JPH01194351A - Thin film semiconductor device - Google Patents

Abstract

PURPOSE:To make an operation speed of a driving TFT faster than that of a switching TFT without generating a ununiformity of a thin film and reducing the image quality, by making a second semiconductor thin film thicker than a first one which is formed on the same substrate where the second semiconductor thin film is formed. CONSTITUTION:About 30,000 pieces of switching TFTs (thin film transistors) 20 are arranged in the form of a matrix in an area 2 on a glass substrate 1 and about 3,000 pieces driving TFT's 30 are arranged in an area 3. Each of the TFTs 20 is a multi-crystal silicon film 200 formed on the substrate 1, having a gate electrode 5 on it with a gate film 4 put between. In a like manner, each of the TFTs 30 is a multi-crystal silicon film 300 formed on the substrate 1, having a gate electrode 5 on it with a gate film 4 put between. Each TFT 20 and 30 also have source areas 21 and 31, drain areas 22 and 32 and channel areas 23 and 33 respectively. By making the film 300 thicker than the film 200, the operation speed of the TFT 30 can be faster than that of the TFT 20 without injuring the uniformity of the characteristics of the TFTs 30 and without increasing the reverse leak current of the TFTs 20.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a thin film semiconductor device, and particularly to a semiconductor device formed in a matrix corresponding to each pixel and for switching each pixel, or The present invention relates to a thin film semiconductor device that is formed in a matrix and has a semiconductor device functioning as a photosensor and a semiconductor device for driving the semiconductor device on the same substrate.

(Prior art) In recent years, thin film transistors (hereinafter referred to as TPTs) have been formed using semiconductor thin films such as polycrystalline silicon formed at relatively low temperatures on transparent insulating substrates such as glass, and circuits are constructed using these TPTs. 2. Description of the Related Art Thin film semiconductor devices such as liquid crystal display devices are being actively developed.

In liquid crystal display devices, TPTs using amorphous silicon or polycrystalline silicon are formed in a matrix on the surface of a transparent glass substrate, and these TPTs are used as switching elements for each pixel to create an active matrix substrate for liquid crystal display devices. form.

However, TPTs using amorphous silicon or polycrystalline silicon have the drawbacks of lower field effect mobility and lower operating speed than transistors using single crystal silicon.

That is, compared to the field effect mobility of single crystal silicon, the field effect mobility of amorphous silicon is about one order of magnitude smaller.
The field effect mobility of polycrystalline silicon is reduced by about three orders of magnitude.

However, as the number of scanning lines increases as the display area becomes larger and the image quality becomes higher, the TPT is required to operate at a higher operating speed than before.

On the other hand, as display devices become smaller, more energy efficient, and more complex, TPTs for switching each pixel (hereinafter referred to as switching TPTs) and TPTs for switching
Research is also being actively conducted on a TPT active matrix substrate with a built-in drive circuit, which has a TPT for driving a TPT (hereinafter referred to as a driving TPT) on the same substrate.

In order to achieve high image quality and high definition in TPT substrates for liquid crystal display devices, it is necessary to improve the field effect mobility within the semiconductor thin film of the driving TPT. However, as described above, it has been confirmed that the field effect mobility of polycrystalline silicon is smaller than that of single crystal silicon, and becomes even smaller when the film thickness is 1000 Å or less.

Therefore, in order to achieve high image quality and high definition using polycrystalline silicon, it is required that the thickness of the polycrystalline silicon film of the driving TPT be approximately 800 Å or more.

However, in the switching TPT for switching each pixel of the liquid crystal in a liquid crystal display device, when the thickness of the semiconductor thin film is increased, a problem arises in that reverse leakage current increases and image quality deteriorates. Therefore, in the switching TPT, the thickness of the semiconductor thin film must be approximately 800 Å or less.

Furthermore, in a liquid crystal display device, in order to maintain accurate circuit operation timing, it is desirable that the operating speed of the switching TPT be slower than the operating speed of the driving TPT.

Therefore, in a thin film semiconductor device such as a liquid crystal display device in which a switching TPT and a driving TPT are formed on the same substrate, only the thickness of the semiconductor thin film constituting the driving TPT is increased, and the driving TPT is It is desirable to increase only the operating speed of.

As a means for reducing the field effect mobility as described above, as described in the specification of Japanese Patent Application No. 62-143136, the semiconductor thin film in the region where the field effect mobility is desired to be improved is heated. Techniques for recrystallizing the semiconductor thin film have been proposed.

(Problem to be solved by the invention) The above-mentioned conventional technology had the following problems.

In other words, when the area where you want to increase the operating speed is locally irradiated with a beam such as a laser beam and heated, the surface of the semiconductor thin film melts and the area recrystallizes. Since the lateral epitaxial growth effect does not occur, a uniform film quality cannot be obtained, and there is a problem in that the characteristics of 'rF T vary.

