JPH0210882A - Semiconductor thin film magnetoresistance element and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain sufficient reliability even in high temperature use such as a gear sensor for a vehicle by forming a material layer made of alkaline earth metal fluoride on a board, and forming a high mobility semiconductor material thin film on the layer. CONSTITUTION:After alkaline earth fluoride and particularly a material layer 2 made of any selected from CaF2, SrF2, BaF2 is formed on a board made of insulator or semiconductor or a surface insulated board 1, a high mobility semiconductor material thin film and particularly a thin film 3 made of InSb is formed. The layer 2 made of the alkaline earth metal fluoride and particularly BaF2 is similar to the lattice constant of InSb, a mixed crystal suitably mixed with CaF2, SrF2, etc. is employed in response to the adaptability of lattice constant with a base board material. Thus, the BaF2, CaF2, SrF2, etc., are oriented in a specific direction on the board, becoming a nucleus forming material of the InSb thin film, and its adhesive properties are satisfactory. Thus, stability at high temperature and high mobility can be imparted thereto.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for manufacturing a semiconductor thin film of a semiconductor thin film magnetoresistive element used in a rotation sensor or the like.

2. Description of the Related Art In general, there are various types of rotation sensors including optical type and magnetic type. Among these, the magnetic method, which is less susceptible to such influences, is the most advantageous, particularly in applications that are affected by the atmosphere, such as dirt and dust. On the other hand, in this magnetic method, there are various methods such as an electromagnetic pickup, a Hall element, and a magnetoresistive element.

In recent years, with the electronicization of automobiles, various sensor elements have been installed for this purpose. Until now, electromagnetic pickups (inductance type) have been used as rotation sensors, especially gear sensors, due to their simplicity and good temperature characteristics. has been used. However, one of the properties recently required of automotive rotation sensors is that they can be detected at very low speeds (0 km/h and up). From this point of view, although the electromagnetic pickup described above has been put into practical use because it is originally impossible to detect low speeds (0 to 50 RPM) and is difficult to miniaturize, it does not necessarily meet current requirements. It does not match.

On the other hand, the Hall element (Hall IC), the ferromagnetic thin film magnetoresistive element, and the semiconductor magnetoresistive element are all capable of detection from the aforementioned low speed. Each of these elements has advantages and disadvantages, but when used as an automotive rotation sensor,
The deciding factors are: (1) it should be possible to directly detect parts that are originally installed in the car (such as toothed rotors) as much as possible.

(2) The operating temperature range of the element must be 150 to +160°C.

02 points are possible.

For (1), what is specifically required is, for example, the distance between the toothed rotor and the element (hereinafter referred to as the gap)
To this end, it is desirable that the drop in output due to widening the gap be small, since the tolerance for this is large. If you think about it from this point of view, it is a Hall element.

Hall ICs and ferromagnetic thin-film magnetoresistive elements have low output and small gaps, making them difficult to use as gear sensors. On the other hand, semiconductor magnetoresistive elements have originally large output and large gap tolerance, and Since it uses the same detection method as current electromagnetic pickups, it is easy to replace, so it is considered suitable for gear sensors.

On the other hand, regarding the temperature characteristic (2), at present, only a Ga1g Hall IC satisfies this.

However, as described above, this GaAs Hall IC must have a small gap and is not necessarily suitable as an automobile gear sensor.

Taking all these points together, it can be said that a semiconductor magnetoresistive element is the most suitable element for an automobile gear sensor, provided that the temperature resistance is improved. As is well known, the characteristics of this semiconductor magnetoresistive element are determined by the mobility of the material. That is, the output in a low magnetic field is proportional to the square of the mobility, and the output in a high magnetic field is proportional to the mobility.

Therefore, InSb, which has the highest mobility among semiconductors, is often used as a material for semiconductor magnetoresistive elements. On the other hand, as is well known, the forbidden band width of InSb is 0.17 eV
It exhibits intrinsic conduction even at room temperature, and the temperature coefficient of resistance of the material is as large as -2%/deg.

