JP2002083966A - Manufacturing method of thin-film transistor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a thin-film transistor, where a sufficient field-effect mobility is assured while degradation of reliability is suppressed. SOLUTION: An active layer is formed as a polysilicon film on a glass substrate. the active layer is hydrogenized for 20-180 seconds with a plasma hydrogen in an atmosphere of hydrogen concentration 90% or higher with a glass substrate at 300-420 deg.C. It is heated continuously at the glass substrate temperature at hydrogenization or higher for 60 seconds or longer. Thus the active layer to be a channel region of the thin-film transistor is appropriately hydrogenized. Sufficient field-effect mobility of the thin-film transistor is assured while degradation in reliability of the thin-film transistor characteristics is suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a thin film transistor having a channel region formed of a polysilicon film.

[0002]

2. Description of the Related Art Conventionally, this kind of polysilicon film (Pol)
y-Si) Thin Film Transistor
Generally, as shown in FIG. 4, in order to improve characteristics such as mobility increase or threshold value reduction, hydrogen plasma treatment is performed after device completion to fill defects in the channel region of the thin film transistor with hydrogen. .

The effect of terminating defects by hydrogenation is that diffusion of hydrogen in a gate insulating film of a thin film transistor as a first step and diffusion of hydrogen in a polysilicon film as a second step, ie, lateral diffusion There are two stages.

For this reason, as shown in FIG. 5, when the hydrogenation time of the channel region of the thin film transistor is short, the field-effect mobility with respect to the hydrogenation time hardly changes for the first fixed time, but only for a certain fixed time. Later, it gradually rises, and the absolute amount of hydrogen terminating the defect of the polysilicon film is small, so that the mobility cannot be sufficiently increased.

[0005] On the other hand, when the channel region is hydrogenated for an appropriate hydrogenation time, the lateral diffusion of hydrogen is sufficiently achieved, so that the field effect mobility is greatly increased. Furthermore, those having a sufficiently long hydrogenation time have sufficiently large field effect mobility because lateral diffusion occurs during hydrogenation.

As a result, by securing a certain hydrogenation time, a required amount of hydrogen accumulates in the polysilicon film,
It diffuses in this polysilicon film.

As shown in FIG. 6, a BTS (Bias Temperature Stres) is plotted against the hydrogenation time of the thin film transistor.
s) The threshold value (Vt) of this thin film transistor after the test
The shift amount of h) hardly changes when hydrogenation is performed within the first fixed time, and increases rapidly when hydrogenation is performed for a certain time or more, and the reliability of the characteristics of the thin film transistor is increased. Is greatly lost. It is considered that the characteristics are deteriorated by the BTS test due to excessive hydrogen in the polysilicon film.

The BTS test is a test for applying a voltage to the gate electrode of a thin film transistor and heating the thin film transistor to examine the characteristics of the thin film transistor, such as reliability and acceleration of deterioration.

[0009]

However, in the above-described thin film transistor, the hydrogenation process of the channel region is used to improve characteristics such as the improvement of the field effect mobility. Due to the defect between the channel region and the gate insulating film, sufficient hydrogenation time is required to reach the minimum value of the field effect mobility required for the thin film transistor,
There is a problem that excessive hydrogenation causes deterioration of the reliability of the characteristics of the thin film transistor in the BTS test due to excess hydrogen.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method of manufacturing a thin film transistor capable of securing sufficient field effect mobility and suppressing deterioration in reliability.

[0011]

SUMMARY OF THE INVENTION The present invention comprises a step of forming a polysilicon film on a substrate and a step of hydrogenating the polysilicon film, and using the polysilicon film as a channel region. In the method for manufacturing a thin film transistor, the step of performing hydrogenation is performed by plasma-forming the hydrogen in an atmosphere having a hydrogen concentration of 90% or more and the substrate temperature is 300 to 420 ° C for 20 to 180 seconds. After the completion of the hydrogenation, the substrate is continuously heated at a temperature not lower than the substrate temperature during the hydrogenation for not less than 60 seconds.

In this configuration, a polysilicon film is formed on a substrate, and hydrogen plasmanized in an atmosphere having a hydrogen concentration of 90% or more is subjected to hydrogen treatment at a substrate temperature of 300 ° C. to 420 ° C. for 20 seconds to After hydrogenating the polysilicon film for 180 seconds, the polysilicon film is appropriately hydrogenated by continuously heating the polysilicon film at a substrate temperature higher than the hydrogenation for 60 seconds or more. As a result, the polysilicon film becomes a channel region of the thin film transistor, so that a sufficient field effect mobility of the thin film transistor is secured, and deterioration of reliability of the thin film transistor characteristic is suppressed.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration of an embodiment of the liquid crystal display device of the present invention will be described below with reference to FIGS.

