Method of making aggregate of semiconductor micro-needles

Details Method of making aggregate of semiconductor micro-needles Method of making aggregate of semiconductor micro-needles

2000-02-08

2001-01-23

Chaudhari, Chandra (Department: 2813)

Semiconductor device manufacturing: process

Making device or circuit emissive of nonelectrical signal

Groove formation

C438S947000, C438S962000

Reexamination Certificate

active

06177291

ABSTRACT:

BACKGROUND OF THE INVENTION
In recent years, there has been developed an optical element in which porous silicon is formed to be used as a light emitting element. Japanese Laid-Open Patent Publication No. 4-356977 discloses such an optical element, in which a large number of micro-pores
102
are formed in the surface region of a silicon substrate
101
by anodization, as shown in FIG.
33
. If the porous silicon is irradiated with light, photoluminescence having its absorption edge in the visible region is observed, which implements a light-receiving/light-emitting element using silicon. That is, in a normal semiconductor apparatus composed of single-crystal silicon, an excited electron makes an indirect transition to a lower energy level so that the energy resulting from the transition is converted into heat. which renders light emission in the visible region difficult. However, there has been reported a phenomenon that, if silicon has a walled structure, such as porous silicon, and its wall thickness is about 0.01 &mgr;m, the band width of the silicon is enlarged to 1.2 to 2.5 eV due to the quantum size effects, so that an excited electron makes a direct transition between the bands, which enables light emission.
It has also been reported that two electrodes are provided on both ends of the porous silicon so that electroluminescence is observed by the application of an electric field.
However, if electroluminescence is to be obtained by the application of an electric field or photoluminescence is to be obtained by the irradiation with light of the porous silicon formed by anodization in the surface region of the silicon substrate
101
as shown in
FIG. 33
, the following problems are encountered.
That is, the diameter and depth of the micro-pore
102
formed by anodization are difficult to control. In addition, the configuration of the micro-pore
102
is complicated and the distribution of its wall thickness is extremely random. As a result, if etching is intensely performed in order to reduce the wall thickness, the wall portions may be partially torn and peeled off the substrate. Moreover, since the distribution of the wall thickness is random, the quantum size effects are not generated uniformly over the whole wall portions, so that light emission with a sharp emission spectrum cannot be obtained. Furthermore, the wall surface of the micro-pore in the porous silicon readily adsorbs molecules and atoms during anodization, due to its complicated configuration. Under the influence of the atoms and molecules attached to the surface of the silicon, the resulting optical element lacks the capability of reproducing a required emission wavelength and its lifespan is also reduced.
On the other hand, with the development of the present information-oriented society, a semiconductor apparatus in which a semiconductor integrated circuit is disposed has presented an increasing tendency toward the personalization of advanced info-communication appliances with large capacities. In other words, there has been a demand for appliances which enable advanced information transmission to and from a hand-held computer or cellular phone. To meet the demand, it is required to not only enhance the performance of the conventional semiconductor apparatus, which processes only electric signals, but also implement a multi-function semiconductor apparatus which processes light, sounds, etc., as well as electric signals.
FIG. 34
shows the cross sectional structure of a three-dimensional integrated circuit system that has been developed in order to satisfy the requirements. Such a three-dimensional integrated circuit system is expected to surmount the miniaturization limit inherent in the conventional two-dimensional integrated circuit system as well as improve and diversify functions to be performed. In the drawing, a PMOSFET
110
a
consisting of a source
103
, a drain
104
, a gate oxide film
105
, and a gate
106
is formed in the surface region of an n-well
102
, which is formed in a p-type silicon substrate
101
a
as a first layer. In the surface region of the first-layer silicon substrate
101
a
are formed semiconductor apparatus including an NMOSFET
110
b
consisting of the source
103
; drain
104
, gate oxide film
105
, and gate
106
. There are also formed a connecting wire
107
between the source and drain regions and an inter-layer insulating film
108
for covering each region, which has been flattened. On the inter-layer insulating film
108
is formed a second-layer silicon substrate
101
b
made of single-crystal silicon. On the second-layer silicon substrate
101
b
are also formed semiconductor apparatus such as the PMOSFET
110
a
and NMOSFET
110
b
, similarly to the semiconductor apparatus on the above first-layer silicon substrate
101
a
. The semiconductor apparatus in the first layer and the semiconductor apparatus in the second layer are electrically connected via a metal wire
109
(see, e.g., “Extended Abstracts of 1st Symposium on Future Electron Devices,” p. 76, May 1982).
However, such a three-dimensional integrated circuit system has the following problems. The wire
109
is formed by a deposition method in which, after a contact hole was formed, a wiring material is deposited and buried in the contact hole. Since the resulting contact hole becomes extremely deep, deficiencies such as an increase in resistance value and a break in wiring are easily caused by a faulty burying of the wiring material, resulting in poor reliability. With such problematic manufacturing technology, it is difficult to implement a three-dimensional integrated circuit system which can be used practically. In particular, it is extremely difficult to implement an integrated circuit system in more than three dimensions.
SUMMARY OF THE INVENTION
The present invention has been achieved by focusing on the fact that, if a structure in which a large number of semiconductor micro-needles are arranged is used instead of a porous structure, the diameters of the semiconductor micro-needles become uniform. It is therefore a first object of the present invention to provide a quantized region for implementing intense light emission with a narrow wavelength distribution, such as electroluminescence or photoluminescence, and conversion of optical signals to electric signals.
A second object of the present invention is to provide a semiconductor apparatus with an advanced information processing function by incorporating an aggregate of semiconductor micro-needles with various signal converting functions into an integrated circuit system.
To attain the above first object, an aggregate of semiconductor micro-needles according to the present invention comprises, as their basic structure, a large number of semiconductor micro-needles juxtaposed in a substrate, each of said semiconductor micro-needles having a diameter sufficiently small to cause the quantum size effects.
With the basic structure, the band width of a semiconductor material composing the semiconductor micro-needles is expanded due to the so-called quantum size effects. As a result, the direct transitions of electrons occur even in a semiconductor material such as silicon in which excited electrons make indirect transitions in the proper size to cause the quantum size effects. Consequently, it becomes possible to constitute a light emitting element, wavelength converting element, light receiving element, or the like in which the aggregate of semiconductor micro-needles is disposed by using the photoluminescence and electroluminescence resulting from the quantum size effects of each semiconductor micro-needle, variations in electric characteristics caused by the radiation of light, and the like. In this case, unlike a conventional quantized region composed of silicon with a porous structure or the like, the quantized region according to the present invention is constituted by the aggregate of semiconductor micro-needles, so that the diameter of each semiconductor micro-needle becomes sufficiently small to cause significant quantum size effects

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