Method of making a barrier layer for via or contact opening of integrated circuit structure

Described is a barrier layer in an integrated circuit structure which is formed in a via or contact opening over an underlying material in which diffusion of the underlying material (or filler material deposited over the barrier layer) through the barrier layer is inhibited without unduly increasing the thickness and resistivity of the barrier layer. This is accomplished by substituting an amorphous material for the crystalline titanium nitride to thereby eliminate the present of grain boundaries which are believed to provide the diffusion path through the titanium nitride material. In a preferred embodiment, the amorphous barrier layer comprises an amorphous ternary Ti--Si--N material formed using a source of titanium, a source of silicon, and a source of nitrogen. None of the source materials should contain oxygen to avoid formation of undesirable oxides which would increase the resistivity of the barrier layer. In a particularly preferred embodiment, an organic source of titanium is used, and either or both of the silicon and nitrogen sources are capable of reacting with the organic portion of the organic titanium reactant to form gaseous byproducts which can then be removed from the deposition chamber to inhibit the formation of carbon deposits in the chamber or on the integrated circuit structure.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to materials used in vias or contact openings in 
integrated circuit structures. More particularly, this invention relates 
to improved barrier materials used in vias or contact openings to prevent 
diffusion between the underlying material and the material used to fill 
the vias or contact openings. 
2. Description of the Related Art 
In the filling of vias between metal layers, or the filling of contact 
openings which connect portions of an underlying active device with metal 
interconnects such as a wiring level, titanium nitride has been used in 
the past to provide a barrier layer between the underlying material and 
the material used to fill the via or contact opening to prevent or inhibit 
diffusion between the underlying material and the filler material. Such a 
titanium nitride barrier layer might, for example, be about 200 Angstroms 
in wall thickness (for a 2000 Angstrom diameter via or contact opening), 
or as much as 400 Angstroms thick (for a 5000 Angstrom diameter opening). 
However, particularly when aluminum or aluminum-copper alloys are used as 
via/contact opening filler materials (and/or as the underlying material in 
the case of vias), there is a tendency for the aluminum and/or copper to 
diffuse through the titanium nitride along the grain boundaries if the 
titanium nitride layer is not thick enough. 
The thickness of the titanium nitride barrier layer is usually controlled 
because the titanium nitride, while electrically conductive, has a higher 
electrical resistance than the metal via/contact opening filler material. 
Also if the deposited titanium nitride is too thick, there is an overhang 
problem wherein too much of the titanium nitride deposits not only in the 
via/contact opening, but also on the exposed surface of the insulation 
layer adjacent the via or contact opening. The deposition of too thick of 
a titanium nitride barrier can also result in void formation in the via or 
contact opening. This is shown in prior art FIG. 1, wherein an integrated 
circuit structure 2 is shown with an insulation layer 10 formed thereon 
with a via 12 etched through insulation layer 10 to underlying integrated 
circuit structure 2. A barrier layer 20 of titanium nitride is shown 
formed on the surfaces of via 12, as well as on the exposed surface of 
integrated circuit structure 2 at the bottom of via 12. As shown in FIG. 
1, however, the titanium nitride simultaneously deposits on opposite sides 
of the via/contact opening sidewall adjacent the top of the via/contact 
opening, causing a necking-in, as shown at 22 in prior art FIG. 1, which 
could eventually result in a closing of the via/contact opening at the 
top, leaving an unfilled void therein. 
Thus, while the obvious answer to the problem of undesired diffusion of 
metals through the titanium nitride barrier layer might appear to be to 
increase the thickness of the deposited barrier layer of titanium nitride, 
such an increase in the titanium nitride thickness is also fraught with 
problems. 
It would, therefore, be desirable to provide a barrier layer for a via or 
contact opening which will prevent the difflusion of metal therethrough 
without the need to unduly increase the barrier layer thickness so that 
the electrical resistance of the barrier layer is not increased to 
unacceptable levels, and the other above discussed problems associated 
with increases in the thickness of the titanium nitride barrier layer may 
also be avoided. 
