JPH10321881A - Manufacture of variable capacitance diode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a variable capacitance diode which secures a predetermined breakdown voltage and has a series resistance reduced. SOLUTION: In a variable capacitance 1, constituted by a semiconductor substrate 11 containing an N-type impurity at a high concentration and an epitaxial layer containing an impurity at a predetermined concentration NVB, in which the breakdown voltage of a PN junction found in advance becomes a breakdown voltage Vb, an N-type epitaxial layer 12 having a predetermined thickness d0 substantially equal to a depletion layer width d at the time of the application of the predetermined breakdown voltage Vb is formed. After that, an n<+> -diffusion layer 14 and a p<+> -diffusion layer 15 are formed by an ion implantation method, thereby forming a P-N junction of the variable capacitance 1. Thus, a variable capacitance having high reliability and high performance can be produced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a variable capacitance diode, and more particularly, to a method for manufacturing a variable capacitance diode having a predetermined breakdown voltage and a reduced series resistance.

[0002]

2. Description of the Related Art A variable capacitance diode (varicap) uses a phenomenon in which the junction capacitance of a diode having a PN junction formed on the surface of a semiconductor substrate is changed by a voltage applied in the reverse direction of the diode. These varicaps are frequently used in tuners of TV receivers and tape recorders, and the performance of varicaps is an important factor in determining tuner performance.

Here, an example of a conventional method for manufacturing a varicap will be described with reference to FIG. First, as shown in FIG. 3, an N-type epitaxial layer 12 doped with a low-concentration impurity is formed on the surface of a low-resistance N-type semiconductor substrate 11 doped with a high-concentration impurity. In the initial stage of the formation of the epitaxial layer 12, an auto-doping phenomenon occurs in which impurities are mixed into the epitaxial layer 12 from the low-resistance N-type semiconductor substrate 11 doped with a high-concentration impurity. The layer 12a is formed. Then, the epitaxial layer 1
2. A thin thermal oxide film 13 is formed on the surface
Photoresist is applied on top and patterned. Next, using the patterned photoresist as a mask,
Using an ion implantation method, ions serving as N-type impurities are implanted into the epitaxial layer 12 through the thin thermal oxide film 13, and then heat treatment is performed to form an n ⁺ diffusion layer 1 having a predetermined impurity concentration profile on the surface of the epitaxial layer 12.
4 is selectively formed.

Next, using a new patterned photoresist as a mask for ion implantation, ions serving as P-type impurities are implanted into the epitaxial layer 12 through the thin thermal oxide film 13 by an ion implantation method, and then heat-treated. A p ⁺ diffusion layer 15 is formed. This p ⁺ diffusion layer 1
The size of 5 is larger than the periphery of the surface of the n ⁺ diffusion layer 14 by a predetermined width to reduce the electric field in the periphery of the PN junction, thereby improving the breakdown voltage (breakdown voltage).

Next, a CVD oxide film 16 is deposited by the CVD method, and thereafter, the CVD oxide film 16 is patterned to
⁺ A contact hole 17 of the diffusion layer 15 is formed. After that, an Al alloy film such as an Al film containing 1% Si is deposited,
By patterning this Al alloy film to form an electrode 18 that contacts the p ⁺ diffusion layer 15, a varicap is manufactured.

[0006] The performance evaluation of varicap 1, and the capacitance variation index n indicating the magnitude of the change in capacitance with respect to the applied voltage changes, such as the following, there is a cut-off frequency f _{c. ^{Cα (V + V bi) -n}} , f c = (2πR S C) -1 , where, C is the junction capacitance, V is the applied voltage, V _bi is the diffusion potential, R _S is the series resistance inserted in series in the junction capacitance C It is. In order to increase the capacitance change index n, as shown in the above-described method for manufacturing the varicap 1, the n ⁺ diffusion layer 14 in contact with the p ⁺ diffusion layer 15 at the PN junction is formed by ion implantation and thermal diffusion. It has a functional concentration distribution. The impurity concentration profile of the varicap 1 manufactured as described above is as shown in FIG. 4, and the relationship between the applied voltage and the capacitance of the varicap 1 having this impurity profile is as shown in FIG. Become. Meanwhile, in order to increase the cut-off frequency f _c, since the cutoff frequency f _c is inversely proportional to the product of the junction capacitance C and series resistance R _S as described above,
Epitaxial layer 12 which substantially controls series resistance R _S
, That is, the impurity concentration of the epitaxial layer 12 is increased, and the distance between the n ⁺ diffusion layer 14 and the low-resistance N-type semiconductor substrate 11 is reduced.

