JPH02152278A - Manufacture of thin film semiconductor element - Google Patents

Abstract

PURPOSE:To prevent the scattering of VG-IDS characteristics among several transistors by making the roughness due to etching on an active layer surface smooth on the occasion of dry etching on a doping layer and stabilizing an interface between protetching and active layers. CONSTITUTION:After forming source and drain electrodes 16 and 17, a part of a doping layer 15 which is exposed between these electrodes is removed selectively by using the fore-going electrodes 16 and 17 as masks with a dry etching process where a fluorine-containing gas is used. After that, wet etching by the use of ammonium fluoride solution on the surface of an active layer 14 which becomes rough by etching makes the roughness on the surface of the active layer 14 smooth. Such a step stabilizes an interface between protecting and active layers 18 and 14 which are covered later on. When VG-IDS characteristics of respective transistors (for example 5 pieces) in a matrix array in which a plurality of this film transistors are formed are examined, it is obvious that they have superior characteristics which are free from scattering among several transistors.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Field of Application) The present invention relates to a method for manufacturing a thin film semiconductor device, and particularly to a method for manufacturing a thin film semiconductor device used for driving and switching active matrix liquid crystal devices, etc. It is related to the method.

(Prior Art) Conventionally, thin film semiconductor devices (for example, thin film transistors having an inverted staggered electrode structure) have been manufactured by the method shown in FIGS. 4(A) to 4(C).

First, a gate metal layer (e.g. Mo-T
After forming the gate electrode 2, a gate insulating film 3 is formed. Subsequently, an active layer and a doping layer made of amorphous silicon are sequentially formed, and after patterning these to form an island-shaped active layer 4 and a doping layer 5, an electrode material layer is deposited and photolithographically etched. The material layer is selectively etched using a resist pattern formed by the method as a mask to form a source electrode 6 and a drain electrode 7 (as shown in FIG. 4A). Next, source electrode 6
Then, the doped layer 5 between the drain electrodes 7 is removed by dry etching using a fluorine-based gas to form doped layers 5a and 5b separated from each other (as shown in FIG. 3B). Next, after performing a water washing process, a protective film 8 of SiNx or the like is formed to manufacture the thin film transistor shown in FIG.

Source electrode 6 in manufacturing the above-mentioned thin film transistor
In the process of removing the doped layer 5 between the drain electrodes 7, etching is performed to the surface of the active layer 3 made of amorphous silicon below the doped layer 5, so the etching selectivity between the doped layer 5 and the active layer 4 is improved. Dry etching is performed using a fluorine-based gas that can be used.

However, if the doped layer 5 is removed by such dry etching, the surface of the active layer 4 becomes rough as shown in FIG. If the protective film 8 is coated with such roughness on the surface of the active layer 4, the active layer 4 and the protective film 8
The interface becomes unstable, degrading transistor characteristics. That is, a matrix array is formed by forming a plurality of the transistors, and V of five transistors, for example. -I
When examining the DS characteristics, variations occur between individual transistors as shown in FIG. Like this c-Io
When a matrix array consisting of transistors with varying s-characteristics is incorporated for driving and switching of a liquid crystal display device, image unevenness occurs in the liquid crystal display.

(Problems to be Solved by the Invention) The present invention has been made to solve the above-mentioned conventional problems, and is to manufacture a thin film semiconductor element having good characteristics without variations in v61DS characteristics between individual transistors. It is intended to provide a method.

[Structure of the Invention] (Means for Solving the Problem) The present invention provides a structure in which a gate electrode, a gate insulating film, a gate insulating film, and a gate electrode are formed on a glass substrate.
In manufacturing a thin film semiconductor device in which an active layer made of amorphous silicon, a doped layer, a source electrode, and a drain electrode are sequentially formed, the doped layer portion exposed between them is exposed to a fluorine-based gas using the source electrode and drain electrode as a mask. A method for manufacturing a thin film semiconductor device, comprising the steps of: selectively removing the active layer by dry etching; and forming a protective film after smoothing the active layer surface roughened by the etching. be.

In order to smooth the surface of the active layer roughened by the above-mentioned etching, a method of wet etching using, for example, an ammonium fluoride solution, a hydrofluoric acid solution, or a mixed solution of hydrofluoric acid and nitric acid may be employed.

