JP3944585B2 - Vertical surface fabrication method by dry etching - Google Patents

Description

  According to the present invention, when dry-etching a three-dimensional shape of a MEMS using a semiconductor material by an RIE apparatus, a vertical surface can be manufactured with high accuracy in order to improve the performance of a reflective surface such as an optical switch. The present invention relates to a vertical side surface manufacturing method by dry etching, and a dry etching processing apparatus for performing the manufacturing method.

  2. Description of the Related Art An RIE (Reactive Ion Etching) apparatus that performs high-speed dry etching of silicon with high-density plasma has been widely used for three-dimensional shape fabrication of MEMS (Micro Electro Mechanical Systems) using semiconductor materials. Etching anisotropy can be strengthened by processing using an RIE apparatus, and a substantially vertical etching side surface can be realized. Various MEMS devices have been developed using this.

  Among the various MEMS devices described above, optical application MEMS such as an optical switch that uses the vertical side as a mirror greatly affects the performance because the angle and surface roughness of the vertical side greatly affect the performance. It is said.

  When forming a mirror structure by conventional etching, for example, a mask pattern 31 as shown in FIG. 4A is used. In this mask pattern 31, a mask light-shielding portion provided with a contour 34 that coincides with the upper surface shape of a mirror structure 32 as finally produced (c) and defines a mirror surface 33 that is an etching side surface. 35 is formed, and the periphery thereof is a mask transparent portion 36.

  Using this mask pattern 31, the positive resist applied to the surface 38 of the silicon substrate 37 is optically removed as shown in FIG. 4B to form a resist 39 corresponding to the mask light shielding portion 34. . When this silicon substrate 37 is dry-etched, the light-shielding portion of the mask pattern is protected, and portions other than the resist 39 are peeled off and removed by etching. Therefore, the mirror structure 32 as shown in FIG. And a mirror surface 33 which is an etching side surface thereof is formed.

  A dry etching apparatus performs etching by forming a high-density plasma of a reactive gas on the front surface of a workpiece and irradiating the workpiece with ions or radicals in the plasma. In such dry etching, the action of ions / radicals contributing to etching is changed by changing the etching conditions such as the type of reaction gas, gas pressure, high frequency applied power, bias voltage and the like. In particular, when etching is performed under such a condition that most ions are perpendicularly incident on the workpiece, the etching anisotropy becomes extremely strong and the etching proceeds in a direction perpendicular to the surface of the workpiece. At this time, if a pattern of an etching mask is prepared with a photoresist or the like, a vertical side surface can be formed with the contour. These changes in etching shape due to changes in conditions are reported in detail in Non-Patent Document 1 below.

  In addition, a processing technique called the Bosch process, in which etching is performed while protecting the etching side surface by alternately switching between a gas that causes etching by plasma and a gas that causes deposition of a protective film by plasma, is also practical. It has become. A number of MEMS devices such as an optical communication switch for controlling a light signal by combining the vertical side surface with an actuator or the like to form a movable mirror have been proposed in, for example, Patent Document 1 below.

In addition, by using various methods as described above, a mold whose shape is transferred using a technique such as plating based on an original made of silicon is used, and the same shape as the original is made using a molding process. Research on the production of plastic and glass ultra-compact parts having the above has been reported, for example, in Non-Patent Document 2 below.
JP 2001-56440 A Henri Jansent, Han Gardeniers, Meint de Boer, Miko Elwenspoek, Jan Fluitman, J. Micromech. Microeng. 6 (1996) 14-28.A survey on the reactive ion etching of silicon in microtechnology Yusuke Hashiura, Tsuyoshi Ikehara, Akiko Kitajima, Hiroshi Goto, Ryutaro Maeda, Device and Process Technologies for MEMS and Microelectronics ll, Jung-Chiao, Editor, Proceedings of SPIE Vol. 4592 (2001), 414-421, Optical switch array based on microforming process

  When a groove having a relatively narrow width of about several μm to 100 μm is produced by dry etching as described above, the verticality of the etching side surface is kept well, and by adjusting the etching conditions such as gas pressure, the conventional technique can also be ± A vertical accuracy of about 0.1 degree can be realized.

