JPH0748571B2 - Semiconductor optical sensor - Google Patents

Description

TECHNICAL FIELD The present invention relates to a high withstand voltage shutter barrier semiconductor optical sensor.

[Problems to be Solved by Conventional Techniques and Inventions]

An optical sensor that detects light and converts it into an electric signal is indispensable not only for measuring light itself, but also for non-contact measurement using light. Various types of optical sensors such as vacuum tube type are known, but optical sensors using semiconductors are
It has features such as small size, light weight, and long life, so it is being actively developed.

By the way, in a semiconductor optical sensor, there is a demand for a higher band having sensitivity to light in a wide wavelength range and an improvement in high-speed response capable of accurately responding to light such as high-frequency modulated light. In order to increase the band, it is an issue to improve the sensitivity to ultraviolet light.

Many semiconductor optical sensors are used in a reverse bias state. Increasing the reverse voltage at this time effectively achieves high bandwidth and high-speed response. That is, when the reverse voltage is increased, the depletion layer that spreads at the junction becomes wider accordingly. Therefore, the junction capacitance is reduced and the high speed response is improved. On the other hand, a small number of carriers (electrons or holes) mainly generated in the depletion layer due to light incidence flow as a photocurrent. The shorter the wavelength of light is infrared light, visible light, and ultraviolet light, the shorter the reaching distance from the semiconductor surface to the inside. Therefore, when the depletion layer is wide, light in a wide wavelength range causes carriers to be generated in the depletion layer, resulting in a higher band. In order to improve the sensitivity to ultraviolet light, a semiconductor optical sensor of the type having a junction as close as possible to the incident surface is preferable. For example, a semiconductor photosensor of a shutter barrier type is suitable as an ultraviolet light sensor because it forms a thin metal layer of several hundred liters on a semiconductor surface as a barrier metal forming a shutter barrier. However, in a semiconductor barrier type semiconductor device, the peripheral breakdown voltage (breakdown voltage around the shutter barrier) is significantly lower than the bulk breakdown voltage (breakdown voltage at the center of the shutter barrier), and it is difficult to obtain a high breakdown voltage semiconductor device.

Therefore, an object of the present invention is to improve the peripheral withstand voltage of a shutter barrier type semiconductor optical sensor to achieve a high withstand voltage, thereby achieving a high bandwidth and a high speed response.

[Means for Solving the Problems]

The present invention for achieving the above object comprises: a semiconductor region; and a barrier electrode made of a thin metal layer formed on the surface of the semiconductor region so that a Schottky barrier can be formed between the semiconductor region and the semiconductor region. A semiconductor photosensor having an ohmic electrode connected to the semiconductor region, wherein the barrier electrode is provided with a light-receiving surface, and the barrier electrode is surrounded by a ring on the surface of the semiconductor region. A thin resistance layer is formed, the high resistance thin layer is made of a material capable of generating a Schottky barrier with the semiconductor region, and has a sheet resistance of 10 kΩ / □ or more. The present invention relates to a semiconductor photosensor characterized in that the entire peripheral edge is in contact with and electrically connected to the entire outer peripheral edge of the barrier electrode.

[Operation and Effect of the Invention] When a reverse bias voltage is applied between the barrier electrode and the ohmic electrode of the semiconductor photosensor of the present invention, a depletion layer is generated in the semiconductor region based on the barrier electrode and the high resistance thin layer is formed. A depletion layer based on the high resistance thin layer is also generated by the Schottky barrier action of. Since the high resistance thin layer is in contact with the entire outer peripheral edge of the barrier electrode, the depletion layer based on the barrier electrode and the depletion layer based on the high resistance thin layer are continuous. In addition, since the potential gradually decreases from the inner peripheral edge to the outer peripheral edge of the high resistance thin layer formed in an annular shape, the depletion layer also tapers from the inner peripheral edge to the outer peripheral edge. As a result, the depletion layer does not change abruptly in the semiconductor region corresponding to the outer peripheral edge of the barrier electrode, and the breakdown voltage increases. When the breakdown voltage of the semiconductor optical sensor becomes high, it becomes possible to use the semiconductor optical sensor at a high reverse bias voltage, and it is possible to achieve a high band and an improvement in responsiveness.

