JPH0799326A - Micromechanic sensor and its preparation - Google Patents

Abstract

PURPOSE: To provide a micromechanic sensor that is stable mechanically, can be manufactured easily, and can be formed in one piece with a bipolar process or a mixing process without any additional expenses. CONSTITUTION: A sensor consists of a support made of a silicon substrate 1 and an epitaxy layer 5 that is made of silicon covering the silicon substrate 1. One portion of the epitaxy layer 5 is released as at least one micromechanic displacement part 12-15 by the etching process, the released displacement parts 12-15 are made of polycrystal silicon, and the silicon migrates to the single crystal silicon at the connection part to the silicon substrate 1 of a support region.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention comprises a support made of a silicon substrate and an epitaxy layer made of silicon coated on the silicon substrate, a part of the epitaxy layer being formed by at least one etching process. It is open as a micromechanical displacement part, this part is connected to the silicon substrate at at least one of the support areas, and it can be displaced with respect to other sensor structures when a force is applied to the sensor. Starting from a micromechanical sensor for measuring vibrations, tilts, accelerations or pressures, in particular having means for

[0002]

2. Description of the Related Art German Patent Application No. 400903.
From 3.09, a micromechanical sensor as an acceleration sensor manufactured based on silicon microtechnology is known. This sensor consists of a support made of a silicon substrate and an epitaxy layer made of silicon coated on the silicon substrate, and a part of the epitaxy layer is opened in the form of a tongue as a micromechanical displacement portion by the etching process. Has been done. To that end, one or more tongues are hooked onto one or more webs and are displaced relative to other sensor structures when a force is applied to the sensor. Furthermore, means for evaluating this displacement are provided. From German Patent Application No. 4003473.9.09,
It is further known to take into account the crystallographic angle of single crystal silicon wafers in form and arrangement and for the etching process.

As a means for assessing the displacement of the tongue, electrodes are arranged which are electrically insulated from the tongue, so that the capacitance variation between the tongue and the electrode can be measured.

The opening of the tongue as part of the epitaxy layer is carried out by backside etching. This is an additional process compared to the normal bipolar process.

From the specification of WO92 / 03740, a low pressure chemical vapor deposition method (L
It is known to coat a layer of polycrystalline silicon on a silicon oxide layer having a contact window by PCVD, Low Pressure Chemical Vapor Disposed). The silicon oxide layer is removed by an etching process, whereby a polycrystalline silicon layer is present on the support, which is spaced apart from the silicon substrate, as tongues or as electrodes, in the contact window. LPCVD with low mechanical stress-The deposition rate of poly is about 60Å
/ Min and is therefore very low compared to the deposition rate of epitaxy polysilicon of about 1 μ / min. Therefore, for reasons of manufacturing costs, only relatively thin LPCVD layers can be manufactured, which limits the actuation capacity of lateral acceleration sensors, in particular, by the correspondingly low layer density of the tongue. In this case, an additional silicon deposition is required as compared with the conventional bipolar process.

[0006]

On the other hand, the open displacement portion is made of polycrystalline silicon, and this silicon is transferred to single crystal silicon at the connecting portion to the silicon substrate in the supporting region. The sensor according to the invention enables the production of open displacement parts or the production of mechanically active layers of polycrystalline silicon within a bipolar process or a MOS process without additional costs, It has the advantage that no additional silicon deposition is required. Epitaxy is a well-known special process for producing monocrystalline layers of silicon, whereas in the present invention polycrystalline (on silicon oxide) or other amorphous layers are deposited. An epitaxial layer is used, which is coated according to conventional bipolar processes.

The epitaxy deposition rate is much higher than that of the LPCVD process, and is therefore 10-30 μm according to the invention.
A relatively thick layer of m can be realized, which increases the actuation capacity of the lateral sensor.

