TWI571053B - Impedance Matching Network for Plasma Reactors - Google Patents

Description

Impedance matching network for plasma reactor

The present invention relates to the field of semiconductor device fabrication, and more particularly to the field of impedance matching technology for plasma reactors.

Plasma processing apparatuses are widely used in manufacturing processes for manufacturing integrated circuits (ICs) or MEMS devices. One of the notable uses is in plasma reactors for etching semiconductor substrates. The plasma contains a large number of active particles such as electrons, ions, excited atoms, molecules and radicals. These active particles undergo various physical and chemical reactions on the surface of the semiconductor substrate, thereby changing the surface properties of the semiconductor substrate. Generally, as a method of generating plasma, a plasma processing module can be roughly classified into a method using a glow discharge or a high-frequency discharge, and a method using microwaves.

In the high-frequency discharge plasma processing module, in order to efficiently load the RF power of the excitation plasma into the discharge system, an impedance matching network needs to be connected between the RF power supply and the discharge system, and the impedance matching network usually includes Capacitance and inductance, when the impedance of the impedance matching network needs to be changed, the impedance matching network is usually adjusted by changing the size of the capacitor. Since the change of process parameters (such as RF power, air pressure, process materials or gases) in practical applications will lead to rapid changes in plasma impedance, especially for applications where the RF power source is pulse modulated output, pulsed RF output power control reaction plasma The bulk etching process has been widely used. The basic principle is that the RF power source outputs the pulsed RF power for generating plasma. The density of the generated plasma changes with the pulse, and the number of charged particles (electrons and ions). Intermittent changes, so that the etching of the plasma is controlled and buffered. In this application, the RF power source in a plasma application changes the high and low frequency power loaded on the discharge system in microseconds, causing a rapid change in plasma impedance in microseconds, which requires impedance matching. The network is capable of providing impedance matching for the same order of magnitude to maintain a continuous, stable discharge of the plasma. In the traditional matching network, the variable capacitor is driven by the motor, which cannot meet the rapid adjustment of the variable capacitor in the microsecond range. As a result, the impedance matching network cannot adjust its size in time, so that the RF power can not be effectively activated in time. The loading is on the discharge system, which in turn does not produce the plasma distribution required for the process.

In order to solve the above technical problem, the present invention provides an impedance matching network for a plasma reactor, comprising at least one inductor and a variable capacitor unit, the variable capacitor unit including at least one variable vacuum capacitor, The vacuum capacitor includes two electrode plates, and an annular piezoelectric ceramic plate is disposed between the two electrode plates, the ring-shaped piezoelectric ceramic plate is connected to a driving power source, and an arc-shaped electrode plate is disposed in a hollow region of the annular piezoelectric ceramic plate. .

Preferably, the variable vacuum capacitor unit comprises a plurality of variable vacuum capacitors connected in parallel or in series.

Preferably, a high power MOSTFET FET unit is connected between the variable capacitance unit and the driving power source, and the high power MOSTFET FET unit comprises a plurality of high power MOSTFET FETs.

Preferably, the number of the high power MOSTFET FETs is equal to the number of the variable vacuum capacitors, and each of the high power MOSTFET FETs is connected to a variable vacuum capacitor.

Preferably, the high power MOSTFET FET unit is connected to a micro control unit MCU.

Preferably, the capacitance of the variable vacuum capacitor is adjusted in the order of microseconds.

Preferably, the plurality of variable vacuum capacitors are connected in parallel or in series to one circuit according to impedance matching requirements, and the circuit is connected to a driving power source.

Preferably, the impedance matching network is connected to a radio source power source or a radio frequency bias power source.

Preferably, the RF source power source and the RF bias power source output are pulse modulated outputs.

Preferably, the annular piezoelectric ceramic plate is connected to the driving power source through a piezoelectric ceramic driving electrode.

The invention has the advantages that the variable vacuum capacitor in the impedance matching network of the invention is made of piezoelectric ceramic material, and the reverse piezoelectric effect of the piezoelectric ceramic material is used when an alternating driving voltage is applied to the piezoelectric ceramic. Piezoelectric ceramics can rapidly expand and contract along the voltage loading direction, thereby rapidly changing the capacitance of the variable vacuum capacitor, which can usually be changed in the order of microseconds. By using multiple variable vacuum capacitors in parallel, high-power MOSTFET FET units and MCU control can be used to achieve any combination of variable vacuum capacitors, thus enabling flexible adjustment of matching impedance. The technical solution described in the present invention subverts the conventional adjustment method of the conventional variable vacuum capacitor driven by the motor, and uses the inverse piezoelectric effect of the piezoelectric ceramic material to fabricate the vacuum variable capacitor, so that the vacuum variable capacitor can be in the order of microseconds. The size adjustment is implemented to meet the need for the plasma impedance to rapidly change with the output of the RF power source.

The technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention. It is a partial embodiment of the invention, and not all of the embodiments. All other embodiments obtained by a person of ordinary skill in the art based on the embodiments of the present invention without departing from the scope of the present invention are within the scope of the present invention.

In plasma industry applications, in order to efficiently load the RF power source that excites the plasma into the discharge system, an impedance matching network is required between the power supply and the discharge system. 1 is a schematic view showing the connection structure of the impedance matching network and the plasma reactor of the present invention. As shown in FIG. 1, the plasma reactor includes a vacuum reaction chamber 100 including an upper electrode 105 and a lower electrode 110 below the upper electrode 105, the semiconductor substrate to be processed being located above the lower electrode 110. When the RF power of the RF power source is applied to the lower electrode 110, a plasma 120 is formed between the upper electrode 105 and the lower electrode 110, and the plasma 120 physically oscillates and chemically reacts the surface of the semiconductor substrate to complete the etching. process. The RF power source of the plasma reactor generally includes at least one RF bias power source and one RF source power source. In this embodiment, one RF bias power source 170 and one RF source power source 160 are simultaneously applied to the lower electrode 110. on. The RF bias power source 170 and the RF source power source 160 effectively apply RF power to the lower electrode 110 through the impedance matching network 140 and the impedance matching network 150, respectively.

It will be readily apparent to those skilled in the art that in a plasma reactor, the impedance matching network must be arranged to ensure that the impedance of the RF power source matches the impedance of the plasma 120 generated within the vacuum reaction chamber 100 due to process parameters such as RF in practical applications. Changes in power, gas pressure, process materials, or gases can cause rapid changes in plasma impedance, particularly when the RF power output is a pulsed output, to ensure that the plasma 120 impedance changes in the vacuum reaction chamber 100 and the RF power source pulse. The output changes consistently, and the impedance matching network between the RF power source and the plasma needs to be equal to the pulse output frequency of the RF power source. Generally, the impedance matching network includes at least one inductor and one variable capacitor. In the prior art, the impedance adjustment of the impedance matching network is mainly through the inductance of the fixed impedance matching network, and the variable capacitance of the impedance matching network is changed. to realise. In a plasma reactor, the variable capacitance is typically a variable vacuum capacitance. The traditional variable vacuum capacitor is driven by the motor and cannot change the capacitance value quickly. Especially in the application where the RF power source is pulse output, the RF power source will be in microseconds when the RF power source is pulse output. Changing the high frequency and low frequency power loaded on the plasma during the time period causes the plasma impedance to change rapidly in the order of microseconds, which requires the impedance matching network to provide impedance matching for the same order of magnitude. Continuous stable discharge of plasma. Conventional motor-driven variable vacuum capacitors do not meet this requirement.

2 is a schematic view showing the structure of a variable vacuum capacitor according to the present invention, the variable vacuum capacitor 1510 includes two parallel electrode plates 1511 and 1512, and a space substantially parallel to the two electrode plates is disposed between the two electrode plates. Annular piezoelectric ceramic plate 1513. The annular piezoelectric ceramic plate 1513 is connected to a driving power source 153 through a piezoelectric ceramic driving electrode 1515. The hollow region of the annular piezoelectric ceramic plate 1513 is provided with an arc electrode plate 1514. The electrode plate 1512 and the arc electrode plate 1514 form a parallel plate vacuum. Capacitor, FIG. 3 is a schematic view showing the connection structure of the annular piezoelectric ceramic plate and its curved electrode plate. Piezoelectric ceramic is a functional ceramic material capable of mutually converting mechanical energy and electrical energy. In the present invention, an alternating driving power source 153 is connected to the annular piezoelectric ceramic plate 1513, and the inverse piezoelectric effect of the piezoelectric ceramic material is utilized. The piezoelectric ceramic material is mechanically driven by the alternating electric field, that is, when an alternating electric field is applied to the annular piezoelectric ceramic plate 1513, the shape of the annular piezoelectric ceramic plate 1513 is expanded and contracted in the voltage loading direction. The telescopic movement forces the arc electrode plate 1514 in the hollow region to undergo compression or stretching motion, resulting in a change in the distance d between the arc electrode plate 1514 and the electrode plate 1512, and the capacitance value of the known variable vacuum capacitor is calculated. Formula is , (where For the vacuum dielectric constant, S is the plate area, and d is the plate spacing), thus achieving a rapid change in capacitance. According to the technical solution of the present invention, different capacitance change rates and capacitance value adjustment response times of the variable vacuum torch can be realized by selecting curvatures, mass design and materials of different arc electrode plates. In the present embodiment, the driving power source 153 acting on the annular piezoelectric ceramic plate 1513 is an alternating current power source.

