JPH06166198A - Thin-film protective layer and thermal head - Google Patents

Abstract

PURPOSE:To form, with one film making batch, a thin-film protective layer having excellent heat resistance, excellent insulating property and abrasion resistance at bottom and surface layers by adding a specific quantity of boron, phosphorus, silicon, nitrogen, and oxygen to the surface and bottom layers, and making the content of the oxygen in the bottom layer larger than that of the surface layer. CONSTITUTION:In a thermal head 1, a heat generating resistance layer 4 is arranged on a heat accumulating glaze layer 3 provided on a substrate 2. A pair of lead layers 51 and 53 are connected oppositely at a predetermined interval. On almost the whole area of the top face of the base of the thermal head as a laminate, a thin film protective layer 7 is provided as an utmost upper layer. In the thin film protective layer 7, content of boron is 40-80at%, content of phosphorus is 5-20at%, content of silicon is 10-50at%, and content of nitrogen is 2-20at%. Further, for content of oxygen, at the time that the thin film protective layer 7 is divided into 5 in the direction of thickness, average content in a thickness of 1/5 at the bottom layer starting from the base interface is 10-30at% and average content in a thickness of 1/5 at the surface layer starting from the top face is 0-5at%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film protective layer and a thermal head having the thin film protective layer.

[0002]

2. Description of the Related Art Conventionally, a thermal head for a thermal printer used as one of the output systems of a video printer, a ticket vending machine, a facsimile, a computer terminal device, a printing device, a recorder, etc. is constructed as shown in FIG. It That is, the heat generating resistor layer 4 is formed on the substrate 2 through the heat storage glaze layer 3, and the pair of lead layers 51 and 53 are connected to the heat generating resistor layer 4. The uppermost layer is provided with a thin film protective layer 7 having abrasion resistance in order to prevent abrasion and damage of the heating resistor layer 4 and the lead layers 51 and 53 due to sliding contact with the thermal paper. ing. At this time, the insulating layer 6 is usually separately formed under the thin film protective layer 7, and the thin film protective layer as the uppermost layer, the heating resistor layer 4, and the lead layers 51, 53 are formed.
It has a function for insulation between and.

During use, the heating resistor layer 4 is energized via the lead layers 51 and 53 to heat the heating resistor layer 4 in the region between the lead layers 51 and 53,
This heat is applied through the insulating layer 6 and the thin film protective layer 7 to the thermal paper which is relatively slidably contacted with the thermal protection paper to perform thermal recording.

Among the performances which determine the life of the thermal head having such a structure, the wear resistance of the surface paper-contacting portion, the heat resistance for repeatedly using high temperature and low temperature, the lead layer 51,
The insulating property of the insulating layer 6 for preventing the dot opening caused by the electrical corrosion of 53, and the peeling due to the poor adhesion between the thin film protective layer 7 and the insulating layer 6 and the lead layers 51, 53 and the heating resistor layer. The stress relaxation property for preventing the above is particularly important.

Of these, a thin film satisfying abrasion resistance and heat resistance is disclosed in Japanese Patent Application Laid-Open No. 56-120512, under normal pressure C.
A thin film containing B, P and Si formed by the VD method has been proposed. However, since this thin film alone has a low insulating property, the dot open occurrence rate due to the electrical corrosion of the lead layers 51 and 53 becomes high. Further, since the atmospheric pressure CVD method is used, it is necessary to form the film at a high temperature of about 600 to 700 ° C., and when selecting the lead layers 51 and 53 electrodes, there is a restriction that only a high melting point material can be used. This is the lead layer 5
This is a major limitation when selecting the material of the 1,53 electrodes.

Further, as a method capable of improving wear resistance and heat resistance to improve the durability of the thermal head and further lowering the film forming temperature, Japanese Patent Application Laid-Open No. 61-447.
In JP-A-03-2003, it is proposed to form a thin film containing B, P and Si using a plasma CVD method. When the film is formed by this method, since the film can be formed at a lower temperature, the selection range of the material of the lead layers 51 and 53 electrodes is greatly expanded,
Further, in terms of durability of the thin film protective layer 7, progress has been made as compared with the atmospheric pressure CVD method, but the volume resistivity of the thin film protective layer 7 is as low as that by the atmospheric pressure CVD method, and further,
The film formed by this method has a high internal stress, and has a problem that in a thermal head manufacturing process, peeling easily occurs between the thin film protective layer 7 and a lower layer in a part of the product.