Claim 2 By the means described in claim 2 and below,
Advantageous configurations of the described sensor are possible. A particular advantage of the sensor according to the invention is that the method according to the invention can be universally used in different configurations, in particular the cantilever tongue and the plate supported edge region are arranged in a number of layers. It is possible to do. Another major advantage is that integrated electronic circuits, in particular displacement evaluation circuits, can be manufactured in addition to micromechanical sensors on the same support using the same process without significant additional expense. Similarly, it is possible to electrically insulate the micromechanical sensor member from other electronic components on the same support together with other manufacturing steps.

[0009]

The present invention will be described in detail with reference to the drawings.

FIG. 1 shows a support 1 made of a silicon substrate, which is covered with a silicon oxide layer 2 and contact window openings 3, 4 for the silicon substrate 1 are provided around the silicon oxide layer 2. Being manufactured.

The silicon oxide layer 2 may be undoped or doped with phosphorus, boron or arsenic. Doping can advantageously also be used for doping Si structures which result in shorter etching steps in the removal of this silicon oxide layer 2 relatively later or mechanical movement.

The oxide layer can optionally be coated with yet another layer, for example silicon nitride or polysilicon.

According to FIG. 1b, an epitaxy layer 5 of silicon is deposited on the support 1 or the silicon oxide layer 2 and the contact window openings 3, 4 by another process. Epitaxy is a special process known per se for producing monocrystalline layers of silicon. In the process according to the invention, the epitaxy layer 5 is grown as a single crystal on the silicon substrate 1 only in the support regions 6, 7. On the other hand, on the silicon oxide layer 2, an epitaxy layer is grown in polycrystal in the region 8 corresponding to the width of the arrow 9 (indicated by hatching).

As a silicon wafer, the support is preferably oriented in the crystallographic direction. Orientation in the (100) direction is technically important for MOS and BICMOS processes, and orientation (111) is important for bipolar processes. The orientation (110) is technically less important.

In order to improve the properties of the polycrystalline epitaxy layer (region 8), the silicon oxide layer 2 is coated with a polystart layer 10 before epitaxy, which is shown in dashed lines in FIG. 1a. .

A special configuration of the sensor requires a conductor or counter electrode that is sterically restricted by a pn junction underneath the open and etched sensor material on the substrate. A HF resistant dielectric layer can be deposited on the substrate (eg, nitride) prior to depositing the sacrificial oxide for electrical passivation. This layer avoids much leakage current through the pn junction opened by the sacrificial oxide etch.

The micromechanical displacement portion is released from the polycrystalline epitaxy layer in the region 8. For that, 1
As shown in c, a deep and narrow etching groove, a so-called trench, is dug through the polycrystalline epitaxial layer 8 in the trenching process. Therefore, for example, a corresponding mask is required as a resist. Fabrication of trenches is performed using anisotropic plasma etching techniques as a highly anisotropic dry etching process. Due to the five trenches 11 shown, four tongue-shaped displacement parts 12, 1
The lateral structural limit portions 3, 14 and 15 are removed by etching.

Silicon oxide layer 2 as a sacrificial layer in another process
To remove. This removal is performed with high selectivity compared to silicon using hydrofluoric acid (HF).

Therefore, as is apparent from FIG. 1d, the micromechanical sensor 16 can be manufactured together with the displacement parts 12, 13, 14, 15 made of polycrystalline silicon, these parts being attached to the silicon substrate 1 in the support region. In the connection part of, it is converted to single crystal silicon. When a force is applied to the sensor, these displaced portions 12, 13, 14, 15 are displaced with respect to other sensor structures, particularly the silicon substrate 1. This displacement can be evaluated capacitively or by piezoresistance for measuring purposes.

Obviously, the above method can be used in multiple superpositions by alternately coating the silicon oxide layer 2, the other layers 10 and the epitaxy layer 5, and thus the corresponding etching steps. Displaced by 1
Many layers of 2, 13, 14 and 15 can be manufactured in superposition. Such a configuration is particularly suitable for a capacitive acceleration sensor.

