JPH07211492A - Method and device for plasma processing - Google Patents

Abstract

PURPOSE:To generate a stable discharge under medium pressure using simple constitution so as to make possible ashing at high speed by supplying the required reaction gas in a predetermined quantity to a rare gas generating a plasma. CONSTITUTION:An electric field, generated by a feeding electrode 11 having a dielectric substance 13 and by an opposite electrode 11 serving also as a casing, ionizes a rare gas introduced from a gas introducing pipe 20, to generate a plasma. A gas for supplying oxygen to the rare gas is added to the rare gas as a reaction gas by 3% or less. Then the reaction gas is allowed to pass through the plasma and blown toward a substrate, ashing any organic material on the surface of the substrate at high speed. The plasma generator generates a stable discharge under medium pressures of 5-150Torr and has simple constitution into which the dielectric substance is inserted so as to eliminate the need for forming each electrode surface into a specific shape.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of using stable discharge at a medium pressure of 5 to 150 Torr for processing a substrate and an apparatus for realizing the method. Disclosed is a method and apparatus for inexpensively and simply providing an organic substance removal method effective for LSI processes, active matrix LCD processes, etc., such as removal of organic substances such as resist (ashing) and removal of residual organic substances after cleaning a glass substrate. It is a thing.

[0002]

2. Description of the Related Art In semiconductor processes such as LSI and active matrix LCD, photoresist of photosensitive resin is used for mask formation. The photoresist is removed after a predetermined process, but it is usually removed by ashing. In general, the reason is that the resist film is hardened and carbonized so that it cannot be removed by the stripping solution.

Ashing removes organic substances by chemically reacting active oxygen molecules or ozone molecules or oxygen atoms generated by electric discharge with a resist film which is an organic substance to ash it. It can be said that it is a kind.

In order to proceed with the combustion reaction, it is necessary to generate radicals (generally collectively referred to as chemically active molecules, atoms, etc.) that cause an oxidation reaction. Radicals related to the oxidation reaction include oxygen atoms / molecules such as oxygen molecule, excited oxygen molecule, oxygen molecule ion, oxygen atom, oxygen atom ion, ozone molecule, excited ozone molecule, and ozone molecule ion. The oxygen atoms / molecules have energy levels of a ground state and various excited states. In addition to oxygen atoms / molecules, ground state or excited state oxygen dinitride (N
₂ O), carbon monoxide, carbon dioxide and other oxygen compounds.

Generally, the more reactive the radical, the faster the reaction rate. As is well known, the reactivity increases in the order of oxygen molecules, ozone molecules, and oxygen atoms, so an atmosphere with more oxygen atoms has higher throughput and higher productivity, which is advantageous for ashing. Become. On the other hand, if the number of highly reactive radicals is too large, the damage to the substrate becomes large, which is not preferable. Therefore, appropriate process conditions exist depending on the substrate.

Since the combustion reaction is a reaction on the surface, the reaction temperature as well as the number of radicals is an important factor for the reaction rate. Generally, the higher the reaction temperature (substrate temperature), the higher the reaction rate. However, since most resists are thermosetting resins, if the substrate temperature is set too high, the removal rate will rather decrease. Generally, it is common to process at a temperature of about 200 degrees Celsius.

As a method of generating radicals involving oxygen, a method using discharge and a method using ultraviolet irradiation are known.

As a method using electric discharge, there are a method of generating glow discharge plasma under reduced pressure and a method of corona discharge under atmospheric pressure.

