JP2008264951A - Machining method of inclined shape - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a machining method of an inclined shape low in cost and favorable in productivity, capable of inclining the inner side face of a recessed section or a hole section in forming the recessed section or the hole section on the surface of a substrate. <P>SOLUTION: This machining method comprises a process for forming a first mask 11 on the substrate 10, a process for forming an opening by performing etching by using the first mask 11, a deposit process for forming a polymer membrane, an etch back process for performing etch-back throughout the entire surface of the polymer membrane and forming a second mask 16 (14) on the inner side face of the first mask 11 and the inner side face of the opening, and an in-opening etching process for performing etching in the opening by using the first mask 11 and the second mask 16. By repeating the deposit process and the etch-back process, the thickness of the second mask 16 (18) is adjusted to have a desired thickness, and by repeating the thickness adjustment of the second mask and the in-opening etching process, the inner side face of the opening (the recessed section 19) is substantially inclined. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method of processing an inclined shape when a recess or a hole is formed on the surface of a substrate.

  In recent years, a technique called MEMS (Micro Electro Mechanical System), which uses a micromachining technology that applies semiconductor micromachining technology to produce a very small structure having a size of several hundreds [μm], has attracted attention. Yes. Such microstructures, that is, MEMS devices, are being studied for application to various sensors, optical switches in the field of optical communication, radio frequency (RF) components, and the like.

  In the etching technique in the three-dimensional mounting of the MEMS device or the IC chip, silicon is used as a workpiece, that is, a substrate. In the microfabrication technology of silicon, anisotropic etching (dry etching) independent of the crystal orientation of silicon is effective particularly when a recess or a hole is formed.

  Conventionally, a “method for anisotropic etching of silicon” described in Patent Document 1 is known as an anisotropic etching technique widely applied to three-dimensional mounting of MEMS devices and IC chips. This technique provides a method for anisotropically etching microstructures and nanostructures in a silicon substrate using an etching process and a polymer deposition process that are alternately and continuously controlled in a plasma and independently controlled, and the amount of polymer deposited is reduced. It is a method characterized in that it decreases in the course of the polymer precipitation process, and in particular, the inner surface of the recess and hole can be formed more perpendicular to the substrate surface (processed surface) and has excellent verticality. It is a processing method.

By the way, especially in the processing of MEMS devices, for example, a nozzle trumpet shape (tapered shape) for ejecting droplets is not vertical processing, but in the direction of the substrate processing surface in the vertical direction (processing direction). In some cases, a tilting process is required to tilt the side surface at a relatively large angle, for example, an angle of 30 ° to 60 °.
Special Table 2001-505001

  However, in the method of Patent Document 1, it is possible to incline the inner surface of the recess and the hole at an angle close to perpendicular to the substrate processing surface (for example, about 85 ° or more). It is difficult to have an inclination angle of from 60 ° to 60 °.

  Therefore, when forming a mask on the processed surface 1a of the substrate 1 made of silicon as shown in FIG. 3 (a), the mask 2 is formed by stacking thin mask patterns 2a in multiple stages, That is, it is conceivable that the shape of the hole 3 is, for example, substantially reverse tapered. That is, when the mask pattern 2a is stacked in multiple stages, the size of the opening is gradually increased, and the inner surface of the hole 3 of the resulting mask 2 is expanded stepwise so that the hole 3 The shape is substantially inversely tapered.

Then, the base body 1 is processed by etching using such a mask 2. At this time, after etching the base body 1 to a predetermined depth as shown in FIG. For example, as shown in FIG. 3C, the mask pattern 2a is selectively removed by one step by RIE (reactive ion etching). Then, by alternately repeating the step of etching the substrate 1 having the predetermined depth and the step of etching and removing the mask pattern 2a by one step, the hole 3 of the mask 2 is formed as shown in FIG. A pattern corresponding to the shape, that is, a concave pattern 4 is formed on the processed surface 1 a of the substrate 1.
By adopting such a processing method, the inner surface of the concave pattern 4 is expanded stepwise in correspondence with the shape of the hole 3 that is substantially inversely tapered. The side surface can be a substantially inclined surface.

