JP2676787B2 - 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 (No voids or cracks are generated during heating.) (3) Electric corrosion of the heating resistor, conductor layer, etc. formed under the wear-resistant protective film should not occur. (It is generated when driving under moisture absorption of paper etc., it has good step coverage, it is pinhole free, and it is dense and has no hygroscopicity.) (4) As a base for heating resistors, conductor layers, substrates, etc. Adhesion of is good.

(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.

Regarding the above-mentioned matters, particularly (3) is an important problem in terms of reliability, and the plasma CVD (chemical vapor deposition) method is effective for such a problem. Because the plasma CVD method is basically a method of depositing a film by decomposing the source gas and promoting the surface reaction, the energy (electric power) required for film formation can be small, and the granularity due to abnormal discharge can be used. Defects such as protrusions and pinholes are unlikely to occur, and since the density and the step coverage are excellent, galvanic corrosion of the lower layer film is unlikely to occur, and the reliability is significantly improved. By the way, as a protective film using this plasma CVD, it is usually used in semiconductor ICs and the like, SiH ₄ , N ₂ gas, Si
H _4, NH ₃ gas, SiH _4, N _2, NH ₃ gas or the like used as a raw material gas
A SiN (silicon nitride) film is 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 when it is usually thickened or heat is applied,
Causes stress cracking. 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 JP-A-62-145735, a silicon oxynitride film (hereinafter
SiON film), and SiH ₄ , N ₂ O, N ₂ as source gas
A film formed by a plasma CVD method using is useful. In addition to these, SiH ₄ , NH ₃ and N are used as the source gas for the SiON film.
₂ O and SiH ₄ , NH ₃ , N ₂ , N ₂ O, etc. have been reported.
Both of them are mainly considered to reduce the power consumption of film formation, but when pulse heating is required in a short time like a thermal head, the surface temperature rises up to about 500 ° C. In this case, many hydrogen content in the feed gas, which, in the film, Si-H, Si-H 2, O-H, in the form of such N-H _2, as a low product relatively binding energy , A lot remains. Hydrogen existing in these forms can be relatively easily released to the outside of the film in the form of H ₂ , H ₂ O, etc. 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 requiring heat resistance for a long period of time, such as a wear-resistant protective film of a thermal head. In this respect, when SiH ₄ , N ₂ O, N ₂ is used as a source gas, the hydrogen content in the original source gas is small, and the dissociation energy of N ₂ O gas is small as O.845eV,
O is generated by the decomposition of N ₂ O → N ₂ + O, and hydrogen is extracted, so that the amount of hydrogen existing in the film is reduced. Therefore,
Heat resistance is improved. However, even when a film is formed with this source gas system, hydrogen remains in the form of Si-H, OH, N-H, etc.
Particularly in the former two cases, that is, hydrogen remaining in the form of Si-H, OH is a cause of heat resistance deterioration, and NH is high heat resistance, so from the viewpoint of high heat resistance, Si-H It is important to reduce each O, H bond and increase N-H bond. For this, it is necessary to increase the incident power,
This is not always a preferable direction, especially in the case of a large-scale production apparatus, because the electric power becomes extremely high and the occurrence of abnormal discharge is promoted, and therefore, the heat resistance deterioration of Si-H, O-H, etc. still remains. Difficult to reduce the resulting coupling,
Therefore, in order to reduce the residual amount of hydrogen, the oxygen generated by the decomposition of N ₂ O gas, by abstracting hydrogen, which had been reduced hydrogen content, in this way, an increase in the N ₂ O Inevitably, the Si—O bond also increases, leading to a decrease in hardness. Therefore, it has been difficult to satisfy both the high hardness and the high heat resistance required for the wear resistant protective film of the thermal head at the same time.

