JP6991934B2 - Plasma processing equipment - Google Patents

Description

The present invention relates to a plasma processing apparatus.

Conventionally, a plasma generator has been used in the 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 where a reactive gas is introduced into a processing chamber which is a vacuum vessel, and the plasma is generated and placed on a lower electrode. Materials (eg, silicon wafers) can be etched.

By applying the bias power in 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 typical dimension of the device shape called a CD (Critical Dimensions) such as the width of a gate electrode and the width of a wiring.

In the example of gate processing, the width of the gate structure called the gate length directly affects the switching characteristics of the semiconductor device, so it is important to process this according to the design dimensions. As an example of CD control, CD variation within the same linear pattern, shape variation due to the difference in circuit pattern density in the chip, CD variation in the wafer surface, etc. may be caused, and these CD variations are suppressed and a high product yield is achieved. Is required to be achieved. CD variation varies depending on the wafer temperature, ion energy, amount of reaction by-products, and amount of ions / radicals at the time of processing. For example, the techniques disclosed in Patent Documents 1 and 2 are known in order to suppress CD variation.

Patent Document 1 discloses a technique for adjusting the composition and / or the flow rate of the processing gas introduced from a plurality of introduction ports provided in the processing chamber. Further, Patent Document 2 discloses a technique that provides a chamber design that allows symmetrical, electrical, thermal, and gas flow conductance.

Japanese Unexamined Patent Publication No. 2005-56914 Japanese Unexamined Patent Publication No. 2013-179055

By the way, in the etching process of semiconductor manufacturing, a silicon wafer having a laminated film made of various materials formed on its surface is exposed to plasma generated by applying a high frequency to a reactive gas introduced into a vacuum processing chamber. The circuit pattern exposed and developed on the mask layer at the top of the laminated film is transferred to the lower layer. It is necessary to process the CD after this pattern transfer according to the design required value. Therefore, in order to suppress CD variation in the wafer surface from another viewpoint, for example, wafer temperature control, plasma distribution control technology, 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, the residence time of gas molecules, etc. are uniform on the silicon wafer. There was a problem that CD variation was caused by not doing so. In specific examples, the consumption of ion radicals and the amount of reaction products emitted at the outer periphery of the wafer change at the outermost edge of the wafer, the plasma distribution becomes non-uniform, and the gas is generated. The spatial distribution of radicals and reaction products becomes non-uniform according to the flow velocity distribution, resulting in CD variation.

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

In order to solve the above problems, one of the representative plasma processing devices of the present invention is a vacuum processing chamber in which a sample is plasma-processed, and a microwave high-frequency power for generating plasma is transmitted through a waveguide. The first high-frequency power supply supplied from the above, the cavity resonance portion arranged above the vacuum processing chamber by adjusting the electromagnetic field distribution of the microwave transmitted via the waveguide to a predetermined distribution, and the sample. In a plasma processing apparatus equipped with a sample table on which the
This is achieved by supplying high-frequency microwave power from a second high-frequency power source different from the first high-frequency power source and further providing an excitation line arranged in the cavity resonance portion.

According to the present invention, it is possible to provide a plasma processing apparatus capable of suppressing CD variation by controlling the density distribution of plasma.
Issues, configurations and effects other than those described above will be clarified by the following description of the embodiments.

It is a block diagram of the plasma etching apparatus in this invention. It is a block diagram of the plasma etching apparatus which can be excited in a high order mode which concerns on 1st Embodiment. It is a figure which shows the example of the electric field distribution by the synthesis of the low-order mode and the high-order mode of a microwave. It is a figure which shows the time change of a microwave power. It is a block diagram of the plasma etching apparatus which can be excited in a high order mode which concerns on 2nd Embodiment. It is a block diagram of the plasma etching apparatus which can be excited in a high order mode which concerns on 3rd Embodiment.

As used herein, the term "different mode" means both a different mode type (TM mode, TE mode) and a different mode order.

