Process for thin film deposition through controlled formation of vapor phase transient species

Abstract

A method for deposition of a thin film onto a substrate is provided. The method includes providing a source precursor containing on or more of elements constituting the thin film, generating a transient species from the source precursor, and depositing a thin film onto the substrate from the transient species. The transient species being a reactive intermediate that has a limited lifetime in a condensed phase at or above room temperature.

Claims

1. A method for deposition of a cobalt-based thin film onto a substrate surface, the method comprising: providing a deposition chamber containing a substrate; providing a synthesis chamber which is distinct from but connected to the deposition chamber; connecting the synthesis chamber to the deposition chamber with a vacuum interlock or valving system; providing a cobalt source precursor to the synthesis chamber; maintaining the working pressure in the synthesis chamber in the range of 5 to 150 ton; generating a cobalt-containing vapor phase transient species from the source precursor in the synthesis chamber; wherein the vapor phase transient species is generated independently from the substrate surface; wherein the temperature of the synthesis chamber during generation of the vapor phase transient species is maintained at a temperature of about 150° C. to about 250° C.; controlling a concentration or partial pressure of the vapor phase transient species in the synthesis chamber using a vacuum, inert gas, or a stabilizing gas to prevent self-reaction of the transient species; (a) maintaining the partial pressure of the vapor phase transient species at 5 to 50 Torr and maintaining the substrate at a temperature of about 100° C. to about 400° C.; or (b) maintaining the partial pressure of the vapor phase transient species at 5 to 20 Torr and maintaining the substrate at a temperature of about 100° C. to about 500° C.; and delivering the vapor phase transient species to the deposition chamber, wherein the vapor phase transient species decomposes to form a cobalt-based thin film on the substrate.

2. The method of claim 1, wherein the cobalt source precursor has a cobalt oxidation state of zero.

3. The method of claim 1, wherein the vapor phase transient species is Co(CO).sub.2NO* and/or Co(CO).sub.2*.

4. The method of claim 2, wherein the cobalt source precursor is dicobalt octacarbonyl, dicobalt hexacarbonyl t-butylacetylene, or cobalt tricarbonyl nitrosyl.

5. The method of claim 1, wherein hydrogen is used as a co-reactant in the synthesis chamber, optionally in combination with an inert gas.

6. The method of claim 5, wherein the vapor phase transient species is HCo(CO).sub.2NO* and/or HCo(CO).sub.3*.

7. The method of claim 1, wherein the method for deposition of the cobalt-based thin film onto the substrate surface is a method selected from the group consisting of chemical vapor deposition, atomic layer deposition, molecular layer deposition, and self-assembled monolayer deposition.

8. A method for deposition of a cobalt-based thin film onto a substrate in a deposition chamber, the method comprising: providing a deposition chamber containing a substrate; equipping the deposition chamber with a vacuum manifold and a pumping system to maintain pressure in the deposition chamber; providing a cobalt source precursor to the deposition chamber; heating the deposition chamber to a conversion temperature between about 150° C. and about 250° C. to generate a vapor phase transient species from the cobalt source precursor in-situ in the deposition chamber, wherein the vapor phase transient species is generated independently from the substrate surface; controlling a concentration or partial pressure of the vapor phase transient species in the deposition chamber using a vacuum, inert gas, or a stabilizing gas to prevent self-reaction of the transient species; (a) maintaining the partial pressure of the vapor phase transient species at 5 to 50 Torr and maintaining the substrate at a temperature of about 100° C. to about 400° C.; or (b) maintaining the partial pressure of the vapor phase transient species at 5 to 20 Torr and maintaining the substrate at a temperature of about 100° C. to about 500° C.; wherein the vapor pressure of the transient species and the substrate temperature are controlled to inhibit self-reaction of the transient species during their synthesis and prevent gas phase depletion; and subsequently depositing a cobalt-based thin film on the substrate from the vapor phase transient species.

9. The method of claim 8, wherein the cobalt source precursor has a cobalt oxidation state of zero.

10. The method of claim 8, wherein the vapor phase transient species is Co(CO).sub.2NO* and/or Co(CO).sub.2*.

11. The method of claim 9, wherein the cobalt source precursor is dicobalt octacarbonyl, dicobalt hexacarbonyl t-butylacetylene, or cobalt tricarbonyl nitrosyl.

