JP3070669B2 - Manufacturing method of silicon microsensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a silicon microsensor having a microbridge structure formed by surface micromachining.

[0002]

2. Description of the Related Art Surface micromachining using silicon as a material has a large accumulation of technology and is easy to increase the degree of integration. Therefore, it is used for manufacturing technology of digital mirror displays, accelerometers, vibrating gyroscopes or uncooled infrared sensors. Widely applied. These devices have a diaphragm and a microbridge structure consisting of a cantilever or a cantilever that mechanically connects the substrate and the diaphragm. An example of surface micromachining is shown with an uncooled infrared sensor of the shape shown in FIG.

Here, a general manufacturing process of a bolometer type uncooled infrared sensor will be described. FIG. 1 is a sectional view of FIG.
A part of a manufacturing process of a microbridge corresponding to a cross section taken along line A ′ is shown. FIG. 1A shows a CMO for signal reading.
Polonphosphosilicate glass (BPSG) for planarization on the silicon substrate 1 on which the S circuit is formed
Layer 2, polysilicon layer 5 as a sacrificial layer, titanium (Ti) layer 10 for wiring, bolometer layer 11, and bolometer layer 1
1 shows a state in which a protective film 8 on the lower surface side of No. 1 is formed. FIG. 1B shows a titanium nitride (TiN) layer 13 for infrared absorption.
Is formed. FIG. 1C shows the through hole 14.
Is formed, and the polysilicon layer 5 is partially exposed. FIG. 1D shows a state in which the etching of the polysilicon layer 5 by the alkali etchant via the through hole 14 is completed. The lower part of the diaphragm 16 is filled with the alkaline etchant 30. Next, the microbridge structure is immersed in running water, washed and dried in an oven at a high temperature, and the microbridge structure is in the state of FIG. The water below the diaphragm 16 is removed to form the cavity 15.

[0004]

However, FIG.
The microbridge structure shown in FIG.
5B, the diaphragm 16 frequently adheres to the base as shown in FIG. 5B at the stage of washing with flowing water after the selective etching and high-temperature drying with an oven. Hereinafter, this phenomenon is referred to as “sticking”. Furthermore, when the wafers in which the microbridge structures were arranged in an array were set up vertically and dried, the in-plane distribution of the sticking became extremely non-uniform. The problem with this sticking is
It has become a widespread problem in the field of surface micromachining, and methods for avoiding sticking have been proposed. For example, a method of lyophilizing after replacing the etching solution with water / methanol (H. Guckel et al., Sensors and Actuato
rs, 20 (1989) 117-122), a method in which the etchant is replaced with a suitable various organic solvent and finally replaced with a resist, and then removed with oxygen plasma (M. Orpana et al., Proc.
6th Int. Conf.Solid-State Sensors and Actuators
(Transducers'91), San Francisco, CA, USA, (1991),
958-964), Method of reducing the contact area by forming bumps on the base (F. Kozlowski et al., Sensors and Actuators A, 54
(1996) 659-662), Rapid Annealing after methanol replacement (T. Abe et al., J. Microelectromechanical Syst.
ems, 4 (2), (1995), 66-75), a method in which a pulse current is applied to the diaphragm after sticking occurs and the diaphragm is lifted by Lorentz force (BP Gogoi and CHMastrangelo, J. Microelectrom
Various methods such as echanical Systems, 4 (4), (1995), 185-192) have been proposed. However, any of these methods has an unclear effect or requires a large number of steps, and a simple and effective method for avoiding sticking has been desired.

[0005]

According to a method of manufacturing a silicon microsensor of the present invention, when a microbridge structure is formed using a surface micromachining manufacturing process, a sacrificial layer is selectively etched with an etchant to form a cavity. After the formation of, the etching liquid in the cavity is replaced with an inert liquid medium, and the liquid medium is allowed to stand in a high-temperature vapor of isopropyl alcohol for a certain time while the liquid medium remains, Is characterized in that the isopropyl alcohol vapor is gradually replaced with air.

