JPH1070130A - Heat-treating conductive thin film using a-c magnetic field - Google Patents

Abstract

PROBLEM TO BE SOLVED: To heat-treat a conductive thin film uniformly at a good reproducibility and low cost for a short time. SOLUTION: An a-c magnetic field 15 perpendicular to the surface of a conductive thin film 1 formed on an insulation structure 17 is applied to the substrate and the film 1 classified in semiconductors such as amorphous Si having specific resistivity of less than 10<10> Ωcm at a frequency f>=1Hz and field intensity H>=1V/cm to generated an induced current 16 in the conductive film which selectively inductively heats only the semiconductor even in a laminate of insulators and semiconductor.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to heat treatment of a substance.

[0002]

2. Description of the Related Art First, a process diagram of a memory will be described below to explain a conventional heat treatment method for a semiconductor circuit. FIG. 8 is a sectional process view of a DINOR type flash memory. As shown in FIG. 8A, S having a specific resistance of 30 Ωcm
The conductive thin film 1 on the i-wafer surface has a local oxide film 2 on the element side for separating elements.

On the conductive thin film 1, a lower insulating film 3 made of silicon oxide, a floating gate 4 made of polycrystalline silicon annealed after ion implantation, and an upper insulating film 5 made of silicon nitride are sequentially deposited. ing. The upper insulating film 5 has thereon a high-resistance layer 6 made of polycrystalline silicon with very few impurities.

In this state, in order to form a control gate, source or drain of the flash memory, ions 7 are formed in a direction perpendicular to the surface of the conductive thin film 1 as shown in FIG.
Inject. Then, as shown in FIG.
In addition, an implanted film 8 having a relatively high ion concentration is formed on the surface of the conductive thin film 1.

The implanted film 8 has no activated ions,
Since the resistance is high as it is, it is heated by light 9 from a xenon lamp or the like. Since the ions are activated and diffused by light, the control gate 10 is formed on the upper insulating film 5 and the low-resistance film 11 serving as a source or a drain is formed on the conductive thin film 1 as shown in FIG. 8C. You can do each.

Subsequently, a sub-bit line is provided to connect between the flash memories. As shown in FIG. 8d,
A contact hole is opened in the insulating film, and a sub-bit line 12 made of polycrystalline silicon in the lower layer and aluminum in the upper layer is formed on the low-resistance film 11. After a new insulating film is deposited on the sub-bit line 12, a word line 13 made of aluminum is arranged.

Further, a main bit line 14 crossing the word line 13 is provided above the word line with an insulating film interposed therebetween. FIG.
Comparison between FIG. 8A and FIG. 8C shows that in the conventional heat treatment method, the annealing step of each conductive thin film is performed for each film. This is because the temperature reached in the heat treatment step performed in FIG. 8B differs depending on the depth from the surface.

For this reason, when heating a plurality of layers at once, 1
Even if the yield for each layer is 99%, the yield for four layers is (0.9%).
9) It is even lower than ⁴ = 96%. Here, conventionally, the following three methods are generally known as a method for heat-treating a thin film. (A) Electric furnace (b) Lamp annealing (c) Laser annealing

[0009]

However, since the heat treatment method (a) heats the entire furnace, it takes a long time to stabilize the temperature of the furnace, and it is not preferable that the object is transferred from the heated furnace to an object. Impurities may diffuse. Also,
In the heat treatment method (b), since the light transmittance greatly varies depending on the film thickness, the object may not reach a predetermined temperature.

In the heat treatment method (c), a large number of plane patterns of several tens μm are scanned over several tens of cm.
Problems may occur in reproducibility, and long processing time and high cost are required. SUMMARY OF THE INVENTION An object of the present invention has been made in view of the above-mentioned circumstances, and it is an object of the present invention to heat-treat a target object, especially a conductive thin film, uniformly and reproducibly in a short time and at low cost without adverse effects.

[0011]

The heat treatment method of the present invention comprises:
The method is characterized in that the conductive thin film is heated by applying an alternating magnetic field. Further, the heat treatment method of the present invention is characterized in that an insulating substrate is used as a substrate for supporting the conductive thin film.

Further, the heat treatment method of the present invention is characterized in that a semiconductor film subjected to ion doping is used as the conductive thin film. Alternatively, the heat treatment method of the present invention is characterized in that an a-Si thin film is used as a semiconductor film and the a-Si thin film is used for p-Si conversion. The heat treatment method of the present invention is characterized in that a glass substrate is used as an insulating substrate.

