JPH0573256B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to glass plasma processing of semiconductor wafers, particularly to a magnetically enhanced reactive ion etching apparatus.

(Prior Art) In recent years, in the manufacturing process of semiconductor devices, single wafer processing has become mainstream rather than batch processing as semiconductor wafers have become larger.

In particular, in the etching process, conventionally
The batch method, which processes about 10 semiconductor wafers, was often used. The reason for this is that even though one process takes a certain amount of time, the throughput per unit time is relatively high, for example, 60 sheets per hour.

In order to obtain this level of throughput with a single wafer method, it is necessary to increase the etching rate (etching speed), but for this purpose it is necessary to increase the power of radio frequency (RF). but,
Increasing the RF power causes damage to the wafer (also called substrate) surface. Therefore, in order to increase the etching rate without increasing the RF power, it was considered to increase the plasma density within the reactor chamber.

Conventionally, a planar magnetron cathode method used in sputtering has been known as a method of increasing plasma density.In this method, electrons move in a cycloid manner surrounding magnetic lines of force on the cathode surface, so these electrons move between particles. This is a magnetic enhancement method that increases the number of collisions and increases the density of plasma.

(Problems to be Solved by the Invention) Recently, it has been proposed to utilize this magnetic enhancement method in reactive ion etching processing. For example, conventionally proposed devices are configured to arrange magnets under the wafer, thereby forming a high concentration region of plasma near the surface of the wafer.

A magnetically enhanced reactive ion etching apparatus having a structure as schematically shown in a perspective view in FIG. 8 has also been proposed. This device has solenoid coils 2 and 3 on both ends of a reactive chamber 1.
These coils 2
and 3, while passing a direct current from a direct current power supply 4 to
It is constructed so that a high frequency current is passed through a wafer (substrate) 5 provided in a chamber 1 from a high frequency power supply 6.

In this device, for example, if the magnetic field (or magnetic flux density) is B and the direction of the flow (or particle velocity) of positively charged particles q at a certain point is E, then the charged particles q have the principle diagram shown in Fig. 9. Lorentz force F acts as shown. In this type of device, the wafer 5 is generally placed so that its surface is parallel to the direction of the magnetic field B, so when the wafer surface is viewed from the direction opposite to the direction of the flow E of charged particles, The etching speed varies greatly between the left and right regions. The reason for this is that, as can be understood from FIG. 10, the plasma density varies greatly on the wafer surface. In other words, when considering positively charged plasma particles q, suppose that the flow direction of the plasma particles q is from the back side of the page to the front side (indicated by E), and the magnetic field B is directed from the top to the bottom in the figure. , the force f acting on the positively charged plasma particles is parallel to the wafer surface and in the direction from left to right in the figure, so the plasma high concentration area (area Q shown with diagonal lines in the figure) is on the right side of the figure. , and the etching rate in this region increases. Also, if the direction of the current in the coil is reversed, the high concentration area of the plasma will be located to the left, increasing the etch rate in that area.

However, in the case shown in FIG. 8, the positively charged plasma particles q are subjected to a force within the surface of the wafer 5 in the direction shown by the arrow a in the direction perpendicular to the direction of the magnetic field B, while the negatively charged particles q are The charged particle is b in the figure.
receive a directional force. Therefore, the positively and negatively charged particles move in the directions a and b, respectively, and as a result, the plasma concentration within the chamber 1 becomes non-uniform.

FIG. 11 is a diagram illustrating the non-uniformity of plasma concentration obtained through experiments using such a conventional apparatus in terms of the difference in etching rate (Å/min) on the wafer surface. In this case, 4 inches (1 inch is approximately 2.54 inches)
Etching was performed on a SiO ₂ film grown on a wafer (cm). The conditions are: gas (CHF ₃ + 5% CO ₂ ) flow rate into the chamber is 140 SCCM, magnetic field B is 240 Gauss, and high frequency power is 1.91 W/cm ²
It was obtained with a plasma gas pressure of 13Pa. In this case, the difference (non-uniformity) between the etching rate at the center of the wafer surface and the etching rate at 85% of the surrounding area is as large as ±26%.
In the figure, the etching rate at typical locations is shown in numerical values (unit: Å/min).

