WO2012074511A2

WO2012074511A2 - Deposition of alkaline earth metal fluoride films in gas phase at low temperature

Info

Publication number: WO2012074511A2
Application number: PCT/US2010/058340
Authority: WO
Inventors: Changhee Ko; Julien Gatineau; Christian Dussarrat
Original assignee: L'air Liquide, Societe Anonyme Pour L'etude Et L'exploitation Des Procedes Georges Claude
Priority date: 2009-11-30
Filing date: 2010-11-30
Publication date: 2012-06-07
Also published as: WO2012074511A3

Abstract

Disclosed are thermal and/or plasma-enhanced CVD, ALD, and/or pulse CVD processes to deposit alkaline earth metal fluoride-based films, such as MgF₂, at temperatures ranging from about 25C to about 300°C, preferably from about 50°C to about 250°C, and more preferably from about 100°C to about 200°C.

Description

DEPOSITION OF ALKALINE EARTH METAL FLUORIDE FILMS IN GAS PHASE AT LOW TEMPERATURE

Cross-Reference to Related Applications

This application claims the benefit under 35 U.S.C. § 119(e) to provisional application No. 61/265,130, filed November 30, 2009, the entire contents of which are incorporated herein by reference.

Technical Field

Disclosed are thermal and/or plasma-enhanced CVD, ALD, and/or pulse CVD processes to deposit alkaline earth metal fluoride-based films, such as MgF₂, at temperatures ranging from about 25°C to about 300°C, preferably from about 50°C to about 250°C, and more preferably from about 100°C to about 200°C.

Background

Anti-refractive layers (ARL) or coatings (ARC) are important in many manufacturing processes, such as optical coatings. These coatings have been introduced to the Complementary metal-oxide-semiconductor

(CMOS) image sensor manufacturing process. The CMOS Image Sensor (CIS) is an alternative to the Coupled Charge Detector (CCD) for light sensor applications. Anti-reflective coatings are deposited on the top of the image sensor, onto the micro-lens. The coating protects the micro-lens and increases the CIS sensitivity. The coating layer must have a refractive index lower than that of the micro-lens, which may be made of S1O2. In that situation, the ARC requires a refractive index <1.46.

Some materials with low dielectric constant (low-k) used in the manufacturing process of many electronic devices also exhibit a low refractive index (<1.35) that may allow them to be used as coatings.

However, the use of a UV curing post-process is sometimes required to improve the film characteristics and this step may generate damages in the CIS sub-layers. MgF₂ has a Rl of 1.35 (at 400 nm) and does not need a UV curing step. Mg-containing films have been deposited using ALD (see, e.g., US Pat. App. Pub. No. 2008/210973 to Chen et al.). However, in that application, the Mg served as a doping agent in a zinc oxide film. The reference does not disclose whether the process would produce a satisfactory MgF₂ film.

One issue encountered in the deposition of MgF₂ films is

incorporation of impurities, such as other metals or oxygen. MgO has a refractive index of 1.7, resulting in too high a refractive index for the ARL application.

A need remains for deposition methods of suitable alkaline earth metal fluoride films at temperatures below approximately 300°C, preferably below 250°C, and more preferably below 200°C.

Notation and Nomenclature

Certain abbreviations, symbols, and terms are used throughout the following description and claims and include: the term "alkyl group" refers to saturated functional groups containing exclusively carbon and hydrogen atoms. Further, the term "alkyl group" refers to linear, branched, or cyclic alkyl groups. Examples of linear alkyl groups include without limitation, methyl groups, ethyl groups, propyl groups, butyl groups, etc. Examples of branched alkyls groups include without limitation, t-butyl. Examples of cyclic alkyl groups include without limitation, cyclopropyl groups, cyclopentyl groups, cyclohexyl groups, etc.

