JPH11168232A - Manufacture of semiconductor light-receiving device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress slightly an irregularity in the thicknesses of substrates by a simple means, to lessen an irregularity in positions where signal light is made incident in a photoabsorption layer, to lessen the area of a light- receiving region and to reduce the parasitic capacitance of a semiconductor light-receiving device. SOLUTION: An element substrate 13 consisting of a hard material in comparison with an InP material is pasted together with a support substrate 11 via an intermediate layer 12, the substrate 13 is polished from the surface thereof to form the substrate 13 in a prescribed thickness, a light-receiving element film PD comprising at least a photo-absorption layer 15 consisting of the InP material is pasted together with the surface of the substrate 13 and after that, after an impurity diffused region, a P side electrode and the like are formed, the layer 12 is dissolved to separate the substrate 13 from the substrate 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
The present invention relates to a manufacturing method for improving the performance of a semiconductor light receiving device formed by using an InP-based material to cope with light in a band.

[0002] At present, a subscriber system for drawing an optical fiber to each home is being realized, and for this realization, a reduction in the price of an optical module is required.

For example, in the case of a chamfered light-receiving element capable of receiving a signal light from an end face, a mounting means can be made the same as a semiconductor laser when an optical module is manufactured.
The equipment for manufacturing the module is simplified, and the cost can be reduced.

Generally, a PON (passive opt) is used.
A light receiving element for an optical network (for a station of a subscriber system) requires a wide dynamic range. Therefore, it is important to reduce the capacitance in addition to the characteristics of the conventional light receiving element. .

However, in the case of a structure in which signal light passes through the substrate and reaches the light receiving region, as in the case of the above-mentioned chamfered light receiving element, it is difficult to reduce the capacitance. One means for solving the problem is disclosed.

[0006]

2. Description of the Related Art FIG. 11 is a cutaway side view of a principal part showing a chamfered light receiving element and an optical fiber for explaining problems in the prior art.

In the figure, 1 is a substrate, 1A is a light incident surface (chamfered portion), 2 is a light absorbing layer, 3 is a window layer, 4 is an impurity diffusion region, 5 is an optical fiber, 6 is an optical path, and L is The diameter of the light receiving region 4 is shown.

In this light receiving element, the signal light from the optical fiber 5 is taken in at the light incident surface 1A, which is a chamfered portion, passes through the substrate 1, and is photoelectrically converted in the light receiving region of the light absorbing layer 2. Therefore, when mounted as an optical module, it can be handled in the same manner as a semiconductor laser.

As is apparent from this configuration, when the thickness of the substrate 1 changes, the position of the light incident on the light absorbing layer 2 shifts and moves out of the light receiving region, and the light receiving sensitivity decreases. Will be.

In order to cope with such a situation and to obtain a sufficient light receiving sensitivity, it is necessary to form the light receiving area wider in consideration of the variation in the thickness of the substrate 1. .

At present, in the process of manufacturing the illustrated light receiving element, the substrate 1 is polished using an abrasive between the steps of forming the p and n electrodes to have a thickness of 100 [μm].

[0012] However, it is difficult to uniformly polish a soft substrate such as InP.
It is inevitable that a variation of about [μm] occurs, and such a variation causes the light absorption layer 2 of the signal light.
Since the position of incidence on the substrate greatly changes, the light receiving region, that is, the impurity diffusion region 4 must be formed large accordingly.

Specifically, when the variation when the substrate 1 is 100 μm is ± 5 μm, the diameter L in the light receiving region needs to be 147.7 μm. In this case, the parasitic capacitance is 0.50 [pF].

However, when the thickness variation on the substrate 1 is ± 1 μm, the diameter L of the light receiving region is 1 μm.
25 [μm] and the capacity in that case is 0.36 [p
F].

[0015]

SUMMARY OF THE INVENTION By simple means,
Variations in substrate thickness in semiconductor light receiving devices are reduced, and variations in the position where signal light is incident on the light absorbing layer are also reduced. As a result, it is not necessary to provide a large margin in the area of the light receiving region. Attempts to reduce capacity.

[0016]

According to the present invention, a semiconductor such as an InP-based semiconductor is used as a material of a light receiving element film including a light absorbing layer, and a relatively hard GaAs is used as a material of a substrate whose thickness is reduced by polishing. Basically, a technique of using a semiconductor such as a system or a Si system and bonding a substrate or a semiconductor layer or the like is used in many cases.

For example, a relatively hard semiconductor such as GaAs or Si can reduce the variation in thickness when it is polished, and can sufficiently reduce the variation to ± 1 [μm] or less.