  However, considering use as a mirror on the vertical side, a space of 500 μm or more is usually required in front of the mirror surface in order to ensure a light path, and the etching width must be increased.

  For example, in the example of the dry etching processing apparatus 41 shown in FIG. 6, a workpiece wafer 47 is fixed on the lower electrode 48 between the opposed upper electrode 42 and lower electrode 48, and high frequency is applied to both electrodes in a reactive gas atmosphere. When a voltage is applied, a plasma glow 43 is generated from the upper electrode 42 to the workpiece wafer 47 on the lower electrode 48, and ions and radicals 45 are generated from the boundary of the plasma glow toward the surface of the workpiece wafer 47. When processing conditions with strong anisotropy are applied, all of these ions and radicals initially proceed perpendicular to the surface of the workpiece wafer 47.

  Thereafter, in the portion where the etching mask 46 is not formed on the surface of the workpiece wafer 47, etching proceeds by the ions / radicals 45. When the width of the portion where the etching mask 46 is not formed is narrow, a groove as shown as a narrow groove 49 in the drawing is formed. When the width of the portion is wide, the groove as shown as a wide groove 50 in the drawing. Is formed. As apparent from FIG. 6, in the portion where the narrow groove 49 is formed, the etching proceeds vertically, so that grooves whose groove side walls are parallel to each other are formed. On the other hand, in the portion where the wide groove 50 is formed, the plasma glow boundary deforming portion 44 protrudes toward the groove bottom which is processed as shown in the drawing as the etching progresses and the groove bottom advances downward. To occur.

  Since the side surface of the boundary deformation portion 44 of the plasma glow 43 as described above has a gentle protruding deformation unlike the shape of the groove to be formed, the side surface has an inclined shape. Therefore, ion radicals radiated from the boundary of the plasma glow 43 are radiated from the side surface of the boundary deformation portion 44 so that the groove sidewall 51 of the wide groove 50 is formed to be inclined by side etching.

  Thus, when the groove formed in the workpiece wafer 47 is a narrow groove 49, the groove side wall 51 is formed at a right angle from the surface, whereas when the groove 50 is wide, the groove side wall 51 is illustrated. Inclined to. Therefore, when a rectangular mirror having a width of 500 .mu.m, a thickness of 100 .mu.m and a height of 120 .mu.m is produced when performing etching by the conventional method shown in FIG. 4, as shown in the micrograph of FIG. An inclined side surface having an inverse taper angle is formed. In the illustrated example, the angle of the etching side surface was 87 degrees to 89.5.

  In FIG. 7, when the silicon single crystal is dry-etched under two different conditions while alternately switching between two kinds of gases, the etching gas SF6 and the deposition gas C4F8, the angle of the etching side surface changes depending on the etching groove width. The actual measurement result is shown. When the groove width is about 10 μm to 100 μm, it is possible to make the side surface angle almost 90 degrees by adjusting the etching conditions. However, when the groove width is 200 μm or more, it becomes difficult under any condition, and the surface angle is 1 mm or more. The groove width causes a large deviation from the vertical, and the remaining mirror structure has an inversely tapered shape as described above. Therefore, the angle of the vertical side surface manufactured using an etching mask having a wide opening is only about 89.5 degrees even if the etching conditions are optimized.

  From the experimental results shown in FIG. 6, by adjusting the etching conditions, the side surface formed by etching is set to be formed at a right angle as much as possible, and conversely, the side surface is inclined as much as possible. It can be seen that the processing can be performed by arbitrarily selecting these in the case of setting to do so. In the present invention, by utilizing this property, it is possible to select a case where it is formed at a right angle from a side surface to be formed and a case where it is formed with a large inclination, as will be described later. .

