Plasma processing with energy supplied

Details Plasma processing with energy supplied Plasma processing with energy supplied

1999-07-22

2002-02-19

Kornakov, Michael (Department: 1746)

Etching a substrate: processes

Gas phase etching of substrate

Application of energy to the gaseous etchant or to the...

C216S063000, C216S064000, C216S065000, C216S069000, C216S061000, C427S569000, C427S575000, C438S730000

Reexamination Certificate

active

06348158

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and apparatus for processing a semiconductor substrate by use of a plasma, and more particularly to a plasma processing of a semiconductor substrate with energy supplied.
2. Description of the Related Art
Integration density of an integrated circuit as a main device of microelectronics has been increased. With the increase of the integration density, a pattern width becomes narrower so that the processing such as etching and deposition to a semiconductor substrate with large irregularity is required. To fill the above-mentioned requirement, there are provided a lot of methods of processing of a semiconductor device by use of plasma.
For example, a plasma etching method at a low pressure (under high vacuum) has been developed as an etching technique for a thin film (Japanese Laid Open Patent Applications: JP-A-Showa 61-256727, JP-A-Showa 62-194623, JP-A-Heisei 5-247673, and JP-A-Heisei 6-132252). In these conventional techniques, various dry etching apparatuses are used such as a plasma etching apparatus, a sputtering apparatus, an electron cyclotron resonance (ECR) etching apparatus, a magnetron etching apparatus, and an ion beam etching apparatus. An etching rate increases by employing a gas containing halogen such as Freon based gas (for example, CF
4
and the like) during processing of a semiconductor substrate by a dry etching method using plasma. Consequently, a fine pattern processing can be realized. Also, in a thin film deposition technique, a halogen based gas such as TiCl
4
, WF
6
is dissociated, and the deposition at a low temperature and at a high rate can be realized.
However, there has been limitations in processing precision, when the etching for fine patterns is performed, or a film is deposited on a micro-processed irregular surface.
First, a problem of the fine pattern etching will be described below. For example, when contact holes are formed in an SiO
2
insulating film of a semiconductor device by an etching method, the limitation of a selection ratio is known to be about 50 when an etching rate is kept at a value not less than 1 &mgr;m/min. Here, the selection ratio is a ratio of an etching rate to a SiO
2
film formed on a silicon substrate or a nitride film to an etching rate of the silicon substrate or the nitride film.
That is, when the contact holes are formed, over-etching is performed to completely open the holes in consideration of the deviation of processes. This means that the silicon substrate or the nitride film is simultaneously etched away by {fraction (1/50)} of the thickness of the SiO
2
film. As a result, the silicon substrate is inevitably etched away to some extent.
In the semiconductor device such as a metal oxide semiconductor large-scale integrated device (MOSLSI device), there arises a problem in which a silicon substrate is etched to a p-n junction layer which has been formed under the contact hole in conjunction with the increase of the integration density. For this reason, new countermeasures such as deposition of a polymer on the silicon substrate or a nitride film using a fluorocarbon gas are required.
The reason in which a satisfactory selection ratio can not be attained will be described below. Let's consider a case where an etching process is performed at a high rate by use of a high density plasma. When a C
4
F
8
gas plasma is generated, radicals and C
x
F
y
+
ions having high energy are generated in the plasma through a complex dissociation process such as C
4
F
8
→C
4
F
7
→C
3
F
5
→C
2
F
4
→CF
2
→CF →C+F. In the plasma, electron energy is not less than about 5 eV, which is relatively high. Therefore, a dissociation rate of the C
4
F
8
gas becomes high. Thus, radical species such as CF
2
are rare which act as a precursor necessary for obtaining a high selection ratio. Therefore, an important problem is that desired radical species or desired ion species are selectively generated.
To address the above-described problem, there is disclosed conventional methods in which electron energy is reduced in a low pressure and high density plasma (Japanese Laid Open Patent Applications: JP-A-Heisei 5-029613, and JP-A-Heisei 6-122978). In these methods, dissociation in the plasma is relatively restrained, and a lot of radicals contributing to an improvement in selectivity are generated, compared with the conventional methods. However, a problem is remaining in that an ion current density injected into a semiconductor substrate is reduced and the etching rate is also reduced, since an amount of high-energy electrons which contribute to ionization is relatively small. On the other hand, there is known a method in which a plasma is generated by supplying electrons whose energy is controlled by an electron beam. In this method, although dissociation and ionization can be accurately controlled, ionization requiring high energy and dissociation requiring low energy cannot simultaneously occur. Also, a plasma having a high density cannot be homogeneously generated across a large diameter. As a result, there gives rise to problems for practical use.
Next, deposition on an irregular surface of a semiconductor substrate will be described below. For example, when a thin film is deposited on the semiconductor substrate by use of a UHF plasma using a C
4
F
8
gas as a process gas, it is preferable that a lot of CF radicals are generated. In such a case, low permittivity, high heat resistance, and superior embedding property are attained. However, in the above-described UHF plasma, CF
2
and CF
3
are mainly generated, so that satisfactory properties are not accomplished.
In conjunction with the above description, a dry etching apparatus is described in Japanese Laid Open Patent Application (JP-A-Showa 62-76627). In this reference, a gas inside a chamber is exhausted by an exhausting unit. Then, a reactive gas is introduced into a chamber. A power is applied between opposing parallel plate electrodes to generate a discharge between the electrodes. A sample is located on one of the opposing electrodes. An electron beam is supplied into a discharge plasma generated between the electrodes. In this dry etching apparatus, however, a parallel plate electrode structure is adopted. Therefore, an electron energy distribution is broad. As a result, it is difficult to apply the apparatus to a very fine pattern processing.
Also, a plasma reacting apparatus is described in Japanese Laid Open Patent Application (JP-A-Showa 64-90534). In this reference, opposing parallel plate electrodes are provided in a chamber and a plasma is generated between the electrodes. An electron beam is supplied between the electrodes. Thus, etching or deposition is performed to a substrate located on one electrode.
Also, a dry etching apparatus is described in Japanese Laid Open Patent Application (JP-A-Heisei 4-181727). In this reference, an etching gas is introduced in a chamber, and opposing electrodes are provided in the chamber. A high frequency power is applied to the electrodes to cause a glow discharge to generate a plasma. An electron gun outputs an electron beam toward the electrodes and the electron beam is scanned on the semiconductor wafer.
Also, a plasma surface processing apparatus is described in Japanese Laid Open Patent Application (JP-A-Heisei 6-181185). In this reference, an electron beam is irradiated to a plasma source gas to generate a plasma. At this time, an electron distribution of electrons irradiated is modulated with respect to space and time. A high frequency bias is applied to a wafer holder in synchronous with the modulation so that the plasma is modulation with respect to time. Thus, a semiconductor wafer is etched.
Also, an electron beam exciting plasma film forming apparatus is described in Japanese Laid Open Patent Application (JP-A-Heisei 8-27577). In this reference, two electron beams with high energy and low energy are provided. A plasma is generated through excitation by the electron beam. When the e

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