JP4203066B2 - Semiconductor device - Google Patents

Description

  The present invention relates to a glass substrate on which a semiconductor device is formed. In particular, a base film formed on the surface of a glass substrate and a manufacturing method thereof. Furthermore, it is related with the heat processing method of a glass substrate.

  As a thin film semiconductor device formed on a glass substrate, a thin film transistor (hereinafter referred to as TFT) is known. The TFT formed on such a glass substrate is disposed in a pixel driving portion or a peripheral circuit of a liquid crystal display device, and is used when displaying a high image. It is also used for image sensors and other integrated circuits.

Using a glass substrate as the substrate
Since it is optically transparent to visible light, it is easy to use when light is transmitted through the device as in a liquid crystal display device.
·Cheap price.
However, there is a problem that the upper limit of the heat treatment temperature is limited by the heat resistant temperature of the glass substrate.

  Corning 7059 glass is generally used as the glass substrate because of problems such as precipitation of impurities from the glass substrate and price. The transition temperature of this 7059 glass is 628 ° C., and the strain point is 593 ° C. As other practical industrial glass materials having a strain point of 550 to 650 ° C., those shown in Table 1 below are known.

  On the other hand, when an amorphous silicon film formed on a glass substrate by a vapor phase method is crystallized by heating, a temperature of 600 ° C. or higher is generally required. When a 7059 glass substrate is used, the substrate is heated. Will shrink.

  As a device using TFTs formed on a glass substrate, an active matrix type liquid crystal display device is known. In this case, tens of thousands to millions of TFTs are formed in a matrix on a glass substrate. There is a need to. In order to form a TFT, a process using a large number of masks is required, and the problem of shrinkage of the substrate is a major obstacle in the manufacturing process.

In particular, when it is necessary to perform mask alignment before the heat treatment, there is a problem that the substrate shrinks according to the heat treatment.
On the other hand, in the process of heat-treating the substrate, due to the problem of the processing speed, it is common to place a plurality of substrates vertically in a heating furnace, but in the heat treatment above the strain point temperature of the substrate, Will become prominent.

Further, when a TFT is formed on a glass substrate, particularly when a TFT capable of passing a large current is formed, heat generation according to the operation becomes a problem. The problem of this heat generation is caused by the fact that the thermal conductivity of silicon is 148 Wm ⁻¹ K ⁻¹ (300 K) and the thermal conductivity of the glass substrate is 1.38 Wm ⁻¹ K ⁻¹ (300 K). (However, the thermal conductivity of silicon is that of single crystal silicon, and the thermal conductivity of the glass substrate is that of quartz glass.)

  As described above, since the thermal conductivity of the glass substrate is significantly lower than that of silicon, the heat generated in the TFT cannot escape during the operation of the TFT. Thermal breakdown becomes a problem.

  This problem is particularly prominent when crystalline silicon is used. That is, in a TFT using an amorphous silicon film, since the current value to be handled is small, there is no need to worry about the problem of heat generation. However, in a TFT using a crystalline silicon film, a large current flows. Heat generation is a big problem.

The present invention solves the problem of shrinkage of the glass substrate, the problem of bending of the glass substrate, and the problem of heat generation during the operation of the TFT in the heating process in manufacturing the semiconductor device using the glass substrate. It is an object of the invention.

  In the present invention, the glass substrate is heat-treated at a temperature higher than its strain point, and gradually cooled at a rate of 0.01 ° C./min to 0.5 ° C./min. The fact is that the shrinkage of the glass substrate at this time can be suppressed to 50 ppm or less by performing the cooling at a temperature lower than the point and quenching at a rapid descending speed of 10 ° C./min to 300 ° C./sec. Is based.

  By performing the treatment as described above, it is possible to obtain a glass substrate generally having a strain point of 550 ° C. to 690 ° C. and shrinkage in a heat treatment step of 600 ° C. or less of 50 ppm or less.

  In the present invention, in order to solve the problem of bending of the substrate at the time of heat treatment of the glass substrate, it is preferable to heat the glass substrate while being held substantially horizontally. An example of an apparatus for performing heat treatment while holding the substrate approximately horizontal is shown in FIG.

  FIG. 1 shows an outline of a heating furnace, and shows a reaction tube 11 made of quartz, a substrate holding means (substrate holder) 12, and a substrate 13 arranged horizontally. Although not shown in the figure, this apparatus is provided with a heater for heating the reaction tube 11 from the outside. Also provided are means for supplying a predetermined gas into the reaction tube and means for moving the substrate holding means from the reaction tube to the outside.

  FIG. 1 shows a state in which the glass substrate 13 is held horizontally by the substrate holding means 12. Here, the reason why the glass substrate is held horizontally is to prevent the substrate from being bent and its planarity from being impaired by holding the substrate horizontally and performing the heat treatment. Such a configuration is useful when a process for applying a temperature higher than the strain point to the glass substrate is required.

