Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01C—MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
  • G01C9/00—Measuring inclination, e.g. by clinometers, by levels
  • G01C9/02—Details
  • G01C9/06—Electric or photoelectric indication or reading means
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01H—MEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES
  • G01H11/00—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by detecting changes in electric or magnetic properties
  • G01H11/06—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by detecting changes in electric or magnetic properties by electric means
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
  • G01P15/00—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration
  • G01P15/02—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses
  • G01P15/08—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values
  • G01P15/0802—Details
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
  • G01P15/00—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration
  • G01P15/02—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses
  • G01P15/08—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values
  • G01P15/125—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values by capacitive pick-up
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
  • G01P15/00—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration
  • G01P15/02—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses
  • G01P15/08—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values
  • G01P2015/0805—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values being provided with a particular type of spring-mass-system for defining the displacement of a seismic mass due to an external acceleration
  • G01P2015/0808—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values being provided with a particular type of spring-mass-system for defining the displacement of a seismic mass due to an external acceleration for defining in-plane movement of the mass, i.e. movement of the mass in the plane of the substrate
  • G01P2015/0811—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values being provided with a particular type of spring-mass-system for defining the displacement of a seismic mass due to an external acceleration for defining in-plane movement of the mass, i.e. movement of the mass in the plane of the substrate for one single degree of freedom of movement of the mass
  • G01P2015/0817—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values being provided with a particular type of spring-mass-system for defining the displacement of a seismic mass due to an external acceleration for defining in-plane movement of the mass, i.e. movement of the mass in the plane of the substrate for one single degree of freedom of movement of the mass for pivoting movement of the mass, e.g. in-plane pendulum

