JPH0250197B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved plasma etching method and apparatus.

In recent years, gas plasma etching has become commonly used in the manufacture of semiconductor devices. The electrode structures used to perform this gas plasma etching include the cylindrical coaxial type, the cylindrical induction type, and the parallel plate type. Among these, the parallel plate type electrode is different from other types of electrodes. In comparison, this method is attracting particular attention because it has the advantage of producing highly accurate etching that is faithful to ultra-fine patterns with less side etching.

However, with this parallel plate type electrode, the processing power output must be kept low because (1) the etching speed is slow and productivity is low, and (2) the resist mask and sample to be processed are easily damaged by plasma ion bombardment. (3) Requires post-treatment to recover from damage caused by plasma ions after etching; (4) Etching silicon nitride (Si ₃ N) films, which are important as insulating gate films and protective films for semiconductor devices. In this case, there are practical problems such as the photoresist used as the mask has a large film loss and also has low selectivity with respect to the silicon dioxide (SiO ₂ ) film that is often used as the underlayer.

In order to solve these problems, a device was developed in which an electrode plate made of a porous plate was inserted between parallel plate electrodes and connected to one electrode to function as an intermediate electrode (Japanese Patent Laid-Open No. 56-76242). Public bulletin). This device makes the active species generated by the plasma discharge rod uniform and high-density, enables highly uniform and precise etching, protects the sample from plasma ion bombardment, and increases the etching rate from 5 to 10 times faster than the conventional etching rate. Although it has the advantage of doubling the improvement, it has become clear that the following problems occur in a device using this intermediate electrode. That is, it has been found that when an aluminum porous plate is used as an intermediate electrode, a new problem arises in that aluminum is sputtered and contaminates the material to be etched, degrading its electrical properties.

In view of these circumstances, the present inventors have overcome the shortcomings of the conventional plasma etching method using parallel plate electrodes, improved the selectivity for silicon nitride, photoresist films, and silicon dioxide films, and improved the etching target material. As a result of extensive research into a plasma etching method using a parallel plate electrode type device that prevents contamination, it was discovered that the objective could be achieved by interposing an insulating plate between the electrodes, and the present invention was developed. .

That is, in plasma etching an electronic component forming material having a resist pattern, the present invention places the object to be processed on a lower electrode, arranges an upper electrode opposite to this, and places a gap between the two electrodes. A plasma etching method characterized by applying a high frequency voltage to an upper electrode through an insulating flat plate having a large number of pores, and an apparatus equipped with an insulating flat plate having a large number of pores suitable for carrying out the method. This is what we provide.

Next, the present invention will be explained in more detail with reference to the accompanying drawings.

FIG. 1 is a cross-sectional view for explaining the structure and main parts of the device of the present invention, showing a bell-shaped lid 1 and a bottom plate 2.
A flat upper electrode 3 and a lower electrode 4 are arranged in parallel in a sealed container, and an insulating flat plate 5 having a hole is inserted between them. The upper electrode 3 is suspended by fitting and fixing its support column 6 into a hole 7 provided at the top of the bell-shaped lid 1, and the lower electrode 4 is fitted into the center of the bottom plate 2. Alternatively, it is constructed integrally with the bottom plate 2, and its upper surface also serves as a mounting table for an electronic component forming material to be processed having a resist pattern. The upper electrode 3 is connected to a high frequency power source via a support column 6, and the lower electrode 4 is grounded.

An insulating flat plate 5 having a large number of holes disposed between the upper electrode 3 and the lower electrode 4 is supported by suitable supports 8, 8', and the supporting means may be any known method. May be used. The supporting position of this flat plate 5 is, for example, a distance of 50 mm between the upper and lower electrode plates.
In this case, the position is preferably 30 mm or more below the upper electrode 3 and 10 mm or more above the lower electrode 4 where the object to be treated is placed, especially the lower electrode 4.
It is preferable to arrange it within a range of 15 to 20 mm above. Further, the shape of the flat plate 5 is preferably a shape that is compatible with a normal plasma etching apparatus, and for example, a disk-like shape is suitable for the bell shape shown in FIG.

However, the shape is not particularly limited as long as the object of the present invention is not hindered, and the size of the surface of the flat plate 5 is not particularly limited as long as the effects of the present invention are effectively achieved. , usually the lower electrode 4 and the object to be processed placed on its upper surface, that is,
It is preferable to select the material so as to sufficiently cover the electronic component forming material having the resist pattern.

The insulating flat plate 5 having a large number of pores used in the method and apparatus of the present invention is made of an insulating material and has a plate-like shape in which a large number of small through holes 9 are formed throughout the plate. It is preferable that the pores are uniformly distributed throughout the plate. As the insulating material, for example, ceramics, glass, etc. are used, and ceramics are particularly preferred.

FIG. 2 is a plan view showing a preferred example of the flat plate 5 used in the present invention, and FIG. 3 is a plan view showing another example of the flat plate. In FIG. 2, a circular flat plate 5 has a large number of pores 9,...
However, as shown in FIG. 3, depending on the purpose, it may be advantageous to use a donut-shaped flat plate with a relatively large hole 9' formed in the center of the disk. You can also do it.

A large number of pores formed in an insulating flat plate can have any shape such as square, rectangular, circular, triangular, etc., but it is desirable that the pores be uniformly distributed over the entire flat plate. In addition, the size of this pore is
less than 10 mm, preferably in the range of 5 to 8 mm,
It is appropriate to make holes at a rate of about 1 to 5 per 1 cm ² .

