JP6205017B2 - Method for manufacturing transistor - Google Patents

Description

The present invention relates to a method for producing a transistor.

  In recent years, sensor elements that detect a specific substance contained in a solution (electrolyte solution), such as an ion sensor that detects an ion concentration in a solution or a biosensor that detects an organic substance such as protein or glucose in a solution, Research and development is actively conducted. As one kind of such sensor element, a source electrode and a drain electrode are formed on a diamond thin film, and an electric field in which the surface of the diamond thin film between the source electrode and the drain electrode and in contact with the above solution functions as a gate. Some have an effect transistor. Such a field effect transistor has advantages that the portion in contact with the solution is a diamond thin film, has high stability, is easy to manufacture, and is low in cost.

  Patent Document 1 below discloses an ion sensor including the above-described field effect transistor. Specifically, a reference electrode and a working electrode are provided so that a solution to be detected is sandwiched, and each of the reference electrode and the working electrode is formed by the above-described field effect transistor (p-channel field effect transistor). A configured ion sensor is disclosed. Further, this Patent Document 1 also has a point of controlling ion sensitivity by performing hydrogen termination treatment on the surface of a diamond thin film functioning as a gate and then partially terminating it with oxygen termination or fluorine termination. It is disclosed.

  Moreover, the following patent documents 2 to 4 disclose techniques for treating the surface of diamond (fluorine treatment). Specifically, Patent Document 2 below discloses that a conductive substrate coated with conductive diamond is subjected to a fluorination treatment (thermal fluorination treatment, electrolytic fluorination treatment) to extend the life. . Patent Document 3 below discloses that the hole density is increased by exposing the surface of diamond to plasma made of a mixed gas of hydrogen and fluorine sulfide and treating the surface of the diamond substrate. In Patent Document 4 below, diamond powder and perfluoroazoalkane are present in a solution and irradiated with ultraviolet rays to perform a process of chemically bonding a perfluoroazoalkyl group to the surface of the diamond powder. The point of introducing a functional group is disclosed.

JP 2012-168120 A JP 2006-97054 A Japanese Patent No. 3886922 Japanese Patent No. 4119973

  By the way, as disclosed in Patent Document 1 described above, it is considered that the ion sensitivity of the field-effect transistor can be freely changed if a part of the diamond-terminated diamond surface is terminated with fluorine. . However, according to the research of the inventors of the present application, it has been found that when a diamond surface is treated with fluorine, a deposited film of fluorocarbon is deposited depending on the treatment method.

  As is well known, fluorocarbon is a general term for organic compounds having a carbon-fluorine bond (C—F), and has a property that a chemical reaction hardly occurs and is stable even when the temperature is changed. For this reason, when such a fluorocarbon deposit is deposited on the diamond surface when a part of the hydrogen-terminated diamond surface is terminated with fluorine, the characteristics (property) of the diamond surface are originally intended. May be different. Then, the ion sensitivity of the field effect transistor becomes different from the originally intended ion sensitivity, and as a result, a sensor element different from the original characteristic may be manufactured. Problems arise.

  From the above, in order to manufacture a sensor element having the intended characteristics, it is extremely important to control the presence or absence of a deposited film of fluorocarbon when processing the diamond surface functioning as the gate of the field effect transistor. Although Patent Documents 2 to 4 described above disclose a technique for treating the surface of diamond (fluorine treatment), these Patent Documents 2 to 4 are all made of fluorocarbon when the surface of diamond is treated. No mention is made of the point where the deposited film is deposited.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for manufacturing a transistor capable of making a diamond surface have desired characteristics by controlling the presence or absence of a deposited film of fluorocarbon. .

In order to solve the above problems, the surface treatment method for a diamond thin film of the present invention is a surface treatment method for a diamond thin film (12, 22) formed on a substrate (11, 21, 40), which is necessary. In accordance with the surface characteristics of the diamond thin film, a first substitution treatment in which part of the hydrogen terminus of the diamond thin film is replaced with a fluorine terminus without depositing a fluorocarbon deposition film on the surface of the diamond thin film; One of the processes (S15) of the second substitution process in which a part of the hydrogen terminal of the diamond thin film is replaced with a fluorine terminal while depositing a fluorocarbon deposition film on the surface is performed.
According to the present invention, the first substitution treatment in which part of the hydrogen terminal of the diamond thin film is replaced with fluorine termination without depositing the fluorocarbon deposited film on the surface of the diamond thin film, and the fluorocarbon deposited film is deposited on the surface of the diamond thin film. In this manner, either one of the second substitution process is performed in which a part of the hydrogen terminal of the diamond thin film is replaced with a fluorine terminal.
In the diamond thin film surface treatment method of the present invention, before any one of the first and second substitution processes is performed, a terminal other than hydrogen on the surface of the diamond thin film is replaced with a hydrogen terminal ( S14) is performed.
In the diamond thin film surface treatment method of the present invention, the first substitution treatment is realized by performing an exposure treatment using a fluorine gas or a fluorine-based gas on the entire surface or a partial region of the diamond thin film. Or a reactive ion etching process using a fluorine-based gas or an inductively coupled reactive ion etching process on the entire surface or a part of the diamond thin film. .
In the diamond thin film surface treatment method of the present invention, the second substitution treatment may be reactive ion etching treatment or inductively coupled reactive ion etching using a fluorine-based gas for the entire surface or a part of the diamond thin film. It is a process realized by performing the process.
The diamond thin film surface treatment method of the present invention is characterized in that the fluorine-based gas used in the exposure treatment of the first substitution treatment is a gas containing XeF ₂ or COF ₂ .
In the diamond thin film surface treatment method of the present invention, the fluorine-based gas used in the reactive ion etching treatment or inductively coupled reactive ion etching treatment of the first substitution treatment is C _x F _y , C _x H _y. At least one of F _z , S _x F _y , N _x F _y , C _x O _y F _z , N _x O _y F _z , and S _x O _y F _z (x, y, z are integers of 1 or more) It is characterized by being gas containing.
In the diamond thin film surface treatment method of the present invention, the fluorine-based gas used in the reactive ion etching process or inductively coupled reactive ion etching process of the second substitution process is C _x F _y , C _x H _y. At least one of F _z , S _x F _y , N _x F _y , C _x O _y F _z , N _x O _y F _z , and S _x O _y F _z (x, y, z are integers of 1 or more) It is characterized by being gas containing.
The method of manufacturing a field effect transistor according to the present invention includes a diamond thin film (12, 22) formed on a substrate (11, 21, 40), a source electrode (13, 23) and a drain formed on the diamond thin film. And a surface of the diamond thin film between the source electrode and the drain electrode functions as a gate (16, 26), wherein the diamond is formed on a substrate. A first step of forming a thin film (S13), and a second process of performing at least a portion functioning as the gate on the surface of the diamond thin film using the surface treatment method for a diamond thin film according to any one of the above. It has the process (S14, S15).
A third step (S16) of forming the source electrode and the drain electrode on the diamond thin film is provided between the first step and the second step.
In the field effect transistor manufacturing method of the present invention, the third step includes a step of forming a protective film (15, 25) for protecting the source electrode and the drain electrode so as to cover the source electrode and the drain electrode. It is characterized by that.
The sensor element of the present invention includes at least one detection electrode (10, 20) in contact with the solution (W) containing the specific substance, and the specific substance contained in the solution is detected based on the output of the detection electrode. A sensor element (1, 2) for detection, wherein the field effect transistor manufactured by the above-described method for manufacturing a field effect transistor has at least the surface of the diamond thin film functioning as the gate in contact with the solution. It is characterized by being provided on one detection electrode.

