Patent Description:
An inertial sensor manufactured based on a micro-electro-mechanical system (MEMS) has drawn extensive attention due to its advantages such as simple structure, good compatibility with a microelectronics manufacturing process, mass manufacturing, and small volume.

In the existing process, a forming method of the inertial sensor generally includes: first providing a first substrate and a second substrate which are mutually bonded; and then, etching the second substrate to form a movable comb tooth structure and suspending the movable comb tooth structure above the first substrate. However, the inertial sensor prepared based on the existing process usually has the problem that side walls of comb teeth of the movable comb tooth structure are damaged.

Inertial sensors according to the state of the art are known, for instance, from prior art documents <CIT>, and <CIT>.

An objective of the present invention is to provide a forming method of an inertial sensor, so as to alleviate damage to side walls of comb teeth of a formed movable comb tooth structure.

To solve the above technical problem, the present invention provides a forming method of an inertial sensor, according to claim <NUM>, which includes:.

Optionally, a thickness of the thin film layer is less than a depth of the trench.

Optionally, after bonding the second conducting material layer and the first conducting material layer, the forming method further includes: forming a plurality of electrodes on the second conducting material layer, where at least part of the plurality of electrodes are used for being electrically connected to the movable comb tooth structure.

Optionally, first openings are further formed in the first conducting material layer, and when etching the second conducting material layer, second openings are further formed in the second conducting material layer. The second openings communicate with the first openings to form separation openings, and the plurality of electrodes are electrically isolated from each other by the separation openings.

Optionally, the first substrate further includes a first base and a first insulating layer formed between the first base and the first conducting material layer.

Optionally, a first cavity is formed in the first conducting material layer, and after bonding the first conducting material layer and the second conducting material layer, the comb tooth region is suspended above the first cavity.

Optionally, the second conducting material layer is further provided with a cantilever region, a second cavity and a stopper are further formed in the first conducting material layer, and after bonding the first conducting material layer and the second conducting material layer, the second cavity and the stopper are both located directly under the cantilever region.

Optionally, the second substrate further includes a second base and a second insulating layer formed between the second base and the second conducting material layer. Before etching the second conducting material layer, the forming method further includes: grinding the second base to partially remove the second base, then etching the remaining second base by an etching process, stopping etching at the second insulating layer, and then removing the second insulating layer to expose the second conducting material layer.

Optionally, the method for etching the second conducting material layer to form the movable comb tooth structure includes: adopting a plasma etching process for etching the second conducting material layer.

Another objective of the present invention is to provide an inertial sensor, according to claim <NUM>, which includes:.

A first cavity is further formed in the first conducting material layer, and the movable comb tooth structure is suspended above the first cavity.

Optionally, the second conducting material layer is further provided with a cantilever region, a second cavity and a stopper are further formed in the first conducting material layer, and the second cavity and the stopper are both located directly under the cantilever region.

In the forming method of the inertial sensor provided by the present invention, the trench is formed in the comb tooth region of the second conducting material layer, so that the movable comb tooth structure formed in the comb tooth region can be spaced from the first conducting material layer; and the thin film layer is further arranged at the bottom of the trench, and the thin film layer can be used for realizing etching blocking while etching the second conducting material layer, so that etching on the second conducting material layer can be stopped at the thin film layer without damaging the first conducting material layer below. Moreover, when etching the second conducting material layer to form the movable comb tooth structure, the bottoms of the comb teeth of the movable comb tooth structure are all fixed to the thin film layer, thereby avoiding damage to the side walls of the comb teeth due to torsion of the comb teeth during etching. In addition, in the forming method provided by the present invention, the thin film layer with a small thickness can be arranged, and thus, only a small etching amount is required for removing the thin film layer, and at this time, other film layers cannot be largely eroded, which is conducive to guaranteeing stability of modules in a device.

Reference numerals are as follows: <NUM>-first substrate; <NUM>-first base; <NUM>-first insulating layer; <NUM>-first conducting material layer; 130a-first cavity; 130b-second cavity; 130c-first opening; <NUM>-stopper; <NUM>-second substrate; <NUM>-second base; <NUM>-second insulating layer; <NUM>-second conducting material layer; <NUM>-movable comb tooth structure; 230a-trench; <NUM>-thin film layer; <NUM>-electrode; <NUM>-separation opening; <NUM>-seal-capping base plate; <NUM>-seal-capping cavity; and <NUM>-bonding sealing ring.