Further, according to the present invention, when manufacturing a silicon microsensor having a microbridge structure using a manufacturing process of surface micromachining, after selectively etching a sacrificial layer by wet etching to form a cavity, a drying step is performed. The sample, which sometimes adhered to the base of the microbridge structure, was immersed in an isopropyl alcohol solution, applied with a weak ultrasonic wave for a certain period of time, pulled up, and then immersed in the cavity with the isopropyl alcohol solution remaining. This is a method for manufacturing a silicon microsensor, wherein the silicon microsensor is allowed to stand for a predetermined time in alcohol vapor.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS It is considered that the surface tension and electrostatic attraction of a solution are the main causes of sticking of a diaphragm in a microbridge structure which occurs when the microbridge structure is pulled up from an aqueous solution and dried. ing. The surface tension is generated at the boundary area between the solid layer / liquid layer / gas layer on the back surface of the diaphragm. The electrostatic attraction is generated by charging the base of the diaphragm and the microbridge structure.

In the present invention, the etchant for etching the sacrificial layer is replaced with an inert liquid medium, and then, instead of a drying step using a normal oven, isopropyl alcohol is vaporized using an isopropyl alcohol vapor apparatus as shown in FIG. Drying in steam. In the drying step in the isopropyl alcohol vapor, the liquid on the back surface of the microbridge structure is first replaced with isopropyl alcohol vapor. At this time, the solid layer / liquid layer / gas layer
The change of the gas layer at the boundary between the layers from the atmosphere to isopropyl alcohol vapor reduces the surface tension.
In addition, since the electric charge on the base of the diaphragm and the microbridge structure is removed by isopropyl alcohol vapor or minute droplets of isopropyl alcohol, the electrostatic attraction decreases. The fact that isopropyl alcohol is effective in removing static electricity has been reported, for example, by T. 0hmi et.
al., IEEE Transaction on semiconductor Manufacturi
ng, 7 (4) (1994) 440-446.

As a result, sticking of the microbridge structure is avoided. In addition, compared to water in a liquid state, isopropyl alcohol vapor molecules at a higher temperature are less susceptible to the effects of gravity, and act uniformly on the top and bottom of a vertically placed sample, thereby avoiding in-plane non-uniformity.

[0010] The inert liquid medium of the present invention is a liquid medium which does not affect the microbridge structure at all, and is usually preferably water, especially pure water. Further, once the etchant in the formed cavity is replaced with pure water, the pure water is immersed in an isopropyl alcohol solution with the pure water remaining in the cavity, and after a certain period of time, the pure water is removed. The water may be further replaced with isopropyl alcohol. As the inert liquid medium in the present invention, those in which some impurities remain in the microbridge structure, such as water containing a surfactant, are not preferred. Also,
If the microbridge structure is dried before being introduced into the isopropyl alcohol vapor apparatus, the effect of the present invention will not be exhibited, and therefore, the inert liquid medium preferably has a low vapor pressure. In this respect, water, especially pure water, or isopropyl alcohol is suitable, but methyl alcohol or ethyl alcohol may be used if attention is paid to drying.

FIG. 4 shows an example of an isopropyl alcohol vapor apparatus used in the present invention, and shows an embodiment of isopropyl alcohol vapor drying. After the selective etching of the sacrificial layer is completed, the sample immersed in the inert liquid medium is pulled up, immediately placed on the sample stage 24, and lowered by the elevator 23,
The sample is left in the isopropyl alcohol vapor area 20. After standing still for a certain period of time, preferably for 1 minute to 10 minutes, it is raised by the elevator 23. At this time, the sample reaches the atmosphere region 22 after passing through the isopropyl alcohol concentration transition region 21 over several minutes and is in a dry state.

Drying with isopropyl alcohol vapor is generally performed under atmospheric pressure, but may be performed under reduced pressure or under increased pressure.

Further, the present invention provides a method for recovering a microbridge structure in which sticking to a substrate has occurred by performing conventional oven drying. Therefore, in the present invention,
The sample with the sticking is immersed in an isopropyl alcohol solution, applied with a weak ultrasonic wave for a certain period of time, pulled up, and allowed to stand in the isopropyl alcohol vapor for a certain period of time with the isopropyl alcohol solution remaining in the cavity. . Alternatively, pure water to which a surfactant is added can be used instead of the above immersion in the isopropyl alcohol solution.

Here, the weak ultrasonic waves to be applied are 20
It is an ultrasonic wave having a frequency of kHz to 50 kHz and an intensity of 50 W or less. By applying the ultrasonic wave for about 1 to 30 minutes, the attached microbridge structure can be lifted. Subsequent standing for a certain time in isopropyl alcohol vapor can be performed in the same manner as described above.

