WO1997041598A1

WO1997041598A1 - Apparatus and method for improved deposition of conformal liner films and plugs in high aspect ratio contacts

Info

Publication number: WO1997041598A1
Application number: PCT/IB1997/000522
Authority: WO
Inventors: Corey A. Weiss; Bruce Gittleman; Jeffrey M. Bulson
Original assignee: Sony Corporation; Materials Research Corporation
Priority date: 1996-04-26
Filing date: 1997-04-15
Publication date: 1997-11-06
Also published as: JPH11509049A; TW417223B; AU2400497A; CA2225446A1; KR19990028451A; EP0843890A1

Abstract

A sputter deposition system and method comprises a vacuum system (36), target (44), collimator (46), and substrate (38). The target (44) is biased and sputtered to deposit a material layer onto the substrate (38) through the collimator (46). The substrate (38) can be biased to allow contemporaneous etching with deposition.

Description

APPARATUS AND METHOD FOR IMPROVED DEPOSITION OF

CONFORMAL LINER FILMS AND PLUGS IN HIGH ASPECT RATIO

CONTACTS

Field of the Invention

This invention relates generally to the formation of

conductive liners and the formation of conductive plugs or non-

conductive plugs for creating electrical interconnections or circuit

elements for integrated circuits (IC's) . More particularly, the

invention relates to the formation of conductive liners and

conductive plugs in substrate contacts or apertures having high

aspect ratios.

Background of the Invention

In the manufacturing of integrated circuits, and

particularly, logic and memory circuits, the circuit structures utilized

are increasingly dense and compact. Furthermore, current integrated circuits are utilizing an increasingly larger number of

interconnecting metal levels as well as increasingly higher

interconnect densities per level. During IC fabrication, patterned

series of holes, apertures and trenches are formed in the substrate,

and specifically the holes/apertures are formed in the material layers

of an IC substrate to provide for interconnection between the

material layers. For example, when one substrate material layer is

formed on top of another layer, a hole is made in the top layer to

provide for interconnection to a lower layer. These holes and

apertures are oftentimes referred to in the art as contacts or vias

and will be collectively referred to herein as "contacts" . When

making an interconnection between the layers, the contacts are

filled with an appropriate metal plug. Sometimes the metal plug is

preceded by the deposition of a liner film.

In the fabrication of IC devices, the various metal

interconnect layers make electrical contact to the semiconductor

substrate or to other levels of interconnections through the

contacts. The contacts are formed in the various metal

interconnect layers by etching, masking or other techniques known

to a person of ordinary skill in the art. Once a contact is formed,

the interconnecting metal layers or plugs are deposited into the contact to provide for the electrical interconnection between the

layers. Such films and layers can be deposited by generally known

techniques such as chemical vapor deposition (CVD) or physical

vapor deposition (PVD).

One conventionally known physical vapor deposition

technique is sputter deposition. In sputter deposition, a target of

material, such as a metal target, is positioned in a vacuum chamber

generally opposite a substrate which is to receive a layer or plug of

material. A working gas is introduced into the vacuum chamber

proximate the target and is electrically excited to create a gas

plasma including positively charged gas ions. The target is

negatively biased and the ionized plasma species bombard the

negative target, thus dislodging material or "sputtering" the target.

The dislodged or sputtered material deposits onto the substrate

surface and thus covers the substrate surface and thereby lines or

fills any contacts formed in the exposed substrate surface.

In the drive toward more dense and compact circuit

structures on a substrate, the critical dimensions of the

interconnect contacts are made increasingly smaller. The "aspect

ratio" of a contact is the ratio of the contact length to its width (or

diameter if the contact hole is circular). With smaller contact dimensions, the contact aspect ratios are becoming increasingly

higher. Such high aspect ratio contacts are difficult to fill due to

the obstruction of the sputtered material by the high contact walls

and resulting shadowing of portions of the contacts interior.

However, the smaller architecture of current IC technology is

desirable for improved performance and lower cost.

While sputter deposition has proven to be generally

useful for conductive liner films and conductive plugs, the

conventional sputter deposition techniques present problems when

depositing such films and plugs into contacts having very high

aspect ratios, e.g., aspect ratios ≥ 1 .5. As such, when the aspect

ratio of a contact exceeds 1 , conventional sputter deposition

becomes less effective at depositing material into the bottom and

sides of the contact. The physical shadowing of the contact side

walls results in a tapered sidewall deposition, and the contact has

little deposition in the bottom corner. As may be appreciated, this

problem becomes worse as the contact aspect ratios increase.

One known technique of improving bottom and side

wall coating or coverage in high aspect ratio contacts is to use a

plate collimator. The plate collimator is typically positioned parallel

to the substrate. A collimator has a series of tubes, the walls of which intercept some of the material sputtered from the target.

