JP2008243926A - Method for reforming thin film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reform a thin film by a process at a temperature lower than 400°C. <P>SOLUTION: The thin film for a substrate which has passed through a CVD process is reformed by utilizing surface heating by the ultraviolet light absorption of the thin film on the substrate by an annealing treatment furnace 2. Partial heating by the absorption of ultraviolet light at a defective site of the thin film is utilized. A pulse laser or a continuous wave laser is used as a light source 6 irradiating the ultraviolet light. The thin film may also be supplied with irradiating light from the light source emitting light in a visible-light region except an ultraviolet wavelength region when reforming the thin film. The light source 6 irradiating the ultraviolet light irradiates light having a wavelength longer than 210 nm. The thin film is reformed by utilizing the surface heating by the ultraviolet light absorption of the thin film in an atmosphere separately supplied with an oxidizing gas from a bomb 3, a reducing gas from a bomb 4 and an inert gas from a bomb 5. An ozone gas is supplied as an oxidizing gas. A dilution hydrogen gas is supplied as the reducing gas. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a technique for modifying a thin film exemplified by a gate oxide film or a polysilicon film of a semiconductor element such as a semiconductor polysilicon TFT or FET element.

In recent years, TFT LCD devices have been widely used as display devices. In this LCD device, TFTs (thin film transistors) are formed in a matrix on a glass substrate, and the liquid crystal above and below the TFTs is driven by the TFTs. A TFT is formed by laminating an insulating film or a polysilicon film on a glass substrate. Recently, soda glass, which is cheaper than quartz glass, is used as the glass substrate. Soda glass has a softening point as low as about 500 ° C. compared to quartz, and Na contained in the soda glass diffuses in a high temperature environment, so that a film forming technique of 400 ° C. or less is required. In addition, the quality of the produced film is required to be high quality close to that of a film formed at a high temperature. In recent years, as represented by a flexible information terminal (flexible PC, mobile phone), silicon device fabrication technology on an organic (flexible) substrate such as plastic (polyimide) has become important. In this case, the process temperature is 250 ° C. or lower from the heat resistant temperature of polyimide or the like. In the future, production of higher quality oxide films at lower temperatures will be required. As these insulating films, silicon oxide films are mainly used. In the gate oxide film manufacturing method at a low temperature, the plasma CVD method at 350 ° C. is usually the current mainstream (Japanese Patent Laid-Open No. 2002-92358). However, since the plasma CVD film forming temperature of 350 ° C. is higher than the melting point of the above-mentioned element, a film forming technique at a lower temperature will be required in the future.
JP 2002-92358 A

In order to form a TFT gate insulating film at a low temperature, ozone CVD or photo-ozone excitation CVD is considered to be effective. However, at a film forming speed required from a practical standpoint (for example, 20 nm / min, 200 ° C.), the leakage current amount is 10 ⁻⁶ A / cm at 4 MV / cm, which is a slightly higher value. Reforming is necessary. The main cause of film quality degradation is residual impurities. This is because it is difficult to completely remove impurities in the film because the CVD reaction rate is not sufficient in the low temperature process. As other factors, structural defects of Si—O—Si, for example, oxygen excess defects (POL) and oxygen deficiency defects (ODC) also deteriorate the film quality. In the conventional TFT fabrication technology, the CVD film could be annealed at a high temperature of 450 ° C. or higher once in the subsequent process, so that these defects could be removed to some extent. However, when the process proceeds only at a low temperature in the future, annealing at a high temperature cannot be performed, and thus a technique for removing the defect by a low temperature process is required.

  Therefore, a thin film modification method for solving the above problems is characterized in that the thin film of the substrate that has undergone the CVD process is irradiated with ultraviolet light and modified using surface heating due to ultraviolet light absorption of the thin film. . According to the present invention, the surface of the thin film formed by the CVD process is heated by the ultraviolet light absorption of the thin film, and the thin film can be modified at 400 ° C. or lower. This is because the ultraviolet light has a penetration length of about several nm with respect to the silicon crystal, so that only the surface of the thin film can be heated. Further, the diffusion of impurities in the thin film is promoted by heating the thin film.

In the modification of the thin film, local heating by absorption of ultraviolet light at the defect site of the thin film may be used. Since the ultraviolet light has an absorption edge with respect to the impurity site Si—OH bond and Si—CH ₃ bond of the thin film, the binding force is changed by irradiation with ultraviolet light.

  A pulse laser or a continuous wave laser may be used as the light source for irradiating the ultraviolet light. These types of light sources increase the photoreaction rate at the impurity sites in the thin film.

