JPH0770510B2 - Plasma processing device - Google Patents

Description

Description: (a) Field of Industrial Application The present invention relates to a plasma processing apparatus used for etching or depositing, and more particularly to improvement of a plasma processing apparatus using microwaves.

Preliminarily, many processes using plasma have been performed in the manufacturing process of semiconductor devices.

Plasma contains a lot of electrons, ions, radicals (activated neutral particles) and stable neutral molecules therein, and most plasma treatments are performed by mainly using the ions and radicals therein. ing.

In particular, since ions have an electric charge, they can be electrostatically accelerated, and the directionality and acceleration energy can be easily controlled, and the range of use is wide.

On the other hand, since radicals are electrically neutral, they cannot be electrostatically manipulated and their directionality cannot be controlled.

Therefore, when performing anisotropic etching suitable for forming a fine pattern, it is common to accelerate ions by an electric field.

(B) Conventional Technology The reactive ion etching (RIE) processing schematically shown in FIG. 2 is the most commonly used conventional anisotropic etching processing.

The RIE process is performed by the etching electrode 2 on which the workpiece 1 is mounted.
A high frequency voltage RF is applied between the counter electrode 3 and the counter electrode 3 for etching. At this time, the ion 4 is a sheath (ion sheath) of ions formed between the plasma 5 and the etching electrode 2 (surface of the workpiece). It is electrostatically accelerated by 6 and is incident on the surface of the workpiece. The acceleration energy at this time is usually 10
It is said that it is about 0 eV, and one of the major characteristics of the RIE processing is that the ions accelerated by the acceleration energy can perform processing in the direction perpendicular to the etching electrode surface. (In the figure, 7 is a susceptor, 8 is a shield, 9 is an insulator, In is a gas introduction pipe, Ex is an exhaust pipe, RF is a high-frequency oscillator, and GND is a ground part.) Reactive as an attempt to utilize the directionality of ions・ Beam ・ Ion etching (RIBE) processing is available.
This is done by electrostatically extracting ions by plasma and irradiating the beam to the work piece, and the ion shower device of Matsuo et al. Is a typical one (JP-A-55-55).
141729). The acceleration energy of ions in this RIBE process is
Generally about 500 to 1000 eV.

As described above, various processing mainly using ions has been carried out, but on the other hand, many drawbacks due to the large acceleration energy of ions have been pointed out, for example, device damage and resist damage have become problems. Here, device damage is a phenomenon in which the characteristics of the device are impaired due to defects caused by ion bombardment, and resist damage is a phenomenon in which the resist surface is carbonized by ion bombardment and removal of the resist becomes difficult.

Many attempts have been made to avoid the damage caused by ions and electrons from such plasma, and the representative one is chemical dry etching (CDE) by Horiike et al.
The law (Japanese Patent Publication No. 53-14472). Since this is a method of extracting active particles generated by plasma rather than ions and etching, it has a drawback that the processing direction cannot be controlled and only isotropic etching can be performed.

Therefore, a method that can perform anisotropic processing with less damage is being studied, one of which is a method of lowering the acceleration energy of ions, and the other is a method of spraying neutral active particles with a differential pressure. A typical method for lowering the acceleration energy is the low-energy ion beam method (J. Electrochem, Soc Vol 128 No.5 May 1981 “Low Ene” by HR Kaufman et al.
rgy Ion Beam Etching ") and the other is microwave plasma etching (J. Electrochem, Soc) by Suzuki et al.
Vol 126 No 6June 1979 “The Roles of Ions and Neutr
al Active Species in Microwave Plasuma Etching ")
Is.

Both of them basically use the floating potential of plasma to anisotropically etch the work piece, and the acceleration energy of the ions at this time is about 20 eV, and the damage is very small.
However, the former has a drawback that the etching rate is extremely slow because it depends on only ions for etching, and the latter has a workpiece to be processed in the plasma, so that electrons are incident and the temperature rises. If the number increases, there is a defect that anisotropic etching cannot be performed.

Akitani is trying to spray the neutral particles with a differential pressure (3rd Dry Process Symposium October 26
−27,1981 Tokyo “Directional dry etching of silico
n by a reactive nozzl-jet ").