  According to the present invention, the first substitution treatment in which part of the hydrogen termination of the diamond thin film is replaced with fluorine termination without depositing the fluorocarbon deposition film on the surface of the diamond thin film, and the fluorocarbon deposition film on the surface of the diamond thin film. While being deposited, any one of the second substitution treatment in which part of the hydrogen termination of the diamond thin film is replaced with a fluorine termination is performed, so that the surface of the diamond can have desired characteristics. There is an effect.

It is sectional drawing which shows the structure of the pH sensor as a sensor element by 1st Embodiment of this invention. It is a plane perspective view of the pH sensor as a sensor element by a 1st embodiment of the present invention. It is a circuit diagram which shows an example of the pH measurement circuit using the pH sensor as a sensor element by 1st Embodiment of this invention. It is a figure which shows an example of the characteristic of the p channel field effect transistor currently formed in the pH sensor as a sensor element by 1st Embodiment of this invention. 3 is a flowchart illustrating a method for manufacturing a field effect transistor according to the first embodiment of the present invention. It is a figure which shows the analysis result of the diamond thin film processed by the processing method of the diamond thin film by 1st Embodiment of this invention. It is a figure which shows typically the surface state of the diamond thin film processed by the processing method. It is sectional drawing which shows the structure of the pH sensor as a sensor element by 2nd Embodiment of this invention. It is a figure which shows the example of the diamond substrate which can be used by embodiment of this invention. It is a flowchart which shows the manufacturing method of the field effect transistor in 1st Example. It is a figure which shows an example of the characteristic of the field effect transistor obtained in 1st Example. It is a flowchart which shows the manufacturing method of the field effect transistor in 2nd Example. It is a figure which shows an example of the current-voltage characteristic of the field effect transistor obtained in 2nd Example. It is a flowchart which shows the manufacturing method of the field effect transistor in 3rd Example. It is a figure which shows an example of the current-voltage characteristic of the field effect transistor obtained in 3rd Example. It is a figure which shows an example of the pH sensitivity of the field effect transistor obtained in 3rd Example. It is a flowchart which shows the surface treatment method of the diamond thin film in 4th Example.

  Hereinafter, a surface treatment method of a diamond thin film, a method of manufacturing a field effect transistor, and a sensor element according to an embodiment of the present invention will be described in detail with reference to the drawings. In the following, the case where the sensor element is a pH sensor will be described as an example, and the surface treatment method of the diamond thin film and the method of manufacturing the field effect transistor will be described in the case of manufacturing the field effect transistor included in the pH sensor. An example will be described.

[First Embodiment]
<Sensor element>
FIG. 1 is a cross-sectional view showing a configuration of a pH sensor as a sensor element according to the first embodiment of the present invention. FIG. 2 is a perspective plan view of the pH sensor. 1 is a cross-sectional view taken along the line BB in FIG. 2, and FIG. 2 is a plan perspective view when the pH sensor 1 is viewed from the direction AA in FIG. As shown in FIG. 1 and FIG. 2, the pH sensor 1 includes a reference electrode 10 (detection electrode) and a working electrode 20 (detection electrode) provided so as to face each other, and these reference electrode 10 and working electrode. 20, the pH of the liquid W (solution) to be measured introduced between the two is measured.

  The reference electrode 10 includes a silicon wafer 11 (substrate), a diamond thin film 12, a source electrode 13, a drain electrode 14, and a protective film 15. The diamond thin film 12 is formed on the surface of the silicon wafer 11, and the source electrode 13 and the drain electrode 14 are formed so as to face each other on the surface of the diamond thin film 12. The protective film 15 is formed on the diamond thin film 12 so as to cover the source electrode 13 and the drain electrode 14. In the reference electrode 10, a region sandwiched between the source electrode 13 and the drain electrode 14 (the surface of the diamond thin film 12) functions as the gate 16.

  That is, a p-channel field effect transistor including a source electrode 13, a drain electrode 14, and a gate 16 is formed on the reference electrode 10. This p-channel field effect transistor can be referred to as an ion-sensitive field-effect transistor (ISFET) because the liquid to be measured W is guided to the gate 16. The ion-sensitive field effect transistor is also called a diamond ISFET because it has the diamond thin film 12. Moreover, it is also called diamond SGFET (electrolyte solution-gate FET) because it has a diamond thin film and does not have an oxide in the wetted part of diamond.

  Here, the dimension of the gate 16 is appropriately set according to the characteristics of the pH sensor. For example, as shown in FIG. 2, the gate length α is set to a value of about 10 to 1000 μm, and the gate width β is set to a value of about 0.01 to 50 mm. Further, the length γ of the source electrode 13 (drain electrode 14) is set to a value of about 0.01 to 50 mm, and the width δ of the source electrode 13 (drain electrode 14) is a value of about 0.01 to 100 mm. Set to

In addition, the surface of the diamond thin film 12 functioning as the gate 16 has a stable potential in a hydrogen ion concentration range of 1.0 × 10 ^{−1 to} 1.0 × 10 ⁻¹⁴ mol / L, or ion sensitivity is practical. The termination element is controlled so that the potential is kept constant to the extent that does not cause a problem. That is, the surface of the diamond thin film 12 functioning as the gate 16 is an ion-insensitive termination. Details of the surface treatment of the diamond thin film 12 will be described later.

  The working electrode 20 has the same configuration as the reference electrode 10 and includes a silicon wafer 21 (substrate), a diamond thin film 22, a source electrode 23, a drain electrode 24, and a protective film 25. The diamond thin film 22 is formed on the surface of the silicon wafer 21, and the source electrode 23 and the drain electrode 24 are formed so as to face each other on the surface of the diamond thin film 22. The protective film 25 is formed on the diamond thin film 22 so as to cover the source electrode 23 and the drain electrode 24. In this working electrode 20, a region sandwiched between the source electrode 23 and the drain electrode 24 (the surface of the diamond thin film 22) functions as the gate 26.

  That is, the p-channel field effect transistor including the source electrode 23, the drain electrode 24, and the gate 26 is formed on the working electrode 20. This p-channel field effect transistor can be referred to as an ion sensitive field effect transistor (ISFET) because the liquid to be measured W is guided to the gate 26.

  Here, it is desirable that the source electrode 23 and the drain electrode 24 have the same shape as the source electrode 13 and the drain electrode 14 of the reference electrode 10, respectively, as shown in FIG. The size and interval of the source electrode 23 and the drain electrode 24 may be different from the size and interval of the source electrode 13 and the drain electrode 14 of the reference electrode 10. However, the gate length α, the gate width β, the length γ of the source electrode 23 (drain electrode 24), and the width δ of the source electrode 23 (drain electrode 24) are preferably set to values in the above-described ranges. is there.

