JPH0888218A - Method and device for plasma etching - Google Patents

Abstract

PURPOSE: To increase the etching speed ratio and etching characteristics by impressing pulsative high-frequency electric power upon a coil and making the frequency of the high-frequency electric power for generating plasma the same as that of bias power, and then, changing the phase difference between the frequencies of both electric powers. CONSTITUTION: The output of a high-frequency power source 12 is impressed upon a coil 3 through a matching device 7. Then high-density plasma is generated in a reaction chamber 2 by generating helicon waves in the chamber 2. At the same time, the output of a bias power source 10 is impressed upon a planar electrode 5 through another matching device 9. Under such a condition, a workpiece is etched by utilizing a self-bias voltage or AC electric field generated from the electrode 5. When the frequency of pulse modulation is made the same as that impressed upon the electrode 5, the phase difference between both frequencies is appropriately set by means of a phase shifter 13.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an etching method, which is one of semiconductor manufacturing processes, and more particularly to a plasma etching method and apparatus for dry etching using plasma.

[0002]

2. Description of the Related Art Conventionally, as a method for generating plasma, a pair of flat plate electrodes are provided facing each other, a reaction gas is supplied under a reduced pressure atmosphere, and high frequency power is applied between both electrodes to generate plasma. And ECR (Electroron Cy) that generates plasma by microwave and magnetic field.
Clotoron Resonance) method and magnetic field induction method of generating plasma by using helicon wave generated by applying high frequency power to the space to which magnetic field is applied. With the magnetic field induction method, it is possible to generate a higher density plasma than the above-mentioned two.

Referring to FIG. 12, a conventional plasma etching apparatus of a magnetic field induction method for generating plasma using a helicon wave will be described.

A cylindrical reaction chamber 2 made of an insulating material is airtightly connected to an upper side of an airtight processing chamber 1 made of a conductive material, and two coils 3 are provided outside the reaction chamber 2. A magnetic field generating coil 4 for generating a magnetic field in the axial direction of the reaction chamber 2 is provided outside the coil 3 in a wound manner. On the bottom surface of the reaction chamber 2, there is provided a flat plate electrode 5 which also serves as a mounting table for an object to be processed such as a semiconductor sample via a pedestal 6 made of an insulating material.

The coil 3 includes a matching unit 7 and a high frequency power source 8
Are connected in series so that the output of the high frequency power source 8 can be applied to the coil 3 through the matching unit 7.
A matching unit 9 and a bias power supply 10 are connected in series to the plate electrode 5, and the output of the bias power supply 10 can be applied to the plate electrode 5 through the matching unit 9.

In the above-mentioned conventional example, the processing chamber 1,
The inside of the reaction chamber 2 is evacuated by a vacuum pump (not shown), the reaction gas is supplied into the reaction chamber 2 after exhaustion, and the pressure in the reaction chamber 2 is kept constant. The reaction chamber 2 is formed by the magnetic field generating coil 4.
With the magnetic field generated therein, the output of the high frequency power source 8 is applied to the coil 3 through the matching unit 7 to generate a helicon wave in the reaction chamber 2 to generate high density plasma.

At the same time, the output of the bias power source 10 is applied to the plate electrode 5 through the matching unit 9, and the plate electrode 5
Using the self-bias voltage or the alternating electric field generated above, the object 11 to be processed placed on the plate electrode 5 is etched.

[0008]

As described above, when plasma is generated using a helicon wave, there is an advantage that high density plasma can be obtained. However, dissociation of the reaction gas introduced into the reaction chamber, and There is a phenomenon that a reaction product generated by etching is dissociated.

When etching a silicon oxide film (SiO ₂ film) on a silicon (Si) wafer which is a semiconductor sample, a C _X F _Y system is used as a reaction gas, but a high density plasma as in the conventional example is used. In the apparatus for generating and etching, the dissociation of the reaction gas proceeds, so that the generation ratio of fluorine (F) becomes large, which causes the etching of silicon as the base of the silicon oxide film due to fluorine to proceed, resulting in a selective ratio (etching rate ratio). ) Decreases.

