TWI566644B - A radio frequency system for controllable harmonics of a plasma generator - Google Patents

Description

Radio frequency system for controllable harmonics of plasma generators

The present invention relates to a radio frequency system for a plasma generator, and more particularly to a radio frequency system for controllable harmonics of a plasma generator.

At present, in the manufacturing process of a semiconductor device, plasma of a reaction gas introduced therein is generally generated in a vacuum processing chamber of a plasma generator, and a substrate placed in the processing chamber is etched or the like.

In the existing dual-frequency capacitively coupled plasma generator, a flat upper electrode and a lower electrode are arranged in parallel in the vacuum reaction chamber. For example, a first RF source and a second RF source separated by a certain frequency are simultaneously applied to the lower electrode, wherein the first RF source having a higher frequency (eg, 60 MHz) is used to control ion dissociation or plasma density in the reactive gas; A low second RF source (e.g., 2 MHz) introduces a bias voltage to control the ion energy and energy distribution incident on the substrate.

However, due to the nonlinear effects caused by the interaction of the plasma with the RF source, secondary, tertiary or other harmonics of the high frequency RF source are generated, affecting the plasma distribution in the reaction chamber: the base placed on the lower electrode The plasma density above the center position is higher, and the plasma density at the edge position of the corresponding substrate is lower; the higher the frequency of the RF source, the more obvious the uneven distribution of the plasma, thus causing the substrate to be etched. Uneven.

It is an object of the invention to provide a controllable harmonic for a plasma generator The wave radio frequency system is provided with a harmonic control device capable of outputting a tuning impedance in a matching box between the RF source and the vacuum reaction chamber, and suppressing or adjusting the harmonic current of the high frequency RF source to control the plasma at the base The distribution of the surface of the sheet.

In order to achieve the above object, the technical solution of the present invention provides a radio frequency system for controlling harmonics of a plasma generator, which applies radio frequency energy to a driving electrode, and forms a reaction gas in a vacuum reaction chamber of the plasma generator. Plasma processing the substrate, wherein the radio frequency system includes: a first RF source that provides RF energy to generate the plasma; and a matching box coupled to the first RF source and the drive electrode Between the matching circuit, the load impedance of the plasma in the reaction chamber is matched with the output impedance of the first RF source; and the matching box is further provided with a harmonic control device. Connected to the first RF source, the harmonic control device generates a tuning impedance with an adjustable impedance value to adjust the harmonic impedance of the first RF source.

The harmonic current of the first RF source is proportional to the power of the first RF source; when the power of the first RF source is constant, the harmonic current thereof and the tuning impedance output by the harmonic control device The impedance value is inversely proportional.

The substrate is placed in the bottom of the reaction chamber; the plasma on the surface of the substrate has a density at a position corresponding to the center of the substrate and decreases toward the edge of the substrate; the plasma corresponds to the center of the substrate and The density difference of the edge is proportional to the harmonic current of the first RF source, i.e., inversely proportional to the impedance value of the tuning impedance.

The harmonic control device is an inductor, a low pass filter or a band rejection filter disposed in series between the first RF source and the drive electrode; or the harmonic control device is at the first A capacitor, a high pass filter or a band pass filter connected in parallel between the RF source and the drive electrode.

The harmonic control device is the inductor arranged in series, and has an inductance value of 0.1 μH to 100 μH.

The harmonic control device is the low pass filter, further comprising two inductors arranged in series between the first RF source and the drive electrode, and grounded in parallel between the two inductors Capacitor; the two inductors are 66nH; the capacitor is 53pF.

The radio frequency system further includes a second radio frequency source for controlling ion energy and energy distribution in the reaction chamber; the frequency of the second radio frequency source is smaller than the frequency of the first radio frequency source by a certain interval.

The selectable frequency of the first RF source comprises 27 MHz, 40 MHz, 60 MHz, 100 MHz or 120 MHz; the selectable frequency of the second RF source comprises 13 MHz, 2 MHz or 400 KHz.

The invention is particularly applicable to said first RF source having a frequency greater than 40 MHz.

The driving electrode includes an upper electrode and a lower electrode disposed in parallel in the reaction chamber; the first RF source is applied to one of the upper electrode or the lower electrode through the matching box; The first RF source is configured with the matching circuit and a harmonic control device; the second RF source is applied to the same or another matching box The upper electrode or the lower electrode is applied to the same or different radio frequency electrode as the first radio frequency source; and the matching circuit is configured in the matching box for the second radio frequency source.

