JP2002343980A - Variable capacity diode and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable a discrete variable diode to be operated at a low voltage by increasing the rate of change in voltage capacity, and to improve high-frequency characteristics of the variable diode. SOLUTION: By forming an anode electrode 7 using aluminum silicon having the silicon content between 3% and 5%, an aluminum spike into a p<+> diffusion layer 4 can be prevented. Thereby, p<+> diffusion layer 4 and an n<+> diffusion layer 3 can be formed shallow, making a steep distribution profile of impurity concentration. Furthermore, the impurity concentration can be kept low with a diffusion potential kept low. Consequently, the rate of change in voltage capacity can be increased, allowing the operation of the diode at a low voltage. By lowering the diffusion potential, carriers can move easily, thereby improving high-frequency characteristics.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a variable capacitance diode, and more particularly to a discrete variable capacitance diode used in a high frequency circuit.

[0002]

2. Description of the Related Art A variable capacitance diode is a diode that utilizes the fact that a depletion layer of a pn junction acts as a capacitor when a reverse bias voltage is applied. The capacitance of the depletion layer of the variable capacitance diode is adjusted by changing the magnitude of the reverse bias. Utilizing such a change in the capacitance of the depletion layer, the variable capacitance diode is tuned, frequency-multiplied,
It is used for frequency conversion and automatic frequency control.

[0003] Discrete variable capacitance diodes are:
For example, an n-type substrate, a high-concentration n ⁺ diffusion layer formed on the n-type substrate, and a p-type layer formed on the surface of the n ⁺ diffusion layer
^A diffusion layer, an anode electrode formed of aluminum above the p ⁺ diffusion layer, and a cathode electrode formed of Au, Ag, or the like below the n-type substrate. In such a variable capacitance diode, the cathode electrode is reverse-biased to have a higher potential than the anode electrode, and a depletion layer generated near the junction between the p ⁺ diffusion layer and the n ⁺ diffusion layer is used as a variable capacitance capacitor. are doing.

[0004]

In such a variable capacitance diode, aluminum of the anode electrode is deposited on the p ⁺ diffusion layer to cause aluminum spikes. If p ⁺ diffusion layer is thin, the aluminum spike penetrates the p ⁺ diffusion layer, and the p ⁺ diffusion layer and the n ⁺ diffusion layer to lead to a short circuit. Conventionally, a high concentration deep p ⁺ diffusion layer is formed to prevent a short circuit due to an aluminum spike.
However, since ion implantation is performed in a deep region, it is difficult to control the impurity concentration, and the distribution of the p-type impurity concentration cannot be formed steeply. Further, in order to form the p ⁺ diffusion layer at a high concentration and deep, even in the step of forming the n ⁺ diffusion layer thereunder,
It is necessary to implant impurities at a high concentration and deeply, it is difficult to control the impurity concentration, and the distribution of the n-type impurity concentration cannot be formed steeply.

When the impurity concentration is reduced in this manner, it is difficult to remove carriers from the junction between the p ⁺ diffusion layer and the n ⁺ diffusion layer at the time of reverse bias, and the ratio of the change of the depletion layer capacitance to the change of the reverse bias voltage ( Voltage change rate) cannot be increased.

When the rate of change in voltage capacity is small, it is necessary to increase the change in reverse bias voltage for changing the capacity of the depletion layer, and the variable capacity diode cannot be driven at a low voltage. In this case, it becomes difficult to use a variable capacitance diode in a VCO (Voltage Controlled Oscillator) or a tuner circuit of a mobile phone or the like that requires driving at a low voltage.

Further, since the p-type and n-type impurity concentrations are high, carrier movement is slow, and it is difficult to use them in a high-frequency circuit. SUMMARY OF THE INVENTION An object of the present invention is to improve the high-frequency characteristics of a discrete variable diode by increasing the rate of change in voltage capacity so that the diode can be driven at a low voltage.

[0008]

A variable capacitance diode according to a first aspect of the present invention is a variable capacitance diode formed on a semiconductor substrate, the first conductivity type impurity diffusion region formed on a surface of the semiconductor substrate, A second conductivity type impurity diffusion region formed in the first conductivity type impurity diffusion region; and aluminum silicon formed on a surface of the second conductivity type impurity diffusion region and having a silicon content of 3 w% or more and 10 w% or less. And a second electrode formed on the back surface of the semiconductor substrate.
Electrodes.

In the variable capacitance diode according to the first invention,
Since the first electrode is formed of aluminum silicon, aluminum spikes can be prevented, and the second conductivity type impurity diffusion region can be formed shallow.
Since the second conductivity type impurity region is formed shallow, the impurity concentration can be easily controlled by ion implantation, and the concentration distribution of the second conductivity type impurity can be made steep. Further, since the second conductivity type impurity region is formed shallow, the first conductivity type impurity region may be formed shallow, and for the same reason, the concentration distribution of the first conductivity type impurity can be made steep. The steep distribution of the impurity concentration improves the rate of change in voltage capacity, and the variable capacity diode can be driven at a low voltage.

Further, since the first conductivity type impurity diffusion region and the second conductivity type impurity diffusion region are formed shallow, the high resistance region between the second electrode and the first conductivity type impurity diffusion region can be made thin. , The series resistance between the first and second electrodes can be reduced. Also, since the impurity region is made thin, p
The impurity concentration of the n-type and n-type can be reduced, the movement of carriers becomes faster, and the high-frequency characteristics of the variable capacitance diode can be improved.

The reason why the silicon content of aluminum silicon of the first electrode is set to 3 wt% or more and 10 wt% or less is as follows. In a high-density integrated circuit (LSI), an aluminum silicon electrode having a silicon content of 1 w% to 2 w% has conventionally been used to prevent aluminum spikes. However, since a discrete variable capacitance diode has a large junction area between an electrode and a diffusion layer, even if an aluminum silicon electrode having a silicon content of 1 w% to 2 w% is used, it is possible to sufficiently prevent aluminum spikes. Can not. Therefore, by setting the silicon content of aluminum silicon to 3 w% or more, aluminum spikes are suppressed and a short circuit of the pn junction is prevented. On the other hand, when the silicon content increases, a high-resistance silicon crystal is formed in the aluminum silicon electrode (silicon nodule), and the contact resistance between the first electrode and the second impurity diffusion region increases, deteriorating high-frequency characteristics. Therefore, by setting the silicon content to 10 w% or less,
The contact resistance is not increased.

A method of manufacturing a variable capacitance diode according to a second aspect of the present invention is a method of manufacturing a variable capacitance diode on a semiconductor substrate, comprising: forming a first conductivity type impurity diffusion region on a surface of the semiconductor substrate; Forming a second conductivity type impurity diffusion region on the surface so as to overlap with the first conductivity type impurity diffusion region; and forming aluminum silicon having a silicon content of 3 w% or more and 10 w% or less on the surface of the second conductivity type impurity diffusion region. Forming a first electrode, and forming a second electrode on the back surface of the semiconductor substrate.

According to the variable capacitance diode manufacturing method of the second invention, the same function and effect as described in the variable capacitance diode of the first invention can be obtained.

[0014]

FIG. 1 is a sectional structural view showing a variable capacitance diode according to an embodiment of the present invention. This variable capacitance diode includes an n-type semiconductor substrate 1,
An n-type epitaxial layer 2 formed by epitaxial growth on an n-type semiconductor substrate 1, and n ⁺ in which n-type impurities are heavily implanted into a predetermined region of the n-type epitaxial layer 2.
Diffusion layer 3, p ⁺ diffusion layer 4 formed on the surface of n-type epitaxial layer 2 so as to overlap n ⁺ diffusion layer 3, and heat formed so as to have an opening in a predetermined region of the p ⁺ diffusion layer An oxide film 5; a CVD oxide film 6 formed on the surface of the thermal oxide film 5 in the same pattern as the thermal oxide film 5;
Anode electrode 7 of a variable capacitance diode formed of Al-Si so as to be electrically connected to p ⁺ diffusion layer 4 through an opening of oxide film 6, and a part of CVD oxide film 6 and anode electrode 7 A protective film 8 formed so as to cover
A cathode electrode 9 of a variable capacitance diode formed of Au, Ag, or the like is provided on the back surface of the mold semiconductor substrate 1.

[Manufacturing Process] FIGS. 2 to 7 are cross-sectional views for explaining a manufacturing process of the variable capacitance diode shown in FIG. Hereinafter, the manufacturing process of the variable capacitance diode according to the present embodiment will be described with reference to FIGS.

First, as shown in FIG. 2, 10 ¹⁹ -5 × 1
N-type semiconductor substrate 1 containing 0 ¹⁹ atoms / cm ³ As
Next, Si is epitaxially grown to form an n-type epitaxial layer 2. n-type epitaxial layer 2 is 1 μm
３3 μm.

Next, as shown in FIG. 3, the surface of the n-type epitaxial layer 2 is thermally oxidized to form a thermal oxide film 5, and a photoresist pattern is formed and then etched to form an n ⁺ diffusion layer 3. An opening 10 is formed at a position to be formed. After a further thin thermal oxidation, via the thermal oxide film 5,
The surface of the n-type epitaxial layer 2 below the opening 10
As is ion-implanted at 0 ¹⁶ to 10 ¹⁸ atoms / cm ³ . Thereafter, the n-type epitaxial layer 2 is annealed to
The type impurities are thermally diffused to form a thermal oxide film 5 and an n ⁺ diffusion layer 3 as shown in FIG. In this embodiment, the n ⁺ diffusion layer 3
Is formed to a thickness of 1 μm to 2 μm.

Next, as shown in FIG. 5, by etching after forming a photoresist pattern on the thermal oxide film 5, an opening 11 wider than the opening 10 is formed in the thermal oxide film 5.
To form After further thermal oxidation, B ions of 10 ¹⁹ to 10 ²⁰ atoms / cm ³ are implanted into the surface of the n-type epitaxial layer 2 below the opening 11 through the thermal oxide film 5.

Next, as shown in FIG. 6, a CVD oxide film 6 is formed, and thereafter, p-type impurities are diffused by annealing, and a p-type impurity is formed on the surface of the n-type epitaxial layer 2 wider than the n ⁺ diffusion layer 3. ^{+ A} diffusion layer 4 is formed. In this embodiment, the p ⁺ diffusion layer 4 is formed to have a thickness of 0.3 μm to 0.6 μm.

Next, after forming a photoresist pattern on the CVD oxide film 6, the CVD oxide film 6 and the thermal oxide film 5 are etched to form an opening 12 in a region where the anode electrode 7 is to be formed. The p ⁺ diffusion layer 4 is exposed.

After exposing the p ⁺ diffusion layer 4, Al-Si is deposited by sputtering using an Al-Si target. Thereafter, a photoresist pattern is formed on the Al-Si, and the Al-Si is etched to leave the anode electrode 7 only on the p ⁺ diffusion layer 4 as shown in FIG. Thereafter, a protective film 8 such as Si ₃ N ₄ is formed on the CVD oxide film 6 and the anode electrode 7 by CVD. After forming a photoresist pattern on the protective film 8, the protective film 8 is etched to expose the anode electrode 7. Finally, after polishing the back surface of the n-type semiconductor substrate 1, A
The cathode electrode 9 is formed by depositing u, Ag, or the like.

Here, the silicon content of the anode electrode 7 is set to 3 w% or more and 10 w% or less. In a high-density integrated circuit (LSI), Al-Si having a silicon content of 1 w% to 2 w% is conventionally used to prevent aluminum spikes.
Electrodes were used. However, in a discrete variable capacitance diode, the junction area between the anode electrode 7 and the p ⁺ diffusion layer 4 is large, and the silicon content is 1 w% to 2 w
% Al-Si anode electrode 7 cannot sufficiently prevent aluminum spikes. Therefore, in the variable capacitance diode according to the present embodiment, by setting the silicon content to 3 w% or more, aluminum spikes are suppressed, and short-circuit of the pn junction is prevented. on the other hand,
When the silicon content increases, a phenomenon (silicon nodule) in which a high-resistance silicon crystal is formed in the aluminum silicon electrode occurs. When the joule of silicon occurs, the contact resistance between the anode electrode 7 and the p ⁺ diffusion layer 4 increases, deteriorating the high frequency characteristics. Therefore, the silicon content is set to 10 w% or less so that the contact resistance does not increase.

FIG. 8A is a schematic diagram showing the distribution of impurity concentrations of a conventional discrete variable capacitance diode and the discrete variable capacitance diode according to the present embodiment. In the figure, the horizontal axis represents the depth Xj from the surface of the p ⁺ diffusion layer 4, and the vertical axis represents the p-type or n-type impurity concentration. In addition, the impurity concentration according to the related art is represented by a dotted line, and the impurity concentration according to the present embodiment is represented by a solid line. As shown in the figure, in the conventional variable capacitance diode, the anode electrode 7 is formed of Al, and the n ⁺ diffusion layer 3 and the p ⁺ diffusion layer 4 are formed in order to prevent the short circuit of the pn junction due to the aluminum spike. It is formed deeply and has a high impurity concentration. On the other hand, in this embodiment, since the anode electrode 7 is formed of Al—Si to suppress aluminum spikes, n ⁺
The diffusion layer 3 and the p ⁺ diffusion layer 4 can be formed shallower than before,
The impurity concentration can also be kept low. Therefore, the control of the impurity concentration becomes easy, and the distribution of the impurity concentration can be made sharp.

The steep distribution of the impurity concentration improves the voltage capacity change rate, and enables the variable capacity diode to be driven at a low voltage. By making the impurity concentration shallow and sharp, the high resistance region between n ⁺ diffusion region 3 and n-type semiconductor substrate 1 can be made thin, that is, n-type epitaxial layer 2 can be made thin, and anode electrode 7 and cathode electrode 9 can be reduced. Further, since the impurity region is thinned, the p-type and n-type impurity concentrations can be reduced, carriers can move faster, and the high-frequency characteristics of the variable capacitance diode can be improved.

