JP2012109579A - Semiconductor device and manufacturing method for the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem in which: TFTs with a lightly-doped drain (LDD) structure and a gate-drain overlapped LDD (GOLD) structure are conventionally manufactured through a complicated process including a large number of steps.SOLUTION: After low-concentration impurity regions 24 and 25 are formed through a second doping step, a fourth etching step is performed. Thus, the width of the low-concentration impurity region overlapping with a third electrode 18c and the width of the low-concentration impurity region not overlapping with the third electrode can be adjusted freely. The region overlapping with the third electrode 18c can relax the electric field concentration and prevent a deterioration caused by hot carriers. The region not overlapping with the third electrode 18c can suppress an off current value.

Description

  The present invention relates to a semiconductor device having a circuit formed of a thin film transistor (hereinafter referred to as TFT) and a manufacturing method thereof. For example, the present invention relates to an electro-optical device typified by a liquid crystal display panel, an EL (electroluminescence) display device, an EC display device, and the like and an electronic apparatus in which such an electro-optical device is mounted as a component.

  Note that in this specification, a semiconductor device refers to all devices that can function by utilizing semiconductor characteristics, and an electro-optical device, a semiconductor circuit, and an electronic device are all semiconductor devices.

  In recent years, a thin film transistor (TFT) is formed using a semiconductor thin film (thickness of about several to several hundred nm) formed on a substrate having an insulating surface, and a semiconductor device having a large-area integrated circuit formed using this TFT is developed. Is progressing. Active matrix liquid crystal display devices, EL display devices, and contact image sensors are known as representative examples. In particular, TFTs (hereinafter referred to as polysilicon TFTs) using a crystalline silicon film (typically polysilicon film) as an active layer have high field effect mobility, so that various functional circuits can be formed. It is.

  For example, in an active matrix liquid crystal display device, a pixel circuit for displaying an image for each functional block, a pixel circuit such as a shift register circuit based on a CMOS circuit, a level shifter circuit, a buffer circuit, and a sampling circuit are controlled. A drive circuit is formed on a single substrate.

  In a pixel circuit of an active matrix liquid crystal display device, a TFT (pixel TFT) is disposed in each of tens to millions of pixels, and a pixel electrode is provided in each of the pixel TFTs. A counter electrode is provided on the counter substrate side with the liquid crystal interposed therebetween, and a kind of capacitor using the liquid crystal as a dielectric is formed. Then, the voltage applied to each pixel is controlled by the switching function of the TFT, and the liquid crystal is driven by controlling the charge to this capacitor, and the transmitted light quantity is controlled to display an image.

  The pixel TFT is composed of an n-channel TFT, and is driven by applying a voltage to the liquid crystal as a switching element. Since the liquid crystal is driven by alternating current, a method called frame inversion driving is often employed. In this method, in order to keep power consumption low, it is important that the characteristics required for the pixel TFT have a sufficiently low off-current value (drain current that flows when the TFT is off).

  As a TFT structure for reducing the off-current value, a lightly doped drain (LDD) structure is known. In this structure, a region to which an impurity element is added at a low concentration is provided between a channel formation region and a source region or a drain region formed by adding an impurity element at a high concentration, and this region is referred to as an LDD region. I'm calling. A so-called GOLD (Gate-drain Overlapped LDD) structure in which an LDD region is disposed so as to overlap with a gate electrode through a gate insulating film is known as means for preventing deterioration of an on-current value due to hot carriers. . With such a structure, it is known that a high electric field in the vicinity of the drain is relaxed, hot carrier injection is prevented, and the deterioration phenomenon is effective.

  In addition, the GOLD structure has a high effect of preventing deterioration of the on-current value, but on the other hand, there is a problem that the off-current value becomes larger than that of a normal LDD structure. Therefore, it is not a preferable structure for application to the pixel TFT. Conversely, the normal LDD structure has a high effect of suppressing the off-current value, but has a low effect of relaxing the electric field in the vicinity of the drain and preventing deterioration due to hot carrier injection. As described above, in a semiconductor device having a plurality of integrated circuits such as an active matrix liquid crystal display device, such a problem is enhanced particularly in a crystalline silicon TFT, and in the active matrix liquid crystal display device. It has become apparent as the required performance increases.

  Conventionally, when a TFT having an LDD structure or a TFT having a GOLD structure is formed, there is a problem that the manufacturing process becomes complicated and the number of processes increases. It is clear that an increase in the number of processes not only increases the manufacturing cost but also decreases the manufacturing yield.

  The present invention is a technique for solving such problems. In an electro-optical device and a semiconductor device typified by an active matrix liquid crystal display device manufactured using TFTs, the operating characteristics and reliability of the semiconductor device are disclosed. It is intended to reduce the manufacturing cost and improve the yield by reducing the number of steps while reducing the power consumption.

  In order to realize a reduction in manufacturing cost and an improvement in yield, reducing the number of processes can be considered as one means. Specifically, the number of photomasks required for manufacturing the TFT is reduced. A photomask is used in photolithography to form a resist pattern as a mask on a substrate during an etching process. Therefore, the use of a single photomask means that, in addition to steps such as film formation and etching in the steps before and after that, resist stripping, washing and drying steps are added, and even in the photolithography step, It means that complicated steps such as resist coating, pre-baking, exposure, development, and post-baking are performed.

  The present invention is characterized in that the number of photomasks is reduced as compared with the prior art, and TFTs are manufactured by the following manufacturing process. An example of the manufacturing method of the present invention is shown in FIGS.

  The manufacturing method of the present invention disclosed in this specification includes a first step of forming a semiconductor layer 12 on an insulating surface, a second step of forming an insulating film 13 on the semiconductor layer, and the insulating film 13. A third step of forming a first electrode comprising a stack of a first conductive layer 18a having a first width (W1) and a second conductive layer 17b; and As a mask, a fourth step of adding an impurity element to the semiconductor layer 12 to form the high-concentration impurity regions 20 and 21; and etching the second conductive layer 17b to form the first width (W1) A fifth step of forming a second electrode made of a laminate of a first conductive layer 18b having a second width (W2) and a second conductive layer 17c having a second width (W2); and As a mask, an impurity element is added to the semiconductor layer to form a low concentration impurity region 24, A first conductive layer 18c having a third width (W3) and a second width (W2) by etching the first conductive layer 18b. And a seventh step of forming a third electrode formed of a laminate with two conductive layers 17c.

  In the above manufacturing method, as a material for forming the first conductive film and the second conductive film, a heat-resistant conductive material is used, which is typically made of tungsten (W), tantalum (Ta), or titanium (Ti). It is formed from a selected element or a compound or alloy containing the element as a component.

  In the third step, the shape of the first electrode is a so-called taper shape in which the thickness gradually increases from the end toward the inside at the end.

  In order to etch the first conductive film and the second conductive film made of a heat-resistant conductive material at high speed and with high accuracy and to further taper the end portion, a dry etching method using high-density plasma is used. Apply. An etching apparatus using microwaves or inductively coupled plasma (ICP) is suitable for obtaining high-density plasma. In particular, the ICP etching apparatus can easily control the plasma and can cope with an increase in the area of the processing substrate.

  A plasma processing method and a plasma processing apparatus using ICP are disclosed in JP-A-9-293600. In this publication, as a means for performing plasma processing with high accuracy, high-frequency power is applied to a multi-spiral coil in which four spiral coil portions are connected in parallel via an impedance matching device to form plasma. The method is used. Here, the length of each coil portion is set to 1/4 times the wavelength of the high frequency. Further, a bias voltage is additionally applied to the lower electrode holding the object to be processed by separately applying high frequency power.

  When using an etching apparatus using an ICP to which such a multi-spiral coil is applied, the angle of the taper portion (taper angle) changes greatly depending on the bias power applied to the substrate side, further increasing the bias power, and increasing the pressure. By changing the angle, the angle of the tapered portion can be changed from 5 ° to 45 °.

  In the fourth step, in order to form the high-concentration impurity regions 20 and 21 in a self-aligned manner, an ionized impurity element is accelerated by an electric field to form a gate insulating film (in the present invention, the first electrode and Add to the semiconductor layer by passing through the insulating film provided in close contact with the semiconductor layer and the insulating film extending from the insulating film to the surrounding area (referred to as a gate insulating film) The method to be used is used. In this specification, this impurity element addition method is referred to as a “through doping method” for convenience.

  Note that in this specification, an impurity element refers to an impurity element imparting n-type conductivity (phosphorus or arsenic) or an impurity element imparting p-type conductivity (boron) to a semiconductor.

  In the fifth step, the second conductive layer is selectively etched using an etching apparatus using ICP, and the second conductive layer 17c constituting the second electrode is secondly etched. The width (W2) is made narrower than the first width (W1). The taper angle at the end of the first conductive layer in the second electrode is smaller than the taper angle at the end of the second conductive layer.

  In the present invention, by using the second electrode having such a shape, the through-doping method is used in the sixth step, and the tapered portion of the first conductive layer constituting the second electrode ( Low concentration impurity regions 24 and 25 that continuously increase in concentration as the impurity element moves away from the channel formation region are formed in the semiconductor layer existing below the taper portion in a self-aligned manner. However, even though it is continuously increased, there is almost no difference in concentration in the low concentration impurity region.

  In order to form the low-concentration impurity regions 24 and 25 having such a gentle concentration gradient in a self-aligned manner, the ionized impurity element is accelerated by an electric field to form the second conductive layer of the first conductive layer constituting the second electrode. It is added to the semiconductor layer through the tapered portion and the gate insulating film. Thus, by performing the through-doping method on the tapered portion of the first conductive layer constituting the second electrode, the concentration of the impurity element added to the semiconductor layer is controlled by the thickness of the tapered portion of the first conductive layer. Thus, it is possible to form the low concentration impurity regions 24 and 25 in which the concentration of the impurity element gradually changes over the channel length direction of the TFT.

  Note that immediately after the sixth step in which the through doping is performed, the low-concentration impurity regions 24 and 25 overlap the tapered portion of the first conductive layer constituting the second electrode through the gate insulating film.

  Further, the tapered portion of the first conductive layer is selectively etched by the seventh step. The etching in the seventh step is etching using the RIE method, and is different from the etching method used in the third step and the fifth step. However, the present invention is not limited to the RIE method, and can be performed using an ICP dry etching apparatus if conditions are appropriately selected. Etching using the RIE method can also be performed after using the ICP method. . By this seventh step, the taper angle of the first conductive layer in the third electrode becomes substantially the same as the taper angle of the first conductive layer in the second electrode. The third width (W3) is narrower than the first width (W1) and wider than the second width (W2). In addition, simultaneously with the seventh step, the insulating film is removed, and a part of the high concentration impurity region is exposed.

  Note that immediately after the step 7, the low-concentration impurity region has a region 25a that overlaps the tapered portion of the first conductive layer that constitutes the third electrode through the gate insulating film, and the third region through the gate insulating film. It can be distinguished from the region 25b that does not overlap with the tapered portion of the first conductive layer constituting the electrode.

  Further, the third width (W3) can be freely adjusted by appropriately changing the etching conditions. Therefore, according to the present invention, by appropriately changing the etching conditions in the seventh step, the width of the low concentration impurity region that overlaps the third electrode and the width of the low concentration impurity region that does not overlap the third electrode can be obtained. Can be adjusted freely. However, the low-concentration impurity region has a gradual concentration gradient regardless of the width of the third electrode, and the region overlapping the third electrode achieves relaxation of the electric field concentration and thus hot carriers. In addition, the off-current value can be suppressed in a region that does not overlap with the third electrode.

