JP4214930B2 - Silicon material etching method, etching solution, and inkjet head manufacturing method - Google Patents

Description

  The present invention relates to a method for etching a silicon material used for manufacturing a silicon microstructure such as an ink jet head, and more particularly, a silicon material that performs anisotropic etching on the surface of a silicon material using a silicon oxide film as a mask material. This is related to the etching method.

  Silicon single crystals can be anisotropically etched with greatly different etching rates depending on the crystal plane orientation. Silicon anisotropic etching is used to accurately manufacture various silicon microstructures. For example, it is used for manufacturing an inkjet head or a silicon pressure sensor diaphragm. Patent Document 1 discloses a method of manufacturing an inkjet head with high precision by silicon anisotropic etching.

  In silicon anisotropic etching, a silicon oxide film is generally used as an etching resistant mask material for protecting a non-etched portion on the surface of a silicon material. The silicon oxide film is generally formed by performing a thermal oxidation process on the surface of a silicon substrate in an atmosphere to which oxygen and water vapor are supplied. In addition, an alkaline solution containing KOH or the like is generally used as an etching solution for a silicon material.

The silicon oxide film used as the mask material is also slightly removed when the silicon substrate is etched with an alkaline solution, and the film thickness is reduced. Therefore, it is necessary to set the thickness of the silicon oxide film to a predetermined value or more so that the silicon substrate can be reliably masked until the etching is completed.
JP-A-6-8449

  Here, if the thickness of the silicon oxide film used as the etching resistant mask material can be reduced, the oxidation time (lead time) required for the thermal oxidation process for forming the oxide film can be shortened, and the processing cost can be reduced. Can also be reduced. Further, if the silicon oxide film can be made thinner, the accuracy of the mask pattern formed there can be increased, and as a result, the etching accuracy of the silicon substrate can be improved.

  In view of these points, an object of the present invention is to propose a method for etching a silicon material in which the thickness of a silicon oxide film used as a mask material can be smaller than that in the prior art.

  Another object of the present invention is to propose an etching solution used in such a new etching method.

  Another object of the present invention is to propose a method for manufacturing an inkjet head using a new etching method.

In order to solve the above problems, the present invention is characterized in that, in an etching method for a silicon material using a silicon oxide film as a mask material , an alkaline solution containing an alkali metal and an alkaline earth metal is used as an etching solution. It is said.

  Here, it is desirable to use calcium as the alkaline earth metal. The calcium concentration is preferably 100 ppb or more, and particularly preferably 500 ppb or more.

  Next, the present invention relates to an etching solution used for etching a silicon material using a silicon oxide film as a mask material, wherein the etching solution is an alkaline earth metal, preferably an alkaline solution containing calcium. It is said. The calcium concentration is preferably 100 ppb or more, particularly 500 ppb or more.

  On the other hand, the present invention is a method for manufacturing an ink jet head having an ink nozzle and an ink pressure chamber that generates a pressure for ejecting ink droplets from the ink nozzle. A single crystal substrate is etched to form the ink nozzle and / or the ink pressure chamber.

  In the present invention, an alkaline solution containing an alkaline earth metal is used as an etching solution. It was confirmed that when an alkaline solution containing an alkaline earth metal, particularly calcium, is used, the etching rate of the silicon oxide film can be reduced by increasing the amount of addition. In particular, when etching is performed using an alkaline solution containing calcium of 100 ppb or more, preferably 500 ppb or more, the etching rate of the silicon oxide film can be greatly reduced, so that the silicon oxide film can be thin.

  Therefore, the lead time of the process for forming the silicon oxide film by performing the thermal oxidation process on the surface of the silicon material can be greatly reduced. As a result, the amount of supplied oxygen and power required for the process are reduced. The cost can be greatly reduced. Further, since the silicon oxide film as a mask material can be thin, the amount of side etching can be suppressed, and the pattern accuracy of the mask pattern can be increased. As a result, the etching accuracy of the silicon material can be improved.

  Furthermore, since the heat treatment time for forming the silicon oxide film can be shortened, the thermal load on the silicon material is reduced in the heat treatment step. Therefore, since the thermal distortion of the silicon material is reduced, the silicon material can be etched with high accuracy. In other words, when a heat treatment time similar to the conventional one is ensured, the silicon oxide film can be formed by performing the heat treatment at a lower temperature than the conventional one, so that the thermal distortion of the silicon material can be reduced.

