Thin film using non-thermal techniques

Details Thin film using non-thermal techniques Thin film using non-thermal techniques

1999-10-08

2004-06-01

Wilson, Allan R. (Department: 2815)

Active solid-state devices (e.g., transistors, solid-state diode

With specified dopant

Deep level dopant

C257S610000, C257S611000, C257S612000, C257S635000, C257S656000

Reexamination Certificate

active

06744116

ABSTRACT:

BACKGROUND INFORMATION
(1) Field of the Invention
The present invention generally relates to fabrication of semiconductor devices. More specifically, the present invention relates to fabrication of integrated circuits that utilize prefabricated transistor layers.
(2) Description of Related Art
Modern integrated circuits are generally made up of a silicon substrate containing millions of active and passive devices including transistors, capacitors, resistors, etc. Until recently, the semiconductor industry focused was on reducing the two dimensions, (X-Y) in a Cartesian system of coordinates, of the transistors to reduce the size of the integrated circuit. However, as integration in two dimension has become more and more difficult due to limitations of lithography tools, the exploitation of the third dimension (Z dimension in a Cartesian a system of coordinates) has become increasingly attractive.
FIG. 1
illustrates a conventional integrated circuit
100
that includes substrate
102
(typically made of silicon) onto which a very large number of active devices (transistors
104
) are fabricated. Transistors
104
are intercoupled therebetween and to other devices, thereby forming various circuits, by way of an interconnect system that includes metal lines (
106
). The metal lines may further be connected to other circuits. The various circuits formed are further coupled, by well known techniques, to bond pads
108
of the integrated circuit. Transistors
104
are located on a single layer of silicon at the bottom of the integrated circuit. When the dimension of the gates of transistors
104
goes beyond
193
nanometers, which is shortest wave length of the light used in the present day photolithography process, integration of transistors becomes problematic as lithography tools that are utilized in the process of fabrication of these transistors reach the limit of their performance. One solution to increasing integration without further having to minimize transistors' gates dimensions and thus without resorting to new lithography tools, is to build up further layers of transistors in a third dimension (Z dimension) as illustrated in FIG.
2
.
FIG. 2
illustrates an integrated circuit that includes a first silicon substrate (base substrate
202
) onto which are built a first layer (film)
205
of active devices
204
. A second layer (film)
206
of active devices
208
may be envisioned as being further built in the z dimension (vertically in the Figure). Interconnect lines
207
intercouple the active device
208
of second layer
206
to the active devices
204
of first layer
205
. The second layer
206
of active devices
208
may be coupled to the outside world via bond pads
210
.
In the display area (imaging) attempts have been made to integrate transistors in the third dimension. For example, some digital cameras use chips that have at the bottom thereof (at the base silicon substrate) transistors for logical operations and on top of those transistors are built display sensors. For example, CMOS sensor arrays may be built in the third dimension and used as light sensors. However, these transistors do not have good conducting properties, and therefore their performance is weak.
The second layer transistors are not made of a single-crystal silicon but are made of a polycrystalline silicon or amorphous silicon. The problem in providing a second layer of active devices (transistors) made of single silicon crystal is that the fabrication of the second level of transistors requires processing steps that are performed well beyond the temperature that the interconnect system may withstand. For example, at 400° or 450° Celsius, the metal lines begin to melt. It is desirable to provide an integrated circuit that overcomes the disadvantages associated with conventional devices.


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