JPWO2012063614A1 - Semiconductor device - Google Patents

Abstract

Provided is a protective film that has high atmospheric resistance and does not deteriorate the characteristics of an oxide TFT. An oxide TFT in which a gate electrode 11, a gate insulating film 12, a channel layer 13 made of an oxide semiconductor film, a source electrode 14s and a drain electrode 14d are stacked in this order is formed on the upper surface of the substrate 10. A protective film 15 is formed on the TFT to suppress fluctuations in the characteristics of the oxide TFT. The protective film 15 includes a lower protective film 15L made of a low density silicon oxynitride film and an upper protective film 15U made of a high density silicon oxynitride film or silicon nitride film. The lower protective film 15L is formed so as to cover the upper portion of the channel layer 13 and a region in the vicinity thereof, and the whole including the end portion thereof is covered with the upper protective film 15U.

Description

  The present invention relates to a semiconductor device having a thin film transistor (TFT), and is particularly effective when applied to a semiconductor device in which a protective film having a high atmospheric resistance is formed on top of a thin film transistor using an oxide semiconductor as a channel layer. It is about technology.

  Thin film transistors (hereinafter simply referred to as TFTs) are used as display device driving transistors in various portable electronic devices such as mobile phones, notebook personal computers, and PDAs because they have a small element area and save space.

  Conventionally, most of TFTs have been made of silicon-based semiconductors typified by amorphous silicon and polycrystalline silicon. This is because there is a merit that a TFT can be manufactured using a manufacturing process and manufacturing technology of a conventional semiconductor device.

  However, when manufacturing TFTs using conventional manufacturing processes / techniques, the processing temperature is 350 ° C. or higher, which limits the substrate materials that can be used. In particular, since many flexible resin substrates have a heat-resistant temperature of 350 ° C. or lower, it is difficult to form TFTs on these substrates using conventional manufacturing processes and manufacturing techniques.

  Therefore, recently, research and development of a TFT using a semiconductor made of a metal oxide (oxide semiconductor) for a channel layer (hereinafter simply referred to as an oxide TFT) has been advanced.

  Oxide TFTs are considered as one of the leading candidates for TFTs used when forming circuits on flexible resin substrates because the channel layer is made of a metal oxide that can be formed at a low temperature.

  In addition, the oxide TFT has an advantage that a large current can flow as compared with a conventional TFT using amorphous silicon as a channel layer. Furthermore, there is an advantage that variation between elements is small as compared with a TFT using polycrystalline silicon as a channel layer.

  On the other hand, an oxide semiconductor has a problem that the characteristic variation due to components (moisture, oxygen, etc.) in the atmosphere is larger than that of a silicon-based semiconductor. Therefore, in order to suppress fluctuations in characteristics of the oxide TFT, it is necessary to cover the surface of the oxide TFT with a protective film having high atmospheric resistance. As the protective film having high atmospheric resistance, it is ideal to use a silicon-based insulating material (SiO, SiN, SiON, etc.) that can be deposited by CVD or sputtering in consideration of mass productivity.

  For example, in Patent Document 1 (Japanese Patent Laid-Open No. 2010-073894), a silicon nitride insulating film (oxygen barrier film) is stacked on a silicon oxide insulating film (oxygen permeable film) as a protective film covering the oxide TFT. A two-layer insulating film is disclosed.

JP 2010-073894 A

  According to Patent Document 1, the oxide TFT may deteriorate in characteristics due to oxygen vacancies in the channel layer. In that case, heat treatment is performed in the atmosphere or an atmosphere into which oxygen is introduced, and the channel is thus obtained. It is said that the characteristics need to be restored by supplying oxygen to the layer.

  However, when the protective film covering the channel layer is formed of an insulating film (for example, a silicon nitride film) that hardly allows oxygen to pass through, oxygen does not diffuse into the channel layer even if the above heat treatment is performed. Does not recover. On the other hand, when the protective film is formed of an insulating film (for example, a silicon oxide film) that easily allows oxygen to pass through, oxygen diffuses to the channel layer, so that characteristic fluctuations caused by oxygen vacancies can be recovered. However, in this case, not only oxygen but also moisture and the like diffuse into the channel layer, so that the protective film does not play its original role.

  Therefore, in Patent Document 1, the protective film covering the oxide TFT has a two-layer structure of a silicon oxide-based insulating film (oxygen permeable film) and a silicon nitride-based insulating film (oxygen barrier film). Oxygen vacancies are compensated by diffusing oxygen that has entered the film through the end portion into the channel layer. Further, during the operation of the TFT, the oxygen barrier film becomes an obstacle and the diffusion of oxygen from the channel layer to the outside is suppressed, so that oxygen vacancies can also be suppressed.

  However, when the inventors conducted a test in which the oxide TFT having the protective film having the two-layer structure described above was left in a high humidity atmosphere for a long time, the characteristics of the oxide TFT were deteriorated. This is because even if the upper protective film is composed of a silicon nitride film having high atmospheric resistance, a small amount of moisture that has passed through the upper protective film is formed when the lower protective film is composed of a silicon oxide film. This is presumed to be due to the deterioration of the characteristics of the oxide TFT by passing through the lower protective film and reaching the oxide TFT. In the case of the above protective film, the end of the lower protective film is not covered with the upper protective film, and oxygen is able to enter the protective film of the lower layer from this end. It is presumed that one of the reasons is that moisture easily enters from the part together with oxygen.

  On the other hand, when the protective film covering the oxide TFT is composed of only a silicon nitride film having high atmospheric resistance, oxygen in the oxide semiconductor constituting the channel layer is lost and the channel layer becomes a conductor. It became clear by their experiment. This is because a high-density insulating film such as a silicon nitride film needs to be formed with high energy. However, when a silicon nitride film is directly deposited on the surface of the channel layer, the surface of the channel layer has high energy particles. This is because the oxide semiconductor is exposed to plasma and causes oxygen vacancies.

  An object of the present invention is to provide a protective film that has high atmospheric resistance and does not deteriorate the characteristics of an oxide TFT.

  The above and other objects and novel features of the present invention will be apparent from the description of this specification and the accompanying drawings.

  Of the inventions disclosed in the present application, the outline of typical ones will be briefly described as follows.

A semiconductor device according to a preferred embodiment of the present invention is a semiconductor device in which a thin film transistor is formed on an upper surface of a substrate and a protective film is formed on the thin film transistor,
The thin film transistor includes a gate electrode formed on an upper surface of the substrate, a gate insulating film formed on the gate electrode, a channel layer made of an oxide semiconductor film formed on the gate insulating film, A source electrode and a drain electrode electrically connected to the channel layer;
The protective film is formed on at least a portion of the first silicon oxynitride film formed so as to be in contact with the upper surface of the channel layer, and on the substrate above the first silicon oxynitride film, The multi-layer film includes a second silicon oxynitride film or a silicon nitride film having a film density higher than that of the silicon nitride film.

  The effects obtained by typical ones of the inventions disclosed in the present application will be briefly described as follows.

  A protective film that has high atmospheric resistance and does not deteriorate the characteristics of the oxide TFT can be provided.

It is a top view which shows the oxide TFT which is Embodiment 1 of this invention. It is the sectional view on the AA line of FIG. It is the BB sectional view taken on the line of FIG. It is sectional drawing which shows the manufacturing method of the oxide TFT which is Embodiment 1 of this invention. FIG. 5 is a cross-sectional view showing a method for manufacturing the oxide TFT following FIG. 4. FIG. 6 is a cross-sectional view showing a method for manufacturing the oxide TFT subsequent to FIG. 5. FIG. 7 is a cross-sectional view showing a method for manufacturing the oxide TFT subsequent to FIG. 6. FIG. 8 is a cross-sectional view showing a method for manufacturing the oxide TFT following FIG. 7. FIG. 9 is a cross-sectional view showing a method for manufacturing the oxide TFT following FIG. 8. FIG. 10 is a cross-sectional view showing a method for manufacturing the oxide TFT following FIG. 9. FIG. 11 is a cross-sectional view showing a method for manufacturing the oxide TFT following FIG. 10. It is a graph which shows the Id-Vg characteristic of the oxide TFT which is Embodiment 1 of this invention. It is a graph which shows the Id-Vg characteristic of the oxide TFT which is a comparative example. It is a graph which shows the Id-Vg characteristic of the oxide TFT which is a comparative example. It is a graph which shows the Id-Vg characteristic of the oxide TFT which is a comparative example. It is a graph which shows the Id-Vg characteristic of the oxide TFT which is a comparative example. It is a top view which shows the oxide TFT which is another example of Embodiment 1 of this invention. It is CC sectional view taken on the line of FIG. It is the DD sectional view taken on the line of FIG. It is a top view which shows the oxide TFT which is Embodiment 2 of this invention. It is the EE sectional view taken on the line of FIG. It is the FF sectional view taken on the line of FIG. It is a top view which shows the oxide TFT which is Embodiment 3 of this invention. It is the GG sectional view taken on the line of FIG. It is the HH sectional view taken on the line of FIG. It is sectional drawing which shows the oxide TFT which is Embodiment 4 of this invention. It is sectional drawing which shows the oxide TFT which is another example of Embodiment 4 of this invention. It is a figure which shows schematic structure of the RFID tag using the thin-film transistor of this invention. It is a circuit block diagram which shows an example of the array structure of the semiconductor device using the thin-film transistor of this invention. FIG. 30 is a schematic diagram of an active matrix liquid crystal display device to which the array shown in FIG. 29 is applied.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that components having the same function are denoted by the same reference symbols throughout the drawings for describing the embodiments, and the repetitive description thereof will be omitted. In the embodiments, the description of the same or similar parts will not be repeated in principle unless particularly necessary. Further, in the drawings describing the embodiments, hatching may be given even in plan views in order to make the configuration easy to understand.

