JP2000031503A - Sensor structure and method of mutually connecting separated structures - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sensor structure which permits required electric separation and connection without forming an oxide separation layer. SOLUTION: For a sensor 10, a bridge is built over an open trench 22, using conductive bridges 30-34, and electric connection is given between structures 24, 26 within an integrated circuit. The conductive bridge is useful in a sensor where the measurement of electric properties such as the capacity difference between the structures separated electrically. By forming an open trench around the flank, the structure is electrically separated. The bottom of the structure is electrically separated by an oxide layer. To form a conductive bridge, at first, the trench is filled with sacrificed glass to make firm foundation, and thereon a polysilicon conductor is arranged, and next the sacrificed glass is removed, and a conductive bride is made on the open trench. The open trench gives required separation, and the conductive bridge gives required electric connection.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

FIELD OF THE INVENTION The present invention relates generally to sensors, and more particularly, to sensors having structures that are physically separated and electrically interconnected.

[0002]

2. Description of the Related Art A sensor uses a converter to convert a physical state into an electric signal representing the physical state. One type of sensor is an accelerometer. Accelerometers are commonly used to detect acceleration, deceleration, or other externally applied forces in various applications. For example, an accelerometer can detect a deceleration associated with a vehicle accident and generate an electrical signal to deploy an airbag. Alternatively, the accelerometer is a car suspension,
It is used for vibration control of motors, impact protection for computers, etc.

[0003] Accelerometers are generally integrated in semiconductor devices based on single crystal materials. Accelerometers use a movable structure, arranged as a free-standing element, supported at a corner or anchor points, usually at several points along the structure perimeter.
This movable structure is suspended from the anchor point by a flexible or elastic spring, making the transducer movable. The structure of the transducer displaces in response to externally applied forces. Displacement of the transducer structure causes a change in capacitance between the surfaces of the structure, which is converted into an electrical signal indicative of the magnitude of the displacement.

[0004] As occurs in a car collision, x
To detect axial acceleration or inertial force, accelerometer manufacturers use x-axis oriented transduces.
r) was developed. Such an x-axis converter includes a plurality of fingers extending from a free-standing body. The free-standing body is typically suspended at both ends from a substrate foundation. The body and fingers move as a whole when an x-axis force is applied from the outside. Fingers
It is symmetrically arranged between rigid structures forming a comb structure. The capacitance between each finger and the surface of the rigid structure is differentially balanced. Any displacement that occurs between the finger and the rigid structure due to the x-axis force will unbalance the capacitance between the surfaces and change the electrical signal representing the applied force.

[0005] One of the common problems associated with forming the structure of an x-axis transducer in a monolithic integrated device is the electrical communication between the electrically isolated area of the transducer and other processing circuits. There is a connection. In order to generate capacitance, the body, fingers and rigid structure must be electrically separated.
For example, each finger must be electrically isolated from the substrate and the rigid structure. In order to generate a capacity difference,
The rigid structure on one side of the finger must be electrically isolated from the rigid structure and the substrate on the other side of the finger. Further, to measure the change in capacitance, each capacitance plate of the transducer must be electrically connected to a processing circuit.

[0006]

Prior art x-axis sensors have a rigid structure and a trench formed around an anchor point of a body spring. The rigid structure and the anchor points are surrounded and electrically isolated by oxide regions or layers. The trench is filled with polysilicon and has a solid surface for forming a polysilicon or metal conductor, connecting the rigid structure and anchor points to pads for connection to capacitance measuring circuits on the substrate. Forming oxide regions around the rigid structure and anchor points for electrical isolation adds to the cost and complexity of the manufacturing process.

Therefore, there is a need to form an electrical connection between an x-axis converter and a substrate without forming an oxide isolation layer between the sidewall and the substrate.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG.
Has developed an integrated circuit (I
C). In this example, the sensor 10 is a converter or an accelerometer capable of detecting a change or acceleration of an externally applied force and converting the change into an electric signal.

FIG. 1 is a plan view of the sensor structure. The central mass or spine 12 can be located at various locations, e.g.
At the point, it is fastened to the anchor point 14 by a flexible member. The flexible member is shown as a serpentine spring 16. The anchor point 14 is firmly connected to the substrate 20 on the bottom side. A plurality of fingers 18 are provided with a central mass 12.
And is extending from now on. The center mass 12 and the fingers 18 are free standing with respect to the substrate 20. That is, the center mass 12 and the fingers 18
6, except that it contacts the anchor point 14 via
Does not contact with Area 22 is an open trench.
In the area 22, there is no conductive material, no semiconductor material, no insulating material. The spring 16 allows the central mass 12 and the finger 18 to operate as a movable structure, freeing along the x-axis in response to externally applied forces, such as, for example, acceleration or deceleration associated with a vehicle collision. To be displaced. The external force is generated in the x-axis direction as shown in FIG.