As the surfactant, an anionic surfactant such as sodium cetyl sulfate and a nonionic surfactant such as polyethylene glycol alkyl ether can be used. Cationic surfactants are unsuitable because they may have poor wettability to silicon oxide films.

[0016]

EXAMPLES Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to these examples.

Embodiment 1 An embodiment of the present invention in an uncooled infrared sensor is shown in FIGS.
This is shown using FIG. FIG. 1A to FIG.
As described with reference to (d), the polysilicon layer 5 is selectively etched with an alkaline etching solution, and when the etching is completed, the polysilicon layer 5 is washed with running water to replace the etching solution with pure water. Next, the sample immersed in pure water is immediately moved to the isopropyl alcohol vapor region 20 of the isopropyl alcohol vapor device. At this time, the lower portion of the diaphragm 16 is replaced with isopropyl alcohol vapor 31 as shown in FIG. Next, as shown in FIG. 3, by exposing to the atmosphere, the portion filled with the isopropyl coal vapor 31 is replaced with the atmosphere to form the cavity 15, and the desired microbridge structure 18 is obtained.

FIG. 4 shows an isopropyl alcohol vapor apparatus and details of the isopropyl alcohol vapor drying step. Prior to use, the isopropyl alcohol vapor device introduces isopropyl alcohol from the isopropyl alcohol injection tank 28 into the isopropyl alcohol tank 26 and heats it with heat 27 to heat the isopropyl alcohol vapor region 20.
Is formed. Isopropyl alcohol vapor region 20
Is about 80 ° C. In the upper layer of the isopropyl alcohol vapor region 20, the isopropyl alcohol vapor is cooled by the cooling unit 25, and the isopropyl alcohol concentration transition region 2
1 is formed in advance. After the above-described selective etching of the polysilicon layer 5, the sample immersed in pure water is pulled up, immediately placed on the sample stage 24, lowered by the elevator 23, and left standing in the isopropyl alcohol vapor region 20. After standing still for 5 minutes, the pure water in the cavity 15 was sufficiently replaced with isopropyl alcohol at 80 ° C.
To raise.

At this time, the sample passes through the isopropyl alcohol concentration transition area 21 over several minutes, and after that, the atmosphere area 2
And reaches a dry state.

After the selective etching of the polysilicon layer 5, the incidence of sticking of the sample subjected to the isopropyl alcohol vapor drying and the conventional oven drying was counted. The pixel of the uncooled infrared sensor treated in this embodiment is 256 ×
They are arranged in an array of 256 pixels. Pixels at which sticking occurred in a total of 350 pixels at five locations at the corners and center of the array were counted, and the sticking occurrence rate was calculated. Here, the bolometer layer side protective film 9 and the bolometer layer upper protective film 12
Is made of a silicon nitride film having a strong tensile stress as an internal stress, so that the beam 17 is warped in a concave shape, and the diaphragm 16 is largely lifted upward. However, despite this internal stress, the rate of sticking of the oven-dried sample was 61%.

On the other hand, the sample subjected to isopropyl alcohol vapor drying according to the present invention was 0%.

As described above, in the microbridge structure 18 in which sticking is avoided by the present invention, since the thermal isolation of the diaphragm 16 is ensured, the temperature of the bolometer layer 11 rises sensitively when the diaphragm 16 absorbs incident infrared rays. Then, the temperature of the bolometer layer 11 changes greatly. In this way, an uncooled infrared sensor with high responsiveness was realized.

Embodiment 2 Another embodiment of the present invention in an uncooled infrared sensor will be described. The manufacturing process up to the step of selectively etching the polysilicon layer 5 with an alkaline etchant is the same as in the first embodiment. The difference from the first embodiment is that the bolometer layer side protective film 9 and the bolometer layer upper protective film 1 are different.
2 is made of a silicon nitride film having a low internal stress, so that the beam 17 is slightly warped in a convex shape, and the diaphragm 16 has a feature of slightly sinking downward. At this time, the occurrence rate of sticking of the sample subjected to the conventional oven drying was 73%,
The sample subjected to isopropyl alcohol vapor drying according to the present invention was reduced to 9%.

The rate of sticking of the sample which was pulled up from pure water after the selective etching of the polysilicon layer 5 and washed with running water and immediately dried in an oven was 73%. The sticking rate of the sample immersed in the isopropyl alcohol solution and then oven-dried was 78%, and hardly changed. From this result, it was found that the effect of avoiding sticking cannot be obtained only by selectively etching the polysilicon layer 5 and then immersing it in an isopropyl alcohol solution and drying it in an oven.

