WO2000065126A1

WO2000065126A1 - Cvd tantalum nitride plug formation from tantalum halide precursors

Info

Publication number: WO2000065126A1
Application number: PCT/US2000/011281
Authority: WO
Inventors: John J. Hautala; Johannes F. M. Westendorp
Original assignee: Tokyo Electron Limited; Tokyo Electron Arizona, Inc.
Priority date: 1999-04-27
Filing date: 2000-04-26
Publication date: 2000-11-02
Also published as: JP2002543580A; TW593733B; WO2000065126A9; JP4763894B2; KR20020010612A; KR100668903B1

Abstract

Plasma treated chemical vapor deposition (PTTCVD) method for depositing high quality tantalum nitride (TaNx) films from inorganic tantalum halide (TaX5) precursors and a nitrogen containing gas for filling small contacts having high aspect ratio features with TaNx film and eliminating copper deposition step. The inorganic tantalum halide precursors are tantalum pentafluoride (TaF5), tantalum pentachloride (TaCl5) and tantalum pentabromide (TaBr5). In a thermal CVD process, TaX5 vapor is delivered into heated chamber (11). The vapor is combined with process gas containing nitrogen to deposit TaNx film in feature. In one embodiment, hydrogen gas is introduced in radiofrequency generated plasma to plasma treat TaNx film. Plasma treatment is performed periodically until the feature is filled with TaNx film. Deposited TaNx film is useful for integrated circuits containing copper. The method produces seamless TaN plug fill in high aspect ratio structures.

Description

CVD TANTALUM NITRIDE PLUG FORMATION FROM TANTALUM HALIDE PRECURSORS

This invention relates to the formation of integrated circuits, and

specifically to filling electrical contacts with tantalum nitride films deposited by

chemical vapor deposition from tantalum halide precursors.

Background of the Invention

integrated circuits provide the pathways for signal transport in an

electrical device. An integrated circuit (IC) in a device is composed of a number

of active transistors contained in a silicon base layer of a semiconductor

substrate. To increase the capacity of an IC, large numbers of interconnections

with metal "wires" are made between one active transistor in the silicon base of

the substrate and another active transistor in the silicon base of the substrate.

The interconnections, collectively known as the metal interconnection of a circuit,

are made through features such as holes, vias or trenches that are cut into a

substrate. The particular point of the metal interconnection which actually makes

contact with the silicon base is known as the contact. The remainder of the hole,

via or trench is filled with a conductive material, termed a contact plug. As 00/65126

transistor densities continue to increase, forming higher level IC, the diameter of

the contact plug must decrease to allow for the increased number of

interconnects, multilevel metalization structures and higher aspect ratio vias.

Aluminum has been the accepted standard for contacts and

interconnections in integrated circuits. However, problems with aluminum

electromigration and its hign electrical resistivity require new materials for newer

structures having deep suDπnicron αimensions Cooper (Cu) holαs promise as tne

interconnect material for the next generation of integrated circuits in ultra large

scale integration (ULSI) circuitry, yet tne formation of copper siiiciαe (Cu-Si)

compounds at low temperatures and its electromigration tnrough a silicon oxide

(Sι0₂) layer are αisaαvantages to its use

As the snift occurs from aluminum to cooper as an interconnect

element of choice, new materials are required to serve as a barrier, preventing

copDe^r diffusion into the unαeriying αieiectπc laye^rs of the suDstrate ana to form

an effective "glue" layer for subsequent copper deposition. New materials are

also requireα to serve as a liner, adneπng subsequently αeposited copper to the

suDstrate. Tne liner must also proviαe a low eiectπcal resistance interface

oetween cooDer and the Darner mateπal. Barrier layers that were previously used

witn aluminum, sucn as titanium (Ti) and titanium nitπαe iTiN) barrier layers

αeoositeα eιtne^r DV physical vaoor αeocsition (PVD) sucn as sputtering and/or

cnemicai v aoo' αeoosition (CVD) , are ιne^*fectιvε as αiffusion 03.^rrιε^rs to copper. In addition, Ti reacts with copper to form copper titanium compounds at the

relatively low temperatures used with PVD and/or CVD.

Sputtered tantalum (Ta) and reactive sputtered tantalum nitride (TaN)

have been demonstrated to be good diffusion barriers between copper and a

silicon substrate due to their high conductivity, high thermal stability and

resistance to diffusion of foreign atoms. However, the deposited Ta and/or TaN

film has inherently poor step coverage due to its shadowing effects. Thus the

sputtering process is limited to relatively large feature sizes ( > 0.3 //m) and small

aspect ratio contacts and vias. CVD offers the inherent advantage over PVD of

better conformality, even in small structures ( < 0.25 μm) with high aspect ratios.

However, CVD of Ta and TaN with metal-organic sources such as

tertbutyiimidotris(diethylamido)tantalum (TBTDET), pentakis (dimethylamino)

tantalum (PDMAT) and pentakis (diethylanmino) tantalum (PDEAT) yields mixed

results. Additional problems are that all resulting films have relatively high

concentrations of oxygen and carbon impurities and require the use of a carrier

gas.

A contact plug makes an electrical connection between doped silicon

and metal wires that connect transistors, both with each other and with the

outside world. Contact plugs involving Cu lines currently require the depositions

as follows. A liner of about 100 A Ta is first deposited using PVD. This Ta layer

enhances the electrical contact to the silicon base layer. A liner of about 500 A

TaN is then deposited on the Ta layer by PVD. A seed layer of 1 00 A Cu is then deposited by PVD, and the remainder of the plug is filled with electroplated Cu.