Although the heat treatment method of the present invention uses heating of the conductive thin film by electromagnetic induction, an externally applied alternating magnetic field H and a depth δ at which an induced current generated by the alternating magnetic field penetrates the conductive thin film. And the heat generation amount P generated by the inductive current that has entered, the following relationship is established. δ = √2 / m = √2 / √ (ω · μrμ0 / ρ) = √ (2ρ) / √ (2πf · μr · 4π × 10 ^-7 ) [m] = {10 ² ρ / {2π} (10 ⁻⁷ f · μr) [cm] = (1 / 2π) · (1 / √10 ⁻⁹ ) · {ρ / (f · μr)} [cm] = 1.59 × 10 ² √ ｛ρ / ( f · μr)｝ [cm] where ρ is the specific resistance [Ωcm] of the conductive thin film, f is the frequency [Hz] of the alternating magnetic field, and μr is the relative magnetic permeability [−] of the conductive thin film.

For example, in the case of Fe96-Si4 (wt%) silicon steel, the resistivity ρ = 60 × 10 ^{-6 at} room temperature.
Ωcm, AC magnetic field frequency 50 Hz, relative permeability μr = 7
From 000, the depth δ is δ = 1.59 × 10 ² · {60 × 10 ⁻⁶ /(50×7000)}=0.0658 cm.

The heating value P is represented by the following equation. P = f (a / δ) · H ² · (ρ / δ) [W · cm ⁻² ] where a is the thickness of the conductive thin film [cm], H is the strength of the magnetic field [V / cm], f (a / δ) is a function that converges to 1 as a / δ increases and becomes 0 as a / δ approaches 0.

F (a / δ) = ((sinh (a / δ)-
sin (a / δ)) / (cosh (a / δ) + cos
(A / δ)) + j (sinh (a / δ) + sin (a /
δ)) / (cosh (a / δ) + cos (a / δ))) From the above equation, the relationship between the resistivity ρ and the calorific value P is unknown, but free electrons in the conductive thin film are affected by the magnetic field. The object to be heated needs to have conductivity higher than that of a semiconductor because it is assumed that the object is bound around the line of magnetic force.

Quantitatively, even if the relative magnetic permeability is close to 1 as in a-Si, the specific resistance is desirably 10 ¹⁰ Ωcm or less. As described above, the conductive thin film is heated by the amount of heat generated when free electrons are wound around the AC magnetic field penetrating the conductive thin film under normal pressure. Also, since there are no free electrons on the insulating substrate, only the conductive thin film is heated by the AC magnetic field.

Further, since the conductive thin film made amorphous by the ions is induction-heated, segregation of the ions is small,
The resistance of the conductive thin film after the induction heating is reduced. Alternatively, by using a-Si (amorphous silicon) having lower crystallinity instead of p-Si (polycrystalline silicon) having low resistance, crystal growth during heating becomes isotropic.

By using a glass substrate, an inexpensive support that is not heated can be used. According to the above configuration, without adversely affecting the conductive thin film,
The conductive thin film is heat-treated in a short time and at low cost with good reproducibility.

[0020]

1 to 7 show an embodiment of the present invention.
It will be described based on. FIG. 1 is a principle diagram of a heat treatment method for a conductive thin film using an alternating magnetic field. In FIG. 1, reference numeral 1 denotes an a-Si conductive thin film serving as an operation layer of a thin film transistor used in a liquid crystal display device, 15 denotes an AC magnetic field applied to the conductive thin film 1, and 16 denotes a free electron wound around the AC magnetic field. The induced current that is generated, 17 has a specific resistance of 10 ¹⁴ Ω · cm
This is a glass insulating substrate having high insulating properties.

A-Si has a specific resistance of 10 ¹⁰ Ωcm when off,
It is a semiconductor with a specific resistance of 50 Ωcm when turned on (Shuichi Nonomura: Applied Physics vol 64, p1013, (1995)
Year)). As shown in FIG. 1, the frequency f = 1 to 100
An alternating magnetic field 15 of 0 [Hz] and a magnetic field strength of H = 1 [V / cm] has a relative permeability of 1 and a specific resistance of 10 ¹⁰ Ωcm when off.
When applied to the conductive thin film 1 made of -Si, an induced current 16 is generated in the conductive thin film 1.