The abbreviation "Me" refers to a methyl group; the abbreviation "Et" refers to an ethyl group; the abbreviation "Pr" refers to a propyl group; the abbreviation "iPr" refers to an isopropyl group; the abbreviation "Bu" refers to butyl (n-butyl); the abbreviation "tBu" refers to tert-butyl; the abbreviation "sBu" refers to sec-butyl; the abbreviation "acac" refers to acetylacetonato; the abbreviation "tmhd" refers to 2,2,6, 6-tetramethyl-3,5-heptadlonato; the abbreviation "od" refers to 2,4-octadionato; the abbreviation "mhd" refers to 2-methyl-3,5-hexadinonato; the abbreviation "tmod" refers to 2,2,6,6- tetramethyl-3,5-octanedionato; the abbreviation "ibpm" refers to 2,2,6- trimethyl-3-5-heptadionato; the abbreviation "hfac" refers to

hexafluoroacetylacetonato; the abbreviation "tfac" refers to

trifluoroacetylacetonato; the abbreviation "Cp" refers to cyclopentadienyl; the abbreviation "Cp*" refers to pentamethylcyclopentadienyl; the

abbreviation "dkti" refers to diketimine (whatever the R ligands bonded to the nitrogen atoms); the abbreviation "emk" refers to enaminoketones (whatever the R ligand bonded to the nitrogen atom); the abbreviation "amd" refers to amldlnate (whatever the R ligands bonded to the nitrogen atoms); the abbreviation "formd" refers to formamidinate (whatever the R ligands bonded to the nitrogen atoms); the abbreviation "guam" refers to guamidinate (whatever the R ligands bonded to the nitrogen atoms); the abbreviation "dab" refers to diazabutadiene (whatever the R ligands bonded to the nitrogen atoms); and the abbreviation "PCAI" refers to alkylimino pyrroles (whatever the R ligands bonded to the nitrogen atoms).

For a better understanding, the generic structures of some of these ligands are represented below, wherein each R is independently selected from H; a C₁-C₆ linear, branched, or cyclic alkyl or aryl group; an amino substituent such as NR¹R² or NR¹R²R³, wherein R¹, R², and R³ are independently selected from H or a C₁-C₆ linear, branched, or cyclic alkyl or aryl group; and an alkoxy substituent such as OR, or OR¹R² wherein R¹ and R² are independently selected from H and a C₁-C₆ linear, branched, or cyclic alkyl or aryl group.

Summary

Disclosed are methods for depositing alkaline earth metal fluoride films onto one or more substrates. A reactor is provided containing at least one substrate disposed therein. The vapor of an alkaline earth metal precursor is introduced into the reactor. The alkaline earth metal precursor has the formula:

wherein:

- M is magnesium, calcium, strontium, or barium,

preferably Mg;

- X¹ is selected from the group consisting of

cyclopentadienyl, pentadienyl, cyclohexadienyl, hexadienyl, cycloheptadienyl, heptadienyi,

cyclooctadienyi, and octadienyl, preferably

cyclopentadienyl;

- X² is selected from the group consisting of

acetylacetonate, enamlnoketonate, diketiminate, diaza butadiene, amidinate, formamidinate, and guamidinate;

- L is a Lewis base;

- ox is an integer that represents the oxidation state of the molecule;

- n is an integer selected between 0 and ox, preferably 0 or 2;

- m is an integer selected between 0 and ox, preferably - n and m are selected such as the sum of n and m is equal to ox; and

- p is a integer between 0 and 2, preferably 1.

The vapor is contacted with the substrate to form an alkaline earth metal film selected from the group consisting of MgF₂, CaF₂, SrF₂, and BaF₂ on at least one surface of the substrate in a vapor deposition process. The disclosed methods may include on or more of the following aspects:

• the alkaline earth metal precursor being selected from the group consisting of MgCp₂, Mg(MeCp)2, Mg(EtCp)₂, Mg(PrCp)₂,