The TaN layer serves as a metal diffusion barrier to protect the dielectric layer

from Cu diffusion. TaN also serves as an adhesion layer for the Cu.

As transistor densities continue to increase and structures become

narrower, the proportion of Cu in the plug becomes smaller. Since the probable

TaN barrier layer may remain at greater than about 200 A for robust performance

as a diffusion barrier and the Ta thickness is still required to be 1 00 A, it follows

that the portion of the contact plug that is filled with Cu is diminished. For

example, a structure with a diameter of 0J 3 μm would have a Cu film or "core"

in the center of the plug that is only about 700 A. Therefore, the effective plug

resistance becomes dominated more by the higher resistivity Ta and TaN and,

more importantly, the resistance of the interface between the TaN and Cu layers.

Subsequent filling of the contact plugs with Cu, then, provides an

extra procedural step with no significant effect on the overall resistance of the

contact plug. Accordingly, a process step in the formation of an IC could be

eliminated, manufacturing efficiency could be increased, and significant savings

for the fabrication of these devices couid be realized by filling a via with a contact

plug of TaN only, rather than with TaN and Cu. Therefore, what is needed is a

method of forming a TaN contact plug by CVD and eliminating a Cu layer in the

contact plug in the formation of an IC.

While the absolute thickness of the Cu layer may vary according to

the size of the via to be filled, its relative thickness is about 80% of the via diameter. This is because the deposited film must not only fill the volume of the

via with a contact plug, but it must also fill the "dimple" above the contact plug.

The "dimple," defined as an indentation in the TaN that is formed during filling of

the via, is eliminated by depositing more TaN on top of the plug, resulting in a

capping layer. Thus, for. a 0.2 μm feature, a TaN film having a thickness of

1 600 A (0.8 x 2000 A) is required. For a good plug fill it is also critical that these

thick films be continuous, completely conformal, and seamless.

Thus, what is needed is a method for depositing TaN_x films to fill a

contact plug in and eliminating a copper deposition step. The method would

require deposition temperature less than about 500°C to protect the integrity of

underlying materials such as low k dielectrics, a deposition rate of more than 1 00

A/minute for reasonable throughput, a cracking threshold larger than 2000 A,

sufficiently low electrical resistivities for low interconnect impedances, 100%

conformality in high aspect ratio features, no attack or corrosion of subsequently

deposited fiims such as copper films, minimal impurities in the film, and the film

would provide a good barrier to copper diffusion.

Summary of the Invention

The invention is directed to a method of filling a via with a TaN plug

and eliminating a copper (Cu) deposition step by depositing a tantalum nitride

(TaN_x) film from a tantalum halide precursor on a substrate. The tantalum halide

precursor is delivered at a temperature sufficient to vaporize the precursor to

provide a vaporization pressure to deliver the tantalum vapor to a reaction chamber containing the substrate. The vaporization pressure is greater than

about 3 Torr. The vapor is combined with a process gas containing nitrogen and

TaN_x is deposited by a thermal chemical vapor deposition (thermal CVD) process.

The deposition is halted to plasma treat the film, then deposition is resumed. The

plasma treatments are performed at regular intervals in the thermal CVD process

(PTTCVD) until a desired film thickness is obtained. The tantalum halide

precursor is tantalum fluoride (TaF), tantalum chloride (TaCI) or tantalum bromide

(TaBr), preferably tantalum pentafluoride (TaF₅), tantalum pentachloride (TaCI₅)

or tantalum pentabromide (TaBr₅). The substrate temperature is in the range of

about 300° C-500°C.

The present invention is also directed to a method of completely

filling a high aspect ratio via which is less than about 0.1 6 μm in diameter with

a TaN_x layer from a TaF₅ or TaCI₅ precursor by elevating the precursor

temperature sufficient to vaporize the precursor to provide a pressure to deliver

the vapor. The vapor is combined with a process gas containing nitrogen and

TaN_x is deposited in the feature by a thermal chemical vapor deposition (thermal

CVD) process. The deposition is halted to plasma treat the film surface, then

deposition is resumed. The plasma treatments are performed at regular intervals

in the thermal CVD process until a desired film thickness is obtained.

The invention is further directed to a method of filling a high aspect

ratio via which is less than about 0J 6 μm in diameter with a TaN_x film from a

TaBr₅ precursor on a substrate without a carrier gas. The temperature of the precursor is elevated sufficient to produce a tantalum vapor. The vapor is

combined with a process gas containing nitrogen and TaN_x is deposited in the

feature by a thermal chemical vapor deposition (thermal CVD) process. The

deposition is halted to plasma treat the film surface, then deposition is resumed.

The plasma treatments are performed at regular intervals in the thermal CVD

process until a desired film thickness is obtained.

The fiims deposited by the method of the invention can completely

fill a feature and eliminate the need for a copper deposition step. The films are

deposited at temperature less than about 500°C, thereby protecting the integrity

of the underlying material. The films have a cracking threshold greater than 2000

A, have sufficiently low electrical resistivities, have 1 00% conformality in high

aspect ratio features, and show no attack or corrosion of integral copper films.

The films have minimal impurities and are good barriers to copper diffusion. The

films can be deposited at a rate sufficient for throughput considerations. It will

be appreciated that the disclosed method and substrates of the invention have an

array of applications. These and other advantages will be further understood with

reference to the following drawings and detailed description.

Brief Description of the Drawings

FIG. 1 is a schematic of an apparatus for plasma treated thermal

chemical vapor deposition (PTTCVD) .

