JP2002170962A - Semiconductor pressure sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a semiconductor pressure sensor utilizing a piezoelectric resistance effect which can be used stably at a high temperature and which can attain a high reliability against aging. SOLUTION: An i-Ga1-z1Alz1N layer 16 and a p-GaN piezoelectric resistance layer 17 are grown on a GaN substrate 15'. The p-GaN layer 17 is etched to form a piezoelectric resistance 18. Then an SiN insulating film 19 is formed over the hole surface and the part as the piezoelectric resistance 18 is opened, after which an electrode 20 consisting of Ni/Au is formed. An SiN film 21 is formed over the whole back surface of the GaN substrate 15' by P-CVD method. The SiN film 21 and the GaN substrate 15' are etched by selective etching down to expose the i-Ga1-z1Alz1N layer 16.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor pressure sensor utilizing a piezoresistive effect in which a piezoresistive section is provided on a semiconductor thin film and the applied pressure is detected as a change in the resistance value of the piezoresistive section.

[0002]

2. Description of the Related Art There is known a pressure sensor utilizing a piezoresistive effect in which the electric resistance of a semiconductor or the like is changed by an externally applied stress. 2. Description of the Related Art In recent years, research and development of semiconductor pressure sensors using semiconductor materials have been promoted because of their advantages of realizing space saving and integration. For example, U.S. Pat. No. 5,514,898 reports a semiconductor pressure sensor to which a miniaturization technique is applied using a Si material.

On the other hand, III-V compound semiconductors such as Ga
A semiconductor pressure sensor based on a piezoresistive effect using an As or AlGaAs material has been proposed. Because these materials have a larger band gap than Si,
Stable use at high temperatures is expected for those using Si materials and the like. For example, Compound Semicond published in 1999
In uctor 5 (9) November / December, pp.L68, HANS
Compound Semiconductor MEMS f by L.HARTNAGEL et al.
or Sensing and Optical Communication Applications
Have been reported. This is a structure in which GaAs / AlGaAs / p-GaAs materials are stacked in this order, the GaAs portion is etched in an arch shape, and p-GaAs to be a piezoresistor is arranged on AlGaAs in the edge portion etched in an arch shape. Is a piezo sensor. It is described that a sensor using a III-V compound semiconductor can operate stably at a higher temperature than a conventional Si material. In addition, utilizing these characteristics, AlGaAs
/ InGaAs pressure sensor and MEMS based on InP material
(Micro-Electro-Mechanical Systems) or examples of optical filters are also shown.

[0004]

Other materials exhibiting a high piezoresistance effect include quartz and LN (Lithium niobate).
Alternatively, a ceramic material can be used, but the advantages of the group III-V compound semiconductor are that integration is easy, and application and development to MEMS are expected.

[0005] However, although the GaAs / AlGaAs material has an advantage that the band gap energy is larger than that of the Si material, it is not as strong as the Si material. Therefore, in order to obtain a piezoresistive effect, there is a concern that the aging resistance against plastic deformation such as warpage due to external pressure is not as high as that of the Si material.

SUMMARY OF THE INVENTION In view of the above circumstances, an object of the present invention is to provide a semiconductor pressure sensor having material strength equal to or higher than that of a Si material, high reliability at high temperatures, and high reliability over time. It is.

[0007]

According to a semiconductor pressure sensor of the present invention, a portion of an upper surface of a semiconductor thin film layer supported by a semiconductor supporting portion by exposing a part of a lower surface is formed between an exposed exposed portion and a supporting portion. In a semiconductor pressure sensor provided with a piezoresistive portion near a boundary, the support portion, the semiconductor thin film layer, and the piezoresistive portion are made of a nitride semiconductor.

The nitride semiconductor is made of GaN or AlN
A system is desirable.

The support is made of GaN or AlN,
Preferably, the semiconductor thin film layer is made of i-type AlGaN having a high resistance value, and the piezoresistive section is made of p-type or n-type GaN.

An SiN film having an opening in at least a part of the p-type piezoresistor is formed so as to cover the semiconductor thin film layer and the p-type piezoresistor, and is exposed to the opening. Ni and A on the p-type piezoresistor
It is desirable that an electrode formed by laminating u in this order is formed.

Alternatively, an SiN film having an opening in at least a part of the n-type piezoresistor is formed so as to cover the semiconductor thin film layer and the n-type piezoresistor,
It is preferable that an electrode formed by laminating Ti and Al in this order is formed on the n-type piezoresistor exposed at the opening.

