JP2006338947A - Protective film forming method and protective film - Google Patents

Abstract

A protective film having high barrier properties and relatively low residual stress is obtained.
An element layer including a large number of organic EL elements is formed on a glass substrate, and a protective film is formed to cover the entire element layer. In particular, it is preferable to use a chemical vapor deposition method for the protective film 14, and the formation conditions (temperature, raw material supply amount) at that time are changed during the formation. Thereby, the protective layers 14 having different densities in the thickness direction are obtained. As a result, the residual stress in the vicinity of the element layer 12 is relatively small, and the surface portion is dense and has a high barrier property against moisture and the like.
[Selection] Figure 1

Description

  The present invention relates to a protective film for protecting an internal structure, in particular, a film excellent in both stress relaxation and barrier properties.

  Conventionally, an organic EL display panel is known as a thin flat panel. In this organic EL display panel, a thin film transistor (TFT) is formed on a glass substrate, a peripheral circuit and a pixel circuit are formed using the thin film transistor, and an organic EL element is formed on each pixel.

  Since this organic EL element is composed of an organic substance, it easily changes in quality and has a problem in that it cannot maintain desired light emission when it is changed due to moisture or oxidation.

  Therefore, in the organic EL panel, the interior is maintained in a nitrogen atmosphere and a desiccant is disposed to remove moisture in the internal space, thereby preventing the organic EL element from being altered.

  However, there is always a demand for more reliable protection of the organic EL element, and there are various proposals. For example, Patent Document 1 discloses that a protective film having a high barrier property against moisture and oxygen is formed so as to cover the entire pixel substrate.

  Moreover, as one of the film forming methods, there is a catalytic chemical vapor deposition (Catlytic Chemical Vapor Deposition: Cat CVD), and an effective film formation can be performed at a relatively low temperature of about 300 ° C. (see Patent Document 2).

JP 2003-297549 A JP 2003-309119 A

  However, when the protective film increases the barrier property against moisture and the like, the film becomes quite dense. Likely to happen. On the other hand, a film having a rough structure has a small residual stress, but has a problem of poor barrier properties.

  The present invention provides a protective film having a high barrier property and a relatively small residual stress.

  The present invention is a protective film forming method in which a large number of elements are formed on a substrate, and then a protective film is formed to protect the large number of elements, and the conditions for forming the protective film are changed during the formation of the protective film. Thus, a protective film having a gradient structure in the thickness direction, including a low-stress layer that is formed relatively coarsely and has a small residual stress, and a barrier layer that is formed relatively densely and has excellent isolation performance from the external atmosphere. It is characterized by forming.

  In addition, it is preferable to change the density of the film by changing the temperature during the formation of the protective film so that the film constituent materials are the same.

  The protective film formation is preferably a catalytic chemical vapor deposition method.

  The protective film is preferably a SiN film.

  The protective film covers an electrode covering the whole of a large number of organic EL elements formed on the substrate, and a low stress layer is disposed on the side close to the electrode, and on the side far from the electrode. It is preferred that a barrier layer is disposed.

  Moreover, it is preferable to maintain the substrate temperature at the time of forming the protective film at 100 ° C. or lower.

  The present invention also provides a protective film for protecting a large number of element structures formed on a substrate, which is formed relatively coarsely and has a low stress layer with little residual stress, and is relatively densely formed from an external atmosphere. And a barrier layer having an excellent isolation performance in the thickness direction.

  According to the present invention, the density of the protective film can be controlled appropriately in the thickness direction. For example, the surface portion is made dense with high barrier properties against moisture and the like, and by making the lower structure rough, the residual stress generated in relation to the lower material can be reduced.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram illustrating an overall configuration of a protective film according to an embodiment. An element layer 12 including a large number of organic EL elements is formed on a glass substrate 10 and covers the entire element layer 12. 14 is formed.

Here, in this embodiment, the protective film 14 is SiN, and is formed by catalytic chemical vapor deposition. In particular, the density of the film is gradually changed by raising the film forming temperature halfway. Further, the SiN film is formed while supplying a source gas such as SiH ₄ , H ₂ , and NH ₃ . Therefore, the density of the film can also be reduced by reducing the supply amount of SiH ₄ . Therefore, if the supply amount of the raw material is a SiN film, the density of the film can be changed by changing the supply amount of SiH ₄ , and both the supply amount of the raw material and the film formation temperature can be changed. , The change width of the density can be increased.