For this reason, it is common to connect two magnetoresistive elements in series and use them differentially, and the temperature coefficient of the output in this case is -〇, 2%/dog, and this value is , GaAs
Hall I C+7) Temperature coefficient of output -o, 1%/dog
.

There is no big difference compared to.

In other words, if InSb magnetoresistive elements are used differentially,
The drop in output between room temperature and +150°C is at most 20-3
If it is only a 0% drop and used digitally,
Not a problem.

By the way, most of the InSb magnetoresistive elements currently on the market are of the bulk type, and very few are of the thin film type. The most important reason for this is that, as described above, the output of a semiconductor magnetoresistive element increases as its mobility increases (normally, the mobility required for a semiconductor magnetoresistive element is 200 oOv/Cd or more). That is, bulk single crystals and polycrystals always have higher mobility than thin film non-epitaxial ones. However, when considering the above-mentioned temperature range of -60 to +150'C, the situation is slightly different.

Typically, the operating temperature range of InSb magnetoresistive elements is -20
~+80°C, which is the operating limit for obtaining analog output, and as the temperature increases,
This results in degradation, including device failure, due to increased self-heating as the resistance decreases and therefore the operating power increases.

Normally, in InSb, its mobility is dominated by polar optical scattering in the low temperature region, impurity scattering in the high temperature region, and the peak value of the mobility is at the boundary of each dependent region. On the high temperature side from the peak value, the mobility is -1 of the temperature.
, changes along the seventh power.

In bulk single crystals, etc., the mobility has a steep peak at extremely low temperatures (around 70°C), whereas in thin film types, the mobility peak shifts to the high temperature side and decreases somewhat around room temperature. Has a broad peak. Therefore, for high-temperature applications, the thin-film type is preferable, and in addition, the thin-film type is advantageous because it is easier to increase the resistance, and therefore allows for lower power consumption and miniaturization of the element. It is. Despite these advantages of the thin film type, the reasons why it is not widely used and why it is not used in high temperature applications are considered to be as follows.

First, there is the inherent difficulty in improving mobility with thin-film non-epitaxial devices. (For Evita Kinyal, it is possible to use a CdTe, PbTe substrate, etc., but the substrate cost is extremely high.)
987), it has been revealed that when a cleaved mica substrate is used, a mobility comparable to that of single bond 8 can be obtained, as stated by Line et al. On the other hand, this method is difficult to use in high-temperature applications. This is because the adhesion between InSb and the mica substrate is poor, so a process is used in which this InSb is transferred onto another support substrate via an adhesive layer such as epoxy. Because such a process is used, it is inevitable that the finished device will have a large difference in thermal expansion coefficient between the adhesive layer and the InSb thin film at high temperatures.
In particular, cracks occur in the sb thin film, etc.
It did not have reliability sufficient for practical use in a temperature range of 160°C.

Problems to be Solved by the Invention As mentioned above, an InSb magnetoresistive element is most suitable as a gear sensor, and in high-temperature applications such as automobiles, a thin film type is preferable to a bulk type.
On the other hand, in the thin film type, application of the transfer process due to the poor adhesion between InSb and the mica substrate used for the purpose of improving mobility is due to the fact that the InSb thin film and However, cracks were caused in the InSb due to the difference in thermal expansion coefficient between the adhesive layers (epoxy, etc.), and the InSb did not have sufficient reliability for use in high-temperature applications such as automobiles. From this point of view, the present invention is applicable to gear sensors for automobiles, etc., especially in high-temperature applications.
The main purpose of this invention is to provide a method for manufacturing a semiconductor thin film magnetoresistive element with sufficient reliability.