  In the modification of the thin film, irradiation light of a light source that emits light in a visible light region other than the ultraviolet wavelength region may be provided to the thin film. Irradiation with light in the visible light range has the effect of light absorption heating, so that the heating of the thin film is promoted.

  Also, since silicon crystals have high binding energy, they do not damage the silicon crystal even when irradiated with light having a wavelength longer than 210 nm. Therefore, a light source that emits light having a wavelength longer than 210 nm may be used as the light source that emits ultraviolet light.

  The modification of the thin film using surface heating by absorbing ultraviolet light in polysilicon is preferably performed in an atmosphere in which an oxidizing gas, a reducing gas, or an inert gas is separately supplied. In an atmosphere provided with an oxidizing gas, it is possible to repair oxygen defects in the thin film and remove impurities by an oxidation reaction with impurity sites. In the atmosphere provided with reducing gas, the construction of hydrogen termination is promoted, so the interface characteristics are improved. This is because the structure in the film is changed by light in an atmosphere provided with an inert gas. The pressure of the inert gas is preferably reduced. The lower the gas pressure, the more heat release is avoided, so the heating of the thin film increases. The effect of reforming can be obtained arbitrarily depending on the reactive species and the atmospheric gas species having different diffusion rates in the film.

  An example of the oxidizing gas is ozone gas. Excited oxygen atoms are generated from ozone by ultraviolet absorption and enter the thin film. The excited oxygen atoms react with impurities in the thin film and enter O defect sites, and the thin film is further modified. The ozone gas concentration is not limited to 100%. However, the lower the ozone concentration, the lower the generation efficiency of excited oxygen atoms, the shorter the life time, and the higher the concentration of the gas, the higher the pressure possible. The ozone gas is desirable.

  Examples of the reducing gas include hydrogen dilution gas. Interface properties are improved by facilitating the construction of hydrogen terminations. Further, since hydrogen has a higher diffusion rate in the thin film than ozone and excited oxygen, it can diffuse to the surface even at low temperatures, and the thin film is efficiently modified.

  It is desirable to modify the thin film according to the present invention in a clean chamber. However, it may be performed in a CVD chamber.

  The modification of the thin film may be performed alternately with the CVD process. The diffusion and reaction rate in the thin film can be easily controlled, and the thin film is efficiently modified.

  As an aspect in which the modification of the thin film is alternated with the CVD process, a form in which the thin film is modified in the CVD chamber, or a CVD chamber and an oxide film are produced by vacuum transfer of the substrate on which the thin film is formed. An example is a mode in which the space between the chambers can be freely transferred. According to these aspects, a dedicated chamber for reforming becomes unnecessary. In addition, the light source for reforming can be easily shared with the light source used in other processes. Furthermore, ozone gas, which is one of the reforming gases, can be shared with a gas source used in the film forming process. Therefore, the cost can be reduced when modifying the thin film.

  Examples of the thin film described above include thin films made of polysilicon or metal oxide. The light source used for activating the thin film made of polysilicon is preferably used also as the light source used for modifying the thin film made of metal oxide. As the light source used for photoactivation (crystallization) of polysilicon, laser light in the ultraviolet light region of 254 nm and 308 nm is the mainstream, and is in the same or near frequency region as the light source used in the light annealing treatment according to the present invention. By sharing the light source used for the modification of the film, the thin film can be modified efficiently in terms of energy.

  Therefore, according to the above invention, the thin film can be modified by a process at a temperature lower than 400.degree. The film quality of the thin film after this modification is in an effective range in a low temperature device. In addition, the thin film can be modified without selecting means such as a plasma method or an ozone CVD method.

(Embodiment 1)
1. About Light Irradiation Annealing The light irradiation annealing according to the present embodiment means that the CVD oxide film is irradiated with ultraviolet light. The light source used for light irradiation annealing is desired to have a specification capable of irradiating light including a wavelength region of 200 nm to 300 nm, so-called ultraviolet light region. As an example in which the ultraviolet light region is effective for the modification of the CVD oxide film, there is a technique in which ultraviolet light irradiation is performed to improve etching resistance against SiCOH which is a low dielectric constant film (low-k film) ( 67th Applied Physics Academic Lecture 2nd Volume P747 30P-ZN-5 Kameshima et al., Sony, Toshiba, NEC, 67th Applied Physics Academic Lecture 2nd Volume P747 30P-ZN-6 Hashii et al. Renesas Semiconductor Engineering , Renesas Technology).