  FIG. 2 shows a schematic configuration of a film forming apparatus using a catalytic chemical vapor deposition method. One side of the vacuum chamber 20 is provided with an exhaust port 22 connected to a vacuum pump, from which the gas in the vacuum chamber 20 is exhausted. On the other hand, a sample introduction port 24 is provided on the other side of the vacuum chamber 20 from which a sample substrate 26 that is a target on which a protective film is to be formed is introduced.

  A sample stage 28 is provided below the vacuum chamber 20, and a sample substrate 26 is set on the sample stage 28. A cooler 30 is provided below the sample stage 28. The cooler 30 circulates a refrigerant (for example, water) and maintains the sample stage 28 and the sample substrate 26 at a predetermined temperature. The temperature of the sample substrate 26 can be set to a predetermined value depending on the temperature of the refrigerant, the circulation amount, and the like.

  A heating catalyst body 32 is provided in an intermediate portion of the vacuum chamber 20 above the sample stage 28. Although not shown in the figure, the heating catalyst body 32 is energized from a power source (not shown), whereby the heating catalyst body 32 is heated to a predetermined temperature.

  A gas supply unit 34 is provided above the vacuum chamber 20 above the heating catalyst body 32. The gas supply unit 34 has a hollow disk shape, and a large number of openings are formed on the lower surface thereof, and a source gas is supplied from the outside. Therefore, the supplied source gas is blown out from the opening.

  Note that the heating catalyst body 32 is formed in a mesh shape so that the source gas supplied from the gas supply unit 34 effectively contacts.

  The inside of the vacuum chamber 20 is maintained at a predetermined degree of vacuum by a vacuum pump. In addition, the sample substrate 26 is set on the sample stage 28, and the refrigerant is circulated through the cooler 30 to set the temperature of the sample substrate 26 to a predetermined temperature. In this state, the supply of the source gas is started. And an electric current is sent through the heating catalyst body 32, and it heats to predetermined temperature.

When the SiN film is formed, SiH ₄ , H ₂ , and NH ₃ are used as the source gas, and tungsten is used as the heating catalyst body 32. The heating catalyst body 32 is heated to, for example, about 200 ° C., and when the raw material gas passes through it, radicals such as SiH ₃ , H, and NH ₂ in the raw material gas are generated. A SiN film is formed by depositing on the surface.

In this embodiment, the SiN ₄ flow rate is increased in the middle, and the temperature of the sample substrate 26 by the cooler 30 is increased in the middle, thereby forming a SiN gradient film having a gradually increased density.

  As a result, it is possible to obtain a protective film that keeps the stress below the SiN film small and has improved barrier properties against moisture and the like on the surface.

    FIG. 3 shows the film formation temperature when the film formation temperature is changed in the film formation by catalytic chemical vapor deposition, and the etching of the film with an acid (for example, buffered hydrofluoric acid). It is a figure which shows the relationship of a rate. Here, since this etching rate is proportional to the density of the film, the etching rate may be regarded as the density. As described above, when the film formation temperature is increased, the etching rate is lowered and the density is increased.

  FIG. 4 is a diagram showing the relationship between the residual stress and the etching rate by measuring the residual stress for the same film as FIG. Thus, the higher the residual stress, the lower the etching rate (higher density).

FIG. 5 shows the relationship between the residual stress [MPa] when a 300 nm SiN film is deposited on a Si substrate and the etching rate by buffered hydrofluoric acid when a 300 nm SiN film is deposited on a glass substrate. Further, in the figure, C is a substrate temperature of 60 ° C. and the flow rate of silane (SiH ₄ ) is small, B 60 is a substrate temperature of 60 ° C. and the flow rate of silane (SiH ₄ ) is medium, and B 80 is a silane at a substrate temperature of 80 ° C. When the (SiH ₄ ) flow rate is medium, A60 indicates that the substrate temperature is 60 ° C. and the silane (SiH ₄ ) flow rate is large, and A80 indicates that the substrate temperature is 80 ° C. and the silane (SiH ₄ ) flow rate is large.

  From this, it was confirmed that the density of the generated film can be changed by changing the silane flow rate, changing the substrate temperature, or both.

