Methods for manufacturing MEMS sensor and thin film thereof with improved etching process

A method for manufacturing a MEMS sensor and a thin film thereof includes steps of etching a top surface of a single-crystal silicon wafer in combination of a deposition process, an isotropic DRIE process, a wet etching process and a back etching process in order to form a pressure-sensitive single-crystal silicon film, a cantilever beam, a mass block, a front chamber, a back chamber and trenches connecting the front and the back chambers. The single-crystal silicon film is prevented from etching so that the thickness thereof can be well controlled. The method of the present invention can be used to replace the traditional method which forms the back chamber and the pressure-sensitive single-crystal silicon film from the bottom surface of the silicon wafer.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for manufacturing a MEMS sensor on a same single-crystal silicon wafer, and methods for fabricating a thin film of such MEMS sensor with improved etching processes.

2. Description of Related Art

Micro-Electro-Mechanical Systems (MEMS) is a high technology rapidly developed in recent years. MEMS components can be manufactured by advanced semiconductor manufacturing processes to realize mass production. Compared with the traditional electronic components, the MEMS components are more competitive in profile, power consumption, weight and price etc.

Usually, a MEMS condenser includes micro structures such as a thin film, a mass block and a cantilever beam etc. The traditional method for manufacturing such thin film uses surface sacrificial processes which include steps of: (i) fabricating a sacrificial layer by a Low Pressure Chemical Vapor Deposition (LPCVD) process or a Plasma Enhanced Chemical Vapor Deposition (PEVCD) process or a Physical Vapor Deposition (PVD) process; (ii) fabricating a thin film on the sacrificial layer by the fore deposition methods; and (iii) etching the sacrificial layer under the thin film to release the thin film to be movable micro structures. Such method can be used to fabricate a polysilicon thin film, a metal thin film or a medium thin film etc. However, such method is not suitable to fabricate a single-crystal silicon film.

Pressure sensors are those MEMS sensors earliest appear to be used. The pressure sensors are divided into a piezoresistive type, a capacitive type and a piezoelectric type etc. The piezoresistive pressure sensor has advantages of mass output signals, simple follow-up processing and easy for mass production. However, the piezoresistive pressure sensors are usually fabricated on the single-crystal pressure-sensitive silicon film. In mass production, it is a key guideline to keep the uniformity thickness of the pressure-sensitive silicon films of the piezoresistive pressure sensors. The current method for fabricating the pressure-sensitive silicon film is to anisotropically etch the single-crystal silicon wafer from its bottom side via a kind of alkaline liquor. As a result, a back chamber is formed at the bottom side of the single-crystal silicon wafer, and meanwhile, the pressure-sensitive silicon film is formed at the top side of the single-crystal silicon wafer. In order to control the thickness of the pressure-sensitive silicon film, a time controlling method is selected. However, such method can not uniform the thickness of the inside and outside pressure-sensitive silicon films. Another method is to use the highly doped silicon film to control the thickness of the pressure-sensitive silicon film. However, since the piezoresistances cannot be fabricated on the highly doped silicon film, such method is not suitable to manufacture the pressure-sensitive silicon films of the piezoresistive pressure sensors. Another method is to use electrochemical etching to achieve the lowly doped silicon film which can be used to fabricate piezoresistances. However, such method needs additional apparatus, such as expensive potentiostats and clip tools for protecting the silicon wafer. The cost is accordingly enhanced and the manufacture efficiency is decreased due to additional processes.

Acceleration sensors are other kinds of MEMS sensors and are divided into a piezoresistive type, a capacitive type and a piezoelectric type etc. The piezoresistive type acceleration sensor needs to fabricate piezoresistances on its cantilever beam in order to detect the acceleration. Usually, the cantilever beam is fabricated from a single-crystal silicon film, which still meets the problems described in the above piezoresistive pressure sensors.

Hence, it is desired to have improved methods for manufacturing a MEMS sensor and its thin film.

