JP2001085394A - Method and device for processing surface - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily and effectively reduce the damage on element by charged particles, by allowing the frequency of a plasma generating power source to be different from that of a bias power source for applying a high frequency to a sample, and time-modulating the two power sources periodically while the frequency of time modulation is set to a different value. SOLUTION: Both a high frequency power source 109 for discharge and a microwave power source 101 are made into pulse and the repetition frequency for on/off of both is set to a different value. The high frequency power source 109 and the microwave power source 101 are periodically time-modulated, with the frequency for time modulation set to a different value. In short, phase is not synchronized. With no synchronization, the timing when the on-period of discharge pulse overlaps with off-period of bias pulse is averaged by the micro time fluctuation in frequency, suppressing occurrence of a transient voltage. No synchronization between the high frequency power source 109 and the microwave power source 101 is required for a simple device configuration.

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface treatment of a semiconductor device.
Method, especially using a plasma
The present invention relates to an apparatus for performing etching. [0002] The present invention relates to a method for etching a semiconductor device.
Applied to equipment using plasma. here
A device called ECR (Electron Cyclotron Resonance)
The conventional technology will be described with reference to an example. In this method,
Plasma by microwave in vacuum vessel with applied magnetic field
Occurs. Electrons move in a cyclotron due to the magnetic field,
It is effective by resonating this frequency with the microwave frequency.
Plasma can be generated efficiently. Ions entering the sample
To accelerate, a high frequency voltage is applied to the sample. Less than
Later, the power applied to the sample is called a bias. With plasma
Halogen gas such as chlorine and fluorine
It is. The purpose of this device is mainly to improve the accuracy.
Japanese Unexamined Patent Publication No. 4-69415 is known. With this invention
Modulates microwave power and bias causing discharge
Control the ratio of ions and radicals in the plasma.
Control the ion energy at the same time
Can be etched as much as possible. Similar technology is also a US patent
Also known in USP 4,585,516. here,
A device that generates a discharge by applying high frequency to the electrodes.
Turn on and off at least one of the biases repeatedly to
It describes how to improve the uniformity of the switching speed.
You. Also, Japanese Patent Application Laid-Open No. Hei 1-236629,
In Japanese Patent Publication No. 3-130370, the discharge is pulsed.
And synchronize the discharge on and off with the bias
Describes the means to prevent abnormal voltage generated in the sample.
ing. Also, Japanese Patent Laid-Open Publication No. Hei 8-181125 describes
By pulsing discharge and bias synchronously,
A method for preventing the gate breakdown of the transistor is described. [0004] MOS (metal oxide semi)
conductor) The gate oxide thickness of the transistor is 256
For memory elements after M, it is 6 nm or less. Further processing
The width of the wiring and grooves becomes less than 0.3 μm,
The duty ratio (the dimensional ratio between the vertical direction and the horizontal direction) increases. this
In such a fine element, the plasma in the processing of the element
Gate of MOS transistor by charged particles (electrons and ions)
This causes a problem that the oxide film breaks down. [0005] Hereinafter, the present invention will be described with reference to the reduction of gate dielectric breakdown.
The problem when applied to the system is described. 2 to 4 show the discharge and the battery.
An ECR system with pulsed ias.
The result of having measured the electric potential generated on EHA is shown. In addition,
The microwave frequency is 2.45GHz and high for bias.
The frequency is 400 kHz. Here, S covered with an oxide film
i Line-and-space resist on the wafer
And attach this Si chip (1cm square)
Was connected to a probe wire for measurement. [0006] Fine line and space patterns
Sample is lighter than ion
Electrons at the bottom of the groove do not allow large electrons to enter the bottom of the groove.