The sputtered material or flux incident at an angle far from 0° (with

respect to the collimator perpendicular) are removed. Only the

portion of the flux incident within an angle proportional to the ratio

of the collimator hole diameter to hole height is allowed to pass

through the collimator. As this ratio decreases, the aspect ratio of

the collimator tubes increases, and a greater percentage of the total

flux is incident on the substrate within a very small angle from

perpendicular. However, while high aspect ratio plate collimators

may offer suitable deposition, they produce a large reduction in the

deposition rate and reduce the efficiency of target utilization

because much of the sputtered material is deposited on the

collimator. The invention allows lower aspect ratio collimators to

achieve deposition profiles similar to high aspect collimators and

reduces the impact on deposition rate and target utilization.

Further, the invention allows greater utilization of the collimator by

reducing the rate of material build-up thereon.

Relatively recently, the use of titanium and titanium

nitride has become desirable for lining contacts. Collimator

techniques for depositing conductors such as titanium and titanium

nitride will generally produce films which exhibit low resistivity, low impurity concentrations and regular crystal morphologies.

However, conventional collimation processes still have undesirable

drawbacks which reduce the reliability of subsequent

interconnection processes. One such drawback is that the

deposition inside the contact still may be generally non-uniform

with inadequate material in the corners of the contact. For

example, Fig. 1 illustrates a substrate 10 having an upper surface

1 2 receiving a layer of deposited material 14. A contact 1 6 formed

in substrate 1 0 has sidewall 1 8 and a bottom surface 20. As

shown in Fig. 1 , sputter deposition by conventionally known

collimation techniques produces a liner film 22 on the sidewall 1 8

which is tapered from top to bottom and which can produce

discontinuities in the bottom corners 21 of the contact 1 6. The

tapered sidewall film 22 and the corner discontinuities may result in

electrical failure of the interconnection.

An additional drawback results from the buildup of

material at the opening of the contact 1 6 proximate surface 1 2.

Referring again to Fig. 1 , the rounded buildup 24, which is

commonly referred to as "overhang" , protrudes into the contact

opening and shadows the sidewall 1 8 of the contact 1 6. The

overhang then results in voids, sometimes referred to as keyholes, within the plug subsequently deposited in the contact. Referring to

Fig. 2, a conductive liner film 26, such as titanium or titanium

nitride, might be deposited by sputter deposition or CVD (see Fig.

1 ), and then a plug layer 28, such as aluminum or tungsten, would

be deposited over the liner film 26 to fill the contact 1 6. A plug

layer of aluminum might be deposited by sputtering or a plug layer

of tungsten might be deposited by CVD. During the plug filling

process, the rounded overhang 24 at the contact opening grows

faster than the plug layer 28 resulting in the contact opening

closing off before the contact is completely filled with the deposited

material. Depending upon the processing temperature, the plug

layer 28 may not flow to the bottom of the contact 1 6, leaving a

void 30 therein often referred to as a keyhole. Such keyholes

appear due to premature contact closing both in sputter deposited

aluminum and CVD deposited tungsten and are particularly

troublesome in contacts having high aspect ratios. The keyhole

voids result in an unreliable electrical contact which degrades the

manufacturing yield and reduces the number of usable devices per

substrate.

Accordingly, it is an objective of the invention to

improve the capability of filling contacts with conductive materials. It is a further objective of the present invention to

produce conformal liner layers in contacts having high aspect ratios.

It is a further objective of the present invention to

increase the reliability of the electrical contacts made within high

aspect ratio contact holes.

It is a further objective of the present invention to

reduce the tapered sidewalls and overhang in conductive layers

deposited into contacts.

It is still a further objective of the present invention to

produce conductive plugs which are free from openings, keyholes

or voids and thus provide more reliable electrical interconnections

between wafer layers.

It is another objective of the present invention to

increase the manufacturing yield of substrates having high aspect

ratio contacts and thus increasing the number of usable devices

from a substrate wafer.

It is a further objective of the present invention to

extend collimator lifetime. 598 PCIYIB97/00522

Summary of the Invention

The present invention provides improved bottom and

sidewall coverage during sputter deposition, and particularly

provides improved coverage for substrates utilizing contacts with

high aspect ratios. The invention is utilized to deposit liner films

and conductor plugs which are more uniformly conformal to thus

enhance the electrical reliability of the interconnects formed

therewith. Additionally, the present invention reduces the overhang

buildup at the opening of the contact to provide for void-free

interconnect plugs. The invention further facilitates plugging

contacts with conductive materials.

The present invention utilizes a sputter deposition

system comprising a collimator in combination with an electrical

biasing system which is operably coupled to the substrate during

sputter deposition to bias the substrate. The collimator is

positioned between a material target and a substrate and it is

configured to intercept sputtered particles of a predetermined

angular incidence to promote uniform deposition into the substrate

contacts, and particularly into contacts having high aspect ratios.

