JP2828181B2 - Capacitive element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of a capacitance element having extremely small voltage dependency.

[0002]

2. Description of the Related Art In recent years, in order to improve the accuracy of analog LSIs such as video signal processing LSIs and high-precision A / D converters, and filter elements incorporated in analog-digital LSIs, high-precision and voltage-dependent A small capacitor is desired.

Heretofore, as such a capacitor, a device using a high-concentration diffusion layer or a high-concentration polycrystalline silicon film as a lower electrode, and using a metal film such as a high-concentration polycrystalline silicon film or an aluminum film as an upper electrode has been used. It has been.

Hereinafter, the configuration will be described with reference to FIG. FIG. 5 is a sectional structural view of a conventional capacitive element. An N ⁺ -type polycrystalline silicon film 2 is selectively formed on a silicon oxide film 1 and an interlayer insulating film 3 is formed thereon. Next, a portion of the interlayer insulating film 3 where a capacitor is to be formed is selectively removed by etching using a photoresist, and then a silicon nitride film 4 is grown as a capacitor insulating film. Next, after selectively etching and opening the interlayer insulating film 3 and the silicon nitride film 4 using a photoresist, an aluminum film is grown and patterned with the photoresist to form an upper electrode 5 and a lower electrode 6 of a capacitor. I do. In this way, a capacitive element composed of an N ⁺ type polycrystalline silicon film, a silicon nitride film, and an aluminum film is formed.

[0005]

However, in such a capacitive element, since the N ⁺ -type polycrystalline silicon film 2 is used as the capacitive lower electrode, the lower electrode has a positive voltage relationship with respect to the upper electrode 5. In this case, a depletion layer is formed on the surface of the N ⁺ -type polycrystalline silicon film 2 on the silicon nitride film 4 side, and the capacitance value decreases. Conversely, if a P ⁺ -type polycrystalline silicon film is used at this position, a depletion layer is formed on the surface of the P ⁺ -type polycrystalline silicon film when the capacitance lower electrode has a negative voltage relationship, and the capacitance value decreases. .

Therefore, when a filter is formed using a capacitor having a conventional structure, the capacitance changes with the voltage, so that the signal is distorted and a high-precision analog signal processing circuit or A / D converter is formed. However, it has a drawback that it cannot be used.

An object of the present invention is to solve the above-mentioned conventional problems, and an object of the present invention is to provide a capacitance element whose capacitance value has extremely small voltage dependency.

[0008]

In order to achieve this object, the present invention provides an N type semiconductor layer region and a P type semiconductor in the same plane.
A lower semiconductor layer having a layer region ; and
A capacitor insulating film formed of a single layer or a laminate ,
Upper electrode made of metal thin film formed on capacitive insulating film
And a first lower electrode connected to the N-type semiconductor layer region
A second lower electrode connected to the P-type semiconductor layer region;
Wherein the first lower electrode and the second lower electrode is the same potential
And electrically connected to each other.

[0009]

According to the present invention, since the lower semiconductor layer, which is the lower capacitor electrode, is made of an N-type semiconductor and a P-type semiconductor, the voltage dependency of the capacitance value with respect to the voltage applied to the capacitor is contradictory. . By mutually connecting the capacitance elements having the opposite voltage dependencies in parallel, the mutual voltage dependency is canceled.

[0010]

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

FIG. 1 is a sectional structural view of a capacitive element according to a first embodiment of the present invention. Silicon oxide film 1
A polycrystalline silicon film having a thickness of about 400 nm is grown thereon, and a capacitor lower electrode is patterned using a photoresist.
Next, 1 × 10 ¹⁶ cm ⁻² of As or the like is used as an N-type impurity using a photoresist as a mask, and 1 × 10 ¹⁶ cm ^{−2 is used as} a P-type impurity.
After each ion implantation at 10 ¹⁶ cm ^-2 , a heat treatment is performed in an inert gas to form an N ⁺ -type polycrystalline silicon film 8 and a P ⁺ -type polycrystalline silicon film 9. Next, after an interlayer insulating film 3 such as a silicon oxide film having a thickness of about 500 nm is grown, a portion of the interlayer insulating film 3 where a capacitance is to be formed is opened by etching using a photoresist as a mask. Furthermore, the thickness of the capacitor insulating film is about 50 nm.
Is grown. Next, the interlayer insulating film 3 is selectively etched using a photoresist as a mask to open a contact hole for a lower electrode, and then an aluminum film having a thickness of about 1 μm is grown. Finally, the aluminum film is selectively etched using a photoresist as a mask to form an upper electrode 5, a first lower electrode 6, and a second lower electrode 7.
The first lower electrode 6 and the second lower electrode 7 are electrically connected for use.