In the above manufacturing method, the first photolithography process is performed in the first process and the second photolithography process is performed in the third process. In the other processes (fourth to seventh processes), Since the resist mask used in the second photolithography process is used as it is, the photolithography process is not performed.

  Therefore, after the seventh step, a third photolithography step for forming a contact hole in the interlayer insulating film to be formed, and a fourth photo step for forming a source electrode or a drain electrode reaching the semiconductor layer. A TFT can be manufactured by performing a lithography process.

  Thus, while reducing the number of photomasks, the present invention was able to make the TFT configuration appropriate. The configuration of the present invention is shown below.

  The present invention disclosed in this specification is a semiconductor device including a semiconductor layer formed on an insulating surface, an insulating film formed on the semiconductor layer, and a gate electrode formed on the insulating film. The gate electrode has a first conductive layer having a first width (corresponding to W3 in FIG. 2) as a lower layer, and a second width narrower than the first width (W2 in FIG. 2). The semiconductor layer includes a channel formation region that overlaps with the second conductive layer, and a low concentration that partially overlaps with the first conductive layer. A semiconductor device having an impurity region and a source region and a drain region made of a high-concentration impurity region.

  In the above structure, the low-concentration impurity region is present between the channel formation region and the source region, or between the channel formation region and the drain region.

  In the above structure, an end portion of the first conductive layer has a tapered shape.

  In the above structure, an end portion of the one conductive layer exists between the channel formation region and the source region, or between the channel formation region and the drain region via the insulating film. It is a feature.

  In the above structure, a thickness of a region of the insulating film that overlaps with the low-concentration impurity region decreases as the distance from the channel formation region increases.

  Further, as shown in FIG. 3, in the low-concentration impurity region 25 provided between the channel formation region 26 and the drain region 23, the concentration of the impurity element imparting conductivity type gradually increases as the drain region is approached. A low concentration impurity region 25 having a gentle concentration gradient, and a region 25a (GOLD region) overlapping the gate electrode 18c and a region 25b (LDD region) not overlapping the gate electrode. It is a point.

  Note that in this specification, a low-concentration impurity region that overlaps with the gate electrode through the insulating film is referred to as a GOLD region, and a low-concentration impurity region that does not overlap with the gate electrode is referred to as an LDD region.

  In addition, an electro-optical device typified by a liquid crystal display device or an EL display device is formed using a TFT having the above structure.

The width of the low-concentration impurity region (GOLD region) that overlaps with the gate electrode and the width of the low-concentration impurity region (LDD region) that does not overlap with the gate electrode can be freely adjusted by the etching conditions of the third etching process in the present invention. Further, there is almost no difference in concentration between the GOLD region and the LDD region of the TFT formed according to the present invention. Therefore, the GOLD region overlapping with the gate electrode can be mitigated by electric field concentration and prevented by hot carriers, and the LDD region not overlapping with the gate electrode can suppress the off-current value.

It is a figure which shows the preparation process of TFT. It is a figure which shows the preparation process of TFT. It is a curve which shows the concentration distribution of an impurity element. It is the structure schematic diagram used by simulation. It is a graph of a simulation result (phosphorus dope). It is a graph of a simulation result (voltage / current characteristic of TFT). It is a figure which shows the manufacturing process of AM-LCD. It is a figure which shows the manufacturing process of AM-LCD. It is a figure which shows the manufacturing process of AM-LCD. It is a cross-sectional structure diagram of a transmissive liquid crystal display device. It is an external view of a liquid crystal panel. It is a figure which shows the manufacturing process of AM-LCD. It is a figure which shows the manufacturing process of AM-LCD. It is a figure which shows the manufacturing process of AM-LCD. It is a pixel top view. It is a cross-section figure of a reflection type liquid crystal display. It is a pixel top view in a manufacturing process. FIG. 11 illustrates a structure of an active matrix EL display device. FIG. 11 illustrates a structure of an active matrix EL display device. FIG. 14 illustrates an example of an electronic device. FIG. 14 illustrates an example of an electronic device. FIG. 14 illustrates an example of an electronic device.

  Embodiments of the present invention will be described below with reference to FIGS.

  First, the base insulating film 11 is formed on the substrate 10. As the substrate 10, a glass substrate, a quartz substrate, a silicon substrate, a metal substrate, or a stainless substrate on which an insulating film is formed may be used. Alternatively, a plastic substrate having heat resistance that can withstand the processing temperature may be used.

  As the base insulating film 11, a base film 11 made of an insulating film such as a silicon oxide film, a silicon nitride film, or a silicon oxynitride film is formed. Here, an example in which a two-layer structure (11a, 11b) is used as the base film 11 is shown, but a single-layer film of the insulating film or a structure in which two or more layers are stacked may be used. Note that the base insulating film is not necessarily formed.

  Next, the semiconductor layer 12 is formed over the base insulating film. The semiconductor layer 12 is formed by forming a semiconductor film having an amorphous structure by a known means (sputtering method, LPCVD method, plasma CVD method, etc.), and then performing a known crystallization process (laser crystallization method, thermal crystallization method). And a crystalline semiconductor film obtained by performing a method such as thermal crystallization using a catalyst such as nickel) is formed by patterning into a desired shape using a first photomask. The semiconductor layer 12 is formed with a thickness of 25 to 80 nm (preferably 30 to 60 nm). There is no limitation on the material of the crystalline semiconductor film, but the crystalline semiconductor film is preferably formed of silicon or a silicon germanium (SiGe) alloy.

  Next, an insulating film 13 that covers the semiconductor layer 12 is formed.

  The insulating film 13 is formed by a plasma CVD method or a sputtering method, with a thickness of 40 to 150 nm, and a single layer or a laminated structure of an insulating film containing silicon. The insulating film 13 becomes a gate insulating film.

  Next, a first conductive film 14 with a thickness of 20 to 100 nm and a second conductive film 15 with a thickness of 100 to 400 nm are stacked over the insulating film 13. Here, a first conductive film 14 made of a TaN film and a second conductive film 15 made of a W film are stacked by sputtering. Here, the first conductive film 14 is TaN and the second conductive film 15 is W. However, the first conductive film 14 is not particularly limited, and any element selected from Ta, W, Ti, Mo, Al, Cu, Or you may form with the alloy material or compound material which has the said element as a main component. Alternatively, a semiconductor film typified by a polycrystalline silicon film doped with an impurity element such as phosphorus may be used.

  Next, a resist mask 16a is formed using a second photomask, and a first etching process is performed using an ICP etching apparatus. In this first etching step, the second conductive film 15 is etched to form a second conductive layer 17a having a tapered portion at the end (tapered portion) as shown in FIG. obtain.

  Here, the angle of the tapered portion (taper angle) is defined as the angle formed by the substrate surface (horizontal plane) and the inclined portion of the tapered portion. The taper angle of the second conductive layer 17a can be in the range of 5 ° to 45 ° by appropriately selecting the etching conditions.

  Next, using the resist mask 16a as it is, a second etching process is performed using an ICP etching apparatus. In the second etching step, the first conductive film 14 is etched to form a first conductive layer 18a as shown in FIG. The first conductive layer 18a has a first width (W1). In the second etching step, the resist mask, the second conductive layer, and the insulating film are also slightly etched to form a resist mask 16b, a second conductive layer 17b, and an insulating film 19a, respectively.

  Here, in order to suppress the decrease in the thickness of the insulating film 13, etching (first etching step and second etching step) was performed twice, but an electrode structure (see FIG. 2C) ( There is no particular limitation as long as the second conductive layer 17b and the first conductive layer 18a can be formed), and the etching may be performed once.

  Next, a first doping process is performed while the resist mask 16b is left as it is. Through-doping is performed through the insulating film 19a by this first doping step, and the high concentration impurity regions 20 and 21 are formed. (Figure 1 (D))

Next, a third etching process is performed using the resist mask 16b using an ICP etching apparatus. In the third etching step, the second conductive layer 17b is etched to form a second conductive layer 17c as shown in FIG.
The second conductive layer 17c has a second width (W2). Note that, in the third etching step, the resist mask, the first conductive layer, and the insulating film are also slightly etched to form the resist mask 16c, the first conductive layer 18b, and the insulating film 19b, respectively.

  Next, a second doping process is performed while the resist mask 16c is left as it is. Through this second doping step, through doping is performed through the tapered portion of the first conductive layer 18b and the insulating film 19b, and the low concentration impurity regions 24 and 25 are formed. 2B. Note that, in the second doping, the high-concentration impurity regions are also doped, and high-concentration impurity regions 22 and 23 are formed.

  Next, a fourth etching process is performed using an RIE etching apparatus while the resist mask 16c is left as it is. By this third etching step, a part of the tapered portion of the first conductive layer 18b is removed. Here, the first conductive layer 18b having the first width (W1) became the first conductive layer 18c having the third width (W3). In the present invention, the first conductive layer 18c and the second conductive layer 17c stacked thereon serve as a gate electrode. During the fourth etching, the insulating film 19b is also etched to form the insulating film 19c. Here, an example is shown in which a part of the insulating film is removed to expose the high-concentration impurity region, but the invention is not particularly limited.

  Thereafter, the resist mask 16c is removed, and the impurity element added to the semiconductor layer is activated. Next, after an interlayer insulating film 27 is formed, contact holes are formed using a third mask, and electrodes 28 and 29 are formed using a fourth mask.

  In this manner, a TFT having a structure shown in FIG. 2D can be formed using four photomasks.

  The TFT formed according to the present invention is characterized in that there is almost no difference in concentration in the low-concentration impurity region 25 provided between the channel formation region 26 and the drain region 23, and there is a gradual concentration gradient. A region 25a (GOLD region) overlapping with 18c and a region 25b (LDD region) not overlapping with the gate electrode are provided. The peripheral portion of the insulating film 19c, that is, the region 25b that does not overlap with the gate electrode and the region above the high-concentration impurity regions 20 and 21 are tapered.

In addition, simulation was performed in the process of FIG. For the simulation, the structural schematic diagram shown in FIG. 4 was used. Here, the film thickness of the semiconductor layer is 42 nm, the film thickness of the gate insulating film is 110 nm, and the tapered portion of the first conductive layer is modeled into a stepped structure as shown in FIG. It was assumed that phosphorus was doped in an amount of 1.4 × 10 ¹³ atoms / cm ² .

  The simulation result is shown in FIG. FIG. 5 shows that the concentration of the impurity element (phosphorus) continuously increases as the distance from the channel formation region increases. However, the concentration gradient is gentle, and there is almost no concentration difference in the low concentration impurity region.

  FIG. 6 shows the voltage / current characteristics of a TFT having the concentration distribution obtained in FIG. 5 and formed as a 0.5 μm GOLD region and a 0.5 μm LLD region. By simulation, the TFT threshold (Vth) is 1.881 V, the S value is 0.2878 V / dec, and the on-current is 40 μA when Vds (voltage difference between the source region and the drain region) = 1V. Thus, when Vds = 14V, the value was 119.6 μA.

  The present invention having the above-described configuration will be described in more detail with the following examples.

  Here, a method for simultaneously manufacturing a pixel portion and TFTs (n-channel TFT and p-channel TFT) of a driver circuit provided around the pixel portion on the same substrate will be described in detail with reference to FIGS. .

