The present Invention concerns a procedure for manufacturing a piezoresistive resistance element, by said procedure a piezoresist- ance resistance element, or such elements, being produced on an insulator substrate by gas phase growing.

The invention also concerns an apparatus intended for implementing the procedure of the invention.

The invention furthermore concerns a pick-up manufactured by the procedure and/or apparatus of the invention.

As known in the art, in piezoresistive resistance pressure pick-ups, force pick-ups or equivalent are used for measuring resistance el¬ ements, semiconductor strips or configurations grown by an epitaxial process on the surface of a suitable insulator, for instance a sapphire. The material of the resistance elements may be either silicon, germanium, or another semiconductor which has suitable piezoresistive properties and which may form an epitaxial mono- crystal layer on the surface of the respective insulator, such as a sapphire. The procedure, known in the art, for producing said measuring resistance elements is to form the resistance configuration photolithographically from a continuous epitaxial semiconductor layer by procedures known In the art.

As an example of a pressure pick-up of prior art which may be contemplated in the procedure of the invention, reference is made to the Finnish patent application No. 810667 (filed March 3, 1981) and to the equivalent U.S. Patent No. 4,373,399 (granted Feb. 15, 1983). Furthermore, regarding the state of art reference is made

to the U.S. Patent No. 4,127,840. In these references is disclosed a semiconductor pick-up which contains a measuring resistance, in which capacity serves a monocrystalline strain pick-up or differ¬ ential circuit made on sapphire substrate of silicon which is of p type as to its conductivity. In the silicon of said resistance element, the density of vacancies is in the range from 3.3 x lO-*-^ to 3 x 10 ²⁰ cm ^"3 . The patents cited above are merely cited as an example of the kind of applications with which the present invention may be associated.

The above-mentioned lithographic procedure, known in the art, for producing said resistance elements is a technically exacting process involving a plurality of steps and in which the apparatus invest¬ ments reach considerable magnitude.

The object of the present invention is therefore to provide a novel procedure, a resistance element thereby produced, and an apparatus applying the procedure, by which the apparatus cost may be substan¬ tially reduced, even by one order of magnitude.

It is also an object, to provide a novel procedure and apparatus of which the simplicity had not to be achieved at the expense of the product properties or quality.

Furthermore, it is an object of the invention to provide a procedure and apparatus in which the metallic wiring required in the pick-up can be produced by the same procedure and, if required, in the same connection.

in order to attain the objectives presented above, and others which will become apparent later on, the invention is mainly characterized in that said resistance element, or elements, is/are grown on a monocrystal insulator substrate in laser gas phase growing In such manner that laser light is applied to heat the insulator substrate locally and in this way growth gas molecules are thermally decom¬ posed on the surface of the insulator substrate, whereby as resist-

ance element is produced, from the growth gas, a semiconductor strip or configuration which consists of separate crystals in its main part and which has a given crystal orientation determined by the insulator substrate, and that the insulator substrate and the laser beam "tracing" the resistance element configuration are moved in relation to each other in order to grow a resistance configuration such as is desired.

The apparatus of the invention, again, is mainly characterized in that the apparatus comprises, in combination,

a growth chamber with a suction connector connectable to a vacuum pump and with connectors for gas introduction and removal,

laser unit by which a laser beam can be directed and focussed on the growth substrate,

a substrate base on which the growth substrate can be mounted,

means by which relative movement can be produced between the growth substrate and the focus of the laser beam for tracing the resistance configuration on the growth substrate, and

a control unit by which the operation of the laser and the movement relative to each other of the substrate base and the laser beam focus can be controlled.

The resistance element of the invention, again, is mainly character¬ ized in that the pick-up comprises a resistance configuration produced by laser gas phase growing on an artificial sapphire film or another equivalent insulating material substrate, said resistance configuration being composed in its main parts of monocrystal silicon strips, or of equivalent semiconductor strips, the orien¬ tation of which Is determined by the Insulator substrate.

The laser gas phase growing, LCVD - Laser Chemical Vapour Depo-

sition, of semiconductor material which is applied in the procedure and apparatus of the invention is a process known in the art, regarding which reference is made, by way of example, to the refer¬ ences: Journal of Crystal Growth 22 (1974) 125-148, (H.M. Manasevit) " A survey of the heteroepitaxial growth of semiconductor films on insulating substrates"; D.J. Ehrlich and J.Y. Tsao, "A review of laser-microchemical processing"; and Brit, J.Appl.Phys. , 1976, Vol. 18, (J.D. Filby and Nielsen) "Single-crystal films of silicon on insulators".