(Embodiment 1)
1 is a plan view showing an oxide TFT according to the present embodiment, FIG. 2 is a cross-sectional view taken along line AA in FIG. 1, and FIG. 3 is a cross-sectional view taken along line BB in FIG.

  This embodiment is applied to a bottom gate / top contact type oxide TFT. Here, the bottom gate means a structure in which the gate electrode is arranged below the channel layer (oxide semiconductor film), and the top contact means that the source electrode and the drain electrode are arranged above the channel layer. Means the structure.

  As shown in FIGS. 1 to 3, the oxide TFT of this embodiment includes a gate electrode 11, a gate insulating film 12, a channel layer 13, a source electrode 14 s and a drain electrode 14 d on the upper surface of an insulating substrate 10. It is the structure which laminated | stacked in order. A protective film 15 is formed on the top of the oxide TFT to suppress fluctuations in the characteristics of the oxide TFT caused by components (moisture, oxygen, etc.) in the atmosphere.

  The protective film 15 is composed of a two-layer insulating film in which an upper protective film 15U is stacked on the lower protective film 15L. The lower protective film 15L is composed of a silicon oxynitride (SiON) film, and the upper protective film 15U is a high-density oxynitride having a higher nitrogen composition ratio than the silicon oxynitride film constituting the lower protective film 15L. A silicon film or a silicon nitride (SiN) film that is a higher density than the silicon oxynitride film is used.

  The lower protective film 15 </ b> L is formed so as to cover the upper portion of the channel layer 13 and a region in the vicinity thereof, and a part thereof is in direct contact with the upper surface of the channel layer 13. On the other hand, the upper protective film 15U is formed so as to cover almost the entire surface of the substrate 10. Therefore, the entire lower protective film 15L including its end is covered with the upper protective film 15U so as not to come into contact with the atmosphere.

  Above the upper protective film 15U, an upper wiring 17 that is electrically connected to the drain electrode 14d through a contact hole 16 penetrating the upper protective film 15U is formed. Although illustration is omitted, an upper layer wiring electrically connected to the source electrode 14s through a contact hole penetrating the upper layer protective film 15U may be formed on the upper layer protective film 15U.

  The bottom gate / top contact type oxide TFT of this embodiment is manufactured by the following method.

  First, as shown in FIG. 4, an insulating substrate 10 is prepared. Examples of the material of the substrate 10 include Si (silicon), sapphire, quartz, glass, and a flexible plastic film. Examples of the plastic film material include polyethylene terephthalate, polyethylene naphthalate, polyetherimide, polyacrylate, polyimide, polycarbonate, cellulose triacetate, and cellulose acetate propionate. Moreover, what provided the insulating coating layer on the surface of various materials mentioned above or a metal film as needed can also be used.

  Next, as shown in FIG. 5, a conductive film is deposited on the upper surface of the substrate 10, and then the conductive film is patterned to form the gate electrode 11. As the conductive film constituting the gate electrode 11, Mo (molybdenum), Cr (chromium), W (tungsten), Al (aluminum), Cu (copper), Ti (titanium), Ni (nickel), Ta (tantalum) A single layer film of metal such as Ag (silver), Co (cobalt), Zn, Au (gold), and Pt (platinum), an alloy film containing these metals, and a laminated film of these metals. it can. In addition, a conductive metal oxide film such as ZnO (zinc oxide) to which ITO (In-Sn-O: indium tin oxide), Al, Ga, In, or B (boron) is added, or the conductivity thereof A laminated film of a metal oxide and the metal can also be used. Furthermore, a single layer film of conductive metal nitride such as TiN (titanium nitride), a laminated film of the conductive metal nitride and the metal, or the like can also be used.

  The various conductive films described above are deposited by CVD, sputtering, vapor deposition, or the like, and patterning is performed by dry etching or wet etching using a photoresist film as a mask.

  Next, as shown in FIG. 6, a gate insulating film 12 is formed on the upper surface of the substrate 10 on which the gate electrode 11 is formed.

