JP2676786B2 - Thin film thermal head and manufacturing method thereof - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film thermal head used for thermal recording and a method for manufacturing the same.

2. Description of the Related Art Generally, a thin-film thermal head has a structure in which a large number of heating resistor rows and a conductor layer for supplying electric power to the heating resistor rows are provided on an insulating substrate, and an abrasion-resistant protective film is formed on these. .

By the way, in this structure, the following matters can be mentioned as the properties required for the wear-resistant protective film.

(1) Good wear resistance. (Mechanical wear (related to hardness and friction coefficient) and electrochemical wear (abnormal wear due to reaction between paper and wear resistant protective film) are both small) (2) Good heat resistance thing.

(3) Electrolytic corrosion of the film formed under the wear-resistant protective film, such as the heating resistor and the conductor layer, should not occur. (Good step coverage that occurs when driven under moisture such as paper, pinhole-free, dense and non-hygroscopic) (4) With heating resistors, conductor layers, substrates and other bases Good adhesion.

(5) Static electricity resistance is good. (Especially under dry conditions, like the thermal transfer system, electrostatic damage occurs due to static electricity generated when the abrasion resistant protective film and the PET (insulator) that is the transfer paper slide.) These things are conceivable.

On the other hand, conventionally, the sputtering method has been frequently used for forming the wear-resistant protective film. However, in the sputtering method, when high power is applied during high-speed film formation, splats are likely to be generated, and as a result, granular projections are formed on the wear-resistant protective film and pinholes are generated due to their detachment,
Since the step coverage of the conductor layer pattern (conductor layer thickness of about 1 μm) is insufficient, electric field corrosion of the lower layer film may occur through these defective portions. The plasma CVD (chemical bar pad deposition) method is effective for such problems. Because the plasma CVD method is basically a method of depositing a film by decomposing the raw material gas and accelerating the surface reaction, physically hitting the solid target surface to deposit the target material on the substrate. Compared to the sputtering method, less energy (electric power) is needed, defects such as granular projections and pinholes due to abnormal discharge are less likely to occur, and since it is dense and has excellent step coverage, the electric field corrosion of the lower layer film Is less likely to occur and reliability is significantly improved. By the way, as a protective film using this plasma CVD, SiH ₄ or N ₂ gas, SiH ₄ or NH ₃ gas, SiH ₄ or N ₂ or NH ₃ gas or the like is used as a source gas in a semiconductor IC such as SiH ( Silicon nitride) films are commonly used. This is because the SiN film has a large ability to block alkali ions and has a low hygroscopicity. On the other hand, the stress of the SiN film is extremely large, and usually causes stress cracking when it is applied thickly or when heat is applied. The wear-resistant protective film of the thermal head usually needs to have a thickness of about 5 μm from the viewpoint of wear characteristics and reliability, and therefore cracks easily occur and cannot be used. Therefore, for example, as disclosed in Japanese Patent Laid-Open No. 62-145735, a silicon oxynitride film (hereinafter referred to as SiON film) is used, and SiH ₄ , N ₂ O, and N ₂ are used as a source gas, and a plasma CVD method is used. The film formed by (1) is useful. In addition to these, SiH ₄ , NH ₃ , N ₂ O, SiH ₄ , NH ₃ , N ₂ , N ₂ O, etc. have been reported as the raw material gas for the SiON film. Although it is mainly considered to use electricity, the surface temperature is the highest when pulse heating is required in a short time like a thermal head.
Raises to about 500 ℃. At this time, the raw material gas has a large hydrogen content, and a large amount of this remains in the film in the form of Si—H, Si—H ₂ , N—H ₂ or the like as a product having a relatively low binding energy. There is. Hydrogen existing in these forms can be relatively easily released from the membrane even by heating at about 500 ° C. In this way, when hydrogen in the film is released, bubbles and cracks are generated, and it is difficult to use it in applications where heat resistance for a long period of time is required, such as a wear-resistant protective film of a thermal head.
In this regard, when SiH ₄ , N ₂ O, and N ₂ are used as the source gas, the hydrogen content in the original source gas is low and N ₂ O
Gas dissociation energy is as small as 0.845 eV, and N ₂ O → N ₂ +
Since hydrogen generated by the decomposition of O extracts hydrogen, the amount of hydrogen existing in the film decreases. Therefore, heat resistance is improved. However, even when a film is formed using this source gas system, hydrogen bonds remain in the form of Si—H, and if it is desired to reduce this, a large amount of N ₂ O must be supplied. Hydrogen is reduced, but at the same time Si-O bond is increased,
The hardness is significantly reduced. From the viewpoint of wear, it is absolutely important that the protective film for the thermal head has high hardness. Therefore, at this point, that is, hydrogen existing in the form of low binding energy in the film is reduced, and
To increase the hardness, it is usually necessary to increase the incident power and raise the substrate temperature. By increasing the incident power, the low heat resistance (low binding energy) Si-H bond is decreased, the high heat resistance (high binding energy) N-H bond is increased, and the decomposition of nitrogen and the formation into the film are performed. By increasing the uptake and increasing the substrate temperature, it is possible to reduce the hydrogen taken up in the film. this house,
Increasing the incident power promotes the occurrence of abnormal discharge and is not always a good measure. Therefore, it was difficult to obtain a film having high hardness and high heat resistance. Further, as the wear-resistant protective film for the thermal head, the internal stress is preferably compressive stress,
The cause of this compressive stress is due to the ion bombardment of the film. At this point, since the ionization voltage of N ₂ in the raw material gas is high, sufficient ion bombardment is not given, so the compressive stress is improved. That was difficult.

