JP4153252B2 - Photodiode - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a photodiode, and more particularly to a photodiode that receives monitor light emitted from a semiconductor light emitting element such as a semiconductor laser diode in a semiconductor light source device.
[0002]
[Prior art]
Conventionally, there is JP-A-4-147690 as a technique in such a field. The photodiode provided in the semiconductor light source device described in this publication receives the monitoring laser light emitted downward from the monitoring laser light emitting surface of the semiconductor laser diode. Based on the monitor output from the photodiode, the output of the laser beam emitted upward from the laser beam emission surface opposite to the above-described monitoring laser beam emission surface is controlled. Further, in this semiconductor light source device, the monitoring laser light reflected from the photodiode surface is emitted from the laser light emitting surface by fixing the photodiode on the stem so that the optical axis of the monitoring laser light and the surface of the photodiode are not orthogonal to each other. So that it does not overlap with the laser beam emitted from.
[0003]
[Problems to be solved by the invention]
However, the photodiode provided in the conventional semiconductor light source device has a problem that the light receiving sensitivity largely fluctuates with a change in temperature, and as a result, precise output control of the semiconductor laser diode is difficult. It was.
[0004]
The present invention has been made to solve the above problems, and provides a photodiode capable of obtaining a stable light receiving sensitivity even with respect to a temperature change.
[0005]
[Means for Solving the Problems]
The inventors of the present invention have obtained the following knowledge about the reason why the light receiving sensitivity of the photodiode largely fluctuates due to temperature change in the conventional semiconductor light source device. That is, in the photodiode provided in the conventional semiconductor light source device, the region having the second conductivity type semiconductor layer selectively formed inside the peripheral portion of the surface layer of the first impurity type semiconductor layer having a low impurity concentration is light sensitive. A region (a region in which carriers composed of holes / electrons are generated in response to incident light), and a region in which the second conductivity type semiconductor layer surrounding the photosensitive region is not formed (hereinafter referred to as “variable region”) In addition, it has been found that when the monitoring laser beam is incident, the light receiving sensitivity greatly varies with the temperature change.
[0006]
Therefore, in order to solve the above problems based on such knowledge, the photodiode of the present invention includes a first conductivity type semiconductor substrate and a first conductivity having a lower impurity concentration than the semiconductor substrate formed on the semiconductor substrate. And a second conductivity type semiconductor layer which is formed on the first conductivity type semiconductor layer having the low impurity concentration and forms a pn junction at the interface with the first conductivity type semiconductor layer having the low impurity concentration. A groove is formed to surround the photosensitive region that generates carriers in response to incident light and reaches from the surface of the second conductive semiconductor layer to the first conductive semiconductor substrate, and is cut out from the groove at a predetermined width outer periphery. It is characterized by that.
[0007]
According to the present invention, by forming the groove around the photosensitive region of the photodiode, the pn junction is formed up to the inner surface of the groove existing around the photosensitive region. Can do. As a result, the light receiving sensitivity of the photodiode can be stabilized against temperature changes. Furthermore, since the outer periphery of the predetermined width is cut from the groove by dicing, mechanical damage to the end of the photosensitive region, that is, the pn junction formed on the inner surface of the groove can be prevented. In addition, the first conductive type semiconductor layer and the second conductive type semiconductor layer left on the outer periphery of the groove portion serve as a protection block, and the photosensitive region can be protected.
[0008]
In the photodiode of the present invention, it is preferable that the semiconductor substrate is a silicon substrate, and a silicon thermal oxide film is provided on the inner surface of the groove.
[0009]
According to the present invention, since the thermal oxide film is formed on the inner surface of the groove portion as described above, the pn junction portion formed on the inner surface of the groove portion can be protected.
[0010]
In the photodiode of the present invention, it is preferable that a light shielding member for shielding the incident light is embedded in the groove.
[0011]
According to this invention, since the light shielding member that shields the incident light is embedded in the groove, it is possible to prevent light from entering the pn junction formed on the inner surface of the groove. As a result, this photodiode can obtain more stable device characteristics.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
A photodiode 1 according to an embodiment of the present invention will be described with reference to the accompanying drawings. In the following description of the embodiments, for ease of understanding of the description, the same components are denoted by the same reference numerals as much as possible in each drawing, and redundant description is omitted. Further, the dimensional ratios in the drawings do not necessarily match those described.
