KR20070034747A - Diffusion Method Used in the Manufacturing Process of Avalanche Photodetectors - Google Patents

Abstract

The present invention is a novel diffusion method of forming a guard ring region and a main junction region in one diffusion process in an avalanche photodetector manufacturing process, and forming a pattern of a diffusion control layer that opens the main junction region on the clad layer. And forming a diffusion material layer over the entire structure, allowing the pattern to remain on the main junction region and the guard ring region, and diffusing the diffusion material layer so that the diffusion depths in the main junction region and the floating guard ring region are different from each other. Provide a method of diffusion.

Diffusion Control Layer, Diffusion Material Layer, Avalanche Photodetector

Description

Diffusion Method Used In Manufacturing Process Of Avalanche Photo Detector}

1 is a schematic cross-sectional view of an avalanche photodetector according to an embodiment of the present invention.

2A to 2E are diagrams for describing a diffusion process used in manufacturing an avalanche photodetector according to an embodiment of the present invention.

3A and 3B are graphs showing Zn diffusion profiles in InP grown by substrate, LPE, and MOVPE methods.

4A and 4B are graphs showing the diffusion profile of Zn in In _0.53 Ga _0.47 As grown by substrate, LPE, and MOVPE methods.

* Description of the main parts of the drawings

DESCRIPTION OF SYMBOLS 1 Avalanche photodetector 12 cladding layer

13: electric field control layer 14: transition layer

15: light absorption layer 16: substrate

18, 19: metal electrode 20: diffusion control layer

22: diffusion material layer

The present invention relates to a manufacturing technique of an avalanche photodetector, and proposes a new process for forming a guard ring region and a main junction region in a single diffusion process, thereby enabling a reliable avalanche photodetector manufacturing. will be.

Recently, due to the growing demand for high-speed, high-capacity optical communication systems and image processing systems, research on photodetectors used in these systems has been actively conducted. Most of these studies are about speeding up and increasing sensitivity of the photodetector.

Most conventional photodetectors were simple PIN photodetectors, but APD (Avalanche Photo Detector) replaced PIN photodetectors with various heterojunction structures as well as semiconductor growth technologies such as molecular beam epitaxy and metal organic chemical vapor deposition. Doing. APD has the advantage of having higher sensitivity than PIN photodetectors because it uses avalanche gain.

In general, avalanche photodetectors use ancillary structures that allow a high electric field to be formed only at the desired portion. In the conventional method, the guard ring is used to maintain a high electric field only at the center junction. The guard ring refers to a structure in which a small junction depth is formed around the main joint in order to prevent the bond breakdown easily occurring in the edge region of the main joint.

In this guard ring structure, since the diffusion depth of impurities (for example, Zn) is different from that of the absorbing layer, two Zn diffusion processes must be performed. However, since Zn diffusion processes are generally inferior in reproducibility, there is a problem that it is not easy to precisely control a desired structure in two successive diffusion processes.

In order to solve the above problems, Korean Patent No. 10-399050 (name of the invention "Avalanche Photodetector for Ultra High Speed Communication and Its Manufacturing Method") is a process of forming the guard ring and the main joint surface in one diffusion process. Is disclosed. According to this method, a sacrificial layer is formed to etch the semiconductor cladding layer of the present bonding surface region to a partial depth and to prevent diffusion through the interface between the mask layer and the semiconductor cladding layer in a subsequent process, and the main bonding surface region and the guard are formed. A mask with an open ring region is formed and diffusion is performed to form the guard ring and the main joining surface.

However, according to this conventional technique, the upper part of the device is not flat by the etching process, so process reliability is a problem in a subsequent process, and it is not easy to precisely control the diffusion region, and thus it is still difficult to manufacture a reliable avalanche photodetector. There is an inadequate problem.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a new process for forming the guard ring region and the main junction region in one diffusion process.

Another object of the present invention is to ensure the reproducibility of the impurity diffusion process in the manufacturing process of the avalanche photodetector.

As a technical means for solving the above problems, an aspect of the present invention is a diffusion method used in the avalanche photodetector manufacturing process, the step of preparing a compound semiconductor structure having a light absorption layer and a clad layer on a substrate ;

Forming a pattern of a diffusion control layer on the clad layer to open the main junction region;

Forming a diffusion material layer on the entire structure, wherein the pattern remains on the main junction region and the guard ring region; And

It provides a diffusion method used in the avalanche photodetector manufacturing process comprising the step of diffusing the diffusion material layer so that the diffusion depth in the main junction region and the floating guard ring region are different from each other.

Preferably, when the diffusion material layer is formed on the diffusion control layer, a portion of an edge of the diffusion material layer is formed to cover the diffusion control layer.

Meanwhile, when the clad layer is made of InP material, the diffusion control layer may be made of InGaAs or InGaAsP material.

Hereinafter, with reference to the accompanying drawings will be described a preferred embodiment of the present invention. However, the present invention is not limited to the embodiments disclosed below, but can be embodied in various forms, and only the present embodiments are intended to complete the disclosure of the invention and to those skilled in the art to fully understand the scope of the invention. It is provided to inform you. In the drawings, the same reference numerals refer to the same elements, and descriptions of overlapping elements will be omitted.

