JP3446244B2 - Manufacturing method of micromachine - 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 of manufacturing a micromachine to which a photofabrication technique is applied, and more particularly to a method of simplifying a sacrifice layer forming and removing process.

[0002]

2. Description of the Related Art Today's advanced information society is supported by advanced electronics technology capable of producing more than one million transistors on a semiconductor chip of several millimeters square. In response to such miniaturization of electric elements, miniaturization of mechanical elements that enable spatial movement was proposed in the 1980s. What embodies this is a micromachine,
It is expected to have a wide range of applications such as various sensors, ultrasonic resonators, fine work machines, and narrow work machines.

In order for a micromachine to have a high level of function, it is essential to integrate a sensor, a control circuit, an actuator and the like. However, the work of assembling these microscopic elements of the order of μm cannot be realized by extension of conventional machining techniques. Under such circumstances, most of the micromachines currently being researched are formed on a silicon substrate, and the fine processing technology cultivated in semiconductor integrated circuits is applied to the processing of each part.

Among them, the photofabrication technique for collectively transferring the pattern on the photomask by projection exposure has a characteristic called "preassembly" capable of forming a complicated system into an assembled state. , It has become an extremely important technology for flattening.

This photofabrication technique basically performs planar processing such as patterning a material layer formed on a substrate. However, unlike integrated circuits, micromachines have physically movable parts. Therefore, it is also necessary to perform three-dimensional processing for forming a minute structure separated from the substrate and a complicated structure such as a fitting portion that holds the minute component in a predetermined positional relationship.

[0006] The three-dimensional processing can be realized to some extent by wet etching or the like, which makes good use of the dependence of the etching rate on the crystal plane orientation, but the most distinctive and unique technique in micromachine manufacturing is sacrifice layer etching. . This requires that the periphery of a pattern which will be a movable part in the future is surrounded by a material having a selective ratio with the pattern, that is, a sacrifice layer (also referred to as a separation layer), and finally the pattern needs to be separated from the substrate. This sacrificial layer is sometimes removed under isotropic etching conditions. With this technique, gears, rotors, etc. that rotate away from the substrate are actually created.

As an example, a typical electrostatic micromotor manufacturing process is shown sequentially in FIGS. First, as shown in FIG. 3A, a SiO _x sacrificial layer 13 and a polysilicon layer 14 are sequentially deposited on the entire surface of a substrate 11 on which a polysilicon electrode 12 is formed in a predetermined pattern by a CVD method or the like. Here, the substrate 11 is, for example, a single crystal Si substrate whose surface is thermally oxidized and further Si _x N _y is deposited by, for example, a plasma CVD method. Further, the polysilicon layer 14 is finally formed on the substrate 11
Is a part of the rotor of the electrostatic micromotor which is separated from.

Next, as shown in FIG. 3B, the polysilicon layer 14 and the SiO _x sacrificial layer 13 are etched using a common resist mask (not shown). By this etching, the polysilicon layer 14 is removed to the rotor 1
A prototype of 4a is formed. Next, as shown in FIG. 3C, a SiO _x sacrificial layer 15 is deposited on the entire surface of the base.

Further, as shown in FIG. 3D, the above S is formed by photolithography and dry etching.
The iO _x sacrificial layer 15 is patterned. As a result, the rotor 14a is completely surrounded by the SiO _x sacrificial layers 13 and 15.

Next, as shown in FIG. 4E, a polysilicon layer 16 is deposited on the entire surface of the substrate. Further, this is patterned by photolithography and dry etching, and as shown in FIG.
A hub 16a is formed on the inner peripheral side and a stator 16b is formed on the outer peripheral side. Finally, this wafer is dipped in a dilute hydrofluoric acid solution to remove the SiO _x sacrificial layers 13 and 15 by etching, and as shown in FIG. 4G, the rotatable rotor 14a separated from the surrounding structure is obtained. Can be obtained.

[0011]

By the way, the above-mentioned SiO_x
The sacrificial layer 15 forms the fine rotor 14a during the formation process.
After being completely bent and removed by etching, the circumference of the rotor 14a is
Since it is a part that creates minute voids in the
High-precision photolithography technology required for turning
To be done. In the above process, the process shown in FIG.
The extent is exclusively SiO _xTo pattern the sacrificial layer 15
It is provided in.

