JPS58159367A - MOS capacitor device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an MO8 capacitor device, and more particularly to a complementary MO8 capacitor device.
A so-called complementary MO5 that combines a device and a crystal oscillator.
An MO5 capacitor device useful for stabilizing a crystal oscillator is provided.

Generally 1. In analog or digital electronic watches,
Complementary MO8 crystal oscillators have very good frequency stability, low voltage, and low current consumption characteristics, so they have become widely used. In such electronic watches, frequency stability against fluctuations in power supply voltage is the most important element. The crystal oscillation circuit unit controls frequency fluctuations depending on the power supply voltage.

First, the circuit configuration of the crystal oscillator will be explained.

An example of the configuration of a typical complementary MO8 crystal oscillation circuit is shown in FIG. In FIG. 1, M is an inverting amplifier composed of complementary MO8) transistors, k is a buffer resistor between the amplifier and the resonant circuit, and rtal is a crystal oscillator. (2) and Gg are the resonance capacitances of the crystal resonator.

Next, FIG. 2 shows an internal wiring diagram of the inverting amplifier.

Rf is a resistive element for DC bias, and is usually 10MΩ in order not to affect the gain or positive phase of the oscillation circuit.
The value above is selected. T1 and T2 are P-channel type and N-channel type MO5)7 transistors which are complementary to each other, and their respective sources are connected to the power supplies VDD and Vaa.In practical circuits, the power supply voltage is usually 1 between VDD and Vaa.
．． When 6V is applied, oscillation occurs according to the natural vibration frequency of the crystal resonator.

FIG. 3 is a plan view showing a mask layout of an MO8 capacitor Cg connected to the input side of the inverting amplifier of the crystal oscillator shown in the first figure, which is conventionally used in an electronic watch. Also, the fourth
The figure is a schematic cross-sectional view of the device. M like this
The O8 capacitive element is integrally formed with a complementary MO8 transistor integrated circuit in the following manner. However, complementary MO8
) A detailed explanation of the constituent parts of the transistor will be omitted. Third
figure.

As shown in Figure 4, N-type silicon (specific resistance 1~10Ω・
cIn) After aligning the P-well mask onto the substrate 1, boron ions are implanted at an acceleration voltage of several tens of keV, and annealing is performed.
Drive-in oxidation is performed to form an f diffusion layer 2 and a protective oxide film 3 with a diffusion depth controlled to several μm. Thereafter, the protective oxide film 3 on the f diffusion layer 2 is etched using a mask integrally formed with the MOS transistor channel forming mask, and a dielectric layer of the same composition as the gate oxide film for MO8) is placed in the same place. form 4. Typically, the gate oxide film has a thickness of about 1200 µm, and the dielectric layer 4 has the same thickness. Next, a polycrystalline silicon mask alignment process is performed to form MO-8) transistor gate electrodes and first layer wiring, and after about 6,000 yen, P+ diffusion region 6
The protective oxide film 3 is opened using a mask to form a window, and boron is implanted at an accelerating voltage of several tens of KeV.
Next, an oxide film 7 is deposited on the entire surface, and a contact electrode region 8 is formed using a contact window opening mask, and this contact Lli electrode region 8 and the above-mentioned ? After opening a predetermined window in each of the aluminum mask for forming the 21st interconnection spanning the diffusion region 6 and the contact mask for the polycrystalline silicon film 6 of the first layer interconnection, the aluminum film 9 (, 9 -b is vapor-deposited to form an electrode. Note that the P1 diffusion region 6 and the contact electrode region 8
is fed simultaneously in the process of forming the source and drain regions of the complementary MO+3 transistor. Also, 10
indicates the contact part.

FIG. 6 shows an equivalent circuit of the MO8 capacitive element shown in FIGS. 3 and 4. In FIG. 5, one of the aluminum film electrodes 9-4 is a high potential terminal of a power supply, and the other aluminum film electrode 9-4 is a high potential terminal of a power source. The aluminum membrane electrode 9-b is the other electrode terminal of the MO8 capacitor.

Also D+, 02. Os...Ci and P+,
R2, Rs, R, and R are the capacitance and internal resistance distributed between the f diffusion layer 2 and the polycrystalline silicon film 6, respectively.

The equivalent circuit in Fig. 5 shows the resistance R4l capacity Ci as a distributed constant.
It is considered as a Re distributed constant circuit. Furthermore, when FIG. 6 is simplified to a lumped constant model, it becomes as shown in FIG. In Fig. 6, R and C are R1, R2 in Fig. 6...
・■ and 01.02.・River...It appears as shown in the following equation in relation to C1.

1=1 In the MO8 capacitor ag having a one-note configuration, that is, the MO8 type capacitor formed by the electrode formed by the polycrystalline silicon film 6 and the diffusion layer 2, the diffusion layer 2 directly under the polycrystalline silicon film 6 A time constant constituted by the product of the resistance R formed between and the potential extraction port 9-IL of the diffusion layer 2 and the capacitance C of the MO8 capacitor device becomes large due to the internal resistance component. For this reason, this time constant may become longer than the period of the oscillation circuit, and the reference oscillation of the crystal resonator cannot be followed.