The deposition rate of the epitaxy layer is quite fast,
Therefore, it is possible to realize the epitaxy layer thickness and the displacement portions 12, 13, 14, 15 with the thickness of 10 to 30 μm.

After the drawings of FIGS. 1a-1d, the fabrication and construction of a specific micromechanical sensor 16 is shown in FIG. 2a.
2e will be described in connection with the integration possibilities of the bipolar process of the associated transistor 17. This transistor is typically for IC circuits, especially for sensor 16
It exists as an evaluation circuit for the mechanical displacement of the displacement part of.

FIG. 2a shows as a starting element a support 1 made of a p-doped silicon substrate.

In FIG. 2, n ⁺ diffusion (buried layer diffusion, Burie
d Layer Diffusion) and p diffusion (the following insulation diffusion)
The normal manufacturing process of the bipolar technology according to US Pat. Layers 2 and 10 shown in the left-hand region of FIG. 2b correspond to layers 2 and 10 of FIG. The silicon oxide layer 18 shown in the right-hand part (where the transistor should occur in the right-hand area) is removed for another process, whereas the silicon oxide layer 2 remains with the existing contact windows. Be done. Then, as shown in FIG. 2c, an n-epitaxial layer 5 is coated on this structure, which layer corresponds to the length of the arrow 9 in the region 8 on the remaining silicon oxide layer 2. It grows in polycrystal.

2d, electrical insulation is carried out by means of the p-insulating diffusion part 19 as well as the p-base diffusion part 20. Further, the n ⁺ collector connection diffusion portion 21 and the n ⁺ emitter diffusion portion are attached by a known method corresponding to the bipolar process. Further, the upper silicon oxide layer 23 is covered.

In another process according to FIG. 2e, a trench 11 is dug in the lateral structural boundary of the tongue-shaped displacement portion 12 and the silicon oxide layer 2 is used as a sacrificial layer to open the lower surface, and hydrofluoric acid is used. To corrode and remove. Furthermore, the contact openings and the metallization of the connection part of the sensor 16 and the transistor connection parts E, B, C of the transistor 17 are manufactured.

Therefore, according to FIG. 2e, the tongue-shaped displacement part 12
Of the micromechanical sensor 16 is manufactured, which is displaceable when a force is applied inside the air gap 24. The change in capacitance can be measured and evaluated via the connections 25 and 26.

3a and 3b, the sensor 16 is shown in detail corresponding to the manufacturing process according to the left side of FIGS. To that end, FIG. 3b shows a corresponding cross-sectional view along line 27 in plan view 3a.

From FIG. 3 a, a trench groove 11 is produced using a trenching process, which defines a plate-like structure as the displacement part 12, which member is connected via two webs 28, 29 to each other. It is clear that it is linked to the structure of The sensor can thus be used as an acceleration sensor, which preferably operates perpendicular to the plane of the support.

In another configuration according to FIG. 4, a plate-shaped, substantially square displacement part 30 is held at the corners by means of four webs 31, 32, 33, 34. Such a configuration is particularly suitable as a capacitive acceleration sensor.

From the top view of the third configuration according to FIG. 5, a strip 3 of conductors, possibly conductive, in the sensor using the above technique is shown.
It will be appreciated that configurations having multiple electrodes 36 connected via 5 are also feasible. This fixed electrode 36
To the open silicon material 37 produced by the above method is activated. This material is provided with electrodes which project between the fixed electrodes 36. Therefore, the displacement of the material 37 due to the lateral acceleration can be sensed capacitively.

[Brief description of drawings]

1A to 1D are cross-sectional views of a sensor in various manufacturing processes.

2A to 2E are cross-sectional views of a sensor connected to a transistor by a bipolar process in various manufacturing processes.

FIG. 3a is a plan view of a sensor according to the present invention. b is a sectional view of this sensor.

FIG. 4 is a plan view of a second embodiment of the sensor according to the present invention.

