JPS58170078A - Semiconductor photodetector - Google Patents

Abstract

PURPOSE:To form an avalanche photodiode (APD) which exhibits preferable frequency characteristics with low amplification factor by setting the density of a pi layer of an active region of a hyper abrupt junction structure to a specific value, ion implanting the dosage of a P type layer in a specific value, and setting the width of the P type layer to the specific value, thereby decreasing the amplification factor MRT of reach-through to the vicinity of 1. CONSTITUTION:An Si-APD is selected in impurity density of a P<-> type epitaxial layer to 1X10<14>cm<-3> to 5X10<14>cm<-3> with a P<+> type substrate 1 as a pi layer 2, thereby forming an oxidized film 3 of 1,000Angstrom thick. Then, a resist 4 is coated through a mask, a window 5 is opened at the light absorbing layer part of the APD part, and boron ions are implanted by ion implantation to the layer to form a P type layer 6. The accelerating voltage of the B<+> ions at this time is 300keV and the implantation amount of 2.13X10<12>cm<-2>, and this value is actually preferred in the range of 2-5X10<12>cm<-2>. Then, it is heat treated at 1,200 deg.C. The time at this time relates to the amplification factor and the excess noise coefficient. The implanted boron is doped in the pi layer in response to the gauss distribution. The width of the P type layer at this time is preferably 7-9mum. An oxidized film 3a is formed on the P type layer at this time.

Description

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

(2) Background of the technology Recently, there has been a demand for high sensitivity by applying APD as a light receiving element for long-distance wireless relay transmission. Since analog transmission requires a higher S/N than digital transmission, APD elements are now used in a low multiplication factor region where the multiplication factor M is 10 or less. However, with such a low multiplication factor APD, the frequency characteristics deteriorate significantly and the receiving sensitivity decreases, so ideally it should exhibit good operating characteristics from a multiplication factor close to 1 without a decrease in the band of frequency characteristics. AP
The appearance of L) was desired.

(3) Prior art and problems Figure 1 fan, (bl is N”PπP+ structure APD (7
) This shows a conventional schematic diagram and the relationship between impurity concentrations. It is known that the P layer is epitaxially grown to a thickness of 6.8 .mu.m and the impurity concentration is approximately 3.times.10"cm.sup.-".

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 an impurity concentration as described above, the internal electric field distribution becomes reach-through (Reach-through).
Through ), 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 carriers 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 purpose of this invention is to lower the multiplication factor MRT to around 1 and form an APD that exhibits good frequency characteristics at a low multiplication factor.

(5) Structure of the Invention The present invention is characterized in that, in an avalanche photodiode having a hyperstep junction structure, the π layer concentration in the active region of the hyperstep junction structure is set to 5×to13 to 5×1.
0'LAem-3, and the dose of the P layer is 2 to 5XI.
It is an object of the present invention to provide an optical semiconductor light-receiving device in which the width of the second layer is 7 to 19 μm by implantation of Q'' cm.

(6) Embodiment of the Invention Hereinafter, an embodiment of the present invention will be described with reference to the manufacturing process diagrams shown in FIGS.

In Fig. 2+8), the 5t-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 I x 10'' low (5 x 10'' to 5 x 1
01φcm”) and the oxide film 3 is
0 person thickness is formed.

Next, as shown in Fig. 2~), 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.
Form layer 6. At this time, the accelerating voltage of B+ ions is 3
00 K eν, 2.13×10″cm−”, and in practice this value is preferably in the range of 2 to 5×10 12 □d2.

Next, heat treatment (drive-in) is performed at 1200°C as shown in Figure 2 (C1).The time at this time is related to the multiplication factor and excess noise coefficient as described later depending on the heat treatment time.Ion-implanted boron is doped into the π layer according to the Gaussian distribution described later.The width of the two layers at this time is preferably 7 to 9 μm.At this time, oxidized 1
13a is formed.

Next, as shown in FIG. 2 +dl, a window 77 is formed in the oxide film 3 to serve as a channel stopper 8 for reducing dark current, and B+ ions are implanted.

Next, heat treatment (drive-in) is performed as shown in Figure 2(e).
As a result, the boron ion implanted in the window opening 7.7 becomes π
The channel stopper 8 is formed by penetrating into the layer and forming a P+ region. At this time, new oxide 1113b is formed on the channel stopper.

3b is formed.

Next, as shown in Fig. 2(g), windows 9 and 9 for the gartling are made to diffuse phosphorus and form an N region.
), the oxide films 3C, 3c are formed at the 9° 9 part of the window opening, and the guard rings 10, 10 are formed.

Next, in order to open a window for the N4'' junction of the light receiving part on the oxide film 3, a window 11 is made as shown in Figure 2 (h), and phosphorus is diffused as shown in Figure 2 (il). N + 12 to 0
．． 2~0.3μ! Form to n thickness.

Finally, as shown in Figure 2 (J), SiO2/S i
3 N a / S i O2 passivation 13
And an aluminum electrode 15.15 is formed after a non-reflective coating 14 of S i 3 Na.