  Even if such an error from the vertical is slight, an optical axis shift occurs when used as an optical device, causing an insertion loss of the amount of light and making it difficult to adjust the optical axis at the time of manufacture. Therefore, when the vertical side surface is used as a mirror as described above, when a space of 500 μm or more is provided in front of the mirror surface in order to secure a light path, the portion must be a wide groove, and therefore The mirror has an inclined shape, and a desired vertical mirror surface cannot be formed.

  In addition, since the groove side surface has a reverse taper shape as described above, in addition to manufacturing the optical device as described above, when performing a molding process using a mold made by dry etching as a prototype, In hot embossing and injection molding, there is also a problem that product omission becomes worse.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a method for manufacturing a vertical surface by dry etching, which can easily form an accurate vertical side surface by dry etching, and to provide an apparatus for performing the method. To do.

In order to solve the above problems, a vertical surface manufacturing method by dry etching according to the present invention is a vertical surface manufacturing method in which a wide space is formed by dry etching before a vertical side surface of a structure. The first etching process is performed using the first mask pattern for forming the narrow groove having the matching contour, and the vertical plane formation characteristic by the first etching process for forming the thin groove is used to form the structure. The second mask pattern is used to form a vertical side surface, and then use a second mask pattern to etch away a wide surface having a contour at a position farther from the structure side surface than the groove formed by the first etching process. It was etched by the inclined etched surface forming properties extending in the depth direction caused by a second etching process in the wide surface, the second d A portion adjacent to the space to be removed by the chucking process and adjacent to the first etching groove and not removed by the first and second etching processes is separated from the silicon substrate at the bottom of the groove. By removing the resist of the two-mask pattern and removing the portion separated from the silicon substrate , a wide space is formed by the second etching process in front of the vertical side surface of the structure formed by the first etching process. It is what I did.

  In another vertical surface manufacturing method by dry etching according to the present invention, in the vertical etching method by dry etching, in the first etching process, a processing condition for forming a uniform thin groove in a depth direction is selected. This is what we do.

  According to another aspect of the present invention, there is provided a method for manufacturing a vertical surface by dry etching. In the method for manufacturing a vertical surface by dry etching, in the second etching process, the depth depends on the progress of the process from the processing conditions of the first etching process. The processing conditions for forming the side surfaces inclined in the direction are selected and performed.

  The dry etching is divided into two processes, a first etching process with a narrow width for defining the outline of the groove and a second etching process for removing the remaining large area, thereby performing the first etching process. This makes it possible to stably and precisely control the etching side surface angle, and to form a highly accurate side surface with high accuracy. At this time, the vertical error can be reduced from about ± 0.5 degrees to about ± 0.1 degrees.

  In addition, the second etching process performs etching to remove a large area, thereby forming an etching side surface inclined from the outside to the inside of the part where the first etching is performed, and an unnecessary part remaining in the first etching process. Can be easily removed. Moreover, even if the first mask pattern and the second mask pattern are misaligned, a desired structure can be reliably formed without causing etching residue or double etching as shown in FIG.

  By manufacturing the mirror of the optical switch with this technology, the deflection from the preset optical axis is reduced and precise optical path adjustment is possible, so lower insertion loss can be obtained with less assembly adjustment. It is possible to contribute to high performance and low cost of an optical switch which is a basic component in the optical communication field.

  In addition, it is possible to improve the difficulty of removal due to reverse taper in a molding process in which a mold is manufactured using the manufactured etching shape as a prototype.

  The present invention manufactures a structure that uses a vertical side surface formed by dry etching a region having a wide etching width so that a precise vertical side surface can be easily formed by a dry etching process. In this case, first, a first etching process is performed using a first mask pattern for forming a narrow groove having a contour that matches the side surface of the structure, and then a groove formed by the first etching process is performed. A second etching process is performed using a second mask pattern for etching away a wide surface having a contour at a position farther from the structure side surface than the width, and the contour of the second mask pattern is obtained by the second etching process. And a portion between the contours of the first mask pattern is removed.

