JP2020004672A - Plasma processing apparatus - Google Patents

Abstract

To provide a plasma processing apparatus that can suppress CD variation by controlling the plasma density distribution.SOLUTION: In a plasma processing apparatus, plasma generation means includes a plurality of microwave sources 101 and 201 that oscillates microwaves, a circular waveguide 104 to which one microwave source 101 is connected, an excitation line 205 connected to the other microwave source 201, and a cylindrical cavity resonator 106 to which the circular waveguide 104 and the excitation line 205 are connected, and the distribution of the low-order mode electric field and the high-order mode electric field formed in a vacuum processing chamber 110 connected to the cavity resonator 106 via a microwave introduction window 107 can be adjusted.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a plasma processing apparatus.

  Conventionally, a plasma generator has been used in an etching process of semiconductor manufacturing. According to this plasma generator, plasma is generated by applying high-frequency power (hereinafter referred to as source power) in a state in which a reactive gas is introduced into a processing chamber which is a vacuum vessel, and a processing target placed on a lower electrode is generated. A material (eg, a silicon wafer) can be etched.

  By applying bias power to the lower electrode, the etching rate and the etching shape can be controlled. The most important parameter that determines the performance of a semiconductor device is a representative dimension of a device shape called a CD (Critical Dimension) such as a width of a gate electrode and a width of a wiring.

  In the example of the gate processing, the width of the gate structure, which is called the gate length, directly affects the switching characteristics of the semiconductor device. Therefore, it is important to process this according to the design dimensions. Examples of CD control include CD variations in the same linear pattern, shape variations due to differences in circuit pattern density in the chip, and CD variations in the wafer surface. These CD variations are suppressed and a high product yield is achieved. Is required to be achieved. The CD variation varies depending on the wafer temperature during processing, ion energy, the amount of reaction by-products, and the amount of ions and radicals. Techniques disclosed in, for example, Patent Documents 1 and 2 are known to suppress CD variations.

  Patent Literature 1 discloses a technique for adjusting the composition and / or flow rate of a processing gas introduced from a plurality of inlets provided in a processing chamber. Further, U.S. Pat. No. 6,037,064 discloses a technique for providing a chamber design that allows for symmetric, electrical, thermal, and gas flow conductances.

JP 2005-56914 A JP 2013-179055 A

  By the way, in the etching process of semiconductor manufacturing, a silicon wafer having a laminated film made of various materials formed on the surface is exposed to plasma generated by applying high frequency to a reactive gas introduced into a vacuum processing chamber. Then, the circuit pattern exposed and developed on the uppermost mask layer of the laminated film is transferred to the lower layer. It is necessary to process the CD after the pattern transfer according to design requirements. Therefore, in order to suppress the CD variation in the wafer surface from another viewpoint, for example, a wafer temperature control, a plasma distribution control technique and the like have been used.

  The plasma space distribution and gas flow in the vacuum processing chamber may not always be uniform in the radial or circumferential direction in the vacuum processing chamber, and the collision frequency of ions and radicals and the residence time of gas molecules are uniform on the silicon wafer. Otherwise, there is a problem that CD variation is caused. In a specific example, the consumption of ions and radicals and the amount of the released reaction products at the outer peripheral portion of the wafer change at the outermost end of the wafer as a boundary, non-uniform plasma distribution occurs, gas For example, the spatial distribution of radicals and reaction products becomes non-uniform according to the flow velocity distribution, which results in CD variations.

  The present invention has been made in view of the above-mentioned problems of the related art, and has as its object to provide a plasma processing apparatus capable of suppressing a CD variation by controlling a plasma density distribution.

In order to solve the above problem, one of the typical plasma processing apparatuses of the present invention is a vacuum processing chamber in which a sample is subjected to plasma processing, and a microwave high-frequency power for generating plasma is transmitted through a waveguide. A first high-frequency power supply, a cavity resonating part arranged above the vacuum processing chamber by adjusting an electromagnetic field distribution of a microwave transmitted through the waveguide to a predetermined distribution, and the sample In a plasma processing apparatus comprising a sample stage on which
This is achieved by further comprising an excitation line arranged in the cavity resonance section.

ADVANTAGE OF THE INVENTION According to this invention, the plasma processing apparatus which can suppress CD variation by controlling the density distribution of plasma can be provided.
Problems, configurations, and effects other than those described above will be apparent from the following description of the embodiments.