Mg(BuCp)2, Mg(acac)2, Mg(tmhd)2, Mg(od)₂, Mg(tfac)2, Mg(hfac)₂, Mg(hfac)2 tetraglyme, Mg(mhd)₂, Mg(dibm)₂, Mg(tmod)₂, Mg(ibmp)₂, Mg(Et-dkti)₂, Mg(Et-emk)₂, Mg(iPr-amd)₂, Mg(iPr-form)2, Mg(N,N'- Et₂-N"-Me₂-guam)₂, Mg(N.N'-tBu₂-dab)₂, and combinations thereof, preferably Mg(MeCp)2, Mg(EtCp)₂, Mg(Et-dkti)₂, and Mg(tmhd)₂;

• the vapor including a solvent used to dissolve the alkaline earth

metal precursor;

• the reactor having a temperature ranging from approximately 25°C to approximately 300°C, preferably from approximately 50°C to approximately 250°C, and more preferably from approximately 100°C to approximately 200°C;

• the reactor having a pressure between about 0.0001 Torr (0.013333 Pa) and about 1000 Torr (133,322 Pa), preferably between about 0.1 Torr (13.33 Pa) and about 300 Torr (39,997 Pa);

• the vapor deposition process being selected from the group

consisting of a chemical vapor deposition (CVD) process, an atomic layer deposition (ALD) process, a plasma enhanced CVD process, and a plasma enhanced ALD process;

• introducing co-reactants into the reactor to tune the alkaline earth metal film;

• decreasing the refractive index of the alkaline earth metal film by a post treatment process; • introducing into the reactor a vapor of a co-reactant;

• reacting the vapor of the co-reactant with the vapor of the alkaline earth metal precursor prior to or concurrently with the contacting step;

• the co-reactant containing fluorine but not containing a metal source;

• the co-reactant being selected from the group consisting of NF3, hydrofluoric acid (HF), fluorine (F₂), trifluorochlorine (CIF₃), trifluorobromide (BrF₃), trifluoro iodine (IF₃), and pentafluoroiodlne (IF₅); and

• the co-reactant comprising oxygen, nitrogen, and/or aluminum.

Also disclosed are alkaline earth metal containing thin film-coated substrates comprising the product of any of the processes described above.

Detailed Description of Preferred Embodiments

Disclosed are processes to deposit alkaline earth metal fluoride films by thermal and/or plasma-enhanced CVD, ALD, and pulse CVD at temperatures ranging from approximately 25°C to approximately 300°C, preferably from approximately 50°C to approximately 250°C, more preferably from approximately 100°C to approximately 200°C. The disclosed processes utilize a combination of alkaline earth metal precursors and fluorine co-reactants. The fluorine co-reactants are not a solid at room temperature, but a liquid or a gas, and do not contain any other metal atom.

The disclosed alkaline earth metal precursors have the formula:

MX¹ _ox-nX² _ox-mL_p

M is magnesium, calcium, strontium, or barium, preferably magnesium;

X¹ is selected from the group consisting of

cyclopentadienyl, pentadienyl, cyclohexadienyl, hexadienyl, cycloheptadienyl, heptadienyl,

cyclooctadienyl, and octadienyl, preferably

cyclopentadienyl;

- X² is selected from the group consisting of

acetylacetonate, enaminoketonate, and diketiminate;

- L Is a Lewis base;

- ox is an integer that represents the oxidation state of the molecule;

- n Is an Integer selected between 0 and ox, preferably 0 or 2;

- m is an integer selected between 0 and ox, preferably 0 or 2;

- n and m are selected such as the sum of n+m=ox; and

- p is a number selected between 0 and 2, preferably 1. Each X1 and X2 may each be substituted by C₁-C₄ linear or branched alkyl group; C₃-C₄ cyclic alkyl group; C₁-C₄ alkylamino group; a C₁-C₄ linear or branched fluoroalkyl group; or C3-C4 cyclic fluoroalkyl group. The fluori nation of the fluoroalkyl groups may range from partially fluorinated, with one F molecule in the group, to fully fluorinated, with a F molecule on each available position in the alkyl group (i.e. with no H substituents). The Lewis base may be selected from tetraglyme, triglyme, dimethyl ether, tetrahydrofuran, pyridine, or combinations thereof.