  First, in this embodiment, a substrate 100 made of glass such as barium borosilicate glass represented by Corning # 7059 glass or # 1737 glass or aluminoborosilicate glass is used. The substrate 100 is not limited as long as it is a light-transmitting substrate, and a quartz substrate may be used. Further, a plastic substrate having heat resistance that can withstand the processing temperature of this embodiment may be used.

Next, a base film 101 made of an insulating film such as a silicon oxide film, a silicon nitride film, or a silicon oxynitride film is formed over the substrate 100. Although a two-layer structure is used as the base film 101 in this embodiment, a single-layer film of the insulating film or a structure in which two or more layers are stacked may be used. As a first layer of the base film 101, a silicon oxynitride film 101a formed using SiH ₄ , NH ₃ , and N ₂ O as a reactive gas is formed by using a plasma CVD method to a thickness of 10 to 200 nm (preferably 50 to 100 nm). To do. In this embodiment, a silicon oxynitride film 101a having a film thickness of 50 nm (composition ratio Si = 32%, O = 27%, N = 24%, H = 17%) is formed. Next, as the second layer of the base film 101, a silicon oxynitride film 101 b formed using SiH ₄ and N ₂ O as a reaction gas is formed with a plasma CVD method to a thickness of 50 to 200 nm (preferably 100 to 150 nm). Stacked to a thickness. In this embodiment, a silicon oxynitride film 101b (composition ratio Si = 32%, O = 59%, N = 7%, H = 2%) having a thickness of 100 nm is formed.

Next, semiconductor layers 102 to 105 are formed over the base film. The semiconductor layers 102 to 105 are formed by forming a semiconductor film having an amorphous structure by a known means (a sputtering method, an LPCVD method, a plasma CVD method, or the like), and then a known crystallization treatment (laser crystallization method, heat A crystalline semiconductor film obtained by performing a crystallization method or a thermal crystallization method using a catalyst such as nickel) is formed by patterning into a desired shape. The semiconductor layers 102 to 105 are formed to have a thickness of 25 to 80 nm (preferably 30 to 60 nm). There is no limitation on the material of the crystalline semiconductor film, but it is preferably formed of silicon or silicon germanium (Si _x Ge _1-x (X = 0.0001 to 0.02)) alloy. In this example, a 55 nm amorphous silicon film was formed by plasma CVD, and then a solution containing nickel was held on the amorphous silicon film. This amorphous silicon film is dehydrogenated (500 ° C., 1 hour), then thermally crystallized (550 ° C., 4 hours), and then laser annealing treatment is performed to improve crystallization. Thus, a crystalline silicon film was formed. Then, the semiconductor layers 102 to 105 were formed by patterning the crystalline silicon film using a photolithography method.

  In addition, after forming the semiconductor layers 102 to 105, a small amount of impurity element (boron or phosphorus) may be doped in order to control the threshold value of the TFT.

When a crystalline semiconductor film is formed by a laser crystallization method, a pulse oscillation type or continuous emission type excimer laser, YAG laser, or YVO ₄ laser can be used. When these lasers are used, it is preferable to use a method in which laser light emitted from a laser oscillator is linearly collected by an optical system and irradiated onto a semiconductor film. Crystallization conditions are appropriately selected by the practitioner. When an excimer laser is used, the pulse oscillation frequency is 30 Hz, and the laser energy density is 100 to 400 mJ / cm ² (typically 200 to 300 mJ / cm ^2). ). In the case of using a YAG laser, the second harmonic is used and the pulse oscillation frequency is set to 1 to 10 kHz, and the laser energy density is set to 300 to 600 mJ / cm ² (typically 350 to 500 mJ / cm ² ). Then, when the laser beam condensed linearly with a width of 100 to 1000 μm, for example 400 μm, is irradiated over the entire surface of the substrate, the superposition ratio (overlap ratio) of the linear laser light at this time is 80 to 98%. Good.

  Next, a gate insulating film 106 that covers the semiconductor layers 102 to 105 is formed. The gate insulating film 106 is formed of an insulating film containing silicon with a thickness of 40 to 150 nm by plasma CVD or sputtering. In this embodiment, a silicon oxynitride film (composition ratio: Si = 32%, O = 59%, N = 7%, H = 2%) with a thickness of 110 nm is formed by plasma CVD. Needless to say, the gate insulating film is not limited to the silicon oxynitride film, and another insulating film containing silicon may be used as a single layer or a stacked structure.

When a silicon oxide film is used, TEOS (Tetraethyl Orthosilicate) and O ₂ are mixed by a plasma CVD method to a reaction pressure of 40 Pa, a substrate temperature of 300 to 400 ° C., and a high frequency (13.56 MHz) power density of 0. It can be formed by discharging at 5 to 0.8 W / cm ² . The silicon oxide film thus manufactured can obtain good characteristics as a gate insulating film by subsequent thermal annealing at 400 to 500 ° C.

Next, as illustrated in FIG. 7A, a first conductive film 107 with a thickness of 20 to 100 nm and a second conductive film 108 with a thickness of 100 to 400 nm are stacked over the gate insulating film 106. In this example, a first conductive film 107 made of a TaN film with a thickness of 30 nm and a second conductive film 108 made of a W film with a thickness of 370 nm were stacked.
The TaN film was formed by sputtering, and was sputtered in a nitrogen-containing atmosphere using a Ta target. The W film was formed by sputtering using a W target. In addition, it can be formed by a thermal CVD method using tungsten hexafluoride (WF ₆ ). In any case, in order to use as a gate electrode, it is necessary to reduce the resistance, and the resistivity of the W film is desirably 20 μΩcm or less. The resistivity of the W film can be reduced by increasing the crystal grains. However, when there are many impurity elements such as oxygen in the W film, the crystallization is hindered and the resistance is increased. Therefore, in this embodiment, a sputtering method using a target of high purity W (purity 99.9999%) is used, and the W film is formed with sufficient consideration so that impurities are not mixed in from the gas phase during film formation. By forming, a resistivity of 9 to 20 μΩcm could be realized.

  In this embodiment, the first conductive film 107 is TaN and the second conductive film 108 is W. However, there is no particular limitation, and all of them are Ta, W, Ti, Mo, Al, Cu, Cr, Nd. You may form with the element selected from these, or the alloy material or compound material which has the said element as a main component. Alternatively, a semiconductor film typified by a polycrystalline silicon film doped with an impurity element such as phosphorus may be used. Further, an AgPdCu alloy may be used. In addition, the first conductive film is formed using a tantalum (Ta) film, the second conductive film is formed using a W film, the first conductive film is formed using a titanium nitride (TiN) film, and the second conductive film is formed. The first conductive film is formed of a tantalum nitride (TaN) film, the second conductive film is formed of an Al film, and the first conductive film is formed of a tantalum nitride (TaN) film. The second conductive film may be a combination of Cu films.

Next, resist masks 109 to 112 are formed by photolithography, and a first etching process for forming electrodes and wirings is performed. The first etching process is performed under the first and second etching conditions. In this embodiment, an ICP (Inductively Coupled Plasma) etching method is used as the first etching condition, CF ₄ , Cl ₂ and O ₂ are used as etching gases, and the respective gas flow ratios are 25. Etching was performed by generating plasma by applying 500 W of RF (13.56 MHz) power to the coil type electrode at a pressure of 1 Pa at a pressure of 1/25/10 (sccm). Here, a dry etching apparatus (Model E645- □ ICP) using ICP manufactured by Matsushita Electric Industrial Co., Ltd. was used. 150 W RF (13.56 MHz) power is also applied to the substrate side (sample stage), and a substantially negative self-bias voltage is applied. The W film is etched under the first etching condition so that the end portion of the second conductive layer is tapered. Under the first etching conditions, the etching rate with respect to W is 200.39 nm / min, the etching rate with respect to TaN is 80.32 nm / min, and the selection ratio of W with respect to TaN is about 2.5. Further, the taper angle of W is about 26 ° under this first etching condition. Note that the etching under the first etching conditions here corresponds to the first etching step (FIG. 1B) described in the embodiment mode.

Thereafter, the masks 109 to 112 made of resist are changed to the second etching conditions without removing them, CF ₄ and Cl ₂ are used as etching gases, and the respective gas flow ratios are set to 30/30 (sccm). Etching was performed for about 30 seconds by applying 500 W RF (13.56 MHz) power to the coil electrode at a pressure of 1 Pa to generate plasma. 20 W of RF (13.56 MHz) power is also applied to the substrate side (sample stage), and a substantially negative self-bias voltage is applied. Under the second etching condition in which CF ₄ and Cl ₂ are mixed, the W film and the TaN film are etched to the same extent. The etching rate for W under the second etching conditions is 58.97 nm / min, and the etching rate for TaN is 66.43 nm / min. Note that in order to perform etching without leaving a residue on the gate insulating film, it is preferable to increase the etching time at a rate of about 10 to 20%. Note that the etching under the second etching conditions here corresponds to the second etching step (FIG. 1C) described in the embodiment.

  In the first etching process, the shape of the mask made of resist is made suitable, and the end portions of the first conductive layer and the second conductive layer are tapered due to the effect of the bias voltage applied to the substrate side. It becomes. The angle of the taper portion may be 15 ° to 45 °. Thus, the first shape conductive layers 113 to 116 (the first conductive layers 113 a to 116 a and the second conductive layers 113 b to 116 b) composed of the first conductive layer and the second conductive layer by the first etching treatment. Form. The width of the first conductive layer in the channel length direction here corresponds to W1 described in the above embodiment. Reference numeral 117 denotes a gate insulating film, and a region not covered with the first shape conductive layers 113 to 116 is etched and thinned by about 20 to 50 nm.

Then, a first doping process is performed without removing the resist mask, and an impurity element imparting n-type conductivity is added to the semiconductor layer. (FIG. 7B) The doping process may be performed by an ion doping method or an ion implantation method. The conditions of the ion doping method are a dose amount of 1 × 10 ^{13 to} 5 × 10 ¹⁵ atoms / cm ² and an acceleration voltage of 60 to 100 keV. In this embodiment, the dosage is 1.5 × 10 ¹⁵ atoms / cm ² and the acceleration voltage is 80 keV. As an impurity element imparting n-type, an element belonging to Group 15, typically phosphorus (P) or arsenic (As), is used here, but phosphorus (P) is used. In this case, the conductive layers 113 to 116 serve as a mask for the impurity element imparting n-type, and the high-concentration impurity regions 118 to 121 are formed in a self-aligning manner. An impurity element imparting n-type conductivity is added to the high-concentration impurity regions 118 to 121 in a concentration range of 1 × 10 ²⁰ to 1 × 10 ²¹ atoms / cm ³ . Note that the first doping treatment here corresponds to the first doping step (FIG. 1D) described in the embodiment.

Next, a second etching process is performed without removing the resist mask.
The etching gas used for the first etching process and the second etching process is a chlorine compound gas such as Cl ₂ , BCl ₃ , SiCi ₄ , or CCl ₄ , or a fluorine compound such as CF ₄ , SF ₆ , or NF ₃ . A gas selected from a system gas and O ₂ or a mixed gas containing these as a main component may be used. Here, CF ₄ , Cl _2, and O ₂ are used as etching gases, and the respective gas flow ratios are 25/25/10 (sccm).
Etching was performed by applying 500 W of RF (13.56 MHz) power to the coil electrode at a pressure of 1 Pa to generate plasma. 20 W of RF (13.56 MHz) power is also applied to the substrate side (sample stage), and a substantially negative self-bias voltage is applied.
In the second etching process, the etching rate with respect to W is 124.62 nm / min, the etching rate with respect to TaN is 20.67 nm / min, and the selection ratio of W with respect to TaN is 6.05. Therefore, the W film is selectively etched. By this second etching process, the taper angle of W became 70 °. The second conductive layers 122b to 125b are formed by this second etching process. On the other hand, the first conductive layers 113a to 116a are hardly etched, and the first conductive layers 122a to 125a are formed. Note that the second etching process here corresponds to the third etching step (FIG. 2A) described in the embodiment mode. The width of the second conductive layer in the channel length direction here corresponds to W2 described in the embodiment.