SUMMARY OF THE INVENTION 
In accordance with the invention, in an integrated circuit structure, a 
barrier layer is formed in a via or contact opening over an underlying 
material in which diffusion of the underlying material (or filler material 
deposited over the barrier layer) through the barrier layer is inhibited 
without unduly increasing the thickness of the barrier layer. This is 
accomplished by substituting an amorphous material for the crystalline 
titanium nitride to thereby eliminate the present of grain boundaries 
which are believed to provide the diffusion path through the titanium 
nitride material. In a preferred embodiment, the amorphous barrier layer 
comprises an amorphous ternary Ti--Si--N material formed using a source of 
titanium, a source of silicon, and a source of nitrogen. None of the 
source materials should contain oxygen to avoid formation of undesirable 
oxides which would increase the resistivity of the barrier layer. In a 
particularly preferred embodiment, an organic source of titanium is used 
and either or both of the silicon and nitrogen sources are further capable 
of reacting with the organic portion of the organic titanium reactant to 
form gaseous byproducts which can then be removed from the deposition 
chamber to inhibit the formation of carbon deposits in the chamber or on 
the integrated circuit structure.

DETAILED DESCRIPTION OF THE INVENTION 
Referring now to FIG. 2, an integrated circuit structure is generally 
illustrated at 2 which may or may not have already formed a first metal 
wiring layer thereon. Over integrated circuit structure 2 is formed an 
insulation layer 10 having formed therein an opening 12 extending from the 
upper surface of insulation layer 10 through insulation layer 10 down to 
underlying integrated circuit structure 2. When opening 12 extends down to 
a contact on an active device in integrated circuit structure 2, e.g., to 
a gate contact of an MOS device, opening 12 is usually referred to as a 
contact opening. When opening 12 extends through insulation layer 10 to an 
underlying metal interconnect, i.e., a previously formed wiring level, 
opening 12 may be referred to as a via. Since this invention may be used 
in the filling of either vias or contact openings, these terms may be used 
interchangeably herein, and the use of either term should be deemed to 
include reference to either type of opening, unless otherwise specified. 
In accordance with the invention, a thin layer of a titanium silicon 
nitride barrier layer 30 is then formed over the surface of opening 12 as 
well as the exposed surface 4 of underlying integrated circuit structure 2 
to prevent interaction between the underlying integrated circuit structure 
and the filler material which will be deposited over the barrier layer to 
fill opening 12, while still maintaining a satisfactory resistivity level 
for the barrier layer. 
By use of the term "thin" with respect to the thickness of the barrier 
layer is a barrier layer having a thickness not exceeding about 150 
Angstroms. By use of the term "satisfactory resistivity level" is meant a 
resistivity level not exceeding 1000 .OMEGA./square. 
The titanium silicon nitride barrier layer of the invention is formed by a 
CVD deposition in a CVD chamber using gaseous sources of titanium, 
silicon, and nitrogen which are respectively flowed into a CVD chamber is 
which a semiconductor substrate, having integrated circuit structure 2 
formed thereon with insulation layer 10 and opening 12 therein, formed 
over integrated circuit structure 2. 
a. The Reactants 
The gaseous source of titanium may comprise an inorganic source of titanium 
such as, for example, titanium tetrachloride (TiCl.sub.4). Preferably, 
however, to provide a chlorine-free barrier layer, an organic source of 
titanium is used such as, for example, TDEAT (tetrakis(diethylamido) 
titanium) having the formula TiN(CH.sub.3 CH.sub.2).sub.2 !.sub.4, or 
TDMAT (tetrakis(dimethylamido) titanium) having the formula 
TiN(CH.sub.3).sub.2 !.sub.4. The use of a gaseous organic source of 
titanium is preferred, instead of a gaseous inorganic source of titanium, 
to permit lower temperature formation of the barrier layer which will 
provide a chlorine-free barrier layer and good step coverage while 
preserving a low thermal budget. 
The gaseous nitrogen source may comprise any gaseous nitrogen source 
capable of proving a source of nitrogen, and also capable of reacting with 
organic residues from decomposition of the gaseous titanium source, when 
the gaseous titanium source is an organic material. While the nitrogen 
source could be organic, preferably an inorganic source of nitrogen such 
as ammonia is used as the gaseous source of nitrogen because of the 
liberation of hydrogen therefrom which will react with the organic portion 
of the gaseous organic source of titanium to form a gas or gases which may 
be removed by evacuation from the CVD chamber during the deposition. It 
should be noted, however, that the gaseous source of nitrogen should not 
include any materials which may liberate oxygen or in any way form oxide 
products or byproducts which could co-deposit with the titanium silicon 
nitride barrier layer and thereby increase the resistivity of the barrier 
layer. 