The insulating film constituting the gate insulating film 12 includes a silicon oxide film, a silicon nitride film, an aluminum oxide film, an aluminum nitride film, a Y ₂ O ₃ (yttrium oxide) film, an HfO ₂ (hafnium oxide) film, and a YSZ (yttria stable). Zirconia) film, organic polymer insulating film, and the like. Materials for organic polymer insulating films include polyimide derivatives, benzocyclobutene derivatives, photoacryl derivatives, polystyrene derivatives, polyvinyl phenol derivatives, polyester derivatives, polycarbonate derivatives, polyester derivatives, polyvinyl acetate derivatives, polyurethane derivatives, polysulfone derivatives. Acrylate resin, acrylic resin, epoxy resin, parylene and the like. These insulating films are deposited by a CVD method, a sputtering method, a vapor deposition method, a coating method, or the like.

  Next, as shown in FIG. 7, after depositing an oxide semiconductor film on the gate insulating film 12, the channel layer 13 is formed by patterning the oxide semiconductor film. As the oxide semiconductor constituting the channel layer 13, any one or more elements of In, Zn, Cd (cadmium), Al, Ga, Si, Sn, Ce (cerium), Ge (germanium), and Hf are included. An oxide bonded to oxygen can be exemplified.

  The oxide semiconductor film is deposited by a sputtering method, a CVD method, a pulsed laser deposition (PLD) method, a coating method, a printing method, a co-evaporation method, or the like, and the film thickness is about 5 nm to 50 nm. . The patterning of the oxide semiconductor film is performed by dry etching or wet etching using a photoresist film as a mask. Further, after the channel layer 13 is formed, impurities may be doped as necessary, or the substrate 10 may be annealed.

  Next, as shown in FIG. 8, after depositing a conductive film on the channel layer 13, the conductive film is patterned by dry etching or wet etching using a photoresist film as a mask to form the source electrode 14s. And the drain electrode 14d is formed. Examples of the conductive film include various conductive films that constitute the gate electrode 11 described above. The conductive film is deposited by an electron beam evaporation method, a sputtering method, a CVD method, or the like.

  Next, as shown in FIG. 9, after depositing a silicon oxynitride film on the source electrode 14s and the drain electrode 14d by a CVD method or a sputtering method, the silicon oxynitride film is patterned to form the channel layer 13 A lower protective film 15L is formed to cover the upper part and the area in the vicinity thereof. The silicon oxynitride film is patterned by dry etching using a photoresist film as a mask or a combination of dry etching and wet etching.

As an example, the lower protective film 15L has a film density of less than 2.45 g / cm ³ , a nitrogen ratio (N / O + N) in the film of less than 34 atm%, and a hydrogen concentration in the film of 1.5 × 10 ²² atm / cm It is composed of less than ³ silicon oxynitride films. The thickness of the silicon oxynitride film constituting the lower protective film 15L is preferably at least 20 nm or more in order to prevent damage caused by high energy particles or plasma intrusion.

  Next, as shown in FIG. 10, an upper protective film 15U covering the entire surface of the substrate 10 is deposited by depositing a silicon oxynitride film or a silicon nitride film on the lower protective film 15L by a CVD method or a sputtering method. Form.

For example, the upper protective film 15U has a film density of 2.45 g / cm ³ or more, a nitrogen ratio (N / O + N) of 34 atm% or more (a silicon nitride film when 100 atm%), and a hydrogen concentration in the film. Is made of a silicon oxynitride film or a silicon nitride film having a thickness of 1.5 × 10 ²² atm / cm ³ or more.

  In addition, you may add processes, such as a heating and light irradiation, as needed between the process of forming lower protective film 15L, and the process of forming upper protective film 15U. This is because energy is applied to the oxide TFT in the middle of manufacture, and excess substances such as moisture are removed from the channel layer 13, the lower protective film 15L, and their interfaces.

  Next, as shown in FIG. 11, the contact hole 16 reaching the drain electrode 14d is formed by dry etching the upper protective film 15U using the photoresist film as a mask. Although illustration is omitted, at this time, a contact hole reaching the source electrode 14s is simultaneously formed as necessary. These contact holes 16 are arranged in a region where the lower protective film 15L is not formed so that the lower protective film 15L is not exposed on the side wall of the contact hole 16.

  Thereafter, the conductive film deposited on the upper layer protective film 15U is patterned to form the upper layer wiring 17, thereby completing the oxide TFT shown in FIGS. Examples of the conductive film constituting the upper wiring 17 include the metal film, conductive metal oxide film, and conductive metal nitride film exemplified as the conductive film constituting the gate electrode 11.

  FIG. 12 is a graph showing Id (drain current) -Vg (gate voltage) characteristics of the oxide TFT of this embodiment.