FIG. 2 is a graph of vapor pressure versus temperature for tantalum

(Ta) halides. O 00/65126

-8-

FIG. 3 is a schematic representation of a structure fabricated using

standard plug fills.

FIG. 4 is a scanning electron micrograph (SEM) image of a plug fill

by TaN_x deposited by TaF₅ based thermal CVD.

FIG. 5 is a SEM image of a plug fill by TaN_x deposited by TaF₅ based

plasma treated thermal CVD (PTTCVD).

FIG. 6 is a SEM image of a plug fill by TaN_x deposited by TaBr₅ based

thermal CVD.

FIG. 7 is a SEM image of a plug fill by TaN_x deposited by TaBr₅ based

PTTCVD.

FIG . 8 is a SEM image of a 1 1 50 A TaF₅ based CVD TaN_x film.

FIG. 9 is a SEM image of a 3700 A TaCI₅ based CVD TaN_x film.

FIG. 1 0 is a SEM image of a 1 350 A TaBr₅ based CVD TaN_x film.

FIG. 1 1 is a SEM image of TaF₅ based CVD Ta/TaN_x film deposited

on a copper (Cu) layer.

FIG. 1 2 is a SEM image of TaCI₅ based CVD TaN_x film deposited on

a Cu layer.

FIG. 1 3 is a SEM image of TaBr₅ based CVD Ta/TaN_x film deposited

on a Cu layer.

FIG . 1 4 is an Auger spectrum of a TaBr₅ based CVD TaN_x film

deposited on a Cu layer. -9-

Detailed Description

Refractory transition metals such as tantalum (Ta) and their nitride

films (TaN) are effective diffusion barriers to copper (Cu) . Their effectiveness is

due to their high thermal stability, high conductivity and resistance to diffusion

of foreign elements or impurities. Ta and TaN are especially attractive due to

their chemical inertness with Cu; no compounds form between Cu and Ta or Cu

and N.

Tantalum halides provide a convenient inorganic source for Ta and

TaN. Specifically, the inorganic precursor is a tantalum pentahalide (TaX₅) where

X represents the halides fluorine (F), chlorine (Cl) and bromine (Br). Table 1

shows relevant thermodynamic properties of the tantalum halide precursors,

specifically tantalum pentafluoride (TaF₅), tantalum pentachloride (TaCI₅) and

tantalum bromide (TaBr₅), with tantalum pentaiodide (Tal₅) included for

comparison. The TaF₅, TaCI₅ and TaBr₅ precursor materials are all solids at room

temperature ( 1 8 °C-22 °C).

Table 1

In chemical vapor deposition (CVD) processes, gas precursors are

activated using either thermal energy or electrical energy. Upon activation, the

gas precursors react chemically to form a film. A preferred method of CVD is

illustrated in FIG 1 and is disclosed in a copending application entitled

APPARATUS AND METHODS FOR DELIVERY OF VAPOR FROM SOLID SOURCES

TO A CVD CHAMBER by Westendorp et al. filed on the same date as the present

application and assigned to Tokyo Electron Limited and incorporated by reference

herein in its entirety. A chemical vapor deposition (CVD) system 1 0 includes a

CVD reaction chamber 1 1 and a precursor delivery system 1 2. In the

reaction chamber, a reaction is carried out to convert a precursor gas of, for

example, tantalum chloride (TaCI) or other tantalum halide compound, into a film

such as a barrier layer film of tantalum (Ta) or tantalum nitride (TaN) . The TaN

film is not limited to any particular stoichiometry (TaN_x). Thus, as used herein,

TaN_x encompasses a tantalum nitride film of any stoichiometry.

The precursor delivery system 12 includes a source 13 of precursor

gas having a gas outlet 14, which communicates through a metering system 1 5

with a gas inlet 1 6 to the CVD reaction chamber 1 1 . The source 1 3 generates

a precursor gas, for example a tantalum halide vapor, from a tantalum halide

compound. The compound is one that is in a solid state when at standard

temperature and pressure. The precursor source is maintained, preferably by

controlled heating, at a temperature that will produce a desired vapor pressure of

precursor. Preferably, the vapor pressure is one that is itself sufficient to deliver the precursor vapor to the reaction chamber, preferably without the use of a

carrier gas. The metering system 1 5 maintains a flow of the precursor gas vapor

from the source 1 3 into the reaction chamber at a rate that is sufficient to

maintain a commercially viable CVD process in the reaction chamber.

The reaction chamber 1 1 is a generally conventional CVD reactor and

includes a vacuum chamber 20 that is bounded by a vacuum tight chamber

wall 21 . In the chamber 20 is situated a substrate support or susceptor 22 on

which a substrate such as a semiconductor wafer 23 is supported. The

chamber 20 is maintained at a vacuum appropriate for the performance of a CVD

reaction that will deposit a film such as a Ta/TaN_x barrier layer on the

semiconductor wafer substrate 23. A preferred pressure range for the CVD

reaction chamber 1 1 is in the range of from 0.2 to 5.0 Torr. The vacuum is

maintained by controlled operation of a vacuum pump 24 and of inlet gas sources

25 that include the delivery system 12 and may also include reducing gas sources

26 of, for example, hydrogen (H₂), nitrogen (N₂) or ammonia (NH₃) for use in

carrying out a tantalum reduction reaction, and an inert gas source 27 for a gas

such as argon (Ar) or helium (He). The gases from the sources 25 enter the

chamber 20 through a showerhead 28 that is situated at one end of the

chamber 20 opposite the substrate 23, generally parallel to and facing the

substrate 23.