12. The method of claim 8, wherein hydrogen is used as a co-reactant, optionally in combination with an inert gas.

13. The method of claim 12, wherein the vapor phase transient species is HCo(CO).sub.2NO* and/or HCo(CO).sub.3*.

14. The method of claim 8, wherein the method for deposition of the cobalt-based thin film onto the substrate surface is a method selected from the group consisting of chemical vapor deposition, atomic layer deposition, molecular layer deposition, and self-assembled monolayer deposition.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The foregoing summary, as well as the following detailed description of the invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there are shown in the drawings embodiments which are presently preferred. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown. In the drawings:

(2) FIG. 1 is a schematic rendering of the apparatus for ex-situ formation of transient species that are then transported to a thin film processing chamber where they react to form a thin film on a substrate;

(3) FIG. 2 is a schematic rendering of the apparatus for in-situ formation of transient species in the thin film deposition chamber where they then react to form a thin film on a substrate; and

(4) FIG. 3 is a schematic rendering of a manufacturing cluster tool equipped with modules for ex-situ and in-situ synthesis of transient species that are then reacted in thin film processing chambers.

DETAILED DESCRIPTION OF THE INVENTION

(5) The present invention relates to high-quality thin films formed by CVD, ALD, MLD, or SAM deposition on various substrates, and a method for depositing such films. The method of the present invention may deposit such films as a thin amorphous or polycrystalline film or an epitaxial film on a substrate.

(6) In one embodiment, the present invention relates to silicon-rich or silicon-based films formed from transient species generated from parent silane precursors, and further relates to associated methods for the CVD or ALD of such films on various substrates. As used herein, “silicon-rich films” refers to epitaxial or amorphous silicon and silicon alloys with germanium and carbon, as well as doped silicon thin films. For example, the silicon thin film may be doped with small amounts of arsenic, phosphorus and boron that modify silicon's properties, such as conductivity.

(7) In another embodiment, the present invention relates to cobalt-rich or cobalt-based films formed from transient species generated from parent cobalt precursors, and further relates to associated methods for the CVD or ALD of such films on various substrates. As used herein, “cobalt-rich films” refers to epitaxial and amorphous cobalt and cobalt alloys or compounds, such as cobalt oxide and cobalt nitride.

(8) Such high-quality films are especially useful on substrates such as semiconductor and solar cell substrates. Examples of the substrates that may be utilized for formation of either silicon-rich or silicon-based films or cobalt-rich or cobalt-based films include, for example, metals such as copper, tungsten, cobalt, ruthenium, titanium, and tantalum; metal compounds and alloys such as nitrides and carbides, silicon, silicon alloys with germanium and carbon, silicon dioxide, and the like which are found in IC and solar cell technologies.

(9) There is essentially no limitation on the type of substrate that can be used in the present method. Preferably, however, the substrate is thermally and chemically stable at the conditions used for depositing the film or films onto the substrate. That is, the substrate is preferably stable at temperatures between about 150° C. and about 650° C. It will be understood by those skilled in the art that the thermal stability of the substrate may depend on various factors, such as the type of film to be deposited and the intended use of the coated substrate.

(10) In the embodiment for formation of silicon-rich or silicon-based films, the parent precursors are preferably perhydridosilanes, and more preferably perhydridosilanes having from 2 to 8 silicon atoms. More preferably, the parent perhydridosilane precursor for generating the transient species to form silicon-rich or silicon-based films is isotetrasilane.

(11) Under controlled CVD or ALD processing conditions, including specific temperature, pressure, and key processing conditions (such as providing additional tailored chemical, thermal, plasma, or ionization energy) to the parent perhydridosilane precursors, the parent precursors are converted to specific and desirable silylene transient species that are designed to grow epitaxial or amorphous films with specific composition, morphology and structure. For formation of the transient species, substrate temperatures are preferably in the range of 250°-600° C., and more preferably in the range of 375-500° C. For formation of the transient species, the reactor working pressure is preferably in the range of 10-150 torr, and more preferably in the range of 10-40 torr.