[0013]
FIG. 1 is a plan view of the photodiode 1. As shown in FIG. 1, the photodiode 1 has a square planar shape and has a chip area of 0.68 mm × 0.68 mm. A trench groove GRV having a width of 5 μm is formed at the periphery of the square photosensitive region 1 a having an area of 0.64 mm × 0.64 mm. A light shielding member 1r is embedded in the trench groove GRV. The light shielding member 1r can be used a black dye or insulated with black photoresist or polyimide obtained by mixing a pigment such as carbon black. In addition, an upper surface electrode eu made of aluminum having a square shape of 0.13 mm × 0.13 mm is provided at a position near the corner of the photosensitive region 1a.
[0014]
Next, a sectional view of the photodiode 1 is shown in FIG. FIG. 2 shows a cross-sectional structure of the photodiode 1 shown in FIG. As shown in FIG. 2, the photodiode 1 has an n-type semiconductor substrate 1s made of silicon having a resistance of 0.002 Ω · cm and having a thickness of 240 μm. An n-type semiconductor layer 1n having a resistance of 1 kΩ · cm and a thickness of 30 μm and a p-type semiconductor layer 1p having a sheet resistance of 100Ω / □ and a thickness of 0.35 μm are sequentially formed on the semiconductor substrate 1s. Yes. The boundary between the n-type semiconductor layer 1n and the p-type semiconductor layer 1p forms a pn junction.
[0015]
In the photodiode 1, a trench groove GRV having a U-shaped cross section with a depth of 40 μm and a width of 5 μm formed from the boundary between the n-type semiconductor layer 1n and the semiconductor substrate 1s to the deep part is formed at the periphery of the photosensitive region 1a. An insulating layer ILT made of SiO ₂ is formed on the inner surface of the trench groove GRV and the surface layer portion of the p-type semiconductor layer 1p. As described above, the light shielding member 1r is embedded in the trench groove GRV. Furthermore, it has a top electrode eu having a thickness of 1.1 μm made of aluminum formed after etching the insulating layer ILT at a predetermined position on the p-type semiconductor layer 1p, and has a thickness formed sequentially from the bottom surface of the semiconductor substrate 1s. An aluminum layer 1c having a thickness of 1.1 μm and a bottom electrode el having a thickness of 5 μm made of Ni—Au are provided.
[0016]
Next, a method for manufacturing the photodiode 1 will be described. FIG. 3 is a cross-sectional view illustrating a method for manufacturing the photodiode 1.
[0017]
In order to manufacture the photodiode 1, first, as shown in FIG. 3A, an n-type semiconductor substrate 1s having a thickness of 240 μm is prepared. Then, using an epitaxial growth method on a semiconductor substrate 1s, to form an n-type semiconductor layer 1n a low impurity concentration having a thickness of 30μm as shown in FIG. 3 (b).
[0018]
Next, a p-type impurity (boron) is added from the surface layer portion of the n-type semiconductor layer 1n by diffusion, and the conductivity type of this surface layer portion is reversed, and as shown in FIG. 3C, the thickness is 0.35 μm. The p-type semiconductor layer 1p is formed.
[0019]
Next, an insulating layer ILT made of, for example, silicon oxide having a thickness of 1 μm is deposited on the surface layer portion of the p-type semiconductor layer 1p as shown in FIG. As the volume method, a CVD (chemical vapor deposition) method, a sputtering method, or the like can be used.
[0020]
Next, a mask pattern is formed by using a normal photolithography technique, ICP (inductively coupled plasma) etching is performed on the opening of the mask, and a deep region is formed in the region of the opening as shown in FIG. A trench groove GRV having a thickness of 40 μm and a width of 5 μm is formed.
[0021]
Next, the device is heated in an oxygen and water vapor atmosphere to thermally oxidize the trench groove GRV, whereby an insulating layer ILT made of silicon oxide having a thickness of 66 nm is formed in the trench groove GRV as shown in FIG. Form. In this way, the pn junction exposed in the trench groove GRV is protected. The thermal oxidation temperature is as high as 900 ° C.
[0022]
Next, as shown in FIG. 3G, the light shielding member 1r is embedded in the trench groove GRV. The light shielding member 1r can be embedded in the trench groove GRV by spin coating or the like.
