JPS582449B2 - Control method for minority carrier diffusion length - Google Patents

Description

Detailed Description of the Invention The present invention introduces carrier recombination centers at a desired depth by implanting ions made of light elements such as protons and helium into a semiconductor substrate, thereby increasing the diffusion length of minority carriers. This invention relates to a method of controlling the minority carrier diffusion length to shorten it.

The ion implantation method is a useful method for introducing impurities at a desired concentration to a desired depth, and has been put into practical use in some areas of the semiconductor industry to the extent that it replaces the conventional thermal diffusion method.

However, this method accelerates ionized impurity atoms in a high electric field and forcibly implants them into the semiconductor substrate, resulting in them colliding with the substrate atoms in the process of losing incident energy and coming to rest. This forces them out of the crystal lattice position and induces a large amount of vacancies.

During the annealing process, these vacancies are combined with each other or with atoms constituting the substrate or with impurity atoms to form complex defects such as a vacancy-to-vacant lattice-substrate atom pair, a vacancy-impurity atom pair, and the like.

These defects create various energy levels within the forbidden band, and are expected to become carrier trap levels or recombination centers.

The present invention provides a method of shortening the minority carrier diffusion length by actively utilizing recombination centers generated by ion irradiation damage.

This spatial distribution of recombination centers is the defect distribution, in other words:
It is thought that, to a first approximation, it takes the same form as the distribution of energy released in the nuclear collision process.

The shape of the defect density distribution during ion implantation differs depending on the ion species, the incident energy, and the substrate constituent atoms and density, but generally when light atom ions are implanted, the defect distribution is similar to the substrate surface, as illustrated in Figure 1. It gradually increases as it goes deeper into the interior, reaches its maximum value at a portion (RD) slightly shallower than the projected range (RP) of the primary incident ions, and then rapidly decreases.

Therefore, the density distribution of recombination centers immediately after ion implantation is
This is similar to the defect density distribution in the figure.

Along with this, the depth distribution of the minority carrier diffusion length decreases from the surface to the inside, and after taking the shortest value at the RD position, increases and finally reaches the value when ions are not implanted.

Next, the case where annealing is performed will be described.

Defects disappear through annealing, but the process progresses gradually starting from the portion of FIG. 1 where the defect density is small, and the process ends at the RD position.

Therefore, by setting appropriate annealing conditions, it is possible to leave a recombination center only at the RD position and shorten only the minority carrier diffusion length there.

Furthermore, by adopting a multi-stage ion implantation method and controlling the incident energy and implantation amount, the RD position and the recombination center density there can be continuously changed, and the desired depth direction minority carrier diffusion length distribution can be achieved. Obtainable.

Figure 2 shows N-type GaAS0.62 po. 20 on 38 boards
This figure shows the hole diffusion length measured near the RD of a substrate obtained by implanting 0 KeV H+ ions and then performing various annealing operations.

The substrate is Te-doped GaAsO. 62 P0.33 (10
0) It is a gas phase epitaxial wafer, and the electrical density is 1
．． 9X1016Cm-3, mobility is 4150cm2/V
・It was sec.

200KeV H+ ions are added to this substrate at 1×1013C.
Inject m-2.

In this case, RD is estimated to be about 1.5 μ, and the vacancy density at that position is estimated to be about 1.2×10 cm −3 .

Next, the substrate is annealed at 200 to 500° C. for about 5 minutes in a N2 stream.

As expected, as the annealing temperature increases, defects disappear, that is, the number of recombination centers decreases, and the diffusion length of holes, which are minority carriers, increases. The diffusion length, which was 0.61μ immediately after H0 injection, increased to 0.89μ, 0.99μ, and 1.09μ as the temperature rose to 200℃, 300℃, and 500℃, respectively. It is thought that by annealing, the value approaches the value of 2.20μ when not implanted.

The above results are obtained when 1×10 13 cm −2 of 200 KeV H+ is implanted.

It goes without saying that by selecting appropriate incident energy, implantation amount, and annealing conditions, the minority carrier diffusion length can be shortened to a desired value at a desired depth.

Next, a method for controlling the diffusion length distribution of small and few carriers using the multi-stage ion implantation method according to the present invention will be described in detail below based on examples.

This example was created when manufacturing a photodiode with visibility characteristics, and will be explained step by step in the following.

50 μm of Te-doped N-type GaAs Po. on Si-doped N-type GaAs. 38 (n=1.9×10l6cm-3)
Ordinary Zn selective diffusion method or 50Kev, Zn + ion is 1×1013
˜1×10 14 cm −2 implant to form a planar PN junction photodiode.