(12) In one embodiment, the parent perhydridosilane precursor is preferably isotetrasilane and the silylene transient species generated from the isotetrasilane is bis(trihydridosilyl)silylene ((H.sub.3Si).sub.2Si), with silane as a byproduct Bis(trihydridosilyl)silylene ((H.sub.3Si).sub.2Si) can be generated from isotetrasilane by a variety of methods. In particular, bis(trihydridosilyl)silylene ((H.sub.3Si).sub.2Si) can be generated from isotetrasilane under controlled processing conditions, such as direct or remote plasma-assisted conditions, electron ionization at energy levels of 6 eV or greater (preferably between 6 eV and 15 eV, although energy levels as high as 70 eV can be employed), chemical ionization, and/or thermal decomposition at temperatures at or above 250° C.

(13) Without wishing to be bound by theory, the mechanism for formation of bis(trihydridosilyl)silene appears to be the controlled and reproducible reductive elimination of silane from isotetrasilane, as shown below:

(14) ##STR00001##

(15) Branched perhydridosilanes, such as isotetrasilane, are preferred for the method of the invention, because they necessarily have a relatively greater proportion of Si atoms bonded to three hydrogens than their linear analogs. Branched perhydridosilanes are thus more likely to undergo dissociative adsorption. In this respect, the sticking coefficient ε, defined as the number of adsorbed molecules per number of impacts, of branched perhydridosilanes is expected to be higher than that of their linear analogs.

(16) As such, the invention demonstrates that isotetrasilane is a superior candidate for CVD e-Si, particularly relative to its lower order perhydridosilane counterparts. The advantages of isotetrasilane include (i) the generation of bis(trihydridosilyl)silylene as the transient species for film formation, (ii) reduced particle formation in the reaction zone due to the inhibition of undesirable gas-phase reactions, and (iii) lower decomposition temperature due in part to its higher surface sticking coefficient.

(17) Alternatively, bis(trihydridosilyl)silylene can be generated by the thermally-driven reaction of disilane with trisilane. Other homologs of bis(trihydridosilyl)silylene can be generated, for example, by the reaction of disilane with n-tetrasilane.

(18) In the embodiment for formation of cobalt-rich or cobalt-based films, the parent cobalt precursors are preferably Co.sup.(0) precursors, and more preferably Co.sup.(0) precursors having a Co oxidation state of zero. In one such preferred embodiment, the parent Co.sup.(0) precursor for generating a transient cobalt coordination complex with an unsatisfied coordination sphere to form cobalt based films is cobalt tricarbonyl nitrosyl.

(19) Under controlled CVD or ALD processing conditions, including specific temperature, pressure, and key processing conditions (such as providing additional tailored chemical, thermal, plasma, or ionization energy) to the parent Co.sup.(0) precursors, the parent cobalt precursors are converted to specific and desirable Co(CO).sub.2NO* transient species that are designed to grow epitaxial or amorphous films with specific composition, morphology and structure. For formation of the transient species, substrate temperatures are preferably in the range of 100°-500° C., and more preferably in the range of 250-400° C. For formation of the transient species, the reactor working pressure is preferably in the range of 5-50 torr, and more preferably in the range of 5-20 torr.

(20) In one embodiment, the parent Co.sup.(0) precursor is preferably cobalt tricarbonyl nitrosyl and the cobalt transient species generated from the cobalt tricarbonyl nitrosyl precursor is Co(CO).sub.2NO*. Co(CO).sub.2NO* can be generated from cobalt tricarbonyl nitrosyl by a variety of methods, forming CO or NO as a byproduct In particular, Co(CO).sub.2NO* can be generated from cobalt tricarbonyl nitrosyl under controlled processing conditions, such as direct or remote plasma-assisted conditions, electron ionization at energy levels of 1 eV or greater (preferably between 2 eV and 20 eV), chemical ionization, thermal decomposition, and/or photolysis. Substrate temperatures are preferably in the range of 100°-500° C., and more preferably in the range of 250-400° C. The reactor working pressure is preferably the range of 5-50 torr, and more preferably in the range of 5-20 torr.