The SiCOH film manufactured by TEOS-CVD or the like is irradiated with ultraviolet light (200 nm-300 nm) in a hydrogen atmosphere, whereby the Si—CH ₃ bond is cut and the Si—H bond is improved, thereby improving the etching resistance. . In addition, it has been pointed out that the SiO—H bond can be cut by ultraviolet rays, and it is expected that an effective reaction for improving the characteristics will occur for a film having a small amount of C (carbon) such as a gate oxide film. The

  As described above, the present invention provides a technique for improving oxide film characteristics by light annealing in an arrangement in which ultraviolet rays are directly irradiated onto a CVD film under a specific atmospheric gas without raising the substrate temperature than the CVD film forming temperature.

2. Configuration of Apparatus FIG. 1 is a schematic configuration diagram of a light annealing treatment apparatus 1 according to an embodiment of the invention for modifying an oxide film by light irradiation annealing described above. The optical annealing apparatus 1 includes an annealing furnace 2, cylinders 3, 4, 5, light sources 6, 7 and an exhaust pump 8.

The annealing furnace 2 includes a substrate loading / unloading port, an annealing gas supply port, a vacuum exhaust port, and a leakage inert gas (for example, nitrogen) supply port. The annealing furnace 2 is provided with an irradiation window 21 for introducing ultraviolet light for light annealing and an irradiation window 22 for introducing infrared light for substrate heating. The irradiation window 21 is made of a window material that transmits 200 to 300 nm, for example, synthetic quartz (synthetic silica glass). Alternatively, it may be made of a crystal material such as MgF ₂ . In the case of infrared lamp heating, the irradiation window 22 for introducing infrared light for substrate heating is made of an infrared range transmitting material such as synthetic quartz (synthetic silica glass). Alternatively, it may be made of a crystal material such as MgF ₂ . An O-ring may be interposed at the edge of the opening of the annealing furnace 2 in which the irradiation windows 21 and 22 are installed in order to ensure airtightness. When the O-ring is installed in a place where it can be heated to 200 ° C. or higher, cooling by water cooling or air cooling is necessary.

  Since the annealing furnace 2 has a heating process, the annealing furnace 2 is preferably made of a material that can cope with a medium vacuum (-10-4 Pa) and can cope with a high temperature up to 400 ° C. Further, quartz is desirable from the viewpoint of impurity diffusion and cleaning. However, since it is difficult in terms of work, it may be made of an inner surface processing that does not fly impurities and a metal that does not oxidize into ozone. Examples of the metal include aluminum and SUS304. In this embodiment, aluminum is adopted as the material constituting the annealing furnace 2, and a mechanism for cooling the O-ring is provided by providing a cooling water channel in the vicinity of the O-ring that seals the irradiation window 21 and the irradiation window 22.

  The cylinders 3 and 4 are filled with a light annealing atmosphere gas. The number of cylinders may be increased depending on the type of gas used. However, in the case of a gas that cannot be filled in the cylinder (for example, 100% concentration ozone gas), a gas generator may be installed instead of the cylinder. As the gas species, different gases are introduced depending on the purpose of reforming, such as a gas that promotes an oxidation reaction during annealing (for example, ozone gas), a gas that promotes a reduction reaction (for example, nitrogen-diluted hydrogen), or an inert gas. Valves V1 and V2 are installed between the cylinders 3 and 4 and the annealing furnace 2, respectively.

  The cylinder 5 is filled with leak gas. Examples of the leak gas include nitrogen and argon gas. A valve V3 for supplying and stopping leak gas is installed in a pipe connecting the inert gas supply port for leak of the annealing furnace 2 and the cylinder 5.

  These gases are basically not supplied at the same time. That is, in the annealing furnace 2, the valves V1, V2, and V3 are selectively operated with the gas used for each process.

The light source 6 is a light source that irradiates light with a wavelength band of 210 to 300 nm that promotes modification by light annealing. Light having a wavelength longer than 300 nm may intersect. The light source 6 is installed outside the optical annealing furnace 2 and irradiates the substrate 10 (the substrate 10 on which the oxide film is formed) through an irradiation window 21 made of a light transmitting material exemplified by synthetic quartz. The light source 6 heats the extreme surface of the substrate 10 by light absorption. Therefore, it is desirable to set the length of the optical path 11 as short as possible so that the light in the wavelength band reaches the surface of the substrate 10 as much as possible. As shown in FIG. 1, the annealing furnace 2 is designed so that light is introduced from above, and the annealing furnace 2 is designed to have a height (gap length) as small as possible. For example, when the volume of the annealing furnace 2 is 6000 cm ³ , the gap length is set to 5 cm.

