JP2008108975A - Joining structure of element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an element wherein when directly joining a semiconductor layer such as n<SP>+</SP>-Si and an Al-Ni-based alloy layer, the mutual diffusion of Al and Si can be so prevented as to be able to maintain the ohmic characteristic of the element. <P>SOLUTION: In the element having a semiconductor layer and having an Al-Ni-based alloy layer joined directly to the semiconductor layer, the Al-Ni-based alloy layer joined directly to the semiconductor layer is so formed that the concentration of the nitrogen contained in it is not smaller than 2×10<SP>17</SP>atoms/cm<SP>3</SP>and is smaller than 9×10<SP>21</SP>atoms/cm<SP>3</SP>. Also, the refractive index of the bonding surface side of the Al-Ni-based alloy layer is made preferably not less than 1.9. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

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

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

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

In the case of configuring the element as described above, in consideration of the influence of the aluminum oxide formed in the Al—Ni alloy layer, molybdenum (Mo) or titanium is interposed between the Al—Ni alloy layer and the transparent electrode layer. A refractory metal material such as (Ti) is formed as a so-called cap layer. In addition, in joining the semiconductor layer such as n ⁺ -Si and the wiring circuit, the semiconductor layer and the Al—Ni-based alloy are prevented from interdiffusion between Al and Si by a thermal process during the manufacturing process. The same high-melting point metal material as molybdenum (Mo) or titanium (Ti) as the cap layer is interposed between the layers.

Here, the above-described element structure will be specifically described with reference to FIG. FIG. 1 is a schematic cross-sectional view of an a-Si type TFT relating to a liquid crystal display. In this TFT structure, an electrode wiring circuit layer 2 made of an Al-based alloy wiring material constituting the gate electrode portion G and a cap layer 3 made of Mo, Mo—W, or the like are formed on the glass substrate 1. The gate electrode portion G is provided with a SiNx gate insulating film 4 as protection. On the gate insulating film 4, an a-Si semiconductor layer 5, a channel protective film layer 6, an n ⁺ -Si semiconductor layer 7, a cap layer 3, an electrode wiring circuit layer 2, and a cap layer 3 are sequentially deposited. A drain electrode portion D and a source electrode portion S are provided by appropriately forming a pattern. On the drain electrode portion D and the source electrode portion S, an element surface flattening resin or SiNx insulating film 4 ′ is coated. Further, on the source electrode portion S side, a contact hole CH is provided in the insulating layer 4 ′, and a transparent electrode layer 7 ′ of ITO or IZO is formed in that portion. In the case where an Al alloy wiring material is used for such an electrode wiring circuit layer 2, the transparent electrode layer 7 ′ and the electrode wiring layer 2 between the n ⁺ -Si semiconductor layer 7 and the electrode wiring layer 2 and in the contact hole CH The cap layer 3 is interposed between the two.

  In the element structure shown in FIG. 1, since a cap layer of Mo or the like is formed, an increase in the cost of materials and manufacturing equipment is inevitable, and it has been pointed out that the manufacturing process is complicated.

Therefore, as a technique for omitting the cap layer as described above, a technique has been proposed in which a part of the wiring layer made of an Al-based alloy is nitrided and bonded to the semiconductor layer via the nitrided part (Patent Document). 1), and a technique for nitriding the entire wiring layer made of an Al-based alloy and bonding it to the semiconductor layer has also been proposed (see Patent Document 2).
JP 2003-273109 A JP 2005-123576 A

  However, in response to the above-mentioned Patent Document 1, the resistance of the nitrided portion of the Al-based alloy is increased, and therefore, when the semiconductor layer and the Al—Ni-based alloy layer are directly bonded, ohmic characteristics tend not to be satisfied. . Further, as in Patent Document 2, if all of the Al-based alloy wiring layer is nitrided, the resistance value of the wiring layer itself becomes too large to satisfy satisfactory element characteristics.

The present invention has been made in the background as described above, and in the case of directly joining a semiconductor layer such as n ⁺ -Si and an Al—Ni alloy layer, mutual diffusion between Al and Si can be prevented. An element junction structure capable of reliably maintaining ohmic characteristics is provided.

In order to solve the above-described problems, the present invention provides an Al—Ni alloy directly bonded to a semiconductor layer in a bonding structure of an element including a semiconductor layer and an Al—Ni-based alloy layer bonded directly to the semiconductor layer. The system alloy layer is characterized by containing nitrogen of 2 × 10 ¹⁷ atoms / cm ³ or more and less than 9 × 10 ²¹ atoms / cm ³ .

