JPS63215084A - Semiconductor photodetector - Google Patents

Abstract

PURPOSE:To control the concentrations of a semiconductor layer, wherein a P-N junction and guard rings are formed, and a semiconductor layer having a concentration lower than that of this semiconductor layer with high precision and to improve the yield of the title element by a method wherein both semiconductor layers are formed as a substrate through a joint layer. CONSTITUTION:A P<--> semiconductor layer 2 is deposited on the surface of a P<+> Si substrate 1 and the surface is mirror-polished. Then, the surface of a P<-> Si semiconductor substrate 3 prepared separately from the substrate 1 is mirror-polished and the layer 2 and the substrate 3 are closely bonded to each other to form a composite semiconductor substrate. Subsequently, a thermal oxide film 5 is formed on the surface of the substrate 3 and after apertures are provided at the programming positions for forming guard rings, deposition of of a BSG film 7 and diffusion of B are performed to form the guard rings 6. Then, an annular channel stopper 9 and an N<+> region 10 are formed and a passivation film 11 and a rear electrode 12 are provided to complete an avalanche photo diode.

Description

DETAILED DESCRIPTION OF THE INVENTION <Object of the Invention> (Industrial Application Field) The present invention relates to an improvement in an avalanche photodiode that is used as a light receiving element in optical communications and exhibits high-speed response and amplification.

(Prior Art) Avalanche photodiodes, which provide high-speed response and amplification, have recently been increasingly used as light-receiving elements for light sources that emit wavelengths of 600 nm to 11,000 nm, especially 800 nm, that is, for optical communications.

The structure of this avalanche photodiode will be explained with reference to FIG. 2.
+Prepare the semiconductor substrate 20. This is because the good noise characteristics required for this diode are determined by the ionization rate ratio in the semiconductor single crystal.

In SL, since the ionization rate of electrons is higher than the ionization rate of holes, and it is necessary to select electrons as minority carriers in the avalanche amplification region, a P conductivity type semiconductor substrate is usually used.

This P″″ semiconductor substrate 20 contains B by a normal epitaxial growth method, and has a specific resistance of 100 to 300Ω-c.
A P-semiconductor layer 21 is deposited, and a P-semiconductor layer 22 functioning as an amplification layer is further deposited by an epitaxial growth method. The specific resistance of this P-semiconductor layer is 10~
It is 20Ω-am and contains B as an impurity.

Prior to forming this p-semiconductor layer, a P+ buried layer 23 is provided in the P-semiconductor layer 21 by a conventional method. Specifically, a predetermined position of the insulating layer covering the surface of the P-semiconductor layer 21 is opened, and B is injected into the exposed P'' semiconductor layer 21 at a dose of approximately 2 x 10''/cm''. mosquito.

A resist may be used as this mask.

Also, vapor phase diffusion may be used.

A guard ring 24, a channel stopper 25, and an N4' region 26 are formed on this P-semiconductor layer 22. First, the surface of the P- semiconductor layer 22 is coated with an insulating film 27 by a normal thermal oxidation method, and then an opening is made at the position where the P+ guard ring 24 is planned to be installed, and two BSG films are patterned in eight layers and then contained. 10101 by solid phase diffusion of B
It is formed at a surface concentration of about 9ato/cc.

Next, the predetermined position of the insulating film 27, that is, the channel stopper 2
After removing the portion corresponding to position 5, PAsSG film 2
After turning the membrane surface 8, P and As containing P and As are solid phase diffused to form a channel stopper 25 having a surface concentration of about 10'' atoms/cc.

Next, the insulating film 27 corresponding to the N+ region 26 is dissolved and a new PAsSG film 28 is turned by 8 film surfaces, and the contained P and As are diffused to form an N+ of about 10" atoms/cc.
A region 26 is formed. However, the diffusion depth 4 of this N+ region 26 is considerably deeper than that of the channel stopper 25. -More Final Pa5sivatio
A CVD film 29 of Undop6 was deposited for n,
Further, an electrode 30 is provided on the back surface of the P+ semiconductor substrate 20 to complete an avalanche photodiode.

(Problems to be Solved by the Invention) This avalanche photodiode has the advantage that the P-semiconductor layer 21 and the P-semiconductor layer 22, which operate as a light absorption layer and an amplification layer, can be designed independently by epitaxial growth. , the concentration and thickness of each of these semiconductor layers are determined by this growth method.

Moreover, since the semiconductor layers 21, 22 and the P+ buried layer 23 have a large concentration difference, auto doping occurs during the epitaxial growth process, and the P+ buried layer 23 has a large concentration difference.
- or P- There is a problem in that so-called misfit occurs in the semiconductor layer, and this causes local breakdown, which deteriorates the yield. Furthermore, problems with concentration control and the like cause deterioration in operating voltage and noise characteristics, which also lowers yield.

An object of the present invention is to provide a novel semiconductor light-receiving device that eliminates the above-mentioned drawbacks.

<Structure of the Invention> (Means for Solving the Problems) In order to achieve this object, in the present invention, a P''''- semiconductor layer is formed on a P+ semiconductor substrate by an epitaxial method, and a P'''' semiconductor layer prepared on the other hand is A method is adopted in which a mirror surface provided on the substrate and a mirror surface formed on the surface of this p-semiconductor layer are bonded to form a single semiconductor substrate, and an N+ region channel stopper and guard ring are formed on this p-semiconductor layer. .