However, when photolithography is performed once, it goes without saying that each step of exposure, development, and etching is increased by one extra step, and various steps for producing one photomask are accompanied, and Minute throughput and economy are reduced.

As described above, the SiO _x sacrificial layer 13,
The formation of 15 is generally done by a dry process, while its removal is done by a wet process. Therefore, there is a concern that the number of required facilities will increase, and that the number of processes required for opening the substrate to the atmosphere, cleaning / drying after etching, and the like will decrease, and the throughput will decrease. Therefore, the present invention simplifies the manufacturing process by devising the step of forming the sacrificial layer,
It is an object of the present invention to provide a micromachine manufacturing method capable of improving throughput and economical efficiency.

[0014]

The present invention has been proposed in order to achieve the above-mentioned object, and a sacrificial layer surrounding a first material layer processed into a predetermined pattern is sacrificed. A second overlying layer that partially shields the first layer of material
In the method for manufacturing a micromachine, in which the movable member is formed with the first material layer released from the substrate by isotropically removing the sacrificial layer after forming the material layer of A portion surrounding the side wall portion of the pattern is formed in a self-aligned manner by plasma CVD using a sublimable and / or thermally decomposable deposition material,
The second material layer is formed of amorphous silicon while maintaining the substrate in a temperature range where the sacrificial layer is not sublimated.

Further, according to the present invention, the second material layer is made of polycrystalline silicon when sublimating and removing the portion surrounding the side wall portion of the pattern made of the first material layer in the sacrificial layer.

The present invention further uses at least one of sulfur and sulfur nitride compounds that are dissociated from the source gas as the depositable substance.

[0017]

The inventor of the present invention considers that a sacrificial layer that can be removed isotropically is formed by a dry process that is continuous with the deposition process, not by wet etching, and sublimation and / or thermal decomposition deposition is performed. Focused on organic substances. The sublimable substance having a sublimable property or a thermal decomposable property, or both of these properties is deposited on the surface of the substrate as long as the temperature of the substrate is maintained at a temperature range sufficiently lower than the sublimation point or the decomposition point, and the deposition material as a sacrificial layer Can perform a function. On the other hand, if the substrate is heated to a temperature range higher than the sublimation point or the decomposition point, these depositable substances are easily sublimated or decomposed.
Immediately before the sacrifice layer is removed, the material layer (second material layer) formed on the sacrifice layer is usually dry-etched, so that the substrate is practically heated in the same etching chamber. Alternatively, the sacrificial layer can be removed by transferring the substrate to another chamber connected under high vacuum and heating the substrate there. Sublimation products and decomposition products are discharged to the outside of the chamber by a high vacuum exhaust flow.

Here, if the entire sacrificial layer is formed by using such a depositing material, the wet process for removing the sacrificial layer is completely unnecessary. However, in this case, it is necessary to perform photolithography once in order to pattern the sacrificial layer itself made of a depositable substance. Therefore, it is premised on selection of a depositable substance that can exist stably even after the resist process and establishment of a practical dry etching method for the depositable substance.

On the other hand, when the side wall portion of the pattern of the material layer (first material layer) which will be the movable member in the future is formed of the above-mentioned depositing substance, this portion is self-aligned. There is a merit that you can do it. This is because, for example, on the vertical ion incident surface of the substrate installed facing the plasma, the deposition process of the depositable substance and the sputter removal process are exactly opposed to each other, and the deposition is performed only on the side wall surface of the pattern where vertical ion incidence does not occur. This is possible by adopting conditions that allow the progress. In this case, the sacrificial layer that surrounds the material layer to be the movable member in the vertical direction needs to be formed by using, for example, SiO _x as in the conventional case, but the patterning of the upper and lower sacrificial layers is common to the material layer. Since it can be performed using the resist mask of No. 3, the number of times of photolithography is not increased.

In the present invention, at least one of sulfur (S) and sulfur nitride compounds is used as the depositable substance. The deposition of sulfur as a simple substance is as disclosed in Japanese Patent Application Laid-Open No. 4-84427 by the applicant of the present application, and the sulfur-based compound capable of releasing free S into plasma under discharge dissociation conditions is used. Can be realized. S is removed by sublimation when the substrate is heated to approximately 90 ° C. or higher.

