CA2155659A1

CA2155659A1 - Process for depositing a thin layer on a substrate using a remote cold nitrogen plasma

Info

Publication number: CA2155659A1
Application number: CA002155659A
Authority: CA
Inventors: Franck Callebert; Philippe Supiot; Odile Dessaux; Pierre Goudmand
Original assignee: Individual
Current assignee: Compagnie Europeenne de Composants Electroniques LCC CICE
Priority date: 1993-02-10
Filing date: 1994-02-09
Publication date: 1994-08-18
Also published as: EP0683825A1; KR960701237A; FI953779A0; FR2701492A1; JPH08506381A; DE69404971D1; FR2701492B1; ATE156866T1; DE69404971T2; WO1994018355A1; FI953779L; EP0683825B1

Abstract

A method for applying a thin film to a metal, organic or inorganic substrate (12), wherein a remote cold nitrogen plasma essentially consisting of free nitrogen atoms is produced in an enclosure (5) housing said substrate (12). To form passivation layers, a gaseous organosilica or germanium compound containing CH, Si (or Ge), O or NH groups is fed into said enclosure (5) during the formation of the remote nitrogen plasma. To form dielectric thin films, organometallic compounds may also be added.

Description

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"Process for depositing a thin layer on a substrate using a remote cold nitroqen plasma"

The present invention relat:es to a process for producing homogeneous, thin layers which are adherent to the surface of metallic, organic or inorganic substrates, ~p~hle of being involved in the production of electronic or microelectronic devices.

The present invention also relates to the products obtained by the process.

For a number of decade~s the electronics industry has been employing the technology of materials involving their electronic, dielec:tric, conductive or insulating properties.

The materials employed~ for electronic applications have undergone considerable modifications in order to meet performance requirements in increasingly severe conditions of use. These modifications have driven the elect;ronics industries to perform considerable miniaturization of all of their components. It has therefore been necessary for the latter to be presented in ever thinner layers involving novel deposition techniques.

Among the latter, we shall be concerned essentially with the t~chni~les consisting in depositing on a metal substrate a deposit of a silicon oxide (SiO2) or of a compound of ceramic or polymeric nature, such as SiN or polysiloxanes. This can be done in a number of different ways.

For example, in the case o~ SiO2, the thin film may be obtained by condensation of silicon oxide vapour obtained by bombarding a target of (SiO2) with a high-energy ion beam.

In order to create a fi.lm of (SiO2), some authors employ the technology of plasma-assisted deposition, in which a plasma-forming gas is excited by a radio-frequency, microwave or continuous discharge.

The plasma-forming gas very fre~lently consists of a rare gas, by itself or as a mixture at pressures of 2 1 ~
.~ .

between 10-5 and lO-2 hPa. This ~ischarge plasma is composed of ionic species, of fast electrons, of atoms and/or of electronically and/or vibrationally excited molecules, as well as ultraviolet ;photons. It is into this medium that the precursor gas of the deposit is introduced. The precursor gas of the deposit is generally composed of a mixture of silane (SiH4) and of oxygen or of an organosilicon gas such as tetraethoxysilane (TEOS). This precursor gas is dissociated by the plasma and the products of dissociation, which are in most cases radicals, recombine at the surface of the substrate to form the actual deposit. Polysiloxanes are obtained in the same way from monomers such as, for example, hexamethyldisiloxane.
The main characteristics of this t~-hnique are that it produces a deposit whose sl:oichiometry is that of the precursor gases. It produces a rate of deposition which is limited by the regasifications induced by the action of the high-energy plasma carriers (ions, fast electrons and W photons), and causes rapid heating of the substrate to temperatures that are higher than the melt:Lng t~r~rature of conventional organic materials (T>200C). This technique exposes the substrate to considerable ion and electron bombardments and gives riLsc to processes of photochemical degradation of the substrate and of the deposit formed. The effective area ~f the deposition is determined by the geometry of the electrodes. The latter do not e~c~d a few hundred square centimetres.
The very high viscosity of th:ls type of plasma restricts the application of this t~chn;que to deposits on planar surfaces and prevents the deposition from being carried out correctly on awkward surfaces.
The techniques described above do not provide a suitable solution for depositing an adherent, thin film ensuring a good uniformity of deposition on planar or awkward surfaces, at rates of t;reatment which are compatible with a high-rate process on a substrate that 2 ~
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can be either metallic or polymeric.
The present invention i8 aimed at providing a process making it possible to carry out a deposition of a polymeric thin layer on metallic, inorganic or polymeric substrates at high rate~ of treatment. The deposits produced according to th,a present invention have the property of being homogeneous and adherent to the substrate.
Another objective aimed at by this invention is to provide a process which is c~p~hle of producing at will a thin and homogeneous deposit on a planar substrate, and a homogeneous film on substrates of complex geometry, especially in three ~im~nsions.
According to the inventic,n the process for applying a polymeric thin film onto a metallic, inorganic or organic substrate, in which a remote nitrogen plasma consisting essentiaLly of free nitrogen atoms and of energetically excited dinitrogen species is produced in a vessel in whic,h the substrate is situated, is characterized in that a gaseous organosilicon or -g~rm~nium compound containing CH, Si (or Ge), 0 or NH groups is introdLuced into the said vessel during the formation of t:he remote nitrogen plasma.
The process for forming 1:he remote nitrogen plasma has been described especially in French patent No. 2 616 088.
In contrast to the plasmas obtained by a different process, the above proceC~s makes it possible to produce, in a region which is distant from the discharge region, a plasma consisting essentially of free nitrogen atoms.
Such a plasma virtually does not heat the substrate. In the process described in the above French patent the nitrogen plasma has the effect of treating the surface of the substrate to make it a&erent towards a coating which is appliedL subseqLuently, that is to say outside the treatment vessel.
In the case of the process in accordance with 21~6~