FIG. 1 is a diagram for explaining the variation in thickness of a GaAs wafer after polishing. FIG. 1A shows a section (site) having a size of 15 × 15 [mm ² ] defined on the wafer.
FIG. 7B is a diagram for explaining the definition of the variation in thickness in FIG.
[m ² ] is a diagram showing numerical values of differences in thickness in each section (site: □ in the figure).

The LTV (local th
Ickness variation) is defined as follows.

The wafer is divided into sections of a fixed size, and the total thickness of each section is determined by TTV (total thickness va- sage).
ration), that is, the maximum / minimum thickness difference in the wafer plane, and the maximum value of TTV in each section is defined as LTV.

FIGS. 2A and 2B are diagrams for explaining thickness variations after polishing a GaAs wafer. FIG. 2A is a diagram relating to Warp, FIG. 2B is a diagram relating to TTV, and FIG. 2C is a diagram relating to LTV.
FIG.

In the figure, Warp in (A) shows a focal plane (focal plane) in a free state without chucking the wafer.
Plane) as a reference plane, and is represented by the sum of the maximum values of the deviation in the vertical direction from that plane.
This is a variation of the wafer thickness over the entire wafer of about 10 cm (4 inches), and the LTV of FIG.
This is the maximum value of the variation in wafer thickness in a section of 5 × 15 [mm ² ].

1 and 2, the polished GaAs
It can be recognized that the variation in the thickness of the wafer over the entire wafer can be suppressed to within 1 [μm]. According to the present invention, the wafer having the small variation in the thickness after polishing is bonded to the light receiving element film. Construct a light receiving element.

From the above description, in the method of manufacturing a semiconductor light receiving device according to the present invention, (1) the InP-based material is formed on the supporting substrate (for example, the supporting substrate 11) via the intermediate layer (for example, the intermediate layer 12). A step of bonding an element substrate (eg, the element substrate 13) made of a relatively hard material (eg, GaAs or Si), and then a step of bonding the element substrate made of the hard material to a predetermined thickness (eg, 100 [μm]). A light-receiving element film (for example, a light-receiving element) including at least a light-absorbing layer (for example, a light-absorbing layer 15) made of an InP-based material on the polished surface of the element substrate made of the hard material. a step of bonding the film PD _F), then either characterized in that the support by dissolving the intermediate layer substrate made contains the step of separating the element substrate, certain It is,

(2) In the above (1), the element substrate made of a material harder than the InP-based material is a GaAs-based material and the intermediate layer is an AlAs layer, or ,

(3) The method according to (1), wherein the element substrate made of a material harder than the InP-based material is a Si-based material and the intermediate layer is a SiO ₂ layer. Or,

(4) In the above (1) or (2),
Forming a groove having a triangular cross section (for example, groove 13B) on the back surface of the element substrate separated from the supporting substrate by dissolving the intermediate layer, and then cleaving the element substrate at the bottom of the groove; And forming a light incident surface (for example, the light incident surface 13A) by a surface forming a groove having a triangular cross section.

(5) In any one of the above (1) to (3), a step of dissolving the intermediate layer and forming a lens (for example, a lens 13L) on the back surface of the element substrate separated from the supporting substrate is included. It is characterized by becoming.

By adopting the above configuration, it is possible to obtain a light receiving element having a substrate having a small variation in thickness after polishing, so that the signal light from the optical fiber can reach the light receiving region with high accuracy. Therefore, the area of the light receiving region can be reduced, and as a result, the parasitic capacitance also decreases.
A semiconductor light receiving device having a wide dynamic range is realized, and is suitable for PON.

[0030]

FIG. 3 to FIG. 7 are cutaway side views of a main part of a semiconductor light receiving device in a process step for explaining a first embodiment of the present invention. This will be described with reference to FIG.

FIG. 3A 3- (1) MOCVD (metalorganic chemical)
The intermediate layer 12 is formed on the support substrate 11 by applying an al vapor deposition method.

Various data relating to the support substrate 11 and the intermediate layer 12 are exemplified as follows. About the support substrate 11 Material: GaAs About the intermediate layer 12 Material: AlAs Thickness: 50 [Å]

The intermediate layer 12 is interposed between the support substrate 11 and the element substrate 13 to be bonded in the next step. During the processing of the element substrate 13, the bonding strength between the support substrate 12 and the support substrate 11 is reduced. Needless to say, it is necessary that the etchant be different from at least the element substrate 13 and, if necessary, the support substrate 11 or a material having an extremely high etching rate with respect to the etchant used. And the element substrate 1
When separating the support substrate 3 from the support substrate 12, the two must be easily separable.