  However, in such a processing method, for example, an inductive coupling (ICP) type etching apparatus is used in the etching process of the substrate 1 shown in FIG. 3B, whereas, as shown in FIG. In the process of removing the mask pattern 2a by one step, these processes are performed by different apparatuses, such as using an RIE etching apparatus. Therefore, in order to repeat these steps, time for moving between apparatuses and initial adjustment time for operating the apparatus are required, and therefore, there are significant problems in terms of cost and productivity.

  The present invention has been made in view of the above circumstances. The object of the present invention is to form the recess or hole on the surface of the substrate so that the inner surface of the recess or hole is, for example, about 30 ° to 60 °. An object of the present invention is to provide a method for processing an inclined shape that can be inclined and at the same time has improved cost and productivity.

The inclined shape processing method of the present invention is an inclined shape processing method of substantially inclining the inner surface of the recess or hole when forming the recess or hole on the surface of the substrate,
A first mask forming step of forming a first mask corresponding to the opening shape of the recess or hole on the substrate;
Etching the base using the first mask to form an opening of a recess or hole to be formed; and
Depositing a polymer to form a polymer film on the first mask and in the opening;
Etch back the entire surface of the polymer film, leaving the polymer film on the inner surface of the first mask and the inner surface of the opening, and using this as a second mask;
And an in-opening etching process for etching the inside of the opening using the first mask and the second mask,
By repeating the deposition step and the etch back step a plurality of times, the thickness of the second mask used in the in-opening etching step is adjusted to a desired thickness,
The inner surface of the opening is substantially inclined by adjusting the thickness of the second mask by the deposition process and the etch-back process and repeating the etching process in the opening a plurality of times. .

According to this inclined shape processing method, the adjustment of the thickness of the second mask by the deposition step and the etch back step and the in-opening etching step are repeated a plurality of times, thereby forming the recesses or holes to be formed. The inner surface of the opening can be expanded stepwise, and the inner surface of the recess or hole obtained thereby can be a substantially inclined surface. At that time, by appropriately setting the thickness of the second mask and the etching depth at the time of the in-opening etching step, the inclination angle of the inner surface of the obtained recess or hole can be set, for example, with respect to the surface of the substrate. It can be formed at a desired inclination angle, for example, within a range of 30 ° to 60 °.
In addition, since the adjustment of the thickness of the second mask by the deposition step and the etch-back step and the etching process in the opening can be performed in the same apparatus, Even if the in-opening etching process is repeated a plurality of times, there is no loss such as moving the substrate between apparatuses each time, so that the cost and productivity can be improved.

Moreover, in the said processing method, the substantial inclination angle with respect to the surface of the said base | substrate of the inner surface of the said opening part can be 30 degrees or more and 60 degrees or less as mentioned above.
In the processing method described above, it is preferable that the base is made of silicon. In this way, an existing silicon micro-processing technique can be used for etching and the like.

Hereinafter, the inclined shape processing method of the present invention will be described in detail.
1 (a) to 1 (e) and FIGS. 2 (a) to 2 (d), the inclined shape processing method of the present invention is applied to form and process a concave portion having a reverse taper shape with respect to a silicon substrate. It is process explanatory drawing which shows one Embodiment in the case. In addition, as for the recessed part formed here, the opening shape may be a closed shape such as a circle or a rectangle, or it may be a shape with one end or both ends open, such as an elongated groove shape. Good.

In these drawings, reference numeral 10 denotes a silicon substrate (base). In the present embodiment, first, as shown in FIG. 1A, a first mask 11 corresponding to the opening shape of a recess to be formed on the silicon substrate 10 is shown. Is formed (first mask forming step). That is, the first mask 11 having the same opening as that of the recess to be formed is formed. Here, for the formation of the first mask 11, for example, an oxide film made of SiO ₂ is formed on the silicon substrate 10 by a CVD method or the like, and then a well-known resist technique and exposure / development are formed on the oxide film. A mask made of a resist pattern is formed by a technique. Thereafter, the oxide film is patterned using this resist mask to obtain a first mask 11 made of an oxide film.