〔Example〕

A shutter barrier type semiconductor photosensor and a method of manufacturing the same according to the embodiment of the present invention will be described with reference to FIGS.
A description will be given based on (D).

When manufacturing the semiconductor optical sensor shown in FIG. 1, first,
A semiconductor substrate 1 made of GaAs (gallium arsenide) shown in FIG. 2 (A) is prepared. The semiconductor substrate 1 has a thickness of about 270μ.
m, on the n ^{+ type} region 2 having an impurity concentration of 1 to 3 × 10 ¹⁸ cm ^-3 ,
The n-type region 3 having a thickness of about 45 μm and an impurity concentration of 2 × 10 ¹⁴ cm ⁻³ is epitaxially grown.

Next, as shown in FIG. 2 (B), a Ti (titanium) thin layer 4 and an Al (aluminum) layer 5 are continuously formed on the entire upper surface of the semiconductor substrate 1 by vacuum vapor deposition. The thickness of the Ti thin layer 4 is about 50Å
(0.005 μm), which is extremely thin. The thickness of the Al layer 5 is about 2 μm
Is. An Au (gold) -Ge (germanium) alloy and Au are continuously vacuum-deposited on the entire lower surface of the n ^{+ -type} region 2 to form an ohmic electrode 6.

Next, as shown in FIG. 2 (C), the Al layer 5 around the element is removed to leave the Al layer 5a, and then the air is heated at 300 ° C. for 20 ° C. in air.
Heat treatment for minutes. As a result, the exposed Ti thin layer 4
Is partially oxidized to form the first titanium oxide thin layer 7.
It is considered that the thickness of the titanium oxide thin layer 7 is about 1.5 times that of the Ti thin layer 4, but it is not known exactly because the measurement is difficult. The sheet resistance of the titanium oxide thin layer 7 is about 5000.
It is a thin layer of 0 MΩ / □ and can be regarded as an insulator. Al
Since the lower part of the layer 5a is not oxidized, the Ti thin layer 4a remains.

Next, as shown in FIG. 2 (D), the periphery of the Al layer 5a is removed by etching to leave the Al layer 5b, and then 275 in air.
Heat treatment at ℃ for 15 minutes. As a result, the exposed Ti
Part of the thin layer 4a is oxidized to become the second titanium oxide thin layer 8. The thickness of the second thin titanium oxide layer 8 is substantially the same as that of the first thin titanium oxide layer 7. The second titanium oxide thin layer 8 is a semi-insulating high resistance layer having a sheet resistance of about 100 MΩ / □. The second titanium oxide thin layer 8 is formed in a ring shape so as to surround and adjoin the Ti thin layer 4b remaining under the Al layer 5b having a substantially square planar shape. The first titanium oxide thin layer 7 is formed in an annular shape along the periphery of the element so as to surround and surround the second titanium oxide thin layer 8.

Next, as shown in FIG. 1, a part of the Al layer 5b is removed by etching to leave an Al layer 5c running on the Ti thin layer 4b and running in an annular shape near the periphery of the Ti thin layer 4b. Let Then plasma
The silicon oxide film 9 is formed as a protective film by CVD to a thickness of about 800Å to complete the semiconductor chip of the optical sensor.