In order to improve this non-uniformity, an alternating current was passed through coils 2 and 3 of the apparatus shown in FIG. 8 to generate an alternating magnetic field, and etching was attempted under the same experimental conditions as described above. . The results of the etching rate (Å/min) are shown in FIG. As can be understood from the experimental results, in this case, forces in opposite directions act on the charged particles every half cycle of the alternating current, resulting in the formation of high plasma concentration areas on the left and right sides of the wafer 5. Therefore, the non-uniformity of the plasma concentration is about ±12.2%, and the non-uniformity of the plasma can be improved to some extent, but it is also clear that the plasma concentration in the direction perpendicular to the magnetic field B is asymmetric. Ru.

Unlike the above-mentioned device, as shown in FIG.
A reactive ion etching apparatus has also been proposed in which a three-phase current with a phase lag of 1.5 degrees is passed to form a rotating magnetic field that rotates in the direction shown by arrow c in FIG. 14, for example. In this device, charged particles rotate in the direction indicated by the arrow d (indicated by the dotted line) within a plane parallel to the wafer 5, so that uniform plasma can be obtained over the entire surface of the wafer 5.

Although the method shown in FIG. 13 is theoretically attractive, the configuration shown in FIG. Problems such as inductance matching, heat generation of these coils, and phase matching occur. Furthermore, if an attempt is made to lower the frequency in order to reduce the inductance problem, a new problem arises in that a low frequency oscillator or the like is required.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a magnetically enhanced reactive ion etching apparatus which solves the above-mentioned problem of plasma concentration asymmetry and can obtain a uniform plasma concentration with a simple configuration.

(Means for Solving the Problems) In order to achieve this object, the present invention uses at least two coils to generate two or more types of magnetic fields that repel each other, and by this magnetic repulsion, the semiconductor wafer to be processed is generate a magnetic flux parallel to the surface of the reactor chamber, such that the pattern of this magnetic flux is symmetrical about the longitudinal axis of the reactor chamber, and thus symmetrical about the center point of the semiconductor wafer, and change the current flowing through the solenoid coil into an alternating current. It is characterized by the following.

In a preferred embodiment of the invention, the alternating current may be generated by varying the strength of the direct current flowing through the solenoid coil.

Furthermore, in another preferred embodiment of the present invention, an alternating current can be formed by turning on and off a direct current flowing through a solenoid coil.

Furthermore, in carrying out the present invention, the alternating current is
It is preferable to form the solenoid coil by modulating the direct current flowing through the solenoid coil with alternating current.

Furthermore, in another preferred embodiment of the present invention, the solenoid coil is preferably wound around the outer periphery of the plasma reactor so as to surround the semiconductor wafer inside the reactor.

(Function) In this way, in the present invention, magnetic fields generated by at least two solenoid coils in mutually repelling directions are applied to the vicinity of the wafer surface to be etched, parallel to and parallel to the wafer surface. Since a magnetic flux is formed that is symmetrical about the wafer center point, the distribution of plasma density on the wafer surface, and therefore the etching rate on the wafer surface, is uniform.

Moreover, since the current flowing through the solenoid coil is an alternating current, it is possible to give fluctuations to the distribution of charged particles in the direction along the wafer surface. This fluctuation contributes to making the etching rate uniform on the wafer surface.

(Embodiments) Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that these figures only schematically illustrate the shapes, dimensions, and arrangement relationships of each component to the extent that the configuration of the invention can be understood, and this invention is limited only to the illustrated configuration example. isn't it.

FIG. 1 is a perspective view schematically showing an embodiment of the apparatus of the present invention, FIG. 2 is a cross-sectional view taken along the line -- in FIG. 1, and FIG. 3 is a cross-sectional view taken along the line -- in FIG.

As shown in FIG. 2, in the magnetically enhanced reactive ion etching apparatus of the present invention, a semiconductor wafer 20 is placed on a cylindrical electrode 21 in a well-heated state, and this cylindrical electrode 21 is supported by an insulator 22. A gas introduction section 23 is disposed opposite to the semiconductor wafer 20 at a predetermined distance. The whole outer container 2
4 constitutes a plasma reactor 25, and defines a reactor chamber 26 inside.

