JP2617531B2 - Semiconductor sensor - Google Patents

Description

The present invention relates to a semiconductor sensor.

(Prior Art) Conventionally, a semiconductor acceleration sensor has been manufactured, and for example, an IE TRANSACTIONS ON ELECTRON D
EVICES), VOL.ED-26, P1911, 1979. FIG. 2 shows the structure of the semiconductor acceleration sensor. (A) is a plan view, and (b) is a cross-sectional view along YY '.

Usually, in order to detect acceleration, it is fixed to an object to be accelerated, and vibrates following a reference point for detecting acceleration and external vibration. Requires beams and weights. In a conventional acceleration sensor, a weight 1 for detecting acceleration is formed substantially at the center of the acceleration sensor, and is supported by one beam 2. First, the beam for detecting the acceleration is subjected to anisotropic etching from the back surface of the substrate, the etching is stopped halfway by an appropriate method, a silicon thin film is formed, and the anisotropic etching is again performed from the surface. , Formed into the required shape. In order to detect acceleration efficiently, the weight provided at the tip of the beam is formed by directly using the remaining semiconductor substrate when the beam is manufactured, or by forming a thick metal on the surface. When a weight is directly manufactured from a semiconductor substrate, silicon having <100> plane orientation is used for the substrate, anisotropic etching is applied, and a trench is formed around the portion where the V groove is to be weighted until the substrate is penetrated. It is separated and manufactured except for the cantilever beam portion from the fixed portion. In addition, when adding metal, silicon is poor in electrical conductivity and adhesion, and silicon is poor in electrical conductivity and adhesion. Alternatively, nickel is vapor-deposited in advance, and thereafter, a metal having a large weight density such as gold is thickly applied by an electroplating method or the like. A fixed point 3 for detecting acceleration including a semiconductor circuit is provided on the outer peripheral portion. And
The stress generated in the supporting portion of the beam caused by the vibration of the weight is converted into an electric signal by the gauge resistor 5.

This acceleration sensor detects the acceleration in the vertical direction, so that the vibrators 1 and 2 are displaced up and down with respect to the substrate surface to provide a space in which the vibrator can move. A glass pedestal 8 and a glass cover 7 are provided to prevent breakage of the vibrator.

(Problems to be Solved by the Invention) In the semiconductor acceleration sensor, the acceleration is detected by using a change in the resistance value of a gauge resistor in response to an external acceleration signal. Since the signal is converted into an electric signal, the detection sensitivity has a property proportional to the weight of the weight attached to the tip of the beam. Therefore,
In order to increase the degree of acceleration detection, it is necessary to provide a relatively large mass of silicon or metal at the tip of the beam. Therefore, a conventional acceleration sensor employs a structure in which a large weight is installed at the center of the sensor and supported by a single beam. But,
Usually, a single crystal of silicon <100> orientation is used for the substrate,
Since the weight is made using an anisotropic etching method, there is a V-groove gap with an angle of 54.7 ° between the surrounding part and the weight, and the groove width inevitably corresponds to the substrate thickness. There was a problem that it became large enough to take up space. Furthermore, when the size of the sensor is reduced, it is mainly manufactured. The size of the weight must also be reduced, but when the width of the weight becomes about the thickness of the wafer, if the substrate used to make the acceleration sensor is a <100> oriented silicon single crystal, In this case, undesirable etching occurs in the lateral direction, and it becomes difficult to leave the weight as designed according to the anisotropic etching. Therefore, as the size of the structure becomes smaller in this way, it is extremely difficult to determine the frequency characteristics of the semiconductor acceleration sensor, and it is very difficult to accurately set the weight, which has a large effect. There was a problem. Furthermore, even when forming a weight having a size that can be etched well, it is impossible to form a weight having an arbitrary weight in the space limited by the outer peripheral portion serving as a fixing point. In order to satisfy the weight required for detecting the acceleration, there is no other way than to widen the outer circumference, and it has been difficult to reduce the size.

Only the semiconductor acceleration sensor has been described above. However, dynamic quantity sensors such as semiconductor force sensors and pressure sensors also have similar problems. A semiconductor sensor that converts a physical quantity to be detected (for example, temperature, light, or the like) into a mechanical quantity applied to a weight or a beam can be considered, but this also has a similar problem.

An object of the present invention is to form a weight required for physical quantity detection effectively in a limited space in order to eliminate the above-described problems, to increase the detection sensitivity of the sensor, and to increase the variation in element sensitivity. Another object of the present invention is to provide a sensor structure in which the number is reduced.

(Means for Solving the Problems) The present invention has a fixed point serving as a measurement reference point in a central portion, has a weight around the central portion, and has a predetermined width for connecting the fixed point and the weight. A semiconductor sensor having a beam having a fixed point, a weight, a beam or a film formed integrally by processing a semiconductor wafer.

