JP2014135391A - Piezoresistive element and semiconductor sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoresistive element with less variation in the output voltage, and the like.SOLUTION: A piezoresistive element 10 includes: a semiconductor substrate 11 of a first conductivity type containing a first impurity; a piezoresistive layer 12 of a second conductivity type which is embedded in the semiconductor substrate 11 and contains a second impurity; and a barrier layer 13 of the first conductivity type which is formed between the surface of the semiconductor substrate 11 and the piezoresistive layer 12, and contains a third impurity. When a region in which the concentration of the second impurity is the concentration of the first impurity or more is defined as the piezoresistive layer 12, and a region in which the concentration of the third impurity is the concentration of the first impurity or more is defined as the barrier layer 13, the piezoresistive layer 12 and the barrier layer 13 overlap each other with a predetermined layer width in a thickness direction of the semiconductor substrate 11.

Description

  The present invention relates to a piezoresistive element and a semiconductor sensor.

  Conventionally, a semiconductor sensor using a piezoresistive element is known. As an example of such a semiconductor sensor, a pressure sensor using a piezoresistive element and having a diaphragm formed of a semiconductor can be cited.

  As a method for manufacturing a piezoresistive element, for example, a method of forming a piezoresistive layer (referred to as a first method) by adding impurities to the surface of a semiconductor substrate by diffusion or ion implantation is known. In addition, a method of forming a buried piezoresistive layer (second method) by implanting impurity layers of different conductivity types into a semiconductor substrate with high energy (for example, 1 MeV) is known (for example, Patent Document 1).

  Further, a method of forming a groove in the semiconductor substrate, forming a piezoresistive layer having a different conductivity type from the semiconductor substrate in the groove, and forming a silicon layer having the same conductivity type as the semiconductor substrate on the piezoresistive layer (first step) 3 is known) (see, for example, Patent Document 2).

Japanese Unexamined Patent Publication No. 7-1331035 JP 2007-250869 A

  However, since the piezoresistive element manufactured by the first method has the piezoresistive layer formed on the surface, the piezoresistive element is easily affected by impurity ions and charges in a humidity atmosphere or the like, and the output voltage fluctuates. Arise.

  The piezoresistive element manufactured by the second method is less affected by impurity ions and charges in the humidity atmosphere than the piezoresistive element manufactured by the first method, but the surface of the piezoresistive layer. The barrier effect is weak and the output voltage fluctuation cannot be completely suppressed. That is, the problem that the output voltage fluctuates is not solved.

  In the case of a sensor using a piezoresistive element (for example, a pressure sensor), the sensor sensitivity depends on the position of the piezoresistive layer in the depth direction from the semiconductor substrate surface. It is also known that the higher the ion implantation energy, the deeper the piezoresistive layer is formed from the surface of the semiconductor substrate.

  That is, when ions are implanted with high energy (for example, 1 MeV), the piezoresistive layer is formed at a deep position from the surface of the semiconductor substrate, which causes a problem that the sensitivity of the sensor is lowered. In this case, in order to increase the sensitivity of the sensor, it is necessary to increase the diaphragm of the pressure sensor, which causes a problem that it is difficult to downsize the sensor.

  Moreover, since the piezoresistive element manufactured by the third method requires more manufacturing steps than the first and second methods, it is possible to manufacture a piezoresistive element with less output voltage fluctuation at a low cost. It is difficult to provide a piezoresistive element with low output voltage fluctuation at a mass production level.

  The present invention has been made in view of the above points, and it is an object of the present invention to provide a piezoresistive element or the like with less output voltage fluctuation.

  The piezoresistive element (10) includes a first conductive type semiconductor substrate (11) containing a first impurity and a second conductive type piezo containing a second impurity embedded in the semiconductor substrate (11). A resistance layer (12), and a barrier layer (13) of the first conductivity type including a third impurity formed between the surface of the semiconductor substrate (11) and the piezoresistive layer (12); A region where the concentration of the second impurity is equal to or higher than the concentration of the first impurity is defined as the piezoresistive layer (12), and the concentration of the third impurity is equal to or higher than the concentration of the first impurity. When the region to be defined is defined as the barrier layer (13), the piezoresistive layer (12) and the barrier layer (13) overlap each other in a thickness direction of the semiconductor substrate (11) with a predetermined layer width. It is a requirement to have

  Note that the reference numerals in the parentheses are given for ease of understanding, are merely examples, and are not limited to the illustrated modes.

  According to the disclosed technique, it is possible to provide a piezoresistive element or the like with less output voltage fluctuation.

