JP6893091B2 - Thin film transistor - Google Patents

Description

The present invention relates to a thin film transistor.

In recent years, as thin film transistors (TFTs (Thin-Film Transistor)) intended to be used for display drive elements and the like, oxide semiconductors containing indium, gallium, and zinc (indium gallium oxide zinc (In-Ga-Zn-O)). )) And other oxide semiconductors are attracting attention as channels (active layers). A TFT using In-Ga-Zn-O (hereinafter, IGZO-TFT) has a feature that it exhibits a ^{field effect mobility (10 cm 2 / Vs) that is 10 times or more higher than that of an amorphous silicon TFT.} (See, for example, Non-Patent Document 1).

Further, in recent years, in order to apply it to a large-area, high-definition display, a TFT having a mobility higher than that of the IGZO-TFT has been studied. For example, a TFT using zinc oxynitride (Zn—ON) (hereinafter, ZnON-TFT) is known to exhibit higher mobility than IGZO-TFT (for example, Non-Patent Document 2).

K.Nomura et al., Nature vol.432, p.488 (2004) M.Ryu et al., IEDM Tech.Dig. Vol.432, p.5.6.1 (2012)

By the way, ZnON-TFT, which exhibits high mobility, has a problem that the film quality is unstable and the electrical characteristics are liable to change with time.

Therefore, in a thin film transistor using a semiconductor containing Zn—ON as a main component as an active layer, it is an object of the present invention to provide a thin film transistor having improved stability of electrical characteristics while maintaining high field effect mobility. ..

The thin film transistor according to the embodiment of the present invention is arranged on a semiconductor layer containing at least zinc, oxygen, nitrogen, and silicon, a source disposed on the first surface of the semiconductor layer, and the first surface of the semiconductor layer. It is seen containing a drain set, a gate insulating film disposed on the first surface or the second surface of the semiconductor layer, and a gate connected to the semiconductor layer through the gate insulating film, the semiconductor The proportion of silicon contained in the layer is 0.3 atomic% or more and 5 atomic% or less .

In a thin film transistor using a semiconductor containing Zn—ON as a main component as an active layer, it is possible to provide a thin film transistor having improved stability of electrical characteristics while maintaining high field effect mobility.

It is sectional drawing which shows the thin film transistor 100 of an embodiment. It is a figure which shows the measurement result of the gate voltage-drain current characteristic of the TFT of the comparative example in which Si is not added to the semiconductor layer 140. It is a figure which shows the measurement result of the gate voltage-drain current characteristic of the thin film transistor 100 of Example 1. FIG. It is a figure which shows the measurement result of the gate voltage-drain current characteristic of the thin film transistor 100 of Example 2. It is a figure which shows the measurement result of the gate voltage-drain current characteristic of the thin film transistor 100 of Example 3. It is a figure which shows the measurement result of the gate voltage-drain current characteristic of the thin film transistor 100 of Example 4. It is a figure which shows the measurement result of the gate voltage-drain current characteristic of the thin film transistor 100 of Example 5. It is a figure which shows the measurement result of the gate voltage-drain current characteristic of the thin film transistor 100 of Example 6. It is a figure which shows the characteristic of the change amount (ΔVth) of the threshold voltage with respect to the DC power applied to the Si sputter target in the TFT of Comparative Example and Examples 1 to 6. It is a figure which shows the dependence of the electric field effect mobility with respect to the DC power applied to the Si sputter target in the TFT of Comparative Example and Examples 1 to 6. It is a figure which shows the analysis result by XPS. It is a figure which shows the analysis result by XPS.

Hereinafter, embodiments to which the thin film transistor of the present invention is applied will be described.

<Embodiment>
FIG. 1 is a cross-sectional view showing the thin film transistor 100 of the embodiment. In the following, the positional relationship will be described using the vertical relationship in FIG. 1, but this is merely a positional relationship for convenience of explanation and does not represent a universal positional relationship.