Next, a second doping process is performed to obtain the state of FIG. Doping is performed using the second conductive layers 122b to 125b as masks against the impurity element so that the impurity element is added to the semiconductor layer below the tapered portion of the first conductive layer. In this embodiment, P (phosphorus) was used as an impurity element, and plasma doping was performed at a dose of 3.5 × 10 ¹² and an acceleration voltage of 90 keV. Thus, the low concentration impurity regions 126 to 129 overlapping with the first conductive layer are formed in a self-aligning manner.
The concentration of phosphorus (P) added to the low-concentration impurity regions 126 to 129 is 1 × 10 ¹⁷ to 1 × 10 ¹⁸ atoms / cm ³ and according to the thickness of the tapered portion of the first conductive layer. It has a gentle concentration gradient. Note that in the semiconductor layer overlapping the tapered portion of the first conductive layer, the impurity concentration is slightly lower from the end of the tapered portion of the first conductive layer to the inside, but the concentration is almost the same. . Further, the impurity element is also added to the high concentration impurity regions 118 to 121 to form the high concentration impurity regions 130 to 133. Note that the second doping treatment here corresponds to the second doping step (FIG. 2B) described in the embodiment.

Next, a third etching process is performed without removing the resist mask.
In the third etching process, the tapered portion of the first conductive layer is partially etched to reduce a region overlapping with the semiconductor layer. The third etching process uses CHF ₃ as an etching gas and a reactive ion etching method (RIE method).
To do. In this example, the third etching process was performed at a chamber pressure of 6.7 Pa, an RF power of 800 W, and a CHF ₃ gas flow rate of 35 sccm. By the third etching process, first conductive layers 138 to 141 are formed. Note that the third etching process here corresponds to the fourth etching process (FIG. 2C) described in the embodiment. The width of the first conductive layer in the channel length direction here corresponds to W3 shown in the embodiment.

  At the same time as the third etching process, the insulating film 117 is also etched, and part of the high-concentration impurity regions 130 to 133 is exposed to form insulating films 143a to 143c and 144. In this embodiment, etching conditions in which a part of the high-concentration impurity regions 130 to 133 are exposed are used. However, if the thickness of the insulating film and the etching conditions are changed, a thin insulating film remains in the high-concentration impurity region. It can also be done.

  By the third etching process, impurity regions (LDD regions) 134a to 137a that do not overlap with the first conductive layers 138 to 141 are formed. Note that the impurity regions (GOLD regions) 134b to 137b remain overlapped with the first conductive layers 138 to 141.

  In addition, an electrode formed by the first conductive layer 138 and the second conductive layer 122b serves as a gate electrode of an n-channel TFT of a driver circuit formed in a later step, and the first conductive layer 139 and the second conductive layer 122b The electrode formed with the second conductive layer 123b becomes a gate electrode of a p-channel TFT of a driver circuit formed in a later step. Similarly, an electrode formed using the first conductive layer 140 and the second conductive layer 124b serves as a gate electrode of an n-channel TFT in a pixel portion formed in a later step, and the first conductive layer 141 and The electrode formed with the second conductive layer 125b serves as one electrode of the storage capacitor of the pixel portion formed in a later step.

  In this way, in this embodiment, the impurity concentration in the impurity regions (GOLD regions) 134b to 137b overlapping with the first conductive layers 138 to 141 and the impurity region not overlapping with the first conductive layers 138 to 141 ( The difference from the impurity concentration in the LDD regions 134a to 137a can be reduced, and the TFT characteristics can be improved.

Next, after removing the resist mask, new resist masks 145 and 146 are formed, and a third doping process is performed. By this third doping treatment, an impurity region 147 in which an impurity element imparting a conductivity type (p-type) opposite to the one conductivity type (n-type) is added to the semiconductor layer that becomes the active layer of the p-channel TFT. To 152. (FIG. 8B) The first conductive layers 139 and 141 are used as masks against the impurity element, and an impurity element imparting p-type is added to form an impurity region in a self-aligning manner. In this embodiment, the impurity regions 147 to 152 are formed by an ion doping method using diborane (B ₂ H ₆ ). In this third doping process, the semiconductor layer forming the n-channel TFT is covered with masks 145 and 146 made of resist. By the first doping process and the second doping process, phosphorus is added to the impurity regions 145 and 146 at different concentrations, respectively, and the concentration of the impurity element imparting p-type in each of the regions is 2 ×. By performing the doping treatment so as to be 10 ^{20 to} 2 × 10 ²¹ atoms / cm ³ , no problem arises because it functions as the source region and drain region of the p-channel TFT. In this embodiment, a part of the semiconductor layer that becomes an active layer of the p-channel TFT is exposed by the third etching treatment, so that the impurity element (boron) is exposed.
Has the advantage of being easy to add.

  This third doping process may be performed once or a plurality of times. For example, when doping is performed twice, the first doping condition is 5 to 40 keV and 147 and 150 are formed, and the second doping condition is 60 to 120 keV and 148, 149, 151 and 152 are used. By forming, implantation defects (defects caused by ion doping or ion implantation) in the semiconductor film can be minimized. Furthermore, if doping is performed a plurality of times in this way, the amount of boron element introduced into the source and drain regions 147 and the LDD regions 148 and 149 can be changed, and the degree of freedom in design is improved.

  Through the above steps, impurity regions are formed in the respective semiconductor layers.

  Next, the resist masks 145 and 146 are removed, and a first interlayer insulating film 153 is formed. The first interlayer insulating film 153 is formed of an insulating film containing silicon with a thickness of 100 to 200 nm by using a plasma CVD method or a sputtering method. In this embodiment, a silicon oxynitride film with a thickness of 150 nm is formed by a plasma CVD method. Needless to say, the first interlayer insulating film 153 is not limited to the silicon oxynitride film, and another insulating film containing silicon may be used as a single layer or a stacked structure.

  Next, as shown in FIG. 8C, a step of activating the impurity element added to each semiconductor layer is performed. This activation process is performed by a thermal annealing method using a furnace annealing furnace. As the thermal annealing method, it may be performed at 400 to 700 ° C., typically 500 to 550 ° C. in a nitrogen atmosphere having an oxygen concentration of 1 ppm or less, preferably 0.1 ppm or less. The activation treatment was performed by heat treatment. In addition to the thermal annealing method, a laser annealing method or a rapid thermal annealing method (RTA method) can be applied.

  In this embodiment, at the same time as the activation treatment, nickel used as a catalyst during crystallization is gettered to impurity regions (130, 132, 147, 150) containing high-concentration phosphorus, and mainly the channel. The nickel concentration in the semiconductor layer that becomes the formation region is reduced. A TFT having a channel formation region manufactured in this manner has a low off-current value and good crystallinity, so that high field-effect mobility can be obtained and good characteristics can be achieved.

  In addition, an activation process may be performed before forming the first interlayer insulating film. However, when the wiring material used is weak against heat, it is activated after an interlayer insulating film (insulating film containing silicon as a main component, for example, a silicon nitride film) is formed to protect the wiring and the like as in this embodiment. It is preferable to perform the conversion treatment.

  Furthermore, a heat treatment is performed at 300 to 550 ° C. for 1 to 12 hours in an atmosphere containing 3 to 100% hydrogen to perform a step of hydrogenating the semiconductor layer. In this embodiment, heat treatment was performed at 410 ° C. for 1 hour in a nitrogen atmosphere containing about 3% hydrogen. This step is a step of terminating dangling bonds in the semiconductor layer with hydrogen contained in the interlayer insulating film. As another means of hydrogenation, plasma hydrogenation (using hydrogen excited by plasma) may be performed.

  In the case where a laser annealing method is used as the activation treatment, it is desirable to irradiate a laser beam such as an excimer laser or a YAG laser after performing the hydrogenation.

  Next, a second interlayer insulating film 154 made of an organic insulating material is formed on the first interlayer insulating film 153. In this embodiment, an acrylic resin film having a thickness of 1.6 μm is formed. Next, patterning for forming contact holes reaching the impurity regions 130, 132, 147, 150 is performed.

  Then, in the driver circuit 205, electrodes 155 to 158 that are electrically connected to the impurity region 130 or the impurity region 147, respectively, are formed. Note that these electrodes are formed by patterning a laminated film of a Ti film having a thickness of 50 nm and an alloy film (alloy film of Al and Ti) having a thickness of 500 nm.

  In the pixel portion 206, the connection electrode 160 or the source electrode 159 in contact with the impurity region 132 is formed, and the connection electrode 161 in contact with the impurity region 150 is formed.

Next, a transparent conductive film is formed thereon with a thickness of 80 to 120 nm, and the pixel electrode 162 is formed by patterning. (FIG. 9) Indium oxide-zinc oxide alloy (In ₂ O ₃ —ZnO) and zinc oxide (ZnO) are also suitable materials for the transparent conductive film. Furthermore, in order to increase the transmittance and conductivity of visible light, gallium ( Zinc oxide (ZnO: Ga) to which Ga) is added can be preferably used.

  Further, the pixel electrode 162 is formed in contact with the connection electrode 160 so as to overlap with the drain region of the pixel TFT, and further, a semiconductor layer (impurity region) functioning as one electrode forming a storage capacitor. 150) and an electrical connection is formed.

  Note that although an example in which a transparent conductive film is used as the pixel electrode is described here, a reflective display device can be manufactured if the pixel electrode is formed using a conductive material having reflectivity. In that case, the pixel electrode can be formed at the same time in the step of manufacturing the electrode, and the pixel electrode is made of a highly reflective material such as a film containing Al or Ag as a main component or a laminated film thereof. Is desirable.

  As described above, the driver circuit 205 including the n-channel TFT 201 and the p-channel TFT 202 and the pixel portion 206 including the pixel TFT 203 and the storage capacitor 204 can be formed over the same substrate. In this specification, such a substrate is referred to as an active matrix substrate for convenience.

  The n-channel TFT 201 of the driver circuit 205 includes a channel formation region 163, a low-concentration impurity region 134b (GOLD region) overlapping with the first conductive layer 138 that forms part of the gate electrode, and a low-concentration region formed outside the gate electrode. An impurity region 134a (LDD region) and a high concentration impurity region 130 functioning as a source region or a drain region are provided. The p-channel TFT 202 functions as a channel formation region 164, an impurity region 149 overlapping with the first conductive layer 139 that forms part of the gate electrode, an impurity region 148 formed outside the gate electrode, and a source region or a drain region. An impurity region 147 is formed.

  The pixel TFT 203 of the pixel portion 206 includes a channel formation region 165, a low concentration impurity region 136b (GOLD region) overlapping the first conductive layer 140 forming the gate electrode, and a low concentration impurity region 136a (outside of the gate electrode). LDD region) and a high concentration impurity region 132 functioning as a source region or a drain region. In addition, an impurity element imparting p-type conductivity is added to each of the semiconductor layers 150 to 152 functioning as one electrode of the storage capacitor 204. The storage capacitor 204 is formed of electrodes 125 and 141 and semiconductor layers 150 to 152 and 166 using the insulating film 144 as a dielectric.

