JP3331957B2 - Surface treatment method for structure to be treated - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating a surface of a structure to be treated, and more particularly to a method for treating a surface of a structure to be treated by forming a thin organosilicon polymer film on the surface of the structure.

[0002]

2. Description of the Related Art An acceleration sensor, a yaw rate sensor element, and the like can be manufactured using a minute structure including a movable structure formed on a substrate surface by surface micromachining. In these devices, sticking, as shown in FIG. 1, that is, during formation of the structure or operation of the device, a structure floating in the air, for example, a beam 44 having one end fixed.
A problem that the free end of the substrate adheres to the silicon wafer 40. As one of the methods of preventing sticking, lower the surface energy of the substrate and the silicon-based structure,
It has been reported that preventing sticking is effective. This document describes a method of immersing a silicon-based structure in a solution containing a silylating agent and treating the surface by causing hydrolysis by moisture adsorbed on the surface of the structure (Self). -assembled Monolayer Fi
lms as Durable Anti-Stiction Coatings for Polysili
con Microstructures.Michel R. Houston et al., Solid-
State Sensor and Actuator Workshop, South Carolina
June 2-6, 42, 1996).

However, in this method, it is difficult to control the amount of water to be hydrolyzed. If a large amount of moisture is present, excessive deposits adhere to the surface of the structure, which may cause sticking of the structure or hinder normal operation. Conversely, when the amount of water is small, sufficient surface treatment becomes difficult. Furthermore, a large amount of organic solvent is required for the washing step after the treatment, and when the organic solvent is changed to another solvent, the wettability is deteriorated, so that the flow of droplets due to surface tension occurs, and the surface structure There was a problem such as causing damage to

[0004] In addition to the above-mentioned method, as a method for preventing sticking, there is also a proposal to prevent sticking by coating a water-repellent fluorine-based polymer on the surface of a microstructure by plasma polymerization of fluorocarbon. (A Novel Method to Avo
id Sticking of Surface Micromachined Structures.,
F. Kozlwski, et al., Transducers `95, 220 (1995)).

However, in this method, surface coating is performed by depositing a polymer film of a fluorine-based polymer. Although the polymer is deposited on the upper surface of the microstructure, the polymer is less likely to deposit on the back surface. Insufficient film uniformity, difficult to coat the inner structure in a multi-layer structure such as three-layer structure, change of resonance frequency due to mass increase in micro vibrator, deposition state However, since the surface is thick and the back surface is thin, there are problems such as that uniform vibration is hindered and that the structure is expected to warp due to the stress of the polymer film.

[0006] In order to solve the above problems, it is conceivable to perform surface treatment of the structure to be treated by supplying a silylating agent vapor in a gas phase system.

However, simply supplying vapor of the silylating agent causes condensation and condensation on the surface of the structure to be treated,
There is a problem that the reaction is not sufficiently performed.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a surface treatment method for a structure to be treated, which enables surface treatment in a gas phase system while controlling the thickness of the surface treatment layer of the structure to be treated. Is to do.

[0009]

According to the surface treatment method for a structure to be treated of the present invention, the surface of the structure to be treated is exposed to an atmosphere of water vapor having a predetermined pressure equal to or lower than a saturated vapor pressure, and a hydroxyl group is formed on the surface. And (a) introducing a long-chain alkyl group or a saturated
(B) exposing the hydroxyl group to the organosilicon compound under an atmosphere of an organosilicon compound having a long-chain fluoroalkyl group in the molecule .

In this surface treatment method, the thickness of the coating can be controlled by controlling the water vapor pressure. The reason will be described below.

[0011] By a hydroxyl group of the surface of the object structure and the reactive groups of the organic silicon compound is a condensation reaction, the coating is formed comprising an organic silicon polymer layer. Further, on the hydroxyl group are adsorbed water, the reactive group of the organic silicon compound by the adsorbed water is further hydrolyzed, a hydroxyl group is formed. That is, a coating is selectively formed on the surface of the structure to be processed in which the hydroxyl groups are present. Therefore, in the state of pressure under the saturated vapor pressure of the organic silicon compound, and, in the case where the organosilicon compound is present sufficiently, formation of the organosilicon polymer film, the amount of hydroxyl groups and adsorbed water Depends on. Also, the amount of hydroxyl groups is affected by the amount of water vapor adsorbed in a water vapor atmosphere. Further, the amount of water vapor adsorbed depends on the water vapor pressure. Therefore, the amount of hydroxyl groups on the surface of the structure to be processed can be controlled by controlling the water vapor pressure in the chamber. As a result, by controlling the water vapor pressure in the chamber, it is possible to control the formation of the coating and, consequently, to control the thickness of the coating.