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

A first high frequency power source for the plasma source, eg, a microwave source 101, is connected to the square circular waveguide converter 103 via a square waveguide 102 including an automatic matching machine 105, and is a square circular waveguide converter. 103 is connected to the circular waveguide 104. The automatic matching machine 105 has a function of automatically suppressing reflected waves. 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 resonance portion) 106. The cavity resonator 106 has a function of adjusting the microwave electromagnetic field distribution to a distribution suitable for plasma processing. The microwave introduction path is from the rectangular waveguide 102 to the cavity resonator 106.

A microwave introduction window 107 and a shower plate (gas supply unit) 108 are arranged at the lower part of the cavity resonator 106, and the vacuum processing chamber 110 is inside the vacuum container 109 whose upper part is airtightly sealed by the microwave introduction window. It is configured. The vacuum processing chamber 110 is generated by ECR resonance due to the interaction between the microwave oscillated from the microwave source 101 and propagated to the vacuum processing chamber 110 via the microwave introduction path described above and the static magnetic field formed by the solenoid coil 111. Plasma by the reactive gas is generated inside. It is desirable to use quartz as the 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 while rotating along the magnetic field lines of the magnetic field generated by the solenoid coil 111, and microwaves having a frequency corresponding to the rotation cycle are incident on the plasma to selectively cause electrons. It is a phenomenon of heating, which can effectively heat the plasma. 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 plasma is suppressed in the direction perpendicular to the magnetic force line, and this characteristic can be used to control the diffusion of plasma and reduce the loss of plasma. Due to these effects, the distribution of plasma can be controlled, and therefore the uniformity of plasma processing can be improved. In addition, the distribution of the static magnetic field can be controlled by changing the current that energizes 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 vacuum processing chamber is via a shower plate 108 arranged on a surface facing the lower electrode 112 which is a sample table. It is supplied in 110. The gas supplied into the vacuum processing chamber 110 is exhausted by a turbo molecular pump (hereinafter referred to as TMP) 113. The exhaust conductance adjusting valve 114 arranged in the upstream portion of the TMP 113 is feedback-controlled so that the measured value of the pressure gauge 115 becomes a desired value, and the opening degree thereof is adjusted.

A sample, for example, a silicon wafer (hereinafter, simply referred to as a wafer) can be adsorbed and held on the lower electrode 112 by electrostatic adsorption. Further, the processing performance can be controlled and the processing speed can be controlled by applying an RF (Radio Frequency) wave having a frequency lower than that of the plasma source power supply, for example, 400 kHz, to the lower electrode 112 via the matching unit 117. Can be improved.

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

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

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

(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 cross-sectional view of the plasma etching apparatus according to the present embodiment. In the plasma etching apparatus according to the present embodiment, in addition to the configuration shown in FIG. 1 described above, in addition to the first waveguide 101, a second waveguide 201 and a second automatic matching unit 202 are branched. It has a waveguide 203, a coaxial cable 204, and an excitation wire 205. The parts having the same functions as those shown in FIG. 1 described above are designated by the same reference numerals and the description thereof will be omitted (the same applies to the following embodiments). The second microwave source 201 constitutes a second high frequency power source that supplies high frequency power to the excitation line.

The microwave oscillated from the second microwave source 201 is suppressed in the reflected wave in the automatic matching device 202, and is branched into six in the branched waveguide 203. The branched microwave is transmitted to the six excitation lines 205 arranged in the cavity resonator 106 via the coaxial cable 204 connected via the waveguide-coaxial converter, and is transmitted to the cavity resonator 106. It is radiated inside. In FIG. 2, only two coaxial cables are specified, and chain wires are shown from the outlets of the other branched waveguides. However, excitation lines are also shown at the ends of the coaxial cables indicated by these chain wires. It is connected.

The shape of the branched waveguide 203 is adjusted so that the amplitude and phase of each microwave after branching are the same. By making the lengths of the six coaxial cables the same, it is possible to make the microwaves radiated from the six excitation wires 205 into the cavity resonator 106 having the same amplitude and phase with each other. .. In order to maximize the microwave transmission efficiency, the impedance of the coaxial cable and the excitation line are adjusted to be the same.

