JPH065862A - Production of thin film transistor - Google Patents

Abstract

PURPOSE:To form a thin channel area with excellent controllability and uniformity by single semiconductor layer. CONSTITUTION:Oxygen ions are implanted by ion implantation in a prescribed thickness part at the bottom plane in the channel forming area 2a of a polysilicon layer 2 and the oxygen ion implanted part is changed to be an oxide film 5 by annealing. Then, only the top plane part in the channel forming area 2a is left as a polysilicon part, which forms a thin channel area 6. Since the semiconductor layer uses only the single polysilicon layer 2, the problems due to the usage of a plurality of semiconductor layers are settled. Since the oxygen ions are accurately implanted at the prescribed part by ion implantation, the channel area 6 is thinly formed with excellent controllability and uniformity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a thin film transistor.

[0002]

2. Description of the Related Art In a thin film transistor, a channel region is formed thinner than a source / drain region as one method for increasing the electric field strength to improve the mobility. In that case, as a conventional manufacturing method, first, a first semiconductor layer having a predetermined thickness is formed on a substrate, and then a portion corresponding to a channel formation region in a central portion of the first semiconductor layer is entirely etched. After that, a thin second semiconductor layer is formed on the surface of the etching-removed portion and the remaining first semiconductor layer on both sides of the removed portion.
Annealing is performed to bring the interface between the semiconductor layer and the second semiconductor layer into a good state. According to this method, the channel region is thinly formed only by the second semiconductor layer, and the source / drain regions on both sides thereof are thickly formed by the first and second semiconductor layers.

[0003]

However, in the conventional manufacturing method as described above, the step coverage is formed when the second semiconductor layer is formed on the etching-removed portion of the first semiconductor layer and the remaining first semiconductor layer. In addition, since the first semiconductor layer and the second semiconductor layer are not continuously grown, there is a problem in uniformity of film quality of the semiconductor layer. Furthermore, even if annealing is performed, the first surface of the first semiconductor layer is not
There is a problem that the interface between the semiconductor layer and the second semiconductor layer is not always in a good state. Since the probability of the occurrence of localized levels increases from these problems, the above conventional method has a problem that it may affect the deterioration of the characteristics of the transistor. Further, the above conventional method has a problem that the uniformity is not so good when the channel region is formed thin at a plurality of locations on the same substrate at the same time.

An object of the present invention is to provide a method of manufacturing a thin film transistor in which a channel region can be formed thin with good controllability and uniformity using only a single semiconductor layer.

[0005]

According to the present invention, oxygen ions are implanted into a predetermined portion of a channel formation region of a semiconductor layer in a film thickness direction, and then annealing treatment is performed to convert the oxygen ion implanted portion into an oxide film. Thus, the channel region is formed in a portion of the channel forming region excluding the oxide film.

[0006]

According to the present invention, the channel region can be formed thin with only a single semiconductor layer by utilizing the conversion of the oxide film by the implantation of oxygen ions and the annealing. And, since only a single semiconductor layer is used, there are problems when using multiple semiconductor layers, that is, the problem of step coverage of the semiconductor layer, the problem of uniformity of the film quality of the semiconductor layer, and the problem of the interface of the semiconductor layers. Can be wiped out. Further, since oxygen ions can be accurately injected into a predetermined portion in the channel forming region by ion implantation and a desired portion can be accurately converted into an oxide film, a thin channel region can be formed with good controllability and uniformity.

[0007]

1 to 6 are sectional views showing an embodiment of the present invention in the order of manufacturing steps. An embodiment of the present invention will be described in detail below with reference to these drawings. A substrate 1 shown in FIG. 1 is a silicon substrate whose surface is converted into an oxide film (insulating layer) by thermal oxidation. First, the polysilicon layer 2 is patterned on the substrate 1. Next, a photoresist 3 is formed on the polysilicon layer 2 as shown in FIG.
Apply. Then, the photoresist 3 is exposed and developed to form a photoresist pattern 3a on the surface of the polysilicon layer 2 other than the channel formation region 2a, as shown in FIG. next,
Oxygen ions ( ¹⁶ O ⁺ ) 4 are ion-implanted into the channel formation region 2a of the polysilicon layer 2 using the photoresist pattern 3a as a mask. At this time, the acceleration energy is controlled so that the oxygen ions 4 are implanted into the channel forming region 2a of the polysilicon layer 2 at a predetermined thickness on the lower surface side. After that, as shown in FIG. 4, after removing the photoresist pattern 3a, thermal annealing treatment is performed in a nitrogen atmosphere to activate oxygen ions 4. Then, the channel forming region 2 of the polysilicon layer 2 is formed.
A portion of a having a predetermined thickness on the lower surface side into which the oxygen ions 4 are implanted is oxidized by the oxygen ions 4 and converted into an oxide film 5 as shown in FIG. As a result, only the upper surface side portion of the channel forming region 2a is formed of the polysilicon layer 2, and the channel region 6 thinner than the polysilicon layer 2 on both sides is formed in this upper surface side portion.

