JPH09181329A - Semiconductor device and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form high-resistance impurity regions in a thin film transistor in a self-alignment manner. SOLUTION: Impurities are doped to an active layer 103 using a gate electrode 106, a barrier anode oxide layer 108 and a gate insulating film 104' as masks. The impurities are substantially not doped to the lower part of the electrode 106, the lower part is formed into a channel formation region, the regions, where the film 104' exists, of the layer 103 have little doping amount, are turned into high-resistance impurity regions 111 and 112 of a low impurity concentration and the regions, where the film 104' does not exist, of the layer 103 are turned into low-resistance impurity regions 110 and 113 of a high impurity concentration. The distance (y), which projects from the oxide film 108, of the film 104' is decided according to the film thickness of a porous anode oxide film 107 formed on the side surfaces of the electrode 106.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an insulated gate transistor (TFT) formed on an insulating material such as glass or a material obtained by forming an insulating film such as silicon oxide on a silicon wafer, and an insulating gate type transistor (TFT). It relates to a manufacturing method.
The present invention particularly relates to a TFT formed on a glass substrate having a glass transition point (also called strain temperature or strain point) of 750 ° C. or lower.
It is effective for The semiconductor device according to the present invention is used in an active matrix such as a liquid crystal display, a drive circuit such as an image sensor, or a three-dimensional integrated circuit.

[0002]

2. Description of the Related Art Conventionally, a TF has been used for the purpose of driving an active matrix type liquid crystal display device or an image sensor.
It is widely known to form a T (thin film transistor). In particular, recently, because of the need for high-speed operation, a crystalline silicon TFT having a higher electric field mobility has been developed in place of the amorphous silicon TFT using amorphous silicon in the active layer. However, when higher characteristics and higher durability are required, a high resistance impurity region (high resistance drain (HRD) or low concentration drain (LDD)) as used in semiconductor integrated circuit technology is provided. Was needed. However, unlike the known semiconductor integrated circuit technology, the TFT has many problems to be solved. Especially,
Since the device is formed on the insulating surface and the reactive ion anisotropic etching cannot be sufficiently performed, there is a large restriction that a fine pattern cannot be formed.

FIG. 6 shows an HRD that has been used up to now.
6A to 6D are cross-sectional views of a typical process for manufacturing the. First, a base film 602 is formed over a substrate 601, and an active layer is formed using crystalline silicon 603. Then, an insulating coating 604 is formed on the active layer with a material such as silicon oxide. (FIG. 6 (A))

Next, a gate electrode 605 is formed of polycrystalline silicon (doped with impurities such as phosphorus), tantalum, titanium, aluminum or the like. Further, using the gate electrode as a mask, an impurity element (phosphorus or boron) is introduced by ion doping or the like, and a high-resistance impurity region (HRD) with a small doping amount is self-aligned.
606 and 607 are formed in the active layer 603. The active layer region under the gate electrode into which the impurity has not been introduced becomes a channel forming region. Then, the doped impurities are activated by a heat source such as a laser or a flash lamp. (Fig. 6 (B))

Next, an insulating film 608 of silicon oxide or the like is formed by means of plasma CVD, APCVD or the like (see FIG. 6).
(C)), and by performing anisotropic etching, a side wall 609 is formed adjacent to the side surface of the gate electrode. (FIG. 6D) Then, an impurity element is again introduced by means such as ion doping, and a sufficiently high-concentration impurity region (low-resistance impurity region, source / Drain region) 610,
611 is formed in the active layer 603. Then, the doped impurities are activated by a heat source such as a laser or a flash lamp. (FIG. 6
(E))

Finally, an interlayer insulator 612 is formed, a contact hole is formed in the source / drain region through the interlayer insulator, and a wiring / electrode 613 connected to the source / drain is formed by a metal material such as aluminum.
614 is formed. (FIG. 6 (F))

[0007]

The above method follows the LDD manufacturing process in the conventional semiconductor integrated circuit as it is, and it is difficult to directly apply it to the TFT manufacturing process on the glass substrate. Alternatively, there are processes that are not preferable in terms of productivity.

First, the activation of impurities by irradiation with a laser or the like is required twice. This reduces productivity. In the conventional semiconductor integrated circuit, activation of the impurity element has been performed by thermal annealing. for that reason,
The activation of impurities was performed collectively after the introduction of all impurities was completed.

However, especially on a TFT on a glass substrate
In this case, it is difficult to perform thermal annealing due to the temperature limitation of the substrate, and it is unavoidable to rely on laser annealing or flash lamp annealing (RTA or RTP). However, in these methods, the surface to be irradiated is selectively annealed, so that, for example, the portion below the sidewall 609 is not annealed. Therefore, annealing is required every time impurity doping is performed.