Therefore, an insulating layer 6 having a stress relaxation property and an insulation property is provided separately from the thin film protective layer 7, but it has abrasion resistance, heat resistance, insulation property, and stress relaxation property. The protective layer film that satisfies the requirements, for example, the deep side which is the interface with the substrate is excellent in insulation, heat resistance and stress relaxation, and the surface side which is the paper contact portion is excellent in abrasion resistance, heat resistance and stress relaxation. It is preferable from the viewpoint of simplifying the manufacturing process and the like if it is possible to form such a film in a single film-forming batch.

[0008]

The main object of the present invention is to have low internal strain and excellent heat resistance. Further, the deep layer side has high volume resistivity and excellent insulating property, and the surface layer side has high hardness. It is an object of the present invention to provide a thermal head capable of forming a thin film protective layer having excellent abrasion resistance in a single film forming batch.

[0009]

Such an object is achieved by the following constitutions (1) to (7). (1) contains boron, phosphorus, silicon, nitrogen and oxygen,
A thin film protective layer in which the oxygen content in the deep layer is higher than the oxygen content in the surface layer. (2) The thin film protective layer according to (1) above, which is formed by plasma-decomposing and depositing a source gas containing boron, phosphorus, silicon, nitrogen and oxygen. (3) The thin film protective layer of (1) or (2) above, which contains 40 to 80 at% boron, 5 to 20 at% phosphorus, 10 to 50 at% silicon, and 2 to 20 at% nitrogen. (4) When divided into five in the thickness direction, the average content of oxygen in the thickness of 1/5 on the deep side is 10 to 30 at% (1).
~ The thin film protective layer according to any one of (3). (5) When divided into five in the thickness direction, the average content rate of oxygen having a thickness of 1/5 on the surface layer side is 0 to 5 at% (1) to
The thin film protective layer according to any one of (4). (6) The value obtained by dividing the average oxygen content of the thickness of 1/5 on the deep side by the average oxygen content of the thickness of 1/5 on the surface is 2 or more when divided in five in the thickness direction. The thin film protective layer according to any one of (1) to (5). (7) A thermal head having the thin film protective layer according to any one of (1) to (6) above.

[0010]

The thin film protective layer of the present invention contains B, P, Si, N and O. In particular, O has a large component distribution in the deep layer portion, and a small amount of O in the surface layer portion, and preferably has no component distribution at all. As a result, the surface layer is inferior in insulation due to the low volume resistivity,
It has excellent wear resistance, heat resistance, and stress relaxation properties. The deep layer has less wear resistance than the surface layer due to the addition of O in the composition of the surface layer, but excellent stress relaxation due to low internal stress. In addition, since it has a high volume resistivity, it becomes a thin film protective layer having excellent insulation properties.

In Japanese Patent Laid-Open No. 55-82678, a stress relaxation layer having an insulating property is provided on a heating resistor layer,
It is proposed that a wear-resistant layer is additionally provided on it to form a protective layer for the heating resistor layer and the lead layer by these two layers.

In contrast to the above proposal, in the present invention, B, P, Si
By including O in a thin film containing N and N, it is possible to form a film having low hardness but excellent in insulating property. Therefore, when forming a thin film protective layer near the interface with the substrate at the initial stage of film formation,
When a raw material having a high content rate is supplied to form a film, and then the O content rate in the supplied raw material is changed as necessary to form a film. When forming a film near the surface layer, the raw material contains little or no O. Form without. That is, in the present invention, the protective film for the heating resistor layer and the lead layer, which has been required to have the required performance by forming another layer of two or more layers, is provided with the required performance in one film-forming batch. It is possible to obtain a film having

[0013]

Specific Structure The specific structure of the present invention will be described in detail below. The thin film protective layer of the present invention contains B, P, Si and N, and further contains O whose content changes in the thickness direction of the layer.

The B content in the thin film protective layer is 40 to 80 at%.
And more preferably 50 to 70 at%. If the B content is too high or too low, the hardness of the thin film protective layer is lowered to deteriorate wear resistance, and if the B content is too high, heat resistance is also lowered to deteriorate durability. In addition, there is a problem that the material cost becomes expensive.

The P content is 5 to 20 at%, more preferably 8 to 16 at%. If the P content is too high or too low, the hardness of the thin film protective layer decreases and the wear resistance deteriorates.

