The present invention relates to a method of manufacturing strain-detecting devices.
Elements for detecting strain are categorized into a variety of types of elements. One type of strain-detecting device uses a diaphragm on which a strain gage is arranged. The diaphragm responds to stimulation that has been given, and the strain gage senses the stimulation based on physical changes in the diaphragm. Such strain-detecting devices have been manufactured by using various types of methods.
Referring to FIGS. 1 and 2, one type of manufacturing method will now be described. As shown therein, a jig 1 made up of upper and lower plates 1a and 1b are used. This jig 1 is made to have lot of holes 3 formed at given positions thereof. The holes 3 are responsible for sustaining substrates 2 of the strain-detecting devices with precision concerning their sizes and pitches. The holes 3 are the same in number as the substrates 2. A great deal of substrates 2 (dozens of pieces to several hundreds of pieces) are contained in the single jig 1.
Each substrate 2 is formed into a cylindrical body of which one end closed by a diaphragm 4 (refer to FIG. 2). The dimensions, such as an outer diameter, of each substrate 2 is finished with higher precision, because it is required that each substrate 2 be fit into each hole 3 of the jig 1 with no looseness. As shown in FIGS. 1 and 2, after fitting the substrates 2 to the jig 1, all the substrates 2 are positioned such that the upper surfaces of all the diaphragms 4 take the same height position. This height is determined by regarding the upper surface of the upper plate 1a as a reference position. Thus, the upper surfaces of all the diaphragms 4 constitute the same plane.
The jig 1 which sustain the substrates 2 is then delivered to the next step in which a strain gage portion is formed on each diaphragm 4. In this step, first, both of an insulation layer and a strain gage layer are formed by turns on the upper surface of each diaphragm 4. Relying on accurately worked reference holes 5 formed at given positions of the jig 1, patterning a strain gage is carried out using a photolithography process so that a strain gage is formed simultaneously on all the diaphragms 4. Masks are set over the jig 1 with reference to the reference holes 5, and a physical vapor deposition process is conducted to form electrodes and a strain-gage protection layer on the strain gages by turns.
After completing the strain gage portion, the substrates 2 are detached from jig 1. The detached substrates 2, on which the strain gage portions are formed individually, are used as strain-detecting devices.
A second type of method of manufacturing strain-detecting devices is provided by Japanese Patent Publication No. 2768804, which can be pictorially shown in FIGS. 3 and 4. As shown therein, a jig 7 is employed, on which a plurality of pins 6 are built. Each substrate 2 is put on each pin 6 in such a manner that the pin 6 is pressed into a bottomed opening formed in the substrate 2. The bottom of the opening functions as a diaphragm 4. The upper surfaces of all the diaphragms 4 are kept to be included in the same plane. Various thin layers are then formed by turns on each diaphragm 4. The thin layers on the individual diaphragms 4 are then subjected to micro fabrication and other necessary work. Therefore, a plurality of strain-detecting devices are manufactured at a time.
However, the foregoing conventional manufacturing methods have faced various problems.
In the former manufacturing method shown in FIGS. 1 and 2, a first problem comes from the shape of each substrate 2. The substrate 2 can be summarized as being cylindrical, thus being rotatable around its center axis even when being held by the jig 1. It is therefore difficult to position each substrate 2 in its rotating direction.
A second problem results from a gap between each substrate 2 and the jig 1. This gap causes each substrate 2 to shift, against the jig 1, in the plane direction along which the jig 1 (that is, plates 1a and 1b) extends (that is, the X-Y direction in FIG. 1). This shift will spoil positioning between the gage patterns for strain gages and the mask patterns for electrodes and a protection layer. That is, the strain gages cannot be placed in place on each diaphragm 4, being a defective device.
To avoid the manufacture of such defective devices, both of the substrates 2 and the jig 1 should be positioned precisely with each other. To meet this demand, it should be necessary that the jig 1 as well as the substrates 2 be finished with higher precision. A third problems is therefore that the cost of manufacturing strain-detecting devices has been high, because of higher degrees of finishing precision of both of the jig 1 and the substrates 2.
On the other hand, the foregoing latter manufacturing method represented by FIGS. 3 and 4 is also accompanied by a number of problems. A first problem is also concerned with a manufacturing cost. The diaphragms 4 of all the substrates 2 fitted to the jig 7 should be the same height so as to form the same plane. If this condition is satisfied, dimensional errors of the thin layer patterns can be minimized. In order to realize the same plane configuration, both of the reference positions for positioning the substrates 2 on the jig 7 and intervals of holes into which the pins 6 are inserted respectively should be finished with higher precision. Such higher precision of finish will bring about an increase in manufacturing strain-detecting devices.
A second problem results from the fact that each pin 6 is pressed into the bottomed opening (cavity) of each jig 7. There are some cases where pressing the pin 6 into the opening damages the surface of the opening, thus decreasing the reliability of the devices themselves. If such damaged strain-detecting devices are applied to, for example, pressure vessels, the reliability of the pressure vessels themselves will be spoiled as well. In addition, as the number of uses of the jig 7 is increased, the pins 6 are worn away. Further, during the step of forming the strain gage portion, the pins 6 are exposed to a high-temperature atmosphere. Hence the elasticity of each pin 6 is degraded, thereby weakening a force for sustaining the substrate 2. These drawbacks will also lead to unstable factors in enhancing the reliability.
Further, a third problem is caused by the configuration in which each pin 6 is pressed into the bottomed opening of each substrate 2. Because of this configuration, various types of fluid, such as cleaning fluid, developing fluid, rinsing fluid, and resist separating agent, which have been flowed into the bottomed opening of each substrate 2 during a cleaning step and thin-layer micro-fabrication steps, are apt to remain therein, even after completing such steps. The residue of such fluids often brings about a pollutant problem in the various post-steps for manufacturing strain-detecting devices.