JPH0496379A - Semiconductor device - Google Patents

Abstract

PURPOSE:To increase the heat generation of electron-hole pairs at the lower end section of a depletion layer extending from a P-N joint surface, and to improve sensibility by forming an insulating layer having specific thickness under an element forming region. CONSTITUTION:Light projected to a photodiode PD is reflected by each interface, the interface (a) of an insulating layer 15 and an element forming region 5n and the interface (b) of the insulating layer 15 and a silicon substrate 1p, of the insulating layer 15 by forming the insulating layer 15, and the attenuation of the quantity of light absorption in the depth direction of a depletion layer extending from a P-N joint surface (j) can be inhibited. The quantity of light absorption is increased more remarkably especially when the film thickness (t) of the insulating layer 15 is set so that light reflected by each interface (a) and (b) is maximized by mutual interference action-that is, reflected light is brought to phase-shifting relationship, in which reflected light is intensified mutually, thus augmenting the generation of electron-hole pairs at the lower end section of the depletion layer, then improving the sensibility of the photodiode PD.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a semiconductor device, particularly a PN in an element formation region.
The present invention relates to a semiconductor device in which a photodiode is formed by a junction.

[Summary of the invention]

The present invention provides a semiconductor device in which a light-receiving element is formed by a PN junction formed in an element formation region, in which an insulating layer having a predetermined thickness is provided under the element formation region, so that the PN junction surface is The generation of electron-hole pairs at the lower end of the depletion layer, which extends further, is increased to improve light-receiving sensitivity (quantum efficiency).

Further, in the semiconductor device of the present invention, one of the semiconductor regions forming the PN junction is formed in a comb-tooth shape so that the characteristics and integration degree of other elements are not deteriorated (depletion layer The light-receiving sensitivity is improved by increasing the spread of the light.

[Conventional technology]

Conventional semiconductor devices, especially semiconductor devices in which elements such as photodiodes and transistors coexist, have an N-type buried layer (42) selectively formed on a P-type silicon substrate (41), as shown in FIG. After forming, an N-type epitaxial layer (43) is formed on the entire surface, and then an element isolation region (44) is selectively formed.
A plurality of element formation regions (45) and (46) surrounded by
), and in one element formation region (45),
An NPN transistor (T
r) and also form an N-type impurity diffusion region (50) and a P-type impurity diffusion region (51) in the other element formation region (46), thereby forming a PN junction (j). A photodiode (PD) is formed.

In this photodiode (PD), a cathode electrode (52) is formed on the N-type impurity diffusion region (50), and an anode electrode (53) is formed on the P-type impurity diffusion region (51). , this photodiode (P
A reverse bias is applied to D). Note that (54) indicates an insulating layer made of Sin or the like.

[Problem to be solved by the invention]

Generally, the light receiving sensitivity (quantum efficiency) of a photodiode (PD) is determined by the density of electron-hole pairs generated within the depletion layer extending from the PN junction surface (j), and this density is depends on the amount of light absorbed.

However, as shown in the characteristic diagram of FIG. 11, the amount of light absorbed in a conventional photodiode (PD) has the characteristic that it is maximum at the surface and attenuates as it goes in the depth direction. The amount of light absorbed at the bottom end is small, and accordingly, the amount of electron-hole pairs generated at the bottom end of the depletion layer is also small, which is a disadvantage in that there is a limit to increasing the light receiving sensitivity of the photodiode (PD). There is.

By the way, a photodiode (P
In D), when the width of the depletion layer is narrow, only some minority carriers of the electron-hole pairs generated by light absorption contribute to the generation of photocurrent.

However, if the depletion layer is made thicker so that most of the light is absorbed within it, the generated electrons and holes will definitely be separated and drifted by the electric field within the depletion layer and will contribute to the photocurrent. This makes it possible to obtain high light-receiving sensitivity.

Furthermore, minority carriers generated outside the depletion layer become a diffusion current component and cannot be followed during high-speed response, making little contribution to photocurrent.

Therefore, in order to improve the performance (light receiving sensitivity, frequency characteristics) of a photodiode (PD), it is necessary to widen the depletion layer region.
It is desirable to take out only the carriers generated there.

On the other hand, in the structure of a typical photodiode (PD), as shown in the figure, the photodiode (PD) is
PD), the concentration of the epitaxial layer (43) is the same as that of other elements (NPN here) transistors (Tr).
) cannot be selected freely in consideration of the characteristics of If the concentration of the layer (23) is relatively high, the depletion layer cannot be sufficiently expanded, and high light-receiving sensitivity cannot be obtained. Therefore, if it is desired to obtain a large photocurrent, it is necessary to increase the area of the device, which is a disadvantage in that it becomes a major obstacle in increasing the degree of integration of the device.