The method of generating glow discharge plasma under reduced pressure is generally called low pressure glow discharge. The processed substrate is held in a reaction vessel capable of reducing the pressure, and an appropriate reaction gas (oxygen, nitric oxide, carbon oxide, etc.) in the reaction vessel is controlled to a constant pressure, and a pair of electrodes or inductive coupling is applied to the reaction gas. Is a method of applying an electromagnetic field to ionize the reaction gas. The applied electromagnetic field is 2.4 from DC.
In a wide range up to microwaves of about 5 GHz, electromagnetic energy is generally applied by a pair of electrodes from DC to RF frequencies of about several MHz, and by inductive coupling at RF frequencies or higher. With microwaves of about 2.45 GHz, quartz, which can be a wall material of the vacuum container, can pass through as a traveling wave, and therefore microwave plasma may supply energy as electromagnetic waves and ionize without using electrodes. In this case, the electromagnetic wave is supplied as a traveling wave, a standing wave, or a mode in which the traveling wave and the standing wave are mixed. Generally, the reaction gas is exhausted by an exhaust device attached to the reaction vessel and simultaneously supplied by a reaction gas supply device.

The method using corona discharge under atmospheric pressure is a method in which a nonequilibrium electric field is created under atmospheric pressure and corona discharge is generated under the electric field to mainly generate ozone. In principle, it is not suitable for uniform processing because it uses a non-equilibrium electric field.
The main reason for generating ozone is atmospheric pressure because the mean free path of collision is small, and oxygen atom ions with large internal energy repeatedly collide with other neutral particles, resulting in a metastable state with longer life. This is because it becomes ozone molecules that it has.

The method of irradiating with ultraviolet rays is to use oxygen or dinitrogen monoxide or the like at a wavelength of 200 nm or less and 200 to 300
This is a method of irradiating a light source having a wavelength of nm (generally, a low pressure mercury lamp is often used) to generate ozone and excited ozone. Since the method of irradiating with ultraviolet rays is not a method of generating ions in principle, only ozone is generated in this case. (However, two-photon absorption occurs with a small probability, and ions may be generated.)

The method of generating radicals involving oxygen is roughly classified into a corona discharge method for generating ozone, an ultraviolet irradiation method, and a low pressure glow method for generating various radicals including oxygen atoms and ions. be able to. The former method that mainly generates ozone causes less damage to the substrate, but the method that mainly generates oxygen atoms and ions has a significantly higher processing speed. In reality, a processing method using low-pressure glow discharge is used. It is overwhelmingly adopted.

[0013]

As described above, a low-pressure glow discharge system is often adopted as the ashing device. Although it is certain that the system has a certain processing capacity, various restrictions occur due to the condition that the reaction space must be maintained at a low pressure.

That is, the cost of the apparatus for installing the exhaust device for reducing the pressure increases, the cost of the reaction container for maintaining sufficient mechanical strength in the reduced pressure state, and the transport mechanism under the high vacuum state. Due to the difficulty of automation, the automation mechanism becomes complicated, the equipment weight increases due to the installation of the exhaust device and the weight of the reaction container, the installation floor area increases, and the throughput decreases due to the vacuum evacuation time and the reaction container leak time. is there.

Further, damage to the substrate caused by processing by the action of ions cannot be ignored. This is a problem that has become more prominent due to the recent higher integration and higher performance of semiconductors. It is understood that the ion damage to the substrate is due to the formation of an ion sheath in the plasma. The ion sheath is generated when the electron temperature and the ion temperature in the plasma are not the same and are in a thermally non-equilibrium state. Electron temperature in general low-pressure glow discharge is several e
It is said that V (tens of thousands of degrees) and ion temperature is several tens of meV (several hundred degrees). Generally, the lower the pressure, the higher the electron temperature. (It is said that the electron temperature is a dozen eV in ECR discharge that discharges at a low pressure.) Therefore, it is considered that the damage to the substrate by the ions increases as the pressure decreases, and empirically the damage decreases as the pressure decreases.

Both of the above problems are caused by processing under reduced pressure. On the other hand, the method of generating and treating ozone under atmospheric pressure has advantages such as simplicity of the apparatus, low cost, and damage-free, but its practical use is limited to some applications in terms of treatment speed. Therefore, there has been a demand for a technique for realizing an ashing device that has a simple exhaust device, low device cost, and less damage.