  Moreover, when it is not desired to shrink the glass substrate in the heating process, there is a method in which the glass substrate is preliminarily contracted by heat treatment (pre-heat treatment) to reduce the contraction in the subsequent heating process.

  According to the experiments by the present inventors, when the pre-heat treatment is performed at a temperature higher than the strain point temperature of the glass substrate and is gradually cooled after the heat treatment, the glass substrate is greatly shrunk, and the subsequent heating step is performed at the transition point of the glass substrate. It was found that the glass substrate was hardly shrunk when it was carried out at or near the temperature and quenched after this heat treatment.

  In the pre-heat treatment, it is important to cool the glass substrate slowly at a rate of 0.01 to 0.5 ° C./min, for example, 0.2 ° C./min or less. When the glass substrate shrinks by heating, particularly when it is slowly cooled after the heating, the glass substrate shrinks extremely greatly and at the same time, local stress in the glass substrate is relieved. As a result, the greater the shrinkage, the smaller the shrinkage of the substrate in the subsequent heating step. Moreover, the effect becomes large, so that this heat processing temperature is high.

  Moreover, in the heat treatment necessary for film formation, crystal growth, oxidation, etc. performed after the pre-heat treatment, it is important to rapidly cool after heating at a rate of 10 ° C./min to 300 ° C./sec. In particular, at ± 100 ° C., preferably ± 50 ° C. in the vicinity of the strain point of the glass material, expansion and contraction of the glass material can be suppressed by quenching at the above speed. For example, in a process that requires a processing temperature of 493 to 693 ° C. for Corning 7059 glass, at least rapid cooling to 493 ° C. is effective in suppressing further shrinkage (in some cases, elongation) to 50 ppm or less. .

  The heat treatment process performed after the pre-heat treatment includes crystallization of the amorphous semiconductor formed on the glass substrate by heating, thermal annealing on the semiconductor film or semiconductor device formed on the glass substrate, and on the glass substrate. In addition, a heat treatment required when forming a semiconductor film or an insulating film, a process of applying heat to the glass substrate, and the like can be given.

  The heat treatment (pre-heat treatment) for shrinking the glass substrate described above in advance needs to be performed at a temperature higher than the heating temperature in the heating step performed thereafter.

  Specifically, it is necessary to heat-treat a glass substrate having a strain point of 550 to 690 degrees at a temperature of 600 degrees or more (this temperature needs to be higher than the strain point temperature of the glass substrate).

  In addition, by forming an aluminum nitride (AlN) film as a base film in advance on the glass substrate, the problem of heat generation of the TFT when the TFT is formed on the glass substrate can be solved.

Aluminum nitride has a thermal conductivity of about 200 Wm ⁻¹ K ⁻¹ or more, and is higher than the thermal conductivity of crystalline silicon constituting the TFT (considered to be smaller than 150 Wm ⁻¹ K ⁻¹ of single crystal silicon). Large and functions as a heat sink. Moreover, since the aluminum nitride film is transparent to visible light, there is no problem even if it is used for a liquid crystal display device or the like.

  As a method for producing this aluminum nitride (AlN), a sputtering method, a plasma CVD method, and the like are known. In particular, a positive column type plasma CVD apparatus capable of simultaneously forming films on both surfaces of a glass substrate is used. It is useful. Further, the thicker the thickness, the higher the function as a heat sink of the TFT can be improved, but it is practically useful that the thickness is 500 to 3 μm, preferably 1000 to 1 μm.

  An outline of this positive column plasma CVD apparatus is shown in FIGS. FIG. 7 shows a cross section of FIG. 6 taken along A-A ′. 6 and 7, 58 is a vacuum chamber, 50 and 51 are high frequency power supplies of 13.56 MHz, a high frequency is applied to the pair of electrodes 54 and 55, and a high frequency discharge is generated between these electrodes. . A plurality of substrates 53 on which films are formed are arranged inside a substrate support 56 having a frame structure. The end of the substrate 53 is held inside the substrate support 56 by a substrate support member 57 so that the film is formed on both surfaces of the substrate. Reference numeral 52 denotes a reactive gas or carrier gas introduction system, and unnecessary gas is discharged from the exhaust system 59 by the vacuum exhaust pump 60.

  The usefulness of using the apparatus shown in FIGS. 6 and 7 is that a plurality of substrates can be processed at the same time, and films can be formed on both sides of the substrate. In particular, when an aluminum nitride film is formed on the surface of a glass substrate as a base film, forming an aluminum nitride film on both surfaces of the glass substrate has utility as described below.

(1) By forming an aluminum nitride film on both surfaces of a glass substrate, the influence of precipitates from the glass substrate can be suppressed.
(2) In the subsequent heat treatment step, the substrate can be prevented from warping to one side.