In this method, plasma generated under a pressure of 0.1 to 1 Torr is ejected from a nozzle into a chamber of 10 ^-4 to 10 ^-5 Torr, and anisotropic etching can be realized by neutral active particles. However, this method has a drawback that the nozzle diameter is small (0.5 to 1 mmφ) in order to provide a differential pressure, so that a large area cannot be uniformly etched and the etching rate becomes slow.

(C) Problems to be Solved by the Invention The present invention relates to the above conventional anisotropic plasma processing method,
When the processing rate is increased, the damage to the workpiece is large, and when the damage is reduced, the processing rate is extremely slow, and the temperature of the workpiece rises during the processing. It tries to solve the problem.

(D) Means for Solving Problems The above-mentioned problems are caused by a plasma processing chamber provided with a microwave incidence means and a gas introduction means, and a magnetic field for confining plasma in the microwave irradiation region in the plasma processing chamber. A plasma processing apparatus according to the present invention, comprising: a magnetic field forming means for forming a magnetic field; and a work piece supporting means for holding a work piece outside the magnetic field at a distance less than the mean free path of active particles from the magnetic field. Will be solved by.

(E) Action In the plasma processing using the apparatus of the present invention, the gas pressure of the reaction gas such as etching gas is set to an extremely low gas pressure of about 10 ⁻⁴ Torr, and electrons are generated by electron cyclotron resonance due to the action of microwave and magnetic field. The density is increased and the electrons are accelerated rapidly, which causes the etching gas to be plasma-heated to generate a large amount of ions and neutral active particles in the etching gas.

By doing so, the electrons are confined in the magnetic bottle of the magnetic field, but particles such as neutral active particles and ions with a large mass are not confined in the magnetic field and jump out of the magnetic field only by their thermal kinetic energy. come. At this time, since the low gas pressure is used as described above, the mean free path of these particles is expanded to about 50 cm to improve workability.

Then, the workpiece, for example, the substrate to be processed is arranged at a position away from the magnetic field by a distance equal to or smaller than the mean free path of the particles. Therefore, only primary particles generated by the plasma are incident on the surface to be processed, and secondary particles generated by collision of the primary particles with gas molecules are not incident.

Therefore, by placing a substrate to be processed on which a mask film having a desired thickness is deposited at a distance less than the mean free path of these particles from the above position, that is, the magnetic field, the mask film is formed on the surface of the substrate to be processed. It is possible to selectively apply only particles that are not electrostatically accelerated but are accelerated by only thermal kinetic energy, which particles fly in a direction substantially perpendicular to the surface of the substrate to be processed through the holes of the.

Thus, anisotropic etching in a direction perpendicular to the surface of the substrate to be processed is performed without damaging the surface of the substrate to be processed or the resist mask as in the conventional case, and the neutral particles deposited on the surface of the substrate are also removed. A high etching rate is obtained because it is activated by being hit by ions and contributes to etching.

(F) Example Hereinafter, the present invention will be specifically described with reference to an example shown in FIG.

FIG. 1 is a schematic sectional view showing an embodiment of the plasma processing apparatus of the present invention.

The plasma processing apparatus of the present invention, for example, as shown in FIG.
The upper portion has a μ wave introducing means 13 connected to a waveguide 12 via a microwave (μ wave) transmitting window 11, and the side portion has a reaction gas introducing means 14 made of an introducing pipe, and a lower portion. In order to form a plasma processing chamber 16 having an exhaust means 15 composed of vacuum piping connected to a vacuum device, and a mirror magnetic field 17 for confining plasma (electrons) e in the μ wave irradiation region in the processing chamber 16. Magnetic field forming means 18 composed of magnets and coils arranged around the processing chamber 16, and mean freeness of particles generated by the plasma heating from the magnetic field 17 outside the magnetic field 17 formed inside the processing chamber 16. The workpiece supporting means 20 is comprised of a stage for holding the substrate 19 to be processed at a distance d below the stroke.