The above-mentioned GaN-based material contains at least N and Ga. In addition, it also indicates that the AlN-based material also contains at least N and Al.

[0013]

According to the semiconductor pressure sensor of the present invention, in the semiconductor pressure sensor having the above-described structure, the supporting portion, the semiconductor thin film, and the piezoresistive portion are made of a nitride semiconductor. Band gap is Si
Since it is larger than a system semiconductor, it can be stably operated at a high temperature. Furthermore, since the nitride semiconductor has a smaller lattice constant than the Si or GaAs-based semiconductor and is hard, the vicinity of the boundary between the exposed portion of the semiconductor thin film and the support portion is cracked over time due to bending due to external pressure. Is suppressed. Therefore, high temporal reliability can be obtained.

In the case where GaN or AlN is used for the supporting portion, a strong supporting portion can be realized because the strength is high as described above.

[0015]

Embodiments of the present invention will be described below in detail with reference to the drawings.

A semiconductor pressure sensor according to an embodiment of the present invention will be described along a manufacturing process. FIG. 1 shows a sectional view of the semiconductor pressure sensor in a manufacturing process.
In addition, trimethyl gallium (TMG), trimethyl indium (T
MI), trimethylaluminum (TMA) and ammonia, silane gas as n-type dopant gas, p
Cyclopentadienyl magnesium (Cp ₂ Mg) is used as the type dopant.

As shown in FIG. 1A, a 30-nm-thick GaN low-temperature layer 10 at a growth temperature of 500 ° C. is formed on a (0001) C-plane sapphire substrate 11 by metal organic chemical vapor deposition. The growth temperature is 1100 ° C and the low pressure is 1.33 × 10 ⁴ (P
In a), a GaN buffer layer 12 is formed with a thickness of about 2 μm. A SiO ₂ film 13 having a thickness of 0.1 μm is formed by a P-CVD apparatus,
By a photolithographic etching to form a stripe pattern in 2μm intervals so as to leave the SiO ₂ film 13 film of 5μm wide. On this SiO ₂ film mask pattern, a 20 μm thick GaN
The film 14 is grown. In addition, HVPE (hydride vapor phase
A 200 .mu.m non-doped GaN film 15 is grown at 1000.degree. C. using an epitaxy method.

Next, as shown in FIG. 1B, the non-doped GaN film 15 grown by the HVPE method is cut and polished from the back surface of the sapphire substrate until the thickness of the GaN film 15 becomes 150 μm. The substrate 15 'is manufactured. Then, an i-Ga _{1 -z 1} Al _z1 N layer 16 (about 2 μm thick) and a p-GaN piezoresistive layer 17 are grown on the GaN substrate 15 ′.

Next, as shown in FIG. 1C, p-Ga
N SiO ₂ film on the piezoresistive layer 17 (not shown) and the resist (not shown) is formed, removing the SiO ₂ film except the piezoresistive portion 18 in BHF (buffered hydrofluoric acid solution) by the usual lithography I do. After removing the resist, the p-GaN piezoresistive layer 17 is etched by selective etching with a RIE (reactive ion etching) apparatus using the SiO ₂ film as an etching mask, and the i-Ga _{1 -z 1} Al _z1 N layer 16 is removed. Expose. Thus, piezoresistive portion 18 made of p-GaN piezoresistive layer 17 on the _{i-Ga 1-z1 Al z1} N layer 16 is formed. By making the layer 16 GaAlN,
Etching can be stopped automatically on 16 surfaces.

Next, after removing the SiO ₂ etching mask by BHF, a SiN insulating film 19 is formed on the entire surface by the P-CVD method, the piezoresistive portion 18 is opened by ordinary lithography, and RIE (reactive The SiN insulating film 19 is etched by selective etching with an (ion etching) apparatus. After stripping the resist, an electrode material made of Ni / Au is deposited by EB deposition. By normal lithography, the upper portion is covered with a resist mask so that the electrode material remains on at least the exposed piezoresistive portion 18, and the electrode material in other areas is removed with an iodine-based etchant, and then the resist is peeled off. An electrode 20 made of Ni / Au is formed.