The harmonic control device for adjusting the harmonic impedance of the first RF source is disposed between the output end of the matching circuit of the first RF source and the RF electrode; or the harmonic control device is disposed at Between the output end of the matching circuit of the second RF source and the RF electrode, and connected to the first RF source; or the harmonic control device is disposed at the first and second RF sources a common output end of the matching circuit and the RF electrode; or an output end of the matching circuit of the first RF source and an output end of the matching circuit of the second RF source are respectively connected with a harmonic control device .

Compared with the prior art, the radio frequency system for controlling harmonics of the plasma generator of the present invention has the advantage that the harmonic control device can output a high impedance tuning impedance to suppress the first The secondary and tertiary harmonic currents of an RF source cause the plasma energy on the surface of the substrate to be evenly distributed; or, by adjusting the tuning impedance of the output from high impedance to low impedance, the magnitude of the harmonic current is controlled. Thus, different plasma densities can be obtained at the center and edge surfaces of the substrate, and correspondingly different etching effects are produced.

11‧‧‧First RF source

12‧‧‧second RF source

20‧‧‧match box

21‧‧‧Harmonic control device

30‧‧‧ Vacuum reaction chamber

31‧‧‧ lower electrode

32‧‧‧Upper electrode

33‧‧‧Electrostatic suction cup

40‧‧‧Substrate

50‧‧‧ ion body

60‧‧‧Reactive gas

1 is a general structural diagram of a radio frequency system for controllable harmonics of a plasma generator in accordance with an embodiment of the present invention; and FIG. 2 is a diagram of the radio frequency system according to an embodiment of the present invention. Schematic diagram of the circuit structure when the harmonic control device is a low pass filter; Figure 3 is a schematic illustration of the etch rate of different locations of the substrate for the RF system at different impedances in accordance with an embodiment of the present invention.

Specific embodiments of the present invention will be described below with reference to the accompanying drawings.

The radio frequency system for controlling harmonics of the plasma generator of the present invention sets a harmonic control device in a matching box between the RF source and the RF electrode, which provides a harmonic of the tuning impedance to the high frequency RF source. The wave current is suppressed or regulated. The invention is described below in conjunction with specific embodiments.

1 is a general structural diagram of a radio frequency system for controllable harmonics of a plasma generator according to an embodiment of the present invention. As shown in FIG. 1, a vacuum reaction is provided in the plasma generator. The cavity 30 is provided with a substrate 40 on the electrostatic chuck 33 (ESC) at the bottom thereof. The electrostatic chuck 33 is provided with a lower electrode 31, and an upper electrode 32 parallel to the lower electrode 31 is disposed at the top of the reaction chamber 30. Under the action of the radio frequency system, the reaction gas 60 introduced into the reaction chamber 30 can be dissociated to form the plasma 50, thereby further etching the substrate 40 and the like.

The radio frequency system includes a matching box 20 electrically connected to the lower electrode 31 by a cable or the like, and a first radio frequency source 11 applied to the lower electrode 31 through the matching box 20, Two RF sources 12.

The frequency of the first RF source 11 is relatively high, and the generation and density of the plasma 50 are controlled by forming a radio frequency electric field between the upper and lower electrodes. The second RF source 12 controls the ion energy and energy distribution incident on the substrate 40 by controlling the sheath 50 self-biasing of the plasma. The frequency of the first RF source 11 may be 27 MHz, 40 MHz, 60 MHz, 100 MHz or 120 MHz, etc., and the frequency of the second RF source 12 may be 13MHz, 2MHz or 400KHz, etc.

The matching box 20 matches the load impedance of the plasma 50 in the reaction chamber 30 with the output impedance of the first and second RF sources through a matching circuit (not shown) to reduce the The reflectivity of the first and second RF sources is such that the first and second RF sources are each applied to the lower electrode 31 at the maximum output power.

In order to achieve harmonic control, the radio frequency system of the present embodiment further includes a harmonic control device 21 after the output end of the matching box 20, that is, the common end of the matching circuits of the first and second RF sources. . The harmonic control device 21 provides a tuning impedance with an adjustable impedance value, and adjusts the harmonic impedance of the first RF source 11 in which the high frequency is adjusted, thereby making the second and third harmonics of the first RF source 11 The wave current is controlled.