An electrical biasing system is operably coupled to the substrate

during sputter deposition for biasing the substrate such that ions from the sputtering plasma bombard the substrate surface and

effectively etch the surface contemporaneously with the sputter

deposition. The collimator provides near-normal incidence of the

sputter deposition particles for growing a film in high aspect ratio

contacts. By electrically biasing the wafer negatively with respect

to the collimator, the contemporaneous ion bombardment of the

growing layer occurs. The collimator affects the ion bombardment

of the substrate with near-normal incidence of the ions on the

growing substrate layer to produce the benefits and results of the

present invention.

The contemporaneous sputter deposition and normally

incident ion bombardment effectively redistributes the material

which is contained in the rounded deposits or overhang at the

opening of the contact. The redistributed material is transferred

into the contact and onto the flat field of the substrate resulting in

a more uniformly conformal liner film or plug within the contact.

The present invention provides more uniform conformal liner layer

without a substantial overhang at the opening of the contact.

Material layers subsequently deposited onto the substrate and plugs

deposited into the contacts are generally free of voids or keyholes

thus minimizing electrical failures of the interconnects provided by such layers and plugs. This, in turn, increases manufacturing yield

of devices and circuits from a substrate. Furthermore, the present

invention provides significantly improved flat field uniformity

characteristics over conventional non-biased collimation (i.e.,

collimation without substrate bias). For example, the sheet

resistance uniformity and reflectivity is improved with respect to a

non-biased collimation technique.

In the preferred embodiment of the present invention,

a collimator having an aspect ratio between 1 and 2 is utilized. The

combination of such a collimator and a biased substrate provides

uniformly conformal deposition and reduces the overhang to the

extent that would normally only be possible with a collimator

having a higher aspect ratio, such as 2 to 3. With the lower aspect

ratio collimator utilized with the present invention, the deposition

rate is not as significantly reduced as would be the case with a

higher aspect ratio collimator. That is, less of the sputter deposited

material is collected by the collimator and thus more is available for

deposition on the substrate. The present invention is particularly

useful for deposition of liner layers and plugs within sub-micron

(mm), high aspect ratio contacts. The above and other objects and advantages of the

present invention shall be made apparent from the accompanying

drawings and the description thereof.

Brief Description of the Drawings

The accompanying drawings, which are incorporated in

and constitute a part of this specification, illustrate embodiments of

the invention and, together with a general description of the

invention given above, and the detailed description of the

embodiments given below, serve to explain the principles of the

invention.

Fig. 1 is a cross-sectional view of a contact having a

material layer deposited with conventional collimator;

Fig. 2 is a cross-sectional view of a contact

illustrating a material layer deposited in the substrate contact of Fig.

1 ;

Fig. 3 is a diagrammatic cross-sectional view of a

sputter deposition configuration for practicing the present invention;

Fig. 4A is a graph of deposition rate and substrate

current as a function of RF bias voltage in accordance with the

principles of the present invention, while Fig. 4B is a graph of

deposition rate and substrate current as a function of a DC bias voltage further in accordance with the principles of the present

invention;

Fig. 4C is a graph of the ratio of net sputtered flux

obtained using a collimator and substrate bias to the sputtered flux

using a collimator without substrate bias plotted as a function of

DC bias voltage;

Fig. 4D is a bar graph of deposition rate as a function

of substrate bias voltage;

Fig. 5A is a bar graph of the measured resistivity of a

substrate as a function of substrate bias voltage, while Fig. 5B is a

bar graph of sheet resistance uniformity of a substrate coated in

accordance with the principles of the present invention as a

function of substrate bias voltage.

Figs. 6A, 6B and 6C are sheet resistance uniformity

maps for 0 V, 250 V, and 450 V RF substrate bias voltages,

respectively;

Fig. 7 is a bar graph of the measured reflectivity of

substrates coated in accordance with the principles of the present

invention as a function of substrate bias voltage. Figs. 8A, 8B and 8C are photographs of various

substrate contact liners with a conformal film deposited with 450 V

RF substrate bias in accordance with the invention.

Detailed Description of Specific Embodiments

Fig. 3 illustrates an equipment configuration for

practicing the present invention. Specifically, the sputter deposition

system 30 for practicing the present invention includes a

processing housing 32 which defines therein a processing chamber

34 for containing a substrate. Housing 32 is operably coupled to a

vacuum system 36 for creating a vacuum in chamber 34. A

suitable system for practicing the present invention is the Eclipse

Mark II available from Materials Research Corporation of Congers,

New York. Within chamber 34 a substrate 38 is supported on a

substrate support 40 which is preferably operable to clamp

substrate 38 thereto and provides a backside heating gas (not

shown) between the backside of substrate 38 and a surface of

support 40 for efficient heating of the substrate.

Positioned opposite substrate 38 in the chamber 34 is

a target mount 42 which is bonded to a target 44 of material to be

deposited onto the upper surface 45 of substrate 38. Positioned

between the target 44 and substrate 38 is a collimator 46 having a plurality of apertures 48 defined therein. The apertures 48 may be

either hexagonally or circularly shaped and collimator 46 provides

interception of particles sputtered from target 44 to yield sputter

particles which are properly directed to impinge upon substrate

surface 45 and fill or line contacts formed therein to provide a liner

layer or plug. A shield 50 surrounds target 44 and prevents sputter

deposition particles from depositing onto the walls of chamber 34.