1 to 3, reference numeral 1 denotes a thin film transistor (Poly-Si TFT).
In (r)), the thin film transistor 1 constitutes an array substrate of a liquid crystal display (not shown). A counter substrate (not shown) is provided facing the array substrate, and a liquid crystal as a liquid crystal composition (not shown) is provided between the counter substrate and the array substrate.

The thin film transistor 1 is formed on a glass substrate 11 as an insulating substrate made of a translucent substantially transparent non-alkali glass (SiO 2). On one main surface of the glass substrate 11, an undercoat film 12 as an inorganic insulating film for preventing diffusion of impurities from the glass substrate 11, for example, 2.0 ×
The thickness is about 10-7 m.

Further, on the undercoat film 12,
The active layer 13 which is a polycrystalline silicon, that is, a silicon semiconductor layer formed of a polysilicon film is, for example,
About 10-8m, Plasma CVD (Chemical Vapor Dep.)
osition) method. This active layer 13
It is formed by melting amorphous silicon (a-Si: H) by excimer laser annealing and then crystallization. The active layer 13 has an RF application frequency of 40.
A channel region 14 formed by hydrogenation at 0 Hz to 54 MHz is provided.
Means that the active layer is heated at a temperature of 300 ° C. to 340 ° C. for 40 seconds to 1 hour.
After hydrogenation for 80 seconds, the active layer 13 is formed by heating the active layer 13 at a temperature higher than the temperature of the glass substrate 11 at the time of hydrogenation for 300 seconds or more in the same chamber (not shown) at the time of the hydrogenation.

The active layer 13 on one side of the channel region 14 is made of boron (B2HX +) or phosphorus (PHX
+) Is ion-doped to form (n)
(P type, p type) A source region 15 which is a Poly-Si region is formed. Further, similarly to the source region 15, the active layer 13 on the other side of the channel region 14 facing the source region 15 is made of boron (B2HX +) or phosphorus (PHX +)
Are ion-doped to form (n-type, p-type
(Type) A drain region 16 which is a Poly-Si region is formed.

On the active layer 13, a gate insulating film 17 which is an inorganic insulating film such as a silicon oxide film (SiOX) having an insulating property is formed by, for example, about 1.5 × 10 −7 m by a plasma CVD method. After being deposited, it is formed by patterning.

On the gate insulating film 17, an island-like gate electrode 18 having a thickness of, for example, 2.0 × 10 −7 m is formed.
Are formed. This gate electrode 18 is made of molybdenum-
It is formed by patterning after sputtering a tungsten alloy (MoW) or the like. Also,
The gate electrode 18 is electrically connected integrally to a scanning line (not shown). Then, on the gate insulating film 17 including the gate electrode 18, an interlayer insulating film 19 formed of a silicon oxide film (SiOX) or the like, for example, 5.0 × 10−
The film is formed to a thickness of about 7 m.

Further, an interlayer insulating film 19 and a gate insulating film
In 17, through holes 21 a and 21 b which are open to the source region 15 and the drain region 16 are formed, respectively. Aluminum (Al) is provided in these through holes 21a and 21b.
A source electrode 22 and a drain electrode 23 are formed by depositing a low-resistance metal such as molybdenum (Mo).

The source electrode 22 is connected to the source region 15 via a through hole 21a.
The drain electrode 23 is connected to the drain region 16 via the through hole 21b. Furthermore, these source electrodes 22
The drain electrode 23 is made of, for example, aluminum 3.0.
After depositing x10-7 m, molybdenum was 5.0x10
It is formed by patterning after sputtering in a state where -8 m is deposited.

A protective film (not shown) is formed on the interlayer insulating film 19, the source electrode 22, and the drain electrode 23, and a flattening film (not shown) is formed on the protective film. On the flattening film, pixel electrodes (not shown), which are transparent conductor layers, are arranged in a matrix.
This pixel electrode is connected to the source electrode 22 through a protective film and a planarizing film via a through hole (not shown).

Next, a method of manufacturing the thin film transistor according to the embodiment will be described.