1 is a cross-sectional view illustrating a piezoresistive element according to a first embodiment. It is a figure which illustrates the density | concentration profile of the piezoresistive element which concerns on 1st Embodiment. It is an example of the flowchart which shows the manufacturing method of the piezoresistive element which concerns on 1st Embodiment. 6 is a cross-sectional view illustrating a piezoresistive element according to Comparative Example 1. FIG. It is a figure which illustrates the measurement result of the output voltage variation of the piezoresistive element concerning comparative example 1. 6 is a cross-sectional view illustrating a piezoresistive element according to Comparative Example 2. FIG. It is a figure which illustrates the measurement result of the output voltage variation of the piezoresistive element concerning comparative example 2. It is a figure which illustrates the measurement result of the output voltage variation of the piezoresistive element concerning a 1st embodiment. It is a figure which illustrates the relationship between an ion implantation acceleration voltage and a pressure sensor sensitivity fall rate. It is sectional drawing which illustrates the semiconductor sensor which concerns on 2nd Embodiment. It is a top view which illustrates the diaphragm surface of the sensor element which concerns on 2nd Embodiment.

  Hereinafter, embodiments for carrying out the invention will be described with reference to the drawings. In the drawings, the same components are denoted by the same reference numerals, and redundant description may be omitted.

<First Embodiment>
FIG. 1 is a cross-sectional view illustrating a piezoresistive element according to the first embodiment. Referring to FIG. 1, the piezoresistive element 10 includes a semiconductor substrate 11, a piezoresistive layer 12, a barrier layer 13, and an insulating film 14. A thermal oxide film may be formed on the surface of the semiconductor substrate 11.

  The semiconductor substrate 11 is a portion where the piezoresistive layer 12 and the barrier layer 13 are formed, and is a first conductivity type semiconductor substrate containing a first impurity. The semiconductor substrate 11 is, for example, a silicon substrate containing a first impurity, but a SiC substrate, a polysilicon film, or the like may be used instead of the silicon substrate.

  In the present application, the first conductivity type is N-type or P-type, and the second conductivity type is P-type or N-type opposite to the first conductivity type. For example, if a pentavalent element such as phosphorus (P) is implanted as the first impurity into the semiconductor substrate 11, an N type semiconductor substrate is formed. If a trivalent element such as boron (B) is implanted, a P type semiconductor is formed. It becomes a substrate. In the present embodiment, a case where the semiconductor substrate 11 is an N-type semiconductor substrate in which phosphorus (P) is implanted as the first impurity will be described below as an example.

  The piezoresistive layer 12 is embedded in the semiconductor substrate 11. The piezoresistive layer 12 has a conductivity type different from that of the semiconductor substrate 11. If a pentavalent element such as phosphorus (P) is implanted as the second impurity into the semiconductor substrate 11, an N-type piezoresistive layer 12 is formed. If a trivalent element such as boron (B) is implanted, a P-type piezoresistor is formed. The resistance layer 12 is formed. Hereinafter, a case where the piezoresistive layer 12 is a P-type layer in which boron (B) is implanted as the second impurity in the semiconductor substrate 11 will be described as an example.

  The barrier layer 13 is formed between the surface 11 a of the semiconductor substrate 11 and the piezoresistive layer 12. The barrier layer 13 has the same conductivity type as the semiconductor substrate 11. If a pentavalent element such as phosphorus (P) is implanted as a third impurity into the semiconductor substrate 11, an N-type barrier layer 13 is formed. If a trivalent element such as boron (B) is implanted, a P-type barrier layer is formed. 13 Hereinafter, a case where the barrier layer 13 is an N-type layer in which phosphorus (P) is implanted as the third impurity in the semiconductor substrate 11 will be described as an example.

The insulating film 14 is formed on the surface 11 a of the semiconductor substrate 11. For example, in the semiconductor sensor using the piezoresistive element 10, the insulating film 14 is an interlayer insulating film that insulates the semiconductor substrate 11 from a conductive layer such as wiring formed thereon. As a material of the insulating film 14, for example, SiO ₂ or SiN can be used.

  Here, the depth and layer width of the piezoresistive layer 12 and the barrier layer 13, and the maximum impurity concentration (maximum impurity concentration) will be described. First, the depth and layer width of the piezoresistive layer 12 and the barrier layer 13 will be outlined with reference to FIG. 1, and then the depth and layer of the piezoresistive layer 12 and the barrier layer 13 will be described with reference to FIG. Define the width etc. accurately.

In FIG. 1, D ₁ indicates the depth of the piezoresistive layer 12, and D ₂ indicates the depth of the barrier layer 13. W ₁ represents the layer width of the piezoresistive layer 12, and W ₂ represents the layer width of the barrier layer 13. W ₃ indicates the layer width of the portion where the piezoresistive layer 12 and the barrier layer 13 overlap in the thickness direction of the semiconductor substrate 11 (hereinafter referred to as the overlapping portion layer width).