The present invention has been made in view of the above points, and its purpose is to increase the generation of electron-hole pairs at the lower end of the depletion layer extending from the PN junction surface, thereby increasing the light receiving sensitivity. An object of the present invention is to provide a semiconductor device that can be improved.

Another object of the present invention is to provide a semiconductor device that can increase the spread of the depletion layer and improve the light-receiving sensitivity without deteriorating the characteristics or the degree of integration of other elements.

[Means to solve the problem]

The present invention provides a semiconductor device (AI) in which a light receiving element (PD) is formed by a PN junction (j) formed in an element formation region (5), in which a predetermined thickness is provided below the element formation region (5). An insulating layer (15) having L is provided and configured.

Further, the present invention provides that in the semiconductor device (A2), one semiconductor region (lO) forming the PN junction (j)
is formed into a comb-like shape.

[Effect]

According to the above-described configuration of the present invention, since the insulating layer (15) is provided under the element formation region (5), the incident light is transmitted to each interface (a) and (b) of the insulating layer (15). The amount of light absorbed at the lower end of the depletion layer increases. Furthermore, if the thickness t of the insulating layer (15) is set, for example, so that the reflected light from each interface (a) and (b) is maximized by mutual interference, the amount of light absorption at the lower end of the depletion layer can be increased. more and more,
The generation of electron-hole pairs at the lower end of the depletion layer increases, and the light receiving sensitivity can be improved.

Furthermore, according to the above-described configuration of the present invention, one of the semiconductor regions (10) forming the PN junction (j) is formed in a comb-teeth shape, so that the area of the PN junction surface (j) increases; Thereby, the spread of the depletion layer extending from the PN junction surface (j) can be increased. Therefore, the element formation region (5
) It is possible to increase the spread of the depletion layer without changing the overall concentration and film thickness, and improve the light-receiving sensitivity of the photodetector (PD) without deteriorating the characteristics and integration degree of other elements. I can do it.

〔Example〕

Hereinafter, the present invention will be explained in detail with reference to FIGS. 1 to 9. In each semiconductor region (element formation region, impurity diffusion region, etc.), if the conductivity type is P type, a subscript P is added to the code, and if the conductivity type is N type, a subscript n is added to the code.

FIG. 1 is a configuration diagram showing a semiconductor device (A,) according to a first embodiment.

As shown in the figure, this semiconductor device (A1) includes, for example, an N-type semiconductor region (2n) on a P-type silicon substrate (lp).
By selectively forming a P-type element isolation region (3p) in the element isolation region (3p), a plurality of element formation regions (4n) and (5n) surrounded by this element isolation region (3p) are formed. NPN (NPN) consisting of an N-type collector extraction region (6n), a P-type base region (7p), and an N-type emitter region (8n) surrounded by the base region (7p) in the element formation region (4n). While forming a transistor (Tr),
By forming an N-type impurity diffusion region (9n) and a P-type impurity diffusion region (Lop) in the other element formation region (5n), a photodiode (PD) composed of a PN junction (j) is formed. It forms. NPN transistor (
Tr) base region (7p) and photodiode (PD
) P-type impurity diffusion region (Lop) and NPN l
- Collector extraction region (6n) and emitter region (8n) of transistor (Tr) and N of photodiode (PD)
The type impurity diffusion regions (9n) are formed simultaneously.

In the photodiode (PD), an anode electrode (11) is placed on the P-type impurity diffusion region (10p).
, a cathode electrode (1) is placed on the N type impurity diffusion region (9n).
2) is formed so that a reverse bias is applied to this photodiode (PD). Furthermore, (13)
indicates an insulating layer made of SiO□ or the like, and (14n) indicates an N-type buried layer.

However, in this example, a P-type silicon substrate (1p
) and the element formation region (5n), an insulating layer (15) made of, for example, SiO□ is formed.

According to this first embodiment, due to the formation of the insulating layer (15), the light incident on the photodiode (PD) is transmitted through each interface of the insulating layer (15), that is, between the insulating layer (15) and the element forming area ( 5n) and the interface (b) between the insulating layer (15) and the silicon substrate (1p),
Attenuation of the amount of light absorbed in the depth direction of the depletion layer extending from the PN junction surface (j) can be suppressed. As shown in the characteristic diagram of FIG. 2, in a normal photodiode without the insulating layer (15), the curve I (
As shown by the broken line), the amount of light absorbed decreases as the depth increases. However, as in this example, an insulating layer (15) is placed between the silicon substrate (1p) and the element formation region (5n).
), as shown by the curve (solid line), the amount of light absorbed increases in the depth direction with the minimum at the middle light of the element formation region (5n), compared to the normal case. An increase in absorption amount corresponding to the shaded area (C) can be expected.

