JPH04174514A - Plasma processing equipment - Google Patents

Abstract

PURPOSE:To prevent the generation of abnormal voltage between a substrate and a ground part position when an RF bias voltage is applied so as to be synchronized with microwave pulses, by installing a vacuum chamber, an RF generator, etc., which constitute a plasma forming chamber. CONSTITUTION:Microwaves which are generated from a microwave source and have a rectangular envelope of ms order width are introduced into a vacuum chamber constituting a plasma forming chamber through a waveguide, and used for generating plasma. A signal for exactly monitoring the time variation of the envelope is led out from the microwave source, and delivered to a pulse generator, which is equipped with variable resistors VR1, VR2. By adjusting the resistance values of them, pulses are generated which rise up and fall down with specified delay times from the rise time and the fall time of a microwave monitoring signal. Thereby the RF pulses are applied to a substrate, only during the plasma period in an equibrium state, so that the generation of an abnormal voltage to the ground part position can be prevented, and the damage of a substrate to be treated can be prevented.

Description

[Detailed description of the invention] [! Application field of soil collection] This invention is a C V D (Chemical
Regarding microwave plasma processing equipment capable of forming thin films by vapor deposition, especially RF
It relates to applying a bias voltage to a processing substrate. .

(Prior art) ECR (E
lectron Cyclotron Re5oaap
ce) Process technology using plasma is attracting attention. ECR plasma is based on the principle of accelerating electrons using the resonance effect of a magnetic field and microwaves, and using the kinetic energy of the electrons to form an electric layer on a gas to generate plasma. Electrons excited by microwaves move in a circular motion around magnetic lines of force, and at this time, centrifugal force and Lorentz force act together,
The conditions under which this occurs are called ECR conditions. centrifugal force m
rω8. When the Lorentz force is expressed as -qra+13, the condition for these to be balanced is ω/B = q/m. Here, ω is the angular frequency of the microwave, B is the magnetic flux archive, and Q/m is the specific charge of the electron. The industrially accepted microwave frequency of 2.45 GHz is generally used, and the resonant magnetic flux density in that case is 875 Gauss.

In ECR type plasma CVD and etching equipment, we aim to increase the density of plasma and achieve efficient 1IllI.
In order to perform I formation or etching, it is necessary to introduce microwaves into the plasma generation chamber in the form of pulses with high peak power.

Furthermore, in CVD, surface retention Il! l! Flattening of I.

Forming a so-called conformal film with uniform film thickness on a substrate with an uneven surface, and improving film quality ffi! Achieving film formation, etc.
Alternatively, in etching, in order to perform highly anisotropic processing, an RF bias voltage is applied between the substrate to be processed and plasma. Furthermore, RF means Rad.
io Frequency, also called high frequency in this field, is a frequency in the range of approximately 50 KHz to several + [f. As is well known, the reason why applying an RF bias voltage enables flattening of surface retention, conformal film formation on a substrate with an uneven surface, and dense film formation is due to the When an RF bias voltage is applied to the substrate, a negative potential appears on the substrate surface with respect to the grounded part in the device, and the electric field distribution on the uneven surface due to this negative potential causes the uneven surface to be easily etched by the ions in the plasma. There may be a difference in the film formation speed between the difficult concave portions (this results in the formation of a smooth surface protection layer), or the electric field on the side walls of the convex portions may cause the film to be deposited effectively on the side walls (
This allows the film to be deposited conformally on the uneven surface), and the electric field accelerates the ions and the film receives ion bombardment (this makes the film denser).

As an ECR plasma CVD and etching apparatus as described above, for example, the one shown in FIG. 6 is known. The configuration and operation of this device will be outlined below. First, plasma generation chamber 3. The processing chamber 9 is evacuated by an evacuation means (not shown), and the gas supply means 4 is supplied with, for example, 0! Where the gas flows into the plasma generation chamber 3, pulsed microwaves generated by the microwave generator 17 are introduced into the plasma generation chamber 3 via the waveguide 1 which is a transmission means thereof. A vacuum window 2 is provided between the waveguide 1 and the plasma generation chamber 3 for airtightly sealing the waveguide 1 side under atmospheric pressure and the evacuated plasma generation chamber 3. . A metal plate having a large-diameter open lower portion at the center is attached to the lower part of the plasma generation chamber 3, and this metal plate and the plasma generation chamber 3 constitute a semi-open microwave resonator. An excitation solenoid 6 is disposed outside the resonator, and generates an air field that satisfies the ECR conditions within the resonator to generate plasma within the resonator. This plasma is pushed out into the processing chamber 9 along the line of force, and is supplied from the gas supply means 12 into the space facing the substrate table 10 using, for example, monosilane gas (Si
When L) is supplied and this gas is activated by the plasma, the activated species react with the substrate 11, which is the sample to be processed, to which an RF bias voltage is applied by the RF generator 20, and a thin film is formed on the surface of the substrate. be done. Note that the wiring for applying an RF bias voltage to the substrate 11 is covered with a shield of ground potential.