  In this embodiment, a process for manufacturing an active matrix liquid crystal display device from the active matrix substrate manufactured in Embodiment 1 will be described below. FIG. 10 is used for the description.

First, after obtaining the active matrix substrate in the state of FIG. 9 according to Example 1, an alignment film 167 is formed on the active matrix substrate of FIG. 9 and a rubbing process is performed.
In this embodiment, before forming the alignment film 167, columnar spacers for holding the substrate interval are formed at desired positions by patterning an organic resin film such as an acrylic resin film. Further, instead of the columnar spacers, spherical spacers may be scattered over the entire surface of the substrate.

  Next, a counter substrate 168 is prepared. This counter substrate is provided with a color filter in which a colored layer 174 and a light shielding layer 175 are arranged corresponding to each pixel. Further, a light shielding layer 177 is also provided in the drive circuit portion. A planarizing film 176 that covers the color filter and the light shielding layer 177 is provided. Next, a counter electrode 169 made of a transparent conductive film was formed over the planarizing film 176 in the pixel portion, an alignment film 170 was formed over the entire surface of the counter substrate, and a rubbing process was performed.

  Then, the active matrix substrate on which the pixel portion and the driving circuit are formed and the counter substrate are attached to each other with a sealant 171. A filler is mixed in the sealing material 171, and two substrates are bonded to each other with a uniform interval by the filler and the columnar spacer. Thereafter, a liquid crystal material 173 is injected between both the substrates and completely sealed with a sealant (not shown). A known liquid crystal material may be used for the liquid crystal material 173. In this way, the active matrix liquid crystal display device shown in FIG. 10 is completed. If necessary, the active matrix substrate or the counter substrate is divided into a desired shape. Furthermore, a polarizing plate or the like was appropriately provided using a known technique. And FPC was affixed using the well-known technique.

The structure of the liquid crystal display panel thus obtained will be described with reference to the top view of FIG.
In addition, the same code | symbol was used for the part corresponding to FIG.

  11A is a top view, a pixel portion, a driving circuit, an external input terminal 207 to which an FPC (Flexible Printed Circuit Board: Flexible Printed Circuit) is attached, and wiring that connects the external input terminal to the input portion of each circuit. An active matrix substrate formed with 208 and the like and a counter substrate 168 provided with a color filter or the like are attached to each other with a sealant 171 interposed therebetween.

A light shielding layer 177a is provided on the counter substrate side so as to overlap with the gate wiring side driving circuit 205a, and a light shielding layer 177b is formed on the counter substrate side so as to overlap with the source wiring side driving circuit 205b. In addition, the color filter 209 provided on the counter substrate side over the pixel portion 206 is provided with a light shielding layer and a colored layer of each color of red (R), green (G), and blue (B) corresponding to each pixel. It has been. When actually displaying, red (R)
A color display is formed with three colors, a colored layer of green, a colored layer of green (G), and a colored layer of blue (B). The arrangement of the colored layers of these colors is arbitrary.

  Here, the color filter 209 is provided on the counter substrate for colorization; however, there is no particular limitation. When an active matrix substrate is manufactured, a color filter may be formed on the active matrix substrate.

  In addition, a light-shielding layer is provided between adjacent pixels in the color filter to shield light other than the display area. Here, the light shielding layers 177a and 177b are also provided in the region covering the driver circuit. However, the region covering the driver circuit is covered with a cover when the liquid crystal display device is incorporated later as a display portion of an electronic device. It is good also as a structure which does not provide a light shielding layer. Further, when the active matrix substrate is manufactured, a light shielding layer may be formed on the active matrix substrate.

  Further, without providing the light-shielding layer, the light-shielding layer is appropriately disposed between the counter substrate and the counter electrode so as to be shielded from light by stacking a plurality of colored layers constituting the color filter. Or the drive circuit may be shielded from light.

  Further, an FPC composed of a base film 210 and a wiring 211 is bonded to the external input terminal with an anisotropic conductive resin 212. Furthermore, the mechanical strength is increased by the reinforcing plate.

  FIG. 11B is a cross-sectional view taken along the line AA ′ of the external input terminal 207 shown in FIG. Since the outer diameter of the conductive particles 214 is smaller than the pitch of the wirings 215, if the amount dispersed in the adhesive 212 is appropriate, it is electrically connected to the corresponding wiring on the FPC side without short-circuiting with the adjacent wirings. Can be formed.

  The liquid crystal display panel manufactured as described above can be used as a display portion of various electronic devices.

  In this embodiment, a method for manufacturing an active matrix substrate, which is different from that in Embodiment 1, will be described with reference to FIGS. Although the transmissive display device is formed in the first embodiment, the present embodiment is characterized in that a reflective display device is formed and the number of masks is reduced as compared with the first embodiment.

  First, in this embodiment, a substrate 400 made of glass such as barium borosilicate glass represented by Corning # 7059 glass or # 1737 glass or aluminoborosilicate glass is used. Note that the substrate 400 may be a quartz substrate, a silicon substrate, a metal substrate, or a stainless substrate on which an insulating film is formed. Further, a plastic substrate having heat resistance that can withstand the processing temperature of this embodiment may be used.

Next, a base film 401 made of an insulating film such as a silicon oxide film, a silicon nitride film, or a silicon oxynitride film is formed over the substrate 400. Although a two-layer structure is used as the base film 401 in this embodiment, a single-layer film of the insulating film or a structure in which two or more layers are stacked may be used. As the first layer of the base film 401, a silicon oxynitride film 401a formed using SiH ₄ , NH ₃ , and N ₂ O as a reactive gas is formed by using a plasma CVD method to a thickness of 10 to 200 nm (preferably 50 to 100 nm). To do. In this embodiment, a 50 nm thick silicon oxynitride film 401a (composition ratio Si = 32%, O = 27%, N = 24%, H = 17%) is formed. Next, as a second layer of the base film 401, a silicon oxynitride film 401b formed by using a plasma CVD method and using SiH ₄ and N ₂ O as a reaction gas is formed to a thickness of 50 to 200 nm (preferably 100 to 150 nm). Stacked to a thickness. In this embodiment, a silicon oxynitride film 401b (composition ratio Si = 32%, O = 59%, N = 7%, H = 2%) having a thickness of 100 nm is formed.

  Next, semiconductor layers 402 to 406 are formed over the base film. The semiconductor layers 402 to 406 are formed by forming a semiconductor film having an amorphous structure by a known means (a sputtering method, an LPCVD method, a plasma CVD method, or the like), and then a known crystallization treatment (laser crystallization method, heat A crystalline semiconductor film obtained by performing a crystallization method or a thermal crystallization method using a catalyst such as nickel) is formed by patterning into a desired shape. The semiconductor layers 402 to 406 are formed to have a thickness of 25 to 80 nm (preferably 30 to 60 nm). There is no limitation on the material of the crystalline semiconductor film, but the crystalline semiconductor film is preferably formed of silicon or a silicon germanium (SiGe) alloy. In this example, a 55 nm amorphous silicon film was formed by plasma CVD, and then a solution containing nickel was held on the amorphous silicon film. This amorphous silicon film is dehydrogenated (500 ° C., 1 hour), then thermally crystallized (550 ° C., 4 hours), and then laser annealing treatment is performed to improve crystallization. Thus, a crystalline silicon film was formed. Then, semiconductor layers 402 to 406 were formed by patterning the crystalline silicon film using a photolithography method.

  Further, after forming the semiconductor layers 402 to 406, a small amount of impurity element (boron or phosphorus) may be doped in order to control the threshold value of the TFT.

When a crystalline semiconductor film is formed by a laser crystallization method, a pulse oscillation type or continuous emission type excimer laser, YAG laser, or YVO ₄ laser can be used. When these lasers are used, it is preferable to use a method in which laser light emitted from a laser oscillator is linearly collected by an optical system and irradiated onto a semiconductor film. Crystallization conditions are appropriately selected by the practitioner. When an excimer laser is used, the pulse oscillation frequency is 30 Hz, and the laser energy density is 100 to 400 mJ / cm ² (typically 200 to 300 mJ / cm ^2). ). In the case of using a YAG laser, the second harmonic is used and the pulse oscillation frequency is set to 1 to 10 kHz, and the laser energy density is set to 300 to 600 mJ / cm ² (typically 350 to 500 mJ / cm ² ). Then, when the laser beam condensed linearly with a width of 100 to 1000 μm, for example 400 μm, is irradiated over the entire surface of the substrate, the superposition ratio (overlap ratio) of the linear laser light at this time is 80 to 98%. Good.

  Next, a gate insulating film 407 covering the semiconductor layers 402 to 406 is formed. The gate insulating film 407 is formed of an insulating film containing silicon with a thickness of 40 to 150 nm by using a plasma CVD method or a sputtering method. In this embodiment, a silicon oxynitride film (composition ratio: Si = 32%, O = 59%, N = 7%, H = 2%) with a thickness of 110 nm is formed by plasma CVD. Needless to say, the gate insulating film is not limited to the silicon oxynitride film, and another insulating film containing silicon may be used as a single layer or a stacked structure.

When a silicon oxide film is used, TEOS (Tetraethyl Orthosilicate) and O ₂ are mixed by a plasma CVD method to a reaction pressure of 40 Pa, a substrate temperature of 300 to 400 ° C., and a high frequency (13.56 MHz) power density of 0. It can be formed by discharging at 5 to 0.8 W / cm ² . The silicon oxide film thus manufactured can obtain good characteristics as a gate insulating film by subsequent thermal annealing at 400 to 500 ° C.

Next, as illustrated in FIG. 12A, a first conductive film 408 with a thickness of 20 to 100 nm and a second conductive film 409 with a thickness of 100 to 400 nm are stacked over the gate insulating film 407. In this embodiment, a first conductive film 408 made of a TaN film with a thickness of 30 nm and a second conductive film 409 made of a W film with a thickness of 370 nm are stacked. The TaN film was formed by sputtering, and was sputtered in a nitrogen-containing atmosphere using a Ta target. The W film was formed by sputtering using a W target. In addition, it can be formed by a thermal CVD method using tungsten hexafluoride (WF ₆ ). In any case, in order to use as a gate electrode, it is necessary to reduce the resistance, and the resistivity of the W film is desirably 20 μΩcm or less. The resistivity of the W film can be reduced by increasing the crystal grains. However, when there are many impurity elements such as oxygen in the W film, the crystallization is hindered and the resistance is increased. Therefore, in this embodiment, the sputtering method using a target of high purity W (purity 99.9999% or purity 99.99%) is sufficient so that impurities are not mixed from the gas phase during film formation. By forming the W film in consideration, a resistivity of 9 to 20 μΩcm could be realized.

  In this embodiment, the first conductive film 408 is TaN and the second conductive film 409 is W. However, there is no particular limitation, and all of them are Ta, W, Ti, Mo, Al, Cu, Cr, Nd. You may form with the element selected from these, or the alloy material or compound material which has the said element as a main component. Alternatively, a semiconductor film typified by a polycrystalline silicon film doped with an impurity element such as phosphorus may be used. Further, an AgPdCu alloy may be used. In addition, the first conductive film is formed using a tantalum (Ta) film, the second conductive film is formed using a W film, the first conductive film is formed using a titanium nitride (TiN) film, and the second conductive film is formed. The first conductive film is formed of a tantalum nitride (TaN) film, the second conductive film is formed of an Al film, and the first conductive film is formed of a tantalum nitride (TaN) film. The second conductive film may be a combination of Cu films.

