Patent Application
20070284680
The present invention relates to a method for manufacturing a semiconductor device and the semiconductor device manufactured by using the same, and a micro-device manufactured by using MEMS (Micro Electro Mechanical Systems) technology and its manufacturing method, and more particularly to a manufacturing of an RF-MEMS resonator having electrodes and a gap and a protrusive structure of an RF-MEMS filter.
In present MEMS devices, a structure with electrodes sandwiching a gap in a minute structure is applied to a wide field of devices such as a sensor, an actuator, a switch, a resonator and a filter having a capacitive coupling. Among these devices, in a case that two or more electrodes are arranged in a single protrusive structure, there devices are roughly classified into two kinds of electrode structures, one is a parallel electrode structure in which the electrodes are arranged in a plane with respect to a substrate, and the other is a side electrode structure in which the electrodes are arranged in a plane which is perpendicular to or oblique to the substrate. The methods for making two protrusive structures are different, in the case of the parallel electrode structure, at least two film-deposition steps are required, whereas in the side electrode structure, a single film-deposition step is required to form many electrodes simultaneously so that its manufacturing method is simple.
However, in the case of manufacturing the side electrode structure, it is required that a method for separating a conductive film (electrode film) deposited by the single step into two patterns to form the electrodes. For example, in the method of making an electron gun proposed by Mr. Hashiguchi and Mr. Hara, it was realized that the conductive film was pattern-separated by an etch-back step to form two electrodes (see JP-A-6-310029). In this method, by etching the upper part of the resist covering the conductive film which is stacked on the structure having an inclined face and etching, from above, a desired area of the conductive film can be separated at the upper end since the resist serves as a mask. In this case, in order to pattern the other area such as the other end, only a necessary area must be etched. For this purpose, it is required to protect the area other than an area to be etched by a mask.
To this end, the resist applied onto the entire surface is etched back so that the area to be etched is exposed from the resist. Thereafter, the electrode film in this area is etched to form electrodes. This manufacturing method is shown in
In this method, as shown in
As shown in
As shown in
In this state, as shown in
Further, as shown in
However, the step of etching back a sacrificing layer such as the resist in the above conventional electrode manufacturing methods requires a sophisticated etching controlling technique and so cannot assure sufficient pattern accuracy. For example, it is very difficult to form a sacrificing layer mask with the apex being exposed in the protrusive portion having an inclined face. The resist etch-back method, in which the apex is patterned by controlling an etching rate, must have special functions of precise time management and detection of an end point of the etching mounted, in the manufacturing device.
Further, in the conventional manufacturing using the etch-back step, at least two steps for patterning the apex and electrode are required. As a result, the number of manufacturing steps and costs are increased.
The present invention has been accomplished in view of the above circumstances. An object of the present invention is to form a pattern with high accuracy and high reliability without using precise time management and a special device.
In order to solve the above problem, the present invention provides a method for manufacturing a semiconductor device comprising:
forming a protrusive portion on a surface of a semiconductor substrate;
forming a thin film on the surfaces of the semiconductor substrate and the protrusive portion;
applying a resist on a surface of the thin film so that at least an apex of the protrusive portion on which the thin film is formed is exposed;
etching the thin film formed on the apex of the protrusive portion which is exposed from the resist to separate a pattern of the thin film into a plurality of patterns of the thin film; and
removing the resist.
In accordance with this configuration, the apex of the protrusive portion can be exposed only by adjusting the thickness (height) of an applied resist so that the electrodes can be easily formed.
Specifically, this invention, in a method for manufacturing a semiconductor device such as an MEMS device having an electrode on an inclined face so as to sandwich a gap, permits mask patterns for the apex of the protrusive portion and the electrode to be simultaneously formed. Since the electrodes can be formed with high accuracy by a simple process, the manufacturing method can be realized at low cost.
Preferably, the method, further comprising:
forming an insulating film on the surface of the protrusive portion,
wherein the protrusive portion has an inclined face;
wherein the thin film is a conductive film; and
wherein the conductive film is formed on the surfaces of the semiconductor substrate and the insulating film formed on the protrusive portion in the forming process of the thin film.
In this configuration, the resist is applied on a rugged surface and the conductive film is etched with a part of the convex area being exposed so that it is separated. Therefore, if the bottom of the convex area is matched with that of the conductive film, the heights of the separated conductive films agree with each other.
Preferably, the separating process includes processes of: patterning the resist to expose a part of the conductive film by photolithography process; and etching the part of the conductive film which is exposed from the resist in the patterning process and an apex part of the conductive film disposed on the apex of the protrusive portion.
In accordance with this configuration, patterning of the conductive film can be realized all at once with high efficiency.
Preferably, the semiconductor substrate is an SOI substrate having a single-crystal silicon layer formed on a surface thereof. The forming process of the protrusive portion includes a process of forming the protrusive portion by anisotropic etching so that a (111) plane of the SOI substrate is remained as the inclined face.
In accordance with this configuration, since the anisotropic etching is adopted so that the etching speed in the (111) plane is slow, using the etching selectivity of the (111) plane, the patterning can be performed with high efficiency and good reproducibility.