The Si content is 10 to 50 at%, more preferably 20 to 30 at%. If the Si content is too high, the thin film protective layer will have reduced hardness and poor wear resistance, and if it is too low, the heat resistance will be reduced and durability will deteriorate, and internal strain will cause cracking and peeling. May occur.

The N content is 2 to 20 at%, preferably 10 to 20 when O described later does not coexist in the thin film protective layer.
at%. If the N content is too low, the compressive stress is large and peeling easily occurs. However, N is useful for relaxing the stress of the thin film, and although it does not cause a big problem at most, it is difficult to add a large amount under normal film forming conditions, and since it is too large, the inclusion of other components such as B, P, and Si. It is not preferable in terms of reducing the rate.

When the O content is divided into five in the thickness direction of the thin film protective layer to be formed, the O content starts from the interface on the base side and becomes 1 / on the deep side
The average content of 5 is 10 to 30 at%, more preferably 15 to 25 at%. If the O content is too low on the deep side, the volume resistivity of the film is too low, resulting in poor insulation, resulting in a high dot open occurrence rate due to electrical corrosion and poor durability. On the other hand, if the amount is too large, the content ratio of other composition components is reduced, the hardness and heat resistance of the film are reduced, and tensile stress acts on the film, which tends to cause peeling of the film.

Similarly, when the thin film protective layer is divided into five parts in the thickness direction, the average O content of the surface layer 1/5 of the thickness starting from the surface is 0 to 5 at%, more preferably 0 to 1 at%. . If the O content is too high on the surface side, the hardness is lowered and the wear resistance is deteriorated.

Further, the thickness of the deep side 1/5 and the surface side 1/5
The O content between the thicknesses of A and B may change continuously from the deep layer side to the surface layer side toward the lower side, or may gradually change to the lower side. Rate is 0 to 1 at%
In the range of 1 / in the thickness direction of the thin film protective layer from the surface side.
Up to about 2 is formed. This is because a layer having a low O content and a high hardness on the surface side is as thick as possible within a range not deteriorating the insulation property on the deep side,
This is because the durability based on the abrasion resistance of the thermal head becomes high.

Further, the average content of O having a thickness of 1/5 on the deep layer side and the average content of O having a thickness of 1/5 on the surface layer are
The value obtained by dividing the average oxygen content in the thickness of 1/5 on the deep side by the average oxygen content in the thickness of 1/5 on the surface is preferably 2 or more, and more preferably 1/5 on the deep side. The ratio of the average content of O in the surface layer side to the average content rate of O in the surface layer side ⅕ is 5% on the surface layer side for 10% on the deep layer side and 30% on the surface layer side for 30% in the deep layer side. Should be in the range of 0%. When this ratio is small, that is, the deep side 1/5
When the value obtained by dividing the average oxygen content of the thickness of the surface layer by the average oxygen content of the thickness of the surface layer side is less than 2, if the O content is too small on the large side, the O content on the surface side is small. Is low, the hardness on the surface layer side is insufficient, and if the O content rate is too small on the side where the O content rate is low, the O content rate on the deep layer side is low, resulting in low insulation. On the other hand, if this ratio is higher than this range, the O content on the deep layer side will be too high, and the content ratio of other composition components will be reduced, the hardness and heat resistance of the film will be reduced, and the tensile stress of the film will be reduced. Is likely to cause peeling.

It is also possible to form a film with a uniform O content in the thickness direction without changing the O content in the thickness direction of the thin film protective layer as described above. Since the range of O content is narrow, it is difficult to control the O content during film formation. However, the method of the present invention is also excellent in that the permissible range of controlling the O content during film formation is widened.

Of the above-mentioned components other than O, B, P and S
It is preferable that i has a constant content ratio in the thickness direction of the thin film protective layer, but it may be changed within a range such that it becomes the average content ratio of each component.

In order to analyze the composition of each component of the thin film protective layer at each portion in the thickness direction, secondary ion mass spectrometry may be used.

In addition to the above composition, H and / or halogen may be contained in the thin film protective layer of the present invention due to the raw materials used. In this case, the amount of H and / or halogen is preferably 3 at% or less. This is because when the H or / and halogen content exceeds 3 at%, the heat resistance is lowered and the durability is deteriorated.

Further, other elements may be contained in the range of approximately 1% by weight or less of the whole. Examples of such elements include elements such as Ge, Sn, Pb, Al, Zr, and Nb, and elements derived from stainless steel that is the material of the manufacturing apparatus, such as Ni and Cr.

The thin film protective layer having such a composition usually takes an amorphous or polycrystalline state.