The thin film transistor 100 includes a substrate 110, a gate electrode 120, a gate insulating film 130, a semiconductor layer 140, a source electrode 150, and a drain electrode 160. As an example, the thin film transistor 100 is a bottom gate type and top contact type TFT. The thin film transistor 100 can be used, for example, for driving a display such as a liquid crystal or an organic EL (Electroluminescence).

The substrate 110 is, for example, a glass substrate, a silicon substrate, a resin (plastic) substrate, or the like, and various substrates can be used depending on the intended use. The gate electrode 120 is arranged on the surface of the substrate 110. The substrate 110 shown in FIG. 1 is a part of the whole, and is, for example, a simplified portion included in one pixel of the display.

The gate electrode 120 is arranged on the surface of the substrate 110. The gate electrode 120 can be manufactured by a conventional method for manufacturing a thin film transistor. The gate electrode 120 is, for example, a thin film made of molybdenum or aluminum. A gate insulating film 130 is laminated on the gate electrode 120.

The gate insulating film 130 is arranged on the gate electrode 120. The gate insulating film 130 can be manufactured by a conventional method for manufacturing a thin film transistor. The gate insulating film 130 is, for example, _{a thin film made of silicon oxide (SiO 2} ), and is provided to insulate the semiconductor layer 140 and the gate electrode 120 and apply the gate electrode to the semiconductor layer 140.

The semiconductor layer 140 is arranged on the gate insulating film 130. The semiconductor layer 140 can be manufactured by a conventional method for manufacturing a thin film transistor. The semiconductor layer 140 is, for example, a semiconductor layer containing at least zinc, oxygen, nitrogen, and silicon, and is an active layer in which channels are formed. In other words, such a semiconductor layer 140 is a semiconductor film containing Zn—ON (zinc nitride) as a main component.

Here, the notation Zn-ON of zinc nitride means that it is a compound containing zinc (Zn), oxygen (O), and nitrogen (N) in an arbitrary composition ratio (various composition ratios). To do. The semiconductor layer containing at least zinc, oxygen, nitrogen, and silicon is a semiconductor layer (oxide semiconductor layer) in which silicon is added to zinc oxynitride (Zn—ON).

The source electrode 150 and the drain electrode 160 are arranged on the semiconductor layer 140. The source electrode 150 and the drain electrode 160 can be manufactured by a conventional method for manufacturing a thin film transistor, and are made of, for example, molybdenum or aluminum.

Next, a method for producing a sample of the thin film transistor 100 will be described.

By performing thermal oxidation on a highly doped silicon substrate (110) that also serves as a gate electrode 120, a _{gate insulating film 130 composed of a thermal oxide film made of SiO 2} is formed to a thickness of 100 nm, and a gate insulating film is formed. A semiconductor layer (active layer) 140 having a thickness of 10 nm was formed on the 130 by co-sputtering using a Zn (zinc) sputtering target and a Si (silicon) sputtering target by a sputtering apparatus. Co-sputtering was performed in an atmosphere in which oxygen (O) and nitrogen (N) were added in addition to argon (Ar).

At that time, the value of the DC (Direct Current) power applied to the Si sputtering target was set in the range of 0W to 50W. The larger the value of DC power, the larger the amount of Si added to the semiconductor layer 140. As a result of RBS (Rutherford Backscattering) analysis, when the DC power was 30 W, the composition ratio of Si in the semiconductor layer 140 was 1.8 atomic%. When the DC power was 3 W, the composition ratio of Si was 0.3 atomic% (reference value because it was below the detection limit).

After the formation of the semiconductor layer 140, a heat treatment at 200 ° C. for 1 hour was carried out in the air using a hot plate. Then, a sample of the thin film transistor 100 (TFT) was prepared by forming the source electrode 150 and the drain electrode 160. The produced thin film transistor 100 has a bottom gate-top contact structure, a channel length of 80 μm, and a channel width of 520 μm.