When the polycrystalline silicon layer is patterned on the substrate to be processed in which the polycrystalline silicon layer is formed on the insulating film such as silicon dioxide by the apparatus of the present invention, the thickness of the polycrystalline silicon layer on the polycrystalline silicon layer is increased. After forming a predetermined mask pattern (not shown) made of a resist having a thickness of about 2 μm, the substrate to be processed is mounted on the workpiece support means 20 and, for example, fluorine gas (F ₂ ) is placed in the plasma processing chamber. To
The gas is introduced at a flow rate of 5 cc / min, and a predetermined evacuation is performed by a vacuum device to bring the inside of the plasma processing chamber 16 to a fluorine gas pressure of, for example, about 1 × 10 ⁻⁴ Torr.

Then, for example, 2.45 GHz, about 500w μ wave is introduced by the μ wave introducing unit 13, and, for example, 800 to 9 by the magnetic field forming unit 18.
A magnetic field of about 00 G is formed, and plasma is generated in the magnetic field by the electron cyclotron resonance. At this time, as described above, the electrons are confined in the magnetic field, and particles such as fluorine ions and fluorine radicals generated by heating by the plasma are not confined in the magnetic field and are ejected by thermal kinetic energy. Since the mean free path is about 50 cm at the above gas pressure, the surface of the substrate to be processed 19 and the magnetic field are
The distance of 17 is adjusted to less than that in advance.

As a result, the surface of the substrate to be processed is irradiated with only fluorine ions and fluorine radicals which are directly ejected from the magnetic field due to thermal motion, and fluorine ions and ions which are irradiated from an angle extremely inclined with respect to the substrate surface. Since there are no secondary particles such as fluorine radicals, the lower portion of the resist mask is not greatly laterally etched through the openings of the resist mask.

Further, as the etching progresses, the depth of the recess formed in the polycrystalline silicon layer is added to the depth of the opening of the resist mask, so that the fluorine ion having a direction more perpendicular to the substrate surface is obtained. Only fluorine radicals are selected, and etching having anisotropy substantially perpendicular to the substrate surface proceeds.

Thus, the polycrystalline silicon layer is patterned substantially perpendicular to the substrate surface.

Also, under the above conditions, it is a value that is sufficiently practical to be 500.
A relatively large etching rate of about Å / min is obtained, and fluorine ions and fluorine radicals are not electrostatically accelerated but are accelerated only by the energy of their thermal kinetic energy and collide with the surface of the substrate to be processed. Damage to the processed substrate and resist mask is greatly reduced compared to the conventional one.

Furthermore, since the electrons are confined in the magnetic bottle and are not irradiated on the surface of the substrate to be processed, the temperature rise of the substrate to be processed is prevented.

Of course, there is no problem if a torus magnetic field is used in place of the magnetic mirror shown in the above embodiment to confine the plasma.

In addition, the plasma processing apparatus of the present invention is not limited to the above-described etching processing, but is also applicable to deposit processing of semiconductor layers, insulating layers and the like.

(G) Effects of the Invention As described above, when the plasma processing apparatus of the present invention is used, the damage to the work piece is extremely reduced and it has anisotropy perpendicular to the work surface at a high processing rate. Plasma processing can be performed, and the temperature rise of the workpiece can be prevented.

Therefore, the present invention is extremely effective in the manufacturing process of semiconductor devices.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing an embodiment of a plasma processing apparatus of the present invention, and FIG. 2 is a schematic sectional view of a reactive ion etching apparatus. In the figure, 11 is a microwave transmission window, 12 is a waveguide, 13 is microwave introduction means, 14 is reaction gas introduction means, 15 is exhaust means, 16 is a plasma processing chamber, 17 is a mirror magnetic field, 18 is a magnetic field formation. Means, 19 a substrate to be processed, 20 a means for supporting a workpiece, d
Is a distance less than the mean free path of particles, and e is plasma (electrons).

Claims (1)

[Claims] 1. A plasma processing chamber provided with a microwave incidence means and a gas introducing means, a magnetic field forming means for forming a magnetic field for confining plasma in the microwave irradiation region in the plasma processing chamber, and a magnetic field of the magnetic field. A plasma processing apparatus, further comprising: a workpiece support means for holding a workpiece at a distance less than the mean free path of the active particles from the magnetic field.