The second problem is the difficulty of forming the side wall. The thickness of the insulating film 608 is 0.5 to 2 μm. Usually, the thickness of the base film 602 provided on the substrate is 1000 to 3000Å
Therefore, in this etching process, the base film is often mistakenly etched to expose the substrate, and the yield is lowered. Since the substrate used for manufacturing the TFT contains many elements harmful to the silicon semiconductor, it is necessary to avoid such defects as much as possible. It was also difficult to finish the width of the side wall uniformly. This is reactive ion etching (RIE)
This is because, in plasma dry etching such as the above, unlike the silicon substrate used in the semiconductor integrated circuit, it is difficult to finely control the plasma because the surface of the substrate is insulative.

Since the drain of the high resistance impurity region has a high resistance, it is necessary to make its width as narrow as possible, but it is difficult to mass-produce it due to the above variations, and this self-alignment (that is, the photolithography method is used). The challenge was how to make the process easier to control). Further, in the conventional method, doping was required at least twice, but reducing the number of times of doping was also a problem to be solved.

The present invention solves the above problems and further simplifies the process to form a high resistance impurity region, and a high resistance impurity region (high resistance drain, HRD) thus formed. With respect to the TFT.
Here, the term “high resistance drain (HRD)” means that the impurity concentration is relatively high in addition to the drain having a low impurity concentration and a high resistance, but carbon, oxygen, nitrogen or the like is added to remove the impurities. It also includes a drain which has a high resistance as a result of hindering activation.

[0013]

In forming a high resistance region, the present invention is characterized in that an oxide layer formed by means such as anodic oxidation of a gate electrode is positively used. In particular, the thickness of anodic oxide can be precisely controlled, and the thickness is as low as 1000 Å or less.
Since it has a feature that it can be formed uniformly over a wide range up to a thickness of 000 Å or more, it is preferable as a material replacing the side wall by conventional anisotropic etching.

In particular, the so-called barrier type anodic oxide is not etched unless it is a hydrofluoric acid type etchant, whereas the porous type anodic oxide is selectively etched by an etchant such as phosphoric acid. Therefore, the TFT
It is characterized in that it can be processed without giving any damage (damage) to other materials constituting, for example, silicon and silicon oxide. Further, in both the barrier type and the porous type, anodic oxide is extremely difficult to be etched by dry etching. In particular, the feature is that the selection ratio is sufficiently large in etching with silicon oxide. The present invention is characterized in that a TFT is manufactured by the following manufacturing process. By adopting this process, the HRD can be more surely configured and mass productivity can be improved.

[0015]

DETAILED DESCRIPTION OF THE INVENTION FIG. 1 illustrates the basic steps of the present invention. First, the base insulating film 102 is formed on the substrate 101, and the active layer 103 is further made of a crystalline semiconductor (in the present invention, a semiconductor in which crystals are mixed as much as possible, such as single crystal, polycrystal, or semi-amorphous) is called a crystalline semiconductor. ). Then, an insulating film 104 is formed so as to cover the insulating film 104 with a material such as silicon oxide, and a film is formed with a material capable of anodizing. As the material of this coating, aluminum, tantalum, titanium, silicon or the like which can be anodized is preferable. In the present invention, a gate electrode having a single layer structure using these materials alone may be used, or a gate electrode having a multilayer structure in which two or more layers are stacked. For example, it has a two-layer structure in which titanium silicide is overlaid on aluminum and a two-layer structure in which aluminum is overlaid on titanium nitride.
The thickness of each layer may be determined by a practitioner according to the required device characteristics.

Further, a film serving as a mask in anodic oxidation is formed so as to cover the film, and both are simultaneously patterned and etched to form a gate electrode 105 and a mask film 106 thereon. As a material for the mask film, a photoresist used in a normal photolithography process, a photosensitive polyimide, or a material that can be etched with a normal polyimide may be used.
(Fig. 1 (A))

Next, a porous anodic oxide 107 is formed on the side surface of the gate electrode 105 by applying a current to the gate electrode 105 in an electrolytic solution. This anodic oxidation process is 3
It is carried out using an acidic aqueous solution of citric acid or oxalic acid, phosphoric acid, chromic acid, sulfuric acid, etc. of -20%. The hydrogen ion concentration pH of the solution is preferably less than 2. The optimum pH depends on the type of electrolytic solution, but is 0.9 to 1.0 for oxalic acid. In this case, 10-30
It is possible to form a thick anodic oxide of 0.5 μm or more at a voltage as low as V. (Fig. 1 (B))

Then, the insulating film 104 is etched by a dry etching method, a wet etching method or the like.
This etching depth is arbitrary, and etching may be performed until the underlying active layer is exposed, or may be stopped midway. However, from the viewpoint of mass productivity, yield, and uniformity, it is desirable to etch up to the active layer. At this time, the anodic oxide 107 and the gate electrode 10
The insulating film having the original thickness is left in the insulating film (gate insulating film) below the region covered with 5. The gate electrode is mainly composed of aluminum, tantalum, and titanium.
In the case where the insulating film 104 contains silicon oxide as a main component,
In the case of using a dry etching method, if dry etching is performed using a fluorine-based (eg, NF ₃ , SF ₆ ) etching gas, the insulating film 104 made of silicon oxide is used.
Is etched quickly, but the etching rates of aluminum oxide, tantalum oxide, and titanium oxide are sufficiently low that the insulating film 104 can be selectively etched.

