JPH0815216B2 - Method for manufacturing amorphous silicon thin film transistor - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to a method for manufacturing an amorphous silicon thin film transistor. In particular, in the method for manufacturing an amorphous silicon thin film transistor in which a triple layer of a high-concentration n-type hydrogenated amorphous silicon film, a titanium film, and an aluminum film is used as a source / drain electrode / wiring, the above-mentioned titanium film etching step is performed. Regarding improvements made easily and at high speed.

(2) Background of the technology A switching element for driving a flat panel display device such as a liquid crystal display, an electroluminescence display, an electrochromic display, a plasma display, etc., has the above flat surface on an insulating substrate on which the above flat display device is formed. A thin film transistor manufactured by using mainly the same manufacturing technique (vacuum evaporation method, sputtering method, plasma CVD method, etc.) as the method used for manufacturing a display device is used. It is desirable to form the above flat display device on an amorphous insulating substrate such as a glass plate, but it is difficult to form a semiconductor crystal on such an amorphous substrate, and the semiconductor crystal layer is formed as an operating layer. This is because it is difficult to integrally form a normal transistor with the above flat display device.

By the way, in a thin film transistor, the interface between the source / drain electrode and the operating layer is used as a blocking contact, and the source / drain electrode and the operating layer have ohmic contact with electrons but are non-conducting with respect to holes. Need to be kept. Therefore, there is a thin film transistor having a structure shown in FIG. 1 in which the source / drain electrodes / wirings are triple layers of a high-concentration n-type hydrogenated amorphous silicon film, a titanium film, and an aluminum film. In the figure, 1 is a glass substrate, 2 is a gate electrode made of a metal film such as a chrome film, 3 is a gate insulating film made of a silicon nitride film, and 4 is an n-type impurity of 10 ¹⁶ cm ⁻³ or less. An operating layer made of a hydrogenated amorphous silicon film containing a low concentration,
5 and 6 are high-concentration n-type hydrogenated amorphous silicon films 7
And a source / drain electrode / wiring formed of a triple layer of the titanium film 8 and the aluminum film 9.

(3) Prior Art and Problems In the method according to the prior art for manufacturing the thin film transistor having the above structure, the etching of the above triple layer is (a) dissolving the aluminum film 9 with hot phosphoric acid at about 50 ° C. And (b) a step of dissolving the titanium film 8 with hot phosphoric acid at about 200 ° C., and (c) a high-concentration n-type hydrogenated amorphous silicon film 7 with tetrafluoromethane (CF).
₄ ) and etching using a plasma etching method using a mixed gas of oxygen as a reactive gas.

By the way, of the above steps (a), (b) and (c), there are no problems in (a) and (c), but (b)
In the above process, the etching rate is extremely slow at about 200 Å / min, and the high temperature causes severe damage to the etching mask. Therefore, it is necessary to use a high temperature resistant resist mask to maintain patterning accuracy. is there.

Further, titanium can be chemically etched even with a mixed solution of nitric acid and hydrofluoric acid. Therefore, as a method for etching the titanium film 8, instead of the chemical etching method using hot phosphoric acid, nitric acid and hydrofluoric acid are used. A chemical etching method using a mixed solution can also be used, but the etching rate is extremely high at about 1,000Å / sec even at room temperature, and the high-concentration n-type hydrogen forming the lower layer is used. Since the etching rates of the hydrogenated amorphous silicon film 7 and the low-concentration n-type hydrogenated amorphous silicon film 4 are about the same, control becomes extremely difficult, and this method is practically unusable.

In short, there is no suitable etching method for the titanium film forming the triple layer as described above, which is a bottleneck in the method for manufacturing the amorphous silicon thin film transistor shown in FIG.

(4) Object of the Invention The object of the present invention is to eliminate this drawback, and a source / layer structure comprising a triple layer of a high-concentration n-type hydrogenated amorphous silicon film, a titanium film, and an aluminum film.
It is an object of the present invention to provide a method for manufacturing an amorphous silicon thin film transistor having a drain electrode, which has an advantage that etching of the titanium film can be easily performed at an appropriate speed with high patterning accuracy and easily.