On the other hand, since the insulating substrate 17 has no free electrons, no induced current is generated. Therefore, the specific resistance 10 ¹⁰
Only conductive thin films of less than Ωcm and containing free electrons are selectively heated by the alternating magnetic field. Therefore, a glass substrate having a lower melting point and a lower melting point than quartz can be used as the insulating substrate.

In the case of a-Si, the frequency f of the alternating magnetic field is
= 1 [Hz], the depth δ at which the induced current penetrates from the surface and the calorific value P are δ = 5.03 × 10 ⁷ [cm], P
= 1.95 × 10 ⁻⁹ [W · cm ⁻² ]. Similarly, when the frequency of the magnetic field is increased, the frequency f of the AC magnetic field f = 1000
In [Hz], the depth δ and the calorific value P are δ = 5.03, respectively.
× 10 ⁵ [cm], P = 1.95 × 10 ⁻⁷ [W · c]
m ^-2 ].

From the above values, the semiconductor element made of a-Si is 1 × 10 ⁵ c smaller than the depth of 0.066 cm of iron.
m and the penetration of the AC magnetic field is easy, and when the frequency of the AC magnetic field is increased from 1 Hz to 1000 Hz, 1
The heating value increases from 0 ^-9 W · cm ^-2 to 10 ^-7 W · cm ^-2 , while the penetration depth decreases slightly from 10 ⁷ cm to 10 ⁵ cm, but hinders the heating of the semiconductor circuit. It turns out that there is no.

In general, the interaction between iron (Fe) used for induction heating and an alternating magnetic field is very strong. When the frequency of the alternating magnetic field is increased, a skin effect in which only the surface is heated occurs, and it is difficult to treat a plurality of layers. However, as in the present embodiment, a semiconductor having a relative magnetic permeability close to 1 and a specific resistance of 10 ¹⁰ Ωcm or less can easily process a plurality of layers. FIG. 2 is a perspective view of a substrate on which a conductive thin film is overlapped.

As shown in FIG. 2, an insulating substrate 17 made of borosilicate glass having a thickness of 1 mm is covered with a-Si 18 having a thickness of 1000 ° and having poor crystallinity, and a portion of the a-Si is covered. An insulating film 19 made of silicon oxide and having a thickness of 1000 ° is formed. In FIG. 2, n ⁺ a-Si2
Numeral 0 denotes amorphous silicon obtained by doping n-type impurities such as P into a-Si by about 10 ²⁰ cm ⁻³ .

A plurality of n ⁺ a-Si 20 having a thickness of 1000 ° are scattered on the insulating film. A-Si18 of FIG.
Is more amorphous than that of a silicon film formed by plasma CVD or the like by a so-called ion doping process in which an ion flow of silane (SiHx (0 ≦ x ≦ 4)) is injected without mass separation of the silicon film. It is a thing. on the other hand,
The n ⁺ a-Si 20 is obtained by increasing the ion concentration and amorphousness of the formed silicon film by ion doping of phosphine (PHx (0 ≦ x ≦ 3)).

The frequency of 1000 for the laminated film configuration of FIG.
Hz, an alternating magnetic field 15 of 1 V / cm of magnetic field strength is applied.
Induction heating. In this case, the specific resistance 10^TenΩcm a-S
i18 and n of specific resistance 10Ωcm⁺Induction of a-Si20
The depth δ at which the flow enters the conductive thin film is 5.03, respectively.
× 10 ^Fivecm, 1.59 × 10¹cm, but AC magnetic
There was no problem with the field permeability, and a-Si18 and n⁺a
An equivalent magnetic field is applied to -Si20.

Regardless of the large difference in the resistance value, the heat value is
For a-Si18 and n ⁺ a-Si20,
1.95 × 10 ⁻⁷ Wcm ⁻² , 1.94 × 10 ⁻⁷ Wcm ⁻²
Assuming that the number of free electrons does not change.
Actually, the insulating film placed between the insulating substrate as the base and the conductive thin film is not heated, and the n ⁺ a-Si 20
Heats faster than i18.

The difference from the conventional heat treatment method is that n ⁺ a-
That is, the a-Si 18 in the portion overlapping with the Si 20 is heated in the same manner as the a-Si in the other portion, regardless of the distance from the surface or the number of layers. Although the heat treatment method in FIG. 2 is for heating a flat film, the film need not necessarily be flat.