1 is a schematic cross-sectional view of an avalanche photodetector structure according to an embodiment of the present invention.

The avalanche photodetector is a light absorbing layer 15 sequentially formed on the substrate 16, a transition layer (grading layer, band gap control layer) 14, an electric field control layer 13, a clad layer 12, and a main junction. And a floating guard ring region B having the same polarity as that of the main junction region A. The metal electrodes 18, respectively, are disposed above the main junction region A and below the substrate 16. 20).

A manufacturing example of the avalanche photodetector will be described taking concrete materials of each layer as an example. The avalanche photodetector is an n-type InP substrate 16 and an undoped (hence n-type) InGaAs light absorption layer 15. A multi-layer InGaAsP transition layer 14 formed thereon, an n-type InP electric field control layer 13 formed thereon, and an undoped (and thus n-type) InP cladding layer 12 formed thereon. And a main junction region A and a floating guard ring region B, which are p-InP diffusion regions, through Zn diffusion through a portion of the InP cladding layer 12. Meanwhile, an InP buffer layer (not shown) may be further formed on the n-type InP substrate 16.

The most important step in the manufacturing process of such an avalanche photodetector is a process of forming the bonding surface region and the floating guard ring region by a diffusion process. According to the present invention, such a diffusion process can be easily performed. Hereinafter, a method of manufacturing the avalanche photodetector of the present invention will be described in detail with reference to the accompanying drawings.

2A to 2E are diagrams for describing a diffusion process used in manufacturing an avalanche photodetector according to an embodiment of the present invention.

Referring to FIG. 2A, a compound semiconductor structure including a light absorbing layer 15 and a cladding layer 12 is first prepared on a substrate 16. The compound semiconductor structure shown in FIG. 2 is formed on, for example, an n-type InP substrate 16, an n-type InGaAs light absorption layer 15, an InGaAsP transition layer 14, an n-type InP electric field control layer 13, and an upper portion thereof. The n-type InP cladding layer 12 may be provided. These films are sequentially grown on the n-type InP substrate 16 using crystal thin film growth equipment such as CVD or MBE devices.

Referring to FIG. 2B, the diffusion control layer 20 is formed in such a manner as to open a region where the main junction is to be formed on the compound semiconductor structure. The diffusion control layer 20 has a thickness of 10 to several hundred nm. Then, the diffusion material layer 22 is formed by patterning. The diffusion material layer 22 may be a general metal material such as Zn or a non-metal material. The diffusion material layer 22 is formed such that the pattern remains in regions where diffusion is to be made, in particular, the main junction region and the guard ring region. Preferably, a portion of the edge of the patterned diffusion material layer 22 can be formed into a structure covering the diffusion control layer 20 ("L" in FIG. 2B is a covered length). According to such a structure, a junction curvature becomes large and it is more effective to concentrate an electric field in a center part.

Referring to FIG. 2C, the diffusion process is performed in a state in which the structure of FIG. 2B is completed. In this case, the diffusion material layer 22 on the region where the diffusion control layer 20 is formed is diffused through the diffusion control layer 20, so that the diffusion depth of the diffusion material is reduced and the diffusion control layer 20 is formed. The diffusion material layer 22 over the unused region does not pass through the diffusion control layer 20, and thus diffusion occurs directly, so that diffusion occurs deeper. In this way, two diffusion profiles with different depths of diffusion process can be formed.

When the cladding layer 12 is made of n-type InP, it is preferable that the diffusion control layer 20 use InGaAs material or InGaAsP material. In this case, when Zn is used as the diffusion material, the diffusion depth of the main junction region and the guard ring region can be adjusted. The diffusion control layer 20 can control the fastness of the diffusion of the Zn material in accordance with the deposition method such as LPE or MOVPE, and the diffusion of the Zn material by the degree of doping amount of the material such as Si, S, Te, etc. (See "Dopant accumulation during substitional-interstitial diffusion in semiconductors", Applied Phys. Letter. Vol. 70, p613 (1997)).

 On the other hand, the diffusion rate of Zn in the P-type material increases as doping increases, and the diffusion rate in the n-type material is significantly slowed. Therefore, when the n-type InGaAs material or InGaAsP material is formed in the diffusion control layer 20 on the guard ring region with a layer having a predetermined thickness, the Zn diffusion speed in the main junction region is faster than the Zn diffusion speed in the guard ring region. Therefore, the main junction region and the guard ring region form two diffusion profiles having different depths of the diffusion process. On the other hand, the diffusion control layer 20 may be made of the same material as the cladding layer 12 and may perform the diffusion control function according to the present invention by appropriately selecting the doping material and adjusting the doping amount. More preferably, the diffusion control layer 20 is formed of a different material from the cladding layer 12 and the doping treatment of the diffusion control layer 20 in consideration of the etching selectivity, etc., in the subsequent process, to more effectively control the diffusion rate. It becomes possible. In addition, the degree of diffusion of the Zn material also varies depending on the thickness and material composition of the diffusion control layer 20, and also depending on the deposition method of the diffusion control layer 20, the diffusion process to be used, and the heat treatment temperature to be used during the diffusion process. The degree of diffusion of the Zn material is adjustable. The diffusion process may utilize boat diffusion, As doped or P doped spin-on diffusion, and In doped spin-on diffusion.

