Semiconductor device manufacturing: process – Making device or circuit responsive to nonelectrical signal – Physical stress responsive
Reexamination Certificate
2002-01-30
2003-02-11
Chaudhari, Chandra (Department: 2813)
Semiconductor device manufacturing: process
Making device or circuit responsive to nonelectrical signal
Physical stress responsive
C438S239000
Reexamination Certificate
active
06518083
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a surface shape recognition sensor used to sense a surface shape having a fine three-dimensional pattern such as a human fingerprint or animal noseprint.
Along with the progress in information-oriented society in the environment of the current society, the security technology has received a great deal of attention. For example, in the information-oriented society, a personal authentication technology for establishment of, e.g., an electronic cash system is an important key. Authentication technologies for preventing theft or illicit use of credit cards have also been extensively researched and developed (e.g., Yoshimasa Shimizu et al., “A Study on the Structure of a Smart Card with the Function to Verify the Holder”, Technical Report of IEICE OFS92-32, pp. 25-30 (1992-11)).
There are various kinds of authentication schemes such as fingerprint authentication and voice authentication. Especially, many fingerprint authentication techniques have been developed so far. Fingerprint authentication schemes are roughly classified into an optical reading scheme and a scheme of using the human electric characteristic and detecting the three-dimensional pattern of the skin surface of a finger and replacing it with an electrical signal.
In the optical reading scheme, fingerprint data is read mainly using reflection of light and an image sensor (CCD) and collated (e.g., Seigo Igaki et al., Japanese Patent Laid-Open No. 61-221883). A scheme of reading a pressure difference by the three-dimensional pattern of the skin surface of a finger using a piezoelectric thin film has also been developed (e.g., Masanori Sumihara et al., Japanese Patent Laid-Open No. 5-61965).
An authentication scheme of replacing a change in electric characteristic due to contact of a skin with an electrical signal distribution by detecting a resistive or capacitive change amount using a pressure sensitive sheet so as to detect a fingerprint has also been proposed (e.g., Kazuhiro Itsumi et al., Japanese Patent Laid-Open No. 7-168930).
In the above prior arts, however, the optical reading scheme is difficult to make a compact and versatile system, and its application purpose is limited. The scheme of detecting the three-dimensional pattern of the skin surface of a finger using a pressure sensitive sheet or the like is difficult to put into practical use or is unreliable because a special material is required and fabrication is difficult.
“Marco Tartagni” et al. have developed a capacitive fingerprint sensor using an LSI manufacturing technology (Marco Tartagni and Robert Guerrieri, A 390 dpi Live Fingerprint Imager Based on Feedback Capacitive Sensing Scheme, 1997 IEEE International Solid-State Circuits Conference, pp. 200-201 (1997)).
In this fingerprint sensor, the three-dimensional pattern of a skin is detected using a feedback static capacitance scheme by a sensor chip in which small capacitive detection sensors are two-dimensionally arrayed.
In the capacitive detection sensor, two plates are formed on the uppermost layer of an LSI, and a passivation film is formed on the plates. In this capacitive detection sensor, a skin surface functioning as a third plate is isolated by an insulating layer formed from air, and sensing is performed using the difference in distance, thereby detecting a fingerprint. As characteristic features of a fingerprint authentication system using this structure, no special interface is necessary, and a compact system can be constructed, unlike the conventional optical scheme.
In principle, a fingerprint sensor using a capacitive detection sensor is obtained by forming a lower electrode on a semiconductor substrate and forming a passivation film on the resultant structure. A capacitance between the skin and the sensor is detected through the passivation film, thereby detecting the fine three-dimensional pattern of the skin surface of a finger.
In this sensor chip using capacitive detection sensors, however, since a skin serves as one electrode for capacitive detection, static electricity generated at the fingertip readily causes electrostatic destruction in an integrated circuit such as a sensor circuit incorporated in the sensor chip.
To prevent the above-described electrostatic destruction of an electrostatic capacitance fingerprint sensor, a surface shape recognition sensor having an electrostatic capacitive detection sensor having a sectional structure as shown in
FIG. 15
has been proposed. The sensor shown in
FIG. 15
will be described. The sensor has a lower electrode
1503
formed on a semiconductor substrate
1501
via an interlevel dielectric
1502
, a plate-shaped deformable upper electrode
1504
which is separated from the lower electrode
1503
at a predetermined interval, and a support electrode
1505
laid out around the lower electrode
1503
to support the upper electrode
1504
while being insulated and isolated from the lower electrode
1503
.
In the sensor having the above arrangement, when a finger to be subjected to fingerprint detection comes into contact with the upper electrode
1504
, the pressure from the finger deflects the upper electrode
1504
toward the lower electrode
1503
to change the electrostatic capacitance formed between the lower electrode
1503
and the upper electrode
1504
. This change in electrostatic capacitance is detected by a detection circuit (not shown) on the semiconductor substrate
1501
through an interconnection (not shown) connected to the lower electrode
1503
. In this surface shape recognition sensor, when the upper electrode
1504
is grounded through the conductive support electrode
1505
, static electricity generated at the fingertip and discharged to the upper electrode
1504
flows to ground through the support electrode
1505
. For this reason, the detection circuit incorporated under the lower electrode
1503
is protected from electrostatic destruction.
The above-described deformable upper electrode must be formed with a space under it. An example of a sensor using such a hollow structure is described in a “method of manufacturing a capacitive pressure sensor for detecting a change in pressure by a change in electrostatic capacitance” by “P. Rey et al.” (reference 1: P. Rey, P. Charvet, M. T. Delaye, and S. Abouhassan, “A High Density Capacitive Pressure Sensor Array For Fingerprint Sensor Application”, proceedings of Transducers '97, pp. 1453-1456 (1997)).
To form such a hollow structure, a lower electrode is formed, and then, a sacrificial film is formed on the lower electrode. An upper electrode and a deformable portion to which the upper electrode is fixed are formed on the sacrificial film. After that, the sacrificial film under the deformable portion is removed by etching from the sides of the edge portion of the deformable portion to which the upper electrode is fixed, thereby forming a space under the upper electrode. In such a fine hollow structure, however, since the height of the space under the deformable portion is as small as about 0.5 to 2 &mgr;m, though the deformable portion generally has a length of about 50 &mgr;m in the lateral direction, it is very difficult to completely remove the sacrificial film by etching from the lateral direction. Additionally, in the above-described surface shape recognition sensor, since a plurality of cells formed from a single lower electrode are arrayed, it is almost impossible to completely remove the sacrificial film by etching from the lateral direction.
To the contrary, when an opening portion is formed in the deformable portion formed on the sacrificial film, and the sacrificial film is removed by etching through the opening portion, the sacrificial film can be efficiently removed. Hence, the sacrificial film can be completely removed.
When the upper electrode serving as a deformable portion has an opening portion, a foreign substance or the like may enter the hollow structure from the opening portion to impede the detection operation of the sensor. This may also cause an error in the lower electrode.
Kyuragi Hakaru
Machida Katsuyuki
Morimura Hiroki
Sato Norio
Shigematsu Satoshi
Blakely & Sokoloff, Taylor & Zafman
Chaudhari Chandra
Nippon Telegraph and Telephone Corporation
LandOfFree
Surface shape recognition sensor and method of manufacturing... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Surface shape recognition sensor and method of manufacturing..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Surface shape recognition sensor and method of manufacturing... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3160188