(Function) According to the present invention, after selectively removing the doped layer portion exposed between the source electrode and the drain electrode by dry etching using a fluorine-based gas using the source electrode and the drain electrode as masks, the active layer roughened by the etching is removed. By wet-etching the surface with an ammonium fluoride solution or the like to smooth the surface of the active layer, a thin film semiconductor element can be manufactured in which the interface between the protective film and the active layer to be coated subsequently is stabilized. As a result, it is possible to eliminate variations in the vG IDS characteristics of each element in a matrix array in which a plurality of semiconductor elements are formed, so that when the matrix array is incorporated as a drive or switch in a liquid crystal display device, good image display can be performed. Can be done.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

First, a gate metal layer made of a molybdenum-tantalum alloy was formed on a glass substrate 11 to form a gate electrode I2, and then a gate insulating film 13 made of, for example, 5IOx was formed by a plasma CVD method (see FIG. 1(A)). (Illustrated). Subsequently, after sequentially forming an amorphous silicon layer and an n-type amorphous silicon layer doped with phosphorus by plasma CVD, these amorphous silicon layers and n-type
The active layer 14 and the doped layer 15 were formed by patterning the amorphous silicon layer into an island shape (FIG. 3(B)).
(Illustrated).

Next, a molybdenum layer was sputter-deposited on the entire surface and patterned to form a source electrode 16 and a drain electrode I7 (as shown in FIG. 2C). Subsequently, using the source and drain electrodes 1B and 17 as a mask, the exposed portion of the doped layer 15 between the electrodes 16 and 17 was selectively removed by dry etching using CF4 and 02 gases. At this time, as shown in FIG. 2, which is an enlarged view of the doped layer portion, the surface of the active layer 14 below the doped layer 15 is etched;
This is to completely etch the surface. Also, at this time, doped layers L5a and 15b separated from each other were formed, but the etched surface of the active layer I4 became rough due to dry etching using a fluorine gas. This was followed by wet etching with ammonium fluoride solution. At this time, as shown in FIG. 1(D) and FIG. 3, which is a partially enlarged view of the same figure, the active layer 1 roughened by the etching is
4. The surface became smooth.

After that, a protective film 18 made of 5jNx is coated and the same figure (
A thin film transistor shown in E) was manufactured.

In this embodiment, the source electrode 1B and the drain electrode 1
After forming the electrodes 16 and 17, the portion of the doped layer 15 exposed between them as a mask is selectively removed by dry etching using a fluorine-based gas, and the surface of the active layer 14 roughened by the etching is then etched with fluorine. The subsequently applied protection 1i is smoothed by wet etching with an ammonium chloride solution to smooth the surface of the active layer 14.
! 1g and the active layer 14 can be stabilized. the result,
V of each transistor (for example, five) in a matrix array in which a plurality of such thin film transistors are formed. -I
When examining the D5 characteristics, as shown in FIG. 7, the transistors have good characteristics with no variation between individual transistors.

Although molybdenum-tantalum alloy was used as the gate electrode metal in the above embodiment, tantalum alone or other tantalum alloys may also be used.

In the above embodiment, 510x was used as the gate insulating film, but 5INx may also be used.

[Effects of the Invention] As detailed above, according to the method for manufacturing a thin film semiconductor device of the present invention, the etching roughness generated on the surface of the active layer during dry etching of the doped layer is smoothed and the interface with the protective film is stabilized. As a result, variations in vG 105 characteristics between individual transistors can be eliminated, and further, when incorporated as a driving or switching transistor in a liquid crystal display device, remarkable effects such as good image display can be achieved.

[Brief explanation of the drawing]

Figures 1 (A) to (E) are cross-sectional views showing the manufacturing process of a thin film transistor according to an embodiment of the present invention, and Figure 2 is an enlarged view of the main part showing the state after dry etching the doped layer using a fluorine-based gas. A sectional view, FIG. 3 is an enlarged sectional view of the main part showing the state after wet etching of the active layer surface after dry etching with an ammonium fluoride solution, and FIG. 4 (A)
- (C) are cross-sectional views showing the manufacturing process of a conventional thin film transistor, FIG. Figure 6 is a diagram showing the vc-tos characteristics of a 511M transistor when thin film transistors manufactured by the conventional method are used as a matrix array. FIG. 2 is a diagram showing V610s characteristics of several transistors. 11...Glass substrate, 12...Gate electrode, 13.
... Gate insulating film, 14... Active layer, 15... Doping layer, 16... Source electrode, 17... Drain electrode, 18... Protective film. Applicant's agent Patent attorney Takehiko Suzue (A) (B) Figure 1 Figure (E) Figure 3 Figure 3 VG Figure 6 VG (V) Figure 7

Claims (1)

[Claims] In manufacturing a thin film semiconductor device in which a gate electrode, a gate insulating film, an active layer made of amorphous silicon, a doping layer, a source electrode, and a drain electrode are sequentially formed on a glass substrate, the source electrode and the drain electrode are used as a mask. The method includes a step of selectively removing the doped layer portion exposed between the layers by dry etching using a fluorine-based gas, and a step of forming a protective film after smoothing the surface of the active layer roughened by this etching. A method for manufacturing a thin film semiconductor device, characterized by: