JPS59163827A - Plasma etching device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] [Technical field of invention] The present invention relates to a plasma etching apparatus.

[Technical background of the invention and its problems]

In recent years, integrated circuit manufacturing processes have required microfabrication of elements as they become more highly integrated and faster. For this reason,
A reactive ion etching (R,1,E,) apparatus that can obtain a vertical etched shape without so-called undercuts has been attracting attention. This etching apparatus performs the etching process as follows. First, high frequency power is applied to an electrode on which an object to be etched to form a pattern is placed. This operation causes glow discharge to occur in the reactive gas in the chamber containing the object to be etched. At this time, a negative self-bias is generated in the electrode due to the difference in mobility between electrons and ions and the difference in area ratio between the high frequency electrode and the counter electrode.

This negative self-bias is called cathode drop voltage and is shown as Vde as measured from ground potential. Ground potential (
Positive ions in the plasma accelerated by
The etching species collides perpendicularly with the surface of the object to be etched. This operation promotes the reaction between the etching species and the object to be etched, turning the object into a gas.
Proceed with the etching process. For example, when forming a contact hole in an object to be etched made of silicon oxide, CF4 and H2 gas or CHF gas are used. When the object to be etched is made of polycrystalline silicon, a gas such as CCl2 or C42 is used. Nickel is released, which contaminates the highly etched device with heavy metals and seriously degrades it. To prevent this, covering the electrode with quartz or alumina can prevent heavy metal contamination. However, the oxygen contained in the electrode is released, and this small amount of oxygen generates a large amount of end chamber radicals. As a result, if the object to be etched is formed of polycrystalline silicon, particularly polycrystalline silicon containing phosphorus or arsenic, undercuts are likely to occur during the etching process. These problems can be solved by forming the surface of the electrode with a polymer film made of polyester. However, during the etching process, polymers fly out from the polymer coating and adhere to the surface of the object to be etched. Therefore, residues are likely to be left on the surface of the object to be etched after the etching process. Furthermore, in order to solve the above-mentioned problems, electrodes made of cardin plates have been used in recent years. In this case as well, it has been found that when the object to be processed is formed of a silicon nitride film, this can cause crystal defects to occur in the semiconductor substrate made up of the object to be processed.

Furthermore 1. In the case where the 'r-to-electrode has become extremely thin', if the etching process is performed using the polycrystalline silicon, high melting point gold wire and its silicide compound that constitute the capacitor electrode and electrode as the object to be processed, the object to be processed will be etched. The withstand voltage of the underlying oxide film deteriorates significantly. For this reason, there is a problem in that it is not possible to secure an insulating film having a sufficiently high withstand voltage after the etching process.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a plasma etching apparatus that prevents deterioration of breakdown voltage of an insulating film.

[Summary of the invention]

The present invention is a plasma etching apparatus in which the electrodes are formed of a silicon nitride film, thereby reducing the breakdown voltage deterioration of the insulating film.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings.

In the figure, 1 is a stainless steel vacuum container main body. Inside the vacuum container body 1, an upper electrode 2 and a lower electrode 9 are disposed opposite each other with a predetermined interval. Upper electrode 2 and lower electrode S,
It is integrally attached to the vacuum container body J via a Teflon ring 4.5, and is electrically insulated from the vacuum container body 1. The conductive member '3a of the lower electrode 3 and the two upper electrodes are made of a material such as alumina or quartz. As shown in FIG. 2(A), the lower electrode 3 has a silicon nitride film 3b formed on the surface of a conductive member 3Il. Silicon nitride film? A force is applied so that a silicon wafer, which is the object to be processed 6, is placed on the surface of b. It is sufficient that the silicon nitride film s bl is laid down at least in the area where the object to be processed 6 is installed, as shown in ω) in the figure. At the rear of the upper electrode 2 and the lower electrode 3, water cooling pipes 7 and 8 are attached for cooling each electrode.

Exhaust pipes 9 and 10 are led out from the lower part of the vacuum container body 1. The exhaust pipes 9, 10 are connected to, for example, an oil diffusion pump and a rotary pump (not shown). A dispersion tube 1 for supplying a reactive gas is introduced into the vacuum container body 1 from the outside. The reactive gas is
It is designed to be uniformly supplied into the vacuum container main body 1 from the introduction hole 12 of the dispersion tube 1. A predetermined voltage is applied to the upper electrode 2 and the lower electrode 3 from a high frequency power source 16 via a matching box 13, 14 and a coaxial switch 15. The upper electrode 2 and the lower electrode 3 are provided with switches 17 and 18 for grounding the other electrode when RF power is applied to either one.

Furthermore, a monitoring window 19 is provided on one side wall of the vacuum container main body 1 . An etching monitor 20 is provided outside the monitoring window 19 and facing it. The etching monitor 20 is composed of a spectrometer, a phototube, a recorder, etc., and is designed to monitor the progress of etching by analyzing the gas plasma during the etching process. Below the monitoring window 19, a pressure gauge I\1'2 is provided for measuring the pressure inside the vacuum container body 16-.