Further, the surface of the diamond thin film 22 functioning as the gate 26 has a linear or non-linear potential depending on the pH value in the hydrogen ion concentration range of 1.0 × 10 ^{−1 to} 1.0 × 10 ⁻¹⁴ mol / L. The termination element is controlled to respond. That is, the surface of the diamond thin film 22 functioning as the gate 26 is an ion-sensitive termination. Details of the surface treatment of the diamond thin film 12 will be described later.

  Next, the operation of the pH sensor 1 having the above configuration will be described. As shown in FIG. 1, in the reference electrode 10, a region sandwiched between the source electrode 13 and the drain electrode 14 functioning as the gate 16 (the surface of the diamond thin film 12) is in contact with the liquid W to be measured. On the other hand, since the source electrode 13 and the drain electrode 14 are covered with the protective film 15, the source electrode 13 and the drain electrode 14 do not come into contact with the measured liquid W. In addition, the working electrode 20 is in contact with the liquid W to be measured at a region sandwiched between the source electrode 23 and the drain electrode 24 that function as the gate 26 (the surface of the diamond thin film 22). On the other hand, since the source electrode 23 and the drain electrode 24 are covered with the protective film 25, they do not come into contact with the liquid W to be measured.

  The charge of the liquid W to be measured affects the interface potential between the gate 16 and the gate 26, and the result is taken out at the output terminals T1 and T2 (see FIG. 3).

  FIG. 3 is a circuit diagram showing an example of a pH measurement circuit using the pH sensor as the sensor element according to the first embodiment of the present invention. As shown in FIG. 3, the pseudo reference electrode 30 in contact with the liquid to be measured W (not shown in FIG. 3) is grounded.

  A constant current source C1 and a buffer circuit B11 are connected to the source electrode 13 of the reference electrode 10, and a buffer circuit B12 is connected to the drain electrode 14 of the reference electrode 10. The output terminal T1 is connected to the source electrode 13 of the reference electrode 10 through the buffer circuit B11, and is connected to the drain electrode 14 of the reference electrode 10 through the resistor R1 and the buffer circuit B12. A constant current source C2 and a buffer circuit B21 are connected to the source electrode 23 of the working electrode 20, and a buffer circuit B22 is connected to the drain electrode 24 of the working electrode 20. The output terminal T2 is connected to the source electrode 23 of the working electrode 20 through the buffer circuit B21, and is connected to the drain electrode 24 of the working electrode 20 through the resistor R2 and the buffer circuit B22.

  In the pH measurement circuit of the source follower shown in FIG. 3, the electric charge of the liquid W to be measured affects the interface potential between the gate 16 and the gate 26, thereby causing the gate 16 of the reference electrode 10 and the gate 26 of the working electrode 20 to respectively. Potential is generated. In the pH measurement circuit shown in FIG. 3, a voltage based on the source electrode 13 and the gate 16 of the reference electrode 10 is generated at the output terminal T1. In contrast, a voltage based on the source electrode 23 and the gate 26 of the working electrode 20 is generated at the output terminal T2. The difference between the voltage value at the output terminal T1 and the voltage value at the output terminal T2 has a correlation with the pH of the liquid W to be measured.

  FIG. 4 is a diagram showing an example of the characteristics of the p-channel field effect transistor formed in the pH sensor as the sensor element according to the first embodiment of the present invention. The characteristics shown in FIG. 4 are obtained by evaluating the characteristics of a p-channel field effect transistor formed on the working electrode 20 of the pH sensor 1 with the source grounded, for example. Although the p-channel field effect transistor formed on the reference electrode 10 of the pH sensor 1 is different from the p-channel field effect transistor formed on the working electrode 20 in terms of current and voltage, it is generally shown in FIG. , (B) shows the same characteristics.

  FIG. 4A shows the voltage (Vgs) of the reference electrode and the drain electrode / source when the voltage (Vds) between the drain electrode and the source electrode is set to a constant voltage (−0.5 [V]). It is a figure which shows the relationship with the electric current (Ids) which flows into an electrode. Referring to FIG. 4A, when the voltage (Vgs) of the reference electrode becomes about −0.4 to −0.5 [V], the current (Ids) flowing through the drain electrode and the source electrode increases rapidly. I understand that.

  FIG. 4B shows the voltage (Vds) between the drain electrode and the source electrode when the voltage (Vgs) of the reference electrode is changed in a certain range (range of 0 to −1.4 [V]). It is a figure which shows the relationship with the electric current (Ids) which flows into a drain electrode and a source electrode. Referring to FIG. 4 (b), as the reference electrode voltage (Vgs) increases, the characteristic curve in FIG. 4 (b) rises upward as a whole, and the current (Ids) flowing through the drain electrode / source electrode is increased. You can see that it tends to grow.

  Here, when the pH value of the liquid to be measured W increases, the characteristic curve in FIG. 4B moves upward, and when the pH value of the liquid to be measured W decreases, the characteristic curve in FIG. It becomes the characteristic to move to. In addition, when the current (Ids) flowing through the drain electrode / source electrode is constant, the reference electrode voltage (Vgs) decreases as the pH value of the liquid W to be measured increases. Using this characteristic, the pH value of the liquid W to be measured can be calculated from the value of the reference electrode voltage (Vgs).

<Manufacturing method of field effect transistor and processing method of diamond thin film>
Next, a method for manufacturing the above-described pH sensor 1 will be described. In the following, the manufacturing method of the p-channel field effect transistor formed on the reference electrode 10 and the working electrode 20 and the processing method of the diamond thin film used in this manufacturing method will be mainly described in a series of manufacturing steps of the pH sensor 1. Explained.

  FIG. 5 is a flowchart illustrating a method of manufacturing a field effect transistor according to the first embodiment of the present invention. When the manufacture of the p-channel field effect transistor is started, as shown in FIG. 5A, first, a process of polishing the surfaces of the silicon wafers 11 and 21 is performed (step S11). Specifically, when the silicon wafers 11 and 21 are polished, in order to improve the adhesion between the silicon wafers 11 and 21 and the diamond thin films 12 and 22 formed in a later step, the arithmetic average roughness Ra: It is desirable that the thickness is 0.1 to 15 μm and the maximum height Rz is 1 to 100 μm.

  When the polishing process is completed, a nucleation process for nucleating diamond powder onto the polished silicon wafers 11 and 21 is performed (step S12). This step is performed to grow uniform diamond thin films 12 and 22 on the surfaces of the silicon wafers 11 and 21. Here, as a method for nucleating diamond powder, a solution containing diamond fine particles is applied to the surfaces of the silicon wafers 11 and 21 by an ultrasonic method, a dipping method, or other methods, and the solvent is dried. Can be used.

  When the nucleation of the diamond powder is completed, the diamond thin films 12 and 22 are formed on the surfaces of the silicon wafers 11 and 21 by, for example, a hot filament CVD method (step S13: first step). Specifically, a carbon source (for example, a low molecular organic compound such as methane, alcohol, or acetone) is supplied to the filament together with hydrogen gas or the like. If necessary, a dopant (for example, boron) is also supplied to the filament together with a carbon source and hydrogen gas. Then, the filament is heated to a temperature range where carbon radicals and the like are generated (for example, 1800 to 2800 ° C.), and the silicon wafer 11 is brought to a temperature range (for example, 750 to 950 ° C.) where diamond is deposited in the atmosphere. , 21 are arranged.