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 formation method of decomposing and depositing with plasma, gas may be taken into the film in an undecomposed form. For example, plasma using SiH ₄ and N ₂ as source gases
This is the Si—H bond in the SiN film. Since hydrogen, which has been taken into the film without being decomposed like Si-H, has a relatively small binding energy, hydrogen is released by heating, and at that time, bubbles and cracks are generated in the film, resulting in heat resistance. Cause problems. On the other hand, 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 formed by SiH ₄ , N ₂ , N ₂ O-based or SiH ₄ , NH ₃ , N ₂ O-based as a source gas, the latter is the amount of hydrogen present in the source gas. However, the heat resistance of the film is still inferior because it is accompanied by hydrogen bonds in the film. On the other hand, in the former, that is, SiH ₄ , N ₂ , N ₂ O system, since the hydrogen content in the raw material gas is small, it is possible to reduce the amount of hydrogen present in the film, heat resistance is improved, thermal It can be said that it is suitable for a head protection film. However, this SiH ₄ , N ₂ ,
Even in the case of plasma SiOH film that depends on the source gas of N ₂ O, the following matters still pose a problem. That is, the ionization voltage and dissociation energy of N ₂ are large, so that the incident power must be increased. This means that particularly in a large-scale production apparatus, a very large amount of power must be input, which is a form that promotes the occurrence of abnormal discharge, and is not necessarily the preferred direction. , Si—H bond, O—H bond and the like that cause deterioration of heat resistance, and it is difficult to reduce the bond. On the other hand, in the use of an insulating film that requires ordinary heat resistance, it is possible to increase the N ₂ O gas flow rate to reduce the amount of residual hydrogen and to extract hydrogen by the oxygen generated by this decomposition. Although the hydrogen amount is reduced, increasing the N ₂ O gas flow rate inevitably increases the Si—O bond, resulting in a decrease in hardness. Therefore, it has been difficult to satisfy both the high hardness and the high heat resistance required for the wear-resistant protective film of the thermal head at the same time.

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

Means for Solving the Problems In order to solve this problem, the present invention uses SiH ₄ , N ₂ , N ₂ O as a raw material gas, and at least the N ₂ flow rate of this raw material gas and the SiH ₄ flow rate ratio N ₂ / Provide a thin film thermal head using a silicon oxynitride (SiON) film formed by plasma CVD at a substrate temperature of 350 ° C. or more as a wear-resistant protective film, and a method for manufacturing the same, with SiH ₄ of 10 to 60. It was done.

Action The following effects can be obtained by keeping the N ₂ / SiH ₄ flow rate ratio in the source gas in this configuration within a predetermined range, that is, 10 or more and 60 or less. Nitrogen regard to the lower limit 10, by increasing the N ₂ amount, increases the frequency of collision between electrons and N _2, excitation neutral radicals (▲ N ^※ ₂ ▼) density is increased, therefore, to be incorporated into the film The amount also increases (nitrogen supply rate-controlling region)
It is easy to form N—H bonds with hydrogen of Si—H and O—H, and Si—N bonds increase, while the number of Si—H and O—H decreases, but for this effect, ▲ N ^※ ₂ ▼ The number of excited radicals is required, N ₂ flow rate is required to some extent,
This is the limit value for that. Also, regarding the upper limit value 60,
When the N ₂ flow rate also increases indefinitely, N ₂ originally has a large ionization voltage and dissociation energy, so if the number of N ₂ is too large, the energy added per unit gas molecule decreases and the excitation efficiency decreases, ▲ N ^※ ₂ ▼ The number of excited radicals decreases and N
This gives a limit value in which the -H bond is hard to form, and therefore Si-H and OH cannot be reduced. (Energy supply rate-controlling region) Therefore, by setting the N ₂ / SiH ₄ flow rate to 10 or more and 60 or less, ▲ N ^* ₂ ▼ excited radicals having sufficient energy to form a highly heat-resistant N—H bond are supplied. And Si-H,
Hydrogen, which coordinates to bonds that cause deterioration of heat resistance such as O-H, forms N-H bonds and reduces Si-H and O-H, resulting in high heat resistance of the film, such as bubbles and cracks. No deterioration occurs. In addition, at the same time, some Si-N bonds are formed, and the hardness is not lowered. Therefore, high heat resistance and high hardness of the film can be realized at the same time.By using the SiON film formed by this method as a wear-resistant protective film, it is possible to obtain a highly reliable thin film thermal head. Become.

Example In this example, a parallel plate type (capacitive coupling type) plasma CVD apparatus was used as a film forming apparatus, and the electrode plate shape was 600 mm × 600 m.
In m square, distance between electrodes is 20mm, RF frequency 13.56MHz, RF power
800W, Gas pressure 125Pa Substrate temperature 350 ℃, SiH ₄ : 35sccm, N ₂ O: 35
As sccm (constant), N ₂ flow rate is 35Osccm to 2100sccm (N
_The film was formed by changing the flow rate ratio of ₂ / SiH _{4 of} 10 to 60).

FIG. 1 shows the relative emission intensity of the plasma emission spectrum when the glow discharge is raised by changing the N ₂ flow rate.
Line 1 shows relative emission intensities of ▲ N ^* ₂ ▼ (luminous neutral radicals) at 337 nm and line 2 shows ▲ N ⁺ ₂ ▼ (ions) at 392 nm.