It should be noted that the present invention is particularly applicable to applications in which the radio frequency of the first radio frequency source 11 is greater than 40 MHz. In this case, the invention of the present invention is most effective, and the tuning can be better performed by outputting a high impedance. The impedance suppresses the second and third harmonic currents of the first RF source 11, so that the plasma 50 on the surface of the substrate 40 can be uniformly distributed; or, more effectively, the tuning impedance of the output is high impedance to low impedance. It is adjustable to control the magnitude of the harmonic current. At this time, different plasma densities can be obtained at the center and edge surfaces of the substrate 40, thereby correspondingly producing different etching effects.

Optionally, the harmonic control device 21 is an inductor, a low pass filter or a band rejection filter disposed in series between the first RF source 11 and the driving electrode; or the harmonic control device 21 is a capacitor, a high-pass filter or a band-pass filter that is grounded in parallel between the first RF source 11 and the lower electrode 31.

Optionally, a series inductance of 0.1 μH to 100 μH can be configured as the harmonic The control device 21 is adapted to adjust the harmonic control of the first RF source 11 in a certain frequency range; preferably, the inductance value may be 2 μH~3 μH.

Alternatively, as shown in FIG. 2, a low-pass filter can be configured as the harmonic control device 21, and the harmonics generated at a specific first RF source 11 frequency can be accurately adjusted. Specifically, the low pass filter includes two inductors disposed in series between the first RF source 11 and the lower electrode 31, and a capacitor connected in parallel between the two inductors. Preferably, when the first RF source 11 is 60 MHz, the two inductors are 66 nH, and the capacitance is 53 pF.

Referring to FIG. 1 , FIG. 3 shows a second embodiment of the first RF source 11 in a specific embodiment in which the frequency of the first RF source 11 is 60 MHz and the frequency of the second RF source 12 is 2 MHz. Modulation of subharmonic current: In Fig. 3, the abscissa indicates the diameter of the substrate 40, and the ordinate indicates the rate at which the oxide on the substrate 40 is etched. It can be seen that when the harmonic control device 21 does not output the tuning impedance or outputs a low impedance tuning impedance, the second harmonic current is larger, that is, the plasma 50 corresponding to the center position of the substrate 40 has a higher density, and the edge The lower position, as shown by curve 1 having a larger undulation, the rate at which the center of the substrate 40 is etched above 5400 A/min is much faster than the rate at which the outermost edge of the substrate 40 is etched by about 4200 A/min.

In contrast, if the harmonic control device 21 outputs a high-impedance tuning impedance, the second harmonic current can be made smaller, and the plasma corresponding to the center of the substrate 40 and the edge of the substrate 40 can be correspondingly 50. The difference in density becomes small, that is, the rate at which the center of the substrate 40 is etched is reduced to about 4,700 A/min, and the rate difference between the rate at which the edge of the substrate 40 is etched is about 4,200 A/min, and the curve 2 obtained is relatively flat. .

Therefore, the harmonic control device 21 of the present invention can output a high impedance Tuning the impedance to suppress the second and third harmonic currents of the first RF source 11, so that the plasma 50 on the surface of the substrate 40 can be uniformly distributed; or, by making the output of the tuning impedance between high impedance and low impedance Adjustable to control the magnitude of the harmonic current and to achieve different plasma densities at the center and edge of the substrate 40 to produce different etching effects.

The implementation structure of the present invention is not limited to the above description. For example, the first radio frequency source may also be applied to the upper electrode through a matching box; the second radio frequency source may be applied to be the same as or different from the first radio frequency source. On the upper or lower electrode. The above structure is given after the harmonic control device is disposed at the common end of the matching circuit of the first and second RF sources (Fig. 1); the harmonic control device may also be disposed only after the matching circuit of the first RF source, Or only after the matching circuit of the second RF source; or alternatively, a matching control circuit of the first and second RF sources is respectively provided with a harmonic control device, but the harmonic control device only applies to the first RF of the high frequency The harmonic current of the source is adjusted.

Although the present invention has been described in detail by the preferred embodiments thereof, it should be understood that the foregoing description should not be construed as limiting. Various modifications and alterations of the present invention will be apparent to those skilled in the art. Therefore, the scope of the invention should be limited by the scope of the appended claims.

