Coating processes – Direct application of electrical – magnetic – wave – or... – Plasma
Reexamination Certificate
1999-03-26
2001-01-23
Beck, Shrive (Department: 1762)
Coating processes
Direct application of electrical, magnetic, wave, or...
Plasma
C427S527000, C427S528000, C427S582000, C427S596000, C216S065000, C216S066000, C216S067000
Reexamination Certificate
active
06177147
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a process and apparatus for treating a substrate by using a halogen-containing gas, more especially to a process and apparatus for etching a substrate or depositing a thin film on a substrate by using a halogen-containing gas.
BACKGROUND ART
The integration of an integrated circuit which is a main part of microelectronics has been increased year by year. With the increase of the integration, process technologies, which can provide a fine pattern on a substrate, such as fine etching technology and the like as well as a thin film deposition technology have been required. Under such requirements, various technologies of applying a halogen-containing gas have been put into practice.
In the etching, which is one of the process technologies, there exist various dry etching technologies for processing a semiconductive substrate or a thin film deposited on the substrate through the steps of using a halogen-containing gas under low pressure or high vacuum and exciting this halogen-containing gas by some means. As for this example, there has been known a process of exciting a halogen gas by exposing to plasma, or by the irradiation of an electron beam, an ion beam or a light. Especially, the etching by exposing to plasma has been widely applied since it is highly practicable. Recently, there have been put into practice high-density plasma etching technologies of applying ECR (Electron Cyclotron Resonance) type of plasma, ICP (Induction-Coupled Plasma), or a plasma method (hereinafter referred as to “UHF plasma”) generated in the course of electric discharge caused by applying an electric field of high frequency ranging in VHF to UHF bands, that is, nearly from 100 to 1,000 MHz and the like in addition to parallel-plate type of plasma etching technology. In these etching technologies, using a halogen-containing gas such as fluorocarbon (CF
4
, C
4
F
8
and the like) makes it possible to etch a semiconductive material including silicon (Si) and the like, insulating material including silicon oxide (SiO
2
), silicon nitride (SiN) and the like, and a metallic material including aluminum and the like, or to remove selectively one of these materials by etching. Accordingly, this type of halogen-containing gas is indispensable for forming a fine pattern on the substrate.
In the process technologies other than the etching technology, for example, a thin film deposition technology, a halogen-containing gas also has been widely used as raw materials. As an example of this, a case of depositing a fluorinated amorphous carbon (a-C:F) film by applying a plasma CVD (Chemical Vapor Deposition by using plasma) process is given. As disclosed in Japanese Patent Kokai Publication Nos. JP-A-8-83842 (1996) and JP-A-8-222557 (1996), the a-C:F can be prepared by introducing a fluorocarbon gas such as CF
4
and the like solely or together with a hydrocarbon gas such as CH
4
and the like into plasma. Many type of plasma can be used in this process. The usable plasma includes parallel-plate type of plasma, ECR type of plasma, ICP, helicon type of plasma, UHF plasma and the like. As for other example, a case of depositing a titanium film by using TiCl
4
a case of tungsten by using WF
6
and the like are given.
In these processes of treating the substrate, the species which act on the substrate are not parent molecules of the gas themselves but the active species of radicals and/or ions resulting from the dissociation of these molecules by the action of plasma and the like.
SUMMARY OF THE DISCLOSURE
However, The conventional processes for treating a substrate have the following problems.
The most essential problem among them is that it is impossible to control at desire kind and concentration(density) of radicals and/or ions resulting from dissociation of gas molecules by the action of plasma and the like. For example, in case of plasma etching by using the CF
4
gas, parent molecules of the gas are excited and dissociated by the energy of plasma electrons to produce radicals and ions. This dissociation process is very complicated. For example, even in the simplest case of CF
4
, its dissociation process has the steps of CF
4
→CF
3
→CF
2
→CF→C+F. Further, each content of the radials and ions is determined on complicated mutual balance of various parameters such as pressure of plasma, electron energy, concentrations of all radical and ion species contained in the plasma and the like. Accordingly, it has been hitherto impossible to control the concentrations of the radicals and ions resulting from the dissociation of the halogen-containing gas precisely.
On account that it has been impossible to control the ratio of the radicals and ions resulting from the dissociation of the halogen-containing gas as mentioned above, there has hitherto been the following problems.
Assume an exemplary case of making a contact hole through a substrate of Si by etching a thin film of SiO
2
deposited on the substrate in a CF
4
gas plasma. In this case, a large etching speed is important first of all, and secondary, a large etching selection ratio (etching rate of the SiO
2
film deposited on the Si substrate relative to the Si substrate) is important for ensuring good processability. By the way, there is fluctuation in the etching speed and the thickness of the SiO
2
depending on the surface spot of a wafer now. In order to make contact holes through the wafer over its surface without failure under such conditions, it is necessary to overetch the SiO
2
film for certain overtime additional to an appropriate time. In order to etch the substrate as little as possible during a given short period of the overtime, a large etching selection ratio is required. When a contact hole is made, e.g., through a diffusion layer of a MOS transistor under the condition of an insufficient etching selection ratio, the diffusion layer will be etched. Accordingly, insufficient etching selection ratio will exert adverse effect on the properties of the produced semiconductive element or deteriorate the operational action of the same.
In the conventional plasma etching process in which neither of the radical nor ion species has been control led, it is difficult to satisfy both of high etching speed and etching selection ratio. For example, in case of maintaining at least 1 &mgr;m/min. of the etching speed, attainable etching selection ratio has been limited to around 50. This value is insufficient to the manufacturing of integrated semiconductive devices. Especially, in the above mentioned MOS transistor, a diffusion layer having shallow junction is inclined to be formed with the improvement of integration. Accordingly, the element destruction due to the overtime of etching has been caused easily more and more.
The reason why it has been hitherto impossible to satisfy high etching speed together with high etching selection ratio is considered as follows. In etching a SiO
2
film deposited on a Si substrate termed as “SiO
2
/Si etching”, active species which mainly advance etching are different from those which contribute to the selection of etching. It is generally considered, among the active species resulting from the dissociation of CF
4
gas, that CF
3
+
ion, which is a low dissociation product mainly advances etching and that CF
2
and CF radicals, which are high dissociation products, polymerize to form polymers on the surface to be etched, and thereby contribute to the selection of etching. However, it was difficult to control the ratio of these species in the conventional plasma etching. Accordingly, it has been hitherto impossible to satisfy both of the high etching speed and etching selection rate.
Another problem that the prior art processes for treating a substrate have is that it is difficult to control the fluorine concentration in the a-C:F film deposited by applying plasma CVD. In case that the a-C:F film is used as an interlaminar insulating film, its dielectric constant lowers in proportion to the fluorine content. On the other hand, when the fluorin
Samukawa Seiji
Tsuda Kenichirou
Beck Shrive
Crockford Kristen A.
NEC Corporation
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