In wet etching, 1
A hydrofluoric acid-based etchant such as / 100 hydrofluoric acid may be used. In this case as well, the insulating film 104 made of silicon oxide is etched quickly, but since the etching rates of aluminum oxide, tantalum oxide, and titanium oxide are sufficiently small, the insulating film 104 can be selectively etched. (Figure 1
(D))

After that, the anodic oxide 107 is removed. As the etchant, a phosphoric acid-based solution, for example, a mixed acid of phosphoric acid, acetic acid, nitric acid, or the like is preferable. However, for example, when a gate electrode is made of aluminum and a phosphoric acid-based etchant is used, the gate electrode is also etched at the same time. Therefore, in the present invention, by applying an electric current to the gate electrode in the ethylene glycol solution containing 3 to 10% tartar solution, boric acid and nitric acid in the previous step, A barrier type anodic oxide 108 may be provided on the upper surface. In this anodic oxidation step, the pH of the electrolytic solution may be 2 or more, preferably 3 or more, and more preferably 6.9 to 7.1. In order to obtain such a solution, it is preferable to neutralize using an alkaline solution such as ammonia. The thickness of the obtained anodic oxide is determined by the magnitude of the voltage applied between the gate electrode 105 and the opposing electrode.

It should be noted that although barrier-type anodic oxidation is a later step, barrier-type anodic oxide is not formed outside the porous anodic oxide, but barrier-type anodic oxidation is performed. The object 108 is to be formed between the porous anodic oxide 107 and the gate electrode 105. In the phosphoric acid-based etchant, the etching rate of the porous anodic oxide is 10 times or more that of the barrier type anodic oxide. Therefore, since the barrier type anodic oxide 108 is not substantially etched by the phosphoric acid-based etchant, the inner gate electrode can be protected. (Fig. 1 (C), (E))

Through the above steps, it is possible to obtain a structure in which a part of the insulating film 104 (hereinafter, referred to as a gate insulating film) is selectively left under the gate electrode. Since the gate insulating film 104 ′ originally existed under the porous anodic oxide 107, not only under the gate electrode 105 and under the barrier anodic oxide 108 but also at the barrier anodic oxide 108. , And a width y thereof is characterized by being determined in a self-aligned manner. In other words, a region where the gate insulating film 104 'exists and a region where the gate insulating film 104' does not exist are formed in a self-alignment manner outside the channel formation region below the gate electrode in the active layer 103.

When ions of N-type or P-type impurities accelerated by this structure are implanted into the active layer, a large number of ions are implanted into a region where the insulating film 104 does not exist (or is thin), and (relatively) high. Concentration impurity regions (low resistance impurity regions) 110 and 113 are formed. On the other hand, in the region where the gate insulating film 104 'is present, ions are injected into this gate insulating film, and only the ions that have passed through the gate insulating film are injected into the semiconductor. Low concentration impurity region (high resistance impurity region) 111,
112 is formed. Low concentration impurity regions 111 and 11
The difference in the impurity concentration between the high impurity concentration regions 110 and 113 and the impurity concentration in the high concentration impurity regions 110 and 113 varies depending on the thickness of the insulating film 104 and the like, but is usually 0.5 to 3 digits, which is smaller in the former. Further, substantially no impurity is implanted into the region below the gate electrode, and the intrinsic or substantially intrinsic state is maintained, that is, the region becomes a channel formation region. After the impurities are injected, the impurities may be activated by irradiating a laser or strong light equivalent thereto, but needless to say, this step is substantially sufficient once. (FIG. 1 (E))

As described above, the present invention is characterized in that the width of the high resistance impurity region is controlled in a self-aligned manner by the thickness y of the anodic oxide 107. Further, the end 109 of the gate insulating film 104 ′ and the high-resistance region (HRD) 112
The ends 117 of the can be approximately matched. In the conventional method shown in FIG. 6, it is extremely difficult to control the width of the side wall which plays such a role, but in the present invention, the width of the anodic oxide 107 is determined by the anodic oxidation current (charge amount). Therefore, extremely delicate control is possible.

Further, as is clear from the above steps, the low resistance region and the high resistance region can be formed even if the impurity doping step is substantially performed once, and the subsequent activation step is also performed. It only needs to be processed once. As described above, according to the present invention, mass productivity can be improved by reducing the steps of doping and activation. Conventionally, since the HRD has a large resistance, it has been difficult to make an ohmic contact with the electrode, and this resistance causes a decrease in the drain voltage. However, on the other hand, the presence of HRD also has the advantage that hot carrier generation can be suppressed and high reliability can be obtained. The present invention can solve these contradictory problems all at once, and can obtain ohmic contact with the HRD having a width of 0.1 to 1 μm formed in a self-aligned manner and the source / drain electrodes.