FIG. 2 is an equivalent circuit diagram of the capacitive element according to the first embodiment of the present invention. C _N 21 is an N ⁺ type polycrystalline silicon film 8, a silicon nitride film 4 and an upper electrode 5.
And C _P 22 is a capacitance element composed of the P ⁺ type polycrystalline silicon film 9, the silicon nitride film 4 and the upper electrode 5. The capacitance element of the present invention is a parallel capacitance of the capacitance elements C _N21 and C _P22 . 23 is C _N
A terminal corresponding to the upper electrode 5 of the parallel capacitance of 21 and _CP 22, and a terminal 24 corresponding to the first lower electrode 6 and the second lower electrode 7.

FIG. 3 shows the case where the impurity concentrations of the N ⁺ type polycrystalline silicon film 8 and the P ⁺ type polycrystalline silicon film 9 are equal.
Shows the voltage dependence of each of the capacitance value of the capacitor C _N 21 and the capacitive element C _P 22. In the figure, C _max is the maximum capacitance value and the unit area capacitance value when C _N 21 or C _P 22 is a parallel plate capacitance, and C _min is the minimum capacitance value and the N ⁺ -type polysilicon film 8 and P ^This is a unit area capacitance value when a channel is formed on the surface of the ⁺ type polycrystalline silicon film 9 on the silicon nitride film 4 side. This C _min can be expressed by the following (Equation 1).

[0014]

(Equation 1)

Under the conditions for forming the polycrystalline silicon film of this embodiment, the impurity concentration N _B of the polycrystalline silicon film is 2.5 × 10 ²⁰ cm.
^-3 , so C _max = 1.38 × 10 ^-7 (F / cm ² ), C
_min = 1.34 × 10 ⁻⁷ (F / cm ⁻² ). Further, the voltage dependence of the capacitance value can be expressed by the following depletion approximation formula (Equation 2).

[0016]

(Equation 2)

N⁺Type polycrystalline silicon film 8 is used as a lower electrode.
Capacity C_N21, the applied voltage V of the upper electrode 5 is set to N⁺Type
When increasing in the positive direction with respect to the crystalline silicon film 8,
The quantity value increases and decreases in the negative direction.
You. On the other hand, P⁺Type polycrystalline silicon film 9 is used as a capacitor lower electrode.
Capacity C_P22, the capacity C_NVoltage dependence opposite to 21
have. Using the numerical values of the present embodiment,_N21 and C_P22
And the average voltage change rate ΔC / C of the capacitance values is approximately 50
It becomes 0 ppm / V. 31 and 32 are capacity C_N21 and C _P22
And 33 is the capacitance-voltage curve of_N21 and C_P22 parallel
Capacity C_T5 is a capacitance-voltage curve of FIG. For the reasons mentioned above,
And C_N21 and C_P22 has opposite voltage dependency
C in which both are connected in parallel_TThe capacitance-voltage curve 33 of FIG.
No longer exist.

As described above, according to the present embodiment, the polycrystalline silicon film, which is one electrode of the capacitor, is composed of the N ⁺ type polycrystalline silicon film 8 and the P ⁺ type polycrystalline silicon film 9, and is opposite to each other. By connecting capacitor elements having voltage dependency in parallel, mutual voltage dependency can be canceled out, and a capacitor element with extremely low voltage dependency can be realized.