As mentioned in the background, side walls of comb teeth of a movable comb tooth structure of an inertial sensor prepared by the existing forming method of the inertial sensor are likely to be damaged. Thus, the inventors of the present invention carried out researches and found that one important reason why the side walls of the comb teeth of the movable comb tooth structure are likely to be damaged is that in the process of etching a second substrate to form the movable comb tooth structure, a torsion space of the movable comb tooth structure is released along with constant etching, causing the movable comb tooth structure to easily twist during etching, and at this time, the side walls of the comb teeth are likely to suffer from etching damage.

Therefore, the present invention provides an inertial sensor and a forming method thereof. The forming method includes the following steps.

Step S100: A first substrate with a first conducting material layer and a second substrate with a second conducting material layer are provided, a trench is formed in a surface of a comb tooth region of the second conducting material layer, and a thin film layer is further formed at a bottom of the trench.

Step S200: The second conducting material layer and the first conducting material layer are mutually bonded.

Step S300: At least the comb tooth region of the second conducting material layer is etched, etching is stopped at the thin film layer to form a movable comb tooth structure, and bottoms of comb teeth in the movable comb tooth structure are all fixed to the thin film layer.

Step S400: The thin film layer is removed.

The inertial sensor and the forming method thereof provided by the present invention are further described in detail below in combination with the drawings and specific embodiments. The advantages and features of the present invention will be more clear according to the following description. It should be noted that the drawings all adopt a very simplified form and use an inaccurate scale, which are only intended to conveniently and clearly assist in describing the purposes of the embodiments of the present invention. In addition, relative terms shown in the drawings such as "above", "below", "top", "bottom", "over" and "under" can be used for describing relationships among modules, and these relative terms are intended to cover different orientations among elements besides the orientations depicted in the drawings. For example, if a device is inverted relative to a view in the drawings, it is described that an element above the other element is located below the other element now.

In this embodiment, the forming method of the inertial sensor may include the following step S100 to step S400. The detailed description is made below in combination with <FIG> and <FIG> to <FIG>. <FIG> is a schematic flowchart of a forming method of an inertial sensor according to an embodiment of the present invention, and <FIG> are schematic structural diagrams illustrating a preparation process of a forming method of an inertial sensor according to an embodiment of the present invention.

In step S100, referring to <FIG> for details, a first substrate <NUM> with a first conducting material layer <NUM> and a second substrate <NUM> with a second conducting material layer <NUM> are provided.

A trench 230a is formed in a surface of a comb tooth region A of the second conducting material layer <NUM>, and a thin film layer <NUM> is formed at a bottom of the trench 230a. A material of the thin film layer <NUM>, for example, includes silicon oxide, and the comb tooth region A of the second conducting material layer <NUM> is used for preparing the movable comb tooth structure. In this embodiment, the thin film layer <NUM> is only located in the trench 230a, and a thickness of the thin film layer <NUM> is less than a depth of the trench 230a, so that a top surface of the thin film layer <NUM> is not higher than that of the second conducting material layer <NUM>. For example, the thickness of the thin film layer <NUM> may be only a half of the depth of the trench 230a, and the depth of the trench 230a is, for example, <NUM>-<NUM>.

Further, the second conducting material layer <NUM> is further provided with a cantilever region B, the comb tooth region A is located beside the cantilever region B, and a part of the cantilever region B can constitute a mass block of the inertial sensor.

Further, a first cavity 130a is further formed in the first conducting material layer <NUM>. The first cavity 130a corresponds to the comb tooth region A of the second conducting material layer <NUM> (i.e., after subsequent bonding of the first substrate <NUM> and the second substrate <NUM>, the first cavity 130a is aligned with the comb tooth region A). In addition, a second cavity 130b is further formed in the first conducting material layer <NUM>. The second cavity 130b corresponds to the cantilever region B of the second conducting material layer <NUM> (i.e., after subsequent bonding of the first substrate <NUM> and the second substrate <NUM>, the second cavity 130b is aligned with the cantilever region B), thereby providing a vibration space for the cantilever region B.