As described above, the surface treatment method for a structure to be treated according to the present invention enables surface treatment in a gas phase system while controlling the thickness of the surface treatment layer. Therefore, there is an advantage that post-processing such as cleaning is not required, and surface treatment can be performed on the details of the structure to be processed, and furthermore, there is a problem of excessive sediment, a problem of a large amount of waste liquid, and a problem occurs when removing from the liquid. Problems such as various problems found in the conventional wet method can be solved.

Another object of the present invention is to form a very thin coating layer on the surface of the structure, and to control the film thickness by controlling the partial pressure of water vapor. Accordingly, in a state in which the organic silicon compound of the excess is present, when the step (a), the possibility that the organic <br/> organosilicon compound unreacted undergo hydrolysis, excess coating layer is formed There is. Further, if steam is further supplied in the presence of unreacted steam, the supply amount may not be controlled. For the above reasons, unreacted
Wherein it is desired organosilicon compound and at least one of water vapor comprising the step (c), except from the surface of the object structure.

Further, according to the method for treating the surface of the structure to be processed, wherein the steps (a), (b) and (c) are repeated as one cycle, and the cycle is repeated two or more times, the method further provides a uniform and uniform surface. Coating can be achieved for the following reasons.

The contact angle gradually increases as the process of adsorbing water vapor on the surface of the structure to be treated and silylating it is repeated. When the contact angle between the surface of the coated structure to be treated and water becomes 90 ° or more due to the coating by the silylation, the surface energy of the coating portion becomes smaller than the surface energy of the coating portion in the coating portion covered with water. And it is more stable when it is not adsorbed by water. As a result, even if water having a saturation vapor pressure or less is supplied, almost no water is adsorbed on the coating portion.
Almost no hydroxyl group is introduced into that portion. Therefore, even if the organic silicon compound is adsorbed to the coated portion, in that part, since there is no counterpart to the reaction, does not occur hydrolysis reaction or condensation reaction, silylation reaction hardly occurs, iterating , The coating hardly proceeds. On the other hand, water is adsorbed to a portion having a small contact angle, that is, a portion where the coating does not exist or an insufficient portion, so that the silylation reaction proceeds preferentially. In this way, a uniform and non-excessive coating is possible.

Further, the structure to be processed has a front surface.
It is necessary to form a stable coating layer in which the organosilicon compound is siloxane-bonded. Therefore, at least one selected from the group consisting of single crystal silicon, polycrystalline silicon, amorphous silicon, a silicon nitride film, a silicon oxide film, and a silicon oxynitride film, which is a structural material on which silanol groups can be formed on the surface Desirably, it consists of In this case, even if the entire structure is not made of the above substance, at least the surface may be made of the above substance.

The organosilicon compound is preferably a bifunctional or trifunctional compound having a long-chain alkyl group.

In order to reduce the surface energy in the coating, it is necessary to create a very low surface energy state in which the alkyl groups are vertically densely arranged on the surface of the coating. This requires the presence of freely movable long-chain alkyl groups. In order to sufficiently lower the surface energy, a chain longer than a certain length is necessary, and a chain having 6 or more carbon atoms is desirable. The maximum length is not limited, but preferably has a carbon number of 20 or less from the viewpoint of volatility. Here, in addition to the straight-chain alkyl group, a straight-chain fluoroalkyl group in which at least the hydrogen at the leading end of the straight-chain alkyl group that is not bonded to silicon is replaced with fluorine is used as the long-chain alkyl group. Can be. A straight-chain fluoroalkyl group has a low surface energy even when the ideal structure in which the above long-chain alkyl groups are arranged is disordered, and has high heat resistance and high stability such as oxidation resistance. More preferred than long chain alkyl groups.

The type of the functional group is not limited as long as it causes a condensation reaction with a hydroxyl group. Examples thereof include halogen groups such as chlorine, bromine and iodine, alkoxy groups such as methoxy and ethoxy groups, methylamino groups, and dimethyl groups. An amino group such as an amino group, an acetoxy group, or the like, or a combination thereof can be used. Of these, a halogen group which is particularly easily hydrolyzed, and among them, a compound having a long-chain alkyl group having chlorine as a functional group, which is the cheapest compound, is desirable.

