A pressure-sensitive chip for a semiconductor pressure sensor is formed of a silicon single crystal similar to in an integrated circuit (IC) component, and is provided with, at a center portion of this chip, a diaphragm formed by thinning the thickness of the chip. And, on the surface of this diaphragm, piezoresistive pressure-sensitive gauges (semiconductor strain gauges) are formed. When pressure is applied to the diaphragm, the diaphragm is deformed to change the pressure-sensitive gauges in electric resistance, and this change in electric resistance is detected as an electric signal, whereby a pressure or a change in pressure is measured. Semiconductor pressure sensors include relative pressure-type semiconductor pressure sensors for measuring relative pressures and absolute pressure-type semiconductor pressure sensors for measuring absolute pressures.
A sectional view of an absolute pressure-type semiconductor pressure sensor is shown in FIG. 10. By making a glass substrate 23 adhere to a rear-surface side of a pressure-sensitive chip 21, a vacuum space is formed between a diaphragm 20 and a glass substrate 23. A pressure applied to the front surface of the diaphragm 20 is measured as an absolute pressure with reference to a vacuum pressure of the rear-surface side as a standard. The drawing shows a condition where the diaphragm 20 has been warped owing to pressure applied to the front surface of the pressure-sensitive chip 21.
As a conventional absolute pressure-type semiconductor pressure sensor, one whose pressure-sensitive chip 21 has been protected by a case has been proposed (see Japanese Unexamined Patent Application, First Publication No. 2000-88687, for example). An example of this pressure sensor is shown in FIG. 11. A glass substrate 23 is attached to the pressure-sensitive chip 21 which is provided with piezoresistive pressure-sensitive gauges (unillustrated) formed on a silicon substrate, and a vacuum chamber 24 is formed therebetween. The pressure-sensitive chip 21 and glass substrate 23 are covered with a case 25, and the pressure-sensitive chip 21 is connected to leads 27 via bonding wires 26.
In such an absolute pressure-type semiconductor pressure sensor, due to presence of the case 25, damage to the bonding wires 26 and deterioration of the pressure-sensitive gauge electrodes are prevented. Connecting the pressure-sensitive gauge electrodes to an external electronic measuring device directly by soldering becomes a factor in fluctuation of sensor output since stress occurs owing to a difference in thermal expansion, and therefore, to connect them, the bonding wires 26 and leads 27 are used. As a result, with a structure having the case 25, bonding wires 26, and leads 27, reduction in size is difficult.
In order to realize reduction in size of an absolute pressure-type semiconductor pressure sensor, one whose pressure-sensitive chip and leads have been electrically connected by conductive bumps has been proposed (see Japanese Unexamined Patent Application, First Publication No. 2002-82009). An example of this pressure sensor is shown in FIG. 12. A bump 33 having conductivity is formed on one surface 32 of a pressure-sensitive chip 31, and the bump 33 and a lead 36 are electrically connected in a condition where the one surface 32 of the pressure-sensitive chip 31 and one surface 35 of the base 34 are opposed.
However, in this structure, since the pressure-sensitive chip 31 and lead 36 are firmly connected via the bump 33, when a change in temperature occurs, stress caused by a difference in thermal expansion between the pressure-sensitive chip 31 and an electronic measuring device occurs, and the stress easily concentrates on the bump 33. When strain of the bump 33 becomes great as a result of this stress concentration, there is a possibility that a problem such as electrode exfoliation and an increase in the resistance value occurs. In addition, as a result of occurrence of a fluctuation in the resistance value of a piezoresistive pressure-sensitive gauge owing to this stress, the sensor erroneously detects that a fluctuation in pressure has occurred. Accordingly, when reduction in size is attempted by a connection using bumps 33, it is necessary to provide the bumps 33 with some stress relieving function.
On the other hand, in recent years, with the reduction in size of semiconductor devices, a reduction in size of semiconductor packages has been realized. Of these, one for which reliability of a connecting portion has been improved and reduction in size has been realized by providing a resin post structure in a solder bump portion and a stress concentrated in the bump is relieved by this resin post has been proposed (see Japanese Unexamined Patent Application, First Publication No. 2002-280476, for example). An example of this semiconductor package is shown in FIG. 13. This has been provided by coating a resinous projection 44 provided on a insulating resin layer 43 of a wafer 41 with a conductive layer 45, and connection reliability has been improved and reduction in size of the semiconductor package has been realized by forming a post 46 constructed so as to disperse and absorb a stress by way of deformation of the resinous projection 44.
The present invention has been made in view of the above-described circumstances, and an object thereof is to provide a semiconductor pressure sensor for which reduction in size has been realized without impairing pressure measurement accuracy and connection reliability by connecting a pressure-sensitive chip to an electronic measuring device by use of bumps having a stress relieving function.