I'm jealous of the plasma etching equipment configured like this! The object to be processed 6 is placed on the silicon nitride film 3b of the lower electrode 3.
was installed and etched. As shown in FIG. 3, the +Jυ treated body 6 is made by forming an insulating film 6b with a thickness of 400× on the surface of a silicon substrate 6a of 10zφ by thermal oxidation method, and then forming a polycrystalline silicon layer 6c on the surface by low pressure CVD method. At the same time, phosphorus impurities are diffused into the polycrystalline silicon layer 6c, and a resist film 6d having a predetermined pattern is formed on its surface. The region to be etched is not covered by the polycrystalline silicon layer by the resist film 6d.

The etching conditions are Cl3 as the reactive gas.
c/nin, H2 was set to be supplied from the dispersion tube 11 into the vacuum vessel main body 1 at a rate of 6 cc/m+n. The pressure inside the vacuum container body 1 is 0.07 Torr.

The applied RF power is 13.56 MJ (,0,25 WAf
It was applied to the lower electrode 3 as n2. When the withstand voltage of the insulating film 6b of the object to be processed 6 was measured after the etching process, the fourth
The results shown in the bar graph in the figure were obtained.

The breakdown voltage was measured using the voltage when a current of 1 μA flows as the breakdown voltage. The electrode formation area of the polycrystalline silicon layer 6c is 10 squares. As is clear from the figure, the breakdown voltage is distributed at 10 x Δ and 6 MV/crn. 10 MV/crs is a breakdown voltage specific to the insulating film 6b, and 6 MV/cm is considered to be due to deterioration due to contamination such as dust during formation of the insulating film 6b. This means that the polycrystalline silicon layer 6 of the object 6 to be processed has a similar structure.
This was confirmed because the withstand voltage of the insulating film 6b was examined after etching with a nitric acid solution using the resist film 6d as a mask, and the same results as shown in FIG. 4 were obtained.

Furthermore, in order to compare with the apparatus of the example, a conventional plasma etching apparatus having a structure similar to that of the example except that the lower electrode and the upper electrode were composed of a single carbon electrode was used. A similar etching process was performed. The object to be processed 6 and the etching conditions were exactly the same as those in the example. When the withstand voltage of the insulating film after etching treatment was investigated, the results shown in FIG. 5 were obtained. As is clear from the figure, it can be seen that the insulating film has lost its electrical insulation function.

In this way, the plasma etching apparatus of the embodiment! The reason why the withstand voltage of the insulating film 6b is guaranteed when etching is performed is considered to be due to the following reason. Lower electrode 3
Most of the voltage drop at the (cathode) occurs in the sheath formed between the plasma, the object to be processed 6, and the electrode. Insulating film 6b
If the film thickness of the electrode is 500X or less, the insulating material of the electrode is 1
When the voltage is 0 μ or more, even if the cathode drop voltage is 500 V, the DC voltage applied to the insulating film 6b due to charge accumulation is considered to be several volts at most, and will not be a voltage that would cause dielectric breakdown.

In these steady states, the breakdown voltage of the insulating film 6b does not deteriorate, and the electrode forming material may be a conductive member.

However, since the breakdown voltage actually deteriorates, the silicon substrate 6a that is in contact with the N1 conductive member is removed during the period from immediately after the polycrystalline silicon film 6c completes etching until it reaches a constant state. However, the potential of the polycrystalline silicon film 6c is lower than that of the silicon substrate 6a.

It is thought that this potential difference causes dielectric breakdown of the insulating film 6b. However, if the lower electrode 3 is formed of the conductive material 3a and the silicon oxide film 3b (insulating material) as in the embodiment, the silicon substrate 6a and the polycrystalline silicon film 3b
Since the respective potentials of c reach a constant potential at the same rate of culm even immediately after the etching process, it is considered that no dielectric breakdown occurs. Therefore, the object to be processed 6 has a portion of the insulating film 6b formed by using a silicon dielectric film, or a silicon nitride film and the insulating film 6.
Similarly, even if the polycrystalline silicon film 6c is made of a metal such as aluminum, tungsten, or molybdenum, or a silicide compound thereof, the polycrystalline silicon film 6c has a two-layer structure with
Etching can be performed with excellent dielectric strength.

10- [Effects of the Invention] As explained above, the plasma etching apparatus according to the present invention has remarkable effects such as being able to prevent deterioration of breakdown voltage of an insulating film.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing a schematic configuration of an embodiment of the present invention,
2(4) and 03) are cross-sectional views showing the structure of the lower electrode, FIG. 3 is a cross-sectional view of the object to be processed, and FIGS.
The figure is a characteristic diagram showing the relationship between breakdown voltage and frequency. No... Vacuum vessel body, 2... Upper electrode, 3... Lower electrode, 311... Conductive member, 3b... Silicon nitride film, J15... Teflon ring, 6... Covering Processing body, 7.8... Water cooling pipe, 9.10... Exhaust pipe, 11
...Dispersion tube, 12...Introduction hole, 7.9.14...
Matching box, 15... Coaxial switch, Noro... High frequency power supply, 17° No. 8... Switch, 19... Monitoring window, 2
0... Etching monitor gauge, 2... Pressure gauge, U.
-・Plasma etching equipment.

Claims (1)

[Claims] an upper electrode and a lower electrode arranged opposite each other at a predetermined distance within a vacuum container main body; a silicon nitride film formed on at least a part or all of the object-to-be-processed area of the lower electrode;
A plasma etching apparatus comprising: a dispersion tube for a reaction gas introduced into the vacuum container body.