Next, the result of measuring the electrical characteristics of the sample prepared as described above will be described. The gate voltage-drain current characteristics of the thin film transistor 100 (TFT) were measured using a semiconductor parameter analyzer on the manufacturing date (immediately after manufacturing), 2 months and 3 months after the manufacturing of the thin film transistor 100. For some samples, there is no data 2 months after the production date, only data on the production date and 3 months later.

FIG. 2 is a diagram showing the measurement results of the gate voltage-drain current characteristics of the TFT of the comparative example in which Si is not added to the semiconductor layer 140. The sputter film forming conditions of the semiconductor layer 140 are as follows.

Gas flow rate during film formation: Ar / O ₂ / N ₂ = 5 / 0.5 / 10 sccm
Pressure during film formation: 0.6Pa
Thickness of semiconductor layer (active layer) 140: 10 nm
Applied power: RF100W (Zn sputter target), DC0W (Si sputter target)
As shown in FIG. 2, the gate voltage-drain current characteristic of the TFT of the comparative example is good at the gate voltage at which the drain current rises at about -4 to about -3V on the manufacturing day, but two months after the manufacturing. After 3 months, it was found that the gate voltage at which the drain current rises decreased to about -10, the rise of the drain current became gentle, and the change with time was large.

FIG. 3 is a diagram showing the measurement results of the gate voltage-drain current characteristics of the thin film transistor 100 of Example 1. The sputter film forming conditions of the semiconductor layer 140 are as follows.

Gas flow rate during film formation: Ar / O ₂ / N ₂ = 5 / 0.5 / 10 sccm
Pressure during film formation: 0.6Pa
Thickness of semiconductor layer (active layer) 140: 10 nm
Applied power: RF100W (Zn sputter target), DC3W (Si sputter target)
As described above, in Example 1, silicon was added to the semiconductor layer 140 by applying 3 W of DC power to the Si sputtering target.

FIG. 4 is a diagram showing the measurement results of the gate voltage-drain current characteristics of the thin film transistor 100 of the second embodiment. The sputter film forming conditions of the semiconductor layer 140 are as follows.

Gas flow rate during film formation: Ar / O ₂ / N ₂ = 5 / 0.5 / 10 sccm
Pressure during film formation: 0.6Pa
Thickness of semiconductor layer (active layer) 140: 10 nm
Applied power: RF100W (Zn sputter target), DC5W (Si sputter target)
As described above, in Example 2, 5 W of DC power was applied to the Si sputter target to add silicon to the semiconductor layer 140.

FIG. 5 is a diagram showing the measurement results of the gate voltage-drain current characteristics of the thin film transistor 100 of Example 3. The sputter film forming conditions of the semiconductor layer 140 are as follows.

Gas flow rate during film formation: Ar / O ₂ / N ₂ = 5 / 0.5 / 10 sccm
Pressure during film formation: 0.6Pa
Thickness of semiconductor layer (active layer) 140: 10 nm
Applied power: RF100W (Zn sputter target), DC10W (Si sputter target)
As described above, in Example 3, 10 W of DC power was applied to the Si sputter target to add silicon to the semiconductor layer 140.

FIG. 6 is a diagram showing the measurement results of the gate voltage-drain current characteristics of the thin film transistor 100 of Example 4. The sputter film forming conditions of the semiconductor layer 140 are as follows.

Gas flow rate during film formation: Ar / O ₂ / N ₂ = 5 / 0.5 / 10 sccm
Pressure during film formation: 0.6Pa
Semiconductor layer (active layer) thickness: 10 nm
Applied power: RF100W (Zn sputter target), DC20W (Si sputter target)
As described above, in Example 4, 20 W of DC power was applied to the Si sputter target to add silicon to the semiconductor layer 140.

FIG. 7 is a diagram showing the measurement results of the gate voltage-drain current characteristics of the thin film transistor 100 of Example 5. The sputter film forming conditions of the semiconductor layer 140 are as follows.

