FI78782B - FOERFARANDE FOER FRAMSTAELLNING AV ETT PIEZORESISTIVT MOTSTAONDSELEMENT SAMT EN ANORDNING SOM TILLAEMPAR FOERFARANDET OCH EN MED FOERFARANDET FRAMSTAELLD GIVARE SPECIELLT EN TRYCKGIVARE ELLER MOTSVARANDE. - Google Patents

Description

78782 1 A method of manufacturing a pletsoreslstllvlsen resistance element and an apparatus applying the method and a sensor manufactured by the method, especially a pressure sensor or the like.

The invention relates to a method for the preparation of a piezoresistive resistance element.

The invention also relates to an apparatus for carrying out the method of the invention.

The invention further relates to a sensor manufactured by the method and / or device of the invention.

20

In piezoresistive pressure sensors, force sensors or the like, semiconductor strips or patterns grown epitactically on the surface of a suitable insulating crystal, e.g. an artificial sapphire, are known as measuring resistance elements. The material of the resistor elements 25 may be either silicon, germanium or some other semiconductor having suitable piezoresistive properties and which may form an epitactic discrete layer on the surface of said insulating crystal such as sapphire. The previously known method of manufacturing said dimensional resistance elements is the formation of a resistance pattern from a photolithographically uniform epitactic semiconductor layer by known methods.

For example, one of the previously known pressure sensors which can be used in the method according to the invention is referred to in FI Patent Application No. 810667 (filed March 3, 1981) and the corresponding U.S. Patent No. 35 A 373,399 (issued February 15, 1983). In addition, with respect to the prior art, reference is made to U.S. Patent A 127,8A0. These references disclose a semiconductor pressure sensor incorporating a large-scale fusion with a single-crystal voltage sensor or differential circuit made on a sapphire substrate, a p-type silicon with a conductivity. In said silicon of the resistance element 19 20 -3 the density of the openings is between 3.3 x 10 -3 x 10 cm. The above patents are referred to as only one example of the applications to which this invention may relate.

5

The above-mentioned known lithography method for manufacturing such resistance elements is a technically demanding and multi-step process, the equipment cost of which becomes considerably high.

The object of the present invention is therefore to provide a new method, in which a resistor element is manufactured and a device applying the method, with which the device costs can be substantially reduced by up to about one order of magnitude.

15 It is also an object to provide a new method and apparatus the simplicity of which has not been required by the characteristics or quality of the product to be manufactured.

It is a further object of the invention to provide a method and a device in which the metal wiring required for the sensor 20 can be made by the same method and, if necessary, in the same connection.

In order to achieve the above and later objects, the invention is mainly characterized in that said resistor element or elements are grown on a single crystal insulating substrate by laser gas phase growth so that the insulating substrate is or a pattern having a certain crystal orientation determined by the insulating substrate and that the laser beam "drawing" the insulating substrate and the resistance element pattern is shifted relative to each other to increase the desired resistance pattern.

The device according to the invention, in turn, is mainly characterized in that the device comprises in combination a growth chamber with a suction connection to be connected to a suction pump and connections for importing and removing the growth gas, 3 78782 1 laser unit attachable, 5 devices for providing relative movement between the culture medium and the laser beam focus to draw a resistance pattern on the growth substrate, and 10 control units for controlling the operation of the laser and the relative movement of the substrate substrate and the laser beam focus.

The resistor element according to the invention, in turn, is mainly characterized in that the sensor comprises a resistor pattern made on an artificial sapphire film or a corresponding insulating substrate by laser gas phase growth, which resistor pattern is formed mainly of discrete strips of discrete weft or similar semiconductor tapes.

20

The semiconductor laser chemical vapor deposition, LCVD Laser chemical vapor deposition, used in the method and apparatus of the invention is a prior art process, for which reference is made by way of example to the following publications: Journal of Crystal Growth 22 (1974) 125-148, (HM Manasevit) "A 25 survey of the heteroepltaxial growth of semiconductor Films on Insulating substrates "; D.J. Ehrlich and J.Y. Tsao, "A review of laser-microcochemical processing"; and Brit.J.Appi.Phys., 1976, Vol. 18, (J.D. Fllby and Nielsen) "Single-crystal Films of Silicon on insulators".