The depth _{D 1} of the piezoresistive layer 12 relative to the surface 11a of the semiconductor substrate 11 is preferable to the 0.5μm or 1.1μm or less is optimal when the 0.6μm or 0.7μm below. Layer width _{W 1} of the piezoresistive layer 12 is preferable to be less than 3μm or 1.1 .mu.m, it is optimal when the 2μm or 2.4μm or less.

The maximum impurity concentration of the piezoresistive layer 12 is preferably 1 × 10 ¹⁷ ions / cm ³ or more and 5 × 10 ¹⁸ ions / cm ³ or less, and 4 × 10 ¹⁷ ions / cm ³ or more and 6 × 10 ¹⁷ ions / cm ^3. It is optimal if it is less than cm ³ .

The depth _{D 2} of the barrier layer 13 relative to the surface 11a of the semiconductor substrate 11 is preferable to a 0.01μm or 0.1μm or less is optimal when the 0.01μm or 0.05μm or less.

Layer width _{W 2} of the barrier layer 13 is preferable to the 0.2μm or 0.7μm or less is optimal when the 0.3μm or 0.4μm below. The maximum impurity concentration of the barrier layer 13 is preferably 5 × 10 ¹⁷ ions / cm ³ or more and 1 × 10 ¹⁹ ions / cm ³ or less, and is 8 × 10 ¹⁷ ions / cm ³ or more and 1.2 × 10 ¹⁸ ions / cm 3. ³ or less is optimal.

However, an appropriate numerical value is selected from the above numerical range, and the piezoresistive layer 12 and the barrier layer 13 are set so that the upper side of the piezoresistive layer 12 and the lower side of the barrier layer 13 overlap in the thickness direction of the semiconductor substrate 11. Must be formed. The overlapping portion layer width W ₃ between the piezoresistive layer 12 and the barrier layer 13 is preferably 0.1 μm or more and 0.5 μm or less, and most preferably 0.3 μm or more and 0.4 μm or less.

  Here, the preferable range is a range in which the piezoresistive element 10 functions normally and output voltage fluctuation can be reduced as compared with the conventional piezoresistive element. Further, the optimum range is a range in which the piezoresistive element 10 functions normally, the output voltage fluctuation can be reduced as compared with the conventional piezoresistive element, and the sensor sensitivity reduction rate can be suppressed.

  The sensor sensitivity decrease rate is a numerical value indicating how much the sensor sensitivity has decreased with respect to the sensor sensitivity when the piezoresistive layer 12 is present on the outermost surface of the semiconductor substrate 11. For example, the sensor sensitivity decrease rate can be suppressed to about −25% in the above preferable range, and the sensor sensitivity decrease rate can be suppressed to about −10% in the above optimal range.

  For example, in the example of Patent Document 1, since the sensor sensitivity decrease rate is −40% or more, the piezoresistive element 10 according to the present embodiment does not cause an increase in size, compared with the example of Patent Document 1. Sensor sensitivity decrease rate can be greatly suppressed.

Incidentally, greater than layer width _{W 1} of the piezoresistive layer 12 is 3 [mu] m, and the layer width _{W 2} of the barrier layer 13 is larger than 0.7 [mu] m, piezoresistive element 10 may not function properly. In addition, since the impurity concentration of the piezoresistive layer 12 in the vicinity of the surface 11a of the semiconductor substrate 11 is increased, the thickness of the depletion layer in the barrier layer 13 is reduced, and a sufficient barrier effect cannot be obtained. The output voltage fluctuation increases. In addition, if the high impurity concentration regions of the piezoresistive layer 12 and the barrier layer 13 overlap in the thickness direction, double diffusion occurs, so that a leak current is likely to occur in the semiconductor substrate 11. It becomes a factor that output voltage fluctuation increases.

  Incidentally, in FIG. 1, the depth and the layer width of the piezoresistive layer 12 and the barrier layer 13 are schematically shown. However, they are accurately defined here with reference to FIG. As described above, in this embodiment, as an example, the P-type piezoresistive layer 12 and the N-type barrier layer 13 are formed on the N-type semiconductor substrate 11 (silicon substrate).

In FIG. 2, the horizontal axis represents the depth [μm] with respect to the surface 11 a of the semiconductor substrate 11. That is, the origin of the horizontal axis (intersection with the vertical axis) is the surface 11 a of the semiconductor substrate 11. In FIG. 2, the vertical axis represents the impurity concentration [ions / cm ³ ] of other layers based on the concentration of the first impurity of the semiconductor substrate 11. That is, the origin of the vertical axis (intersection with the horizontal axis) is the concentration of the first impurity (for example, phosphorus which is an N-type impurity) in the semiconductor substrate 11.

