JP2015070114A - Thin film semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thin film semiconductor device comprising a practical conductive barrier material capable of preventing oxidation-reduction reaction.SOLUTION: An amorphous electride is used as a conductive barrier material (5) provided between a semiconductor layer (4) and each of a source electrode (6) and a drain electrode (7). This conductive barrier material (5) is formed through sputter deposition to have a thickness in the range from 2 nm to 15nm, exhibits electric properties comparable to conventional Mo electrode TFTs, and satisfactorily operates as an n-type Oxide-TFT electrode.

Description

  The present invention relates to a thin film semiconductor device that realizes an electrode with low resistance and high reliability.

  In a general thin film semiconductor transistor, a low resistance source / drain electrode and a conductive barrier material for isolating a semiconductor layer are Ti (titanium) or Mo (molybdenum), or Ti-Mo, which is a refractory metal. Alloy is used.

  As an example, FIG. 4 shows a schematic longitudinal sectional view of a general oxide thin film semiconductor transistor. In the oxide thin film semiconductor transistor illustrated in FIG. 4, a gate electrode 20, a gate insulating film 30, and an oxide semiconductor layer 40 are sequentially stacked on a glass substrate 10. A source electrode 60 and a drain electrode 70 are laminated via a conductive barrier material 50.

  More specifically, in the illustration of FIG. 4, the oxide semiconductor layer 40 is composed of indium, gallium, zinc, and oxygen expressed as In—Ga—Zn—O. The source electrode 60 and the drain electrode 70 are made of Al (aluminum), Al—Nd (neodymium) alloy, or Cu (copper). The conductive barrier material 50 for isolating the source electrode 60 / drain electrode 70 and the oxide semiconductor layer 40 is made of Ti (titanium) or Mo (molybdenum), or a Ti—Mo alloy, which is a refractory metal. (For example, refer nonpatent literature 1).

Japanese Patent No. 4245608

"69.2 Highly Reliable Oxide-Semiconductor TFT for AM-OLED Display", Toshiaki Arai et. Al. SID 10 DIGEST p1033-1036

However, the prior art has the following problems.
In order to manufacture a high-performance stable oxide thin film semiconductor transistor (Oxide-TFT), heat treatment at 200 ° C. or higher, desirably 300 ° C. or higher is required. However, Ti or Mo, which is a metal material of the conductive barrier material 50 used to form the source electrode 60 and the drain electrode 70, easily oxidizes with oxygen in Oxide to form titanium oxide or molybdenum oxide. To do.

  As a result, oxygen deficiency occurs in Oxide, and the number of carriers increases. The increase in carriers causes a variation in TFT characteristics, mainly a variation in threshold value (Vth). That is, as long as “a material that can cause an oxidation-reduction reaction” is used as the conductive barrier material 50, such a variation in threshold value cannot be avoided.

  A supplementary explanation will be given of the cause of such a problem. Oxide semiconductors typified by IGZO (In-Ga-Zn-O) have such threshold fluctuations due to carriers carrying charges = electrons are oxygen deficient, that is, oxygen atoms in the semiconductor film are insufficient. It is understood.

  Therefore, if such a threshold value fluctuates in the manufacturing process and further due to an increase in element temperature during operation, the electrical characteristics of the TFT, for example, the threshold value (Vth), current, and the like fluctuate. As a result, there is a possibility that the oxide-TFT becomes unusable.

  From this point of view, in order to realize a highly reliable high-performance Oxide-TFT, the conductive barrier material used for the source electrode and the drain electrode must not undergo an oxidation-reduction reaction with the oxide semiconductor. Here, examples of the metal material that does not oxidize include Au, Ag, and Pt. However, there are problems in workability, adhesion, and cost, and these metal materials cannot be used for products.

  Therefore, as a problem of the prior art, when a metal material that can be practically used is used as a conductive barrier material, none of them can prevent a redox reaction with an oxygen atom in an oxide semiconductor. Is mentioned.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to obtain a thin film semiconductor device provided with a practical conductive barrier material capable of preventing a redox reaction.

  The thin film semiconductor device according to the present invention uses amorphous electride as a conductive barrier material provided between each of a source electrode and a drain electrode and a semiconductor layer.

  According to the thin film semiconductor device of the present invention, a low-resistance and high-reliability electrode is realized by using electride, which is a chemically inert ceramic material having a small work function, as an electrode material of a thin-film semiconductor transistor. By doing so, a thin film semiconductor device provided with a practical conductive barrier material capable of preventing the oxidation-reduction reaction can be obtained.

It is a typical longitudinal cross-sectional view of the thin film semiconductor transistor in Embodiment 1 of this invention. It is explanatory drawing regarding the manufacturing process of the thin film semiconductor device in Embodiment 1 of this invention. It is the figure which showed the result of having performed TFT characteristic evaluation with respect to the prototype in Embodiment 1 of this invention. It is a typical longitudinal section of a general oxide thin film semiconductor transistor.

  First, the gist of the present invention will be described. “Amorphous electride C12A7” (see, for example, Patent Document 1) invented by Professor Hideo Hosono of Tokyo Institute of Technology is a chemically stable (inert) ceramic and has a small work function. By using it as an electron injection layer of a light emitting element (OLED), it is a new material that has a possibility of realizing an OLED with a low driving voltage.

  Therefore, as a result of detailed analysis and evaluation of published papers and published patents, the inventor of the present application pays attention to the fact that this electride C12A7 can be used as a source / drain electrode material of a thin film semiconductor device, particularly an oxide semiconductor transistor. did.

  The reason for this is that amorphous C12A7 is a conductor, and carriers that carry charges are electrons. Therefore, from the category of semiconductor engineering, it can be considered as an n + oxide semiconductor, and is considered to be an optimum material as a source / drain ohmic electrode of an oxide semiconductor transistor (carrier is an electron) that operates n-type. Therefore, a preferred embodiment of the thin film semiconductor device of the present invention will be described below with reference to the drawings.

Embodiment 1 FIG.
FIG. 1 is a schematic longitudinal sectional view of a thin film semiconductor transistor according to Embodiment 1 of the present invention. In the thin film semiconductor transistor according to the first embodiment shown in FIG. 1, a gate electrode 2, a gate insulating film 3, and an oxide semiconductor layer 4 are sequentially stacked on a glass substrate 1, and an oxide semiconductor layer A source electrode 6 and a drain electrode 7 are laminated on 4 with a conductive barrier material 5 interposed therebetween.

  More specifically, in the illustration of FIG. 1, the oxide semiconductor layer 4 is IGZO and is composed of indium, gallium, zinc, and oxygen. The source electrode 6 and the drain electrode 7 are made of Al, an Al—Nd alloy, or Cu. As the conductive barrier material 5 for isolating the source electrode 6 / drain electrode 7 and the oxide semiconductor layer 4, the n-type conductivity which is chemically stable (inactive) and has a small work function is used. The amorphous electride (C12A7) is used instead of the conventional conductive barrier material composed of Ti or Mo. Incidentally, the work function value of the electride used in the present invention is about 3 eV, and the work function value of the conventional Mo or Ti is about 4 eV.

  As described above, by using the conductive barrier material 5 made of amorphous electride, an oxide semiconductor thin film transistor (Oxide-TFT) with low contact resistance and little TFT characteristic variation can be realized. In other words, the use of chemically inert amorphous electride for the material in direct contact with Oxide can prevent oxidation-reduction reactions during heat treatment, etc., and realize a high-performance and highly reliable Oxide-TFT. it can.

  The idea of using electride as a conductive barrier material for an electrode of a thin film semiconductor device will be described in detail below. Electride (C12A7) is a paper or patented material as an electron injection layer of an organic EL light emitting device (OLED). As a result of detailed analysis of the physical properties and chemical characteristics of this electride, the inventor of the present application has found that it can be used as a conductive barrier material for a source / drain electrode of an Oxide-TFT. Furthermore, from basic experiments, TFT characteristics comparable to conventional conductive barrier materials made of Ti or Mo could be confirmed.

  FIG. 2 is an explanatory diagram relating to the manufacturing process of the thin film semiconductor device according to the first embodiment of the present invention. More specifically, FIG. 2A shows a manufacturing process of a bottom gate & top contact type Oxide-TFT as a cross-sectional view divided into steps 1 to 5, and FIG. The top view corresponding to step 3-step 5 is shown. Hereinafter, Step 1 to Step 5 will be described in order.

<Step 1> Substrate preparation A crystalline silicon wafer with a thermal oxide film (100 nm, SiO2) is prepared. Here, the n + silicon wafer (specific resistance value: 0.02 Ω · cm) operates as the gate electrode 2.

<Step 2> Formation of Channel Layer IGZO that is an oxide semiconductor layer is formed by sputtering with a film thickness of 50 nm to form a channel layer.

<Step 3> Processing of channel layer The channel layer is processed into an island shape by photolithography and wet etching.

<Step 4> Electrode formation by lift-off method using photolithography Photoresist is formed on portions other than the source electrode 6 and the drain electrode 7 are formed (S4-1). Thereafter, amorphous electride C12A7 (10 nm) and subsequently, Al (100 nm) as an electrode material are continuously sputtered (S4-2). Further, the photoresist is peeled off, and the amorphous electride C12A7 and Al on the photoresist are removed to form the source electrode 6 and the drain electrode 7 (S4-3).

<Step 5> Heat treatment and characteristic evaluation Heat treatment was performed in air at 300 ° C for 30 minutes, and then TFT characteristic measurement evaluation was performed.

  Compared to a conventional product using a Ti layer or Mo layer (40 nm) as the conductive barrier material 5, the difference is that in step 4, a C12A7 layer (10 nm) is formed instead of the Ti layer or Mo layer. In the manufacturing process itself, a conventional procedure can be used.

  Although description with reference to the drawings is omitted, it is also possible to manufacture an etch stopper type bottom gate & top contact type Oxide-TFT. Also in this case, as compared with a conventional product using a Ti layer or a Mo layer (40 nm) as a conductive barrier material, only a point that a C12A7 layer (10 nm) is formed in place of the Ti layer or the Mo layer is different.

  FIG. 3 is a diagram showing a result of performing TFT characteristic evaluation on the prototype in the first embodiment of the present invention. More specifically, FIG. 3A shows the Ids-Vds characteristic of the Oxide-TFT, and FIG. 3B shows the Ids-Vgs characteristic of the Oxide-TFT. In addition, the vertical axis | shaft of FIG.3 (b) is a logarithmic scale.

  As shown in FIG. 3A, the rise of the linear region in the Ids-Vds characteristic is very good. That is, it can be seen that a good ohmic junction can be formed even when a 10 nm C12A7 layer is used as the conductive barrier material. Furthermore, the saturation characteristics in the saturation region are also good.

  Further, from FIG. 3B, various characteristics of the TFT can be calculated. The threshold value (Vth) is 3.1 V, which is not significantly different from the conventional Mo electrode TFT. Moreover, it has confirmed that a mobility and S value were also equivalent to the TFT of the conventional Mo electrode. In addition, 1stMeas. And 3rdMeas. It was also confirmed that there was no so-called hysteresis phenomenon because the characteristics of these were consistent.

  From the above characteristic evaluation, the C12A7 electrode Oxide-TFT of the present invention has no problem in the ohmic characteristics of the electrode, exhibits the same electrical characteristics as the conventional Mo electrode TFT, and operates well as an n-type Oxide-TFT electrode. I was able to verify that.

  As described above, according to the first embodiment, the electride, which is a chemically inactive ceramic material having a small work function, is applied as a conductive barrier material for a thin film semiconductor transistor, so that low resistance and reliability can be achieved. A practical thin film semiconductor device capable of realizing a highly functional electrode and preventing an oxidation-reduction reaction can be obtained. Furthermore, it was confirmed that characteristics equivalent to those of conventional products were obtained through the verification of characteristics using prototypes.

  In the above-described embodiment, the amorphous electride having a film thickness of 10 nm has been described. However, the film thickness of the conductive barrier material of the present invention is not limited to this. If the film thickness is in the range of 2 nm to 15 nm, it has been verified that the same performance as in the case of the film thickness of 10 nm can be obtained.

  In the above-described embodiment, the oxide thin film semiconductor device using the oxide semiconductor layer has been described. However, the application example of the electride in the present invention is not limited to this. Thin film semiconductor devices using amorphous silicon and thin film semiconductor devices using polycrystalline and microcrystalline silicon can be made of conductive barrier materials instead of conventional refractory metal Ti (titanium) or Mo (molybdenum) barrier layers. A certain electride can also be applied, and the same effect can be obtained. Further, regarding an oxide semiconductor, electride can be applied to any of a crystal system, a microcrystal system, and an amorphous system.

  1 glass substrate, 2 gate electrode, 3 gate insulating film, 4 oxide semiconductor layer, 5 conductive barrier material, 6 source electrode, 7 drain electrode.

Claims (2)

A thin film semiconductor device using amorphous electride as a conductive barrier material provided between a source electrode and a drain electrode and a semiconductor layer. The thin film semiconductor device according to claim 1,
The conductive barrier material is configured as an amorphous electride formed to a thickness in the range of 2 nm to 15 nm by sputtering film formation.

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