  Here, although the supply speed of the mixed gas containing the carbon source, the dopant, and the hydrogen gas depends on the size of the reaction vessel, the pressure is preferably about 2 to 100 [kPa]. On the silicon wafers 11 and 21, a diamond fine particle layer having a particle diameter of generally 0.001 to 2 μm is deposited. The thickness of the diamond fine particle layer can be adjusted by the deposition time, but is preferably 0.5 to 20 μm from the viewpoint of economy. The steps S11 and S12 can be omitted if not necessary. Further, the step S14 described below may also serve as the step S13.

  When the diamond film forming process is completed, a hydrogen termination process is performed on the diamond thin films 12 and 22 (as grown diamonds) formed on the silicon wafers 11 and 21 (step S14: second step). Specifically, a high density hydrogen termination is performed by substituting a terminal other than hydrogen (for example, a carbon terminal or an oxygen terminal) other than hydrogen on the surface of the formed diamond thin films 12 and 22 with a hydrogen terminal. As the hydrogen termination treatment, any of a treatment with an aqueous hydrofluoric acid solution, a hydrogen plasma treatment, a heat treatment in a hydrogen atmosphere, a hydrogen radical treatment, and a cathode reduction method can be selected. Two or more methods may be combined to increase the efficiency of hydrogen termination treatment.

Here, as the hydrogen plasma treatment, for example, the termination hydrogen density on the surfaces of the diamond thin films 12 and 22 is increased under the treatment conditions of 1 [kW], H ₂ -flow 400 [sccm], and plasma irradiation time of 5 hours. it can. As the cathode reduction method, for example, a voltage of about −1.8 [V] is applied to an as-grown conductive diamond electrode and immersed in a 0.1 M sulfuric acid aqueous solution (H ₂ SO ₄ ) for 30 minutes or more. You can use the method you want.

When the hydrogen termination process is completed, a fluorine gas process is performed in consideration of the presence or absence of a fluorocarbon deposition film (step S15: second step). Specifically, one of the following first and second replacement processes is selected and performed according to the required surface characteristics of the diamond thin films 12 and 22.
First substitution process: A process of substituting part of the hydrogen ends of the diamond thin films 12, 22 with fluorine terminations without depositing a fluorocarbon deposition film on the surface of the diamond thin films 12, 22 Second substitution process: Diamond thin films 12, 22 Of substituting fluorine termination for part of the hydrogen termination of diamond thin films 12, 22 while depositing a fluorocarbon deposition film on the surface of the substrate

The first replacement process is realized by performing an exposure process using fluorine gas or fluorine-based gas on the entire surface or a part of the diamond thin films 12 and 22 (areas functioning as the gates 16 and 26). Process. For example, fluorine gas (F ₂ gas) diluted with nitrogen gas (N ₂ gas) is used as the processing gas, the processing temperature is set to 20 ° C., and the processing time is about 10 hours. Alternatively, the first substitution process may be a reactive ion etching (RIE) process using a fluorine-based gas or an inductively coupled plasma-RIE (ICP-RIE) process for the region. This is a process realized by performing the process.

On the other hand, the second substitution process described above is a reactive ion etching (RIE) process using a fluorine-based gas for the entire surface or a part of the diamond thin films 12 and 22 (a region functioning as the gates 16 and 26). This is a process realized by performing an inductively coupled reactive ion etching (ICP-RIE) process. For example, when ICP-RIE processing is performed, octafluoropropane gas (C ₃ F ₈ gas) is used as the processing gas, the ICP power output is 500 [W], and the bias output is 0 to 20 [W ], The gas pressure is set to 3 [Pa], the flow rate of the C ₃ F ₈ gas is set to 20 [sccm], and the processing time is set to 5 [sec].

Here, the above-mentioned fluorine-based gas is a general term for gases containing F in the molecular formula. Examples of the fluorine-based gas include C _x F _y gas (for example, CF ₄ , C ₂ F ₆ , C ₃ F ₈ , C ₄ F _8, etc.), C _x H _y F _z gas (for example, CHF ₃ , CH ₂ F ₂ , CH ₃ F, etc.), S _x F _y gas (eg, SF ₆ etc.), N _x F _y gas (eg, NF ₃ etc.), C _x O _y F _z (eg, COF ₂ etc.) , N _x O _y F _z (eg, F ₃ NO), and S _x O _y F _z (eg, SOF ₂ ). Moreover, the mixed gas containing the said fluorine-type gas is also contained in fluorine-type gas.

The fluorine-based gas used for the exposure treatment in the first replacement treatment can be selected from the above-mentioned fluorine-based gases according to the expected effect, and for example, XeF ₂ , COF ₂ or the like can be used. The fluorine-based gas used for the ICP-RIE process in the first and second replacement processes can be selected from the above-described fluorine-based gases according to the expected effect. For example, CF ₄ , C ₃ F ₈ , C ₄ F ₈ , CHF ₃ , SF _{6 and the} like can be used.

  When the fluorine gas treatment considering the presence or absence of a fluorocarbon deposited film is completed, a step of manufacturing a p-channel field effect transistor is performed (step S16: third step). This process is roughly divided into an electrode forming process and a protective film forming process.

  In the electrode forming process, first, a resist is spin-coated on the surfaces of the diamond thin films 12 and 22, and exposure and development are performed to pattern the resist. Thereafter, Au / Ti sputtering is performed and lift-off is performed, whereby an Au / Ti thin film having a plan view shape shown in FIG. 2 is formed on the diamond thin films 12 and 22. As a result, the source electrode 13 and the drain electrode 14 are formed on the diamond thin film 12, and the source electrode 23 and the drain electrode 24 are formed on the diamond thin film 22.

  In the protective film forming step, there is a process of spin-coating a resist to be the protective films 15 and 25 on the silicon wafers 11 and 21 on which the diamond thin films 12 and 22 and the Au / Ti thin film are formed, and patterning the resist by exposure and development. Done. In the region where the resist is removed, the diamond thin films 12 and 22 are exposed. The region where the diamond thin film 12 is exposed functions as the gate 16, and the region where the diamond thin film 22 is exposed functions as the gate 26.

  By the above processing, the reference electrode 10 and the working electrode 20 in which the p-channel field effect transistor is formed are obtained. The pH sensor 1 shown in FIG. 1 has the reference electrode 10 and the working electrode 20 facing each other so that the source electrodes 13 and 23 overlap in a plan view and the drain electrodes 14 and 24 overlap in a plan view. 20 are arranged apart from each other by a predetermined interval.

  With respect to the qualitative quantification of the diamond surface termination (fluorine termination, oxygen termination, hydrogen termination, etc.) produced through the above steps, for example, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectrophotometer (FT-IR) Etc.) can be inspected by a conventionally known analysis method. In the flow chart shown in FIG. 5A, the step of manufacturing a p-channel field effect transistor (step S16) is performed after the fluorine gas treatment (step S15) in consideration of the presence or absence of a fluorocarbon deposited film. However, as shown in the flowchart of FIG. 5B, the steps S16 and S15 can be reversed.