The gaseous source of silicon must be capable of proving a source of 
silicon, and also should be capable of reacting with organic residues from 
decomposition of the gaseous titanium source, when the gaseous titanium 
source is an organic material. While the silicon source could be organic, 
preferably an inorganic source of silicon such as silane (SiH.sub.4), or a 
substituted silane, e.g., SiH.sub.n X.sub.4-n, where X is a halogen and n 
is an integer from 0-3, is used as the gaseous source of silane. This is 
because of the liberation of hydrogen (and/or halogen) by evacuation from 
the CVD chamber during the deposition. It should also be noted, however, 
that like the gaseous source of nitrogen, the gaseous source of silicon 
should not include any materials which may liberate oxygen or in any way 
form oxide products or byproducts which could co-deposit with the titanium 
silicon nitride barrier layer and thereby increase the resistivity of the 
barrier layer. Other gaseous sources of silicon (in addition to silane or 
a substituted silane) which may be used in the formation of the titanium 
silicon nitride barrier layer of the invention include, for example, 
Si.sub.3 H.sub.9 N. 
b. Proportions and Flow Rates of the Reactants 
The reactant gases are flowed into a CVD chamber in which is already 
mounted on a susceptor the semiconductor substrate, including the 
insulation layer having the contact opening or via into which the barrier 
layer of the invention is to be deposited. The ratio of the flow rates of 
the gaseous silicon source to the gaseous nitrogen source will range from 
about 1 part by volume of the silicon source per 100 parts by volume of 
the nitrogen source (1:100 silicon to nitrogen) to about 2 parts by volume 
of the gaseous silicon source per part by volume of the gaseous nitrogen 
source (2:1 silicon to nitrogen). Preferably the ratio of the gaseous 
silicon source to the gaseous nitrogen source will range from about 1:10 
to about 1:1 in parts by volume. 
The minimum ratio of the gaseous titanium source to the other gaseous 
reactants will be at least about 1 part by volume of the gaseous titanium 
source per 20 parts by volume of the larger amount of either the gaseous 
silicon source or the gaseous nitrogen source (1:20). That is, the ratio 
of the gaseous source of titanium is measured against the gaseous nitrogen 
source, if the amount of the gaseous nitrogen source is larger than the 
amount of the gaseous silicon source, but is measured against the gaseous 
silicon source when the gaseous silicon source amount exceeds the amount 
of the gaseous nitrogen source used. 
The maximum ratio of the gaseous titanium source to the larger of either 
the gaseous nitrogen source or the gaseous silicon source is about 1 part 
by volume of the gaseous titanium source per 1 part per volume of the 
larger amount of either the gaseous silicon source or the gaseous nitrogen 
source (1:1). Preferably the ratio of the gaseous titanium source to the 
larger of the gaseous silicon source or the gaseous nitrogen source will 
range from about 1:10 to about 1:2 in parts by volume. 
The absolute amounts of the individual flow rates of the respective gaseous 
reactant sources, as well as the total gas flow, will depend upon the 
volume of the CVD chamber, with higher flow rates needed for larger 
chambers. For example, for a 35 liter CVD chamber, the flow rate of the 
respective gaseous reactants can be about 1,300 standard cubic centimeters 
per minute (sccm) of gaseous TDEAT, about 13,000 sccm of ammonia, and 
about 1,300 sccm of silane. If desired, a carrier gas may also be 
optionally added to the reactant gases to increase the total gas flow 
through the reactor. 
c. The Reaction Temperature 
The temperature of the semiconductor substrate during the deposition 
reaction should preferably be maintained between about 100.degree. C. and 
about 500.degree. C., and more preferably at a temperature between about 
250.degree. C. and about 400.degree. C. Typically the temperature is 
maintained at about 350.degree. C. Higher temperatures are preferred 
within these temperature ranges for purposes of obtaining lower 
resistivity, while lower temperatures within these temperature ranges are 
preferred from the standpoint of maintaining maximum step coverage of the 
deposited barrier layer. 
d. Use of a Plasma 
The use of a plasma during the CVD formation of the titanium silicon 
nitride barrier layer of the invention is optional, but may be 
particularly desirable when using lower deposition temperatures to improve 
the resistivity and to lower the thermal budget, for example, lower 
deposition temperatures ranging from about 100.degree. C. to about 
350.degree. C. At higher deposition temperatures, a plasma may not be 
needed, but usually the use of a plasma will enhance the overall quality 
of the deposited film, regardless of the deposition temperature. The power 
level of such a plasma may range (expressed as an amount equivalent to the 
power used for a six inch diameter silicon wafer in a 35 liter deposition 
chamber) from about 100 watts to about 1000 watts. 