The precursor gas source 1 3 includes a sealed evaporator 30 that

includes a cylindrical evaporation vessel 31 having a vertically oriented axis 32. The vessel 31 is bounded by a cylindrical wall 33 formed of a high temperature

tolerant and non-corrosive material such as the alloy INCONEL 600, the inside

surface 34 of which is highly polished and smooth. The wall 33 has a flat circular

closed bottom 35 and an open top, which is sealed by a cover 36 of the same

heat tolerant and non-corrosive material as the wall 33. The outlet 14 of the

source 1 3 is situated in the cover 36. When high temperatures are used, such

as with Til₄ or TaBr₅, the cover 36 is sealed to a flange ring 37 that is integral to

the top of the wall 33 by a high temperature tolerant vacuum compatible metal

seal 38 such as a HELICOFLEX seal, which is formed of a C-shaped nickel tube

surrounding an INCONEL coil spring. With materials requiring lower temperatures,

such as TaCI₅ and TaF₅, a conventional elastomeric O-ring seal may be used to

seal the cover.

Connected to the vessel 31 through the cover 36 is a source 39 of

a carrier gas, which is preferably an inert gas such as He or Ar. The source 1 3

includes a mass of precursor material such as tantalum fluoride, chloride or

bromide (TaX), preferably as the pentahalide (TaX₅), at the bottom of the

vessel 31 , which is loaded into the vessel 31 at standard temperature and

pressure in a solid state. The vessel 31 is filled with tantalum halide vapor by

sealing the chamber with the solid mass of Ta_x therein. The halide is supplied as

a precursor mass 40 that is placed at the bottom of the vessel 31 , where it is

heated, preferably to a liquid state as long as the resulting vapor pressure is in an

acceptable range. Where the mass 40 is liquid, the vapor lies above the level of -1 3-

the liquid mass 40. Because wall 33 is a vertical cylinder, the surface area of

TaX mass 40, if a liquid, remains constant regardless of the level of depletion of

the TaX.

The delivery system 1 2 is not limited to direct delivery of a

precursor 40 but can be used in the alternative for delivery of precursor 40 along

with a carrier gas, which can be introduced into the vessel 31 from gas

source 39. Such a gas may be hydrogen (H₂) or an inert gas such as helium (He)

or argon (Ar) . Where a carrier gas is used, it may be introduced into the

vessel 31 so as to distribute across the top surface of the precursor mass 40 or

may be introduced into the vessel 31 so as to percolate through the mass 40

from the bottom 35 of the vessel 31 with upward diffusion in order to achieve

maximum surface area exposure of the mass 40 to the carrier gas. Yet another

alternative is to vaporize a liquid that is in the vessel 31 . However, such

alternatives add undesired particulates and do not provide the controlled delivery

rate achieved by the direct delivery of the precursor, that is, delivery without the

use of a carrier gas. Therefore, direct delivery of the precursor is preferred.

To maintain the temperature of the precursor 40 in the vessel 31 ,

the bottom 35 of the wall 33 is maintained in thermal communication with a

heater 44, which maintains the precursor 40 at a controlled temperature,

preferably above its melting point, that will produce a vapor pressure greater than

about 3 Torr in the absence of a carrier gas (i.e., a direct delivery system), and

a lower vapor pressure such as about 1 Torr when a carrier gas is used. The 00/65126

-14-

exact vapor pressure depends upon other variables such as the quantity of carrier

gas the surface area of the substrate and so on. In a direct system for tantalum,

a vapor pressure can be maintained at the preferred pressure of 5 Torr or above

by heating the a tantalum halide precursor in the 95 °C to 205 °C range as shown

in FIG. 2. For TaX₅ the desired temperature is at least about 95 ° C for TaF₅, the

desired temperature is at least about 1 45 °C for TaCI₅, and the desired

temperature is at least about 205 °C for TaBr₅. The melting points of the

respective fluoride, chloride and bromide tantalum pentahalide compounds are in

the 97 ° C to 265 ° C range. A much higher temperature is required for tantalum

pentaiodide (Tal₅) to produce a sufficient vapor pressure in the vessel 31 .

Temperatures should not be so high as to cause premature reaction of the gases

in the showerhead 28 or otherwise before contacting the wafer 23.

For purposes of example, a temperature of 1 80 °C is assumed to be

the control temperature for the heating of the bottom 35 of the vessel 31 . This

temperature is appropriate for producing a desired vapor pressure with a titanium

tetraiodide (Til₄) precursor. Given this temperature at the bottom 35 of the

vessel 31 , to prevent condensation of the precursor vapor on the walls 33 and

cover 36 of the vessel 31 , the cover is maintained at a higher temperature than

the heater 44 at the bottom 35 of the wall 33 of, for example, 1 90°C, by a

separately controlled heater 45 that is in thermal contact with the outside of the

cover 36. The sides of the chamber wall 33 are surrounded by an annular

trapped air space 46, which is contained between the chamber wall 33 and a surrounding concentric outer aluminum wall or can 47. The can 47 is further

surrounded by an annular layer of silicon foam insulation 48. This temperature

maintaining arrangement maintains the vapor in a volume of the vessel 31

bounded by the cover 36, the sides of the walls 33 and the surface 42 of the

precursor mass 40 in the desired example temperature range of between 1 80°C

and 1 90 °C and the pressure greater than about 3 Torr, preferably at greater than

5 Torr. The temperature that is appropriate to maintain the desired pressure will

vary with the precursor material, which is primarily contemplated as a being

tantalum or titanium haiide compound.