  As in the example shown in FIG. 4, the vertical surface manufacturing method and apparatus according to the present invention is a rectangular single-walled substrate having a vertical wall surface on a silicon single crystal substrate and having a width of 500 μm, a thickness of 100 μm, and a height of 120 μm. A description will be given based on an example of manufacturing a mirror.

  First, a first mask pattern as shown in FIG. The first mask pattern 1 shown in FIG. 1A includes a first central mask light shielding portion 2 similar to the mask light shielding portion 35 of the mask pattern 31 shown in FIG. A peripheral mask light-shielding part 5 is provided that has a peripheral mask contour 4 that is a distance a from the first central mask contour 3, which is the contour of the first central mask light-shielding part 2. In the example shown in the figure, a mask transparent portion 8 having the distance a uniformly set to 70 μm is formed.

  When the resist 7 is formed on the silicon substrate 6 using the first mask pattern 1, as shown in FIG. 1B, the first resist pattern 9 from which the resist 7 having a width of 70 μm is removed is formed. . When the first etching process is performed using this resist 7, grooves 10 having side surfaces parallel to the right angle from the surface of the silicon substrate 6 are formed as shown in FIG.

  At this time, the etching side angle of the etching region having a width of 70 μm can be controlled to 89.9 degrees to 90.1 degrees by adjusting the etching conditions as in condition 2 in FIG.

  When the etching is performed to a predetermined depth, that is, the depth of 120 μm, which is the height of the mirror to be formed, the processing is stopped and the resist 7 on the surface is peeled off. The state is shown in FIG. Thereafter, for the second etching process to be performed next, as shown in FIG. 1E, the second resist 11 is uniformly applied to the entire surface. In this case, the resist is applied by spray coating or the like so that the resist is reliably applied also to the peripheral wall of the narrow groove 10.

  Next, a second mask pattern 12 as shown in FIG. The second mask pattern 12 shown in FIG. 1 (f) has a second central mask light shielding part 13 at the center thereof, and the second central mask light shielding part 13 is a peripheral mask contour 4 in the first mask pattern 1. It is set so as to be located outside by a distance b. In the illustrated example, the distance b is 3 μm.

  When the second resist 11 in FIG. 1E is removed using the second mask pattern 12, a second resist pattern 14 as shown in FIG. 1G is formed. As shown in FIG. 1G, the contour 15 of the second resist pattern 13 formed at this time extends further to the position outside the outer wall 16 of the groove 10 shown in FIG. Covered with a second resist 14.

  At this time, when the alignment error is within 3 μm, the protection length around the groove is 0 μm minimum and 6 μm maximum. Therefore, the groove 10 formed by the first etching process is completely protected by the photoresist.

  Thereafter, a second etching process is performed with the second resist pattern 14 formed as shown in FIG. At this time, if a large etching condition for side etching as shown in condition 1 in FIG. 6 is selected, the etching width may be wide, and the angle α of the side surface 17 is about 87 degrees. The side etching width at this time is 120 μm / tan 87 degrees = 6.3 μm when etching is performed at a depth of 120 μm. Even when the protection length around the groove is 6 μm at the maximum, the first etching groove and its groove Connection occurs at the bottom.

  Next, when the second resist 14 is peeled off, the remaining wafer 18 is removed and discharged as described above. In the final product structure 19 formed in this way, as shown in FIG. 1 (i), the angle of the side surface 20 is maintained at 89.9 to 90.1 degrees during the first etching. FIG. 2 shows a scanning electron micrograph of the actual prototype shape.

  Normally, when etching is performed twice in this way, unnecessary interference structures such as protrusions due to etching residue and grooves due to double etching as shown in FIG. 3 occur due to slight alignment errors during lithography. It will occur. However, the method according to the present invention uses the fact that side etching proceeds in the lateral direction for the second time, and creates a gap of a slight distance b in the first and second etching masks, thereby causing an alignment error. However, the etching connected to the first groove can be performed without generating an unnecessary interference structure.

