WO1999032890A1

WO1999032890A1 - Micromechanical device and corresponding production method

Info

Publication number: WO1999032890A1
Application number: PCT/DE1998/003695
Authority: WO
Inventors: Karlheinz Müller
Original assignee: Siemens Aktiengesellschaft
Priority date: 1997-12-19
Filing date: 1998-12-16
Publication date: 1999-07-01

Abstract

Disclosed is a micromechanical device, more particularly, a micromechanical cantilever sensor, comprising a semiconductor substrate (10) with a basic doping, at least one doping area (20, 22; 25; 28) applied therein differing from the basic doping; at least one epitaxial layer (30a, 30b; 33a, 33b; 36a, 36b, 37a, 37b) lying above the doping area (20, 22; 25; 28) of the substrate (10) and a hollow space (50) beneath one of the epitaxial layers (30a, 30b; 33a, 33b; 36a, 36b, 37a, 37b), wherein the area of the epitaxial layer (30b; 33a; 37a) located above the hollow space has a membrane function.

Description

Micromechanical device and corresponding manufacturing method

The present invention relates to a micromechanical device with a membrane, in particular a micromechanical cantilever sensor, and a corresponding manufacturing method.

Although it can be applied to any micromechanical devices, the present invention and the problem on which it is based are explained in relation to a micromechanical cantilever sensor which is used, for example, as an acceleration sensor. The membrane, in conjunction with corresponding electrodes, serves as a capacitor, the changes in capacitance of which are evaluated as a measured variable.

At the moment there are various basic approaches in the prior art for producing a cantilever sensor. In the vast majority of all cases, the membrane area is made of polycrystalline silicon (polysilicon). If you use polysilicon, you have problems with bending of the cantilever during the process. The problem is partly avoided by increasing the layer thickness of the polysilicon to 400 nm to 2000 nm.

This leads to other problems in the topology. The fact that mechanical stresses develop in the devices with larger layer thicknesses, which severely impair the functionality and the builders of life of these known micromechanical devices, has been found to be disadvantageous in the known approaches above.

It is therefore an object of the present invention to form an improved micromechanical device which is simple to manufacture and is essentially unaffected by mechanical stresses. According to the invention, this object is achieved by the micromechanical device specified in claim 1.

The idea on which the present invention is based is that a sacrificial layer region is provided under an epitaxial layer and is removed to form the cavity.

The micromechanical device according to the invention has the advantage over the known approaches that it can be produced inexpensively by known CMOS, BIPOLAR and BICMOS processes. The area of the epitaxial layer lying above the cavity, which has the membrane function, is characterized by freedom from mechanical stresses and therefore by good functionality and high quality of life.

Advantageous further developments and improvements of the micromechanical device specified in claim 1 are found in the subclaims.

According to a preferred development, the epitaxial layer has a monocrystalline region grown on the doping region and a polycrystalline region grown on an intermediate layer provided above the substrate, the monocrystalline region having a supporting function and the polycrystalline region having the membrane function.

According to a further preferred development, the intermediate intermediate layer is an oxide layer.

According to a further preferred development, the substrate is a p-silicon substrate, the doping region is an n ⁺ doping region and the epitaxial layer is n-doped. According to a further preferred development, the epitaxial layer has a monocrystalline region grown on the doping region and a polycrystalline region grown on an intermediate layer provided over the substrate, the polycrystalline region having a suspension function and the monocrystalline region having the membrane function and the cavity being formed in the doping region is.

According to a further preferred development, the intermediate layer is an oxide layer.

According to a further preferred development, the substrate is a p-silicon substrate, the doping region is an n ⁺ doping region and the polycrystalline region is p ⁺ -doped and the monocrystalline region is p ^~ -doped.

According to a further preferred development, a first monocrystalline epitaxial layer grown on the doping region is provided, a second monocrystalline epitaxial layer grown on the first epitaxial layer, a region of the second monocrystalline epitaxial layer having the membrane function and a region of the first monocrystalline epitaxial layer and the layer having a supporting function Cavity is formed in the first monocrystalline epitaxial layer.

According to a further preferred development, the substrate is a p-silicon substrate, the doping region is an n ⁺ doping region, the supported region of the second monocrystalline epitaxial layer is p ⁺ -doped, the membrane region of the second monocrystalline epitaxial layer is p-doped and the support region is first monocrystalline epitaxial layer n ^" -doped. Embodiments of the invention are shown in the drawings and explained in more detail in the following description.

Show it:

1 shows a schematic cross-sectional illustration of a first embodiment of the micromechanical device according to the invention;

2 shows a schematic cross-sectional representation of a second embodiment of the micromechanical device according to the invention;

3 shows a schematic illustration in plan view of the second embodiment of the micromechanical device according to the invention according to FIG. 2; and

4 shows a schematic cross-sectional representation of a third embodiment of the micromechanical device according to the invention.

In the figures, identical reference symbols designate identical or functionally identical components.

1 shows a schematic cross-sectional representation of a first embodiment of the micromechanical device according to the invention.