  In the case where the above-mentioned utility is obtained by a normal sputtering method or a parallel plate type plasma CVD method, it is necessary to form a film on each side of the substrate, and there is a problem of contamination when the substrate is turned over. A decrease in productivity due to an increase in the number of processes is a problem.

  In addition, an aluminum nitride film formed by a sputtering method or a CVD method may have a small aluminum component and an excessive nitrogen component. In this case, the aluminum nitride film that has just been formed appears colored yellow, and its resistance is not sufficient as an insulator.

  In order to improve this, heat treatment may be performed in a nitrogen atmosphere or a mixed atmosphere of nitrogen and oxygen (for example, air). When heat treatment is performed in a nitrogen atmosphere, an aluminum nitride film having the necessary transmittance and resistance can be obtained. In addition, when heat treatment is performed in a mixed atmosphere of nitrogen and oxygen, an oxidized aluminum nitride film represented by AlNxOy can be obtained. In this case, 0.001 to 10 atomic% of oxygen (O) can be contained. And good transparency and insulation characteristics, and TFT heat sink (Cool sink, means for spreading the heat generation evenly on the substrate even if the local heat generation area exists on the substrate, such as TFT) It can have the function as.

  It is very useful in the manufacturing process to combine the heat treatment process of the aluminum nitride film and the pre-heat treatment process for shrinking the glass substrate in advance. That is, by performing the heat treatment of the aluminum nitride film and the pre-heat treatment of the glass substrate at the same time, an aluminum nitride film optimal for a high mobility TFT is formed as a base film, and even in a process that requires heating, glass A glass substrate capable of minimizing the shrinkage of the substrate can be provided.

  Of course, an aluminum nitride film may be formed after pre-heat treatment of the glass substrate, and then the aluminum nitride film may be heat-treated. In this case, it is important that the pre-heat treatment is performed at a temperature higher than the strain point temperature of the glass substrate, and the heat treatment of the aluminum nitride film is performed at a temperature lower than that of the pre-heat treatment. At this time, the glass substrate is shrunk by slow cooling after the pre-heat treatment, and the aluminum nitride film is rapidly cooled after the heat treatment of the aluminum nitride film, thereby minimizing the shrinkage of the substrate in the heat treatment process of the aluminum nitride film. Can be suppressed.

  Further, according to a study by the present inventors, by introducing Ni, Pb, or Si as impurities that promote crystallization into the amorphous silicon film, the amorphous silicon film can be formed at a temperature of 600 ° C. or lower. Crystallization can be performed, and by selectively introducing Ni, Pb, and Si, which are impurities that promote this crystallization, crystal growth in a direction parallel to the substrate or selective crystal growth can be achieved. It has been found that it can be done.

  In the case of employing such a process, a mask alignment process is required to selectively introduce impurities before crystallization by heating. Therefore, in this case, the present invention capable of suppressing the shrinkage of the glass substrate in the heating process after mask alignment (some glass has anisotropy in expansion and contraction) to 50 ppm or less is extremely effective.

  The present invention is also useful when an oxide film is formed on the semiconductor surface by heating in an oxidizing atmosphere (generally referred to as thermal oxidation). Further, it is also effective when a predetermined film is formed by heating in an atmosphere containing raw materials for forming a film.

  In any case, it is important that these heating steps are performed at a temperature lower than the temperature in the pre-heat treatment step that is initially performed on the glass substrate at a temperature equal to or higher than the strain point temperature of the glass substrate.

  Moreover, it is important to perform slow cooling after the treatment step during the pre-heat treatment, and to perform rapid cooling during the subsequent heat treatment.

  By heat-treating the glass substrate in advance at a temperature equal to or higher than the transition temperature, and gradually cooling after the heat treatment, the substrate is shrunk, and then subjected to heat treatment at a temperature lower than the strain temperature of the glass substrate, and further rapidly cooled, In this case, the shrinkage of the glass substrate can be minimized.

  Further, by providing an aluminum nitride (AlN) film as a base film for the semiconductor film, a margin for the heat generation of the TFT can be obtained, and the reliability and stability of a device using the TFT (for example, an active matrix liquid crystal display device). Can be increased.

  Further, by performing the pre-heat treatment step of the glass substrate in a nitrogen atmosphere or a mixed atmosphere of nitrogen and oxygen, the heat treatment for preliminarily shrinking the glass substrate and the insulation and permeability of the aluminum nitride film can be achieved. A thermal annealing process for enhancing the temperature can be performed simultaneously, which is extremely useful in the manufacturing process.

  In the embodiment of the present invention, the description mainly focused on the Corning 7059 glass substrate, but other glass substrates, for example, Corning 1733, HOYA / LE30, NA35, NA45, NEC, It goes without saying that the same effect can be obtained even with materials such as glass OA2, Asahi glass AN1, and AN2.