Next, resist masks 410 to 415 are formed by photolithography, and a first etching process is performed to form electrodes and wirings. The first etching process is performed under the first and second etching conditions. In this embodiment, an ICP (Inductively Coupled Plasma) etching method is used as the first etching condition, CF ₄ , Cl ₂ and O ₂ are used as etching gases, and the respective gas flow ratios are 25. Etching was performed by generating plasma by applying 500 W of RF (13.56 MHz) power to the coil type electrode at a pressure of 1 Pa at a pressure of 1/25/10 (sccm). Here, a dry etching apparatus (Model E645- □ ICP) using ICP manufactured by Matsushita Electric Industrial Co., Ltd. was used. 150 W RF (13.56 MHz) power is also applied to the substrate side (sample stage), and a substantially negative self-bias voltage is applied. The W film is etched under the first etching condition so that the end portion of the second conductive layer is tapered. FIG. 17A shows a top view of a pixel portion using an optical microscope immediately after etching under the first etching condition.

Thereafter, the masks 410 to 415 made of resist are changed to the second etching conditions without removing them, CF ₄ and Cl ₂ are used as etching gases, and the respective gas flow ratios are set to 30/30 (sccm). Etching was performed for about 30 seconds by applying 500 W RF (13.56 MHz) power to the coil electrode at a pressure of 1 Pa to generate plasma. 20 W of RF (13.56 MHz) power is also applied to the substrate side (sample stage), and a substantially negative self-bias voltage is applied. Under the second etching condition in which CF ₄ and Cl ₂ are mixed, the W film and the TaN film are etched to the same extent. Note that in order to perform etching without leaving a residue on the gate insulating film, it is preferable to increase the etching time at a rate of about 10 to 20%.

  In the first etching process, the shape of the mask made of resist is made suitable, and the end portions of the first conductive layer and the second conductive layer are tapered due to the effect of the bias voltage applied to the substrate side. It becomes. The angle of the tapered portion is 15 ° to 45 °. Thus, the first shape conductive layers 417 to 422 (first conductive layers 417 a to 422 a and second conductive layers 417 b to 422 b) composed of the first conductive layer and the second conductive layer by the first etching treatment. Form. Reference numeral 416 denotes a gate insulating film, and a region not covered with the first shape conductive layers 417 to 422 is etched and thinned by about 20 to 50 nm. FIG. 17B shows a top view of a pixel portion using an optical microscope immediately after etching under the second etching condition.

Then, a first doping process is performed without removing the resist mask, and an impurity element imparting n-type conductivity is added to the semiconductor layer. (FIG. 12B) The doping process may be performed by an ion doping method or an ion implantation method. The conditions of the ion doping method are a dose amount of 1 × 10 ^{13 to} 5 × 10 ¹⁵ atoms / cm ² and an acceleration voltage of 60 to 100 keV. In this embodiment, the dosage is 1.5 × 10 ¹⁵ atoms / cm ² and the acceleration voltage is 80 keV. As an impurity element imparting n-type, an element belonging to Group 15, typically phosphorus (P) or arsenic (As), is used here, but phosphorus (P) is used. In this case, the conductive layers 417 to 421 serve as a mask for the impurity element imparting n-type, and the high concentration impurity regions 423 to 427 are formed in a self-aligning manner. An impurity element imparting n-type conductivity is added to the high-concentration impurity regions 423 to 427 in a concentration range of 1 × 10 ²⁰ to 1 × 10 ²¹ atoms / cm ³ .

Next, a second etching process is performed without removing the resist mask.
Here, CF ₄ , Cl _2, and O ₂ are used as the etching gas, and the W film is selectively etched. At this time, the first conductive layers 428b to 433b are formed by the second etching process. On the other hand, the second conductive layers 417a to 422a are hardly etched, and the second conductive layers 428a to 433a are formed. Next, a second doping process is performed to obtain the state of FIG. Doping is performed using the second conductive layers 417a to 422a as a mask for the impurity element so that the impurity element is added to the semiconductor layer below the tapered portion of the first conductive layer. In this manner, impurity regions 434 to 438 overlapping with the first conductive layer are formed. The concentration of phosphorus (P) added to the impurity region has a gentle concentration gradient according to the thickness of the tapered portion of the first conductive layer. Note that in the semiconductor layer overlapping the tapered portion of the first conductive layer, the impurity concentration is slightly lower from the end of the tapered portion of the first conductive layer to the inside, but the concentration is almost the same. . Impurity elements are also added to the impurity regions 423 to 427 to form impurity regions 439 to 443.

Next, a third etching process is performed without removing the resist mask.
(FIG. 13A) In this third etching process, the tapered portion of the first conductive layer is partially etched to reduce a region overlapping with the semiconductor layer. The third etching process is performed using a reactive ion etching method (RIE method) using CHF ₃ as an etching gas. By the third etching process, first conductive layers 444 to 449 are formed. At this time, the insulating film 416 is also etched to form insulating films 450a to 450d.

  By the third etching process, impurity regions (LDD regions) 434a to 438a that do not overlap with the first conductive layers 444 to 448 are formed. Note that the impurity regions (GOLD regions) 434 b to 438 b remain overlapped with the first conductive layers 444 to 448.

  Thus, in this embodiment, the impurity concentration in the impurity regions (GOLD regions) 434b to 438b overlapping with the first conductive layers 444 to 448 and the impurity region not overlapping with the first conductive layers 444 to 448 ( The difference from the impurity concentration in the LDD regions 434a to 438a can be reduced, and the reliability can be improved.

Next, after removing the resist mask, new resist masks 452 to 454 are formed, and a third doping process is performed. By this third doping treatment, an impurity region 455 in which an impurity element imparting a conductivity type (p-type) opposite to the one conductivity type (n-type) is added to the semiconductor layer serving as the active layer of the p-channel TFT. ~ 460 are formed. The first conductive layers 445 and 448 are used as masks against the impurity element, and an impurity element imparting p-type is added to form an impurity region in a self-aligning manner. In this embodiment, the impurity regions 455 to 460 are formed by ion doping using diborane (B ₂ H ₆ ). (FIG. 13B) In this third doping process, the semiconductor layer forming the n-channel TFT is covered with masks 452 to 454 made of resist. By the first doping process and the second doping process, phosphorus is added to the impurity regions 455 to 460 at different concentrations, and the concentration of the impurity element imparting p-type in each of the regions is 2 ×. By performing the doping treatment so as to be 10 ^{20 to} 2 × 10 ²¹ atoms / cm ³ , no problem arises because it functions as the source region and drain region of the p-channel TFT. In this embodiment, since a part of the semiconductor layer serving as an active layer of the p-channel TFT is exposed, there is an advantage that an impurity element (boron) can be easily added.

  Through the above steps, impurity regions are formed in the respective semiconductor layers.

  Next, the resist masks 452 to 454 are removed, and a first interlayer insulating film 461 is formed. The first interlayer insulating film 461 is formed of an insulating film containing silicon with a thickness of 100 to 200 nm by using a plasma CVD method or a sputtering method. In this embodiment, a silicon oxynitride film with a thickness of 150 nm is formed by a plasma CVD method. Needless to say, the first interlayer insulating film 461 is not limited to the silicon oxynitride film, and an insulating film containing other silicon may be used as a single layer or a stacked structure.

  Next, as shown in FIG. 13C, a step of activating the impurity element added to each semiconductor layer is performed. This activation process is performed by a thermal annealing method using a furnace annealing furnace. As the thermal annealing method, it may be performed at 400 to 700 ° C., typically 500 to 550 ° C. in a nitrogen atmosphere having an oxygen concentration of 1 ppm or less, preferably 0.1 ppm or less. The activation treatment was performed by heat treatment. In addition to the thermal annealing method, a laser annealing method or a rapid thermal annealing method (RTA method) can be applied.

  In this embodiment, at the same time as the activation treatment, nickel used as a catalyst during crystallization is gettered to impurity regions 439, 441, 442, 455, and 458 containing high-concentration phosphorus, and mainly the channel. The nickel concentration in the semiconductor layer that becomes the formation region is reduced. A TFT having a channel formation region manufactured in this manner has a low off-current value and good crystallinity, so that high field-effect mobility can be obtained and good characteristics can be achieved.

  In addition, an activation process may be performed before forming the first interlayer insulating film. However, when the wiring material used is weak against heat, it is activated after an interlayer insulating film (insulating film containing silicon as a main component, for example, a silicon nitride film) is formed to protect the wiring and the like as in this embodiment. It is preferable to perform the conversion treatment.

  Furthermore, a heat treatment is performed at 300 to 550 ° C. for 1 to 12 hours in an atmosphere containing 3 to 100% hydrogen to perform a step of hydrogenating the semiconductor layer. In this embodiment, heat treatment was performed at 410 ° C. for 1 hour in a nitrogen atmosphere containing about 3% hydrogen. This step is a step of terminating dangling bonds in the semiconductor layer with hydrogen contained in the interlayer insulating film. As another means of hydrogenation, plasma hydrogenation (using hydrogen excited by plasma) may be performed.

  In the case where a laser annealing method is used as the activation treatment, it is desirable to irradiate a laser beam such as an excimer laser or a YAG laser after performing the hydrogenation.

  Next, a second interlayer insulating film 462 made of an inorganic insulating film material or an organic insulating material is formed over the first interlayer insulating film 461. In this example, an acrylic resin film having a film thickness of 1.6 μm was formed, but a film having a viscosity of 10 to 1000 cp, preferably 40 to 200 cp, and having an uneven surface formed.

  In this embodiment, in order to prevent specular reflection, the surface of the pixel electrode is formed with the unevenness by forming the second interlayer insulating film having the unevenness on the surface. In addition, a convex portion may be formed in a region below the pixel electrode in order to make the surface of the pixel electrode uneven to achieve light scattering. In that case, since the convex portion can be formed using the same photomask as that of the TFT, it can be formed without increasing the number of steps. In addition, this convex part should just be suitably provided on the board | substrate of pixel part area | regions other than wiring and a TFT part. Thus, irregularities are formed on the surface of the pixel electrode along the irregularities formed on the surface of the insulating film covering the convex portions.

  Alternatively, a film whose surface is planarized may be used as the second interlayer insulating film 462. In that case, after forming the pixel electrode, adding a step such as a known sandblasting method or etching method to make the surface uneven, prevent specular reflection, and increase the whiteness by scattering the reflected light Is preferred.

  In the driver circuit 506, wirings 463 to 467 that are electrically connected to the impurity regions are formed. Note that these wirings are formed by patterning a laminated film of a Ti film having a thickness of 50 nm and an alloy film (alloy film of Al and Ti) having a thickness of 500 nm.

  In the pixel portion 507, a pixel electrode 470, a gate wiring 469, and a connection electrode 468 are formed. (FIG. 14) With this connection electrode 468, the source wiring (lamination of 443b and 449) is electrically connected to the pixel TFT. In addition, the gate wiring 469 is electrically connected to the gate electrode of the pixel TFT. In addition, the pixel electrode 470 is electrically connected to the drain region 442 of the pixel TFT and further electrically connected to the semiconductor layer 458 functioning as one electrode forming a storage capacitor. Further, as the pixel electrode 470, it is desirable to use a highly reflective material such as a film containing Al or Ag as a main component or a laminated film thereof.