However, the capacitance changes, the impurity concentration profile of the n ⁺ diffusion layer 14 to the index n have contributed, the impurity concentration and the n ⁺ diffusion layer 14 of the epitaxial layer 12 contributing to the cutoff frequency f _c of the low-resistance The distance between the N-type semiconductor substrates 11 is related to the breakdown voltage Vb of the varicap 1. Now, assuming that the capacitance change range of the varicap 1 as the specification of the varicap 1 is C ₁ ≧ C ≧ C ₂ , the voltage change range at that time is V ₁ ≦ V ≦ V ₂ . In order to sufficiently ensure that the cap 1 does not cause breakdown, for example, the breakdown voltage Vb of the varicap 1 is set to Vb
≧ 1.2V ₂ .

As described above, the breakdown voltage Vb ≧ 1.2 V ₂ of the varicap 1 is ensured, and a high-performance varicap 1 having a large capacitance change with respect to an applied voltage change and a small series resistance R _S is manufactured. There is a problem that is difficult.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems in the method of manufacturing a variable capacitance diode. That is, an object of the present invention is to provide a method for manufacturing a variable capacitance diode in which a predetermined breakdown voltage is secured and the series resistance is reduced.

[0010]

SUMMARY OF THE INVENTION A method of manufacturing a variable capacitance diode according to the present invention is proposed to solve the above-mentioned problem. Forming an epitaxial layer containing the first conductivity type impurity with a predetermined thickness, and selectively implanting ions serving as the first conductivity type impurity into the epitaxial layer by ion implantation. Forming a PN junction by forming a second conductivity type ion implantation layer in which ions of a second conductivity type impurity are selectively implanted into the epitaxial layer. It is assumed that.

According to the present invention, when the epitaxial layer is made sufficiently thick, the breakdown voltage of the PN junction having the first conductivity type ion implantation layer and the second conductivity type ion implantation layer becomes a predetermined breakdown voltage. The impurity concentration of the epitaxial layer becomes a predetermined concentration, the depletion layer width at the time of applying a predetermined breakdown voltage to the above-mentioned PN junction formed of the epitaxial layer of the predetermined concentration, the predetermined thickness of the epitaxial layer, A varicap having a predetermined breakdown voltage and a reduced series resistance can be obtained. Therefore, a highly reliable and high performance varicap can be manufactured.

[0012]

Embodiments of the present invention will be described below with reference to the accompanying drawings. The same components as those in FIG. 3 referred to in the description of the prior art are denoted by the same reference numerals.

This embodiment is an example in which the present invention is applied to a method of manufacturing a variable capacitance diode, which will be described with reference to FIGS. First, as shown in FIG. 1, a semiconductor substrate containing a high-concentration impurity of the first conductivity type, for example, a semiconductor substrate 11 doped with an N-type impurity having an impurity concentration of 1E19 / cm ³ is formed by vapor phase epitaxial growth. Then, an epitaxial layer containing a first conductivity type impurity of a predetermined concentration, for example, an N-type epitaxial layer 12 having an impurity concentration of 3.5E15 / cm ³ as a predetermined concentration is formed with a predetermined thickness, for example, about 4 μm. In the initial stage of the formation of the epitaxial layer 12, an auto-doping phenomenon occurs in which impurities are mixed into the epitaxial layer 12 from the low-resistance N-type semiconductor substrate 11 doped with a high-concentration impurity. The layer 12a is formed. How to determine the predetermined concentration and the predetermined thickness of the impurity of the epitaxial layer 12 will be described later.

Next, a thin thermal oxide film 13 having a thickness of about 40 nm is formed on the surface of the epitaxial layer 12, a photoresist is applied on the thermal oxide film 13, and patterning for forming the varicap 1 is performed. After that, using the patterned photoresist as a mask, using an ion implantation method,
An ion serving as a first conductivity type impurity, for example, phosphorus (P) ion serving as an N-type impurity is implanted at an energy of about 500 k.
eV, dose of about 1E13 / cm ² , thin thermal oxide film 1
Then, the n ⁺ diffusion layer 14 having a predetermined impurity concentration profile is formed on the surface of the epitaxial layer 12 by performing a heat treatment, for example, about 1000 ° C. for about 20 minutes. The predetermined impurity concentration profile is determined so as to obtain a specified capacitance change range of the varicap 1 without causing a very large voltage change.