(21) Without wishing to be bound by theory, the mechanism for formation of the preferred transient Co(CO).sub.2NO* appears to be the loss of CO from the coordination sphere of cobalt in Co(CO).sub.3NO, as shown below:
Co(CO).sub.3NO.fwdarw.Co(CO).sub.2NO*+CO
The further loss of the nitrosyl group, a so-called non-innocent ligand, to form Co(CO).sub.2* is another preferred transient cobalt species

(22) Referring to FIG. 2, in one embodiment, the parent precursor, and more particularly the parent silane or cobalt precursor, and even more particularly the parent perhydridosilane precursor or parent Co.sup.(0) precursor, is introduced into a CVD or ALD thin film deposition chamber, for production of the transient species directly in the deposition chamber, either in the vapor phase or on the substrate surface. The parent precursors may be introduced in the deposition chamber with or without an inert carrier gas, such as, for example, argon, hydrogen or nitrogen. The inert carrier gas which is utilized may depend upon the type of film to be formed. Preferably, the inert carrier gas is helium or argon.

(23) In such an in-situ embodiment of the method, the deposition chamber is initially set to predetermined parameters particularly suited for transient species generation, in order to enable the conversion of the parent precursors to the transient species within the deposition chamber.

(24) For example, where isotetrasilane is utilized as the parent precursor and thermal decomposition is utilized to convert the isotetrasilane to the transient silylyene species, namely bis(trihydridosilyl)silylene, the deposition chamber is preferably initially operated at a conversion temperature between about 250° C. and about 350° C. Alternatively, where cobalt tricarbonyl nitrosyl is utilized as the precursor and thermal decomposition is utilized to convert the cobalt tricarbonyl nitrosyl to the Co(CO).sub.2NO intermediate (i.e., transient species), the deposition chamber is preferably initially operated at a conversion temperature between about 150° C. and about 250° C.

(25) Concurrently, the substrate is preferably set to predetermined processing parameters (including during substrate introduction into the deposition reactor) to enable thermal decomposition of the transient species and formation of the film from the transient species (i.e., consumption of the transient species). In the thermal deposition processes, the substrate is preferably operated at a deposition temperature between about 250° C. and about 650° C., and more preferably between about 350° C. and about 550° C. The partial vapor pressure of the silylene transient species (e.g., bis(trihydridosilyl)silylene) or the cobalt transient species (e.g., Co(CO).sub.2NO*) within the deposition chamber during the thermal deposition process is preferably less than 40 torr. The total system processing pressure, including that of the carrier gas and other volatile components, during the thermal deposition process is preferably from 1 torr up to 150 torr.

(26) After generation of the transient species, the deposition chamber may then optionally be purged to remove all byproducts.

(27) In one embodiment, hydrogen is used as co-reactant, either individually, or in combination with an inert gas such as argon.

(28) Referring to FIG. 1, in another embodiment, the parent precursor is first introduced into a separate synthesis chamber or vessel (i.e., separate from the deposition chamber), where the transient species are generated controllably and reliably from the parent precursor, and then the transient species are generated and transported in the gas phase (with or without an inert carrier gas, and/or with or without a co-reactant such as hydrogen) to the CVD or ALD deposition chamber, where they are consumed in the thin film deposition process. The transient species may be in the deposition environment with precursor molecules and other carrier and/or reactant gases, as described above.

(29) Preferably, the transient species synthesis chamber is connected under controlled conditions, such as by a vacuum interlock or valving system, to the deposition chamber. More particularly, the effluent or product of the transient species synthesis chamber (i.e., the silylene or Co(CO).sub.2NO* intermediate/transient species) is directly transported via a conduit or manifold system from the transient species synthesis chamber to the film deposition chamber. As such, the transient species synthesis chamber and the deposition chamber are connected directly with each other physically without exposure of the transient species to air or the surrounding environment.

(30) In some embodiments, the controlled environment under which the transient species synthesis chamber is connected to the deposition chamber is one of vacuum, inert gas, hydrogen, reactive gas, or a combination of such gases.

(31) In the transient species synthesis chamber, the silylene transient species can be generated from the perhydridosilane precursor in various manners, such as direct or remote plasma-assisted conditions, electron ionization at energy levels of 6 eV or greater (preferably between 6 eV and 15 eV), chemical ionization, and/or thermal decomposition. In one embodiment, where isotetrasilane is utilized as the parent precursor and thermal decomposition is utilized to convert the isotetrasilane to the silylene transient species, particularly bis(trihydridosilyl)silylene, the transient species synthesis chamber is preferably operated at a conversion temperature between about 250° C. and about 350° C.