FIG. 4 is a sectional structural view of a capacitor according to a second embodiment of the present invention. 5 × 1 As or the like is deposited on an N-type silicon substrate 41 as an N-type impurity using a photoresist as a mask.
After implanting 5 × 10 ¹⁵ cm ⁻² ions of B and the like as a P-type impurity at 0 ¹⁵ cm ⁻² and oxidizing it at 1000 ° C. for about 60 minutes, N ⁺
A type diffusion layer 42, a P ⁺ type diffusion layer 43 and a silicon oxide film 44 having a thickness of about 500 nm are formed. Next, the silicon oxide film 44 is selectively opened by etching using a photoresist as a mask, and a silicon nitride film 45 having a thickness of about 50 nm is grown as a capacitance insulating film. Next, the silicon oxide film 44 and the silicon nitride film 45 are selectively etched using a photoresist as a mask to open a contact hole of a lower electrode, and an aluminum film having a thickness of about 1 μm is grown. Next, this aluminum film is selectively etched to form the upper electrode 46, the first electrode.
A lower electrode 47 and a second lower electrode 48 are formed. The difference from the configuration of FIG. 1 is that a diffusion layer is used instead of the polycrystalline silicon film as one electrode of the capacitor. The second embodiment operates in the same manner as the first embodiment.

When the N-type and P-type impurity concentrations of the lower semiconductor layer are different, the voltage dependency can be canceled by adjusting the area ratio of the N-type and P-type semiconductor layer regions. In the first embodiment, the N ⁺ -type polycrystalline silicon film 8 and the P ⁺ -type polycrystalline silicon film 9 are used as the lower electrode material, but they may be an N ⁺ -type amorphous silicon film and a P ⁺ -type amorphous silicon film, respectively. Although the N-type silicon substrate 41 is used in the second embodiment, a P-type silicon substrate may be used. Further, it goes without saying that a metal silicide film or a high melting point metal can be used instead of the aluminum film.

[0021]

As is apparent from the above embodiments, according to the present invention, since the capacitance elements having the opposite voltage dependencies are connected in parallel to cancel each other's voltage dependence, the voltage dependence is extremely low. There is an effect that a small capacitance element can be realized, and distortion generated in a filter or the like can be significantly reduced.

[Brief description of the drawings]

FIG. 1 is a sectional structural view of a capacitive element according to a first embodiment of the present invention;

FIG. 2 is an equivalent circuit diagram of the capacitive element according to the first embodiment of the present invention.

FIG. 3 is a diagram showing the voltage dependence of the capacitance value of the capacitance element according to the first embodiment of the present invention.

FIG. 4 is a sectional structural view of a capacitive element according to a second embodiment of the present invention;

FIG. 5 is a sectional structural view of a conventional capacitive element.

[Explanation of symbols]

Reference Signs List 4 silicon nitride film 5 upper electrode 6 first lower electrode 7 second lower electrode 8 N ⁺ type polycrystalline silicon film 9 P ⁺ type polycrystalline silicon film 42 N ⁺ type diffusion layer 43 P ⁺ type diffusion layer 45 silicon nitride film 46 Upper electrode 47 First lower electrode 48 Second lower electrode

Claims (3)

(57) [Claims] 1. An N-type semiconductor layer region and a P-type semiconductor in the same plane.
A lower semiconductor layer having a body-layer region, a capacitor insulating film composed of a single layer or a laminated formed on the lower semiconductor layer, before
Upper electrode consisting of a metal thin film formed on the capacitor insulating film
And a first lower electrode connected to the N-type semiconductor layer region
A second lower electrode connected to the P-type semiconductor layer region;
Wherein the first lower electrode and the second lower electrode is the same potential
A capacitor element electrically connected as described above . 2. A first capacitor comprising the N-type semiconductor layer region, the upper electrode, and the capacitor insulating film therebetween, and the capacitor insulator between the P-type semiconductor layer region, the upper electrode, and the capacitor. 2. A parallel capacitance element comprising a second capacitance element comprising a film and a second capacitance element.
The capacitive element described in the above. 3. The method according to claim 1, wherein the upper electrode is made of one of an aluminum film, a metal silicide film, and a refractory metal.
3. The method according to claim 1, wherein the metal film comprises two metal thin films.
4. The capacitive element according to 1.