  The light source 7 is a light source for irradiating infrared rays to heat the substrate 10 in the annealing furnace 2. The substrate 10 is not directly irradiated with the heating light of the substrate 10, but is efficiently heated by placing the substrate 10 on a susceptor 20 (for example, made of SiC) made of a material that absorbs infrared light. it can. The light source 7 is disposed below the annealing furnace 2, and the light provided from the light source 7 is introduced into the annealing furnace 2 from the irradiation window 22 made of a light-transmitting material exemplified by synthetic quartz, and the susceptor 20 is introduced. The substrate 10 is irradiated through. The susceptor 20 is movably provided. The susceptor 20 should not be a substance that contaminates the inside of the annealing furnace 2 and is preferably made of a material that has a high absorption rate of infrared light and does not scatter impurities even when heated. Examples of the susceptor 20 include those made of opaque processed quartz glass, SiC, SiC coating C, or the like. The heating method of the substrate 10 may be a pot plate method. When the hot plate method is adopted, the light source 7 is not necessary. When the annealing furnace 2 is a hot plate system, a susceptor made of aluminum that is inferior in infrared absorption may be employed.

  The exhaust pump (vacuum pump) 8 controls the pressure of the annealing furnace 2 based on the pressure measurement signal supplied from the pressure gauge 23 of the annealing furnace 2. The piping connecting the annealing furnace 2 and the exhaust pump 8 is provided with a valve V4, and when various gases are supplied to the annealing furnace 2, the pressure in the annealing furnace 2 is finely adjusted as appropriate. It is necessary to install the exclusion cylinder 9 immediately before or after the exhaust pump 8 depending on the type of gas to be exhausted. For example, when ozone gas is used, an ozone killer is installed immediately after the exhaust pump 15 as shown in FIG.

  As the pressure gauge 23, a pressure gauge that can be measured in a reduced pressure state is employed. The measurement pressure range of the pressure gauge 23 desirably includes 0.1 Pa to 0.1 MPa (1 atm). In particular, when ozone gas is used, it is essential to be able to measure a low pressure range of 1000 Pa or less because use at an explosion limit pressure or less is required.

  Further, when a moving means for moving the susceptor 20 holding the substrate 10 in the annealing furnace 2 is provided, the light irradiation region can be scanned, so that a large area light annealing process can be performed on the large substrate 10.

  The chamber for performing light irradiation annealing (annealing furnace 2) can be shared with other chambers (for example, a CVD chamber). However, in the case of CVD that does not use a light source, such as plasma CVD, it is necessary to separately provide a chamber as shown in FIG.

  On the other hand, if it is a CVD that can be shared with a light source used for light irradiation annealing, such as photo-excited ozone CVD or ozone CVD, or does not use light, light irradiation is performed in a CVD chamber when a light irradiation window is provided. Annealing can be performed (Embodiment 2).

  Alternatively, in the case of employing a technique (oxidation + CVD) in which a gate oxide film is formed in two stages, it is considered that light irradiation annealing is preferably performed in an oxidation chamber that is a cleaner environment (embodiment). 3).

  Further, light irradiation annealing is performed in the CVD chamber as in the second embodiment. However, in the digital CVD method in which the CVD gas is introduced at different timings and the film formation is controlled digitally, it is effective to incorporate a light irradiation annealing process. .

  In addition, in the activation method (ELA method) by irradiating amorphous silicon or polysilicon with a laser for low-temperature activation of polysilicon, a light source having the same wavelength region as that of light irradiation annealing is used as the light source. A method of sharing a light source for light irradiation and a light source for light irradiation annealing (Embodiment 4) is also conceivable.

3. Restriction of light source for light irradiation annealing (1) Change the bonding force of impurities in the film.

For impurities CH ₃ and OH, it was confirmed that impurities SiOSi—CH ₃ and SiO—H bonds bonded to Si in SiO ₂ were cut with a laser having a wavelength of 248 nm. Irradiation in this peripheral frequency band is desirable.

  (2) Repair of structural defects.

  According to the characteristic diagram of FIG. 2, optical absorption peaks of ODC, NBOHC, E'center, NBOHC, etc. exist over 150 nm to 350 nm. Although it is most effective to irradiate a light source including all of these wavelength ranges, even when a single wavelength such as a laser (for example, KrF excimer laser: 248 nm) is used, the optical absorption edge due to all these defects is reduced. There is no problem because there is.