Shortage and become positively charged. This phenomenon is electronic shading
It is called electronic shading in the processing of fine elements.
Breakdown of the gate oxide film becomes the most serious. [0007] The voltages shown in FIGS.
The potential rise of the Si chip due to
The lower the value, the higher the effect of preventing dielectric breakdown. In each figure, waveform 20
1 is the discharge on / off, and waveform 202 is the bias on / off.
Respectively. Waveforms 203, 301, 401
Indicates the voltage of the Si chip, and the vibrating part indicates the high bias voltage.
Vibration corresponding to the frequency of the frequency (400kHz)
In the figure, the exact description of the wave number is omitted. [0008] Dotted line 204 pulses discharge and bias.
It shows the average value of the voltage of the Si chip in the case where it is not used. Release
The repetition frequency of the electric and bias pulses is 10 kHz,
The duty ratio is 50%. Discharge and bias
The time average of the power when both are pulsed is the
It is set to be the same as power. Discharge and bias
And the phase difference between the pulses is 0 in FIGS.
Degrees, 90 degrees, and 180 degrees. Discharge in both cases
Chip potential is lower than when the bias is continuous
However, when the phase difference is 90 degrees and 180 degrees, the discharge is off.
Transient potentials 304 and 402 occur when bias is applied
This causes gate destruction. The phase difference is 0 degree,
When the discharge is off, the bias is also off, and the discharge is on.
When the bias is also turned on sometimes, the transient potential
The result is good because the rise of the pressure is eliminated. This effect
Known examples are described in Published Japanese Patent Application No. Hei 1-263629.
Is the same as However, this method has the following problems. Ma
Synchronization, that is, the position of the pulse
In order to keep the phase difference constant, the phase control
Separate equipment is required and the price is high. In addition, discharge on
In order to set the condition that bias off does not overlap,
The frequency and duty ratio of the
Narrows. [0010] Further, Patent Publication No. 4-69415 and US Pat.
In USP 4,585,516, the tasks are different,
Specific methods to prevent dielectric breakdown of oxide film are described.
Not in. Thus, conventionally, the discharge and the bias are synchronized
Although pulsing techniques are known, the equipment is complex and expensive.
Valued. An object of the present invention is to provide a semiconductor device using a plasma.
Load during plasma device processing in surface treatment
Easily and effectively reduce damage to devices due to charged particles
Is to provide a way to [0012] _{[Means for Solving the Problems]}  The feature of the present invention is to discharge
Pulse both high frequency power and bias power to generate
And the repetition frequency of both on and off are different.
Values and make sure that the phases are not synchronized.
That is. Turning on and off the discharge power supply and bias power supply
Then, the voltage generated at the gate electrode of the sample can be reduced.
Can prevent the gate oxide film from being destroyed.
When the bias turns on when the zuma turns off
Then, a transient voltage is generated, and the destruction reduction effect is reduced.
According to the method of the present invention, the bias is applied when the plasma is turned off.
Are turned on and the transient voltage is generated.
It is possible to suppress the life and at the same time, two
It is not necessary to synchronize the power supply of
The desired effect can be obtained. [0014] In order to further improve the effect, the present invention
According to other characteristics of the repetition of both
_{The frequency was more than doubled.} [0015] _{BEST MODE FOR CARRYING OUT THE INVENTION [Example 1]} Hereinafter, the embodiment will be described with reference to the drawings.
Will be described. FIG. 1 shows a plasma etchin to which the present invention is applied.
FIG. 1 is an overall configuration diagram of a logging device. From microwave power supply 101
Inside the vacuum vessel 104 via the waveguide 102 and the introduction window 103
A microwave is introduced into the. The material of the introduction window 103 is stone
It is a substance that transmits electromagnetic waves, such as English and ceramic. vacuum
An electromagnet 105 is provided around the container 104,
The magnetic field strength is set to resonate with the microwave frequency.