(Operation) In the sensor, a fixed point is required for making a mechanical connection to the object to be measured for measurement, but the size of the beam is large enough that the beam for detecting the acceleration is sufficiently fixed. What is necessary is just to have the magnitude | size of a certain degree. Therefore, when the fixed point is reduced while keeping the conventional sensor shape, it is understood that the symmetry of the sensor, that is, the position of the center of gravity is located in the weight. In the sensor of the present invention, the fixing point is set in a small area in the center portion of the sensor for measurement, which is completely opposite to the conventional sensor structure, so that it is possible to set the fixing point at the position of the center of gravity. Although the point is very small, a very stable structure can be obtained. Furthermore,
All the semiconductor parts other than the beam part around the fixed point can be used as weights, and the weight for the entire chip area and weight compared to the case where the whole area around the chip is fixed point as before. It is much easier to increase the percentage. Therefore, it is possible to increase the weight of the weight, which is necessary for increasing the detection sensitivity of the physical quantity, without difficulty. Further, since the volume occupied by the weight is large, design accuracy can be easily obtained as compared with the case of a small volume as in the related art, so that the sensitivity variation of the element can be reduced. Further, when the fixed points are provided in this manner, it is easy to provide a plurality of good points and to increase the length thereof, and it is possible to further increase the directivity and the detection sensitivity.

(Embodiment) FIG. 1 shows an acceleration sensor according to an embodiment of the present invention. This sensor is manufactured using the manufacturing steps shown in FIGS. 5 (a) to 5 (e). 5 (a) to 5 (e) show cross sections along the line xx 'shown by the dotted line in FIG. As the substrate, a P-type single crystal silicon 9 of <100> orientation is used. An N-type epi layer 10 is provided on the surface. This epi layer becomes a beam. First, a gauge portion is formed in a normal semiconductor manufacturing process. A silicon oxide film 11 is formed on both surfaces of the substrate. Next, a portion of the silicon oxide film on the surface is removed by etching to form a window for producing a gauge resistor by ion implantation. Boron is implanted into the window to obtain a P-type impurity implanted layer 12 in the N-type epi layer, that is, a P-type strain gauge resistor 5 for acceleration detection as shown in FIG. ). Next, P ⁺ is added to both ends of the P-type resistor.
Diffusion 13 is performed to form an ohmic contact for extracting an electric signal (FIG. 2B). Silicon oxide is deposited thereon by CVD, and after opening the silicon oxide in the contact portion, aluminum is deposited and etched to form wirings 14 and pads 4 (FIG. 3C). After that, a part of the silicon oxide film on the back surface of the semiconductor substrate is removed, and using this as a mask, anisotropic etching is performed using a solution such as KOH or hydrazine. The etching automatically stops near the interface between the epi layer and the substrate by continuously applying an appropriate voltage to the N type epi layer in advance. Therefore, portions other than the center fixing portion and the peripheral weight portion are formed in a diaphragm shape (FIG. 4D). In the conventional example shown in FIG. 2, the weight of the weight 1 is not enough to detect acceleration by using only silicon. Therefore, usually, a metal having a large weight density such as gold is further loaded on the silicon. ing. When placing metal as a weight, the plating method is usually used, but when electrolytic plating is used,
Complicated pretreatment, such as depositing silver, nickel, etc. on silicon to provide good electrical continuity required for plating and to specify the range in which weights are to be formed, and to improve adhesion strength However, there is a problem that the cost increases and the yield decreases. However, in the present invention, such metal plating is not particularly required, and the manufacturing process can be shortened. In the present invention, if it is desired to further increase the detection sensitivity, metal plating may be performed.

Next, the diaphragm 50 manufactured by the above method is
In order to form the beam 2, etching is performed again from the upper surface of the substrate. Thus, the acceleration sensor of the present embodiment is obtained (FIG. 5E). FIG. 1A shows a first embodiment. a
Is a top perspective view of the semiconductor acceleration sensor of the present invention,
(B) is a side perspective view thereof. Reference numeral 1 denotes a weight portion, and when a vertical acceleration is applied, the weight portion 1 moves up and down in proportion to its magnitude. Reference numeral 2 denotes a beam connecting the weight and the reference point. The acceleration is converted into an electric signal based on a change in the gauge resistance 5 formed on the support portion of the beam. Reference numeral 6 denotes a part of the package, which is connected to the fixed part 3 of the acceleration sensor. By providing an arbitrary pedestal 6 in the package in advance, it is possible to provide a space in which the weight 1 can vibrate. The length of the pedestal is arbitrary. The height of the fixed center of the semiconductor acceleration sensor may be defined as the thickness of the substrate, and a space may be provided by cutting the weight portion 1 of silicon. Further, by appropriately setting the gap between the weight 1 and the pedestal 6 in the non-acceleration state, the stopper functions to prevent the vibrator from being broken when a large acceleration is applied to the beam. The pedestal 6 can also be used.

