TWI636484B - Inductively coupled plasma processor - Google Patents

Abstract

An inductively coupled plasma processor comprising: a reaction chamber, a susceptor, a high frequency RF power source and an inductor; the susceptor is located in the reaction chamber, the substrate to be processed is fixed on the susceptor; and the top of the reaction chamber includes insulation a material window, the inductor coil is disposed outside the reaction chamber, and transmits a radio frequency magnetic field into the reaction chamber through the insulating material window; the high frequency RF power source is connected to the input end of the inductor coil through a matching circuit, and the output of the inductor coil The terminal is connected to the grounding end; the first balancing circuit is further included between the matching circuit and the input end of the inductor, and the second balancing circuit is further included between the output end of the inductor and the ground, the first And the second balancing circuit includes an inductor and a capacitor connected in series with each other.

Description

Inductively coupled plasma processor

The present invention relates to the field of semiconductor manufacturing technology, and in particular, to a driving circuit of an inductively coupled plasma processor.

In recent years, computers, communications, automotive electronics, aerospace and other consumer products have placed higher demands on microelectronic packaging, namely smaller, thinner, lighter, more reliable, versatile, and low power. At low cost, many vertical interconnect vias are needed to realize electrical interconnection between different wafers. The via via etching process has gradually become an important technology in the field of micro-nano processing. With the increasing use of microelectromechanical systems and microelectromechanical systems (MEMS) in automotive and electricity electronics, TSV (Through Silicon Via) via etching technology in the future packaging field Broad prospects, deep etching process has gradually become one of the most sought-after processes in the field of MEMS manufacturing and TSV technology. An inductively coupled (ICP) plasma processing apparatus is widely used in these semiconductor processing apparatuses. As shown in FIG. 1, the inductively coupled plasma processing apparatus includes a reaction chamber 100 including a susceptor 120 therein, and the susceptor 120 includes Lower electrode. An electrostatic chuck 121 is included above the susceptor 120, and the substrate 122 to be processed is disposed on the electrostatic chuck 121. A radio frequency power source 40 having a lower frequency (e.g., 2 Mhz to 400 Khz) is connected to the lower electrode through a matcher 50. The top of the reaction chamber 100 includes a top plate made of an insulating material, and an inductor 70 is disposed above the top plate of the insulating material. An RF power source 60 is coupled to the inductor 70 via a matcher 80, and the inductor 70 The other end is grounded. An air supply nozzle 90 is coupled to the gas source 110 via a valve 95. The inductive coil 70 may be an involute or concentric circle, or a combination of various coil shapes of the inner and outer sections, and the like. The RF current flows from the input end of the inductor 70 into the inductor 70 and from the other end to the ground, and the voltage gradually decreases during the RF electric field transfer.

As shown in Figure 2, the voltage amplitude profile of a typical involute coil is linearly reduced from input point A to output B. The voltage on the inductor 70 during plasma processing affects the thickness of the sheath within the reaction chamber 100, which in turn affects the energy of the plasma incident on the top insulating window of the reaction chamber 100. If the incident energy is too large, the bombardment destroys the underlying surface of the insulating material window, causing the particulate matter to fall onto the underlying substrate 122 to form a contamination, and at the same time, since the entire inductor coil 70 has different voltages at different positions, the entire insulating layer is destroyed by bombardment. The degree of difference is different, so the uneven distribution of the voltage of the inductor 70 also causes the difference in the processing effect of the lower substrate 122. To reduce the uneven voltage distribution on the inductor 70, a balancing circuit needs to be provided to obtain a more optimized voltage distribution. To this end, two capacitors are connected at each end of the inductor coil to balance the voltage at various locations within the coil. As shown in FIG. 3a, the inductor 70 driving circuit with the balancing capacitors Cin and Cout is connected. The output power of the RF power source 60 is connected to the series-connected Cin, the inductors 70 and Cout and finally to the ground through a variable capacitor Cv. The capacitance values of the capacitors Cin and Cout across the inductor 70 are carefully calculated and designed to finally reduce the voltage distribution on the inductor 70 to the voltage at terminal A shown in FIG. 3b from the input voltage Vin to half of the original voltage. /2, the voltage at the B terminal is changed from 0 to -Vin/2, and the A terminal and the B terminal are only high-frequency voltages having opposite phases, and the voltage amplitude actually affecting the lower plasma reaction chamber 100 is Vin/2. The inductor 70 is turned into a zero voltage in the middle of the capacitor through the two ends, so that the voltage difference across the inductor 70 is obtained. It is still Vin, but its bombardment effect on the lower reaction chamber is significantly reduced. However, such improvements still have problems. The two series capacitors are designed to match the current plasma reaction chamber 100, but when the impedance within the reaction chamber 100 changes, the inductance of the inductor 70 changes or the frequency of the input RF power source changes. This circuit cannot achieve effective coil voltage balance. It is necessary to replace the new capacitors Cin and Cout for a specific RF power supply or a specific processing technology to adjust the voltage of the coil to achieve a balanced distribution. This is not only costly but also time consuming. It is laborious, so the industry needs to be able to adapt to the impedance of different inductors 70, and also needs to be able to adapt to the drive circuit of the inductor 70 with different frequency output of the RF power source 60.