The vapor flow metering system 1 5 includes a delivery tube 50 of

at least Vi inch in diameter, or at least 1 0 millimeters inside diameter, and

preferably larger so as to provide no appreciable pressure drop at the flow rate

desired, which is at least approximately 2 to 40 standard cubic centimeters per

minute (seem) . The tube 50 extends from the precursor gas source 1 3 to which

it connects at its upstream end to the outlet 14, to the reaction chamber to which

it connects at its downstream end to the inlet 1 6. The entire length of the

tube 50 from the evaporator outlet 14 to the reactor inlet 1 6 and the showerhead

28 of the reactor chamber 20 are also preferably heated to above the evaporation

temperature of the precursor material 40, for example, to 1 95 °C.

In the tube 50 is provided baffle plate 51 in which is centered a

circular orifice 52, which preferably has a diameter of approximately 0.089

inches. The pressure drop from gauge 1 56 to gauge 2 57 is regulated by control valve 53. This pressure drop after control valve 53 through orifice 52 and into

reaction chamber 1 1 is greater than about 10 milliTorr and will be proportional to

the flow rate. A shut-off valve 54 is provided in the line 50 between the

outlet 14 of the evaporator 1 3 and the control valve 53 to close the vessel 31 of

the evaporator 1 3.

Pressure sensors 55-58 are provided in the system 1 0 to provide

information to a controller 60 for use in controlling the system 1 0, including

controlling the flow rate of precursor gas from the delivery system 1 5 into the

chamber 20 of the CVD reaction chamber. The pressure sensors include

sensor 55 connected to the tube 50 between the outlet 14 of the evaporator 1 3

and the shut-off valve 54 to monitor the pressure in the evaporation vessel 31 .

A pressure sensor 56 is connected to the tube 50 between the control valve 53

and the baffle 51 to monitor the pressure upstream of the orifice 52, while a

pressure sensor 57 is connected to the tube 50 between the baffle 51 and the

reactor inlet 1 6 to monitor the pressure downstream of the orifice 52. A further

pressure sensor 58 is connected to the chamber 20 of the reaction chamber to

monitor the pressure in the CVD chamber 20.

Control of the flow of precursor vapor into the CVD chamber 20 of

the reaction chamber is achieved by the controller 60 in response to the pressures

sensed by the sensors 55-58, particularly the sensors 56 and 57 which determine

the pressure drop across the orifice 52. When the conditions are such that the

flow of precursor vapor through the orifice 52 is unchoked flow, the actual flow -1 7- of precursor vapor through the tube 52 is a function of the pressures monitored

by pressure sensors 56 and 57, and can be determined from the ratio of the

pressure measured by sensor 56 on the upstream side of the orifice 52, to the

pressure measured by sensor 57 on the downstream side of the orifice 52.

When the conditions are such that the flow of precursor vapor

through the orifice 52 is choked flow, the actual flow of precursor vapor through

the tube 52 is a function of only the pressure monitored by pressure sensor 57.

In either case, the existence of choked or unchoked flow can be determined by

the controller 60 by interpreting the process conditions. When the determination

is made by the controller 60, the flow rate of precursor gas can be determined by

the controller 60 through calculation.

Preferably, accurate determination of the actual flow rate of

precursor gas is calculated by retrieving flow rate data from lookup or multiplier

tables stored in a non-volatile memory 61 accessible by the controller 60. When

the actual flow rate of the precursor vapor is determined, the desired flow rate

can be maintained by a closed loop feedback control of one or more of the

variable orifice control valve 53, the CVD chamber pressure through evacuation

pump 24 or control of reducing or inert gases from sources 26 and 27, or by

control of the temperature and vapor pressure of the precursor gas in vessel 31

by control of heaters 44, 45.

As shown in FIG. 1 , the solid TaF₅, TaCI₅ and TaBr₅ precursor

material 40 is sealed in a cylindrical corrosion resistant metal vessel 31 that maximizes the available surface area of the precursor material. Vapor from either

TaF₅, TaCI₅ or TaBr₅ was delivered directly, that is, without the use of a carrier

gas, by a high conductance delivery system into a reaction chamber 1 1 . The

reaction chamber 1 1 was heated to a temperature of at least about 1 00° C to

prevent condensation of vapor or deposition by-products.

The controlled direct delivery of tantalum halide vapor into the

reaction chamber 1 1 was accomplished by heating the solid tantalum halide

precursor 40 to a temperature in the range of about 95 ° C-205 °C, the choice

depending upon the particular precursor. The temperature was sufficient to

vaporize the precursor 40 to provide a vapor pressure to deliver the tantalum

halide vapor to the reaction chamber 1 1 . Thus, a carrier gas was not necessary

and preferably was not used. A sufficient vapor pressure was in the range of

about 3-10 Torr. This pressure was required to maintain a constant pressure drop

across a defined orifice in a high conductance delivery system while delivering up

to about 50 seem tantalum halide precursor to a reaction chamber 1 1 operating

in the range of about OJ -2.0 Torr. The temperatures to obtain the desired

pressures in a direct delivery system were in the range of about 83 °C-95 ° C and

preferably about 95 °C with TaF₅, in the range of about 1 30°C-1 50°C and

preferably about 1 45 °C with TaCI₅, and in the range of about 202 °C-21 8 °C and

preferably about 205 °C with TaBr₅. Under these conditions, TaF₅ is a liquid while