Further, the deposition of the sulfur nitride type compound was previously disclosed by the applicant of the present application in Japanese Patent Application Laid-Open No. 4-354331, and the discharge of a mixed gas containing the sulfur type compound and the nitrogen type compound as described above. This can be achieved by Various kinds of compounds are known as sulfur nitride compounds, and the main component of the side wall protective film in this case is polythiazyl (SN) _x .
The sulfur nitride compound is sublimed or decomposed and removed when the substrate is heated to approximately 130 ° C. or higher.

None of these S and sulfur nitride compounds cause any particle contamination on the substrate after sublimation / decomposition.

[0023]

EXAMPLES Specific examples of the present invention will be described below.

[0024]Example 1 This example applies the present invention to the manufacture of an electrostatic micromotor.
The sacrificial layers on the upper and lower surfaces of the rotor_xLayer, on the side wall
This is an example in which the sacrificial layer is composed of a deposited layer of S. This process
Will be described with reference to FIGS. 1 and 2. First, the figure
As shown in Fig. 1 (a), a poly-
A CVD method or the like is applied to the entire surface of the substrate 1 on which the silicon electrode 2 is formed.
Due to SiO_xThe sacrificial layer 3 and the polysilicon layer 4 are sequentially stacked.
The surface of the polysilicon layer 4 by thermal oxidation.
SiO _xThe sacrificial layer 5 was formed. Here, the substrate 1
For example, the surface of a single crystal Si substrate is thermally oxidized.
Si by plasma CVD method_xN_yLayer deposited
Of. Further, the polysilicon layer 4 is finally formed on the substrate.
1 is separated from the electrostatic micromotor rotor 4a.
It is the part that

Next, as shown in FIG. 1B, the above-mentioned SiO _{x is formed} by using a common resist mask (not shown).
The laminated film of the sacrificial layer 5, the polysilicon layer 4, and the SiO _x sacrificial layer 3 was etched to form the rotor 4a. The planar shape of the rotor 4a at this time is such that comb-shaped irregularities are formed on the outer peripheral side of the annular member. The merit of this step is that the rotor 4a in which the upper and lower sides are side-switched by the sacrificial layer can be formed by one photolithography. However, in dry etching, since it is necessary to continuously process a laminated film of material layers having different etching characteristics, a fluorine-based etching species is used and SiO _x and Si are used.
Etching was collectively performed under the condition that the etching selection ratio between and was intentionally lowered. The etching end point was determined by time management based on a previously measured etching rate.

Since the above-mentioned etching is performed using the thin polysilicon electrode 2 as an underlayer, in order to achieve higher underlayer selectivity, SiO _{x is formed} near the boundary of each layer.
It is particularly desirable to carry out etching while switching the etching conditions optimized for each of Si and Si.

Next, in order to form a sacrificial layer made of S on the side wall surface of the pattern, the above wafer was set in a magnetic field microwave plasma CVD apparatus, and as an example, discharge was performed under the following conditions. S ₂ F ₂ flow rate 30 SCCM Gas pressure 1.33 Pa Microwave power 850 W (2.45 GH
z) RF bias power 30 W (2 MHz) Wafer mounting electrode temperature −10 ° C. (using alcohol-based coolant) Under this discharge condition, an appropriate RF bias power is applied and a certain amount of ions are generated on the vertical ion incident surface. It is intended to selectively deposit S, which is dissociated and produced from S ₂ F ₂ by exerting a sputtering action, only on the pattern sidewall surface. As a result, as shown in FIG. 1C, the S sacrificial layer 6 was formed on the sidewall surface of the pattern. Since the S sacrificial layer 6 is formed in a self-aligned manner, photolithography for patterning is unnecessary.

Next, as shown in FIG. 1D, an amorphous silicon layer 7 was deposited on the entire surface of the wafer by the CVD method as an example. The CVD at this time was performed while maintaining the wafer temperature near room temperature so as not to sublime the S sacrificial layer 6. Further, this amorphous silicon layer 7 is patterned by photolithography and dry etching, and as shown in FIG. 2 (e), a hub 7a that partially overlaps the inner peripheral portion of the rotor 4a and a partially overlap the outer peripheral portion of the rotor 4a. The stator 7b is formed. The stator 7b is a plurality of electrodes arranged radially in a plan view, and by sequentially switching the voltage application to each of these electrodes, the rotor 4a is attracted and rotated.