1 is a configuration diagram of a plasma etching apparatus according to the present invention. 1 is a configuration diagram of a plasma etching apparatus according to a first embodiment, which can be excited in a higher-order mode. FIG. 4 is a diagram illustrating an example of an electric field distribution obtained by combining a lower mode and a higher mode of a microwave. It is a figure showing a time change of microwave power. FIG. 9 is a configuration diagram of a plasma etching apparatus according to a second embodiment that can be excited in a higher-order mode. FIG. 9 is a configuration diagram of a plasma etching apparatus according to a third embodiment that can be excited in a higher-order mode.

  In the present specification, the “different modes” are both different modes (TM mode, TE mode) and different modes.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a longitudinal sectional view schematically showing a configuration around a vacuum processing chamber according to a plasma processing apparatus (plasma etching apparatus) of the present embodiment.

  A first high-frequency power source for a plasma source, for example, a microwave source 101, is connected to a square circular waveguide converter 103 via a square waveguide 102 including an automatic matching unit 105, and is connected to the square circular waveguide converter 103. 103 is connected to the circular waveguide 104. The automatic matching machine 105 has a function of automatically suppressing a reflected wave. As the microwave source 101, for example, a magnetron having an oscillation frequency of 2.45 GHz can be used.

  The circular waveguide 104 is connected to a cavity resonator (also referred to as a cavity resonator) 106. The cavity resonator 106 has a function of adjusting the microwave electromagnetic field distribution to a distribution suitable for plasma processing. A microwave introduction path from the rectangular waveguide 102 to the cavity resonator 106 is used.

  A microwave introduction window 107 and a shower plate (gas supply unit) 108 are disposed below the cavity resonator 106, and a vacuum processing chamber 110 is provided inside a vacuum vessel 109 whose upper portion is hermetically sealed by the microwave introduction window. It is configured. The ECR resonance caused by the interaction between the microwave oscillated from the microwave source 101 and propagated to the vacuum processing chamber 110 through the microwave introduction path and the static magnetic field formed by the solenoid coil 111 causes the vacuum processing chamber 110 Plasma is generated therein by the reactive gas. It is desirable to use quartz as a material of the microwave introduction window 107 and the shower plate 108. The solenoid coil 111 constitutes a magnetic field forming means.

  ECR resonance means that electrons move selectively while rotating along the lines of magnetic force of the magnetic field generated by the solenoid coil 111, and microwaves having a frequency corresponding to the period of the rotation are incident on the plasma. This is a phenomenon in which the plasma is heated, whereby the plasma can be effectively heated. Another advantage of using such a static magnetic field is that the position where ECR resonance occurs can be controlled by changing the distribution of the static magnetic field, and the plasma generation region can be controlled.

  Further, it is known that the diffusion of the plasma is suppressed in a direction perpendicular to the lines of magnetic force. By utilizing this characteristic, the diffusion of the plasma can be controlled, and the loss of the plasma can be reduced. With these effects, the distribution of the plasma can be controlled, and therefore, the uniformity of the plasma processing can be improved. The distribution of the static magnetic field can be controlled by changing the current flowing through the electromagnet.

  The flow rate of the reactive gas supplied from a gas source (not shown) is controlled in a gas control device, and the reactive gas is supplied to a vacuum processing chamber via a shower plate 108 disposed on a surface facing the lower electrode 112 serving as a sample stage. Supplied in 110. The gas supplied into the vacuum processing chamber 110 is exhausted by a turbo molecular pump (hereinafter, TMP) 113. The exhaust conductance adjusting valve 114 disposed upstream of the TMP 113 is feedback-controlled so that the measured value of the pressure gauge 115 becomes a desired value, and the opening thereof is adjusted.

  A sample, for example, a silicon wafer (hereinafter simply referred to as a wafer) can be suction-held on the lower electrode 112 by electrostatic suction. Further, by applying an RF (Radio Frequency) wave having a frequency lower than the frequency of the power source for the plasma source, for example, a frequency of 400 kHz, to the lower electrode 112 through the matching unit 117 from the RF power source 116, control of processing performance and processing speed can be achieved. Can be improved.

  The spectroscope 118 is connected to the vacuum processing chamber 110 by an optical fiber 119, and can split the emission of the plasma generated in the vacuum processing chamber 110 to detect the intensity for each wavelength. The spectroscope 118 is connected to a control computer (not shown). The control computer has a function of extracting characteristics of a change in plasma emission detected by the spectroscope 118, determining an end point of etching, and terminating the process.