  Further, by increasing or decreasing the calcium concentration, there is an advantage that the etching rate of the silicon oxide film as the mask material can be adjusted to an appropriate rate according to the etching processing time.

  Furthermore, if the silicon oxide film has been thinned due to defects or scratches in the conventional silicon oxide film, the silicon substrate cannot be masked until the etching is completed. Oxide film defects and scratches have been transferred, but in the present invention, the etching rate of the silicon oxide film can be reduced, so that transfer to a silicon substrate is possible depending on the degree of silicon oxide film defects and scratches. Can be reduced.

  On the other hand, according to the ink jet head manufacturing method of the present invention, the thickness of the silicon oxide film as a mask material required in the etching process for forming the ink nozzles and the ink pressure chambers can be reduced. Lead time and cost can be reduced. In addition, the ink nozzle and the ink pressure chamber can be formed with high accuracy.

  Hereinafter, with reference to the drawings, an example of an etching solution and an inkjet head manufacturing method to which the present invention is applied will be described.

(Etching solution)
The inventor measured the etching rate of a silicon oxide film by using an alkaline solution such as calcium added to an alkaline solution such as KOH or TMAH as an etching solution used for etching a silicon single crystal substrate. . As a result, it was confirmed that the etching rate of the silicon oxide film gradually decreased when the addition amount of the alkaline earth metal was increased.

As an example, using an etching solution obtained by adding calcium to an alkaline solution having a KOH concentration of 25% by weight, the relationship between the calcium concentration (Ca concentration) and the etching rate (SiO ₂ E / R) of the silicon oxide film is shown. Examined. FIG. 1 is a graph showing these relationships.

  As can be seen from this figure, when the calcium concentration is in the range from about 100 ppb to about 500 ppb, the rate of decrease in the etching rate of the silicon oxide film increases with an increase in the calcium concentration. When the calcium concentration exceeds about 500 ppb, the decreasing rate of the etching rate becomes small, and when it exceeds about 1000 ppb, the etching rate hardly fluctuates.

  Therefore, if the calcium concentration is about 100 ppb or more, the etching rate of the silicon oxide film can be reduced as compared with the case where a conventional alkaline solution is used. Therefore, the thickness of the silicon oxide film used as a mask material when etching the silicon material can be reduced. Further, when the calcium concentration is increased or decreased within the range of 100 ppb to 500 ppb, the etching solution for etching the silicon oxide film at an etching rate suitable for the etching process conditions can be easily adjusted. Furthermore, since the etching rate is hardly reduced when the calcium concentration exceeds about 1000 ppb, it is economical to use an alkaline solution having a calcium concentration in the range of about 500 ppb to about 1000 ppb.

(Inkjet head)
Next, an example of an ink jet head capable of forming ink nozzles and the like by an etching method using the above etching solution will be described.

  FIG. 2 is an exploded perspective view of the inkjet head, and FIG. 3 is a cross-sectional configuration diagram of the assembled inkjet head. As shown in these drawings, the inkjet head 1 is a face inkjet type that ejects ink droplets from ink nozzles formed on the upper surface of a substrate. The inkjet head 1 has a three-layer structure in which a cavity plate 3 is sandwiched, a nozzle plate 2 is laminated on the upper side, and a glass plate 4 is laminated on the lower side.

  The cavity plate 3 is made of a silicon single crystal substrate, and has a concave portion 7 that constitutes an ink chamber 6 whose bottom portion functions as the vibration plate 5 on the surface thereof, and an ink supply port 8 provided behind the concave portion 7. The narrow grooves 9 to be formed and the recesses 11 constituting the ink reservoirs 10 for supplying ink to the respective ink chambers 6 are formed by anisotropic wet etching.

  The nozzle plate 2 bonded to the upper side of the cavity plate 3 is formed from a silicon single crystal substrate, similarly to the cavity plate 3. In the nozzle plate 2, a plurality of ink nozzles 21 communicating with each ink chamber 6 are formed at a portion defining the upper surface of the ink chamber 6.

