JP2008078243A - Bonding structure of element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing technology with which damage such as erosion to a wiring circuit is suppressed as much as possible on an element where the wiring circuit formed of Al-based alloy is directly bonded to a transparent electrode and the highly reliable element is achieved. <P>SOLUTION: In a bonding structure of having a transparent electrode and a wiring circuit formed of Al-based alloy which is directly bonded to the transparent electrode, a taper angle of a wiring circuit side is 20°to 75°. It is desirable that Al-based alloy is Al-Ni-based alloy and it is much more desirable that it is Al-Ni-B alloy. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a bonding structure of elements constituting a display device such as a liquid crystal display, and more particularly to a technique for manufacturing an element using an Al-based alloy as a wiring circuit material.

  2. Description of the Related Art In recent years, aluminum (hereinafter, sometimes simply referred to as “Al”)-based alloys are widely used as constituent materials in display devices such as thin-screen televisions typified by liquid crystal displays. This is because a wiring circuit formed of an Al-based alloy has a low specific resistance value and good workability.

For example, in the case of an active matrix type liquid crystal display, a thin film transistor (hereinafter abbreviated as TFT) as a switching element is a transparent electrode (hereinafter referred to as “ITO” (Indium Tin Oxide) or IZO (Indium Zinc Oxide)). And a transparent electrode layer) and a wiring circuit formed of an Al-based alloy (hereinafter also referred to as a wiring circuit layer). In such an element, there is a portion where the Al-based alloy wiring circuit is bonded to the transparent electrode, and a portion where the Al ⁺ -Si (phosphorus-doped semiconductor layer) is bonded in the TFT.

In the case of configuring the above-described element, molybdenum (Mo) or titanium (Ti) is interposed between the wiring circuit layer and the transparent electrode layer in consideration of the effect of aluminum oxide that is easily generated in the Al-based alloy wiring circuit. There is a technique for forming a refractory metal material such as a so-called cap layer. In addition, also in the junction between a semiconductor layer such as n ⁺ -Si and a wiring circuit, in order to prevent Al and Si from interdiffusion due to a thermal process during the manufacturing process, the semiconductor layer and the wiring circuit layer A high melting point metal material such as molybdenum (Mo) or titanium (Ti), which is the same as the cap layer, is interposed therebetween (for example, see Non-Patent Document 1).
Edited by Tatsuo Uchida, “Next Generation Liquid Crystal Display Technology”, first edition, Industrial Research Committee, Inc., November 1, 1994, p. 36-38

In the element structure in which such a cap layer is interposed, the element structure is naturally complicated, and the production cost tends to increase. Therefore, recently, a display device structure has been proposed in which the cap layer is omitted and the Al-based alloy wiring circuit and the transparent electrode layer can be directly joined (see, for example, Patent Document 1 and Patent Document 2).
JP 2004-214606 A JP 2003-89864 A

  In Patent Document 1 and Patent Document 2, direct bonding to the transparent electrode is realized by improving the composition and structure of the Al-based alloy. However, the device manufacturing conditions when the cap layer is omitted are examined. Is not done enough. Specifically, when an element such as a TFT is manufactured, an insulating layer made of SiNx is provided on the wiring circuit layer. However, when a cap layer is interposed as in the prior art, the cap layer itself is a wiring circuit. Since it also serves to protect the layer, no particular problem occurred even when the insulating layer itself had a defect. However, when the cap layer is omitted and the insulating layer is formed directly on the wiring circuit layer, if there is a defect such as a crack in the insulating layer, a chemical solution such as an etchant penetrates from the crack, and Al There is a concern that the wiring circuit layer of the system alloy may be eroded. For example, when the wiring circuit layer is dissolved by a chemical solution such as an etching solution at the direct bonding portion between the wiring circuit layer and the transparent electrode layer, it is considered that the bonding resistance is increased.

  The present invention has been made in the background as described above. In an element structure in which an Al-based alloy wiring circuit layer and a transparent electrode layer are directly bonded, there is a concern with an etching solution that is concerned in the manufacturing process of the element. The present invention proposes an element structure that can suppress damage such as erosion of a wiring circuit as much as possible and realize a highly reliable element.

  In order to solve the above-described problems, the present invention provides a device having a transparent electrode and a wiring circuit made of an Al-Ni alloy that is directly bonded to the transparent electrode. It was assumed to be 20 ° to 75 °.

  In the junction structure of elements according to the present invention, the taper angle is preferably 35 ° to 60 °.

  In the junction structure of the element according to the present invention, the Al-based alloy is preferably an Al-NI-based alloy, and in the case of this Al-Ni-based alloy, it may contain 0.5 at% to 10.0 at% Ni. preferable.

  Moreover, it is preferable that this Al-Ni type alloy further contains B (boron).

  ADVANTAGE OF THE INVENTION According to this invention, the erosion by chemical | medical solutions, such as an etching liquid, of the wiring circuit which consists of Al type alloys can be suppressed as much as possible, and a reliable element can be manufactured.

  Hereinafter, although the best embodiment in the present invention is described, the present invention is not limited to the following embodiment.

  In the element according to the present embodiment, in a bonding structure of an element including a wiring circuit made of an Al—Ni alloy that is directly bonded to a transparent electrode, the taper angle of the side surface of the wiring circuit is 20 ° to 75 °. It is.

The element in this embodiment is a TFT element formed mainly by a five-mask process. More specifically, an Al—Ni alloy is formed on a glass substrate by sputtering, and then gate wiring / electrodes are formed by photolithography. A gate insulating film and a semiconductor film (amorphous i-Si, n ⁺ -Si) are continuously formed thereon. Thereafter, only the semiconductor layer portion is subjected to photolithography, and islands are formed in necessary portions to be TFTs.

On top of that, an Al-based alloy for source / drain is formed by sputtering, and S / D wirings and electrodes are formed by photolithography. Only n ⁺ -Si at a portion to be a channel portion is removed by dry etching. An SiNx insulating layer is formed thereon, and a contact hole for contacting the pixel electrode (transparent electrode) is formed on the drain electrode portion by dry etching. Then, a transparent electrode layer is formed by sputtering, and a pixel electrode is formed by photolithography to produce a TFT.

  In the manufacture of the TFT element as described above, in the present invention, the taper angle on the side surface of the wiring circuit formed of the Al-based alloy is 20 ° to 75 °, but is less than 20 °. Thus, the width of the wiring circuit cannot be reduced, and it becomes difficult to form a thinning circuit. On the other hand, if the taper angle is larger than 75 °, when the SiNx insulating layer is directly formed on the wiring circuit, a crack is generated in the insulating layer. There is a tendency for the chemical solution to permeate and erode the wiring circuit.

  The taper angle in the present invention is an angle (θ) on the bottom angle side of the wiring circuit cross section as shown in FIG. Specifically, in the cross section of the trapezoidal wiring circuit after patterning, from the distance a and the film thickness b from one end (A) of the lower base to the perpendicular dropped from one end (B) of the upper base, b / a = The taper angle θ was determined by tan θ.

  The taper angle is more preferably 35 ° to 60 °. When the angle is 60 ° or less, the occurrence of cracks in the SiNx insulating layer can be reliably prevented. Further, if the angle is less than 35 °, the processing at the time of thinning tends to be somewhat difficult, so a taper angle of 35 ° to 60 ° is considered effective in practical use. However, in the case where the insulating layer is formed by CVD with good coverage, a practical element may be obtained even if the taper angle exceeds 60 °.

  In the case of the element according to the present invention, the Al-based alloy is preferably an Al-Ni-based alloy, and more preferably an Al-Ni-B alloy. This is because the Al—Ni—B alloy is excellent in direct bonding characteristics with a transparent electrode, has a low specific resistance value, and is excellent in wiring circuit characteristics such as heat resistance. The Ni content of the Al—Ni alloy is preferably 0.5 at% to 10.0 at%. In the case of an Al—Ni—B alloy, the Ni content is preferably 0.5 at% to 10.0 at%, and the B content is preferably 0.1 at% to 0.8 at%. By setting it as such a composition, it becomes possible to omit cap layers, such as Mo, used at the time of joining with a semiconductor layer. Furthermore, when reducing the taper angle value, it is preferable to set the Ni content to 3.0 at% to 6.0 at% and the B content to 0.2 at% to 0.4 at%. Further, Al is preferably contained at 75 at% or more from the viewpoint of forming a low-resistance wiring circuit.