  In FIG. 2, Pi is the concentration profile of the second impurity (for example, boron which is a P-type impurity) in the piezoresistive layer 12, and Ba is the third impurity (for example, an N-type impurity in the barrier layer 13). It is a concentration profile of a certain phosphorus).

In the present embodiment, a region where the second impurity concentration is equal to or higher than the first impurity concentration of the semiconductor substrate 11 is defined as the piezoresistive layer 12. That is, when the depth of the piezoresistive layer 12 is defined on the basis of the surface 11a of the semiconductor substrate 11, the piezoresistive layer 12 has the first depth at which the second impurity concentration and the first impurity concentration match. It is having a _{P 1.} Then, further, piezoresistive layer 12, a second depth P ₂ which deeper than the first depth P ₁ concentration of the second impurity is maximized, depth first than the second depth P ₂ 2 and the third depth P _{3 in} which the concentration of the first impurity is the same.

The depth D ₁ from the surface 11 a of the semiconductor substrate 11 to the second depth P _{2 is} the depth of the piezoresistive layer 12. Further, the layer width W ₁ from the _first depth P ₁ to the third depth P _{3 is} the layer width of the piezoresistive layer 12.

Similarly, in this embodiment, a region where the concentration of the third impurity is equal to or higher than the concentration of the first impurity of the semiconductor substrate 11 is defined as the barrier layer 13. That is, when the depth of the barrier layer 13 is defined with reference to the surface 11 a of the semiconductor substrate 11, the barrier layer 13 has a fourth depth B ₄ that coincides with the surface 11 a of the semiconductor substrate 11. Further, the barrier layer 13 is deeper than the fourth depth B ₄ and has a fifth depth B _{5 at} which the concentration of the third impurity is maximum, and a third depth deeper than the fifth depth B ₅ . having a concentration of impurities and the sixth depth B ₆ in which the concentration of the first impurity match.

The depth D ₂ from the surface 11 a of the semiconductor substrate 11 to the fifth depth B _{5 is} the depth of the barrier layer 13. Further, the layer width W ₂ from the _fourth depth B ₄ (= surface 11 a of the semiconductor substrate 11) to the sixth depth B _{6 is} the layer width of the barrier layer 13. Further, the layer width W ₃ from the first depth P ₁ of the piezoresistive layer 12 to the sixth depth B ₆ of the barrier layer 13 is the overlapping portion layer width.

In the example of FIG. 2, the first depth P ₁ of the piezoresistive layer 12 is deeper than the surface 11 a of the semiconductor substrate 11. The concentration may be higher than the concentration of the first impurity. In that case, like the fourth depth B ₄ of the barrier layer 13, the first depth P ₁ of the piezoresistive layer 12 coincides with the surface 11 a of the semiconductor substrate 11, and the overlapping portion layer width W ₃ is It corresponds to the layer width W ₂ of the barrier layer 13.

The preferred ranges are summarized in Table 1, and the optimum ranges are summarized in Table 2. Thus, in the present embodiment, the piezoresistive layer 12 and the barrier layer 13 necessarily have an overlap of the overlapping portion layer width W _{3 in} the thickness direction of the semiconductor substrate 11. That is, in the present embodiment, the overlap layer width W ₃ does not become a zero.

  Next, a method for manufacturing the piezoresistive element 10 will be briefly described with reference to FIG. As an example, an example in which a P-type piezoresistive layer 12 and an N-type barrier layer 13 are formed on an N-type semiconductor substrate 11 is shown.

First, in step S100, an N-type silicon wafer to be the semiconductor substrate 11 is prepared. Next, in step S101, the surface of the silicon wafer is thermally oxidized to form a thermal oxide film (SiO ₂ ).

  Next, in step S102, an opening is formed in the thermal oxide film, and boron, for example, as an impurity is ion-implanted into the silicon wafer from the opening to embed the P-type piezoresistive layer 12 in the silicon wafer. At this time, the ion implantation acceleration voltage and the dose are controlled so that the depth, layer width, and maximum impurity concentration of the piezoresistive layer 12 fall within the ranges shown in Table 1 or Table 2. It should be noted that the relationship between the depth, layer width, and maximum impurity concentration of the piezoresistive layer 12, the ion implantation acceleration voltage, and the dose can be obtained in advance through experiments, calculations, and the like.

  Next, in step S <b> 103, for example, phosphorus is ion-implanted into the silicon wafer from the opening to form an N-type barrier layer 13 between the surface 11 a of the semiconductor substrate 11 and the piezoresistive layer 12. At this time, the ion implantation acceleration voltage and the dose amount are controlled so that the depth, layer width, and maximum impurity concentration of the barrier layer 13 fall within the ranges shown in Table 1 or Table 2. Note that the relationship between the depth, the layer width, and the maximum impurity concentration of the barrier layer 13, the ion implantation acceleration voltage, and the dose can be obtained in advance by experiments, calculations, or the like.

