JPH07321371A - Method for forming light receiving and emitting diode - Google Patents

Abstract

PURPOSE:To form a shallow pn junction and at the same time to form the Zn diffusion region of high concentration in the whole surface of a p-type diffusion layer. CONSTITUTION:An Al2O3 diffusion mask 16 is formed. on an n-GaAsP substrate 14. Next, a diffusion source film 10 comprising the mixed film of ZnO and SiO2 or a ZnO film is formed on a backing 14 exposed through the diffusion window 16a of the mask 16. Next, an AlN annealing cap film 20 is formed on the diffusion source film 10 and the surface 14a of the substrate 14, which is located on the opposite side to the film 10. After that, the substrate 14 is held and heated in the atmosphere of a nitrogen gas to diffuse Zn contained in the diffusion source film into the substrate 14, thereby forming a p-type diffusion layer 22.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a light emitting / receiving diode having both light receiving and light emitting functions, and more particularly to a method for forming a p-type diffusion layer contributing to the light receiving / light emitting.

[0002]

2. Description of the Related Art Conventionally, for the purpose of cost reduction and size reduction, a printing / reading integrated type device using an LED (Light Emitting Diode) as both an exposure light source for electrostatic latent image formation and an image sensor for image reading. Is proposed. In the production of a general LED, a diffusion mask having a diffusion window is formed on a substrate, and impurities are diffused through the diffusion window to form a pn junction. At this time, a deep pn junction is formed over almost the entire inside of the diffusion window, and a shallow pn junction is formed in a narrow region at the window peripheral portion outside the diffusion window by side diffusion of impurities. The integrated printing / reading device
Focusing on the fact that the deep pn junction mainly contributes to light emission and the shallow pn junction mainly contributes to light reception, the LED is used as both an exposure light source and an image sensor.

On the other hand, it is known that the light emission output of an LED is closely related to the depth of a deep pn junction (diffusion depth of impurities). The LED light output increases with increasing depth of the deep pn junction, reaches a maximum at a certain depth, and gradually decreases at a deeper depth. Focusing on such a point, in general, the emission output intensity is generally increased by setting the depth of the deep pn junction to approximately 3 to 7 μm.

[0004]

On the other hand, the shallow pn junction has a high photosensitivity to the green light generally used in the reader, and therefore the area of the shallow pn junction is wide in order to enhance the photosensitivity. It is desired to do. However, in the LED used as the conventional light emitting element, the shallow pn junction is formed only by lateral diffusion (direction along the substrate surface) in the peripheral portion outside the diffusion window, and thus the shallow pn junction is formed. The area of is extremely small.

Therefore, a light emitting / receiving diode (LE that also functions as a light receiving element) is provided with a p-type diffusion layer that contributes to light reception and emission.
In D), a shallow p is formed over the entire surface of this p-type diffusion layer.
A light emitting and receiving diode in which an n-junction is formed is proposed in Japanese Patent Application No. 5-210074 of the same applicant. In this light receiving and emitting diode, a shallow pn junction is formed over the entire surface of the p-type diffusion layer to enhance the light-receiving sensitivity, and the impurity concentration of the p-type diffusion layer is increased to enhance the emission output intensity.

However, conventionally, the impurity diffusion is performed by the sealed tube method, and with this sealed method, it is difficult to diffuse the high concentration impurity over the entire region where the shallow pn junction is formed.

An object of the present invention is to provide a light receiving and emitting diode having a shallow pn junction over the entire surface of a p-type diffusion layer that contributes to light reception and emission, and having a high-concentration impurity diffusion region over the entire surface of the p-type diffusion layer. It is to provide a method suitable for formation.

[0008]

In order to achieve this object, a method of forming a light emitting / receiving diode according to the present invention is a method of forming a light receiving / emitting diode by selectively thermally diffusing Zn on an underlayer made of an n-type compound semiconductor. In forming the p-type diffusion layer that contributes to the diffusion of Zn, a diffusion source film containing Zn is formed on the base so that Zn can be thermally diffused selectively with respect to the base of the planned diffusion region, and an annealing cap film is formed. The step of forming on the diffusion source film, and after forming the annealing cap film, a p-type diffusion layer that contributes to light reception and emission of the light receiving and emitting diode by thermally diffusing Zn contained in the diffusion source film into the base of the diffusion planned region is formed. And a forming step.

