A method of metallization using a tungsten plug is described. A contact hole is opened to the semiconductor substrate through an insulating layer covering semiconductor structures in and on the semiconductor substrate. A glue layer is deposited conformally over the surface of the insulating layer and within the contact opening. A tungsten plug is formed within the contact opening. The glue layer is removed except for portions of the glue layer underneath the tungsten plug and on the lower sides of the tungsten plug. Ditches are left on the upper sides of the tungsten plug where the glue layer has been removed. The ditches around the tungsten plug are filled with a dielectric material. A second metallization is deposited and patterned. The patterned second metallization does not extend over one side portion of the tungsten plug; that is, there is no dog-bone formation. There is no junction damage through the side portion of the tungsten plug not covered by the second metallization because the dielectric material filling the ditches protects the glue layer from being etched away. In a second embodiment of the invention, after the contact hole is opened, the insulating layer is reflowed forming an overhang around the contact hole. A glue layer is deposited conformally over the surface of the insulating layer and within the contact opening. A tungsten plug is formed within the contact opening.

BACKGROUND OF THE INVENTION 
(1) Field of the Invention 
The invention relates to a method of metallization in the fabrication of 
integrated circuits, and more particularly, to a method of tungsten 
metallization resulting in improved step coverage and prevention of 
junction damage in the manufacture of integrated circuits. 
(2) Description of the Prior Art 
Conventional aluminum metallization suffers from bad step coverage, 
electromigration, and dog-bone problems. Tungsten-plug metallization can 
improve step coverage and alleviate electromigration concern since 
tungsten is a kind of refractory metal with high resistance to 
electromigration. However, overetching of the first metal layer results in 
considerable junction damage if the metal layer is designed without the 
dog-bone overlying the tungsten plug. FIG. 1A illustrates the dog-bone 1. 
Contact hole 2 is surrounded by the metal 3 in the shape of a dog-bone. 
Fig. 1B illustrates the contact hole 2 and metal 3 without the dog bone. 
The misalignment problem is overcome by using the dog-bone. 
Referring now to FIG. 2, there is illustrated a conventional tungsten plug 
process of the prior art. There is shown semiconductor substrate 10 in 
which have been formed Field OXide (FOX) region 12 and source/drain 
regions 14. Gate electrode 18 has been formed overlying gate silicon oxide 
layer 16. A contact hole 22 has been opened through insulating layer 20 to 
source/drain region 14. Glue layer 24 has been deposited over the surface 
of the substrate and within the contact hole. Tungsten plug 26 has been 
formed within the contact hole. 
Referring now to FIG. 3, second metallization 34 has been deposited. After 
metal etching, an overetch is required to overcome the nonuniformity 
problem and to remove residue that will cause stringers or shorts at some 
valley regions. The anisotropic overetch of metal layer 34 causes junction 
failure 36. A dog-bone shape 38 (shown in top view in FIG. 1A) would have 
prevented this spiking problem which causes junction failure. However, 
without the dog-bone, the metal line spacing can be designed to the 
minimum to shrink the chip size. It is desirable to avoid the spiking 
problem without using a dog-bone. 
U.S. Pat. No. 5,216,282 to Cote et al shows the formation of a contact stud 
using a sidewall structure for alignment. They partially remove one 
sidewall layer and then replace it with a metal stud material. 
SUMMARY OF THE INVENTION 
A principal object of the present invention is to provide an effective and 
very manufacturable method of metallization with improved step coverage 
and reduced electromigration problems in the fabrication of an integrated 
circuit. 
Another object of the invention is to form a tungsten plug which does not 
require a dog-bone structure. 
Yet another object of the invention is to provide a tungsten plug process 
which protects the contact area from junction failure. 
A further object is to prevent stress in the contact area and to prevent 
junction failure caused by metal overetch. 
In accordance with the objects of this invention a new method of 
metallization using a tungsten plug is achieved. Semiconductor structures 
are formed in and on a semiconductor substrate. An insulating layer covers 
the semiconductor structures and a contact hole has been opened through 
the insulating layer to the semiconductor substrate. A glue layer is 
deposited conformally over the surface of the insulating layer and within 
the contact opening. A tungsten plug is formed within the contact opening. 
The glue layer is removed except for portions of the glue layer underneath 
the tungsten plug and on the lower sides of the tungsten plug. Ditches are 
left on the upper sides of the tungsten plug where the glue layer has been 
removed. The ditches around the tungsten plug are filled with a dielectric 
material. A second metallization is deposited over the insulating layer 
and the tungsten plug. The second metallization is patterned. The 
patterned second metallization does not extend over one side portion of 
the tungsten plug; that is, there is no dog-bone formation. There is no 
junction damage through the side portion of the tungsten plug not covered 
by the second metallization because the dielectric material filling the 
ditches protects the glue layer from being etched away. 
A second method of forming tungsten plug metallization without dog-bone and 
without junction damage in the fabrication of integrated circuits is 
achieved. Semiconductor structures are formed in and on a semiconductor 
substrate. An insulating layer covers the semiconductor structures and a 
contact hole has been opened through the insulating layer to the 
semiconductor substrate. The insulating layer is reflowed forming an 
overhang around the contact hole. A glue layer is deposited conformally 
over the surface of the insulating layer and within the contact opening. A 
tungsten plug is formed within the contact opening wherein a keyhole void 
is formed within the tungsten plug. A second metallization is deposited 
over the insulating layer and the tungsten plug. The second metallization 
is patterned. The patterned second metallization does not extend over one 
side portion of the tungsten plug; that is, there is no dog-bone 
formation. There is no junction damage through the side portion of the 
tungsten plug not covered by the second metallization because the overhang 
of the insulating material protects the glue layer from being etched away.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A first preferred embodiment of the present invention will be described 
with reference to FIGS. 4 through 7. Referring now more particularly to 
FIG. 4, there is illustrated a portion of a partially completed integrated 
circuit. There is shown a semiconductor substrate 10, preferably composed 
of monocrystalline silicon. Field OXide (FOX) region 12 is formed in and 
on the semiconductor substrate. Source/drain regions 14 are formed as is 
understood in the art either before or after formation of the gate 
electrode 18 overlying gate silicon oxide layer 16. 
An insulating layer 20, composed of borophosphosilicate glass (BPSG), 
borosilicate glass (BSG), or phosphosilicate glass (PSG) is deposited over 
the surface of the semiconductor structures to a thickness of between 
about 3000 to 20,000 Angstroms. A contact hole 22 is opened through the 
insulating layer to the source/drain region 14 within the semiconductor 
substrate. A glue layer 24 is deposited conformally over the surface of 
the insulating layer 20 and within the contact hole 22. The glue layer 
preferably is composed of titanium nitride, but could be other materials 
such as titanium tungsten. This glue layer 24 is deposited by physical 
vapor deposition (PVD) or chemical vapor deposition (CVD) to a thickness 
of between about 300 to 2000 Angstroms. 
Tungsten plug 26 is formed by CVD with WF6, H2, or SiH4 as precursors with 
SF6 and He on the like to fill contact hole 22. Referring now to FIG. 5, 
the glue layer 24 is partially removed by either a dry or wet etch, such 
as dipping in a solution of ammonium hydroxide (NH4OH), hydrogen peroxide 
(H2O2), and water (H2O) for between about 3 to 10 minutes. The portions of 
the glue layer underneath the tungsten plug and on the lower sides of the 
tungsten plug are not removed. The etch selectivity of titanium nitride to 
tungsten is greater than 30 to 1, so that the tungsten is not 
significantly etched during partial removal of the glue layer. (The 
selectivity of titanium tungsten to tungsten is less than 3 to 1, which is 
why titanium nitride is preferred.) Ditches 27 are left on the upper sides 
of the tungsten plug. 
Referring now to FIG. 6, a dielectric material 28, such as silicon dioxide, 
silicon nitride, or silicon oxynitride (SiNxOy) is deposited by chemical 
vapor deposition (CVD) over the surface of the substrate and within the 
ditches 27. The dielectric is etched back to fill the ditches. This 
dielectric will protect the lower glue layer 24 from subsequent etching. 
Referring to FIG. 7, the second metallization 34, such as an aluminum 
alloy, is deposited and patterned. No dog-bone is needed; that is, the 
metal 34 does not need to extend over one side of the tungsten plug 26. 
The dielectric 28 protects the underlying glue layer 24 from being etched 
during the etching of the metal layer 34, thus preventing spiking and 
junction failure such as occurs in FIG. 3 of the prior art. The dog-bone 
is not needed for alignment. Even if there is misalignment without the 
dog-bone, the contact structure of the invention keeps its integrity 
without the spiking problem after metal etchback. 
A second preferred embodiment of the present invention will be described in 
reference to FIGS. 8 through 11. Referring now to FIG. 8, there is shown 
the same semiconductor substrate as described for FIG. 4 after the step of 
opening contact hole 22. After contact hole 22 has been opened, the 
insulator layer 20 is reflowed. This is done in a conventional furnace at 
a temperature of between about 850.degree. to 950.degree. C. for between 
about 10 to 30 minutes in a nitrogen or nitrogen and oxygen ambient. 
Alternatively, the reflow could be accomplished by rapid thermal annealing 
at a temperature of between about 950.degree. to 1050.degree. C. for 
between about 10 to 60 seconds. 
FIG. 9 illustrates the overhang 25 over the contact hole 22 that is formed 
as a result of the reflow. This overhang will prevent junction damage. 
Referring now to FIG. 10, glue layer 24 is deposited conformally over the 
surface of the insulating layer 20 and within the contact hole 22. The 
glue layer preferably is composed of titanium nitride, but could also be 
titanium tungsten as in the first embodiment. This glue layer 24 is 
deposited by PVD or CVD to a thickness of between about 300 to 2000 
Angstroms. 
Tungsten plug 26 is formed by CVD with WF6, H2, or SiH4 as precursors and 
etchback with SF6 and He or the like to fill contact hole 22. A keyhole 
void 30 is formed within the tungsten plug. The presence of the keyhole 
can release stress within the tungsten plug. The conformity of the 
tungsten will result in the overhang within the contact hole resulting in 
void 30. 
Referring now to FIG. 11, the second metallization 34, such as an aluminum 
alloy, is deposited and patterned. No dog-bone is needed; that is, the 
metal 34 does not need to extend over one side of the tungsten plug 26. 
The overhang 25 of the insulating layer 20 protects the underlying glue 
layer 24 from being etched during the etching of the metal layer 34, thus 
preventing spiking and junction failure such as occurs in FIG. 3 of the 
prior art. 
While the invention has been particularly shown and described with 
reference to the preferred embodiments thereof, it will be understood by 
those skilled in the art that various changes in form and details may be 
made without departing from the spirit and scope of the invention.