TaCI₅ and TaBr₅ remain solid. FIG. 2 shows the relationship between the measured vapor pressure

and temperature for the precursors TaF₅, TaCI₅ and TaBr₅, with Tal₅ included for

comparison. As previously stated, the desired pressure was greater than about

3 Torr and preferably greater than 5 Torr. Also as previously stated, the vapor

pressure for TaF₅, TaCI₅ and TaBr₅ was desirably low enough to be able to deposit

tantalum in the absence of a carrier gas but yet sufficient to maintain a constant

pressure drop across a defined orifice in a high conductance delivery system and

still be able to deliver up to 50 sscm TaX₅ to a reaction chamber 1 1 operating at

0.1 -2.0 Torr. The vapor pressure for Tal₅ was determined to be too low for

practical implementation in the described apparatus. For TaBr₅ the open circles

represent published values, while closed squares for TaBr₅, TaF₅, TaCI₅ and Tal₅

represent the inventors' experimental data.

A parallel plate RF discharge was used where the driven electrode

was the gas delivery showerhead and the susceptor 22 or stage for the wafer or

substrate 23 was the RF ground. The selected TaX₅ vapor was combined with

other process gases such as H₂ above the substrate, which had been heated to

a temperature between about 300 °C-500 ° C. Ar and He could also be used,

either singularly or in combination, as process gases in addition to H₂.

The thermal CVD is stopped at regular intervals to plasma treat the

film surface. The flow of tantalum halide precursor gas and process gas is turned

off or is directed around the reaction chamber 1 1 and a plasma treatment is then

performed on the surface of the film. For the plasma treatment a parallel plate RF -20- discharge is used where the driven electrode is the gas delivery showerhead and

the wafer stage is the RF ground. H₂ was used to plasma treat the film at a flow

of 7 slm, after which thermal CVD was resumed. The depositing, plasma treating

and resumed depositing steps continued until the desired film thickness was

obtained. The plasma treatment of films deposited by thermal CVD, that is, the

plasma treated thermal CVD (PTTCVD) process, could decrease the film's

electrical resistivity by a factor of greater than ten thousand. In addition,

PTTCVD improves the film's morphology from a relatively rough structure to a

smooth dense film.

Process conditions for deposition of good quality PTTCVD TaN_x films

are given in Table 2.

Table 2

Typical initial film results for TaN_x films deposited by thermal CVD

are given in Table 3. Depositions were on 200 mm Si and SiO₂ substrates. The properties of the deposited TaN_x films as listed in Table 3 were uniform within

plus or minus 20% across the wafer.

Table 3

-23- Typical initial film results for TaN_x fiims deposited by PTTCVD are

given in Table 4. Depositions were on 200 mm Si and SiO₂ substrates. The

properties of the deposited TaN_x films as listed in Table 4 were uniform within

plus or minus 20% across the wafer.

Table 4

As shown in Table 4, the results of the initial tests indicate that

plasma treatment of the TaN_x film deposited by thermal CVD makes this

process potentially viable for TaBr₅ and TaF₅ based TaN_x films. The TaCI₅

based film is expected to perform similarly because the TaCI₅ based films had

properties that were effectively between the TaBr₅ and TaF₅ based TaN_x films.

The improvement of TaN_x electrical resistivity by application of

the H₂ plasma can be seen in Table 4. Resistivities of the films that did not

undergo the plasma treatment were high, greater than 1 X1 0⁷ μΩcm, which

was the limit of the measurement tool. As thinner layers of TaN_x films

deposited by thermal CVD were treated by the hydrogen RF discharge, lower

resistivities were obtained. The electrical resistivity of the PTTCVD TaF₅ based

film decreased from greater than 1 X1 0⁷ μΩcm in the untreated state to

3600 μΩcm when a 70 A thick TaN_x film per cycle was subjected to plasma

treatment. The resistance further decreased to 1 100 μΩcm when a 45 A thick

TaN_x film per cycle was subjected to plasma treatment. Similarly, the

electrical resistivity of the PTTCVD TaBr₅ based film decreased from greater

than 1 X 1 0⁷ μΩcm for untreated fiims to 32,000 μΩcm when a 1 05 A TaN_x

film per cycle was subjected to plasma treatment. A further decrease to 5800

μΩcm was obtained when a 20 A thick TaN_x film per cycle was subjected to

plasma treatment. A TaN_x film deposited using a TaCI₅ precursor would be

expected to perform similarly since other TaN_x based films had properties that

were effectively between TaF₅ and TaBr₅ precursors.

The H₂ plasma treatment process appeared to cause a

fundamental change in the electrical and/or morphological properties of the TaN_x fiims. Plasma treatment times in the range of between 1 0 seconds and

240 seconds have been evaluated. It has been determined that, within this

range, longer treatment times yield films with lower resistivities for the

material. The microstructure of the TaN_x film also changed from a rough to a

smooth surface with the cycled deposition and plasma treatment.

For a plug fill application, seamless fill of the structure requires

a nearly perfect conformality and a 100% step coverage. A conformal fiim is

one that exactly reproduces the surface topography of the underlying

substrate. A seamless fiim is one that contains no cracks. The step coverage

represents the film thickness on the bottom of the feature divided by the film

thickness on the surface of the substrate adjacent the feature, also called the

field. An ideal step coverage is 1 .0 or 1 00%, representing identical thickness

on the bottom as on the field. As shown in FIG. 4 and FIG. 5 for TaF₅ based

TaN_x films, and FIG. 6 and FIG. 7 for TaBr₅ based TaN_x films, the thermal CVD

and PTTCVD TaN_x processes using these tantalum halide precursors meet

these criteria. TaCI₅ based fiims would be expected to exhibit the same

desired conformality and step coverage as the TaF₅ and TaBr₅ precursors since

all of the other measured properties appeared very similar.