[0009]

According to such a forming method, the diffusion source film is formed on the underlayer, the annealing cap film is further formed on the diffusion source film, and then Zn contained in the diffusion source film is to be diffused. Heat is selectively diffused into the underlayer of (the region where a p-type diffusion layer that contributes to light reception and emission is to be formed). The annealing cap film prevents Zn evaporated from the diffusion source film from escaping into the atmosphere holding the base.

As described above, since Zn is diffused from the diffusion source film to the base and the Zn is prevented from escaping by the annealing cap film, the entire surface of the diffusion planned region is covered.
A shallow pn junction can be formed and the Zn concentration can be made high.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. It should be noted that the drawings are merely schematic representations so that the invention can be understood, and therefore the invention is not limited to the illustrated examples.

1 to 3 are sectional views showing step by step the main steps of the first embodiment of the present invention.

(First Step) First, an underlayer 14 made of an n-type semiconductor is prepared, and a diffusion source film 10 containing Zn as a constituent element is selectively subjected to thermal diffusion of Zn with respect to the underlayer 14 in a predetermined diffusion region 12. It is formed on the base 14 as much as possible. The planned diffusion region is a region where a p-type diffusion layer that contributes to light reception and emission of the light emitting and receiving diode is to be formed.

In this embodiment, as the base 14, n-Ga is used.
Prepare an As _x P _1-x epitaxial substrate (Fig. 1
(A)). And in a well-known standard way,
The underlayer 14 is subjected to cleaning and pretreatment before film formation. An organic solvent and an acid may be used as the cleaning liquid. The emission wavelength of the light emitting / receiving diode can be controlled by the composition ratio x. For example, if x = 0.1, the emission wavelength can be 740 nm. In order to obtain direct transition type light emission, x ≦ 0.4
It is good to

Next, the diffusion prevention film 16 is formed on the base 14 (FIG. 1B). Here, an Al ₂ O ₃ film is formed as the diffusion prevention film 16 on the base 14 over the entire surface of the base 14 by the sputtering method. In this formation, preheating of the underlayer 14, pre-sputtering of the target, and main sputtering are performed, as is usually done in the sputtering method.

As is clear from the purpose of selectively diffusing Zn through the diffusion prevention film 16, the diffusion prevention film 16 has a thickness such that Zn permeates the diffusion prevention film 16 and reaches the base 14. The film thickness is set so as not to exist. Although such a film thickness varies depending on the diffusion conditions, the diffusion prevention film 16 having a film thickness of about 2000Å is formed here. Optimum other film forming conditions of the diffusion prevention film 16 differ depending on the sputtering apparatus used, and therefore detailed description thereof will be omitted.

The difference between the coefficient of thermal expansion of the Al ₂ O ₃ diffusion prevention film 16 and the coefficient of thermal expansion of the n-GaAsP underlayer 14 is small,
Therefore, when the diffusion prevention film 16 and the base 14 are heated, the thermal stress generated between them becomes small. Therefore Al
_{By using the 2} O ₃ diffusion prevention film 16 and the n-GaAsP underlayer 14, the strain of the diffusion prevention film 16 and the underlayer 14 due to thermal stress can be reduced.

When Ga of the underlayer 14 diffuses into the diffusion preventive film 16, holes are formed in the underlayer 14, and Zn is abnormally diffused laterally (a direction along the substrate surface) due to the generation of the holes. Is known to do. However constituent elements Ga of n-GaAsP base 14 so hard to diffuse into the Al ₂ O ₃ diffusion preventing film 16, Al ₂ O ₃ diffusion preventing film 16 is suitable for preventing abnormal lateral diffusion. When the Al ₂ O ₃ film is used as the diffusion prevention film 16 to perform selective diffusion, the diffusion depth and the side diffusion distance are almost equal. Therefore, when the light emitting and receiving diodes prepared in this embodiment are arranged in an array, the side diffusion distance is shortened because the diffusion depth of the p-type diffusion layer that contributes to light reception and emission is shallow, which increases the array density of the light receiving and emitting diodes. be able to.