By supplying an etching gas instead of the 03 gas from the gas supply means 4, this apparatus can also be used for etching a substrate.

[The problem to be solved by the invention] In the conventional ECR plasma CVD of this type and for etching processing, when viewed from the RF generator, the plasma is a load, and the presence of this load causes the plasma side of the substrate and the RF generator to This allows for impedance matching with the other side, making it possible to apply an appropriate voltage onto the substrate. However, when microwaves are not being generated and therefore plasma is not being generated, there is no load and a high voltage is applied to the substrate, and this high voltage may be about 1 kV, causing discharge on the substrate surface. This causes problems such as tartar formation on the surface of the substrate and damage. For this reason, in conventional devices, for example, as disclosed in Japanese Patent Application No. 63-275786, a synchronous pulse generation circuit is provided in the device, and two pulse signals output from this circuit are generated, one of which is generated by microwave generation. The other input is to an RF generator so that the microwave pulse and the RF bias voltage are always synchronized and sent into the device body, or the device is equipped with an RF bias modulation circuit and the RF bias voltage is input to the substrate surface. R to the board when the potential exceeds the set value
The application of the F bias voltage is stopped.

However, such a trouble prevention device due to abnormal voltage is sufficient when the response speed of the plasma load impedance to the microwave pulse is fast as seen from the RF generator, but depending on the type of plasma, when the impedance pulse is turned on, The inventor's experiments have revealed that there are some that have poor synchronization characteristics, some that have poor synchronization characteristics when the pulse is OFF, or some that have bad both. As shown in FIG. 5, this tendency particularly occurs immediately after plasma ignition and immediately after the microwave is turned off, with the former appearing as an overshoot of the applied voltage, and the latter appearing as a spike-like normal voltage. Experiments conducted by the inventors have revealed that these abnormal voltages can damage the aluminum wiring in the case of a board with pre-wired LSI mounted, and conventional devices have the drawback that the occurrence of these abnormal voltages cannot be avoided. had.

For example, when an RF pulse is applied to a substrate in synchronization with a microwave pulse having an envelope shown in FIG. 5, 1M+, depending on the type of process gas, (bl, (cl, (d))
An abnormal voltage with the shape of is generated. Table 1 shows the types of plasma gases that correspond to each of these abnormal voltages.

Table 1 An object of the present invention is to produce an ECR plasma C that does not generate abnormal voltage on the substrate to the grounded part of the device when applying the RF bias voltage in synchronization with the microwave pulse.
Our objective is to provide VD and etching equipment.

[Means for solving lIs]

In order to solve the above problems, the present invention includes a pulsed microwave generating means, a means for transmitting the microwave, a means for transmitting the microwave to which the microwave is introduced, and a gas supplying means. an excitation solenoid that generates magnetic lines of force for generating one active atom molecule or ion by converting gas supplied through the means into plasma by a resonance effect with the microwave, and whose axis is the line of magnetic force generated by the solenoid. a plasma generation chamber having an opening on the side facing the microwave transmission means that coincides with the central axis of the bundle; and a plasma generation chamber that is coupled to the plasma generation chamber via the opening and flows out from the opening along the lines of magnetic force. a processing chamber in which a substrate whose surface is etched with a single atomic molecule or ion or an i** is formed;
A plasma processing apparatus equipped with an RF generating means for applying an RF bias voltage to the substrate and a vacuum evacuation means for evacuating the plasma generation chamber and the processing chamber is used to apply the RF bias voltage to the substrate at a time when the generation timing is the pulse. The RF pulse is generated as a pulse synchronized with the microwave pulse, and is provided with means for delaying the start time of the rise of the RF pulse by a significant period of time from the rise time of the microwave pulse, depending on the type of gas supplied to the plasma generation chamber. equipment or RF
The device is equipped with means for delaying the rise start time of the pulse by a significant period of time from the rise time of the microwave pulse and advancing the fall start time of the RF pulse by a significant period of time from the fall time of the microwave pulse, or The rising start time of the RF pulse is the same as the rising time of the microwave pulse, and R
The device is provided with means for advancing the falling start time of the F pulse by a significant period of time compared to the falling time of the microwave pulse.

