JPH0413867B2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a measurement method of a semiconductor pressure sensor in a wafer process, and more specifically,
The present invention relates to a method for measuring a semiconductor pressure sensor that enables the measurement of the pressure sensitivity of a diaphragm type semiconductor pressure sensor, typically a medical semiconductor pressure sensor attached to the tip of a catheter.

<Prior art> Semiconductor pressure sensors were developed based on the fact that when mechanical stress is applied to a semiconductor crystal such as silicon, the piezoresistance effect causes a large change in resistance. A strain gauge resistor was diffused into the surface layer of the crystal, a Wheatstone bridge was assembled with these four strain gauge resistors, and a recess was formed on the back side of the silicon single crystal by etching, and the thin part was used as a diaphragm. , electrodes are placed at appropriate locations on the surface. When pressure is applied to the semiconductor pressure sensor, the diaphragm deforms and the resistance value of the strain gauge resistor changes greatly due to the piezoresistive effect, making it possible to obtain a bridge output proportional to the pressure.

The above-mentioned semiconductor pressure sensors are very small, and in medical applications in particular, multiple semiconductor pressure sensors are attached to the tip of a catheter and inserted into the body, so peripheral circuits such as a temperature compensation circuit and a pressure sensitivity compensation circuit are incorporated. Even if it is a chip, it must be small, with each side of one chip being about 1 mm or less.

Therefore, as described above, applying pressure to the diaphragm from the surface of a very small semiconductor pressure sensor and measuring the bridge output by bringing the electrode of the semiconductor pressure sensor into contact with the measurement probe is as follows:
Very difficult.

For this reason, the conventional method for measuring semiconductor pressure sensors in the wafer process is to place the wafer of the semiconductor pressure sensor on a wafer stage table, and measure the electrodes formed on the surface of the wafer without applying pressure. The method was to make measurements only electrically by making contact with a commercially available probe.

<Problems to be Solved by the Invention> The above method does not perform measurements with pressure applied to the diaphragm, so the diaphragm formed in each semiconductor pressure sensor through processes such as ion implantation and etching There are slight variations in thickness and uniformity, and there are slight variations in the degree of deformation of the diaphragm in response to actually applied pressure, which poses a problem in that highly accurate measurements cannot be performed. In addition, in order to prevent this variation, it is impossible in practice to measure the pressure sensitivity by applying pressure to the diaphragm for each chip after cutting out the wafer, because the chip size is small as described above. Therefore, there was a problem in that it had to be used with slight variations allowed. Furthermore, it is conceivable to measure the pressure sensitivity after mounting the sensor chip on a package, but if the sensor chip does not have the desired pressure sensitivity, it will have to be discarded including the package, resulting in a large amount of cost. The problem was that it was wasted.

<Object of the Invention> The present invention has been made in view of the above-mentioned problems, and provides a semiconductor pressure sensor that makes it possible to easily measure the pressure sensitivity of a semiconductor pressure sensor regardless of chip size in a wafer process. The purpose of this study is to provide a method for measuring

<Means for Solving the Problems> In order to achieve the above object, a measurement method using a semiconductor pressure sensor of the present invention provides a method for measuring pressure between a wafer and a wafer stage having a plurality of holes for vacuum suction. An intermediate member made of a porous material is interposed, and the back side of the wafer is vacuum-suctioned through the hole to deform all the diaphragms facing the intermediate member, and the semiconductor pressure sensor is removed from the front side of the semiconductor pressure sensor. It measures pressure sensitivity.

<Function> If the above semiconductor pressure sensor measurement method is used,
By using multiple holes provided in the wafer stage base and vacuuming the back side of the wafer through an intermediate member made of porous material, a pressure sensor is formed on all semiconductor pressure sensors directly facing the intermediate member. The electrical output of the semiconductor pressure sensor in the deformed state, i.e.,
The pressure sensitivity of the semiconductor pressure sensor can be measured from the front side of the wafer using a measurement probe.

Therefore, it is possible to measure a semiconductor pressure sensor in a wafer process by generating negative pressure corresponding to the pressure applied to the diaphragm from the surface by vacuum suction from the back side of the diaphragm and measuring the electrical output. I can do it.

<Examples> Hereinafter, examples will be described in detail with reference to the accompanying drawings showing examples.

FIG. 2 shows a semiconductor pressure sensor. The semiconductor pressure sensor 1 has a very small total thickness of about 400 μm, and has strain gauge resistors 121, 122, 123 on the surface layer of a silicon single crystal 11. ,12
The four strain gauge resistors are connected in series by the diffusion lead part 13, and the diffusion lead part 1
Al pads 141, 142, 14 in succession with 3
3,144,145 are formed. and,
A recess 15 is formed on the back surface of the silicon single crystal 11, and a thin portion (10 to 30 μm thick) serves as a diaphragm 16.

FIG. 1 is a schematic cross-sectional view showing the measurement method of the semiconductor pressure sensor of the present invention. The wafer stage table 2 is made of a plate material 21 made of stainless steel, synthetic resin, etc., and is slightly wider than the bottom surface of the wafer 3. Then, a recess 22 that is slightly smaller than the bottom surface of the wafer 3 is provided on the top surface, and the intermediate member 4 is placed in the recess 22.
is attached, and a plurality of through holes 5 for vacuum suction are provided on the bottom surface of the recess 22.