Further, a stopper <NUM> may also be arranged in the first conducting material layer <NUM>. The stopper <NUM> corresponds to the cantilever region B of the second conducting material layer <NUM>, so as to limit a vibration range of the cantilever region B, and avoid the problems such as fracture due to excessive vibration of the cantilever region B. Specifically, after subsequent bonding of the first substrate <NUM> and the second substrate <NUM>, the stopper <NUM> is located below the cantilever region B, and in this embodiment, the stopper <NUM> may be further arranged on an edge of the second cavity 130b, so as to perform stopping from the edge of the cantilever region B. Further, a top surface of the stopper <NUM> is not higher than that of the first conducting material layer <NUM>.

Continuing referring to <FIG>, a plurality of first openings 130c are further formed in the first conducting material layer <NUM>, and the first openings 130c penetrate through the first conducting material layer <NUM>. The first openings 130c are used for forming separation openings. It should be noted that in the constituted plurality of separation openings, part of the separation openings may also be used for forming alignment marks, thereby ensuring alignment precision of a subsequent patterning process. The detailed description will be made in subsequent steps.

In this embodiment, trenches and thin film layers are also formed in positions, corresponding to the first openings 130c, of the second conducting material layer <NUM>.

Continuing referring to <FIG>, in this embodiment, the first substrate <NUM> further includes a first base <NUM>, and the first conducting material layer <NUM> is formed on the first base <NUM>. A material of the first conducting material layer <NUM>, for example, is an ion-doped silicon material, and a resistance value of the first conducting material layer <NUM> is, for example, between <NUM>Ω and <NUM>Ω.

In addition, before forming the first conducting material layer <NUM>, a first insulating layer <NUM> may also be formed on the first base <NUM>. After forming the first insulating layer <NUM>, the first conducting material layer <NUM> is formed on the first insulating layer <NUM>, and when etching the first conducting material layer <NUM> for patterning, the first insulating layer <NUM> may also be used as an etching stop layer. A material of the first insulating layer <NUM>, for example, includes silicon oxide.

Continuing referring to <FIG>, the second substrate <NUM> with the second conducting material layer <NUM> may be the second substrate directly constituted only with the second conducting material layer; or, in this embodiment, the second substrate <NUM> further includes a second base <NUM>, and the second conducting material layer <NUM> is formed on the second base <NUM>.

Further, before forming the second conducting material layer <NUM>, a second insulating layer <NUM> is further formed on the second base <NUM>, and after forming the second insulating layer <NUM>, the second conducting material layer <NUM> is formed on the second insulating layer <NUM>. A material of the second insulating layer <NUM>, for example, includes silicon oxide.

In an optional solution, a material of the second conducting material layer <NUM> may be the same as that of the first conducting material layer <NUM>. In this embodiment, the material of the second conducting material layer <NUM> is, for example, an ion-doped silicon material, and a resistance value of the second conducting material layer <NUM> is, for example, between <NUM>Ω and <NUM>Ω. Compared with the low-resistance second conducting material layer <NUM>, the second base <NUM> has a higher resistance value, for example, the resistance value of the second base <NUM> is between <NUM>Ω and <NUM>Ω.

In step S200, referring to <FIG> for details, the second substrate <NUM> and the first substrate <NUM> are bonded in a direction that the second conducting material layer <NUM> faces the first conducting material layer <NUM>.

The specific process of bonding the second substrate <NUM> and the first substrate <NUM> is to mutually bond the first conducting material layer <NUM> in the first substrate <NUM> and the second conducting material layer <NUM> in the second substrate <NUM>. In this embodiment, both the first conducting material layer <NUM> and the second conducting material layer <NUM> are made of the ion-doped silicon material, that is, the first substrate <NUM> and the second substrate <NUM> are in silicon-silicon direct bonding, and the bonding process is simple and has high bonding force.

The comb tooth region A of the second conducting material layer <NUM> corresponds to the first cavity 130a of the first conducting material layer <NUM>, and thus, after bonding the first substrate <NUM> and the second substrate <NUM>, the trench 230a is located above the first cavity 130a. In addition, the cantilever region B of the second conducting material layer <NUM> is located above the second cavity 130b.