Thus the production how as described above by etching a narrow trench in the first etching, almost exactly sides perpendicular structures can be obtained, be dropped all the second etching large areas remaining it can. In particular, by utilizing the side etching effect of the etching side surface that occurs at this time, even if a slight gap is formed between the first and second etching masks, the etching can be connected to the first groove. Interference structures associated with alignment errors can be avoided.

  By manufacturing the mirror of the optical switch using the technology of the present invention, the deflection from the preset optical axis is reduced and precise optical path adjustment is possible, so lower insertion loss and less assembly adjustment And can contribute to higher performance and lower cost of an optical switch which is a basic component in the field of optical communication.

  For example, when the optical path length after reflection by the mirror is 5 mm, the deflection of the spot position due to the side surface angle error is ± 44 μm when the angle error is ± 0.5 degrees, and ± 9 μm when the angle error is ± 0.1 degrees. The diameter of the core of the communication optical fiber is about 9 μm in the case of the thinnest single-mode fiber, so that a light beam that was not incident on the optical fiber at all without adjustment is now incident on the core even without adjustment. The optical axis adjustment can be greatly simplified.

  Since the present invention can realize a highly accurate verticality on the vertical side surface, the present invention is particularly suitably used for an optical switch which is a basic component in the field of optical communication. Can be used in various fields.

It is the figure which demonstrated the example of the vertical surface preparation method by the dry etching of this invention in order. It is a microscope picture which shows the external shape of the mirror structure produced by this invention. It is a figure which shows the influence of the alignment error when not using a side etching effect. It is a figure which shows the conventional dry etching method. It is a microscope picture which shows the cross section of the mirror structure produced by the conventional etching process. It is a schematic cross section which shows the cause which the perpendicularity of a side surface falls with wide etching width. It is a graph which shows the example of a measurement of the angle change of the side surface when changing the etching width.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 1st mask pattern 2 1st center mask light-shielding part 3 1st center mask outline 4 Perimeter mask outline 5 Peripheral mask light-shielding part 6 Silicon substrate 7 Resist 8 Mask transparent part 9 1st resist pattern 10 Groove 11 2nd resist 12 2nd mask pattern 13 2nd center mask light-shielding part 14 2nd resist pattern 15 Outline 16 Outer side wall 17 Side 18 Remaining wafer 19 Structure 20 Side

Claims (3)

In the vertical surface manufacturing method of forming a wide space by dry etching in front of the vertical side surface of the structure,
First, a first etching process is performed using a first mask pattern for forming a narrow groove having a contour matching the side surface of the structure,
Due to the vertical plane formation characteristics of the first etching process that forms the narrow groove, the vertical side surface of the structure is formed,
Next, a second etching process is performed using a second mask pattern for etching and removing a wide surface having a contour at a position farther from the structure side surface than the groove formed by the first etching process,
Due to the inclined etching surface formation characteristic spreading in the depth direction generated by the second etching process on the wide surface, the first etching groove is adjacent to the space removed by the second etching process and adjacent to the first etching groove. Separating a portion not removed by the first and second etching processes from the silicon substrate at the bottom of the groove;
Finally, by removing the resist of the second mask pattern and removing the part separated from the silicon substrate , a large space is obtained by the second etching process in front of the vertical side surface of the structure formed by the first etching process. Forming a vertical surface by dry etching.   2. The method of manufacturing a vertical surface by dry etching according to claim 1, wherein the first etching process is performed by selecting a processing condition for forming a uniform thin groove in the depth direction.   2. The dry etching process according to claim 1, wherein the second etching process is performed by selecting a process condition for forming an inclined side surface extending in a depth direction as the process proceeds from the process condition of the first etching process. Vertical surface production method by etching.