JP2000194825A - Fingerprint sensor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a capacitive fingerprint sensor capable of generally improving surface strength without degrading the sensitivity of the sensor. SOLUTION: In this capacitive fingerprint sensor for sampling a fingerprint by sensing capacitance with a finger, the surface of a protective film 12 for covering a detection electrode 11 provided in a two-dimensional array shape on a sensor part is flattened. The flattening processing is performed by using resist etch-back, the application of spin-on glass and chemical mechanical grinding, etc. The height of the level difference of the surface of the flattened protective film 12 is made equal to or less than 30 nm. The thickness of the detection electrode 11 can be made equal to or less than 0.3 μm or the side face can be made into a gentle forward tapered shape.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a fingerprint sensor device, and more particularly, to a fingerprint sensor device for sampling a fingerprint by sensing capacitance with a finger.

[0002]

2. Description of the Related Art There are various types of fingerprint sensors. Among them, the most excellent in terms of accuracy, size, ease of manufacturing, cost, etc. are shown in FIG. This is a capacitive fingerprint sensor that contacts the surface of the sensor with a sensor unit and senses a capacitance with a finger to collect a fingerprint.

Conventionally, as a capacitive fingerprint sensor, as shown in FIG. 7, a detection electrode 103 is formed on an interlayer insulating film 102 on a chip-like silicon (Si) substrate 101 on which a signal detection circuit and the like are formed. It is known to provide a two-dimensional array and provide a protective film 104 so as to cover these detection electrodes 103 (for example, US Pat. No. 53254).
No. 42), manufactured using a standard CMOS process (1998 ISSCCC SA17.7). The overall configuration of this fingerprint sensor is, for example, as shown in FIG.

FIG. 9 shows an example of a specific structure of the fingerprint sensor. As shown in FIG. 9, in this fingerprint sensor, a field insulating film 202 for element isolation is selectively provided on the surface of a Si substrate 201. Code 20
3 indicates a gate insulating film, 204 indicates a gate electrode, 205 indicates a source region, and 206 indicates a drain region.
An OS transistor is formed. On these surfaces, an interlayer insulating film 207 is provided, on which metal wirings 208 and 209 formed of a first-layer metal film are provided. These metal wirings 208 and 209 are formed on the interlayer insulating film 2.
07 contact holes 207a and 207b
Through contact with the source region 205 and the drain region 206, respectively. These metal wirings 20
8, 209 are provided to cover the interlayer insulating film 210;
A detection electrode 21 formed thereon by a second-layer metal film
1 is provided. The detection electrode 211 is connected to the metal wiring 209 through a contact hole 210a formed in the interlayer insulating film 210. This detection electrode 21
1, a protective film (overpassivation film) 212 is provided.

[0005]

One of the problems of the conventional fingerprint sensor configured as described above is that it is used in a state where the chip surface is exposed. is there. Usually, as the protective film 212, an insulating film such as a SiN film having a thickness of about 1 μm is used. By increasing the thickness of the protective film 212, the mechanical strength of the surface is improved, but if it is too thick, the sensitivity of the sensor deteriorates.

On the other hand, as shown in FIG. 9, a large step exists on the surface of the protective film 212 reflecting the shapes of the field insulating film 202, the metal wirings 208 and 209, the detection electrode 211 and the like thereunder. I have. For example, the detection electrode 211 is usually formed of an Al film having a thickness of about 0.6 to 1 μm, but the surface of the protective film 212 has at least such irregularities. According to the findings of the present inventor, when the surface of the fingertip is brought into contact with the surface of the protective film 212 of the sensor unit at the time of fingerprint collection, the step has a problem that the protective film 212 is easily broken.

This problem will be described in more detail with reference to FIG. That is, as shown in FIG. 10, when the object A comes into contact with the surface of the protective film 212 of the fingerprint sensor, the force F applied to the surface of the protective film 212 is more to a certain degree than when it is perpendicular to the surface. It is generally considered that the direction is oblique. Now, assuming that a force F is applied in a direction of an angle θ with respect to a normal set on the surface of the protective film 212, F is a force F _y = Fcos θ perpendicular to the surface.
And a force F _x = F sin θ parallel to the surface, the only force applied to the surface is F _y , and the object A applying a force to the surface slides on the surface.

The sliding of the object A on the surface of the protective film 212 stops at the step existing on the surface of the protective film 212, and all the external force F is applied to this portion.
For this reason, mechanical stress is concentrated on the step, and the protective film 212 is easily broken.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a fingerprint sensor device capable of greatly improving the overall surface strength without deteriorating the sensitivity of the sensor.

[0010]

According to a first aspect of the present invention, there is provided a fingerprint sensor device for sampling a fingerprint by sensing a capacitance between the finger and a finger. The surface of the film is flattened.