As described above, preferably, a thin film protective layer containing B, P, Si and N and a composition in which O having different contents in the thickness direction is contained in the above proportion is formed by the plasma CVD method under the conditions described later. It is possible to obtain a thin film protective layer having low internal stress, high heat resistance, high hardness especially on the surface side, and high volume resistivity on the deep side at a low film forming temperature.

The film thickness may be appropriately determined according to the application, but is usually 1 to 10 μm, particularly preferably 5 to 10 μm.
m.

For plasma decomposition, a high frequency method is preferably used, but a microwave method can also be used. The commonly used high-frequency method is 0.05 to 1 at 1 to 30 MHz.
Power of about W / cm ² should be applied.

As a raw material source to be used, a boron hydride such as BH ₃ or B ₂ H ₆ may be used as a B source, and a boron halide such as BCl ₃ or BBr ₃ may be used.
As the P source, phosphorus hydride such as PH ₃ , phosphorus halide such as PCl ₃ and PBr ₃ may be used.
As a source, a silane-based gas such as SiH ₄ or Si ₂ H ₆
Etc., silicon halide, SiCl ₄ , SiF _4, etc. may be used, and as the N source, for example, N ₂ O containing N and O, NO _2, etc. represented by the general formula NO _x , N ₂ ,
NH ₃ , NF ₃ or the like may be used, and at this time, if necessary, a material represented by the general formula of NO _x is selected, and this raw material also serves as an O source. From the above raw material sources, a mixed gas containing B, P, Si, N, and optionally O may be used as a raw material gas.

As the carrier gas, hydrogen, argon, helium or the like, especially helium may be used, and the raw material gas may be introduced into the reaction system so that the raw material gas has a predetermined ratio.

The conditions such as the type and composition of the raw material gas and the carrier gas and the flow rate for obtaining the optimum component composition for the thin film protective layer may be determined experimentally. However, since the content of the O source changes in the thickness direction, it is necessary to appropriately change the flow rate depending on the film forming rate and time, but this change condition may be experimentally obtained.

The operating pressure is about 0.01-5 Torr,
The substrate temperature is about 100 to 500 ° C, preferably 300 to
The temperature may be 400 ° C. The film forming rate is 100 to 20.
It may be about 00 A / min.

Referring to FIG. 1, a typical example of a thermal head using the thin film protective layer 7 of the present invention will be described.

That is, the substrate 2 may be made of ceramics such as alumina.

The glaze layer 3 for heat storage provided on the substrate 2 may be formed of ordinary glass. Note that the glaze layer 3 is provided over almost the entire area of the substrate, and the thickness thereof may be 60 to 80 μm, as in the usual case. It may be formed by a screen printing method, a dipping method, or the like. As the substrate on which the glaze layer is formed, a commercially available substrate satisfying the above conditions can be used.

On the other hand, the heating resistor layer 4 is disposed on the glaze layer 3. The heating resistor layer 4 may be formed by various methods, but is preferably a polycrystalline silicon thin film from the viewpoint of its characteristics.

Further, in this polycrystalline silicon thin film,
Impurities such as P, As, B and Sb may be included.
The resistance may be about 2 × 10 ^{−4 to} 5 × 10 ⁻² Ω · cm. Further, only one heating resistor layer 4 may be provided on the substrate in a predetermined shape, but normally, a plurality of heating resistor layers 4 are separated and provided in a predetermined array so as to have, for example, a parallel strip shape. And the thickness is 200 to 20,000.
It may be A, but preferably 500 to 5000A.

A pair of lead layers 51, 53 are connected to the heating resistor layer 4 having a predetermined shape and a predetermined arrangement so as to face each other with a predetermined gap. The lead layers 51 and 53 may be formed as a thin film from various refractory metals according to various methods. Aluminum, gold, nickel, copper,
It is preferably composed of tantalum, titanium, tungsten, molybdenum, chromium or alloys thereof, and further tungsten silicide, molybdenum silicide or the like.

In this case, the lead layers 51 and 53 may be located above or below the heating resistor layer 4. The lead layers 51 and 53 may have a thickness of about 0.5 to 2 μm.

Then, the thin film protective layer 7 of the present invention is provided as the uppermost layer over substantially the entire area of the upper surface of the thermal head base as such a laminated body. At this time,
It is not necessary to provide the insulating layer 6 shown in FIG.

