JPS582463B2 - Manufacturing method of semiconductor strain detection element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a semiconductor strain detection element, and more particularly to a method of manufacturing an element improved to increase mechanical strength.

FIG. 1 shows the manufacturing process of a conventional semiconductor strain sensing element.

Figure 1a is a front cross-sectional view of a wafer that is the material of the detection element.
On one side of the bulk wafer 2, an impurity diffusion layer 3 is provided at regular intervals, and an oxide film 4 and a protective film 5 are provided on the impurity diffusion layer 3.

On the backside of the wafer, only an oxide film and a protective film are applied over the bulk wafer.

The portion of the wafer 1 in which impurities are not diffused is cut along the cutting line 6 using, for example, a rotary saw embedded with fine diamond particles.

FIG. 1b is a front sectional view showing the state in which the wafer is cut.

Such a cut piece may break even if a relatively small strain (approximately 1000 microstrain or less) is applied to it, so it cannot be used as a semiconductor strain detection element unless its mechanical strength is increased.

FIG. 1C is a front sectional view showing a state where the cut surface of FIG. 1B has been chemically etched.

Chemical etching is performed to increase the mechanical strength of the device by removing thin fissures and areas with disordered crystallinity that occur during cutting.

Since the oxide film 4 is difficult to be etched, the etched cut end surface has a concave shape.

FIG. 1d is a perspective view of a conventional semiconductor strain sensing element manufactured as described above.

The dotted portion on the upper surface is the portion where the impurity diffusion layer 3 is present.

When this element is pinched with tweezers or the like, force is applied locally to the sharp edges, which often causes damage and chipping at that part.

There is a drawback that if strain is applied to a partially cut-out element during measurement, the element will be destroyed from that part.

FIG. 2a is a bar graph showing the breaking strength of the conventional semiconductor strain detecting element, in which the vertical axis shows the frequency and the horizontal axis shows the strain applied to the element in με (microstrain).

Eight test pieces were used for this, and when both longitudinal ends were held and bent, the stress at which the element broke was measured.
All elements were destroyed between 1000 and 1500 με.

This value is not much different from the value (approximately 1000 με or less) measured using the same measurement method without the chemical etching described above.

It is an object of the present invention to provide a semiconductor strain sensing element which has high mechanical strength and which has a higher rate of commercialization than raw materials, while eliminating the above-mentioned drawbacks.

The gist of the present invention is to form the side surface of the detection element into a convex shape by taking advantage of the property that the portion with a high impurity concentration is chemically etched at a higher rate than other portions.

FIG. 3d is a perspective view of a semiconductor strain detection element which is an embodiment of the present invention.

The surface on which the impurity diffusion layer 13 is present and its opposite surface are flat, but the etched surface 17 other than that is a convex surface, so the angle of each edge is an obtuse angle.

In order to do this, it is manufactured through the following steps.

FIG. 3a is a front cross-sectional view of the wafer, and a high concentration impurity substance 18 is formed on the front and back surfaces of the bulk wafer 12 wider than the cutting width of the cutting line 16.

The impurity diffusion layers 13 for strain detection are formed on only one side of the bulk wafer at regular intervals as shown in the figure.

Next, an oxide film 14 is formed thereon, but at this time, the oxide film at the high concentration impurity layer 18 is thinner than at other locations.

The protective film 15 is applied to a uniform thickness on the oxide film.

FIG. 3b is a front cross-sectional view of the wafer in the cut state;
FIG. 3C is a front sectional view showing the chemically etched state of FIG. 3B.

Since the high concentration impurity layer 18 is quickly etched, the side surfaces become convex and each edge angle becomes an obtuse angle.

To cut the wafer, the back surface of the wafer is temporarily adhered to a Bakelite plate or the like and cut with a diamond disk saw or the like.

In this way, when the element cutting is finished, there is less damage to the notch and the element can be cut cleanly.

Note that the Bakelite plate does not need to be separated; it is immersed in the etching solution as it is and removed after etching is completed.