Means for Solving the Problems In order to solve the above problems, the present invention uses a substrate made of an insulator or a semiconductor, or a surface-insulated substrate, and coats an alkaline earth fluoride, particularly CaF2. Sr.
F2. After forming a layer of material selected from BILF2(7) (including mixed crystal), a thin film of a high mobility semiconductor material, particularly a thin film of InSb, is formed.

Effect In the above structure, the material layer made of alkaline earth metal fluoride, especially BaF, has a lattice constant close to that of InSb, and depending on the compatibility of the lattice constant etc. with the underlying substrate material, CaF
, SrF2, etc., as well as mixed crystals mixed appropriately, these BaF2. CaF2. SrF, etc. are oriented in a specific direction on the base substrate, and serve as a good nucleation material for the InSb thin film, and also have good adhesion.

From the above points, the above-described configuration makes it possible to construct a semiconductor thin film magnetoresistive element having stability at high temperatures and high mobility.

Example (Example 1) FIG. 1 shows the basic configuration of the method for manufacturing a semiconductor thin film magnetoresistive element of the present invention. In this embodiment, CGW is used as the substrate 1.
#7059 (manufactured by -Y-Ning Co., Ltd.) was used. (CGW
The linear expansion coefficient of gyo69 is 4.6X10 (K
)) Immediately after cleaning this substrate 1, it was introduced into a vacuum evaporation apparatus, and after reducing the degree of vacuum to 1 x 10' Torr or less,
The surface of the substrate 1 is heated at 00 to 900° C. for 10 minutes, or the surface of the substrate 1 is hit with a sputtering effect using gas plasma such as Ar or H2, or an ion beam.
In any case, after cleaning the substrate surface, the substrate temperature is 600-700°C and the vacuum degree is 10' order (To
rr) Below, as shown in FIG. 1 (bl), the material layer 2 made of alkaline earth metal fluoride, in this example, B
A material layer 2 made of aF2 is formed on the substrate 1 by evaporating a BaF2 ingot using a resistance heating method.

In these series of steps, the substrate temperature of the material layer 2 made of BaF2 is in the range of 600 to 700°C, the higher the
Its crystallinity is improved, and the lower the pressure, the better the crystallinity. In addition, in this example, the material layer 2 made of BaF 2 was formed by resistance heating of a BaF 2 ingot. Another reason is that when it is formed with an electron beam or the like, a part of BaF 2 decomposes into its constituent elements. , a deviation from stoichiometry occurs in the material layer 2 made of BaF2, whereas resistance heating can maintain good stoichiometry.

Through the above steps, the material layer 2 made of BaF 2 obtained is sharply oriented in the (111) direction.

Thereafter, as shown in FIG. 1(C), an InSb thin film 3 is formed. This InSb thin film 3 has a substrate temperature of 400 to 50
The film was formed using a three-temperature method in which In and Sb were each used as separate sources and the source temperatures were individually controlled at a vacuum level of 10'0rder (TOrr). The crystallinity of the InSb thin film 3 obtained in this way changes as the substrate temperature increases from 400 to 500''C, the higher the temperature, the slower the initial deposition rate that affects initial nucleation, and the later The faster the film formation rate, the more the damage was improved.
This is different from the case where the film formation rate is slowed down. This is because, in normal thin film crystal growth, a high vacuum of 1 o-8 Torr or less is used, so there is no need to consider gas adsorption to the growth surface, whereas in this example, the vacuum level during film formation was 1 o' order(T
orr), for example, adsorption of oxygen gas occurs within a few seconds of the electrolyte and is therefore required to increase the purity of the membrane.

By forming the film in this way, the InSb thin film 3 with a thickness of about 1 μm has a sufficiently large grain size in the film plane direction (lateral direction), and the mobility at room temperature is aoooooV/d.
I got something of a certain degree.

On the other hand, in the case where the InSb thin film 3 is formed on the substrate 1 under the same conditions as described above without forming the material layer 2 made of BaF2 shown in FIG. 1(kl), the grain size is At most, the mobility at room temperature is only on the order of the film thickness, and the thickness of the InSb thin film 3 is about 1 μm.
It was only about 100oOv/c-.