BRIEF SUMMARY OF THE INVENTION

The present invention discloses a method for manufacturing a thin film of a MEMS sensor, comprising steps of:

a) forming a medium layer on a top surface of a single-crystal silicon wafer via a deposition process, and the medium layer functioning as a mask layer;

b) partly removing the medium layer in order to form a mask diagram;

c) etching the single-crystal silicon wafer from the mask diagram via a Deep Reactive Ion Etching (DRIE) process to form a plurality of trenches extending into an inner side of the single-crystal silicon wafer;

d) partly etching the single-crystal silicon wafer through the mask diagram via an independent isotropic DRIE process, to form an inner chamber and a plurality of remainder single-crystal silicon chips under the medium layer, the trenches being in communication with the inner chamber, the remainder single-crystal silicon chips forming a meshwork silicon film;

e) removing the medium layer from the single-crystal silicon wafer in order to expose the meshwork silicon film, via a dry etching process or a wet etching process; and

f) finally, expanding a single-crystal silicon film based on the meshwork silicon film via an epitaxial growth process, the single-crystal silicon film covering the meshwork silicon film to shield the trenches, the inner chamber being located under the single-crystal silicon film.

A method for manufacturing a thin film of a MEMS sensor comprises steps of:

a) forming a medium layer on a top surface of a single-crystal silicon wafer via a deposition process, and the medium layer functioning as a mask layer;

b) partly removing the medium layer in order to form a mask diagram;

c) etching the single-crystal silicon wafer from the mask diagram via a Deep Reactive Ion Etching (DRIE) process to form a plurality of trenches extending into an inner side of the single-crystal silicon wafer;

d) partly etching the single-crystal silicon wafer through the mask diagram via an anisotropic DRIE process together with an anisotropic etching process, or an independent anisotropic DRIE process, or an independent isotropic DRIE process, to form an inner chamber and a plurality of remainder single-crystal silicon chips under the medium layer, the trenches being in communication with each other through the inner chamber, the remainder single-crystal silicon chips forming a meshwork silicon film;

e) removing the medium layer from the single-crystal silicon wafer in order to expose the meshwork silicon film, via a dry etching process or a wet etching process;

f) forming a deposition layer filled in the trenches so as to close the inner chamber, the deposition layer further covering the top surface of the single-crystal silicon wafer; and

g) finally, removing the unwanted deposition layer which covers the top surface of the single-crystal silicon wafer while leaving the deposition layer filled in the trenches, the meshwork silicon film and the deposition layer filled in the trenches being exposed to an exterior and jointly forming the thin film.

A method for manufacturing a piezoresistive pressure sensor and an acceleration sensor on a same single-crystal silicon wafer, the single-crystal silicon wafer being divided into a first area for fabricating the piezoresistive pressure sensor and a second area for fabricating the acceleration sensor, the method comprising steps of:

a) etching a top surface of the single-crystal silicon wafer to form a first deep hole at the first area and a second deep hole at the second area;

b) depositing a medium layer on the top surface of the single-crystal silicon wafer under an arrangement that the medium layer fills in the first and the second deep holes to form first and second sacrificial layers, respectively;

c) partly etching the single-crystal silicon wafer through the medium layer to form first and second chambers and a plurality of remainder single-crystal silicon chips under the medium layer, the first and the second chambers being located at the first and the second areas, respectively, the single-crystal silicon wafer being etched to terminate at the first sacrificial layer which is located adjacent to the first chamber, and the single-crystal silicon wafer being etched to terminate at the second sacrificial layer which is located adjacent to the second chamber;

d) removing the medium layer from the single-crystal silicon wafer at both the first and the second areas, while leaving the first and the second sacrificial layer;

e) fabricating a single-crystal silicon film at the first and the second areas, and then fabricating a first piezoresistance on the single-crystal silicon film at the first area, and a second piezoresistance on the single-crystal silicon film at the second area, the first and the second piezoresistances being electrically extended to an exterior;

f) forming first and second back cavities from a bottom surface of the single-crystal silicon wafer under a condition that the first back cavity and the first chamber are separated from each other by the first sacrificial layer, and the second back cavity and the second chamber are separated from each other by the second sacrificial layer; and

g) finally, removing the first and the second sacrificial layers so as to communicating the first back cavity with the first chamber, the second back cavity communicating with the second chamber to release a mass block movable in the second chamber, the mass block being adapted for sensing the acceleration.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Please refer toFIGS. 1-7(b), a method for fabricating a thin film of a MEMS sensor according to a first embodiment of the present invention is disclosed and includes the following steps.