  Next, in step S104, annealing is performed under a predetermined condition, and then in step S105, an insulating film 14 that is an interlayer insulating film is formed on the surface of the silicon wafer, whereby the piezoresistive element 10 is completed. In the case of manufacturing a semiconductor sensor using the piezoresistive element 10, a process for forming contact holes, electrodes, diaphragms, and the like is further required. An example of a semiconductor sensor using the piezoresistive element 10 will be described later.

  Here, the effects produced by the piezoresistive element 10 according to the present embodiment will be described with reference to a comparative example. FIG. 4 is a cross-sectional view illustrating a piezoresistive element according to the first comparative example. Referring to FIG. 4, the piezoresistive element 10A according to Comparative Example 1 is different from the first embodiment in that the piezoresistive layer 12 is formed in the vicinity of the surface 11a of the semiconductor substrate 11 and does not have a barrier layer. It differs from the piezoresistive element 10 (refer FIG. 1) which concerns on this form.

  In the piezoresistive element 10 </ b> A, the piezoresistive layer 12 is formed in the vicinity of the surface 11 a of the semiconductor substrate 11. Therefore, although it is preferable in that high sensor sensitivity can be obtained, since the barrier layer is not formed, for example, it is easily affected by impurity ions and charges in a humidity atmosphere or the like, causing a problem that the output voltage fluctuates.

  FIG. 5 is a diagram illustrating the measurement result of the output voltage fluctuation of the piezoresistive element according to Comparative Example 1. Note that the measurement results in FIG. 5 show that a plurality of semiconductor sensors 100 (described later in the second embodiment) on which the piezoresistive element according to Comparative Example 1 is mounted are prepared, and each semiconductor sensor 100 is set in a high temperature and high humidity state. After standing for a period of time, the temperature was returned to room temperature and energized individually, and the output voltage was measured and plotted. That is, the measured output voltage is the output voltage of the Wheatstone bridge circuit of the semiconductor sensor 100.

  As shown in FIG. 5, in the piezoresistive element 10A after the test, the output voltage varies in the range of about ± 0.1 to ± 1.3 mV, and the output voltage variation with time is large. This is presumably because in the piezoresistive element 10A, the piezoresistive layer 12 is formed in the vicinity of the surface 11a of the semiconductor substrate 11, and thus is easily affected by impurity ions and charges in a high temperature and high humidity state.

  FIG. 6 is a cross-sectional view illustrating a piezoresistive element according to the second comparative example. Referring to FIG. 6, the piezoresistive element 10B according to the comparative example 2 is that the piezoresistive layer 12 and the barrier layer 13 are separated from each other and have no overlap at all. 10 (see FIG. 1).

  In the piezoresistive element 10B, the piezoresistive layer 12 is formed to a predetermined depth from the surface 11a of the semiconductor substrate 11, and a barrier layer 13 is further formed. Therefore, it is considered that the influence of impurity ions and charge in a high-temperature and high-humidity state is reduced as compared with the case of the piezoresistive element 10A according to Comparative Example 1.

  However, since the concentration of the barrier layer 13 is low and there is no sufficient depletion layer, the barrier effect is weak, and for example, output voltage fluctuations due to the influence of impurity ions or charge in a humidity atmosphere or the like cannot be completely suppressed.

  FIG. 7 is a diagram illustrating the measurement result of the output voltage variation of the piezoresistive element according to Comparative Example 2. Note that the measurement results in FIG. 7 show that a plurality of semiconductor sensors 100 (described later in the second embodiment) on which the piezoresistive elements according to Comparative Example 2 are mounted are prepared, and each semiconductor sensor 100 is set in a high temperature and high humidity state. After standing for a period of time, the temperature was returned to room temperature and energized individually, and the output voltage was measured and plotted. That is, the measured output voltage is the output voltage of the Wheatstone bridge circuit of the semiconductor sensor 100.

  As shown in FIG. 7, in the piezoresistive element 10B after the test, the output voltage varies in the range of about 0 to +0.3 mV, and the output voltage varies with time. Although the output voltage fluctuation is reduced as compared with the piezoresistive element 10A, it can be confirmed that it is not completely suppressed.

  On the other hand, FIG. 8 is a diagram illustrating the measurement result of the output voltage fluctuation of the piezoresistive element according to the first embodiment. Note that the measurement results in FIG. 8 show that a plurality of semiconductor sensors 100 (described later in the second embodiment) on which the piezoresistive elements 10 are mounted are manufactured, and each semiconductor sensor 100 is left in a high temperature and high humidity state for a predetermined time. The graph is plotted by measuring the output voltage after returning to normal temperature and energizing each individual. That is, the measured output voltage is the output voltage of the Wheatstone bridge circuit of the semiconductor sensor 100.