In the present invention, the positional relationship between the end of the gate electrode and the impurity region can be arbitrarily changed by appropriately utilizing the thickness of the anodic oxide 108 in FIG.
This example is shown in FIG. For example, in a method in which ions are injected without being substantially mass-separated, such as an ion doping method (also referred to as plasma doping), the angle of entry of the ions is different, so there is a considerable spread of impurities in the lateral direction. That is, it is expected that the ions will spread in the lateral direction to the extent that they are added. In the example below, the active layer 4
The thickness of 04 is 800Å.

Therefore, as shown in FIG. 4A, the thickness (for example, 800 °) of the anodic oxide 402 (corresponding to 108 in FIGS. 1 and 108) is substantially the same as that of the active layer 404 outside the metal gate electrode 401. If the thickness is almost the gate electrode 4
01 end 405 and the high resistance impurity region 407 end 40
6 does not overlap and does not separate, resulting in a matched state. FIG.
As in (B), the thickness of the anodic oxide 402 is, for example, 30
In the case where the thickness is larger than 00 ° and the thickness of the active layer is 800 °, the end 405 of the gate electrode and the end 406 of the high resistance impurity region are formed.
Are separated from each other by offset. Conversely, when the thickness of the anodic oxide 402 is reduced as shown in FIG. 4C, the gate electrode and the high-resistance impurity region overlap each other. This overlap is maximum when no anodic oxide exists around the gate electrode 401 as shown in FIG.

Generally, in the offset state, the reverse leak current is reduced and the on / off ratio is improved. For example, as in a TFT (pixel TFT) used for controlling pixels of an active matrix liquid crystal display, It is suitable for applications that require low leakage current. However, the hot carriers generated at the edges of the HRD are trapped in the anodic oxide,
It also has the drawback of deterioration.

In the overlapped state, deterioration due to hot carrier traps as described above is reduced, and the on-current increases, but the leak current increases. Therefore, a TFT (driver TF) which is used in a peripheral circuit of a monolithic type active matrix, for example, which requires a large current driving capability.
Suitable for T). The TFT actually used is shown in FIG.
Which of (D) to (D) should be determined depending on the application of the TFT.

[0030]

【Example】

Embodiment 1 FIG. 1 shows this embodiment. First, a substrate (Corning 7059, 300 mm x 400 mm or 1
A silicon oxide film having a thickness of 1000 to 3000 ° was formed as a base oxide film 102 on (00 mm × 100 mm) 101. As a method for forming this oxide film, a sputtering method in an oxygen atmosphere was used. However, in order to further improve mass productivity, a film obtained by decomposing / depositing TEOS by the plasma CVD method may be used.

Thereafter, an amorphous silicon film is deposited by plasma CVD or LPCVD to a thickness of 300 to 5000 Å, preferably 500 to 1000 Å, which is deposited at 550 to 600.
It was left to stand in a reducing atmosphere at 0 ° C. for 24 hours for crystallization.
This step may be performed by laser irradiation.
Then, the silicon film crystallized in this manner was patterned to form the island regions 103. Further, a silicon oxide film 104 having a thickness of 700 to 1500 Å was formed thereon by a sputtering method.

Thereafter, aluminum having a thickness of 1000Å to 3 μm (1 wt% Si, or 0.1 to 0.3 wt) is used.
% Of Sc (scandium) film was formed by electron beam evaporation or sputtering. Then, a photoresist (for example, OFPR800 / 3 manufactured by Tokyo Ohka)
0 cp) was formed by spin coating. Before forming the photoresist, the thickness of 100 to 1 is formed by the anodic oxidation method.
If a 000Å aluminum oxide film is formed on the surface, the adhesion to the photoresist is good, and the leakage of current from the photoresist is suppressed, so that the porous anodic oxide is used in the subsequent anodic oxidation process. It was effective in forming only on the side surface. Thereafter, the photoresist and the aluminum film are patterned and etched together with the aluminum film to form a gate electrode 105 and a mask film 10.
6. (Fig. 1 (A))

Further, current is anodized in the electrolytic solution by applying an electric current to obtain a thickness of 3000 to 6000Å, for example, a thickness of 50.
A 00Å anodized oxide 107 was formed. Anodic oxidation is 3
~ 30% using an acidic aqueous solution of citric acid or oxalic acid, phosphoric acid, chromic acid, sulfuric acid, etc.
A constant current of V may be applied to the gate electrode. In this example, the voltage was set to 10 V in an oxalic acid solution (30 ° C.) having a pH of 0.9 to 1.0, and anodization was performed for 20 to 40 minutes. The thickness of the anodic oxide was controlled by the anodic oxidation time. (Fig. 1 (B))