Next, after removing the above-mentioned photoresist, a new photoresist is applied, and the photoresist is patterned so that an opening having a predetermined width wider than the peripheral portion of the surface of the n ⁺ diffusion layer 14 is formed. do. Then, using the patterned photoresist as a mask, ions of the second conductivity type, for example, boron (B) ions are implanted by implanting energy of about 15 keV and dose of about 5
At E15 / cm ² , the p ⁺ diffusion layer 15 is formed on the surface of the epitaxial layer 12 by bombarding the surface of the epitaxial layer 12 through the thin thermal oxide film 13 and then performing heat treatment, for example, about 950 ° C. for about 20 minutes. In addition,
The size of the p ⁺ diffusion layer 15 is set to be larger than the periphery of the surface of the n ⁺ diffusion layer 14 by a predetermined width, so that the electric field in the periphery of the PN junction is relaxed and the breakdown voltage (breakdown voltage) is improved. It has become.

Next, a CVD oxide film 16 is deposited to a thickness of about 500 nm, and thereafter, the CVD oxide film 16 is patterned to form a contact hole 17 in the CVD oxide film 16 above the p ⁺ diffusion layer 15 in one portion of the varicap. . Thereafter, an electrode film, for example, an Al alloy film such as an Al film containing 1% Si is deposited to a thickness of about 1.5 μm, and the Al alloy film is patterned to form an electrode 1 which is in contact with the p ⁺ diffusion layer 15.
8 is formed. As described above, the p ⁺ diffusion layer 15 and the n ⁺
The varicap 1 including the diffusion layer 14, the N-type epitaxial layer 12, and the N-type high-concentration semiconductor substrate 11 is manufactured.

The method of determining the predetermined impurity concentration and the predetermined film thickness of the epitaxial layer 12 in the production of the above-described varicap 1 is such that the thickness of the epitaxial layer 12 is made sufficiently thick, for example, about 10 μm. The varicap 1 with the impurity concentration changed is formed, and the relationship between the breakdown voltage (breakdown voltage) of the varicap 1 and the impurity concentration of the epitaxial layer 12 and the varicap 1 immediately before the breakdown voltage Vb of the varicap 1 are formed. The relationship between the junction capacitance C and the relationship between the impurity concentration is determined in advance.

Now, the joining volume as the specification of the varicap 1
The capacity change range of the quantity C is C₁≧ C ≧ C _TwoAnd C₁/ C_Two≒
N to be about 7⁺Predetermined impurity concentration of diffusion layer 14
Fix the profile and adjust the thickness of the epitaxial layer 12
In a state where the thickness is sufficiently thick,
The relationship between the breakdown voltage and the impurity concentration is shown in FIG.
It looks like a graph, and the break of the varicap 1
The junction capacitance C of the varicap 1 immediately before the down voltage Vb is not
The relationship with the pure substance concentration is as shown in the graph of FIG.
Become.

Next, a varicap 1 having a junction capacitance C = C ₂
Application electrode V = V ₂ and then, as the breakdown voltage Vb of the varicap 1 to ensure that in this application electrode V = V ₂ varicap 1 does not cause a breakdown, for example the breakdown voltage Vb ≧ 1. Assuming that 2V ₂ , the impurity concentration N of the epitaxial layer 12 where Vb = 1.2 V _{2 is} obtained from the graph of FIG. 2A as N = N _BV , for example, N _BV = 3.5E15 / cm ² .

Next, the varicap 1 immediately before the breakdown voltage Vb of the varicap 1 when the impurity concentration N = _NBV is used.
From the graph of FIG. 2B, the junction capacitance C
Is obtained as C = C _BV . When the junction capacitance C = C _BV is obtained, the depletion layer width d in the N-type impurity region of the PN junction at this time is d ≒ Sε / C _BV . Where S is PN
The area of the junction. The predetermined thickness d of the epitaxial layer 12
_{As 0} , the width is substantially equal to the depletion layer width d ≒ Sε / C _BV described above. A more as the predetermined thickness d ₀ of the exact epitaxial layer 12, in consideration of the thickness d _1, and a thickness d ₂ of the auto-doped layer 12a of the p ⁺ diffusion layer 15, a predetermined thickness d ₀ ≒ Sε / Let C _BV + d ₁ + d ₂ . As the predetermined film thickness d ₀ , for example, d ≒ Sε / C _BV is about 2.7 μm
Since d ₁ + d ₂ is about 1 μm, it is about 3.7 μm. However, in consideration of the fact that the impurity concentration and the film thickness of the epitaxial layer 12 vary, in the production of the varicap 1, the predetermined film thickness d ₀ of the epitaxial layer 12 was set to about 4 μm.

