JPS6259906B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Technical Field of the Invention The present invention relates to an APD (avalanche photodiode), and particularly to a semiconductor light receiving device that improves the high frequency characteristics and multiplication noise of an APD at a low multiplication factor.

(2) Background of the technology Recently, it has been used as a photodetector for long-distance wireless relay transmission.
There are requests to increase sensitivity by applying APD. Analog transmission requires a higher S/N ratio than digital transmission, so the APD multiplication factor M is
Elements have come to be used in the low multiplication factor region of 10 or less. However, with such a low multiplication factor APD, the frequency characteristics deteriorate significantly and the reception sensitivity decreases, so ideally it should show good operating characteristics from a multiplication factor close to 1 without a decrease in the frequency band.
The appearance of APD was requested.

(3) Prior art and problems Figures 1a and b show a conventional schematic diagram of an N ⁺ PπP ⁺ structure APD and the relationship between the impurity concentration. It is known that the value is about 3×10 ¹⁵ cm ^-3 .

In an APD with such a structure, the P and π layers are active regions, and carriers generated in these regions contribute to the output photocurrent.

When a reverse bias is applied to an APD having the impurity concentration as described above, the internal electric field distribution becomes a state after reach-through, and the entire active region becomes a depletion layer. When the reverse bias voltage is low, reach-through is not reached and the P layer is not depleted, so the optically excited carrier cannot follow high-speed modulation.

(4) Purpose of the Invention In view of the above-mentioned conventional drawbacks, the present invention provides reach-through by selecting the ion implantation concentration and diffusion (drive) conditions into the P layer of an N ⁺ PπP ⁺ type silicon (Si) APD. The multiplication factor M _RT of is made low to around 1,
The purpose is to form an APD that exhibits good frequency characteristics with a low multiplication factor.

(5) Structure of the Invention The present invention is characterized in that an avalanche photodiode having a hyperstep junction structure includes:
The π layer concentration in the active region of the above hyperstep junction structure is 5
×10 ¹³ to 5 × 10 ¹⁴ cm ^-3 , and the P layer dose was 2 to 5 × 10 ¹² cm ^-2 by ion implantation, and the P layer width was 7 to 5 × 10 14 cm -3.
An object of the present invention is to provide an optical semiconductor light receiving device having a thickness of 9 μm.

(6) Embodiment of the Invention An embodiment of the present invention will be described below with reference to manufacturing process diagrams shown in FIGS. 2a to 2j.

In Fig. 2a, the Si-APD of the present invention has a P ^- epitaxial layer as a π layer 2 on a P ⁺ substrate 1 with an impurity concentration of 1 x 10 ¹⁴ cm ^-3 (5 x 10 ¹³ to 5 x 10 ¹⁴
cm ^-3 ), and the oxide film 3 is formed to a thickness of 1000 Å.

Next, as shown in FIG. 2b, a resist 4 is applied through a mask to open a window 5 in the light absorption layer portion of the APD portion, and then boron (B ⁺ ) is injected into the π layer by ion implantation to form a P layer. Form layer 6. At this time
The accelerating voltage for B ⁺ ions is 300KeV, 2.13×10 ¹² cm ^-2
In reality, this value is 2 to 5 × 10 ¹²
A range of cm ^-2 is preferred.

Next, as shown in FIG. 2c, heat treatment (drive-in) is performed at 1200°C. The time at this time is related to the multiplication factor and excess noise coefficient, as will be described later, depending on the heat treatment time. The implanted boron ions are doped into the π layer according to a Gaussian distribution, which will also be described later. The width of the P layer at this time is preferably 7 to 9 μm. At this time, an oxide film 3a is formed on the P layer.

Next, as shown in FIG. 2d, windows 7, 7 are formed in the oxide film 3 to serve as channel stoppers 8 for reducing dark current, and B ⁺ ions are implanted.

Next, by heat treatment (tribe-in) as shown in FIG. 2e, the boron ions implanted into the window openings 7 and 7 enter the π layer and form a P ⁺ region, forming the channel stopper 8. . At this time, new oxide films 3b, 3 are formed on the channel stopper.
b is formed.

Next, as shown in FIG. 2 f, windows 9 and 9 for the guard ring are made to diffuse phosphorus and form an N region.
By performing tribe-in as shown in FIG. 2g, oxide films 3c, 3c are formed at the window openings 9, 9, and guard rings 10, 10 are formed.

Next, in order to open a window for the N ⁺ junction of the light receiving part in the oxide film 3, a window 11 is made as shown in Fig. 2h, and phosphorus is diffused as shown in Fig. 2i ^.
Layer 12 is formed to have a thickness of 0.2 to 0.3 μm.

Finally, as shown in Figure 2j, SiO ₂ /Si ₃ N ₄ /
Aluminum electrode 1 after passivation 13 of SiO ₂ and anti-reflection coating 14 of Si ₃ N ₄
5 and 15.