  As shown in FIG. 8, in the piezoresistive element 10 after the test, the output voltage fluctuation is in the range of about 0 to +0.01 mV, and the output voltage fluctuation hardly occurs. The output voltage fluctuation of the piezoresistive element 10 is suppressed to 1/10 or less as compared with the piezoresistive element 10B according to the comparative example 2.

  This is because, in the piezoresistive element 10, the piezoresistive layer 12 and the barrier layer 13 have a predetermined layer width overlap in the thickness direction of the semiconductor substrate 11. That is, in the piezoresistive element 10, a thick depletion layer is formed in the overlapping portion of the layer widths of the piezoresistive layer 12 and the barrier layer 13, and the effect of suppressing the influence of impurity ions and charges is improved by the formed thick depletion layer. It is.

  The results shown in FIG. 8 can be obtained for both the piezoresistive element 10 manufactured under the preferable conditions shown in Table 1 and the piezoresistive element 10 manufactured under the optimal conditions shown in Table 2. The inventors have confirmed.

  However, as shown in FIG. 9, as the ion implantation acceleration voltage increases, the pressure sensor sensitivity decrease rate increases. When manufacturing under the preferable conditions shown in Table 1, it is necessary to increase the ion implantation acceleration voltage as compared with the case of manufacturing under the optimal conditions shown in Table 2. Therefore, the sensitivity of the pressure sensor is reduced accordingly. The rate increases.

  However, even in the case of manufacturing under the preferable conditions shown in Table 1, it is not necessary to perform ion implantation with high energy (for example, 1 MeV) as in the above-mentioned Patent Document 2, so that it is possible to manufacture under the preferable conditions shown in Table 1. Compared with the conventional piezoresistive element, the pressure sensor sensitivity reduction rate can be reduced. It should be noted that the ion implantation acceleration voltage in the case of manufacturing under suitable conditions shown in Table 1 is about 500 [keV] at the maximum.

  Thus, in the first embodiment, the second conductivity type piezoresistive layer 12 containing the second impurity is embedded in the first conductivity type semiconductor substrate 11 containing the first impurity, and the semiconductor substrate 11 A first conductivity type barrier layer 13 containing a third impurity is formed between the surface 11 a and the piezoresistive layer 12. At this time, the piezoresistive layer 12 and the barrier layer 13 are overlapped with each other with a predetermined layer width in the thickness direction of the semiconductor substrate 11.

  As a result, a thick depletion layer that did not exist in the past is formed in the overlapping part of the layer width, and the effect of suppressing the influence of impurity ions and charge is improved by the formed thick depletion layer, so the output voltage fluctuations than before Can be suppressed.

  The piezoresistive element 10 according to the first embodiment can also provide the following effects. That is, the rate of decrease in sensitivity of the pressure sensor can be reduced as compared with a conventional piezoresistive element in which ions are implanted with high energy (for example, 1 MeV). Thereby, the semiconductor sensor using the piezoresistive element 10 can be miniaturized, and the degree of freedom in designing the semiconductor sensor can be improved.

  In addition, by setting the depth of the piezoresistive layer to 0.5 μm to 1.1 μm, it becomes possible to reduce the area where crystal defects occur in the diaphragm of the semiconductor sensor, which will be described later. Impairment of impact can be prevented.

  Further, a PN junction diode is formed by the piezoresistive layer 12 and the barrier layer 13 having different conductivity types, and the reverse breakdown voltage is lowered. For this reason, when ESD (electro-static discharge) is applied, current flows from the piezoresistive layer 12 to the semiconductor substrate 11 and the density of current flowing through the wiring of the semiconductor sensor is reduced, so that the ESD withstand voltage of the semiconductor sensor can be improved.

<Second Embodiment>
In the second embodiment, an example of a semiconductor sensor including the piezoresistive element 10 according to the first embodiment is shown. In the second embodiment, the description of the same components as those already described is omitted.

  FIG. 10 is a cross-sectional view illustrating a semiconductor sensor according to the second embodiment. Referring to FIG. 10, a semiconductor sensor 100 according to the second embodiment includes a sensor element 200, an adhesive resin 300, a control IC (Integrated Circuit) 400, an adhesive resin 500, a substrate 600, and the like. , A bonding wire 700 and a lid 800.

  Here, the sensor element 200 includes a diaphragm portion 210 and a pedestal 220. The diaphragm portion 210 has a diaphragm surface 250 and a diaphragm support portion 260. Further, a groove 230 is formed in the central portion of the pedestal 220, and the lid 800 has a through hole 810.