The above-mentioned impurity concentration of the epitaxial layer 12 is set to N = N _BV and the thickness d ₀ ≒ S of the epitaxial layer 12 is set.
Assuming that ε / C _BV + d ₁ + d ₂ , when a predetermined breakdown voltage Vb is applied to the varicap 1, as shown in FIG.
2a, the breakdown voltage Vb does not decrease due to the depletion layer being restricted to the high-concentration auto-doping layer 12a and not expanding, and there is almost no extra epitaxial layer 12 to which almost no voltage is applied. Therefore, the series resistance R _s of the varicap 1, which is related to the distance between the depletion layer and the auto-doping layer 12 a in the voltage change range of the varicap 1, can be reduced. Accordingly, in the method for manufacturing a varicap 1 described above, by forming the epitaxial layer 12 having a predetermined concentration N _BV and a predetermined thickness d ₀ of the impurities discussed above, to ensure a predetermined breakdown voltage Vb, the series resistance R _s can be reduced and a high-performance varicap 1 can be manufactured.

The present invention has been described with reference to the embodiments.
The present invention is not limited to this embodiment. For example, in the embodiment of the present invention, the first conductivity type impurity is described as an N-type impurity, and the second conductivity type impurity is described as a P-type impurity. However, the first conductivity type impurity is a P-type impurity, and the second conductivity type impurity is an N-type impurity. It may be a type impurity. Further, in the embodiment of the present invention, the predetermined impurity concentration and the predetermined film thickness of the epitaxial layer for securing the predetermined breakdown voltage are determined by experiments, but the breakdown critical electric field and the predetermined impurity concentration of the n ⁺ diffusion layer are determined. Based on the profile, a breakdown voltage when the impurity concentration of the epitaxial layer is changed and a depletion layer width at the time of the breakdown voltage are obtained by simulation, and the maximum impurity concentration of the epitaxial layer that secures a predetermined breakdown voltage Vb is determined. Predetermined concentration,
Further, the predetermined film thickness may be obtained as a film thickness substantially equal to the depletion layer when a predetermined breakdown voltage is applied at the predetermined concentration. In addition, the process conditions can be appropriately changed within the scope of the technical idea of the present invention.

[0023]

As is apparent from the above description, the method of manufacturing a variable capacitance diode according to the present invention provides a predetermined breakdown voltage Vb by forming an epitaxial layer having a predetermined impurity concentration and a predetermined thickness. This ensures that the series resistance R _s is minimized. Therefore, a highly reliable and high performance varicap can be manufactured.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of a varicap for explaining a process of an embodiment to which the present invention is applied.

FIGS. 2A and 2B are characteristic diagrams of a varicap formed to obtain a predetermined impurity concentration and a predetermined film thickness of an epitaxial layer according to an embodiment of the present invention, and FIG. 2A shows a relationship between a breakdown voltage and an impurity concentration; FIG. 4B is a diagram illustrating a relationship between the junction capacitance of the varicap and the impurity concentration immediately before the breakdown voltage.

FIG. 3 is a schematic cross-sectional view of a varicap for explaining a conventional method of manufacturing a varicap.

FIG. 4 is a diagram showing an impurity concentration profile of a conventional varicap.

FIG. 5 is a diagram showing a relationship between an applied voltage of a conventional varicap and a junction capacitance.

[Description of Symbols] 1 ... Varicap, 11 ... Semiconductor substrate, 12 ... Epitaxial layer, 12a ... Auto-doping layer, 13 ... Thermal oxide film, 14 ... N ⁺ diffusion layer, 15 ... P ⁺ diffusion layer, 16 ... CV
D oxide film, 17 contact hole, 18 electrode

Claims (3)

[Claims] A step of forming an epitaxial layer containing a predetermined concentration of the first conductivity type impurity on a semiconductor substrate containing a high concentration of the first conductivity type impurity with a predetermined thickness; Forming a first conductivity type ion-implanted layer by selectively implanting ions into the epitaxial layer; and forming a second conductivity-type ion-implanted layer by selectively implanting ions of a second conductivity type into the epitaxial layer. And a step of forming a PN junction. 2. The method according to claim 1, wherein the predetermined concentration of the first conductivity type impurity in the epitaxial layer is substantially equal to an impurity concentration at which a breakdown voltage of the PN junction becomes a predetermined breakdown voltage when the epitaxial layer is sufficiently thick. The method for manufacturing a variable capacitance diode according to claim 1, wherein: 3. The depletion when a predetermined breakdown voltage is applied to the PN junction when the impurity concentration of the epitaxial layer is the predetermined concentration and the epitaxial layer is sufficiently thick. 2. The method according to claim 1, wherein the thickness of the variable capacitance diode is substantially equal to the layer width.