Here, as the lower protective film 15L, the film density = 2.40 g / cm ³ , the ratio of nitrogen in the film (N / O + N) = 31 atm%, the hydrogen concentration in the film = 0.8 × 10 ²² atm / cm ³ A silicon oxynitride film having a film thickness of 20 nm was used. As the upper protective film 15U, the film density = 2.45 g / cm ³ , the ratio of nitrogen in the film (N / O + N) = 34 atm%, the hydrogen concentration in the film = 1.5 × 10 ²² atm / cm ³ A silicon oxynitride film was used.

  The film density was measured by X-ray reflectivity measurement using GXR300 manufactured by Rigaku, and the ratio of nitrogen in the film was measured by fluorescent X-ray analysis using PW2800 manufactured by Philips. The hydrogen concentration in the film was measured by secondary ion mass spectrometry (SIMS) using PHI ADEPT-1010 manufactured by ULVAC-PHI, and the film thickness was measured using MARY-102 manufactured by Fibravo. It was measured by single wavelength ellipsometry or electron microscope observation.

  When the characteristics of the oxide TFT were measured after being left in a high humidity environment for 500 hours or longer, the characteristics were the same as those measured immediately after production. This revealed that the protective film 15 has sufficiently high atmospheric resistance.

  13 to 16 are graphs showing Id-Vg characteristics of oxide TFTs manufactured for comparison.

  FIG. 13 shows Id-Vg characteristics of an oxide TFT in which the protective film is composed of only one silicon oxide film. In this case, the initial characteristics were good, but when left in a high humidity environment for 24 hours, the characteristics of the oxide TFT were greatly deteriorated. That is, this protective film had insufficient atmospheric resistance.

  FIG. 14 shows Id-Vg characteristics of an oxide TFT having a protective film having the same configuration as that of Patent Document 1. That is, it is the Id-Vg characteristic when the protective film has a two-layer structure of a silicon oxide film (lower protective film) and a silicon nitride film (upper protective film).

  In this case, the initial characteristics were as good as those of the oxide TFT (FIG. 13) in which the protective film was composed of only one layer of silicon oxide film, but the characteristics deteriorated over time when left in a high humidity environment. It began to. Although the atmospheric resistance of this protective film was improved over that of a protective film composed of only one silicon oxide film, it was still insufficient.

  FIG. 15 shows Id-Vg characteristics of an oxide TFT in which the protective film is composed of only one layer of a high-density silicon oxynitride film (a silicon oxynitride film having the same composition as the upper protective film 15U in FIG. 12). In this case, since the energy for forming the silicon oxynitride film is too high, the oxide semiconductor forming the channel layer 13 has oxygen vacancies as in the case where the protective film is formed of only one silicon nitride film. As a result, the channel layer 13 became a conductor.

  FIG. 16 shows Id-Vg characteristics of an oxide TFT in which the protective film is composed of only one layer of a low-density silicon oxynitride film (a silicon oxynitride film having the same composition as the lower protective film 15L in FIG. 12). As in the case of FIGS. 13 and 14, the initial characteristics were good, but when left in a high humidity environment, the characteristics deteriorated over time. Although the atmospheric resistance of this protective film was improved over that of FIGS. 13 and 14, it was still insufficient.

  From the above, as the protective film for the oxide TFT, the lower protective film 15L made of a low-density silicon oxynitride film and the upper protective film 15U made of a high-density silicon oxynitride film (including a silicon nitride film) It has been found that the laminated structure is optimal, which can significantly improve the atmospheric resistance of the oxide TFT.

  The lower layer protective film 15L of the oxide TFT shown in FIGS. 1 to 3 is configured to cover the entire upper portion of the channel layer 13, but FIG. 17 (plan view) and FIG. As shown in FIG. 19 (cross-sectional view taken along line C) and FIG. 19 (cross-sectional view taken along line DD in FIG. 17), the lower protective film 15 </ b> L may cover part of the upper portion of the channel layer 13.

  In the oxide TFT shown in FIGS. 1 to 3, the protective film 15 is composed of two insulating films in which the upper protective film 15U is laminated on the lower protective film 15L. The protective film 15 can also be constituted by a film.

In this case, the lowermost protective film in contact with the channel layer 13 has a film density of less than 2.45 g / cm ³ , a ratio of nitrogen in the film (N / O + N) of less than 34 atm%, and a hydrogen concentration in the film of 1 It is composed of a silicon oxynitride film of less than 5 × 10 ²² atm / cm ³ . The uppermost protective film has a density of 2.45 g / cm ³ or more, a nitrogen ratio (N / O + N) of 34 atm% or more, and a hydrogen concentration in the film of 1.5 × 10 ²² atm / cm. It is composed of ^three or more silicon oxynitride films or silicon nitride films. Between the two protective films, the film density, the ratio of nitrogen in the film, and the hydrogen concentration in the film are higher than the lowermost silicon oxynitride film and higher than the uppermost silicon oxynitride film. A low-layer silicon oxynitride film or a lower layer may be sandwiched.