Next, the mask was removed, and a current was again applied to the gate electrode in the electrolytic solution. This time, 3-1
PH = 6.9 containing 0% tartar solution, boric acid and nitric acid
An ethylene glycol ammonia solution of 7.1 was used.
A better oxide film was obtained when the temperature of the solution was lower than room temperature around 10 ° C. As a result, a barrier-type anodic oxide 108 was formed on the upper and side surfaces of the gate electrode. The thickness of the anodic oxide 108 is proportional to the applied voltage, and the applied voltage is 150
2000 V of anodic oxide was formed. The thickness of the anodic oxide 108 was determined by the size of the required offset, overlap, as shown in FIG.
250V to obtain anodic oxide with a thickness of 3000Å or more
Since the above high voltage is required and the characteristics of the TFT are adversely affected, the thickness is preferably 3000 Å or less.
In this example, the voltage was raised to 80 to 150 V and the voltage was selected according to the required thickness of the anodic oxide film 108. (Fig. 1 (C))

After that, the silicon oxide film 104 was etched by the dry etching method. In this etching, a plasma mode of isotropic etching or a reactive ion etching mode of anisotropic etching may be used. However, it is important to prevent the active layer from being etched deeply by sufficiently increasing the selectivity between silicon and silicon oxide. For example, if CF ₄ is used as an etching gas, the anodic oxide is not etched, and only the silicon oxide film 104 is etched. Also,
The silicon oxide film 104 'under the porous anodic oxide 107 remained without being etched. (Fig. 1 (D))

After that, the anodic oxide 107 was etched using a mixed acid of phosphoric acid, acetic acid and nitric acid. In this etching, only the anodic oxide 107 was etched, and the etching rate was about 600 Å / min. The gate insulating film 104 'thereunder remained as it was. Then, an impurity is implanted into the active layer 103 of the TFT in a self-aligned manner by using the gate electrode portion (that is, the gate electrode and the anodic oxide film around the gate electrode) and the gate insulating film as a mask by an ion doping method. Source / drain region) 11
0, 113 and high resistance impurity regions 111, 112 were formed. Since phosphine (PH ₃ ) was used as the doping gas, an N-type impurity region was formed. Diborane (B ₂ H ₆ ) may be used as a doping gas to form a P-type impurity region. The dose is 5 × 10 ^{14 to} 5 ×
10 ¹⁵ cm ^-2 and the acceleration energy were 10 to 30 keV. Thereafter, a KrF excimer laser (wavelength 248 n)
m, a pulse width of 20 nsec) to activate the impurity ions introduced into the active layer.

According to the result of SIMS (secondary ion mass spectrometry), the impurity concentration of the regions 110 and 113 is 1 × 10.
^{20 to} 2 × 10 ²¹ cm ⁻³ , 1 × 1 in the regions 111 and 112
0 ^{17 to} 2 × 10 ¹⁸ cm ⁻³ . In dose conversion,
The former is 5 × 10 ^{14 to} 5 × 10 ¹⁵ cm ⁻² and the latter is 2 × 10
¹³ was ~5 × 10 ¹⁴ cm ^-2. This difference is brought about by the presence or absence of the gate insulating film 104 ', and generally, the impurity concentration of the low resistance disordered cormorant region is 0.5 to 3 orders of magnitude higher than that of the high resistance impurity region. . (Figure 1
(E))

Finally, the inter-layer insulator 114 is formed on the entire surface.
A silicon oxide film having a thickness of 3000 Å was formed by the CVD method. Contact holes were formed in the source / drain of the TFT, and aluminum wiring / electrodes 115 and 116 were formed. Further, hydrogen annealing was performed at 200 to 400 ° C. Thus, the TFT was completed. (Figure 1
(F))

An example in which a plurality of TFTs are formed on one substrate by using the method shown in FIG. 1 is shown in FIG. In this example, three TFTs, TFT1 to TFT3, are formed. TFT
1 and 2 are used as driver TFTs, and an oxide 501 corresponding to the anodic oxide 108 in FIG.
The thickness of the gate electrode 502 and the high resistance region (HR) are slightly reduced to a thickness of 200 to 1000 °, for example, 500 °.
D) was made to overlap. In the figure, TF
Connect the drain of T1 and the source of TFT2 to each other,
In addition, an example is shown in which the source of the TFT1 is grounded and the drain of the TFT2 is connected to the power source so as to form a CMOS inverter. As the peripheral circuit, there are various other circuits, but such a CMOS type circuit may be used according to the specifications of each circuit.