  FIG. 6 is a diagram showing an analysis result of the diamond thin film processed by the diamond thin film processing method according to the first embodiment of the present invention. Moreover, FIG. 7 is a figure which shows typically the surface state of the diamond thin film processed by the processing method. Here, FIG. 6A and FIG. 7A are diagrams respectively showing the analysis result and the surface state of the diamond thin film subjected to the first substitution process described above, and FIG. 6B and FIG. (b) is a figure which each shows the analysis result and surface state of a diamond thin film in which the 2nd substitution process mentioned above was performed. The analysis result shown in FIG. 6 is an analysis result using the above-mentioned X-ray photoelectron spectroscopy (XPS).

  First, referring to FIG. 6A, it can be confirmed that a large peak indicating a carbon-carbon bond (C—C) and a small peak indicating a carbon-fluorine bond (C—F) appear. No peaks other than these peaks appear. For this reason, as shown in FIG. 7A, the surface state of the diamond thin film that has been subjected to the first substitution treatment described above is partially hydrogen-terminated, but most of it is hydrogen-terminated. The deposited film is not deposited (or hardly deposited).

Next, referring to FIG. 6B, in addition to a large peak indicating a carbon-carbon bond (C—C) and a small peak indicating a carbon-fluorine bond (C—F), a carbon-fluorinated carbon bond ( It can be seen that three new peaks appear indicating C—CF) and carbon-fluorine bonds (C—F ₂ , C—F ₃ ). For this reason, the surface state of the diamond thin film that has been subjected to the second substitution process described above is a state in which a part of the diamond thin film is fluorine-terminated and a fluorocarbon deposition film D is deposited as shown in FIG. It is.

  As described above, in this embodiment, when the first substitution process described above is performed on the diamond thin film, a part of the hydrogen terminal of the diamond thin film is made fluorine-terminated without depositing a fluorocarbon deposited film on the surface of the diamond thin film. Can be replaced. On the other hand, if the second substitution process described above is performed on the diamond thin film, a part of the hydrogen terminal of the diamond thin film can be replaced with a fluorine terminal while depositing a fluorocarbon deposition film on the surface of the diamond thin film. For this reason, in this embodiment, it is possible to make the surface of diamond have desired characteristics.

  Here, when the surface of the diamond thin film becomes an ion-sensitive termination by performing the first substitution process described above, the p-channel field effect transistor is formed on the working electrode 20 (specifically, the diamond thin film 22). The first replacement process described above may be performed when the surface is processed. Further, when the surface of the diamond thin film becomes an ion-insensitive terminal by performing the second substitution process described above, when the p-channel field effect transistor is formed on the reference electrode 10 (specifically, the diamond thin film 12 When the surface is processed), the above-described second replacement process may be performed.

  Contrary to the above example, the surface of the diamond thin film becomes an ion-insensitive termination by performing the above-described first substitution treatment, and the surface of the diamond thin film becomes an ion-acute sensitive termination by performing the above-described second substitution treatment. It may be possible. In such a case, the first replacement process described above is performed when the p-channel field effect transistor is formed on the reference electrode 10, and the second replacement process described above is performed when the p-channel field effect transistor is formed on the working electrode 20. Just do it.

  Thus, in the present embodiment, a field effect transistor in which a fluorocarbon deposition film is not deposited on the surface of the diamond thin film 12 or 22, or a field effect transistor in which a fluorocarbon deposition film is deposited on the surface of the diamond thin film 12 or 22. Any of these can be manufactured. Thereby, a field effect transistor having intended ion sensitivity can be easily manufactured.

  Further, the pH sensor 1 in the present embodiment is formed on the working electrode 20 while the surface of the diamond thin film 12 functioning as the gate 16 of the p-channel field effect transistor formed on the reference electrode 10 is in contact with the liquid W to be measured. The surface of the diamond thin film 22 that functions as the gate 26 of the p-channel field effect transistor is in contact with the liquid W to be measured. For this reason, the pH sensor 1 is excellent in high temperature / high pressure and acid / alkali resistance. Accordingly, it is possible to accurately measure the pH value even under strong acid / strong alkali conditions in a semiconductor manufacturing process and even in a bioprocess that handles biologically related substances such as proteins.

[Second Embodiment]
FIG. 8 is a cross-sectional view showing a configuration of a pH sensor as a sensor element according to the second embodiment of the present invention. In FIG. 8, members corresponding to those shown in FIG. In the pH sensor 1 according to the first embodiment described above, the reference electrode 10 and the working electrode 20 are formed using different silicon wafers 11 and 12, respectively, and the measurement target guided between the reference electrode 10 and the working electrode 20. The pH of the liquid W was measured. On the other hand, in the pH sensor 2 of the present embodiment, the reference electrode 10 and the working electrode 20 are formed using a common silicon wafer 40 (substrate), and the silicon wafer 40 (on the reference electrode 10 and the working electrode 20). ) To measure the pH of the liquid W to be measured. As the pseudo reference electrode 30 (not shown), a conductive material (metal or the like) is used.

  As shown in FIG. 8, the reference electrode 10 includes a diamond thin film 12, a source electrode 13, a drain electrode 14, and a protective film 15. The diamond thin film 12 is formed on the surface of the silicon wafer 40, and the source electrode 13 and the drain electrode 14 are formed on the surface of the diamond thin film 12 so as to be arranged in parallel to the same substrate. The protective film 15 is formed on the diamond thin film 12 so as to cover the source electrode 13 and the drain electrode 14. In the reference electrode 10, a region sandwiched between the source electrode 13 and the drain electrode 14 (the surface of the diamond thin film 12) functions as the gate 16.

In addition, the surface of the diamond thin film 12 functioning as the gate 16 has a stable potential in a hydrogen ion concentration range of 1.0 × 10 ^{−1 to} 1.0 × 10 ⁻¹⁴ mol / L, or ion sensitivity is practical. The termination element is controlled so that the potential is kept constant to the extent that does not cause a problem. That is, as in the first embodiment described above, the surface of the diamond thin film 12 functioning as the gate 16 is an ion-insensitive termination.

  The working electrode 20 includes a diamond thin film 22, a source electrode 23, a drain electrode 24, and a protective film 25. The diamond thin film 22 is formed on a portion of the surface of the silicon wafer 40 that is different from the portion where the reference electrode 10 is formed, and the source electrode 23 and the drain electrode 24 face each other on the surface of the diamond thin film 22. It is formed as follows. The protective film 25 is formed on the diamond thin film 22 so as to cover the source electrode 23 and the drain electrode 24. In this working electrode 20, a region sandwiched between the source electrode 23 and the drain electrode 24 (the surface of the diamond thin film 22) functions as the gate 26. It is desirable that the source electrode 23 and the drain electrode 24 have the same shape as the source electrode 13 and the drain electrode 14 of the reference electrode 10, respectively.

Further, the surface of the diamond thin film 22 functioning as the gate 26 has a linear or non-linear potential depending on the pH value in the hydrogen ion concentration range of 1.0 × 10 ^{−1 to} 1.0 × 10 ⁻¹⁴ mol / L. The termination element is controlled to respond. That is, the surface of the diamond thin film 22 functioning as the gate 26 is an ion-sensitive termination.

  Here, the termination control of the surface of the diamond thin film 12 functioning as the gate 16 and the surface of the diamond thin film 22 functioning as the gate 26 can be performed by the same method as in the first embodiment. That is, the termination of the surfaces of the diamond thin films 12 and 22 can be controlled by performing a fluorine gas treatment in consideration of the presence or absence of a fluorocarbon deposited film (see step S15 in FIG. 5).

