KR100385674B1 - A Sensor for Breath Alcohol Measurement Using Porous Silicon, and Fabrication Method Thereof - Google Patents

Abstract

The present invention relates to an alcohol sensor for alcohol measurement using porous silicon as a sensing material. Conventional alcohol sensors include an electrochemical alcohol sensor using platinum and an electrically conductive alcohol sensor using tin oxide and the like. However, the alcohol sensor using platinum is expensive, high operating current, high battery consumption, and has a problem that the measurement interval should be more than 10 minutes to remove alcohol in the container. On the other hand, an alcohol sensor using a metal oxide has a disadvantage in that selectivity and linearity are weak.

The present invention provides an alcohol sensor using a silicon integration process technology using a porous silicon layer as an alcohol sensing material, comprising: a porous silicon layer which is an alcohol sensing region formed in a portion of a high concentration silicon substrate; An epitaxial layer formed on the high concentration silicon substrate to isolate the exposed area from the porous silicon layer while maintaining a portion of the high concentration silicon substrate in an exposed state; Electrodes formed on an upper portion of the porous silicon layer, the alcohol sensing region, and on a portion of the exposed high concentration silicon substrate; And an element passivation layer formed on the epitaxial layer and on the other region of the exposed high concentration silicon substrate. According to the present invention, the integration of the alcohol sensor is easy, miniaturization and low cost is possible.

Description

A sensor for breath alcohol measurement using porous silicon, and fabrication method thereof}

The present invention relates to an alcohol sensor for measuring alcohol, and more particularly, to an alcohol sensor using porous silicon as a sensing material. The present invention also relates to an alcohol sensor manufacturing method using the porous silicon.

There are three types of sensors for measuring alcohol, which have been developed so far: electrochemical method using platinum, conductivity change method by surface adsorption using metal oxide semiconductor, and infrared absorption spectrum analysis method using laser. Among these, the platinum-based electrochemical breathalyzer, which is used by traffic policemen in Korea, uses two platinum electrode detectors to detect small voltages caused by electrochemical reactions when breathing gas is delivered to the detector. The blood alcohol level of the subject is measured indirectly. This platinum-based breathalyzer is currently used in many countries as a breathalyzer because of its reliability and linearity. However, since the price is high and the operating current is higher than 100 mA, the battery needs to be replaced frequently. In addition, this platinum-based breathalyzer measures blood alcohol levels by analyzing samples collected in a closed container. If the alcohol is not removed from the container, the cumulative result is displayed. There is a problem to leave more than 10 minutes.

Meanwhile, a breathalyzer using a metal oxide semiconductor uses tin oxide (SnO ₂ ), and detects gas concentration by using a change in electrical conductivity according to the concentration of alcohol gas adsorbed on the surface. The breathalyzer using the metal oxide semiconductor is generally used for self-measurement at home and abroad because it is generally inexpensive, has excellent sensitivity, and has excellent advantages in response speed and long-term stability.

Since the study of the moisture effect on the porous silicon layer was published in 1990, the research on the humidity sensor using the porous silicon continued. As a humidity sensor using this porous silicon, there is an internal capacitive sensor using a change in dielectric constant of the porous silicon layer between the upper and lower electrodes due to moisture adsorbed on the surface. Kim Seong-jin, one of the applicants of the present invention, filed on October 22, 1998 about such an internal capacitance type humidity sensor. However, the applicant of the present invention has learned through various experiments that the internal capacitive humidity sensor is more excellent in response to alcohol than in response to moisture.

An object of the present invention devised to solve the above problems of the prior art, to provide an alcohol sensor using a porous silicon as the alcohol sensing material and a method of manufacturing the same.

1 is a structural diagram of an alcohol sensor using porous silicon according to an embodiment of the present invention,

2A to 2J are process diagrams illustrating a method of manufacturing an alcohol sensor using porous silicon according to an embodiment of the present invention.