In the first aspect of the present invention, any method may be basically used for the planarization process. For example, a protective film is formed, and a resist is formed on the protective film. After applying so that the surface becomes flat, the surface of the protective film is flattened by performing etch back, or the surface of the protective film is flattened by applying spin-on glass as the protective film, or the protective film is formed. After that, the surface of the protective film can be planarized by polishing the protective film using a chemical mechanical polishing method. By such a flattening process, the height of the step on the surface of the protective film can be made sufficiently small, for example, 30 nm or less. As a method of flattening the surface of the protective film, the thickness of the detection electrode immediately below the protective film is sufficiently thin, for example, 0.3 μm or less, or the side surface of the detection electrode is wet-etched. It may have a forward tapered shape.

According to a second aspect of the present invention, there is provided a fingerprint sensor device for sampling a fingerprint by sensing the capacitance with a finger, wherein the height of the step on the surface of the protective film of the sensor portion is three.
0 nm or less.

In the first aspect of the present invention configured as described above, since the surface of the protective film of the sensor portion is flattened, there is no step on the surface.
Because it is greatly eased, it is difficult to break when force is applied to the surface of the protective film of the sensor part from outside at the time of fingerprint collection etc., and not only scratch strength but also overall surface strength is greatly improved Can be done.

[0014] In a second aspect of the present invention,
When the height of the step on the surface of the protective film of the sensor unit is 30 nm or less, that is, when there is substantially no step on the surface, external force is applied to the surface of the protective film of the sensor unit when fingerprints are collected. When added, breakage is less likely to occur, and not only scratch strength but also overall surface strength can be significantly improved.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. In all the drawings of the embodiments, the same or corresponding portions are denoted by the same reference numerals.

FIG. 1 shows a capacitive fingerprint sensor according to a first embodiment of the present invention, and is a cross-sectional view of a main part including one of a plurality of detection electrodes provided in a two-dimensional array. The overall configuration of this fingerprint sensor is, for example, the same as that shown in FIG.

As shown in FIG. 1, in this fingerprint sensor, a field insulating film 2 made of a SiO ₂ film for element isolation is selectively provided on the surface of a chip-shaped Si substrate 1. Reference numeral 3 denotes a gate insulating film made of, for example, an SiO ₂ film, 4 denotes a gate electrode made of, for example, an impurity-doped polycrystalline Si film or a polycide film, 5 denotes a source region, 6 denotes a drain region, and these are MOS transistors. Are formed. On these surfaces, for example, Si
An interlayer insulating film 7 made of an O ₂ film is provided, on which are provided first-layer metal films, for example, metal wirings 8 and 9 formed of an Al film. These metal wirings 8 and 9 are
Contact holes 7a and 7b formed in interlayer insulating film 7
Are in contact with the source region 5 and the drain region 6, respectively. An interlayer insulating film 10 made of, for example, an SiO ₂ film is provided so as to cover these metal wirings 8 and 9, and a detection electrode 11 formed of a second metal film, for example, an Al film is provided thereon. . This detection electrode 1
1 is a contact hole 1 formed in the interlayer insulating film 10
Oa is connected to the metal wiring 9. A protective film 12 such as a SiN film formed by, for example, a plasma CVD method is provided so as to cover the detection electrode 11.

In the first embodiment, the surface of the protective film 12 in the sensor section is flattened, and the height of the step on the surface is 30 nm or less. Further, the thickness of the protective film 12 above the detection electrode 11 is selected to be a thickness that can suppress the deterioration of the sensitivity of the sensor and ensure sufficient surface strength. For example, about 1 to 2 μm.

The flattening treatment of the surface of the protective film 12 can be specifically performed by the following method, for example. That is, in the first method, an SiN film is formed as the protective film 12 on the entire surface of the substrate by, for example, a plasma CVD method, and a resist is applied on the SiN film by a spin coating method or the like so that the surface becomes flat. For example, the surface of the SiN film is planarized by performing etch-back using, for example, a reactive ion etching (RIE) method. In the second method, the surface is flattened by applying, for example, spin on glass (SOG) as the protective film 12. In the third method, the protective film 12
After forming a SiN film over the entire surface of the substrate by, for example, a plasma CVD method, the SiN film is subjected to chemical mechanical polishing (Chemic
The surface is flattened by polishing using an al mechanical polishing (CMP) method. FIG. 2 shows the state of the surface after the surface of the protective film 12 is actually flattened by these methods.