Please refer toFIGS. 1 and 2, firstly, a medium layer102is formed on a top surface of a single-crystal silicon wafer101via a deposition process, such as a Low Pressure Chemical Vapor Deposition (LPCVD) process or a Plasma Enhanced Chemical Vapor Deposition (PEVCD) process or a thermal oxidation process. The medium layer102is made of silicon oxide or silicon nitride to function as a mask layer in subsequent etching processes.

Secondly, referring toFIG. 3, the medium layer102is partly removed via an etching process, such as a photo etching process or a dry etching process or a wet etching process, in order to form a meshwork mask diagram103.

Thirdly, referring toFIG. 4, a plurality of trenches104are formed by etching the single-crystal silicon wafer101through the mask diagram103via a Deep Reactive Ion Etching (DRIE) process. The trenches104further extend into an inner side of the single-crystal silicon wafer101. As shown inFIGS. 8 and 9, the shapes of the trenches104can be square or rectangular or round. The dimensions of the trenches104are determined by the actual design.

Fourthly, referring toFIGS. 5(a) and5(b), the single-crystal silicon wafer101is then partly etched through the mask diagram103via an anisotropic DRIE process together with an anisotropic etching process, or an independent anisotropic DRIE process, or an independent isotropic DRIE process, to form an inner chamber105and a plurality of remainder single-crystal silicon chips107located under the medium layer102. Such remainder single-crystal silicon chips107form a meshwork silicon film. The trenches104are in communication with each other through the inner chamber105inside the single-crystal silicon wafer101. Referring toFIG. 5(a), the anisotropic etching process includes infusing KOH or tetramethylammonium hydroxide (TMAH) into the trenches104so as to etch the single-crystal silicon wafer101. Because of the anisotropic characteristic of such etching process, each remainder single-crystal silicon chip107is etched to form a contractive end1071facing the inner chamber105. According to the preferred embodiment of the present invention, the contractive end1071has an inverted triangle shaped cross section taken along a vertical plane. Alternatively, the cross section can be of other shapes, such as rectangular etc.

If the anisotropic DRIE process is selected as an etching process, a reactive ion is radiated into the single-crystal silicon wafer101through the trenches104. Under suitable technical parameter, the meshwork silicon film107can be formed as well.

Referring toFIG. 5(b), if the isotropic DRIE process is selected as an etching process, because of the isotropic characteristic of such etching process, the inner side of the inner chamber105is of curved surfaces.

Besides, the above-mentioned anisotropic DRIE process together with the anisotropic etching process can be combined to form the meshwork silicon film213as well.

Fifthly, referring toFIGS. 6(a) and6(b), the medium layer102is then removed from the single-crystal silicon wafer101in order to expose the meshwork silicon film, via a dry etching process such as a reactive ion etching process, or a wet etching process such as using the Buffered Oxide Etchant (BOE). Thereafter, a plurality of small holes108are formed at the top surface of the single-crystal silicon wafer101. The small holes108and the trenches104have the same transverse dimensions.

Finally, referring toFIGS. 7(a) and7(b), an integrate single-crystal silicon film106is then expanded based on the meshwork silicon film via an epitaxial growth process. The single-crystal silicon film106fills in the small holes108because the epitaxial growth process is isotropic. Since the small holes108are small in size, the reactive gas cannot easily enter the inner chamber105. As a result, the single-crystal silicon film106covers the meshwork silicon film and shields the trenches104. The thickness of the independent single-crystal silicon film106is easy to control because the single-crystal silicon film106lastly grows. The inner chamber105is located under the single-crystal silicon film106. The single-crystal silicon film106can be used as a pressure-sensitive film of a pressure sensor or a diaphragm of other components.

Besides, the single-crystal silicon film106can not be etched in the subsequent etching processes as a result that the thickness of the single-crystal silicon film106can be well controlled. The traditional etching process with the silicon wafer etched from its bottom surface can't prevent the diaphragm from further being etched. As a result, the thickness of the diaphragm can't be well controlled. However, the current fabrication method of the first embodiment of the present invention can overcome such difficulty of the traditional method. Besides, the current fabrication method is simple and useful because no additional apparatus, such as the expensive potentiostats or clip tools for protecting the silicon wafer, is needed.