4 is a schematic structural diagram of the impedance matching network according to the present invention. In this embodiment, an impedance matching network 150 matching the RF source power source 160 is selected for detailed description, and an impedance matching network connected to the RF bias power source 170 is described. The road 140 can adopt the same technical solution as the impedance matching network 150, and details are not described herein again. In the schematic diagram shown in FIG. 4, the RF source power source 160 is coupled to the impedance matching network 150. The impedance matching network 150 includes an inductor 152 and a variable vacuum capacitor unit 151, a variable vacuum capacitor unit 151, and a driving power source 153. A high power MOSTFET FET unit 155 is connected between them, and a microprocessor MCU 154 is connected to the high power MOSTFET FET unit 155. The variable vacuum capacitor unit 151 employed in this embodiment includes a plurality of variable vacuum capacitors 1510. Since the annular piezoelectric ceramic plate 1513 of the variable vacuum capacitor 1510 has a limited expansion and contraction amplitude, it drives the stretching and compression amplitude of the arc electrode plate 1514. Smaller, the distance between the arc electrode plate 1514 and the two parallel electrode plates changes little, and finally the change of the capacitance value of the variable capacitor is small, which cannot meet the adjustment requirement of the impedance matching network. In the present invention, a plurality of variable vacuum capacitors 1510 are connected in parallel or in series to form a variable vacuum capacitor unit 151, and the variable vacuum capacitor unit 151 is disposed by setting the number of variable vacuum capacitors 1510 and the magnitude of change of each variable vacuum capacitor. The equivalent capacitance value is adjusted. Since a plurality of variable vacuum capacitors 1510 are connected in parallel or in series to form one circuit, the same driving power source 153 can be applied to the circuit. 5 is a schematic structural view showing a connection between a high power MOSTFET field effect transistor and a variable vacuum capacitor; in the embodiment illustrated in FIG. 5, the high power MOSTFET FET unit 155 includes a large number corresponding to the variable vacuum capacitor 1510. A power MOSTFET FET 1551, each high power MOSTFET FET 1551 is coupled to a variable vacuum capacitor 1510. The high-power MOSTFET FET control driving power source 153 loads the driving voltage to the ring-shaped piezoelectric ceramic plate of the variable vacuum capacitor 1510, and drives the variable vacuum capacitor 1510 through the switching of the high-power MOSTFET FET. Further, the combination of the variable vacuum capacitor units 151 participating in the impedance matching is determined. In addition, the high power MOSTFET FET unit 155 is also coupled to a microprocessor MCU 154. The MCU 154 can select the variable vacuum capacitor 1510 by controlling the switching of each high power MOSTFET FET when a high power MOSTFET field effect is applied. When the tube 1551 is in the on state, the variable vacuum capacitor connected thereto is moved by the internal piezoelectric ceramic under the driving voltage, thereby changing the capacitance value, when a certain high-power MOSTFET FET 1551 is in a blocking state, The size of the connected variable capacitor remains unchanged. By using the MCU 154 to control the on and off of the high power MOSTFET FET unit, the variable vacuum unit 151 can be controlled to realize the combination of the number of arbitrary variable vacuum capacitors, thereby implementing the impedance matching network 150. The impedance is flexibly adjusted to ensure stable power input to the discharge system.

The variable vacuum capacitor in the impedance matching network of the present invention is made of piezoelectric ceramic material, and the piezoelectric ceramic can be rapidly applied when an alternating driving voltage is applied to the piezoelectric ceramic by using the inverse piezoelectric effect of the piezoelectric ceramic material. The telescopic movement occurs along the voltage loading direction, which in turn rapidly changes the capacitance of the variable vacuum capacitor, which is usually changed in the order of microseconds. By using multiple variable vacuum capacitors in parallel, high-power MOSTFET FET units and MCU control can be used to achieve any combination of variable vacuum capacitors, thus enabling flexible adjustment of matching impedance. The technical solution described in the present invention subverts the adjustment mode of the conventional variable vacuum capacitor driven by the motor in the past, and uses the inverse piezoelectric effect of the piezoelectric ceramic material to fabricate the vacuum variable capacitor, so that the vacuum variable capacitor can be in the order of microseconds. The size adjustment is implemented to meet the need for the plasma impedance to rapidly change with the output of the RF power source.

The present invention is disclosed in the above preferred embodiments, but it is not intended to limit the present invention, and any one skilled in the art can make possible variations and modifications without departing from the spirit and scope of the invention. The scope of protection shall be subject to the scope defined by the claims of the present invention.

100‧‧‧vacuum reaction chamber
105‧‧‧Upper electrode
110‧‧‧ lower electrode
120‧‧‧ Plasma
140, 150‧‧‧ impedance matching network
151‧‧‧Variable vacuum capacitor unit
1510‧‧‧Variable vacuum capacitor
1511, 1512‧‧‧electrode plates
1513‧‧‧Circular Piezoelectric Ceramic Plate
1514‧‧‧Arc electrode plate
1515‧‧‧ Piezoelectric ceramic drive electrode
152‧‧‧Inductance
153‧‧‧Drive power supply
154‧‧‧MCU
155‧‧‧High-power MOSTFET FET unit
1551‧‧‧High Power MOSTFET FET
160‧‧‧RF source power source
170‧‧‧RF bias power source
D‧‧‧distance

1 is a schematic view showing the connection structure of the impedance matching network and the plasma reactor of the present invention; FIG. 2 is a schematic view showing the structure of the variable vacuum capacitor of the present invention; FIG. 3 is a view showing the annular piezoelectric ceramic board of the present invention; FIG. 4 is a schematic structural view of the impedance matching network of the present invention; FIG. 5 is a schematic structural view showing the connection of a high power MOSTFET FET and a variable vacuum capacitor.

1510‧‧‧Variable vacuum capacitor

1511, 1512‧‧‧electrode plates

1513‧‧‧Circular Piezoelectric Ceramic Plate

1514‧‧‧Arc electrode plate

1515‧‧‧ Piezoelectric ceramic drive electrode

153‧‧‧Drive power supply

D‧‧‧distance

Claims (10)

An impedance matching network for a plasma reactor, comprising at least one inductor and a variable capacitor unit, wherein the variable capacitor unit comprises at least one variable vacuum capacitor, the variable vacuum capacitor comprising two electrode plates, An annular piezoelectric ceramic plate is disposed between the two electrode plates, the annular piezoelectric ceramic plate is connected to a driving power source, and an arc-shaped electrode plate is disposed in a hollow region of the annular piezoelectric ceramic plate. The impedance matching network of claim 1, wherein the variable vacuum capacitor unit comprises a plurality of variable vacuum capacitors, the plurality of variable vacuum capacitors being connected in parallel or in series. The impedance matching network of claim 2, wherein a high power MOSTFET FET unit is connected between the variable capacitance unit and the driving power source, the high power MOSTFET FET unit comprising a plurality of high power MOSTFET FET. The impedance matching network of claim 3, wherein the number of the high power MOSTFET FETs is equal to the number of the variable vacuum capacitors, and each of the high power MOSTFET FETs is connected to a variable vacuum capacitor. The impedance matching network of claim 3, wherein the high power MOSTFET FET unit is coupled to a micro control unit MCU. The impedance matching network of claim 1, wherein the capacitance of the variable vacuum capacitor is adjusted in the order of microseconds. The impedance matching network of claim 2, wherein the plurality of variable vacuum capacitors are connected in parallel or in series to one circuit according to impedance matching requirements, the circuit being connected to a driving power source. The impedance matching network of claim 1, wherein the impedance matching network is connected to a radio source power source or a radio frequency bias power source. The impedance matching network of claim 8, wherein the RF source power source and the RF bias power source output are pulse modulated outputs. The impedance matching network of claim 1, wherein the annular piezoelectric ceramic plate is connected to the driving power source through a piezoelectric ceramic driving electrode.