The six excitation lines 205 are arranged below the upper surface (ceiling surface) in the cylindrical cavity resonator 106, parallel to the central axis of the cavity resonator 106 and axisymmetric with respect to the central axis. Further, the microwave radiated from the excitation wire 205 forms a magnetic field surrounding each excitation wire 205 and an electric field oscillating in the direction along the excitation wire 205, and forms a cavity resonator 106 and a vacuum processing chamber 110. The TM mode can be excited in a cylindrical waveguide composed of.

In this embodiment, six excitation lines 205 are arranged axisymmetrically near the side wall of the cavity resonator 106. Six antinodes of standing waves generated in the cavity resonator 106 can exist directly under the excitation line 205 and between the excitation lines 205 adjacent to each other in the circumferential direction (12 in total). In such a case, an electric field in TM61 mode is formed. Since the position of the maximum electric field in the TM mode is clearly fixed in this way, stable excitation is possible in the TM61 mode regardless of the presence or absence of the circular waveguide 104 connected to the cavity resonator.

In order to suppress disturbance due to reflection on the wall surface and obtain a desired mode, the position where the excitation wire 205 is arranged is preferably a distance of 1/4 wavelength from the side wall of the cavity resonator 106, specifically, the position thereof. The distance should be 20-40 mm.

The calculation result of the microwave electric field distribution in the vacuum processing chamber 110 in this embodiment is shown in FIG. FIG. 3 shows the electric field distribution in the vacuum processing chamber 110 in a plane parallel to the microwave introduction window 107 and 200 mm below the introduction window, and the microwave power P1 introduced from the circular waveguide 104. It is a 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 the microwave is introduced only from the circular waveguide 104, that is, when P1: P2 = 100: 0, the TE11 mode (low-order mode) of the microwave propagating in the circular waveguide 104 is basic. It shows the electric field distribution, which is equivalent to the microwave distribution in the device without excitation lines (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 selected according to the microwave power ratio. An electric field distribution in which is linearly combined appears, 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 in the low-order mode and the electric field distribution in the high-order mode can be formed at a desired ratio. As a result, the electric field distribution in the vacuum processing chamber 110 can be arbitrarily controlled from the convex type to the 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 excitation lines 205 is 6, but the number 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 excitation lines 205 is set to n, and the number of coaxial cables 204 and the number of branches of the branched waveguide 203 are set accordingly. May be n respectively. That is, since the number of n corresponds to the order of the mode, if n is small, the mode is low, and if n is large, the mode is high.

When the number of excitation lines 205 is reduced, the electric field strength amplitude in the circumferential direction becomes large, and when the number of excitation lines is increased, the region with strong electric field strength is localized near the side wall of the cavity resonator 106, and the plasma density in the central portion is required. It is desirable that the number of excitation lines 205 is 6 to 10 because the size may become smaller and there is a concern that the outer wall of the vacuum processing chamber 110 may be damaged.

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

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

The frequency of each of the pulses 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%, the duty ratio of the graph 402 is B%, and A + B = 100%. There may be a case where there is a time when there is no supply, or there is a case where there is a time when A + B> 100%, that is, 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 frequency, so that the TE11 mode has a convex density distribution. Plasma and plasma having a concave density distribution in the TM61 mode are alternately generated 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 strength distribution in the center, the high-order mode having a strong electric field strength distribution near the outer wall of the cylinder of the vacuum processing chamber 110 is simultaneously excited or temporally separated. It is possible to control the density distribution of the plasma by repeatedly and alternately exciting the two modes and synthesizing them on a time average.