For example, if the frequency is 2.45GHz, the magnetic field strength
Is 875 Gauss. The sample 107 is placed on the sample stage 108
Is installed. To accelerate ions entering the sample
The high frequency voltage power supply 109 is connected to the sample stage 108
I have. There is no particular limitation on the frequency of the high frequency voltage power supply.
Normally the frequency is practically in the range of 200kHz to 20MHz
It is. Microwave power supply 101 and bias power supply 109
Is a pulse signal generator 110 for controlling on / off of each of them.
And 111 are provided. Discharge pulse frequency 20kH
z, the bias pulse frequency is set to 10 kHz, and
There is no control to synchronize the two. That is,
The pulse phase difference is an arbitrary value that depends on the lighting time.
You. FIG. 5 shows the method of the present invention, that is,
The high frequency power supply and bias power together for
Set the on / off repetition frequency to different values
To avoid synchronizing the phase
5 shows a voltage waveform 501 of a chip. Some transient voltage 502
Occurs but is small and not a problem. The transient voltage is
From the experiment, it was determined that the discharge was turned off and the bias was turned on.
Frequency is high, but because of the lack of synchronization, the frequency
Turn on and via of discharge pulse due to minute time fluctuation
The timing at which spurs turn off overlaps is averaged,
It is considered that the generation of the passing voltage was suppressed. Also discharge
Changes in the Si chip potential change
It is also considered that averaging was not possible. This one
Method, even if there is some variation in the frequency setting, the phase difference
Are averaged with a shift over time, so the frequency setting
There is an advantage that accuracy is not required. FIG. 6 shows the pulse frequency of the discharge and the bias.
4 shows the relationship between the ratio and the transient voltage. The difference between the two is twice
The pressure is reduced to about 1/2. DRAM of 256M class at this level
The problem of gate destruction in the above processing is eliminated. If further improvement is required depending on the device,
If the ratio of the loudspeaker frequency is made 4 times or more, the transient voltage will be almost
The waveform becomes like a waveform 701 shown in FIG. Also release
If the power-off time is set to 50 μs or less,
Transient voltage is generated because some ions do not completely disappear.
Is more suppressed. FIG. 8 is a graph showing the effects of the present invention.
The duty ratio of the pulse (repetition frequency 10 kHz) and S
The relationship between the average values of voltages generated in the i-chip is shown. In FIG.
Pulse continuous bias and bias (duty
Comparison with 50% ratio and 2kHz repetition frequency)
You. Just pulse discharge or bias
Voltage also decreases, which is effective in reducing gate breakdown.
The voltage is further reduced by pulsing. Discharge pulse
The cause is unknown when the duty ratio of 20% or less
Since the voltage rises, the duty ratio is 20% or more 6
0% or less is appropriate. Also, the bias pulse duty
The same range is appropriate for the tee ratio. In the above embodiment, the frequency of the discharge pulse is
Although it was set higher than the bias pulse frequency,
Has the same effect. However, in general, the frequency of the bias high frequency
The number is from 13.56MHz to accelerate ions efficiently
It is set small, the high frequency of the discharge is higher
Good. Therefore, the repetition frequency when pulsed is also
Making the discharge pulse bigger enters the on-period
Since the wave number of the high-frequency power is made uniform, the pulse width can be set.
Increases the margin. Next, FIG. 9 shows the actual application of the present invention.
The results of measuring the breaking rate of the sheet are shown. 4nm thickness for evaluation
Antenna of poly Si (0.2 nm thick) is in contact with the gate oxide film of
A continuous element was used. Antenna poly Si is line and scan
Each width of the pace is 0.5 μm resist (thickness is 1 μm).
m), and the gate is broken by electronic shading.
You can evaluate the destruction. Antenna ratio ((space area) / (game
Oxide film area)) is about 8000. Such an element
121 pieces are placed on an 8-inch wafer, and poly Si is etched.
After the etching, the dielectric breakdown of the gate was measured. Etchin