Next, the silicon substrate 10 is etched using the first mask 11 to form an opening 12 of a target recess as shown in FIG. 1B (opening forming step). The opening width d of the opening 12 is, for example, about 20 to 30 μm. Here, the etching of the silicon substrate 10 is performed by using, for example, an inductively coupled (ICP) etching apparatus and using SF ₆ gas plasma. That is, the silicon substrate 10 is etched by F radicals (F ^* ) and F ⁺ ions generated by SF ₆ gas plasma. The etching mechanism of the silicon substrate 10 is mainly caused by a chemical reaction between silicon and F radicals, as will be described later. When etching is performed in this manner, this etching acts as isotropic etching on silicon.

  However, in the present invention, in the step of forming the opening 12 and the etching process in the opening described later, the etching depth is sufficiently shallow, for example, several μm (about 1 to 5 μm). Etching is stopped in a state where the etching in the direction hardly proceeds. Thereby, in this opening part formation process, it can be made to act as anisotropic etching rather than substantially isotropic.

Next, a polymer is deposited on the silicon substrate 10 on which the opening 12 is formed, and a polymer film 13 is formed on the first mask 11 and in the opening 12 as shown in FIG. 1C (deposition step). The polymer film 13 is formed by using C ₄ F ₈ gas plasma by the inductively coupled (ICP) etching apparatus. That is, by polymerizing CxFy radicals generated by C ₄ F ₈ gas plasma, fluorocarbon is deposited on the first mask 11 and in the opening 12 to form the polymer film 13. However, in such a method for forming the polymer film 13, although it is possible to form a thick film by taking a long time, in that case, it becomes difficult to control an etch back process of the polymer film 13 described later.

That is, according to the present invention, the SF ₆ gas is etched by the same inductive coupling (ICP) etching apparatus in the etching back process of the polymer film 13 to be described later, similarly to the opening forming process and the etching process in the opening to be described later. This is done by using plasma. That is, the F ⁺ ions generated by the SF ₆ plasma collide with the polymer film 13 on the first mask 11 and the polymer film 13 at the bottom in the opening 12, and these sites are generated by the ion impact force of the F ⁺ ions. The polymer film 13 is removed. However, in the removal of the polymer film 13 by such ion bombardment, if the etching is performed excessively, the polymer film 13 is removed and the exposed silicon substrate 10 is etched. Therefore, when the thickness of the polymer film 13 is increased, the control becomes very difficult as described above. Therefore, in the present invention, in order to obtain a desired thickness by a plurality of film forming processes, the polymer film 13 is formed to a thickness that is a fraction of the desired thickness.

Next, the entire surface of the obtained polymer film 13 is etched back to leave the polymer film 13 on the inner side surface of the first mask 13 and the inner side surface of the opening 12 as shown in FIG. 14 (etch-back process). As described above, the etch back process of the polymer film 13 is performed by using SF ₆ gas plasma by the same inductive coupling (ICP) etching apparatus as the opening forming process. This etch-back is obtained by, for example, obtaining the time required to remove the polymer film 13 on the first mask 11 and the polymer film 13 at the bottom in the opening 12 in advance by experiments or simulations. The second mask 14 is formed by performing etching for a predetermined time.

  However, in the second mask 14 formed in this way, the thickness of the polymer film 13 is only a fraction of the desired thickness as described above. The thickness of 14 is also thinner than the desired thickness. Therefore, in the present invention, the deposition process shown in FIG. 1C is repeated while leaving the second mask 14 to form the polymer film 13 on the first mask 11 and in the opening 12.

  Subsequently, the entire etch back process of the polymer film 13 shown in FIG. 1D is repeated, and the polymer film 13 on the first mask 11 and the polymer film 13 at the bottom in the opening 12 are removed again. Then, the polymer film 13 remaining on the inner side surface of the first mask 13 and the inner side surface of the opening 12 by this etch back is laminated on the second mask 14 previously formed, so that the film thickness is increased. Thus, a new second mask 14 is obtained.