[0023]
Next, as shown in FIG. 3 (h), the upper electrode eu and aluminum layer 1c having a thickness of 1.1μm made of Al is formed by sputtering or vapor deposition, further having a thickness of 5 [mu] m by electroless plating A bottom electrode el (Ni—Au) is formed. And, finally, in the middle of the two trench GRV, by cutting the lower electrode el insulating layer ILT by dicing, photodiode 1 is obtained as shown in FIG. 3 (i). By dicing in this way, a block having a width of 15 μm is left from the outside of the inner surface of the trench groove GRV to the end of the photodiode 1.
[0024]
In the photodiode 1 manufactured in this way, a pn junction is formed up to the inner surface of the trench groove GRV, and there is no fluctuation region at the periphery of the photosensitive region 1a as in the conventional photodiode, and the trench groove GRV Even if light enters the block left outside, there is no sensitivity at all, so that stable light receiving sensitivity can be obtained with respect to temperature changes. Further, since the photodiode 1 cuts the outer periphery of the predetermined width from the trench groove GRV by dicing, mechanical damage to the end portion of the photosensitive region 1a, that is, the pn junction formed in the inner surface of the trench groove GRV is prevented. be able to. Furthermore, the block composed of the p-type semiconductor layer 1p and the n-type semiconductor layer 1n left on the outer periphery of the trench groove GRV can be a protective block and protect the photosensitive region 1a. In addition, since the insulating layer ILT is formed on the inner surface of the trench groove GRV as described above, the pn junction formed on the inner surface of the trench groove GRV can be protected. In addition, since the light shielding member 1r is embedded in the trench groove GRV, it is possible to prevent light from entering the pn junction formed on the inner surface of the trench groove GRV. As a result, the photodiode 1 can obtain more stable element characteristics.
[0025]
Here, an example of a semiconductor light source device on which the photodiode 1 is mounted will be described. FIG. 4 is an explanatory diagram for explaining an example of the semiconductor light source device 10.
[0026]
The semiconductor light source device 10 is emitted from a semiconductor laser diode 12 fixed to a side surface of a support 20 on a column fixed on a stem 11 on a disk, and from a monitoring laser light emitting surface 15 of the semiconductor laser diode 12. The optical axis 17 of the monitoring laser beam 16 is provided with a photodiode 1 that is incident on a region off the center. The semiconductor laser diode 12 is made of a nitride material and emits laser light having a wavelength of 409 nm. The normal line 19 of the photodiode 18 is inclined at a predetermined angle with respect to the optical axis 17 of the monitoring laser beam 16 emitted from the monitoring laser beam emitting surface 15 of the semiconductor laser diode 12. With such a configuration, the monitoring laser light 16 reflected by the surface of the photodiode 18 is overlapped with the laser light 14 emitted from the laser light emitting end face 13 facing the monitoring laser light emitting face 15. I try to avoid it. The laser beam 14 emitted from the semiconductor laser diode 12 is controlled based on the monitor output from the monitor laser beam 16 incident on the photodiode 18.
[0027]
When the photodiode 1 is mounted as in the semiconductor light source device 10, the photodiode 1 has a stable light receiving sensitivity even with respect to a temperature change, so that a laser beam having a stable intensity can be output without being affected by the temperature change. it can.
[0028]
Here, FIG. 5 shows the light receiving sensitivity characteristic with respect to temperature change when the photodiode 1 is irradiated with laser light having a wavelength of 409 nm. For reference, FIG. 6 shows the same characteristics of a photodiode used in a conventional semiconductor light source device. 5 and 6, the horizontal axis represents the photodiode temperature, and the vertical axis represents the photocurrent ratio, that is, the photocurrent variation ratio [%] at other temperatures based on the photocurrent at a temperature of 25 ° C. In FIGS. 5 and 6, the line connecting the black square plots indicates the light receiving sensitivity with respect to the temperature change when only the light sensitive region is irradiated with the laser light. In FIG. 5, the line connecting the black circle-shaped plots shows the same characteristics when the chip end of the photodiode 1 is irradiated with laser light. In FIG. 6, the fluctuation region around the photosensitive region is shown. Also shows the same characteristics when irradiated with laser light. As shown in FIG. 6, in the photodiode used in the conventional semiconductor light source device, the photocurrent ratio is higher when the laser beam is also irradiated to the fluctuation region than when the laser beam is irradiated only to the photosensitive region. In other words, it can be seen that the light receiving sensitivity greatly fluctuates due to temperature changes. As described above, in the photodiode used in the conventional semiconductor light source device, the temperature coefficient when the fluctuation region is irradiated with the laser light, that is, the change amount of the photocurrent ratio accompanying the temperature change of 1 ° C. is −0.35. [% / ° C] and large. On the other hand, as shown in FIG. 5, the photodiode 1 has a temperature coefficient of −0.08 [% / ° C.] even when the chip end is irradiated with laser light, and a stable light receiving sensitivity with respect to temperature change can be obtained. Can be confirmed.