(32) Similarly, in the transient species synthesis chamber, the cobalt transient species can be generated from the parent Co.sup.(0) precursor in various manners, such as direct or remote plasma-assisted conditions, electron ionization at energy levels of 1 eV or greater (preferably between 1 eV and 20 eV), chemical ionization, photolysis and/or thermal decomposition. In one embodiment, where cobalt tricarbonyl nitrosyl is utilized as the parent precursor and thermal decomposition is utilized to convert the cobalt tricarbonyl nitrosyl to the Co(CO).sub.2NO* transient species, the synthesis chamber is preferably operated at a conversion temperature between about 150° C. and about 250° C.

(33) In one embodiment, the transient species synthesis chamber contains a mechanism for separating reaction byproducts, such as a selective adsorption bed (e.g., activated carbon), a molecular sieve, a metal-organic framework that removes the byproducts from the vapor transport stream, a specific chamber design, or specialized chamber flow dynamics that enable separation of byproducts from reaction intermediates.

(34) The deposition chamber, to which the transient species are transferred from the synthesis chamber, is preferably operated at a deposition temperature between about 150° C. and about 650° C., more preferably between about 350° C. and about 550° C. The partial processing pressure of the transient species (e.g., bis(trihydridosilyl)silylene or Co(CO).sub.2NO*) within the deposition chamber during thermal deposition is preferably less than 40 torr. The total system processing pressure, including that of the carrier gas and other volatile components, is preferably from 1 torr up to 150 torr.

(35) With respect to the above-described embodiments, the deposition chamber is preferably equipped with a vacuum manifold and a pumping system to maintain an appropriate pressure. It is also preferred that the deposition chamber includes a temperature control system, and gas or vapor handling capability to meter and control the flow of reactants and products resulting from the process.

(36) In all of the above-described embodiments, the deposition process typically takes from about 30 seconds to about 30 minutes, most preferably about 5 minutes. However, it will be understood that the time may vary dependent upon the type of film to be deposited, the processing conditions and the desired film thickness.

(37) In one embodiment, under specific low temperature and low reaction vapor pressure parameters in CVD or ALD processing, and low precursor partial vapor pressure in an inert carrier gas or hydrogen stream, as discussed above, the parent isotetrasilane is converted reliably and controllably to the transient species bis(trihydridosilyl)silylene through the reductive elimination of silane from isotetrasilane. The bis(trihydridosilyl)silylene has the capacity to be stable and long-lived (i.e., half-lives consistent with transport time requirements). Further, the bis(trihydridosilyl)silylene retains two trihydridosilyl groups that undergo dissociative adsorption with the substrate, in order to produce high quality epitaxial silicon films capable of n and p-type doping, such as phosphorus and boron, as well as tensile and compressive strained epitaxial Si (e-Si), when deposited in combination with germanium or carbon-containing precursors, germane, or trisilapentane.

(38) In another embodiment, the silylene transient species is pentahydrdidosilylene generated from the parent precursor n-tetrasilane at temperatures greater than 650° C. Pentahydrdidosilylene can be used directly for the deposition process at temperatures below 600° C., but it also can be engineered to rearrange to bis(trihydridosilyl)silylene, a preferred transient species.

(39) In another embodiment, bis(trihydridosilyl)silylene is formed by the reliable and reproducible reaction of disilane with trisilane at temperatures above 350° C. Without being bound by theory, the reaction is thought to occur by the decomposition of disilane to silylene (H.sub.2Si:), hydrogen and silane. The silylene inserts into trisilane forming isotetrasilane which, in turn, forms bis(trihydridosilyl)silylene and silane.

(40) In one embodiment, under low temperature and low reaction vapor pressure in CVD or ALD processing, and low precursor partial vapor pressure in an inert carrier gas or hydrogen stream, as discussed above, the parent cobalt tricarbonyl nitrosyl molecule was reliably and controllably converted to the transient species Co(CO).sub.2NO* through the elimination of CO from cobalt tricarbonyl nitrosyl. The Co(CO).sub.2NO* transient species has the capacity to be stable and long-lived (i.e., half-lives consistent with transport time requirements). Further, the Co(CO).sub.2NO* retains CO and NO groups that undergo dissociative adsorption with the substrate, in order to produce high quality cobalt films.