Exemplary alkaline earth metal precursors include MgCp₂,

Mg(MeCp)2, Mg(EtCp)2, Mg(PrCp)₂, Mg(BuCp)2, Mg(acac)₂, Mg(tmhd)2, Mg(od)2, Mg(tfac)2, Mg(hfac)₂, Mg(hfac)2 tetraglyme, Mg(mhd)2, Mg{dibm)2, Mg(tmod)₂, Mg(ibmp)2, Mg(Et-dkti)₂, Mg(Et-emk)₂, Mg(iPr-amd)₂, Mg(iPr- form)₂, Mg(N,N'-Et2-N"-Me2-guam)2, Mg(N,N'-tBu2-dab)2, and combinations thereof. Preferable alkaline earth metal precursors include Mg(MeCp)₂, Mg(EtCp)2, Mg(Et-dkti)₂, or Mg(tmhd)2. Many of these examples are commercially available. Those that are not may be synthesized by methods known in the art. The disclosed fluorine co-reactants do not contain metal elements, which helps to reduce contamination of the resulting alkaline earth metal fluoride films. Exemplary fluorine co-reactants Include NF₃, hydrofluoric acid (HF), fluorine (F₂), trifluorochlorine (CIF3), trifluorobromide (BrF₃), trifluoro iodine (IF₃), and pentafluoroiodine (IF5). The exemplary fluorine co-reactants are commercially available.

The disclosed alkaline earth metal precursors and fluorine co- reactants are utilized in the disclosed methods of forming alkaline earth metal fluoride layers on a substrate using a vapor deposition process. The method may be useful in the manufacture of semiconductor, photovoltaic, LCD-TFT, or flat panel type devices. The method includes: providing a reactor having at least one substrate disposed in it; providing the alkaline earth metal precursor; vaporizing the alkaline earth metal precursor;

introducing the vapors of the alkaline earth metal precursor into the reactor; and depositing at least part of the vapor of the alkaline earth metal precursor onto the substrate to form an alkaline earth metal containing film.

The alkaline earth metal precursors (hereinafter the "precursors") may be deposited to form alkaline earth metal-containing films using any vapor deposition methods known to those of skill in the art. Examples of suitable deposition methods include without limitation, conventional chemical vapor deposition (CVD), low pressure chemical vapor deposition (LPCVD), atomic layer deposition (ALD), pulsed chemical vapor deposition (P-CVD), plasma enhanced atomic layer deposition (PE-ALD), or combinations thereof.

The type of substrate upon which the film will be deposited will vary depending on the final use intended. In some embodiments, the substrate may be chosen from oxides which are used as dielectric materials in Metal Insulator Metal (MIM - a structure used in capacitors), dynamic random access memory (DRAM), ferroelectric random access memory (FeRam technologies or gate dielectrics in complementary metal-oxide- semiconductor (CMOS) technologies (for example, HfO₂ based materials, TiO₂ based materials, ΖrO₂ based materials, rare earth oxide based materials, ternary oxide based materials, etc.) or from nitride-based films (for example, TaN) that are used as an oxygen barrier between copper and the low-k layer. Other substrates may be used in the manufacture of semiconductors, photovoltaics, LCD-TFT, or flat panel devices. (Examples of such substrates include, but are not limited to, solid substrates such as metal substrates (for example, Au, Pd, Rh, Ru, W, Al, Ni, Ti, Co, Pt and metal silicides, such as TiSi₂, CoSi₂, NiSi, and NiSi₂); metal nitride containing substrates (for example, TaN, TIN, WN, TaCN, TiCN, TaSiN, and TiSiN); semiconductor materials (for example, Si, SiGe, GaAs, InP, diamond, GaN, and SiC); insulators (for example, SiO₂, S13N4, SiON, HfO₂₎ Ta₂O₅, ZrO₂, TiO₂, Al₂O₃, and barium strontium titanate); or other substrates that include any number of combinations of these materials. The actual substrate utilized may also depend upon the specific precursor embodiment utilized. In many instances though, the preferred substrate utilized will be selected from HfiV, TiOr, or ZrO^based substrates.

