JP3113344B2 - Dual frequency excitation plasma device using rotating magnetic field - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the manufacture of semiconductor devices such as ICs and LSIs, and more particularly to a plasma processing apparatus using a rotating magnetic field used in a dry etching apparatus.

[0002]

2. Description of the Related Art With the increase in the degree of integration of semiconductor integrated circuits, miniaturization of devices has been required, and development of three-dimensional integrated circuits has been promoted. ing. The concept of the dry etching method using a rotating magnetic field was introduced in 1981.
Since it was announced by BM's Hymen, it has been widely used as a method for increasing the plasma density together with a triode type reactive ion etching apparatus.

In the magnetron system in which an electric field and a magnetic field are orthogonal to each other, so-called cyclotron motion occurs in a direction (E × B) perpendicular to a plane formed by the electric field E and the magnetic field B due to a synergistic effect of the electric field and the magnetic field. The electron collides with the molecules to improve the ion efficiency and increase the etching rate. In addition, the mobility of electrons is significantly reduced by the magnetic field,
The speed of electrons reaching the electrode which is in a DC floating state is reduced, the energy of ions colliding with the electrode can be reduced, and damage to the wafer surface can be reduced.

In a device using a rotating magnetic field, a high-density plasma is rotated on a wafer by rotating a magnetic field generated by two or three pairs of electromagnetic coils, thereby promoting plasma ionization. However, the conventional apparatus has the following problems. First of all, wafers can have a maximum diameter of 8 inches (about 20.3 cm) to 12 inches (30.3 cm).
The diameter is increasing to 0.5 cm). In order to apply a uniform magnetic field on these large-diameter wafers, a large electromagnetic coil having a diameter of 1 m or more is required. When such a large-sized device is used, it cannot be used in the current semiconductor manufacturing line in consideration of the floor occupied area of the device and the working space.

Second, regardless of the magnetic field strength distribution, in the parallel plate electrode type magnetron device, the electrons move in the E × B direction as described above, so that the plasma becomes denser in the direction. The current flowing in plasma using high-frequency discharge is
J (E) = j (ωε 0 -n e (x) e / ωm e) × E (E.Everha
rt, SCBrown, Phys. Rev., 76, 839, 1949). Here, J (E) represents current, _ne represents density, ω represents frequency, _me represents mass, and E represents an alternating electric field. In this equation, ωε _{0 in} the first term on the right side is a displacement current in a vacuum and does not depend on the density of the plasma, but the second term increases in proportion to the density of the plasma. Therefore, as the density of electrons and ions in the plasma increases, the current increases and the electric field decreases. In such a plasma state, if the magnetic force direction is assumed to be north, the amplitude of the AC voltage on the wafer is substantially uniform in the north-south direction, but the voltage amplitude on the west side is east (E × B) in the east-west direction.
Be larger. Like reactive ion etching,
When the etching shape and the etching rate are controlled by the direction and intensity of the ions, the ions are accelerated in the dark portion of the plasma by the sum of the plasma potential and the self-bias and collide with the film to be etched. When the ion current Ji is charged e, ni is the ion density, μ is the ion mobility, and E is the electric field, Ji = e · ni · μ · E (where Ji is the ion current, e is the charge, ni represents the ion density, μ represents the ion mobility, and E represents the electric field.) As shown in FIG. That is, due to the movement of the plasma in the E × B direction, both the ion irradiation density and the ion irradiation energy become non-uniform on the wafer, and the etching rate and the etching shape become extremely non-uniform.

The density phenomenon of plasma mainly depends on the magnetic field strength and the pressure (degree of vacuum). In particular, etching in a low-pressure atmosphere is indispensable in order to realize etching having a high aspect ratio and extremely small pattern size required for a next-generation device, and the density phenomenon caused by a magnetic field becomes remarkable. Further, not only the etching rate and the etching shape, but also the plasma density is periodically decreased with the rotation of the magnetic field in the outer peripheral portion of the wafer as compared with the central portion, the impedance of the plasma is increased, and the amplitude of the AC voltage is increased. Therefore, the ion irradiation energy determined by the plasma potential and the self-bias of the electrode increases, and is susceptible to damage by ion irradiation,
There is a problem that the yield in the peripheral portion is significantly reduced depending on the device.

Further, in the prior art, the damage caused by the difference in the etching rate between the periphery and the center of the wafer to be etched and the periodic change in ion energy in the periphery is large, and is not suitable for a large-diameter wafer.

[0008]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its object to make the plasma density on the wafer uniform and the ion irradiation energy distribution uniform.
A plasma processing apparatus using a rotating magnetic field capable of improving the yield of devices by making the etching rate in a wafer more uniform as a dry etching apparatus, and capable of forming a uniform film as a plasma CVD apparatus. It is to provide.