  The vacuum processing chamber 110, the lower electrode 112, and the TMP 113 each have a substantially cylindrical shape, and the axes of the cylinders are the same. The lower electrode 112 is supported in the vacuum processing chamber 110 by a beam or the like (not shown).

  All of the above components are connected to a control computer PROC (see FIG. 2), which is a control unit, and the timing and amount of operation are controlled so as to operate in an appropriate sequence. The detailed parameters of the operation sequence are called a recipe, and an operation based on a preset recipe is performed.

(First embodiment)
In the first embodiment, an example of a plasma etching apparatus having a microwave electric field distribution control function will be described. FIG. 2 is a sectional view of the plasma etching apparatus according to the present embodiment. The plasma etching apparatus according to the present embodiment includes, in addition to the configuration shown in FIG. 1 already described, a second microwave source 201, a second automatic matching device 202, It has a waveguide 203, a coaxial cable 204, and an excitation line 205. Portions having the same functions as those of the configuration shown in FIG. 1 already described are denoted by the same reference numerals and description thereof will be omitted (the same applies to the following embodiments). The second microwave source 201 constitutes a second high frequency power supply for supplying high frequency power to the excitation line.

  The microwave oscillated from the second microwave source 201 has its reflected wave suppressed by the automatic matching unit 202 and is branched into six in the branch waveguide 203. The branched microwaves are transmitted to six excitation lines 205 arranged in the cavity resonator 106 via a coaxial cable 204 connected via a waveguide-coaxial converter, and are transmitted to the cavity resonator 106. Radiated into. In FIG. 2, only two coaxial cables are clearly shown, and chain lines are shown from the exits of the other branch waveguides. Excitation lines are similarly provided at the ends of the coaxial cables indicated by the chain lines. It is connected.

  The shape of the branch waveguide 203 is adjusted so that the amplitude and phase of each microwave after branching become the same. By making the lengths of the six coaxial cables the same, the microwaves radiated from the six excitation lines 205 into the cavity resonator 106 can have the same amplitude and the same phase. . In order to maximize the microwave transmission efficiency, the impedance of the coaxial cable is adjusted to be the same as the impedance of the excitation line.

  The six excitation lines 205 are arranged below the upper surface (ceiling surface) in the cylindrical cavity resonator 106 in parallel with the central axis of the cavity resonator 106 and symmetrically with respect to the central axis. The microwaves radiated from the excitation lines 205 form a magnetic field surrounding each excitation line 205 and an electric field oscillating in a direction along the excitation lines 205, and the cavity resonator 106 and the vacuum processing chamber 110 The TM mode can be excited in the cylindrical waveguide constituted by the above.

  In the present embodiment, the six excitation lines 205 are arranged axially symmetrically near the side wall of the cavity resonator 106. The antinodes of the standing wave generated in the cavity resonator 106 can be six each (a total of 12) immediately below the excitation line 205 and between the excitation lines 205 adjacent in the circumferential direction. In such a case, a TM61 mode electric field is formed. As described above, the position where the maximum electric field of the TM mode is obtained is clearly fixed, so that the excitation can be stably performed in the TM61 mode regardless of the presence or absence of the circular waveguide 104 connected to the cavity resonator.

  In order to suppress the disturbance due to the reflection on the wall surface and obtain a desired mode, the position where the excitation line 205 is disposed is preferably set at a distance of １ ／ wavelength from the side wall of the cavity resonator 106. The distance is preferably set to 20 to 40 mm.

  FIG. 3 shows a calculation result of the microwave electric field distribution in the vacuum processing chamber 110 in the present embodiment. FIG. 3 shows an electric field distribution in a plane parallel to the microwave introduction window 107 and 200 mm below the introduction window in the vacuum processing chamber 110, and shows the microwave power P1 introduced from the circular waveguide 104. And the calculation result when the ratio of the microwave power P2 introduced from the excitation line 205 is changed.

  When microwaves are introduced only from the excitation line 205, that is, when P1: P2 = 0: 100, only the TM61 mode (higher-order mode) appears, and a strong electric field distribution appears along the outer wall of the processing chamber. On the other hand, when microwaves are introduced only from the circular waveguide 104, that is, when P1: P2 = 100: 0, the TE11 mode (lower-order mode) of the microwave propagating in the circular waveguide 104 is basically used. , Which is equivalent to the microwave distribution in a device having no excitation line (FIG. 1).