The shield 50 is preferably grounded and may be removed and

replaced during periodic maintenance of the system 30.

The target support 42 and target 44 are electrically

connected to a DC power supply for biasing the target 44. As

illustrated in Fig. 3, target 44 is negatively biased with respect to

collimator 46 which is maintained at ground potential. During

deposition, gas is introduced into chamber 34 from a process gas

supply 54. The gas is preferably introduced between the cathode

target 44 and collimator 46. Power is coupled to the process gas

in chamber 34 to ignite a plasma which is illustrated in Fig. 3 as a

plasma cloud 56. Contained within plasma cloud 56 are various

positively charged ions 58 which are attracted to the negative

cathode target 44 and thereby bombard the target. Target particles

are dislodged or sputtered from target 44 as illustrated by reference numeral 60 and appropriate arrows. Some of the sputtered

particles 60 travel in the process chamber 34 toward substrate 38.

Some of these particles 60 have angles of flight which cause them

to collide with the collimator 46 at or exceeding a predetermined

angle of incidence such that they are intercepted. Those target

particles 60 which have angles of incidence relative to the plane of

the collimator below the predetermined angle are not intercepted by

collimator 46 and deposit upon substrate surface 45. The

predetermined angle of incidence below which sputtered particles

are intercepted by the collimator is a function of the diameter and

depth of the collimator apertures 48, as is well known to those

skilled in the art and therefore not further discussed herein.

The apertures 48 of collimator 46 have a defined

height or depth 62 and width or diameter 64. The ratio of the

depth 62 to the width 64 is defined as the aspect ratio of the

collimator 46. As may be appreciated, collimator apertures 48 with

high aspect ratios have deep depths 62 and/or narrow widths 64

and will generally intercept a greater number of sputter particles 60

than will collimator apertures having smaller aspect ratios (i.e., wide

and/or shallow apertures). For example, sputter particle 60b has an

angle of incidence φ from target surface 57 relative to the plane of the collimator which will ensure that it strikes the sidewalls of one

of the apertures 48. However, sputtered particle 60a has a flight

path which is more normal to surface 57 and thus has an angle of

incidence θ which will avoid collision with the sidewalls of

collimator apertures 48 to pass through the collimator and deposit

onto substrate surface 45 and thus contribute to creating a material

layer or plug in a contact located on the substrate surface 45.

Collimators generally are utilized to provide sputter deposition of

particles which have an angle of incidence to surface 45 which is

close to normal incidence. Those sputter particles 60 having flight

paths which are angled away from a 90° or normal flight path will

generally be intercepted by collimator 46. The greater the aspect

ratio of the collimator apertures, the greater the percentage of

sputtered particles which will be intercepted. As discussed

hereinabove, collimators provide assistance in filling contacts by

removing those sputtered particles which tend to deposit as an

overhang close the opening of the contact. However, it is

appreciated the interception of sputter particles by the collimator 46

will reduce the deposition rate of the sputter deposition and will

decrease the efficiency of target utilization because a large number of the sputtered particles deposit onto the collimator 46 rather than

substrate 38.

To fill contacts having very high aspect ratios, a

collimator with a high aspect ratio apertures, such as 2.5 or above,

might be utilized. However, the resulting reduction in the

deposition rate reduces the efficiency of the sputter deposition

process and increases the overall cost thereof. The present

invention provides conformal coating of high aspect ratio contacts

utilizing a collimator 46 having an aspect ratio which is lower than

the aspect ratio normally required with conventional collimator

techniques. The invention thereby effectively increases the

deposition rate over that achieved with a conventional collimator.

In other words, the present invention provides a conformal liner in a

sub-micron, high aspect ratio contact which would normally only be

possible with a collimator having a relatively high aspect ratio.

In accordance with the principles of the present

invention, substrate support 40 and substrate 38 are operably

connected to a biasing source to provide a bias to the substrate 38

during sputter deposition. Referring to Fig. 3, substrate 38 is

coupled to either an AC or pulsed DC source 70 or a DC source 72

for biasing the substrate. Substrate 38 is negatively biased with respect to the

collimator 46 which is typically maintained at ground potential.

Ionized plasma particles of plasma cloud 56, such as particles 59,

are attracted to the negatively biased substrate 38 to bombard

surface 45. For example, while some of the particles 58 are

attracted to the negative cathode target 44, other of the ionized

particles 59 in the plasma 56 are attracted to the negatively biased

substrate 38. Ionized particles 59 are attracted to surface 45 and

bombard the surface and thereby etch the layer of sputter

deposited material thereon.