In particular, the film thickness t of the insulating layer (15) is set at each interface (a) and (
If the setting is made so that the reflected light in step b) is maximized by mutual interference, that is, the reflected light has a mutually reinforcing phase relationship, the increase in the amount of light absorption becomes more remarkable, and the depletion layer The generation of electron-hole pairs at the lower end increases, and the light receiving sensitivity of the photodiode (PD) improves.

Next, a method for manufacturing the semiconductor device (A,) according to the first embodiment will be explained with reference to FIG.

First, as shown in FIG. 3A, an N-type silicon substrate (2
1n) is prepared, and an N-type high concentration region, ie,
After forming an N-type buried layer (14n), the surface is oxidized to form a SiO□ film (15a). At this time, Si
n, and the film thickness of the film (15a) is t. In addition, if frequency characteristics are not an issue, use the N-type buried layer (14n) as described above.
does not need to be formed.

Next, as shown in FIG. 3B, another P-type silicon substrate (1p) is prepared, and the surface of this silicon substrate (1p) is oxidized to form a SiO□ film (15b). The thickness of the SiO□ film (15b) at this time is defined as t2.

Next, as shown in FIG. 3C, using a normal wafer bonding technique, the two silicon substrates (21n) and (1p) are bonded with the Si0g films (15a) and (15b) facing each other, respectively. and paste it together.

In this example, the 5tO2 films (15a) and (15b) are arranged so that the reflected light at each interface (a) and (b) of the 5iOzWA (15a) and (15b) with respect to the incident light is maximized.
It is preferable to select the total thickness t (-t+ + tz) of the film. Specifically, as shown in the characteristic diagram of FIG.
is selected as the film thickness t.

Next, as shown in the third diagram, a silicon substrate (21n)
After polishing the main surface to a desired thickness, a P-type element isolation region (3p) is formed, and an element formation region (5n) surrounded by the element isolation region (3p) is formed.

After that, a P-type impurity diffusion region (10p), an N-type impurity diffusion region (9n), a surface protection film (insulating film) (13), an anode electrode (11) and a cathode made of Af etc. are formed in the element formation region (5n). An electrode (12) is formed to obtain a semiconductor device t(At) according to the first example.

According to this manufacturing method, a silicon substrate (
A semiconductor device (80) in which an insulating layer (15) is interposed between the element formation region (5n) and the semiconductor device (A) can be easily formed.
In order to further increase the reflection of light, P in No. 3-8
The surface of the silicon substrate (1p) may be silicided in advance before the oxidation treatment of the silicon substrate (1p).

Next, the semiconductor device (A2) according to the second embodiment, especially the PN
The structure of a photodiode (PD) with an improved junction surface will be explained based on the process diagram of FIG.

For this photodiode (PD), first, as shown in FIG. 5A, an N-type buried layer (14n) and a P-type buried layer 1i (22p) are formed on a P-type silicon substrate (1p).

Next, as shown in FIG. 5B, after forming an N-type epitaxial layer (23n) on the silicon substrate (1p),
Upper element bone 1tl reaching the P-type embedded layer (22p)
A region (3p) is formed, and a P-type buried layer (2p) is formed.
In the element formation region (5n) surrounded by the element isolation region (3p) and the element isolation region (3p), there is a relatively narrow P-type impurity diffusion region ( 24P)
Form multiple pieces. The element isolation region (3p) and the impurity wave 'h' region (24p) are formed using the same mask.

Next, as shown in FIG. 5C, a relatively shallow P-type impurity diffusion region (10p) is formed in the element formation region (5n), and as shown in FIG. , so as to include the plurality of previously formed impurity diffusion regions (24p) in its surface portion. That is, each impurity diffusion region (lop) and (24p) form a comb-like shape to increase the area of the PN junction surface (j). The impurity diffusion region (Lop) is an NP (not shown).
N) Formed at the same time as forming the base region of the transistor. Thereafter, an N-type impurity diffusion region (9n), an insulating film (13), an anode electrode (11) and a cathode electrode (12) made of M or the like are formed to obtain a photodiode (PD) according to the second embodiment. Here, the N-type impurity diffusion region (9n) is formed simultaneously with the collector lead-out region and emitter region of an NPN (not shown) transistor.

According to this second embodiment, the element formation region (5n) and the PN
Since the semiconductor region forming the junction (j) is formed in a comb-like shape with a plurality of impurity diffusion regions (24p) extending in the depth direction and one impurity diffusion region (10p) extending in the plane direction, the PN As the area of the bonding surface (j) increases, the spread of the alternating layers extending from the PN bonding surface (j) increases accordingly. Therefore, in the element formation region (5n), that is, in this second embodiment, it is possible to increase the spread of the depletion layer without changing the concentration and film thickness of the entire epitaxial layer (23n), and other elements ( NPN not shown
The light-receiving sensitivity of a photodiode (PD) can be improved without deteriorating the characteristics and degree of integration of transistors, etc.).