Next, the wafer was dipped in a dilute hydrofluoric acid solution to remove the SiO _x sacrificial layer 5 as shown in FIG. 2 (f). Next, the wafer is heated to 500 to 600 ° C.,
As shown in FIG. 2G, the S sacrificial layer 6 was removed by sublimation. If only the sublimation of the S sacrificial layer 6 is intended, 90 ° C.
Although heating to some extent is sufficient, high temperature heating is performed here to serve also as crystallization annealing of amorphous silicon. As a result, the hub 7a and the stator 7b are changed to the hub 7ap and the stator 7bp, respectively.

Furthermore, SiO _x sacrificial layer 3 as shown in FIG. 2 (h) is immersed in a dilute hydrofluoric acid solution again the wafer
Was removed to completely separate the rotor 4a from the surrounding structure.

In the manufacturing process of the electrostatic micromotor described above, the photolithography was performed on the rotor 4a.
Patterning [FIG. 1 (b)] and patterning the hub 7a and the stator 7b [FIG. 2 (f)] twice, once compared to the conventional process described with reference to FIGS. I was able to reduce.

Example 2 In this example, the deposition efficiency of the S sacrificial layer 6 was improved in the same manufacturing process of the electrostatic micromotor. The process of this example is almost as described above in Example 1. However, the conditions for forming the S sacrificial layer 6 were changed as follows.

S ₂ F ₂ flow rate 30 SCCM H ₂ flow rate 5 SCCM Gas pressure 1.33 Pa Microwave power 850 W (2.45 GH
z) RF bias power 30 W (2 MHz) Wafer mounting electrode temperature 0 ° C. (water cooling) Here, H ₂ is added because a part of F ^* dissociated from S ₂ F ₂ is captured. This is because the S / F ratio (ratio of the number of S atoms and the number of F atoms) of the reaction system is increased by removing the hydrogen in the form of HF (hydrogen fluoride) to relatively facilitate the deposition of S. As a result, the S sacrificial layer 6 could be deposited efficiently even though the wafer cooling conditions were relaxed as compared with the first embodiment.

Example 3 In this example, a sulfur nitride nitride sacrificial layer was formed in the same manufacturing process of an electrostatic micromotor. The process of this example is also substantially as described in Example 1.
However, in this example, plasma CVD was performed under the following conditions as an example in order to generate a sulfur nitride-based compound.

S ₂ F ₂ flow rate 30 SCCM N ₂ flow rate 5 SCCM Gas pressure 1.33 Pa Microwave power 850 W (2.45 GH
z) RF bias power 30 W (2 MHz) Wafer mounting electrode temperature 10 ° C (water cooling)

In this plasma CVD process, S ₂ F ₂
The S atom generated from N reacts with the N atom generated from N _2, and a sulfur nitride compound represented by polythiazyl (SN) _x is generated. Since this sulfur nitride-based compound has a higher sublimation / decomposition temperature than the above-mentioned simple substance of S, vertical ion incidence does not occur even though the temperature of the wafer mounting electrode is higher than that of each of the previous examples. The sulfur nitride-based sacrificial layer 8 was formed by efficiently depositing on the side wall surface of the pattern.

Also in this embodiment, it is necessary to maintain the wafer temperature in a range where the sulfur nitride based sacrificial layer 8 is not removed when the amorphous silicon layer 7 is formed in the subsequent step. I was able to raise it a little.

The present invention has been described above based on the three embodiments, but the present invention is not limited to these embodiments. For example, as the raw material gas for forming the S sacrificial layer, in addition to the above S ₂ F ₂ , SF ₂ , S
F ₄ , S ₂ F ₁₀ , S ₃ Cl ₂ , S ₂ Cl ₂ , SCl ₂ ,
Various halogenated sulfur such as S ₃ Br ₂ , S ₂ Br ₂ and SBr ₂ or a gas containing a sulfur compound such as H ₂ S can be used.

As a raw material gas for forming the sulfur nitride based sacrificial layer, a gas obtained by adding a nitrogen based compound to the above sulfur based compound may be used. As the nitrogen-based compound at this time, NF ₃ may be used instead of N ₂ described above. NH ₃ is not recommended because it reacts with S to form ammonium sulfide with a low vapor pressure. As the compound for increasing the S / F ratio of the reaction system in order to promote the formation of the S sacrificial layer and the sulfur nitride-based sacrificial layer, other than H ₂ described above, H ₂
S or a silane compound can be used.