The finger 18 is provided with electrode plates 24, 26
It has a comb structure alternately arranged between them. Finger 1
The number of eights and the height of the fingers 18 can vary and can be selected to achieve the desired volume. Increasing the number of fingers 18 or lengthening the fingers 18 increases the capacity. The electrode plates 24, 26
Since it is firmly connected to the substrate 20 on the bottom side, it does not move with respect to the substrate 20 when a force is applied from the outside. Except for contact on the bottom side, the electrode plates 24,
26 is separated from substrate 20 by open trench area 22. That is, the side walls of the electrode plates 24, 26 are electrically separated from each other and from the substrate 20 by the open trench area 22.

In the neutral state, that is, when no external force is applied, the distance between any finger 18 and the surface of the adjacent electrode plate is fixed and equal. For example, the distance between one surface 18a of the finger 18 and the surface 24a of the electrode plate 24, and the distance between the surface 18b of the finger 18 and the surface 26a of the electrode plate 26 is about 0.5 to 5 microns. Range. In this embodiment, this distance is 1 micron. The other fingers 18 are equally spaced from adjacent surfaces of the electrode plates 24,26. Surface 24
There is a capacitance C1 between a and the opposing surface 18a of the finger 18. Similarly, a capacitance C2 is formed between the surface 26a and the opposing surface 18b of the finger 18. The capacitances C1 and C2 are balanced and equal. Therefore, the capacitance difference C1-C2 becomes zero.

If the x-axis force is not zero, the central mass 12 and the fingers 18 will be displaced from their neutral position. The magnitude of the displacement is a function of the applied force.
The distance between surface 18a and surface 24a is no longer
The distance between 8b and surface 26a is not equal. As a result, the capacitance C1 is no longer equal to the capacitance C2. The capacitance difference C1-C2 becomes unbalanced. That is, it is not zero. The magnitude of the capacitance difference C1-C2 is a function of the displacement of the central mass 12 and the fingers 18, while the displacement is determined by the mass of the structure, the spring constant, and the magnitude of the x-axis force. The magnitude of the capacitance difference C1-C2 is similarly measured by the capacitance-voltage conversion circuit 28 located on the substrate 20, and changes its operation. Alternatively, the circuit 28
Can be placed on a separate substrate (not shown). Central mass 12, finger 18 and electrode plate 2
The behavior of 4, 26 operates as an x-axis converter, converting a physical state such as acceleration along the x-axis into an electrical signal representing the physical state.

As shown in FIG. 1 and discussed above, the central mass 1
The 2 and the finger 18 do not contact the substrate 20 except through the spring 16. The electrode plates 24, 26 contact the substrate 20 at their bottom surfaces, as described below. The side walls of the electrode plates 24 and 26 have open trenches.
The area 22 separates from the substrate 20, that is, is physically separated. Open trench area 22 provides electrical isolation and eliminates the need for an oxide insulating layer between electrode plates 24, 26 and substrate 20, which is common in the prior art. By removing any oxide layers from the sidewalls of the electrodes 24, 26, the manufacturing process of the sensor 10 is simplified.

The circuit 28 comprises the finger 18 and the electrode plate 2
In order to measure, ie, respond to, the change in capacitance between the finger 18 and the circuit 28, the electrode plate 24 and the circuit 28, and the electrode plate 2
There must be an electrical connection between 6 and the circuit 28.
Further, in order to measure the capacitance difference, the electrode plate 24,
Electrode plate 26 and finger 18 must each be electrically isolated from each other and from substrate 20.

As part of the present invention, a conductive microbridge 30 is formed between the electrode plates 24 to bridge the open trench area 22 and the contact pads on the substrate 20 and to connect to the input of the circuit 28 through conductive paths. Lead. The circuit 28 can be located on the substrate 20 or on a separate substrate connected to a multi-chip module or printed circuit board. Another conductive microbridge 32 is formed, connecting the electrode plates 26 together and further to the contact pads on the substrate 20, leading to the inputs of the circuit 28 through the conductive paths. A further conductive microbridge 34 is formed between the anchor point 14 and the contact pad of the substrate 20, and the circuit 2 is connected through a conductive path.
Leads to the input of 8. The conductive bridges 30-34 form an open trench area 22 between adjacent electrode plates and between the electrode plates or anchor points and the substrate 20.
To bridge.