  Further, when the ratio of P1: P2 is changed via the control computer PROC which is a control unit for driving and controlling the microwave source 101 and the microwave source 201, the TE11 mode and the TM61 mode are switched according to the microwave power ratio. Appear, and it can be seen that the electric field distribution can be controlled. That is, by changing the ratio of the microwave powers P1 and P2, the electric field distribution of the lower-order mode and the electric field distribution of the higher-order mode can be formed at a desired ratio. Thus, the electric field distribution in the vacuum processing chamber 110 can be arbitrarily controlled from a convex type to a concave type, and as a result, the radial distribution in which the plasma is distributed can be easily adjusted.

  In the present embodiment, the number of the excitation lines 205 is six, but may be less or more. For example, in order to excite the TMn1 mode in which the number of antinodes of the standing wave is 2 × n, the number of the excitation lines 205 is set to n, and accordingly, the number of the coaxial cables 204 and the number of the branch waveguides 203 are set. May be set to n. That is, since the number n corresponds to the order of the mode, the smaller the n, the lower the mode, and the larger the n, the higher the mode.

  When the number of the excitation lines 205 is reduced, the amplitude of the electric field intensity in the circumferential direction increases, and when the number of the excitation lines is increased, the region where the electric field intensity is strong is localized near the side wall of the cavity resonator 106, and the plasma density in the center is required. The number of the excitation wires 205 is desirably 6 to 10 because the size of the excitation wires 205 is reduced or the outer wall of the vacuum processing chamber 110 may be damaged.

(Second embodiment)
A second embodiment will be described with reference to FIG. The second embodiment is different from the first embodiment in that the microwave TE11 mode introduced from the circular waveguide 104 and the microwave TM61 mode by the six excitation lines 205 are simultaneously subjected to vacuum processing. Instead of synthesizing in the room 110, TE11 mode and TM61 mode are alternately introduced and time-averaged. Such control can be performed by a control computer.

  In the figure, a graph 401 shows a time change of the microwave power introduced from the circular waveguide 104, and a graph 402 shows a time change of the total of the microwave power introduced from the six excitation lines 205. As shown in FIG. 4, what is shown by the graphs 401 and 402 is a pulse wave having the same frequency, a different phase and a duty ratio, and indicates that the supply and the stop of the supply of the microwave power are periodically repeated. ing.

  The frequency of each pulse is preferably in the range of 10 Hz or more and 10 kHz or less in view of the life of the plasma. In the example shown in FIG. 4, the duty ratio of the graph 401 is A%, and the duty ratio of the graph 402 is B%, and A + B = 100%. However, A + B <100%, that is, the microwave power is There may be a case where there is a non-supplied time or a case where A + B> 100%, that is, a time where the graph 401 and the graph 402 overlap.

As described above, by periodically and alternately exciting the TE11 mode and the TM61 mode, the plasma disappears during the time when the pulse is turned off at the above-mentioned frequency, and thus has a convex density distribution due to the TE11 mode. The plasma and the plasma having a concave density distribution in the TM61 mode are generated alternately without interfering with each other, and the etching distribution can be easily adjusted by the respective duty ratios.
According to the above embodiment, in addition to the low-order mode having a strong electric field intensity distribution at the center, the higher-order mode having a strong electric field intensity distribution near the cylindrical outer wall of the vacuum processing chamber 110 is simultaneously excited or separated in time. By exciting the two modes repeatedly and alternately and synthesizing them in a time-average manner, it is possible to control the plasma density distribution.

(Third embodiment)
A third embodiment will be described with reference to FIG. In this embodiment, six microwave sources (second high-frequency power sources) 501 are used instead of branching the microwave oscillated from one microwave source 201 into six as described in the first embodiment. Are different. Note that the control computer is omitted in FIG. 5 and FIG. 6 described later.

  Each of the microwave sources 501 is connected to the excitation line 205 via the coaxial cable 204. The microwave sources 501 are connected to the controller 502, respectively, and are driven in the same phase based on a signal from the controller 502. As a result, unnecessary interference between microwaves transmitted from the plurality of excitation lines 205 in the cavity resonator 106 can be suppressed, and a standing wave in a desired mode can be obtained.

  The plurality of microwave sources 501 may have a total output corresponding to the output of the microwave source 201 shown in the first embodiment, and in the case of using six excitation lines 205, each one-sixth. I just need output. More specifically, a microwave source 501 having an output of about 100 W to 300 W may be used. As the microwave source 501, a microwave source having a solid-state oscillator and an amplifier may be used instead of using a magnetron. It is known that these microwave sources have good frequency characteristics, and by using this, the controllability of the standing wave mode can be improved.

