Active solid-state devices (e.g. – transistors – solid-state diode – Responsive to non-electrical signal – Electromagnetic or particle radiation
Reexamination Certificate
2000-01-24
2001-10-16
Meier, Stephen D. (Department: 2822)
Active solid-state devices (e.g., transistors, solid-state diode
Responsive to non-electrical signal
Electromagnetic or particle radiation
C257S458000, C257S452000, C257S457000
Reexamination Certificate
active
06303968
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor light-receiving element.
2. Description of Related Art
A common conventional semiconductor light-receiving element (photodiode) performs optoelectric conversion in which light incident on a light-receiving surface is diverted to the depletion layer of a light-absorbing layer immediately below a diffusion region.
An example of such a semiconductor light-receiving element is disclosed in Reference I (Japanese Unexamined Patent Application (Kokai) 8-18088). The semiconductor light-receiving element of Reference I prevents stray light from being generated because light from outside the light-receiving surface is blocked by a shielding metal film provided along the perimeter of the light-receiving surface. In addition, the shielding metal film does not create stray capacitance because this shielding metal film is electrically connected to a window layer via an ohmic electrode. Consequently, using the technique of Reference I makes it possible to realize a semiconductor light-receiving element having excellent element characteristics.
It is known, however, that outside force, stress, or the like causes cracking or chipping on the surface of a semiconductor light-receiving element during production or operation of this element. Consequently, the substrate around the light-receiving surface is commonly cracked or chipped during production or operation. Such cracking of chipping is not limited to the technique disclosed in Reference I.
For example, dicing, scribing or the like (hereinafter referred to as “dicing or the like”), is used in an element splitting process in which a plurality of semiconductor light-receiving elements formed as an array on a wafer are cut and separated. Wafers are commonly cut while being bonded to a wafer sheet or the like. When cracks form near the cutting surface during the cutting of wafers by dicing or the like, these cracks grow during the operation of the semiconductor light-receiving element, sometimes reaching the diffusion region. In a common semiconductor light-receiving element, a crack reaching all the way into the diffusion region alters element characteristics or causes element failure. The above-described excellent element characteristics are adversely affected as a result.
In the semiconductor light-receiving element of Reference I, an ohmic electrode is provided, for example, on opposite sides (areas that face each other) of a substrate surface, but these opposite-side areas of the substrate surface occasionally break off.
Such breakage occurs, for example, when a semiconductor light-receiving element is handled by pincers or the like during the mounting of the element. In the process, the shielding metal film is brought into an electrically floating state if the ohmic electrode on the opposite sides of the substrate surface has broken off. The above-described excellent element characteristics are adversely affected as a result.
SUMMARY OF THF INVENTION
In view of the above, an object of the present invention is to provide a semiconductor light-receiving element whose element characteristics are only minimally affected by the cracking, chipping, or the like occurring during the fabrication or mounting of the semiconductor light-receiving element.
To attain the stated object, the following unique structure has been adopted for the semiconductor light-receiving element of the present invention. Specifically, the semiconductor light-receiving element of the present invention comprises a light-absorbing layer of a first conduction type and a window layer of the first conduction type sequentially formed on the first principal surface of a substrate of the first conduction type. In the present invention, part of the window layer is provided with a diffusion region of a second conduction type that reaches as far as the boundary between the window layer and the light-absorbing layer. Another feature of the present invention is that a shielding film cladding is formed on the window layer around the diffusion region. Yet another feature of the present invention is that the shielding film cladding is constructed by cladding a shielding metal film and an insulating film. Still another feature of the present invention is that the shielding metal film is part of the shielding film cladding and is electrically connected to the window layer by means of an ohmic electrode. According to the present invention, the ohmic electrode is provided such that it is in contact with the window layer and encircles the diffusion region.
In this structure, the shielding metal film contained in the shielding film cladding is electrically connected to the window layer by the ohmic electrode, and this ohmic electrode encircles the diffusion region. It is therefore possible to suppress generation of stray light because light coming from outside the light-receiving surface can be blocked by the shielding metal film provided around the light-receiving surface. In addition, the shielding metal film does not generate any stray capacitance because this shielding metal film is electrically connected to the window layer by means of the ohmic electrode. In other words, the excellent characteristics of the semiconductor light-receiving element in Reference I can be easily afforded.
In particular, actions and effects (1) and (2) below can be achieved because the ohmic electrode in the above-described structure is provided such that it is in electrical contact with the window layer and encircles the diffusion region.
(1) When cracks form at the edges of the cutting surfaces or other areas of a semiconductor light-receiving element substrate during pincer handling or element splitting, these cracks can be prevented from reaching all the way inside the ohmic electrode because the ohmic electrode is formed such that it is in contact with the window layer. This is because the material for forming the ohmic electrode diffuses (usually by thermal diffusion) into the area of the substrate provided with the ohmic electrode, increasing the strength of the substrate in this area. With this structure, therefore, cracks are less likely to reach the diffusion region, and the adverse effect of cracks on the element characteristics can be controlled.
(2) When, for example, the ohmic electrode provided to the opposite sides of an element breaks off during mounting, the excellent characteristics of the semiconductor light-receiving element in Reference I are still prevented from being adversely affected because the ohmic electrode maintains electric conductivity between the window layer and the shielding metal film in areas outside these sections. This structure therefore makes it possible to control deterioration in element characteristics due to cracking or chipping.
In working the present invention, the substrate should preferably be an indium/phosphorus-based substrate.
Indium/phosphorus-based substrates are generally useful for obtaining wide-ranging photosensitive wavelengths, but these substrates are known to be weak materials. For this reason, semiconductor light-receiving elements obtained using indium/phosphorus-based substrates are apt to develop cracks, chips, or the like, causing the above-described element characteristics to decline considerably. When, however, an ohmic electrode is provided in the manner described above, the deterioration of element characteristics can be controlled, as described in (1) and (2) above.
In working the present invention, it is particularly preferable that a connection electrode be further provided for electrically connecting the ohmic electrode and the shielding metal film.
When an ohmic electrode and a shielding metal film are connected directly, an inadequate connection occasionally forms between the two because step coverage defects develop during the formation of the ohmic electrode. Such connection defects are less likely to develop, however, when the ohmic electrode and the shielding metal film are connected by means of a connection electrode.
The dif
Burdett James R.
Meier Stephen D.
Oki Electric Industry Co. Ltd.
Venable
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