On the other hand, the TFT 3 is used as a pixel TFT, and the anodic oxide 503 is thickened to 2000 Å to make it in an offset state (corresponding to FIG. 4B) to suppress the leak current. One of the source / drain electrodes of the TFT 3 is connected to the pixel electrode 501 of ITO. To change the thickness of anodic oxide in this way,
What is necessary is just to separate so that the voltage of the T gate electrode can be controlled independently. Note that TFT1 and TFT3 are N-channel TFTs, and TFT2 is a P-channel TFT.

Example 2 FIG. 2 shows this example. First, a substrate having an insulating surface (eg Corning 705)
9) Using the steps (A) and (B) of Example 1 on the base 201, the base oxide film 202, the island-like silicon semiconductor region (for example, crystalline silicon semiconductor) 203, the silicon oxide film 204, and the aluminum film ( A gate electrode 205 (thickness: 200 nm to 1 μm) and a porous anodic oxide (thickness: 3000 to 1 μm, for example, 5000 °) 206 are formed on side surfaces of the gate electrode. (FIG. 2 (A)) And, as in the first embodiment, the thickness of the barrier mold is 1000-2.
A 500 Å anodic oxide 207 was formed. (Figure 2
(B))

Further, using the porous anodic oxide 206 as a mask, the silicon oxide film 204 was etched to form a gate insulating film 204 '. After that, the barrier type anodic oxide film 2
Using 07 as a mask, the porous anodic oxide film 206 was removed by etching. Thereafter, the gate electrode portions (205, 20)
7) and impurity implantation is performed by ion doping using the gate insulating film 204 ′ as a mask to form low-resistance impurity regions 208 and 211, high-resistance impurity regions 209 and
Formed 10. The dose amount was 1 to 5 × 10 ¹⁴ cm ⁻² , and the acceleration voltage was 30 to 90 kV. Phosphorus was used as an impurity. (Fig. 2 (C))

Further, a film of an appropriate metal, for example, titanium, nickel, molybdenum, tungsten, platinum, palladium or the like, for example, a titanium film 212 having a thickness of 50 to 500 Å is formed on the entire surface by sputtering. As a result, the metal film (here, titanium film) 212 was formed in close contact with the low resistance impurity regions 208 and 211. (Figure 2
(D))

Then, a KrF excimer laser (wavelength 248 nm, pulse width 20 nsec) is irradiated to activate the doped impurities, and at the same time react the metal film (titanium in this case) with silicon in the active layer to form a metal silicide ( Here, regions 213 and 214 of titanium silicide) are formed.
Laser energy density is 200-400 mJ / cm
² , preferably 250 to 300 mJ / cm ² . In addition, the substrate is 200 to 500 during laser irradiation.
Preheating the titanium film could suppress the peeling of the titanium film.

In this embodiment, the excimer laser is used as described above, but it goes without saying that another laser may be used. However, when using a laser, a pulsed laser is preferable. Since the irradiation time of the continuous wave laser is long, there is a risk that the object to be irradiated expands due to heat and peels off.

Regarding the pulse laser, Nd: YAG
Infrared laser such as laser (preferably Q-switched pulse oscillation) and its visible light such as its second harmonic, Kr
Various ultraviolet lasers using excimers such as F, XeCl and ArF can be used, but when laser irradiation is performed from the upper surface of the metal film, it is necessary to select a laser having a wavelength that is not reflected by the metal film. However, there is almost no problem when the metal film is extremely thin. Further, the laser light may be applied from the substrate side. In this case, it is necessary to select a laser beam that passes through the underlying silicon semiconductor film.

The annealing may be lamp annealing by irradiation with visible light or near infrared light.
When performing lamp annealing, the surface to be irradiated is 600
The lamp irradiation is performed at 600 ° C. for several minutes, and at 1000 ° C. for several tens of seconds so that the temperature becomes about 1000 ° C. In annealing with near infrared rays (for example, infrared rays of 1.2 μm), the near infrared rays are selectively absorbed by the silicon semiconductor, do not heat the glass substrate so much, and shorten the irradiation time once, thereby heating the glass substrate. It can be suppressed and is extremely useful.

After that, the Ti film was etched with an etching solution in which hydrogen peroxide, ammonia and water were mixed at 5: 2: 2. The titanium film (for example, the titanium film existing on the gate insulating film 204 and the anodic oxide film 207) other than the portion in contact with the exposed active layer remains in a metal state as it is, but can be removed by this etching. On the other hand, the titanium silicides 213 and 214, which are metal silicides, are not etched and can be left. (FIG. 2 (E))

Finally, as shown in FIG. 2F, a silicon oxide film having a thickness of 2000 Å to 1 μm, for example 3000 Å, is formed as an interlayer insulator 217 on the entire surface by a CVD method to make contact with the source / drain of the TFT. A hole is formed and the aluminum wiring / electrodes 218, 219 are set to 200
It was formed to a thickness of 0Å to 1 μm, for example, 5000Å. In this example, the contact portion of the aluminum wiring was made of titanium silicide, and the stability of the interface with aluminum was better than that of silicon, so a highly reliable contact was obtained. The aluminum electrode 21
8 and 219 and the silicide regions 213 and 214, for example, titanium nitride is further formed as a barrier metal,
Reliability can be improved. In this example, the sheet resistance in the silicide region was 10 to 50 Ω / □. On the other hand, in the high resistance impurity regions 209 and 210, 10 to 100
kΩ / □, resulting in good frequency characteristics and
TF with little hot carrier deterioration even at high drain voltage
It was possible to make T.