  By joining the nozzle plate 2 to the cavity plate 3, the recesses 7, 11 and the narrow groove 9 are closed, and the ink chamber 6, the ink supply port 8, and the ink reservoir 10 are respectively formed in a compartment. A hole 12a for supplying ink to the ink reservoir 10 is provided in a portion defining the bottom surface of the ink reservoir 10, and after the substrate is joined, the ink supply hole 12 is provided together with a hole 12b provided in the glass plate 4 described later. Form. An ink tank (not shown) is connected to the ink supply hole 12 via a connection tube (not shown). The ink supplied from the ink supply hole 12 is supplied to each independent ink chamber 6 via each ink supply port 8.

  Here, each ink chamber 6 is provided with an electrostatic actuator for temporarily raising the pressure in each ink chamber and discharging an ink droplet from the corresponding ink nozzle. Each electrostatic actuator has an individual electrode and a common electrode arranged to face each other with a minute gap. In this example, the individual electrode is an ITO film described later formed in the recess 16 of the glass plate 4, and the common electrode is a deformable diaphragm 5 formed at the bottom of the ink chamber 6.

  Next, the glass plate 4 bonded to the lower side of the cavity plate 3 is a borosilicate glass plate having a thermal expansion coefficient close to that of silicon. In the glass plate 4, concave portions 16 that form gaps 15 are formed at portions facing the respective vibration plates 5. An individual electrode 17 is formed on the bottom surface of the recess 16 so as to face the diaphragm 5. The individual electrode 17 has a segment electrode portion 18 and a terminal portion 19 made of ITO.

  By bonding the glass plate 4 to the cavity plate 3, the diaphragm 5 defining the bottom surface of each ink chamber 6 and the segment electrode portion 18 of the individual electrode 17 face each other with a very narrow gap. The external communication port 15 a of the space (gap portion) 15 between these is hermetically sealed by a sealing material 20 made of low melting point glass disposed between the cavity plate 3 and the glass plate 4.

  A voltage applying device 25 is connected between the diaphragm 5 and the individual electrode 17. One output of the voltage application device 25 is connected to the terminal portion 19 of each individual electrode 17, and the other output is connected to a common electrode terminal 26 formed on the cavity plate 3. Since the cavity plate 3 itself has conductivity, a voltage can be supplied from the common electrode terminal 26 to the diaphragm (common electrode) 5.

  In the inkjet head 1 having this configuration, when the drive voltage from the voltage application device 25 is applied between the opposing electrodes, a Coulomb force is generated by the charge charged between the opposing electrodes, and the diaphragm 5 has the segment electrode portion 18. And the volume of the ink chamber 5 increases. Next, when the driving voltage from the voltage application device 25 is released and the electric charge between the opposing electrodes is discharged, the diaphragm 5 is restored by its elastic restoring force, and the volume of the ink chamber 6 is rapidly reduced. Due to the internal pressure fluctuation generated at this time, a part of the ink stored in the ink chamber 6 is ejected from the ink nozzle 21 communicating with the ink chamber 6 toward the recording paper.

  FIG. 4 is an explanatory view showing a manufacturing process of the cavity plate 3 of the inkjet head 1 having the above-described configuration. First, a silicon single crystal substrate 3A having a (100) plane orientation is prepared (FIG. 4A), a silicon oxide film 31 as an etching resistant material is formed on the surface, and ink supply holes 12a are formed in the silicon oxide film 31. Then, a recess 12A corresponding to the ink supply hole 12a is formed by dry etching such as ICP (FIG. 4C).

  Next, after the silicon oxide film 31 is removed, a thermal oxidation process is performed again, for example, at 1100 ° C. for 3 hours in an atmosphere in which oxygen and water vapor are supplied, and the surface of the silicon substrate 3A is used as an etching resistant mask material. A functioning silicon oxide film 32 of 400 nm, for example, is formed. A photoresist pattern (not shown) corresponding to the pressure chamber recess 7, the ink supply port recess 9 and the ink reservoir recess 11 is formed on the silicon oxide film 32, and silicon is etched using a hydrofluoric acid-based etching solution. The exposed portion of the oxide film 32 is removed by etching, the silicon oxide film 32 is patterned, and the photoresist pattern is removed (FIG. 4D).