Please refer toFIGS. 41-48, another method for fabricating a thin film of a MEMS sensor according to an alternative embodiment of the present invention is disclosed and includes the following steps.

Please refer toFIGS. 41 and 42, firstly, a medium layer402is formed on a top surface of a single-crystal silicon wafer401via a deposition process, such as a Low Pressure Chemical Vapor Deposition (LPCVD) process or a Plasma Enhanced Chemical Vapor Deposition (PEVCD) process or a thermal oxidation process. The medium layer402is made of silicon oxide or silicon nitride to function as a mask layer in subsequent etching processes.

Secondly, referring toFIG. 43, the medium layer402is partly removed via an etching process, such as a photo etching process or a dry etching process or a wet etching process, in order to form a meshwork mask diagram403.

Thirdly, referring toFIG. 44, a plurality of trenches404are formed by etching the single-crystal silicon wafer401through the mask diagram403via a Deep Reactive Ion Etching (DRIE) process. According to different etching selectivities of the single-crystal silicon wafer401and the medium layer402, the plurality of trenches401can be finally formed. The trenches404are similar to the trenches104as shown inFIGS. 4,8and9. The trenches404further extend into an inner side of the single-crystal silicon wafer401. The shapes of the trenches404can be square or rectangular or round etc. and the dimensions of the trenches404are determined by the actual design.

Fourthly, referring toFIG. 45, a passivation layer is formed covering the inner sides of the trenches404in a passivation process. Then an isotropic DRIE process is selected by radiating reactive ion into the single-crystal silicon wafer401through the trenches404. As a result, because of the isotropic characteristic of such etching process, an inner chamber405is formed and a plurality of remainder single-crystal silicon chips407are located under the medium layer402. Such remainder single-crystal silicon chips407form a meshwork silicon film. The trenches404are in communication with each other through the inner chamber405inside the single-crystal silicon wafer401. Referring toFIG. 45, each remainder single-crystal silicon chip407is etched to form a contractive end4071facing the inner chamber405. According to the preferred embodiment of the present invention, the contractive end4071has an inverted triangle shaped cross section taken along a vertical plane. Alternatively, the cross section can be of other shapes, such as rectangular etc.

Fifthly, referring toFIG. 46, the medium layer402is then removed from the single-crystal silicon wafer401in order to expose the meshwork silicon film, via a dry etching process such as a reactive ion etching process, or a wet etching process such as using the Buffered Oxide Etchant (BOE). Thereafter, a plurality of small holes408are formed at the top surface of the single-crystal silicon wafer401. The small holes408and the trenches404have the same transverse dimensions.

Sixthly, referring toFIG. 47, a deposition layer406is formed covering the top surface of the single-crystal silicon wafer401in a deposition process. The deposition layer406is made of polycrystalline silicon or silicon oxide. Because of the isotropic characteristic of the deposition process, the deposition layer406fills in the trenches404so as to close the inner chamber405. Besides, the deposition layer406further covers the remainder single-crystal silicon chips407of the meshwork silicon film when the deposition layer406is thick enough. Since the small holes408are small in size, reactive gas produced in the deposition process can not easily enter into the inner chamber405through the trenches404so that the inner side of the inner chamber405is prevented from being deposited with the deposition layer406.

Finally, referring toFIG. 48, the unwanted deposition layer406covering the remainder single-crystal silicon chips407of the meshwork silicon film is then removed via etching processes. However, the deposition layer406filled in the trenches404are saved in the etching processes. As a result, the meshwork silicon film and the deposition layer406filled in the trenches404are combined and exposed to ultimately form the thin film409of the MEMS sensor according to the alternative embodiment of the present invention. The thin film409can be used as a pressure-sensitive film or a pressure sensor or as a diaphragm of other components. The remainder single-crystal silicon chips407of the meshwork silicon film are exposed to the exterior to provide a base for fabricating piezoresistances.

Besides, the thin film409can not be etched in the subsequent etching processes as a result that the thickness of the thin film409can be well controlled. The traditional etching process with the silicon wafer etched from its bottom surface can't prevent the diaphragm from further being etched. As a result, the thickness of the diaphragm can't be well controlled. However, the current fabrication method of the alternative embodiment of the present invention can overcome such difficulty of the traditional method. Besides, the current fabrication method is simple and useful because no additional apparatus, such as the expensive potentiostats or clip tools for protecting the silicon wafer, is needed.