  (3) Expectation of surface heating effect and restriction of substrate damage.

The frequency band with a wavelength of 210 nm or less is called a vacuum ultraviolet light region, and oxygen does not pass through in the air due to an ozone generation reaction. For this reason, installation of special specifications (vacuum light path) is required between the light source and the irradiation object. Vacuum ultraviolet light has an absorption edge for structural defects in SiO ₂ (FIG. 1). By irradiating a (poly) silicon substrate with light in this wavelength band, Si—Si bond (˜7.0 eV) Affects the substrate and damages the board. Therefore, it is desirable not to irradiate light in the vacuum ultraviolet region.

  There is no concern of damaging the substrate particularly in the wavelength range of 300 nm or more. However, it does not affect the impurities and structural defects in the oxide film as much as ultraviolet light. In other words, this wavelength range may be included.

  From the viewpoint of substrate surface heating, light irradiation of 210 nm or more is desirable. However, the substrate heating effect is not essential in the present invention.

(4) Continuous light source / discontinuous light source In particular, it does not matter whether the light source is continuous or discontinuous. However, since the discontinuous light source becomes a single wavelength light source such as a laser, the irradiation area is small at this time, but since there is a sufficient number of photons, a heating effect on the substrate surface can be expected more.

  On the other hand, although a continuous light source such as a Deep UV lamp can increase the irradiation area, it has a feature that the surface heating effect is poorer than that of a laser, so that it is necessary to use it according to the application.

  From the above, there is a light source restriction that necessarily includes the wavelength range of 210 to 300 nm, and may include the wavelength range of about 300 nm or more.

4). About the type of annealing gas and its effect The type of annealing gas is selected according to the characteristics of the film to be modified.
There are three possible types: oxidizing atmosphere gas, reducing atmosphere gas, inert gas, or vacuum.

In an oxidizing gas atmosphere, removal by Si repair in the film and oxidation reaction with impurity sites can be expected. In particular, when ozone gas is used, photoreaction of ozone molecules occurs due to the ultraviolet light of light annealing, and it is taken into the film in which excited oxygen atoms with higher reactivity are generated. it can. However, pay attention to pressure and flow rate when using ozone gas. This is because when ozone is excessive in the gas phase, light cannot reach the substrate, while when it is small, the number of supplied atoms is insufficient. In the embodiment, a KrF excimer laser is used as a light annealing light source, an irradiation area of 3 cm ² , an irradiation intensity of 200 to 250 mJ / cm ² , and a repetition frequency of 100 Hz, 100% ozone gas as an annealing gas is 50 sccm, 250 Pa, a temperature of 20 to 250 ° C. Supplied with.

  In a reducing atmosphere gas, for example, nitrogen diluted hydrogen gas, in addition to the above effects, improvement of the interface characteristics of the interface characteristics can be expected by promoting the construction of hydrogen termination. In addition, since hydrogen has a higher diffusion rate in the film than the above-described excited oxygen, it can be expected to be effectively reformed in a short time.

  Modification can also be achieved using an inert gas or vacuum. This is because the structure in the film is changed by light. Moreover, the effect by the heating effect which arises on the very surface of a substrate by light irradiation can also be expected. The heating effect varies greatly depending on the pressure of the gas atmosphere. The lower the gas pressure, the greater the heating effect because heat release can be avoided. In the case of a vacuum atmosphere, the effect of surface heating can be expected most.

5. Verification of light annealing effect The conditions for annealing are shown below.

1) Conditions for light source Annealing light source: KrF excimer laser (wavelength 248 nm)
Laser repetition frequency: 100Hz
Irradiation area: 3 cm ²
Irradiation intensity: 200 to 240 mJ / cm ²
2) Gas-related conditions Annealing gas: (1) 100% ozone gas, (2) hydrogen 3% + nitrogen gas, (3) vacuum 100% ozone gas (manufactured by Meidensha's Ozonizer MPOG-SM1C1): 50 sccm, 250 Pa
3% hydrogen + nitrogen gas: confined at 0.1 atm Vacuum: 1 Pa or less 3) Conditions for annealing target annealing target: 250 ° C. photoexcited ozone CVD film (thickness ˜30 nm, 60 nm)
Sample size: chip 15cm x 15cm
[1] Improvement of film compression effect and etching rate by UV irradiation annealing FIG. 3 shows film shrinkage under the conditions of 3% hydrogen + 0.1 atm nitrogen and annealing time: 20 minutes (optical film thickness comparison before and after annealing) And a comparison of the etching rate (0.25 wt% HF). It is expected that the etching rate is reduced due to film shrinkage caused by the modification by annealing. That is, in the case of thermal annealing at 400 ° C. (no light irradiation), it was confirmed that although the film shrinks slightly, the etching rate does not change. Further, it was confirmed that when thermal annealing at 250 ° C. was performed after thermal annealing at 400 ° C., film shrinkage occurred and the etching rate decreased. From this, it is clear that irradiation with light is a driving source that promotes modification. In the case of light annealing at 400 ° C., the film compression and the etching rate decrease, but it was also confirmed that both the compression rate and the etching rate were almost the same as in the case of light annealing at 250 ° C.