(Embodiment 2)
20 is a plan view showing the oxide TFT of this embodiment, FIG. 21 is a cross-sectional view taken along line EE in FIG. 20, and FIG. 22 is a cross-sectional view taken along line FF in FIG.

  In the oxide TFT of the first embodiment, two insulating films (lower protective film 15L and upper protective film 15U) are formed on the source electrode 14s and the drain electrode 14d. On the other hand, the oxide TFT of this embodiment has a configuration in which the source electrode 14s and the drain electrode 14d are sandwiched between two insulating films (the lower protective film 15L and the upper protective film 15U). The density of the two insulating films (the lower protective film 15L and the upper protective film 15U), the ratio of nitrogen in the film, and the hydrogen concentration in the film are the same as in the first embodiment.

  When manufacturing the oxide TFT of this embodiment, first, the gate electrode 11, the gate insulating film 12, and the channel layer 13 are formed in this order on the upper surface of the substrate 10 by the same method as in the first embodiment. Next, after depositing a low-density silicon oxynitride film on the channel layer 13, this silicon oxynitride film is etched to form a lower protective film 15L.

  Next, after depositing a conductive film on the lower protective film 15L, the conductive electrode is etched to form the source electrode 14s and the drain electrode 14d. Thereafter, an upper layer protective film 15U is formed by depositing a high-density silicon oxynitride film or silicon nitride film on the source electrode 14s and the drain electrode 14d.

  As described above, when the lower protective film 15L is disposed under the source electrode 14s and the drain electrode 14d, when the conductive film constituting the source electrode 14s and the drain electrode 14d is etched, the surface of the channel layer 13 becomes the lower protective film. Since it is covered with 15L, the surface of the channel layer 13 is not damaged by etching. That is, since the lower protective film 15L functions as an etching stopper layer, it is possible to prevent deterioration of the characteristics of the oxide TFT due to damage to the channel layer 13.

  In addition, according to the present embodiment, when the lower protective film 15L is formed by dry etching the low density silicon oxynitride film, the substrate bias or plasma power is increased to contact the source electrode 14s or the drain electrode 14d. The resistance of the channel layer 13 in the region can be reduced by deficiency. Thereby, the contact resistance between the source electrode 14s and the channel layer 13 and the contact resistance between the drain electrode 14d and the channel layer 13 can be lowered, so that the performance of the oxide TFT can be improved.

  In the present embodiment also, the protective film 15 can be composed of three or more silicon oxynitride films having different film densities, nitrogen ratios in the film, and hydrogen concentrations in the film. Also in this case, the lowermost layer is composed of a silicon oxynitride film having the lowest film density, and the uppermost layer is composed of a silicon oxynitride film or a silicon nitride film having the highest film density. And, between the two silicon oxynitride films, the film density, the ratio of nitrogen in the film, and the hydrogen concentration in the film are higher than the lowermost silicon oxynitride film, and the uppermost silicon oxynitride film A lower layer or layers of silicon oxynitride films may be sandwiched.

(Embodiment 3)
FIG. 23 is a plan view showing the oxide TFT of this embodiment, FIG. 24 is a cross-sectional view taken along the line GG of FIG. 23, and FIG. 25 is a cross-sectional view taken along the line H-H of FIG.

  This embodiment is applied to a bottom gate / bottom contact type oxide TFT. Here, the bottom contact means a structure in which the source electrode 14 s and the drain electrode 14 d are disposed below the channel layer 13.

  The manufacturing method of the oxide TFT of the present embodiment is the same as that of the first embodiment except that the order of the step of forming the source electrode 14s and the drain electrode 14d and the step of forming the channel layer 13 are reversed. is there.

  According to the present embodiment, since it is not necessary to consider the damage of the channel layer 13 when forming the source electrode 14s and the drain electrode 14d, the material of the conductive film that forms the source electrode 14s and the drain electrode 14d, the film formation The selection range of methods and processing methods can be expanded.

  In the present embodiment also, the protective film 15 can be composed of three or more silicon oxynitride films having different film densities, nitrogen ratios in the film, and hydrogen concentrations in the film. Also in this case, the lowermost layer is composed of a silicon oxynitride film having the lowest film density, and the uppermost layer is composed of a silicon oxynitride film or a silicon nitride film having the highest film density. And, between the two silicon oxynitride films, the film density, the ratio of nitrogen in the film, and the hydrogen concentration in the film are higher than the lowermost silicon oxynitride film, and the uppermost silicon oxynitride film A lower layer or layers of silicon oxynitride films may be sandwiched.