As described above, the protective film formed by the plasma CVD method is
Dense, with reduced defects such as granular projections and pinholes, excellent step coverage, and has a great effect on preventing corrosion of the lower layer film, significantly improving reliability. Since this is a method of decomposing and depositing, the gas may be taken into the film in an undecomposed form. For example,
This is the Si—H bond in the plasma SiN film using SiH ₄ . Hydrogen which is not decomposed and remains in the film like Si-H is
Since the binding energy is relatively small, hydrogen is released by heating, and at that time, problems such as bubbles and cracks in the film may occur, which may cause a problem in heat resistance. For this,
A silicon oxynitride film (SiON film) obtained by introducing oxygen into a SiN film is useful in improving crack resistance. This SiON film is usually used as a source gas for SiH ₄ , N ₂ and N ₂
O-based or SiH ₄ , NH ₃ , N ₂ O-based films are formed, but the latter is still inferior in heat resistance because the amount of hydrogen present in the source gas is large and hydrogen bonds are involved in the film. On the other hand, the former can be said to be suitable as a protective film for a thermal head because the amount of hydrogen present in the film can be reduced because the hydrogen content in the source gas is small and the heat resistance can be improved. However, this Si
In the plasma SiON film which depends on the source gas of H ₄ , N ₂ and N ₂ O, the following matters become problems. The reason is that the ionization voltage and dissociation energy of N ₂ are large, so the incident power must be increased. Therefore, unless the incident power is increased, the incorporation of nitrogen into the film is reduced, and highly heat-resistant bonds such as NH are less likely to occur. Also, factors such as Si-N bonds that are important for increasing hardness are reduced, and only the decomposition of N ₂ O gas is promoted. This oxygen causes Si-H hydrogen to be abstracted and reduced, but at the same time, Si- Since a large amount of O-bonds are also generated, the hardness is remarkably reduced, which gives an impediment factor to the "high hardness" required as a wear-resistant protective film for a thermal head.
As described above, the plasma SiON film using SiH ₄ , N ₂ , and N ₂ O gas has a high incidence that is likely to cause abnormal discharge in order to achieve both high heat resistance and high hardness required for the protective film for the thermal head. It is necessary to form a film in the power region, and there is a problem in the stability of the film forming apparatus.