※ Explanation of code about main part of drawing ※

10 silicon substrate 20 porous silicon layer

30: epi layer 40: oxide film

50 electrode 60 aluminum electrode pad

70: wire bonding

An alcohol sensor according to the present invention for achieving the above object, the porous silicon layer which is an alcohol sensing region formed in a portion of the high concentration silicon substrate; An epitaxial layer formed on the high concentration silicon substrate to isolate the exposed area from the porous silicon layer while maintaining a portion of the high concentration silicon substrate in an exposed state; Electrodes formed on an upper portion of the porous silicon layer, the alcohol sensing region, and on a portion of the exposed high concentration silicon substrate; And an element passivation layer formed on an upper portion of the epitaxial layer and on another region of the exposed high concentration silicon substrate.

In addition, the alcohol sensor manufacturing method according to the present invention comprises: a first step of growing an epitaxial layer of a second conductivity type on a silicon substrate of the first conductivity type; Converting at least two regions of the epitaxial layer of the second conductivity type into a high concentration region of the first conductivity type using a mask pattern, and forming a porous silicon layer in the high concentration region of the first conductivity type using an anode reaction Two steps; A third step of exposing the high concentration silicon substrate by converting and removing one region of the at least two regions of the porous silicon layer into the porous silicon oxide film through a thermal oxidation process; Forming a protective film for shielding the resultant product from the outside; And a fifth step of forming electrodes in the exposed region of the high concentration silicon substrate and the porous silicon layer, respectively.

Porous silicon based on silicon, which is a typical semiconductor material, has excellent reactivity to alcohol (in detail, permeability), and can be integrated, thereby making it possible to manufacture lower cost, lighter, and more versatile alcohol sensors than conventional alcohol sensors. Suitable.

Hereinafter, with reference to the accompanying drawings will be described in detail "an alcohol sensor using a porous silicon and a method of manufacturing the same" according to an embodiment of the present invention.

1 is a structural diagram of an alcohol sensor using porous silicon according to an embodiment of the present invention.

Referring to FIG. 1, the epitaxial layer 30 of the second conductivity type is formed on the high concentration silicon substrate 10 of the first conductivity type. As the high concentration silicon substrate 10, a high concentration p ⁺ type substrate having a specific resistance of 0.01 Ωcm is used. Thus, ohmic bonding may be performed immediately without depositing a separate metal electrode during an anode reaction to form porous silicon. . The epi layer 30 uses n type. A detailed process of forming the porous silicon will be described later.

In some regions inside the n-type epitaxial layer 30, a porous silicon layer 20, which is an alcohol sensing region, is formed on the high concentration silicon substrate 10 through ion implantation of impurities and selective anodic reaction. In addition, an exposed area of the high concentration silicon substrate 10 separated from the porous silicon layer 20 by the epi layer 30 is formed in another area inside the epi layer 30. The porous silicon layer 20 and the exposed region are formed with an electrode portion for sensing the alcohol concentration on the surface. That is, two electrodes 50 are formed on the porous silicon layer 20 and a part of the exposed area, respectively, and the upper part of the remaining area (the entire area of the epi layer 30 and the remaining area of the exposed area) is used to protect the device. The protective film 40 is formed.

As described above, the alcohol sensor using porous silicon according to the present invention can limit the distance between the two electrodes 50 to only the porous silicon layer 20 in order to obtain a large capacitance value as much as possible. The positions of the electrodes 50 are all formed on the top of the wafer.

Hereinafter, a process of manufacturing the alcohol sensor using the porous silicon having the above-described structure will be described sequentially with reference to FIGS. 2A to 2J.

In the present invention, in order to form a porous silicon layer having a micro structure, a very high concentration p ⁺ type single crystal silicon substrate having a resistivity of 0.01? Cm or less is used. The doping concentration of the wafer has a great influence on the size of the pores of the porous silicon layer, and when making the device by processing the porous silicon layer, structurally stable microporous is suitable even if the porosity is slightly reduced.