  When the pH of the liquid W to be measured is measured by the pH sensor 2 shown in FIG. 8, the liquid W to be measured is guided onto the silicon wafer 40 (on the reference electrode 10 and the working electrode 20). Thereby, in the reference electrode 10, a region (a surface of the diamond thin film 12) between the source electrode 13 and the drain electrode 14 functioning as the gate 16 is in contact with the measured liquid W. On the other hand, since the source electrode 13 and the drain electrode 14 are covered with the protective film 15, the source electrode 13 and the drain electrode 14 do not come into contact with the measured liquid W.

  In addition, the working electrode 20 is in contact with the liquid W to be measured at a region sandwiched between the source electrode 23 and the drain electrode 24 that function as the gate 26 (the surface of the diamond thin film 22). On the other hand, since the source electrode 23 and the drain electrode 24 are covered with the protective film 25, they do not come into contact with the liquid W to be measured.

  In this way, when the pH sensor 2 measures the pH of the liquid to be measured W, the region functioning as the gate 16 of the reference electrode 10 (the surface of the diamond thin film 12) is the liquid to be measured, like the pH sensor 1. A region that functions as the gate 26 of the working electrode 20 (the surface of the diamond thin film 22) is in contact with the liquid W to be measured. For this reason, the pH of the liquid W to be measured is measured by the same principle as the pH sensor 1 of the first embodiment.

  The diamond thin film surface treatment method, the field effect transistor manufacturing method, and the sensor element according to the embodiment of the present invention have been described above. However, the present invention is not limited to the above embodiment, and is freely within the scope of the present invention. Can be changed. For example, in the above embodiment, an example in which the surfaces of the diamond thin films 12 and 22 formed on the silicon wafers 11, 21 and 40 are processed has been described. However, the diamond thin film to be processed does not necessarily have to be formed on a substrate (silicon substrate or carbon substrate), and may be a substrate from which the substrate has been removed (diamond bulk body). The diamond thin film may have a polycrystalline structure or a single crystal structure.

  FIG. 9 is a diagram showing an example of a diamond substrate that can be used in the embodiment of the present invention. In FIG. 9, the silicon wafers 11 and 21 in FIG. 1 or the silicon wafer 40 in FIG. 8 are shown as the substrate SB. The diamond substrate shown in FIG. 9A is a substrate in which an undoped diamond thin film (non-doped diamond thin film L1) is formed on the substrate SB, and the diamond substrate shown in FIG. 9B is a substrate SB. This is a substrate on which an impurity-added diamond substrate (doped diamond thin film L2) is formed.

  The diamond substrate shown in FIG. 9 (c) is a substrate made of only the non-doped diamond thin film L1 that does not have the substrate SB, and the diamond substrate shown in FIG. 9 (d) does not have the substrate SB and is non-doped. This is a substrate in which a doped diamond thin film L2 is formed on a diamond thin film L1. Note that the diamond substrate shown in FIGS. 9C and 9D does not have the substrate SB, and can be called a diamond self-solid.

  The diamond substrate shown in FIG. 9 (e) is a substrate in which a doped diamond thin film L2 is formed on the diamond substrate shown in FIG. 9 (a). When this substrate is used as a sensor element such as the pH sensor 1, a synergistic effect between the semiconductor characteristics of the doped diamond thin film L2 and the insulator characteristics of the non-doped diamond thin film L1 can be expected.

The diamond substrate shown in FIGS. 9 (f), 9 (g), and 9 (h) has silicon on the substrate SB of the diamond substrate shown in FIGS. 9 (a), 9 (b), and 9 (e). An oxide film (SiO ₂ ) L0 is formed, and at least one of a non-doped diamond thin film L1 and a doped diamond thin film L2 is formed on the silicon oxide film L0. When this substrate is used for a sensor element such as the pH sensor 1, an insulating effect by a silicon oxide film can be expected.

  In the above embodiment, an example in which the pseudo reference electrode based on the reference electrode 10 and the pseudo reference electrode based on the working electrode 20 are common has been described. However, these may be provided individually. Moreover, although the example which uses a silicon wafer as a board | substrate was shown in the said embodiment, the material of a board | substrate is arbitrary. In the above embodiment, an example in which the hydrogen termination process is performed before the first and second substitution processes described above has been described. However, even if the hydrogen termination process is omitted, the necessary surface characteristics of the diamond thin film can be obtained. In this case, the hydrogen termination process may be omitted.

  Moreover, the method of forming a diamond thin film on a board | substrate is not limited to said method, Arbitrary things can be used. As a typical formation method, a vapor phase synthesis method can be used, and examples of the vapor phase synthesis method include a CVD (chemical vapor deposition) method, a physical vapor deposition (PVD) method, and a plasma jet method. Examples of the CVD method include a hot filament CVD method and a microwave plasma CVD method.

In addition, regardless of which diamond film forming method is used, the synthesized diamond thin film is polycrystalline, and amorphous carbon and graphite components may remain in the diamond thin film. Amorphous carbon or graphite component from the viewpoint of the stability of the diamond film is preferably lesser, in Raman spectroscopic analysis, and around 1332 cm ^-1 attributable to the diamond peak present in (1321～1352Cm range of ^-1) intensity I (D) , the ratio I (D) / I of the peak intensity near 1580 cm ^-1 attributable to the G band of graphite (range ^{1560~1600cm -1) I (G) (} G) is not less than 1, the content of diamond It is preferable that the content be higher than the graphite content.

  Moreover, although the pH sensor was mentioned as an example and demonstrated in the said embodiment as a sensor element, this invention is applicable also to sensor elements (for example, biosensor) other than a pH sensor. Some biosensors include only one detection electrode corresponding to the reference electrode 10 or the working electrode 20 described above, but the present invention is also applicable to such a biosensor. .

  In the above-described embodiment, the example in which the field effect transistors having different ion sensitivities are manufactured by performing the above-described first and second substitution processes in step S15 illustrated in FIG. 5 has been described. It is also possible to manufacture field effect transistors having different values. That is, the present invention can manufacture a field effect transistor suitable for the application.

  The inventors of the present application actually processed the surface of the diamond thin film using the diamond thin film surface treatment method described above, or actually manufactured the field effect transistor using the field effect transistor manufacturing method described above. . And the characteristic of the processed diamond thin film was measured, or the characteristic of the manufactured field effect transistor was measured. Hereinafter, first to third examples in which a field effect transistor was manufactured by performing the first substitution process described above on the surface of the diamond thin film, and a second example in which the second substitution process described above was performed on the surface of the diamond thin film. The four examples will be described in order.

[First embodiment]
In this embodiment, the ICP-RIE process is performed using SF ₆ gas, so that a part of the hydrogen terminal of the diamond thin film is replaced with a fluorine terminal without depositing a fluorocarbon film, and a field effect is obtained. Manufactures transistors. FIG. 10 is a flowchart showing a method of manufacturing the field effect transistor in the first embodiment.