In FIG. 2(b) when configured as described above, B+
After ion implantation, heat treatment was performed as shown in FIG. 4(C), resulting in an N+P structure similar to that shown in FIGS.
The impurity concentration distribution of APD with πP4″ structure is shown in Figure 3+a)
, tb), the impurity concentration distribution in the P layer region is given by a Gaussian curve 16. The measurement results are shown in FIG. In FIG. 4, the horizontal axis represents the distance of the P layer region, and the vertical axis represents the impurity concentration. Curves 17a and 18a represent the dose 115.
B+ was diffused as XIQcsn, curve 17a was driven in at 1200°C for 7 hours,
d is the case where the product was driven in for 15 hours at the same temperature.

Moreover, curves 18b and 17b represent the dose amount I
curve 17b is 12
00℃ for 7 hours, song IQ18b was driven in for 15 hours, curve 20.21.22.23 is B+
ion implantation at 300KeV with a dose of 2.13X
Curve 20 is 1200 when it is 10" cm
℃, the drive-in (heat treatment) time was selected to be 5 hours, curve 21 was 7 hours, curve 22 was 10 hours, and curve 23 was 15 hours.

Figure 5 shows boron (B+) at 300K eV, heat treatment temperature 1200°C, dose il 2.13X 10=CIl
-'', the horizontal axis is the depletion layer width L (μm), and the vertical axis is the multiplication factor M. Curve 24 shows the drive-in time of 7 hours 9 Oil line 25 shows the 10 hours 9 curve 26 is 1
This is the case when it is taken for 5 hours.

Furthermore, what is shown in Fig. 6 shows the multiplication factor M on the horizontal axis and the excess noise coefficient F on the vertical axis.The ion implantation conditions are the same as in Fig. 5, and the curves 27.28°29 are the drive This is when the time is set to 7 hours, 10 hours, and 15 hours.

As shown in FIGS. 4 to 6 above, N"PπP+ type 5i
If the heat treatment time of the two layers 6 after the APD B+ ion implantation is too short, the surface concentration will increase and the electric field will become larger, resulting in an increase in the excess noise factor F. Furthermore, if the heat treatment time is too long, M'RT (multiplication factor in reach-through) increases and frequency characteristics at low amplification factors (bias voltage) deteriorate.

In the present invention, if the amount of ion implantation into the second 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. (The reach-through RT is reached at nearly 60 V in the present invention, which was conventionally around 80 V). That is, in the present invention, the width of 21w may be selected to be 7 to 9 μm.

Furthermore, it can be seen from FIG. 6 that if the drive time after B+ ion implantation into the second layer 6 is longer, the excess noise factor F is significantly reduced. Further, as shown in FIG. 4, it can be seen that the Gaussian distribution curve 16 for the second layer 6 can be controlled relatively easily by selecting the drive time after setting the ion implantation dose constant.

However, in the present invention, by forming a P layer with a low concentration and a relatively short length (7 to 9 μm), an APD exhibiting good high frequency characteristics at a low multiplication factor can be formed. In the above embodiment, the N''PπP4 type Al)D was described, but it is clear that the present invention can be applied to the P+π■)N+ type etc. in which light is incident from the P side.

(7) Effects of the invention In view of the above-mentioned conventional drawbacks, the present invention provides a PF of N"P7CP".
By selecting a low IT concentration, selecting a relatively short P layer, and selecting a low value of 7M12T close to approximately 1 through ion implantation and drive-in, the high frequency characteristics are improved with a low multiplication factor. This has the effect that noise APD can be easily obtained.

[Brief explanation of drawings]

Figure 1 (al, (bl is A of the conventional N''PπP+ structure)
This is a schematic diagram of PD and impurity concentration distribution.
Figures (al to (jl) are APs of the N''PπP+ structure of the present invention.
Figures 3(a) and 3(b) are curves showing the schematic structure and impurity concentration distribution of the N+■)πP+ structure APD of the present invention, and Figure 4 shows the impurity concentration and P of the present invention. FIG. 5 is a curve showing the relationship between the layer distance, FIG. 5 is a curve showing the multiplication factor M of the present invention and the active region depletion interval, and FIG. 6 is a curve showing the relationship between the excess noise coefficient and the multiplication factor. l...substrate, 2...π layer, 3... oxide film,
4...Resist, 5.7,9.11...Window opening, 6...P layer, 8...Channel stopper, 10...Guard ring. Figure 7 Trust → JI 2nd cause

Claims (2)

[Claims] (1) In an avalanche photodiode having a B-step junction structure, the π layer concentration of the active region of the hyper-step junction structure is set to 5×10” to 5×10″’low’;
1. An optical semiconductor light-receiving device characterized in that the P layer is ion-implanted at a dose of 2 to 5×10 cm to have a P layer width of 7 to 9 μm. (2) The optical semiconductor light-receiving device according to claim 1, wherein the hyper-step junction structure is an N''PπP4 type silicon avalanche photodiode.