# Patent

## Title
Chemical vapor deposition precursors for deposition of tantalum-based materials

## Abstract

Tantalum precursors suitable for chemical vapor deposition of tantalum-containing material, e.g., tantalum, TaN, TaSiN, etc., on substrates. The tantalum precursors are substituted cyclopentadienyl tantalum compounds. In one aspect of the invention, such compounds are silylated to constitute tantalum/silicon source reagents. The precursors of the invention are advantageously employed in semiconductor manufacturing applications to form diffusion barriers in connection with copper metallization of the semiconductor device structure.

## Background
CROSS-REFERENCE TO RELATED APPLICATION
This is a continuation of U.S. patent application Ser. No. 10/345,616 filed Jan. 16, 2003 now U.S. Pat. No. 6,989,457 in the names of Smuruthi Kamepalli, et al. for CHEMICAL VAPOR DEPOSITION PRECURSORS FOR DEPOSITION OF TANTALUM-BASED MATERIALS. The priority of such earlier application is claimed under the provisions of 35 USC 120.


FIELD OF THE INVENTION
The present invention relates to the deposition of tantalum-based materials, and to precursor compositions having utility for chemical vapor deposition of such materials on substrates, e.g., in the manufacture of semiconductor products.
DESCRIPTION OF THE RELATED ART
The ability to deposit conformal tantalum-based diffusion barriers is critical to the widespread adoption of copper metallization technology in semiconductor manufacturing operations.
Although the use of physical vapor deposition (PVD) is commonly employed for forming Ta, TaN and TaSiN thin film diffusion barrier layers, there are substantial and unresolved issues concerning the suitability of PVD processes for deposition at dimensions below 0.13 μm, as is required in the fabrication of future high performance microelectronic devices.
Considering chemical vapor deposition as a potential deposition technique, currently available organometallic tantalum precursors suffer from the incorporation of high levels of carbon, nitrogen and oxygen in the deposited tantalum film, which render the deposited tantalum-based material unsatisfactory for use as a diffusion barrier for copper metallization.
Accordingly, there is a compelling need in the art for suitable tantalum precursors for forming diffusion barriers in connection with copper metallization.
SUMMARY OF THE INVENTION
The present invention relates to the deposition of tantalum-based materials, and to precursor compositions having utility for the chemical vapor deposition of such materials on substrates, e.g., in the manufacture of semiconductor products.

    
    
        In one aspect, the invention relates to a compound of the formula:
    
    






    
    
        wherein:
        n is an integer having a value of from 1 to 5;
        each R can be the same or different and each is independently selected from the group consisting of Deuterium (hereinafter referred to as “D”), H, CH3, C2H5, i-C3H7, C4H9 and Si(R′′)3 wherein each R′′ is independently selected from H and C1-C4 alkyl; and
        each of R′ can be the same or different and each is independently selected from the group consisting of D, H, C1-C4 alkyl, and Si(R′′)3 wherein each R′′ is independently selected from H and C1-C4 alkyl;
        with the proviso that each of the R and R′ groups are not simultaneously all H.
    
    


Another aspect of the invention relates to specific preferred compounds of the above formula (I), viz.,




In another aspect, the invention relates to a method of forming a tantalum-containing material on a substrate, comprising contacting the substrate with a vapor of a tantalum precursor under chemical vapor deposition conditions, wherein the tantalum precursor comprises a compound of the above formula (I).
A further aspect of the invention relates to a method of synthesizing a cyclopentadienyl tantalum compound of the formula [(R)nCp]2Ta R′3 

    
    
        wherein:
        n is an integer having a value of from 1 to 5;
        each R can be the same or different and each is independently selected from the group consisting of D, H and Si(R′′)3 wherein each R′′ is independently selected from H and C1-C4 alkyl; and
        each of R′ can be the same or different and each is independently selected from the group consisting of H, C1-C4 alkyl, and Si(R′′)3 wherein each R′′ is independently selected from H and C1-C4 alkyl;
        with the proviso that each of the R and R′ groups are not simultaneously all H;
        such method comprising reacting tantalum pentachloride with cyclopentadienyllithium compound of the formula [(R)nCp]Li in a 1:2 ratio, and stepwise addition of sodium borohydride compound of the formula NaBH4, to yield said cyclopentadienyl tantalum hydride or deuteride compound.
    