  Next, examples of the present invention will be described. Here, as an example, an Al-5.0 at% Ni-0.4 at% B alloy is used as the Al-based alloy to form a wiring circuit with a changed taper angle. As characteristic evaluation, the junction resistance with the transparent electrode when the taper angle of the wiring circuit was changed and the junction state with the SiNx insulating layer (element non-defective rate) were investigated.

Each evaluation sample subjected to the characteristic evaluation was produced by the following procedure. First, an Al alloy target having the above composition is used on a glass substrate, the sputtering conditions are an input power of 3.0 Watt / cm ² , an argon gas flow rate of 100 ccm, an argon pressure of 0.5 Pa, and a magnetron sputtering apparatus, and a thickness of 3000 mm. A wiring circuit layer was formed. The wiring circuit layer surface is coated with a resist (TFR-970: manufactured by Tokyo Ohka Kogyo Co., Ltd./coating conditions: spin coater 3000 rpm, post-baking resist thickness 1 μm target), and pre-baking treatment (110 ° C., 1.5 Minutes). Note that it is desirable that the Al—Ni-based alloy is not subjected to heat treatment before patterning for circuit formation. When heat treatment is performed, it is desirable that the heat treatment is performed in a vacuum or in an inert gas atmosphere.

Then, a pattern film for forming a circuit with a width of 20 μm was placed and subjected to an exposure process (Mask Anyler MA-20: Mikasa Co., Ltd./exposure conditions 15 mJ / cm ² ). Subsequently, development processing was performed with an alkali developer containing tetramethylammonium hydroxide having a concentration of 2.38% and a solution temperature of 23 ° C. (hereinafter abbreviated as TMAH developer). After the development processing, post baking processing (100 ° C., 3 minutes) was performed using a hot plate, and circuit formation was performed using a phosphoric acid mixed acid etching solution (manufactured by Kanto Chemical Co., Inc.). In the wiring circuit of each evaluation sample, the taper angle was changed by adjusting the post-baking treatment conditions and the composition of the phosphoric acid mixed acid etching solution (specifically, as shown in Table 1, the taper angle). 9 types of evaluation samples having a wiring circuit with 10 to 85 ° changed.

  After the etching treatment, the resist was removed with a stripping solution (ST106: manufactured by Tokyo Ohka Kogyo Co., Ltd.).

Thereafter, pure water cleaning and drying treatment were performed, and an SiNx insulating layer (thickness 4200 mm) was formed on the surface. This insulating layer was formed using a sputtering apparatus under sputtering conditions of input power RF 3.0 Watt / cm ² , argon gas flow rate 90 ccm, nitrogen gas flow rate 10 ccm, pressure 0.5 Pa, and substrate temperature 300 ° C.

Subsequently, a positive resist (manufactured by Tokyo Ohka Kogyo Co., Ltd .: TFR-970) is coated on the surface of the insulating layer, a 10 μm × 10 μm square pattern film for opening a contact hole is placed, exposed, and subjected to TMAH development. Development processing was performed with the solution. Then, contact holes were formed using a dry etching gas of CF ₄ or SF ₆ . A contact hole formation conditions in the case of a CF ₄ gas, CF ₄ gas flow rate 50 ccm, the oxygen gas flow rate 5 ccm, pressure 4.0 Pa, an output 150 W, in the case of SF ₆ gas, SF ₆ gas flow rate 60 ccm, the oxygen gas flow rate 5 ccm, The pressure was 4.0 Pa and the output was 125 W. After the contact hole was formed, the resist was removed using a stripping solution (ST106: manufactured by Tokyo Ohka Kogyo Co., Ltd.).

  About the evaluation sample which performed the peeling process of the resist, after removing the residual peeling liquid using isopropyl alcohol, it washed with water and performed the drying process.