The intermediate member 4 attached to the recess 22 is made of a porous material (specifically, a metal or glass foam,
or hard foam such as polystyrene).

When the wafer 3 is placed on the intermediate member 4 mounted on the wafer stage base 2 and vacuum suction is applied using the through hole 5, the porous holes of the intermediate member 4 cause the through hole 5 and the wafer 5 to be separated. It communicates with the back surface of the wafer 3 to generate negative pressure almost uniformly over the entire back surface of the wafer 3.

Therefore, the negative pressure applied to the recesses 15 of all the semiconductor pressure sensors 1 formed on the wafer 3 becomes almost uniform, and when the diaphragms 16 formed in all the semiconductor pressure sensors 1 receive pressure from the front side. Deform it in the same way as Al pad 141,1
45 and Al pad 143 (between bridge input terminals),
By bringing the measurement probe 6 into contact with the Al pad 142 and the Al pad 141 (between the bridge output terminals), power can be supplied to the bridge and the output (pressure sensitivity) can be measured.

FIG. 3 shows a state in which the diaphragm 16 is deformed, and four strain gauge resistors 121, 122, 123, configuring the bridge circuit shown in FIG.
Of the strain gauge resistors 121 and 123 diffused in the center of the diaphragm 16, the strain gauge resistors 121 and 123 are compressed as the diaphragm 16 deforms, and the strain gauge resistors 1 diffused in the periphery of the diaphragm 16 are compressed as the diaphragm 16 deforms.
22 and 124 are expanded as the diaphragm 16 deforms.

As the above strain gauge resistors, those whose resistance value increases in proportion to the compressive stress are used, and the resistance values of the strain gauge resistors 121, 122, 123, and 124 are R1, R2, R3, and R4, respectively. , as the diaphragm 16 deforms, R2 and R4 increase, and R1 and R3 decrease. In other words, the potential between the terminals of R2
V ₁ increases and the potential V ₂ across R3 decreases.

Therefore, as the diaphragm 16 deforms, the bridge output, ie, V ₁ -V ₂ increases.

By measuring the bridge output by scanning the measurement probe 6 over the surface of the wafer 3, the pressure sensitivity of the semiconductor pressure sensor 1 can be measured before cutting out the wafer 3 into chips.

In summary, by performing electrical measurements from the front side of the semiconductor pressure sensor 1 and setting pressure from the back side of the semiconductor pressure sensor 1, the pressure sensitivity of the semiconductor pressure sensor 1 can be measured in the wafer process. It can be easily performed regardless of chip size.

It should be noted that the present invention is not limited to the above-mentioned embodiments. For example, by providing the measurement probes 6 in correspondence with the Al pad positions of all the semiconductor pressure sensors 1 formed on the wafer 3, It is possible to measure all the semiconductor pressure sensors in one time, and various design changes can be made without changing the gist of the present invention.

<Effects of the Invention> As described above, according to the measurement method of a semiconductor pressure sensor of the present invention, a negative pressure corresponding to the pressure applied to the surface of the diaphragm can be generated using the vacuum suction hole of the wafer stage table. The diaphragms of all semiconductor pressure sensors formed on the wafer are deformed almost uniformly by generating pressure on almost the entire back surface of the wafer, and the pressure sensitivity can be measured using a measurement probe in this state. It is now possible to measure the pressure sensitivity of semiconductor pressure sensors during the wafer process without having to move the wafer stage relative to the wafer stage, simplifying the measurement process and reducing costs for semiconductor pressure sensors. It has a unique effect.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-section showing an embodiment of a method for measuring a semiconductor pressure sensor according to the present invention, and FIG. 2 is a plan view and a front sectional view of the semiconductor pressure sensor. Figure 3 shows
FIG. 4 is a state diagram when pressure is applied to the semiconductor pressure sensor, and FIG. 4 is an electric circuit diagram showing the electrical configuration of the semiconductor pressure sensor. DESCRIPTION OF SYMBOLS 1...Semiconductor pressure sensor, 2...Wafer stage base, 3...Wafer, 4...Intermediate member, 5...Through hole, 6
...Measurement probe, 16...Diaphragm.

Claims (1)

[Claims] 1. A method for measuring the characteristics of a semiconductor pressure sensor by setting a wafer on which a diaphragm-type semiconductor pressure sensor is formed on a wafer stage,
An intermediate member made of a porous material is interposed between the wafer and a wafer stage base provided with a plurality of holes for vacuum suction, and the back side of the wafer is vacuum-suctioned through the holes, and the back surface of the wafer is vacuum-suctioned. 1. A method for measuring a semiconductor pressure sensor, comprising: deforming all diaphragms for the semiconductor pressure sensor, and measuring the pressure sensitivity of the semiconductor pressure sensor from the surface side of the semiconductor pressure sensor using a measurement probe. 2. A method for measuring a semiconductor pressure sensor according to claim 1, wherein pressure sensitivity is measured by scanning a measurement probe over a wafer.