Definitions

• the invention relates to a sensor for measuring motion according to the preamble of the main claim.
• Acceleration sensors based on silicon micromechanics are already known from patent application P 38 14 952, in which a paddle which is suspended from one or more webs is deflected perpendicularly to the wafer surface. The deflection is evaluated piezoresistively. Due to the required seismic mass and the direction of movement of the paddle, such sensors occupy a relatively large part of the wafer surface.
• the fiction, contemporary sensor with the characterizing features of the main claim has the advantage that it is very easy to implement sensors with a small chip surface by taking advantage of the natural crystallographic surfaces of the monocrystalline silicon wafer in the arrangement and dimensioning of the sensor paddles vertically to the wafer surface.
• a further advantage is that the capacitive evaluation of the sensor signals requires small trench widths, which are particularly easy to manufacture when using the (111) crystal planes as vertical etch stop boundaries for the lateral undercut.
• sensors can advantageously be etched out, the evaluation of which is carried out capacitively, as well as those whose evaluation is piezoresistive.
• a particular advantage of the capacitive sensors is that * the working capacity can be increased as required by connecting several capacitors in parallel. If the (111) crystal planes perpendicular to the wafer surface are used as the etch stop limit for the lateral undercut, etch trenches with an aspect ratio of up to 100: 1 can be produced, which is particularly advantageous since it can be used to produce paddles which have a very low rigidity exhibit.
• Another advantage is that, due to the high aspect ratio, the entire thickness of the wafer can be etched through. Paddles and electrodes with a particularly large working capacity can be manufactured with a small footprint.
• Sensor structures in wafers that consist of a silicon substrate and one applied to it can also be advantageously implemented There are epitaxial layers, a pn junction occurring between the substrate and the epitaxial layer due to their different doping.
• a p / n junction can also advantageously be introduced into a p- or n-doped wafer by means of a corresponding diffusion. If this pn junction is polarized in the reverse direction, it serves on the one hand as an etching stop and on the other hand it has an insulating effect on the substrate.
• the sensor structure can be isolated particularly advantageously either by means of a pn junction, which is polarized in the reverse direction, as well as by means of an isolation trench which completely penetrates the epitaxial layer and extends into the silicon substrate.
• the paddles can advantageously be exposed either by isotropic wet-chemical undercutting of webs from the front of the wafer or by means of a backside etching.
• a particular advantage of taking advantage of the crystallographic conditions is to select a simple parallelogram as the etching window for the rear side etching, the angles of which have the same dimensions as the angles which form the (111) planes in the (110) wafer surface.
• the fixed electrodes are not completely exposed by a rear side etching, but are connected to the silicon substrate at their two ends.
• a particular advantage in the production of sensors according to the invention proves that when using KOH or other alkalis, dielectrics known as etches can be used as the masking layer.
• Another advantage of producing sensor structures in (I ⁇ O) wafers using the crystallographic conditions by anisotropic wet chemical etching is that a combined etching attack from the front and back is possible.
• FIG. 1 shows the top view of a sensor
• FIG. 2 shows the top view of a further sensor
• FIG. 1 shows the top view of a sensor
• the silicon wafer 10 in this exemplary embodiment can have a uniform doping or else consist of a silicon substrate and an epitaxial layer applied thereon, at whose interface there is a pn junction due to the different doping of the substrate and the epitaxial layer.
• the p / n transition is essential.
• B. can also be generated by diffusion of foreign atoms in the silicon wafer.
• (111) planes are etched particularly slowly.
• the (111) planes are perpendicular to the wafer surface and therefore allow deep trenches with a high aspect ratio to be etched. Deep etching can be achieved a hundred times faster than lateral etching.
• oblique silicon areas 141 are also formed in the acute angles of the parallelogram with an angle of inclination to the wafer surface of 35.26 °. At the obtuse angles, oblique silicon areas are also formed on the bottom of the etching pit (FIG. 2).
• the inclined silicon surfaces 141 make design reservations necessary because they can restrict the movement of the paddles 151, 152, 153.
• the aspect ratio in the anisotropic wet chemical etching of (I ⁇ O) wafers is so high that it is possible to etch through the entire wafer.
• a combined etching attack from the front and back can be implemented.
• the height of the paddles or the depth of the etched trenches corresponds to the entire thickness of the wafer.
• the paddles and electrodes are isolated by The structures are separated from the silicon wafer, for example by sawing.
• the sensor should be applied beforehand, for example by anodic bonding, to a carrier made of a suitable material such as silicon or glass, it being important to note that the paddles remain capable of vibrating. This can be achieved, for example, by means of a cavern in the carrier or Si wafer or else by means of selective epitaxy.
• FIG. 2 shows a sensor structure in which vibratable paddles 161, 162 are formed within the epitaxial layer.
• a fixed electrode 151, 152 is assigned to each of the paddles 161, 162, so that each pair of electrode paddles forms a capacitance.
• the two capacitances shown are connected in parallel with a conductive connection 256 for the movable electrodes and a further conductive connection 255 for the fixed electrodes.
• An isolation trench 21 provides electrical isolation of the sensor structure within the expitaxial layer.
• the parallelogram denoted by 22 represents the starting surface for the rear side etching, which takes place starting from the rear side of the silicon wafer 10 up to the pn junction, which serves as the etching stop limit in the reverse direction.
• the parallelogram denoted by 22 represents the starting surface for the rear side etching, which takes place starting from the rear side of the silicon wafer 10 up to the pn junction, which serves as the etching stop limit in the reverse direction.
• the etching in 30% KOH at 80 ° C y 0.544 t.
• y depends on the etching conditions.
• the inclined silicon surfaces 141, 142 must be taken into account, since their position at the base of the rear-side etching pit can hinder the swinging of the paddles 161, 162.
• the fixed electrodes 151, 152 are only exposed by the rear side etching 22 in a central region. At their end, they are at least at a length d that corresponds to the thickness of the epitaxial layer, but are usually connected to the substrate in a length of 2d. This measure is intended to ensure the immobility of the electrodes 151, 152.
• FIG. 3 shows a silicon wafer with a (110) crystal orientation, from which a sensor structure according to the invention is etched out, at various stages of the method.
• FIG. 3a shows the silicon wafer 10, which consists of a silicon substrate 12 and an epitaxial layer 13 applied thereon. At the interface between the epitaxial layer 13 and the silicon substrate 12 there is a pn junction due to their different doping, which can be polarized in the reverse direction by means of a pn etching connection 27. To passivate the surface, there is a silicon oxide layer 311 on the epitaxial layer, which contains only recesses for the pn-etching connection 27 and a contact 26. The contact 26 serves for the electrical connection of the sensor. Both contact 26 and pn-etch connection 27 are in a plasma nitride layer 321 is embedded so that only a small recess remains.
• the recess in the plasma nitride layer 321 above the contact 26 is covered by a low-temperature oxide layer 331.
• the pn-etching connection 27 is exposed through a recess 23.
• a plasma nitride layer 322 is applied to mask the back of the silicon wafer 10, since a simple thermal oxide has an etching rate that is too high and would therefore not withstand etching with KOH.
• a silicon oxide layer 312 is located between the plasma nitride layer 322 and the silicon substrate 12 in order to avoid stresses between the silicon substrate 12 and the plasma nitride layer 322.
• the front and rear sides of the silicon wafer 10 are structured using means of photo masking technology.
• the resulting recesses 23 in the silicon oxide layer 311 on the front side of the silicon wafer 10 and the recess 22 for the etching of the rear side in the plasma nitride layer 322 and the silicon oxide layer 312 are shown in FIG. 3b.
• the front is etched in a further process step.
• the etching stop results from the duration of the etching treatment, which is chosen such that the isolation trench 21, which is not opposite the backside etching 22, completely penetrates the epitaxial layer 13 and extends into the silicon substrate 12.
• the etched trenches 20, which lie opposite the rear side etching 22, form until they encounter the low-temperature oxide layer 332, which serves to passivate the rear side of the silicon wafer 10.
• the silicon wafer 10 at this stage is shown in Figure 3d.
• the low-temperature oxide layer 332 and 331 on the back and the front of the silicon wafer 10 are removed.
• the silicon oxide layer 311 on the front side of the silicon wafer 10 is removed in the sensor region.
• two fixed electrodes 161, 162 have been created.
• the contact 26 was exposed by removing the plasma nitride layer 321, so that the desired sensor structure of FIG. 3e is produced.
• the etching of the rear and the front are carried out in an aligned manner.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• Radar, Positioning & Navigation (AREA)
• Remote Sensing (AREA)
• Pressure Sensors (AREA)
• Weting (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

ID=6399525

Family Applications (1)

Country Status (4)

Cited By (1)

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Family Cites Families (7)

• 1990
  • 1990-02-06 DE DE19904003473 patent/DE4003473A1/de active Granted
• 1991
  • 1991-01-22 JP JP3502377A patent/JPH05503994A/ja active Pending
  • 1991-01-22 WO PCT/DE1991/000058 patent/WO1991012497A1/de not_active Application Discontinuation
  • 1991-01-22 EP EP19910902254 patent/EP0514395A1/de not_active Ceased

Non-Patent Citations (1)

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