Although a typical example of the construction of the thermal head has been described above, various other intervening layers may be provided in the thermal head, or a portion corresponding to the heat generating portion of the substrate as shown in FIG. It is possible to make various shapes such as making the shape concave, or making the portion corresponding to the heat generating portion convex as shown in FIG.

When evaluating a thermal head having a thin film protective layer formed as described above, in order to evaluate abrasion resistance, a thermal test was performed on a thermal head formed with an applied power of 0.2 W as an abrasion test. The recording paper is run and the wear rate is measured. The evaluation criteria vary greatly depending on the usage conditions and the shape of the thermal head, but as an example, when a thermal head having the shape shown in FIG. 3 is formed and temperature, humidity, paper quality, etc. are evaluated under standard conditions, the wear rate is 0. 0.04 μm / km or less, more preferably 0.03 μm / km
It is less than km. If this value is large, the wear rate will be high and the life of the head will be short.

Further, in order to evaluate the insulating property, the lead layers 51 and 53 of the formed thermal head are subjected to an electrolytic corrosion test.
The dot open rate due to corrosion is measured by applying a voltage of 24 V to a temperature of 60 ° C. and a humidity of 90% for 96 hours. This value is preferably 2% or less, more preferably 0%. Is. The dot open is caused by electrical corrosion of the lead layer, and if this value is large, the life of the head is also short.

Further, in order to evaluate the occurrence of internal stress, as a scratch test, the scratch strength is measured on the surface of the formed thermal head by a scratch method with a maximum load of 120 g. The measured value is preferably 100 g or more, more preferably 120 g or more. This value is used to evaluate the adhesion evaluation between the thin film protective layer and the lead layer and the heat generating resistance layer.If this value is small, the adhesion is poor, that is, a large tensile or compressive stress occurs in the formed thin film. It shows that it is doing.

[0047]

EXAMPLE A thermal head as shown in FIG. 3 was prepared and the effect of the present invention was confirmed. First, for the substrate 2,
Alumina of 100 × 150 mm, thickness of 1 mm and purity of 96% is used, and the glaze layer 3 having the maximum thickness of 60 μm is formed on one surface thereof.
A width of 1.5 mm was formed only on the portion of the heating resistor layer 4 where the heating portion was formed. Then, according to the low pressure CVD method, silane and diborane as sources and 1 at% of boron are included.
A polycrystal silicon thin film having a thickness of 00A was deposited, and a plurality of parallel thin strip-shaped polycrystal silicon thin film heating resistor layers 4 having a width of 100 μm and a gap of 30 μm were formed by photolithography.

Thereafter, a tungsten thin film having a thickness of 0.8 μm is deposited on the thin film, and a 100 μm thick film is formed on the central portion of each of the strip-shaped heat-generating resistor layers 4 by photolithography.
Tungsten lead layers 51 and 53 were formed so that a window of 230 μm was formed.

A thin film protective layer 7 having a thickness of 6 μm was applied to the entire surface of the thermal head underlayer laminate thus formed under the following conditions 1 to 6.

<Condition 1> 5% B ₂ H ₆ / He as a raw material
At a flow rate of 600 SCCM and 25% PH ₃ / He at 30 SCCM
Flow rate of 20% SiH ₄ / He at a flow rate of 150 SCCM, N ₂ at a flow rate of 120 SCCM, and the flow rate of N ₂ O is 50 SCCM from the initial 60 SCCM film formation every 20 minutes by setting the mass flow controller. , 30SCCM, 5SCCM, 0
The flow rate was changed from SCCM to 0SCCM and flowed for 120 minutes. Substrate temperature is 300 ° C, RF power is 0.4 W / cm ² , 1.3 Torr
Glow discharge decomposition was carried out to form the thin film protective layer 7 at a film forming rate of 500 A / min.

This thin film protective layer was subjected to composition analysis of film components in the depth direction of the film by secondary ion mass spectrometry. The O content is 1 on the deep side and the surface side in the thickness direction of the film.
The values at the center of the thickness of / 5 were read and the results are shown in Table 1. The average contents of B, P, Si and N are 52 at%, 9 at%, 26 at% and 5 at, respectively.
%Met.

<Condition 2> The flow rate of N ₂ O is set to 30 at the initial stage of film formation.
SCCM, 25SCCM, 20SCCM, 15SCCM, 10SC below
Condition 1 except that CM and 5SCCM were changed every 20 minutes.
A thin film protective layer 7 was formed in the same manner as in. The components of the obtained thin film were analyzed in the same manner as in Condition 1, and the analysis results of O are shown in Table 1. The average contents of B, P, Si and N were 53 at%, 9 at%, 27 at% and 5 at%, respectively.