In the subsequent process, the second conducting material layer <NUM> is patterned to form the movable comb tooth structure. In this embodiment, the second conducting material layer <NUM> further has the second insulating layer <NUM> and the second base <NUM>, and thus, before patterning the second conducting material layer <NUM>, the forming method further includes: the second base <NUM> and the second insulating layer <NUM> are removed.

Details are shown in combination with <FIG> and <FIG>, the method for removing the second base <NUM> and the second insulating layer <NUM> may include: firstly, the second base <NUM> is ground to partially remove the second base <NUM>, then the remaining second base <NUM> is etched by an etching process, etching is stopped at the second insulating layer <NUM>, and then the second insulating layer <NUM> is removed to expose the second conducting material layer <NUM>.

Specifically, the second base <NUM> is partially removed by the grinding process, and part of the second base <NUM> is retained, which can effectively relief mechanical stress of the grinding process acting on the second conducting material layer <NUM>, and avoid hide cracks in the second conducting material layer <NUM>. Then, the remaining second base <NUM> is etched by the etching process, and when etching the remaining second base <NUM>, the second insulating layer <NUM> can be utilized for constituting the etching stop layer, thereby avoiding losses of the second conducting material layer <NUM> below under the protection of the second insulating layer <NUM>, and effectively guaranteeing accurate control over the thickness of the second conducting material layer <NUM>. Further, the remaining second base <NUM> can be etched by a plasma etching process, so as to improve etching precision of the second base <NUM>. Then, the second insulating layer <NUM> can be removed by a wet etching process. For example, the material of the second insulating layer <NUM> may include silicon oxide, and thus, an etching agent adopted in the wet etching process for removing the second insulating layer <NUM> is, for example, hydrofluoric acid solution.

In an optional solution, before grinding the second base <NUM>, the forming method further includes: a trim process is performed on an edge of the second base <NUM>, so as to remove an edge part of the second base <NUM>, and accordingly, when subsequently performing the grinding process on the second base <NUM>, the problem that the edge part of the thinned second base <NUM> is suspended and is likely to fracture can be avoided.

In step S300, referring to <FIG> and <FIG> for details, at least the comb tooth region A of the second conducting material layer <NUM> is etched; etching is stopped at the thin film layer <NUM> to form the movable comb tooth structure <NUM>; and the bottoms of the comb teeth in the movable comb tooth structure <NUM> are all fixed to the thin film layer <NUM>.

Specifically, a pattern of the movable comb tooth structure can be defined by a second mask layer, and the second conducting material layer <NUM> is etched based on the second mask layer, so as to form the movable comb tooth structure <NUM>, and the method, for example, includes the following steps.

Step <NUM>: Referring to <FIG>, a second mask layer <NUM> is formed on the second conducting material layer <NUM>, and the pattern of the movable comb tooth structure is defined in the second mask layer <NUM>.

Step <NUM>: Referring to <FIG>, the second conducting material layer <NUM> is etched with the second mask layer <NUM> as a mask, so as to form the movable comb tooth structure <NUM>, and when etching the second conducting material layer <NUM>, the thin film layer <NUM> is used as the etching stop layer to stop etching at the thin film layer <NUM>. Specifically, the method for etching the second conducting material layer <NUM> is, for example, to use the plasma etching process for etching the second conducting material layer <NUM>, so as to improve the etching precision.

It should be noted that by arranging the thin film layer <NUM>, on the one hand, the function of etching blocking can be realized, and accurate control over the etching process of the second conducting material layer <NUM> is improved; and on the other hand, based on the blocking of the thin film layer <NUM>, a film layer below the thin film layer <NUM> can be effectively protected against etching damage. In addition, it should be understood that the bottoms of the comb teeth in the formed movable comb tooth structure <NUM> are all fixed to the thin film layer <NUM>, and thus, as the etching process continues, a torsion space of the movable comb tooth structure <NUM> is released, but because all the comb teeth are fixed to the thin film layer <NUM>, the comb teeth cannot twist at random, thereby avoiding damage to the side walls of the comb teeth due to torsion of the comb teeth during etching. Particularly, to ensure that patterns of the comb teeth can be completely and accurately etched, a certain over etching amount can be generally increased, and the plasma etching process with higher precision can be adopted for etching. In this embodiment, the comb teeth can be stably fixed by the thin film layer <NUM>, and thus, even under the large etching amount, damage to the side walls of the comb teeth from plasma can still be effectively relieved.