As shown in FIG. 10, in this example, the surface of the silicon wafer was first polished, and the surface of the polished silicon wafer was nucleated with diamond powder (step S21). Next, a non-doped diamond thin film is formed on the surface of the silicon wafer subjected to the nucleation process by a hot filament CVD method (step S22), and boron (boron) is formed on the non-doped diamond thin film by a microwave plasma CVD method. A doped diamond thin film was formed (step S23). Here, as the film formation conditions, for example, the methane (CH ₄ ) concentration was set to 0.01 to 1%, the B / C ratio was set to 1000 to 15000 ppm, and the film formation time was set to 1 to 10 minutes. .

Subsequently, hydrogen termination was performed by microwave plasma CVD (step S24), and then a field effect transistor was manufactured (step S25). Finally, the surface of the diamond thin film functioning as a gate was subjected to ICP-RIE treatment using SF ₆ gas (step S26). Through the above steps, a field effect transistor having a fluorine terminated gate was obtained. Here, as the ICP-RIE processing conditions, for example, the ICP power output is set to 10 to 1000 [W], the degree of vacuum is set to about 1.33 to 13.3 [Pa], and the processing time is set to 2-3. Set to minutes.

  FIG. 11 is a diagram showing an example of the characteristics of the field effect transistor obtained in the first embodiment. In FIG. 11, the analysis results of pH sensitivity and X-ray photoelectron spectroscopy (XPS) are given as the characteristics of the field effect transistor. As shown in FIG. 11, the pH sensitivity of the field effect transistor obtained in this example was about 8 to 11 [mV / pH]. Moreover, the analysis result (F1s / (C1s + F1s)) of XPS was about 30 to 60 [%]. In FIG. 11, only the XPS analysis result of 30 [%] is shown. Thus, in the field effect transistor obtained in this example, it was confirmed that the surface of the diamond thin film functioning as a gate was fluorine-terminated at a predetermined ratio.

[Second Embodiment]
In this example, by performing an exposure process using xenon fluoride (XeF ₂ ), a part of the hydrogen terminal of the diamond self-solid (see FIG. 9D) is made fluorine without depositing a fluorocarbon deposition film. A field effect transistor is manufactured while performing a process of replacing the terminal. FIG. 12 is a flowchart showing a method for manufacturing a field effect transistor in the second embodiment.

As shown in FIG. 12, in this example, first, the surface of the polycrystalline diamond substrate was cleaned (acid cleaning, organic solvent cleaning) (step S31). Next, a boron-doped diamond thin film was formed on the surface of the cleaned polycrystalline diamond substrate by microwave plasma CVD (step S32). Here, as the film formation conditions, for example, the methane (CH ₄ ) concentration was set to 0.01 to 1%, the B / C ratio was set to 1000 to 15000 ppm, and the film formation time was set to 1 to 10 minutes. .

Subsequently, a hydrogen termination process is performed by a microwave plasma CVD method (step S33), followed by an exposure process by sublimating solid XeF _2, and hydrogen at a specific portion (portion serving as a gate) of the boron-doped diamond thin film. A part of the terminal was replaced with a fluorine terminal (step S34). Here, as the processing conditions of the exposure processing using XeF ₂ described above, for example, the degree of vacuum was set to about 133 [Pa], and the processing time was set to 5 minutes. Finally, a field effect transistor was manufactured so that the above-mentioned specific location became a gate (step S35). Through the above steps, a field effect transistor having a fluorine terminated gate was obtained.

  FIG. 13 is a diagram illustrating an example of current-voltage characteristics of the field effect transistor obtained in the second embodiment. The characteristic shown in FIG. 13 is that the current of a field effect transistor in which the source electrode and the drain electrode are made of gold (Au), the gate length is 500 [μm], and the gate width is 10 [mm]. Voltage characteristics (the relationship between the voltage between the drain electrode and the source electrode (Vds) and the current flowing through the drain electrode and the source electrode (Ids) when the voltage between the gate electrode and the source electrode (Vgs) is changed) is there.

  Referring to FIG. 13, as in FIG. 4B, as the voltage (Vgs) increases, the characteristic curve in FIG. 13 generally rises upward, and the current (Ids) flowing through the drain electrode / source electrode is increased. You can see that it tends to grow. Thereby, it was confirmed that it was operating as a field effect transistor. Although not shown, the pH sensitivity of the field effect transistor obtained in this example is about 5 to 12 [mV / pH], and the XPS analysis result (F1s / (C1s + F1s)) is It was about 5%.

[Third embodiment]
In this example, by performing an ICP-RIE process using C ₃ F ₈ gas, a part of the hydrogen termination of the diamond self-solid (see FIG. 9D) is made fluorine without depositing a fluorocarbon deposition film. A field effect transistor is manufactured while performing a process of replacing the terminal. FIG. 14 is a flowchart showing a method for manufacturing a field effect transistor according to the third embodiment.

  As shown in FIG. 14, in this example, as in the second embodiment, the surface of the polycrystalline diamond substrate is cleaned (acid cleaning, organic solvent cleaning) (step S31), and the surface of the cleaned polycrystalline diamond substrate is processed. On top of this, a treatment for forming a boron-doped diamond thin film by a microwave plasma CVD method (step S32) and a hydrogen termination treatment by a microwave plasma CVD method (step S33) were sequentially performed. The film forming conditions in the above step S32 were set in the same manner as in the second example.

Thereafter, ICP-RIE treatment using C ₃ F ₈ gas was performed, and a part of hydrogen termination at a specific location (location to be a gate) of the boron-doped diamond thin film was replaced with a fluorine termination (step S40). Here, as processing conditions of the ICP-RIE process, the ICP power output was set to 100 [W], and the processing time was set to 30 seconds. Finally, a field effect transistor was manufactured so that the above-mentioned specific location became a gate (step S35). Through the above steps, a field effect transistor having a fluorine terminated gate was obtained.

  FIG. 15 is a diagram illustrating an example of the current-voltage characteristics of the field effect transistor obtained in the third embodiment. The characteristics shown in FIG. 15 are the same as in FIG. 13, in which the source electrode and the drain electrode are made of gold (Au), the gate length is 500 [μm], and the gate width is 10 [mm]. The current-voltage characteristics of the field effect transistor. Referring to FIG. 15, although the change width (lifting width) of the characteristic curve when the voltage (Vgs) changes is smaller than that in FIG. 13, the current-voltage characteristics are the same as those in FIG. It was confirmed that it was operating as a transistor.

  FIG. 16 is a diagram showing an example of the pH sensitivity of the field effect transistor obtained in the third example. In FIG. 16, the horizontal axis represents the pH value, and the vertical axis represents the voltage (Vgs) between the gate electrode and the source electrode. Referring to FIG. 16, the voltage (Vgs) tends to decrease slightly as the pH increases. Thus, the pH sensitivity of the field effect transistor obtained in this example was about -1 [mV / pH].

Although not shown, the XPS analysis result (F1s / (C1s + F1s)) of the field effect transistor obtained in this example was about 30%. When only the processing time of the ICP-RIE processing is changed from 30 seconds to 1 minute (the other processing conditions are not changed), the XPS analysis result (F1s / (C1s + F1s)) is about 20%. Met. Further, in the present example, in the XPS analysis result, a peak indicating a carbon-fluorine bond (C—F ₃ ) does not appear in the vicinity of the C1s peak (region having a binding energy of 280 to 295 [eV]). It was confirmed that there was no deposited film.