The present invention has been made in view of the above points, and a main object of the present invention is to achieve both high hardness and high heat resistance and heat even at relatively low incident power.

Means for Solving the Problem In order to solve this problem, the present invention, as a source gas, SiH ₄ or Si ₂ H ₆ and N ₂ , N ₂ O and Ar or He gas system, or Ar or He Diluted SiH ₄ or
Thin-film thermal head that uses Si oxynitride (SiON) film as a wear protection film by plasma CVD method using Si ₂ H ₆ and N ₂ , N ₂ O gas system, especially at substrate temperature of 350 ° C or higher And a method for manufacturing the same.

Action The ionization energy of Ar or He in the source gas in this configuration is smaller than that of N ₂ . Accordingly, in the same incident power, depending on the fact that Ar, He is ionized, the positive ions, the electron density is increased, therefore, also increased collision probability of the SiH _4, promoting the degradation of SiH _4, film formation Higher speed, reduction of Si-H bond in the film can be achieved, and ion bombardment of the film increases, and due to this heating effect, the film becomes dense and
The dangling bonds on the film surface increase, the surface reaction is promoted, the uptake of nitrogen is increased, and the bonds with low bond energy are excluded. Therefore, the film formation speed is improved and the hardness is increased.
Along with achieving high heat resistance, the ion bombardment of the film increases and the compression reaction intensifies, resulting in SiON formed using this method.
By using the film as the wear-resistant protective film, it is possible to obtain a highly reliable thin film thermal head.

Example In this example, conventional SiH ₄ , N ₂ , N ₂ O was used as a source gas, a SiON film deposited by a plasma CVD method, and as an example of the present invention, SiH ₄ , N ₂ , N ₂ A description will be given while comparing SiON films deposited by the plasma CVD method using O and Ar as source gases.

FIG. 1 shows the N ₂ O flow rate when using conventional SiH ₄ , N ₂ , N ₂ O as the source gas and when using SiH ₄ , N ₂ , N ₂ O, Ar of the present invention. Shows the relationship between Vickers hardness and internal stress.

The apparatus used for film formation is a parallel plate type (capacitive coupling type) plasma CVD apparatus, the electrode plate shape is 600 mm × 600 mm square, the distance between electrodes is 20 mm, RF frequency 13.56 MHz, RF power 800 W, gas pressure
125Pa, substrate temperature 350 ℃, SiH ₄ : 35sccm constant, SiH ₄ ,
In N ₂ and N ₂ O system, N ₂ : 500sccm, SiH ₄ , N ₂ , N ₂ O and Ar system, N ₂ :
400 sccm, Ar: 100 sccm (N ₂ + Ar total flow rate 500 sccm), each N ₂ O flow rate is changed from 0 to 50 sccm to form a film.

