JPH03126269A - Manufacture of inp avalanche photodiode - Google Patents

Abstract

PURPOSE:To improve characteristics and reproducibility and also a yield by conducting annealing at a specified temperature and for a specified time after implantation of Be ions in an InP layer. CONSTITUTION:An n<-> InP layer 2 is formed on an n<+> InP substrate 1, and in an n<-> InP layer 3 formed thereon, Be ions are implanted in the shape of a ring surrounding a light-sensing region of APD, with a resist pattern 4 used as a mask, so as to form a girdling 5. Thereafter a water is annealed to acti vate Be, the time for annealing being set to be five hours or longer at a tempera ture of 700 deg.C approximately. A much higher breakdown voltage can be attained for the girdling when the annealing is executed for a longer time. As for the ion-implanted Be, a p-n junction is formed only of a later component in the long-time annealing. Thereby a depth is made easy to control and a high reproducibility is attained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an InP-based avalanche photodiode (A
The present invention relates to a method for manufacturing PD), and particularly to a method for forming a guard ring thereof.

[Conventional technology]

An example of a method for forming a guard ring of a conventional InP-based APD will be described with reference to FIG. First, n” −I
An n-InP layer 2 is formed on an nP substrate 1, and Be is ion-implanted into the n--InP layer 3 formed thereon in a ring shape surrounding the light receiving area of the APD using a resist pattern 4 as a mask. Then, a guard ring 5 is formed.

The implantation conditions at this time are generally an acceleration energy of ~150 K.
e V , the dose is ˜7×10″c+n−′.

After this, the wafer is typically annealed (
heat treatment) to activate Be. The duration of this annealing is 20 to 30 minutes.

The concentration distribution of Be in the depth direction of the guard ring 5 formed under such conditions is as shown in FIG.

[Problem to be solved by the invention]

The breakdown voltage of the guard ring 5 of the APD needs to be higher than that of the light receiving device. However, when the guard ring 5 is formed under the above conditions, a sufficiently high breakdown voltage cannot be obtained with good reproducibility.

This invention was made to solve the above-mentioned problems, and aims to obtain APDs with good characteristics at a high yield.

[Means to solve the problem]

The method for manufacturing an InP-based avalanche I diode according to the present invention involves implanting Be ions into InPiJ, followed by annealing at approximately 700° C. for 5 hours or more.

[Effect]

In this invention, a guard ring with a high breakdown voltage can be obtained with good reproducibility by performing annealing for a long time.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

Fig. 1 is a diagram showing the relationship between the breakdown voltage of the guard ring and the annealing time of the present invention, and Fig. 2 is a diagram showing the concentration distribution of Be in the depth direction, and the annealing time is 5 hours. The temperature is approximately 700°C.

First, by performing long-time annealing as in the present invention, two qualitative differences that cannot be obtained with conventional annealing time will be explained below.

■ When the pn junction of the guard ring is assumed to be a one-sided stepped junction, the breakdown voltage is n - I n P impurity concentration NI
(this breakdown voltage is defined as vNil).

Furthermore, assuming a sloped junction, the breakdown voltage is determined by the concentration gradient a of Be (this breakdown voltage is V). In the pn junction of the guard ring, the impurity concentration distribution on the p side is sloped, and n The impurity concentration on the side is approximately constant. Incidentally, when the impurity concentration distribution is sloped in both p and n (slope type junction), the breakdown voltage is Vl.

Further, when the impurity concentration on the n side is constant and the impurity concentration on the p side is sufficiently higher than that on the n side (stepped junction), the breakdown voltage is V Nl! It is. The breakdown voltage v■ of the pn junction of the guard ring is a little higher than the higher of the above-mentioned V and VNII.

Here, if the concentration gradient a J' at the intersection of V Na and V is a 6, Va increases as a becomes smaller, but there is not much change when a) a6. However, in the region a(a, , with ao as the boundary), as a becomes smaller, V- suddenly becomes larger.