FIG. 3 shows a second embodiment. As shown in the figure, two beams are provided, and the acceleration signal in directions other than the direction perpendicular to the substrate surface can be ignored. In this case, it is possible to form a piezoresistor on the two beams, so that the sensitivity can be increased. Furthermore, as shown in FIG. 4 of the third embodiment, if the number of beams is four, the directivity and sensitivity can be further increased. By thus increasing the number of beams and providing a plurality of beams, it is possible to achieve an acceleration sensor structure with higher sensitivity and directivity.

In the first to third embodiments, the shape of the weight is limited to a quadrangle, but may be another polygon, a circle or an ellipse. Similarly, the number of beams is limited to 1, 2, and 4 in the embodiment, but any other number may be used. Also, there is no need to install them symmetrically. Although the detailed position of the circuit part that processes the actual signal is not shown in the embodiment, since the sensor receives the signal of the physical quantity for each package, even in the conventional sensor, even if it is a weight part, it is a fixed part. Since a similar acceleration impact is also received, the semiconductor circuit may be formed not only at the fixed portion at the center portion but also at a wide weight portion formed at the periphery.

This sensor functions not only as an acceleration sensor as described above but also as a force sensor by directly applying a load to a weight portion. Therefore, by using this, it is possible to manufacture a very minute balance. To apply a load directly, for example, a minute rod may be brought into contact with the weight portion. Also, if the beam is made thicker than in the case of the above-described embodiment, a larger force can be measured. For example, in the above embodiment, even if only a force on the order of mg can be measured, a force on the order of g or kg can be measured by increasing the thickness of the beam.

Furthermore, the sensor of the present invention can also detect physical quantities other than the physical quantities such as acceleration and force, if they can be converted into the physical quantities by any method. For example, if you want to detect the temperature, you can form a film of a material (metal, insulator, etc.) that has a different coefficient of thermal expansion from the semiconductor that composes the beam, and the beam acts as a bimetal and stresses the gauge resistance. May be measured, and this may be measured. In addition, although the use of a minute rod has been described when used as a force sensor, detection is possible if a physical quantity other than a mechanical quantity such as temperature can be converted into the movement of the rod.

If the temperature change caused by the irradiation of the intense light is detected by the above-mentioned “bimetal” structure beam, the light intensity and the like can be measured through the temperature. That is, the physical quantity to be detected may be converted into another physical quantity, and then converted into a physical quantity and detected.

(Effect of the Invention) In the present invention, the reference point for detecting the physical quantity is set at the center of the sensor, which is completely opposite to the conventional sensor. For this reason, the structure of the sensor is very stable even though the fixed part is smaller than the conventional one.
Moreover, since the weight for detecting the physical quantity is formed not on the center but on the outer periphery, it is possible to increase the weight of the weight in proportion to the square of the distance from the center. Can be used very effectively. Therefore, the area of the chip can be easily reduced to ４ or less as compared with the case where the weight having the same mass as the conventional one is used. As a result, the number of sensors manufactured from one substrate is four times or more, and the cost is reduced by one-half.
It becomes below. Further, the acceleration sensor can usually change the acceleration detection frequency range and sensitivity depending on the weight of the weight used. However, in the present invention, since the weight exists in the outer peripheral portion and is larger than the conventional one, it is necessary to separate the chip. According to the scribe method, an acceleration sensor having an arbitrary acceleration detection range and acceleration sensitivity can be easily obtained with high accuracy. Furthermore, by using a plurality of beams, the directivity can be increased, and an acceleration sensor with small crosstalk can be easily obtained.

[Brief description of the drawings]

1A and 1B are perspective views of an acceleration sensor according to a first embodiment of the present invention, FIGS. 2A and 2B are perspective views of a conventional acceleration sensor, and FIG. FIG. 4 is a perspective view of an acceleration sensor of a second embodiment, FIG. 4 is a perspective view of an acceleration sensor of a third embodiment according to the present invention, and FIGS. 5 (a) to (e) are manufacturing process diagrams of the semiconductor acceleration sensor of the present invention. 1 ... weight, 2 ... beam, 3 ... fixed part, 4 ... aluminum pad, 5 ... gauge resistance, 6 ... pedestal, 7 ... glass cover, 8 ... glass pedestal, 9 ... P type Silicon semiconductor substrate, 10 ... N-type epi layer, 11 ... Silicon oxide film, 12 ... Ion implantation layer, 13 ... P ⁺ diffusion layer, 14 ... Aluminum wiring, 50 ... Diaphragm.

Claims (1)

(57) [Claims] 1. A beam having a fixed point at a central portion serving as a reference point for measurement, having a weight around the central portion, and having a predetermined width connecting the fixed point and the weight. A semiconductor sensor, wherein the fixed point, the weight, and the beam are integrally formed by processing a semiconductor wafer.