First, referring to FIG. 2A, phosphorus is doped with 10 ¹⁴ to 10 ¹⁵ doses on a low resistivity of 0.01 Ωcm or less and a high concentration p ⁺ type single crystal silicon substrate 10 of 10 ¹⁹ cm ⁻³ . An n-type epitaxial layer 30 is grown. At this time, the epi layer 30 is grown to a thickness of about 2 to 4 ㎛ at a rate of 0.2 ㎛ / min at a growth temperature of 1050 ℃. The n-type epitaxial layer 30 plays a role of suppressing porous formation when forming a selective porous silicon layer due to a difference in doping concentration and type of dopants in a subsequent process.

2B and 2C illustrate the step of forming the porous silicon layer 20.

First, referring to FIG. 2B, a mask pattern PR1 for defining an alcohol sensing region is formed on the resultant of FIG. 2A, and then boron is used as an ion implantation mask to about 10 ¹⁵ cm ⁻² per unit area. In order to activate the injected boron, annealing is performed at a temperature of about 1000 ° C. in a nitrogen gas atmosphere for 1 hour to adjust the minimum specific resistance to be approximately 0.01Ωcm.

Through this process, the surface of the resultant is divided into p ⁺ region and n region. Since the porous silicon layer is easily formed in the region having high doping concentration, it is predominantly formed in the p ⁺ layer by this reaction selectivity.

Next, the resultant covered with the mask pattern PR1 is applied with a constant current in an anode reaction to form a locally porous silicon layer 20 as shown in FIG. 2C. The porous silicon layer 20 is formed by anodic reaction for 2 minutes at a current density of about 13 mA / cm ² in a 25% hydrogen fluoride (HF) solution in the anode reaction cell. Subsequently, a process of washing with distilled water may be added to remove the hydrogen fluoride solution that may remain in the formed porous silicon layer 20.

Referring to FIG. 2D, when the porous silicon layer 20 is formed as shown in FIG. 2C, the mask pattern PR1 is removed and a nitride film is applied to the entire surface of the resultant product. Subsequently, the nitride film pattern 24 is formed by etching the nitride film in the remaining regions except for the portion of the porous silicon layer 20 that senses alcohol through a photolithography process. The nitride film pattern 24 serves as a barrier film (protective film) to prevent the oxide film from being formed on a portion of the porous silicon layer, which is an alcohol sensing region, in a process of growing an oxide film, which is a subsequent process.

2E illustrates a thermal oxidation process. Specifically, the resultant of FIG. 2D is oxidized at a temperature of about 1000 ° C. to form a thermal oxide film 26 having a thickness of about 3000 kPa over the entire surface of the resultant. In this case, the porous silicon layer 20 exposed to the thermal oxidation process is converted into an oxidized porous silicon layer 28 because the surface is oxidized deep even in a short time.

Referring to FIG. 2F, the thermal oxide layer 26 and the converted porous silicon layer 28 formed through the thermal oxidation process are immersed in a buffered oxide etchant (BOE) etching solution to be removed, and the nitride layer pattern 24 used as a protective layer. ) Is removed using a phosphate solution. As a result, as shown in FIG. 2F, a part of the p ⁺ substrate 10 is exposed, which is called an exposure area.

Next, referring to FIG. 2G, a protective film 40 is formed on the resultant of FIG. 2F to shield the device from the outside. At this time, the protective film 40 is deposited to a thickness of about 5000 kW by using a plasma enhanced chemical vapor deposition (PECVD) method capable of low temperature processing so as not to affect the redistribution of the dopant. Subsequently, a lift-off photoresist film PR2 is formed on the upper portion of the protective film in order to form a subsequent translucent electrode by a lift off method. The photoresist film PR2 and the oxide film 40 applied through this process form an alcohol sensing window and a contact hole by a photolithography process using a predetermined mask.