e. The Reaction Pressure 
The pressure in the CVD reactor may be maintained within a range of from 
about 100 milliTorr to about 100 Torr during the deposition. However, if 
the CVD deposition is carried out in the presence of a plasma, i.e., a 
plasma enhanced CVD (PECVD) deposition, the pressure is preferably 
maintained higher than 100 milliTorr, i.e., at least about 1 Torr, and 
typically about 30 Torr. When the gaseous source of titanium is an organic 
source, e.g., TDMAT or TDEAT, the pressure should be at least about 1 
Torr, regardless of whether or not a plasma is used. 
f. The Deposition Time and Thickness of the TiSiN/Barrier Layer 
The time of the deposition reaction will depend upon the desired thickness 
of the deposited barrier layer. This, in turn, usually depends upon the 
desired amount or thickness of the TiSiN barrier layer needed to prevent 
diffusion of the aluminum and/or copper metal through the barrier layer, 
since this is the principal reason for use of the barrier layer in the 
via. As previously discussed, the thickness of the TiSiN barrier layer 
should not exceed about 150 Angstroms. Usually, the minimum amount of 
TiSiN barrier layer needed will be about half of the thickness needed in 
conventional TiN barrier layers to provide the same degree of diffusion 
protection. However, the minimum thickness of the TiSiN barrier layer 
should be at least about 40 Angstroms, and preferably at least about 75 
Angstroms. If the diameter of the via or contact opening will permit it, 
the minimum thickness will be slightly higher. For example, for a 2000 
Angstrom diameter via, the thickness of the barrier layer of the invention 
could typically be about 100 Angstroms to provide the desired barrier 
against diffusion of metals such as aluminum or copper through the barrier 
layer of the invention. 
g. Example 
To further illustrate the practice of the invention, two silicon 
substrates, each having the same integrated circuit structure formed 
thereon and each having an insulation layer formed thereon with a 3000 
Angstrom diameter contact opening extending therethrough to an underlying 
silicon layer, can be processed as follows: One of the substrates was 
processed in accordance with the invention to form the TiSiN barrier layer 
of the invention, while the other substrate was processed in accordance 
with the prior art to form the prior art TiN barrier layer. 
In accordance with the invention, the first substrate can be mounted in a 
35 liter CVD chamber on a susceptor and heated to a temperature of about 
350.degree. C. Into the chamber will be flowed about 1,300 sccm of TDEAT, 
about 13,000 sccm of ammonia, and about 1,300 sccm of silane and a plasma 
will be ignited in the chamber at a power level of about 400 watts, while 
the pressure is maintained in the chamber at about 25 Torr. After 25 
seconds, the flow of gases would be shut off and the plasma extinguished. 
A layer of CVD copper can then be conventionally deposited over the 
structure, to fill the barrier layer-coated contact. When the structure is 
then sectioned and examined under SEM, the barrier layer formed in 
accordance with the invention will be found to have a thickness of about 
100 Angstroms and the respective silicon and CVD copper layers below and 
over the barrier layer will be found to not have diffused through the 
barrier layer of the invention. A resistivity measurement of the resulting 
TiSiN film will show a resistivity of as low as about 450 .OMEGA./square, 
a satisfactory resistivity. 
In contrast, a second substrate, representing the prior art, can be 
processed in the same 35 liter CVD chamber at the same temperature of 
about 350.degree. C. and at the same pressure. Into the CVD chamber would 
be flowed about 1,300 sccm of TDEAT and about 13,000 sccm of ammonia (but 
without any silane). Again a plasma can be ignited in the chamber at a 
power level of about 400 watts. After 25 seconds, the flow of gases would 
be shut off and the plasma extinguished. A layer of CVD copper can then be 
conventionally deposited over the structure, to fill the barrier 
layer-coated contact. When the structure is then sectioned and examined 
under SEM, the TiN barrier layer formed in accordance with the prior art 
will be found to have a thickness of about 100 Angstroms and portions of 
the respective Si and CVD copper layers below and over the prior art TiN 
barrier layer will be found to have diffused through the prior art TiN 
barrier layer. 
Thus, the invention provides an improved barrier layer for a via or contact 
opening formed in an insulating layer which will prevent diffusion of 
either underlying metal such as aluminum and/or copper, or filler metal in 
the via from diffusing through the barrier layer without the need for 
using an unduly thick barrier layer which would adversely impact the 
resistivity of the barrier layer, as well as create other problems 
associated with thick barrier layers.