Active solid-state devices (e.g. – transistors – solid-state diode – Combined with electrical contact or lead – Of specified material other than unalloyed aluminum
Reexamination Certificate
1998-04-21
2001-11-20
Crane, Sara (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Combined with electrical contact or lead
Of specified material other than unalloyed aluminum
C250S297000, C250S297000, C250S382000, C250S383000, C250S384000
Reexamination Certificate
active
06320261
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a contact interface within a contact opening for a shallow junction device, which contact interface is in electrical communication with an active surface of a semiconductor substrate, and methods of forming the same. More particularly, the present invention relates to altering an Ionized Metal Plasma (“IMP”) process to form a contact interface having a substantially continuous profile along sides of a depression formed in the active surface of the semiconductor substrate, wherein the depression is formed by an etching process to form a contact opening through a dielectric layer.
2. State of the Art
In the processing of integrated circuits, electrical contact must be made to isolated active-device regions formed within a semiconductor substrate, such a silicon wafer. Such active-device regions may include p-type and n-type source and drain regions used in the production of NMOS, PMOS, and CMOS structures for production of DRAM chips and the like. The active-device regions are connected by conductive paths or lines which are fabricated above an insulative or dielectric material covering a surface of the semiconductor substrate. To provide electrical connection between a conductive path and active-device regions, openings in the insulative material are generally provided to enable a deposited conductive material to contact the desired regions, thereby forming a “contact.” The openings in the insulative material are typically referred to as “contact openings.”
Higher performance, lower cost, increased miniaturization of components, and greater packaging density of integrated circuits are goals of the computer industry. However, as components become smaller and smaller, tolerances for all semiconductor structures (such as circuitry traces, contacts, and the like) become more and more stringent. In fact, each new generation of semiconductor device technology has seen a reduction in contact size of, on average, about 0.7 times. Unfortunately, interconnect delays have also increased at a rate of about two times per each new generation. Interconnect delays have a limiting effect on clock speeds which lowers performance. Although the reduction in size creates technical problems, the future advancement of the technology requires the capability for forming sub-0.25 &mgr;m contact openings with aspect ratios (height to width) as high as 8 to 1.
Moreover, the reduction in contact size (i.e., diameter) has resulted in intolerable increases in resistance between the active-device regions and the conductive material. Various methods have been employed to reduce the contact resistance at the interface between the conductive material and active-device region. One such method includes the formation of a metal silicide contact interface atop the active-device region within the contact opening prior to the application of the conductive material into the contact opening. A common metal silicide material formed is titanium silicide (TiSi
X
, wherein x is predominately equal to 2) generated from a deposited layer of titanium.
FIGS. 7-11
illustrate a conventional method of forming a titanium silicide layer on an active-device region.
FIG. 7
illustrates an intermediate structure
300
comprising a semiconductor substrate
302
having an active-device region
304
formed therein with a dielectric layer
306
disposed thereover. A contact opening
308
is formed, by any known technique, such as patterning of a photoresist and subsequent etching, in the dielectric layer
306
to expose a portion of the active-device region
304
, as shown in
FIG. 8. A
thin layer of titanium
310
is applied over the dielectric layer
306
and the exposed portion of the active-device region
304
, as shown in
FIG. 9. A
high temperature anneal step is conducted in an inert atmosphere to react the thin titanium layer
310
with the active-device region
304
in contact therewith which forms a titanium silicide layer
312
, as shown in FIG.
10
. The non-reacted titanium layer
310
may then be removed to result in a final structure
314
with a titanium silicide layer
312
formed therein, as shown in FIG.
11
.
Naturally, as contact opening aspect ratios increase, thicker conductive material layers must be deposited, usually by DC magnetron sputtering, to obtain the required amount and depth of conductive material on the active-device region at the bottom of the contact opening. However, with contact openings approaching dimensions of 0.25 &mgr;m in diameter and aspect ratios of greater than 4 to 1, currently utilized processing techniques, such as physical vapor deposition, do not provide adequate step coverage for depositing conductive materials. Even the use of filtering techniques, such as physical collimated deposition and low-pressure long throw techniques, which are used to increase the number of sputtered particles contacting the bottom of the contact opening, have proven ineffective for contact opening diameters less than about 0.35 &mgr;m (for 0.25 &mgr;m diameter contact opening, the deposition efficiency is less than about 15%) and as contact opening aspect ratios increase beyond about 3 to 1 (bottom step coverage of less than 20%). Both collimated deposition and low-pressure long throw techniques also tend to create excessive film buildup at the top corner or rim of the contact opening, causing shadowing of bottom corners of the contact openings. The result is little or no deposited film at the bottom corners of the contact opening and consequently poor step coverage. Although increasing collimator aspect ratio results in improved step coverage, it also reduces deposition rate which reduces product throughput and, in turn, increases the cost of the semiconductor device.
Recently, physical vapor deposition (“PVD”) has been revived with the introduction of the Ionized Metal Plasma (“IMP”) process. Ionizing sputtered metal particles allows for highly directional PVD for depositing material in contact openings with up to about 6 to 1 aspect ratios and having 0.25 &mgr;m diameter openings. The IMP process can result in up to about 70% bottom coverage and up to about 10% sidewall coverage, even with such high aspect ratios and small diameter contact openings.
As illustrated in
FIG. 12
, an apparatus
320
used in the IMP process consists of a deposition chamber
322
having a pedestal
324
to support a semiconductor substrate
326
to be coated and a target
328
, such as a titanium plate. The pedestal
324
has an RF bias power source
330
, the deposition chamber
322
includes an RF power source
332
, and the target
328
has an RF or a DC power source
334
.
In the IMP process, metal particles (atoms, ions, etc.) (not shown) are sputtered from the target
328
. These metal particles pass through a high-density plasma
336
(e.g., usually between about 10
11
/[cm
3
] and 10
12
/[cm
3
]) formed between the target
328
and semiconductor substrate
326
where they become ionized. The ionization of the material particles enables a user to control the angular distribution of material arriving at the substrate for maximum bottom coverage in the bottom of the contact openings (not shown) by the manipulation of the electric field at the substrate.
In the deposition chamber
322
, the plasma
336
is maintained by inductively coupling RF energy from the RF power source
332
into the plasma
336
. An electric field, or bias voltage, develops in a sheath layer
338
around the plasma
336
, accelerating the metal ions (not shown) in a vector substantially perpendicular to the semiconductor substrate
326
by electrostatic coupling. The potential difference between the plasma
336
and the semiconductor substrate
326
can be optionally modulated by applying independent bias power from RF pedestal power bias source
330
to the semiconductor substrate
326
.
The degree of ionization of sputtered metal particles depends on their residence time in the plasma
336
(i.e., the longer the residence time, the great
Burton Randle D.
Givens John H.
Crane Sara
Micro)n Technology, Inc.
Tran Thien F
TraskBritt
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