  Next, anisotropic etching is performed on the silicon single crystal substrate 3A using a solution obtained by adding about 800 ppb of calcium to an alkali solution containing 25% by weight of KOH containing isopropyl alcohol as an etching solution, and the pressure chamber recess 7 and ink supply A mouth recess 9 and an ink reservoir recess 11 are formed (FIG. 4E).

  Thereafter, the silicon oxide film 32, which is an etching resistant mask material, is completely removed with a hydrofluoric acid-based etchant, and heat treatment is applied to the surface of the silicon single crystal substrate 3A to provide the cavity plate 3 with heat treatment. Completed (FIG. 4F).

  Here, FIG. 5 is a chart showing changes in the required film thickness of the silicon oxide film 32 due to changes in the etching rate of the silicon oxide film 32 under the same etching conditions. In this example, an etching solution having a calcium concentration of about 800 ppb is used, and the etching rate (E / R) of the silicon oxide film 32 is about 1 nm / min. The required film thickness is 400 nm, and the required thermal oxidation time is about 3 hours. Even when an etching solution having a calcium concentration of about 250 ppb is used, the etching rate is 2 nm / min, the required film thickness is about 600 nm, and the necessary oxidation time is about 6 hours. On the other hand, in the case of using a conventional etching solution that does not contain calcium, the etching rate is about 3 nm / min, which is three times that of this example, so that the required film thickness is 1200 nm, and the necessary oxidation time for that purpose. Is about 9 hours.

  Thus, it can be seen that by reducing the etching rate, the film thickness of the silicon oxide film used as the mask material can be reduced, and as a result, the thermal oxidation processing time for forming the silicon oxide film can be greatly shortened. In this example, an alkaline solution containing calcium having a low etching rate for the silicon oxide film is used as the etching solution for the silicon substrate. Therefore, it can be seen that the thermal oxidation treatment time can be shortened as compared with the prior art, so that the amount of supplied oxygen and power supplied in the thermal oxidation treatment can be reduced, and the processing cost can be reduced.

  In the above description, the silicon oxide film as the mask material is described as a wet oxide film formed in a water vapor atmosphere, but a similar effect can be obtained even with a dry oxide film. The same effect can be obtained not only for such a thermal oxide film but also for a silicon oxide film formed by a CVD process.

  On the other hand, the above example is an example in which the etching method of the present invention is applied to the manufacture of the cavity plate of the ink jet head. Of course, the invention is equally applicable.

It is a graph which shows the relationship between a calcium concentration and the etching rate of a silicon oxide film. It is a disassembled perspective view of the inkjet head which can apply the method of this invention. It is a schematic sectional drawing of the inkjet head of FIG. It is explanatory drawing which shows the manufacturing process of the cavity plate of the inkjet head of FIG. It is a table | surface which shows the relationship between the etching rate of a silicon oxide film, required oxide film thickness, etc. FIG.

Explanation of symbols

1 ink jet head, 2 nozzle plate, 3 cavity plate, 3A silicon single crystal substrate, 4 glass substrate, 5 vibration plate, 6 ink pressure chamber, 7 ink pressure chamber recess, 8 ink supply port, 9 ink supply port recess, DESCRIPTION OF SYMBOLS 10 Ink reservoir, 11 Ink reservoir recessed part, 12, 12a, 12b Ink supply hole, 31, 32 Silicon oxide film

Claims (3)

A silicon material etching method using a silicon oxide film as a mask material,
As an etchant, an alkali solution containing an alkali metal and an alkaline earth metal is used .
The alkali metal is potassium, the alkaline earth metal is calcium,
_ Concentration of calcium contained in the alkaline solution 1000ppb der Ru etching method for a silicon material inclusive 100 ppb. The said alkaline solution used for the etching method of the silicon | silicone material of Claim 1 . An ink jet head manufacturing method comprising: an ink nozzle; and an ink pressure chamber that generates a pressure for discharging an ink droplet from the ink nozzle,
A method for manufacturing an ink jet head, wherein the ink nozzle and / or the ink pressure chamber is formed by etching a silicon single crystal substrate using the etching method according to claim 1 .

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