The precursor is introduced as a vapor into a reaction chamber containing at least one substrate. The reaction chamber may be any enclosure or chamber of a device in which deposition methods take place, such as, without limitation, a parallel-plate type reactor, a cold-wall type reactor, a hot-wall type reactor, a single-wafer reactor, a multi-wafer reactor, or other such types of deposition systems.

The reaction chamber may be maintained at a pressure ranging from about 0.0001 Torr (0.013 Pa) to about 1000 Torr (13.33 x 10⁴ Pa), preferably from about 0.1 Torr (13.33 Pa) to about 300 Torr (40 x 10³ Pa). In addition, the temperature within the reaction chamber may range from about 25°C to about 300°C, preferably between about 50°C and about 250°C, and more preferably from about 100°C to and about 200°C.

The substrate may be heated to a sufficient temperature to obtain the desired film at a sufficient growth rate and with desired physical state and composition. A non-limiting exemplary temperature range to which the substrate may be heated includes from about 25°C to about 300°C. Preferably, the temperature of the substrate is between about 100°C and about 200°C.

The precursors may be fed in liquid state to a vaporizer where it is vaporized before it is introduced into the reaction chamber. Prior to its vaporization, the precursor may optionally be mixed with one or more solvents, one or more metal sources, and a mixture of one or more solvents and one or more metal sources. The solvents may be selected from the group consisting of toluene, ethyl benzene, xylene, mesitylene, decane, dodecane, octane, hexane, pentane, or others. The resulting concentration may range from approximately 0.05 to approximately 2 M. The metal source may include any metal precursors now known or later developed.

Alternatively, the precursor may be vaporized by passing a carrier gas into a container containing the precursor or by bubbling the carrier gas into the precursor. The carrier gas and precursor are then introduced into the reaction chamber. If necessary, the container may be heated to a temperature that permits the precursor to be in its liquid phase and to have a sufficient vapor pressure. The carrier gas may include, but is not limited to, Ar, He, N₂,and mixtures thereof. The precursor may optionally be mixed in the container with a solvent, another metal precursor, or a mixture thereof. The container may be maintained at temperatures in the range of, for example, 0-150°C. Those skilled in the art recognize that the

temperature of the container may be adjusted in a known manner to control the amount of precursor vaporized.

The temperature and the pressure within the reactor are held at conditions suitable for ALD or CVD depositions. In other words, the previously disclosed conditions within the chamber are such that at least part of the vapor introduced into the reaction chamber is deposited on the substrate to form an alkaline earth metal-containing layer on the substrate.

In addition to the optional mixing of the precursor with solvents, metal precursors, and stabilizers prior to introduction into the reaction chamber, the precursor may be mixed with co-reactant species inside the reaction chamber. Preferably, the co-reactant species are the disclosed fluorine co-reactants.

Depending upon the desired use of the resulting film, the co-reactant may also include a pore forming agent, such as bicycloheptadiene or other non-saturated carbon ring molecules. The resulting film may undergo subsequent processing to form pores, such as UV curing or heating, but preferably not to temperatures above 250°C. Incorporation of pores in the alkaline earth metal fluoride film will lower the refractive index of the film. However, as oxygen penetration may damage the micro-lens in the CIS, porosity should be used judicially in such applications.

Other exemplary co-reactant species include, without limitation, H2, metal precursors such as trimethyl aluminum (TMA) or other aluminum- containing precursors, other silicon-containing precursors, tertiary butylimido tris(diethylamino) tantalum (Ta[N(C₂H₅)₂]₃[NC(CH₃)₃] or

TBTDET), tantalum tetraethoxide dimethylaminoethoxide (TAT-DMAE), pentaethoxy tantalum (PET), tertiary butylimido tris(diethylamino) niobium (TBTDEN), pentaethoxy niobium (PEN), and any combination thereof.