Furthermore, in accordance with the principles of the

present invention, some of the ionized particles 59 attracted to

substrate 38 will collide with the collimator as illustrated by particle

59a to be intercepted by the collimator and prevented from etching

surface 45. Other ionized particles, for example particle 59b, will

pass through the collimator 46 to etch surface 45. In that way, the

invention provides collimated etching and focuses the etching

particles to have generally normal incidence upon surface 45. The

invention provides more effective etching and redistribution of

sputter deposited material within the contacts than conventional

collimation. One particular advantage of the invention is the

redistribution of the sputter deposited material in the contacts to

eliminate voids formed in the corners at the junctures of the

sidewalls and bottom. Additionally, the contemporaneous sputter

etch provided by the invention redistributes the overhang material

into the contacts to provide a more uniform conformal liner layer.

Reduction of the overhang will also aid in elimination of voids in the

corners. While the present invention is useful with all contacts, it is

particularly useful with sub-micron contacts having high aspect

ratios. By providing a more uniform conformal liner, with little

overhang at the contact opening, subsequent conductive plugs may

be deposited into the contact without creating voids or keyholes

therein. Therefore, the invention provides increased yield of

devices and chips from a substrate and further provides increased

reliability of the devices. In addition, the flat field properties of

substrates yielded by the contemporaneous sputter deposition and

etching of the invention are acceptable for the industry.

Various process runs were made utilizing the present

invention to determine the flat field properties. For the process

runs, an Eclipse Mark II system available from MRC was utilized as

noted above. Substrates were processed with no bias (zero volts), 200 and 400 volt DC bias, and 250 and 450 volt RF bias (at 1 3.56

MHz). A series of 1 500-5000 Λ films were deposited between one

and five wafers to obtain flat field data as discussed hereinbelow.

The wafer-to-wafer flat field properties were measured at the center

of the wafers, and averaged over two to five wafers depending

upon the total number of wafers run at a given bias condition. Film

thicknesses of 2000 A titanium (Ti) were deposited on virgin silicon

(Si) wafers with 10 kλ silicon dioxide (SiO₂) to obtain reflectivity

and sheet resistance data. Film thicknesses of 2000 A Ti were

deposited on virgin Si wafers with native oxide to obtain stress

data. Film thicknesses of 2000-5000 A Ti were deposited on

patterned/active wafers for contact fill information.

The collimator utilized had an aspect ratio of 1 .5, and

it is preferable to utilize a collimator with aπ aspect ratio in the

range of 1 .25-2.0 for the invention. The holes of the collimator

were hexagonal and had a diameter of .625 inch, while the

thickness of the collimator plate was .938 inch. The spacing

maintained between the collimator and the substrate was 1 .500

inches.

The sputter cathode utilized was an ICC-1 2 rotating

magnet with a Ti target. The target to collimator spacing was maintained at 1 .452 inches. The rotating magnet behind the target

to provide uniform sputter deposition was rotated at 1 40 rpm. 1 5

kW of power was delivered to the cathode target, and the substrate

support 40 or backplane was maintained at 300°C with a

backplane pressure of 6-8 Torr for thermal heat exchange purposes.

A flow rate of 25 seem argon (Ar) was utilized and resulted in a 1 .1

mTorr operating pressure maintained within chamber 34.

Process Results

Deposition Rate

Deposition rate was measured as a function of RF and

DC bias. Total backplane current was also measured. DC

backplane to ground current was measured with a multi-meter

connected in series with the DC power supply or as a voltage drop

over a series-connected precision resistor. The RF current

measurements were made with a current transformer, such as a

Current Monitor Model 41 00 available from Pearson of Palo Alto,

California, which had a sensitivity of 0.50 V/A and a ± 3dB

bandwidth of 140 Hz to 35 MHz. The current transformer output

was terminated in 50 ohms at a monitoring oscilloscope.

The deposition rates were calculated from thickness

measurements by using a pen-stripping lift-off process wherein a strip of the sputter deposited layer is removed and the thickness of

the film proximate the strip is measured for calculation of the

deposition rate. The thickness measurements were made with a

profiler, such as the Model P-1 Long Scan Profiler available from

Tencor Instruments of Mountain View, California.

Fig. 4A illustrates graphs of measured wafer-to-ground

current and the deposition rate for various RF bias voltages. As

illustrated by Fig. 4A, for the deposition measurements more bias

values were utilized than for determining the other flat-field

properties. The reference arrows indicate which X-axis in the figure

is associated with the particular curve. Referring to Fig. 4A, the

current increased with RF bias whereas the deposition rate

decreased.

Fig. 4B illustrates a graph of deposition rate and wafer-

to-ground current as a function of the DC bias voltage. Fig. 4B

shows a similar inverse relationship between the current and

deposition rate as that illustrated in Fig. 4A wherein the current

increases with increased DC bias whereas the deposition rate

generally decreases. The increasing bias of the substrate reduces

the effective deposition rate due to the resputtering that occurs at the substrate 38 as increasing numbers of plasma ions 59 are

attracted to the negatively biased substrate.