The chemical etching solution is a mixture of hydrofluoric acid, nitric acid, etc. in an appropriate ratio, and is used to etch the wafer piece shown in FIG. 3B while stirring well.

Both surfaces of the wafer piece are not etched because they have protective films, but the mechanically cut sides are particularly exposed to the high concentration impurity layer 1.
8 is quickly etched to form a convex cylindrical surface.

FIG. 4 is a diagram showing the relationship between electrical resistivity and chemical etching rate of silicon in which impurities are diffused.

The vertical axis shows the etching rate in μ/min, and the horizontal axis shows the electrical resistivity in Ω/d.

It is well known that when impurities are diffused into silicon, the electrical resistivity decreases as the impurity concentration increases, but Figure 4 also shows that the etching rate increases rapidly when the impurity concentration exceeds a certain value. I can say that.

The concentration of impurities that rapidly increases the etching rate is
For example, in an n-type silicon semiconductor, it is approximately 4 x 1012 cm-3
, p-type silicon semiconductor is approximately 1×10 18 cm −3 .

If the high concentration impurity 18 is set higher than the concentration at which the etching rate rapidly increases as shown in FIG. 4, a convex side surface will be obtained as shown in FIG. 3C.

Although the oxide film 14 is etched relatively slowly, the high concentration impurity tube 18 underneath disappears and the area that comes into contact with the etching solution increases, so that the etching progresses and only this part remains protruding. do not have.

On the other hand, the etching rate near the center of the bulk wafer 12 remains as a substrate, so the etching rate is low.

Therefore, the side surface of the element forms a smooth convex circular tube surface.

When the element is pinched with tweezers or the like, the convex portion of the cylindrical side surface is naturally held down, so that the ridgeline portion of the element is not damaged.

In conventional elements, the oxide film layer, which has a slow etching rate, protrudes and the remaining edge angles are acute, so they are easily damaged when pinched with tweezers.

FIG. 2b is a bar graph showing the breaking strength of the detection element of this example, in which the vertical axis shows the frequency and the horizontal axis shows the strain in με.

There were 12 samples used in the test, and the measurement method was the same as in Figure 2 a, but there were measured values between 3000 and 5000 με, with 7 being between 3500 and 4000 με, the most common. .

That is, it exhibited three times the strength as the conventional detection element shown in FIG. 2a.

As described above, the semiconductor strain detection element of this embodiment has a remarkable effect of exhibiting mechanical strength three times that of the conventional one.

In FIG. 3, a semiconductor strain detection element having an impurity diffusion layer on only one side has been described as an example, but the present invention can also be applied to an element having impurity diffusion layers on both sides.

Elements made in the manner described above are more likely to be commercialized than wafers, and are also useful for improving quality.

As described above, the present invention increases the mechanical strength of a semiconductor strain sensing element by chemically etching the cut surface into a convex shape.
This has the effect of significantly increasing the ratio of wafers to products.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the manufacturing process of a conventional semiconductor strain sensing element, Fig. 2 is a bar graph comparing the breaking strength of the conventional semiconductor strain sensing element and the one according to the embodiment of the present invention, and Fig. 3 is a diagram showing the manufacturing process of a conventional semiconductor strain sensing element.
The figure is a diagram showing the manufacturing process of a semiconductor strain sensing element according to an embodiment of the present invention, and FIG. 4 is a diagram showing the relationship between electrical resistivity and chemical etching rate of silicon in which impurities are diffused. Explanation of symbols, 1, 11... Wafer, 2, 12... Bulk wafer, 3, 13... Impurity diffusion layer, 4, 14... Oxide film, 5, 15... Protective film, 6, 16... Cutting line ,7,1
7...Etched surface.

Claims (1)

[Claims] 1. In a method of manufacturing a semiconductor strain sensing element by mechanically cutting a wafer in which impurities are diffused at intervals on at least one surface and then chemically etching the wafer, the width of the wafer is smaller than the width removed by cutting the wafer. 1. A method for manufacturing a semiconductor strain sensing element, which comprises diffusing impurities over a wide area at a high concentration, mechanically cutting off the ib portion of the impurity, and then chemically etching it.