From the figure, line 1, ▲ N ^* ₂ ▼ shows N ₂ flow rate of 350scc
It increases with the increase from m, and this tendency is exhibited up to about 1000 sccm, and thereafter, gradually up to 2100 sccm, ▲ N ^* ₂ ▼
It can be seen that is decreasing.

On the other hand, from line 2, ▲ N ⁺ ₂ ▼ shows a decreasing tendency as the N ₂ flow rate increases. This is to a region where there is N ₂ flow, if Maze the N ₂ flow rate increases the collision of electrons and N _2, but the number of pumping radicals increases, the flow (flow supply rate-determining regions) somewhat more N _2, This means that the number of excited radicals decreases because the excitation energy cannot be applied. (Power supply rate-controlling region) N ₂ flow rate 350s in the figure
The infrared absorption spectrum of the film at ccm and 1000 sccm is shown in FIG. In the figure, line 3 is N ₂ flow rate 350 sccm, line 4
Are infrared absorption spectra of the films at a N ₂ flow rate of 1000 sccm, respectively.

As is clear from lines 3 and 4, the N ₂ flow rate from 350 sccm,
By increasing the 1000 sccm, 2150 cm ^-1 vicinity Si-H bonds and reduces the absorption due to O-H bond 3680Cm ^-1 vicinity
The absorption due to the N—H bond near 3350 cm ⁻¹ increased. Under these two conditions, on the thermal head substrate,
FIG. 3 shows the breakdown state mode when a SiON film was deposited to a thickness of 5 μm and its heat resistance was evaluated by continuous pulse current application. The maximum surface temperature during pulse energization is 600 to 650.
° C.

In FIG. 3, a is N ₂ flow rate of 350 sccm, b is 1
The case of 000 sccm is shown, but it can be seen that the breakdown mode is different. In FIG. 6A, a bubble-like abnormality (with interference fringes) as shown by 6 occurs in the area of the heating resistor portion 5 where the temperature is the highest. On the other hand, in FIG. 7B, as shown by 7, cracks were generated in the wear-resistant protective film due to the bulging portion due to the plastic deformation of the underlying substrate glass due to repeated pulse heating.
(No bubbles are generated) In the normal wear-resistant protective film, the destruction mode is predominantly in FIG. 3b described above, and the life deterioration when bubbles are generated as shown in FIG. It is remarkable as compared with b. Therefore, the mode shown in FIG. The cause of this bubble generation is shown in FIG.
As is clear from FIG. 2, the cause of generation is extra-membrane release due to heating of hydrogen coordinated to a bond having a small bond energy such as Si-H and O-H. That is, as shown in line 1 in FIG. 1, when the N ₂ flow rate is 350 sccm and 1000 sccm, the latter with a large flow rate has a larger number of ▲ N ^* ₂ ▼ excited neutral radicals. Therefore, when the N ₂ flow rate is high, it is bonded to hydrogen such as Si—H and O—H generated when the N ₂ flow rate is low, and NH bond having a large bond energy (high heat resistance) is easily generated. Hydrogen coordinating to this N—H bond is stable because it is not easily released from the film even by heating at about 650 ° C. Si-H and O-H decrease with the generation of N-H. This is shown in Fig. 2, and the heat resistance is N ₂ flow rate 350scc.
It improves with the increase from m to 1000 sccm.

Incidentally, the bubble 6 in FIG. 3a is in the case of the maximum surface temperature of 600 to 650 ° C. in the case of pulse energization heating in the case of this figure, but this bubble lowers the energizing pulse power and lowers the surface temperature. The number of the bubbles decreased with the increase in temperature, and no bubbles were generated at a surface temperature of 400 ° C or lower. Normally, the maximum surface temperature of a thermal head that is generally used is about 350 ° C at most, except when used under some severe conditions.
Even under the condition of, that is, the N ₂ flow rate of 350 sccm, it can be practically used. Incidentally, when the N ₂ flow rate was increased from 1000 sccm to 2100 sccm, this time, as shown in FIG. 1, ▲ N ^* ₂ ▼ excited radicals were gradually decreased to produce Si--H, OH hydrogen. The bond of nitrogen is reduced, NH is less likely to be generated, Si-H, O
-H also does not decrease and heat resistance deteriorates. However, at a N ₂ flow rate of about 2100 sccm, no bubbles were observed even when the maximum surface temperature was about 500 ° C during pulsed current heating (600 ~
At 650 ° C, it was sufficiently observed (slightly observed).

When the SiH ₄ gas flow rate is increased or decreased, Si-H, OH also
As the SiH ₄ increases, the N ₂ flow rate also needs to increase with the increase in SiH ₄ , which can be roughly captured by the flow rate ratio.As can be seen in this example, the N ₂ / SiH ₄ flow rate ratio If at least 350/35 = 10 or more and 2100/35 = 60 or less,
The heat resistance of the film is improved. Another method for improving the heat resistance of the film is to raise the substrate temperature. In this embodiment, the substrate temperature is set to 350 ° C., but if the temperature is raised to a higher temperature, the total amount of hydrogen originally present in the film is also reduced, so that the original Si—H and O—H are also reduced, and the temperature is further increased. Heat resistance is possible.

FIG. 4 shows the relationship between N ₂ flow rate and Vickers hardness.
In the figure, the N ₂ O flow rate is also changed at 15 sccm and 35 sccm. Even if the N ₂ flow rate is changed within the range of this embodiment from the lines 8 and 9 in the figure, the hardness does not decrease. In addition, Fig. 5 shows the relationship between the N ₂ flow rate and the internal stress as the N ₂ O flow rate of 15 sccm and 35 sccm.
The above cases are shown in lines 10 and 11, respectively. The internal stress of the film is relaxed as the N ₂ flow rate increases. This has a large correlation with ▲ N ⁺ ₂ ▼ ions in Fig. 1, and N ₂
This is due to the decrease in the N ⁺ ₂ ions and hence the ion bombardment of the membrane as the flow rate increases. As can be seen from FIG. 5, the internal stress is generally small, which is due to the fact that in a production apparatus in which it is necessary to continuously form a thick film of about 5 μm, such as a wear-resistant protective film of a thermal head, The peeling of the film deposited on the electrode plate causes a film defect, but as described above, the internal stress of the film is small, so even if the film is deposited on the electrode plate of several 100 μm, it is not easily peeled off. Bring

As described above, according to the present, according to the present invention, i.e., SiH ₄ as, N _2, N ₂ O source gas, the N ₂ flow rate and the flow rate _of SiH ₄ ratio N ₂ / SiH ₄ for at least material gas A SiON film formed by the plasma CVD method with a thickness of 10 or more and 60 or less simultaneously satisfies both high heat resistance and high hardness. Therefore, by using this SiON film as a wear resistant protective film for a thin film type thermal head. It is possible to provide a highly reliable thin film thermal head.

[Brief description of the drawings]

Figure 1 in one embodiment of the present invention, contributes to the quality of when changing the N ₂ flow rate ▲ N ^※ ₂ ▼ neutral radicals 1
FIG. 4 is a characteristic diagram showing changes in ▲ N ⁺ ₂ ▼ ion 2.
Fig. 2 is a characteristic diagram showing changes in infrared absorption spectra due to differences in N ₂ flow rate, Figs. 3a and 3b are top views showing changes in breakdown mode, and Figs. 4 and 5 are, respectively, FIG. 6 is a characteristic diagram showing a change in hardness internal stress of a film due to a difference in N ₂ flow rate. Line 3 ... infrared absorption spectrum when the N ₂ flow rate is low (350 sccm), line 4 ... infrared absorption spectrum when the N ₂ flow rate is moderately high (1000 sccm).

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takashi Hirao 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Masatoshi Kitagawa 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd. (56) References JP-A-53-65066 (JP, A) JP-A-58-118275 (JP, A) JP-A-58-163677 (JP, A) JP-A-62-167058 (JP, A) Japanese Patent Laid-Open No. 50-62774 (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 , N ₂ , N ₂ O is used as the source gas, and at least the N ₂ flow rate of this source gas and SiH ₄
A thin film thermal head which is a silicon oxynitride film formed by a plasma CVD method with a flow rate ratio N ₂ / SiH ₄ of 10 or more and 60 or less. 2. SiH ₄ , N ₂ , N ₂ O is used as a source gas on a large number of heating resistor arrays provided on an insulating substrate, and at least the N ₂ flow rate of this source gas and the SiH ₄ flow rate ratio N. _A method for 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 with ₂ / SiH _{4 set} to 10 or more and 60 or less. 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 a source gas and a substrate temperature of 350 ° C. or higher. Type thermal head manufacturing method.