When the desired film also contains oxygen, such as, for example and without limitation, magnesium oxide, the co-reactant species may include an oxygen source which Is selected from, but not limited to, O₂, O3, H₂O, H₂O₂, acetic acid, formalin, para-formaldehyde, and combinations thereof. Alternatively, the oxygen source may be selected from O₂, H₂O, 03, H₂O₂, carboxylic acid, or combinations thereof.

When the desired film also contains nitrogen, such as, for example and without limitation, MgON, the co-reactant species may include a nitrogen source which is selected from, but not limited to, nitrogen (N2), ammonia and alkyl derivatives thereof, hydrazine and alkyl derivatives thereof, N-containing radicals (for instance N , NH , NH₂ ), NO, N₂O, NO₂, amines, and any combination thereof.

When the desired film also contains carbon, such as, for example and without limitation, magnesium carbide, the co-reactant species may include a carbon source which is selected from, but not limited to, methane, ethane, propane, butane, ethylene, propylene, t-butylene, isobutylene, CCl₄, and any combination thereof.

When the desired film also contains silicon, such as, for example and without limitation, MgSiO_x, the co-reactant species may include a silicon source which is selected from, but not limited to, SiH₄, Si₂H₆, Si₃H₈, tris(dimethylamino) silane (TriDMAS), bis(dimethylamino) silane (BDMAS), bis(diethylamino) silane (BDEAS), tetrakis-diethylamino silane (TDEAS), tris(dimethylamino) silane (TDMAS), tetrakis-ethylmethylamino silane (TEMAS), (SiH₃)₃N, (SiH₃)₂O, trisilylamine, disiloxane, trisilylamine, dlsilane, trisilane, an alkoxysilane SiH_x(OR¹ )_4-x. a silanol Si(OH)_x(OR¹ )_4-x (preferably Si(OH)(OR¹ )3 ; more preferably Si(OHXOtBu)3 an aminosilane SiH_x(NR¹R²)_4-x (where x is 1 , 2, 3, or 4; R¹ and R² are independently H or a linear, branched or cyclic C1-C6 carbon chain; preferably TriDMAS,

BTBAS, and/or BDEAS), and any combination thereof. The targeted film may alternatively contain germanium (Ge), in which case the above- mentioned Si-containing reactant species could be replaced by Ge- containing reactant species.

When the desired film also contains another metal, such as, for example and without limitation, Ti, Ta, Hf, Zr, Nb, Mg, Al, Sr, Y, Ba, Ca, As, Sb, Bi, Sn, Pb, or combinations thereof, the co-reactant species may include a second precursor which is selected from, but not limited to, metal alkyls such as SbR^l' ₃ or SnR^l+ 4 (wherein each R¹ is independently H or a linear, branched, or cyclic C1-C6 carbon chain), metal alkoxides such as Sb(oRⁱ)3 or Sn(ORⁱ)4 (where each R¹ is independently H or a linear, branched, or cyclic C1-C6 carbon chain), and metal amines such as

Sb(NR¹R²)(NR³R⁴XNR⁵R⁶) or Ge(NR¹R²)(NR³R⁴XNR⁵R⁶)(NR⁷R⁸) (where each R¹, R², R³, R⁴, R⁵, R⁶, R⁷, and R⁸ is independently H, a C1-C6 carbon chain, or a trialkylsilyl group, the carbon chain and trialkyisilyl group each being linear, branched, or cyclic), and any combination thereof.

The precursors and one or more co-reactant species may be introduced into the reaction chamber simultaneously (chemical vapor deposition), sequentially (atomic layer deposition), or in other combinations. For example, the precursor may be introduced In one pulse and two additional metal sources may be introduced together in a separate pulse [modified atomic layer deposition]. Alternatively, the reaction chamber may already contain the co-reactant species prior to introduction of the precursor. The co-reactant species may be passed through a plasma system localized remotely from the reaction chamber, and decomposed to radicals. Alternatively, the precursor may be introduced to the reaction chamber continuously while other metal sources are introduced by pulse (pulsed-chemical vapor deposition). In each example, a pulse may be followed by a purge or evacuation step to remove excess amounts of the component introduced. In each example, the pulse may last for a time period ranging from about 0.01 s to about 10 s, alternatively from about 0.3 s to about 3 s, alternatively from about 0.5 s to about 2 s.