    


Other aspects, features and embodiments of the invention will be more fully apparent from the ensuing disclosure and appended claims.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an ORTEP diagram of bis(cyclopentadienyl)dihydrido-t-butylsilyl tantalum.



DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS THEREOF
The present invention is based on the discovery of novel cyclopentadienyl tantalum compounds that have surprising and unexpectedly superior utility for deposition of tantalum-based materials on substrates, e.g., as diffusion barrier layers in connection with copper metallization on such substrates.
The cyclopentadienyl tantalum compounds of the invention have the general formula (I):




    
    
        wherein:
        n is an integer having a value of from 1 to 5;
        each R can be the same or different and each is independently selected from the group consisting of D, H, CH3, C2H5, i-C3H7, C4H9 and Si(R′′)3 wherein each R′′ is independently selected from H and C1-C4 alkyl; and
        each of R′ can be the same or different and each is independently selected from the group consisting of D, H, C1-C4 alkyl, and Si(R′′)3 wherein each R′′ is independently selected from H and C1-C4 alkyl;
        with the proviso that each of the R and R′ groups are not simultaneously all H.
    
    


The compounds of the above general formula afford surprising and unexpected advantages over compounds such as bis(cyclopentadienyl)trihydridotantalum, in which the presence of hydrogen and cyclopentadienyl (Cp) moieties provide a facile route for metal center reduction and protonation of the Cp moieties to form stable CpH compounds and leaving behind pure tantalum films under appropriate process conditions. While superficially appearing highly advantageous in application to chemical vapor deposition usage, such compound, bis(cyclopentadienyl)trihydridotantalum, in fact has the severe deficiency that it decomposes immediately after melting to eliminate H2 and form Cp2TaH, which thereupon polymerizes. The polymer product of course is wholly unsuitable for CVD application, and the polymeric deposit on the surfaces of the vaporization chamber and associated vapor flow lines renders the CVD process system equipment incapable of operation and susceptible to dangerous over-pressurization as a result of occlusion of vapor flow passages of the system with the deposited polymeric residue.
Thus, bis(cyclopentadienyl)trihydridotantalum is not useful as a precursor for CVD formation of Ta and Ta-based films on substrates.
Such deficiency of Cp2TaH3 is overcome by the compounds of the present invention, which are stable under volatilization conditions and evidence good transport properties in application to CVD processes.
The compounds of the present invention therefore may be volatilized to form precursor vapor for contacting under CVD process conditions with substrates to form tantalum- and tantalum containing films thereon. The substrate for such purpose can comprise a semiconductor substrate, on which the deposited tantalum can be converted to tantalum nitride by CVD conducted in a nitrogen atmosphere, or by post-deposition nitridation of the deposited tantalum.
In a further embodiment, the tantalum precursors of the invention can be employed to form tantalum silicon nitride films, e.g., TaSiN, by concurrent chemical vapor deposition of silicon from a suitable silicon source reagent compound, and with the deposition being conducted under CVD process conditions including a nitrogen atmosphere, or with post-deposition nitridation of the deposited tantalum/silicon material.
Tantalum silicon nitride films can also be formed in accordance with the invention by tantalum/silicon source compounds within the aforementioned general formula, where at least one of the R, and R′ groups is a silicon-containing group, e.g., a silyl or substituted silyl group, and the TaSiN film is formed by CVD of material from the precursor in the presence of a nitrogen source material, e.g., a nitrogen atmosphere.
Specific examples of illustrative tantalum/silicon precursor compounds of the invention are set out below:




In the compounds of the general formula (I) above, the C1-C4 alkyl substituents can be of any suitable type having such carbon numbers, with methyl, isopropyl, and tertiary butyl (t-butyl) being most preferred.
The substituent groups (R, and R′) of the compounds of the invention can be tailored to provide a precursor compound having a specific desired volatilization and transport characteristic for the intended CVD application. The specific CVD process conditions can be widely varied in respective of temperature, pressure, flow rate of precursor and optional carrier gas or nitrogen source gas, and concentration partial pressure) of precursor vapor in the CVD reactor chamber, etc., as is readily determinable without undue effort by those skilled in the art, based on the disclosure herein, by selective empirical variation of specific process conditions and analysis of the resulting tantalum-based material deposited on the substrate.
The compounds of formula (I) are readily synthesized from (RCp)2TaH3 for which one general synthetic scheme is set out below:

TaCl5+2[(R)nCp]Li+3NaBH4→[(R)nCp]2TaH3+Na/Li salts  (A)

wherein the reaction is conducted in tetrahydrofuran or other suitable aprotic solvent medium. Preferred process conditions include reaction under reflux conditions for suitable length of time, e.g., on the order of 4 hours, followed by hydrolysis with 2 equivalents of water, and reflux operation for a relatively short period of time, e.g., on the order of about 4 minutes.