The thickness of the second mask 14 thus obtained is the thickness obtained by multiplying the thickness of the polymer film 13 formed in one deposition step (film formation process) by the number of times this deposition step is repeated. Almost equal to Therefore, in order to set the thickness of the second mask 14 to a desired thickness by setting the thickness of the polymer film 13 formed in one deposition step (film formation process) in advance, the deposition is performed. It can be seen how many times the process and the etch-back process should be repeated.
Therefore, in the present invention, the second mask 14 having a desired thickness is obtained by repeating the deposition step and the etch back step a predetermined number of times. That is, by repeating the deposition step and the etch back step a plurality of times, the thickness of the second mask 14 to be used in the in-opening etching step to be described later is set to a desired thickness, for example, 1 μm to several μm (3 to 5 μm). Adjust to the degree.

  When the thickness of the second mask 14 is adjusted to a desired thickness in this way, the inside of the opening 12 is etched using the second mask 14 and the first mask 11 as shown in FIG. Then, an opening 12a having an opening narrower than the previously formed opening 12 is formed. Thereby, the recessed part 15 which combined the opening part 12 formed previously and the newly formed opening part 12a is obtained (etching process in opening part).

Here, in the etching in the opening 12, that is, the etching of the silicon substrate 10, SF ₆ gas plasma is generated by the same inductively coupled (ICP) etching apparatus in the same manner as in the opening forming process and the etch back process. Do it by using. However, the etching of the silicon substrate 10 has a mechanism different from that in the case where the polymer film 13 is removed by etch back (etch back process), and is a chemical reaction between F radicals (F ^* ) generated by SF ₆ gas plasma and silicon. Progresses and thus causes an isotropic etching reaction.

  However, in the present invention, in the etching process in the opening, as in the opening forming process, the etching depth is sufficiently shallow, for example, several μm (about 1 to 5 μm), and the side wall of the opening 12 thus obtained is obtained. Etching is stopped in a state where the etching in the direction hardly proceeds. Thereby, even in this in-opening etching process, it can be made to act as anisotropic etching which is not substantially isotropic.

  In addition, by adjusting the thickness of the second mask 14 by the deposition step and the etch back step and performing the in-opening etching step once, respectively, as shown in FIG. One stepped step 16 can be formed on the side wall. At this time, the width of the step portion 16 is equal to the thickness of the second mask 14, and the height (depth) of the step portion 16 is equal to the etching depth in the in-opening etching step.

  Next, the polymer film 13 deposition step shown in FIG. 1C and the etch-back step shown in FIG. 1D are sequentially performed, and these steps are repeated a predetermined number of times, so that FIG. As shown in FIG. 3, a polymer film having a desired thickness is further laminated on the inner surface of the recess 15, that is, on the second mask 14 previously formed. Thereby, the thickness of the second mask is adjusted to obtain a new second mask 16.

Next, as shown in FIG. 2B, the recess 15 (in the opening 12) is etched using the second mask 16 and the first mask 11, and an opening having an opening narrower than the previously formed recess 15 is formed. A portion 15a is formed. Thereby, the recessed part 17 which combined the recessed part 15 formed previously and the newly formed recessed part 15a is obtained.
Hereinafter, the adjustment of the thickness of the second mask shown in FIG. 2A and the etching process in the recess 17 (in the opening 12) shown in FIG. 2B are repeated a desired number of times. As shown in FIG. 2C, the second mask 18 and the corresponding recess 19 are formed.

Thereafter, the second mask 18 and the first mask 11 are selectively removed by removing means such as plasma etching having a selectivity with respect to silicon or wet etching, for example, as shown in FIG. Then, for example, a silicon substrate 10 having a recess 19 having a depth of about 70 μm is obtained.
The recess 19 processed in this way has an inner surface that expands in a stepped manner toward the opening, and each step is very small, for example, about 1 to 5 μm. The side surface is substantially an inclined surface.