  As described above, a CMOS circuit including an n-channel TFT 501 and a p-channel TFT 502, a driver circuit 506 having an n-channel TFT 503, and a pixel portion 507 having a pixel TFT 504 and a storage capacitor 505 are formed over the same substrate. can do. Thus, the active matrix substrate is completed.

  The n-channel TFT 501 of the driver circuit 506 includes a channel formation region 471, a low concentration impurity region 434 b (GOLD region) overlapping with the first conductive layer 444 that forms part of the gate electrode, and a low concentration formed outside the gate electrode. An impurity region 434a (LDD region) and a high-concentration impurity region 439 functioning as a source region or a drain region are provided. A p-channel TFT 502 which is connected to the n-channel TFT 501 and the electrode 466 to form a CMOS circuit has a channel formation region 472, an impurity region 457 overlapping with the gate electrode, an impurity region 456 formed outside the gate electrode, and a source region Alternatively, a high concentration impurity region 455 which functions as a drain region is provided. The n-channel TFT 503 includes a channel formation region 473, a low concentration impurity region 436 b (GOLD region) that overlaps with the first conductive layer 446 that forms part of the gate electrode, and a low concentration impurity formed outside the gate electrode. A region 436a (LDD region) and a high-concentration impurity region 441 functioning as a source region or a drain region are provided.

  The pixel TFT 504 in the pixel portion includes a channel formation region 474, a low concentration impurity region 437 b (GOLD region) that overlaps with the first conductive layer 447 constituting a part of the gate electrode, and a low concentration impurity region formed outside the gate electrode. 437a (LDD region) and a high concentration impurity region 443 functioning as a source region or a drain region. In addition, an impurity element imparting p-type conductivity is added to each of the semiconductor layers 458 to 460 functioning as one electrode of the storage capacitor 505. The storage capacitor 505 is formed of an electrode (stack of 448 and 432b) and semiconductor layers 458 to 460 using the insulating film 451 as a dielectric.

  In the pixel structure of this embodiment, the end of the pixel electrode overlaps with the source wiring so that the gap between the pixel electrodes is shielded from light without using a black matrix.

  A top view of a pixel portion of an active matrix substrate manufactured in this embodiment is shown in FIG. In addition, the same code | symbol is used for the part corresponding to FIGS. A chain line A-A ′ in FIG. 14 corresponds to a cross-sectional view taken along the chain line A-A ′ in FIG. 15. Further, a chain line B-B ′ in FIG. 14 corresponds to a cross-sectional view taken along the chain line B-B ′ in FIG. 15.

  Further, according to the steps shown in this embodiment, the number of photomasks necessary for manufacturing the active matrix substrate can be five. As a result, the process can be shortened, and the manufacturing cost can be reduced and the yield can be improved.

  In this embodiment, a process for manufacturing a reflective liquid crystal display device from the active matrix substrate manufactured in Embodiment 3 will be described below. FIG. 16 is used for the description.

  First, after obtaining an active matrix substrate in the state shown in FIG. 14 according to Embodiment 3, an alignment film 471 is formed on at least the pixel electrode 470 on the active matrix substrate shown in FIG. In this embodiment, before forming the alignment film 471, an organic resin film such as an acrylic resin film is patterned to form columnar spacers (not shown) for maintaining the substrate interval at a desired position. Further, instead of the columnar spacers, spherical spacers may be scattered over the entire surface of the substrate.

  Next, a counter substrate 471 is prepared. Next, colored layers 472 and 473 and a planarization film 474 are formed over the counter substrate 471. The red colored layer 472 and the blue colored layer 473 are overlapped to form a light shielding portion. Further, the light shielding portion may be formed by partially overlapping the red colored layer and the green colored layer.

  In this embodiment, the substrate shown in Embodiment 3 is used. Therefore, in FIG. 15 showing a top view of the pixel portion of Example 3, at least the gap between the gate wiring 469 and the pixel electrode 470, the gap between the gate wiring 469 and the connection electrode 468, and the gap between the connection electrode 468 and the pixel electrode 470 are shown. It is necessary to shield the light. In this example, the respective colored layers were arranged so that the light-shielding portions formed by the lamination of the colored layers overlapped at the positions where light shielding should be performed, and the counter substrate was bonded.

  As described above, the number of steps can be reduced by shielding the gap between the pixels with the light shielding portion formed by the lamination of the colored layers without forming a light shielding layer such as a black mask.

  Next, a counter electrode 475 made of a transparent conductive film was formed over the planarization film 474 in at least the pixel portion, an alignment film 476 was formed over the entire surface of the counter substrate, and a rubbing process was performed.

  Then, the active matrix substrate on which the pixel portion and the driver circuit are formed and the counter substrate are attached to each other with a sealant 477. A filler is mixed in the sealing material 477, and two substrates are bonded to each other with a uniform interval by the filler and the columnar spacer. Thereafter, a liquid crystal material 478 is injected between both substrates and completely sealed with a sealant (not shown). A known liquid crystal material may be used for the liquid crystal material 478. Since the present embodiment is a reflection type, the substrate interval is about half that of the first embodiment. In this way, the reflection type liquid crystal display device shown in FIG. 16 is completed. If necessary, the active matrix substrate or the counter substrate is divided into a desired shape. Further, a polarizing plate (not shown) was attached only to the counter substrate. And FPC was affixed using the well-known technique.

  The liquid crystal display panel manufactured as described above can be used as a display portion of various electronic devices.

  In this example, an example in which an EL (electroluminescence) display device is manufactured using the present invention will be described. FIG. 18 is a cross-sectional view of the EL display device of the present invention.

  In FIG. 18, a switching TFT 603 provided over a substrate 700 is formed using the n-channel TFT 503 in FIG. Therefore, the description of the n-channel TFT 503 may be referred to for the description of the structure.

  Note that although a double gate structure in which two channel formation regions are formed is used in this embodiment, a single gate structure in which one channel formation region is formed or a triple gate structure in which three channel formation regions are formed may be used.

  A driver circuit (an n-channel TFT 601 and a p-channel TFT 602) provided over the substrate 700 is formed using the CMOS circuit in FIG. Therefore, for the description of the structure, the description of the n-channel TFT 501 and the p-channel TFT 502 may be referred to. In this embodiment, a single gate structure is used, but a double gate structure or a triple gate structure may be used.

  Further, the wirings 701 and 703 function as source wirings of the CMOS circuit, and the wiring 702 functions as a drain wiring. The wiring 704 functions as a wiring that electrically connects the source wiring 708 and the source region of the switching TFT, and the wiring 705 functions as a wiring that electrically connects the drain wiring 709 and the drain region of the switching TFT.

  Note that the current control TFT 604 is formed using the p-channel TFT 502 of FIG. Accordingly, the description of the p-channel TFT 502 may be referred to for the description of the structure. In this embodiment, a single gate structure is used, but a double gate structure or a triple gate structure may be used.

  A wiring 706 is a source wiring (corresponding to a current supply line) of the current control TFT, and 707 is an electrode that is electrically connected to the pixel electrode 710 by being overlaid on the pixel electrode 710 of the current control TFT.

  Reference numeral 710 denotes a pixel electrode (EL element anode) made of a transparent conductive film. As the transparent conductive film, a compound of indium oxide and tin oxide, a compound of indium oxide and zinc oxide, zinc oxide, tin oxide, or indium oxide can be used. Moreover, you may use what added the gallium to the said transparent conductive film. The pixel electrode 710 is formed on the flat interlayer insulating film 711 before forming the wiring. In this embodiment, it is very important to flatten the step due to the TFT using the flattening film 711 made of resin. Since an EL layer to be formed later is very thin, a light emission defect may occur due to the presence of a step. Therefore, it is desirable to planarize the pixel electrode before forming the pixel electrode so that the EL layer can be formed as flat as possible.

After the wirings 701 to 707 are formed, a bank 712 is formed as shown in FIG.
The bank 712 may be formed by patterning an insulating film or organic resin film containing silicon of 100 to 400 nm.

Note that since the bank 712 is an insulating film, attention must be paid to electrostatic breakdown of elements during film formation. In this embodiment, carbon particles or metal particles are added to the insulating film that is the material of the bank 712 to reduce the resistivity and suppress the generation of static electricity. At this time, if the addition amount of carbon particles or metal particles is adjusted so that the resistivity is 1 × 10 ⁶ to 1 × 10 ¹² Ω · m (preferably 1 × 10 ⁸ to 1 × 10 ¹⁰ Ω · m). good.

An EL layer 713 is formed over the pixel electrode 710. Although only one pixel is shown in FIG. 18, in this embodiment, EL layers corresponding to each color of R (red), G (green), and B (blue) are separately formed. In this embodiment, a low molecular organic EL material is formed by a vapor deposition method. Specifically, a laminated structure in which a copper phthalocyanine (CuPc) film having a thickness of 20 nm is provided as a hole injection layer and a tris-8-quinolinolato aluminum complex (Alq ₃ ) film having a thickness of 70 nm is provided thereon as a light emitting layer. It is said.
The emission color can be controlled by adding a fluorescent dye such as quinacridone, perylene, or DCM1 to Alq ₃ .

However, the above example is an example of an organic EL material that can be used as an EL layer, and is not necessarily limited to this. An EL layer (a layer for emitting light and moving carriers therefor) may be formed by freely combining a light-emitting layer, a charge transport layer, or a charge injection layer. For example, in this embodiment, an example in which a low molecular weight organic EL material is used as an EL layer is shown, but a high molecular weight organic EL material may be used. It is also possible to use an inorganic material such as silicon carbide for the charge transport layer or the charge injection layer.
As these organic EL materials and inorganic materials, known materials can be used.

  Next, a cathode 714 made of a conductive film is provided over the EL layer 713. In this embodiment, an alloy film of aluminum and lithium is used as the conductive film. Of course, a known MgAg film (magnesium and silver alloy film) may be used. As the cathode material, a conductive film made of an element belonging to Group 1 or Group 2 of the periodic table or a conductive film added with these elements may be used.

  When the cathode 714 is formed, the EL element 715 is completed. Note that the EL element 715 here refers to a capacitor formed by a pixel electrode (anode) 710, an EL layer 713, and a cathode 714.

  It is effective to provide a passivation film 716 so as to completely cover the EL element 715. As the passivation film 716, an insulating film including a carbon film, a silicon nitride film, or a silicon nitride oxide film is used, and the insulating film is used as a single layer or a combination thereof.

At this time, it is preferable to use a film with good coverage as the passivation film, and it is effective to use a carbon film, particularly a DLC (diamond-like carbon) film. Since the DLC film can be formed in a temperature range from room temperature to 100 ° C., it can be easily formed over the EL layer 713 having low heat resistance. In addition, the DLC film has a high blocking effect against oxygen and can suppress oxidation of the EL layer 713. Therefore, the problem that the EL layer 713 is oxidized during the subsequent sealing process can be prevented.

  Further, a sealing material 717 is provided over the passivation film 716 and a cover material 718 is attached thereto. As the sealing material 717, an ultraviolet curable resin may be used, and it is effective to provide a substance having a hygroscopic effect or a substance having an antioxidant effect inside. In this embodiment, the cover material 718 is formed by forming a carbon film (preferably a diamond-like carbon film) on both surfaces of a glass substrate, a quartz substrate, or a plastic substrate (including a plastic film).