FIG. 3 is a perspective view of a substrate in which a conductive thin film overlaps a step. As shown in FIG. 3, a slightly n-type a-Si 18 is laminated on an insulating substrate 17 made of glass. The p ⁺ a-Si 21 is formed by ion doping of borane (BHx (0 ≦ x ≦ 3)) so as to form a diode on the a-Si 18, and the insulating film 19 made of silicon oxide is formed by plasma CVD. .

An n ⁺ a-Si 20 is deposited on the flat surface of the insulating film 19 and on the step between the a-Si. When the AC magnetic field 15 is applied to the substrate having the configuration shown in FIG. 3, the depth at which the AC magnetic field penetrates into the semiconductor is large, and there is little dependence on the amount of heat generated in the specific resistance. Heating is independent of the difference and the difference between the p-type and n-type conductivity.

For this reason, the heat treatment method of the present embodiment can heat, for example, a CMOS including p-type and n-type semiconductor films at a time, and can shorten the process time of the semiconductor device. FIG. 4 is a process diagram of heat-treating the flash memory with an AC magnetic field. As shown in FIG. 4A, an implanted film 8 is formed on the surface of the a-Si conductive thin film 1 on the insulating substrate 17 by ion doping.

The lower insulating film 3, the high resistance film 6, the injection film 8, the upper insulating film 5, the high resistance film 6, and the injection film 8 are sequentially formed on the conductive thin film 1 on which the injection film 8 is not formed. Laminated. Conventionally, the implanted film is annealed for each implantation. However, in the present embodiment, the two-layer structure after the implantation remains as it can be annealed simultaneously. After covering the conductive thin film 1 with an insulating film, a contact hole is formed, and the conductive thin film 1 is formed on the uppermost layer.
The high resistance film 6 to be connected is laminated.

The uppermost high resistance film 6 is ion-doped with ions 7 having various ion forms. Then, FIG.
An injection film 8 is formed on the surface of the uppermost high resistance film 6 as shown in FIG. An AC magnetic field 15 is applied to the semiconductor element in this state.

By applying an AC magnetic field, the sub-bit line 12, the control gate 10, the floating gate 4, and the low resistance film 11 are formed at one time from the front side of the semiconductor element as shown in FIG. 4c. In the case where the base of the conductive thin film 1 is the insulating substrate 17, the local oxide film 2 is not necessarily required because the separation between the elements is improved. FIG. 5 is a manufacturing process diagram of a liquid crystal display device when a heat treatment method for a conductive thin film using an AC magnetic field is applied.

As shown in FIG. 5A, a central portion of a transparent insulating substrate 17 such as a glass substrate is provided with a large number of a-Si
18 and a-Si 18 whose major axes are orthogonal to each other are formed in the peripheral portion on the insulating substrate 17. further,
In FIG. 3A, an insulating film is provided on the peripheral a-Si 18 with an insulating film interposed therebetween.
A large number of implanted films 8 are produced by implanting ions into a-Si by ion doping.

Further, a-Si 18 at the center of the insulating substrate passes through a step at the boundary from the a-Si 18 at the periphery of the insulating substrate.
An elongated injection film 22 is formed on Si 18 so as to overlap with an insulating film therebetween. An AC magnetic field is applied to a substrate having such a configuration from a direction perpendicular to the substrate. Then, FIG.
As shown in b, a-Si is heated by the AC magnetic field to become polycrystalline Si23 having relatively high mobility, while the ions contained therein are activated and the low-resistance film 11 is activated. Becomes

At the same time, the elongated injection film overlapping the a-Si film scattered in the center of the insulating substrate is heated,
The gate line 24 controls on / off of the thin film transistor. Subsequently, as shown in FIG. 5C, after an interlayer insulating film is provided so as not to contact the gate line, the wiring 2 made of Al
5 and a transparent ITO display electrode 26, a TFT substrate of a liquid crystal display device is manufactured.

Usually, a liquid crystal display device is completed by further depositing a liquid crystal on an alignment film made of polyimide and then sealing the liquid crystal between the counter substrate and the TFT substrate. FIG. 6 is a cross-sectional view showing how to apply an alternating magnetic field to the conductive thin film. As shown in FIG. 6, an AC magnetic field 15 passes from above and below to an insulating substrate 17 on which the conductive thin film 1 that moves from left to right in the figure is placed.