In the first embodiment shown in FIG. 1, 10 denote a p-substrate made of silicon, 20, 22 a respective n ⁺ region, 40 an oxide layer, 30a a monocrystalline region of an n-epi provided on the n ⁺ region 20 or 22 - Taxie layer and 30b, 30c a polycrystalline part of the n-epitaxial layer provided on the oxide layer 40, 50 a cavity and Z a coalescence area. The monocrit stalline region 30a supports the polycrystalline region 30b, which has the membrane function.

The method for producing this first embodiment is explained in more detail below.

The n ⁺ doping regions 20 and 22 are formed in the p-substrate 10 by a conventional method, for example an implantation of phosphorus. This is followed by annealing and then oxidation to form the oxide layer as an intermediate layer 40. The oxide layer 40 is then structured photolithographically in order to expose the n ⁺ doping region 20 and 22, respectively. This is followed by an n-doped selective epitaxy, through which the monocrystalline silicon regions 30a, which serve as supports for the cantilever, form on the highly doped n ⁺ doping regions 20 and 22, respectively.

When the monocrystalline region 30a of the epitaxial layer reaches the thickness of the oxide, overgrowth begins, a polycrystalline region 30b, 30c of the epitaxial layer forming on the oxide layer 40. Z denotes the area of convergence of two polycrystalline areas 30b starting from adjacent n ⁺ doping areas 20, 22.

Finally, the oxide layer 40 below the polycrystalline region 30b is removed to form the cavity 50 below the membrane region. This is advantageously done using a known isotropic wet etching process.

As can be seen from FIG. 1, the

Structure of a capacitive sensor in parallel with a diode structure.

2 shows a schematic cross-sectional illustration of a second embodiment of the micromechanical device according to the invention. In the second embodiment, 10 denotes a p-type substrate made of silicon, 25 an n ⁺ region, 40 an oxide layer, 33a a monocrystalline region grown epitaxially on the n ⁺ -doped region 25, and 33b a polycrystalline region 33b grown epitaxially on the oxide layer 40 , and 50 a cavity that is formed in the doping region 25. The polycrystalline region 33b performs a suspension function and the monocrystalline region 33a performs the membrane function.

The process for producing this second embodiment is explained in more detail below.

First, the n ⁺ doping region 25 is formed by a common method, such as phosphorus implantation. The intermediate layer 40 then heals and forms an oxidation. The oxide layer 40 is then structured in such a way that the n ⁺ doping region 25 is exposed. A p-doped monocrystalline region 33a is epitaxially grown on the exposed n ⁺ doping region 25, which, as in the first exemplary embodiment, merges into a polycrystalline region 33b when the oxide thickness is reached. The areas 33b are p ⁺ doped.

This is followed by a deposition of auxiliary layers, such as oxide and nitride, and a structuring of the cantilever area 33a and support area 33b. This is expediently carried out by means of dry etching of the nitride, oxide, monosilicon and polysilicon. FIG. 3 shows a schematic illustration in a top view of the second embodiment of the micromechanical device according to the invention according to FIG. 2 to illustrate this structuring.

This is followed by wet chemical etching to form the cavity 50 under the cantilever region 33a. For this purpose, the holes denoted by 35 are etched into the cantilever region 33 and the n ⁺ region is then selectively etched out. The holes in the cantilever area 33a are then closed again using a conventional method. The latter undercut of the cantilever area 33a is known from the earlier application DE 197 00 290.0, which was registered on 3.1.97.

4 shows a schematic cross-sectional illustration of a third embodiment of the micromechanical device according to the invention.

In the third embodiment, 10 denotes a p-type substrate made of silicon, 28 an n ⁺ doping region, 3βa a first monocrystalline epitaxial layer grown on the n ⁺ doping region 28 and 37a a second monocrystalline epitaxial layer grown on the first epitaxial layer 36a. 50 denotes a cavity. The area 37a of the second monocrystalline epitaxial layer performs the membrane function, and the area 36a of the first monocrystalline epitaxial layer performs a support function. The cavity 50 is formed in the first monocrystalline epitaxial layer.

The method for producing this third embodiment is explained in more detail below.

After the n ⁺ doping region 28 has been formed in accordance with a customary method, such as, for example, phosphorus implantation, healing takes place. The n ^" -doped epitaxial layer is then epitaxially grown on the n ⁺ doping region and the surrounding substrate 10. The second p-doped epitaxial layer is grown on the first epitaxial layer. Subsequently, auxiliary layers, such as oxide or nitride, are deposited Structuring of the auxiliary layers, etching of the auxiliary layers and the p-doped epitaxial layer in an anisotropic, dry manner. Finally, the cantilever is exposed by wet-chemical etching, using the selectivity between high and low-doped regions. The formation of the cavity takes place as in the two th embodiment of forming holes in the second epitaxial layer.

For this cantilever sensor structure, too, the electrical equivalent circuit diagram is the parallel connection of a diode and a capacitor. The regions 36b of the first epitaxial layer and 37b of the second epitaxial layer are doped to form an electrical connection.

Although the present invention has been described above on the basis of preferred exemplary embodiments, it is not restricted to these but can be modified in a variety of ways.