The electrode plate 24 includes a conductive bridge 30
Through the circuit 28. Open trench area 2
2 keeps the electrode plate 24 electrically separated from the electrode plate 26 and the fingers 18. The electrode plate 26 is connected to a circuit 28 through a conductive bridge 32.
Contact with. Open trench area 22 holds electrode plate 26 electrically isolated from electrode plate 24 and fingers 18. Finger 18 contacts circuit 28 through conductive bridge 34. The open trench area 22 connects the fingers 18 to the electrode plates 24,
26 and is kept electrically separated from it. By electrically connecting to the circuit 28 through the conductive bridges 30 to 34, it is possible to convert the capacitance difference into a voltage V _OUT representing the physical state applied to the sensor 10.

The description of the microfabrication process for manufacturing the sensor 10 will begin with FIG. FIG. 2 is a cross-sectional view of the sensor 10 passing through a reference point A in FIG. A single crystal silicon layer 40 is formed or grown to a thickness of about 600 microns. The silicon layer 40 is doped with a P-type dopant. Alternatively, silicon layer 40 can be an N + type semiconductor material. The silicon layer 40 forms the basis of the substrate 20 in FIG. Buried oxide layer 42
Is an electrically insulating material formed on the silicon layer 40 to a thickness of about 1 to 6 microns. On the oxide layer 42, a single crystal silicon layer 44 having a thickness of about 2 to 200 microns.
Is formed, but a thickness larger than this is within the scope of the present invention. The silicon layer 44 is doped with either a P-type or N-type dopant. Silicon layer 44 and oxide layer 42 provide a silicon-on-insulator (SOI) structure.

By growing or depositing a layer of silicon dioxide or silicon nitride on silicon layer 44,
A hard mask is formed. A layer of photoresist is applied over the silicon dioxide layer and exposed to ultraviolet light according to a mask pattern to cure portions of the photoresist. During the photolithographic process, the uncured areas of the photoresist are removed by development and the underlying silicon dioxide areas are removed by etching. Dry etching is typically used to remove silicon dioxide. This is because highly accurate control is possible. The hardened photoresist is stripped or removed by ashing or plasma oxidation, leaving an oxide hard mask as shown in FIG. The silicon dioxide area 46 typically has a width of about 3
Micron and can be scaled as technology advances. Silicon dioxide area 46 defines electrode plate 24. Silicon dioxide area 48 is approximately 1 micron in width and defines finger 18. Silicon dioxide area 50 is approximately 3 microns wide and defines electrode plate 26.

Using an anisotropic reactive ion etchant, as shown in FIG.
Between 48 and 50, a high degree of directional precisi
on) to create a trench. The trench is a silicon layer 4
4 and reaches the buried oxide layer 42. The trench is formed below the silicon dioxide area 46 by the silicon layer 4.
Four rows 52 are formed. The trench also forms a row 54 of silicon layers 44 under the silicon dioxide area 48 and a silicon layer 44 under the silicon dioxide area 50.
Is formed. In another embodiment, a perforated structure is formed in the row 54 to increase the rigidity of the movable structure 12.

The trench is filled with a temporary sacrificial glass, such as, for example, phosphosilicate glass (PSG) or borophosphosilicate glass (BPSG). This is the silicon dioxide area 46,4
It reaches up to 8,50. The sacrificial glass provides a solid surface on which to form conductive bridges 32. The surface of the sacrificial glass is passivated with a layer of nitride.

To form a contact with column 56,
The sacrificial glass and silicon dioxide areas 50 are cut to form vias. To perform a cut to form a via,
The photoresist layer is patterned and the developed areas are removed by etching. Next, the excess photoresist is removed, the polysilicon layer is deposited and patterned to form the desired contacts and guide the conductive bridge to the desired path. Instead of polysilicon, tungsten, tungsten silicide, platinum, platinum silicide, copper, copper alloy, tantalum, tantalum silicide, titanium, titanium silicide, titanium nitride, aluminum, aluminum silicon, aluminum copper, aluminum copper silicide, conductive polyimide Other materials such as, conductive epoxy, and lead / tin can also be used for the conductive bridge. Deposit another nitride layer and passivate the polysilicon. The anchor point allows the conductive bridge 32
Is connected to the column 56 of the silicon layer 44. Other anchor points form electrical contacts to provide electrical interconnection between rows 56 that will eventually become electrode plates 26.

Turning to FIG. 4, a sacrificial oxide etchant is administered to remove the sacrificial glass. Once the sacrificial glass has been removed, the conductive bridge 32 remains open over the open trench area 22. The conductive bridge 32 provides electrical connections between the plurality of columns 56 and also provides electrical connections to pads on the substrate 20 for connection to the circuit 28. The conductive bridges 30, 34 are formed using the same microfabrication process as previously described in FIGS.