As taught by the invention, the semiconductor resistance configur¬ ations can be formed directly by laser gas phase growing (LCVD) in that one only grows an epitaxial semiconductor crystal strip having the shape of the desired resistance configuration, by appropriately moving the laser beam and the growth substrate in relation to each other. The heteroepitaxial gas phase growing (LCVD) of silicon according to the invention is for instance accomplished in that a suitable gaseous semiconductor compound, e.g. silane, is decomposed with the aid of the laser at elevated temperature on the surface of the substrate. The substrate is, for instance, an o-aluminium oxide crystal, i.e., an artificial sapphire, quartz or spinel.

The gas phase growing accomplished by the procedure of the invention is not decisively different as to its nature from homoepitaxial laser growing of silicon, which has been dealt with e.g. in the reference: D. Bauerle et al.: Appl.Phys. A 30 147-149 (1983). An important difference Is, however, that sapphire is highly trans¬ parent at the wavelengths that are employed, and therefore its heating with the laser is mainly based on the ability of the silicon or equivalent already deposited on the surface to absorb radiation in sufficient quantity so that the process can be made continuous. It is also possible within the scope of the invention that the growing is done on the surface of a substrate on which has already been provided a silicon layer or equivalent of uniform thickness and which is later etched off. The temperature has to be rather high locally at the point of growth (about 1300-1400 °C) in order

that monocrystal silicon or equivalent might be produced. In order to counteract excessive temperature differences, preheating of the substrate may be applied if necessary.

As taught by the invention, the resistance configuration of the pick-up is formed by moving the laser beam relative to the substrate surface in accordance with a predetermined programme. It is possible by controlling the pressure of the growing gas, e.g. silane, the laser output power, its aiming and/or the speed of movement of the laser beam, to influence the thickness, breadth and quality of the semiconductor strip that is growing. One may furthermore use for control parameter, if required, the preheating of the substrate, already mentioned. In the following, the invention is described in detail, referring to certain embodiment examples, presented in the figures of the attached drawings, yet to the details of which the invention is in no way narrowly confined.

Fig. 1 presents, partly as a block diagram, the apparatus applying the procedure of the invention.

Fig. 2 presents a central axial section through a piezoresistive pressure pick-up according to the invention.

Fig. 3 presents the same as Fig. 2, viewed from above.

Fig. 4 illustrates, in a schematic elevational view, the growth event of the resistance configuration of the invention.

Fig. 5 presents the same as Fig. 4, viewed from above.

The laser growing apparatus depicted in Fig. 1 comprises a laser 10, e.g. an Nd:YAG, by which over the mirror 11 is directed a laser beam LB through the optics 18 onto the insulator substrate 20, on which the resistance configuration 35 is being grown. The apparatus com- prises a chamber 12, which is evacuated with the suction pump 16 through the connector 17. The chamber 12 is connected to the connec-

tors 14,15, through the connector 14 being introduced (G^ _n ) into the chamber gas which contains silicon, e.g. silane (SiH.4) . The growing gas is circulated in the chamber by drawing it out (G _out ) through the connector 15. The growing gas pressure is e.g. p - 0.1 bar. Within the growing chamber 12 has been disposed a base 19, which is moved by means 21 and 22. The means 21 and 22 may for instance be x-y coordinate mechanisms known in themselves in the art. The oper¬ ation of the apparatus is controlled by the control unit 25 in accordance with a preset programme. The control unit 25 monitors the operation of the laser 10 and the control unit 24 for the movements of the base 19, the latter in its turn controlling the actuating means 23 of the movement mechanism 21,22. In connection with the base 19 may be provided a heating resistance 27, to which a control¬ lable heating current is supplied by the heating unit 26, which is controlled by the control unit 25 if required.

In the wall enclosing the chamber 12 has been provided a window 13, as transparent as possible to the light of the laser 10. On the base 10 has been mounted, for substrate 20, e.g. a polished sapphire crystal, on which growing of the resistance configuration 35 takes place. The laser beam LB has been directed with the aid of optics 18 in such manner that the focus of the beam LB exactly hits the surface of the sapphire crystal 20. The crystal 20 is heated with the heating means 26,27 of the base 19 e.g. to temperature about x _ 200-600 °C.