According to the invention, the semiconductor resistor patterns can be formed directly by laser gas phase growth (LCVD) so that only an epltaktlne semiconductor strip having the desired resistance pattern is grown by suitably moving the laser beam and the growth medium relative to each other. Silicon heteroepltactic gas phase growth (LCVD) 35 according to the method of the invention takes place, for example, by decomposing a suitable gaseous semiconductor compound, for example silane, by means of a laser at an elevated temperature on the surface of the substrate. The substrate is, for example, o (alumina) crystal, i.e. artificial sapphire, quartz or Spinelli.

a 78782 1 The gas phase growth obtained by the process according to the invention is not fundamentally different in nature from the homoepitactic laser culture of silicon, which is discussed, for example, in the following reference D. Bauerle et al., Appl Phys. A 30 147-149 (1983). However, one important difference is that sapphire is very transparent at the wavelengths used, so its heating with a laser is mainly based on the ability of silicon or the like already grown on the surface to absorb enough radiation so that the process is continuous. Within the scope of the invention, it is also possible for the growth to be carried out on a surface of the substrate in which a uniformly strong silicon layer or the like is already prepared, which is subsequently etched away. The temperature at the point of growth must be quite high locally (about 1300..1400 ° C) in order to produce monocrystalline silicon or the like. In order to avoid large temperature differences in the lilac, substrate preheating can be used if necessary.

15

According to the invention, the resistance pattern of the sensor is formed by moving the laser beam relative to the surface of the substrate according to a set program. By adjusting, for example, the pressure of the growth gas, the power of the laser, its alignment and / or the speed of movement of the laser beam, the thickness, width and quality of the increasing semiconductor strip can be influenced. In addition, said preheating of the substrate can be used as a control parameter, if necessary. The invention will now be described in detail with reference to some embodiments of the invention shown in the figures of the accompanying drawing, to the details of which the invention is in no way narrowly limited.

Figure 1 shows, partly in block diagram form, an apparatus applying the method according to the invention.

Figure 2 shows a central axial section of a Piet sorescent pressure sensor according to the invention.

Figure 3 shows the same as Figure 2 seen from above.

Figure 4 illustrates a schematic side view of a resistance pattern growth event according to the invention.

5,78782 1 Figure 5 shows the same as Figure 4 seen from above.

The laser education apparatus shown in Figure 1 comprises a laser 10 e.g.

Nd: YAG, by means of which, by means of the mirror 11, the laser beam LB is directed through the optics 5 18 to the insulating substrate 20, on which the resistance pattern 35 is grown.

The apparatus comprises a chamber 12 which is evacuated by a vacuum pump 16 together 17. The chamber 12 is connected to common 14, 15, one of which 14 is charged with (G 2) silicon-containing gas inside the chamber, e.g. silane (SiH 2). The growth gas is circulated in the chamber 12 by sucking 10 (G) together through 15. The pressure of the growing gas is, for example, p - 0.1 bar. A base 19 is arranged inside the growth chamber 12, which is moved by devices 21 and 22. The devices 21 and 22 can be, for example, x-y coordinate mechanisms known per se. The operation of the equipment is controlled by the control unit 25 according to the set program. The control unit 25 monitors the operation of the laser 15 10 and the movement control unit 24 of the base 19, which in turn controls the actuator 23 of the transfer mechanism 21,22 of the base 19.

20

The wall of the chamber 12 has a window 13 which transmits the light of the laser 10 as well as possible. A polished sapphire crystal, e.g. a polished sapphire crystal, on which the resistance pattern 35 is grown, is attached to the substrate 19. The laser beam LB is aligned by means of the optics 18 so that the focal point of the beam LB hits the surface of the safflower ridge 20. The crystal 20 is heated by a heating device 26.27 of the substrate 19, e.g. to a temperature of about T · = 200 ° C to 600 ° C.

