JP3603087B2 - Method for forming electrode of β-FeSi2 element - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method of manufacturing a semiconductor device in the field of electronics, in which an electrode for conducting an electric current onto an element material plate or a thin film substrate is formed without depositing a metal material from the outside or bonding it by coating. More specifically, the present invention relates to a method of heating a part of β-FeSi ₂ to convert it into a metal phase to form an electrode.
[0002]
[Prior art]
2. Description of the Related Art In a conventional semiconductor device, a functional material thin film is formed on a silicon (Si) substrate or a flat substrate material, and electrodes for inputting and outputting signals are provided thereon. In the case of an electrode of a relatively large sample piece of ceramic or a functional material, an electrode wire is wound around the sample end, or the electrode wire is fixed to a part of the surface using a metal paste or various solders.
[0003]
On the other hand, in order to perform fine wiring such as light emission / light reception / memory / IC circuit device using Si or III-V compound semiconductor material, various electrode forming methods have been conventionally developed.
[0004]
In general, an element has been formed by depositing a deposited film, a sputtered film, and an ion plating film of a metal conductor on the element surface and processing it into a fine pattern using photolithography technology.
[0005]
[Problems to be solved by the invention]
A semiconductor element requires a semiconductor material and an electrode material. Since the function of the electrode is to introduce or draw a current to or from the functional semiconductor material, a so-called ohmic contact must be made at the interface between the two, which mechanically adheres to each other and shows normal electrical conduction.
[0006]
To that end, (1) a metal that is a good conductor is selected as an electrode material. Generally, aluminum (Al), copper (Cu), silver (Ag), gold (Au), or the like is used. Although a material having high conductivity is desirable, problems such as corrosion after long-term use may occur depending on the potential difference depending on the atmosphere or temperature used and the combination with a semiconductor material. Since changes due to these phenomena must be avoided, it is important to select an electrode material.
[0007]
In addition, in order to maintain a good bonding state between the semiconductor material and the electrode material, at least foreign substances that hinder mechanical contact must be removed. For example, (2) the surfaces of both are washed well to remove organic impurities, and (3) oxides and dust are removed to increase the degree of mechanical adhesion. As a method of bringing the electrode material into contact with the cleaned surface, a metal film is deposited in a vacuum or a film is formed by a sputtering method.
[0008]
However, the operation of keeping this surface clean is a factor that increases the number of steps and increases the price.
[0009]
Furthermore, in order to process the laminated conductive film into an arbitrary electrode pattern shape, (4) using an expensive photolithographic apparatus, fabricating a pattern original mask → applying resist on the semiconductor film surface → exposing → removing the resist film by etching → acid And the process of etching the metal film with an alkaline solution and completing the electrode pattern.
[0010]
However, after forming a fine metal pattern by this photolithography method, (5) when forming a further metal film electrode thereon, a multilayer metal thin film is formed across the etching step formed in the pretreatment. Is formed. At that time, the phenomenon that the film connecting the lower surface and the upper surface of the step is not sufficiently connected, that is, the so-called step coverage is poor occurs, which causes peeling of the electrode film and disconnection.
[0011]
As described above, in these conventional forming methods, in order to increase the production yield and achieve the high quality and low cost targets of the product, expensive equipment is used, and many process inspections are performed. There was a problem of having to spend time and effort.
[0012]
An object of the present invention is to provide a method for forming an electrode of a β-FeSi ₂ element, which can eliminate the above problems, significantly simplify the manufacturing process, and reduce the manufacturing cost.
[0013]
[Means for Solving the Problems]
The present invention, in order to achieve the above object,
[1] A method of forming an electrode for forming an element on a semiconductor β-FeSi ₂ thin film or a flat plate, wherein the surface of the β-FeSi ₂ material is previously heated to about 600 ° C. in the air or an inert gas atmosphere. while heating to a part of its cause phase conversion into α-Fe ₂ Si ₅ phase by heating between the beta-FeSi ₂ material surface portion to 1212 ° C. at least 982 ° C., was said phase conversion The portion is used as an electrode having good conductivity.
[0014]
[2] The electrode forming method of the beta-FeSi ₂ element described in [1], a heat source for heating a portion of said material surface with a laser beam, irradiating said material surface near the focal point of focused laser beam The temperature is raised by heating to cause conversion into a conductive metal crystal phase, and then the laser beam is shut off and the material is rapidly cooled to around room temperature, thereby leaving the metal crystal phase in a conductive portion. And an electrode in which the conductive portion has a predetermined shape is formed.
[0015]
[3] The method for forming an electrode of a β-FeSi ₂ element according to the above [2], wherein the heating temperature of the material surface by the laser beam is between 982 ° C. and 1212 ° C., and the α-Fe ₂ Si ₅ phase is formed. The laser beam irradiation portion is heated, and then the laser beam is cut off and rapidly cooled to around room temperature to leave the α-phase, and an electrode pattern is formed by repeating this process.