Therefore, the oscillation operation becomes unstable, and the counter connected at the subsequent stage performs erroneous frequency division, resulting in unstable characteristics as a crystal oscillation circuit. The same thing can be said in the case where the capacitor ω connected to the output side of the inverting amplifier is formed by an MO8 capacitor device in the circuit configuration shown in FIG.

In the present invention, the MO8 capacitor cg or capacitance connected to the input side or the output side of the complementary MO8 crystal oscillation circuit is determined by the internal resistance R (that is, the resistance of the f diffusion layer 2) that is necessarily present in its structure. This is intended to eliminate the drawback that occurs when the crystal oscillator does not perform a specific reference oscillation due to the size of the time constant, that is, the counter connected to the subsequent stage incorrectly divides the frequency. The purpose of the present invention is to provide an MO8 capacitor device that can reduce the internal resistance component associated with the capacitive element, reduce the time constant determined by the capacitive element, and reliably follow the reference frequency of the crystal resonator.

The configuration of the present invention will be explained below. MO8 of the present invention
The capacitive device is shown in the configuration of FIG. FIG. 8 is a schematic cross-sectional view taken along line B-B' in FIG. 7. 1 Figures 7 and 8
In the figure, the same numbers as in FIGS. 3 and 4 indicate the same parts, and the MO8 capacitor electrode g-a19-b' is formed in a comb shape. Therefore, a large number of contacts of the f-diffusion layer 2 and f-diffusion regions 6' are formed in the p-diffusion layer 2.

Figure 9 shows the MO8 capacitor device with the structure shown in Figure 8 as an RC distributed constant circuit with resistors and capacitors.The major difference from the conventional example is the simplified wiring element 1 shown in Figure 9.
1, the internal resistance elements R+, R2, etc. are arranged in parallel when viewed from the external terminal side.

Furthermore, when FIG. 9 is simplified to a lumped constant model, it becomes as shown in FIG. 10. However, the method for manufacturing an MO8 capacitor according to the present invention does not require any change in the manufacturing process for the conventional MO8 capacitor.

In the structure of the MO8 capacitor shown in FIGS. 7 and 8, f
Provided within the diffusion layer 2? The diffusion regions 6' are distributed in an elongated planar shape, and these are distributed over the aluminum film 9-a of the second layer wiring.
′ is connected to the electrode. In this way, since one contact electrode body of the MO8 capacitive device is comb-shaped, the effective distance of the P- diffusion layer 2 connected to the high potential terminal 9-a' of the power source is reduced. Therefore, the F array part terminal 9-&' and the P
-The internal resistance between the diffusion layers 2 is reduced. That is, by configuring the built-in MO8 capacitor as shown in Fig. 8,
The internal resistance between the high potential terminal lead a of the power supply and the f diffusion layer 2 is coupled to the same potential within the same p diffusion layer 2, as if
By effectively parallelizing each distributed resistance by connecting them by the wiring element 11 shown in FIG. 9, the internal resistance of the equal cylinders is reduced. Therefore, the time constant is smaller than the MO8 capacitor with the conventional configuration, and it sufficiently follows the operation of the complementary MO3 oscillation circuit of the high frequency crystal resonator. In addition,
The polycrystalline silicon film 6 and the dielectric layer 4' immediately below it are also
The external terminals d-b are arranged parallel to the high-potential terminals cd-& and intertwined with each other between the comb-shaped electrode bodies, and the external terminals d-b are formed in a comb-shaped symmetry.

Therefore, complementary M
The O8 crystal oscillator circuit does not have the problem of incorrect frequency division of the counter connected to the subsequent stage, and can be applied to a clock IC to ensure the accuracy of the time.

In the MO8 capacitor device of the present invention, although the process of the above-mentioned embodiment is explained for P-well type CMO5, it is exactly the same for N-well type 0MO8. and monolithic IC
By incorporating the device into the device, the number of man-hours required for assembling the watch is reduced, and only the trimming capacity needs to be externally attached.

As described above, the present invention can provide an MO8 capacitor device that can reduce the internal resistance of the MO8 capacitor with a simple configuration, and therefore has great industrial value.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram of a typical complementary MO8 crystal oscillator.
Figure 2 is a circuit diagram of the complementary MO8 inverter in the oscillation circuit of Figure 1, Figures 3N and 4 are a schematic plan view and a cross-sectional view of the conventional complementary MO+3 capacitor, and Figure 6 is the equivalent. Figure 6 is an equivalent lumped constant circuit diagram.
Figures 7 and 8 are a schematic plan view and a B-Br sectional view of the MO8 capacitor of the present invention, Figure 9 is an equivalent distributed constant circuit diagram of the same device, and Figure 10 is an equivalent lumped constant diagram of the same device. A circuit diagram is shown for each. 1...1 type silicon substrate, 2...P-
Diffusion layer, 3... Protective oxide film, 4... Dielectric layer, 5... Polycrystalline silicon film, d...
・? Diffusion region, 7...Silicon oxide film, 8...
...Contact electrode area, 9-a', eb'
...Aluminum film electrode. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 4m 27 Figure 5 Figure 6 Figure 7 Figure 8

Claims (1)

[Claims] A forceps device in which a predetermined diffusion region of a semiconductor substrate is used as one electrode, and a polycrystalline silicon film is provided on the diffusion region via a dielectric layer to serve as the other electrode. An MO8 capacitor device characterized in that polycrystalline silicon film electrodes are alternately arranged and each formed in a comb shape.