Net deposition rates were calculated for the measured

DC bias currents. Assuming that the actual neutral and ion fluxes

are spatially uniform, an estimate of the net deposition rate is given

by the following equation:

EQUATION 1 Where φ is the particle fjux, _and subscript! c and w refer to wafer net c w net ^ c ^ w deposition from the cathode, and wafer sputtering, respectively,

which occurs in the present invention. The flux of particles

received by the wafer from the cathode is given by equation 2:

EQUATION 2 The flux of particles sputtered frorrt_j^he wafer is given by equation

EQUATION 3

Where p = target material mass deputy, R = deposition rate, N_A

= Avogadro's number, w = target material atomic weight

(mass/mol), I = ion current through wafer, Y = sputtering yield, e

= process gas ion charge, and A = wafer area. Yield Y for the

argon/titanium system was obtained from the following equation:

EQUATION 4 Where t

atomic

number, and U = binding energy of surface atom in eV (from

Applied Physics A36, 37 ( 1 985)).

Both the theoretical and observed flux ratios Φ_neI / Φ_c

are shown in Fig. 4C. The theoretical curve 80 of Fig. 4C

accurately predicts the measured reduction in deposition rate with

increasing DC bias as a result of resputtering at the substrate 38.

However, at 400 volts DC bias there is an anomalously high

deposition rate which may be due to an uncertainty in the actual

thickness measurement of the deposition.

Referring to Fig. 4D, the deposition rates are plotted in

a bar format as a function of bias voltage. From the measured

deposition rates, there is evidence that the DC bias may be more

effective at resputtering the substrate than RF biasing for a given

bias level.

Sheet Resistance

The sheet resistance was measured at the wafer

centers with a 4D Automatic Four Point Probe Meter, Model 280C

available from Prometrics. Resistivity was derived by multiplying

the sheet resistance measurement by the thickness of the deposited

film, both at the center of the wafer. Resistivity is plotted in a bar

graph format as a function of the bias voltage in Fig. 5A. As

illustrated, the resistivity of the wafer tended to increase with the

increasing bias voltage. The higher resistivity probably results from

increased film defects and degradation of the film grain structure in

the deposited layer as it is contemporaneously etched during

deposition. Additionally, the incorporation of argon into the

titanium is expected during biased deposition which will also act to

increase the resistivity.

Fig. 5B illustrates the sheet resistance uniformity

within a wafer (WiW) as a function of the bias voltage. As is

illustrated, the sheet resistant uniformity generally improves with

increased bias voltage. That is, there is a smaller percentage

variation within the wafer for increased wafer bias.

Figs. 6A, 6B and 6C illustrate the improved sheet

resistance uniformity for increasing RF bias. Fig. 6A illustrates the interwafer sheet resistance uniformity for zero volts bias, whereas

Figs. 6B and 6C illustrate the interwafer sheet resistance uniformity

for 250 volt RF bias and 450 volt RF bias, respectively. As seen,

the substrate of Fig. 6C has a substantially improved sheet

resistance uniformity contour at 450 volt bias.

Reflectivity

Reflectivity measurements were made with a

NanoSpec/AFT Microarea Gauge, available from Nanometrics of

Sunnyvale, California, and are illustrated in a bar-graph format in

Fig. 7. The range in reflectivity was predominantly above a typical

acceptable lower limit of 1 20% for most of the biasing conditions.

Stress

Stress measurements were also made using a Model

F2300 available from Flexus of Sunnyvale, California. The results

of the stress measurements indicate that the residual stress

decreased as RF bias was increased.

Process Run Data

Tables 1 -4 below illustrate the various raw data

measurements from several of the process runs made utilizing the

present invention. Results of the process runs shown in the tables

hereinbelow and from the Figs, discussed hereinabove illustrate that the present invention produces acceptable flat-field performance as

compared to standard, non-colhmated processes.

The present invention further provides improved step

coverage performance and deposition of conformal films and plugs

within high aspect ratio, sub-micron contacts and in fact produces

significant improvements in liner and plug deposition over prior art

apparatus and methods. Figs. 8A, 8B and 8C are photographs of

various contacts of substrates processed in accordance with the

principles of the present invention and illustrating the improved step

coverage and conformal film coverage.

Figs. 8A-8C show a deposition of titanium in sub-0.5

micron contacts in accordance with the principles of the present

invention using a collimator having an aspect ratio of 1 .5: 1 and a

450 volt RF bias on the wafer. Fig. 8A illustrates a contact 90

having an aspect ratio of 3.5: 1 . The deposited film 92 is conformal

and does not taper dramatically to the bottom corners to leave

voids in the corners as resulted with prior art devices and methods

(see Fig. 1 ). Furthermore, overhang 96 at the top of the contact is

significantly reduced. Fig. 8B illustrates a more narrow contact 98

having a higher aspect ratio of 4.5: 1 , while Fig. 8C is an enlarged

portion of the contact of Fig. 8B. As illustrated in Fig. 8B, and 8 PCΪ7IB97/00522

more clearly in 8C, even with a sub-0.5 micron contact having a

high aspect ratio of 4.5: 1 , the film 1 00 is very conformal and does

not drastically taper down to the bottom corner 1 02 or produce

voids in the corner 1 02. As illustrated in Fig. 8C, the film 1 00 is

conformal on the sidewalls 1 04 and bottom 1 06 of the contact 98

and overhang 1 08 at the top of the contact is reduced (see Fig.