[0016]
[4] The method for forming an electrode of a β-FeSi ₂ element according to the above [2], wherein an Nd-doped YAG laser is used as the laser light source.
[0017]
In the present invention, when an electrode is formed on the surface of a semiconductor material to form an element, without using a special electrode material to be selected, a special cleaning for obtaining ohmic contact and baking heating after adhesion, and vapor deposition and The step of forming a sputtering film is omitted, and when a film other than an electrode is required, the step coverage problem does not occur.There is no need for a step such as a mask or light exposure, and a high quality β-FeSi film is formed in air or in an inert gas atmosphere. _It provides a means for forming _two element electrodes.
[0018]
That is, a part of the sample material is heated to a transformation temperature of a semiconductor crystal phase or higher by irradiating a laser, and the part is converted into a metal crystal phase to form a conductor, which is used as an electrode.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0020]
FIG. 1 is a schematic view of an apparatus for converting a part of the β-FeSi ₂ phase into α-Fe ₂ Si ₅ phase by laser heating according to an embodiment of the present invention, and FIG. 2 is a β-FeSi ₂ phase according to an embodiment of the present invention. FIG. 4 is a sectional view of an electrode forming step of the device.
[0021]
As shown in FIG. 1, a sample plate (silicon substrate) 1 on which a β-FeSi ₂ film has been grown in advance on a Si crystal substrate is placed on a stage 10 which is controlled by a computer 9 and moves so as to draw an electrode pattern. Has been placed.
[0022]
Similarly, a laser beam 6 emitted from an Nd: YAG laser 8 controlled by a computer 9 passes through a mirror 5 for optimally constructing the optical path of the apparatus, a beam switch 7 also controlled by a computer, and a condensing lens. 4 focuses on the heating point 3 on the sample surface. The electrode 2 is formed by patterning a portion of the metal film formed by the heating. The scattered light reflected from the sample surface is absorbed by the absorber 11.
[0023]
A feature of the present invention resides in the fact that the β-FeSi ₂ thin film of the device material utilizes a transformation of crystals by heating operation to convert it into α-Fe ₂ Si ₅ of a metal body.
[0024]
Hereinafter, a method for forming an electrode of a β-FeSi ₂ element of the present invention will be described in detail with reference to FIG.
[0025]
(1) First, as shown in FIG. 2A, a semiconductor β-FeSi ₂ thin film 22 is formed on a silicon substrate 21.
[0026]
(2) Next, as shown in FIG. 2 (b), a predetermined portion of the β-FeSi ₂ thin film 22 is irradiated with a laser beam 23, and heated to 982 ° C. or more, to thereby form a metal α-Fe ₂ Convert to Si ₅ 24.
[0027]
(3) Next, as shown in FIG. 2C, the metal body α-Fe ₂ Si ₅ 24 is rapidly cooled to near room temperature to form a permanent electrode 25.
[0028]
FIG. 3 is a principle diagram for explaining a binary phase diagram of iron and silicon and a phenomenon at the time of metallization by heating.
[0029]
The phase of the intermetallic compound β-FeSi ₂ formed with a composition ratio of Fe and Si of 1: 2 is a semiconductor, and this composition exists at a point A on the _binary phase diagram. When this material is heated by a laser annealing method or the like, it reaches the β phase decomposition temperature (982 ° C.) point B, and the β-FeSi ₂ phase structure is maintained up to this temperature. When the temperature further rises to the point C beyond the point B, the β-FeSi ₂ phase structure of the heated portion is decomposed, and a small amount of the ε-FeSi phase D point material and most of the α-Fe ₂ The mixed crystal phase is separated into the Si ₅ phase E point material. The α-Fe ₂ Si ₅ phase formed here is a metal phase, which is used as an electrode material.
[0030]
The point in the phase diagram of the material in which most of the heating points have been converted to the α-Fe ₂ Si ₅ phase is point E. Next, when the material converted to the α phase at the point E is rapidly cooled as it is and lowered to the point F near the room temperature, the material is not separated into a mixed crystal phase of β-FeSi ₂ and Si which is a stable thermal equilibrium phase. -Fe ₂ Si ₅ remains. Since this crystal phase is a metal, it becomes a good conductor of electricity and functions as an electrode material.
[0031]
If the material at point E is allowed to stand at around 900 ° C. to 650 ° C. for a good time without being rapidly cooled to around room temperature, the α-Fe ₂ Si ₅ phase is separated and precipitated again into β-FeSi ₂ semiconductor phase and Si. No metal properties. In order to use the portion converted from the β-FeSi ₂ phase by heating to the α-Fe ₂ Si ₅ phase as an electrode, it is important to rapidly cool to a point F near room temperature.