Further, before patterning the second conducting material layer <NUM>, the forming method further includes: a plurality of electrodes <NUM> are formed on the second conducting material layer <NUM>. At least part of the plurality of electrodes <NUM> are used for being electrically connected to the movable comb tooth structure <NUM>. Specifically, the plurality of electrodes <NUM> include two first electrodes which are electrically isolated from each other, and the two first electrodes are respectively electrically connected to two sets of comb teeth in the movable comb tooth structure <NUM>.

Further, the plurality of electrodes <NUM> further include a second electrode, and the second electrode is used for being electrically connected to the cantilever region B of the second conducting material layer <NUM>.

In this embodiment, the plurality of electrodes <NUM> can be electrically isolated from each other by separation openings <NUM>. Specifically, through the separation openings <NUM>, the first electrodes and the second electrode in the plurality of electrodes cannot be mutually connected by the conducting material layers (including the first conducting material layer <NUM> and the second conducting material layer <NUM>).

A forming method of the separation openings <NUM> may include: during patterning the second conducting material layer <NUM>, second openings are further formed in the second conducting material layer <NUM>, bottoms of the second openings are stopped at the thin film layer as well and located above the first openings 130c of the first conducting material layer <NUM>, and thus, the first openings 130c and the second openings are in up-down mutual communication to form the separation openings <NUM>, thereby utilizing the separation openings <NUM> for dividing the plurality of mutually separated electrodes.

It should be understood that based on layout limitations, the drawings only exemplarily illustrate two separation openings <NUM> and two electrodes <NUM>, and it should be understood that the electrodes <NUM> for connecting different modules are electrically isolated by the separation openings <NUM>. In addition, the first electrodes can be electrically connected to the movable comb tooth structure <NUM>, and the second electrode can be electrically connected to the cantilever region B through other interconnection structures.

In step S400, referring to <FIG> for details, the thin film layer <NUM> is removed. In this embodiment, the forming method further includes: the second mask layer <NUM> is removed. At this time, the movable comb tooth structure <NUM> is suspended above the first cavity 130a.

As mentioned above, the thin film layer <NUM> is relatively thin, and thus, the thin film layer <NUM> can be depleted with a small etching amount. Specifically, the thin film layer <NUM> can be eroded by a gas phase corrosive agent. In this embodiment, the thin film layer <NUM> is removed by a vapor phase hydrogen fluoride (VHF) fumigation corrosion process. Compared with the wet etching process, the gas phase corrosive agent is utilized for eroding the thin film layer <NUM>, which can effectively avoid the problems such as adhesion and torsion likely to occur between the adjacent comb teeth caused by corrosive liquid in the wet etching process.

In addition, in an optional solution, the material of the first insulating layer <NUM> may be the same as that of the thin film layer <NUM> (e.g., both including silicon oxide), and accordingly, when etching the thin film layer <NUM>, a trace amount of the first insulating layer <NUM> will be consumed. However, as mentioned above, the etching amount of the thin film layer <NUM> is small, and thus, the first insulating layer <NUM> cannot be largely consumed, which is conducive to guaranteeing the stable supporting of the first insulating layer <NUM> to a film layer above the first insulating layer.

In a further solution, referring to <FIG> for details, the forming method of the inertial sensor further includes: a seal-capping base plate <NUM> is bonded onto the second conducting material layer <NUM>. A seal-capping cavity <NUM> is formed in a surface, facing towards the second conducting material layer <NUM>, of the seal-capping base plate <NUM>, and the seal-capping cavity <NUM> faces the comb tooth region A and the cantilever region B. Part of the plurality of electrodes <NUM> may be sealed and capped within the seal-capping cavity <NUM>, and the other part of electrodes may be located outside the seal-capping cavity <NUM> for electrically connecting an external circuit.

Continuing referring to <FIG>, the seal-capping base plate <NUM> and the second conducting material layer <NUM> may be specifically mutually bonded through two bonding rings. For example, a first bonding ring is formed on a top surface, surrounding the seal-capping cavity <NUM>, of the seal-capping base plate <NUM>, a second bonding ring is formed at a corresponding position of the second conducting material layer <NUM>, and during bonding, the first bonding ring and the second bonding ring are mutually bonded and connected to form a bonding sealing ring <NUM>.

