JPH07125273A - Thermal head - Google Patents

Abstract

PURPOSE:To provide a thermal head having a primary film in which, even if charged power density in a heat generating resistor is increased, releasing from a glazed layer is small, a dry etching selection ratio of Ta-SiO2, Nb-SiO2 to a resistance film is large, adherence force to a protective film is excellent and step coverage of the film is preferable. CONSTITUTION:A thermal head comprises a support board 1 provided at its upper part with a glazed layer, a primary layer 3 containing Si, O and N and disposed on the glazed layer, a plurality of heat generating resistors 4 disposed on the layer 3, electrodes 5, 6 connected to the resistors 4, and a protective layer 7 so formed as to cover at least heat generators of the resistors 5, 6, wherein the primary layer contains at least 7 atomic % or less of a content of N.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal head which has a high energy density applied to a heating resistor and is effective for a high definition type.

[0002]

2. Description of the Related Art Thermal heads have the advantages of low noise, easy maintenance, and low running costs.
It is used in various recording devices such as facsimiles and printers for word processors. In addition, 400dpi (dots per inch
) Higher definition thermal heads are used for hole printing.

By the way, regarding the high-definition type thermal head, in order to further improve the resolution, it is required to further miniaturize the shape of the heating resistor and to increase the input energy density.

When the shape of the heating resistor is miniaturized and the input energy density is increased accordingly, the peak value of the heating temperature rises, for example, in the central portion of the heating resistor. Therefore, the solid phase reaction is promoted between the resistance film forming the heating resistor and the glaze layer located below the resistance film, or between the resistance film and the protective film located above the resistance film. When the solid-state reaction occurs, the resistance value of the heating resistor increases during actual operation. As a result, the resistance value of the heating resistor deviates from the specified value, and it may not be usable.

For example, when the temperature of the heating resistor exceeds 600 ° C., the reaction between the resistance film and the glaze layer becomes remarkable due to the solid phase reaction, and the resistance value of the heating resistor increases. In order to suppress the reaction between the resistance film and the glaze layer, SiNxOy is provided between the resistance film and the glaze layer.
There is a method of forming an underlayer of (0.2 <x <1.1, 0.2 <y <1.8) to prevent impurities from diffusing from the glaze layer to the resistance film (see Japanese Patent Laid-Open No. 61-297159).

[0006]

In the case of the thermal head using the underlayer having the above-mentioned composition, if the applied power density is increased in order to operate with high precision, peeling easily occurs between the glaze layer and the underlayer. This is because the thermal expansion coefficient of the glaze layer is different from that of the underlayer, so that stress is generated at the interface between the two when the thermal head operates. Then, it is considered that such heat stress is repeated and peeling occurs. Therefore, the input power density during operation is large,
Further, this is a problem when used in a high-definition thermal head in which the temperature of the heating resistor becomes high. Further, when the resistance film is formed of Ta-SiO ₂ or Nb-SiO ₂ and the resistance film is patterned by dry etching. However, a problem occurs in the base film having the above composition.

In this case, the etching selectivity between the resistance film and the base film is small. Therefore, when the resistive film between the leads is completely etched over the entire area of the substrate,
The base film is etched up to unnecessary portions. When the unnecessary portion of the base film is etched, a step is formed between the resistance film and the lead at that portion, and the step coverage of the protective film is deteriorated when the protective film is formed in a later step.

Further, when the surface of the underlayer film is etched, fine irregularities are formed in that portion, and fluoride tends to remain on the surface of the underlayer film during dry etching. In this case, when the protective film is formed thereafter, the fluoride remains between the base film and the protective film, and the adhesion force between the two becomes weak.

The present invention solves the above-mentioned drawbacks. Even if the power density applied to the heating resistor is large, the peeling from the glaze layer is small, and the Ta-SiO ₂ and N are not separated.
It is an object of the present invention to provide a thermal head having a base film having a large dry etching selection ratio with respect to a resistance film of b-SiO ₂ , excellent adhesion to a protective film, and good step coverage of the protective film.

[0010]

According to the present invention, there is provided a support substrate having a glaze layer formed thereon, an underlayer containing Si, O, and N and located on the glaze layer, and the underlayer. In a thermal head comprising a plurality of heat generating resistors arranged in, a electrode connected to the heat generating resistors, and a protective layer formed so as to cover at least the heat generating portion of the heat generating resistors, the base layer is , N content is approximately 7 atomic% or less.

[0011]

According to the thermal head having the above structure, Si, O, and N are used as the material of the underlayer, and the composition of the conventional thermal head (see Japanese Patent Laid-Open No. 61-297159) and the underlayer is It's different. The configuration of the present invention has the following features (1) and (2).