The number of functional groups is 2 or 3, but a trifunctional compound having a stitch structure and capable of forming a strong coating layer is desirable.

Examples of the compound satisfying the above conditions include, for example, long-chain alkyltrichlorosilane such as hexadecyltrichlorosilane, heptadecyltrichlorosilane, and octadecyltrichlorosilane;
1,2,2-tetrahydrohexyltrichlorosilane,
Long-chain fluoroalkyltrichlorosilane such as tridecafluoro-1,1,2,2-tetrahydrooctyltrichlorosilane can be used.

Further, the steps (a), (b),
The step (c) can be performed in an inert gas in addition to the vacuum. Although the method of this later consideration has the advantage of not using a vacuum vessel, it is not possible to sufficiently replace the atmosphere under steam and the atmosphere under organosilicon vapor in order to uniformly coat the inside of a minute multilayer structure. Problems are conceivable, such as that there is a possibility and that when the coexistence state of both water vapor and the organic compound is created, the mixing may be uneven. In addition, when a large amount of gas is flowed in order to attach dust to the particles in the gas or perform sufficient replacement, there is a problem that the microstructure may be damaged by the gas. Therefore, 10 to 10
It is desirable to perform the coating treatment under a vacuum of 00 Pa.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (Surface Treatment Apparatus) FIG. 2 is a diagram schematically showing an example of a surface treatment apparatus used in an embodiment according to the present invention.

This surface treatment apparatus includes:
It has a holder 12 supported by columns 11. The chamber 10 includes an exhaust unit 22 for evacuating or exhausting the inside of the chamber 10, and a valve 24 for introducing steam generated in the first container 30 into the chamber 10.
The first gas supply path 26 to which is attached, the second container 3
A second gas supply path 28 provided with a valve 27 for introducing the gaseous organosilicon compound generated in 2 into the chamber 10, and a side wall of the chamber 10 for maintaining the inside of the chamber 10 at a predetermined temperature. Heater 16
The structures to be processed 14 are placed on the holder 12 and b and 16c, and a heater 16a is provided on the lower surface of the holder 12. The temperature of the structure to be processed is adjusted by the heater 16a. Further, a thermocouple 34 for measuring the temperature of the holder 12 is attached to the holder 12.

(Processing Method) An example of a processing method for a structure to be processed will be described below.

(A) First, after forming a precursor of a structure to be processed, in order to form a structure to be processed floating in the air, for example, when the sacrificial layer is silicon oxide, etching of a sacrificial layer using hydrogen fluoride is performed. Etching is performed. At this time, a state terminated with hydrogen is formed on the silicon surface. In the case of using hydrofluoric acid, which is a liquid etchant, the structure is immersed in hydrogen peroxide to perform an oxidation treatment. Also,
In the case of etching with a gaseous hydrogen fluoride gas, an oxidation treatment is performed by performing an ultraviolet treatment in an oxygen atmosphere, or by holding in an atmosphere for a long time. Thus, an oxide film is formed on the surface of the structure. When hydrofluoric acid, which is a liquid, is used, a drying step is required before performing the coating of the present invention. This means that after the oxidation process is completed, the structure to be cleaned and replaced with pure water is sufficiently replaced and washed with an organic solvent mixed with water such as isopropanol.
It is immersed in molten paradichlorobenzene, replaced and washed, taken out into the atmosphere, and dried in a step of sublimating and removing paradichlorobenzene.

[0027] (b) Next, is placed on the holder 12 in the chamber 10 of the surface treatment apparatus according to the object to be processed structure in FIG.
Thereafter, the pressure in the chamber 10 is reduced to a vacuum of 1 × 10 −2 Pa or less by the exhaust unit 22, and the temperature in the chamber 10 is maintained at 30 to 50 ° C. This temperature is
The setting is made in consideration of preventing condensation and condensation of the organosilicon compound and preventing excessive coating.

(C) Next, water vapor is introduced into the chamber through the first gas supply path 26 until the pressure in the chamber 10 becomes 10 to 500 Pa, and the structure to be processed is placed in an atmosphere of water vapor. To introduce hydroxyl groups on the surface of the structure to be treated.