A general synthetic scheme for compounds of formula (1) is set out below when addition of R′ groups to the tantalum center are desired:

[(R)nCp]2TaH3+R′Li→(RCp)2TaH2R′+1⁄2H2  (B)

which can be repeated in a stepwise manner until addition of same or differing R′ groups is complete.

In the above synthesis reactions (A and B), the substituent groups (R, and R′ groups) have the same definitions as those set forth in connection with formula (I) above.
Alternatively, the tantalum precursor of reaction (A) above can be used to form Ta/Si precursor compounds of the invention, by subsequent silylation reaction with suitable silane material. An example is the synthesis of cyclopentadienylsilyltantalum compounds of the formula (RnCp)2TaH2(RSiH2) by reaction (C):

(RCp)2TaH3+RSiH3→(RCp)2TaH2(RSiH2)+H2  (C)

Another example is the synthesis of (RCp)2TaH(R′′SiH2)2 by reaction (D):

(RCp)2TaH3+2R′′SiH3→(RCp)2TaH(R′′SiH2)2+H2  (D)

The features and advantages of the invention are more fully shown by the following illustrative examples, wherein all parts and percentages are by weight, unless otherwise expressly stated.
EXAMPLE 1
Synthesis of TMSCp2TaH3
To 5.6 grams of freshly distilled trimethylsilylcyclopentadiene (TMSCp) in tetrahydrofuran (THF) was added 10% excess solution of BuLi in hexane. Upon completion of addition the mixture was stirred for 12 hours. The color of the reaction solution at the completion of the reaction was yellow. No solid formation was observed, due to the high solubility of the material in THF. To the freshly prepared solution of TMSCpLi (40 mmol) in THF and NaBH4 (1.125 grams) was added slowly 3.5 grams of TaCl5. On completion of addition, the mixture was refluxed for 4 hours following which 0.54 milliliter of degassed distilled water was added very slowly. After completion of the addition, the mixture was refluxed for an additional 5 minutes following which the volatiles were removed under vacuum. The compound was extracted with pentane and stored in the freezer. Brown crystals of TMSCp2TaH3 were obtained and washing these crystals with pentane gave very pure white crystals of the material (yield 35%).
Characterization
1H NMR (C6D6): 5.00 (m, 4H, Cp), 4.72 (m, 4H, Cp), 0.30 (s, TMS), −2.06 (t, 1H), −3.28 (d, 2H). STA thermal analysis of the compound yielded a melting point of 90° C. and a residue of 28.7% for TMSCp2TaH3.
Stability Study
TMSCp2TaH3 does not decompose upon melting at 90° C. The compound can be sublimed intact at 74° C. to obtain pure white crystals.
Thus, in contrast to Cp2TaH3, the trimethylsilyl-substituted compound of this example has a low melting point, has high thermal stability and sublimes cleanly.
EXAMPLE 2
Synthesis of Cp2TaH2(t-Bu)SiH2
To 0.5 gram of Cp2TaH3 in toluene was added 0.35 gram of t-BuSiH3 in toluene. The reaction mixture was heated in a quartz reaction vessel at 135° C. for 6 days with three freeze-pump-thaw cycles each day. The solution was bright yellow in color. The solution was filtered and pumped to dryness. Pumping the solvent resulted in crystalline white material. 96% yield was achieved.
Characterization
1H NMR (C6D6): −4.73 (s, 2H, TaH2), 1.37 (s, 9H, t-Bu), 4.57 (s, 10H, Cp), 4,81 (s, 2H, SiH2). 13C NMR (C6D6): 30.42 (t-Bu), 85.81 (Cp).
Crystal Structure
The crystal structure of the product Ta/Si compound, Cp2TaH2(t-Bu)SiH2, is shown in the ORTEP diagram of FIG. 1 hereof.
The Ta/Si compound of this example is usefully employed to form silicon-doped tantalum material layers as barrier layers on substrates in the fabrication of microelectronic devices and device precursor structures.