Gas flow rate during film formation: Ar / O ₂ / N ₂ = 5 / 0.5 / 10 sccm
Pressure during film formation: 0.6Pa
Semiconductor layer (active layer) thickness: 10 nm
Applied power: RF100W (Zn sputter target), DC30W (Si sputter target)
As described above, in Example 5, silicon was added to the semiconductor layer 140 by applying a DC power of 30 W to the Si sputtering target.

FIG. 8 is a diagram showing the measurement results of the gate voltage-drain current characteristics of the thin film transistor 100 of Example 6. The sputter film forming conditions of the semiconductor layer 140 are as follows.

Gas flow rate during film formation: Ar / O ₂ / N ₂ = 5 / 0.5 / 10 sccm
Pressure during film formation: 0.6Pa
Semiconductor layer (active layer) thickness: 10 nm
Applied power: RF100W (Zn sputter target), DC50W (Si sputter target)
As described above, in Example 6, silicon was added to the semiconductor layer 140 by applying a DC power of 50 W to the Si sputtering target.

As shown in FIGS. 2 to 8, when the gate voltage is gradually increased from −20 V in a state where the drain voltage is fixed at 1 V, Examples 1 to 6 (FIG. 2) are compared with Comparative Example (FIG. 2). In FIGS. 3 to 8), it can be confirmed that the change with time after 2 months and 3 months of production is reduced. The source electrode 150 is grounded.

Further, comparing Examples 1 to 6 (FIGS. 3 to 8), when the DC power applied to the Si sputtering target is relatively low as 3W and 5W as in Examples 1 and 2 (FIGS. 3 and 4), Since the gate voltage at which the drain current rises is as low as -10 V or less, a very good sample cannot be obtained.

Further, when the DC power applied to the Si sputtering target is relatively high as 10W, 20W, and 30W as in Examples 3 to 5 (FIGS. 5 to 7), the gate voltage at which the drain current rises is about -8V to about. A value close to 0V of -4V was obtained, and a good sample was obtained.

In the case of Examples 3 to 5 (FIGS. 5 to 7), the change with time after 2 months and 3 months of production is very small, and in the case of Example 4 (Fig. 6: 20 W), the production date and production It can be confirmed that the values of the drain currents after 3 months are almost the same.

Further, when the DC power applied to the Si sputtering target is as high as 50 W as in Example 6 (FIG. 8), the drain current rises and the gate voltage at which the thin film transistor 100 is turned on becomes 0 V, which is about -4 V. Close values were obtained and good samples were obtained. Compared with Examples 3 to 5 (FIGS. 5 to 7), the decrease in drain current after 3 months of fabrication is slightly larger, so that the DC power applied to the Si sputtering target may be 50 W, but 10 W, 20 W, and 30 W. Turned out to be more suitable.

FIG. 9 is a diagram showing the characteristics of the amount of change (ΔVth) in the threshold voltage with respect to the DC power applied to the Si sputter target in the TFTs of Comparative Examples and Examples 1 to 6.

Here, when the drain voltage is 1 V, ^{the gate voltage when the drain current becomes 10-7} A is defined as the threshold voltage. The amount of change in the threshold voltage (ΔVth) was defined as the absolute value of the difference between the threshold voltage measured on the manufacturing date of the TFT and the threshold voltage measured 3 months after the manufacturing.

As can be seen from FIG. 9, the magnitude of the threshold voltage change is such that Si is added as in Examples 1 to 6 as compared with the case where Si is not added (in the case of the comparative example where the DC power is 0 W). This made it smaller, and when the DC power was 20 W, the threshold voltage change was minimized.

FIG. 10 is a diagram showing the dependence of the field effect mobility on the DC power applied to the Si sputter target in the TFTs of Comparative Examples and Examples 1 to 6.

