JPH04280427A - Processing of silicon substrate - Google Patents

Abstract

PURPOSE:To enable a laver portion to be shortened by setting a side-wall of a recessed part vertically for a substrate surface when forming a canrilever with a thin lever part at a base part by machining the recessed part and a penetration groove at the silicon substrate. CONSTITUTION:A recessed part with a sidewall which is vertical to a substrate surface is machined by dry etching using a mixed gas SF6 and O2. Both surfaces are formed by aluminum or the mask on one surface is formed by aluminum and the other is formed by a silicon oxide as the mask in that case. However, the mask may be formed by a silicon oxide for both surfaces when the substrate is thin. An anode coupling system parallel flat plate type device is used for dry etching.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for processing a silicon substrate, in which a mask is provided on the surface of the silicon substrate and dry etching is performed to form recesses for forming cantilevers and through grooves in the substrate.

0002

2. Description of the Related Art In order to manufacture sensors and the like, it is required to form cantilevers of a predetermined size on a silicon substrate. In such a case, the thin part that will become the lever part and the through groove part surrounding the cantilever are processed. Conventionally, a thin film made of silicon oxide and a thin film made of silicon nitride are stacked on the surface of a silicon substrate, a part of which is removed by photolithography, etc., and the removed part is treated with a hydrofluoric acid solution or an alkaline solution. A method of etching was used.

0003

[Problem to be solved by the invention] Figures 2(a) and (b)
2 shows a wet etching method using a hydrofluoric acid solution, and the silicon oxide film 2 and silicon nitride film laminated on the surface of the silicon substrate 1 are partially removed by photolithography. ), openings 41, 42, 43 are provided. Among these, openings 42 and 43 are located at positions facing each other. Then, the openings 41 and 42 are etched using a hydrofluoric acid etching solution.
, 43, the same figure (b) is obtained.
As shown in FIG. 2, the recess 5 and the through groove 6 are machined to form a lever portion 8 to which a thick portion 7 is connected at the tip. However, in the wet etching method using a hydrofluoric acid solution, the etching progresses isotropically, so that the shape of the concave portion 5 of the lever portion formed is rounded and a vertical shape cannot be obtained. Therefore, the length of the lever part 8 becomes shorter than the overall size of the cantilever, and the side wall of the entire cantilever becomes rounded. Therefore, when designing the cantilever when using it as a sensor, etc., there are limited conditions. The disadvantage is that there are many. Furthermore, a processing mask 2,
3, since the thickness of the mask is limited to some extent, there is a limit to the etching depth of the processing recess of the lever part, and this wet etching is necessary when processing a depth of 400 μm or more. Law is not appropriate. Furthermore, this method has a problem in that the shapes of the recesses 5 of the lever portions formed in large numbers within the same silicon substrate vary widely within the silicon substrate 1, resulting in a decrease in yield.

FIGS. 3A and 3B show a wet etching method using an alkaline solution, and parts common to those in FIG. 2 are given the same reference numerals. In the wet etching method using an alkaline solution, which takes advantage of the fact that the etching rate differs depending on the plane orientation of the single crystal silicon substrate,
It is possible to form the accurate shape of the concave portion 5 of the lever part depending on the surface orientation of the single crystal silicon substrate, but since etching depends on the surface orientation, any arbitrary shape can be formed on a single crystal silicon substrate with an arbitrary surface orientation. It is difficult to form a cantilever shape. In addition, since etching cannot be performed from both sides with an alkaline solution, one side must be etched with a hydrofluoric acid solution, and the shape of the through groove 6 on this side is 6.
As shown by 1, the shape of the through groove 6 becomes complicated, which causes a decrease in yield. Furthermore, since both methods use acids and alkalis, there is a problem in that workability is very poor.

[0005] An object of the present invention is to provide a method for processing a silicon substrate in which a recess and a through groove having side walls perpendicular to the silicon substrate surface can be formed due to the cantilever shape.

[0006]

[Means for Solving the Problems] In order to achieve the above object, the present invention has a cantilever that has a thin lever portion at the base by processing a recess and a through groove, and is surrounded by the through groove. In the method for processing the silicon substrate to be formed, masks are formed on both sides of the silicon substrate, and etching is performed from both sides by dry etching using a mixed gas of sulfur hexafluoride and oxygen. Advantageously, the mask is made of aluminum or silicon oxide. Then, a mask made of aluminum or a mask made of silicon oxide may be formed on both sides of the silicon substrate, or a mask made of aluminum may be formed on one side of the silicon substrate, and a mask made of silicon oxide may be formed on the other side. may be formed.

[0007]

[Operation] The dry etching reaction mechanism of the present invention is considered to be as follows. First, a mixed gas of SF6 and O2 dissociates in the plasma to generate F radicals and O radicals. Next, the Si atoms of the silicon substrate and O radicals react, and SiO is produced as an intermediate product. This intermediate product, SiO, reacts with F radicals, resulting in SiF
4 is produced, and since this SiF4 has a very low boiling point, it is naturally exhausted. During etching, as described in Japanese Patent Application No. 1-275222 filed by the present applicant, the sidewalls of the recesses are exposed to the oxygen present in the plasma.
It is temporarily oxidized by radicals and the like, and the etching progresses while the side wall is protected by the temporary oxide. This state is maintained until a predetermined recess is formed in the silicon substrate. Therefore, a recess is formed having sidewalls perpendicular to the main surface of the silicon substrate.

When aluminum is used as a mask, it has a high etching selectivity with respect to silicon, so it is suitable for forming deep recesses and through grooves in thick substrates. However, a silicon oxide film mask can also be used to form a shallow recess or a through groove in a thin substrate.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1(a), 1(b), and 1(c) show an embodiment of the present invention, and parts common to those in FIGS. 2 and 3 are given the same reference numerals. As shown in Figure (a), on both sides of a silicon substrate 1 with a thickness of approximately 500 μm,
A thin film 9 made of aluminum with a thickness of μm is formed. Furthermore, the aluminum thin film 9 is removed using a phosphoric nitric acid-based etching solution so that the silicon substrate 1 of the parts to be processed 41, 42, 43 is exposed, and an aluminum mask pattern is formed on the silicon substrate 1. Next, one side at a time is etched using an anodic bonding type parallel plate type dry etching apparatus as shown in FIG. This device is described in Japanese Patent Application No. 1-102028 filed by the present applicant, in which a lower electrode 12 which also serves as a stage and an upper electrode 13 are placed in a reaction chamber 11 with a width of 10 to 90 mm. They are facing each other at a distance within range. Exhaust pipes 15 are distributed around the bottom plate 14 of the reaction chamber and open toward the center of the lower electrode 12 in parallel with the bottom plate. A high frequency power source 17 is connected to the upper electrode 13 via a matching tuner 16. A gap 20 between the top 18 of the reaction chamber 11 and the connecting body 19 of the upper electrode 13 serves as an introduction port for the reaction gas 21 . A silicon substrate 1 with an aluminum mask 9 pattern formed thereon as shown in FIG. 1(a) is placed on the lower electrode stage 12 in the reaction chamber 11 of such an anodic bonding type parallel plate dry etching apparatus. Oxygen gas mixture ratio is 1 to 11.
A mixed gas 21 of sulfur hexafluoride gas and oxygen gas selected in the range of 50% is introduced, and the inside of the reaction chamber 11 is heated to 10 to 80 Pa.
A high-frequency power of 0.3 to 1.5 W/cm2 is applied between the lower electrode 12 and the upper electrode 13 while maintaining the pressure at 100 to 1000 nm, so that the silicon exposed in the mask openings 41, 42, and 43 and the inside of the plasma 22 are heated. The exposed silicon is removed by causing a physicochemical reaction between the radicals and reactive gas ions present in the silicon substrate 1, and as shown in Figure 1(b), a silicon substrate 1 with a thickness of about 30 μm and a width is formed. A recess 5 having a side wall perpendicular to the substrate surface is formed, leaving a lever portion 8 of approximately 800 μm. At this time, a recess 60 forming a part of the through groove 6 is also formed. Next, the silicon substrate 1 is turned over and placed on the lower electrode stage 12 so that the mask opening 43 is exposed, and the silicon substrate 1 is processed from the mask opening 43 as shown in FIG. 1(c). Width perpendicular to the board surface 400
A through groove 6 of about μm size is formed. Thereby, a cantilever consisting of the lever portion 8 to which the thick portion 7 is connected can be formed. A plurality of such cantilevers can be simultaneously formed on one silicon wafer.

Another embodiment of the present invention shown in FIGS. 5(a) and 5(b) has a thickness of approximately 500 mm as shown in FIG.
A thin film 2 made of a silicon oxide film with a thickness of about 1 μm is formed on one side of a silicon substrate 1 with a thickness of about 1 μm, and a thin film 9 made of aluminum with a thickness of about 1 μm is formed on the opposite side. Further, the silicon oxide film 2 and the aluminum film 9 are removed using a hydrofluoric acid-based etching solution so that the silicon substrate 1 of the parts to be processed 41, 42, 43 is exposed, and a mask pattern is formed on the silicon substrate 1. Silicon oxide film 2
is formed by, for example, a thermal oxidation method. Next, etching was performed from both sides under the same conditions as in the example described in FIG. 1, and as shown in FIG. Can be formed at the same time. In particular, when processing the opening 43 of the silicon oxide film mask 2 by dry etching as in this embodiment, the side side Since the etching time is halved, this method is extremely advantageous when creating cantilevers surrounded by narrow through grooves in silicon substrates. It is also effective when an aluminum mask cannot be used, such as when a semiconductor element is formed on a cantilever.

However, since the silicon oxide film 2 has a smaller selectivity to silicon than aluminum in dry etching using a mixed gas of SF6 and O2,
Although it cannot be used as a double-sided mask when machining deep recesses 5 or machining through grooves 6 in thick substrates 1,
It can be used as a double-sided mask when processing a silicon substrate with a size of about μm or less.

0012

[Effects of the Invention] According to the present invention, by dry etching using a mixed gas of SF6 and O2 with a mask made of aluminum, silicon oxide, etc., the concave portion of the lever portion in the silicon substrate has side walls perpendicular to the substrate surface. A cantilever can be formed. Therefore, since the length of the lever portion can be made longer than the overall size of the cantilever, there is an advantage that there is more leeway in the design when the cantilever is used as a sensor or the like. In addition, high productivity is ensured because a large number of cantilevers having side walls perpendicular to the surface can be formed uniformly and simultaneously within a large-diameter silicon wafer. Furthermore, in the case of the present invention,
Since silicon cantilevers of the same size can be formed at any location using a mask, it is possible to form cantilevers of a size that meets the requirements for manufacturing acceleration sensors and micromechanical parts on a silicon substrate.

[Brief explanation of the drawing]

[Fig. 1] (a), (b) shows a processing method according to an embodiment of the present invention.
), (c) in this order.

[Figure 2] Cross-sectional views showing an example of a conventional processing method in the order of (a) and (b)

[Figure 3] Cross-sectional views showing other examples of conventional processing methods in the order of (a) and (b)

[Fig. 4] Cross-sectional view of a dry etching apparatus used in an embodiment of the present invention

FIG. 5 shows processing methods of different embodiments of the present invention (a),
Cross-sectional views shown in the order of (b)

[Explanation of symbols]

1 Silicon substrate 2 Silicon oxide film 41 Mask opening 42 Mask opening 42 Mask opening 5 Recessed part 6 Through groove 8 Lever part 9 Aluminum film

Claims (6)

[Claims] 1. A method for processing a silicon substrate in which a cantilever having a thin lever portion at the base and surrounded by the through groove is formed by processing a recess and a through groove, wherein masks are formed on both sides of the silicon substrate. A method for processing a silicon substrate, characterized in that the silicon substrate is etched from both sides by dry etching using a mixed gas of sulfur hexafluoride and oxygen. 2. A method for processing a silicon substrate according to claim 1, wherein the mask is made of aluminum. 3. The method according to claim 1, wherein the mask is made of silicon oxide. 4. The method according to claim 1 or 2,
A silicon substrate processing method that forms masks made of aluminum on both sides of the silicon substrate. 5. The method according to claim 1 or 3,
A silicon substrate processing method that forms masks made of silicon oxide on both sides of the silicon substrate. 6. A method of processing a silicon substrate according to claim 1, wherein a mask made of aluminum is formed on one side of the silicon substrate and a mask made of silicon oxide is formed on the other side.