  Further, as described above, by setting the thickness of the second mask and the etching depth at the time of the in-opening etching step as appropriate, the inclination angle of the inner surface of the obtained recess 19 can be changed to the processing of the silicon substrate 10. It can be formed at a desired inclination angle, for example, within a range of 30 ° to 60 ° with respect to the surface (surface) 10a. That is, as described above, the width of the stepped step portion is equal to the thickness of the second mask, and the height (depth) of the step portion is equal to the etching depth in the in-opening etching process. By setting appropriately, the inclination angle of the inner surface of the obtained recess 19 can be formed to a desired inclination angle.

  In such a method of forming the concave portion 19, that is, a method of processing an inclined shape on the inner surface, the inclination angle of the inner surface can be formed to a desired inclination angle. In addition, since the adjustment of the thickness of the second mask by the deposition step and the etch-back step and the etching process in the opening can be performed in the same apparatus, the adjustment of the thickness of these second masks can be performed. Even if the in-opening etching process is repeated a plurality of times, there is no loss of moving the silicon substrate 10 (base) between apparatuses each time, and therefore the cost and productivity can be dramatically increased.

  The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the gist of the present invention. For example, in the above embodiment, the recess is formed in the silicon substrate (base). However, when the hole (through hole) penetrating the silicon substrate is formed instead of the recess having such a bottom surface, the processing of the present invention is performed. The method can also be applied. When the present invention is applied to processing such a through hole, for example, a trumpet shape (tapered shape) of a nozzle in a droplet discharge head can be obtained by the processing method of the present invention.

  Moreover, in the said embodiment, although each level | step difference in the staircase shape of the inner surface of the formed recessed part 19 was made into the substantially inclined surface by making it very small, for example about 1-5 micrometers, each said level | step difference was made comparatively. By increasing the size, for example, the present invention can be applied to processing of a step shape for an adhesive relief groove of a cavity in a droplet discharge head, for example.

Furthermore, in the above-described embodiment, the silicon substrate is used as the base. However, when a silicon chip having a predetermined function is used as the base and a recess or a hole is formed for the purpose of adding another function to the base, for example, You may make it apply invention.
Further, the present invention can be applied to various fine processing such as etching processing in three-dimensional mounting of an IC chip and a manufacturing method of a semiconductor device in addition to processing of a MEMS device.

(A)-(e) is process explanatory drawing which shows one Embodiment of the processing method of this invention. (A)-(d) is process explanatory drawing which shows one Embodiment of the processing method of this invention. (A)-(d) is process explanatory drawing which shows an example of the conventional processing method.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Silicon substrate (base | substrate), 11 ... 1st mask, 12, 12a ... Opening part, 13 ... Polymer film, 14, 16, 18 ... 2nd mask, 15, 15a, 17, 19 ... Recessed part (opening part)

Claims (3)

When forming a recess or a hole in the surface of the substrate, an inclined shape processing method for substantially inclining the inner surface of the recess or hole,
A first mask forming step of forming a first mask corresponding to the opening shape of the recess or hole on the substrate;
Etching the base using the first mask to form an opening of a recess or hole to be formed; and
Depositing a polymer to form a polymer film on the first mask and in the opening;
Etch back the entire surface of the polymer film, leaving the polymer film on the inner surface of the first mask and the inner surface of the opening, and using this as a second mask;
And an in-opening etching process for etching the inside of the opening using the first mask and the second mask,
By repeating the deposition step and the etch back step a plurality of times, the thickness of the second mask used in the in-opening etching step is adjusted to a desired thickness,
The inner surface of the opening is substantially inclined by adjusting the thickness of the second mask by the deposition step and the etch-back step and repeating the etching process in the opening a plurality of times. Inclined shape processing method.   2. The inclined shape processing method according to claim 1, wherein a substantial inclination angle of an inner side surface of the opening with respect to a surface of the base is set to 30 ° or more and 60 ° or less.   3. The inclined shape processing method according to claim 1, wherein the substrate is made of silicon.

Images