasma system 3 is a fourth architectural diagram of an ECR plasma system; FIG. 11 is a flow chart of a first embodiment of a method for obtaining a stable plasma source according to the present invention; A flow chart of a second embodiment of the method of slurry source; FIG. 13A to FIG. 13F are data plots of voltage-instant current measured at a first height to a sixth height of the probe in the working chamber; FIG. A graph of the voltage-average instantaneous current measured by the probe in the working chamber.

S1~S5‧‧‧ method steps

Claims (9)

A method for obtaining a stable plasma source is applied to an ECR plasma system (Electron Cyclotron Resonance), wherein the ECR plasma system includes at least a gas supply device, a microwave generator, and a A plasma generating chamber, a magnetic system, a working chamber, and a pumping and pressure maintaining device; the method for obtaining a stable plasma source comprises the steps of: (1) extending a probe into the working chamber (2) activating the pumping and pressure maintaining device to maintain the interior of the plasma generating chamber and the working chamber in a first low pressure vacuum state; (3) starting the gas supply device to pass a work Gas into the plasma generating cavity, and starting the microwave generator and the magnetic system to generate a plasma in the plasma generating cavity; (4) introducing the plasma into the working cavity; 5) supplying a specific bias voltage to the probe with a power supply, and determining that the plasma source in the working chamber meets a specific process condition; and then connecting to the power supply through An electric meter records the specific bias voltage and a specific current collected by the probe; wherein the specific current is used as a stable plasma parameter, and the engineer can adjust and set the ECR plasma system to generate a stable plasma source. Meet the specific process conditions described. A method for obtaining a stable plasma source according to claim 1, wherein the microwave generator provides a microwave having a frequency range of 1 GHz to 3 GHz to the plasma generating chamber. A method of obtaining a stable plasma source as described in claim 1 wherein the specific process condition can be any of: an etch rate, a deposition rate, or a cutting rate. A method of obtaining a stable plasma source as described in claim 1 wherein the probe is a conductor electrode. The method for obtaining a stable plasma source according to claim 1, wherein a drain electrode of the working chamber is electrically connected to the power supply, and the drain electrode becomes the probe. A method for obtaining a stable plasma source according to claim 1, wherein a measuring surface of the probe is located in a uniform plasma region of the working chamber. A method for obtaining a stable plasma source according to claim 1, wherein a measuring surface of the probe is in the same plane as a target stage in the working chamber. The method for obtaining a stable plasma source according to claim 1, wherein a measuring surface of the probe and a target carrier in the working chamber are oppositely Has an angle. The method for obtaining a stable plasma source as described in claim 1 further includes the step of automatically regulating and stabilizing the plasma source, and the step of automatically regulating and stabilizing the plasma source comprises the following detailed steps: (6) restarting The gas supply device and the gas supply device maintain the interior of the plasma generating chamber and the working chamber in a second low pressure vacuum state; wherein the second low pressure vacuum state is the same or similar to the first low pressure a vacuum state; (7) restarting the microwave generator and the magnetic system; (8) measuring an instantaneous current collected by the probe through the electric meter connected to the power supply; (9) transmitting through the electric meter A regulating device determines whether a current difference between the instantaneous current and the specific current is zero, and if so, performing step (11); if not, performing step (10); (10) the adjusting device adjusts the current limit The power of the microwave generator is repeated and the step (8) is repeated; and (11) the plasma source in the working chamber has satisfied the particular process condition.