  The Al—Ni-based alloy layer in the present invention preferably has a refractive index of 1.9 or more on the bonding surface side that is directly bonded to the semiconductor layer.

Moreover, it is preferable that the semiconductor layer in this invention consists of amorphous n ^<+>- Si.

  The Al—Ni alloy in the present invention preferably contains 0.5 at% to 10 at% of Ni.

  Furthermore, in the junction structure of the element according to the present invention, an Al—Ni alloy layer in which an Al—Ni alloy not containing nitrogen and an Al—Ni alloy containing nitrogen are laminated may be used.

According to the present invention, even if a cap layer is omitted and a semiconductor layer such as n ⁺ -Si and an Al—Ni alloy layer are directly joined, mutual diffusion between Al and Si can be prevented and ohmic characteristics are maintained. Therefore, an element having the low resistance characteristics of the Al—Ni alloy layer itself can be realized.

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

  The present inventors examined interdiffusion between Al and Si in order to realize direct bonding between the semiconductor layer and the Al—Ni-based alloy layer, and found that an Al—Ni-based alloy layer to be bonded to the semiconductor layer was found. It has been found that when a predetermined amount of nitrogen is contained, good direct bonding can be realized. The interdiffusion between Al and Si is known to be affected by temperature, crystallinity, and interatomic connectivity, but the crystallinity and interatomic properties of the Al-Ni-based alloy layer with a predetermined nitrogen content. It is presumed that the bonding state or the like suppresses interdiffusion with Si.

The Al—Ni-based alloy layer in the junction structure of the element according to the present invention needs to contain nitrogen of 2 × 10 ¹⁷ atoms / cm ³ or more and less than 9 × 10 ²¹ atoms / cm ³ . This is because if it is less than 2 × 10 ¹⁷ atoms / cm ³ , direct bonding with the semiconductor layer becomes difficult, and if it is 9 × 10 ²¹ atoms / cm ³ or more, the on / off ratio of the transistor characteristics deteriorates. The Al—Ni-based alloy layer containing nitrogen should contain nitrogen at a junction interface directly joining the semiconductor layer, that is, at a depth of at least about 50 to 500 mm from the surface of the Al—Ni-based alloy layer. . For this reason, an Al—Ni alloy not containing nitrogen and an Al—Ni alloy containing nitrogen may be laminated.

  In the device junction structure according to the present invention, the Al—Ni alloy layer directly bonded to the semiconductor layer preferably has a refractive index of 1.9 or more on the bonding surface side. When the refractive index is less than 1.9, mutual diffusion between Al and Si tends to occur. This refractive index means that an Al-based alloy film for forming an Al-Ni-based alloy layer is formed on a glass substrate with a thickness of 100 mm, the surface of the Al-based alloy film is irradiated with light having a wavelength of 589 nm, and an ellipsometer is used. Measure.

The semiconductor layer in the present invention is preferably made of amorphous n ⁺ -Si. The Al—Ni-based alloy layer and the amorphous semiconductor layer tend to interdiffuse easily, but according to the present invention, interdiffusion is suppressed and so-called Si spiking phenomenon can be eliminated.

  In the device junction structure of the present invention, the Al—Ni alloy layer preferably contains 0.5 to 10 at% of Ni. In the case of an Al—Ni alloy having a predetermined Ni content, it is easy to make the resistance of the Al—Ni alloy layer itself 10 μΩcm or less, and it is easy to realize direct bonding with good element characteristics. It is. Specific examples of the Al—Ni alloy include an Al—Ni alloy, an Al—Ni—C alloy, an Al—Ni—B alloy, an Al—Ni—Nd alloy, an Al—Ni—La alloy, and an Al—Ni—. Examples include Ge alloys. When B is contained, the content is preferably 0.1 to 0.8 at%, and when Nd, La, or Ge is contained, the content is preferably 0.1 to 2 at%. The Al—Ni alloy of the present invention desirably contains 75 at% or more of Al itself from the viewpoint of low resistance characteristics.

Next, examples of the present invention will be described. In this embodiment, as an Al—Ni—B alloy layer, an Al-5.0 at% Ni-0.4 at% B film (specific resistance value 4.2 μΩcm) is used and directly bonded to a Si semiconductor layer. The characteristics of the device were evaluated. When direct bonding with Si was performed, control was performed so that an Al—Ni—B—N alloy layer was formed at the interface between Si and the Al—Ni—B alloy layer.