As described above, according to the first embodiment, the surface of the protective film 12 in the sensor section is flattened,
When the height of the step on the surface is 30 nm or less, mechanical destruction of the protective film 12 in the sensor portion can be effectively prevented. That is, as shown in FIG. 3, F added when the object A comes into contact with the surface of the protective film 12 is decomposed into _Fx and _Fy as in the case shown in FIG. Since the surface of the protective film 12 is flattened and there is substantially no step, the object A slides on the surface forever without being caught at the tip, and the object A rotates in a direction in which θ increases. As a result, the force F _y (= Fcos θ) applied to the surface of the protective film 12
Is getting smaller and smaller. Therefore, the strength of the surface of the protective film 12 can be significantly improved. In addition, since the thickness of the protective film 12 does not need to be increased, deterioration of the sensitivity of the sensor can be prevented. Further, since it is only necessary to planarize the surface after forming the protective film 12, the process is simple and the production cost hardly increases. As a result, while minimizing the increase in manufacturing cost, and without impairing the sensitivity of the sensor,
Not only the scratch strength but also the overall surface strength of the fingerprint sensor can be significantly improved.

FIG. 4 shows a capacitive fingerprint sensor according to a second embodiment of the present invention, and is a cross-sectional view of a main part including one of a plurality of detection electrodes provided in a two-dimensional array. The overall configuration of this fingerprint sensor is, for example, the same as that shown in FIG.

As shown in FIG. 4, in this fingerprint sensor, the field insulating film 2 and the interlayer insulating films 7, 10
Both surfaces are flattened. The detection electrode 11 has a thickness of 0.3 μm or less, and its side surface has a forward tapered shape inclined at a sufficiently small angle with respect to the substrate surface, for example, an angle of 45 ° or less. Then, a protective film 12 is provided so as to cover the detection electrode 11. Here, in order to form the side surface of the detection electrode 11 into a forward tapered shape, for example, an Al film is formed on the entire surface of the substrate by a vacuum evaporation method or a sputtering method, and a resist pattern is formed thereon by lithography. The Al film may be wet-etched using the pattern as a mask. The other points are the same as those of the fingerprint sensor according to the first embodiment, and the description is omitted.

According to the second embodiment, the surfaces of the field insulating film 2 and the interlayer insulating films 7, 10 are flattened, and the thickness of the detecting electrode 11 is 0.3 μm. The surface of the protective film 12 is flattened, and the surface thereof has almost no step due to the fact that the side surface has a forward tapered shape with a gentle slope. For this reason, the force applied to the surface of the protective film 12 from the outside during fingerprint collection or the like is reduced, and the strength of the surface of the protective film 12 can be significantly improved. In addition, since the thickness of the protective film 12 does not need to be increased, deterioration of the sensitivity of the sensor can be prevented. As described above, not only the scratch strength but also the overall surface strength of the fingerprint sensor can be significantly improved without impairing the sensitivity of the sensor.

Here, the relationship between the ratio of the signal component due to the unevenness of the fingerprint in the capacitance value detected by the capacitance type fingerprint sensor and the relative dielectric constant and thickness of the protective film will be examined. Now, as shown in FIG. 5, consider a structure in which an interlayer insulating film is provided on a Si substrate, a detection electrode is provided thereon, and a protective film is provided so as to cover the detection electrode. The thickness of the interlayer insulating film, a thickness of the respective d _x of the gap between the thickness and the surface and finger surfaces of the protective film of the protective film on the detection electrode (air layer), d _y and d _z, Si substrate C _x , C _y, and C _z , respectively, and the relative dielectric constant of the interlayer insulating film as ε.
_x , and the relative dielectric constant of the protective film is ε _y .

As shown in FIG. 5, the capacitance value C _out detected at the time of fingerprint collection is C _out = C _x + C _y C _z / (C _y + C _z ).

The detected capacitance value C _out becomes maximum when d _z = 0 (C _z → ∞). At this time, the capacitance value C _out (m
ax) is C _out (max) = C _x + C _y .

The detected capacitance value C _out becomes minimum when d _z → large (C _z → 0), and the capacitance value C _out (m
in) is C _out (min) = C _x .

Therefore, the ratio of the signal component due to the unevenness of the fingerprint in the detected capacitance value is {C _out (max) −C _out (min)} / C _out (max) = C _y
/ (C _x + C _y ). The greater the ratio, the higher the sensitivity of the fingerprint sensor, which is advantageous.

[0029] C _x, C _y is the area of the detection electrode when the S, are expressed as _{C x = ε 0 ε x S} / d x C y = ε 0 ε y S / d y. Where ε ₀ is the dielectric constant of vacuum and ε _0
0 = 8.85 × 10 ⁻¹² [F / m]

Now, as an example, let the area S of the detection electrode be S
= 80 [μm] × 80 [μm] = 6400 [μm ² ], the material of the interlayer insulating film is SiO ₂ (ε _x = 3.90), and the material of the protective film is SiO ₂ (ε _y = 3.90). ), SiO (ε _y = 4.1) formed by plasma CVD.
0), a SiN film formed by plasma CVD (ε _y
= 7.5), the ratio C _y / (C _x +) of the signal component due to the unevenness of the fingerprint in the detected capacitance value when changing to three types.
The result of calculating C _y ) is shown below.