The method according to the invention works as follows. When the focus L of the laser beam LB hits the surface of the insulating substrate 20, e.g. safflower, due to the locally elevated temperature, silicon crystallizes in the region 28 'from the growth gas, e.g. SiH 2, to separate crystals to form the single crystal strip 28 shown in Figures 4 and 5. and single crystals as the substrate 20 is moved in Figures 4 and 5, the arrow A direction. In the method of the invention, the laser beam LB 35 locally heats the surface of the substrate 20 to such a high temperature that the gas molecules in the immediate vicinity of the surface decompose. They produce silicon and possibly a small amount of the desired alloying agent.

6 78782 1 The temperature is so high and the other conditions such that silicon grows on the surface of the sapphire 20 to form a strip-like single crystal 28 when the laser F is shifted from focus F. Essential to the growth event according to the invention is that the orientation of the plate 28 is determined by the orientation 5 of the sapphire crystal 20 as the exact orientation ratio.

In addition to a suitable semiconductor gas, the gas phase of the culture may also contain an inert carrier gas, such as hydrogen or nitrogen, and, if necessary, a gas containing a small amount of 10 substances for semiconductor doping, e.g. diborane (p-type) or arslin.

AsH 2 (n-type). By moving the substrate according to the program set by the x-y coordinate mechanism 21,22 or the like, a piezoresistive resistance pattern 35 suitable for the sapphire substrate 20 is "drawn" with the focus F of the laser beam LB, an example of which is shown in Fig. 3.

15

The growth of the resistance pattern 35 can be controlled by adjusting the power of the laser 10, the size of the focal point (adjusted by optics 18 or changing the distance of the substrate 19 in the direction of the laser beam LB), the focus F and the substrate 20, the growth gas composition, the pressure and / or the growth substrate 20 temperature.

The following is a non-limiting example illustrating the invention.

Figures 2 and 3 show an example of a piezoresistive pressure sensor made by the method and apparatus of the invention, comprising a body part 30 inside which a chamber 31 is bounded, into which the pressure P to be measured is introduced. The body part 30 has a thread 32 with which the pressure sensor is connected, for example, to a threaded body in a pressure transmitter or the like. The other end of the body portion 30 is closed by a sapphire film 20 (30) having a piezoresistive dimensional resistance pattern 35 made by the method of the invention. Wires 36a, 36b, 36c, -36d are soldered to said metallizations 37, which are connected to the measuring electronics.The metallizations 37 connecting the piezoresistive resistance elements 35 on the surface 35 of the sapphire film 33 are preferably a metal-containing gas, from which the metallizations 37 between the resistor elements 35 are drawn with the focus of the laser beam F.

The pressure sensor shown in Figures 2 and 3 operates in such a way that the pressure P 5 to be measured causes deformations in the crystal film 20, which in turn causes changes in the resistance of the resistance elements 35 like strain gauge strips. The resistance element 35a, 35b, 35c, 35d is connected, for example, as a bridge, the balance of which changes under different effects of the deformations of the film 20 on the different resistance elements 35a, 35b, 35c, 35d. The balance of the bridge is detected by a measuring electron (not shown), and an electrical signal proportional to the measured pressure P is obtained from the bridge connection formed by the resistor elements 35.

In this connection, it should be emphasized that the method and apparatus of the invention are in no way limited to the pressure sensor shown in the figure and which is described only as one of the fields of application of the invention, for example.

The following is a non-limiting experimental example of the invention in which it was found that growth occurs under the following conditions:

20 laser Nd: YAG

wavelength 1,319 pm laser power 20 W (continuous) growth gas approx. 50 Z SIR. +50 Z Ar 4 gas bellows approx. 360 mbar 25 focal lengths approx. 10 pm beam transfer rate approx. 10-30 pm / s at substrate temperature 25 ° C.