Preferably, The method further includes:
forming an embedded insulating layer (BOX layer) on the surface of the semiconductor substrate prior to the forming process of the protrusive portion; and
removing the insulating layer (a first insulating film) between the conductive film and the protrusive portion and the embedded insulating layer (a second insulating film) formed below the protrusive portion.
Preferably, the forming process of the embedded insulating layer includes a process of forming a deep groove from a back face of the semiconductor substrate.
In accordance with this configuration, by removing the embedded insulating film, the hollow structure can be realized with very high efficiency.
Also, by removing the first and second insulating films, the hollow structure can be realized with very high efficiency. Further, if the first and second insulating films are formed of the same material, they can be simultaneously etched. The first and second insulating films may not be formed of the same material as long as they can be etched under the same condition.
Preferably, the embedded insulating film is formed so as to have a step portion at an area on which the protrusive portion is to be formed such that the step portion is higher than other area of the surface of the semiconductor substrate.
In accordance with this configuration, the resist for protruding the apex of the protrusive portion can be made thick so that its uniformity and selectivity can be improved.
Preferably, the forming process of the protrusive portion includes a process of forming a concave portion on an apex plane of the protrusive portion.
In accordance with this configuration, by filling the concave area with the resist, a discontinuous area can be formed so that the pattern-separation can be realized.
Preferably, the apex plane of the protrusive portion has a flat face.
In accordance with this configuration, the pattern structure separated between flat areas can be formed with good controllability.
Preferably, the insulating film is an oxide film which is formed by oxidation of the semiconductor substrate.
In accordance with this configuration, the oxide film having an accurate film thickness can be formed with high efficiency.
Preferably, the oxide film having a thickness of several nms is formed by a chemical reaction of the surface of the semiconductor substrate in substrate cleaning (RCA or SPM cleaning).
In accordance with this configuration, by the oxide film obtained in the cleaning step as the insulating film, the thin oxide film can be easily formed with high efficacy. The “RCA” cleaning is a cleaning technique developed by RCA Corporation which combines SC-1 cleaning (Standard Clean 1) consisting of aqueous ammonia and aqueous hydrogen peroxide for the purpose of removal of particles and SC-2 cleaning (Standard Clean 2) consisting of hydrochloric acid and aqueous hydrogen peroxide for the purpose of removal of metallic impurities. The “SPM” cleaning is a cleaning technique of treatment at a high temperature of 100° C. or more by concentrated sulfuric acid doped with aqueous hydrogen peroxide for the purpose of removal of an organic material.
According to the present invention, there is also provided a semiconductor device formed by the method for manufacturing the semiconductor device, comprising:
an oscillator which is formed to be mechanically oscillatable;
an electrode which is arranged apart by a predetermined interval from the oscillator,
wherein the oscillator serves as an MEMS resonator configured by the protrusive portion.
In accordance with this configuration, a fine and reliable lead-like oscillator can be formed.
Preferably, the oscillator has a triangular section.
In accordance with this configuration, by using the sectional triangle having the (111) plane as one side, the pattern can be formed with high accuracy and good reproducibility.
Preferably, the electrode has a step portion.
Preferably, the oscillator has a square section.
Preferably, the oscillator has at least one groove on an upper face thereof.
In accordance with this configuration, if the upper face is flat so that it is difficult to form a gap (separating area), the groove having a predetermined width is formed and filled with the resist. Thus, the upper gap can be formed with high efficiency.
Namely, the manufacturing method according to the present invention is a method for providing an electrode in a protrusive portion having a gap, comprising: forming an insulating film in the protrusive portion having an inclined face; forming a conductive film on the insulating film; applying a resist to the conductive film so that an thickness of the resist is smaller than the height of the protrusive portion; exposing the apex of the protrusive portion by spin-coating the resist; patterning a mask of the conductive film by exposure and development of the resist; etching the patterned conductive film and the exposed apex; and removing the insulating film.
In accordance with this configuration, using the reproducibility of the film thickness by spin-coating, the gap with high size accuracy can be formed, thereby forming the gap with high accuracy and reliability.
In accordance with the method according to the present invention, there is provided an MEMS device which makes unnecessary the etch-back step of the resist whose control is difficult, and can simultaneously form, by a single etching step, the apex and electrode, which was conventionally impossible. Therefore, the manufacturing method capable of forming the apex and a large number of electrodes simply and accurately can be realized. This manufacturing method can be applied to various MEMS devices which form the electrodes through the gap.
The above objects and advantages of the present invention will become more apparent by describing in detail preferred exemplary embodiments thereof with reference to the accompanying drawings, wherein:
Now referring to the drawings, an explanation will be given of various embodiments of the present invention.