In FIG. 2b when configured as described above,
When heat treatment is performed as shown in Figure 4c after B ⁺ ion implantation, N ⁺ P similar to Figure 1a and b is obtained.
The impurity concentration distribution of APD with πP ⁺ structure is shown in Figure 3a,
As shown in b, the impurity concentration distribution in the P layer region is given by a Gaussian curve 16. The measurement results are shown in FIG. In Figure 4, the horizontal axis shows the distance of the P layer region, and the vertical axis shows the impurity concentration.Curves 17a and 18a are for B ⁺ diffusion at a dose of 5 x 10 ¹² cm ^-2 , and curve 17a is for 7 hours. , 1200°C drive-in, and curve 18a is the case where drive-in was carried out at the same temperature for 15 hours.

In addition, curves 18b and 17b have a dose of 1×10 ¹²
Curve 17b is obtained by diffusing B ⁺ as cm ^-2 .
Curve 18b was driven in for 15 hours at 1200°C for 7 hours, and curves 20, 21, 22, 2
3: B ⁺ is ion-implanted at 300KeV and the dose is 2.13.
×10 ¹² cm ^-2 , curve 20 is 1200℃
drive-in (heat treatment) time for 5 hours, curve 2
1 is also 7 hours, curve 22 is 10 hours, curve 23
indicates when 15 hours is selected.

Figure 5 shows boron (B ⁺ ) at 300KeV and heat treatment temperature.
Curve 24 shows the relationship between the depletion layer width L (μm) on the horizontal axis and the multiplication factor M on the vertical axis when the temperature is 1200°C and the dose is 2.13×10 ¹² cm ^-2 . Curve 25 is for 10 hours and curve 26 is for 15 hours.

Furthermore, the one shown in FIG. 6 has the multiplication factor M on the horizontal axis and the excess noise coefficient F on the vertical axis, and the ion implantation conditions are the same as those in FIG.
28 and 29 have a tribe time of 7 hours and 10 hours respectively.
The time is assumed to be 15 hours.

As shown in Figures 4 to 6 above, N ⁺ PπP ⁺ type
If the heat treatment time of the P layer 6 after B ⁺ ion implantation in the SiAPD is too short, the surface concentration increases and the electric field increases, resulting in an increase in the excess noise factor F. Also, if the heat treatment time is too long, M _RT (multiplication factor at reach-through)
increases, and the frequency characteristics at low amplification factors (bias voltages) deteriorate.

In the present invention, if the amount of ions implanted into the P layer 6 and the heat treatment time are appropriately selected, reach-through RT is reached at an amplification factor close to 1 and extremely close to the origin as shown in FIG. 5, so the bias voltage is also extremely low. (Conventionally, the voltage was around 80V, but with the present invention,
reach-through RT (near 60V) is reached. That is, in the present invention, the P layer width may be selected to be 7 to 9 μm. Furthermore, it can be seen from FIG. 6 that the longer the drive time after implanting B ⁺ ions into the P layer 6, the greater the excess noise factor F decreases. Furthermore, as shown in FIG. 4, if the drive time is selected after setting the ion implantation dose to a constant value, a Gaussian distribution curve 1 for the P layer 6 can be obtained.
It can be seen that 6 can also be controlled relatively easily.

That is, in the present invention, by forming a relatively short (7 to 9 μm) P layer with a low concentration, the APD exhibits good high frequency characteristics at a low multiplication factor.
can be formed. In the above embodiment, N ⁺ PπP ⁺ type APD
As mentioned above, P ⁺ πPN ⁺ allows light to enter from the P side.
It is clear that the present invention can also be applied to molds and the like.

(7) Effects of the invention In view of the above-mentioned conventional ^drawbacks , ^the present invention provides
The layer concentration is selected to be low, the P layer is selected to have a relatively short length, and the M
Since _RT can be selected to a value close to about 1, high frequency characteristics are improved with a low multiplication factor, and a low-noise APD can be easily obtained.

[Brief explanation of the drawing]

Figures 1a and b show a schematic diagram and impurity concentration distribution of a conventional APD with N ⁺ PπP ⁺ structure.
Figures a to j are manufacturing process diagrams of the APD with the N ⁺ PπP ⁺ structure of the present invention, Figures 3 a and b are curves showing the schematic structure and impurity concentration distribution of the APD with the N ⁺ PπP ⁺ structure of the present invention, and Figure 4 The figure shows a curve showing the relationship between the impurity concentration and the distance of the P layer according to the present invention, FIG. This is a curve showing the relationship between 1... Substrate, 2... π layer, 3... Oxide film, 4...
...Resist, 5, 7, 9, 11...Open window, 6...
...P layer, 8...Channel stopper, 10...
Guard ring.

Claims (1)

[Claims] 1. In an avalanche photodiode having a hyper-step junction structure, the π layer concentration in the active region of the hyper-step junction structure is set to 5×10 ¹³ to 5×10 ¹⁴ cm ^-3 ,
1. An optical semiconductor light-receiving device characterized in that the P layer is ion-implanted at a dose of 2 to 5×10 ¹² cm ⁻² and the width of the P layer is 7 to 9 μm. 2. The optical semiconductor light receiving device according to claim 1, wherein the hyperstep junction structure is an N ⁺ PπP ⁺ type silicon avalanche photodiode.