  In this embodiment, a P-channel TFT (PTFT) and an N-channel TFT (NTFT) using a crystalline silicon film formed on the glass substrate shown in FIGS. This is an example of forming a circuit combined with a mold. The configuration of this embodiment can be applied to a pixel electrode switching element and a peripheral driver circuit of an active liquid crystal display device, as well as an image sensor and a three-dimensional integrated circuit. In particular, it is useful to use the TFT for the peripheral driver circuit when the peripheral circuit of the active matrix type liquid crystal display device is also formed on the same substrate. This is because the TFT of the peripheral driver circuit is driven with a large current, and therefore it is necessary to improve the reliability due to the heat generation.

  In this embodiment, NA35 (see Table 1) is used as the substrate. This NA35 has a strain point of 650 ° C., has higher heat resistance than Corning 7059 glass (strain point 593 ° C.), and is useful when a high temperature treatment step is required.

First, an aluminum nitride (AlN _x O _y , where y is 0) film 202 is formed on a glass substrate to a thickness of 4000 mm by using a positive column plasma CVD apparatus shown in FIG. The film is formed to a thickness of 2 μm to 0.5 μm, here 0.3 μm. In film formation, Al (C ₄ H ₉ ) ₃ and N ₂ gas were used as source gases. By this step, the aluminum nitride film 202 is simultaneously formed on both surfaces of the glass substrate.

  Next, the glass substrate is preheated. This step simultaneously performs a pre-heat treatment for shrinking the glass substrate in advance and an annealing step for the previously formed aluminum nitride film.

  This step is performed for 4 hours at a temperature of 690 ° C. higher than the strain point (650 ° C.) of the NA35 glass substrate. The atmosphere is 100% nitrogen and the pressure is normal.

  This step is performed by holding a plurality of substrates 13 horizontally using the heating furnace shown in FIG. The heat treatment atmosphere is a nitrogen atmosphere (normal pressure). This heat treatment is desirably performed at an angle of ± 30 degrees or less from the horizontal in order to prevent the substrate from being bent.

  As described above, when an aluminum nitride film is formed on both surfaces of the glass substrate, the risk of the substrate being warped by the heat treatment is reduced, so this heat treatment may be performed with the substrate standing. Is possible.

After completion of the heat treatment, the glass substrate is cooled at a rate of 0.01 to 0.5 ° C./min, for example, 0.2 ° C./min. The cooling rate is controlled by using a gas containing nitrogen such as nitrogen gas (N ₂ ), ammonia (NH ₃ ), nitrous oxide (N ₂ O), and changing the inflow amount. Moreover, you may mix 1-25 atomic% of oxygen in nitrogen gas. In this slow cooling process, shrinkage of 1000 ppm or more occurs in the glass substrate. Further, when nitrogen, ammonia, or nitrous oxide is used in cooling after the pre-heat treatment, the vicinity of the surface of the glass substrate can be further nitrided with these gases. This makes it possible to realize a structure that prevents the precipitation of boron impurities such as boron, barium, and sodium, which are glass impurities, in a semiconductor formed in a later process at the same time as annealing the aluminum nitride film, and a highly reliable semiconductor device. It is effective in forming.

  Further, before or after the above process, a silicon oxide film may be further formed on the aluminum nitride film 202 as a base film. In this case, however, the function of the aluminum nitride film as a heat sink is reduced.

  Alternatively, an aluminum nitride film may be formed after pre-heat treatment for shrinking the substrate, and thermal annealing may be performed on the aluminum nitride film.

  Then, an intrinsic (I-type) amorphous silicon film 203 having a thickness of 300 to 1500 mm, for example, 800 mm is formed by plasma CVD. Further, a silicon oxide film 204 having a thickness of 100 to 800 mm, for example 200 mm, is deposited thereon by plasma CVD. This serves as a protective film in the following thermal annealing process and prevents the film surface from being rough. (Fig. 2 (A))

  Next, thermal annealing is performed at 600 ° C. for 8 hours in a nitrogen atmosphere (atmospheric pressure). By this thermal annealing, the amorphous silicon film 203 is crystallized to become a crystalline silicon film. Then, rapid cooling is performed from a strain point of the glass to a temperature below 100 ° C., that is, to 493 ° C. in this case, at a rate of 10 to 300 ° C./minute, for example, approximately 50 ° C./minute or more. At this time, shrinkage of 0 to 44 ppm (20 ppm or less on average) was observed on the glass substrate. In this process, the heating furnace shown in FIG. 1 is also used.