(Third embodiment)
The third embodiment will be described with reference to FIG. In this embodiment, instead of branching the microwave oscillated from one microwave source 201 into six as shown in the first embodiment, six microwave sources (second high frequency power source) 501 are used. Is different. 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. Each of the microwave sources 501 is connected to the controller 502 and is driven in the same phase based on the 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 total output of a plurality of mounted microwave sources 501 may correspond to the output of the microwave source 201 shown in the first embodiment, and when six excitation lines 205 are used, each of them is one sixth. All you need is an output. More specifically, a microwave source 501 with an output of about 100 W to 300 W may be used. As the microwave source 501, in addition to using a magnetron, a microwave source having an oscillator and an amplifier composed of solid elements may be used. It is known that these microwave sources have good frequency characteristics, and by using them, the controllability of the standing wave mode can be improved.

(Fourth Embodiment)
The fourth embodiment will be described with reference to FIG. The present embodiment is characterized in that it has an excitation line arrangement for exciting a higher-order TE mode, whereas the object of the present embodiment is to excite a higher-order TM mode.

In this embodiment, the excitation wire 601 is installed vertically on 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 excitation lines 601 is, for example, six as in the first embodiment, and each of them is 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 in a direction parallel to the excitation line 601 and excites the TE mode, as in the first embodiment. By arranging six excitation wires, the position where the maximum electric field strength is obtained is determined between the insertion position of the excitation wire 601 and the adjacent excitation wire, and the TE61 mode can be stably excited. The distance between the excitation wire 601 and the upper surface of the cavity resonator 106 is preferably about 1/4 wavelength in order to suppress the influence of reflection from the wall surface, and may be selected from about 30 mm or 20 to 40 mm.

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

Further, the synthesis with the TE11 mode propagated from the circular waveguide 104 may be performed by the power ratio as in the first embodiment, or may be performed by 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 apparatus, for example, a plasma CVD apparatus or a plasma PVD apparatus, has the same effect. Further, in the above embodiments, the case of microwaves having a frequency of 2.45 GHz has been described, but in the case of ECR discharge, the same effect can be obtained even at a lower frequency or a higher frequency.

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 in order to explain the present invention in an easy-to-understand manner, and are not necessarily limited to those having all the described configurations. Further, it is possible to replace a part of the configuration in one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. .. Further, it is also possible to add / delete / replace a part of the configuration in each embodiment with another configuration.

101 Microwave Source,
102 rectangular waveguide,
103 Square Circular Waveguide Converter,
104 Circular Waveguide,
105 Automation 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 Matcher,
118 spectroscope,
119 optical fiber,
201 Second microwave source,
202 Second automation matcher,
203 branch waveguide,
204 coaxial cable,
205 Excitation line,
401 Graph of microwave power introduced from circular waveguide,
402 Graph of microwave power introduced from excitation line,
501 Second Microwave Source,
502 Microwave Source Controller,
601 Excitation line

Claims (5)

A vacuum processing chamber in which a sample is plasma-processed, a first high-frequency power source that supplies high-frequency power of microwaves for generating plasma via a waveguide, and microwaves transmitted via the waveguide. In a plasma processing apparatus provided with a cavity resonance portion arranged above the vacuum processing chamber and a sample table on which the sample is placed by adjusting the electromagnetic field distribution of the above to a predetermined distribution.
A plasma processing apparatus characterized in that high-frequency microwave power is supplied by a second high-frequency power source different from the first high-frequency power source, and an excitation line arranged in the cavity resonance portion is further provided . In the plasma processing apparatus according to claim 1 ,
The first high frequency power supply so that the combined ratio of the electric field formed by the microwave transmitted through the waveguide and the electric field formed by the microwave excited by the excitation line becomes a predetermined ratio. A plasma processing apparatus further comprising a control unit for controlling the second high frequency power supply. In the plasma processing apparatus according to claim 1 or 2 .
The plasma processing apparatus, characterized in that the excitation line is arranged on the upper surface or the side surface of the cavity resonance portion. In the plasma processing apparatus according to claim 3 ,
The number of the excitation lines is plural,
A plasma processing apparatus characterized in that the excitation lines are arranged symmetrically with respect to the central axis of the cavity resonance portion. The plasma processing apparatus according to any one of claims 1 to 4 .
A plasma processing apparatus characterized in that the electric field mode excited by the excitation line is a TM mode or a TE mode.

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