When performing plasma etching by applying a high frequency voltage to the upper electrode in an atmosphere of plasma gas using the apparatus of the present invention, it is necessary to perform plasma etching by applying a high frequency voltage to the upper electrode in an atmosphere of plasma gas. Plasma discharge is generated between the insulating flat plate, and the generated active species pass through the pores of the insulating flat plate and reach the object to be processed, such as a wafer, placed on the top surface of the lower electrode, effectively etching it. will be held. When using the apparatus of the present invention, the object to be treated is not directly exposed to the plasma discharge region, and the flat plate interposed in the middle is made of an insulating material, so unlike the case of a conductive flat plate, the object to be treated is not exposed directly to the plasma discharge region. The reaching active species are moderately suppressed and reduced, and the object to be etched is etched with a relaxed force. As a result, highly uniform and precise etching can be obtained, and furthermore, damage to the resist and various objects to be processed due to plasma ion bombardment can be effectively prevented, so that selectivity to the photoresist and the underlying material is significantly improved. Such an effect is not practical if a conductive material is used for the flat plate because the object to be processed will be contaminated. Furthermore, when plasma etching is performed using the apparatus of the present invention, the processing power output is increased to reduce the etching rate, and the adverse effects of plasma ion bombardment can also be suppressed, thereby improving productivity.

According to the present invention, dry etching of silicon nitride films, which has been problematic in the past, can be easily performed.
Deterioration of the properties of the processed object and other disadvantages caused by using the intermediate electrode can be advantageously overcome.

When the apparatus of the present invention is used as a cathode-coupled parallel plate apparatus, the upper electrode is grounded, and a high-frequency voltage is applied to the lower electrode on which the object to be processed is placed.
Plasma is generated and acts between the lower electrode and the insulating flat plate with many pores supported in the middle, so the resist and the object to be processed are directly bombarded with plasma ions and are damaged, causing damage to the underlying layer. No improvement in selectivity can be expected. Therefore, in the device of the present invention, it is important to apply a high frequency voltage to the upper electrode.

In the above description, a parallel plate electrode type in which the upper and lower electrodes are placed horizontally has been described, but in the present invention, it is not particularly necessary to make them horizontal, and there is no problem even if they are placed vertically.

Next, the present invention will be explained in more detail with reference to Examples.

Example: OAPM, a single-wafer automatic plasma etching device in which an upper electrode with a diameter of 140 mm and a lower electrode with a diameter of 140 mm that also serves as a workpiece mounting table are arranged in parallel at 50 mm intervals.
−301B (manufactured by Tokyo Ohka Kogyo Co., Ltd.), a 1.5-inch hole with a diameter of 6 mm is made in a ceramic plate with a diameter of 160 mm and a thickness of 2 mm.
A flat plate uniformly formed at a ratio of 30 mm/cm ² was placed parallel to the electrode plate at a position 30 mm below the upper electrode.
A 4-inch silicon wafer with a silicon nitride film of 1000 Å to be processed is placed approximately in the center of the lower electrode surface, and oxygen gas 8 8 is used as the plasma treatment gas.
Using carbon tetrafluoride gas that contains
The silicon nitride film was plasma etched at 200W for 75 seconds. As a mask, a resist film of OMR85 (trade name, manufactured by Tokyo Ohka Kogyo Co., Ltd.) with a thickness of 1 μm was used.
Although a silicon dioxide layer with a thickness of 1000 Å was used as the underlayer, there was almost no reduction in the resist film, and high-precision etching was performed evenly and uniformly over the entire wafer surface.

The etching rate of silicon nitride film is 800 Å/min.
The etching rate of the underlying silicon dioxide layer was 300 Å/min, and the selectivity with respect to the silicon nitride film was 2.7.

For comparison, when an insulating flat plate with many pores was removed from the above device and etching was performed under the same conditions as above, the etching time was 67 seconds, but the resist film was only 3000 Å thick. Diminished. In addition, the etching rates of the silicon nitride film and photoresist film were 900 Å/min and 2700 Å/min, respectively.
The etching rate of the underlayer is 600Å/min, and the selectivity with silicon nitride is 0.3.
It was 1.5.

[Brief explanation of drawings]

FIG. 1 is a side sectional view showing the main parts of the device of the present invention, FIG. 2 is a plan view showing one example of an insulating flat plate, and FIG. 3 is a plan view showing another example of an insulating flat plate. It is a diagram. In the figure, numeral 1 is a bell-shaped lid, 2 is a bottom plate, 3 is an upper electrode, 4 is a lower electrode, and 5 is an insulating flat plate having many pores.

Claims (1)

[Claims] 1. When performing plasma etching on an electronic component forming material having a resist pattern, an object to be processed is placed on a lower electrode, an upper electrode is placed opposite it, and an object is placed between the two electrodes. A plasma etching method characterized by applying a high frequency voltage to an upper electrode through an insulating flat plate having a large number of pores. 2. In a parallel plate plasma etching apparatus having an upper electrode for applying a high-frequency voltage and a lower electrode disposed opposite to the upper electrode and on which the object to be processed is placed, a space between the upper electrode and the lower electrode is A plasma etching apparatus characterized by having an insulating flat plate having a large number of pores. 3. The device according to claim 2, wherein the insulating flat plate is a ceramic plate.