On the other hand, when a base film and an amorphous silicon film are formed on a glass substrate that is not subjected to pre-treatment heating at 640 ° C. for the glass substrate, and thermal annealing is performed at 600 ° C. for 8 hours as described above, 1000 ppm or more Shrinkage was observed.
Prior to crystallization of the amorphous silicon film by heating, Ni or Pb is used as a crystallization promoting material to form a film on the upper or lower surface of the amorphous silicon film, or the material is made amorphous by ion implantation. By injecting into the crystalline silicon film, crystal growth can be performed in the direction parallel to the substrate from the region where the crystallized material is introduced. Further, even when silicon ions are selectively implanted, selective crystal growth can be performed.

In such a case, a mask must be formed before the heating step for crystallization, and a film formation or ion implantation step must be performed. It is necessary to suppress the occurrence of shrinkage of the substrate in the heating step as much as possible. Don't be. Therefore, in such a case, the present invention that can suppress the shrinkage of the glass substrate is effective.
The shrinkage data of the glass substrate (Corning 7059) in this example is shown in FIG. FIG. 3 shows a case where the substrate is pre-heated under the same conditions, and then a base film is formed, an amorphous silicon film is further formed, and heat crystallization is performed under different conditions. This shows the final shrinkage of the substrate.
As is apparent from FIG. 3, the heat treatment is performed at a transition point (in this case, 628 ° C.) or lower of the glass substrate, that is, at least in the range of 100 ° C. up and down from the glass strain point, Is small.

  After the crystallization step of the amorphous silicon film 203 by the heating, the protective film 204 is removed, and the silicon film 203 is patterned to form an island-shaped active layer 205 of the TFT. The size of the active layer 205 is determined in consideration of the channel length and channel width of the TFT. The smaller one is 50 μm × 20 μm, and the larger one is 100 μm × 1000 μm.

Next, infrared light having a peak at 0.6 to 4 μm, here 0.8 to 1.4 μm, is irradiated for 30 to 180 seconds to anneal the active layer 205. This annealing is performed to further improve the crystallinity of the active layer 205.
At this time, the active layer 205 is heated to 800 to 1300 ° C., typically 900 to 1200 ° C., for example, 1100 ° C., by irradiation with infrared light. This temperature is not the actual temperature on the glass (since glass transmits infrared light), but is the temperature on the silicon wafer used as a monitor. Here, the irradiation is performed in an H ₂ atmosphere in order to improve the surface state of the active layer. Since this step selectively heats the active layer, the heating of the glass substrate can be minimized. And it is very effective in reducing defects and non-solid bonds in the active layer. (Fig. 2 (B))

  A halogen lamp was used as an infrared light source. The intensity of the visible / near infrared light was adjusted so that the temperature on the single crystal silicon wafer of the monitor was between 800 and 1300 ° C., typically between 900 and 1200 ° C. Specifically, the temperature of the thermocouple embedded in the silicon wafer was monitored and fed back to the infrared light source. It is estimated that the temperature of the silicon surface on the glass substrate has dropped to about 2/3 of that. In this embodiment, the temperature rise is constant, the speed is 50 to 200 ° C./second, and the temperature drop is natural cooling rapid cooling at 20 to 100 ° C./second.

Note that it is preferable to form a silicon oxide or silicon nitride film as a protective film on the surface of infrared light irradiation. This is to improve the surface state of the silicon film 205. In this embodiment, in order to improve the state of the surface of the silicon film 205 has been carried out in _{H 2} atmosphere, HCl of 0.1 to 10 volume% in _{H 2} atmosphere, other hydrogen halides or fluorine or chlorine A bromine compound may be mixed.

Since the visible / near infrared light irradiation selectively heats the crystallized silicon film, heating of the glass substrate can be minimized. And it is very effective in reducing defects and non-solid bonds in the silicon film. It is also effective to reduce defects by performing hydrogen annealing at 200 to 500 ° C., typically 350 ° C. after the completion of this step. This is performed by ion doping of hydrogen in an amount of 1 × 10 ¹³ to 1 × 10 ¹⁵ cm ⁻² , and the same effect can be obtained by heat treatment at 200 to 300 ° C.

After the infrared light irradiation step, a silicon oxide film 206 having a thickness of 1000 mm is formed as a gate insulating film by plasma CVD. As the CVD source gas, TEOS (tetraethoxysilane, Si (OC ₂ H ₅ ) ₄ ) and oxygen are used, and the substrate temperature during film formation is set to 300 to 550 ° C., for example, 400 ° C.
After the formation of the silicon oxide film 206 to be the gate insulating film, light annealing by irradiation with visible / near infrared light is performed again under the same conditions as the infrared light irradiation step. By this annealing, levels at the interface between the silicon oxide film 206 and the silicon film 205 and in the vicinity thereof can be eliminated. This is extremely useful for an insulated gate field effect semiconductor device in which the interface characteristics between the gate insulating film and the channel formation region are extremely important.