In a specific implementation solution, a material of one of the first bonding ring and the second bonding ring is aluminum, and a material of the other bonding ring is germanium, thereby realizing aluminum-germanium bonding between the first bonding ring and the second bonding ring. Alternatively, in another solution, the material of both the first bonding ring and the second bonding ring is gold, thereby realizing gold-gold bonding between the first bonding ring and the second bonding ring. Alternatively, the material of one of the first bonding ring and the second bonding ring is gold, and the material of the other bonding ring is silicon, thereby realizing gold-silicon bonding between the first bonding ring and the second bonding ring.

Based on the above forming method, this embodiment further provides an inertial sensor. Referring to <FIG> and <FIG> for details, the inertial sensor includes: a base (i.e., a first base <NUM> shown in <FIG>); a first conducting material layer <NUM> formed on the base; and a second conducting material layer <NUM> directly bonded to the first conducting material layer <NUM>. A movable comb tooth structure <NUM> is formed in the second conducting material layer <NUM>, and an end portion, close to the base, of the movable comb tooth structure <NUM> is contracted inward relative to a bonding surface of the second conducting material layer <NUM>, so as to enable the movable comb tooth structure <NUM> to be suspended.

A first cavity 130a may also be formed in the first conducting material layer <NUM>, and the movable comb tooth structure <NUM> is suspended above the first cavity 130a. Further, the second conducting material layer <NUM> is further provided with a cantilever region B, and a second cavity 130b and a stopper <NUM> are further formed in the first conducting material layer <NUM>. The second cavity 130b and the stopper <NUM> are both located directly under the cantilever region B. In this embodiment, a top surface of the stopper <NUM> is lower than a bonding surface of the first conducting material layer <NUM>.

In this embodiment, the first conducting material layer <NUM> and the second conducting material layer <NUM> are, for example, directly bonded based on a silicon-silicon bonding process, and the process is simple and has high bonding force.

Continuing referring to <FIG>, the inertial sensor further includes: a plurality of electrodes <NUM> formed on the second conducting material layer <NUM> and electrically isolated from each other. A part of the plurality of electrodes <NUM> are used for being electrically connected to the movable comb tooth structure <NUM>, and a part of the plurality of electrodes <NUM> are used for being electrically connected to the cantilever region B. It should be understood that the drawings in this embodiment only exemplarily illustrate two electrodes <NUM>, however, in practical application, the number, location and connection mode with corresponding modules of the electrodes can be correspondingly adjusted according to specific conditions.

Further, up-down communicating openings are further formed in both the first conducting material layer <NUM> and the second conducting material layer <NUM>, so as to form separation openings <NUM>, and the plurality of electrodes <NUM> are electrically isolated from each other by the separation openings <NUM>, so as to be respectively and independently electrically connected to the corresponding movable comb tooth structure <NUM> and the corresponding cantilever region B, and the like.

It should be understood that the end portion of the movable comb tooth structure <NUM> is contracted inward through the trench in the second conducting material layer <NUM>, and thus, the movable comb tooth structure <NUM> can be suspended. Compared with a conventional process in which a suspended movable comb tooth structure is realized through a spacer layer, this embodiment not only can guarantee that the movable comb tooth structure <NUM> is spaced from the second conducting material layer, but also can combine the thin film layer to further improve the quality of the formed comb tooth structure.

Claim 1:
A forming method of an inertial sensor, comprising:
providing a first substrate (<NUM>) with a first conducting material layer (<NUM>) and a second substrate (<NUM>) with a second conducting material layer (<NUM>), wherein the second conducting material layer (<NUM>) has a comb tooth region, a trench (230a) is formed in a surface of the comb tooth region, and a thin film layer (<NUM>) is further formed at a bottom of the trench (230a);
mutually bonding the second conducting material layer (<NUM>) and the first conducting material layer (<NUM>); and
etching at least the comb tooth region of the second conducting material layer (<NUM>), and stopping etching at the thin film layer (<NUM>) to form a movable comb tooth structure (<NUM>), wherein bottoms of comb teeth in the movable comb tooth structure (<NUM>) are all fixed to the thin film layer (<NUM>); and
removing the thin film layer (<NUM>).