FIG. 8B is a schematic diagram showing the rate of change in voltage capacity between the conventional discrete variable capacitance diode and the discrete variable capacitance diode according to the present embodiment. In the figure, the horizontal axis is the magnitude V of the reverse bias applied to the variable capacitance diode, and the vertical axis is the depletion layer capacitance C of the variable capacitance diode. As shown in the figure, in the discrete variable capacitance diode according to the present embodiment, the change of the depletion layer capacitance C is larger than that of the conventional variable capacitance diode, and the voltage capacitance change rate is larger.

[Summary] According to the variable capacitance diode of the present embodiment, the voltage capacitance change rate can be improved by the steep distribution of the impurity concentration, and the variable capacitance diode can be driven at a low voltage. By making the impurity concentration shallow and steep, the n-type epitaxial layer 2 can be thinned, and the series resistance between the anode electrode 7 and the cathode electrode 9 can be reduced. Further, since the impurity region is thinned, the p-type and n-type impurity concentrations can be reduced, carriers can move faster, and the high-frequency characteristics of the variable capacitance diode can be improved.

Further, by setting the silicon content of the anode electrode 7 to 3 w% or more, in a discrete variable capacitance diode, aluminum spikes can be suppressed and a short circuit of a pn junction can be prevented. Further, by setting the silicon content of the anode electrode 7 to 10 w% or less, it is possible to prevent joule of silicon and to reduce the contact resistance between the anode electrode 7 and the p ⁺ diffusion layer 4.

[Other Embodiments] In the above embodiment, the case where the anode electrode 7 is formed of Al-Si is shown. However, in FIG. 1, the p-type and the n-type are exchanged, and the anode and the cathode are exchanged. , The cathode electrode is Al-
When formed of Si, the same operation and effect as in the above embodiment can be obtained.

[0029]

According to the present invention, the anode electrode is made of Al-
Since it is formed of Si, the impurity concentration distribution can be made steep, the voltage capacity change rate can be improved, and the variable capacitance diode can be driven at a low voltage. Further, according to the present invention, since the impurity diffusion region can be formed shallowly, the thickness of the semiconductor substrate can be reduced, the series resistance can be reduced, and the high-frequency characteristics can be improved.

[Brief description of the drawings]

FIG. 1 is a sectional structural view showing a variable capacitance diode according to an embodiment of the present invention.

FIG. 2 is a view for explaining the manufacturing process (part 1).

FIG. 3 is a view for explaining the manufacturing process (part 2).

FIG. 4 is a view for explaining the manufacturing process (part 3).

FIG. 5 is a view for explaining the manufacturing process (part 4).

FIG. 6 is a view for explaining the manufacturing process (part 5).

FIG. 7 is a view for explaining the manufacturing process (part 6).

FIG. 8A is a schematic diagram showing the depth and concentration distribution of an impurity diffusion layer, and FIG. 8B is a schematic diagram showing a voltage capacity change rate.

[Explanation of symbols]

Reference Signs List 1 n-type semiconductor substrate 2 n-type epitaxial layer 3 n ⁺ diffusion layer 4 p ⁺ diffusion layer 5 thermal oxide film 6 CVD oxide film 7 anode electrode (Al-Si electrode) 8 protective film 9 cathode electrode

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[Procedure amendment]

[Submission date] June 25, 2001 (2001.6.2)
5)

[Procedure amendment 1]

[Document name to be amended] Drawing

[Correction target item name] Fig. 5

[Correction method] Change

[Correction contents]

FIG. 5

Claims (2)

[Claims] 1. A variable capacitance diode formed on a semiconductor substrate, comprising: a first conductivity type impurity diffusion region formed on a surface of the semiconductor substrate; and a first conductivity type impurity diffusion region on a surface of the semiconductor substrate. A second conductivity type impurity diffusion region formed so as to overlap with the region; and a first conductivity type impurity diffusion region formed on the surface of the second conductivity type impurity diffusion region, the first silicon content ratio being 3 wt% or more and 10 wt% or less. A variable capacitance diode comprising: an electrode; and a second electrode formed on a back surface of the semiconductor substrate. 2. A method for manufacturing a variable capacitance diode on a semiconductor substrate, comprising: forming a first conductivity type impurity diffusion region on a surface of the semiconductor substrate; and forming the first conductivity type on a surface of the semiconductor substrate. Forming a second conductivity type impurity diffusion region so as to overlap the impurity diffusion region; and forming a first electrode on the surface of the second conductivity type impurity diffusion region using aluminum silicon having a silicon content of 3 wt% or more and 10 wt% or less. And a step of forming a second electrode on the back surface of the semiconductor substrate.