In this embodiment, the low resistance impurity region 211 and the metal silicide region could be made to substantially coincide with each other. In particular, the end 215 of the gate insulating film 204 'and the high-resistance impurity region 2
10 and the boundary 216 between the low-resistance impurity region 211 and the end portion 215 and the metal silicide region 214 at the same time.
4 (A) to (D) as a result of making the ends of FIG.
It will be clear that the low resistance impurity regions in ## EQU3 ## can be replaced by metal silicide regions.

FIG. 5B shows an example in which a plurality of TFTs are formed on one substrate by using the technique shown in FIG. In this example, three TFTs, TFT1 to TFT3, are formed. TFT
1 and 2 are CMOS-configured driver TFTs, which are used here as inverter configurations.
The thickness of the oxides 505 and 506 corresponding to the anodic oxide 207 was set to a thin thickness of 200 to 1000 Å, for example, 500 Å, so that they slightly overlap each other. on the other hand,
The TFT 3 is used as a pixel TFT, and the thickness of the anodic oxide 503 was set to 2000 Å to make it an offset state to suppress the leak current. One of the source / drain electrodes of the TFT 3 is connected to the pixel electrode 502 of ITO. In order to change the thickness of the anodic oxide in this manner, it is sufficient to separate the anodic oxide so that the voltage of the gate electrode of each TFT can be controlled independently. Note that TFT1 and TF
T3 is an N-channel type TFT, TFT2 is a P-channel type T
FT.

In this embodiment, the titanium film forming step is arranged after the ion doping step, but the order may be reversed. In this case, since the titanium film covers the entire surface at the time of ion irradiation, it is very effective in preventing abnormal charge (charge-up) which has been a problem in the insulating substrate. Alternatively, after the ion doping, annealing may be performed with a laser or the like, a titanium film may be formed, and then titanium silicide may be formed by irradiation with a laser or the like or thermal annealing.

[Third Embodiment] FIG. 3 shows the present embodiment. First, a base oxide film 302, an island-shaped crystalline semiconductor region, for example, a silicon semiconductor region 303, a silicon oxide film 304, is formed on a substrate (Corning 7059) 301 by using the steps (A) and (B) of Example 1. Aluminum film (thickness 2000Å ~ 1
μm), and a porous anodic oxide (thickness 6000 °) 306 was formed on the side surface of the gate electrode 305. (FIG. 3 (A)) Then, similarly to the first embodiment, the thickness of the barrier mold is 1000-2.
A 500Å anodic oxide 307 was formed. (Fig. 3
(B))

Further, using the porous anodic oxide 306 as a mask, the silicon oxide film 304 was etched to form a gate insulating film 304 '. Then, the porous anodic oxide 30
6 was selectively etched to expose a part of the gate insulating film 304 '. After that, an appropriate metal, for example, a titanium film 308 having a thickness of 50 to 500 Å was formed on the entire surface by sputtering. (FIG. 3 (C)) Then, a KrF excimer laser (wavelength 248 nm,
Irradiation was performed with a pulse width of 20 nsec) to react titanium with silicon in the active layer, thereby forming titanium silicide regions 309 and 310. Laser energy density is 200-400mJ
/ Cm ² , preferably 250 to 300 mJ / cm ² . When irradiating the laser, the substrate is 200 ~
By heating to 500 ° C., the peeling of the titanium film could be suppressed. This step may be performed by lamp annealing by irradiation with visible light or near infrared light.

After that, the Ti film was etched with an etching solution in which hydrogen peroxide, ammonia and water were mixed at 5: 2: 2. The titanium film (for example, the titanium film existing on the gate insulating film 304 'and the anodic oxide film 307) other than the portion in contact with the exposed active layer remains in a metal state as it is, but can be removed by this etching. On the other hand, titanium silicide 3
Since 09 and 310 are not etched, they can be left. (FIG. 3 (D))

Thereafter, impurities are implanted by an ion doping method using the gate electrode portion and the gate insulating film 304 as a mask to form low-resistance impurity regions (≒ titanium silicide regions) 311, 314 and high-resistance impurity regions 312, 313.
Was formed. The dose amount was 1 to 5 × 10 ¹⁴ cm ⁻² , and the acceleration voltage was 30 to 90 kV. Phosphorus was used as an impurity. (FIG. 3 (E))

Then, the KrF excimer laser (wavelength 248 nm, pulse width 20 nsec) was irradiated again to activate the doped impurities. This step may be performed by lamp annealing by irradiation with visible light or near infrared light. Finally, the gate insulating film 30 is formed by using the gate electrode portions (305, 307) as a mask.
4'was etched. This was done to avoid instability due to impurities doped in the gate insulating film 304 '. As a result, the gate insulating film 304 ″ remained only under the gate electrode.