[0009]

SUMMARY OF THE INVENTION The present invention comprises a vacuum chamber containing two or more electrodes, a supply means for supplying a predetermined gas into the vacuum chamber, a discharge means for discharging a gas from the vacuum chamber, In a plasma processing apparatus using a rotating magnetic field that is provided around a vacuum chamber and includes an electromagnetic coil that generates a rotating magnetic field that rotates in a plane perpendicular to the direction of an electric field, a first object on which an object to be processed is mounted is provided. A first high-frequency power supply is connected to the electrodes, and a second electrode is provided facing the first electrode, and the second high-frequency power supply is connected to the second electrode. Thereby, an electric field in the opposite direction to the electric field between the first electrode and the plasma is generated between the second electrode and the plasma.
This is to make the plasma density distribution on the wafer uniform by canceling out the non-uniformity due to the movement of the plasma by B.

[0010]

[Action] By simply rotating the magnetic field, the instantaneous magnetic field on the east side with respect to the north direction when the electrode is viewed from above as described above.
The plasma density in the (E × B direction) increases. The second electrode is controlled to a negative potential in a direction opposite to the electric field E1 between the self-bias (negative) of the first electrode on which the object is placed and the plasma potential (positive), and the first electrode is connected to the first electrode. it is possible to move the plasma by an electric field E ₂ and the magnetic field between the second electrode and the plasma in a direction opposite to the direction of the plasma between the plasma (E ₁ × B). Therefore, the plasma density becomes more uniform on the wafer, and the amplitude of the AC voltage that determines the ion irradiation energy and the ion irradiation density can be made more uniform.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings. Embodiment 1 FIG. 1 shows a sectional view of a dry etching apparatus. The apparatus has a vacuum chamber 1, a gas supply port (not shown) for introducing an etching gas such as CF4, and a gas exhaust port (not shown) for evacuating the vacuum chamber 1 and setting it to a required pressure. The gas supply port is connected to a gas supply source via a valve, and the gas exhaust port is connected to an exhaust valve via a valve.

The first electrode 2 for mounting a wafer is a non-ground electrode provided in the vacuum chamber 1. To this, the first high frequency power supply 3 is connected via a matching circuit, and high frequency power for wafer bias is applied. FIG. 2 shows a flow rate of carbon tetrafluoride (CF ₄ ) and argon (Ar) gas of 7 sc.
In the case of mixing at a ratio of cm and 133 sccm, the correlation between the frequency and the power of the high frequency power supply applied to the substrate and the DC potential of the wafer is shown. As can be seen from FIG. 2, when 100 MHz and 100 W are applied to the upper electrode for plasma generation, the self-bias of the upper electrode is constant regardless of the frequency and power applied to the substrate. On the other hand, it can be seen that the self-bias of the substrate changes greatly depending on the frequency and power applied thereto. Therefore, by controlling the frequency and power of the first high-frequency power supply, the potential of the wafer, that is, the spatial potential of the plasma that determines the ion irradiation energy and the DC potential of the wafer can be precisely controlled.

The second electrode 4 for the purpose of controlling the plasma density is a non-ground electrode provided in the vacuum chamber 1 so as to face the first electrode 2. To this, a second high frequency power supply 5 is connected via a matching circuit, and high frequency power for plasma generation is applied. FIG. 3 shows the emission spectrum intensity of the plasma when the power applied to the second electrode 4 is changed. The numbers shown on the left side of the spectrum show the power (W) introduced to the second electrode and the relative emission intensity of argon at a wavelength of 419.9 nm. For example, 150W / 9
144 indicates that the power introduced into the second electrode is 150 W and the emission intensity at that time is 9144.

Around the vacuum chamber 1, two opposing electromagnetic coils 6 are arranged such that their axes are orthogonal to each other.
When low-frequency currents with phases shifted by 90 degrees are applied to one pair of electromagnetic coils and the other pair of electromagnetic coils, respectively, a rotating synthetic magnetic field is generated in a direction orthogonal to the electric field between the two opposing non-grounded electrodes. Occur. By applying the rotating magnetic field in this manner, high-density plasma can be generated on the wafer. However, as described above, if the plasma is generated only by the first electrode 2 and the bias is controlled, The above-described problem occurs that the instantaneous plasma density is high in the direction of E × B and low in the opposite direction.

By configuring the dry etching apparatus of the present invention as described above, the plasma and the plasma generating electrode (the second electrode) are opposite to the direction of the electric field between the plasma and the wafer mounting electrode (first electrode). Since an electric field can be applied between the electrodes, the non-uniformity due to the movement of the plasma is canceled each other, and the density of the plasma between the electrodes can be made uniform.