  Such a SiN film is suitable as a protective film that covers the pixel substrate in the organic EL display panel. In particular, in this embodiment, a refrigerant is circulated through the cooler 30 to cool the substrate temperature to 100 ° C. or lower (preferably 60 to 80 ° C.). Thereby, a suitable SiN film can be obtained by being formed on the surface of the EL element. That is, in the conventional chemical vapor deposition method, the substrate temperature is heated to about 300 ° C. However, it has been found that film formation at a low temperature of 100 ° C. or lower is suitable particularly for a SiN film formed on an organic EL electrode. Moreover, at 100 degrees C or less, there also exists a merit that water can be used as a refrigerant | coolant.

  FIG. 6 is a cross-sectional view showing the configuration of the light emitting region of one pixel and the portion of the driving TFT. Each pixel is provided with a plurality of TFTs, and the driving TFT is a TFT that controls a current supplied from the power supply line to the organic EL element.

A buffer layer 111 made of a stack of SiN and SiO ₂ is formed on the entire surface of the glass substrate 130, and a polysilicon active layer 122 is formed on the buffer layer 111 in a predetermined area (an area for forming a TFT).

A gate insulating film 113 is formed on the entire surface covering the active layer 122 and the buffer layer 111. This gate insulating film 113 is formed, for example, by laminating SiO ₂ and SiN. Above this gate insulating film 113 and on the channel region 122c, for example, a Cr gate electrode 124 is formed. Then, by doping the active layer 122 with impurities using the gate electrode 124 as a mask, the active layer 122 has a channel region 122c that is not doped with impurities under the gate electrode in the central portion, and impurity impurities on both sides thereof. Doped source region 122s and drain region 122d are formed.

  Then, an interlayer insulating film 115 is formed on the entire surface so as to cover the gate insulating film 113 and the gate electrode 124, and contact holes are formed above the source region 122s and the drain region 122d in the interlayer insulating film 115. Thus, a source electrode 153 and a drain electrode 126 disposed on the upper surface of the interlayer insulating film 115 are formed. Note that a power supply line (not shown) is connected to the source electrode 153. Here, the drive TFT thus formed is a p-channel TFT in this example, but may be an n-channel.

  A planarization film 117 is formed on the entire surface so as to cover the interlayer insulating film 115, the source electrode 153, and the drain electrode 126, and a transparent electrode 161 that functions as an anode is provided thereon. In addition, a contact hole is formed in the planarizing film 117 above the drain electrode 126, and the drain electrode 126 and the transparent electrode 161 are connected through the contact hole.

  Note that an organic film such as an acrylic resin is usually used for the interlayer insulating film 115 and the planarizing film 117, but an inorganic film such as TEOS can also be used. The source electrode 153 and the drain electrode 126 are made of metal such as aluminum, and the transparent electrode 161 is usually made of ITO.

  The transparent electrode 161 is usually formed in most of the area of each pixel, and has a substantially quadrangular shape as a whole, and a contact portion for connection with the drain electrode 126 is formed as a protruding portion, and extends in the contact hole. .

  On the transparent electrode 161, an organic layer 165 composed of a hole transport layer 162, an organic light emitting layer 163, and an electron transport layer 164 formed on the entire surface, and an opposing electrode 166 made of, for example, Al are formed as a cathode.

  A planarization film 167 is formed below the hole transport layer 162 on the peripheral portion of the transparent electrode 161, and the planarization film 167 allows the light emitting region of each pixel to be on the transparent electrode 161, thereby transporting holes. A portion where the layer 162 is in direct contact with the transparent electrode 161 is limited, and this is a light emitting region. Note that an organic film such as an acrylic resin is usually used for the planarizing film 167, but an inorganic film such as TEOS can also be used.

  The counter electrode 166 is formed over the entire pixel region, and a protective film 170 made of SiN is formed so as to cover the entire counter electrode 166. As described above, the protective film 170 has an inclined structure in which the portion in contact with the counter electrode 166 is rough and the surface portion thereof is dense, whereby the residual stress in the portion in contact with the counter electrode 166 is small and dense. The surface has very low moisture permeability and effectively prevents moisture and other organic layers from entering the organic layer.

  For the hole transport layer 162, the organic light emitting layer 163, and the electron transport layer 164, materials usually used for organic EL elements are used. The organic light-emitting layer 163 has an emission color determined by its material (usually a dopant) and is appropriately selected.

  In such a configuration, when the driving TFT is turned on according to the set voltage of the gate electrode 124, a current from the power supply line flows from the transparent electrode 161 to the counter electrode 166, and light is emitted from the organic light emitting layer 163 by this current. This occurs and this light is emitted through the glass substrate 130.