[0032]
The feature of the present invention is that a portion of the sample film is converted into a metal by causing a crystal transformation by a heating operation, so that when manufacturing a device for forming an electrode on a semiconductor element, a metal for an electrode is attached and deposited from the outside. You don't have to. Since a part of the sample material becomes an electrode with no flat surface on the sample material surface, the contamination between the material and the electrode, which occurred during the conventional electrode formation, was eliminated in principle, Excessive cleaning of the surface is unnecessary. Further, since the contact surface of the material is a flat continuous surface, an electrode in which ohmic contact is completely obtained is formed.
[0033]
The method for forming an electrode of a β-FeSi ₂ element of the present invention is characterized in that a necessary portion is heated and converted into a metal phase, so the heating method is not limited to the laser annealing method, and a high-heat flame or a high-heat metal piece tip may be used. A method such as pressure bonding is also possible.
[0034]
Generally, the electrodes of a semiconductor device have a width of 1 mm or less and are formed in a fine pattern of several hundred μm to several tens μm. Therefore, as a heating method for heating and metallizing such a fine part, a heat source is used. It is desirable to use a laser beam that can be made minute. When the laser beam is narrowed down using a lens, the beam diameter applied to the focal point becomes several μm to several tens of μm. This part is metallized, so the beam and sample position can be moved to connect the heating points continuously and freely. An electrode pattern is formed.
[0035]
Laser beams used for heating have various wavelengths. For example, an excimer laser having a strong output in the ultraviolet wavelength range, a semiconductor easily obtained in the green or red visible light range, a He or Ne gas laser, a Cd or Ne: YAG solid laser, and a 10 μm long wavelength CO ₂ gas laser. Each has its own characteristics and can be heated, but in order to efficiently absorb light and speed up heating, the light absorption coefficient and reflection coefficient of the material must be selected. That is, light having a wavelength of 0.9 μm to 2 μm has a high absorption coefficient for the β-FeSi ₂ film. In this respect, the Nd: YAG laser is most suitable as a light source for implementing the present invention. Although an ultraviolet laser can provide a large energy power, it is not suitable as a heating light source because it has a high energy and causes atoms and molecules of a material to collide and scatter.
[0036]
Also, visible light is highly reflective and is not efficient as a heat source. Long-wavelength lasers have a large focal area, are not suitable for fine electrode patterns, and have low light absorption.
[0037]
The energy required for heating depends on the light absorptivity, thermal conductivity, melting point, specific heat, etc. of the material to be irradiated. However, in order to heat a region having a radius of several 10 μm to around 1000 ° C., 10 ⁺⁶ W / cm ² . Energy density is required, and short time in seconds is sufficient. If an ordinary laser having a beam diameter of 1 to 2 mm has an output of several W, a sufficient energy density can be obtained when focusing is performed.
[0038]
When a Nd: YAG laser having a wavelength of 1.06 μm is used for β-FeSi ₂ , its light absorption is as high as 10 ^5, and the thermal conductivity of this material is used for thermoelectric power generation materials. Because the temperature is very low as described above, heating a minute region having a diameter of 50 μm to around 1000 ° C. may be achieved by narrowing down the 10 W output light and irradiating for several seconds.
[0039]
FIG. 4 shows an enlarged cross section of a portion where the laser beam is focused and the sample surface is irradiated.
[0040]
As shown in this figure, when a laser beam 33 is condensed and radiated onto a portion (heating point) 34 on the surface of a β-FeSi ₂ phase 32 grown on a sample plate (silicon substrate) 31, the material Heated by light absorption. The temperature of the heating point 34 is high at the center and the heated portion is spread by heat conduction, but the temperature decreases as the distance from the center increases. The line 35 is an isotherm along the heat diffusion direction at this time. Reference numeral 36 denotes an electrode, 37 denotes a scanning direction of the laser beam 33, and 38 denotes a trajectory of the scanning by the laser beam 33.
[0041]
Here, the portion heated sufficiently until the β-FeSi ₂ → α-Fe ₂ Si ₅ phase conversion is caused is converted to a metal phase. In order to use the converted portion as an electrode line, if the position where the beam hits is moved linearly or curvedly, the converted α-Fe ₂ Si ₅ phase remains on the locus 38. If a single sweep does not have a sufficient width as an electrode, if the beam hit position is shifted from the previous trajectory 38 by the width to convert to the α phase and is swept next to the direction 37, a wider width is obtained. An electrode pattern will be obtained.
[0042]
By repeating this operation to form a desired shape pattern, a device electrode can be obtained.
[0043]
Since the energy density can be increased by narrowing the laser beam, this method is suitable for heating a small area.However, when the energy density cannot be increased, for example, when heating the image irradiation of an incandescent lamp, the irradiation target specimen It is effective to apply a heating bias beforehand. That is, a heater is placed between the sample plate (silicon substrate) and the movable stage, or the entire surface of the sample is irradiated with lamp heater light to raise the sample temperature to a level not exceeding 500 ° C.