On the other hand, when the SiO ₂ film used in the conventional LED is used as the diffusion prevention film 16, n-GaA
The constituent element Ga of the sP underlayer 14 is the SiO ₂ diffusion prevention film 16
It is very easy to diffuse in, and therefore SiO ₂ diffusion preventive film 1
When 6 is used, the side diffusion distance becomes longer than that of the Al ₂ O ₃ diffusion prevention film 16 due to the lateral abnormal diffusion of Zn. The thermal expansion coefficient of the SiO ₂ diffusion prevention film 16 is n-GaAsP.
Since it is about 1/10 of that of the underlayer 14, the difference in thermal expansion coefficient between the SiO ₂ diffusion prevention film 16 and the n-GaAsP underlayer 14 is the difference in thermal expansion coefficient between the Al ₂ O ₃ diffusion prevention film 16 and the n-GaAsP underlayer 14. Will be larger than. As a result, S
The iO ₂ diffusion prevention film 16 has a larger strain due to thermal stress than the Al ₂ O ₃ diffusion prevention film 16. Thus, A
The l ₂ O ₃ diffusion preventing film 16 is suitable for preventing abnormal diffusion in the lateral direction and reducing strain due to thermal stress.

Next, a diffusion window 16a exposing the underlying layer 14 of the diffusion planned region 12 is formed in the diffusion prevention film 16 (FIG. 1C). The diffusion window 16a is formed by standard photolithography and etching processes. That is, a resist 18 is applied on the diffusion prevention film 16 and the resist 18
Is exposed and developed to form the window 18a in the resist 18. The diffusion prevention film 16 in the planned diffusion region 12 is exposed through the window 18a. After that, the diffusion prevention film 16 in the planned diffusion region 12 is etched through the window 18a to form the diffusion window 16
a is formed on the diffusion prevention film 16. The base 14 of the planned diffusion region 12 is exposed through the diffusion window 16a. The diffusion prevention film 16 may be etched by wet etching using hot phosphoric acid.

Next, the diffusion source film 1 is formed on the underlayer 14 in the diffusion planned region 12 through the diffusion window 16a of the diffusion prevention film 16.
0 is formed, so that the base 14 of the diffusion planned region 12 is formed.
The diffusion source film 10 enables Zn to be thermally diffused selectively.
Are formed (FIG. 2 (A)). Here, the diffusion source film 1
0, a mixed film of ZnO and SiO ₂ (hereinafter ZnO
-SiO ₂ film), or to form a ZnO layer. The film thickness of the diffusion source film 10 is set to 200 Å or more. ZnO-S
Both of the iO ₂ film and the ZnO film are preferably formed by sputtering. This is because if the film is formed by sputtering, the uniformity of the film thickness and the uniformity of the composition in the film surface can be improved. According to the experiment, it was confirmed that the film thickness and the composition uniformity can be improved by the sputtering method rather than the CVD method. By increasing the uniformity of the film thickness and composition, the Zn concentration in the p-type diffusion layer that contributes to light reception and emission can be made uniform.

The target used in sputtering is ZnO.
And a mixed target of SiO ₂ or a ZnO target, the value of the molar concentration ratio of SiO _{2 to} ZnO is 1 or less in the mixed target of ZnO and SiO ₂ . ZnO formed using these targets
-SiO ₂ diffusion source film 10 or ZnO diffusion source film 1
0 is suitable for reducing the diffusion depth of the p-type diffusion layer which contains Zn in a high concentration and therefore contributes to light reception and emission, and to increase the Zn concentration. ZnO-Si formed using these targets
According to the O ₂ or ZnO diffusion source film 10, the Zn concentration on the surface of the p-type diffusion layer is high even when the diffusion depth of the p-type diffusion layer that contributes to light reception and emission is shallow, for example, 2 μm or less. For example, it was confirmed experimentally that it could be 5 × 10 ¹⁹ to 10 ²¹ cm ⁻³ . If the molar concentration ratio of SiO _{2 to} ZnO exceeds 1, the Zn concentration on the surface of the p-type diffusion layer cannot be increased in this way.