<Condition 3> The flow rate of N ₂ O is set to 60 at the initial stage of film formation.
SCCM, below 60SCCM, 30SCCM, 30SCCM, 0SCC
Condition 1 except that M and 0 SCCM were changed every 20 minutes.
A thin film protective layer 7 was formed in the same manner as in. The components of the obtained thin film were analyzed in the same manner as in Condition 1, and the analysis results of O are shown in Table 1. The average contents of B, P, Si and N were 52 at%, 9 at%, 26 at% and 5 at%, respectively.

<Condition 4> The thin film protective layer 7 was formed in the same manner as in Condition 1 except that the flow rate of N ₂ O was 50 SCCM and the flow rate was not changed. The components of the obtained thin film were analyzed in the same manner as in Condition 1, and the analysis results of O are shown in Table 1. B, P, Si
And the average contents of N are 47 at%, 8 at%,
It was 23 at% and 4 at%.

<Condition 5> The thin film protective layer 7 was formed in the same manner as in Condition 1 except that the flow rate of N ₂ O was 5 SCCM and the flow rate was not changed. The components of the obtained thin film were analyzed in the same manner as in Condition 1, and the analysis results of O are shown in Table 1. Further, the average contents of B, P, Si and N are 56 at%, 9 at% and 2 respectively.
It was 8 at% and 5 at%.

<Condition 6> A thin film protective layer 7 was formed in the same manner as in Condition 1 except that N ₂ O was not flown. The components of the obtained thin film were analyzed in the same manner as in Condition 1, and the analysis results of O are shown in Table 1. The average contents of B, P, Si and N were 57 at%, 10 at%, 28 at% and 5 at%, respectively.

The wear test and electrolytic corrosion test of the thermal head obtained as described above were carried out by the above-mentioned methods. The results are summarized in Table 1. Further, as a scratch test by the scratch method, a test was conducted in the length direction of the formed glaze layer 3, and all the results showed that the maximum load was 110 g or more, and the internal stress was in the preferable range under all the above conditions. .

[0058]

[Table 1]

Heads A, B and C to which the present invention is applied
Is clearly superior to the heads D, E, and F from the wear test result and the electrolytic corrosion test result, and the effect of the present invention is clear.

[0060]

The thin film protective layer having the component distribution of the present invention is
It has low internal strain and excellent heat resistance. Furthermore, the deep layer has high volume resistivity and excellent insulating properties, and the surface layer has high hardness and excellent abrasion resistance. It is possible to provide a thermal head that is more excellent than ever because it can be formed in a film forming batch.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing one example of the configuration of a thermal head according to the present invention.

FIG. 2 is a cross-sectional view showing one of typical configuration examples of existing thermal heads.

FIG. 3 is a cross-sectional view showing the configuration of the thermal head of the embodiment.

[Explanation of symbols]

 1 Thermal Head 2 Substrate 3 Glaze Layer 4 Heating Resistor Layer 51, 53 Lead Layer 6 Insulating Layer 7 Thin Film Protective Layer

Claims (7)

[Claims] 1. A thin film protective layer containing boron, phosphorus, silicon, nitrogen and oxygen, wherein the oxygen content in the deep layer is higher than the oxygen content in the surface. 2. The thin film protective layer according to claim 1, which is formed by plasma-decomposing and depositing a source gas containing boron, phosphorus, silicon, nitrogen and oxygen. 3. 40-80 at% boron and 5-20 at%
% Phosphorus, 10-50 at% silicon, 2-20 at%
3. The thin film protective layer according to claim 1, which contains nitrogen. 4. When divided into five in the thickness direction, the deep side 1 /
The thin film protective layer according to any one of claims 1 to 3, wherein the average content of oxygen having a thickness of 5 is 10 to 30 at%. 5. When divided into 5 in the thickness direction, the surface side 1 /
The thin film protective layer according to any one of claims 1 to 4, wherein the average content of oxygen having a thickness of 5 is 0 to 5 at%. 6. When divided into 5 in the thickness direction, the deep side 1 /
The thin film protective layer according to any one of claims 1 to 5, wherein a value obtained by dividing the average oxygen content of the thickness of 5 by the average oxygen content of the thickness of 1/5 on the surface layer side is 2 or more. 7. A thermal head having the thin film protective layer according to claim 1.