8B). Accordingly, the invention provides improved step coverage

and conformality for the deposition in very small, high aspect ratio

contacts. The reduction in overhang provided by the invention

further reduces keyholing when a subsequent layer or plug is

deposited in the lined contact (see Fig. 2) .

TABLE 1

TABLE 2

TABLE 3

TABLE 4

While the present invention has been illustrated by a

description of various embodiments and while these embodiments

have been described in considerable detail, it is not the intention of

the applicants to restrict or in any way limit the scope of the

appended claims to such detail. Additional advantages and

modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the

specific details, representative apparatus and method, and

illustrative example shown and described. Accordingly, departures

may be made from such details without departing from the spirit or

scope of applicant's general inventive concept.

What is claimed is:

Claims

1 . A sputter deposition system including a vacuum

chamber containing a sputtering plasma therein for sputter

depositing a layer of material into substrate contacts having very

small dimensions, the sputter deposition system comprising:

a target of deposition material positioned in the

vacuum chamber and coupled to a target bias source for negatively

biasing the target such that ions from the sputtering plasma

bombard the target and produce material particles to deposit on a

surface of a substrate in the chamber and into the substrate

contacts;

a collimator positioned opposite the target and

configured to intercept sputtered particles of a predetermined

angular incidence to the substrate surface to promote uniform

deposition into the substrate contacts;

an electrical biasing system operably coupled to the

substrate during sputter deposition, the biasing system operable to

bias the substrate such that ions from the sputtering plasma

bombard the substrate surface and effectively etch the surface

generally contemporaneously with the sputter deposition and

redistribute the deposited particles in the contacts to reduce deposition overhang in the contacts and to further promote uniform

deposition into the contacts;

whereby substrate contacts having large aspect ratios

may be uniformly coated with a layer of material and filled with

material with reduced numbers of voids.

2. The sputter deposition system of claim 1 wherein the

collimator is operably coupled to the substrate biasing system and

the target bias source and acts as a common reference potential to

both the target and the biased substrate.

3. The sputter deposition system of claim 1 wherein the

substrate biasing system includes one of an AC source and a pulsed

DC source for biasing the substrate during sputter deposition.

4. The sputter deposition system of claim 3 wherein the

biasing source operates under 200 MHz.

5. The sputter deposition system of claim 3 wherein the

biasing source operates under 20 MHz.

6. The sputter deposition system of claim 1 wherein the

substrate biasing system includes a DC source for biasing the

substrate with DC voltage during sputter deposition.

7. The sputter deposition system of claim 1 wherein the

substrate biasing system is operable to bias the substrate in the

range of 1 0 to 5000 Volts.

8. A sputter deposition system including a vacuum

chamber containing a sputtering plasma therein for sputter

depositing a layer of material into substrate contacts having very

small dimensions, the sputter deposition system comprising:

a target of deposition material positioned in the

vacuum chamber and coupled to a target bias source for negatively

biasing the target such that ions from the sputtering plasma

bombard the target and produce material particles to deposit on a

surface of a substrate in the chamber and into the substrate

contacts;

a collimator positioned opposite the target and

configured to intercept sputtered particles of a predetermined

angular incidence to the substrate surface to promote uniform

deposition into the substrate contacts.

an electrical biasing system operably coupled to the

substrate during sputter deposition, the biasing system operable to

negatively bias the substrate such that ions from the sputtering

plasma bombard the substrate surface and effectively etch the

surface generally contemporaneously with the sputter deposition

and redistribute the deposited particles in the contacts to reduce deposition overhang in the contacts and to promote uniform

deposition into the contacts;

whereby substrate contacts having large aspect ratios

may be uniformly coated with a layer of material and filled with

material with reduced numbers of voids.

9. A sputter deposition system for sputter depositing a

layer of material into substrate contacts having very small

dimensions, the sputter deposition system comprising:

a vacuum chamber;

a gas supply for providing gas into the chamber;

an excitation system for exciting the gas into a

sputtering plasma containing ions;

a support for supporting, inside the chamber, a

substrate with contacts having small dimensions;

a target support for supporting a target of deposition

material in the chamber opposite the substrate support, the target

support operable to bias a target thereon such that ions from the

sputtering plasma bombard the target and produce material particles

to deposit on a surface of the substrate and into the contacts;

a collimator positioned between the target support and

the substrate support and configured to intercept sputtered

particles of a predetermined angular incidence to the substrate

surface to promote uniform deposition into and to promote voidless

filling of the substrate contacts; an electrical biasing system operably coupled to the

substrate support during sputter deposition to bias the substrate

thereon such that ions from the sputtering plasma bombard the

substrate surface and effectively etch the surface

contemporaneously with the sputter deposition and redistribute the

deposited particles in the contacts to reduce deposition overhang in

the contacts and to further promote uniform deposition into the

contacts;

whereby substrates with contacts having very small

aspect ratios may be uniformly coated with a layer of material and

filled with material with reduced numbers of voids.