Then, as shown in FIG. 3F, a silicon oxide film having a thickness of 6000Å is formed as an interlayer insulator 315 on the entire surface by a CVD method, contact holes are formed in the source / drain of the TFT, and an aluminum wiring is formed.・ Electrode 3
16 and 317 were formed. Through the above steps, TFT
Was completed.

[0059]

According to the present invention, the high resistance impurity region (HRD) can be formed by substantially one-time doping and one-time laser annealing, and an activation process such as RTA. This shortening of the process improves mass productivity and
This is effective in reducing the amount of investment in the T manufacturing line.
Further, in the present invention, since the width of the HRD is formed with extremely high accuracy, a TFT having excellent yield and uniformity can be obtained.

In the present invention, in order to further improve the characteristics, more doping, laser annealing or RTA may be performed, and the number of times of doping or laser annealing or RTA is not limited to once. Not a thing. Needless to say, the TFT of the present invention is formed in the same manner whether a three-dimensional integrated circuit is formed on a substrate on which a semiconductor integrated circuit is formed or when it is formed on glass, organic resin, or the like. Is formed on the insulating surface in any case. In particular, the effect of the present invention is remarkable for an electro-optical device such as a monolithic active matrix circuit having peripheral circuits on the same substrate.

In the present invention, in addition to ion implantation or ion doping of P or N type impurities, carbon,
Oxygen and nitrogen may be added at the same time. By doing so, the reverse leakage current is reduced and the breakdown voltage is also improved. For example, it is effective when used as a pixel TFT of an active matrix circuit. In this case, the thickness of the anodic oxide layer of the TFT 3 shown in FIG. 5 can be the same as that of the TFT 1 and the TFT 2.

[Brief description of the drawings]

FIG. 1 shows a method of manufacturing a TFT according to a first embodiment.

FIG. 2 shows a method of manufacturing a TFT according to a second embodiment.

FIG. 3 shows a method of manufacturing a TFT according to a third embodiment.

FIG. 4 shows the relationship between offset and overlap in the present invention.

FIG. 5 shows an example of an integrated circuit of TFTs obtained in Examples 1 and 2.

FIG. 6 shows a method of manufacturing a TFT by a conventional method.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 101 Insulating substrate 102 Base oxide film (silicon oxide) 103 Active layer (crystalline silicon) 104 Insulating film (silicon oxide) 104 'Gate insulating film 105 Gate electrode (aluminum) 106 Mask film (photoresist) 107 Anodic oxide (porous) Aluminum oxide) 108 anodic oxide (barrier type aluminum oxide) 109 edge of gate insulating film 110, 113 low resistance impurity region 111, 112 high resistance impurity region (HRD) 114 interlayer insulating film (silicon oxide) 115, 116 metal wiring -Electrode (aluminum) 117 Boundary between low-resistance impurity region and high-resistance impurity region

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hideto Onuma 398 Hase, Atsugi City, Kanagawa Prefecture, Semiconducting Energy Laboratory Co., Ltd. (72) Inventor Naoaki Yamaguchi 398, Hase, Atsugi City, Kanagawa Prefecture, Semiconducting Energy Laboratory Co. (72) Inventor Hideomi Suzawa 398 Hase, Atsugi, Kanagawa Prefecture, Semiconducting Energy Laboratory Co., Ltd. (72) Hideki Uochi 398, Hase, Atsugi, Kanagawa, Ltd. Semiconducting Energy Laboratory, Ltd. (72) Inventor, Yasuhiko Takemura 398 Hase, Atsugi City, Kanagawa Prefecture Semiconductor Energy Research Institute Co., Ltd.

Claims (2)

[Claims] 1. A thin film transistor formed on an insulating surface, comprising: an active layer; a gate insulating film formed on the active layer; and a gate electrode formed on the gate insulating film. The active layer includes an intrinsic or substantially intrinsic channel forming region, a pair of high resistance impurity regions adjacent to the channel forming region, and a pair of high resistance impurity regions provided outside the pair of high resistance impurity regions. A semiconductor device having a low resistance impurity region, wherein the gate insulating film covers at least the channel formation region and the pair of high resistance impurity regions. 2. A first step of forming an active layer on an insulating surface, a second step of forming an insulating film covering the active layer, and selectively removing the insulating film to form the active layer. A third step of selectively exposing the surface of the layer, and a fourth step of introducing a P-type or N-type impurity element into the active layer using the insulating film remaining in the third step as a mask
And a step of manufacturing a semiconductor device.