the present invention the presence of the organosilicon or -g~rm~ni um compound in the plasma vessel makes it possible to obtain on the substrate a layer that can adhere to any substrate. The rate of formation of this layer is fast, because it i8 produced in a medium devoid of ion or photon bombardment effects which are destructive to the formation of the layer.
The said gaseous silicon compound is preferably chosen from alkoxysilanes, siloxanes and silazanes.
According to a preferred version of the invention, a gaseous compound con~ining oxygen is ~ to the gaseous compound :introduced into the vessel and outside the discharge.
This gaseous compound containing oxygen may be molecular oxygen.
It has been found, surE)risingly, that the presence of an oxygen-containing sras~ such a~ oxygen, in the medium containing the nitrogen plasma and the gaseous organosilicon compound makes it possible to increase considerably the rate of formation of the dielectric layer on the substrate.
This surprising finding makes the process according to the invention particularly advantageous from the industrial viewpoint, because of its high production efficiency in relation to the low energy used .
It has been found, fur~h~rmore, that the nature of the layer deposited on the substrate varied not only according to the nature of the gaseous organosilicon compound employed, but also as a function of the oxygen content introduced into the plasma vessel.
Still other special features and advantages of the invention will appear in the description below.
The attached single figure~, given by way of nonlimiting example, shows the diagram of a device for making use of the process according to the invention.
Shown on the left of this figure is a source 1 of nitrogen supply, connected to a tube 2 which comprises a cavity 3 in which a discharge, maintained 2~56~
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and connected to a microwave generator 4, takes place.
The nitrogen pressurQ in~3ide thQ tube 2 is between 1 and 20 hPa. The frequeIlcy generated by the microwave generator may be 2450, 915 or 433 MHz, or any other legal frequency.
The tube 2 i8 connected to a treatment vessel 5 equipped with a gauge 6 for measuri,ng the pressure. The vessel 5 is connected to a vacuum pump 7. An injector 8 is introduced into the part of the tube 2 situated just above the vessel, serving to inject: into the vessel 5 a gaseous organosilicon compound 9, oxygen 10 or another additional reactive gas 11.
A substrate 12 onto which it is desired to deposit a dielectric and highly adherent thin layer is situated inside the vessel 5.
The flowing remote cold plasma is initiated by the effect of the microwave dischlarge on the plasma-forming gas consisting of nitrogen (N2), optionally doped and ~comrressed in the tube called "discharge tube".
The flowing remote cold p].asma is obtained by extraction, in a dynamic regime and from the vessel 5 situated outside the electromagn,atic field, of the species which are excited by the discharge (vibrationally or electronically excited electrons, ions, atoms and molecules).
Only thQ particles which have a sufficiently long "lifetime" succeed in reac:hing the treatment region situated downstream of the discharge.
This reactive medium is c:haracterized by the fact that it does not contain any ions or electrons in an appreciable quantity.
It is composed of free nitrogen atoms generally in the ground state - whc)se reactivity arises from their radical nature. Thus, the nitrogen atoms are in the free N(4S) triradical form.
It should be noted that t~he special mechanics of the nitrogen plasmas enables them to have a lifetime and a volume extension which are much greater than 2~6~3 .~ .

those, for example, of oxygen plasm~s. Furthermore, the existence of other plasma-forming gases such as CO, CO2, NO, NO2, CO and H2O must also be noted.
Finally, tha propertiQs of a flowing cold plasma can be directed by a doping agent, for example 2~ NH3, NF3, CF4 or SF6 The process according to the present invention consists in depositing an adherent and homogeneous thin layer onto the surface of the metallic or other substrate 12. This layer is formed by heterogeneous r~co~in~tion reactions of radical species at the surface of the substrate. These species originate from the reaction between the gaseous precursor (organosilicon compound) and the flowing remote cold plasma.
The organosilicon compounds introduced into the treatment vessel may be:
an alkoxysilane of formula R1 [ Si ]n R3 with n s5 I

H

R1, R2 and R3 denoting CH3, C2H5~ C6H6~ H~ NH2 QtC.
a siloxanQ of formula:

I

Rl- t - si-o ]n~R3 with n ~4 I
H

or a silazane of formula:

215~6~9 Rl-t-Si-NH~n-Si-R1 wit;h n <4 H H

or a mixturQ of thQ abovementioned monomer compounds.
It has been found that in all cases the presencQ of oxygen introduced into thQ vessel 5 at the same time as the organosilicon compound considerably promote~ the rate of formation O.e the layer on the substrate 12.
When an alkoxysilane i8 .introduced into the plasma vessel 5 and when the oxygen content introduced into the vessel i~ lower than a few per cent, an amorphous silica layer is obtained on the substrate 12.
When an alkoxysilane i8 introduced into thQ
plasma vQssel 5 and when the oxygen content is higher than a few per cent, a layer of a mixture of amorphous silica and of polymerized silica is obtained on the substrate 12.
Furthermore, when a siloxane is introduced into the plasma vessel 5 and when the oxygen content introduced into the vessel is low~r than a few per cent, a layer formed by the mixture of the following compounds is obtained on the substr,ate 12:
crosslinked polymer (Si-O-Si) -Si-~CH3)1 -Si-OH
-Si-NH-Si When a siloxanQ is introduced into the plasma vessel 5 and when the oxygen conl:ent introduced into the ~essel i~ higher than a few per ceri~, a layer formed by the mixture of the fol.lowing compounds is obtained on the substrate:
crosslinked polymer (Si-O-Si) 2155~

-Si-~CH3)2 -Si-(CH3)3 -Si-OH
-Si-NH-Si The presence of the -OH, -NH or -NH2 radicals i8 important insofar as it gov~arns the dielectric properties of the deposit.
When a silazane is introduced into the plasma vessel 5, a layer formed by t;he mixture of the following compounds is obtained on the substrate 12:
-Si-NH-Si --si--o--s --si--c--s The substrate may be metallic or made of ceramic or polymer.
The layer obtained may have a controlled thickness that may be between 500 ~. and 50 ~m. The rate of deposition of the layer may be of the order of 1 ~m/min.
Substrates coated with such a layer may be employed as co~rone~ts comprising a passivating layer for electrical or thermal protection, especially in on-board electronics.
The introduction of an additional reactive gas into the reactor (5) simultaneously with one or more of the abovementioned organosilicon compounds enables electrical or dielectric properties of the thin layer deposited to be controlled.
The gases introduced ar~a ions (anions or cations comprising metals) introduced into the gas phase in the form of halides, oxy,halides or complexes such as acetylacetonates, fluoroacetylacetonates etc., or of other complexing agents.
Composite thin layers (ceramic polymer) with controlled electrical or dielectric properties are thus formed.

Claims

1. Process for applying a polymeric thin layer onto a metallic, inorganic or organic substrate (12), in which a remote nitrogen plasma consisting essentially of free nitrogen atoms is produced in a vessel (5) in which the substrate (12) is situated, characterized in that a gaseous organosilicon or -germanium compound containing CH, Si (or Ge), O or NH
groups is introduced into the said vessel (5) during the formation of the remote nitrogen plasma.

2. Process in accordance with Claim 1, characterized in that the said gaseous siliceous compound is chosen from alkoxysilanes, siloxanes and silazanes.

3. Process in accordance with either of Claims 1 and 2, characterized in that a gaseous compound containing oxygen is added to the gaseous compound introduced into the vessel (5).

4. Process in accordance with Claim 3, characterized in that the gaseous compound containing oxygen is molecular oxygen.

5. Process in accordance with one of the preceding claims, characterized in that an anion or cation containing a metal, in the form of gaseous compound, is additionally introduced into the plasma vessel.

6. Process in accordance with Claim 5, characterized in that the said gaseous compound is chosen from halides, oxyhalides and organometallic compounds such as acetylacetonates and fluoroacetylacetonates.

7. Process for deposition of a polymeric thin layer onto a metallic, inorganic or organic substrate (12), the said deposition being performed in a vessel (5) by recombination at the surface of the substrate of the products originating from the! dissociation of a precursor gas by a plasma-forming gas originating from a plasma generated in a discharge cavity (3), characterized in that the said plasma is a remote nitrogen plasma and in that the precursor gas is an organosilicon or organogermanium gas.

8. Process according to Claim 7, characterized in that the remote plasma is a flowing remote cold plasma.

9. Process according to Claim 8, characterized in that the flowing remote cold plasma consists essentially of free nitrogen atoms.

10. Process according to either of claims 8 and 9, characterized in that the nitrogen pressure is between 1 hPa and 20 hPa.

11. Process according to any one of Claims 7 to 10, characterized in that the precursor gas of the deposit is introduced between the exit of the cavity (3) in which the discharge generating the plasma is maintained and the entry of the vessel (5).

12. Process according to any one of Claims 7 to 11, characterized in that the organosilicon compound is chosen from the alkoxysilanes of formula:

with n smaller than or equal to 5, the siloxanes of formula:

with n smaller than or equal to 4, or the siloxanes of formula:

with n smaller than 4, R1, R2 and R3 denoting CH3, C2H5, C6H6, H or NH2.

13. Process according to any one of claims 7 to 12, characterized in that oxygen is introduced during the said deposition into the said vessel (5) so as to accelerate the rate of deposition of the polymeric layer.

14. Process according to any one of Claims 7 to 13, characterized in that a doping component, chosen from the bodies of chemical formula NH3, NF3, CF4 or SF6, is introduced into the vessel (5).