As a result, a P-N junction depth of 0.1μ or less is achieved, but the spectral sensitivity characteristics of this diode have large sensitivity on the long wavelength side, as shown by the normalized curve (a) in Figure 3. , the desired target human visual sensitivity characteristics (curve (b)
) was very different.

The reasons why long wavelength sensitivity predominates despite the extremely shallow P-N junction are (1); short wavelength sensitivity does not increase due to the large surface recombination characteristic of compound semiconductors; (2)
By adopting a low-concentration N-type substrate, the depletion layer greatly expands to the 1N layer side, (3) the hole diffusion length on the N side is large (2.2
μ), etc.

Therefore, one possible way to approach the relative luminous efficiency is to cut off unnecessary long wavelength sensitivity, but as is obvious in principle, it is effective to shorten the diffusion length of holes on the N side.

This is where the invention applies. That is, next, high-energy H+ ions are implanted in multiple stages into a planar diode substrate having the spectral sensitivity characteristic of curve (a).

As for the implantation conditions for H+ ions, in order to effectively cut the long-wavelength photosensitivity (focusing on 6400 Å light as an example), the amount of H+ implanted at each RD position is set to 6400 Å carriers at that depth. It was set to be proportional to the production rate.

That is, 4.3X10cm-2,200K at 180KeV
3.2XIO12Cm2 at eV, 2.5 at 240KeV
Inject in three stages at x1012cm-2.

After that, annealing is performed for 5 minutes in a N2 gas flow in order to leave recombination centers only near each RD position.

As a result, the hole diffusion length is the shortest at a depth of about 1.3μ,
Since a diffusion length distribution is obtained in which the hole diffusion length gradually increases as it goes deeper, long wavelength light
Most of the holes generated in the deep side are recombined by diffusion before entering the drift region (approximately 1.2 μm from the surface) due to space charges, and are no longer taken out as external output.

The normalized spectral sensitivity of the photodiode thus obtained is shown in FIG. 3 as curve + (C).

As is clear from Fig. 3, we were able to maintain the normalized sensitivity at short wavelengths almost at the same level as when H was injected, and effectively reduce the sensitivity at long wavelengths of about 5300 Å or more. ), we were able to get it much closer to the relative luminous efficiency.

By the way, curve (d) shows 200KeV H+ ion at 1×
It shows the characteristics of a photodiode obtained by one-stage injection of 1013Cm-2, and the curve (C It is clear from the figure that )) is superior.

The above is an application example to a normal P-N junction type photodiode, but based on the principle that the present invention can control (shorten) the diffusion current component due to minority carriers, it is possible to apply the present invention to an avalanche photodiode, a transistor, etc. It goes without saying that the present invention is widely applied to semiconductor devices, such as improving the response speed of semiconductor devices.

In addition, the example is GaAs042 PO. 38, similar effects can be expected for all semiconductor materials such as Si, Ge, GaAs, and GaP.

[Brief explanation of drawings]

FIG. 1 shows GaAsO, 62 Po. 38 to 200KeV
The vacancy density distribution and the H atom density distribution when 1×10 cm −2 of protons are injected are shown. In the figure, Rp and RD indicate the positions where the H atom density and the hole density are maximum, respectively. Figure 2 shows proton-implanted N-GaAsg, 62 P0,3
8 shows the annealing temperature dependence of hole diffusion length in No. 8. Figure 3 shows GaAso,62 P0 prepared by various methods.
．． 38 shows the normalized spectral sensitivity characteristics of the No. 38 photodiode when equal energy light is incident. Each curve represents the following: (a) Ordinary CaASO. 62 P0,3
Spectral sensitivity characteristics of 87 Otodiode, (b) Specific luminous efficiency characteristics, (c) QaAsO. Spectral sensitivity characteristics of 62 PO, 38 photodiode, (d) GaAso. 62 P.O. Spectral sensitivity characteristics of 38 photodiode.

Claims (1)

[Scope of Claims] 1 Light element ions are implanted into a semiconductor substrate in multiple stages by setting a plurality of ion implantation conditions such as incident energy and implantation amount to introduce vacancies that serve as minority carrier recombination centers, and then annealing is performed. 1. A method for controlling minority carrier diffusion length, comprising controlling minority carrier diffusion length distribution by continuously or substantially continuously changing minority carrier recombination center density. 2. The method of controlling minority carrier diffusion length according to claim 1, wherein the carrier recombination center density is continuously changed by setting a plurality of ion implantation conditions and performing multi-stage ion implantation.