If the thickness of the ZnO-SiO ₂ or ZnO diffusion source film 10 is set to 200 Å or more, the impurity concentration on the surface of the p-type diffusion layer that contributes to light reception and emission is desired to be, for example, 5 × 10 ¹⁹ to 10 ²¹ cm. ^-Z which is necessary and sufficient to be about ^-3
The diffusion source film 10 is used as an infinite diffusion source for supplying n.
Can function. However, the coefficient of thermal expansion of the ZnO-SiO ₂ or ZnO diffusion source film 10 has a large difference from the coefficient of thermal expansion of the Al ₂ O ₃ diffusion prevention film 16 and the n-GaAsP underlayer 14, so the thickness of the diffusion source film 10 should be set to If it is made too thick, the Al ₂ O ₃ diffusion preventive film 16 and n due to thermal stress and n
-The strain of the GaAsP underlayer 14 becomes large. Therefore Zn
It is preferable to make the thickness of the O—SiO ₂ or ZnO diffusion source film 10 as thin as possible.

(Second Step) Next, the annealing cap film 20 is formed on the diffusion source film 10.

In this embodiment, an AlN film having a film thickness of about 1000Å is used as the annealing cap film 20, and the lower ground surface 14 on the diffusion source film 10 and on the side opposite to the diffusion source film 10 is formed.
It is formed on a and a (FIG. 2 (B)).

The annealing cap film 20 may be a film in which at least Zn is difficult to permeate or diffuse, but more preferably, in addition to this, the constituent element of the base 14 is G here.
It is preferable that a, As, and P are films that are difficult to permeate or diffuse. The AlN annealing cap film 20 is excellent as a film in which Zn and the constituent elements Ga, As and P of the underlayer 14 are less likely to permeate. If Zn is difficult to permeate, it is possible to prevent Zn evaporated from the diffusion source film 10 from escaping into the atmosphere holding the underlayer 14 during thermal diffusion of Zn. It is suitable for forming a high Zn concentration in the diffusion layer. If the constituent elements of the underlayer 14 are difficult to permeate, it is possible to prevent the constituent elements of the underlayer 14 from escaping into the atmosphere holding the underlayer 14 during thermal diffusion of Zn. Occurrence can be prevented.

Although the annealing cap film 20 may be formed only on the diffusion source film 10, in order to prevent the constituent elements of the underlayer 14 from escaping and / or to reduce the warp of the underlayer 14, the diffusion source film is formed. It is preferable to form the annealing cap film 20 not only on 10 but also on the lower ground surface 14 a opposite to the diffusion source film 10.

(Third Step) Annealing Cap Film 2
After the formation of 0, Zn contained in the diffusion source film 10 is thermally diffused into the base 14 of the planned diffusion region 12 to form the p-type diffusion layer 22 that contributes to the light reception and emission of the light emitting and receiving diode.

In this example, the substrate 14 was held at atmospheric pressure in an atmosphere of 100% nitrogen gas, and the substrate 14 was
At about 750-850 ° C, for example 750 ° C, for about 20 minutes. Thereby, the Zn contained in the diffusion source film 10
Is diffused into the underlying layer 14 of the planned diffusion region 12 to obtain a p-GaAsP diffusion layer 22 having a diffusion depth (pn junction depth) of about 2 μm (FIG. 2 (C)). Diffusion source film 10 and base 1
4, the diffusion prevention film 16 is interposed between
Since the underlayer 14 of the planned diffusion area 12 is selectively exposed through the diffusion window 16a of FIG.
4, Zn can be diffused selectively to form the p-type diffusion layer 22. Zn diffusion for forming the p-type diffusion layer 22 is performed by the annealing cap film 20 and the diffusion source film 1.
Zn diffusion by the open tube method using 0.

After that, the AlN annealing cap film 2 is formed.
0 and the ZnO—SiO ₂ diffusion source film 10 are removed by etching (FIG. 3A). Hot phosphoric acid was used to remove the AlN annealing cap film 20, and ZnO-SiO _{2 was used.}
Buffered HF may be used for the removal.

(Fourth Step) Next, the electrode 24 electrically connected to the p-type diffusion layer 22 and the electrode 2 electrically connected to the base 14.
6 is formed. In this embodiment, EB (Electron Beam
) An Al film having a film thickness of about 2.5 μm is formed on the p-type diffusion layer 22 by a vapor deposition method, and then the Al film is processed into an electrode shape by a photolithography and etching process to form an Al film.
The electrode 24 is formed (FIG. 3B). The Al electrode 24 is electrically connected to the p-type diffusion layer 22 through the diffusion window 16a of the diffusion prevention film 16, so that the diffusion prevention film 16 also serves as an interlayer insulating film.