11‧‧‧First RF source

12‧‧‧second RF source

20‧‧‧match box

21‧‧‧Harmonic control device

30‧‧‧ Vacuum reaction chamber

31‧‧‧ lower electrode

32‧‧‧Upper electrode

33‧‧‧Electrostatic suction cup

40‧‧‧Substrate

50‧‧‧ ion body

60‧‧‧Reactive gas

Claims (11)

A radio frequency system for controlling harmonics of a plasma generator, applying radio frequency energy to a driving electrode, and forming a plasma (50) pair of a reactive gas (60) in a vacuum reaction chamber (30) of the plasma generator The substrate (40) is processed, wherein the radio frequency system comprises: a first radio frequency source (11) that provides radio frequency energy for generating the plasma (50); a matching box (20) connected to the first Between a radio frequency source (11) and the driving electrode, wherein a matching circuit is disposed to make a load impedance of the plasma (50) in the reaction chamber (30) and an output impedance of the first RF source (11) Matching, characterized in that: the matching box (20) is further provided with a harmonic control device (21) connected to the first RF source (11), and the harmonic control device (21) generates an impedance Adjustable tuning impedance, adjusting the harmonic impedance of the first RF source (11), thereby suppressing or adjusting the harmonic current of the first RF source (11) to control the plasma (50) The distribution of the surface of the substrate (40). The controllable harmonic radio frequency system for a plasma generator according to claim 1, wherein the harmonic current of the first RF source (11) is opposite to the first RF source (11) Power is proportional; at the first radio frequency When the power of the source (11) is constant, its harmonic current is inversely proportional to the impedance value of the tuning impedance output by the harmonic control device (21). A controllable harmonic radio frequency system for a plasma generator according to claim 2, wherein the substrate (40) is placed in the bottom of the reaction chamber (30); the substrate (40) The plasma (50) of the surface has a density at a position corresponding to the center of the corresponding substrate (40) and decreases toward the edge of the substrate (40); the plasma (50) corresponds to the center of the substrate (40) and The density difference of the edge is proportional to the harmonic current of the first RF source (11), i.e., inversely proportional to the impedance value of the tuning impedance. A radio frequency system for controllable harmonics of a plasma generator according to claim 3, wherein the harmonic control device (21) is at the first RF source (11) and the drive An inductor, a low pass filter or a band rejection filter disposed in series between the electrodes; or the harmonic control device (21) is grounded in parallel between the first RF source (11) and the drive electrode Capacitor, high pass filter or band pass filter. The radio frequency system for controllable harmonics of a plasma generator according to claim 4, wherein the harmonic control device (21) is the inductor arranged in series, and the inductance value is 0.1 μH~ 100μH. A radio frequency system for controlling harmonics of a plasma generator according to claim 4, wherein the harmonic control device (21) is the low a pass filter further comprising two inductors arranged in series between the first RF source (11) and the drive electrode, and a capacitor connected in parallel between the two inductors; the two inductors It is 66 nH; the capacitance is 53 pF. A radio frequency system for controllable harmonics of a plasma generator according to claim 1, wherein the second radio frequency source (12) for controlling ion energy and energy distribution in the reaction chamber (30) is further included; The frequency of the second RF source (12) is smaller than the frequency of the first RF source (11) by a certain interval. The radio frequency system for controllable harmonics of a plasma generator according to claim 7, wherein the selectable frequency of the first radio frequency source (11) comprises 27 MHz, 40 MHz, 60 MHz, 100 MHz or 120 MHz; The selectable frequency of the second RF source (12) comprises 13 MHz, 2 MHz or 400 KHz. The radio frequency system for controllable harmonics of a plasma generator according to claim 1 or 7, wherein the frequency of the first radio frequency source (11) is greater than 40 MHz. A controllable harmonic radio frequency system for a plasma generator according to claim 7, wherein the drive electrode comprises an upper electrode (32) and a lower portion disposed in the reaction chamber (30) An electrode (31); the first RF source (11) is applied to one of the upper electrode (32) or the lower electrode (31) through the matching box; the first RF source is in the matching box (11) configured with the matching circuit and harmonic control device (21); The second RF source (12) is applied to the upper electrode (32) or the lower electrode (31) through a matching box provided with the same or separately, and is applied to the first RF source (11) The same or different of the RF electrodes; the matching box is configured with the matching circuit for the second RF source (12). The radio frequency system for controllable harmonics of a plasma generator according to claim 10, wherein the harmonic control device (21) for adjusting a harmonic impedance of the first radio frequency source (11) is And disposed between the output end of the matching circuit of the first RF source (11) and the RF electrode; or the harmonic control device (21) is disposed on the matching circuit of the second RF source (12) The output end is connected to the RF electrode and connected to the first RF source (11); or the harmonic control device (21) is disposed on the matching circuit of the first and second RF sources Between the common output end and the RF electrode; or the output end of the matching circuit of the first RF source (11) and the output end of the matching circuit of the second RF source (12) are respectively connected to a harmonic Wave control device (21).