10. The sputter deposition system of claim 9 wherein the

collimator is operably coupled to the substrate biasing system and

the biased target support and acts a common reference potential to

both the target and the biased substrate.

1 1 . The sputter deposition system of claim 9 wherein the

target support is operable to bias the target in the range of

approximately 1 0 to 1 ,000 volts.

1 2. The sputter deposition system of claim 9 wherein the

substrate biasing system is operable to bias the substrate in the

range of approximately 1 0 to 5,000 Volts.

1 3. The sputter deposition system of claim 9 wherein the

substrate biasing system includes one of an AC source and a pulsed

DC source for biasing the substrate during sputter deposition.

1 4. The sputter deposition system of claim 1 3 wherein the

biasing source operates between approximately DC and 20 MHz.

1 5. The sputter deposition system of claim 1 3 wherein the

AC or pulsed DC source operates between approximately 1 00 kHz

and 20 MHz.

1 6. The sputter deposition system of claim 9 wherein the

substrate biasing system includes a DC source for biasing the

substrate with DC voltage during sputter deposition.

1 7. A method of sputter depositing a layer of material into

substrate contacts having very small dimensions comprising:

positioning a substrate in a vacuum chamber;

exciting a sputtering plasma containing ions within the

chamber;

positioning a target of deposition material in the

chamber opposite the substrate and biasing the target such that

ions from the sputtering plasma bombard the target to produce the

deposition of sputtered material particles onto a surface of the

substrate and into contacts formed in the substrate surface;

intercepting sputtered particles of a predetermined

angular incidence to the substrate surface to promote uniform

deposition into and promote voidless filling of the substrate

contacts;

biasing the substrate such that ions from the

sputtering plasma bombard the substrate surface and effectively

etch the surface generally contemporaneously with the sputter

deposition and redistribute the deposited particles in the contacts to

reduce deposition overhang in the contacts and to further promote

uniform deposition into the contacts; whereby substrates with contacts having large aspect

ratios may be uniformly coated with a layer of material and filled

with material with reduced numbers of voids.

1 8. The method of claim 1 7 wherein the intercepting step

includes positioning a collimator between the target and substrate

to intercept sputtered particles, the method further comprising

electrically coupling the substrate and the target to the collimator

such that the collimator acts as a common reference potential to

both the target and the biased substrate.

1 9. The method of claim 1 7 further comprising negatively

biasing the substrate to etch the substrate surface with positively

biased ions from the plasma.

20. The method of claim 1 7 further comprising biasing the

target in the range of approximately 1 0 to 1 ,000 Volts.

21 . The method of claim 1 7 further comprising biasing the

substrate in the range of approximately 10 to 5,000 Volts.

22. The method of claim 1 7 further comprising biasing the

substrate with AC voltage during sputter deposition.

23. The method of claim 22 further comprising biasing the

substrate between approximately DC and 20 MHz.

24. The method of claim 22 further comprising biasing the

substrate between approximately 100 kHz and 20 MHz.

25. The method of claim 1 7 further comprising biasing the

substrate with DC voltage during sputter deposition.

26. A method of sputter depositing a layer of material into

substrate contacts having very small dimensions comprising:

positioning a target of material inside of a sputter

deposition chamber;

positioning a substrate in the chamber opposite the

target with a substrate surface having contacts formed therein

facing the target;

bombarding the target with particles from an excited

gas plasma to sputter deposit a material layer onto the

substrate surface and into the contacts;

bombarding the substrate surface with particles to

etch the substrate surface and material layer generally

contemporaneously with the sputter deposition of the layer to

redistribute the deposited material in the contacts to reduce

deposition overhang in the contacts and to promote uniform

deposition into the contacts;

whereby substrates with contacts having large aspect

ratios may be uniformly coated with a layer of material and filled

with material with a reduced number of voids.

27. The method of claim 26 further comprising

intercepting sputtered particles of a predetermined angular

incidence to the substrate surface to further promote uniform

deposition into the substrate contacts.

28. The method of claim 26 wherein the intercepting step

includes positioning a collimator between the target and substrate

to intercept sputtered particles.

29. The method of claim 26 further comprising electrically

coupling the substrate and the target to the collimator such that the

collimator acts as a common reference potential to both the target

and the substrate.

30. The method of claim 26 further comprising biasing the

substrate to etch the substrate surface with positively biased ions

from the plasma.