Please refer toFIGS. 10-16, a method for fabricating a mass block of a MEMS sensor according to a second embodiment of the present invention is disclosed and includes the following steps.

Please refer toFIGS. 10 and 11, firstly, a top surface of a single-crystal silicon wafer201is etched via an etching process, such as a photo etching process or a dry etching process or a wet etching process, in order to form a deep hole202. The deep hole202further extends into an inner side of the single-crystal silicon wafer201.

Secondly, referring toFIG. 12, a medium layer203is then formed on the top surface of the single-crystal silicon wafer201via a deposition process, such as a Low Pressure Chemical Vapor Deposition (LPCVD) process or a Plasma Enhanced Chemical Vapor Deposition (PEVCD) process or a thermal oxidation process. The medium layer203is made of silicon oxide or silicon nitride and fills in the deep hole202to form a sacrificial layer207.

Thirdly, referring toFIG. 13, the medium layer203is removed by Buffered Oxide Etchant (BOE). However, the sacrificial layer207is not etched by the prior etching process and still exists because of the protection characteristics of such etching process. Then, an integrate single-crystal silicon film204is expanded via an epitaxial growth process to cover the top surface of the single-crystal silicon wafer201.

Fourthly, referring toFIG. 14, the single-crystal silicon film204is then etched to form a diagram of a mass block205.

Fifthly, referring toFIG. 14, a back cavity206is then formed by etching a bottom surface of the single-crystal silicon wafer201. The mass block205and the corresponding single-crystal silicon wafer201are separated from each other by the sacrificial layer207.

Finally, referring toFIGS. 15 and 16, the sacrificial layer207is then removed via a reactive ion etching process or a wet etching process in order to communicating the mass block205with the corresponding single-crystal silicon wafer201. As a result, the mass block205is released to be a movable structure.

According to the second embodiment of the present invention, the single-crystal silicon film204can not be etched in the following etching processes as a result that the thickness of the single-crystal silicon film204can be well controlled.

Please refer toFIGS. 17-27, a method for fabricating a cantilever beam of a MEMS sensor according to a third embodiment of the present invention is disclosed and includes the following steps.

Please refer toFIGS. 17 and 18, firstly, a top surface of a single-crystal silicon wafer201is etched via an etching process, such as a photo etching process or a dry etching process or a wet etching process, in order to form a deep hole202. The deep hole202further extends into an inner side of the single-crystal silicon wafer201.

Secondly, referring toFIG. 19, a medium layer203is then formed on the top surface of the single-crystal silicon wafer201via a deposition process, such as a Low Pressure Chemical Vapor Deposition (LPCVD) process or a Plasma Enhanced Chemical Vapor Deposition (PEVCD) process or a thermal oxidation process. The medium layer203is made of silicon oxide or silicon nitride and fills in the deep hole202to form a sacrificial layer207. The medium layer203functions as a mask layer in the following etching processes.

Thirdly, referring toFIG. 20, the medium layer203is partly removed by Buffered Oxide Etchant (BOE) to form a mask diagram on the medium layer203. However, the sacrificial layer207is not etched by the prior etching process and still exists because of the protection characteristics of such etching process.

Fourthly, referring toFIG. 21, the single-crystal silicon wafer201is then etched through the mask diagram via a Deep Reactive Ion Etching (DRIE) process to form a plurality of trenches209.

Fifthly, referring toFIG. 22, the single-crystal silicon wafer201is then partly etched through the medium layer203via an anisotropic DRIE process together with an anisotropic etching process, or an independent anisotropic DRIE process, or an independent isotropic DRIE process, to form an inner chamber210and a plurality of remainder single-crystal silicon chips213located under the medium layer203. Such remainder single-crystal silicon chips213form a girder-shaped silicon film. The trenches209are in communication with each other through the inner chamber210inside the single-crystal silicon wafer201.