The procedure of the invention operates as follows, when the focus F of the laser beam LB hits the surface of the substrate, e.g. a sapphire crystal, thereon starts, owing to the locally elevated temperature, from the growing gas, e.g. from SIH4, to crystallize in the area 28' silicon in monocrystal form so that a strip 28 of separate crystals, shown in Figs 4 and 5, will be produced when at the same time the base 19 and the monocrystal substrate 20 thereon are moved in the direction of the arrow A in Figs 4 and 5. In the procedure of the invention, the laser beam LB heats the surface of the substrate 20 locally to such high temperature that the gas

molecules in the immediate vicinity of the surface are decomposed. For them is produced silicon and, possibly, a minor quantity of desired doping substance.

The temperature is so high, and other conditions are such, that the silicon grows on the surface of the sapphire 20 to form a strip- shaped monocrystal 28 when the laser focus F is being moved. The essential circumstance in the growth event of the invention is that the orientation of the silicon crystal 28 will be determined in conformity with the orientation of the sapphire crystal 20, in epi¬ taxial orientation relationship.

The gas phase in the growing process may in addition to a suitable, semiconductor-loaded gas, also contain an inert carrier gas, such as hydrogen or nitrogen and, when required, gas containing a small quantity of a substance needed to dope the semiconductor, e.g. diborane H_ _* ^6 (p type) or arsine AsH (n type) . By moving the base with the aid of the x-y coordinate mechanism 21,22 or equivalent in accordance with a preset programme, with the aid of the focus F of the laser beam LB is "traced" on the sapphire substrate 20 the desired piezoresistive resistance configuration 35, of which an example is shown in Fig. 3.

The growth of the resistance configuration 35 can be controlled by controlling the output of the laser 10, the size of the focus (regulated with the aid of the optics 18 or by changing the distance of the substrate 19 in the direction of the laser beam LB) , the speed of travel of focus F and substrate 20, the composition of the growing gas, the pressure, and/or the temperature of the growth substrate 20.

In the following is presented a non-restrictive test example of the invention. It was found that growth takes place under the following conditions:

Laser - Nd:YAG

Wavelength - 1.319 μm

Laser output - 20 W (continuous)

Growing gas - about 50 % Sil.4 + 50 % Ar Gas pressure - about 360 mbar

Focus size - about 10 μm

Beam moving speed - about 10-30 μm/s

Substrate temperature - 25 °C

In the above example, growing was performed in the manner that the laser beam was at first kept stationary until growth came under way, whereafter the laser beam was moved with such speed that the strip grew uniformly. Optimum conditions were reached by regulating the laser output, which in its turn has its influence on the moving speed.

In the following is presented a non-restrictive example illustrating the invention.

In Figs 2 and 3 is presented a piezoresistive pressure pick-up pro¬ duced using the procedure and apparatus of the invention, said pick¬ up comprising a frame part 30, inside which is confined a chamber 31, into which the pressure P that shall be measured is conducted. The frame part 30 has a thread 32 by which the pressure pick-up is connected to a threaded element e.g. on a pressure transducer or equivalent. One end of the frame part is closed with a sapphire film 20, on which by the procedure of the invention has been provided a piezoresistive measuring resistance configuration 35. The measuring resistance configuration 35 consists of resistance elements 35a, 5b, 35c,35d, which have been connected with metallizations 37a, 7b,37c, 37d to form a bridge circuit. To said metallizations 37 have been soldered leads 36a,36b,36c,36d, which are connected to measuring electronics. The metallizations 37 interconnecting the piezoresis¬ tive resistance elements 35 on the surface of the sapphire film 30 are advantageously produced in connection with producing the resist¬ ance elements 35. This involves leading into the chamber 12 a gas

containing metal and from which the metallizations 37 between the resistance elements are traced using the focus F of the laser beam.

The pressure pick-up of Figs 2 and 3 operates in the manner that the pressure P that is to be measured causes deformations of the crystal film 20, which in their turn give rise to changes of resistance in the resistance elements 35 in the manner of strain gauges. The re¬ sistance elements 35a,35b,35c,35d have been connected for instance to form a bridge circuit, of which the equilibrium is changed, as the deformations of the film 20 act in different ways on the dif¬ ferent resistance elements 35a,35b,35c,35d. The equilibrium of the bridge is observed with the aid of measuring electronics (not depicted) , and from the bridge circuit constituted by the resistance elements 35 is obtained an electrical signal, which is proportional to the pressure P being measured.

It should be emphasized in this connection that the procedure and apparatus of the invention are in no way restricted to the pressure pick-up presented in the figures and in the text, this pick-up having in fact only been described as an example of an application of the invention.

In the following are stated the claims, various details of the invention being allowed to vary within the scope of the inventive idea defined by these claims and to deviate from that which has been presented in the foregoing by way of example only.