(5) Structure of the Invention According to the structure of the present invention, a gate electrode is formed on an insulating substrate, a gate insulating film is formed on the insulating substrate so as to cover the gate electrode, and hydrogenation is performed on the gate insulating film. An operating layer made of an amorphous silicon film is formed, a triple layer of a high-concentration n-type hydrogenated amorphous silicon film, a titanium film, and an aluminum film is formed on the operating layer, and the triple layer is patterned to form a source. In the method for manufacturing an amorphous silicon thin film transistor in which a drain electrode / wiring is formed, in the patterning step of the triple layer, 1 to 8% of hydrofluoric acid with respect to ammonium fluoride and ammonium fluoride and 10 to with hydrofluoric acid are used. Amorphous silicon thin film transistor comprising a step of chemically etching the titanium film using a mixed aqueous solution containing 80% nitric acid. Lies in the way of production.

It is well known that a mixed aqueous solution of hydrofluoric acid and ammonium fluoride is used as an etchant for silicon dioxide, but this mixed aqueous solution is water-repellent and has no ability to etch silicon. Further, it is known that a mixed solution of nitric acid and hydrofluoric acid functions as a high speed etchant for titanium as described above.

Therefore, the idea is to mix the above two kinds of etchants to obtain an etchant that functions as an etchant for titanium but has water repellency for hydrogenated amorphous silicon and does not function as an etchant. Then, the experiment was repeated by changing the mixing ratio variously.

First, hydrofluoric acid _{(HF40%, H 2 O60%} ) 20cc and ammonium fluoride _{(NH 4 F50%, H 2} O50%) on a standard silicon dioxide etchant containing a 225cc water 685Cc, mixing ratio hydrofluoric acid Mix nitric acid to 0-10%,
When a 000Å thick titanium film was etched at a temperature of 40 ° C, most of the titanium film was etched in about 20 seconds (50
(Å / sec), but needle-like residue remained in the direction parallel to the film.
After that, etching was continued for another 5 minutes, but the needle-like residue did not disappear. Repeating the same experiment with increasing nitric acid mixture ratio, the mixture ratio of nitric acid to hydrofluoric acid becomes
At 10 to 80%, the titanium film could be etched without leaving the above needle-shaped residue. When the mixing ratio of nitric acid to hydrofluoric acid was further increased, the etching rate gradually decreased, and the etching rate of 100% nitric acid was zero. The optimum condition is 25 to 50% within the above range of the mixing ratio of 10 to 80%. In this optimum range, the etching rate is about 67Å / sec, side etching is not recognized, and the width is It was confirmed that it is possible to form a fine pattern of about 10 μm. The new etchant (mixed aqueous solution of hydrofluoric acid, ammonium fluoride and nitric acid) does not function as an etchant for hydrogenated amorphous silicon regardless of the above mixing ratio.
It was confirmed to have excellent selectivity.

(6) Embodiment of the Invention Hereinafter, a method of manufacturing an amorphous silicon thin film transistor according to an embodiment of the present invention will be further described with reference to the drawings.

See Fig. 2. On the glass substrate 1, a chrome film is vapor-deposited to a thickness of about 1,000 Å, and this is deposited by photolithography.
The gate 2 is formed by removing the gate 2 except the region where the gate electrode and the gate wiring are formed.

A silicon nitride (SiN) film is formed thereon to a thickness of about 3,000Å to form the gate insulating film 3. This process is
300 ℃, using argon or hydrogen as carrier gas with an equal amount of mixed gas of ammonia and monosilane as reactive gas
It is possible to use the plasma CVD method with a substrate temperature of about 10 ^-1 Torr and a radio frequency in a vacuum.

That is, the hydrogenated amorphous silicon film 4 containing n-type impurities at a low concentration of about 10 ¹⁶ cm ^-3 or less has a thickness of 1,000 to 3,0.
Form around 00Å. This process uses monosilane (SiH ₄ )
It is possible to use a plasma CVD method in which argon and hydrogen are used as carrier gases with phosphine (PH ₃ ) as a reactive gas.