Referring toFIG. 22, the anisotropic etching process includes infusing KOH or tetramethylammonium hydroxide (TMAH) into the trenches209so as to etch the single-crystal silicon wafer201. Because of the anisotropic characteristic of such etching process, each remainder single-crystal silicon chip213is etched to form a contractive end (not labeled) facing the inner chamber210. According to the illustrated embodiment of the present invention, the contractive end has an inverted triangle shaped cross section taken along a vertical plane. Alternatively, the cross section can be of other shapes, such as rectangular etc.

If the anisotropic DRIE process is selected as an etching process, reactive ion is radiated into the single-crystal silicon wafer201through the trenches209. Under suitable technical parameter, the meshwork silicon film213can be formed as well.

Similar toFIG. 5(b), it is easy to be understood that the isotropic DRIE process can also be selected as an etching process to form the meshwork silicon film213.

Besides, the above-mentioned anisotropic DRIE process together with the anisotropic etching process can be combined to form the meshwork silicon film213as well.

Sixthly, referring toFIG. 23, the medium layer203is then removed from the single-crystal silicon wafer201in order to expose the girder-shaped silicon film, via a dry etching process such as a reactive ion etching process, or a wet etching process such as using the Buffered Oxide Etchant (BOE).

Seventhly, referring toFIG. 24, a single-crystal silicon film211is then expanded based on the girder-shaped silicon film via an epitaxial growth process. The thickness of the independent single-crystal silicon film211is easy to control. The single-crystal silicon film211is integrated because the epitaxial growth process is isotropic. As a result, the single-crystal silicon film211covers the girder-shaped silicon film and shields the trenches209. The inner chamber210is located under the single-crystal silicon film211. The single-crystal silicon film211can be used as a pressure-sensitive film of a pressure sensor or a diaphragm of other components.

Eighthly, as shown inFIG. 25, a diagram of at least one cantilever beam214is then fabricated on the single-crystal silicon film211. However, the amount of the diagram can be single or multiple so that the amount of the cantilever beam214can be single or multiple, accordingly.

Ninthly, referring toFIG. 26, a back cavity212is then formed from a bottom surface of the single-crystal silicon wafer201via a photo etching process or a DRIE process. The back cavity212and the inner chamber210are not communicated with each other and are separated from each other by the sacrificial layer207. Under this condition, the thickness of the cantilever beam214can not be influenced by the etching processes so that the thickness can be well controlled.

Finally, referring toFIG. 27, the sacrificial layer207is then removed via a reactive ion etching process or a wet etching process in order to communicate the back cavity212with the inner chamber210. As a result, the cantilever beam214is released to be a movable structure.

The single-crystal silicon film211can not be etched in the following etching processes as a result that the thickness of the single-crystal silicon film211can be well controlled. In the traditional etching process, the diaphragm will further be etched when the silicon wafer is etched from its bottom surface. As a result, the thickness of the diaphragm can't be well controlled. However, the current fabrication method of the third embodiment of the present invention can overcome such difficulty of the traditional method. Besides, the current fabrication method is simple and useful because no additional apparatus, such as the expensive potentiostats or clip tools for protecting the silicon wafer, is needed.

Please refer toFIGS. 28-40, a method for fabricating a MEMS sensor, such as a piezoresistive pressure sensor and an acceleration sensor on a same single-crystal silicon wafer, according to a fourth embodiment of the present invention is disclosed based upon the combination of the above methods of the first, the second and the third embodiments, and some additional processes of piezoresistance fabrication and metal trace fabrication. The single-crystal silicon wafer is divided into a first area for fabricating the piezoresistive pressure sensor and a second area for fabricating the acceleration sensor. The piezoresistive pressure sensor and the acceleration sensor are separated from each other by a broken line. Such method includes the following steps.

Please refer toFIGS. 28 and 29, firstly, a plurality of deep holes302are formed by etching a top surface of a single-crystal silicon wafer301. The deep holes302can be used to communicate with a chamber in order to fabricate the piezoresistive pressure sensor, or can be used to release a mass block and a cantilever beam in order to fabricate the acceleration sensor.

Secondly, as shown inFIG. 30, a medium layer303is then formed on the top surface of the single-crystal silicon wafer301via a deposition process, such as a Low Pressure Chemical Vapor Deposition (LPCVD) process or a Plasma Enhanced Chemical Vapor Deposition (PEVCD) process or a thermal oxidation process. The medium layer303is made of silicon oxide or silicon nitride and fills in the deep hole302to form a sacrificial layer304. The medium layer303functions as a mask layer in the following etching processes.