[0029]
The present invention is not limited to the above-described embodiment, and various modifications can be made. For example, as the light shielding member 1r embedded in the trench groove GRV, non-doped silica or the like can be used. Even in this case, it is possible to prevent light from entering the pn junction formed on the inner surface of the trench groove GRV.
[0030]
Further, the light shielding member 1r may not be embedded in the trench groove GRV. In this case, since light is incident on the pn junction exposed on the trench groove GRV side, the characteristics of the photodiode 1 are slightly deteriorated, but the area of the photosensitive region of the photodiode 1 can be increased and stable. The effect that the obtained device characteristics can be obtained, the effect that the pn junction formed in the inner surface of the trench groove GRV is not mechanically damaged, etc. still remain.
[0031]
In the present embodiment, in the photodiode 1, the n-type semiconductor layer 1n functions as a light absorption layer, but the conductivity types of the p-type semiconductor layer 1p and the n-type semiconductor layer 1n may be reversed. In this case, the p-type semiconductor layer 1p functions as a light absorption layer.
[0032]
In the present embodiment, the semiconductor light source device using the semiconductor laser diode, which is the most suitable light source, has been described as an example of the semiconductor light source device to which the photodiode 1 is applied. However, the photodiode 1 is applied to the semiconductor light source device. In this case, a light emitting diode (LED) can be used as the light source.
[0033]
【The invention's effect】
According to the photodiode of the present invention, a pn junction is formed up to the end of the photosensitive region, that is, the inner surface of the groove by forming the groove around the photosensitive region of the photodiode. Therefore, as a result of eliminating the fluctuation region around the photosensitive region, the light receiving sensitivity of the photodiode can be stabilized against temperature changes. Furthermore, since the outer periphery of the predetermined width is cut from the groove by dicing, mechanical damage to the end of the photosensitive region, that is, the pn junction formed on the inner surface of the groove can be prevented. In addition, the first conductive type semiconductor layer and the second conductive type semiconductor layer left on the outer periphery of the groove portion serve as a protection block, and the photosensitive region can be protected.
[Brief description of the drawings]
FIG. 1 is a plan view of a photodiode according to an embodiment.
FIG. 2 is a cross-sectional view of the photodiode according to the embodiment.
FIG. 3 is a cross-sectional view showing a method of manufacturing the photodiode according to the embodiment.
FIG. 4 is an explanatory diagram for explaining an example of a semiconductor light source device on which the photodiode according to the embodiment is mounted.
FIG. 5 is a graph showing a light receiving sensitivity characteristic with respect to a temperature change of the photodiode according to the embodiment.
FIG. 6 is a graph showing a light receiving sensitivity characteristic with respect to a temperature change of a conventional photodiode.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Photodiode, 1a ... Photosensitive area | region, 1s ... Semiconductor substrate, 1n ... n-type semiconductor layer, 1p ... p-type semiconductor layer, 1c ... Aluminum layer, 1r ... Light shielding member, ILT ... insulating layer, GRV ... trench groove, eu ... upper surface electrode, el ... lower surface electrode

Claims (3)

A first conductivity type semiconductor substrate;
A first conductivity type semiconductor layer having a lower impurity concentration than the semiconductor substrate formed on the semiconductor substrate;
A second conductivity type semiconductor layer formed on the first conductivity type semiconductor layer having a low impurity concentration and forming a pn junction at an interface with the first conductivity type semiconductor layer having the low impurity concentration, and sensitive to incident light. Then, a groove portion is formed that surrounds the photosensitive region that generates carriers and reaches the first conductive semiconductor substrate from the surface of the second conductive semiconductor layer,
A photodiode cut out at an outer periphery of a predetermined width from the groove. The semiconductor substrate is a silicon substrate;
2. The photodiode according to claim 1, wherein a thermal oxide film of silicon is provided on the inner surface of the groove. The photodiode according to claim 1, wherein a light shielding member that shields the incident light is embedded in the groove.

Images