In an ALD or PEALD process, an annealing or flash annealing step may be performed between each ALD cycle or, preferably, after multiple ALD cycles (for instance every 2 to 10 ALD cycles). The number of deposition cycles performed between each annealing step may be tuned to maximize film properties and throughput. The substrate may be exposed to a temperature ranging from approximately 400°C and approximately 1000°C for a time ranging from approximately 0.1 second to approximately 120 seconds under an inert, a N-containing atmosphere, an O-containing atmosphere, or combinations thereof. The resulting film may contain fewer impurities and therefore may have an improved density resulting in improved leakage current. The annealing step may be performed in the same reaction chamber in which the deposition process is performed.

Alternatively, the substrate may be removed from the reaction chamber, with the annealing/flash annealing process being performed in a separate apparatus.

In one non-limiting exemplary atomic layer deposition type process, the vapor phase of the alkaline earth metal precursor is introduced into the reaction chamber, where it is contacted with a suitable substrate. (Excess precursor may then be removed from the reaction chamber by purging and/or evacuating the reaction chamber. The fluorine co-reactant is introduced into the reaction chamber where it reacts with the absorbed precursor in a self-limiting manner. Any excess fluorine co-reactant is removed from the reaction chamber by purging and/or evacuating the reaction chamber. If the desired film is an alkaline earth metal fluoride film, this two-step process may provide the desired film thickness or may be repeated until a film having the necessary thickness has been obtained.

Alternatively, if the desired film is an alkaline earth metal fluoride film containing a second metal, the two-step process above may be followed by introduction of the vapor of a second precursor into the reaction chamber. The second precursor will be selected based on the nature of the alkaline earth metal fluoride film being deposited and may Include a carbon- containing precursor. After introduction into the reaction chamber, the second precursor is contacted with the substrate. Any excess second precursor is removed from the reaction chamber by purging and/or evacuating the reaction chamber. Once again, the fluorine co-reactant may be introduced into the reaction chamber to react with the second precursor. Excess fluorine co-reactant is removed from the reaction chamber by purging and/or evacuating the reaction chamber. If a desired film thickness has been achieved, the process may be terminated. However, if a thicker film is desired, the entire four-step process may be repeated. By alternating the provision of the precursor, second precursor, and fluorine co-reactant, a film of desired composition and thickness can be deposited.

The alkaline earth metal fluoride films resulting from the processes discussed above may include MgF₂, CaF₂, SrF₂, and BaF₂, One of ordinary skill In the art will recognize that by judicial selection of the appropriate precursor and co-reactant species, the desired film composition may be obtained.

Examples

The following examples illustrate experiments performed in conjunction with the disclosure herein. The examples are not intended to be all inclusive and are not intended to limit the scope of disclosure described herein.

Prophetic Example 1

Deposition of MgF₂ films using Mg(EtCp)₂ and F₂ Mg(EtCp)₂ is a liquid molecule with a relatively high vapor pressure of 0.18 Torr at 52°C. Vapors of Mg(EtCp)₂ may be mixed in a reactor with a F₂- containing mixture. The F₂-containing mixture may be 1% of F₂ in nitrogen. The reaction may take place at temperatures below 200°C and lead to

MgF₂ films of high purity (no carbon, but also no oxygen, as it is not present in the process).

It will be understood that many additional changes in the details, materials, steps, and arrangement of parts, which have been herein described and illustrated in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims. Thus, the present invention is not intended to be limited to the specific embodiments in the examples given above and/or the attached drawings.