FIG. 4 shows the results of FTIR (Fourier transform infrared) analysis. According to this analysis result, it can be confirmed that the OH impurity peak (˜950 cm ⁻¹ ) in the film is reduced by optical annealing (comparison between (2) and (3) in FIG. 4). It can be confirmed that heat alone does not decrease. In addition, it can be confirmed that the position of the Si—O—Si peak (−1068 cm ⁻¹ ) does not change by light annealing (comparison between (2) and (3) in FIG. 4). This means that the CVD film before annealing is of good quality and the rate of structural change caused by film compression accompanying annealing can be ignored from the whole. It can be confirmed that there is no significant difference in the results of optical annealing at temperatures of 400 ° C. and 250 ° C.

  From the above, it is clear that light irradiation is important and dependency on annealing temperature is small.

[2] Influence on Etching Rate for Ultraviolet Light Annealing Time / Annealing Atmosphere FIG. 5 is a characteristic diagram showing how the etching rate varies with the pressure of the annealing gas and the annealing time. The horizontal axis represents the etching time, and the vertical axis represents the SiO ₂ film thickness. The slope means the etching rate. The smaller the slope, the smaller the etching rate. According to this characteristic diagram, it can be confirmed that the etching rate decreases as the annealing time is increased. In the result of the annealing time of 5 minutes (▲ plot shown in FIG. 5), the slope of the line becomes gentle where SiO ₂ is thin. That is, it can be confirmed that the reforming proceeds from the Si / SiO ₂ interface. It can also be confirmed that the vacuum atmosphere is more effective for the etching rate. That is, it can be confirmed that the effect of annealing for 10 minutes in vacuum is larger than the effect of annealing for 60 minutes at a gas pressure of 0.1 atm. It can also be confirmed that as the laser intensity increases, the change in the etching rate increases.

  From the above, it is clear that an annealing time is required to some extent and the surface heating effect has an important function.

[3] Difference in effect depending on the type of annealing gas in terms of electrical characteristics FIG. 6 is a characteristic diagram showing a comparison of JE characteristics in the MIS structure before and after optical annealing. The horizontal axis is normalized by the film thickness. According to this characteristic diagram, when there is no annealing, the leakage current is large at a low electric field (<7 MV / cm), but by performing optical annealing, the leakage current is reduced and the tunnel current is generated (overlapping with the FN curve). It can be confirmed that the reforming progresses. In addition, in the high electric field region (> 7 MV / cm), the FN curve after annealing with ultraviolet light is overlapped with the JE curve, so that the ultraviolet light irradiation is modified. Is clear. The improvement proceeds even if any of the annealing atmosphere gas (1) hydrogen 3% + nitrogen gas (2) 100% ozone gas is used. By comparing the ultraviolet irradiation annealing (Δ plot) at 400 ° C. in 100% ozone atmosphere and the ultraviolet irradiation annealing (◯ plot) in H ₂ + N ₂ atmosphere at 400 ° C. shown in FIG. It can be considered that the ozone gas atmosphere is more modified by ultraviolet light irradiation annealing.

  Furthermore, with respect to the light irradiation temperature, it can be considered that the modification proceeds more by annealing at a higher temperature than the comparison between 200 ° C. (□ plot) and 400 ° C. (◯ plot). Since the annealing temperature affects the diffusion rate in the film, it can be seen that annealing at a low temperature requires a longer time.

FIG. 7 is a CV curve in the MIS structure. The frequency is 100 MHz. According to the characteristic diagram of FIG. 7, it is clear that the modification progressed by the ultraviolet light irradiation annealing because the flat band shift is reduced. Although both 100% ozone gas and H ₂ + N ₂ gas have the effect of reforming, it is clear that the reforming further proceeds when annealed in an atmosphere of H ₂ + N ₂ . Since the flat band shift is determined by the impurity density in the vicinity of the interface, it can be considered that H ₂ + N ₂ is effective for modifying the interface. Since hydrogen has a higher diffusion rate than ozone, it can reach the interface from the gas phase, so it is considered that interface modification is possible.