  More specifically, the semiconductor sensor 100 has the following configuration. That is, the control IC 400 is bonded to the lower surface of the substrate 600 having three surfaces by the adhesive resin 500, and the pedestal 220 of the sensor element 200 is bonded to the control IC 400 by the adhesive resin 300.

  The adhesive resin 500 exists on the entire lower surface of the control IC 400, but the pedestal 220 has a groove 230 formed in the center, and the adhesive resin 300 exists only in a region where no groove is formed. Pads (not shown) are provided as wiring terminals on the diaphragm surface 250 and the control IC 400 of the sensor element 200, and the pads are electrically connected by bonding wires 700.

  Also, pads are provided as wiring terminals on the middle surface of the substrate 600 (not shown), and the pads of the control IC 400 and the substrate 600 are also electrically connected by bonding wires 700. A lid 800 is installed on the upper stage of the substrate 600 and covers the sensor element 200. A through hole 810 is provided at the center of the lid 800 so that the diaphragm surface 250 can sense an external pressure.

  The sensor element 200 is an element for detecting a predetermined physical quantity, and the semiconductor sensor 100 detects an absolute pressure. Here, the absolute pressure is a pressure based on a complete vacuum (or an absolute vacuum). Therefore, the sensor element 200 has a vacuum reference chamber 240 maintained in a vacuum state. In the present embodiment, the sensor element 200 is described as an example of a pressure sensor element. However, the present invention is applied to various sensor elements 200 that need to eliminate the influence of stress from the substrate 600. Can be used.

  The sensor element 200 includes a diaphragm unit 210 and a pedestal 220. The diaphragm unit 210 is a component that constitutes the sensor surface of the sensor element 200, and detects stress generated by pressure by converting it into an electrical signal. The diaphragm part 210 has a diaphragm surface 250 and a diaphragm support part 260.

  The diaphragm surface 250 is a surface for detecting pressure and is formed in a thin film shape. Diaphragm surface 250 is configured to bend when pressure is applied, and the absolute pressure applied to diaphragm surface 250 can be detected by the deflection. Further, the diaphragm support portion 260 is a support portion that supports the diaphragm surface 250.

  The diaphragm unit 210 may be formed of a semiconductor. For example, by using an SOI (Silicon on Insulator) substrate, the diaphragm surface 250 is formed by a silicon active layer, and the diaphragm support unit 260 is formed by a buried oxide film and a backside silicon substrate. Can be formed.

  The pedestal 220 is a support member that supports the diaphragm portion 210. For example, the back surface of the diaphragm support portion 260 of the diaphragm portion 210 is bonded and fixed onto the surface of the end portion along the outer periphery of the pedestal 220. The pedestal 220 may be composed of, for example, a glass substrate or a silicon substrate. In the case of a glass substrate, a multilayered glass substrate may be used.

  The back surface of the pedestal 220 constitutes the mounting surface of the sensor element 200 and is bonded and fixed to the upper surface of the control IC 400, which is the mounted surface, using an adhesive resin 300.

  FIG. 11 is a plan view illustrating a diaphragm surface of the sensor element. Referring to FIG. 11, the diaphragm surface 250 includes the piezoresistive element 10, an impurity resistance wiring 252, a metal wiring 253, and a pad 254. The piezoresistive element 10 and the impurity resistance wiring 252 constitute a Wheatstone bridge circuit so that an output voltage can be detected.

  The piezoresistive element 10 is a kind of piezoelectric element, and its resistance value changes according to the applied pressure. Therefore, the Wheatstone bridge circuit using the piezoresistive element 10 is configured so that the pressure applied to the diaphragm surface 250 can be detected by the change in the output voltage. That is, the pressure applied to the diaphragm surface 250 can be detected by a change in output voltage corresponding to a change in resistance value of the piezoresistive element 10.

  The metal wiring 253 is a wiring for forming a Wheatstone bridge circuit, and the pad 254 is a terminal or an electrode for electrical connection with the outside. Power is supplied to the pad 254 from the outside to apply a voltage to the Wheatstone bridge circuit, and a change in the output voltage of the Wheatstone bridge circuit is detected from a change in the resistance value of the piezoresistive element 10 due to the application of pressure. Thereby, the absolute pressure applied to the diaphragm surface 250 can be detected. For example, the sensor element 200 can detect the absolute pressure by configuring the diaphragm surface 250 as shown in FIG.

  The preferred embodiment of the present invention has been described in detail above. However, the present invention is not limited to the above-described embodiment, and various modifications can be made to the above-described embodiment without departing from the scope of the present invention. And substitutions can be added.