(Embodiment 4)
FIG. 26 is a cross-sectional view showing the oxide TFT of this embodiment. In the first to third embodiments, the protective film 15 covering the oxide TFT is composed of a plurality of insulating films. However, the protective film 15S of the present embodiment has a film growth direction (perpendicular to the upper surface of the substrate 10). (Direction), and a single layer of silicon oxynitride film in which density, nitrogen ratio, and hydrogen concentration continuously increase.

The silicon oxynitride film constituting the protective film 15S has a film density in a region in contact with the channel layer 13 of less than 2.45 g / cm ³ , a nitrogen ratio (N / O + N) in the film of less than 34 atm%, The hydrogen concentration is less than 1.5 × 10 ²² atm / cm ³ , the film density on the outermost surface in contact with the atmosphere is 2.45 g / cm ³ or more, and the ratio of nitrogen in the film (N / O + N) is 34 atm%. As described above, the hydrogen concentration in the film is 1.5 × 10 ²² atm / cm ³ or more. The vicinity of the outermost surface of the protective film 15S may be a silicon nitride film that is a film that does not substantially contain oxygen.

The silicon oxynitride film as described above, for example, gradually deposits the ratio of ammonia gas to O ₂ gas when the film is deposited by a CVD method using a reaction gas composed of monosilane (SiH ₄ ) + ammonia (NH ₃ ) + O _2. It can be formed by increasing the height. In another example, when the film is deposited by a CVD method using a reaction gas composed of monosilane (SiH ₄ ) + nitrogen (N ₂ ) + O ₂ , the ratio of N ₂ gas to O ₂ gas is gradually increased. Can also be formed.

  The protective film 15S of the present embodiment configured by a silicon oxynitride film whose film density continuously changes is the same as that of the first to third embodiments configured by a plurality of layers of silicon oxynitride films having different film densities. Since a rapid change in stress can be suppressed as compared with the protective film 15, deterioration of the oxide TFT due to film peeling or the like can be suppressed.

  This embodiment can be applied not only to the bottom gate / top contact type oxide TFT as shown in FIG. 26 but also to the bottom gate / bottom contact type oxide TFT as shown in FIG.

(Embodiment 5)
FIG. 28 shows a schematic configuration of the RFID tag 20 in which the antenna resonant circuit 21, the rectifier 22, the modulator 23, the digital circuit 24, and the like are formed using the oxide TFT of the present invention described in the first to fourth embodiments. Show.

  The RFID tag 20 can communicate wirelessly with an external reader / writer 25 using, for example, a high frequency of 13.56 MHz. Moreover, since the oxide semiconductor (13) constituting the channel layer of the oxide TFT is a transparent material, an almost transparent circuit can be formed in the IC chip.

  For example, by forming the electrodes and wiring of the IC chip with a transparent conductive film such as ITO and the circuit element with the oxide TFT of the present invention, a transparent wireless that transmits and receives at a high frequency (RF) of 13.56 MHz, for example. An IC tag can be manufactured. Such a wireless IC tag is different from a conventional RFID tag in that an IC chip and an antenna are almost transparent. Therefore, when the wireless IC tag is attached to a film or a card, the design printed on the film or the card is not damaged. .

(Embodiment 6)
FIG. 29 is a circuit block diagram showing an example of an array configuration of a semiconductor device using the oxide TFT of the present invention described in the first to fourth embodiments. The semiconductor device of this embodiment has a configuration in which elements including the oxide TFT of the present invention are arranged in an array on a substrate 30. Of course, the oxide TFT is used as a switching transistor or a driving transistor of each element in the array, as well as a gate line driving circuit 32 for sending a signal to the gate wiring 31 connected to the gate electrode (11) of the oxide TFT. The transistor may be used in a data line driving circuit 34 that sends a signal to the data wiring 33 connected to the source electrode (14s) of the oxide TFT. In this case, the oxide TFT of each element and the oxide TFT in the gate line driving circuit 32 or the data line driving circuit 34 can be formed in parallel.

  When the array described above is applied to an active matrix liquid crystal display device, each element has a configuration as shown in FIG. 30, for example. When a scanning signal is supplied to the gate wiring 31 extending in the x direction in the figure, the TFT 35 is turned on, and the video signal from the data wiring 33 extending in the y direction in the figure is passed through the turned on TFT 35. It is supplied to the pixel electrode 36.