Next, the lower ground surface 14a opposite to the p-type diffusion layer 22 is polished. After that, an Au alloy film having a film thickness of about 1000 Å is formed over the entire under surface 14a by the EB vapor deposition method, and the electrode 26 made of this Au alloy film is obtained. In order to obtain a good ohmic contact between the Al electrode 24 and the Au alloy electrode 26, after the electrodes are formed, sintering is performed at about 500 ° C. to complete the light emitting / receiving diode 28 (FIG. 3C). The light emitting / receiving diodes 28 are suitable for use in forming an array having both the functions of the exposure light source and the image sensor, and a plurality of light receiving / emitting diodes 28 may be arranged in a linear array to form an array. .

According to this embodiment, the following can be confirmed experimentally. That is, even when a shallow pn junction is formed with the diffusion depth of the p-type diffusion layer 22 being about 2 μm, the impurity concentration in the surface layer of the p-type diffusion layer 22 is 10 ^20.
The p-type diffusion layer 22 can be formed to have a high concentration of about 10 ²¹ cm ⁻³ . As a result, good ohmic contact is obtained between the p-type diffusion layer 22 and the Al electrode 24,
This ohmic contact resistance can be as low as 10 ⁻³ Ω · cm or less, more typically as low as 10 ⁻⁵ Ω · cm.

Moreover, the impurity concentration in the surface layer of the p-type diffusion layer 22 is set to 1 over almost the entire surface layer of the p-type diffusion layer 22.
The concentration can be as high as 0 ²⁰ to 10 ²¹ cm ^-3 .

FIG. 4 is a diagram showing the distribution of the impurity concentration in the p-type diffusion layer 22 of the light emitting / receiving diode 28 manufactured in the first embodiment. In the figure, the horizontal axis indicates the distance D [μ
m] and the impurity concentration [cm ⁻³ ] on the vertical axis, and the distance D from the surface of the p-type diffusion layer 22 in the depth direction of the p-type diffusion layer 22 (direction normal to the surface of the p-type diffusion layer 22). The impurity concentration of the p-type diffusion layer 22 at the position is shown. This impurity concentration is obtained by experimental measurement. Distance D
Please refer to FIG.

FIG. 5 is a diagram showing a near-field pattern of emission intensity obtained by measuring the light receiving and emitting diode 28 manufactured in the above-described embodiment, and FIG. 6 shows the light receiving and emitting diode 28 manufactured by the conventional method by the sealed tube method. It is a figure which shows the near field pattern of the light emission intensity obtained by measurement. In these figures, FIG. 1A is a plan view showing the configuration of the light emitting diode 28, FIG. 2B is a diagram showing the relative emission intensity at the position X, and FIG. It is a figure which shows luminescence intensity. Positions X and Y are p-type diffusion layer 2
2 Positions on the X-axis and Y-axis set on the surface, the Y-axis is set so as to overlap with the electrode 24 when viewed in plan along the electrode 24 electrically connected to the p-type diffusion layer 22. At the same time, the X axis is set to be orthogonal to the Y axis and not overlapped with the electrode 24 when seen in a plan view.

Since the sheet resistance of the p-type diffusion layer 22 can be lowered by making the impurity concentration in the surface layer of the p-type diffusion layer 22 high over the entire surface as described above, the shallow diffusion depth, for example, the diffusion depth. Even if the thickness is set to 2 μm, carriers are uniformly injected into the pn junction regardless of the distance from the electrode 24, and almost uniform emission intensity is obtained over the entire surface of the p-type diffusion layer 22.

On the other hand, when the impurity concentration of the surface layer of the p-type diffusion layer 22 is low, the sheet resistance of the shallow p-type diffusion layer 22 becomes high, so that the current concentrates near the electrode 24. Therefore, as shown also in FIG. 6, it is not possible to obtain a practically satisfactory light emission intensity over the entire p-type diffusion layer 22, and as a result, a light emitting / receiving diode 28 having a light emitting function suitable for practical use is obtained. Becomes difficult.

FIG. 7 is an explanatory view of a modification of the first embodiment. Hereinafter, differences from the first embodiment will be described, and detailed description of the same points as the first embodiment will be omitted.