  For example, in the first embodiment, an example in which the P-type piezoresistive layer 12 and the N-type barrier layer 13 are formed on the N-type semiconductor substrate 11 is shown. The piezoresistive layer 12 and the P-type barrier layer 13 may be formed.

  Further, the impurity of the semiconductor substrate 11 and the impurity of the barrier layer 13 may be different. For example, the impurity of the semiconductor substrate 11 may be phosphorus (P), and the impurity of the barrier layer 13 may be arsenic (As).

  In the second embodiment, the pressure sensor is exemplified as the semiconductor sensor 100 on which the piezoresistive element 10 according to the first embodiment is mounted. However, the piezoresistive element 10 can be mounted not only on the pressure sensor but also on a semiconductor sensor such as an acceleration sensor or a gyro sensor.

DESCRIPTION OF SYMBOLS 10 Piezoresistive element 11 Semiconductor substrate 11a Surface 12 Piezoresistive layer 13 Barrier layer 14 Insulating film 100 Semiconductor sensor 200 Sensor element 210 Diaphragm part 220 Base 230 Groove 240 Vacuum reference chamber 250 Diaphragm surface 252 Impurity resistance wiring 253 Metal wiring 254 Pad 260 Diaphragm Support part 300, 500 Adhesive resin 400 Control IC
600 Substrate 700 Bonding wire 800 Lid 810 Through hole

Claims (10)

A first conductivity type semiconductor substrate containing a first impurity;
A second conductivity type piezoresistive layer containing a second impurity embedded in the semiconductor substrate;
A barrier layer of the first conductivity type formed between the surface of the semiconductor substrate and the piezoresistive layer and containing a third impurity;
A region where the concentration of the second impurity is equal to or higher than the concentration of the first impurity is defined as the piezoresistive layer, and a region where the concentration of the third impurity is equal to or higher than the concentration of the first impurity is defined as the barrier. When defined as a layer, the piezoresistive layer and the barrier layer have a predetermined layer width overlap in the thickness direction of the semiconductor substrate. When defining the depth of the piezoresistive layer and the barrier layer with reference to the surface of the semiconductor substrate,
The piezoresistive layer has a depth at which the concentration of the second impurity and the concentration of the first impurity coincide with each other, or the concentration of the second impurity at the surface side of the semiconductor substrate is higher than the concentration of the first impurity. If it is higher, a first depth that is the same as the surface of the semiconductor substrate, a second depth that is deeper than the first depth and at which the concentration of the second impurity is maximized, and the second depth And a third depth at which the concentration of the second impurity and the concentration of the first impurity coincide with each other deeper than the depth of
The barrier layer includes a fourth depth coinciding with the surface of the semiconductor substrate, a fifth depth deeper than the fourth depth and a maximum concentration of the third impurity, and the fifth depth. And a sixth depth at which the concentration of the third impurity and the concentration of the first impurity coincide with each other,
The piezoresistive element according to claim 1, wherein the predetermined layer width is a thickness between the first depth and the sixth depth.   3. The layer width of the barrier layer matches the predetermined layer width when a thickness between the fourth depth and the sixth depth is defined as a layer width of the barrier layer. Piezoresistive element.   The piezoresistive element according to claim 2 or 3, wherein the maximum value of the concentration of the third impurity is larger than the maximum value of the concentration of the second impurity.   5. The piezo according to claim 2, wherein the second depth is not less than 0.5 μm and not more than 1.1 μm, and the fifth depth is not less than 0.01 μm and not more than 0.1 μm. Resistance element.   6. The piezoresistive element according to claim 5, wherein the second depth is 0.6 μm or more and 0.7 μm or less, and the fifth depth is 0.01 μm or more and 0.05 μm or less. The maximum value of the concentration of the second impurity is 1 × 10 ¹⁷ ions / cm ³ or more and 5 × 10 ¹⁸ ions / cm ³ or less, and the maximum value of the concentration of the third impurity is 5 × 10 ¹⁷ ions. The piezoresistive element according to any one of claims 2 to 6, wherein the piezoresistive element is not less than / cm ^{3 and not} more than 1 x 10 ¹⁹ ions / cm ³ . The maximum value of the concentration of the second impurity is 4 × 10 ¹⁷ ions / cm ³ or more and 6 × 10 ¹⁷ ions / cm ³ or less, and the maximum value of the concentration of the third impurity is 8 × 10 ¹⁷ ions. The piezoresistive element according to claim 7, which is not less than / cm ^{3 and not} more than 1.2 × 10 ¹⁸ ions / cm ³ .   A semiconductor sensor equipped with the piezoresistive element according to claim 1.   The semiconductor sensor according to claim 9, wherein the stress applied to the diaphragm surface is detected by a change in output voltage corresponding to a change in resistance value of the piezoresistive element.

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