Embodiment 3 An embodiment similar to Embodiment 1 of the present invention in an uncooled infrared sensor will be described with reference to FIGS. 1A to 1D, the polysilicon layer 5 is selectively etched with an alkaline etchant. When the etching is completed, the polysilicon layer 5 is washed with running water to remove the alkaline etchant with pure water. Replace with Next, the sample immersed in pure water is immediately immersed in isopropyl alcohol solution, and the cavity 15 is replaced with pure water by isopropyl alcohol solution. Next, the sample immersed in the isopropyl alcohol liquid is immediately moved to the isopropyl alcohol vapor region 20 of the isopropyl coal vapor apparatus. At this time, FIG.
The cavity 15 is replaced by isopropyl alcohol vapor 31 as shown in FIG. Next, as shown in FIG. 3, the cavity 15 is dried by exposing the sample to the atmosphere to obtain a desired microbridge structure 18. In this example, a protective film was formed under the same conditions as the sample described in Example 1. As a result, the incidence of sticking of the sample subjected to the conventional oven drying was 78%, whereas the sample subjected to the isopropyl alcohol vapor drying according to the present invention was 4%.
The same effect as in Example 1 was obtained.

Example 4 An example in which the sample described in Example 1 which had been subjected to conventional oven drying and in which the sticking rate was 61% was repaired was described. Immerse this sample in isopropyl alcohol solution,
Weak ultrasonic waves were applied to the solution for 5 minutes. Next, the sample immersed in pure water is immediately moved to the isopropyl alcohol vapor region 20 of the isopropyl alcohol vapor device. At this time, the lower portion of the diaphragm 16 is replaced with isopropyl alcohol vapor 31 as shown in FIG. Next, as shown in FIG. 3, the portion filled with the isopropyl alcohol vapor 31 is replaced with the atmosphere by exposing it to the atmosphere to form the cavity 15, and the desired microbridge structure 18 is obtained. At this time, almost all of the pixels where sticking occurred could be lifted upward.

Example 5 Another example described in Example 1 in which the conventional oven drying was performed to repair the sticking of the sample having the sticking rate of 61% after oven drying was described. This sample was treated with a nonionic surfactant (N
CW-601A (manufactured by Wako Pure Chemical Industries, Ltd.) was added to pure water, and weak ultrasonic waves were applied for 5 minutes to wash with running water. The sample immersed in pure water was immediately transferred to the isopropyl alcohol vapor region 20 of the isopropyl alcohol vapor device and dried as in Example 4. At this time, almost all of the pixels where sticking occurred could be lifted upward.

Embodiment 6 An embodiment of the present invention in the manufacturing process of the vibrating gyroscope will be described. FIG. 6 shows a general manufacturing process of a vibration gyroscope. As shown in FIG. 6A, a phosphorus diffusion layer 41 is formed on a capacitance detection portion and a substrate electrode portion of a p-type silicon substrate 40, and a silicon oxide film 42 and a silicon nitride film 43 are formed. A phosphor silicate glass (PSG) layer 44 and a polysilicon layer 45 are formed on the capacitance detecting unit.

Next, as shown in FIG. 6B, a through hole 46 is formed. Next, as shown in FIG. 6C, after the detection electrode 47 on the diaphragm side and the detection electrode 48 on the substrate side are formed, the PSG layer 44 is etched with a hydrofluoric acid solution.
A microbridge structure is formed by washing with running water and drying in an oven. At this time, the microbridge structure is mechanically connected to the substrate by only a few beams, and has a structure in which the diaphragm 49 can be excited in a fixed direction parallel to the substrate by electrostatic force. When a rotational force to be observed acts on the diaphragm 49, a Coriolis force is generated in a direction perpendicular to the substrate. At this time, the capacitance between the diaphragm 49 and the substrate 41 changes, and by detecting this, the rotational force can be obtained. The above steps are performed, for example, in Y. Mochida et a
l., The Second International Micromachine Symposiu
m, Tokyo, Proceeding 123-126, (1996).