Em. in the example, the growth was carried out by first holding the laser beam at 00 pay until growth began, after which the laser beam was moved at such a rate that the resulting tape grew evenly. Optimal conditions were achieved by adjusting the laser power, which in turn affected the transfer rate.

The following claims set forth within the scope of the inventive idea, the various details of the invention may vary and differ from those set forth above by way of example only.

Claims (12)

1 Claims A method of manufacturing a piezoresistive resistor element (35), which method comprises applying a piezoresistive resistor element or elements (35) to a chemical substrate (CVD) of an insulating substrate (20), characterized in that said resistor element or elements (35) are grown on a crystalline insulating substrate (20). as laser gas phase growth (LCVD) such that the insulating substrate (20) is locally heated by laser light and thus the growth gas molecules are thermally decomposed on the surface of the insulating substrate to form a resistor element that the laser beam (LB) "drawing" the insulating substrate (20) and the resistor element pattern (35) is shifted relative to each other to increase the desired resistance pattern. Method according to Claim 1, characterized in that a suitable insulating crystal is used as the growth substrate (20), on the surface of which the growth of the resistance pattern is performed epitactically. 20 A method according to claim 2, characterized in that an artificial sapphire crystal is used as said growth substrate (20), the surface of which on which the growth is performed is polished. Method according to one of Claims 1 to 3, characterized in that the metal conductors (37) or other similar conductive parts between the piezoresistive resistance elements (35) are grown with the same equipment and preferably in the same connection from the metal gas by laser gas phase growth (LCVD). 30 Method according to one of Claims 1 to 4, characterized in that a gas containing silane (SiH 2) or another similar semiconductor and, if necessary, an inert carrier gas is introduced into the growth chamber (12). 35 Process according to Claim 5, characterized in that a suitable amount of doping gas, such as diborane B'H or arsine AsH, is added to the growth gas. L O j 9 78782 Apparatus for carrying out the method according to one of Claims 1 to 6, characterized in that the apparatus comprises, in combination, a growth chamber (12) with a suction connection (17) to be connected to the suction pump (16) and connections (14, 15) for importing the production gas and for removal (Gout), devices (21,22,23) of a laser unit (10) having an alignable and focusable laser beam 10 (LB) on the growth substrate (20), a substrate substrate (19) to which the growth substrate (20) can be attached, 24) having relative motion between the medium (19) and the focus (F) of the laser beam (LB) to draw a resistance pattern 35 on the growth substrate (20), and a control unit (20) controllable by the operation of the laser (10) and the substrate (19). ) and 20 movements of the focus (F) of the laser beam (LB). Apparatus according to claim 7, characterized in that the position (F) of the focus (F) of the laser beam (LB) is arranged substantially fixed and that the growth medium (19) is arranged to be displaced in a plane substantially perpendicular to the incoming direction of the laser beam (LB) by an xy coordinate mechanism or the like. . Apparatus according to Claim 7, characterized in that the culture medium is fixed and the laser beam is arranged to be movable. 30 Device according to Claim 7, 8 or 9, characterized in that the laser beam (LB) is directed inside the growth chamber (12) via a window (13) made in its wall. Device according to one of Claims 7 to 9, characterized in that in connection with the substrate base (19) there is a heating resistor (27) to which an adjustable heating electric current is supplied from the heating unit (26). Sensor made by a method according to one of Claims 1 to 6 and / or by an apparatus according to one of Claims 7 to 11, in particular a pressure or force sensor, characterized in that the sensor comprises an artificial sapphire film (20) or a corresponding insulating substrate. laser gas phase growth (LCVD) resistance patterning (35), which resistance pattern is formed mainly of discrete crystalline lead strips (28) or similar semiconductor strips whose orientation is determined by the insulating substrate. Piezoresistive force or pressure sensor according to Claim 12, characterized in that the metal conductors (37) connecting the resistance elements (35a-d) and / or other patterns, such as conductive parts, are made as laser gas phase growth in connection with silicon-grown resistance patterns (35). . 15 20 25 30 35 il 78782