(D) Subsequently, the organosilicon compound is introduced into the chamber through the second supply passage 28 until the pressure in the chamber becomes 20 to 600 Pa. While maintaining the pressure state for 5 to 30 minutes, the structure to be treated is exposed to an atmosphere of an organosilicon compound, and a coating comprising an organosilicon polymer film is formed by a condensation reaction between a hydroxyl group and a reactive group of the organosilicon compound.

(E) By exhausting the inside of the chamber 10 by the exhaust means 22, unreacted organosilicon compounds and water vapor are removed from the interior of the chamber.

By repeating the above-described steps (b) to (d) as one cycle and repeating a plurality of cycles, it is possible to obtain a uniform coating having a desired film thickness, for example, a film thickness of a monolayer level. it can.

(Evaluation TEG) FIG. 3 is a schematic diagram showing an example of the evaluation TEG.

The TEG for evaluation has a silicon wafer 40 and a beam 44 having a cantilever structure formed on the silicon wafer 40. Beam 4 of silicon wafer 40
The lower electrode 42 and the lower structure 4
3 is provided, and the lower electrode 42 and the beam 44
6 and a structure in which a voltage is applied between the lower electrode 42 and the beam 44. After the beam 44 is forcibly pulled by the lower electrode 42 and once adhered to the lower structure 43, the voltage is turned off and the change in adhesion is observed. When sticking occurs, that is, when sticking occurs, the beam 44 is distorted by sticking to the lower structure 43, and the sticking phenomenon can be measured by observation with an interference microscope.

(Experimental Example 1) First, a hydrofluoric acid-treated structure (sample) having a silicon wafer and a microstructure having a cantilever structure was immersed in hydrogen peroxide, and oxidized. went. Next, the structure to be processed which has been dried in the drying step is placed on the holder 12 in the chamber 10 of the surface treatment apparatus shown in FIG. 2 , and then the pressure in the chamber 10 is set to 1.3 by the exhaust means 22. A vacuum state of × 10 ⁻² Pa or less was maintained, the temperature in the chamber 10 was maintained at 35 ° C., and the temperature of the holder was maintained at 40 ° C. Next, water vapor is supplied to the chamber 10 at a pressure of 1
The structure was introduced into the chamber 10 through the first gas supply path until the pressure reached 30 Pa, and the structure to be processed was exposed to an atmosphere of water vapor. Subsequently, tridecafluoro-1,1,2,2-tetrahydrooctyltrichlorosilane was introduced into the chamber 10 through the second gas supply passage 28 until the pressure in the chamber 10 became 170 Pa. The state of the pressure is 10
And then treat the structure to be treated with tridecafluoro-1,1,2,2-
The exposed coating was formed under an atmosphere of tetrahydrooctyltrichlorosilane.

Thereafter, the pressure in the chamber 10 is increased to 1.3 ×
The gas was exhausted by the exhaust means 22 to 10 ⁻³ Pa or less. Supply of the steam, then the tridecafluoro-1,1,2,2-
The operation of supplying and exhausting tetrahydrooctyltrichlorosilane was defined as one cycle, and two more cycles were repeated.

When the silicon wafer and the microstructure after the surface treatment were examined, no abnormality such as white turbidity was observed in both of them. In addition, when the contact angle of the silicon wafer with water was measured, it was as high as 108 °, and it was confirmed that the water repellent treatment was performed by this method. In addition, as a result of infrared spectroscopic measurement of the wafer, it was confirmed that the coating layer was below the detection limit and was a very thin coating layer.

Further, in the method using the TEG for evaluation shown in FIG. 3, a silicon wafer and a microstructure (beam) are used.
Was once contacted, and the degree of recovery thereafter was examined. FIG. 4 shows the results. As shown in FIG. 4, when the surface treatment is not performed, when the beam length is 400 nm or more,
Although the adhesion phenomenon, that is, sticking has occurred, it can be seen that sticking did not occur at any beam length when the surface treatment of this method was performed. As a result, it was found that, similarly to the conventional wet method, the back surface of the microstructure (beam) having the cantilever structure can be sufficiently coated and is effective in preventing sticking.