  From the above, it is clear that the gas used for annealing has different targets for modification. Also, 100% ozone gas annealing is effective when aiming for bulk modification in the film. Furthermore, it is effective to use a gas containing hydrogen when aiming at reforming of the interface. Further, since annealing is performed at a low temperature, the diffusion rate is slow, and it is clear that the annealing time and film thickness must be determined appropriately.

  In consideration of these points, the following embodiment provides an effective technique for an actual process.

(Embodiment 2)
1. Continuous flow type apparatus system in which an annealing furnace is also used as a CVD furnace The apparatus system of this embodiment executes an ultraviolet light irradiation annealing process and a CVD process in the same chamber. A specific apparatus system includes a cylinder that supplies CVD gas in the same row as a cylinder that supplies annealing gas to the annealing furnace 2 shown in FIG. Thus, the annealing furnace 2 becomes a chamber that can be used for both the CVD process and the light irradiation annealing process.

  As shown in FIG. 1, the annealing furnace 2 is provided with means for supplying atmospheric gas used for ultraviolet irradiation annealing, an irradiation window 22 for introducing ultraviolet light, and piping for separately supplying the atmospheric gas. Supply and exchange gases used in the process.

  In the ozone supply CVD process while irradiating ultraviolet light, 100% ozone gas used for the CVD gas can be shared with the atmospheric gas in the ultraviolet irradiation annealing. In the CVD process, the light source 7 for the annealing process may be shared and ultraviolet light irradiated from the light source 7 through the irradiation window 22 may be used.

  As the timing of the ultraviolet light irradiation process, there are a method in which a predetermined film thickness is deposited by CVD and a method in which CVD is alternately performed as illustrated in FIG. FIG. 8 is a time chart illustrating the continuous flow type process according to the present embodiment in terms of changes over time in the process gas pressure. In the CVD process in step S1, a CVD gas is introduced into the annealing furnace 2 to form a film for t1 time. In the gas exchange process in step S2 after the CVD process for t1, the CVD gas is exhausted and an annealing gas is introduced. In the light irradiation annealing process S3 after the inside of the annealing furnace 2 reaches a predetermined pressure, ultraviolet light is irradiated for t2 hours. In the gas exchange process in step S4, the annealing gas is exhausted and the CVD gas is introduced. The above steps are repeated, and finally, the light irradiation annealing process S3 is executed and finished.

  The CVD process time t1 and the annealing process time t2 are optimized by the process temperature and the film forming speed. If the time t1 is set short, the number of repetitions increases. On the other hand, if the time t1 is lengthened, the number of repetitions is reduced, but there is a possibility that the modification by annealing is insufficient due to the limitation of the diffusion rate. In addition, if an annealing process (hydrogen + nitrogen) for the purpose of interface modification is separately provided after the final light irradiation annealing process is completed, a film with a higher reforming effect can be produced.

  As an example, in the embodiment which provided the characteristic diagram showing the relationship between the etching rate and the film thickness in FIG. 5, the reforming proceeds by annealing for 10 minutes with respect to the film thickness of 20 to 30 nm by UV light irradiation annealing at 200 ° C. Can be confirmed. Therefore, based on the characteristic diagram of FIG. 5, it is clear that one of the conditions for the light irradiation annealing is to set the time t1 to a process time that allows the film thickness of 20 to 30 nm and the time t2 to 10 minutes.

2. An alternating process type apparatus system in which an annealing furnace is also used as a CVD furnace. The apparatus system of the present embodiment is based on a digital CVD process disclosed in Japanese Patent Application Laid-Open No. 2006-80474. The digital CVD process is characterized by excellent film thickness controllability and uniform film formation on a large substrate. This CVD process repeats the process of supplying the raw material gas, supplying ozone gas, confining the gas for a certain period of time, forming the CVD film, and then exhausting the reacted gas.

  In the apparatus system according to the present embodiment, the annealing furnace 2 is also used as a CVD furnace, and an ultraviolet light irradiation annealing process is incorporated in the digital CVD process as shown in the time chart of FIG. That is, in the CVD process of step S11, a raw material gas is supplied to the annealing furnace 2, and after the inside of the annealing furnace 2 reaches a predetermined pressure, ultraviolet light is irradiated for a certain period of time to form a film. Next, in the gas exchange process of step S12, the CVD gas (raw material gas + ozone gas) is exhausted and the annealing gas is introduced. In the light irradiation annealing process of step S13 after the inside of the annealing furnace 2 reaches a predetermined pressure, ultraviolet light is irradiated for a certain time. After completion of step S13, the annealing gas is exhausted. One cycle 1C consisting of the above steps is repeated, and finally, the light irradiation annealing process S13 is executed and the process ends.