3 (B) 3- (2) An element substrate 13 made of n ⁺ -GaAs is placed on the intermediate layer 12 made of AlAs, and the temperature is set to, for example, 800 ° C., for example, 200 kg. Is applied, the support substrate 11 and the element substrate 13 are bonded via the intermediate layer 12.

FIG. 4 (A) 4- (1) CMP (chemical mechanical p)
By applying the polishing method, the surface of the element substrate 13 is polished to remove the others except for a thickness of 100 [μm].

Needless to say, the thickness variation in the element substrate 13 made of n ⁺ -GaAs that has undergone this polishing step falls within a range of ± 1 [μm].

Referring to FIG. 4B, 4- (2) a buffer layer 14, a light absorbing layer 15,
Placing the light-receiving element film PD _F consisting of the window layer 16, and the temperature, for example 750 [℃], for example 200
By applying a pressure of (kg) bonding the element substrate 13 and the light receiving element film PD _F. In addition, the light receiving element film PD
The manufacturing process of _F will be described later.

FIG. 5 (A) 5- (1) CVD (chemical vapor deposition)
), a resist process in a lithography technique, and a wet etching method using an etchant as a buffered hydrofluoric acid. S
A mask film (not shown) made of iO ₂ is formed.

5- (2) By applying the thermal diffusion method, Zn is diffused, and p ⁺ having an impurity concentration of, for example, 2 × 10 ¹⁸ [cm ^-3 ] is obtained ^.
An impurity diffusion region 17 is formed.

5 (B) 5- (3) After removing the mask film used for the thermal diffusion, a resist process in lithography technology, a vacuum deposition method, a lift process
By applying the off method, a thickness of 100 [Å] / 80 [Å] / 320 [Å] / 50 is formed on the impurity diffusion region 17.
Au / Zn / Au / Ti / P of 0 [Å] / 500 [Å]
A p-side electrode 18 made of t / Au is formed.

6 (A) 6- (1) When immersed in a hydrofluoric acid-based etching solution, the intermediate layer 12 made of AlAs is rapidly etched, and the supporting substrate 11 made of GaAs and the element substrate 13 made of GaAs are separated. Since it is separated, only the element substrate 13 is taken out.

6 (B) 6- (2) By applying a resist process of a lithography technique, an opening is formed on a back surface side of the element substrate 13 at a portion where a groove having a triangular cross section is to be formed. A resist film (not shown) is formed.

6- (3) By applying a wet etching method using an etchant as a sulfuric acid-based etching solution, the element substrate 13 is etched using a resist film as a mask, and the width is, for example, 40.
[Μm] and a groove 13B having a depth of, for example, 50 [μm] and a triangular cross section is formed.

7 (A) 7- (1) A triangular groove 13B on the back surface of the element substrate 13 is formed by applying a resist process, a vacuum evaporation method, and a lift-off method in the lithography technique. 50 thick inside
An n-side electrode 19 made of AuGe / Au of 0 [Å] / 1500 [Å] is formed.

7- (2) 7- (2) Cleaving is performed in the triangular groove 13B to form a chip, thereby completing a semiconductor light receiving device.

Of course, one surface 13A of the triangular groove 13B remaining at the corner on the back side of the substrate 13 after the cleavage is formed as a light incident surface, that is, a chamfered portion.

[0047] Here, the In Step 4- (2), steps of manufacturing the light receiving element film PD _F was bonded to the element substrate 13.

FIG. 8 is a cutaway side view showing a main part of a semiconductor light receiving device in a process step for explaining a method of manufacturing a light receiving element film, and will be described below with reference to this figure.
The same symbols as those used in FIGS. 3 to 7 represent the same parts or have the same meaning.

8A. 8- (1) The buffer layer 14, the light absorbing layer 15, and the window layer 16 are formed on the support substrate 21 by applying the MOCVD method.

The following is an example of main data relating to each semiconductor portion described above. (1) About the support substrate 21 Material: InP (2) About the buffer layer 14 Material: n ⁻ -InP Impurity concentration: 5 × 10 ¹⁵ [cm ⁻³ ] Thickness: 2 [μm] (3) About the light absorbing layer 15 Material: Non-doped InGaAs Impurity concentration: 1 × 10 ¹⁵ [cm ⁻³ ] Thickness: 2 [μm] (4) About window layer 16 Material: n ⁺ -InP Impurity concentration: 2 × 10 ¹⁸ [cm ⁻³ ] Thickness : 1 [μm]

8 (B) 8- (2) A necessary portion such as the surface of the window layer 16 is wax 22
And immersed in a hydrochloric acid-based etching solution to remove the support substrate 21 made of InP.