In this modification, the steps up to forming the diffusion window 16a are the same as in the first embodiment. After forming the diffusion window 16a, then, the base protection film 30 and the diffusion source film 10 are sequentially formed on the base 14 in the planned diffusion region 12 through the diffusion window 16a of the diffusion prevention film 16 (FIG. 7). Here, the base protective film 30 is a SiO ₂ film having a film thickness of about 100 Å, and the diffusion source film 10 is a Zn film or a ZnO film having a film thickness of about 200 Å or more.

The base protection film 30 is a protection film for preventing the diffusion source film 10 and the base 14 from reacting with each other and damaging the base 14. Therefore, a film other than the SiO ₂ film, for example, Z.
An oxide film or a nitride film not containing n may be used as the base protective film 30. In the first embodiment, the diffusion source film 10 is formed by directly contacting the underlayer 14 of the planned diffusion region 12, but when the reactivity between the diffusion source film 10 and the underlayer 14 is high, this modification is similar. The diffusion source film 10 and the base 14
It is preferable to interpose the undercoat protection film 30 between and. It is preferable that the thickness of the base protective film 30 be thin so as not to prevent the Zn contained in the diffusion source film 10 from being thermally diffused into the base 14.

Next, an annealing cap film 20 and an active layer 22 are formed, and after that, the annealing cap film 2 is formed.
0, the base protection film 30 and the diffusion source film 10 are removed.
The subsequent steps are the same as those in the first embodiment.

FIG. 8 is an explanatory view of another modification of the first embodiment. In this modification, the diffusion source film 10 is a Zn film. Others are the same as those in the first embodiment. The Zn diffusion source film 10 also reduces the diffusion depth of the p-type diffusion layer 22 and Z
Suitable for increasing the n concentration.

9 to 11 are sectional views showing stepwise the main steps of the second embodiment of the present invention.

(First Step) First, an underlayer 14 made of an n-type semiconductor is prepared, and the diffusion source film 10 containing Zn is selectively diffusible with respect to the underlayer 14 in the planned diffusion region 12 by thermal diffusion of Zn. It is formed on the base 14.

In this embodiment, n-Ga is used as the base 14.
An As _x P _1-x epitaxial substrate is prepared, and the underlayer 14 is subjected to cleaning and pretreatment before film formation by a well-known standard method.

Next, the diffusion source film 10 is formed on the underlayer 14 (FIG. 9A). Here, ZnO-SiO
_{2 The} diffusion source film 10 is formed on the entire surface of the base 14 by the sputtering method.

Next, the diffusion source film 10 is etched by a photolithography and etching process to form a diffusion source film 10 having the same planar shape as the planned diffusion region 12, and thereby the base 14 of the planned diffusion region 12 is formed. On the other hand, the diffusion source film 10 is formed so that Zn can be thermally diffused selectively (FIG. 9B). The diffusion source film 10 is a planned diffusion region 1
Diffusion source film 1
0 is removed by etching.

(Second Step) Next, the annealing cap film 20 is formed on the diffusion source film 10.

In this embodiment, the AlN annealing cap film 20 is formed on the diffusion source film 10 and the diffusion source film 10.
Are formed on the lower ground surface 14a on the opposite side to the entire ground surface (FIG. 9C).

(Third Step) Annealing Cap Film 2
After the formation of 0, Zn contained in the diffusion source film 10 is thermally diffused into the base 14 of the planned diffusion region 12 to form the p-type diffusion layer 22 that contributes to the light reception and emission of the light emitting and receiving diode.

In this embodiment, the underlayer 14 is held in a nitrogen gas atmosphere to heat the underlayer 14, thereby diffusing Zn contained in the diffusion source film 10 into the underlayer 14 in the planned diffusion region 12 to about 2 μm. A p-GaAsP diffusion layer 22 having a diffusion depth (pn junction depth) is obtained (FIG. 10).
(A)). Since the diffusion source film 10 having the same planar shape as that of the planned diffusion region 12 is left only in the planned diffusion region 12, the Z of the diffusion planned region 12 is selectively formed on the underlayer 14 of the planned diffusion region 12.
It is possible to diffuse n and thus form the p-type diffusion layer 22.