First, a manufacturing method for Al—Ni—B alloy layers having different nitrogen contents will be described. About the evaluation sample, it produced as follows. First, an Al alloy target having the above composition was used on a glass substrate, a sputtering condition, 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 were used. A Ni—B alloy layer was formed. At the time of this sputtering, nitrogen gas is introduced into the argon gas and adjusted so that the actual nitrogen flow rate becomes 0% to 40% with respect to the total actual gas flow rate (argon actual flow rate + nitrogen actual flow rate). -Various samples were produced by changing the nitrogen content on the surface of the B-based alloy layer.

The nitrogen content of the Al—Ni—B based alloy layer was measured by a secondary ion mass spectrometer (Dynamic SIMS) when it was 10 ¹⁸ atoms / cm ³ or more. When nitrogen in the Al—Ni—B alloy layer is measured by a secondary ion mass spectrometer (Dynamic SIMS), an analysis result as shown in FIG. 2 is obtained. In the figure, the result of analyzing nitrogen in an Al—Ni—B alloy wiring film containing nitrogen in the depth direction by a secondary ion mass spectrometer is conceptually shown. For example, when nitrogen is contained in the film, nitrogen is detected at a portion corresponding to the thickness containing nitrogen. The nitrogen content shown in FIG. 2 indicates the average value of the portion detected as nitrogen. The average nitrogen concentration indicates an average value in a range of measurement depths where a certain fixed measurement value is detected. Specifically, in the case of 2.5 × 10 ¹⁸ (solid line data) shown in FIG. 2, the average value was obtained from the measurement values in the range of ¹⁸ nm to 75 nm, excluding the measurement values in the measurement depth range of 0 to 18 nm.

When the nitrogen content is 10 ¹⁸ atoms / cm ³ or less, sputtering is performed in the depth direction of the Si semiconductor layer by an X-ray photoelectron spectrometer (XPS) about 50 to 100 mm, and then the sputtered portion is converted into X The nitrogen content was calculated by comparison with the integrated intensity of the nitrogen detection peak obtained from the measurement result of a sample having a known nitrogen content, as measured by a line photoelectron spectrometer (XPS). This nitrogen content can be measured by either a secondary ion mass spectrometer or an X-ray photoelectron spectrometer, but if the content is near the detection limit of the secondary ion mass spectrometer, the measurement In some cases, measurement by an X-ray photoelectron spectrometer is performed from the viewpoint of reliability of values.

  The specific resistance value of each Al—Ni—B alloy layer having a different nitrogen content was measured with a four-terminal resistance measurement device after heat treatment at 300 ° C. for 30 minutes.

  Next, the result of investigating the bondability between each Al—Ni—B alloy layer having a different nitrogen content and the semiconductor layer will be described. Here, the diffusion heat resistance and the switching characteristics (on / off ratio) of the element when bonded to the semiconductor layer were examined.

For diffusion heat resistance evaluation, an n ⁺ -Si semiconductor layer (300 mm) was formed on a glass substrate (Corning Corp. # 1737) by CVD, and an Al-Ni-B alloy layer (2000 mm) was formed on the semiconductor layer. The formed sample was used as an evaluation sample. At this time, an Al—Ni—B—N alloy layer was formed to a thickness of 100 μm on the n ⁺ —Si layer, and an Al—Ni—B alloy layer was formed to a thickness of 1900 μm thereon. The Al—Ni—B—N alloy layer is formed under sputtering conditions (magnetron sputtering apparatus, input power 3.0 Watt / cm ² , argon gas flow rate 100 sccm, argon pressure 0.5 Pa). Nitrogen gas was introduced therein, and the actual nitrogen flow rate was adjusted in the range of 0% to 40% with respect to the total actual gas flow rate (argon gas actual flow rate + nitrogen actual flow rate). Moreover, the Al—Ni—B alloy layer formed thereon was performed under the above conditions without introducing nitrogen gas.