FIG. 5 is a plan view of a third embodiment of the sensor according to the present invention.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Horst Münzel, Federal Republic of Germany Reutlingen Gru Obachstraße 60 (72) Inventor Michael Offenberg, Germany, Tübingen Obdeer Grafenharde 17 (72) Inventor Vin Fleet Waldvogel Germany Kirchentellingsfurth Hardenweg 33

Claims (15)

[Claims] 1. A support comprising a silicon substrate (1),
The silicon substrate (1) is covered with an epitaxy layer (5) made of silicon, and a part of the epitaxy layer (5) is formed by an etching process to form at least one micromechanical displacement part (12 to 15, 30). Three
6) is open, this part is connected to the silicon substrate (1) on at least one of the support areas and is displaceable with respect to other sensor structures when a force is applied to the sensor (16), In the micromechanical sensor (16) having means for evaluating this displacement, the open displacement parts (12 to 15, 30, 37) are made of polycrystalline silicon, and this silicon is transferred to the silicon substrate (1) in the supporting region. A micromechanical sensor characterized by migrating to single crystal silicon at the connection part of. 2. The micromechanical sensor according to claim 1, wherein the displacement is evaluated by a capacitance method or a piezo resistance. 3. A cantilevered piece (12) having one or more displacement parts.
15. The micromechanical sensor according to claim 1 or 2, comprising: 4. Micromechanical sensor according to claim 1 or 2, wherein the displacement part comprises a plate (30) supported in the edge region. 5. The micromechanical sensor according to claim 1, wherein a large number of layers of the displacement portion, which are composed of epitaxy layers that overlap each other, are open. 6. The micromechanical sensor according to claim 1, wherein the support (1) is oriented as a silicon wafer in the crystallographic direction (111) or (100). 7. The micromechanical sensor according to claim 1, wherein an integrated electronic circuit (17) is arranged on the same support (1) in addition to the micromechanical sensor (16). . 8. Other components on the same support (1)
Micromechanical sensor according to claim 7, wherein the micromechanical sensor part (16) is electrically insulated from the (17) by an insulating diffusion part (19) or by trenching. 9. A method of manufacturing a micromechanical sensor according to claim 1, wherein
Micromechanic displacement part (12-15, 30, 3
6) The silicon substrate (1), from which the silicon substrate (1) is to be opened, is coated with a silicon oxide layer (2), the contact window openings (3, 4) for the silicon substrate (1) being provided around this silicon oxide layer (2). A silicon oxide layer (2) and contact window openings (3, 4)
An epitaxy layer (5) made of silicon is deposited on
This epitaxy layer is polycrystalline (region 8) on the silicon oxide layer (2) and monocrystalline (region 6, in the region of the contact window openings (3, 4) as a direct connection to the silicon substrate (1). 7) A method of manufacturing a micromechanical sensor, which comprises growing and removing the silicon oxide layer (2) below the polycrystalline epitaxy layer region (8) as a sacrificial layer by an etching process. 10. Displacement portions (12-15, 30, 36, 3 in the form of narrow etching trenches as trenches (11) in a trenching step before removing the silicon oxide layer (2).
10. The method according to claim 9, wherein the lateral structural boundaries of 7) are removed by etching through the polycrystalline epitaxy layer (8) using anisotropic plasma etching techniques. 11. The silicon oxide layer (2) is coated with a polystart layer (10) before epitaxy.
The method described in 0. 12. The method according to claim 9, wherein a HF-resistant dielectric layer is deposited on the substrate for electrical passivation prior to depositing the sacrificial oxide. 13. The method according to claim 9, wherein the silicon oxide layer (2) is doped. 14. The method according to claim 9, wherein the removal of the silicon oxide layer (2) is carried out using hydrofluoric acid. 15. The method according to claim 9, wherein the integrated electronic circuit (17) is manufactured on the same support (1) using the manufacturing process of the micromechanical sensor (16). .