After this step, the laminated buffer layer 14, light absorbing layer 15, and window layer 16 remain.
This is the light receiving element film PD _F.

In the present invention, many modifications can be realized without being limited to the above-described embodiment. Next, some examples will be described. This can be realized by slightly changing the described steps.

In the following description, cutaway side views of main parts of the semiconductor light receiving device shown in FIGS. 9A, 9B, 10A and 10B for explaining another embodiment are shown. It shall be referred to at any time, and in FIGS. 9 and 10,
The same symbols as those used in FIGS. 3 to 8 represent the same parts or have the same meanings.

Second Embodiment of the Present Invention (1) In step 3- (2) in the first embodiment, the material of the element substrate 13 bonded to the support substrate 11 is changed from n ⁺ -GaAs to n. ⁺ -Si can be substituted. It is well known that Si is a harder material than GaAs.

(2) In that case, the support substrate 11 and n ⁺ −
As a material of the intermediate layer 12 interposed between the Si element substrate, SiO ₂ is preferably used, and as an etchant for the intermediate layer 12, buffered hydrofluoric acid is preferably used.
AuGe / Au can be used as the material of the side electrode.

Third Embodiment of the Present Invention (1) In step 4- (2) in the first embodiment, the light receiving element film PD bonded to the element substrate 13
_As shown in FIG. 9A, the material of the buffer layer 14 made of n ⁻ -InP constituting _F is, for example, 2 × 10
Instead of n ⁺ -InP doped with S of about ¹⁸ [cm ^-3 ], the window layer 16 and the light absorbing layer 15 are selectively etched to expose a part of the buffer layer 14, where the buffer layer 14 is exposed. The n-side electrode 23 can be formed, so that both the p-side electrode 18 and the n-side electrode 23 are on the surface side. still,
Symbol 24 indicates a bonding pad.

(2) In this case, the material of the element substrate 13 can be changed from n ⁺ -GaAs to semi-insulating GaAs, and the material of the n-side electrode 23 has a thickness of, for example, 500 [Å]. It is preferable to use AuGe / Au which is / 1500 [Å].

Fourth Embodiment of the Present Invention (1) In the step 5- (2) in the first embodiment, the p ⁺ impurity diffusion region 17 is formed in the window layer 16 as shown in FIG. As shown in B), at the same time, the second p ⁺ impurity diffusion region 25 is formed in the window layer 16, and the step 5- (3) in the first embodiment is also performed.
In this case, the p-side electrode 18 is formed on the impurity diffusion region 17. However, as shown in FIG. 9B, at the same time, the second p-side electrode 18 is formed on the second p ⁺ impurity diffusion region 25. An electrode 26 is formed. (2) Accordingly, a pip-type semiconductor light receiving device can be realized.

Fifth Embodiment of the Present Invention (1) In the step 5- (2) in the first embodiment, the p ⁺ impurity diffusion region 17 is formed in the window layer 16 as shown in FIG. As shown in A), instead of this, a first n ⁺ impurity diffusion region 27 and a second n ⁺ impurity diffusion region 28 are formed, and the process 5- () in the first embodiment is also performed. In 3), the impurity diffusion region 17 is formed.
The p-side electrode 18 is formed on the first n ⁺ impurity diffusion region 27, as shown in FIG.
The side electrode 29 and the second n ⁺ impurity diffusion region 28
A second n-side electrode 30 is formed on each. (2) Accordingly, a nin type semiconductor light receiving device can be realized.

In each of the above embodiments, basically,
Although the chamfer type in which the signal light is incident from the end face of the semiconductor light receiving device was used, the present invention may be applied to a semiconductor light receiving device in which a lens is formed on the back surface of the substrate and the signal light is incident through the lens. Good results are obtained.

Sixth Embodiment of the Present Invention (1) In step 5- (3) in the first embodiment, the p-side electrode 18 is formed on the p ⁺ impurity diffusion region 17. As shown in FIG. 10B, an n-side electrode 23 is formed outside the p-side electrode 18. In this case, Si is used as the material of the element substrate 13 as in the second embodiment. Symbol 31 indicates an n ⁺ impurity diffusion region.

(2) Step 6 in Embodiment 1
After removing the support substrate 11 and the intermediate layer 12 in the same manner as (1), a lens-shaped resist film is formed on the back surface of the element substrate 13 by using the surface tension of the resist material, and the ion beam etching method is performed. By applying and etching the entire surface until the resist film disappears, the element substrate 1
3 is formed with a lens 13L to which the lens shape of the resist film is transferred.