The alternating magnetic field is generated by periodically reversing the direction of the current flowing through the coil 27. Lines of magnetic force generated between the coils 27 mainly pass through a laminated core 28 in which plates of an iron group compound having a high relative magnetic permeability are laminated. As described above, a method of passing a magnetic flux perpendicularly to the plane of the conductive thin film is generally called a horizontal axis magnetic flux method (Transverse f.
lux heating).

Since a-Si and p-Si have an absorption wavelength in the visible light region and have a property that free electrons increase due to light, the surface of the opposed laminated iron core is mirror-finished and light is transmitted from the side surface to the conductive thin film. Irradiation is more desirable. FIG. 7 shows a characteristic diagram with respect to time and place of the heat treatment method using an AC magnetic field. As shown in FIG. 7, according to the present embodiment, it is possible to perform a heat treatment having both the high speed of the lamp annealing and the selectivity of the laser annealing in the conventional example.

[0043]

As described above, according to the heat treatment method of heating a conductive thin film with an AC magnetic field, the conductive thin film is not adversely affected by contamination or melting due to melting. Processing can be performed with good reproducibility. Further, since an insulating substrate is used as a substrate for supporting the conductive thin film in an AC magnetic field, the insulating substrate is not heated, and a material having a low melting point can be used.

Furthermore, since the Si thin film subjected to the ion doping treatment is used as the conductive thin film, the crystallinity of the thin film is lost from the surface to a deep portion due to various implantation depths due to the difference in mass, and the crystal grain boundaries are lost. In addition, the segregation of impurities at the crystal grain boundaries does not progress, and in addition, impurities of various energy levels are present, and the energy gap may be smaller than that in the case of a single crystal. Can be.

Since the a-Si thin film is used as the Si thin film and is used for converting the a-Si thin film into p-Si, the crystallinity is poor and the crystal growth in a specific direction does not develop. it can. In addition, since a glass substrate is used as the insulating substrate, an inexpensive material can be used.

[Brief description of the drawings]

FIG. 1 is a perspective view of a method for heat-treating a conductive thin film using an alternating magnetic field according to the present invention.

FIG. 2 is a perspective view of a heat treatment method for a laminated conductive thin film using an alternating magnetic field according to the present invention.

FIG. 3 is a perspective view of a method for heat-treating a bent conductive thin film using an alternating magnetic field according to the present invention.

FIG. 4 is a view showing a heating process of a flash memory using an AC magnetic field according to the present invention.

FIG. 5 is a view showing a heating process of a liquid crystal display device using an AC magnetic field according to the present invention.

FIG. 6 is a sectional view of an apparatus for generating an alternating magnetic field according to the present invention.

FIG. 7 is a characteristic view of a heat treatment method using an alternating magnetic field according to the present invention.

FIG. 8 is a view showing a heating process of a flash memory by a conventional heat treatment method.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Conductive thin film 2 Local oxide film 3 Lower insulating film 4 Floating gate 5 Upper insulating film 6 High resistance film 7 Ion 8 Injection film 9 Light 10 Control gate 11 Low resistance film 12 Sub bit line 13 Word line 14 Main bit line 15 AC Magnetic field 16 Induction current 17 Insulating substrate 18 a-Si 19 Insulating film 20 n ⁺ a-Si 21 p ⁺ a-Si 22 Slender injection film 23 Polycrystalline Si 24 Gate line 25 Wiring 26 Display electrode 27 Coil 28 Laminated core δ Depth a Thickness ρ Resistivity μr Relative permeability H Magnetic field strength f Frequency

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical indication location H01L 29/792 H01L 29/78 627F 29/786 21/336

Claims (5)

[Claims] 1. A heat treatment method comprising heating an electroconductive thin film by applying an alternating magnetic field. 2. The heat treatment method according to claim 1, wherein an insulating substrate is used as a substrate for supporting the conductive thin film. 3. The heat treatment method according to claim 1, wherein a semiconductor film subjected to an ion doping process is used as the conductive thin film. 4. An a-Si thin film is used as a semiconductor film.
The heat treatment method according to claim 3, wherein the heat treatment method is used for p-Si conversion of a -Si thin film. 5. The heat treatment method according to claim 2, wherein a glass substrate is used as the insulating substrate.