With reference to FIGS. 8-10, thick TaN_x films deposited by CVD

are shown. FIG. 8 is a scanning electron micrograph (SEM) image of a 1 1 50

A thick crack-free TaF₅ based CVD TaN_x fiim. FIG. 9 is a SEM image of a

3700 A thick crack-free TaCI₅ based CVD TaN_x film. FIG. 10 is a SEM image

of a 1 350 A crack-free TaBr₅ based CVD TaN_x film. A continuous, completely

conformal film with no cracks is required for a good piug fill. Cracking would be problematic for adhesion of the film to the underlying layers, to prevent

flaking off of the film that would compromise subsequent processes. Cracking

would also be problematic because it would be expected to increase the

electrical resistivity of the plug. As shown in each of FIGS. 8-1 0, each film

from the three precursors were free of cracks.

The compatibility of the precursor chemistries of the TaN_x plug

fills of the present invention with copper was determined. Since in practice

the TaN_x film will be integral, that is, in direct contact with copper, little or no

attack or etching of the copper should take place during TaN_x deposition. TaN_x

compatibility with copper was tested by placing a Si wafer containing a 500

A layer of TaN_x deposited by PVD and a 2000 A layer of copper deposited by

PVD into the deposition reaction chamber 1 1 . A TaN_λ film was deposited by

CVD on top of the copper layer using the process of the invention with either

a TaF₅ or TaCI₅ precursor.

Photographs of SEM of the resulting films are shown in

FIGS. 1 1 -1 3. FIG. 1 1 shows a TaF₅ based Ta/TaN_x film deposited directly on

the Cu surface. FIG. 1 2 shows a TaCI₅ based TaN_x film on deposited directly

on the Cu surface. FIG. 1 3 shows a TaBr₅ based Ta/TaN_x fiim deposited

directly on the Cu surface. For each of FIGS. 1 1 -1 3, the tantalum pentahalide

based Ta and TaN_x based films deposited directly on the Cu layer showed no

visible evidence of etching or attack of Cu.

With reference to FIG. 14, a TaBr₅ based TaN_x film deposited by

thermal CVD directly on a Cu layer was analyzed by Auger analysis. The

Auger spectrum confirms a clean interface between the TaN_xfilm and the- other layers. FIG. 14 indicates that the thermal TaN_x film is nitrogen rich (x > 1 .0),

which was consistent with the results shown in Table 3. Nitrogen rich TaN_x

films (x > 1 ) are expected to have a relatively high electrical resistivity. FIG.

14 also shows a good sharp interface between the TaN_x layer and Cu, which

suggests little or no attack of the Cu surface during TaN_x deposition. The

bromide concentration was determined to be less than 2 atomic percent.

Copper diffusion barrier properties of the resulting TaN_x films are

expected to be good. One contributing factor may be the nitrogen rich

process, since this is known to improve barrier performance. Another factor

may be the generally amorphous structure of the material, since it is known

that an amorphous material, defined as having a low fraction of crystalline

structure, provides a better barrier.

Therefore, a method of producing high quality PTTCVD TaN_x films

suitable for integration with IC interconnect elements that contain Cu has been

demonstrated. The method is based on the vapor delivery of either TaF₅, TaCI₅

or TaBr₅ precursors. All of the resulting TaN_x fiims demonstrated excellent

step coverage, low residual impurity concentrations, sufficiently high

deposition rates and no signs of TaN_x etching of Cu. The introduction of a H₂

RF plasma treatment between thermal CVD cycles resulted in a greater than

ten thousand times reduction in the electrical resistivity of the TaN_x film. The

H₂ RF plasma treatment also significantly improved the microstructure of the

film with no change in step coverage. The TaF₅ based fiims initially appear to

be the most promising due to their lower resistivities and smoother

microstructure. -29-

it should be understood that the embodiments of the present

invention shown and described in the specification are only preferred

embodiments of the inventors who are skilled in the art and are not limiting in

any way. For example, Ta films may be deposited by PECVD, and TaN films

may be deposited by either thermal CVD, PECVD, or plasma treated thermal

CVD as disclosed in, respectively, PECVD OF Ta FILMS FROM TANTALUM

HALIDE PRECURSORS, THERMAL CVD OF TaN FILMS FROM TANTALUM

HALIDE PRECURSORS, PECVD OF TaN FILMS FROM TANTALUM HALIDE

PRECURSORS, and PLASMA TREATED THERMAL CVD OF TaN FILMS FROM

TANTALUM HALIDE PRECURSORS, all of which are invented by Hautala and

Westendorp, assigned to Tokyo Electron Limited, are copending applications

filed on the same date as the present application and are expressly

incorporated by reference herein in their entirety. As another example, TiN

from titanium halide precursors deposited by CVD can be used for plug

formation as disclosed in the copending application entitled CVD TiN PLUG

FORMATION FROM TITANIUM HALIDE PRECURSORS, invented by Hautala et

al., assigned to Tokyo Electron Limited, filed on the same date as the present

application and expressly incorporated by reference herein in its entirety.