  Subsequently, aluminum having a thickness of 6000 to 8000 mm, for example, 6000 mm (including a rare earth element of 0.01 to 0.25% by weight of the periodic table IIIa) is formed by sputtering. In addition to aluminum, a group IIIb element may be used. Then, the aluminum film is patterned to form gate electrodes 207 and 209. Further, the surface of the aluminum electrode is anodized to form oxide layers 208 and 210 on the surface. This anodization is performed in an ethylene glycol solution containing 1 to 5% tartaric acid. The thickness of the obtained oxide layers 208 and 210 is 2000 mm. Since the oxides 208 and 210 have a thickness for forming an offset gate region in a subsequent ion doping step, the length of the offset gate region can be determined by the anodic oxidation step.

Next, by ion doping (also referred to as plasma doping), the gate electrode portion (that is, the gate electrode 207 and the surrounding oxide layer 208 and the gate electrode 209 and the surrounding oxide layer 210) is used as a mask in a self-aligning manner. Impurities imparting P or N conductivity type are added to the silicon film 205. As the doping gas, phosphine (PH ₃ ) and diborane (B ₂ H ₆ ) are used. In the former case, the acceleration voltage is set to 60 to 90 kV, for example, 80 kV, and in the latter case, 40 to 80 kV, for example, 65 kV. The dose amount is 1 × 10 ¹⁴ to 8 × 10 ¹⁵ cm ⁻² , for example, phosphorus is 2 × 10 ¹⁵ cm ⁻² and boron is 5 × 10 ¹⁵ cm ⁻² . In doping, each region is selectively doped by covering one region with a photoresist. As a result, N-type impurity regions 214 and 216 and P-type impurity regions 211 and 213 are formed, and a P-channel TFT (PTFT) region and an N-channel TFT (NTFT) region can be formed. it can.

Thereafter, annealing is performed by laser light irradiation. As the laser light, a KrF excimer laser (wavelength 248 nm, pulse width 20 nsec) was used, but other lasers may be used. The laser light was irradiated under the conditions of an energy density of 200 to 400 mJ / cm ² , for example, 250 mJ / cm ^2, and ² to 10 shots, for example, 2 shots were irradiated at one place. The effect may be increased by heating the substrate to about 200 to 450 ° C. during the laser light irradiation. (Fig. 2 (C))

Further, this step may be a method by lamp annealing using visible / near infrared light. Visible and near infrared rays are easily absorbed by crystallized silicon, or amorphous silicon to which phosphorus or boron is added at 10 ¹⁷ to 10 ²¹ cm ⁻³ , and effective annealing comparable to thermal annealing at 1000 ° C. or higher. It can be performed. When phosphorus or boron is added, light is sufficiently absorbed even in the near infrared due to the impurity scattering. This can be fully inferred from the fact that it is black even when observed with the naked eye. On the other hand, it is difficult to be absorbed by the glass substrate, so it does not heat the glass substrate to a high temperature and requires only a short processing time, so it can be said that it is an optimal method in the process where shrinkage of the glass substrate is a problem. .

Subsequently, a silicon oxide film 217 having a thickness of 6000 mm is formed by plasma CVD as an interlayer insulator. As the interlayer insulator, polyimide or a two-layer film of silicon oxide and polyimide may be used. Further, contact holes are formed, and TFT electrodes and wirings 218, 220, and 219 are formed of a metal material, for example, a multilayer film of titanium nitride and aluminum. Finally, annealing is performed at 350 ° C. for 30 minutes in a hydrogen atmosphere of 1 atm to complete a semiconductor circuit in which TFTs are configured in a complementary manner. (Fig. 2 (D))
The circuit shown above has a CMOS structure in which PTFT and NTFT are provided in a complementary manner. However, in the above process, two TFTs are formed at the same time, and two independent TFTs are manufactured simultaneously by cutting at the center. Is also possible.

  This embodiment is an example in which an N-channel TFT is provided in each pixel as a switching element in an active liquid crystal display device. In the following, one pixel will be described, but many other (generally several hundred thousand) pixels are formed with the same structure. Needless to say, a P-channel TFT may be used instead of an N-channel TFT.

  An outline of the manufacturing process of this example is shown in FIG. In this example, a Corning 7059 glass substrate (thickness 1.1 mm, 300 × 400 mm) was used as the substrate 400. First, an aluminum nitride film 401 having a thickness of 1000 to 5000 mm, typically 2000 mm, was formed by sputtering or reactive sputtering. This aluminum nitride film has high transparency and suppresses the movement of ions, so that it is effective in blocking the diffusion of mobile ions from the substrate 400 to the TFT region. Further, a silicon oxide film 402 was formed as a base film to a thickness of 2000 mm by a plasma CVD method.