These differences in mobility depending on the presence or absence of the material layer 2 made of BaF2 are ultimately due to the lattice constants (o, e+
snm ) and the lattice constant of BaF 2 layer 2 (0,62
nm) are relatively close to each other, and InSb has a cubic ZnS type and BaF2 has a fluorite type, and their crystal structures are similar.In addition, along the orientation plane of the Ba72 layer 2,
An InSb thin film 3 is grown, that is, the Ba72 layer 2 is InS
In contrast, in the absence of the BIL72 layer 2, homogeneous nucleation is difficult to occur, and the growth direction of the particles constituting the InSb thin film 3 becomes random. , the grain size becomes a polycrystalline film whose grain size is at most on the order of the film thickness direction, and the mobility is subject to scattering at the grain boundary and is regulated thereby. Further, as shown in this example, the CGW#7059 glass (linear expansion coefficient 4.6X10 (K)) substrate 1 is made of InSb
Linear expansion coefficient of thin film 3 (5,04X10'(K'))
The tensile stress is smaller and enters the InSb thin film 3.

As is well known, better mobility results can be obtained under tensile stress. In this respect, the substrate 1 may also be a quartz substrate (5.4×10 (K)).

CGW#7740 (3,25X10 (K)
).

The InSb thin film 3 with high mobility can be obtained even by using CGW$79oo (a×1o (K )) or the like. Still, in this example, the substrate 1 BaF2 layer 2, In
The adhesion between the eyebrows of each of the 5b thin films 3 was good, and no peeling occurred even after repeated temperature cycles between -60 and +160°C.

(Example 2) In this example, a (111) Si wafer is used as the substrate. As shown in Figure 2(a), (111
) The Si wafer 4 was cleaned, and an oxide film of 5 in 2 ts was formed thereon by a thermal oxidation method as shown in FIG.
Thereafter, the alkaline earth metal fluoride, especially BaF2
Even if the material layer 6 and the InSb thin film 7 are sequentially laminated, it is possible to obtain a material with high mobility and good interlayer adhesion, as in Example 1. On the other hand, an alkaline earth metal fluoride 6 is directly formed on the (111) Si wafer 4 without forming an oxide film 5 in 25 on the (111) S1 wafer 4, and an InSb thin film 7 is formed thereon. It is also possible to form In this case, it is important to pay attention to the degree of vacuum (I
108 Torr or less), cleaning treatment of the (111) Si substrate before formation, and selection of alkaline earth metal fluoride 6. When forming the alkaline earth metal fluoride 6 directly on the (111) Si wafer 4, the lattice constant is
CaF2 is 0.548 nm, SrF2 is 0
．． 580 nm, BaF2 is 0.620 nm,
Si is 0.543 nm, InSb is 0.64 nm
8 nm relationship, at the initial stage of formation of the alkaline earth metal fluoride 6, CaF2 with a similar lattice constant was formed on the (111) Si wafer 4, and then Sr was gradually added to the (ljaF2).
The mixed crystal composition mixed with F2 is SrF2! Then, gradually change the mixed crystal composition of SrF2 and BaF2 to
ILF2! It is also possible to obtain an InSb epitaxially grown film oriented in the (111) plane by making a J-touch and making BaF 2 the interface that finally contacts the In8b thin film 7. Also in this case, the adhesion between each layer is good.

In Example 1.2 described above, InSb was used as the high mobility semiconductor material thin film, but InAs (
Lattice constant o, soanm), InGaSb (Lattice constant InSb: o, e 48 nm ~Garb
: o, 61 onm) is also CaF2. SrF2. Ba
By forming a film using a suitable mixed crystal of F2 and matching the lattice constant, a film with good crystallinity, high mobility, and good interlayer adhesion can be obtained.