In addition, a technique has been proposed in which the entire substrate surface is recrystallized by scanning the beam uniformly over the entire surface of the substrate using beam scanning adjustment. It is difficult to crystallize, and there are also problems from the viewpoint of productivity.

The purpose of the present invention is to solve the above-mentioned problems, without impairing the uniformity of the semiconductor thin film, and further without increasing the reverse leakage current of the switching TPT.
An object of the present invention is to provide a thin film semiconductor device that can increase the operating speed of a driving TPT.

(Means for Solving the Problems) In order to solve the above problems, the present invention provides first and second semiconductor thin films formed on the surface of an insulating substrate; In a thin film semiconductor device comprising a switching TPT formed in a portion of the second semiconductor thin film and a driving TPT formed in a portion of the second semiconductor thin film for driving the switching TPT, the thickness of the second semiconductor thin film is is characterized in that it is made thicker than the first semiconductor thin film.

(Function) As the thickness of the semiconductor thin film increases, the field effect mobility increases, so when a thin film semiconductor element is formed using the semiconductor thin film, its operation speed improves compared to when the semiconductor thin film is thin. .

Therefore, as described above, by making the second semiconductor thin film thicker than the first semiconductor thin film, the uniformity of the characteristics of the driving TPT is not impaired, and furthermore, the switching TPT can be made thicker than the first semiconductor thin film. The operating speed of the driving TPT can be increased to the switching TP without increasing reverse leakage current.
The operating speed can be faster than that of T.

(Example) The present invention will be described in detail below with reference to the drawings.

FIG. 1 is a plan view of a TPT substrate for a liquid crystal display device incorporating a driving circuit according to an embodiment of the present invention.

1 is a transparent insulating substrate, and in this embodiment, a glass substrate is used. 2 indicates an area in which TPTs for switching each pixel are formed in a matrix, and approximately 3
Tens of thousands of TPTs are arranged. 3 indicates a region where TPTs for driving the switching TPTs are formed, and about 3,000 TPTs are arranged.

FIG. 2 is a sectional view taken along line A-A in FIG.
(a) is an enlarged sectional view of the driving TFT 30, and (b) is an enlarged sectional view of the driving TFT 30.
) is an enlarged sectional view of the switching TFT 20.

In the figure, a polycrystalline silicon film 200 with a thickness of 500 and a polycrystalline silicon film 300 with a thickness of 1000 are formed on the surface of a glass substrate 1, and a gate insulating film 4 is further formed on the surface. A gate electrode 5 is formed through the gate electrode 5.

21.31 is the source region, 22.32 is the drain region,
23.33 represents the channel region.

The feature of the present invention is as shown in FIG.
In a thin film semiconductor device in which a TFT and a switching TPT are formed on the same substrate, the thickness of the polycrystalline silicon film 300 of the driving TFT 30 is made thicker than the thickness of the polycrystalline silicon film 200 of the switching TPT 20. It is.

FIG. 3 is a diagram showing a method of manufacturing a TPT substrate for a liquid crystal display device incorporating a driving circuit according to an embodiment of the present invention. In particular, the right half shows a method of manufacturing a TPT for switching;
The left half shows a method of manufacturing the driving TPT.

In this figure, the same reference numerals as in FIGS. 1 and 2 represent the same or equivalent parts.

First, a polycrystalline silicon film 300 having a thickness of 1,000 wafers is formed on the surface of the glass U plate 1 by the CVD method [FIG. 4(a)]. The heating temperature at this time is 600°C.

□ Next, use a resist to mask the polycrystalline silicon film (left half) in the area where the driving TPT will be formed.
Only the polycrystalline silicon film of the switching TPT is etched to obtain a polycrystalline silicon film 200 with a thickness of 500 mm [FIG. 4(b)].

Next, on the surface of the polycrystalline silicon film 200.300,
Gate insulating film 4 and gate electrode 5 are formed at the same time.

Next, impurities are doped using the gate electrode 5 as a mask, and the source regions 21 and 31 and the drain region 2 are doped with impurities.
2.32 is formed.

At this time, the gate electrode 5 is also doped with impurities [FIG. 4(C)].

Next, after forming the passivation film 7, a contact window is opened and A! Electrode 6 is deposited [FIG. 6(d)].

FIG. 4 is a diagram showing a method for manufacturing a TPT substrate for a liquid crystal display device with a built-in driving circuit according to another embodiment of the present invention. Similar to FIG. 3, the right half shows a method for manufacturing a TPT for switching. The left half shows the manufacturing method of the driving TPT.

In this example, first, a polycrystalline silicon film 200 with a thickness of 500 wafers is formed on the surface of a glass substrate 1 [FIG. 2(a)].

Subsequently, the polycrystalline silicon film in the area where the driving TPT is to be formed is masked using a resist, and only the polycrystalline silicon film of the switching TPT is removed by etching [FIG. 4(b)].