(1) The difference in the coefficient of thermal expansion from the glaze layer is small, and the thermal shock resistance is good.

The mechanical characteristics and coefficient of thermal expansion of a film containing Si, O, and N are intermediate values between the characteristics of SiO ₂ and Si ₃ N ₄ depending on the composition. This is Si-O,
Alternatively, it is considered that an amorphous structure determined by the Si-N bond ratio controls these characteristics. For example, as the O content increases, the Si—O bond ratio increases, and the characteristics approach those of SiO ₂ . Conversely, increased binding ratio of the Si-N the greater the content of N, Si ₃ N ₄
Approaching the natural characteristics.

For example, taking the Knoop hardness of the film,
As shown in FIG. 2, when the N concentration is 12 atomic% or more, the value becomes almost constant. When the N concentration is 12 atomic% or less, the Knoop hardness decreases as the N content decreases. In FIG. 2, the vertical axis represents Knoop hardness (kg · f / mm ² ).
The horizontal axis represents the N content (atomic%). The hardness of the glaze layer is indicated by arrow Y.

When the content of N is 12 atomic%, approximately one of four bonds of Si atoms is bonded to N and the remaining three are bonded to O. If the content rate of N becomes higher than that, most of the stochastically Si is always one or more N.
Will be combined with. It is considered that in such a composition range, structural freedom is limited, and mechanical properties closer to those of the Si ₃ N ₄ film than the SiO ₂ film are exhibited.

When the N content is 12 atomic% or less,
When the ratio of N decreases, a structure such as SiO ₂ , that is, a structure in which silicic acid tetrahedra are connected by sharing the O atom at the apex becomes dominant. For this reason, the characteristics such as film hardness and film stress that greatly depend on the bond structure approach the characteristics of the SiO ₂ film as the N content decreases.

It is difficult to measure the coefficient of thermal expansion related to thermal shock in a thin film state. But Si
By comparing the thermal expansion coefficients of O ₂ (quartz) and Si ₃ N ₄ ,
It is considered that the thermal expansion coefficient increases as the N concentration decreases.
Also, from the relationship between the N concentration in the film and the Knoop hardness shown in FIG. 2, it is expected that if the N concentration decreases from around 12 atomic%, the coefficient of thermal expansion increases accordingly.

Further, when the underlayer film of the thermal head described in the conventional example and the underlayer film of the present invention are compared, the thermal expansion coefficient of the underlayer film of the conventional example is close to that of the Si ₃ N ₄ film, and the underlayer film of the present invention is also Is considered to be close to SiO ₂ . Therefore, the underlayer film of the present invention is closer to the thermal expansion coefficient of the glass glaze containing SiO ₂ as a main component and is more effective as the underlayer provided on the glaze layer.

Particularly, in the case of a high-definition thermal head, the energy density applied to the heating resistor is large and the temperatures of the base film and glaze are high, so that the thermal expansion coefficients of the base film and glaze are close to each other. Is large, and peeling of the base film and the glaze during operation is reduced.

The electrical or optical characteristics of the underlayer film are affected by film defects and impurities which depend on the apparatus for forming the underlayer film and its forming conditions. However, the mechanical properties and coefficient of thermal expansion are governed by the basic structure, which is largely determined by the composition of the film. Therefore, as in the present invention,
When the mechanical properties and the coefficient of thermal expansion are considered to be problems, it is considered that the forming method and forming conditions have almost no effect.

(2) The dry etching resistance of the base film is improved.

For example, Ta-SiO ₂ or Nb-SiO ₂
When patterning the thin-film resistance film of, CF ₄ and O ₂ are used as etching gases and the CDE method is used.
At this time, it is desirable that the underlying film has as small an etch rate as possible (difficult to be etched). If the etch rate is large, unnecessary portions of the base film are also etched, resulting in unevenness on the surface of the base film and formation of unnecessary steps. As a result, the protective film is not sufficiently formed in the step portion, and the adhesive force is reduced.

From the viewpoint of film composition, the etching rate of the Si, O, and N films by the CDE method is smaller as the O concentration is higher (that is, the N concentration is lower). This is because the Si—N bond is more susceptible to F radicals than the Si—O bond. Also, the CDE of Si ₃ N ₄ and SiO ₂
Comparing the rates, this is an expected result because the former is an order of magnitude larger. Since the underlayer of the present invention has a large O concentration and a small N concentration, the etching rate by the CDE method is small. Therefore, it is possible to realize a thermal head in which irregularities are less likely to occur on the surface of the base film, the protective film is well formed, and the adhesive force is excellent.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIG.

1 is a supporting substrate, and the supporting substrate 1 is Al ₂ O ₃
Is formed by. Further, on the supporting substrate 1, a glass glaze layer 2 containing SiO ₂ as a main component and having a thickness of about 60 μ is formed. The material of the support substrate 1 is not limited to Al ₂ O ₃ , and other metal or non-metal substrate can be used. Further, the glass glaze layer 2 can also be selected from those containing various additive materials.

Next, the glass glaze layer 2 is formed on the supporting substrate 1.
On the heat-resistant resin substrate on which was formed the sputtering method, the base film 3 containing Si, O, and N as the main components was changed in the flow rate of oxygen (O ₂ ) as shown in a to f (Table 1 ) Under a plurality of conditions. In this case, the target is
Powders of Si ₃ N ₄ and SiO ₂ were mixed at a molar ratio of 1: 1 and hardened by hot pressing and then sintered.

(Table 1) Sputtering conditions Target input power density; 4.3 W / cm ² sputtering gas and flow rate; Ar, 24 sccm O ₂ a) 2.4 sccm b) 3.6 sccm c) 4.8 sccm d) 7. 2sccm e) 9.6sccm f) 12.0sccm Sputtering gas pressure; 3.0 × 10 ⁻¹ Pa substrate heating temperature; 220 ° C. Note that the O ₂ flow rate when forming the underlayer is set to 5 levels, and XPS (ESCA ) The film composition was analyzed by the relative sensitivity method. The value of the film composition is a depth profile of 200 nm in 10 nm steps from the surface of the underlayer,
Each composition is averaged. The results are shown in (Table 2).

[0028] In addition, the Nb—SiO ₂ system heating resistor 4 is formed on the base film 3.
Then, the individual electrode 5 and the common electrode 6 made of Al were sequentially formed.

A mixed acid composed of phosphoric acid, acetic acid and nitric acid was used for etching the Al electrode. In addition, Nb-SiO ₂
The CDE method was used for etching the resistance film. In this embodiment, CF ₄ and O ₂ are used as the introduction gas, and the ratio is 7:
It was set to 3.

The material of the heating resistor and the electrode material are not limited to those mentioned above, and other materials may be used. Further, as the film forming method and the patterning method, various process techniques can be used.

Next, a protective film 7 was formed of Si, O and N so as to cover most of the Al electrode and the heating resistor portion. The protective film 7 was formed to have a thickness of 3 μm by the sputtering method. The prototype was subjected to a power resistance test and an environment resistance test after the mounting process. Further, a protective film adhesion test by a tape peeling method and an observation of step coverage by SEM were also performed. The results are shown in (Table 3).

(Table 3) Evaluation results Conditions Power resistance Environment resistance Protection film adhesion Step coverage a) △ △ △ △ b) △ △ △ △ c) ◇ △ ◇ △ d) ◇ ◇ ◇ ◇ e) ○ ○ ○ ◇ f) ○ ○ ○ ◇ (Table 3), ○, ◇, △ are displayed in order of good results. And when looking at (Table 3) comprehensively, e),
Good evaluation results were obtained in f), that is, in the composition range of the Si, O, and N underlayers according to the present invention.

As described above, according to the structure of the present invention, the difference in the coefficient of thermal expansion between the glaze layer and the underlayer is reduced, and
The peeling of the film between the glaze layer and the underlying layer can be reduced even in the operation in which the input energy density is increased. Further, in the resistance film patterning step, it is possible to obtain a thermal head in which unnecessary etching of the underlayer is suppressed, the adhesion with the protective film is strong, and the step coverage of the protective film is good.

[0034]

According to the present invention, a thermal head having excellent power resistance and reliability can be realized.

[Brief description of drawings]

FIG. 1 is a diagram illustrating an embodiment of the present invention and is a perspective view showing a part of the present invention in an exploded manner.

FIG. 2 is a diagram showing a relationship between oxygen content of Si, O and N underlayers and Knoop hardness.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Supporting substrate 2 ... Glass glaze layer 3 ... Underlayer 4 ... Heating resistor 5 ... Individual electrode 6 ... Common electrode 7 ... Protective layer

Claims (1)

[Claims] 1. A support substrate on which a glaze layer is provided, a base layer containing Si, O, and N and located on the glaze layer, and a plurality of heating resistors arranged on the base layer. In a thermal head including a body, an electrode connected to the heating resistor, and a protective layer formed so as to cover at least the heating portion of the heating resistor, the underlayer has an N content of approximately 7%. A thermal head characterized by being at most atomic%.