In order to suppress the etching of Si by F, there is a method of using H ₂ as an additive gas. For example, when etching is carried out by using C ₄ F ₈ and H ₂ as etching gases, the selection ratio of SiO ₂ film and Si is If the proportion of H ₂ is increased to improve the etching rate, the etching rate of SiO ₂ also decreases, and as a result, the selectivity does not improve.

In view of the above situation, the present invention increases the etching rate ratio, improves the etching characteristics, and further improves the process condition margin when the high density plasma is generated by utilizing the helicon wave for etching. Is to spread.

[0012]

The present invention utilizes a plasma generated by applying a magnetic field in the axial direction of the reaction chamber and applying high-frequency power to a coil wound around the reaction chamber. In plasma etching for etching a processed object, the high frequency power applied to the coil is pulsed,
Further, the high frequency power for generating plasma and the bias power have the same frequency, and the phase difference between the frequencies of both powers is changed.

[0013]

Function: The high-frequency power is pulsed and intermittently applied to improve the etching characteristics, and the frequencies of the high-frequency power and the bias power are made the same, and the phase difference between the frequencies of both powers is changed, Increase the margin of conditions.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, the same components as those shown in FIG. 12 are designated by the same reference numerals.

A cylindrical reaction chamber 2 made of an insulating material is airtightly connected to the upper side of an airtight processing chamber 1 made of a conductive material, and two coils 3 are provided outside the reaction chamber 2. A magnetic field generating coil 4 for generating a magnetic field in the axial direction of the reaction chamber 2 is provided outside the coil 3 in a wound manner. On the bottom surface of the reaction chamber 2, there is provided a flat plate electrode 5 which also serves as a mounting table for an object to be processed such as a semiconductor sample via a pedestal 6 made of an insulating material.

It should be noted that one turn of the coil 3 is sufficient in consideration of the uniformity of the generated plasma, and one turn of the coil 3 is preferable in view of simplification of the apparatus. FIG. 2 illustrates an embodiment in which the coil 3 has one turn. The magnetic field generating coil 4 may be a permanent magnet as long as it can generate a magnetic field in the axial direction of the reaction chamber 2.

A matching device 7 and a high frequency power source 12 capable of pulse modulation are connected in series to the coil 3, and the high frequency power source 1
The output of 2 can be applied to the coil 3 through the matching device 7. A matching unit 9 and a bias power supply 10 are connected in series to the plate electrode 5, and the output of the bias power supply 10 can be applied to the plate electrode 5 through the matching unit 9.

The frequency of the fundamental wave of the high frequency power source 12 is usually 13.56 MHz, but it is of course possible to use a frequency other than this. Also, the means for performing pulse modulation is
It may be built in the high frequency power source 12, or may be a combination of a separate amplifier and a commercially available arbitrary signal generator,
It may be any high-frequency power applying means for applying pulsed high-frequency power to the coil.

FIG. 3 shows a mode of pulse modulation, (a) shows a fundamental wave of high frequency power applied to the coil 3, (b).
Shows pulse modulation, and (c) shows a state in which the fundamental wave of (a) is modulated by the pulse modulation shown in (b).

When a phase shifter 13 is connected to the matching box 7 and the matching box 9 and the frequency of the pulse-modulated wave output from the high frequency power source 12 and the bias power output from the bias power source 10 are the same, a pulse is generated. The phase difference between the modulated wave and the bias power can be set arbitrarily.

The operation will be described below.

The inside of the processing chamber 1 and the reaction chamber 2 is evacuated by a vacuum pump (not shown), and after exhaustion, the reaction gas is supplied into the reaction chamber 2 to keep the pressure inside the reaction chamber 2 constant. With the magnetic field generated in the reaction chamber 2 by the magnetic field generation coil 4, the output of the high frequency power source 12 is applied to the coil 3 through the matching device 7 to generate a helicon wave in the reaction chamber 2, Generate a plasma of density.

At the same time, the output of the bias power source 10 is applied to the plate electrode 5 through the matching unit 9, and the plate electrode 5
Using the self-bias voltage or the alternating electric field generated above, the object 11 to be processed placed on the plate electrode 5 is etched.