In FIG. 1, the straight line 1 indicates the Vickers hardness, and the curve 2
Indicates internal stress. Line 3 and curve 4 show the Vickers hardness and internal stress in the conventional SiH ₄ , N ₂ and N ₂ O gas system, respectively, and line 5 and curve 6 show the SiH ₄ , N of the present invention.
Vickers hardness and internal stress are shown for ₂ , ₂ , N ₂ O and Ar gas systems, respectively. As is clear from these, the SiON film of the present invention to which Ar gas is added has higher hardness and stronger compressive stress than the SiON film formed using the conventional gas system. This is because by adding Ar gas, Ar has a smaller ionization energy than N ₂ , so that the ionization of Ar is promoted, and therefore the ion bombardment of the film is increased and the film is densified. . In addition, dangling bonds are likely to occur on the surface due to ion bombardment of the film, which also has some influence on the uptake of nitrogen into the film. FIG. 2 shows the infrared absorption spectra at points 7 and 8 in FIG. 1 when the N ₂ O flow rate was 15 sccm. In FIG. 2, 9 is an infrared absorption spectrum of SiH ₄ , N ₂ , N ₂ O gas system, and 10 is an infrared absorption spectrum of SiH ₄ , N ₂ , N ₂ O, Ar gas system of the present invention. As is clear from the figure, Si-O bond, Si-
In absorption by N-linked, but significant change is not observed, the absorption by Si-H based bond at around 2150 cm ^-1 and 3350 cm ^-1
Differences are seen in the absorption due to nearby NH bonds. When Ar is added, the absorption of Si-H decreases and N
The absorption of -H is increased to some extent, which means that Ar has a smaller ionization energy as compared with N ₂ , and therefore ionization is promoted, and the decomposition of SiH ₄ gas is promoted. It means that ion bombardment of the film surface increases, dangling bonds are generated (Si—H decreases), and bond energy is applied to the film surface, so that N—H bond which is a highly heat-resistant bond increases. As is well known, hydrogen coordinated to Si-H bond starts to be easily released at 400 to 450 ° C, and hydrogen coordinated to N-H bond is not easily released even at about 650 ° C. In this way, when hydrogen is released, bubble cracks occur in the film, impairing reliability. Therefore, in order to increase the heat resistance of the film, it is preferable that the number of Si-H bonds is small and the number of N-H bonds is large. Therefore, the SiON film formed by adding Ar gas has higher heat resistance. I can say.

The above matters are applied to the wear-resistant protective film of the thin-film thermal head as follows. That is, what is required as the characteristics of the wear-resistant protective film of the thin-film thermal head is that the hardness is large, the compressive stress is strong, and the heat resistance is high, the conventional SiH ₄ , N _{2 as} described above. , N ₂ O was used as the source gas, and SiH ₄ , N ₂ , N ₂ O, Ar
It can be said that the SiON film in which is used as the source gas is more suitable. FIG. 3 shows the acceleration test results when actually applied to the wear-resistant protective film of the thin-film thermal head. In the figure, the pulse width is 1.0 msec, the repetition period is 10 msec, voltage pulses are continuously applied, and the number of pulse application times when the resistance value increases by + 5% or more of the initial resistance value is defined as the life at the applied power. The specified method is used to specify the life of the wear-resistant protective film. In the figure, 11 is a SiON film made of conventional SiH ₄ , N ₂ and N ₂ O, 1
2 is the life line of the SiON film of SiH ₄ , N ₂ , N ₂ O and Ar of the present invention. From the figure, SiH ₄ , N ₂ , N ₂ O, Ar Si of the present invention
It can be seen that the ON film has a longer life.

By the way, in addition to this, by using SiH ₄ , N ₂ , N ₂ O, and Ar of the present invention as a source gas, the following points are improved.

First, the film formation rate is improved. (The illustration is omitted.) This is because, as is apparent, the addition of Ar increases the positive ion and electron densities, as described above, and promotes the decomposition of SiH ₄ that governs the film formation rate. Is. Secondly,
The resistivity of the film decreases. (It is advantageous to avoid electrostatic breakdown by leak current.) The resistivity of SiON film with conventional SiH ₄ , N ₂ and N ₂ O gas is 10
¹⁴ Ω · cm, but SiON of SiH ₄ , N ₂ , N ₂ O and Ar of the present invention
In the film, it is possible to reduce the resistivity by at least 2 to 3 digits, although it depends on the Ar flow rate. This is because the ion bombardment of the film increases with the addition of Ar, and the dangling bond density (defect density) increases, so that hopping conduction in the film increases. These two additional improvements mentioned above are also necessary for the wear-resistant protective film of the thermal head. The SiON film formed by SiH ₄ , N ₂ , N ₂ O and Ar of the present invention is a thermal head. It can be said that it is suitable as a wear-resistant protective film.