Next, the structure of a semiconductor device, particularly a photodiode (PD), according to a modification of the second embodiment will be described with reference to FIG.

As shown in the figure, this photodiode (PD) has a configuration in which the conductivity type of each semiconductor region in the second embodiment is reversed. Also in this modification, the N-type impurity diffusion region (Ion) forming the PN junction (j) with respect to the P-type element formation region (5p) is formed in a comb-like shape, so that the PN junction surface (j) The area of the photodiode (PD) increases, and the light receiving sensitivity of the photodiode (PD) can be improved.

Next, an example of how to make the above modification will be explained based on the process diagram of FIG. 8.

First, as shown in FIG. 8A, a P-type silicon substrate (1
p) A P-type buried layer (31p) is selectively formed on the layer p). After that, as shown in FIG. 8B, a silicon substrate (1p
) After forming an N-type epitaxial layer (23n) on the device isolation region (3p), a P-type element isolation region (3p) is formed, and a plurality of element formation regions (Ion) surrounded by the element isolation region (3p) are formed.
) and (4n) are formed. At this time, in one element formation region (Ion), a P-type buried layer (
31p) are formed, and this structure constitutes a photodiode (PD) shown in FIG. After this, for example, in the other element formation region (4n), a P-type well region (32p), a P-type collector extraction region (6p), an N-type base region (7n), and a P-type well region (32p) are formed.
A PNP transistor (Tr) consisting of a type emitter region (8p) is formed.

According to this modification, a highly concentrated PN junction (j) is formed at a position relatively deeper than the surface, so that frequency characteristics can be improved. In addition, since the element formation region (Ion) forming the PN junction (j) has a comb-like shape,
It is also possible to improve the light receiving sensitivity of the photodiode (PD).

In each of the above embodiments, that is, in the first embodiment, the amount of light absorbed at the lower end of the depletion layer is increased to increase the light receiving sensitivity of the photodiode (PD), and in the second embodiment, the light receiving sensitivity of the photodiode (PD) is increased. Although the area of the surface (j) was increased to increase the light receiving sensitivity of the photodiode (PD), as shown in FIG. 9, the structure of the first embodiment and the structure of the second embodiment are of course A combination is also possible. In this case, the synergistic effect of the effect of the insulating layer (15) and the effect of the comb-like shape of the P-type impurity diffusion region (Lop) makes it possible to further improve the light-receiving sensitivity.

〔Effect of the invention〕

According to the semiconductor device according to the present invention, the generation of electron-hole pairs at the lower end of the depletion layer extending from the PN junction surface is increased,
The light receiving sensitivity of the light receiving element can be improved.

Further, according to the semiconductor device according to the present invention, the light-receiving sensitivity of the light-receiving element can be improved by increasing the spread of the depletion layer without deteriorating the characteristics and integration degree of other elements.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing a semiconductor device according to the first embodiment, FIG. 2 is a characteristic diagram showing changes in the amount of light absorption in the depth direction of this embodiment, and FIG. 3 is a diagram showing the structure of the semiconductor device according to the first embodiment. A process diagram showing an example of a method for manufacturing a semiconductor device, FIG. 4 is a characteristic diagram showing changes in light reflectance with respect to film thickness of an insulating layer, and FIG. 5 is a process diagram showing the configuration of a semiconductor device according to a second embodiment. Fig. 6 is a plan view showing the main parts, Fig. 7 is a configuration diagram showing a modification of the second embodiment, Fig. 8 is a process diagram showing an example of its manufacturing method, and Fig. 9 is a diagram showing another embodiment. FIG. 10 is a block diagram showing a conventional semiconductor device, and FIG. 11 is a conventional characteristic diagram showing changes in the amount of light absorbed in the depth direction. (AI) and (^2) are semiconductor devices, (PD) is a photodiode, (1p) is a silicon substrate, (3p) is an element isolation region, (4n) and (5n) are element formation regions, (9
n) is an N-type impurity diffusion region, (10ρ) and (24p
) is a P-type impurity diffusion region, (11) is an anode electrode,
(12) is a cathode electrode, (14n) is an N-type buried layer, (15) is an insulating layer, and (j) is a PN junction (plane).

Claims (1)

[Scope of Claims] 1. A semiconductor device in which a light-receiving element is formed by a PN junction formed in an element formation region, in which an insulating layer having a predetermined thickness is provided below the element formation region. 2. A semiconductor device in which a light-receiving element is formed by a PN junction formed in an element formation region, in which one semiconductor region forming the PN junction is formed in a comb-like shape.