By the way, the Be concentration gradient a of the guard ring formed with the conventional annealing time is a□>ao, and the Be concentration gradient a2 of the guard ring formed with the annealing time of the present invention is ao)a, be. In other words, this long-time annealing provides a much higher breakdown voltage of the guard ring.

(2) The implanted Be is diffused by annealing. This Be has two components: a fast component that diffuses about 1 μff1 in the order of several tens of minutes, and a slow component that diffuses about 1 μm in the order of several hours. With conventional annealing times, a pn junction is formed by both fast and slow components, as shown in FIG. However, in this long-time annealing, a pn junction is formed only by the slow component as shown in FIG.

The depth of the pn junction formed by both the fast and slow components is difficult to control, and variations occur. Further, at this time, the curve of the concentration distribution of Be often becomes convex downward (having a negative curvature) near the pn junction.

However, the depth of a pn junction formed only by slow components is easy to control and has high reproducibility. Further, at this time, the curve of the concentration distribution of Be often becomes upwardly convex (having a positive curvature) near the pn junction.

For the above two reasons, when the annealing time of the present invention is used, a guard ring portion with a high breakdown voltage can be obtained with good reproducibility.

From Figure 5, Be concentration gradient a□ with conventional annealing time
is 6X10'°crn-', and from FIG. 3, the Be concentration gradient a2 at the annealing time of this invention is 3X1020cr.
It is n-'. Boundary point a0 is 4.3X1020C,,-
4, the above-mentioned relationship ax>ao>a2 holds true. As a result, a high breakdown voltage that cannot be obtained under conventional conditions can be obtained under the conditions of the present invention.

By the way, as the annealing time increases, the concentration gradient a
However, as shown in FIG. 1, when the annealing time becomes longer than 4 hours, ■- suddenly increases. This is because when the annealing time is 4 hours, a to ao, and when the annealing time is less than 4 hours, a) a,
, and the dependence of Va on the annealing time is small. Conversely, when the annealing time is longer than 4 hours, a (a 6), and the dependence of VB on the annealing time is large. In other words, when the annealing time is longer than 4 hours, the dependence of VB on the annealing time is large. Although Va does not become very high even if ) is made a little longer, a high vlI guard ring part can only be obtained by annealing for 5 hours or more, which is about 10 times the conventional method, as in the present invention.

Further, the curve of the concentration distribution of Be near the pn junction in FIG. 5 (conventional annealing time) has a downwardly convex shape (negative curvature). This is because, as described above, both the fast-diffusing component and the slow-diffusing component form a pn junction.

However, the Be concentration distribution curve near the pn junction in Figure 2 (annealing time of this invention) is upwardly convex (curvature is positive).
It has the shape of In other words, the pnJ & combination is formed only by the slow component, and characteristics with good reproducibility can be obtained.

〔Effect of the invention〕

As explained above, in the present invention, annealing is performed at approximately 700° C. for 5 hours or more after ion implantation, so that an InP-based APD with good characteristics can be obtained with good reproducibility.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between the breakdown voltage of the guard ring and the one-nil time for explaining one embodiment of the present invention, and FIG.
The figure shows B in the depth direction when implanted under the same conditions as in Figure 1, annealed at the same temperature, and annealed for 5 hours.
Figure 3 is a diagram showing the relationship between impurity concentration gradient and breakdown voltage, Figure 4 is a cross-sectional diagram to explain the method for forming the guard ring of APD, and Figure 5 is a diagram showing the concentration distribution of the impurity. A diagram showing the impurity concentration distribution in the depth direction of the ring,
6 and 7 are diagrams showing the impurity concentration distribution depending on the depth of the pn junction, showing the formation process of the pn junction with respect to the annealing time of the conventional method and the present invention. In the figure, 1 is an n''-InP substrate, 2 is an n-InP layer, 3 is an n''-InP layer, 4 is a resist pattern, and 5 is a guard ring. Figure 1

Claims (1)

[Claims] An InP-based method of implanting Be ions into an InP layer and then annealing to form a guard ring for an avalanche photodiode, characterized in that the annealing time after the ion implantation is approximately 5 hours or more at 700° C. Method of manufacturing an avalanche photodiode.