[0017]

In order to solve the above-mentioned problems, the present inventors have 5-150 Torr, preferably 50-Torr.
A stable discharge was obtained under a pressure of -100 Torr, which was solved by applying it to the ashing process.

The discharge device of the present inventors has a structure in which a pair of concentric cylindrical or parallel plate electrodes are provided, and a dielectric is inserted on one side or both sides of the opposing surfaces of the electrodes. The shape of the electrode surface does not need to be comb-shaped or needle-shaped. A rare gas (helium, neon, argon, xenon, krypton) is applied to the gap between the dielectrics or between the dielectric electrodes.
The rare gas is ionized by applying an alternating electric field to the electrode while flowing in a flow state at a pressure of about 0 Torr.

In consideration of application to process plasma, line plasma formed by parallel plate electrodes is preferable to beam plasma formed by concentric cylindrical electrodes.

The line plasma formed by the parallel plate electrodes will be described below with reference to FIG. Feeding electrode (1
1) and a counter electrode (12) which also serves as a casing, and a dielectric (13) provided therebetween are arranged. These electrodes are held by the front housing (16), the upper lid (17), the insulator structural member (18), and the insulator electrode holding member (19). Power supply (14) to the electrode through the power supply terminal (15)
More electric field is applied. The rare gas is supplied from the gas introduction pipe (20) and flows out to the outside through the plasma generation region (21). The gas is supplied via a flow rate adjusting mechanism (not shown). The material of the electrode (11) may be a conductor, but when a reactive gas is added to a rare gas to use it for etching, ashing, deposition, etc.,
Materials that are not attacked by reactive gases are preferred. For example, when a halogen-based gas is added, a chemically stable material such as gold, silver, platinum, or stainless steel is preferable rather than an etchable material such as tungsten.

The surface of the electrode (11) does not need to be positively provided with irregularities such as a comb shape or a needle shape, and can be a flat surface. By making it flat, the gas flow becomes closer to an ideal laminar flow, and the plasma can be made more uniform. There is no particular flatness agreement, but there is no problem if it is sufficiently flat compared to the size of the electrode. In terms of numerical values, a 5-point average roughness (Ra) of about 10 μm is sufficient.

The dielectric material (13) prevents generation of arcing, and preferably has a dielectric constant as high as possible. The higher the dielectric constant, the lower the frequency of discharge possible. It is preferable that the dielectric (13) is thin, but if it is too thin, dielectric breakdown occurs, which is not preferable. In the case of a sintered body, it is necessary to be careful to use an insulator without pinholes. This is because if there is a pinhole, dielectric breakdown will occur from that part. Dielectric (1
As the material of 3), the dielectric constant of alumina or more (relative dielectric constant =
Materials having about 9) are preferred. Specifically, it is alumina, zirconia, PZT, YSZ, STO or the like. Quartz is not so preferable because it has a low relative dielectric constant, but it can be used when the frequency of the applied voltage is set to an RF frequency of 13.56 MHz or higher. Empirically, the thickness of the dielectric (13) is preferably 50 μm or more and 50 mm or less. If it is thinner than 50 μm, dielectric breakdown occurs, and if it is thicker than 50 mm, it becomes difficult to start discharge.

The frequency of the electric field applied to the electrode (11) can be used from a commercial frequency of 50 Hz to a microwave of about 2.45 GHz. The higher the frequency, the easier the discharge can start, but the cost of the power supply (14) increases. When power is applied is expressed by the power density normalized by the electrode area, 5000 W from 5W / cm ² / cm ²
Between is suitable. The value is larger than that in the low-pressure glow discharge, but in consideration of the medium pressure of 5 Torr or more, it is an appropriate value as the electric field strength consumed per gas particle. The lower limit of the above value means the lower limit of the voltage required for sustaining the discharge, and the upper limit indicates the device breakdown limit caused by heating in plasma. Therefore, the upper limit may be further increased by taking measures such as cooling the device.