After that, the annealing cap film 20 and the diffusion source film 10 are removed by etching (FIG. 10).
(B)).

(Fourth Step) Next, the electrode 24 electrically connected to the p-type diffusion layer 22 and the electrode 2 electrically connected to the base 14.
6 is formed.

In this embodiment, the interlayer insulating film 32 is formed over the entire surface of the lower ground surface 14a on which the p-type diffusion layer 22 is formed (FIG. 10C). After that, a light transmitting window 32a is formed in the interlayer insulating film 32 by a photolithography and etching process, and the p-type diffusion layer 2 is formed through the light transmitting window 32a.
2 is exposed (FIG. 11 (A)). Next, the transparent window 32
An Al electrode 24 that is electrically connected to the p-type diffusion layer 22 via a is formed (FIG. 11B). Then, an Au alloy electrode 26 electrically connected to the base 14 is formed on the entire surface of the lower ground surface 14a opposite to the p-type diffusion layer 22 to complete the light emitting / receiving diode 28 (FIG. 11C).

FIG. 12 is an explanatory diagram of a modification of the second embodiment. Hereinafter, differences from the second embodiment will be described, and detailed description of the same points as the second embodiment will be omitted.

In this modification, the base protective film 30 and the diffusion source film 10 are sequentially formed on the base 14 (FIG. 1).
2). Here, the base protective film 30 is an Al ₂ O ₃ film, and the diffusion source film 10 is a Zn film or a ZnO film. The base protection film 30 may be formed over the entire surface of the base 14, or, like the diffusion source film 10, the base protection film 30 having the same planar shape as the planned diffusion region 12 may be formed.

Next, the annealing cap film 20 and p
The mold diffusion layer 22 is formed, and then the annealing cap film 20, the base protection film 30, and the diffusion source film 10 are removed. The subsequent steps are the same as those in the second embodiment.

The present invention is not limited to the above-mentioned embodiment, and therefore, the size, shape, arrangement position, forming material, film forming method and other conditions of each constituent are within the scope of the present invention. It can be changed as desired.

For example, the underlayer 14 is not limited to GaAsP, but other than GaAsP such as GaAs or AlGaAs.
It is also possible to use the base 14 made of.

The base 14 is, for example, GaAsP base, GaA
In either case of s substrate or AlGaAs substrate,
An Al ₂ O ₃ film or a SiN film can be used as a film that hardly transmits or does not transmit Zn and the constituent elements of the underlayer 14.

As the annealing cap film 20 for preventing the escape of Zn, a film other than the AlN film, for example, Zn
It is possible to use an oxide film or a nitride film that does not contain, for example, an Al ₂ O ₃ film, a SiN film, a PSG film or a SiO ₂ film can be used as the annealing cap film 20. When a GaAsP underlayer, GaAs underlayer or AlGaAs underlayer is used as the underlayer 14, an Al ₂ O ₃ film, Si
The N film, the PSG film and the SiO ₂ film also have an effect of suppressing the escape of the constituent elements of the underlayer 14. Further, as the base 14, Ga
When an AsP base, a GaAs base, or an AlGaAs base is used and an SiN film or a SiO ₂ film is used as the annealing cap film 20, the difference in the thermal expansion coefficient between the base 14 and the annealing cap film 20 becomes large, so the annealing cap film 20. If the film thickness is too thick, cracks may occur during heating. However, even in this case, if the film thickness is less than 500 Å, the occurrence of cracks can be considerably suppressed. Further, as the base 14, a GaAsP base, G
When an aAs base or an AlGaAs base is used, an AlN film or Al ₂ O ₃ is used as the annealing cap film 20.
When a film is used, the difference in the coefficient of thermal expansion between the underlayer 14 and the annealing cap film 20 becomes small, which is effective in suppressing the occurrence of cracks.