Claims

What is claimed is:

A method for depositing an alkaline earth metal fluoride film onto more substrates, comprising:

a) providing a reactor and at least one substrate disposed in the reactor

b) introducing into the reactor a vapor of an alkaline earth metal precursor having the formula:

MX¹ _ox-nX² _ox-mLp (I)

wherein:

- M is magnesium, calcium, strontium, or barium,

preferably Mg;

- X¹ is selected from the group consisting of

cyclooctadienyl, and octadienyl, preferably

cyclopentadienyl;

- X² is selected from the group consisting of

acetylacetonate, enaminoketonate, diketiminate, diazabutadiene, amidinate, formamidinate, and guamidinate;

- L is a Lewis base;

- ox Is an integer that represents the oxidation state of the molecule;

- n is an integer selected between 0 and ox, preferably 0 or 2;

- m is an integer selected between 0 and ox, preferably 0 or 2;

- n and m are selected such as the sum of n and m is equal to ox; and

- p is a integer between 0 and 2, preferably 1 ; c) contacting the vapor with the substrate to form an alkaline earth metal film selected from the group consisting of MgF₂, CaF₂, SrF₂, and BaF₂ on at least one surface of the substrate In a vapor deposition process.

2. The method of claim 1 , wherein the alkaline earth metal precursor is selected from the group consisting of MgCp₂, Mg(MeCp)₂, Mg(EtCp)₂, Mg{PrCp)₂, Mg(BuCp)₂, Mg(acac)₂, Mg(tmhd)₂, Mg(od)2, Mg(tfac)₂,

Mg(hfac)2, Mg(hfac)2 tetraglyme, Mg(mhd)2, Mg(dibm)₂, Mg(tmod)₂,

Mg(ibmp)2, Mg(Et-dktl)₂, Mg(Et-emk)2, Mg(iPr-amd)2, Mg(IPr-form)₂, Mg(N,N'-Et₂-N"-Me₂-guam)₂, Mg(N.N'-tBurdab)₂, and combinations thereof, preferably Mg(MeCp)2, Mg(EtCp)₂, Mg(Et-dkti)2, and Mg(tmhd)₂.

3. The method of claim 1 or 2, wherein the vapor includes a solvent used to dissolve the alkaline earth metal precursor.

4. The method of any one of claims 1 to 3, wherein the reactor has a temperature ranging from approximately 25°C to approximately 300°C, preferably from approximately 50°C to approximately 250°C, and more preferably from approximately 100°C to approximately 200°C.

5. The method of any one of claims 1 to 4, wherein the reactor has a pressure between about 0.0001 Torr (0.013333 Pa) and about 1000 Torr (133,322 Pa), preferably between about 0.1 Torr (13.33 Pa) and about 300 Torr (39,997 Pa).

6. The method of any one of claims 1 to 5, wherein the vapor deposition process is selected from the group consisting of a chemical vapor deposition (CVD) process, an atomic layer deposition (ALD) process, a plasma enhanced CVD process, and a plasma enhanced ALD process.

7. The method of any one of claims 1 to 6, further comprising introducing co-reactants into the reactor to tune the alkaline earth metal film.

8. The method of any one of claims 1 to 7, further comprising decreasing the refractive index of the alkaline earth metal film by a post treatment process.

9. The method of any one of claims 1 to 8, further comprising:

a) introducing into the reactor a vapor of a co-reactant; and b) reacting the vapor of the co-reactant with the vapor of the alkaline earth metal precursor prior to or concurrently with the contacting step.

10. The method of claim 9, wherein the co-reactant contains fluorine but does not contain a metal source.

11. The method of claim 10, wherein the co-reactant is selected from the group consisting of NF₃, hydrofluoric acid (HF), fluorine (F₂),

trifluorochlorine (CIF₃), trifluorobromide (BrF₃), trifluoro iodine (IF₃), and pentafluoroiodine (IF5).

12. The method of claim 7, wherein the co-reactant comprise oxygen, nitrogen, and/or aluminum.

13. An alkaline earth metal containing thin film-coated substrate comprising the product of the process of any one of claims 1 to 12.