When the DC power applied to the Si sputter target is up to 3W, 5W, 10W, and 20W, the field effect mobility higher than that when Si is not added (0W) is obtained, and when Si is not added at 30W ( The field effect mobility was almost the same as 0W), and in the case of 50W, the field effect mobility was less than that when Si was not added (0W). In the cases of Examples 1 and 2 (DC power is 3W, 5W), the field effect mobility is high, but since the date voltage at which the drain current rises is -10 or less, the operating characteristics and the field effect mobility are It was found that a well-balanced sample with DC power of 10 W, 20 W, and 30 W is preferable.

FIG. 11 is a diagram showing analysis results by XPS (X-ray Photoelectron Spectroscopy). In FIG. 11, the horizontal axis represents the binding energy (eV) and the vertical axis represents the signal strength (arbitrary scale).

Here, the amount of oxygen-based bonds contained in the semiconductor layer 140 between the TFT of Comparative Example (without Si addition) and the TFT (Thin Film Transistor 100) of Examples 3, 5 and 6 (DC powers 10W, 30W, 50W). Was measured.

In FIG. 11, the solid line shows the signal strength of Si—O and the metal (metal-OH) to which a hydroxyl group (OH: hydroxyl group) is bonded, the alternate long and short dash line shows the signal strength of Zn—O, and the fine solid line shows the signal strength. The sum of the solid line (signal strength of Si—O and the like) and the alternate long and short dash line (signal strength of Zn—O) is shown, and the thin broken line represents the measured value. In FIG. 11, the signal strength of Si—O and the like is mainly examined. Values other than the measured values can be obtained by fitting a Gauss-Lorentz type composite function or the like to the measured values by the least square method or the like.

Si—O is a bond between silicon and oxygen, and includes those having a composition ratio other than 1: 1. The metal-OH is a bond between a metal and a hydroxyl group, and includes those having a composition ratio other than 1: 1. Zn—O is a bond between zinc and oxygen, and includes those having a composition ratio other than 1: 1.

As shown in FIG. 11, when Si was not added (comparative example) and the DC power was 10 W, the signal strength of the oxygen system was substantially the same. The DC power of 10 W corresponds to 0.7 atomic% of Si.

Further, it was found that the signal strength of the oxygen system was clearly increased in the case of DC powers of 30 W and 50 W, and the signal strength was higher in the case of 50 W than in the case of 30 W. The DC power of 30 W corresponds to 2.7 atomic% of Si, and the DC power of 50 W corresponds to 4.3 atomic% of Si.

From the above, when performing sputtering for forming a semiconductor layer 140 containing Zn—ON as a main component, argon gas to which oxygen and nitrogen are added is used by using a Zn sputtering target and a Si sputtering target. By doing so, it was confirmed that Si can be added to the semiconductor layer 140 in the form of Si—O.

FIG. 12 is a diagram showing the analysis results by XPS. In FIG. 12, the horizontal axis represents the binding energy (eV) and the vertical axis represents the signal strength (arbitrary scale).

Here, the amount of nitrogen bonds contained in the semiconductor layer 140 between the TFT of Comparative Example (without Si addition) and the TFT (Thin Film Transistor 100) of Examples 3, 5 and 6 (DC powers 10W, 30W, 50W) is determined. It was measured.

In FIG. 12, the solid line indicates the signal strength of Si—N, the alternate long and short dash line indicates the signal intensity of Zn—N, and the fine solid line indicates the solid line (signal intensity of Si—N) and the alternate long and short dash line (Zn—N signal intensity). ) Is shown, and the dashed line represents the measured value. In FIG. 12, the signal strength of Si—N is mainly examined. Other than the measured values, it can be obtained by fitting a Gauss-Lorentz type composite function or the like to the measured values by the minimum squared method or the like.

In addition, Si—N is a bond of silicon and nitrogen, and includes those having a composition ratio other than 1: 1 and the composition ratio is an arbitrary value. Zn—N is a bond of zinc and nitrogen, and includes those having a composition ratio other than 1: 1, and the composition ratio is an arbitrary value.