Further, as shown in FIG. 3, on the InSb thin film B formed by any method of Example 1.2, Cu/Tl double layer, Cu layer, Ag layer, single layer, etc. forming an electrode 9;
After patterning the shorting electrode 10, a photoresist pattern 11 for separating the elements is formed, and in the wet method, HF is used.

In a dry method such as a mixed solution of HNO3, the InSb thin film 8 is etched away using a mixed gas of CF4 and 02.

At this time, the alkaline earth metal fluoride 12 is
It is not eroded by etching and becomes a good etching prevention material. Thereafter, a passivation film such as a 5iON film is applied to prevent moisture absorption, and the device is completed. The device thus completed was subjected to repeated temperature cycles of 60 to +150° C., moisture resistance tests, etc., but it was confirmed that the device did not suffer from the deterioration that occurred in the past, and had extremely high reliability.

Effects of the Invention As described above, in the present invention, a material layer made of an alkaline earth metal fluoride is formed on a substrate made of an insulator or a semiconductor, or a surface insulated substrate, and this material layer - First, since a thin film of high mobility semiconductor material is to be formed, the orientation of alkaline earth metal fluoride is utilized and this is used as a nucleation material to improve the crystallinity of the thin film of high mobility semiconductor material. In addition to improved mobility, the adhesion between layers is also good, and as a result, there is no characteristic deterioration due to film cracks, etc., which occurs in the past, and it is fully reliable in the temperature range of -60 to +160°C. This results in a semiconductor thin-film magnetoresistive element with properties.

[Brief explanation of the drawing]

FIGS. 1(&) to (0) are cross-sectional views showing a basic example of the method for manufacturing a semiconductor thin film magnetoresistive element of the present invention, and FIGS.
((13 is a sectional view of one embodiment of the present invention, FIG. 3(&)
~((il is a perspective view of another embodiment of the present invention. 1.4.13...Group &, 2,6.12...
... Material layer made of alkaline earth metal fluoride, 3, 7.
8... High mobility semiconductor material thin film (InSb). Name of agent: Patent attorney Toshio Nakao and one other person

Claims (6)

[Claims] (1) A substrate made of an insulator or a semiconductor, or
A semiconductor thin film magnetoresistive element in which a material layer made of alkaline earth metal fluoride is formed on a surface-insulated substrate, and a high mobility semiconductor material thin film is formed on this material layer. (2) The material layer made of alkaline earth metal fluoride is Ba
A material layer made of a material selected from F_2, SrF_2, and CaF_2 (including a mixed crystal), and the high mobility semiconductor material thin film is a thin film made of InSb, InAs, or InGaSb. The semiconductor thin film magnetoresistive element according to item 1. (3) The material layer made of alkaline earth metal fluoride is Ba
The semiconductor thin film according to claim 1, wherein the high mobility semiconductor material thin film is a thin film made of InSb, which is a material layer made of a material selected from F_2, SrF_2, and CaF_2 (including mixed crystal). Magnetoresistive element. (4) A substrate made of an insulator or a semiconductor, or
A method for manufacturing a semiconductor thin film magnetoresistive element, comprising the steps of forming a material layer made of an alkaline earth metal fluoride on a surface-insulated substrate, and forming a high mobility semiconductor material thin film on this material layer. (5) The material layer made of alkaline earth metal fluoride is Ba
A material layer made of a material selected from F_2, SrF_2, and CaF_2 (including a mixed crystal), and the high mobility semiconductor material thin film is a thin film made of InSb, InAs, or InGaSb. 4. A method for manufacturing a semiconductor thin film magnetoresistive element according to item 4. (6) The material layer made of alkaline earth metal fluoride is Ba
The semiconductor according to claim 4, wherein the high mobility semiconductor material thin film is a thin film of InSb, in which the material layer is made of a material selected from among F_2, SrF_2, and CaF_2 (including mixed crystal). A method for manufacturing a thin film magnetoresistive element.