(Fourth embodiment)
A fourth embodiment will be described with reference to FIG. The present embodiment aims at exciting a higher-order TM mode in the above-described embodiment, but is characterized by having an excitation line arrangement for exciting a higher-order TE mode.

  In the present embodiment, the excitation line 601 is installed perpendicular to the cylindrical side wall (side surface) of the cavity resonator 106. As a result, the excitation line 601 is arranged in a plane perpendicular to the central axis of the cavity resonator 106 and on a straight line passing through the central axis. The number of the excitation lines 601 is, for example, six, as in the first embodiment, and the excitation lines 601 are configured to be supplied with microwaves having the same amplitude and the same phase.

  The microwave oscillated from the excitation line 601 forms an electric field parallel to the excitation line 601 as in the first embodiment, and excites the TE mode. By arranging the six excitation lines, the position where the maximum electric field strength is reached is determined between the insertion position of the excitation line 601 and the middle of the adjacent excitation line, and the TE61 mode can be stably excited. The distance between the excitation line 601 and the upper surface of the cavity resonator 106 is preferably about 1/4 wavelength in order to suppress the influence of the reflection from the wall surface, and may be selected from about 30 mm or 20 to 40 mm.

  Although the microwave source is the same as in the first embodiment in FIG. 6, a plurality of microwave sources may be used as in the third embodiment.

  Further, the combination with the TE11 mode propagated from the circular waveguide 104 may be performed at the power ratio as in the first embodiment, or may be performed at the time ratio as in the second embodiment.

  In the above embodiment, the etching apparatus using the microwave ECR discharge has been described as an example, but other microwave plasma processing apparatuses, for example, a plasma CVD apparatus or a plasma PVD apparatus have the same operation and effect. Further, in the above embodiment, the case of the microwave having the frequency of 2.45 GHz has been described. However, in the case of the ECR discharge, the same operation and effect can be obtained even at a lower frequency or a higher frequency.

  Note that the present invention is not limited to the above-described embodiment, and includes various modifications. For example, the above-described embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described above. In addition, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of one embodiment can be added to the configuration of another embodiment. . In addition, for a part of the configuration in each embodiment, it is also possible to add, delete, or replace another configuration.

101 microwave source,
102 rectangular waveguide,
103 square circular waveguide converter,
104 circular waveguide,
105 automatic matching machine,
106 cavity resonator,
107 microwave introduction window,
108 shower plate,
109 vacuum container,
110 vacuum processing chamber,
111 solenoid coil,
112 lower electrode,
113 turbo molecular pump,
114 exhaust conductance control valve,
115 pressure gauge,
116 RF power supply,
117 matching box,
118 spectrometer,
119 optical fiber,
201 a second microwave source,
202 second automatic matching device,
203 branch waveguide,
204 coaxial cable,
205 excitation line,
401 graph of microwave power introduced from circular waveguide,
402 a graph of microwave power introduced from the excitation line,
501 a second microwave source;
502 microwave source controller,
601 excitation line

Claims (6)

A vacuum processing chamber in which a sample is subjected to plasma processing, a first high-frequency power supply for supplying high-frequency microwave power for generating plasma through a waveguide, and a microwave transmitted through the waveguide. In a plasma processing apparatus comprising: a cavity resonating section that adjusts an electromagnetic field distribution to a predetermined distribution and is disposed above the vacuum processing chamber; and a sample table on which the sample is mounted.
The plasma processing apparatus further comprising an excitation line disposed in the cavity resonance section. The plasma processing apparatus according to claim 1,
A plasma processing apparatus, wherein the excitation line is supplied with microwave high-frequency power from a second high-frequency power supply different from the first high-frequency power supply. The plasma processing apparatus according to claim 2,
The first high-frequency power source such that a combined ratio of an electric field formed by the microwave transmitted through the waveguide and an electric field formed by the microwave excited by the excitation line becomes a predetermined ratio. And a control unit for controlling the second high-frequency power supply. The plasma processing apparatus according to any one of claims 1 to 3,
The said excitation line is arrange | positioned at the upper surface or side surface of the said cavity resonance part, The plasma processing apparatus characterized by the above-mentioned. The plasma processing apparatus according to claim 4,
The number of the excitation lines is plural,
The said excitation line is arrange | positioned symmetrically with respect to the central axis of the said cavity resonance part, The plasma processing apparatus characterized by the above-mentioned. The plasma processing apparatus according to any one of claims 1 to 5,
An electric field mode excited by the excitation line is a TM mode or a TE mode.