Referring to FIG. 2H, a thin film of about 300 mW or less is vacuum deposited on the entire surface of the resultant with chromium (Cr) and gold (Au), and the electrode material of the unnecessary region is removed together with the photoresist pattern PR2 by a lift-off method. The translucent electrode 50 is simultaneously formed on the exposed porous silicon layer 20 and the exposed region of the silicon substrate 10.

Finally, the aluminum electrode pad 60 and the wire bonding 70 process are performed as shown in FIG. 2I to connect the external electrodes, thereby completing the manufacture of the alcohol sensor as shown in FIG. 2J.

The alcohol sensor is capacitive, and the alcohol gas that has penetrated into the porous silicon layer changes the total dielectric constant of the sensing region in which the oxide film, alcohol, and water vapor including the porous silicon layer is mixed according to the alcohol concentration. The porous silicon layer, which is a sensing region, is a dielectric in which porous silicon, oxide film, alcohol, water vapor, and air are mixed. The total dielectric constant (x) depends on the dielectric constant (x _i ) of each component and the volume ratio (σ _i ) of each component. Approximated as in Equation 1.

In the electrostatic field, the dielectric constant of silicon is 12, the dielectric constant of oxide is 3.9, and the dielectric constant of pure alcohol and water is 25 and 80, respectively, and as the alcohol concentration increases, the volume ratio of alcohol per unit volume increases, so the capacitance increases. This allows the alcohol concentration to be measured.

While the invention has been described above based on the preferred embodiments thereof, these embodiments are intended to illustrate rather than limit the invention. It will be apparent to those skilled in the art that various changes, modifications, or adjustments to the above embodiments can be made without departing from the spirit of the invention. Therefore, the protection scope of the present invention will be limited only by the appended claims, and should be construed as including all such changes, modifications or adjustments.

According to the present invention as described above, since the reactivity with the alcohol of the porous silicon layer is excellent and can be integrated, there is an effect of manufacturing an alcohol sensor capable of low cost, light weight, and multifunctionality.

Claims (3)

A high concentration silicon substrate; A porous silicon layer which is an alcohol sensing region formed in a portion of the high concentration silicon substrate; An epitaxial layer formed on said high concentration silicon substrate so as to isolate said exposed region of said high concentration silicon substrate and said porous silicon layer while maintaining said other partial region of said high concentration silicon substrate; Electrodes formed on the porous silicon layer, the alcohol sensing region, and on the exposed region of the high concentration silicon substrate, respectively; An element protection film formed on an upper portion of the remaining region except for the region in which the electrodes are formed; Aluminum electrode pads connected to the respective electrodes; Alcohol sensor using porous silicon, characterized in that the wire bonded to each of the aluminum electrode pad. In the method of manufacturing an alcohol sensor using porous silicon, A first step of growing an epitaxial layer of a second conductivity type on a high concentration silicon substrate of a first conductivity type; The mask pattern is used to convert at least two partial regions of the epitaxial layer of the second conductivity type into a high concentration region of the first conductivity type, and a porous silicon layer is formed in the high concentration region of the first conductivity type using an anode reaction. Performing a second step; A third step of converting one partial region of the porous silicon layer of the at least two partial regions into a porous silicon oxide film through a thermal oxidation process and removing the exposed silicon substrate by exposing the high concentration silicon substrate to generate an exposed region of the high concentration silicon substrate Wow; A fourth step of forming an element protection film on the resultant of the third step to shield the outside from the outside; Removing a exposed portion of the high concentration silicon substrate and the device protection layer formed on the porous silicon layer, and forming an electrode on an upper portion of the exposed area of the high concentration silicon substrate and an upper portion of the porous silicon layer, respectively; And forming a sixth electrode pad to connect the external electrode to each of the electrodes, and bonding a wire to each of the aluminum electrode pads. The alcohol sensor using porous silicon according to claim 2, wherein the epitaxial layer of the second conductivity type is an n-type epilayer having a thickness of 2 to 3 µm and a doping concentration of 10 ¹⁴ to 10 ¹⁵ cm ^-3 . Manufacturing method.