(3) In this case, since the element substrate 13 is made of a material harder than InP, the lens 13L can be manufactured accurately while maintaining a required shape.
Therefore, the signal light incident through the lens 13L accurately reaches the set light receiving area.

In the present invention, many other modifications can be realized without being limited to the above-described embodiment. For example, GaAs or Si is used as a rigid substrate material. For example, SiC or AlN can be used.

[0066]

According to the method of manufacturing a semiconductor light receiving device of the present invention, an element substrate made of a hard material is bonded to a support substrate via an intermediate layer, and the element substrate made of a hard material is polished from the surface to obtain a hard substrate. InP on the surface of the element substrate made of material
A light-receiving element film including at least a light-absorbing layer made of a system material is attached, and then, the intermediate layer is dissolved to separate the element substrate from the supporting substrate.

By adopting the above configuration, a light receiving element having a substrate with a small thickness variation after polishing can be obtained, so that the signal light from the optical fiber can reach the light receiving region with high accuracy. Therefore, the area of the light receiving region can be reduced, and as a result, the parasitic capacitance also decreases.
A semiconductor light receiving device having a wide dynamic range is realized, and is suitable for PON.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a variation in thickness of a GaAs wafer after polishing.

FIG. 2 is a diagram illustrating a variation in thickness after polishing a GaAs wafer.

FIG. 3 is a cutaway side view of a main part of the semiconductor light receiving device in a process step for explaining the first embodiment of the present invention;

FIG. 4 is a fragmentary side view showing a semiconductor light receiving device at a key point in the process for explaining the first embodiment of the present invention;

FIG. 5 is a fragmentary side view showing a semiconductor light receiving device at a key point in the process for explaining the first embodiment of the present invention;

FIG. 6 is a fragmentary side view showing a semiconductor light receiving device at a key point in the process for explaining the first embodiment of the present invention;

FIG. 7 is a fragmentary side view showing a semiconductor light receiving device at a key point in the process for explaining the first embodiment of the present invention;

FIG. 8 is a fragmentary side view showing a semiconductor light-receiving device in a process step for explaining a method of manufacturing a light-receiving element film.

FIG. 9 is a cutaway side view showing a main part of a semiconductor light receiving device for describing Embodiments 3 and 4;

FIG. 10 is a cross-sectional side view of a main part of a semiconductor light receiving device for describing Embodiments 5 and 6.

FIG. 11 is a cutaway side view of an essential part showing a chamfered light-receiving element and an optical fiber for explaining a problem in the conventional technique.

[Explanation of symbols]

Reference Signs List 11 support substrate 12 intermediate layer 13 element substrate 13A light incident surface (chamfered portion) 13B groove 13L lens 14 buffer layer 15 light absorption layer 16 window layer 17 impurity diffusion region 18 p-side electrode 19 n-side electrode 21 support substrate 22 wax 23 n Side electrode 24 Bonding pad 25 Second p ⁺ impurity diffusion region 26 Second p-side electrode 27 First n ⁺ impurity diffusion region 28 Second n ⁺ impurity diffusion region 29 First n-side electrode 30 Second n-side electrode PD _F receiving element film

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hiroki Murakami 1000 Azagami Azaishi, Showa-cho, Nakakoma-gun, Yamanashi Prefecture Fujitsu Quantum Device Co., Ltd.

Claims (5)

[Claims] 1. A step of bonding an element substrate made of a material harder than an InP-based material to a supporting substrate via an intermediate layer, and then forming an element substrate made of the rigid material into a predetermined thickness. Polishing from the surface, and then bonding a light receiving element film including at least a light absorbing layer made of an InP-based material to the polished surface of the element substrate made of the hard material, and then dissolving the intermediate layer Separating the element substrate from the support substrate. 2. An element substrate made of a material harder than an InP-based material is made of a GaAs-based material, and the intermediate layer is made of AlA.
2. The method according to claim 1, wherein the semiconductor light receiving device is an s layer. 3. The method according to claim 1, wherein the element substrate made of a material harder than the InP-based material is a Si-based material and the intermediate layer is a SiO ₂ layer. . 4. A step of forming a groove having a triangular cross section on the back surface of the element substrate separated from the supporting substrate by dissolving the intermediate layer, and cleaving the element substrate at the bottom of the groove. 3. A method of manufacturing a semiconductor light receiving device according to claim 1, further comprising the step of forming a light incident surface with a surface forming a groove having a triangular cross section. 5. The semiconductor light receiving device according to claim 1, further comprising a step of forming a lens on the back surface of the element substrate separated from the supporting substrate by dissolving the intermediate layer. Manufacturing method.