JP2000208806A - Semiconductor epitaxial wafer and semiconductor device - Google Patents

Abstract

(57) [Problem] To provide an epitaxial wafer for a light receiving element having a small dark current value and less malfunction. SOLUTION: The semiconductor epitaxial wafer is a semiconductor epitaxial wafer for a light receiving element which receives an electromagnetic wave having a wavelength of 1.1 μm or more and 1.6 μm or less.
A group-V compound semiconductor substrate; and an epitaxial layer formed on the group-III-V compound semiconductor substrate. The center line average roughness Ra measured at a length of 50 to 200 μm on the outermost surface of the epitaxial layer is 3 nm or less. The semiconductor epitaxial wafer is a semiconductor epitaxial wafer for a light receiving element that receives an electromagnetic wave having a wavelength of 1.8 μm or more and 3.0 μm or less, and is measured at a length of 50 to 200 μm on the outermost surface of the epitaxial layer. The center line average roughness Ra is 6 nm or less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor epitaxial wafer and a semiconductor device, and more particularly to a semiconductor epitaxial wafer and a light receiving element for a light receiving element used for optical communication.

[0002]

2. Description of the Related Art In recent years, with the development of optical communication, the production of light receiving elements such as photodiodes has been increasing.

FIG. 7 is a diagram showing a conventional light receiving element.
Referring to FIG. 7, light receiving element 101 includes semiconductor substrate 102.
, Buffer layer 103, light receiving layer 104, window layer 105
, Passivation film 107 and impurity diffusion region 10
8, a p-type electrode 109, and an n-type electrode 110.

A buffer layer 103 made of an indium-phosphorus compound is formed on an upper surface of a semiconductor substrate 102 made of an indium-phosphorus compound (InP). Buffer layer 103 is n-type. On the buffer layer 103, a light receiving layer 104 made of an indium-gallium-arsenic compound (InGaAs) is formed. The light receiving layer 104 is n-type. On the light receiving layer 104, a window layer 105 made of an indium-phosphorus compound is formed.

[0005] In the window layer 105 and the light receiving layer 104, an impurity diffusion region 108 formed by diffusion of zinc is formed. A p-type electrode 109 is formed so as to be in contact with impurity diffusion region 108. A passivation film 107 made of silicon nitride (SiN) is formed so as to cover the surface of window layer 105. On the lower surface of the semiconductor substrate 102, an n-type electrode 110 is formed.

The impurity diffusion region 108 is p-type, and a pn junction is formed at a portion where the impurity diffusion region 108 and the n-type light receiving layer 104 are in contact. Therefore, when light is irradiated to the pn junction, a current is generated. p-type electrode 10
9 and n-type electrode 110 are connected to DC power supply 112, and the pn junction is biased in the reverse direction.

When light is incident from the direction indicated by arrow 111, the light reaches a pn junction where the impurity diffusion region 108 and the light receiving layer 104 are in contact. This light generates a current at the pn junction. This current flows between the p-type electrode 109 and the n-type electrode 110, which are reversely biased, and further flows through the circuit 113. Thus, the light incident on the light receiving element 101 is converted into an electric signal.

[0008]

The above-mentioned light receiving element 101
In, current flows through the circuit 113 only when light enters from the direction indicated by the arrow 111, but current may flow through the circuit 113 even when light does not enter from the direction indicated by the arrow 111. Such a current is called a dark current, and there has been a problem that the yield of the light receiving element 101 decreases as the value of the dark current increases.

Therefore, the present invention has been made to solve the above-mentioned problems, and a semiconductor epitaxial wafer capable of manufacturing a light receiving element having a small dark current.
It is an object of the present invention to provide a semiconductor device manufactured from the epitaxial wafer.

[0010]

The inventors of the present invention have analyzed the cause of the occurrence of dark current and found that the dark current is caused by crystal defects formed in the light receiving layer of the light receiving element. When the light receiving layer has a crystal defect, the surface of the light receiving layer becomes rough. Since the surface of the layer formed on the light receiving layer also has a large roughness, the outermost surface of the epitaxial layer has a large roughness. Therefore, it was found that when the roughness of the outermost surface of the epitaxial layer was equal to or less than the predetermined value, the dark current value was small.

A semiconductor epitaxial wafer according to one aspect of the present invention, which has been made based on such knowledge, is a semiconductor epitaxial wafer for a light receiving element that receives an electromagnetic wave having a wavelength of 1.1 μm to 1.6 μm. And a III-V compound semiconductor substrate and the III-V compound semiconductor substrate.
An epitaxial layer formed on the group III compound semiconductor substrate. 50 μm length at the outermost surface of the epitaxial layer
The center line average roughness Ra measured in the range from m to 200 μm is 3 nm or less.

In the semiconductor epitaxial wafer thus configured, the roughness of the surface of the light receiving layer formed in the epitaxial layer is reduced, and the crystal defects of the layer are reduced. And the center line average roughness Ra at the outermost surface of the epitaxial layer is 3 nm.
Less than the following. As a result, if a light receiving element is manufactured from this semiconductor epitaxial wafer, a light receiving element with a small dark current value can be manufactured.

A semiconductor epitaxial wafer according to another aspect of the present invention is a semiconductor epitaxial wafer for a light receiving element for receiving an electromagnetic wave having a wavelength of 1.8 μm or more and 3.0 μm or less, comprising a III-V compound semiconductor substrate. When,
An epitaxial layer formed on the III-V compound semiconductor substrate. The center line average roughness Ra measured in a range of 50 μm or more and 200 μm or less on the outermost surface of the epitaxial layer is 6 nm or less.

In the semiconductor epitaxial wafer thus configured, the surface of the layer in the epitaxial layer that receives light has a small roughness and the number of crystal defects in this layer is small. Has a small center line average roughness Ra of 6 nm. As a result, if a light receiving element is manufactured from this semiconductor epitaxial wafer, a light receiving element with a small dark current value can be manufactured.

The light receiving element for receiving an electromagnetic wave having a wavelength of 1.1 μm to 1.6 μm is preferably an optical communication element.

It is preferable that the light receiving element for receiving an electromagnetic wave having a wavelength of not less than 1.8 μm and not more than 3.0 μm is a sensor element.

The epitaxial layer includes a light-receiving layer containing a group III-V compound formed on a group III-V compound semiconductor substrate and a layer III formed on the light-receiving layer and constituting the outermost surface of the epitaxial layer. And a window layer containing a group V compound. In this case, in the window layer on the outermost surface of the epitaxial layer, the center line average roughness Ra is reduced, so that the surface roughness of the light receiving layer formed thereunder is also reduced, and the crystal defects in the light receiving layer are reduced. as a result,
The dark current value can be reduced.

Preferably, the light receiving layer contains an InGaAs compound or an InGaAsP compound, and the window layer contains an InP compound or an InAsP compound.

Further, a semiconductor device manufactured from the above-described semiconductor epitaxial wafer is preferable because the dark current value is small.

[0020]

Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) FIG. 1 shows Embodiment 1 of the present invention.
FIG. 2 is a diagram showing a light receiving element according to FIG. Referring to FIG. 1, light receiving element 1 (pin photodiode, hereinafter referred to as “PIN-P
D ". ) Indicates the semiconductor substrate 2 and the buffer layer 3
Light-receiving layer 4, window layer 5, passivation film 7,
The semiconductor device includes an impurity diffusion region, a p-type electrode, and an n-type electrode.

The semiconductor substrate 2 is formed of an indium-phosphorus compound. The thickness of the semiconductor substrate 2 is 350 μm. The semiconductor substrate 2 is doped with sulfur as an impurity, and the concentration of sulfur is about 5 × 10 ¹⁸ to 8 × 10 ¹⁸ atoms / cm ³ .

On the semiconductor substrate 2, a buffer layer 3 is formed. The buffer layer 3 functions to prevent impurities in the semiconductor substrate 2 from diffusing. The thickness of the buffer layer 3 is 2 μm. The buffer layer 3 is made of n-type indium-
It is composed of a phosphorus compound. The impurity concentration in the buffer layer 3 is 2 × 10 ¹⁵ atoms / cm ³ .

On the buffer layer 3, a light receiving layer 4 is formed. The thickness of the light receiving layer 4 is 3.5 μm. Light receiving layer 4
Is composed of an n-type indium-gallium-arsenic compound. The light receiving layer 4 converts the irradiated light into electric current.

A window layer 5 made of an n-type indium-phosphorus compound is formed on the light-receiving layer 4. The impurity diffusion region 8 is formed in the window layer 5 and the light receiving layer 4. In the impurity diffusion region 8, zinc as a p-type impurity is diffused. Pn is provided at the interface between the light receiving layer 4 and the impurity diffusion region 8.
A bond has been formed. On the impurity diffusion region 8, a ring-shaped p-type electrode 9 is formed. The inner diameter D of the p-type electrode 9 is 300 μm. The p-type electrode 9 is formed of a gold-zinc alloy. A passivation film 7 made of silicon nitride is formed so as to cover the surface of window layer 5.

Under the semiconductor substrate 2, an n-type electrode 10 is formed. The n-type electrode 10 is made of a gold-germanium-nickel alloy. p-type electrode 9 and n-type electrode 1
0 is connected to the DC power supply 12, and a voltage is applied so that the pn junction at the interface between the impurity diffusion region 8 and the light receiving layer 4 becomes reverse biased. The semiconductor substrate 2, the buffer layer 3, the light receiving layer 4, and the window layer 5 are obtained by manufacturing a semiconductor epitaxial wafer having a window layer surface roughness Ra of 3 nm or less and cutting the wafer.

When light is applied to the light receiving element 1 from the direction indicated by the arrow 11, the light passes through the window layer 5 and reaches the light receiving layer 4. Light generates a current in the light receiving layer 4. This current is amplified by the window layer 5 and flows through the circuit 13, whereby light is converted into an electric signal.

Since the light receiving element 1 thus constructed is manufactured from a semiconductor epitaxial wafer having an outermost surface (window layer surface) having a roughness of 3 nm or less, the surface of the light receiving layer 4 has a small roughness. There are few crystal defects in the light receiving layer 4.
As a result, the dark current decreases.

Next, a method for manufacturing this light receiving element will be described. FIG. 2 is a schematic diagram showing a vapor phase epitaxial growth apparatus. FIG. 3 is a schematic view of a semiconductor epitaxial wafer manufactured according to the present invention.

Referring to FIG. 2, a vapor phase epitaxial growth apparatus 61 comprises a reactor 62, a driving means 63, a heater 6
4a and 64b, source boards 65 to 67, and source containers 68 to 70 are provided.

In the reactor 62, source boards 65 and 67 containing indium (In) and a source board 66 containing gallium (Ga) are provided.

The driving means 63 is provided for rotating the substrate 22 in the direction shown by the arrow. Hydrogen is fed into the source containers 68 and 69 containing AsCl ₃ and the source container 70 containing PCl ₃ via pipes 71 to 73, respectively. The source container 68 and the source board 65
They are connected by a pipe 74. The source container 69 and the source board 66 are connected by a pipe 75. Source container 7
0 and the source board 67 are connected by a pipe 76.
Heaters 64a and 64b heat reactor 62.

Using such a device, first, the heater 64
By adjusting the outputs of a and 64b, a temperature distribution was formed in the reactor 62 as shown in FIG. Next, the substrate 22 as a semiconductor substrate made of an InP substrate doped with a predetermined concentration of sulfur was set in the driving unit 63. Substrate 2
2 had a diameter of 50 mm and a thickness of 450 μm. The radius R of the cross section at the end of the substrate 22 was 0.25 mm.

The substrate 22 was rotated by the driving means 63 and moved downward in FIG. In this state,
By sending hydrogen gas into the source container 70 via the pipe 73, the following chemical reaction (1) occurred in the source container 70.

[0035]

Embedded image

The P ₄ generated by the reaction shown in the above (1)
And HCL were sent to the source board 67, and the chemical reaction shown in the following (2) occurred.

[0037]

Embedded image

P ₄ sent to the source board 67,
InCl and H ₂ generated by the reaction shown in the above (2) caused a chemical reaction shown in the following (3) on the substrate 22.

[0039]

Embedded image

From the equation shown in (3), as shown in FIG.
An InP buffer layer 23 having a thickness of 2 μm was grown on the substrate 22.

Next, the substrate 22 was rotated and moved upward in FIG. 2A by using the driving means 63. By sending hydrogen gas to the source containers 68 and 69 via the pipes 71 and 72, the source containers 68 and 69 caused a chemical reaction shown in the following (4).

[0042]

Embedded image

A produced by the reaction shown in the above (4)
s ₄ and HCl is fed to the source board 65 through the pipe 74, the chemical reaction occurs as indicated by the following (5).

[0044]

Embedded image

Further, As ₄ and HCl generated by the reaction shown in the above (4) are supplied to the source board 6 through the pipe 75.
As a result, the chemical reaction shown in the following (6) occurred.

[0046]

Embedded image

As ₄ sent to source board 65
InCl generated on the source board 65, GaCl generated on the source board 66, and source boards 65 and 6.
H ₂ generated in 6 caused a chemical reaction shown in the following (7).

[0048]

Embedded image

From the equation shown in (7), as shown in FIG.
3.5 μm thick indium-gallium-on the substrate 22
The light receiving layer 24 made of an arsenic compound was formed.

Next, the substrate 22 is moved downward in FIG. 2A, hydrogen gas is fed into the source container 70 via the pipe 73, and the light-receiving layer 24 is supplied according to the above-mentioned equation (3).
A window layer 25 made of an indium-phosphorus compound having a thickness of about 1.5 μm was formed thereon. Thus, a semiconductor epitaxial wafer shown in FIG. 3 was obtained.

The surface roughness was measured using a surface roughness meter at the six outermost portions (portions 1 to 6) of the window layer shown in FIG. The measurement conditions are as follows.

Measurement distance: 1000 μm Horizontal resolution: 0.125 μm / sample Measurement range: 65 KA Needle contact pressure: 11 mg FIG. 4 shows data on the part 1 obtained under these conditions.

FIG. 4 shows that the outermost surface of the window layer has a thickness of about 0.1 μm.
It can be seen that the surface roughness varies in the range of m.

Based on such measurement results, parts 1 to 6
, The center line average roughness Ra was calculated in the range of 50 μm or more and 200 μm or less.

Table 1 shows the results.

[0056]

[Table 1]

Next, after selectively diffusing zinc at a predetermined concentration into the light receiving layer and the window layer, the window layer 25 was polished. On the window layer 25, a passivation film, a p-type electrode, and an n-type electrode were formed. By cutting the semiconductor substrate to predetermined dimensions,
A plurality of PIN-PDs (samples 1 to 6) were produced.
Sample 1 includes portion 1, sample 2 includes portion 2, ..., sample 6 includes portion 6.

The obtained samples 1 to 6 were subjected to IV measurement of each sample using an auto-probing apparatus. From this measurement result, the value of the dark current was calculated. The result is shown in FIG. In FIG. 5, points 201, 202 and 20
, 206 are points corresponding to sample 1, sample 2, sample 3, ..., sample 6, respectively.

As shown in FIG. 5, Samples 1 to 4 each had a small dark current and exhibited very good dark current characteristics.
This is presumably because the center line average roughness Ra of the surface of the window layer before polishing was small, so that the surface roughness of the light receiving layer was small and the number of crystal defects in the light receiving layer was small.

On the other hand, in samples 5 and 6, the dark current value was large. This is presumably because the surface roughness of the window layer before polishing was large, so that the surface roughness of the light receiving layer was large and crystal defects existed in the light receiving layer.

According to the present invention, the PIN-
In order to manufacture a PD, a semiconductor epitaxial wafer is manufactured according to the above-described steps, and the surface roughness Ra is measured before polishing. In this epitaxial wafer, only the portion where the center line average roughness of the outermost surface of the window layer before polishing is 3.0 nm or less is defined as PIN-PD, and from the portion where the surface roughness Ra of the window layer before polishing exceeds 3.0 μm. Is PIN-PD
Is not manufactured, so that a PIN-
PD can be manufactured.

Example 2 In Example 2, a light receiving element for a sensor was manufactured.

Specifically, first, a buffer layer 23, a light receiving layer 24 and a window layer 25 having the same composition as in Example 1 were formed on a substrate 22 in accordance with the steps of Example 1. In addition, these thicknesses were thicker than those in Example 1.
Next, the window layer 2 was formed using a surface roughness meter in the same manner as in Example 1.
The surface roughness of the outermost surface of No. 5 was measured. Based on the measurement results, the center line average roughness Ra in the range of 50 μm or more and 200 μm or less in the outermost surface portions 11 to 18 of the window layer 25 was calculated. Table 2 shows the results.

[0064]

[Table 2]

Next, zinc is diffused into the window layer of the semiconductor epitaxial wafer at a concentration different from that of the first embodiment.
The surface of the window layer was polished. Thereafter, a passivation film was formed on the surface of the window layer, and a p-type electrode and an n-type electrode were formed.
The inner diameter D of the p-type electrode was 1 mm. By cutting this wafer to a predetermined size, the wavelength is 1.8.
PIN-PDs (samples 11 to 18) were formed as sensors for receiving electromagnetic waves of not less than μm and not more than 3.0 μm.
Sample 11 includes portion 11 and sample 12 includes portion 1
2,..., Sample 18 includes portion 18.

With respect to the obtained PIN-PD, IV measurement of each sample was performed using an auto-probing apparatus. The value of the dark current was calculated from the measurement result. FIG. 6 shows the result.

In FIG. 6, points 301, 302, 303,.
Reference numeral 308 is a point corresponding to Sample 11, Sample 12, Sample 13,..., Sample 18, respectively. According to this graph, in Samples 11 to 14, the dark current value is small and good dark current characteristics are shown. This is because the center line average roughness Ra of the outermost surface of the window layer before polishing is small.
It is considered that the dark current value was reduced because the surface roughness of the light receiving layer was small and the number of crystal defects in the light receiving layer was small.

In Samples 15 to 18, the dark current value was large, and the dark current characteristics deteriorated. This is considered to be because the center line average roughness Ra of the outermost surface of the window layer before polishing is large, so that the surface roughness of the light receiving layer is large, and many crystal defects occur in the light receiving layer. When the dark current value exceeds 500 nA as in samples 15 to 18, malfunctions are excessive, and
It cannot be used as a light receiving element for a sensor.

The PIN- having a small dark current value described above
To manufacture a PD, a semiconductor epitaxial wafer is manufactured by the above-described method, and the surface roughness Ra of the window layer is measured before polishing. Then, a PIN-PD is manufactured from a portion having a surface roughness Ra of 6 nm or less, and a PIN-PD is not manufactured from a portion having a surface roughness Ra exceeding 6 nm. Can be manufactured.

Example 3 In Example 3, a light receiving element for a sensor was manufactured.

More specifically, a plurality of semiconductor epitaxial wafers for manufacturing a light receiving element for a sensor were manufactured in accordance with the same steps as those in the above-described Example 2. The surface roughness of the outermost surface of the window layer of this epitaxial wafer was measured.
Based on this measurement result, in a plurality of semiconductor epitaxial wafers, the center line average roughness Ra in the range of 50 μm or more and 200 μm or less was calculated at 800 of the outermost surface portions 101 to 900 of the window layer. . Table 3 shows the results.

[0072]

[Table 3]

Next, zinc was diffused into the window layers of these semiconductor epitaxial wafers in the same manner as in Example 2, and the surfaces of the window layers were polished. Thereafter, a passivation film was formed on the surface of the window layer, and a p-type electrode and an n-type electrode were formed. This wafer is cut into a predetermined size, so that a PIN-PD (sample 101 to sample 101) serving as a sensor for receiving an electromagnetic wave having a wavelength of 1.8 μm or more and 3.0 μm or less is obtained.
Sample 900) was formed. Sample 101 is part 1
01, sample 102 includes portion 102,.
Sample 900 includes portion 900.

The obtained PIN-PD was subjected to IV measurement of each sample using an auto-probing apparatus. From this measurement result, the value of the dark current was calculated. Those having a dark current exceeding 400 nm were regarded as defective. FIG. 8 shows the relationship between the roughness Ra of the outermost surface of the window layer before polishing and the defect rate.

In FIG. 8, points 501, 502, 503,.
Reference numeral 508 is a point corresponding to samples 101 to 200, samples 201 to 300, samples 301 to 400,..., Samples 801 to 900, respectively. For the defective rate (%), for example, samples 101 to 200
At the point 501 corresponding to, the number of samples 101 to 200 having a dark current value of more than 400 nm was defined as the defect rate.