Gas is a mixed gas of Cl2 (80sccm) and BCl3 (20sccm)
To set the pressure to 1 Pa. The output of the microwave power supply 101
It was 700 W. 10k repetition frequency during pulse discharge
Hz and the duty ratio were 50%. Bias power supply 10
The frequency of 9 is 800KHz, and the power of continuous output is 70W.
Was. At pulse, repetition frequency 2kHz, duty ratio 4
0%. Discharge and bias, average power at pulse
Is set to the same value as during continuous operation. FIG. 9A shows the case of continuous discharge and continuous bias.
Approximately 93% of the gates were destroyed by the
Gates). Fig. 9 (2) shows that both discharge and bias are
This shows the gate destruction in the case of a loosening. As shown in Fig. 9 (2)
As described above, the destruction rate is reduced to 0% by pulsing.
The fruit is clear. This effect also equates discharge and bias.
Pulse at the same frequency and synchronize with zero phase difference
This is the same as the case where the adjustment is made. That is, the present invention
Therefore, even if a device for synchronization is not provided,
The effect is obtained. Next, the gas used for etching will be described.
Bell. This invention uses high aspect ratio lines and spaces.
Suitable for processing. These lines and spaces are mainly
Connected to the gate electrode or gate of the transistor
It corresponds to the metal wiring part. Gate electrode is poly Si, pol
y Si and metal alloy, high melting point metal such as tungsten
Or it is made of a multilayer film of these materials. These materials
Etching of chlorine, HBr, mixed gas of chlorine and oxygen, H
Mixed gas of Br and oxygen, or mixed gas of chlorine, HBr and oxygen
Gas is suitable. Salt is used for etching metal wiring.
Gas, mixed gas of chlorine and BCl3, mixed gas of chlorine and HCl,
Alternatively, a mixed gas of chlorine, BCl3 and HCl is suitable. Also
In the case of a multi-layer device, the gate is destroyed by processing the insulating film between layers.
Becomes a problem. Here, CF4, CHF3, CH2F2, C4F
8, C4F5 or a mixture of these CO2, CO, rare gas, etc.
The used gas is used. The present invention is not limited to etching,
The same applies to a device that deposits a film on a substrate using
effective. [0025]_{[Example 2]}FIG. 10 applies the present invention.
With another device structure, this device has a frequency of several hundred kHz to several tens of MHz.
Inductive coupling at radio frequency (rf) frequencies
Causes zuma. Vacuum container 1001 is made of alumina or quartz
It is made of materials that transmit electromagnetic waves such as. That time
In addition, an electromagnetic coil 1002 for generating plasma
Is wound. An rf power supply 1003 is connected to the coil
I have. A sample stage 1004 is provided in the vacuum
A power supply 1005 is connected. In this type of apparatus, the rf power supply 1003
Signal generator 1 for pulsing to bias power supply 1005
006 and 1007, respectively, and
To suppress the rise in pattern potential and break the gate oxide film.
Breakage can be prevented. [0027]_{[Example 3]}FIG. 11 applies the present invention
In another device structure, this device uses capacitive coupling of rf power.
Generates plasma. In the vacuum vessel 1101, two sheets
The electrodes 1102 and 1103 are arranged in parallel. On the electrode
Are connected to the rf power supply 1104 and the bias power supply 1105, respectively.
Continued. The electrode 1103 serves as a sample stage. Gas is a trial
Tube 110 through the hole opened in the electrode 1102 facing the material.
6 into the container. In this type of apparatus, the rf power supply 1104 and the
Signal generator 1 for pulsing to bias power supply 1105
107 and 1108 are connected respectively,
To suppress the rise in pattern potential and break the gate oxide film.
Breakage can be prevented. As described above, according to the present invention, the plasma
The timing when the bias is turned on when the power is off is averaged
At the same time as the transient voltage can be suppressed.
In addition, there is no need to synchronize the two power supplies as in the conventional method.
Become. There is no need to synchronize the two power supplies as in the conventional method.
Therefore, with a simple device configuration, the rise in pattern potential is suppressed.
The dielectric breakdown of the gate oxide film can be prevented.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of an apparatus to which the present invention is applied.