In the manufacturing process of the vibratory gyroscope in this embodiment, the PSG layer 44 was etched with hydrofluoric acid and then washed with running water and oven-dried.
Sticking of the diaphragm 41 to the silicon substrate occurred. According to the present invention, after washing with running water, isopropyl alcohol vapor drying described in Example 1 was performed instead of oven drying, and sticking was avoided.

[0031]

The first effect is an improvement in the yield of the process for forming the microbridge structure. The reason is that the isopropyl alcohol vapor reduces the external force applied to the microbridge structure in the sticking direction.

The second effect is an improvement in the in-plane uniformity of the process for forming the microbridge structure. This is because isopropyl alcohol vapor molecules at a higher temperature are less affected by gravity than isopropyl alcohol in a water or solution state, and act uniformly above and below a vertically placed sample.

[Brief description of the drawings]

1 (a) to 1 (d) are schematic cross-sectional views of a manufacturing process of a general microbridge structure.

FIG. 2 is a schematic cross-sectional view showing a state of a microbridge structure in a drying step using isopropyl alcohol vapor according to the present invention.

FIG. 3 is a schematic sectional view of a completed microbridge structure.

FIG. 4 is a schematic diagram of an isopropyl alcohol vapor device.

FIG. 5A is a top view of a microbridge structure of an uncooled infrared sensor. (B) is a side view showing sticking of the diaphragm of the uncooled infrared sensor generated by using the conventional manufacturing method.

FIGS. 6A to 6C are schematic cross-sectional views of a vibration type gyroscope manufacturing process according to an embodiment of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 silicon substrate 2 BPSG layer 3 infrared reflection film 4 silicon oxide film 5 polysilicon layer 6 silicon nitride film 7 silicon oxide film 8 bolometer layer lower protection film 9 bolometer layer side protection film 10 electrode wiring titanium 11 bolometer layer 12 bolometer layer upper protection Film 13 Infrared absorbing film 14 Through hole 15 Cavity 16 Diaphragm 17 Beam 18 Micro bridge structure 19 Wiring aluminum 20 Isopropyl alcohol vapor region 21 Isopropyl alcohol concentration transition region 22 Atmospheric region 23 Elevator 24 Sample stand 25 Cooling unit 26 Isopropyl alcohol tank 27 Heater 28 Isopropyl alcohol injection tank 29 Waste liquid tank 30 Alkaline etchant 31 Isopropyl alcohol vapor 40 P-type silicon substrate 41 Phosphorus diffusion layer 42 Silicon oxide film 43 Silicon nitride film 44 PSG layer 45 Polysilicon layer 46 Through hole 47 Electrode 48 Substrate electrode 49 Diaphragm

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 29/84 H01L 37/00 H01L 21/306 H01L 27/14

Claims (6)

(57) [Claims] When manufacturing a silicon microsensor having a microbridge structure using a manufacturing process of surface micromachining, a step of selectively etching at least a sacrificial layer by wet etching to form a cavity, and inactivating an etching solution. A method of manufacturing a silicon microsensor, comprising: a step of replacing the liquid medium with a liquid medium; and a step of allowing the liquid medium to remain in the isopropyl alcohol vapor for a predetermined time while remaining in the cavity. 2. The method according to claim 1, wherein the liquid medium is pure water. 3. The method for manufacturing a silicon microsensor according to claim 1, wherein the liquid medium is an isopropyl alcohol solution in which an etching solution is replaced with pure water and then the pure water is replaced. 4. The method according to claim 1, wherein the isopropyl alcohol vapor in the cavity of the microbridge structure, which is left standing in the isopropyl alcohol vapor for a predetermined time, is gradually replaced with air.
13. The method for manufacturing a silicon microsensor according to the above item. 5. When manufacturing a silicon microsensor having a microbridge structure using a manufacturing process of surface micromachining, after selectively forming a cavity by selectively etching a sacrificial layer by wet etching, said microbridge is formed in a drying step. The sample having the structure adhered to the base is immersed in an isopropyl alcohol solution, applied with a weak ultrasonic wave for a certain period of time, pulled up, and placed in the isopropyl alcohol vapor with the isopropyl alcohol solution remaining in the cavity. A method for manufacturing a silicon microsensor, comprising allowing the silicon microsensor to stand for a predetermined time. 6. A liquid for immersing a sample in which the microbridge structure has adhered to a base is pure water to which a surfactant is added instead of the isopropyl alcohol liquid. A method for manufacturing the silicon microsensor described in the above.