If the frequency of the pulse modulation and the frequency of the bias power applied to the flat plate electrode 5 are made the same if necessary, the phase difference between them is appropriately set by the phase shifter 13.

Next, a case where the high frequency power applied to the coil 3 is pulse-modulated will be described.

[0027] Figure 4 is a mixing ratio of the reactive gas, a line diagram showing the relationship between the selection ratio of the etching rate and SiO ₂ and Si of the SiO ₂ and Si (etching rate ratio), the diagram above pulse modulation The following high-frequency power is applied to the coil 3, and the lower diagram is a diagram when the high-frequency power is continuously applied to the coil 3. In the figure, the solid line shows the etching rate and the broken line shows the selection ratio. The etching conditions are as follows.

・ Etching gas: C ₄ F ₈ + H ₂・ Pressure: 5 mTorr ・ High-frequency output power: 13.56 MHz, 1.0 KW ・ Pulse modulation specifications: ON time 5 μsec OFF time 120 μsec ・ Bias voltage: -200V

The bias voltage described in the etching conditions means a DC voltage generated in the plate electrode 5 when bias power is applied to the plate electrode 5 in a state where plasma is generated in the reaction chamber 2.

As shown in the lower half of FIG. 4, when a high frequency power is continuously applied to the coil 3, the etching rate of SiO ₂ and Si and their selection are increased by increasing the mixing ratio of H _2. The ratio gradually decreases, and the mixing ratio of H ₂ is 40%
It decreases sharply in the vicinity. When the mixture ratio of H ₂ becomes 50%, the etching rate and the selection ratio thereof are almost 0.
become.

As shown in the upper half of FIG. 4, when the applied high frequency power is pulse-modulated, the etching rate of SiO ₂ becomes higher than that of the continuous wave shown in the lower half of FIG.
Further, when the high-frequency power is pulse-modulated and the H ₂ mixing ratio is increased, the selection ratio increases, and the Si etching rate becomes 0 (μ / min) when the H ₂ mixing ratio is around 38%. The selectivity, (SiO ₂ etching rate) / (Si etching rate) becomes infinite.

The reason why the selection ratio is increased by the pulse modulation is that the dissociation of HF is suppressed especially in the reaction product by adjusting the ON / OFF time of the pulse modulation, and Si by F generated by the dissociation is suppressed. It is considered that this is because the increase in the etching rate is suppressed.

FIG. 5 shows that the ON time of pulse modulation is 5 μsec.
OFF time and SiO ₂ and S when fixed to
The relationship between i and the etching rate is shown, and the etching conditions are as follows.

Etching gas: C ₄ F ₈ with H ₂ 50
% Addition → H ₂ flow rate ÷ (H ₂ flow rate + C ₄ F ₈ flow rate) × 10
0 = 50% ・ Pressure: 5mTorr ・ High frequency power output: 13.56MHz, 1.0KW ・ Pulse modulation specification: ON time fixed at 5μsec ・ Bias voltage: 200V

Under the above etching conditions, when the pulse modulation OFF time is in the range of 5 to 20 μsec, Si
The etching rate is 0 μ / min.

When the OFF time becomes 10 μsec or more, S
The etching rate of io ₂ decreases and reaches 0 at 20 μsec.
Since it is μ / min, it is considered that it is necessary to shorten the OFF time as a general tendency to maintain the etching rate of SiO ₂ .

In FIG. 6, the OFF time of pulse modulation is set to 5 μse.
The relationship between the ON time and the etching rate of SiO ₂ and Si in the state of being fixed to c is shown, and the etching conditions are as follows.

Etching gas: C ₄ F ₈ with H ₂ 50
% Addition → H ₂ flow rate ÷ (H ₂ flow rate + C ₄ F ₈ flow rate) × 10
0 = 50% ・ Pressure: 5mTorr ・ High frequency power output: 13.56MHz, 1.0KW ・ Pulse modulation specification: OFF time fixed at 5μsec ・ Bias voltage: 200V

When the ON time is 20 μsec, the etching rate of SiO ₂ is 0 / min. However, if the ON time is increased in this way, the etching rate of SiO ₂ decreases.
As a general tendency, it is considered necessary to shorten the ON time.