## Claims

1. A tantalum precursor vapor, comprising vapor of a compound of the formula:




wherein:
n is an integer having a value of from 1 to 5;
each R can be the same or different and each is independently selected from the group consisting of D, H, CH3, C2H5, i-C3H7, C4H9 and Si(R′′)3 wherein each R′′ is independently selected from H and C1-C4 alkyl; and
each of R′ can be the same or different and each is independently selected from the group consisting of D, H, C1-C4 alkyl, and Si(R′′)3 wherein each R′′ is independently selected from H and C1-C4 alkyl;
with the provisos that (i) each of the R groups and R′ are not simultaneously all H, and (ii) when each of R′ is H, and n is 1, both R groups are not simultaneously trimethylsilyl.

2. The compound of claim 1, wherein at least one of R, R′ is Si(R′′)3 wherein each R′′ is independently selected from H and C1-C4 alkyl.

3. The compound of claim 1, wherein at least one of R, R′ is trimethylsilyl.

4. The compound of claim 1, wherein n is 1 for each cyclopentadienyl ring.

5. The compound of claim 4, wherein R on each cyclopentadienyl ring is trimethylsilyl.

6. The compound of claim 1, wherein each of the R groups and R′ are independently selected from H, methyl, isopropyl, t-butyl, trimethylsilyl, and t-butylsilyl.

7. The compound of claim 6, wherein at least one of the R groups and R′ is trimethylsilyl.

8. The compound of claim 7, wherein n is 1 for each cyclopentadienyl ring.

9. The compound of claim 8, wherein R on each cyclopentadienyl ring is trimethylsilyl.

10. The compound of claim 1, wherein each of the R groups and R′ are independently selected from H and Si(R′′)3 wherein each R′′ is independently selected from H and C1-C4 alkyl.

11. The compound of claim 10, wherein n is 1 for each cyclopentadienyl ring.

12. The compound of claim 11, wherein R on each cyclopentadienyl ring is trimethylsilyl.

13. The compound of claim 11, wherein each R is H.

14. The compound of claim 13, wherein at least one of R′ is Si(R′′)3 wherein each R′′ is independently selected from H and C1-C4 alkyl.

15. The compound of claim 14, wherein one of R′ is Si(R′′)3 wherein each R′′ is independently selected from H and C1-C4 alkyl.

16. A tantalum precursor vapor, comprising vapor of a compound selected from among compounds of the formula:




wherein TMS is trimethylsilyl and R′ is selected from the group consisting of D, C1-C4 alkyl, and Si(R′′)3 wherein each R′′ is independently selected from H and C1-C4 alkyl.

17. A method of synthesizing a cyclopentadienyl tantalum compound, comprising conducting the following reaction:


[(R)nCp]2TaH3+R′Li→(RCp)2TaH2R′+1⁄2H2

wherein:
each R can be the same or different and each is independently selected from the group consisting of D, H, CH3, C2H5, i-C3H7, C4H9 and Si(R′′)3 wherein each R′′ is independently selected from H and C1-C4 alkyl; and
each of R′ can be the same or different and each is independently selected from the group consisting of D, H, C1-C4 alkyl, and Si(R′′)3 wherein each R′′ is independently selected from H and C1-C4 alkyl.

18. A method of synthesizing a cyclopentadienyl tantalum compound, comprising conducting the following reaction:


(RCp)2TaH3+RSiH3→(RCp)2TaH2(RSiH2)+H2

wherein:
each R can be the same or different and each is independently selected from the group consisting of D, H, CH3, C2H5, i-C3H7, C4H9 and Si(R′′)3 wherein each R′′ is independently selected from H and C1-C4 alkyl.

19. A method of synthesizing a cyclopentadienyl tantalum compound, comprising conducting the following reaction:


(RCp)2TaH3+2R′′SiH3→(RCp)2TaH(R′′SiH2)2+H2

wherein:
each R can be the same or different and each is independently selected from the group consisting of D, H, CH3, C2H5, i-C3H7, C4H9 and Si(R′′)3 wherein each R′′ is independently selected from H and C1-C4 alkyl.