In addition, the type of micromachine to be manufactured, the structure of the sample wafer, the conditions for forming the sacrificial layer, the manufacturing equipment used, the details of the process, etc. can be changed as appropriate without departing from the spirit of the present invention. Needless to say.

[0041]

As is apparent from the above description, according to the present invention, at least a part of the sacrificial layer is formed by using a sublimable and / or thermally decomposable deposition material, so that the sacrificial layer can be formed. Removal becomes easy and productivity can be improved. In particular, when the sacrificial layer on the side wall portion of the pattern is formed in a self-aligned manner, it is possible to omit the photolithography which has been conventionally performed for patterning the sacrificial layer, which can reduce the manufacturing cost. it can. The S and sulfur nitride-based compounds used as the depositable substance in the present invention are substances that can be deposited or removed in a practical temperature range and have no fear of particle contamination.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing an example of a process in which the present invention is applied to manufacture of an electrostatic micromotor in the order of steps, in which (a) is a polysilicon layer on a substrate and S above and below the polysilicon layer.
A state in which a laminated film including an iO _x sacrificial layer is formed, (b) is a state in which the laminated film is patterned into a rotor shape,
(C) shows a state in which a sacrificial layer made of S or a sulfur nitride compound is formed on the side wall surface of the rotor pattern, and (d) shows a state in which an amorphous silicon layer is deposited on the entire surface of the wafer.

2 is a schematic cross-sectional view showing a continuation of the process example of FIG. 1, (e) is a state in which the amorphous silicon layer is patterned to form a hub and a stator, and (f) is SiO on the upper surface side of the rotor. _The state where the _x sacrificial layer is removed, (g) shows the state where the sacrificial layer made of S or the sulfur nitride compound is removed, and (h) shows the state where the SiO _x sacrificial layer on the lower surface side of the rotor is removed.

FIG. 3 is a schematic cross-sectional view showing an example of a typical manufacturing process of a conventional electrostatic micromotor in the order of steps, in which (a) shows a laminated film composed of a SiO _x sacrificial layer and a polysilicon layer on the lower surface side. (B) is a state in which this laminated film is patterned in the shape of a rotor, (c) is a state in which the upper surface side SiO _x sacrificial layer is deposited on the entire surface of the wafer,
(D) shows the states in which this SiO _x sacrificial layer is patterned.

FIG. 4 is a schematic cross-sectional view showing a continuation of the process example of FIG.
(E) deposits a polysilicon layer on the entire surface of the wafer
(F) is a patterning of this polysilicon layer.
With the hub and stator formed, (g) shows wet
SiO for _xWith all the sacrificial layers removed
Represent each.

[Explanation of symbols]

1 ... substrate 2 ... polysilicon electrodes 3, 5 ... SiO _x sacrificial layer 4 ... polysilicon layer 4a ... rotor 6 ... S sacrifice layer 7 ... amorphous silicon layer 7a , 7ap ... Hub 7b, 7bp ... Stator 8 ... Sulfur nitride-based sacrificial layer

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) B81C 1/00 B81B 5/00 H02N 1/00 H02N 11/00 H01L 21/3065

Claims (2)

(57) [Claims] The method according to claim 1 sacrificial layer to囲撓the first material layer which is processed into a predetermined pattern is formed on the substrate and the first material layer to form a second material layer to partially shield by the isotropically removing the sacrifice layer after, in the manufacturing method of the micromachine to create a movable member with said first material layer liberated from the substrate, made of the first material layer of the sacrificial layer Side of the pattern
The part surrounding the wall is self-aligned by plasma CVD using sublimable and / or pyrolyzable deposition material
The substrate and maintain the substrate in a temperature range where the sacrificial layer does not sublime.
The second material layer is formed of amorphous silicon, and the side of the pattern made of the first material layer in the sacrificial layer is formed.
When sublimating and removing the portion surrounding the wall portion, the second
A method for manufacturing a micromachine, characterized in that the material layer is polycrystalline silicon . 2. The method of manufacturing a micromachine according to claim 1, wherein the depositable substance is at least one of sulfur and a sulfur nitride-based compound that are dissociated and produced from a source gas.