The electrode forming method in a microscopic protrusive portion according to the present invention is mainly applicable to forming an MEMS resonator. In the electrode forming method according to this embodiment, first, as shown in
In this way, the structure of the resonator can be obtained by forming the triangular sectional beam 1 through crystal anisotropic etching using a tetramethylammonium hydroxide (TMAH) water solution. At this time, for example, by anisotropic etching of an SOI substrate with a silicon layer having a thickness of 1.5 μm, the silicon is etched along a (111) side plane to etch the triangular section beam with an angle of 54.7° from a silicon surface. Thus, since the width (2.1 μm) of the beam is determined by the thickness of the substrate for manufacture, a beam-type oscillator can be formed with high accuracy.
After the beam-type oscillator having the triangular sectional beam is formed in this way, an oxide film for forming a gap is formed. Since the gap width is related with the RF characteristic of the resonator, the oxide film employed in this case is preferably a uniform and thin film. For example, in a case that the thermally oxidized film is employed as a sacrificing layer, an oxide film having a thickness of 50 nm is grown on the side of the triangular sectional beam in an oxidizing furnace. Thereafter, by the LPCVD method, a doped poly-silicon (conductive film) constituting an electrode film is deposited.
Incidentally, in the manufacturing method according to the present invention, in order to make a narrower gap, an oxide film having a thickness of several nms which gives a silicon surface of the triangular sectional beam 1 by a chemical reaction through a treating step of substrate cleaning (RCA, SPM) required before the step of
Next, the steps of exposing the apex of the triangular sectional beam and forming the mask pattern of the electrode will be performed by photolithography steps. Their details will be explained below.
A positive type resist (Shipley 1805;®) is used as a resist. Using a spin coater, coating is performed with the number of revolutions of 4000 rpm for 30 seconds. Thereafter, using a hot plate at 90° C., baking is performed for about two minutes so that the resist is coated with its uniform thickness (410 nm) being kept so as to give a flat surface on the entire substrate. Since the height of the triangular sectional beam is determined by the thickness (1500 nm) of the silicon layer of the SOI substrate, there is less variations. Thus, the apex (1090 nm) of the beam can be exposed with high accuracy.
Specifically, a conductive film 11 is uniformly deposited by CVD method or the like as shown in
Further, as shown in
In this way, after exposure of the apex by spin-coating, a photo-mask is formed. The resist is exposed and thereafter developed to form a mask pattern for forming an electrode pattern. The state after this step is shown by SEM photographs of
Next, as shown in
In this way, the exposed apex and electrode are dry-etched by using an RIE device, and thereafter, the resist is completely removed from the substrate.
Next, as shown in
In a final step, since a forming of the gap and an opening of the triangular section beam from the substrate are required, the oxide film between the electrodes and the beam and the oxide film existing in a low layer portion of the beam are removed by using hydrofluoric acid, thereby making the beam-type resonator. The manufactured resonator is shown in
Thus, as compared with the conventional electrode forming method using the etch-back step, the electrode pattern can be formed with high accuracy and a less number of steps.
In accordance with the present invention, the feature is to form the groove 17 in the BOX layer to provide the level difference. Thus, the resist 19 can be made thick in order to protrude the apex of a nano-protrusive portion 15, thereby improving uniformity and selectivity and also removing necessity of using a special thin film resist.
The method of the nano-protrusive portion forming the electrode according to the present invention is mainly applied to making the MEMS resonator. First, the single-crystal layer on the surface of an SOI substrate 100 is patterned by anisotropic etching to form a triangular sectional beam 15 having a width of 1 μm or less. The SOI substrate 100 is configured by a BOX layer 2, a silicon supporting substrate 3 and a protecting film 4 on a rear surface of the silicon supporting substrate 3 which are stacked. By thermal oxidation of the surface, an insulating film (silicon oxide film) 16 is deposited on the beam 15.
Next, as shown in
As shown in
Next, as shown in
The electrode manufacturing method according to this embodiment is characterized in that by making at least one small groove 28 at the apex of a sectional square protrusive portion 51, an area through which resist flows can be assured in an apex plane, thereby completely exposing the upper face of the protrusive portion 51.
In this embodiment, first, as shown in
Next, as shown in
Further, in this embodiment, after the groove 28 is formed, as shown in
Further, as shown in
As shown in
Next, as shown in
For example, by performing wet etching, the substrate 25 can be etched from both sides so that the oxide film 26 and the insulating film 29 can be removed simultaneously. Further, if the insulating film 29 is removed in this step, the electrode 33 formed in the groove 28 is opened so that the electrode does not stay in the groove 28 of the protrusive portion 51. After the etching, gaps 35 are formed and grooves 36 for opening the protrusive portions are formed, thereby completing the hollow structures of the square protrusive portions 50, 51 having the electrodes.
In the above embodiments, although the pattern-separation of the conductive film is explained, the present invention can be applied to not only the pattern-separation of the conductive film but also to the pattern-separation of a thin film such as the insulating film or other functional films.
The manufacturing method of forming electrodes according to the present invention can eliminate the need of a resist etch-back step whose control is difficult and simultaneously execute separation of a convex apex and formation of electrodes easily and precisely, and particularly is useful as the MEMS resonator in an application field of the MEMS.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-116411 | Apr 2006 | JP | national |