This gas introduction part 23 is connected to the front wall part 2 of the reactor 25.
It is connected to a gas supply (not shown) via a conduit 28 passing through 7. In addition, the rear wall portion 2 of the reactor 25
9 is provided with a gas exhaust section 30, which is communicated with the reactor chamber 26 through a plurality of through holes 31 formed in the insulating support 22. This cylindrical electrode 2
1 is connected to a high frequency energy source 33 via a conductor 32.

Further, according to the present invention, two solenoid coils 34 and 35 are wound around the outer periphery of the plasma reactor 25, for example, the outer container 24, and in this case, the semiconductor wafer 20 is surrounded by these solenoid coils 34 and 35 around the container 24. Wrap it like this.
For example, the coils 34 and 35 are arranged facing each other so that the semiconductor wafer 20 in the reactor chamber 26 is located between the coils 34 and 35. These coils 34 and 35 are supplied with a direct current from an alternating current power supply 36 (shown in FIG. 1) to form magnetic fields that repel each other. FIG. 4 shows the state of such a magnetic field. That is, the two opposing coils 34 and 3
Direct currents in opposite directions are applied to the wafers 20 and 5.
so as to form opposing magnetic fields near the
The alternating current power supply 36 repeatedly turns on and off the direct current that forms this magnetic field to supply alternating current to the coil.

Next, another embodiment of the invention will be described with reference to FIG. FIG. 5 is a diagram schematically showing the main parts for explaining a modification of the device according to the present invention, and the same components as those shown in FIGS. 1 to 3 are the same. Indicated with a code.

In this embodiment, on the outer periphery of the reactor 25, for example, on the left side of the outer container 24 constituting the reactor 25, there is a
Two solenoid coils 37 and 38 are respectively wound on the opposite side of the wafer placement position, that is, on the right side of the outer container 24.
9 and 40, respectively. The wafer 20 is positioned between the set of coils 37 and 38 and the set of coils 39 and 40, and currents in opposite directions are passed through the coils of each set, so that the polarity shown by S and N, respectively, in FIG. mutually repelling magnetic fields are formed in the reactor chamber 26 at a location corresponding to the vicinity of the wafer surface. Due to this repulsive magnetic field, the central axis d of the chamber 26 is within a plane perpendicular to the longitudinal center axis d of the chamber 26 and
A magnetic flux φ is generated radially outward from the radial direction. The appearance of this magnetic flux φ when viewed in the cross-sectional direction taken along the line - in FIG. 5 is schematically shown in FIG. 6 by a line with an arrow.

Solenoid coil 34, 35, 37, 38, 3
When the direct current supplied to coils 9 and 40 is turned on and off to form a repelling magnetic field, the device operates as a magnetically enhanced reactive ion etching device, and when the current is turned off for all coils, it operates as a normal reactive ion etching device. It operates as. In addition, by adjusting the strength of the DC current between each coil, the concentration of plasma can be controlled.
Therefore, the etching speed can be changed freely.

FIG. 7 shows the vector relationship between the strength of the magnetic field B in the chamber 26 of the device shown in FIG. 5 and the force F acting on positively charged particles due to the electrolysis E when viewed in the cross-sectional direction taken along the line - in FIG. FIG. In this example,
This force F acts to rotate the positively charged particles clockwise about the center point 41 of the chamber 26, thus creating a plasma concentrically on the wafer surface, and thus A uniform plasma distribution can be obtained. Furthermore, since an alternating current is passed through the coil, the strength of the Lorentz force exerted on the charged particles varies, resulting in fluctuations in the distribution of the charged particles in the direction along the wafer surface. This fluctuation contributes to making the etching rate uniform on the wafer surface.

It is clear that if the direction of the current flowing through the coil is reversed, the force F will rotate the positively charged particles counterclockwise, and in this case as well, a uniform plasma distribution will be formed on the wafer as described above. I can do it. Therefore, the alternating current flowing through the coil may be alternating current.