The etchant is administered long enough to remove the sacrificial glass and the entire portion of the buried oxide layer 42 under the row 54 of silicon layers 44. Columns 52 and 56 are column 5
4 so that the etching process involves the buried oxide layer 4 under columns 52, 56 of silicon layer 44.
Not all of 2 are removed. Therefore, column 5
2,56 remain physically and firmly connected to the substrate 20. Columns 52 and 56 are electrically isolated from each other and from substrate 20 by oxide layer 42 and open trench area 22. Row 54 is electrically separated from rows 52 and 56 by open trench area 22.

The row 54 becomes the finger 18. Central mass 1
2 and finger 18 are separated and released from substrate 20 in all areas except anchor point 14 defined by spring 16. The row 52 becomes the electrode plate 24 and the row 56 becomes the electrode plate 26. Finger 18
Can move freely when an external force is applied. The movement of the finger 18 causes a non-zero capacitance difference with respect to the surfaces of the electrode plates 24, 26,
This indicates the magnitude of the force.

This capacitance difference can be measured by a circuit 28 having three or more electrical connections. Electrode plate 2
4 is connected to the circuit 28 by a conductive bridge 30. The electrode plate 26 is open trench area 2
Interconnected by a conductive bridge 32 bridging the two. The electrode plate 26 is further connected to the circuit 28 by the same conductive bridge 32. Finger 1
8 are electrically connected by a spring 16 and a conductive bridge 34. This electrical connection allows the circuit 28
_Can provide an output signal V _OUT representative of the applied force by measuring or responding to the change in capacitance difference.

The conductive bridge is also applicable in other semiconductor structures where it is necessary or convenient to provide a conductive path on the open trench.

In summary, the present invention provides a conductive bridge that bridges open trenches for electrical connection between structures in an integrated circuit. Conductive bridges are useful in sensors that need to measure the capacitance difference between electrically isolated structures. These structures are electrically isolated by forming open trenches around the sidewalls. The bottom surface of the structure is firmly connected to the substrate and electrically isolated from the substrate by an oxide layer. To form a conductive bridge, first fill the trench with sacrificial glass and provide a rigid substrate, place a polysilicon conductor over it, then remove the sacrificial glass and place the conductive bridge over the open trench. Leave.

In the prior art, the electrode plate was separated from the substrate by a solid material containing an oxide layer for electrical isolation. Solid materials provide the basis for arranging conductive channels that make electrical connections with the capacitance measurement or detection circuits. According to the present invention, a manufacturing process is simplified by bridging a conductive bridge on an open trench. This is because there is no need to provide an oxide layer for electrical isolation between the side wall of the electrode plate and the substrate. Open trenches provide the necessary isolation and conductive bridges provide the necessary electrical connections.

[Brief description of the drawings]

FIG. 1 is a plan view of a sensor in an integrated circuit package.

FIG. 2 is a diagram showing a process for manufacturing the sensor of FIG. 1;

FIG. 3 is a diagram showing a process for manufacturing the sensor of FIG. 1;

FIG. 4 is a diagram showing a process for manufacturing the sensor of FIG. 1;

[Explanation of symbols]

 Reference Signs List 10 sensor 12 central mass 14 anchor point 16 spring 18 finger 20 substrate 22 open trench area 24, 26 electrode plate 28 capacitance-voltage conversion circuit 30, 32, 34 conductive microbridge 40 single-crystal silicon layer 42 buried oxide layer 44 Single crystal silicon layer 46,48,50 Silicon dioxide area 54,56 rows

 ──────────────────────────────────────────────────続 き Continuing the front page (72) Inventor Guan X Li 1698, West Lee Lane, Gilbert, Arizona, USA (72) Inventor Paul El Bergstrom South Chestnut, Chandler, Arizona, USA Place 2408 (72) Inventor Jargan A. Forstner 539 (72) Inventor North Fraser Drive, Mesa, Arizona, USA John E. Schisming West Citation Lane 35, Tempe, Arizona, United States of America Frank 72. Lee, junior United States Phoenix, Arizona, East Mountain Sky Abenyu over 1905

Claims (3)

[Claims] 1. A semiconductor structure comprising: a substrate (20); a first region (26) connected to the substrate; a first region connected to the substrate and separated from the first region by an open trench (22). A semiconductor structure comprising: two regions (26); and a conductive bridge (32) formed over the open trench and providing electrical connection between the first and second regions. 2. A transducer comprising: a semiconductor structure having first and second regions (26) separated by an open trench (22); and a conductive bridge (32) formed on said open trench. A converter comprising: 3. A method for interconnecting first and second regions of a semiconductor structure separated by an open trench, comprising: forming a conductive bridge over the open trench, between the first and second regions. Providing an electrical connection to the method.