Furthermore, Ta/TaN_x bilayers may be deposited by CVD as disclosed in the

copending application CVD INTEGRATED Ta AND TaN_x FILMS FROM

TANTALUM HALIDE PRECURSORS, invented by Hautala and Westendorp,

assigned to Tokyo Electron Limited, filed on the same date as the present

application and expressly incorporated by reference herein in its entirety.

Therefore, various changes, modifications or alterations to these embodiments may be made or resorted to without departing from the spirit of the invention

and the scope of the following claims.

What is claimed is:

Claims

1 . A method of filling a feature in a substrate comprising depositing

a tantalum nitride (TaN_x) fiim in said feature by providing a vapor of a tantalum

halide precursor to a reaction chamber containing said substrate by heating

said precursor to a temperature sufficient to vaporize said precursor, then

combining said vapor with a process gas containing nitrogen, depositing said

TaN_x film in said feature by a thermal chemical vapor deposition (CVD) process

and plasma treating said deposited TaN_x.

2. The method of claim 1 further comprising repeating said

depositing by thermal CVD and said plasma treating to produce a desired

thickness of said film in said feature.

3. The method of claim 1 wherein said tantalum halide precursor is

selected from the group consisting of tantalum fluoride, tantaium chloride and

tantalum bromide.

4. The method of claim 1 wherein said providing of said vapor

includes producing said vapor at a pressure of at least about 3 Torr.

5. The method of claim 1 wherein said precursor is tantalum

pentafluoride and said temperature is about 95 °C.

6. The method of claim 1 wherein said precursor is tantalum

pentachloride and said temperature is about 145 ° C.

7. The method of claim 1 wherein said precursor is tantalum

pentabromide and said temperature is about 205 °C.

8. The method of claim 1 wherein said heating of said precursor is

to a temperature sufficient to provide a vapor pressure of said tantalum halide

precursor of at least 3 Torr.

9. The method of claim 1 wherein said feature has an aspect ratio

greater than 8.0.

1 0. The method of claim 1 wherein said feature has a diameter less

than about 0.1 6 μm.

1 1 . The method of claim 1 wherein said substrate is heated to a

temperature in the range of about 300-500°C.

1 2. The method of claim 1 wherein said precursor is provided at a

rate in the range of about 1 -50 seem.

1 3. The method of claim 1 wherein said nitrogen containing gas is

ammonia.

1 4. The method of ciaim 1 3 wherein said ammonia is at a flow rate

in the range of about 0J -5.0 slm. 00/65126

-33- 1 5. The method of claim 1 wherein said process gas is selected from

the group consisting of hydrogen, nitrogen, argon, helium and combinations

thereof.

1 6. The method of claim 1 wherein said depositing occurs at a

pressure of said chamber in the range of about 0.2-5.0 Torr.

1 7. The method of claim 1 wherein said fiim is integral with a copper

layer of said substrate.

1 8. The method of claim 1 wherein said depositing is stopped prior

to beginning said plasma treatment.

1 9. The method of claim 1 8 wherein said depositing is stopped by

halting a flow of said precursor gas and said process gas in said chamber.

20. The method of claim 1 8 wherein said depositing is stopped by

redirecting a flow of said precursor gas and said process gas in said chamber.

21 . The method of claim 1 wherein said plasma treatment is

generated by a radiofrequency energy source.

22. The method of claim 1 wherein a hydrogen gas is used for said

plasma treatment.

23. The method of claim 1 wherein said tantalum haiide precursor is

delivered to said reaction chamber without a carrier gas.

24. The method of claim 1 further comprising depositing and treating

said TaN_x film sequentially with a tantalum film.

25. A method of filling a feature in a substrate comprising providing

a vapor of a tantalum halide precursor selected from the group consisting of

tantalum fluoride and tantalum chloride to a reaction chamber containing said

substrate by elevating a temperature of said precursor sufficient to produce a

vapor of said precursor to provide a pressure to deliver a tantalum vapor,

combining said vapor with a process gas containing nitrogen, depositing a

tantalum nitride (TaN_x) fiim in said feature by a thermal chemical vapor

deposition (CVD) process and plasma treating said deposited TaN_x fiim.

26. The method of claim 25 further comprising repeating said

depositing by thermal CVD and said plasma treating to produce a desired

thickness of said film in said feature.

27. The method of claim 25 wherein said elevated temperature is less

than a temperature that would cause a reaction between said precursor vapor

and said process gas.

28. The method of claim 25 wherein said pressure to deliver said

tantalum vapor is at least about 3 Torr.

29. The method of claim 25 wherein said precursor is tantalum

pentafluoride and said temperature is about 95 °C.

30. The method of claim 25 wherein said precursor is tantalum

pentachloride and said temperature is about 1 45 °C.

31 . The method of claim 25 wherein said thermal CVD is stopped

prior to beginning said plasma treatment.

32. A method of filling a feature in a substrate comprising providing

a vapor of a tantalum pentabromide precursor to a reaction chamber containing

said substrate without a carrier gas by elevating a temperature of said

precursor sufficient to produce a vapor of said precursor, combining said vapor

with a process gas containing nitrogen, depositing a tantalum nitride (TaN_x)

film in said feature by a thermal chemical vapor deposition (CVD) process and

plasma treating said deposited TaN_x film.

33. The method of claim 32 wherein said precursor is tantalum

pentabromide and said temperature is in the range of about 1 90° to about

208 ° C.

34. The method of claim 33 wherein said precursor is tantalum

pentabromide and said temperature is about 205 °C.

35. The method of claim 32 further comprising repeating said

depositing by thermal CVD and said plasma treating to produce a desired

thickness of said film in said feature.