(41) The above examples of transient species are exemplary and are not intended to be limiting. Those skilled in the art recognize that other transient species may also be formed and used in thin film deposition applications for copper (Cu), ruthenium (Ru), tantalum (Ta), titanium (Ti), tungsten (W), and their nitrides, oxides and carbides as well as dielectric, organic, polymeric, and insulating films.

(42) In one embodiment, as shown in FIG. 3, the inventive process may utilize a manufacturing cluster tool equipped with modules for ex-situ and in-situ synthesis of the transient species that are then reacted in thin film processing chambers.

(43) The invention will now be described in terms of the following, non-limiting examples.

EXAMPLES

(44) Example 1: The transient species bis(trihydrosilyl)silylene was generated in situ by the reductive elimination of silane from isotetrasilane. The results of these experiments are shown in Table 1.

(45) TABLE-US-00001 TABLE 1 Selected Comparative Results for CVD e-Si Studies from bis(trihydridosilyl)silylene Deposition Total System Process Process Growth Temperature Pressure Rate Gas Phase Example Precursor (° C.) (torr) (nm/min) Reactions 1 Silane 650° 80 11 No (comparative) 2 Silane 750° 100 97 Yes. Gas (comparative) phase depletion* 3 Disilane 650° 100 18 No (comparative) 4 Disilane 700° 100 28 Yes. Gas (comparative) phase depletion* 5 n-Tetrasilane 600° 100 <10 No (comparative) 6 Isotetrasilane 550° 100 13 Yes. Gas (comparative) phase depletion* 7 Isotetrasilane 550° 40 26 Yes. Gas (comparative) phase depletion* 8 Bis(trihydridosilyl)silylene 550° 10 35 No (innovative) 9 Isotetrasilane 525° 100 18 Yes. Gas (comparative) phase depletion* 10 Bis(trihydridosilyl)silylene 500° 100 12 No (innovative) *Thermodynamic pathways that lead to gas-phase depletion reactions and, ultimately, formation of particles in the gas-phase. The latter are believed to be caused by the occurrence of ring systems due to cyclization, leading to the manifestation of gas-phase clusters (nanoparticles) which consist of neutral or negatively charged hydrogenated silicon compounds. B. Arkles et al., Inorganic Chemistry, 2019, 58, 3050-3057.

(46) The data shows that if the processing parameters are not tightly controlled, e.g., if the substrate temperature and/or parent precursor partial pressure are too high, the parent precursor self-reacts or reacts either with other silylenes or volatile species and causes gas phase particle formation, instead of forming the desired transient species.

(47) Example 2: Various experiments were conducted utilizing Co(CO).sub.2NO* in accordance with the present method. The Co(CO).sub.2NO* was generated in situ by the elimination of CO from cobalt tricarbonyl nitrosyl. The results of these experiments are shown in Table 2.

(48) TABLE-US-00002 TABLE 2 Selected Results for CVD Co Studies from Co(CO).sub.2NO*. Deposition Deposition Process Process Temperature Pressure, Gas Phase Precursor (° C.) (torr) Film Composition Reactions cobalt tricarbonyl 200° 1.5 CoO contaminated No nitrosyl with N (comparative) cobalt tricarbonyl 250° 1.5 CoO contaminated No nitrosyl with N (comparative) Co(CO).sub.2NO* 350° 1.5 Pure Co No (innovative) Co(CO).sub.2NO* 390° 1.5 Pure Co No (innovative) Co(CO).sub.2NO* 420° 1.5 Pure Co No (innovative) Co(CO).sub.2NO* 450° 1.5 Pure Co No (innovative) Co(CO).sub.2NO* 480° 1.5 Pure Co No (innovative) *See above note with respect to Table 1.

(49) The data shows a reduction in contaminants with temperature, with pure Co forming above 350° C. Significantly, if the temperature is too low, the parent precursor is partially decomposed without the formation of the desired intermediate, which causes film contamination.

(50) It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the present invention as defined by the appended claims.