First, on one main surface of a glass substrate 11, a silicon oxide film or the like is coated with an undercoat film 12 by a plasma CVD method.
Is formed.

Next, after an amorphous silicon thin film, that is, an amorphous silicon film is formed on the undercoat film 12 by a plasma CVD method or the like, the amorphous silicon film is polycrystallized by an excimer laser annealing method or the like. ,
This polycrystallized polysilicon film is etched into an island shape to form an active layer 13, the elements of each thin film transistor 1 are made independent, and a gate insulating film 17 is formed on the active layer 13 by plasma CVD.
It is deposited by the D method.

Further, a molybdenum film is formed on the gate insulating film 17.
The gate electrode 18 is formed by sputtering and patterning a tungsten alloy, and this gate electrode
The source region 15 is doped with ions using
And a drain region 16 are formed. Then, after the doped ions are activated by heating, hydrogenation described below is performed. Next, an interlayer insulating film 19 which is a silicon oxide film is formed on the gate insulating film 17 including the gate electrode 18.

Thereafter, an interlayer insulating film 19 and a gate insulating film
After opening through holes 21a and 21b in 17 and sputtering aluminum and molybdenum, patterning is performed to form a source electrode 22 and a drain electrode 23, thereby forming the thin film transistor 1.

Here, the hydrogenation step will be described in detail.

In a 100% hydrogen atmosphere chamber, a radio frequency (Radio Frequency) power of 2 kW, RF
The frequency is 13.56 MHz, the distance between the electrodes is about 17 mm,
Hydrogen flow rate 1000 sccm and reaction pressure 2.7 P
Under the conditions of a, the temperature of the glass substrate 11 was set to 380 ° C., the hydrogenation time was set to 80 seconds, and the plasma was stopped at the temperature at the time of hydrogenation.
Heat for 2 seconds. Note that the hydrogen atmosphere may be 90% or more.

Then, hydrogen by plasma accumulates in the active layer 13 by hydrogenation for 80 seconds. At this time, some hydrogen has caused lateral diffusion. Then, lateral diffusion without accumulation by hydrogen occurs in the subsequent holding time of 180 seconds, which contributes to the termination of the recess of the active layer 13.

At this time, if the hydrogenation time is short, the amount of hydrogen accumulated is small, so that the amount of hydrogen necessary for the termination cannot be sufficiently accumulated, and even if the retention time is extended, the hydrogenation termination effect is not sufficiently obtained. .

If the hydrogenation time is long, for example, about 200 seconds, the effect of termination by hydrogenation is satisfied, but since the amount of accumulation is large, the shift amount of the threshold value of the thin film transistor 1 becomes zero due to the influence of excess hydrogen. .5V or more, B
The reliability of the characteristics of the thin film transistor 1 is affected by the TS test.

Further, the speed of diffusion in the gate insulating film 17 and the speed of lateral diffusion are greatly affected by the temperature of the glass substrate 11, and are functions of the glass substrate 11.

As described above, according to the above-described embodiment, as shown in FIG. 1, when the hydrogenation time is short, the field-effect mobility with respect to the hydrogenation time hardly changes for the first fixed time. However, it gradually increases after a certain period of time. However, since the hydrogenation time is short, the absolute amount of hydrogen terminating the defects in the active layer 13 is small, so that the mobility cannot be sufficiently increased.

When the hydrogenation time is appropriate, the lateral diffusion of hydrogen is sufficiently increased as the heating time of the active layer 13 after the hydrogenation increases, so that the field-effect mobility is greatly increased.

Further, when the hydrogenation time is long enough,
Since lateral diffusion occurring during the heating time of the active layer 13 after the hydrogenation occurs during the hydrogenation time, the field effect mobility is sufficiently high from the beginning and does not largely depend on the heating time.

As a result, after the active layer 13 which is a polysilicon film is disposed on the insulating substrate 11 having a light transmitting property, the active layer 13 is kept at a temperature of 300 ° C. to 340 ° C. for 40 seconds to 180 seconds. After hydrogenation at 400 Hz to 54 MHz, the required amount of hydrogen diffuses into the active layer 13 by heating the hydrogenated active layer 13 at a temperature equal to or higher than the temperature of the glass substrate 11 at the time of hydrogenation for 300 seconds or more, Further, this hydrogen diffuses in active layer 13.