  And after setting heat processing temperature for every 10 degreeC in the temperature range of 200-380 degreeC for each evaluation sample and performing heat processing for 30 minutes in nitrogen gas atmosphere, phosphoric acid type Al etching liquid (Kanto Chemical Co., Ltd.) Made by immersing in an Al mixed acid etchant / composition (volume ratio) phosphoric acid: succinic acid: acetic acid: water = 16: 1: 2: 1) for 10 minutes. Dissolved to expose the semiconductor layer. The exposed surface of the semiconductor layer was observed with an optical microscope (200 times) to examine whether mutual diffusion between Si and Al occurred.

  3 and 4 show typical optical micrographs on the exposed semiconductor layer surface. FIG. 3 shows the surface of the semiconductor layer where no interdiffusion is observed (evaluation result: ◯), and FIG. 4 shows the trace of interdiffusion (black spots in the photograph) (evaluation result: x). And in each heat processing temperature, the highest temperature of evaluation result (circle) was made into the diffusion heat resistant temperature of the evaluation sample. Note that the observation photographs shown in FIGS. 3 and 4 are image photographs used as a reference when evaluating the diffusion heat resistance, and do not indicate the specific sample results of this example.

  Next, the switching characteristics of the TFT element were measured by measuring an on / off ratio. The evaluation sample was produced according to the following procedure.

First, an Al-based alloy film serving as an Al—Ni—B alloy layer having a thickness of 3000 mm was formed on a glass substrate (manufactured by Corning: # 1737). The sputtering conditions were as follows: substrate heating temperature 100 ° C., DCPower 1000 W (3.1 Watt / cm ² ), argon gas flow rate 100 sccm, and argon pressure 0.5 Pa.

Subsequently, the Al-based alloy film was etched by photolithography to form a gate wiring width of 50 μm and a gate electrode width of 15 μm (see FIG. 5). Photolithographic conditions were such that the Al-based alloy film surface was coated with a resist (TFR-970: manufactured by Tokyo Ohka Kogyo Co., Ltd./application conditions: spin coater 3000 rpm, post-baking resist thickness 1 μm target) and pre-baked (110 ° C. 1.5 minutes), a predetermined pattern film was placed, and an exposure process (Mask Anyler MA-20: manufactured by Mikasa Co., Ltd./exposure conditions 15 mJ / cm ² ) was performed. Subsequently, the film was developed with an alkali developer containing tetramethylammonium hydroxide having a concentration of 2.38% and a liquid temperature of 23 ° C. (hereinafter abbreviated as TMAH developer). 110 ° C., 3 minutes), and a circuit is formed by using a phosphoric acid mixed acid etching solution (manufactured by Kanto Chemical Co., Inc./composition phosphoric acid: nitric acid: acetic acid: water = 16: 1: 2: 1 (capacity ratio)). went. By forming the circuit under such conditions, the circuit was controlled to have a taper angle of 45 °.

After the etching treatment, the resist was removed with a stripping solution (ST106: manufactured by Tokyo Ohka Kogyo Co., Ltd.). After forming the gate wiring circuit, a SiNx film having a thickness of 4200 mm was formed by RF sputtering. The film forming conditions were substrate heating temperature 350 ° C., RF Power 1000 W (3.1 Watt / cm ² ), argon gas flow rate 90 sccm, nitrogen gas flow rate 10 sccm, and pressure 0.5 Pa. Further, amorphous i-Si and phosphorus-doped n ⁺ -Si were formed on this insulating layer as needed by CVD. The film formation conditions for i-Si (non-doped Si film) were a substrate heating temperature of 200 ° C., RF Power 100 W (0.31 Watt / cm ² ), SiH ₄ flow rate (10% argon gas dilution) 300 sccm, and a thickness of 2000 mm. The deposition conditions of nitrogen-added n ⁺ -Si (P (phosphorus) doped film) are: substrate heating temperature 200 ° C., RF Power 100 W (0.31 Watt / cm ² ), SiH ₄ flow rate (8% argon gas dilution) 300 sccm, An n ⁺ -Si layer having a PH ₃ flow rate (diluted with 8% argon gas) and a thickness of 50 sccm and a thickness of 500 mm was formed.

Thereafter, an Al-based alloy film having the same composition as that first formed on the glass substrate was formed on the n ⁺ -Si layer with a thickness of 2000 mm. At this time, an Al—Ni—B—N alloy layer was formed to a thickness of 100 μm on the n ⁺ —Si layer, and an Al—Ni—B alloy layer was formed to a thickness of 1900 μm thereon. The film forming conditions of the Al—Ni—B—N alloy layer are as follows. Nitrogen gas is introduced into the argon gas at the time of sputtering, and the actual nitrogen flow rate is 0 with respect to the total gas actual flow rate (argon gas actual flow rate + nitrogen actual flow rate). It adjusted in the range of% -40%. Further, the Al—Ni—B alloy layer formed thereon was performed under the same conditions as in the case of the gate wiring. The film forming conditions were the same as those for the gate wiring.