  The gate lines 31 are arranged in parallel in the y direction in the figure, and the data lines 33 are arranged in parallel in the x direction in the figure and are surrounded by a pair of adjacent gate lines 31 and a pair of adjacent data lines 33. A pixel electrode 36 is arranged in the area (pixel area). In this case, for example, the data line 33 is electrically connected to the source electrode, and the pixel electrode 36 is electrically connected to the drain electrode. Alternatively, the data wiring 33 may also serve as the source electrode. Further, the above-described array may be applied not only to a liquid crystal display device but also to an organic EL display device. In this case, an oxide TFT is applied to a transistor constituting the pixel circuit. Further, the above-described array may be applied to a memory element, and an oxide TFT may be applied to a selection transistor.

  As mentioned above, the invention made by the present inventor has been specifically described based on the embodiment. However, the present invention is not limited to the embodiment, and various modifications can be made without departing from the scope of the invention. Needless to say.

  The present invention can be applied to a semiconductor device having an oxide TFT.

10 substrate 11 gate electrode 12 gate insulating film 13 channel layer 14d drain electrode 14s source electrode 15, 15S protective film 15L lower protective film 15U upper protective film 16 contact hole 17 upper wiring 20 RFID tag 21 antenna resonance circuit 22 rectifier 23 modulator 24 Digital circuit 25 Reader / writer 30 Substrate 31 Gate wiring 32 Gate line driving circuit 33 Data wiring 34 Data line driving circuit 35 TFT
36 pixel electrodes

Claims (12)

A semiconductor device in which a thin film transistor is formed on an upper surface of a substrate and a protective film is formed on the thin film transistor,
The thin film transistor includes a gate electrode formed on an upper surface of the substrate, a gate insulating film formed on the gate electrode, a channel layer made of an oxide semiconductor film formed on the gate insulating film, A source electrode and a drain electrode electrically connected to the channel layer;
The protective film is formed on at least a portion of the first silicon oxynitride film formed so as to be in contact with the upper surface of the channel layer, and on the substrate above the first silicon oxynitride film, A semiconductor device comprising a multilayer film including a second silicon oxynitride film or a silicon nitride film having a film density higher than that of a silicon nitride film. The first silicon oxynitride film has a film density of less than 2.45 g / cm ³ , and the second silicon oxynitride film or the silicon nitride film has a film density of 2.45 g / cm ³ or more. The semiconductor device according to claim 1.   The first silicon oxynitride film has a ratio of nitrogen to the total amount of nitrogen and oxygen in the film of less than 34 atm%, and the second silicon oxynitride film has a ratio of nitrogen to the total amount of nitrogen and oxygen in the film. 2. The semiconductor device according to claim 1, wherein the semiconductor device is at least 34 atm%. The first silicon oxynitride film has a hydrogen concentration of less than 1.5 × 10 ²² atm / cm ³ , and the second silicon oxynitride film has a hydrogen concentration of 1.5 × 10 ^{22 in the} film. The semiconductor device according to claim 1, wherein the semiconductor device is atm / cm ³ or more.   2. The semiconductor device according to claim 1, wherein the first silicon oxynitride film has a thickness of 20 nm or more.   2. The semiconductor device according to claim 1, wherein the first silicon oxynitride film is entirely covered with the second silicon oxynitride film including an end portion thereof.   The source and drain electrodes are disposed above the channel layer, and the first silicon oxynitride film is disposed above the source and drain electrodes, and the second silicon oxynitride film or the silicon nitride film The semiconductor device according to claim 1, wherein the semiconductor device is disposed in an upper layer than the first silicon oxynitride film.   The first silicon oxynitride film is disposed above the channel layer, and the source and drain electrodes are disposed above the first silicon oxynitride film, and the second silicon oxynitride film or the nitride 2. The semiconductor device according to claim 1, wherein the silicon film is arranged in an upper layer than the source and drain electrodes.   The semiconductor device according to claim 1, wherein the channel layer is disposed above the source and drain electrodes.   The oxide semiconductor film is made of an oxide in which any one or more elements of In, Zn, Cd, Al, Ga, Si, Sn, Ce, Ge, and Hf are combined with oxygen. Item 14. A semiconductor device according to Item 1. A semiconductor device in which a thin film transistor is formed on an upper surface of a substrate and a protective film is formed on the thin film transistor,
The thin film transistor includes a gate electrode formed on an upper surface of the substrate, a gate insulating film formed on the gate electrode, a channel layer made of an oxide semiconductor film formed on the gate insulating film, A source electrode and a drain electrode electrically connected to the channel layer;
The protective film is formed of a silicon oxynitride film which is formed so that at least a part thereof is in contact with the upper surface of the channel layer and whose density continuously increases along the growth direction of the film. Semiconductor device. The silicon oxynitride film has a film density in a region in contact with the upper surface of the channel layer of less than 2.45 g / cm ³ and a film density of an outermost surface of 2.45 g / cm ³ or more. Item 12. A semiconductor device according to Item 11.

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