FIG. 7 shows that the OFF time of pulse modulation is 5 μse.
The relationship between the ON time and the deposition rate of the reaction product in the state of being fixed at c is shown. The etching conditions are as follows.

Etching gas: C ₄ F ₈ with H ₂ 50
% Addition → H ₂ flow rate ÷ (H ₂ flow rate + C ₄ F ₈ flow rate) × 10
0 = 50% ・ Pressure: 5mTorr ・ High frequency power output: 13.56MHz, 1.0KW ・ Pulse modulation specification: ON time fixed at 5μsec ・ Bias voltage: 200V

The shorter the ON time, the higher the deposition rate of the reaction product. Since it is expected that the selection ratio can be improved by increasing the deposition rate, it is generally considered necessary to shorten the ON time in order to improve the selection ratio.

From the results shown in FIGS. 6 and 7, it can be seen that the shortening of the ON time tends to improve the etching rate of SiO ₂ and also the deposition rate of the reaction product.
The conditions for increasing the selection ratio and the discharge conditions can be oriented.

FIG. 8 shows the relationship between the pulse modulation ON time and the electron density when the pulse modulation OFF time is fixed at 5 μsec and 20 μsec, respectively. The discharge conditions are as follows. On the street.

-Etching gas: Ar-Pressure: 2 mTorr-High frequency power output: 13.56 MHz, 1.0 KW

Even if the ON time is changed, the electron density does not change greatly, but when this phenomenon is pulse-modulated,
This is considered to be one of the reasons why the etching rate of SiO ₂ does not decrease.

FIG. 9 shows the relationship between the pulse modulation ON time and the electron temperature when the pulse modulation OFF time is fixed at 5 μsec and 20 μsec, respectively. The discharge conditions are as follows. On the street.

-Etching gas: Ar-Pressure: 2 mTorr-High frequency power output: 13.56 MHz, 1.0 KW

When the OFF time is 20 μsec, the electron temperature shows a large change when the ON time is changed, but this phenomenon changes the dissociated state of the gas. OFF time is 5
In the case of μsec, there is no large change in the electron temperature, so when changing the gas dissociation state, it is necessary to set the OFF time to an appropriate length.

Further, FIG. 9 shows that when the OFF time is 20 μsec, the change in electron temperature is large, and therefore the effect of changing the dissociation state of the reaction gas is large.

FIG. 10 shows the mixing ratio of the reactive gas and SiO ₂
3 is a diagram showing the relationship between the etching rate of Si and Si and the selection ratio (etching rate ratio) of SiO ₂ and Si.

In both (A) and (B), high frequency power pulse-modulated at 100 KHz is applied to the coil 3.
This is a characteristic when the frequency of the bias power applied to the flat plate electrode 5 on which the semiconductor sample is placed is 100 KHz and the mutual phase difference is 0 degrees and 180 degrees. The etching conditions are as follows.

・ Etching gas: C ₄ F ₈ + H ₂・ Pressure: 5 mTorr ・ High-frequency output power: 13.56 MHz, 1.0 KW ・ Pulse modulation specification: ON time 5 μsec OFF time 5 μsec ・ Bias power frequency: 100 KHz ・ Bias voltage: -200V

FIG. 11 shows the phase relationship between the pulse-modulated high-frequency power applied to the coil 3 and the bias power applied to the plate electrode 5 on which the semiconductor sample is placed. (A) in the figure
Shows a pulse-modulated waveform, and FIG. 9B shows a state in which the bias power becomes “−” when the pulse-modulated wave is ON and “+” when it is OFF. (C) is the state of (b) and "+"
"-" Is reversed. When the phase difference is 0 degree, the selection ratio becomes infinite when the mixing ratio of H ₂ is 50%, but when the phase difference is 180 degrees, the mixing ratio of H ₂ is 40%.
%.