2D and 2E, after the diffusion process is completed, the pattern of the diffusion control layer 20 is removed. Thereafter, the metal electrodes 18 and 20 are formed on the bonding surface 11 and the substrate 16, respectively. For example, after forming the p-metal electrode 18 and the silicon nitride surface protective film (not shown), then lapping and polishing the back surface, the silicon nitride antireflective film (not shown) and the n- metal electrode (19) is formed and manufactured.

In order to examine whether the present invention is practically implemented, graphs showing that diffusion rates differ from each other by preparing a sample of InP and In _0.53 Ga _0.47 As and performing a Zn diffusion process on each of them are introduced.

3A and 3B are graphs showing Zn diffusion profiles in InP grown by the substrate, LPE, and MOVPE methods, and FIGS. 4A and 4B are Zn at In _0.53 Ga _0.47 As grown by the substrate, LPE, and MOVPE methods. Are graphs showing the diffusion profile of.

Referring to the graphs above, Zn diffusion at In _0.53 Ga _0.47 As is different from Zn at In _0.53 Ga _0.47 As, although the deposition degree and diffusion method of InP and In _0.53 Ga _0.47 As are different. Can be. Using this principle, InP can be used as a cladding layer and In _0.53 Ga _0.47 As can be used as a diffusion control layer in the fabrication of an avalanche photodetector.

On the other hand, the detailed manners for producing the samples shown in the graphs are described in detail as follows.

The samples were manufactured by laminating by a liquid phase epitaxy (LPE) or a molecular vapor phase epitaxy (MOVPE) method. The thickness is 3 to 4 um and the n-type doping concentration (Doping Concentration) is about 5 X 10 ¹⁵ cm ^{-3 without} doping. InP substrates (bulk) have a doping concentration of about 2 × 10 ¹⁵ cm ⁻³ . Types of performing the diffusion process are boat diffusion, As doped or P doped spin-on diffusion, and In doped spin-on diffusion.

In the case of the boat diffusion method, Zn diffusion is performed in a vacuum in a sealed graphite boat. The graphite boat consists of two thick graphite plates, one of which is a graphite plate with a recess for the wafer and two deep recesses mounted with a Zn source on either side, which is capped by another graphite plate. do. The boat is equipped with wafers and Zn ₃ P ₂ materials (Zn and P sources) and the graphite boat is fixed in vacuum thermal electrodes. Graphite boats generate heat by the current passing through the graphite and allow periodic heat treatment and cooling. The diffusion temperature was 560 degrees and InGaAs was 600 degrees. The time for the diffusion process was about 2 minutes when 80% of the diffusion temperature was used as the starting point and the end point.

In the case of spin-on diffusion, Zn diffusion occurs from about 0.3 um of spin-on SiO ₂ film. Spin-on solutions consist mainly of solvents, Silicic ester and methylglycol. The films contain ZnO (10 mol%), from which diffusion is possible. Diffusion barriers of group V elements are formed by adding Arsenic or phospheric acid to the spin-on solution for the purpose of preventing thermal decomposition of the semiconductor and investigating the effects of residual P or As. Diffusion experiments were performed with In ₂ O ₃ -doped spin-on films to evaluate the effect of In concentration in the diffusion process. After drying at room temperature or 200 degrees, a diffusion process was performed. The diffusion process was heat-treated in a furnace of flowing hydrogen atmosphere. The diffusion temperature was 600 ° C for InP and InGaAs, and the diffusion time was 2 minutes.

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the technical spirit of the present invention. Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification but should be defined by the claims.

According to the present invention, the guard ring region and the main junction region are formed in one diffusion process, whereas the guard ring region and the main junction region are formed in two diffusion processes in the impurity diffusion process in the manufacturing process of a typical avalanche photodetector. As a result, the process is simple and the reproducibility can be ensured, thus enabling the manufacture of reliable devices.

Claims (4)

In the diffusion method used in the avalanche photodetector manufacturing process, Preparing a compound semiconductor structure having a light absorption layer and a cladding layer on a substrate; Forming a pattern of a diffusion control layer on the clad layer to open the main junction region; Forming a diffusion material layer on the entire structure, wherein the pattern remains on the main junction region and the guard ring region; And And diffusing the diffusion material layer so that the diffusion depths in the main junction region and the floating guard ring region are different from each other. According to claim 1, And a portion of an edge of the diffusion material layer covering the diffusion control layer when forming the diffusion material layer on the diffusion control layer. According to claim 1, If the cladding layer is made of InP material, the diffusion control layer is used in the avalanche photodetector manufacturing process made of InGaAs or InGaAsP material. The method of claim 3, wherein The diffusion control layer is a diffusion method used in the n-doped avalanche photodetector manufacturing process.

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