  Next, a heat treatment at 640 ° C. for 4 hours is performed in a nitrogen atmosphere, and is gradually cooled in ammonia at a cooling rate of 0.1 ° C./min. This step is effective when performed at a rate of 0.5 ° C./min or less. By this step, the glass substrate on which the base film is formed can be shrunk in advance. This process also serves as an annealing process for the aluminum nitride film. Also in this example, the heating furnace shown in FIG. 1 was used for the heating process.

  Further, an amorphous silicon film is formed to a thickness of 1000 mm by plasma CVD. Next, a mask is formed with a photoresist, and silicon ions are implanted into a portion to be a channel formation region. At this time, the projected range of implanted silicon ions is set to be near the center of the silicon film.

  Then, the mask is removed and thermal annealing is performed at 550 ° C. for 8 hours. In this step, the region previously implanted with silicon ions is selectively crystallized. Then, after this step, rapid cooling is performed at a cooling rate of 50 ° C./min or more. In this step, a method of taking the substrate out of the heating furnace and naturally cooling it may be adopted.

Next, the silicon film is patterned to leave only the island-like active layer 403 of the TFT. At this time, the central portion of the island-like active layer 403 is a region into which silicon ions have been previously implanted, and is a portion for forming a channel formation region. The reason for adopting such a configuration is to make the channel formation region portion selectively have a highly crystalline structure. Then, the island-like active layer 403 is irradiated with visible / near infrared light in an oxygen or nitrous oxide atmosphere to improve the crystallinity of the silicon film, and the surface has a thickness of 50 to 200 mm, typically 100 mm. The silicon oxide film 404 is formed. The temperature was 1100 ° C. and the time was 30 seconds. The step of forming the silicon oxide film 404 can be performed even when heated to 550 to 650 ° C. in an oxygen or nitrous oxide atmosphere.
In that case, needless to say, the apparatus shown in FIG. 1 may be used. (Fig. 4 (A))

  Further, an aluminum nitride gate insulating film (thickness 500 to 3000 mm, typically 1200 mm) 406 is formed by sputtering using aluminum nitride as a target or reactive sputtering using aluminum as a target. The substrate temperature is 350 ° C. As a result, a two-layer structure of a thin silicon oxide film 404 by thermal oxidation and an aluminum nitride film 406 by sputtering is obtained. Since aluminum nitride has a ferroelectric constant 5 times or more that of silicon oxide, it is effective in reducing the threshold voltage of TFTs, particularly the threshold voltage of P-channel TFTs. In addition, unlike silicon nitride, aluminum nitride has a low probability of generating a local center and is preferable as a gate insulating film material. Thereafter, the aluminum nitride film 406 is annealed by heat annealing in a nitrogen atmosphere or lamp irradiation.

  Next, a gate electrode 407 is formed by forming a known film mainly composed of polycrystalline silicon by LPCVD and performing patterning. At this time, 0.1 to 5 atomic% of phosphorus is introduced as an impurity in the polycrystalline silicon in order to improve conductivity. (Fig. 4 (B))

Thereafter, phosphorus is implanted as an N-type impurity by an ion doping method, and a source region 408, a channel formation region 409, and a drain region 410 are simultaneously formed in a self-aligned manner. Then, irradiation with KrF laser light improves the crystallinity of the silicon film whose crystallinity has deteriorated due to ion implantation. The energy density of the laser beam at this time is set to 250 to 300 mJ / cm ² . By this laser light irradiation, the sheet resistance of the source / drain of this TFT becomes 300 to 800 Ω / cm ² . In the case of a low concentration drain (LDD) structure in which the doping concentration is lowered than usual, the sheet resistance is 10 to 200 kΩ / □. The annealing step by laser irradiation may be performed by lamp annealing of visible / near infrared light.

  Thereafter, an interlayer insulator 411 is formed from silicon oxide or polyimide, and a pixel electrode 412 is formed from ITO. Then, contact holes are formed, and electrodes 413 and 414 are formed of a chromium / aluminum multilayer film in the source / drain regions of the TFT, and one of the electrodes 414 is also connected to the ITO 412. Finally, hydrogenation is performed by annealing in hydrogen at 200 to 400 ° C. for 2 hours. In this way, the TFT is completed. (Fig. 4 (C))

  The present embodiment will be described with reference to FIG. In this embodiment, as the substrate 501, a glass substrate (Corning 7059) in which an aluminum nitride film (not shown) having a thickness of 5000 mm is formed on both surfaces by the positive column plasma CVD method shown in FIGS. .

  The substrate is annealed in advance at 640 ° C. in nitrogen for 4 hours in order to anneal the aluminum nitride film and prevent shrinkage. After the completion of this annealing, it is gradually cooled in nitrogen to 450 ° C. at 0.1 ° C./min, and then removed from the heating furnace.