Then, a source wiring, a drain wiring, and an electrode were formed by photolithography. The photolithography conditions are the same as those for the gate wiring. At this time, after etching the Al-based alloy film, dry etching of the n ⁺ -Si layer was performed. Dry etching conditions were RF Power 50W, SF ₆ gas flow rate 30 sccm, and pressure 10 Pa. Thereafter, the resist was removed with a stripping solution (ST106: manufactured by Tokyo Ohka Kogyo Co., Ltd.).

Next, a passivation SiNx insulating film having a thickness of 2500 mm was formed, and only the gate, source, and drain electrode portions were exposed by dry etching. Dry etching conditions were RF Power 100W, SF ₆ gas flow rate 30 sccm, O ₂ gas flow rate 5 sccm, and pressure 10 Pa. Under the above conditions, a transistor having a channel width of 25 μm and a channel length of 5 μm was formed (see FIG. 5).

  About the evaluation sample produced as mentioned above, the on / off ratio of the switching characteristic of an element was measured by the 3 terminal method. Vg-Id measurement was performed using a B1500A apparatus manufactured by Agilent Technologies. The on / off ratio was calculated from the Id values at Vg = −10V and + 10V.

  Further, the refractive index was measured by forming an Al—Ni—B alloy layer having a thickness of 100 mm containing nitrogen on a glass substrate, and irradiating light with a wavelength of 589 nm on this surface to produce an ellipsometer (manufactured by ULVAC). ).

  Table 1 shows the evaluation results for the nitrogen content, refractive index, specific resistance, and diffusion heat resistance on / off ratio described above.

As shown in Table 1, when the amount of nitrogen introduced during sputtering (the actual nitrogen flow rate relative to the total gas actual flow rate) is 5% to 20%, the diffusion heat resistance is 250 ° C. or more, and the on / off ratio is 5 digits ( It was found that the on / off ratio when the on current was 10 ⁻⁵ A and the off current was 10 ⁻¹⁰ A was 5 digits or more. Further, it was found that when the nitrogen introduction amount is 10% to 18%, the diffusion heat resistance is 300 ° C. or more and the on / off ratio can be 6 digits. From this result, the nitrogen content of the Al—Ni—B—N alloy wiring material is preferably 2 × 10 ¹⁷ atoms / cm ³ to 8 × 10 ²¹ atoms / cm ³ , and 2.5 × 10 ¹⁸ atoms. / Cm ^{3 to} 7.7 × 10 ²¹ atoms / cm ³ was found to be more preferable. Furthermore, it has been found that the refractive index is preferably 1.9 or more. Since the refractive index of the AlN alloy is 1.46, it is considered that the nitrogen contained in the Al—Ni alloy of this example is very small.

TFT schematic sectional drawing. The conceptual graph which shows the nitrogen analysis result in the Al-Ni-B alloy film containing nitrogen by the secondary ion mass spectrometer. Photomicrograph of Si diffusion heat resistance evaluation. Photomicrograph of Si diffusion heat resistance evaluation. The plane conceptual diagram which shows the wiring structure of a TFT element.

Claims (5)

In a junction structure of an element comprising a semiconductor layer and an Al-Ni alloy layer that is directly joined to the semiconductor layer,
The Al—Ni-based alloy layer directly bonded to the semiconductor layer contains nitrogen at 2 × 10 ¹⁷ atoms / cm ³ or more and less than 9 × 10 ²¹ atoms / cm ³ . The element bonding structure according to claim 1, wherein the Al—Ni-based alloy layer has a refractive index of 1.9 or more on the bonding surface side. The element junction structure according to claim 1, wherein the semiconductor layer is made of amorphous n ⁺ -Si. The Al—Ni-based alloy contains 0.5 at% to 10 at% of Ni, according to any one of claims 1 to 3. 5. The device junction structure according to claim 1, wherein the Al—Ni-based alloy layer is a laminate of an Al—Ni-based alloy not containing nitrogen and an Al—Ni-based alloy containing nitrogen. .