By controlling the phase difference between the phase of the pulse-modulated high frequency power applied to the coil 3 and the bias power applied to the flat plate electrode 5 on which the semiconductor sample is mounted,
Since it is possible to change the etching conditions such as the gas mixture ratio to obtain the same selection ratio (etching rate ratio),
By using the method of controlling the phase, a margin can be given to the etching conditions.

[0056]

As described above, according to the present invention, the high-frequency power for plasma generation is pulse-modulated to improve the selectivity between the film and the base (etching rate ratio) without lowering the etching rate. Further, by making the frequency of the pulse modulation and the frequency of the bias power the same and controlling the phase difference between the high frequency powers, it is possible to widen the margin of the etching condition.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an outline of an embodiment of the present invention.

FIG. 2 is a configuration diagram showing an outline of another embodiment of the present invention.

FIG. 3 is an explanatory diagram illustrating a pulse modulated wave.

FIG. 4 is a diagram showing a relationship between a gas mixture ratio, an etching rate, and a selection ratio.

FIG. 5 is a diagram showing the relationship between the OFF time of pulse modulation and the etching rates of SiO ₂ and Si.

FIG. 6 is a diagram showing the relationship between the ON time of pulse modulation and the etching rates of SiO ₂ and Si.

FIG. 7 is a diagram showing the relationship between the ON time of pulse modulation and the deposition rate of reaction products.

FIG. 8 is a diagram showing a relationship between ON time of pulse modulation and electron density.

FIG. 9 is a diagram showing a relationship between ON time of pulse modulation and electron temperature.

10 (A) and (B) are diagrams showing a relationship between a gas mixture ratio, an etching rate, and a selection ratio.

FIG. 11 is a diagram showing the relationship between the phase of pulse-modulated high-frequency power and the phase of bias power.

FIG. 12 is a configuration diagram showing an outline of a conventional example.

[Explanation of symbols]

 1 Processing Room 2 Reaction Chamber 3 Coil 4 Magnetic Field Generating Coil 5 Plate Electrode 6 Pedestal 7 Matching Machine 8 High Frequency Power Supply 9 Matching Machine 10 Bias Power Supply 11 Workpiece 12 High Frequency Power Supply 13 Phase Shifter

Claims (8)

[Claims] 1. A plasma etching for etching an object to be processed by using a plasma generated by applying a magnetic field in the axial direction of the reaction chamber and applying high-frequency power to a coil wound around the reaction chamber. In the plasma etching method, the high frequency power applied to the coil is pulsed. 2. The plasma etching method according to claim 1, wherein the etching rate is changed by fixing the ON time of the pulsed high-frequency power and changing the OFF time. 3. The plasma etching method according to claim 1, wherein the etching time is changed by fixing the OFF time of the pulsed high frequency power and changing the ON time. 4. The OFF time of the pulsed high frequency power is fixed and the ON time is changed to change the deposition rate of the reaction product and change the etching rate ratio between the film to be etched and the underlayer. Dry etching method. 5. A cycle of pulsed high frequency power applied to a coil wound around a reaction chamber made of an insulator and a cycle of AC power for bias voltage generation applied to a flat electrode on which a semiconductor sample is mounted. And a phase difference of those frequencies is 0 degree or 180 degrees, and a margin is given to the etching conditions, especially the gas mixture ratio. 6. A magnetic field generating means for applying a magnetic field in the axial direction of the reaction chamber, a coil wound around the reaction chamber, and a high frequency power applying means for applying pulsed high frequency power to the coil, A plasma etching apparatus comprising: a flat plate electrode on which a processed object is placed, and a bias power source for applying a bias power to the flat plate electrode. 7. The plasma etching apparatus according to claim 6, further comprising means for independently changing the ON time and the OFF time of the ON / OFF time of the pulsed high frequency power. 8. A phase shifter for making the pulse modulation frequency of the high frequency power applied to the coil and the frequency of the bias power applied to the plate electrode the same and for setting the phase of the frequency of both powers arbitrarily. Alternatively, the plasma etching apparatus according to claim 7.