A hydrogenated amorphous silicon film 7 containing n-type impurities at a high concentration of about 10 ¹⁸ cm ^-3 is formed to a thickness of about 200 to 300 Å. This step can also be performed by the same method as above.
Then, the titanium film 8 is deposited to a thickness of about 1,000Å, and further the aluminum film 9 is deposited to a thickness of about 500Å.

See FIG. 3. An etching mask (not shown) made of a photoresist film is formed on the source / drain electrode / wiring formation area (area excluding the area facing the gate 2 and the area unnecessary as the source / drain wiring). Then, the aluminum film 9 is chemically etched using hot phosphoric acid at about 50 ° C.

1-8% hydrofluoric acid for 100% ammonium fluoride
The titanium film 8 is chemically etched at a temperature of 40 [deg.] C. using a mixed aqueous solution obtained by mixing 25 to 50% nitric acid with respect to the hydrofluoric acid to the mixed mixed aqueous solution as an etchant.

In this chemical etching process, the etching rate is 50 Å / sec or more, which is sufficiently fast, and the etching temperature is as low as 40 ° C. Even if a normal resist mask is used, the etching mask is not damaged. It is possible to realize as much patterning as possible.

Then, an etching mask is formed again in the same region, and the high concentration n-type hydrogenated amorphous silicon film 7 is etched by the plasma etching method using methane tetrafluoride (CF ₄ ) and oxygen. Source / drain electrodes 51 and 61 are formed. At this time, the low-concentration n-type hydrogenated amorphous silicon film 4, which is the lower layer of the high-concentration n-type hydrogenated amorphous silicon film 7, is tetrafluoromethane (CF ₄ ).
Since the etching rate is extremely slow (about 1/5) with respect to the plasma etching method using, it is possible to obtain good control accuracy.

(7) Effects of the Invention As described above, according to the present invention, an amorphous silicon thin film transistor having a source / drain electrode composed of a triple layer of a high concentration n-type hydrogenated amorphous silicon film, a titanium film and an aluminum film. In the above manufacturing method, it is possible to provide a manufacturing method of an amorphous silicon thin film transistor which has an advantage that the above-mentioned titanium film can be easily etched at an appropriate speed with high patterning accuracy.

[Brief description of drawings]

FIG. 1 is a sectional view of an amorphous silicon thin film transistor having a source / drain electrode / wiring formed of a triple layer of a high-concentration n-type hydrogenated amorphous silicon film, a titanium film, and an aluminum film. 2 and 3 are cross-sectional views of the amorphous silicon thin film transistor according to the embodiment of the present invention after completion of main manufacturing steps. 1 ... Glass substrate, 2 ... Gate (chrome film), 3 ...
Gate insulating film (silicon nitride film), 4 ... Hydrogenated amorphous silicon film (operating layer), 5, 6 ... Source / drain electrode / wiring, 7 ... High concentration n-type hydrogenated amorphous silicon film, 8 ... … Titanium film, 9… Aluminum film, 51, 61… Source / drain electrodes.

Claims (1)

[Claims] A gate electrode is formed on an insulating substrate, a gate insulating film is formed on the insulating substrate so as to cover the gate electrode, and an operating layer made of a hydrogenated amorphous silicon film is formed on the gate insulating film. And forming a triple layer of a high-concentration n-type hydrogenated amorphous silicon film, a titanium film, and an aluminum film on the operating layer, and patterning the triple layer to form a source / drain electrode / wiring. In the method for manufacturing an amorphous silicon thin film transistor, the triple layer patterning step includes ammonium fluoride, 1-8% hydrofluoric acid with respect to ammonium fluoride, and 10-80% nitric acid with respect to hydrofluoric acid. A method of manufacturing an amorphous silicon thin film transistor, comprising the step of chemically etching the titanium film using a mixed aqueous solution.