Next, a resist protective film is formed on the entire surface of the p-GaN piezoresistor 18 side, and a P
A SiN film 21 is formed by a -CVD method, the inside thereof is opened by normal lithography so as to leave near the left and right side surfaces of the GaN substrate 15 ′, and the SiN film 21 is selectively etched by a RIE (reactive ion etching) apparatus. And GaN
The substrate 15 'is etched. Etching can be automatically stopped at the surface of the layer 16 by making the layer 16 GaAlN. Next, the resist on the front surface and the back surface is simultaneously peeled off, and a semiconductor pressure sensor is manufactured.

The semiconductor pressure sensor according to this embodiment is
A central portion of the GaN substrate 15 'is etched to have a support portion in which the GaN substrate 15' near the left and right side surfaces of the paper is left, and a semiconductor thin film layer 16 is formed thereon. The piezoresistive portion 18 is provided near the boundary with the semiconductor thin film layer 16 and on the upper surface of the semiconductor thin film layer 16.

In the semiconductor pressure sensor according to the present embodiment, when pressure is applied, the piezoresistor bends, and the flexure changes the resistance of the piezoresistor 18. The change is detected by the electrode 20 as an electric signal.

The shape of the region removed from the GaN substrate 15 'where the support is formed as viewed from above the sensor is not limited to the shape described in the above embodiment, but may be the GaN near the four end faces of the sensor. The substrate 15 'may be removed in a polygonal shape or a circular shape (including an elliptical shape) so as to leave the substrate 15'. There may be a plurality of areas to be removed.

Further, in the present embodiment, GaN is used as the support, but AlN may be applied. AlN has a higher melting temperature and band gap than GaN,
Stable operation is possible at high temperatures.

Since the semiconductor pressure sensor according to the present embodiment is made of a nitride semiconductor, it has a large band gap as compared with the Si-based materials proposed so far, so that high reliability can be obtained even at high temperatures. Can be.
Further, since the lattice constant is smaller than that of the Si or GaAs-based material, the material is hard, and the generation of cracks or the like due to bending can be suppressed, and high temporal reliability can be obtained. Therefore, the reliability at high temperatures and the reliability over time are higher than those of conventional semiconductor pressure sensors made of a Si material or a GaAs material.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a manufacturing process of a semiconductor pressure sensor according to an embodiment of the present invention.

[Explanation of symbols]

11 substrate 10 GaN low-temperature layer 12 GaN buffer layer 13 SiO ₂ film 14 GaN film 15 non-doped GaN film 15 ′ GaN substrate 16 i-Ga _1-z1 Al _z1 N layer 17 p-GaN piezoresistive layer 18 piezoresistive part 19 SiN insulation Film 20 Ni / Au electrode 21 SiN film

Continued on the front page F-term (reference) 2F055 AA40 BB20 CC02 DD04 EE14 FF38 FF49 GG01 GG12 4K030 AA11 BA38 BB12 CA05 FA10 HA03 LA14 4M112 AA01 BA01 CA03 CA07 CA11 DA03 DA06 DA07 EA07 EA09 EA10 EA11 AC01 AB05 AC05 AD08 AD09 AD14 AD15 DA53 HA21

Claims (5)

[Claims] A piezoresistive portion provided on a top surface of a semiconductor thin film layer supported by a semiconductor support portion with a part of a lower surface exposed, near a boundary between the exposed portion and the support portion; A semiconductor pressure sensor according to claim 1, wherein said support portion, said semiconductor thin film layer, and said piezoresistive portion are made of a nitride semiconductor. 2. The semiconductor pressure sensor according to claim 1, wherein the nitride semiconductor is a GaN-based or AlN-based. 3. The semiconductor thin film layer according to claim 1, wherein said support portion is made of GaN or AlN, and said semiconductor thin film layer is an i-type AlGa
N, and the piezoresistive portion is a p-type or n-type G
3. The semiconductor pressure sensor according to claim 1, wherein the semiconductor pressure sensor is made of aN. 4. An SiN film having an opening in at least a part of the p-type piezoresistor so as to cover the semiconductor thin film layer and the p-type piezoresistor, and is exposed to the opening. 4. The semiconductor pressure sensor according to claim 1, wherein an electrode formed by laminating Ni and Au in this order is formed on the p-type piezoresistive portion. 5. An SiN film having an opening in at least a part of the n-type piezoresistor so as to cover the semiconductor thin film layer and the n-type piezoresistor, and is exposed to the opening. 4. The semiconductor pressure sensor according to claim 1, wherein an electrode formed by laminating Ti and Al in this order is formed on the n-type piezoresistive portion.