(Experimental Example 2) The same method as in Experimental Example 1 except that the oxidation step after the hydrofluoric acid treatment was performed by drying without performing the hydrogen peroxide treatment and then performing UV irradiation in oxygen. For surface treatment. As a result, when the contact angle of the silicon wafer to water was measured, it was very large at 108 °, and it was found that the water repellent treatment was completed by this method. Figure 3
In the method using the TEG for evaluation shown in (1), a silicon wafer and a microstructure (beam) subjected to the surface treatment of this method
Was once contacted, and the degree of recovery thereafter was examined. As in Experimental Example 1, sticking was not observed.
According to this method, the back surface of the microstructure (beam) having the cantilever structure can be sufficiently coated, and it is found that the method is effective in preventing sticking.

(Experimental Example 3) Surface treatment was carried out in the same manner as in Experimental Example 2 except that the oxidation step was carried out in the atmosphere for 2 days. Also in this method, Experimental Example 1
Similarly to the above, it was found to be effective in preventing sticking.

(Experimental Example 4) Instead of the treatment in a vacuum, the treatment was performed in a nitrogen atmosphere at atmospheric pressure. A silicon wafer heated to 50 ° C. and a structure to be processed having a cantilevered microstructure are placed in a container, and nitrogen gas is used as steam and a carrier gas for the organosilicon compound. It was bubbled and supplied into the container. afterwards,
Unreacted raw materials were removed by flowing only nitrogen gas. These operations were repeated three times. When the contact angle of the silicon wafer with water was measured, it was very large at 108 °, and as a result, it was confirmed that the water repellent treatment was performed by this method. In the method using the TEG for evaluation shown in FIG. 3 , the silicon wafer was once brought into contact with the microstructure (beam), and the degree of recovery thereafter was examined.
Similarly to the above, sticking was not observed, and it was found that this method could sufficiently coat the back surface of the microstructure (beam) having the cantilever structure and was also effective in preventing sticking.

(Experimental Example 5) The treatment was carried out in the same manner as in Experimental Example 1 except that octadecyltrichlorosilane was used as the organosilicon compound. When the contact angle of the silicon wafer with water was measured, it was as large as 113 °, and it was confirmed that the water repellent treatment was also performed by this method. In the method using the TEG for evaluation shown in FIG. 3 , the silicon wafer subjected to the surface treatment of the present method is once brought into contact with the microstructure,
The degree of subsequent recovery was examined. As a result, similar to Experimental Example 1, sticking was not observed.
It was found that the backside of the microstructure (beam) having a cantilever structure can be sufficiently coated, and that it is also effective in preventing sticking.

[0042]

[Brief description of the drawings]

FIG. 1 is a diagram schematically illustrating an example of a sticking phenomenon.

FIG. 2 is a diagram schematically illustrating an example of a surface treatment apparatus.

FIG. 3 is a diagram schematically illustrating an example of an evaluation TEG.

FIG. 4 is a diagram showing the results of evaluation of sticking prevention ability.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Chamber 11 Support pillar 12 Holder 14 Structure to be processed 16a Heater 16b Heater 16c Heater 22 Exhaust means 24 First valve 26 First gas supply path 27 Second valve 28 Second gas supply path 30 First container 32 second container 34 thermocouple 40 silicon wafer 42 lower electrode 43 lower structure 44 microstructure (beam) 46 conductive wire

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-7-335758 (JP, A) JP-A-8-190204 (JP, A) JP-A-4-287308 (JP, A) JP-A-11- JP-A-5-86353 (JP, A) JP-A-5-70761 (JP, A) JP-A-10-194784 (JP, A) Table 10-512675 (JP, A) (58) Field surveyed (Int.Cl. ⁷ , DB name) C09K 3/18 G03F 7/38 H01L 21/312 H01L 29/84

Claims (3)

(57) [Claims] 1. A step (a) of exposing a surface of a structure to be processed to an atmosphere of water vapor having a predetermined pressure equal to or lower than a saturated vapor pressure to introduce a hydroxyl group into the surface; , Long pressure below the saturated vapor pressure
Intramolecular alkyl or long-chain fluoroalkyl groups
Exposed to an atmosphere of an organic silicon compound having the step of reacting the hydroxyl group and organic silicon compound (b)
A surface treatment method for a structure to be treated, comprising: 2. The method according to claim 1, further comprising the step (c) of removing at least one of the unreacted organosilicon compound and water vapor from the surface of the structure. 3. The method according to claim 2, wherein the step (a), the step (b), and the step (c) are performed.
Is a cycle, and a surface treatment method for a structure to be treated is repeated for two or more cycles.