Embodiment 2 FIG. 4 shows an embodiment in which permanent magnets are arranged around the wafer mounting electrode (first electrode) 2 for the purpose of equalizing the plasma density at the center of the wafer and at the periphery of the wafer. Show. As the diameter of the wafer increases, the diameter of the device at the peripheral portion of the wafer increases. Therefore, it is very important to improve the yield of the device at the peripheral portion of the wafer.

With the conventional rotating magnetic field alone, electrons are drifted in the E × B direction and recombine on the inner wall of the chamber 1, but ions are not affected. The plasma potential is determined by the difference between the density of ions and electrons in the plasma. Since only electrons become sparse due to Lorentz force due to the difference in mobility (mass) between electrons and ions, the plasma potential in the E × B direction increases according to Poisson's equation. The ion irradiation energy is determined by the difference between the plasma potential and the self-bias of the substrate. If the irradiation energy is too high, many problems on the process occur, so it is desirable to control the conditions to the optimal conditions. However, since the plasma potential is determined by the device configuration, the control range is limited.

The main configuration of this embodiment is the same as that of FIG. 1, but in this embodiment, a permanent magnet 7 for generating a _second magnetic field B ₂ is further provided around the wafer to generate a plasma. Electrons are confined in the plasma while forming the plasma in a closed loop in the direction of E ₂ × B ₂ perpendicular to the electric field E ₂ . The ion irradiation energy is determined by the difference between the plasma potential and the self-bias of the substrate. If the irradiation energy is too high, many problems in the process occur, so it is desirable to control the conditions to optimal conditions. However, since the plasma potential is determined by the configuration of the apparatus, the control range is limited. For this reason, the rise of the plasma potential could be suppressed within the allowable range. In addition, since high-density plasma always exists around the wafer, high-density plasma can always be generated in a space above the wafer without being affected by the above-described plasma drift.

When the thermal oxide film was etched using the CF ₄ plasma according to the present embodiment, there was a variation of ± 8% within 10 mm from the wafer edge in the conventional apparatus, but 3 mm from the edge in the present embodiment. ± except for the part
It was 2%, and very uniform etching could be performed. In the above embodiment, use of a high-frequency power source to generate a second electric field E _2, towards the DC power supply can be simplified the structure of the apparatus. When a DC power supply is used, it is a matter of course that the electrode surface is always conductive. Further, in the above-described embodiment, the dry etching apparatus is used as an example.
Of course, it can also be used as a VD device.

[0020]

As described above, according to the present invention, since the movement of electrons in the plasma can be controlled and the distribution of the plasma potential can be made uniform, the etching rate of the object to be processed can be increased by using it as a dry etching apparatus. It can be uniform. In addition, it is possible to reduce the damage of the surface of the processing object due to the irradiation of ions and to form a film having a uniform thickness on the surface of the processing object by using the plasma CVD apparatus.

[Brief description of the drawings]

FIG. 1 shows a sectional view of an embodiment of a dry etching apparatus according to the present invention.

FIG. 2 shows the correlation between the frequency and power of a high-frequency power supply applied to an electrode and the DC potential of a wafer.

FIG. 3 shows the emission spectrum intensity of plasma when the applied power is changed.

FIG. 4 shows another embodiment of the dry etching apparatus according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Vacuum chamber 2 1st electrode 3 1st high frequency power supply 4 2nd electrode 5 2nd high frequency power supply 6 Electromagnetic coil 7 Permanent magnet

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-4-346225 (JP, A) JP-A-5-287559 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H05H 1/46 C23C 16/50 C23F 4/00 H01L 21/3065

Claims (2)

(57) [Claims] 1. A vacuum chamber containing two or more electrodes, a gas supply means for supplying a predetermined gas into the vacuum chamber, a discharge means for discharging gas in the vacuum chamber, and a gas supply means disposed around the vacuum chamber. A plasma processing apparatus using a rotating magnetic field having an electromagnetic coil generating a rotating magnetic field rotating in a plane perpendicular to the direction of an electric field, wherein a first electrode on which an object to be processed is mounted and the first electrode electrode
Negative self-bias is applied to the second electrode
A first potential and a second potential, respectively.
To generate a plasma with a positive potential between the electrodes
By generating an electric field (E ₂ ) between the second electrode and the plasma in a direction opposite to the electric field (E ₁ ) between the first electrode and the plasma, the electric field between the first electrode and the plasma is increased. In the
In the opposite direction (E ₂ × B) to the plasma direction (E ₁ × B),
A plasma processing apparatus using a rotating magnetic field, wherein a plasma is moved . 2. The plasma processing apparatus according to claim 1, wherein a DC magnetic field generating means is provided around the first electrode.