[Effect]

Microwave plasma is non-polar plasma, and if an electrode to which RF power is supplied (hereinafter referred to as RF electrode) is placed in it, and RF power is applied between both electrodes with the chimney plate as the ground electrode, RF・The voltage-current characteristics at the electrode are equal to the voltage-current characteristics of the Langminier probe, and the voltage-current characteristics at the 7th W
It becomes like j.

In the figure, the horizontal axis shows the potential of the RF electrode with respect to the grounding site in the device, and the vertical axis shows the current flowing through the RF electrode. Here, a positive value on the vertical axis indicates that the electron current is more dominant than the ionic current. A negative value indicates that the ionic current is more dominant than the electronic current.

As is well known, when an alternating electric field is applied to such a probe, an alternating potential with a negatively biased center potential appears at the probe due to the difference in mobility between electrons and ions in the plasma. This potential goes back and forth between approximately 0 and V, and this potential is ■.

The ratio between the electric potential *lp and the electric potential *lp at the potential ■ is an index of the plasma load impedance as seen from the RF generator. Current! , is determined by the ion flow, so it can be assumed that it takes the following value.

Here, e: Coulomb quantity of one electron n,: Plasma density: Bormann constant T,: Electron temperature e゛: Base of natural logarithm M: Mass of ion Among these physical quantities, changes over time due to flickering of the plasma Therefore, in a plasma with poor pulse rise responsiveness, it takes a long time for the plasma to reach an equilibrium state, and within this time it exhibits a large load impedance, and the connection between the substrate and the grounding part in the device increases. A large abnormal voltage occurs between the two.

In addition, plasma with poor pulse fall response has a long period of afterglow, in which the load impedance increases discontinuously, compared to steady plasma, and RF
Since the J'1lll wave number is significantly lower than the microwave frequency, even if the RF power is cut off at the same time as the microwave, the time for the RF bias voltage to reach the zero value is much later than the microwave, so the RF bias voltage is subjected to afterglow, and a large abnormal voltage is generated between the board and the grounded part within the device. This is the time interval in which these abnormal voltages occur. The time it takes for the plasma to reach an equilibrium state after applying a microwave pulse and the time for afterglow to exist are both determined by the collision cross section between the source gas and electrons, and the collision cross section depends on the type of gas and electrons. Since it varies greatly depending on the temperature, it is interpreted that the pulse response exhibits various aspects.

For the above reasons, depending on the type of plasma gas, (1) In the case of a plasma gas with poor pulse rise response, the plasma processing equipment may be delayed by a significant period of time from the rise time of the microwave pulse to generate the RF pulse. The device is equipped with a means for applying the voltage to the substrate, and (1) in the case of a plasma gas with poor pulse fall response, a means for cutting off the RF pulse by moving the plasma processing device a significant period earlier than the fall time of the microwave pulse. The device shall be equipped with

As a result, the plasma processing apparatus can be made into an apparatus in which no abnormal voltage is generated between the substrate and the grounded part within the apparatus.

C Embodiment] Figure 1 shows an embodiment of the invention, in which 1m+ is a simulated envelope of microwaves generated in a pulsed manner, and (bl is the timing of the rise of the RF pulse). This figure shows the envelope of RF when the generation of abnormal voltage at the time of rise is suppressed by delaying the rise of the microwave by time τ1. RF when the occurrence of abnormal voltage at falling edge is suppressed by advancing by 8
(d) shows the envelope line of The time τ is set so that the time to cut off the RF pulse is sufficiently earlier than the time to cut off the microwave pulse.Specific types of plasma gas and measures to prevent abnormal voltage for each plasma gas. Examples are shown in Table 2.

Table 2 An example of a specific circuit for implementing such countermeasures is shown in Figure 2.A microwave having a rectangular envelope with a width of the order of as generated by a microwave source passes through a waveguide. The microwave is guided into the vacuum chamber that constitutes the plasma generation chamber and used to generate plasma. A signal that faithfully monitors the time change of this envelope is extracted from the microwave source
This is sent to a pulse generator. Variable resistors VRI and VR2 are attached to the pulse generator, and by adjusting these resistance values, as shown in FIG. 4, the time τ is determined from the rise time of the microwave monitor signal.

It generates a pulse that rises with a delay of τ and falls with a delay of τ. An RF generator is provided with this pulse signal. If the input signal is input to the remote control terminal that controls the output of the RF generator and the RF generator is driven, the desired RF
Pulses can be generated. In addition, in the figure,
The munching box connects the plasma side of the substrate to be processed and the RF
It is a box with a built-in circuit for impedance matching with the generator side.

Another example of a specific circuit is shown in FIG. 3. In this example, no variable resistor is used, and τ1. Input τ8- to calculate τ3, and calculate τ1. τ, is digitized and sent to the D/A converter. τ1 converted to an analog value with desired accuracy. Input τ3 to the pulse generator to obtain the desired pulse signal. After that, the desired RF pulse is output in the same manner as in the above example. Note that when using a normal CR oscillation type pulse generator, for example, by applying the output analog signal from the D/A converter as a bias to the capacitor of the CR oscillator, the pulse generation time point can be adjusted to a specified value. You can move forward or backward from that point.

〔Effect of the invention〕

As described above, in the present invention, there is provided a pulsed microwave generation means, a microwave transmission means, a gas supply means which is coupled to the microwave transmission means to introduce the microwave, and a gas supply means. is provided with an excitation solenoid that generates magnetic lines of force for generating one active atom molecule or ion by turning gas supplied through the microwave into plasma by resonance effect with the microwave, and the axis thereof is a line of magnetic flux generated by the solenoid. a plasma generation chamber having an opening on the side opposite to the microwave transmission means that coincides with the central axis of the plasma generation chamber; and the active atoms that are coupled to the plasma generation chamber via the opening and flow out from the opening along the lines of magnetic force. A processing chamber in which a substrate whose surface is etched or a thin film is formed by one molecule or ion is disposed, and an R is applied to the substrate.
A plasma processing apparatus including an RF generation means for applying an F bias voltage and a vacuum evacuation means for evacuating the plasma generation chamber and the processing chamber, the RF bias voltage is
Generate the pulse as a pulse whose generation time is synchronized with the pulsed microwave, and delay the rise start time of the RF pulse by a significant period of time from the rise time of the microwave pulse in accordance with Ii [of the gas supplied to the plasma generation chamber. Either the rising start time of the RF pulse is delayed by a significant period of time from the rising time of the microwave pulse, and the falling start time of the RF pulse is delayed by a significant time period from the falling time of the microwave pulse. Alternatively, the rising start time of the RF pulse should be the same as the rising time of the microwave pulse, and the falling start time of the RF pulse should be the same as the falling time of the microwave pulse. Since the device is equipped with a means for increasing the time period more significantly, the RF pulse is applied to the substrate only during the equilibrium plasma period, thereby preventing the generation of abnormal voltage between the substrate and the grounded part of the device. be done. This prevents the generation of discharge between the substrate and the grounded portion due to abnormal voltage, thereby preventing damage to the substrate to be processed.

Note that control to output the RF bias voltage only during the plasma period in the equilibrium state is performed based on the waveform of the microwave pulse, so R
High-precision control for advancing the fall start time of the F pulse by a certain period of time than the fall time of the microwave pulse can be easily achieved by configuring the control means using a microcomputer. 11
m can be performed with high precision. Thereby, damage to the substrate due to abnormal voltage can be reliably prevented.

[Brief explanation of drawings]

FIG. 1 shows an example of how to shift the rise start time and fall start time of the RF pulse waveform applied to the substrate in the plasma processing apparatus according to the present invention from the rise time and fall time of the microwave pulse waveform, respectively. (al) is a waveform diagram showing the waveform of a microwave pulse, and (b) is a waveform diagram showing the waveform of the RF pulse applied to the substrate when a gas with poor pulse rise response is used as the gas to be turned into plasma. Waveform diagram, Figure 1 (C1 is a waveform diagram of the RF pulse applied to the substrate when a gas with poor pulse fall response is used as the target gas for plasma generation, Figure 1)
dl is a waveform diagram of the RF pulse applied to the substrate when a gas with poor responsiveness at both the rise and fall of the pulse is used as the gas to be turned into plasma. Figures 2 and 3 are the start of the rise and fall of the RF pulse waveform. A block diagram showing mutually related configurations of the control means for controlling the deviation from the rise and fall times in the microwave pulse waveform at each time, and FIG. 4 shows the pulse generation in the control means shown in FIGS. 2 and 3. output from the device. A waveform diagram showing the pulse signal waveform for RF pulse generation at W in comparison with a monitor signal waveform indicating the microwave pulse waveform. FIG. Figure 1a) is a waveform diagram showing an example of a waveform, and Figure 1a) is a waveform diagram of a microwave pulse, and Figure 1a) is a waveform diagram of a voltage appearing on a substrate when a gas with poor pulse rise response is used as a gas to be turned into plasma. , the same figure (C1 is a waveform diagram of the voltage that appears on the substrate when a gas with poor response at the pulse fall is the target gas for plasma generation, +d in the same figure) is a waveform diagram of the voltage that appears on the substrate when a gas with poor response at both the rise and fall of the pulse is converted into plasma. FIG. 6 is a sectional view showing the basic configuration of an example of a plasma processing apparatus to which the present invention is applied;
The figure is a diagram showing a method for determining plasma impedance from the relationship between the potential of a substrate to which an RF bias voltage is applied relative to the ground and the current flowing into the substrate from the plasma. 1's wave tube (microwave transmission means), 3: plasma generation chamber, 4: gas supply means, 6: excitation solenoid, 7:
Opening, 9: Processing chamber, 1: Substrate, 17: Microwave generator (microwave generation means), 20: RF generator (RF generation means). Agent G Physician Yamaguchi i-'- 1 Figure 1 Figure 2 Figure 3 Figure 4 Figure 5
fertilizer

Claims (1)

[Scope of Claims] 1) A pulsed microwave generating means, a means for transmitting the microwave, and a device coupled to the microwave transmitting means to which the microwave is introduced and supplied via a gas supply means. an excitation solenoid that generates magnetic lines of force for generating active atoms, molecules or ions by converting the gas into plasma through a resonance effect with the microwave, and the axis thereof is the central axis of the magnetic line of force generated by the solenoid. a plasma generation chamber having a matching aperture on the side opposite the microwave transmission means; and the active atoms, molecules or ions coupled to the plasma generation chamber via the aperture and flowing out from the aperture along the magnetic field lines. a processing chamber in which a substrate whose surface is etched or a thin film is formed is disposed, and an RF chamber for applying an RF bias voltage to the substrate;
In a plasma processing apparatus comprising a generating means and a vacuum evacuation means for evacuating the plasma generation chamber and the processing chamber, the RF bias voltage is generated as a pulse whose generation timing is synchronized with the pulsed microwave. A plasma processing apparatus characterized by comprising means for delaying the rise start time of the RF pulse by a significant period of time from the rise time of the microwave pulse. 2) A pulsed microwave generating means, a microwave transmitting means, which is coupled to the microwave transmitting means to introduce the microwave, and a gas supplied via the gas supply means to the microwave. It is equipped with an excitation solenoid that generates magnetic lines of force to produce active atoms, molecules, or ions that turn into plasma through a resonance effect with waves, and an opening whose axis coincides with the central axis of the magnetic flux generated by the solenoid. a plasma generation chamber disposed on a side facing the wave transmission means; and a surface is etched by the active atoms, molecules or ions that are coupled to the plasma generation chamber through the opening and flow out from the opening along the lines of magnetic force; a processing chamber in which a substrate on which a thin film is to be formed or a thin film is disposed, and an RF chamber for applying an RF bias voltage to the substrate;
In a plasma processing apparatus comprising a generating means and a vacuum evacuation means for evacuating the plasma generation chamber and the processing chamber, the RF bias voltage is generated as a pulse whose generation timing is synchronized with the pulsed microwave. It is characterized by comprising means for delaying the rising start time of the RF pulse by a significant period of time from the rising time of the microwave pulse and advancing the falling start time of the RF pulse by a significant period of time from the falling time of the microwave pulse. Plasma processing equipment. 3) A pulsed microwave generating means, a microwave transmitting means, which is coupled to the microwave transmitting means to introduce the microwave, and a gas supplied via the gas supply means to the microwave. It is equipped with an excitation solenoid that generates magnetic lines of force to produce active atoms, molecules, or ions that turn into plasma through a resonance effect with waves, and an opening whose axis coincides with the central axis of the magnetic flux generated by the solenoid. a plasma generation chamber disposed on a side facing the wave transmission means; and a surface is etched by the active atoms, molecules or ions that are coupled to the plasma generation chamber through the opening and flow out from the opening along the lines of magnetic force; a processing chamber in which a substrate on which a thin film is to be formed or a thin film is disposed, and an RF chamber for applying an RF bias voltage to the substrate;
In a plasma processing apparatus comprising a generating means and a vacuum evacuation means for evacuating the plasma generation chamber and the processing chamber, the RF bias voltage is generated as a pulse whose generation timing is synchronized with the pulsed microwave. It is characterized by comprising means for making the rising start time of this RF pulse the same as the rising time of the microwave pulse, and for making the falling start time of the RF pulse earlier by a significant period of time than the falling time of the microwave pulse. Plasma processing equipment.