FIG. 2 shows a pulse waveform of a discharge and a bias and a voltage waveform generated in a Si chip according to a conventional method.

FIG. 3 shows a discharge and bias pulse waveform and a voltage waveform generated in a Si chip according to a conventional method.

FIG. 4 shows a pulse waveform of discharge and bias and a voltage waveform generated in a Si chip according to a conventional method.

FIG. 5 shows a pulse waveform of discharge and bias and a voltage waveform generated in a Si chip according to the method of the present invention.

FIG. 6 is a diagram showing the relationship between the ratio between the frequency of the discharge pulse and the frequency of the bias pulse and the transient voltage according to the method of the present invention.

FIG. 7 is a diagram showing a pulse waveform of a discharge and a bias and a voltage waveform generated in a Si chip according to the method of the present invention.

FIG. 8 is a diagram illustrating a relationship between a pulse duty ratio and a voltage waveform generated in a Si chip, for describing an effect of the present invention.

FIG. 9 is a diagram showing a breakdown distribution of a gate oxide film for explaining the effect of the present invention.

FIG. 10 is a diagram showing an overall configuration diagram of another apparatus to which the present invention is applied.

FIG. 11 is a diagram showing an overall configuration diagram of another apparatus to which the present invention is applied.

[Explanation of symbols]

101-microwave power supply, 102-waveguide, 103-introduction window, 104, 1001, 1101-vacuum vessel, 105
-Magnet, 106-plasma, 107-sample, 108, 1
004-sample stage, 109, 1005, 1105-bias power supply, 110, 111, 1006, 1007, 110
7, 1108-pulse signal generator, 201, 202, 2
03, 301, 401, 501, 701-waveform, 204
-Dotted line, 302, 402, 502-transient voltage, 1002
-Electromagnetic coil, 1003, 1104-rf power, 110
2, 1103-electrode, 1106-introduction tube.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor, Seiichi Watanabe 794, Higashi-Toyoi, Kazamatsu, Kamamatsu City, Yamaguchi Prefecture Inside Kasado Plant, Hitachi, Ltd. Hitachi, Ltd. Kasado Works (72) Inventor Takashi Sato 794, Higashi-Toyoi, Kazamatsu City, Yamaguchi Prefecture F-term (reference) 4G075 AA30 AA61 AA62 BA05 BC06 BD14 CA12 CA47 EB44 5F004 AA16 BA14 BB11 CA03 DA00 DA01 DA04 DA15 DA16 DB02 DB10 DB15 EB02

Claims (7)

[Claims] 1. A surface treatment method for treating a surface of a sample with plasma, wherein the frequency of a power supply for plasma generation and the frequency of a bias power supply for applying a high frequency to the sample are different, and the two power supplies are periodically switched. Wherein the frequency of the time modulation is set to a different value. 2. The surface treatment method according to claim 1, wherein the modulation frequencies of the two power supplies are not synchronized. 3. The surface treatment method according to claim 1, wherein the time modulation frequency of the two power supplies has a difference of two times or more. 4. The surface treatment method according to claim 2, wherein a time modulation frequency of the power supply for plasma generation is set higher than a time modulation frequency of the bias power supply. 5. The surface treatment method according to claim 1, wherein a duty ratio of time modulation of the two power supplies is set to 20% or more and 60% or less. 6. The method according to claim 1, wherein the on-time of the time modulation of the power supply for plasma generation is 50 μs.
A surface treatment method characterized by the following. 7. A surface treatment apparatus comprising a power supply for plasma generation and a bias power supply for applying a high frequency to a sample, wherein the frequency of the power supply for plasma generation and the frequency of the bias power supply are adjusted. Be different, periodically time-modulate the two power supplies,
And a time modulation frequency set to a different value.