In the practice of the present invention, in order to obtain a practically satisfactory emission intensity, the impurity concentration in the surface layer of the p-type diffusion layer 22 should be approximately 5 × 10 ¹⁹ cm ⁻³ or more and approximately 10 ²¹ c.
It is preferably m ^-3 or less. When the diffusion depth is shallow, for example, 2 μm or less, the impurity concentration is 5 × 10 ^19.
If it is less than cm ⁻³ , practically satisfactory emission intensity cannot be obtained, and if the impurity concentration exceeds 10 ²¹ cm ⁻³ , the p-type diffusion layer 22 is obtained.
This is because the crystal damage in (3) becomes severe and the function of the light emitting / receiving diode is impaired. At the same time, in order to obtain good light receiving sensitivity for visible light, particularly visible light of short wavelength, p
The diffusion depth (pn junction depth) of the type diffusion layer 22 is about 0.
The thickness is preferably 3 μm or more and about 2 μm or less. This is because when the diffusion depth is less than 0.3 μm and when the diffusion depth exceeds 2 μm, good light receiving sensitivity for visible light of short wavelength cannot be obtained. According to the experiments conducted by the inventors of the present application, for example, it is possible to enhance the light receiving sensitivity to visible light having a short wavelength such as green light which is important for a reading device and to form a near-field uniform in-plane pattern, which is practically sufficient. In order to obtain the emission intensity, the diffusion depth of the p-type diffusion layer 22 is set to 1
Most preferably, the thickness is ˜2 μm.

[0064]

As is apparent from the above description, according to the method for forming a light emitting and receiving diode of the present invention, a shallow pn is formed over almost the entire surface of the p-type diffusion layer that contributes to light reception and emission.
Since Zn can be diffused in a high concentration while forming a junction,
It is possible to provide a light emitting and receiving diode which has practically satisfactory light receiving sensitivity and can obtain practically satisfactory light emission output intensity.

Further, as compared with the conventional method of forming the p-type diffusion layer by the sealed tube method, the number of steps of the diffusion step can be reduced and the p-type diffusion layer can be formed in a shorter time, so that the manufacturing cost can be reduced. Can be achieved. Further, since the light receiving and emitting diodes are formed by the shallow pn junction, when the light receiving and emitting diodes are arranged in an array, the light receiving and emitting diodes can be arranged at a high density.

[Brief description of drawings]

FIG. 1A to FIG. 1C are process drawings for explaining a first embodiment of the present invention.

2 (A) to (C) are process drawings for explaining a first embodiment of the present invention.

FIGS. 3A to 3C are process drawings for explaining the first embodiment of the present invention.

FIG. 4 is a diagram showing a distribution state of impurity concentrations in a depth direction of an active layer.

FIG. 5 is a diagram showing a distribution state of relative emission intensity in an active layer.

FIG. 6 is a diagram showing a distribution state of relative emission intensity in an active layer.

FIG. 7 is a diagram for explaining a modified example of the first embodiment.

FIG. 8 is a diagram for explaining another modification of the first embodiment.

9A to 9C are process drawings for explaining a second embodiment of the present invention.

10 (A) to 10 (C) are process drawings for explaining the second embodiment of the present invention.

11 (A) to (C) are process drawings for explaining a second embodiment of the present invention.

FIG. 12 is a diagram for explaining a modification of the second embodiment.

[Explanation of symbols]

 10: Diffusion source film 12: Diffusion planned region 14: Base 16: Diffusion prevention film 16a: Diffusion window 20: Annealing cap film 22: P-type diffusion layer 28: Light emitting / receiving diode 30: Base protection film

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takaatsu Shimizu 1-7-12 Toranomon, Minato-ku, Tokyo Oki Electric Industry Co., Ltd.

Claims (3)

[Claims] 1. A diffusion source film containing Zn is diffused in forming a p-type diffusion layer that selectively diffuses Zn on an underlayer made of an n-type compound semiconductor to contribute to light reception and emission of a light emitting and receiving diode. A step of forming on the underlayer so that Zn can be thermally diffused selectively with respect to the underlayer of the predetermined region; a step of forming an annealing cap film on the diffusion source film; and a step of forming the annealing cap film and then forming the diffusion source film. Forming a p-type diffusion layer that contributes to the light reception and emission of the light emitting and receiving diode by thermally diffusing Zn contained in the above into the base of the diffusion planned region. 2. The method for forming a light emitting and receiving diode according to claim 1, wherein the diffusion source film is a ZnO film, or ZnO and Si.
A method of forming a light emitting and receiving diode, which comprises forming a mixed film of O ₂ or a Zn film. 3. The method for forming a light receiving and emitting diode according to claim 1, wherein the annealing cap film is also formed on the lower ground opposite to the diffusion source film.