As shown in FIG. 12, the signal strength of Si—N is zero when no Si is added (comparative example), but when the DC power is 10 W, the signal strength of Si—N is as shown in the enlarged view on the right. The signal strength is increasing. The DC power of 10 W corresponds to 0.7 atomic% of Si.

Further, it was found that the signal strength of Si—N was further increased in the case of DC powers of 30 W and 50 W, and the signal strength was higher in the case of 50 W than in the case of 30 W. The DC power of 30 W corresponds to 2.7 atomic% of Si, and the DC power of 50 W corresponds to 4.3 atomic% of Si.

From the above, when performing sputtering for forming a semiconductor layer 140 containing Zn—ON as a main component, argon gas to which oxygen and nitrogen are added is used by using a Zn sputtering target and a Si sputtering target. By doing so, it was confirmed that Si can be added to the semiconductor layer 140 in the form of Si—N.

By adding Si to the semiconductor layer 140 in the form of Si—O and Si—N, the time-dependent change (deterioration) of Zn-ON can be significantly suppressed, and the change over time (deterioration) is small and stable. It was found that the semiconductor layer 140 can be produced. As described above, the stable semiconductor layer 140 with little aging (deterioration) maintains high field effect mobility for a long period of time.

Therefore, according to the embodiment, a thin film transistor capable of maintaining high field effect mobility for a long period of time and improving the stability of electrical characteristics while using a semiconductor containing Zn—ON as a main component for the active layer. 100 can be provided.

Further, when a semiconductor containing Zn—ON as a main component is used for the semiconductor layer 140, the threshold voltage of the TFT tends to decrease particularly when aging (deterioration) occurs (see FIG. 2).

However, by adding an appropriate amount of Si, the threshold voltage of the thin film transistor 100 using the semiconductor containing Zn—ON as the main component in the semiconductor layer 140 can be suppressed to a value close to 0V. In other words, by adding an appropriate amount of Si, it is possible to suppress a change in the threshold voltage of the thin film transistor 100 using a semiconductor containing Zn—ON as a main component in the semiconductor layer 140.

The silicon contained in the semiconductor layer 140 is preferably 0.3 atomic% or more. Further, the silicon is more preferably 0.3 atomic% or more and 5 atomic% or less.

In the above description, the thin film transistor 100 is a bottom gate type and a top contact type TFT, but the thin film transistor 100 is not limited to such a type of TFT. For example, it may be a top gate type TFT having a gate insulating film and a semiconductor layer in order under the gate electrode, or a bottom contact type TFT in which the source electrode and the drain electrode are under the semiconductor layer.

Although the thin film transistor according to the exemplary embodiment of the present invention has been described above, the present invention is not limited to the specifically disclosed embodiment and can be various without departing from the scope of claims. Can be transformed and changed.

100 Thin film transistor 110 Substrate 120 Gate electrode 130 Gate insulating film 140 Semiconductor layer 150 Source electrode 160 Drain electrode

Claims (4)

With a semiconductor layer containing at least zinc, oxygen, nitrogen, and silicon,
A source disposed on the first surface of the semiconductor layer and
A drain disposed on the first surface of the semiconductor layer and
A gate insulating film disposed on the first surface or the second surface of the semiconductor layer, and
Look including a gate connected to the semiconductor layer through the gate insulating film,
A thin film transistor in which the proportion of silicon contained in the semiconductor layer is 0.3 atomic% or more and 5 atomic% or less. The thin film transistor according to claim 1, wherein the semiconductor layer further contains silicon nitride. The thin film transistor according to claim 2, wherein the semiconductor layer further contains silicon oxide. The thin film transistor according to claim 1 or 2, wherein the proportion of silicon contained in the semiconductor layer is 0.7 atomic% or more and 2.7 atomic% or less.

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