Although a silicon substrate was assumed in the above examples, another semiconductor substrate, e.g. Gallium arsenide, usable.

Furthermore, the doping can of course be reversed, i.e. n can replace p and vice versa.

In particular, in the second embodiment, the doping region 50 can also be n ^~ -doped instead of n ⁺ .

Claims

claims

1. Micromechanical device, in particular micromechanical cantilever sensor, with

a semiconductor substrate (10) with a basic doping with at least one doping region (20, 22; 25; 28) incorporated therein, different from the basic doping;

at least one epitaxial layer (30a, 30b; 33a, 33b; 36a, 36b, 37a, 37b) lying over the doping region (20, 22; 25; 28) of the substrate (10); and

a cavity (50) under one (30b; 33a; 37a) of the epitaxial layers (30a, 30b; 33a, 33b; 36a, 36b, 37a, 37b);

the region of the epitaxial layer (30b; 33a; 37a) lying above the cavity (50) having a membrane function.

2. Device according to claim 1, characterized in that the epitaxial layer (30a, 30b) has:

a monocrystalline region (30a) grown on the doping region (20, 22); and

a polycrystalline region (30b) grown on an intermediate layer (40) provided above the substrate (10);

wherein the monocrystalline region (30a) has a support function and the polycrystalline region (30b) has the membrane function.

3. Apparatus according to claim 2, characterized in that the intermediate intermediate layer (40) is an oxide layer.

4. Device according to one of claims 2 or 3, characterized in that the substrate (10) is a p-silicon substrate, that the doping region (20, 22) is an n ⁺ doping region and that the epitaxial layer (30a , 30b) is n-doped.

5. The device according to claim 1, characterized in that the epitaxial layer (33a, 33b) has:

a monocrystalline region (33a) grown on the doping region (25); and

a polycrystalline region (33b) grown on an intermediate layer (40) provided over the substrate (10);

wherein the polycrystalline region (33b) has a suspension function and the monocrystalline region (33a) has the membrane function; and

wherein the cavity (50) is formed in the doping region (25).

6. The device according to claim 5, characterized in that the intermediate layer (40) is an oxide layer.

7. Device according to one of claims 5 or 6, characterized in that the substrate (10) is a p-silicon substrate, that the doping region (25) is an n ⁺ doping region and that the polycrystalline region (33b) p ⁺ is doped and the monocrystalline region (33a) is p-doped.

8. The device according to claim 1, characterized by

a first monocrystalline epitaxial layer (36a, 36b) grown on the doping region (28); and a second monocrystalline epitaxial layer (37a, 37b) grown on the first epitaxial layer (36a, 3βb);

wherein a region (37a) of the second monocrystalline epitaxial layer (37a, 37b) has the membrane function and a region (36a) of the first monocrystalline epitaxial layer (36a, 36b) has a supporting function; and

wherein the cavity (50) is formed in the first monocrystalline epitaxial layer (36a, 36b).

9. The device according to claim 8, characterized in that the substrate (10) is a p-silicon substrate, that the doping region (28) is an n ⁺ doping region, that the supported region (37b) of the second monocrystalline epitaxial layer (37a , 37b) is p ⁺ -doped, that the membrane region (37a) of the second monocrystalline epitaxial layer (37a, 37b) is p-doped and in that the support portion (36a) of said first monocrystalline epitaxial layer (36a, 36b) n ^~ -doped.

10. A method for producing the device according to claim 2, characterized by the steps:

Providing the substrate (10);

Forming the doping region (20, 22);

Forming the intermediate layer (40);

Structuring the intermediate layer (40) to expose at least a part of the doping region (20, 22);

Growing the monocrystalline region (30a) of the epitaxial layer (30a, 30b) on the exposed part of the doping region (20, 22); and Growing the polycrystalline region (30b) of the epitaxial layer (30a, 30b) on the intermediate layer (40); and

Removal of the intermediate layer (40) under the polycrystalline region (30b) of the epitaxial layer (30a, 30b) in the region of the cavity (50).

11. A method for producing the device according to claim 5, characterized by the steps:

Providing the substrate (10);

Forming the doping region (25);

Forming the intermediate layer (40);

Structuring the intermediate layer (40) to expose at least part of the doping region (25);

Growing the monocrystalline region (33a) of the epitaxial layer (33a, 33b) on the exposed part of the doping region (25); and

Growing the polycrystalline region (33b) of the epitaxial layer (33a, 33b) on the intermediate layer (40); and

Removal of the doping region (25) under the monocrystalline region (33a) of the epitaxial layer (33a, 33b) in the region of the cavity (50).

12. A method for producing the device according to claim 8, characterized by the steps:

Providing the substrate (10);

Forming the doping region (28); Growing the first monocrystalline epitaxial layer (36a, 36b) on the doping region (28);

Growing second monocrystalline epitaxial layer (37a, 37b) on the first monocrystalline epitaxial layer (36a, 36b); and

Removing the first epitaxial layer (36a, 38b) under the second epitaxial layer (37a, 37b) in the region of the cavity (50).