[0031] _{---------------------------------- ε x d x C x ε} y d y C y C _y / (C _x + C _y ) [μm] [fF] [μm] [fF] [%] −−−−−−−−−−−−−−−−−−−−−−−−− -------------------- 1.60 138.06 4.10 3.00 77.41 35.93 3.90 1.60 138.06 4.10 4.00 58.06 29.60 3.90 1.60 138.06 7.50 1.00 424.80 75.47 3.90 1.60 138.06 7.50 2.00 212.40 60.61 3.90 1.60 138.06 7.50 3.00 141.60 50.63 3.90 1.60 138.60 1.90 1.60 138.60 1.90 1.60 138.60 1.90 1.00 138.06 10.00 2.00 283.20 67.23 3.90 1.60 138.06 10.00 3.00 188.80 57.76 3.90 1.60 138.06 10.00 4.00 141.60 50.63 −−−− ---------------------------------------------------------- From the viewpoint of performing pattern detection with higher accuracy, generally, C _y / (C _x + C _y ) ≧ 0.2
5 (25 [%]), and preferably C
It is designed so that _y / (C _x + C _y ) ≧ 0.50 (50 [%]).

Although the embodiments of the present invention have been specifically described above, the present invention is not limited to the above embodiments, and various modifications based on the technical idea of the present invention are possible.

For example, the numerical values, materials, structures, and the like described in the first and second embodiments are merely examples, and different numerical values, materials, structures, and the like may be used as necessary. .

In the first embodiment, for example, the surfaces of the field insulating film 2 and the interlayer insulating films 7, 10 are flattened, or the thickness of the detecting electrode 11 is set to 0.3 μm. Alternatively, the side surface of the detection electrode 11 may have a forward tapered shape with a gentle slope.

[0035]

As described above, according to the present invention, the surface of the protective film of the sensor is flattened, or the height of the step on the surface of the protective film of the sensor is 30 nm or less. In some cases, the surface strength can be generally improved without deteriorating the sensitivity of the sensor.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a main part of a capacitive fingerprint sensor according to a first embodiment of the present invention.

FIG. 2 is a sectional view showing a main part of the capacitive fingerprint sensor according to the first embodiment of the present invention.

FIG. 3 is a schematic diagram illustrating an advantage of the capacitive fingerprint sensor according to the first embodiment of the present invention.

FIG. 4 is a sectional view showing a main part of a capacitive fingerprint sensor according to a second embodiment of the present invention.

FIG. 5 is a schematic diagram for explaining a ratio of a signal component due to unevenness of a fingerprint in a capacitance value detected by a capacitance type fingerprint sensor according to the present invention.

FIG. 6 is a schematic diagram for explaining how to use a capacitive fingerprint sensor.

FIG. 7 is a schematic diagram illustrating a main part of a conventional capacitive fingerprint sensor.

FIG. 8 is a schematic diagram illustrating an entire configuration of a conventional capacitive fingerprint sensor.

FIG. 9 is a cross-sectional view illustrating a main part of a conventional capacitive fingerprint sensor.

FIG. 10 is a cross-sectional view for explaining a problem of a conventional capacitive fingerprint sensor.

[Description of Signs] 1 ... Si substrate, 7, 10 ... Interlayer insulating film, 11
..Detection electrodes, 12 ... Protective films

Claims (8)

[Claims] 1. A fingerprint sensor device for collecting a fingerprint by sensing a capacitance with a finger, wherein a surface of a protective film of a sensor portion is flattened. 2. The method according to claim 1, wherein the protective film is formed, a resist is applied on the protective film so that the surface is flat, and then the surface of the protective film is flattened by performing etch back. The fingerprint sensor device according to claim 1, wherein 3. The fingerprint sensor device according to claim 1, wherein the surface of the protective film is flattened by applying spin-on glass as the protective film. 4. The fingerprint sensor according to claim 1, wherein after forming the protective film, the surface of the protective film is flattened by polishing the protective film using a chemical mechanical polishing method. apparatus. 5. The fingerprint sensor device according to claim 1, wherein the thickness of the detection electrode immediately below the protective film is 0.3 μm or less. 6. The fingerprint sensor device according to claim 1, wherein a side surface of the detection electrode immediately below the protective film has a forward tapered shape. 7. The height of the step on the surface of the protective film is 30n.
The fingerprint sensor device according to claim 1, wherein m is equal to or less than m. 8. A fingerprint sensor device for collecting a fingerprint by sensing a capacitance with a finger, wherein a height of a step on a surface of a protective film of a sensor portion is 30 nm or less. .