In the optical sensor shown in FIG. 1 thus manufactured, the Ti thin layer 4b is a barrier electrode serving as a light-receiving surface, and a shutter barrier is formed between the Ti thin layer 4b and the n-type region 3 to form a shutter barrier optical sensor. The Al layer 5c is an electrode for connection to the barrier electrode (Ti thin layer) 4b, and has a bonding pad portion of the lead wire in a part thereof although not shown. The second titanium oxide thin layer 8 is a feature of the present invention, and contributes to a high breakdown voltage as a field plate. However, it is not a well-known high resistance field plate arranged on the insulating film. That is, the titanium oxide thin layer 8 forms a shutter barrier with the n-type region 3, and should be called a shutter barrier type field plate. The first titanium oxide thin layer 7 should be regarded as a surface stabilizing film, and seems to exert a strong effect of fixing the surface state of the n-type region 3 to a state in which the depletion layer is likely to spread. The light 10 to be detected is irradiated on the barrier electrode (Ti thin layer) 4b, passes through the silicon oxide film 9 and the barrier electrode (Ti thin layer) 4b, reaches the n-type region 3, and then within the n-type region 3. Generate pairs of electrons and holes. Between the Al layer 5c as the connecting electrode and the ohmic electrode 6, the ohmic electrode 6 is provided.
Since a reverse voltage having a positive side is applied, the carrier generated by photoexcitation becomes a photocurrent flowing between the Al layer (connection electrode) 5c and the ohmic electrode 6.

If the semiconductor optical sensor has a structure in which the second titanium oxide thin layer 8 is provided as shown in FIG. 1, a withstand voltage of about 800 V can be obtained. When the titanium oxide thin layer 8 is removed, the breakdown voltage drops to about 200V. Therefore, the depletion layer can be widened and used by applying a reverse voltage significantly higher than the conventional one. As a result, the semiconductor photosensor of the shutter barrier type has a high sensitivity to ultraviolet rays and also a good sensitivity to light on the long wavelength side that reaches a relatively deep position of the n-type region 3. In this example, an unprecedented high-bandwidth semiconductor optical sensor having practical sensitivity to light in the wavelength range of about 8300Å to about 1800Å was realized. The fact that the light receiving sensitivity is attenuated on the short wavelength side of 1800 Å or less is due to the light transmission characteristics of the silicon oxide film 9. In addition, the wide depletion layer significantly reduced the depletion layer capacitance and improved the fast response.

The high breakdown voltage is achieved because the titanium oxide thin layer 8 effectively acts as a field plate as described above. That is, the titanium oxide thin layer 8
Is a high resistance field plate having a larger electric field concentration relaxation effect than a field plate made of a conductor. Therefore, due to the potential gradient generated in the lateral direction of the titanium oxide thin layer 8, the reverse voltage applied to the shutter barrier becomes smaller as it goes to the tip side of the titanium oxide thin layer 8, which is shown schematically in FIG. As shown in FIG.
A depletion layer 11 with a narrowed width is formed in the area. Further, since the titanium oxide thin layer 8 is a field plate of a type in which no insulating layer is interposed between the thin layer 8 of titanium oxide and the n-type region 3, instability of characteristics due to the insulating layer does not occur.
An effective electric field relaxation phenomenon occurs in the n-type region 3. Furthermore, from the barrier electrode (Ti thin layer) 4b to the titanium oxide thin layer 8
Is connected to the shutter barrier on the surface of the n-type region 3, the electric field concentration hardly occurs in this connection portion.

[Modification]

The present invention is not limited to the embodiments, but can be modified as follows, for example.

(1) It is desirable that the first titanium oxide thin layer 7 is formed in order to suppress the reverse current to a small value, but even if it is not formed, a high breakdown voltage can be achieved. If the first thin titanium oxide layer 7 is not formed, breakdown will occur in the minute region at the tip of the second thin titanium oxide layer 8. But,
The reverse current due to the breakdown in this minute region is
Even if it is limited by the resistance value of the titanium oxide thin layer 8, the leakage current remains at the current level and does not cause a decrease in device breakdown voltage. When the first titanium oxide thin layer 7 is formed, the breakdown voltage of the Schottky barrier at the tip of the second titanium oxide thin layer 8 is improved, and the breakdown of the above-mentioned minute region moves to the high pressure side, so that the optimum design is performed. For example, the bulk breakdown is reached without the breakdown in the above-mentioned minute region appearing. That is, since the reverse current does not increase due to the breakdown of the minute region, the reverse current becomes small.