Thereafter, as shown in FIG. 6, a gate insulating film 7 is formed on the surface of the polysilicon layer 2 and the surface of the substrate 1. Further, a gate electrode 8 is formed on the gate insulating film 7 so as to correspond to the channel region 6. And
Impurity ions are implanted using the gate electrode 8 as a mask to form source / drain regions 9 in the polysilicon layer 2 on both sides of the channel region 6. further,
A passivation film 10 covering the gate electrode 8 and covering the entire surface.
To form. A contact hole 11 is opened in the passivation film 10 and the gate insulating film 7. Then, the source / drain electrodes 12 connected to the source / drain regions 9 through the contact holes 11 are formed to complete the thin film transistor.

In the above-described embodiment, oxygen ions 4 are implanted into a portion of the polysilicon layer 2 having a predetermined thickness on the lower surface side of the channel forming region 2a and the portion is converted into an oxide film 5. Since the thin channel region 6 is formed in the portion on the upper surface side of the channel forming region 2a excluding the film 5, the thin channel region 6 can be formed only by the single polysilicon layer 2. Therefore, there are no problems when using multiple semiconductor layers, that is, step coverage of semiconductor layers, uniformity of film quality of semiconductor layers, and interface of semiconductor layers. There is no impact on the decline. In addition, since the ion implantation of the oxygen ions 4 can be accurately performed on the predetermined thickness portion of the channel formation region 2a by controlling the acceleration energy, the desired portion can be accurately converted into the oxide film 5 and the thin channel with good controllability can be obtained. Area 6
Can be formed. Further, since there is little variation in the ion implantation, it is possible to form the thin channel regions 6 with good uniformity in the plurality of polysilicon layers 2 on the substrate 1 at the same time as described above. Further, in the above-described embodiment, since the oxide film 5 is provided below the thin channel region 6, it is possible to expect an effect of reducing or eliminating the back gate effect that occurs when a nitride film is used as the base film.

Although the above embodiment is for a high temperature process, it may be a low temperature process. In the case of the low temperature process, a glass substrate is used as the substrate 1, and an amorphous silicon layer is formed as a semiconductor layer formed on the glass substrate. Further, the annealing after the oxygen ion implantation is performed with a laser. Further, although the above-mentioned one embodiment is a case of manufacturing a top gate type thin film transistor, the present invention can be applied to a method of manufacturing a bottom gate type thin film transistor. In that case, a thin channel region is formed on the lower surface side of the semiconductor layer by implanting oxygen ions into the predetermined thickness portion on the upper surface side of the channel forming area of the semiconductor layer and converting the portion into an oxide film. To do.

[0011]

As described above, according to the present invention, a predetermined portion in the film thickness direction of the channel forming region of the semiconductor layer is selectively converted into an oxide film by implantation of oxygen ions and annealing, and this oxide film is formed. Since the thin channel region is formed in the other channel forming region portion, the channel region can be formed thin with good controllability and uniformity using only a single semiconductor layer. If a thin channel region can be formed with only a single semiconductor layer, the problems in the case of using a plurality of semiconductor layers can be eliminated, and the deterioration of transistor characteristics will not be affected.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a step of forming a polysilicon layer in an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a step that follows FIG. 1 in an embodiment of the present invention.

FIG. 3 is a cross-sectional view showing a step that follows the step of FIG. 2 in one embodiment of the present invention.

FIG. 4 is a cross-sectional view showing a step that follows FIG. 3 in one embodiment of the present invention.

FIG. 5 is a cross-sectional view showing a step that follows the step of FIG. 4 in one embodiment of the present invention.

FIG. 6 is a cross-sectional view showing a step that follows the step of FIG. 5 in one embodiment of the present invention.

[Explanation of symbols]

 2 polysilicon layer 2a channel forming region 4 oxygen ion 5 oxide film 6 channel region

Claims (1)

[Claims] 1. A method for implanting oxygen ions into a predetermined portion of a channel formation region of a semiconductor layer in a film thickness direction, and then performing annealing treatment to convert the oxygen ion implanted portion into an oxide film, thereby forming a portion of the channel formation region. A method of manufacturing a thin film transistor, wherein a channel region is formed in a portion excluding the oxide film.