Then, an ITO transparent electrode layer was formed in and around the contact hole, using an ITO target (composition In ₂ O ₃ -10 wt% SnO ₂ ), for each evaluation sample for which the resist peeling process was completed. The transparent electrode layer is formed by sputtering (substrate temperature 250 ° C., input power 1.8 Watt / cm ² , argon gas flow rate 80 ccm, oxygen gas flow rate 1.9 ccm, pressure 0.37 Pa), and a crystallized ITO having a thickness of 500 mm. A membrane was obtained.

  A resist (Tokyo Ohka Kogyo Co., Ltd .: TFR-970) is coated on the surface of the ITO film, a pattern film is placed and exposed to light, and a TMAH developer having a concentration of 2.38% and a liquid temperature of 23 ° C. Development processing was performed, and a 20 μm wide circuit was formed with a nitric acid-based etching solution (ITO02N: manufactured by Kanto Chemical Co., Inc.). The etching time was 3 minutes. After forming the ITO film circuit, the resist was removed with a stripping solution (ST106: manufactured by Tokyo Ohka Kogyo Co., Ltd.).

  With the above procedure, the junction resistance value of the evaluation sample in which the wiring circuit layer of the Al—Ni alloy and the transparent electrode layer were directly bonded via the contact hole was measured. This junction resistance value measurement method was based on the four-terminal method as shown in FIG. 2, and the resistance value of each evaluation sample was measured after annealing the element as the evaluation sample in the atmosphere at 250 ° C. for 30 minutes.

  Further, regarding the non-defective product ratio, the quality of each element was evaluated by observing the cross section of each evaluation sample and confirming the bonding state between the wiring circuit and the insulating layer. The non-defective rate was specified by counting the number of elements whose junction resistance value could be measured out of the total 64 elements prepared in the evaluation sample and calculating the ratio. Table 1 shows the results of the evaluation samples for each taper angle.

  3 and 4 show representative photographs obtained by observing a cross section of the evaluation sample. FIG. 3 shows a sample with a taper angle of 20 °, and FIG. 4 shows a sample with a taper angle of 85 °. In this cross-sectional observation, a cross-section of the evaluation sample was processed by FIB (focused ion beam), and a SIM image (ion-excited secondary electron image) of the cross-section was taken. 3 and 4, the black portion on the lower side of the photograph is a glass substrate, and a wiring circuit, a SiNx insulating layer, and a transparent electrode layer are sequentially stacked thereon.

  From the results shown in Table 1, when the taper angle is 85 °, the junction resistance value greatly exceeds 50Ω / □ 10 μm. As shown in FIG. 4, the junction resistance value increased in this manner because a crack (occurring from the upper corner of the wiring circuit) occurred in the SiNx insulating layer on the wiring circuit, and etching was performed from this portion. This was thought to be because the chemical solution such as the liquid entered, corroded the wiring circuit layer, and the corrosion proceeded to the joint with the transparent electrode. A junction resistance value of 50Ω / □ 10 μm or less is considered practically preferable as element characteristics.

  On the other hand, in the case where the taper angle is 75 ° or less, the junction resistance value is smaller than 50Ω / □ 10 μm, so that it was considered that there is no practical problem. In this way, when the taper angle is 75 ° or less, the junction resistance value becomes small as shown in FIG. 3 because the SiNx insulating layer on the wiring circuit has a good coverage state and the insulating layer itself has cracks or the like. This is considered to be because no defects occurred and the wiring circuit was not corroded by chemicals.

Definition conceptual diagram of taper angle. Schematic of junction resistance measurement by the four probe method. A cross-sectional observation photograph when the taper angle is 20 °. Sectional observation photograph when taper angle is 85 °.

Claims (5)

In the junction structure of the element comprising a transparent electrode and a wiring circuit made of an Al-based alloy directly joined to the transparent electrode,
A junction structure for an element, wherein a taper angle of a side surface of the wiring circuit is 20 ° to 75 °. The device junction structure according to claim 1, wherein the taper angle is 35 ° to 60 °. 3. The device junction structure according to claim 1, wherein the Al-based alloy is an Al-Ni-based alloy. The Al—Ni-based alloy contains 0.5 at% to 10.0 at% of Ni, according to claim 3. The element-junction structure according to claim 3 or 4, wherein the Al-Ni-based alloy further contains B.