Various processes can be performed by adding a reaction gas to the rare gas. The reaction gas is preferably supplied via a flow rate adjusting mechanism. The reaction gas may be supplied as a mixture with a rare gas from the gas introduction pipe (20), or after the rare gas has passed through the plasma generation region (21), it may be supplied to the vicinity of the processing substrate through a nozzle (not shown). May be supplied.

When the reaction gas is mixed with the rare gas and supplied, the inventors of the present invention have conducted experiments and found that the time during which the reaction gas is present in the plasma generation region is important for the substrate processing ability. ing. That is, the processing capacity greatly changes depending on the relationship between the length of the plasma generation region in the gas flow direction and the gas flow rate. If the gas residence time in the plasma generation region is short (that is, the gas flow rate is high or the length of the plasma generation region in the gas flow direction is short), the reaction gas is pushed out of the plasma region before being sufficiently excited. Get lost. On the contrary, when the gas retention time in the plasma generation region is long (that is, the gas flow rate is small or the length of the plasma generation region in the gas flow direction is long), the excited reaction gases frequently collide with each other, and the active radicals are not separated from each other. It is considered that the reactivity is lost due to the association and the like. The optimum residence time for ashing is 10 μsec to 100
I liked msec. The length of the plasma generation region in the gas flow direction can be approximately represented by the length of the power supply electrode.

In the case of ashing, oxygen can be used as a reaction gas. The relationship between the oxygen concentration and the ashing rate decreases as the oxygen concentration increases, as shown in FIG. Since the ashing is not performed when the oxygen concentration is 0%, it indicates that the optimum value exists between 0 and 0.25%. This is because oxygen is negatively charged,
It is suggested that when oxygen is present more than necessary, electrons in the plasma are trapped in oxygen and the plasma density is reduced (quenching). Therefore, the oxygen concentration is preferably 3% or less, more preferably 1% or less. This is a relationship that holds in the length of the plasma generation region in the gas flow direction and the gas flow rate as long as the gas retention time is within the above range.

The effective discharge length of this device can be increased as long as there is a machining accuracy that can ensure the uniformity of the electrode spacing. However, at the current processing accuracy (100 μm), the effective discharge length is about 1 m at most. However, it goes without saying that the effective discharge length becomes longer as the processing accuracy is improved. The upper limit of the electrode interval is limited by whether or not a voltage capable of starting discharge can be applied. Further, the lower limit is limited to the extent that the gas flow velocity does not become too fast. Specifically, 50 μm to 50 mm is suitable.

[0028]

EXAMPLE In this example, oxygen is used as a reaction gas and argon is used as a rare gas. The line plasma generator used previously was used for the plasma generator.

[Preparation of Substrate] As the substrate, a 100 mm square glass substrate was used. This substrate is used in the production process of TFTs for LCDs, and the ashing performance in resist stripping after ion doping for channel formation was examined.

The resist is a positive type resist (manufactured by Tokyo Ohka O
FPR-800) with a viscosity of 30 cps was used. First, a resist was applied on the substrate by spin coating and prebaked at 80 degrees Celsius for 20 minutes.

Next, a mask was applied, and the film was exposed to ultraviolet rays (2 mW) having a central wavelength of 365 nm for 20 seconds, and then developed with a developer NMD3 (manufactured by Tokyo Ohka) for 1 minute. After washing with water, post-baking was performed at 130 degrees Celsius for 30 minutes. The resist film thickness after post-baking was 2 μm.

Then, 1 × 10 boron was added by implantation.
Ion doping was performed at ¹⁹ atom / cm ² .

Since the resist film which has undergone the above-mentioned steps was heated by ion-impantation, it could hardly be stripped by the stripping solution stripper 10 (manufactured by Tokyo Ohka).