[Fourth embodiment]
In this embodiment, the ICP-RIE process is performed using C ₃ F ₈ gas to perform a process of substituting a part of the hydrogen terminal of the diamond thin film with a fluorine terminal while depositing a fluorocarbon deposition film. FIG. 17 is a flowchart showing a diamond thin film surface treatment method according to the fourth embodiment. As can be seen from a comparison between FIG. 17 and FIG. 14, in this embodiment, the surface of the diamond thin film is treated by the same process as in the third embodiment.

  As shown in FIG. 17, in this example, as in the third embodiment, the surface of the polycrystalline diamond substrate is cleaned (acid cleaning, organic solvent cleaning) (step S31). On top of this, a treatment for forming a boron-doped diamond thin film by a microwave plasma CVD method (step S32) and a hydrogen termination treatment by a microwave plasma CVD method (step S33) were sequentially performed. The film forming conditions in the above step S32 were set in the same manner as in the third example.

Thereafter, ICP-RIE treatment using C ₃ F ₈ gas was performed, and a part of hydrogen termination at a specific location (location to be a gate) of the boron-doped diamond thin film was replaced with a fluorine termination (step S40). Here, as processing conditions for the ICP-RIE process, the ICP power output was set to about 300 to 500 [W], and the processing time was set to 30 seconds.

Although not shown, the XPS analysis result (F1s / (C1s + F1s)) of the field effect transistor obtained in this example is about 58 [%] when the ICP power output is 300 [W]. When the ICP power output is 500 [W], it was about 62 [%]. Here, in the present example, in the XPS analysis result, a peak indicating a carbon-fluorine bond (C—F ₃ ) appears in the vicinity of the C1s peak (a region where the binding energy is 280 to 295 [eV]). It was confirmed that a deposited film of fluorocarbon was deposited.

As described above, when the ICP-RIE process is performed using the C ₃ F ₈ gas, the diamond thin film on which the fluorocarbon deposition film is deposited and the fluorocarbon deposition film are merely changed by changing the processing conditions of the ICP-RIE process. It is possible to obtain both a diamond thin film on which no is deposited. Note that if step S35 shown in FIG. 14 is performed after step S40 shown in FIG. 17, a field effect transistor having a fluorine-terminated gate can be obtained as in the third embodiment.

  In the third and fourth embodiments described above, a process for forming a boron-doped diamond thin film (process S32), a hydrogen termination process (process S33), and a process for replacing part of the hydrogen termination with a fluorine termination (process) S40) and the field effect transistor manufacturing process (step S35) were performed in order. However, the field effect transistor manufacturing process (process S35) may be performed between the process of forming a boron-doped diamond thin film (process S32) and the hydrogen termination process (process S33). You may implement between S33) and the process (process S40) which substitutes a part of hydrogen termination | terminus by the fluorine termination | terminus.

1, 2 pH sensor 10 Reference electrode 11 Silicon wafer 12 Diamond thin film 13 Source electrode 14 Drain electrode 15 Protective film 16 Gate 20 Working electrode 21 Silicon wafer 22 Diamond thin film 23 Source electrode 24 Drain electrode 25 Protective film 26 Gate 30 Pseudo reference electrode 40 Silicon wafer W Liquid to be measured

Claims (15)

Forming a diamond film,
The diamond thin film is not deposited on the surface of the diamond thin film by subjecting at least a part of the surface of the diamond thin film to an exposure treatment using a fluorine gas or a fluorine-based gas containing no carbon. Performing a process of substituting a part of the hydrogen terminal of the thin film with a fluorine terminal;
Forming a gate on a portion of the surface of the diamond film ;
A method for manufacturing a transistor , comprising: forming a source electrode and a drain electrode on the diamond thin film between the formation of the diamond thin film and the substitution treatment . 2. The method for manufacturing a transistor according to claim 1 , wherein the formation of the source electrode and the drain electrode includes forming a protective film for protecting the source electrode and the drain electrode so as to cover the source electrode and the drain electrode.   2. The method of manufacturing a transistor according to claim 1, further comprising: performing a process of substituting a terminal other than hydrogen on the surface of the diamond thin film with a hydrogen terminal before performing the replacement process. The transistor manufacturing method according to claim 1, wherein the fluorine-based gas used in the exposure treatment is a gas containing XeF ₂ . Forming a diamond film,
At least a part of the surface of the diamond thin film is subjected to inductively coupled reactive ion etching using a fluorine-based gas not containing carbon, so that no fluorocarbon deposition film is deposited on the surface of the diamond thin film. A process of substituting a part of the hydrogen terminal of the diamond thin film with a fluorine terminal;
Forming a gate on a portion of the surface of the diamond film ;
A method for manufacturing a transistor , comprising: forming a source electrode and a drain electrode on the diamond thin film between the formation of the diamond thin film and the substitution treatment . The method for manufacturing a transistor according to claim 5 , wherein a treatment for replacing a terminal other than hydrogen on the surface of the diamond thin film with a hydrogen terminal is performed before the replacement processing. The fluorine-based gas used in the inductively coupled reactive ion etching process is S _x F _y , N _x F _y , N _x O _y F _z , and S _x O _y F _z (x, y, z is 1 or more). The method for manufacturing a transistor according to claim 5 , wherein the gas contains at least one of an integer of (1). Forming a diamond film,
Doping the surface of the diamond thin film with boron;
A fluorocarbon deposition film is formed on the surface of the diamond thin film by subjecting at least a part of the surface of the diamond thin film doped with boron to inductively coupled reactive ion etching using a fluorine-based gas containing carbon. A process of substituting a part of the hydrogen terminal of the diamond thin film with a fluorine terminal without depositing,
Forming a gate on a portion of the surface of the diamond film ;
A method for manufacturing a transistor , comprising: forming a source electrode and a drain electrode on the diamond thin film between the formation of the diamond thin film and the substitution treatment . 9. The method of manufacturing a transistor according to claim 8 , wherein a treatment for replacing a terminal other than hydrogen on the surface of the diamond thin film with a hydrogen terminal is performed before the replacement processing. The fluorine-based gas used in the inductively coupled reactive ion etching process is at least C _x F _y , C _x H _y F _z , and C _x O _y F _z (x, y, z are integers of 1 or more). The method for manufacturing a transistor according to claim 8 , wherein the transistor comprises one gas. Forming a diamond film,
Using a fluorine-based gas containing carbon, depositing a fluorocarbon deposition film having a crystal structure different from that of the diamond thin film on the surface of the diamond thin film while using a part of the hydrogen termination of the diamond thin film as a fluorine termination. Performing the replacement process,
Forming a gate on a part of the surface of the diamond thin film. The method for manufacturing a transistor according to claim 11 , wherein a process of replacing a terminal other than hydrogen on the surface of the diamond thin film with a hydrogen terminal is performed before the replacement process. The method of manufacturing a transistor according to claim 11 , wherein the substitution treatment is a reactive ion etching treatment using a fluorine-based gas for at least a part of the surface of the diamond thin film. The method of manufacturing a transistor according to claim 13 , wherein the reactive ion etching process is an inductively coupled reactive ion etching process. Fluorine-based gas used in the reactive ion etching _{process, C x F y, C x} H y F z, and _{C x O y F z (x} , y, z is an integer of 1 or more) at least one of The method for manufacturing a transistor according to claim 13 , wherein the gas is a gas.

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