Thirdly, referring toFIG. 31, the single-crystal silicon wafer301is partly etched from trenches defined through the medium layer303to form a chamber305and a plurality of remainder single-crystal silicon chips3051under the medium layer303, via an anisotropic DRIE process together with an anisotropic etching process, or an independent anisotropic DRIE process, or an independent isotropic DRIE process disclosed in theFIGS. 10-16and17-27. The remainder single-crystal silicon chips3051form a meshwork silicon film and each remainder single-crystal silicon chip3051has an inverted triangle shaped cross section taken along a vertical plane. The single-crystal silicon wafer301is etched to terminate at the sacrificial layer304.

Fourthly, referring toFIG. 32, the medium layer303is removed by Buffered Oxide Etchant (BOE) to expose the meshwork silicon film. However, the sacrificial layer304is not etched by such etching process and still exists because of the protection characteristics of such etching process. Then, a single-crystal silicon film306is expanded based on the meshwork silicon film via an epitaxial growth process so as to cover the meshwork silicon film.

Fifthly, referring toFIG. 33, a plurality of piezoresistances307are fabricated on the single-crystal silicon film306via a photo etching process, an injection process and annealing process etc.

Sixthly, referring toFIG. 34, a passivation layer308is then fabricated on the single-crystal silicon film306and covering the single-crystal silicon film306, via a LPCVD process or a PEVCD process. The passivation layer308can be made of silicon oxide or silicon nitride.

Seventhly, referring toFIG. 35, a plurality of through holes3081corresponding to and connecting the piezoresistances307are formed by etching the passivation layer308.

Eighthly, as shown inFIG. 36, a plurality of metal pads312and metal traces310are formed on the passivation layer308, via a metal deposition process or a photo etching process or a metal etching process. The metal traces310fill in the through holes3081, and connect the corresponding metal pads312and the piezoresistances307in order to extend the piezoresistances307beyond a top surface of the passivation layer308. The passivation layer308is adapted for insulate the single-crystal silicon film306and the metal traces310.

Ninthly, referring toFIG. 37, diagrams309of a cantilever beam and a mass block are then formed on the passivation layer308.

Tenthly, referring toFIG. 38, a back cavity311is then formed from a bottom surface of the single-crystal silicon wafer301via a photo etching process or a DRIE process. The back cavity311and the chamber305are not communicated with each other and are separated from each other by the sacrificial layer304. Under this condition, the thickness of the single-crystal silicon film306can not be influenced by the following etching processes so that the thickness thereof can be well controlled.

Finally, referring toFIG. 39, the sacrificial layer304is then removed via a reactive ion etching process or a wet etching process in order to communicate the back cavity311and the chamber305. As a result, the cantilever beam and the mass block are both released to be movable structures to form the piezoresistive pressure sensor and the acceleration sensor, respectively. The part shown at the left side of the broken line is the piezoresistive pressure sensor, and the part shown at the right side of the broken line is the acceleration sensor. According to the fourth embodiment of the present invention, the piezoresistive pressure sensor and the acceleration sensor are commonly fabricated by a single single-crystal silicon wafer301to realize cost-effective manufacturing.

It is noted that the above ninthly step of the fourth embodiment is not needed when only the piezoresistive pressure sensors are fabricated. Under this condition, the single-crystal silicon film306will be driven to deform when the outer pressure is applied thereto. As a result, the piezoresistance of the single-crystal silicon film306is changed, which will result in a signal outputted by the metal traces310. However, when the MEMS sensor is an acceleration sensor, the above ninthly step of the fourth embodiment is needed. Under this condition, the mass block will be driven to offset a distance when the outer acceleration is applied thereto. As a result, the cantilever beam deforms to output a changed signal transmitted by the metal traces310. Besides, an additional mass block similar toFIGS. 10-16can be fabricated on the single-crystal silicon film306. The additional mass block is moveable and is in communication with the chamber305. The additional mass block increases the stress raiser to improve resolution so that the MEMS sensor can be more suitable for slight pressure measurement.