Therefore, the active layer 13 can be appropriately hydrogenated, and the active layer 13
Since the value is 14, by setting the hydrogenation conditions and the subsequent setting of the heating time, it is possible to secure a sufficient field effect mobility of the thin film transistor 1 and to suppress the deterioration in the reliability of the characteristics of the thin film transistor 1.

Further, since the active layer 13 is heated in the same chamber when the active layer 13 is hydrogenated, appropriate hydrogenation of the active layer 13 can be easily performed, so that the productivity of the thin film transistor 1 is improved. it can.

In the above embodiment, the active layer 13, which is a polysilicon film, is formed at a temperature of 300.degree.
After hydrogenation for 0 to 180 seconds, the glass substrate 11 at the time of hydrogenation
Although the configuration in which the channel region 14 is formed by heating at a temperature of 300 ° C. or more for 300 seconds or more has been described, the present invention is not limited to such a configuration, and a sufficient field-effect mobility of the thin film transistor 1 can be secured. Any configuration can be used as long as deterioration in the reliability of the characteristics can be suppressed.

For example, after the active layer 13 is hydrogenated at a temperature of 340 ° C. to 380 ° C. for 40 seconds to 120 seconds, the active layer 13 after hydrogenation is heated at a temperature equal to or higher than the temperature of the glass substrate 11 at the time of hydrogenation.
Even when heating for more than 80 seconds, the active layer
13 is hydrogenated at a temperature of 380 ° C. to 420 ° C. for 20 seconds to 100 seconds, and then the active layer 13 after the hydrogenation is heated at a temperature higher than the temperature of the glass substrate 11 at the time of hydrogenation for 60 seconds or more. Is also good. With such a configuration, the same operation and effect as those of the above-described embodiment can be obtained.

[0042]

According to the present invention, the substrate temperature is 300 ° C.
At 420 ° C., the polysilicon film formed on the substrate is hydrogenated for 20 seconds to 180 seconds with hydrogen plasmatized in an atmosphere having a hydrogen concentration of 90% or more. By heating the polysilicon film at a substrate temperature or higher for 60 seconds or longer, the polysilicon film can be appropriately hydrogenated. Therefore, a sufficient field effect mobility of the thin film transistor can be secured, and deterioration in reliability of the thin film transistor characteristics can be suppressed. .

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the heating time after hydrogenation and the field-effect mobility as a function of the hydrogenation time in one embodiment of the thin film transistor of the present invention.

FIG. 2 is a sectional view showing a part of the thin film transistor.

FIG. 3 is a top view showing a part of the thin film transistor.

FIG. 4 is a graph showing changes in characteristics of a conventional thin film transistor due to hydrogenation.

FIG. 5 is a graph showing the relationship between hydrogenation time and field-effect mobility in the thin film transistor at a plurality of substrate temperatures.

FIG. 6 shows hydrogenation time and BTS in the same thin film transistor.
It is a graph which shows the relationship with the shift amount of the threshold value in a test.

[Explanation of symbols]

 1 thin film transistor 11 glass substrate as substrate 13 active layer as polysilicon film 14 channel region

Continued on front page F-term (reference)

Claims (5)

[Claims] 1. A method for manufacturing a thin film transistor using a polysilicon film as a channel region, comprising: forming a polysilicon film on a substrate; and hydrogenating the polysilicon film. Is performed in an atmosphere having a hydrogen concentration of 90% or more, and the hydrogen is turned into plasma, and the substrate temperature is set to 300 ° C.
A method for producing the thin film transistor, wherein the heating is performed at a temperature not lower than the substrate temperature during the hydrogenation for 60 seconds or more after the hydrogenation is completed. . 2. The hydrogenation according to claim 1, wherein the substrate temperature is 300 ° C. to 3 ° C.
The heating is performed at 40 ° C. for 40 seconds to 180 seconds, and the heating time is 3 seconds.
2. The method according to claim 1, wherein the time is at least 00 seconds. 3. The method according to claim 1, wherein the hydrogenation is performed at a substrate temperature of 340.degree.
The heating is performed at 80 ° C. for 40 seconds to 120 seconds, and the heating time is 1
2. The method according to claim 1, wherein the time is 80 seconds or more. 4. The method according to claim 1, wherein the hydrogenation is performed at a substrate temperature of 380 ° C. to 4 ° C.
The heating is performed at 20 ° C. for 20 seconds to 100 seconds, and the heating time is 6 seconds.
2. The method according to claim 1, wherein the time is 0 second or more. 5. The method according to claim 1, wherein the hydrogenation and the heating are performed in the same chamber.