The problem to be solved by the present invention is to provide an inductively coupled plasma processor comprising: a reaction chamber, a susceptor, a high frequency RF power source and an inductor; the susceptor is located in the reaction chamber, and the substrate to be processed is fixed on the pedestal The top of the reaction chamber includes an insulating material window disposed outside the reaction chamber, and the RF magnetic field is transmitted into the reaction chamber through the insulating material window; the high frequency RF power source is connected to the inductor coil through a matching circuit An input end, the output end of the inductor is connected to the ground; wherein: the matching circuit and the input end of the inductor further comprise a first balancing circuit, and the second end of the inductor and the ground further comprise a second A balancing circuit, the first and second balancing circuits comprising an inductor and a capacitor connected in series with each other.

The first balancing circuit and the second balancing circuit have the same impedance and can realize automatic balancing at different RF frequencies.

The first balancing circuit includes an input inductor connected to the output of the matching circuit, an input capacitor connected between the input inductor and the inductor; the second balancing circuit includes an output inductor connected to the ground at one end The other end passes an output Connected to the output of the inductor.

The input capacitor and the output capacitor may have the same capacitance.

The input inductor and the output inductor may be selected from air core inductors.

The pedestal is connected to the low frequency RF power supply through a second matching circuit, and the output power of the high frequency RF power source or the low frequency RF power source alternates between the high power output and the low power output. The output frequency of the high frequency RF power source or the low frequency RF power source is also synchronized with the output power. The invention has outstanding advantages in application to variable frequency applications, and the prior art can achieve automatic balancing in applications where the frequency is variable.

One of the first balancing circuit or the second balancing circuit of the present invention includes an inductor that cooperates with the capacitance in the first balancing circuit and the second balancing circuit to achieve matching of different impedances at different process parameters.

100‧‧‧plasma reaction chamber

105‧‧‧Adjustment ring

110‧‧‧ gas source

120‧‧‧Base

121‧‧‧Electrostatic chuck

122‧‧‧Substrate

130‧‧‧Pneumatic valve

40‧‧‧RF power supply

50‧‧‧matcher

60‧‧‧RF power supply

70‧‧‧Inductance coil

80‧‧‧matcher

90‧‧‧Air supply nozzle

95‧‧‧ Valve

1 is a schematic structural view of a prior art inductively coupled plasma processor.

2 is a voltage distribution diagram of a prior art inductor coil.

Fig. 3a is a circuit diagram of an improved inductor driving circuit of the prior art.

FIG. 3b is a voltage distribution diagram of the inductor coil after the prior art application improves the inductor driving circuit.

Fig. 4 is a circuit diagram showing an inductor driving circuit of the first embodiment of the present invention.

Fig. 5 is a circuit diagram showing an inductor driving circuit of a second embodiment of the present invention.

Please refer to FIG. 4 for understanding the driving circuit of the inductor coil on the inductively coupled plasma processing apparatus of the present invention. As shown in FIG. 4, the inductor driving circuit of the present invention comprises a RF power source 60 connected to an input terminal of an input inductor Lin through a variable capacitor Cv, and an output terminal of the input inductor Lin is connected to an input terminal of an input capacitor Cin, the input capacitor The output is connected to the input A of the inductor 70. The output of the inductor 70 is connected to the input of an output capacitor Cout, the output B of the output capacitor Cout is connected to the input of an output inductor Lout, and the output of the output inductor Lout is grounded.

The inductively coupled drive circuit of the present invention can accommodate an RF power supply 60 having an automatic frequency tuning function. With the increasing precision of plasma processing, the control accuracy of plasma energy and concentration is also getting higher and higher, and pulsed plasma is also widely used. When a semiconductor substrate is processed by a pulse-type plasma, the RF power applied to the plasma reaction chamber is abrupt, and in order to accommodate the mutated RF power and the abrupt plasma impedance, a faster matching capability is required, a conventional matcher, The matchers 50, 80 as in the present invention require a mechanically driven variable impedance component, such as the variable capacitor Cv of FIG. The variable capacitance Cv is mechanically driven during the adjustment matching process to match the impedance between the matching circuit and the plasma reaction chamber, so that the output power of the RF power source is delivered to the reaction chamber as much as possible. However, when the pulsed plasma is used to process the semiconductor substrate, since the pulse frequency reaches several kilohertz or several tens of kilohertz, the matching time is required to be less than 1 ms, which is a failure of the ordinary mechanical drive to achieve the response speed. Therefore, the applicant proposed in another Chinese patent application CN201210393470.X that the instantaneous output power frequency is used to achieve fast impedance matching. The output frequency of the RF power source 60 of the present invention may be hopped between two close frequencies (eg, 12.9Mhz-13.1Mhz), thus achieving electronic switching, the corresponding speed can reach the required speed. The output power of the biased RF power source 40 connected to the lower electrode can also be pulsed. The present invention achieves voltage balance by a balancing circuit connected in series across the inductor 70 while achieving matching and voltage distribution balance over such variable output frequency range. The balancing circuit of the present invention comprises an inductor and a capacitor connected in series, wherein the input capacitor Cin and the output capacitor Cout need to calculate their capacitance so that the voltage balance on the coil can be achieved when connected across the inductor 70, as shown in FIG. 3b. Voltage distribution. Similarly, the sense values of the input inductor Lin and the output inductor Lout in the present invention also need to be selected according to the plasma processing process performed. The different processing processes (power, gas pressure, gas composition, etc.) performed in the plasma reaction chamber 100 may cause different impedances of the plasma, and different plasma impedances may cause different actual inductance values of the inductor coil 70, so as shown in FIG. 3a. The prior art uses only two capacitors at both ends to match the actual application where the plasma impedance varies within a certain range. The inventors have found that the application of a composite impedance including a series inductor and a capacitor combination can match a wider range of impedances within the plasma reaction chamber 100 due to different processing processes, and can also match the RF power source 60 or the RF power source. 40 The impedance caused by the abrupt output frequency varies within a certain range.

Preferably, by selecting the input and output inductance and the capacitance parameter, the balancing circuit at both ends of the inductor 70 of the present invention has the same impedance value, so that the voltage across the inductor 70 can be automatically balanced, wherein the input capacitors Cin and Cout With the same capacitance value, the input inductor Lin and the output inductor Lout can also have the same sense value, so that the balance circuits at both ends have symmetry. The balanced circuit with symmetry can change the impedance of the balanced circuit at both ends when the input frequency changes, so the inductor coil can also automatically obtain the voltage distribution in the equilibrium state as shown in FIG. 3b, and the present invention passes through the balanced circuit. Set the inductor to better adapt to the reaction chamber The internal impedance of 100 varies within a certain range depending on the processing.

The present invention can also be combined between the front end Lin of the inductor 70 and the Lout of the rear end of the inductor 70 to be disposed between the matching circuit and the input capacitor. The specific circuit is as shown in FIG. Of course, the combined Lin' can also be placed between the output capacitor and the ground after the output capacitor Cout. The second embodiment of the present invention as shown in FIG. 5 has no symmetrical characteristics because the inductor Lin' is disposed only at one end of the inductor coil, and the input capacitor Cin and the output capacitor Cout are different when the parameters are selected, and thus vary in a wide frequency. Automatic balancing is also not possible in the range. However, compared with the prior art, the second embodiment of the present invention can adapt to the impedance change brought by different processing technologies, and can still work efficiently in an application where the frequency range is not required or the frequency variation range is not large.

In the balancing circuit of the present invention, a plurality of inductors or a plurality of capacitors may be provided to form other impedance values in combination, and the object of the present invention can still be achieved, which is a modified embodiment of the technical solution of the present invention. In the present invention, the positions of the inductor and the capacitor can be interchanged. For example, the input capacitor is at the front end of the input inductor, and the input inductor is connected to the inductor 70. Since the inductors Lin and Lout in the present invention mainly function to adapt to the impedance change in the reaction chamber 100, a large inductance value is not required, and an air core inductance having a low inductance value can be selected.

The top insulating material window of the inductively coupled plasma processor of the present invention may be dome-shaped in addition to a flat top shape, and even an insulating material portion may be disposed on the top side of the reaction chamber sidewall, and the corresponding inductor coil 70 may also be covered in the reaction. The top or a portion of the side wall of the cavity 100.

Although the present invention has been disclosed above, the present invention is not limited thereto. Any changes and modifications may be made by those skilled in the art without departing from the spirit and scope of the invention, and the scope of the invention should be determined by the scope defined by the appended claims.

Claims (5)

An inductively coupled plasma processor comprising: a reaction chamber, a susceptor, a high frequency RF power source and an inductor; the susceptor is located in the reaction chamber, the substrate to be processed is fixed on the susceptor; and the top of the reaction chamber includes insulation a material window, the inductor coil is disposed outside the reaction chamber, and transmits a radio frequency magnetic field into the reaction chamber through the insulating material window; the high frequency RF power source is connected to the input end of the inductor coil through a matching circuit, and the output of the inductor coil The terminal is connected to the grounding end; the first balancing circuit is further included between the matching circuit and the input end of the inductor, and the second balancing circuit is further included between the output end of the inductor and the ground, the first And the second balancing circuit includes an inductor and a capacitor connected in series with each other, the first balancing circuit including an input inductor connected to the matching circuit output, and an input capacitor connected between the input inductor and the inductor coil; The second balancing circuit includes an output inductor connected to the ground end at one end and the other end connected to the inductor line through an output capacitor An output terminal, the input capacitance of the output capacitor having the same capacitance, the output power of the high frequency RF power alternates between a high power output and low power output. The inductively coupled plasma processor according to claim 1, wherein the first balancing circuit and the second balancing circuit have the same impedance. The inductively coupled plasma processor according to claim 1, wherein the input inductor and the output inductor are air core inductors. The inductively coupled plasma processor of claim 1, wherein the susceptor is connected to a low frequency RF power source via a second matching circuit. The inductively coupled plasma processor according to claim 4, wherein the output frequency of the high frequency radio frequency power source or the low frequency radio frequency power source is also synchronized with the output power.