Alternatively, the direct current flowing through each coil may be modulated by alternating current, and the alternating current may be used to equalize the magnetic field and, therefore, equalize the plasma distribution and the charged particle distribution in the direction along the wafer surface.
Alternatively, the strength of the direct current flowing through each coil may be changed periodically, and the magnetic field may be equalized by this alternating current.

Further, a cylindrical electrode 2 for supporting the wafer 20 is provided.
When 1 is made of divalent iron material, the chamber 26
It is possible to control the magnetic flux pattern in the wafer, and therefore the concentration of active species in the plasma, and ultimately the uniform processing of the wafer surface.

Furthermore, the arrangement relationship of each coil described above can be appropriately set according to the design.

(Effects of the Invention) As is clear from the above description, according to the present invention, a uniform magnetic field can be obtained with a simple configuration, and therefore a wafer can be etched uniformly.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an embodiment of a magnetically enhanced reactive ion etching apparatus according to the present invention, FIG. 2 is a cross-sectional view taken along the - line in FIG. 1, and FIG. 3 is a cross-sectional view taken along the - line in FIG. 4 is an explanatory diagram showing the state of the magnetic field generated in the coil of the device shown in FIG.
FIG. 5 is an explanatory diagram showing a modified example of the apparatus shown in FIG. 1, FIGS. 6 and 7 are cross-sectional views taken along the - line in FIG. 5, and FIG. 8 is a conventional magnetically enhanced reactive ion etching apparatus. FIG. 9 is an explanatory diagram of the Lorentz force acting on charged particles in the device shown in FIG. 8, and FIG. 10 is a diagram showing the force acting on the wafer in the device shown in FIG. 8 and the force generated thereby. 11 and 12 are explanatory diagrams showing the state of plasma concentration. FIGS. 11 and 12 are distribution diagrams of plasma concentration in the chamber. FIG. 13 is a perspective view showing another example of a conventional magnetically enhanced reactive ion etching apparatus. FIG. 14 is an explanatory diagram showing the state of the magnetic field generated in the apparatus of FIG. 13. 20... Semiconductor wafer, 21... Cylindrical electrode,
22... Insulator (support) body, 23... Gas introduction part,
24... Outer container, 25... Plasma reactor,
26...Reactor chamber, 27...Front wall, 2
8... Conduit, 29... Rear wall part, 30... Gas discharge part, 31... Through hole, 32... Conductive wire, 33... High frequency energy source, 34, 35, 37, 38, 3
9, 40... Solenoid coil, 36... Alternating current power supply, 41... Center point of the chamber.

Claims (1)

[Claims] 1. Gas plasma is generated by applying a radio frequency (RF) alternating voltage between two or more electrodes provided in a plasma reactor chamber, and the ionization of this plasma is enhanced by a magnetic field to generate plasma. In a magnetically enhanced reactive ion etching system that processes semiconductor wafers in a reactor, two or more types of magnetic fields that repel each other are generated, and this magnetic repulsion generates magnetic flux parallel to the surface of the semiconductor wafer to be processed. at least two solenoid coils arranged such that the pattern of magnetic flux is symmetrical about the longitudinal axis of the reactor chamber and therefore symmetrical about the center point of the semiconductor wafer;
A magnetically enhanced reactive ion etching device characterized in that the current flowing through the solenoid coil is an alternating current. 2. The magnetically enhanced reactive ion etching apparatus according to claim 1, wherein the alternating current is generated by changing the intensity of a direct current flowing through the solenoid coil. 3. The magnetically enhanced reactive ion etching apparatus according to claim 1, wherein the alternating current is formed by turning on and off a direct current flowing through the solenoid coil. 4. The magnetically enhanced reactive ion etching apparatus according to claim 1, wherein the alternating current is formed by modulating the direct current flowing through the solenoid coil with alternating current. 5. Claim 1, characterized in that the solenoid coil is wound around the outer periphery of the plasma reactor so as to surround the semiconductor wafer inside the reactor.
The magnetically enhanced reactive ion etching apparatus described in 2.