  Thus, an EL display device having a structure as shown in FIG. 18 is completed. Note that it is effective to continuously process the steps from the formation of the bank 712 to the formation of the passivation film 716 using a multi-chamber type (or in-line type) film formation apparatus without releasing to the atmosphere. . Further, it is possible to continuously process the process up to the step of bonding the cover material 718 without releasing to the atmosphere.

  Thus, the n-channel TFTs 601 and 602, the switching TFT (n-channel TFT) 603, and the current control TFT (n-channel TFT) 604 are formed on the insulator 700 having the plastic substrate as a base. The number of masks required in the manufacturing process so far is smaller than that of a general active matrix EL display device.

  That is, the TFT manufacturing process is greatly simplified, and the yield can be improved and the manufacturing cost can be reduced.

  Furthermore, as described with reference to FIGS. 14A and 14B, an n-channel TFT which is resistant to deterioration due to the hot carrier effect can be formed by providing an impurity region overlapping with the gate electrode through an insulating film. Therefore, a highly reliable EL display device can be realized.

  Further, in this embodiment, only the configuration of the pixel portion and the drive circuit is shown. However, according to the manufacturing process of this embodiment, other logic circuits such as a signal dividing circuit, a D / A converter, an operational amplifier, and a γ correction circuit are provided. Can be formed on the same insulator, and a memory and a microprocessor can also be formed.

  Furthermore, the EL light-emitting device of this example after performing the sealing (or sealing) process for protecting the EL element will be described with reference to FIG. In addition, the code | symbol used in FIG. 18 is quoted as needed.

  FIG. 19A is a top view illustrating a state where the EL element is sealed, and FIG. 19B is a cross-sectional view taken along line A-A ′ in FIG. 19A. Reference numeral 801 indicated by a dotted line denotes a source side driver circuit, 806 denotes a pixel portion, and 807 denotes a gate side driver circuit. Reference numeral 901 denotes a cover material, reference numeral 902 denotes a first sealing material, reference numeral 903 denotes a second sealing material, and a sealing material 907 is provided on the inner side surrounded by the first sealing material 902.

  Reference numeral 904 denotes a wiring for transmitting signals input to the source side driver circuit 801 and the gate side driver circuit 807, and receives a video signal and a clock signal from an FPC (flexible printed circuit) 905 serving as an external input terminal. Although only the FPC is shown here, a printed wiring board (PWB) may be attached to the FPC. The EL display device in this specification includes not only the EL display device main body but also a state in which an FPC or PWB is attached thereto.

  Next, a cross-sectional structure will be described with reference to FIG. A pixel portion 806 and a gate side driver circuit 807 are formed above the substrate 700, and the pixel portion 806 is formed by a plurality of pixels including a current control TFT 604 and a pixel electrode 710 electrically connected to a drain thereof. . The gate side driver circuit 807 is formed using a CMOS circuit (see FIG. 14) in which an n-channel TFT 601 and a p-channel TFT 602 are combined.

  The pixel electrode 710 functions as an anode of the EL element. A bank 712 is formed at both ends of the pixel electrode 710, and an EL layer 713 and a cathode 714 of the EL element are formed on the pixel electrode 710.

  The cathode 714 also functions as a wiring common to all pixels, and is electrically connected to the FPC 905 via the connection wiring 904. Further, all elements included in the pixel portion 806 and the gate side driver circuit 807 are covered with a cathode 714 and a passivation film 716.

  Further, a cover material 901 is bonded to the first seal material 902. Note that a spacer made of a resin film may be provided in order to secure a gap between the cover material 901 and the EL element. A sealing material 907 is filled inside the first sealing material 902. Note that an epoxy-based resin is preferably used as the first sealing material 902 and the sealing material 907. The first sealing material 902 is desirably a material that does not transmit moisture and oxygen as much as possible. Further, a substance having a hygroscopic effect or a substance having an antioxidant effect may be contained in the sealing material 907.

  The sealing material 907 provided so as to cover the EL element also functions as an adhesive for bonding the cover material 901. In this embodiment, FRP (Fiberglass-Reinforced Plastics), PVF (polyvinyl fluoride), Mylar, polyester, or acrylic can be used as the material of the plastic substrate 901a constituting the cover material 901.

  In addition, after the cover material 901 is bonded using the sealing material 907, the second sealing material 903 is provided so as to cover the side surface (exposed surface) of the sealing material 907. The second sealing material 903 can use the same material as the first sealing material 902.

  By encapsulating the EL element in the sealing material 907 with the above structure, the EL element can be completely shut off from the outside, and a substance that promotes deterioration due to oxidation of the EL layer such as moisture or oxygen enters from the outside. Can be prevented. Therefore, an EL display device with high reliability can be obtained.

  The TFT formed by implementing any one of the first to fifth embodiments can be used for various electro-optical devices (active matrix liquid crystal display, active matrix EL display, active matrix EC display). That is, the present invention can be implemented in all electronic devices in which these electro-optical devices are incorporated in the display unit.

  Such electronic devices include video cameras, digital cameras, projectors, head-mounted displays (goggles type displays), car navigation systems, car stereos, personal computers, personal digital assistants (mobile computers, mobile phones, electronic books, etc.), etc. Can be mentioned. Examples of these are shown in FIGS. 20, 21, and 22.

  FIG. 20A illustrates a personal computer, which includes a main body 2001, an image input portion 2002, a display portion 2003, a keyboard 2004, and the like. The present invention can be applied to the display portion 2003.

  FIG. 20B illustrates a video camera, which includes a main body 2101, a display portion 2102, an audio input portion 2103, operation switches 2104, a battery 2105, an image receiving portion 2106, and the like. The present invention can be applied to the display portion 2102.

  FIG. 20C illustrates a mobile computer, which includes a main body 2201, a camera unit 2202, an image receiving unit 2203, an operation switch 2204, a display unit 2205, and the like. The present invention can be applied to the display portion 2205.

  FIG. 20D illustrates a goggle type display, which includes a main body 2301, a display portion 2302, an arm portion 2303, and the like. The present invention can be applied to the display portion 2302.

FIG. 20E shows a player using a recording medium (hereinafter referred to as a recording medium) on which a program is recorded, and includes a main body 2401, a display portion 2402, a speaker portion 2403, a recording medium 2404, an operation switch 2405, and the like. This player uses a DVD (Digital Versatile Disc), CD, or the like as a recording medium, and can perform music appreciation, movie appreciation, games, and the Internet.
The present invention can be applied to the display portion 2402.

  FIG. 20F illustrates a digital camera, which includes a main body 2501, a display portion 2502, an eyepiece portion 2503, an operation switch 2504, an image receiving portion (not shown), and the like. The present invention can be applied to the display portion 2502.

  FIG. 21A illustrates a front type projector including a projection device 2601, a screen 2602, and the like. The present invention can be applied to the liquid crystal display device 2808 constituting a part of the projection device 2601 and other driving circuits.

  FIG. 21B shows a rear projector, which includes a main body 2701, a projection device 2702, a mirror 2703, a screen 2704, and the like. The present invention can be applied to the liquid crystal display device 2808 constituting a part of the projection device 2702 and other driving circuits.

  FIG. 21C is a diagram showing an example of the structure of the projection devices 2601 and 2702 in FIGS. 21A and 21B. The projection devices 2601 and 2702 include a light source optical system 2801, mirrors 2802 and 2804 to 2806, a dichroic mirror 2803, a prism 2807, a liquid crystal display device 2808, a phase difference plate 2809, and a projection optical system 2810. Projection optical system 2810 includes an optical system including a projection lens. Although the present embodiment shows a three-plate type example, it is not particularly limited, and for example, a single-plate type may be used. Further, the practitioner may appropriately provide an optical system such as an optical lens, a film having a polarization function, a film for adjusting a phase difference, or an IR film in the optical path indicated by an arrow in FIG. Good.

  FIG. 21D illustrates an example of the structure of the light source optical system 2801 in FIG. In this embodiment, the light source optical system 2801 includes a reflector 2811, a light source 2812, lens arrays 2813 and 2814, a polarization conversion element 2815, and a condenser lens 2816. Note that the light source optical system illustrated in FIG. 21D is an example and is not particularly limited. For example, the practitioner may appropriately provide an optical system such as an optical lens, a film having a polarization function, a film for adjusting a phase difference, or an IR film in the light source optical system.

  However, the projector shown in FIG. 21 shows a case where a transmissive electro-optical device is used, and an application example in a reflective electro-optical device and an EL display device is not shown.

  FIG. 22A illustrates a mobile phone, which includes a main body 2901, an audio output portion 2902, an audio input portion 2903, a display portion 2904, operation switches 2905, an antenna 2906, and the like. The present invention can be applied to the display portion 2904.

  FIG. 22B illustrates a portable book (electronic book) which includes a main body 3001, display portions 3002 and 3003, a storage medium 3004, operation switches 3005, an antenna 3006, and the like. The present invention can be applied to the display portions 3002 and 3003.

  FIG. 22C shows a display, which includes a main body 3101, a support base 3102, a display portion 3103, and the like. The present invention can be applied to the display portion 3103. The display of the present invention is particularly advantageous when the screen is enlarged, and is advantageous for displays having a diagonal of 10 inches or more (particularly 30 inches or more).

  Incidentally, the display shown in FIG. 22C is a medium or small-sized display, for example, a screen size of 5 to 20 inches. Further, in order to form a display portion having such a size, it is preferable to use a substrate having a side of 1 m and perform mass production by performing multiple chamfering.

  As described above, the application range of the present invention is extremely wide and can be applied to electronic devices in various fields. Moreover, the electronic apparatus of a present Example is realizable even if it uses the structure which consists of what combination of Examples 1-5.

Claims (3)

A semiconductor layer provided on an insulating surface;
An insulating film provided on the semiconductor layer;
A semiconductor device having a gate electrode provided on the insulating film,
The gate electrode has a stacked structure in which a first conductive layer having a first width is formed as a lower layer, and a second conductive layer having a second width smaller than the first width is formed as an upper layer,
The first conductive layer and the second conductive layer are formed using an element selected from tungsten, tantalum, and titanium, or a compound or alloy containing the element as a component,
The semiconductor layer includes a channel formation region that overlaps the second conductive layer, a low concentration impurity region that partially overlaps the first conductive layer, and a source to which an impurity having a higher concentration than the low concentration impurity region is added. A region and a drain region;
The semiconductor device is characterized in that an end portion of the insulating film has a tapered shape.   A video camera, a digital camera, a projector, a goggle type display, a car navigation system, a personal computer, a portable information terminal, a digital video disc player, or an electronic game machine using the semiconductor device according to claim 1. A first step of forming a semiconductor layer on the insulating surface;
A second step of forming an insulating film on the semiconductor layer after the first step;
After the second step, a third step of forming a first electrode comprising a stack of a first conductive layer and a second conductive layer on the insulating film;
A fourth step of forming a high concentration impurity region by adding an impurity element to the semiconductor layer using the first electrode as a mask after the third step;
After the fourth step, a fifth step of etching the second conductive layer to form a second conductive layer that is narrower than the width of the second conductive layer in the third step;
After the fifth step, a sixth step of forming a low concentration impurity region by adding an impurity element to the semiconductor layer using the second conductive layer as a mask;
After the sixth step, the first conductive layer is etched so that it is narrower than the width of the first electrode in the third step and larger than the width of the second conductive layer in the fifth step. Forming a wide first conductive layer and etching the insulating film,
In the semiconductor device, the first conductive layer and the second conductive layer are formed using an element selected from tungsten, tantalum, and titanium, or a compound or alloy containing the element as a component. Manufacturing method.

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