(2) The sheet resistance of the second titanium oxide thin layer 8 is 10
kΩ / □ to 5000 MΩ / □, preferably 10 MΩ / □ to 1000 MΩ
It is better to choose / □. The thickness of the titanium oxide thin layer 8 is 20.
~ 300Å is suitable. The length of the titanium oxide thin layer 8 (length in the horizontal direction in FIG. 1) is preferably selected to be 30 to 500 μm.

(3) In order to obtain good contact with the semiconductor surface, it is desirable to oxidize the Ti thin layer coated on the semiconductor surface to form the titanium oxide thin layer 8. However, the titanium oxide itself may be formed by vacuum vapor deposition, sputtering, or the like.

(4) A structure in which an annular Ti layer is left in the middle of the titanium oxide thin layer 8 to stabilize the lateral potential distribution of the titanium oxide thin layer 8, or the titanium oxide thin layer 8 has a large sheet resistance. As a two-layer structure of a lower layer and an upper layer having a small sheet resistance, it is possible to modify the structure for reducing the reverse current.

(5) A titanium oxide thin layer is suitable as the high-resistance thin layer, but it can be replaced with, for example, a tantalum (Ta) oxide thin layer.

(6) The barrier electrode (Ti thin layer) 4b can be replaced with an Au thin layer or the like.

(7) The material of the semiconductor region may be replaced with GaP (gallium phosphide), GaAsP (gallium arsenide phosphide), Si (silicon), etc. depending on the purpose. The titanium oxide thin layer 8 is particularly effective in combination with a III-V group compound semiconductor.

(8) It may be combined with a well-known guard ring structure in which a p ^{+ -type} annular region is formed so as to be adjacent to the peripheral portion of the barrier electrode (Ti thin layer) 4b. In this case, the titanium oxide thin layer 8
Does not form a shock barrier with this p ⁺ -shaped annular region. Therefore, the shutter barrier formed by the barrier electrode (Ti thin layer) 4b and the shutter barrier formed by the titanium oxide thin layer 8 do not directly connect to each other, and the guard ring region p ^{+ -type} annular region and the n-type region 3 are formed. It is continuous with a pn junction formed therebetween. That is, it is common to the embodiments in that the connecting portion of the two shutter barriers is continuous as a rectifying barrier (a generic name including a pn junction and a shutter barrier).

[Brief description of drawings]

FIG. 1 is a sectional view showing a semiconductor photosensor according to an embodiment of the present invention, and FIGS. 2A to 2D are sectional views showing the semiconductor photosensor of FIG. 1 in the order of manufacturing steps. 1 ... semiconductor substrate, 2 ... n ^{+ type} region, 3 ... n type region,
4b …… Ti thin layer, 5c …… Al layer, 6 …… Omic electrode, 7
...... First titanium oxide thin layer, 8 …… Second titanium oxide thin layer, 9 …… Silicon oxide film.

Claims (1)

[Claims] 1. A semiconductor region, a barrier electrode made of a thin metal layer formed on a surface of the semiconductor region so that a Schottky barrier can be formed between the semiconductor region, and the barrier electrode connected to the semiconductor region. In the semiconductor photosensor having a light receiving surface on the barrier electrode, a high resistance thin layer is formed on the surface of the semiconductor region so as to surround the barrier electrode in a ring shape. The high-resistance thin layer is made of a material capable of forming a Schottky barrier with the semiconductor region and has a thickness of 10k.
A semiconductor optical sensor having a sheet resistance of Ω / □ or more, wherein an inner peripheral edge of the high resistance thin layer is in contact with an outer peripheral edge of the barrier electrode and is electrically connected thereto.