  By this step, the glass substrate is greatly shrunk, and shrinkage in the subsequent heating step can be suppressed to 50 ppm or less. At the same time, the aluminum nitride (AlN) film can be annealed, and its insulation and permeability can be improved.

  First, a base film 502 was formed on a substrate 501, and an amorphous silicon film having a thickness of 300 to 800 mm was formed by plasma CVD. Then, heat annealing was performed at 600 ° C. for 1 hour. After thermal annealing, the substrate was rapidly cooled to 450 ° C. at a rate of 2 to 200 ° C./second, preferably 10 ° C./second or more. This is to prevent the substrate from shrinking due to this thermal annealing step. In such a heating furnace that cannot be rapidly cooled, the same effect can be obtained by taking the substrate out of the furnace and leaving it at room temperature. In this embodiment, the heating furnace shown in FIG. 1 was used for the heating process.

In this embodiment, since the thermal annealing temperature is higher than the strain point (593 ° C.) of Corning 7059, it is difficult to suppress the shrinkage of the substrate even if the heat treatment / annealing treatment is performed in advance. In such a case, rapid cooling from the annealing temperature as described above is effective.
Next, the silicon film is patterned to form island-shaped active layer regions 505 and 506. The active layer was etched by the RIE method having anisotropy in the vertical direction. (FIG. 5A))

  Next, a silicon oxide or silicon nitride film 507 having a thickness of 200 to 3000 mm is formed by a plasma CVD method. Low pressure CVD or photo CVD may be used to form the silicon oxide film. Then, optical processing of visible / near infrared light is performed. The conditions are the same as in Example 1. In this embodiment, a protective film of silicon oxide or silicon nitride is formed on the surface of the active layer during irradiation with visible / near infrared light. Can be prevented. (Fig. 5 (B))

  After the visible / near infrared light irradiation, the protective film 507 is removed. Thereafter, the gate insulating film 508, the gate electrode and the surrounding oxide layer 509, the gate electrode and the surrounding oxide layer 510 are formed as in Example 1, and the impurity region is formed by ion doping. This is activated by laser irradiation. (Fig. 5 (C))

Further, an interlayer insulator 511 is formed, contact holes are formed therein, and metal wirings 512, 513, and 514 are formed. (Fig. 5 (D))
In this way, a complementary TFT circuit is formed. In this embodiment, a protective film is formed on the surface of the active layer during irradiation with visible / near infrared light, and surface roughness and contamination are prevented. For this reason, the characteristics (electric field mobility and threshold voltage) and reliability of the TFT of this example were extremely good. Further, as is clear from this example, the present invention was particularly effective for a substrate material having a glass strain point of 550 to 650 ° C. Furthermore, in the present invention, when the slow cooling step is performed in an atmosphere containing nitrogen-based gas such as nitrogen, ammonia, nitrous oxide, etc., the glass is nitrided, and various impurity elements contained in the glass are glass. Since diffusion and precipitation on the surface can be suppressed, high reliability can be obtained in forming a semiconductor element.

The structure of a heating furnace is shown. The manufacturing process of an Example is shown. The shrinkage | contraction data of a glass substrate are shown. The manufacturing process of an Example is shown. The manufacturing process of an Example is shown. The structure of the CVD apparatus used in the examples is shown. The structure of the CVD apparatus used in the examples is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Reaction tube 12 Substrate holding means 13 Substrate 201 Glass substrate 202 Base film (aluminum nitride film)
203 silicon film 204 silicon oxide film 205 island-like silicon film (active layer)
206 Gate insulating film (silicon oxide film)
207 Gate electrode (aluminum)
208 Anodized layer (aluminum oxide)
209 Gate electrode 210 Anodized layer 211 Source (drain) region 212 Channel formation region 213 Drain (source) region 214 Source (drain) region 215 Channel formation region 216 Drain (source) region 217 Interlayer insulator 218 Electrode 219 Electrode 220 Electrode

Claims (2)

A film mainly composed of aluminum nitride formed on a glass substrate and mixed with 0.001 atomic% to 10 atomic% of oxygen;
An island-like silicon film having a source region, a drain region, and a channel formation region on the coating;
A silicon oxide film on the island-like silicon film;
An aluminum nitride film on the silicon oxide film;
A semiconductor device comprising: a gate electrode on the aluminum nitride film. A film mainly composed of aluminum nitride formed on a glass substrate and mixed with 0.001 atomic% to 10 atomic% of oxygen;
An island-like silicon film having a source region, a drain region, and a channel formation region on the coating;
A silicon oxide film on the island-like silicon film;
An aluminum nitride film on the silicon oxide film;
A gate electrode on the aluminum nitride film,
A film mainly composed of aluminum nitride mixed with 0.001 atomic% to 10 atomic% of oxygen is formed on a surface opposite to the surface of the glass substrate on which the film is formed. Semiconductor device.

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