(Function) By the way, a technology has already been developed for bonding and integrating semiconductor substrates that have different concentrations of impurities and are of the same type or different conductivity type, but this technology cannot be applied to semiconductor photodetectors. The present invention has been completed based on the fact that the amplification effect and noise characteristics are significantly improved and the yield is improved.

(Example) An example according to the present invention will be described in detail with reference to FIG. 1, and new numbers will be assigned to descriptions that overlap with those in the conventional technology section.

A P"Si semiconductor substrate 1 containing B and having a specific resistance of about 5 mΩ-cm is prepared, and the surface thereof contains B and has a specific resistance of 100 mΩ-cm.
~300Ω-cIl P-semiconductor layer 2 with a thickness of 30-40 μm
accumulate. This deposition is performed using a known epitaxial growth method, and the auto doping that occurs at this time is at most about 5 μm, so it is not a problem. 3
After preparation, proceed to the above-mentioned bonding process.

This P″″-semiconductor layer 2 and I″Si semiconductor substrate 3
The surface is polished to a mirror surface with a roughness of 500 Å or less, and depending on the surface condition after this polishing process, oils and fats are dissolved out in a pretreatment process. Next, after rinsing with clean water for several minutes, excess moisture is removed by dehydration treatment such as spinner treatment, leaving the moisture that is assumed to have been adsorbed on the mirror surface as it is. 100 evaporates
Avoid heating and drying above 0℃.

The P-5i semiconductor substrate 3 and the P-semiconductor layer 2 that have undergone this treatment are placed in a clean atmosphere of class 1 or lower, for example, and are brought into close contact with each other with substantially no foreign matter (dust) intervening between the mirror surfaces. A composite semiconductor substrate is formed by bonding. This composite semiconductor substrate can be heat-treated at 200°C or higher, preferably 1000°C to 2000°C, to increase the bonding strength, and the atmosphere during the bonding process can be air, oxygen, or a mixture of both. These atmospheres can also be used to increase bonding strength.

By the way, in this bonding process, polar groups are formed by the water washing process on the mirror surface, and the bonding caused by this causes B
It is assumed that a composite semiconductor substrate is obtained because a bonding layer 4 different from the ulkM weave is formed.

Since the boundary of this bonding layer 4 may change depending on the applied heat load, the present invention does not only mean clearly dividing the boundary, but also includes this changing state. It is.

A step of forming a guard ring 6, a channel stopper 9, and an N+ region 10 starts from the surface of this composite semiconductor substrate, that is, the surface of the P- semiconductor substrate 3 toward the inside.

A thermal oxide film 5 is formed on the surface of this P ~ semiconductor substrate by a normal method, and an opening is made by a known photolithography method at a position corresponding to the position where an annular Pigard ring is to be formed.
A film 7 is deposited and patterned, and B contained therein is diffused in a solid phase to form a guard ring 6 at a surface concentration of about 1'O'' atoms/cc.

Next, the thermal oxide film 7 corresponding to the planned formation position of the N" channel stopper 9 is removed and exposed using a conventional method.
A PAsSG film 8S is coated on a semiconductor substrate, and after further patterning, P and As are diffused to a surface concentration of about 101.
An annular channel stopper 9 of approximately 9 atoa+s/cc is formed.

Subsequently, the thermal oxide film 5 and PAsS corresponding to the N+ region 10 are formed at the middle position of this channel stopper 9.
After removing the G layer, a new PAsSG layer is coated and patterned, and the P and As are in-phase diffused to form the N4'' region 10. The depth of the N+ region 10 is far greater than that of the channel stopper 9. The shape is small and continuous, and the P content is larger than the As content.

Further, an undoped CVD film 11 is deposited as a final Pa5sivation layer 11, and an Au-V-Ni electrode 12 is provided on the back surface of the P+ semiconductor substrate to complete an avalanche photodiode.

<Effects of the Invention> The operating voltage and noise characteristics, which are important characteristics of an avalanche photodiode, are determined by the punch-through voltage and breakdown voltage of the p-grown semiconductor layer, which functions as a light absorption layer, and the amplification layer, that is, the p-semiconductor, when the operating voltage is applied. Depends on the voltage strength of the board. However, it is the concentration profile obtained by these two layers that determines these characteristics, and since the present invention uses bonding technology to obtain a structure that is extremely close to the design value, devices that satisfy these characteristics have a high yield. It became possible to form it well.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a semiconductor light receiving element according to the present invention, and FIG. 2 is a sectional view showing its conventional structure.

Claims (1)

[Claims] A semiconductor substrate exhibiting a certain conductivity type, a grown semiconductor layer of a conductivity type with a low concentration provided on the surface of the semiconductor substrate, and a semiconductor layer of a certain conductivity type having a concentration intermediate between the grown semiconductor layer and the semiconductor substrate and laminated on the grown semiconductor layer. a bonding layer provided at the boundary between the semiconductor layer of a certain conductivity type and the grown semiconductor layer of the certain conductivity type; a region of the opposite conductivity type formed from the surface of the semiconductor layer of the certain conductivity type inward; and a region of the opposite conductivity type. and a guard ring provided surrounding the PN junction formed between the certain conductivity type semiconductor layers.