[Ashing] The resist film on the substrate was ashed by using the above apparatus. The discharge conditions are described below. Electrode material Stainless steel (SUS416) Effective discharge length 150 mm Electrode dielectric spacing 5 mm Electrode length 20 mm Dielectric thickness 1 mm Dielectric material Zirconia gas retention time 10 msec Reaction pressure 100 torr Applied electric field frequency 13.56 MHz Applied power 100 W / cm ² Reaction gas Oxygen reaction gas mixing method Noble gas (argon) mixing method

When plasma was generated under the above conditions and the resist on the substrate was ashed, it was confirmed that the resist was ashed and removed. The distance between the opening of the discharge device and the surface of the substrate was 2 mm.

However, in this embodiment, since ashing can be performed only in a line shape, a method of arranging a plurality of lines and scanning the lines in the direction perpendicular to the line direction is useful.

Further, the characteristics of the TFT manufactured by using this example were sufficiently good, and no result was found that the TFT was damaged by the substrate treatment of the present invention.

[0038]

As described above, when ashing is performed by the substrate processing method of the present invention, the ashing speed is improved and the substrate is almost free from damage, so that a highly reliable semiconductor device can be manufactured. Further, since the vacuum exhaust device is simple, the device configuration is simple and the device cost can be kept low.

[Brief description of drawings]

FIG. 1 shows a cross-sectional view of a discharge device of the present invention.

FIG. 2 shows the ashing rate dependence of oxygen concentration with respect to a rare gas.

[Explanation of symbols]

 11 Feeding Electrode 12 Counter Electrode that also serves as a Housing 13 Dielectric 14 Power Supply 15 Feeding Terminal 16 Front Housing 17 Upper Lid 18 Insulator Structural Member 19 Insulator Electrode Holding Member 20 Gas Introducing Tube 21 Plasma Generation Region

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical indication location H01L 21/3065 (72) Inventor Shunpei Yamazaki 398 Hase, Atsugi-shi, Kanagawa Semiconductor Conductor Energy Research Co., Ltd. In-house

Claims (7)

[Claims] 1. A dielectric is disposed between a pair of concentric cylindrical or parallel plate electrodes in contact with one or both of the electrodes, and between the electrodes and the dielectric or between the pair of dielectrics. A rare gas is caused to flow in the vicinity of a pressure of 5 to 150 Torr, and a reactive gas which is added to the rare gas and supplies active oxygen is mixed with plasma generated by ionizing the rare gas by an electric field applied between the electrodes. When the reactive gas that has passed through the plasma is blown onto the substrate by the flow of the rare gas, active species generated by receiving plasma energy from the reactive gas may ash organic substances on the substrate surface. Characteristic plasma processing method 2. The rare gas according to claim 1, wherein the rare gas is argon or helium or a mixed gas of argon and helium, and the reactive gas for supplying the active oxygen is one selected from oxygen, dinitrogen monoxide, and carbon monoxide. Processing method characterized in that it is a mixed gas or a plurality of mixed gases 3. The reaction gas for supplying the active oxygen according to claim 1, is 3% or less with respect to the rare gas, preferably 1
% Or less, a plasma processing method. 4. The plasma processing method according to claim 1, wherein the organic substance on the surface of the substrate is a resist. 5. A dielectric is disposed between a pair of concentric cylindrical or parallel plate electrodes in contact with one or both of the electrodes, and between the electrodes and the dielectric or between the pair of dielectrics. In a plasma processing apparatus, in which a rare gas is caused to flow near a pressure of 5 to 150 Torr, and the rare gas is ionized by an electric field applied between the electrodes to generate plasma.
Means for mixing a reactive gas for supplying active oxygen into the plasma, and the reactive gas that has passed through the plasma and the activated species generated by the reactive gas receiving plasma energy together with the rare gas are blown to the substrate. Plasma processing apparatus having means for attaching 6. The gas according to claim 5, wherein the rare gas is argon or helium or a mixed gas of argon and helium, and the reactive gas for supplying the active oxygen is one selected from oxygen, dinitrogen monoxide, and carbon monoxide. Plasma processing apparatus characterized in that it is a mixed gas or a plurality of mixed gases 7. The plasma processing apparatus according to claim 5, wherein the organic substance on the surface of the substrate is a resist.