From this graph, it can be seen that the defect rate is small when the surface roughness Ra before polishing is 6 nm or less. This is presumably because the center line average roughness Ra of the outermost surface of the window layer before polishing was small, so that the surface roughness of the light receiving layer was small, and the dark current value was small because there were few crystal defects in the light receiving layer.

On the other hand, in Samples 501 to 900, the defect rate increased due to the increase in the dark current value. This is considered to be because the center line average roughness Ra of the outermost surface of the window layer before polishing is large, so that the surface roughness of the light receiving layer is large, and many crystal defects occur in the light receiving layer.

Although the embodiment of the present invention has been described above, the embodiment shown here can be variously modified. First, materials constituting the substrate, the buffer layer, the light receiving layer, and the window layer are not limited to those shown in the embodiments, and other III-V compounds may be used. further,
Each film thickness or the like can be changed as needed.

It should be understood that the embodiments disclosed this time are illustrative in all respects and are not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

[0080]

According to the present invention, the dark current value is small,
It is possible to provide a light receiving element that does not easily malfunction.

[Brief description of the drawings]

FIG. 1 is a diagram showing a light receiving element according to a first embodiment of the present invention.

FIG. 2 is a schematic view showing a vapor phase epitaxial growth apparatus.

FIG. 3 is a schematic view of a semiconductor epitaxial wafer manufactured according to the present invention.

FIG. 4 is a graph showing the roughness of the outermost surface of the window layer.

FIG. 5 is a graph showing the relationship between the roughness Ra of the outermost surface of the window layer before polishing and the dark current in the light receiving element for communication;

FIG. 6 is a graph showing a relationship between surface roughness Ra of a window layer before polishing and dark current in a light receiving element for a sensor.

FIG. 7 is a schematic diagram of a conventional light receiving element.

FIG. 8 is a graph showing a relationship between a surface roughness Ra of a window layer before polishing and a defect rate in a light receiving element for a sensor.

[Explanation of symbols]

 2 Semiconductor substrate 4 Light receiving layer 5 Window layer

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5F045 AB12 AB17 AB18 AB33 AC03 AD10 AF04 BB12 BB16 CA13 CB04 DA51 DA53 DA65 DQ08 EE03 EK06 5F049 MA02 MB07 MB12 NA05 NB01 NB03 PA03 SE05 SS04 SZ12 WA01

Claims (7)

[Claims] 1. A semiconductor epitaxial wafer for a light receiving element for receiving an electromagnetic wave having a wavelength of 1.1 μm or more and 1.6 μm or less, comprising: a III-V compound semiconductor substrate; A length of 50 μm or more at the outermost surface of the epitaxial layer.
Center line average roughness R measured in the range of 00 μm or less
A semiconductor epitaxial wafer wherein a is 3 nm or less. 2. A semiconductor epitaxial wafer for a light-receiving element for receiving an electromagnetic wave having a wavelength of 1.8 μm or more and 3.0 μm or less, comprising: a III-V compound semiconductor substrate; and a III-V compound semiconductor substrate. A length of 50 μm or more at the outermost surface of the epitaxial layer.
Center line average roughness R measured in the range of 00 μm or less
A semiconductor epitaxial wafer wherein a is 6 nm or less. 3. The semiconductor epitaxial wafer according to claim 1, wherein said light receiving element is an optical communication element. 4. The semiconductor epitaxial wafer according to claim 2, wherein said light receiving element is a sensor element. 5. The method according to claim 1, wherein the epitaxial layer is
A light receiving layer containing a group III-V compound formed on a group V compound semiconductor substrate, and a window layer containing a group III-V compound formed on the light receiving layer and constituting the outermost surface of the epitaxial layer The semiconductor epitaxial wafer according to claim 1, comprising: 6. The semiconductor epitaxial wafer according to claim 5, wherein said light receiving layer contains an InGaAs compound or an InGaAsP compound, and said window layer contains an InP compound or an InAsP compound. 7. A semiconductor device manufactured from the semiconductor epitaxial wafer according to claim 1.