Here, when a polycrystalline silicon film is again formed to a thickness of 500 mm over the entire surface by the CVD method, the driving TPT
A polycrystalline silicon film 300 with a thickness of 1000 is formed in the region where the switching TFT is formed, and a polycrystalline silicon film 300 with a thickness of 5 is formed on the switching TFT.
A polycrystalline silicon film 200 of 0.000 mm is formed [see the same figure (
C)].

In this example, in the process explained in FIG.
Since the polycrystalline silicon film is removed until it is exposed, the thickness of the polycrystalline silicon film can be adjusted more accurately than in the embodiment shown in FIG.

The subsequent steps are the same as those in the embodiment described in FIG. 3, so their explanation will be omitted.

FIG. 5 is a diagram illustrating a method of manufacturing a TPT substrate for a liquid crystal display device incorporating a driving circuit according to still another embodiment of the present invention, in which the right half is a switching TPT substrate as described above.
The left half shows the manufacturing method of the driving TPT.

In this figure, the same reference numerals as in FIGS. 1 to 4 represent the same or equivalent parts.

In this example, first, a polycrystalline silicon film 200 with a thickness of 500 wafers is formed on the surface of a glass substrate 1 [FIG. 2(a)].

Next, the region where the driving TPT is formed, the source region of the switching TPT, and the drain region are masked using resist, and the channel region of the polycrystalline silicon film 200 of the switching TPT is masked. Only the portion that becomes , is removed by etching [Figure (b)].

Here, when a polycrystalline silicon film is again formed to a thickness of 500 mm over the entire surface by the CVD method, the driving TPT
A film thickness of 1 is applied to the region where TPT is formed, the source region of the switching TPT, and the drain region.
A polycrystalline silicon film 300 with a thickness of 500 mm is formed, and a film thickness of 50 mm is formed in the portion that will become the channel region of the switching TPT.
0 polycrystalline silicon film 200 is formed [FIG.
)].

Subsequently, as in the case of the embodiment described in FIG. 3, the gate electrode 5, passivation PIk7, etc. are formed.
! (d) of the same figure] in which the electrode 6 is deposited.

In this example, even in the switching TPT, the polycrystalline silicon film in the source region and the drain region is formed thickly, and the polycrystalline silicon film in the channel region is thinly formed, so that reverse leakage occurs. A switching TPT that is less prone to process defects can be obtained without increasing the current.

In the above description, the insulating substrate was explained as a glass substrate, but a quartz substrate may be used as long as it is a transparent insulating substrate.

Further, in the above description, the present invention has been explained by applying it to a liquid crystal display device, but the present invention is not limited to this, and is applied to a liquid crystal switch array for a liquid crystal printer or a line sensor for an image reading device. Thus, the present invention can be applied to any thin film semiconductor device as long as the TPT functioning as a switching element and the driving TPT for driving the switching element are formed on the same substrate.

Note that, as described above, when the present invention is applied to a line sensor, the insulating substrate does not need to be transparent.

(Effects of the Invention) As is clear from the above description, according to the present invention, the following effects can be achieved.

In a TPT active matrix substrate with a built-in driving circuit that has a switching semiconductor device and a driving semiconductor device on the same substrate, the reverse leakage current of the switching semiconductor device is not increased, and the driving semiconductor device is The operating speed of the driving semiconductor device can be made faster than the operating speed of the switching semiconductor device without impairing the uniformity of the surface of the semiconductor thin film.

[Brief explanation of the drawing]

FIG. 1 is a plan view of a liquid crystal display device according to an embodiment of the present invention. FIG. 2 is a partial sectional view of a liquid crystal display device according to an embodiment of the present invention. FIG. 3 is a sectional view showing a manufacturing method according to an embodiment of the present invention. FIG. 4 is a sectional view showing a manufacturing method of another embodiment of the present invention. FIG. 5 is a sectional view showing a manufacturing method of still another embodiment of the present invention.

Claims (5)

[Claims] (1) an insulating substrate, first and second semiconductor thin films formed on the surface of the insulating substrate, a first thin film semiconductor element formed in a portion of the first semiconductor thin film, and a first thin film semiconductor element formed on a portion of the first semiconductor thin film; 2
a second thin film semiconductor element formed in a portion of a semiconductor thin film, the second thin film semiconductor element driving the first thin film semiconductor element, A thin film semiconductor device, wherein the film thickness is greater than that of the first semiconductor thin film. (2) The thin film semiconductor device according to claim 1, wherein the first thin film semiconductor elements are arranged in a matrix on the surface of the insulating substrate. (3) The thin film semiconductor device according to claim 1 or 2, wherein the insulating substrate is a transparent glass substrate or a quartz substrate. (4) The thin film semiconductor device according to any one of claims 1 to 3, wherein the first thin film semiconductor element is a switching element. (5) The thin film semiconductor device according to any one of claims 1 to 3, wherein the first thin film semiconductor element is an optical sensor.