  In this example, a bottom emission type in which light is emitted from the glass substrate 130 side is used. However, the present invention is not limited to this, and a top emission type may be used. In this case, the counter electrode 166 is made of a transparent conductive material such as ITO, and a reflective film such as Ag is disposed on the lower surface of the transparent electrode 161.

  In addition, a large number of pixels are arranged in a matrix on the glass substrate 130, and peripheral circuits are formed in the periphery thereof, whereby a pixel substrate is formed. Then, a sealing substrate is disposed facing the pixel substrate, and the peripheral portions of both are hermetically connected using a sealing material. Therefore, since the upper space of the pixel substrate is airtight and the surface of the pixel substrate is covered with the protective film 170, moisture can be effectively prevented from entering the organic layer.

  In the present embodiment, a SiN film is employed as the protective film, thereby protecting the organic EL element. However, the present invention is not limited to this, and can also be used as a protective film in various semiconductor devices.

  Alternatively, the film formation conditions may be gradually changed to gradually change the film composition, or a laminated structure of films having different conditions may be employed.

  Furthermore, depending on the composition of the lower film on which the protective film is formed, it may be better to form the denser as the lower side of the protective film. In this case, the temperature is gradually lowered during film formation or the raw material is supplied. What is necessary is just to reduce an amount gradually.

It is a figure which shows schematic structure of embodiment. It is a figure which shows the structure of the film-forming apparatus. It is a figure which shows the relationship between film-forming temperature and an etching rate. It is a figure which shows the relationship between a residual stress and an etching rate. It is a figure which shows the residual stress and etching rate in various conditions. It is a figure which shows the structure of a pixel part.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Glass substrate, 12 Element layer, 14 Protective film, 20 Vacuum chamber, 22 Exhaust port, 24 Sample inlet, 26 Sample substrate, 28 Sample stand, 30 Cooler, 32 Heating catalyst body, 34 Gas supply part, 60, 80 Substrate temperature, 111 buffer layer, 113 gate insulating film, 115 interlayer insulating film, 117 planarization film, 122 active layer, 122c channel region, 122d drain region, 122s source region, 124 gate electrode, 126 drain electrode, 130 glass substrate, 153 source electrode, 161 transparent electrode, 162 hole transport layer, 163 organic light emitting layer, 164 electron transport layer, 165 organic layer, 166 counter electrode, 167 planarization film, 170 protective film.

Claims (10)

A protective film forming method for forming a large number of elements on a substrate and then forming a protective film for protecting the large number of elements,
By changing the protective film formation conditions during the protective film formation,
A low-stress layer that is relatively rough and has little residual stress,
A barrier layer that is formed relatively densely and has excellent isolation performance from the external atmosphere;
Forming a protective film having an inclined structure in the thickness direction including the protective film. In the protective film formation method of Claim 1,
A method for forming a protective film, characterized by changing the temperature during the formation of the protective film to change the density of the film with the same film constituent material. In the protective film formation method of Claim 1 or 2,
The protective film formation method is characterized in that the protective film formation is a catalytic chemical vapor deposition method. In the protective film formation method of any one of Claims 1-3,
The method for forming a protective film, wherein the protective film is a SiN film. In the protective film formation method of any one of Claims 1-4,
The protective film covers an electrode covering the whole of a large number of organic EL elements formed on a substrate, and a low stress layer is disposed on the side close to the electrode, and a barrier layer on the side far from the electrode. A protective film forming method, wherein: In the protective film formation method of any one of Claims 1-5,
A method for forming a protective film, comprising maintaining a substrate temperature at 100 ° C. or lower when forming the protective film. A protective film for protecting a large number of element structures formed on a substrate,
A low-stress layer that is relatively rough and has little residual stress,
A barrier layer that is relatively dense and has excellent isolation performance from the external atmosphere;
A protective film having an inclined structure in the thickness direction including The protective film according to claim 7,
The barrier layer and the low stress layer have the same constituent material. The protective film according to claim 7 or 8,
The protective film is a SiN film. In the protective film as described in any one of Claims 7-9,
The protective film covers an electrode covering the whole of a large number of organic EL elements formed on a substrate, and a low stress layer is disposed on the side close to the electrode, and a barrier layer on the side far from the electrode. A protective film characterized by being arranged.

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