[0044]
In this temperature range, the β-FeSi ₂ phase of the sample does not change and, of course, does not convert to the α-Fe ₂ Si ₅ phase or the ε-FeSi phase. By irradiating the sample surface in this state with a light source, even a light source having a low power can sufficiently reach a temperature of 982 ° C. or more in a short time, and can be converted into an α-Fe ₂ Si ₅ phase. If the light source is rapidly turned off after the conversion to the metal phase, and the light source is rapidly cooled, the temperature will be around 500 ° C., so that a patterned electrode is formed with the α-phase metal as it is.
[0045]
The method of obtaining the desired electrode pattern by the continuous repetitive sweeping by converting the focal position of the laser beam to the metal phase has been described above. However, the entire surface of the material is irradiated with the projected image of the electrode pattern, and the entire electrode pattern is formed at once. Is also conceivable. However, a laser light source for heating a large area of the entire electrode portion requires a very large power, and a large amount of heat is applied to the original pattern, which may burn the pattern. Since the above-mentioned preheating method produces an effect of suppressing the power of the original laser, it may be an effective method for heating and irradiating a part of the electrode pattern with one irradiation.
[0046]
It should be noted that the present invention is not limited to the above embodiment, and various modifications are possible based on the spirit of the present invention, and these are not excluded from the scope of the present invention.
[0047]
【The invention's effect】
As described above in detail, according to the present invention, by heating a part of the β-FeSi ₂ thin film to 982 ° C. or higher, the part is converted into the α-Fe ₂ Si ₅ phase, and the part is converted to the α-Fe ₂ Si ₅ phase. Since the electrodes are used as conductive electrodes, the manufacturing process can be significantly omitted with a flat surface without forming device electrodes, which were conventionally formed by depositing a metal film by photolithography. It is now possible to construct an inexpensive device.
[Brief description of the drawings]
FIG. 1 is a schematic view of an apparatus for performing a method of forming an electrode of a β-FeSi ₂ element according to an embodiment of the present invention.
FIG. 2 is a sectional view of an electrode forming process of a β-FeSi ₂ element showing an embodiment of the present invention.
FIG. 3 is a principle diagram illustrating a binary phase diagram of iron and silicon and a phenomenon at the time of metallization by heating.
FIG. 4 is an enlarged view near the formation of an electrode irradiated with a laser focus.
[Explanation of symbols]
1,31 Sample plate (silicon substrate)
2,36 Electrode 3 Heating point 4 Condenser lens 5 Mirror 6,23,33 Laser beam 7 Beam switch 8 Nd: YAG laser 9 Computer 10 Stage 11 Absorber 21 Silicon substrate 22 Semiconductor β-FeSi ₂ thin film 24 Metal body α -Fe ₂ Si ₅
25 permanent electrode 32 β-FeSi ₂ phase 34 site (heating point)
35 Isothermal line 37 Laser beam scanning direction 38 Trajectory of laser beam scanning

Claims (4)

A method of forming an electrode for forming an element on a semiconductor β-FeSi ₂ thin film or a flat plate,
While heating to a pre-600 ° C. vicinity of the beta-FeSi ₂ material surface in air or in an inert gas atmosphere, As a by heating between the beta-FeSi ₂ material surface portion to 1212 ° C. at least 982 ° C. the part is phase converted to α-Fe ₂ Si ₅ phase, electrode forming method of the beta-FeSi ₂ element characterized by using a portion obtained by said phase transformation as a good electrode conductivity. _{2. The} method for forming an electrode of a β-FeSi ₂ element according to claim 1, wherein a heat source for heating a part of the material surface is a laser beam, and the material surface is irradiated near the focal point where the laser beam is narrowed. Then, a conversion to a conductive metal crystal phase is caused, and thereafter, the laser beam is shut off and the material is rapidly cooled to around room temperature to make that part a conductive part in the metal crystal phase, A method for forming an electrode of a β-FeSi ₂ element, comprising forming an electrode having a conductive portion having a predetermined shape. 3. The method for forming an electrode of a β-FeSi ₂ element according to claim 2, wherein a heating temperature of the material surface by the laser beam is between 982 ° C. and 1212 ° C., and the α-Fe ₂ Si ₅ phase is formed by the laser. An electrode of a β-FeSi ₂ element, characterized in that, after heating the irradiated portion, the laser beam is cut off and rapidly cooled to around room temperature to leave the α-phase, and an electrode pattern is formed by repeating this process. Forming method. In the electrode forming process of beta-FeSi ₂ element according to claim 2 wherein, the electrode forming method of the beta-FeSi ₂ element characterized by using a Nd-doped YAG laser as the laser light source.

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