In this example, the substrate temperature during film formation was 350 ° C. (constant), but this is also due to Si-
H-bonds increased with a decrease in the substrate temperature, and, for example, in a film formed at a substrate temperature of 300 ° C., when the film was heated at 500 ° C., hydrogen was released to cause a crack in the film. Meanwhile, the substrate temperature is 35
The film formed at 0 ° C. or higher did not crack in the film even under heating at about 500 ° C., which is required as a wear-resistant protective film for a thermal head.

Therefore, the substrate temperature at the time of film formation must be at least 350 ° C or higher.

In this example, SiH ₄ , N ₂ , N ₂ O, and Ar were used as the source gas, and the SiON film formed by the plasma CVD method at the substrate temperature of 350 ° C. was described. Even if the source gas SiH ₄ is changed to Si ₂ H ₆ , this is
Since the composition of hydrogen is small, the same results as in the present embodiment can be obtained and the film formation rate is improved. Even if Ar of the source gas is changed to He, since He has a low ionization energy, the ion impact of the film increases like Ar, and the same result can be obtained. In addition, the source gas does not have to be an independent gas source, for example, Si diluted with Ar or He.
H ₄ or Si ₂ H ₆ , N ₂ , N ₂ O or SiH ₄ diluted with N ₂ or
Needless to say, the same result can be obtained by using a gas system of Si ₂ H ₆ , N ₂ O, Ar or He. Further, regarding the substrate temperature, in this embodiment, the heat resistance of the wear-resistant protective film of the thermal head is set to 500 ° C. This is a story in consideration of considerably strict specifications, and the normal operating temperature is , 300 ~ 3
About 50 ° C is sufficient, and the substrate temperature should be adjusted according to this specification.
It may be set at 350 ° C or lower.

As described above, according to the present invention, that is, SiH ₄ or Si
Plasma C using ₂ H ₆ , N ₂ , N ₂ O, Ar or He as source gas
The SiON film formed by the VD method has higher hardness, higher heat resistance, and stronger compressive stress than the SiON film made of conventional SiH ₄ , N ₂ , and N ₂ O. In addition, the film formation rate is high and the resistivity is low. Therefore, by using this film as the wear-resistant protective film of the thin film thermal head, it becomes possible to easily provide a highly reliable thin film thermal head.

[Brief description of the drawings]

FIG. 1 to FIG. 3 are characteristic charts showing differences in Vickers hardness and internal stress, infrared absorption spectrum, and heat-resistant pulse life of the film formed in one example of the present invention from the film formed by the conventional method, respectively. Is. Straight line 5, curve 6: Vickers hardness and internal stress of the SiON film formed according to the embodiment of the present invention, respectively. Curve 10: Infrared absorption spectrum of a SiON film according to an example of the present invention. Line 12: Heat-resistant pulse life of a thermal head using a SiON film according to an embodiment of the present invention as a wear-resistant protective film.

Front page continued (72) Inventor Takashi Hirao 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. ) Reference JP 53-65066 (JP, A) JP 58-118275 (JP, A) JP 58-163677 (JP, A)

Claims (3)

(57) [Claims] 1. An insulating substrate, a large number of heating resistor arrays provided on the substrate, and a wear-resistant protective film provided on the heating resistor array, wherein the wear-resistant protective film is made of SiH. ₄ or Si
_A thin-film thermal head made of a silicon oxynitride film formed by plasma CVD using ₂ H ₆ , N ₂ , N ₂ O, and Ar or He as source gases. 2. SiH ₄ or Si ₂ H ₆ , N ₂ , N ₂ O, Ar or H on a large number of heating resistor arrays provided on an insulating substrate.
A method of manufacturing a thin-film thermal head in which a wear-resistant protective film made of a silicon oxynitride film is formed by a plasma CVD method using e as a raw material gas. 3. The thin film according to claim 2, wherein the wear-resistant protective film is a silicon oxynitride film formed by a plasma CVD method using the source gas at a substrate temperature of 350 ° C. or higher. Type thermal head manufacturing method.