  The presence or absence of ultraviolet light irradiation in the CVD process does not matter. In the case of ultraviolet light irradiation, the film is formed when the ultraviolet light is irradiated, so that after sufficiently mixing the raw material gas, the film can be uniformly formed on a large area substrate by using a large area irradiation UV lamp. At this time, if the same large area irradiation UV lamp is used in the ultraviolet light irradiation annealing process, a large area process can be performed and a CVD gas can be used efficiently.

(Embodiment 3)
In general, low-temperature CVD films have poor interface characteristics. As one solution to this problem, there is a two-stage film forming process, that is, a method in which a buffer layer having an excellent interface is formed by oxidation, and then a film having an insufficient film thickness is formed by a CVD process. In creating the film forming method according to the present embodiment, the inventors of the present embodiment have successfully oxidized single crystal silicon and polysilicon using ultraviolet light irradiation and ozone gas, and have a film quality that can sufficiently function as a buffer layer at room temperature. A method that can be manufactured has been proposed.

  The two-stage film forming process is a method in which an oxidation chamber and a CVD chamber are separately prepared, and a material is vacuum-transferred between both chambers. In this embodiment, a light irradiation annealing process is applied to this two-stage film forming process.

  FIG. 10 is a schematic configuration diagram of a film forming apparatus according to a third embodiment of the invention.

  The film forming apparatus 30 includes an oxidation furnace 31 and a CVD furnace 32, and conveys an oxidized sample between the oxidation furnace 31 and the CVD furnace 32 in a vacuum. A valve 33 is provided in the conveyance path that connects the oxidation furnace 31 and the CVD furnace 32. The valve 33 is closed except during the vacuum transfer of the sample to prevent the gas from flowing into the chambers (the oxidation furnace 31 and the CVD furnace 32). A pipe is connected to either the oxidation furnace 31 or the CVD furnace 32 so that ozone gas can be supplied. The ozone gas is supplied from an ozone gas cylinder (generator) 35. The piping connected to the oxidation furnace 31 is provided with a valve 36 while the CVD furnace 32 is provided with a valve 37 so that ozone gas can be supplied individually. In addition, piping for supplying an annealing gas is connected to the oxidation furnace 31. An annealing gas is provided from an annealing gas cylinder 38. The piping is provided with a valve 39 for supplying and stopping the annealing gas. When plasma is used in the CVD process, the CVD furnace 32 does not need to be provided with piping for supplying ozone gas.

  The film forming apparatus 30 includes a light source 34 that emits ultraviolet light. The ultraviolet light emitted from the light source 43 is supplied to the oxidation furnace 31 via the beam split 41. The oxidation furnace 31 includes an irradiation window 311 for introducing the ultraviolet light. When ultraviolet light is used for the CVD process, the CVD furnace 32 also includes an irradiation window 321 for introducing ultraviolet light from the light source 43. The ultraviolet light is supplied to the irradiation window 321 through the beam split 42.

  The film forming apparatus 30 returns the sample to the oxidation furnace 31 when the CVD process is completed in the CVD furnace 32. In this oxidation furnace 31, a light irradiation annealing process is executed. Since the degree of cleanliness of the oxidation furnace 31 is higher than that of the CVD furnace 32, as compared with the case where annealing is performed in the CVD furnace 32 by performing ultraviolet irradiation annealing in the oxidation furnace 31 as in the film forming apparatus 30. It is expected that reforming will proceed.

  An example of the operation of the film forming apparatus 30 will be described with reference to FIG. First, ozone gas is supplied to the oxidation furnace 31 with the valves 33, 37, 39 closed and the valve 36 set open, and the sample in the oxidation furnace 31 is oxidized to form an oxide film of several nm. It is formed. Next, the sample is vacuum transferred into the CVD furnace 32 through a transfer path in which the valve 33 is set to open. Here, ozone gas is supplied to the chamber 2 in a state where the valves 33, 36, and 39 are set to be closed and the valve 37 is set to be open to perform CVD film formation of the sample. Next, the sample formed by CVD with the valve 33 set to open is again vacuum transported to the oxidation furnace 31 by vacuum transport. Then, with the valves 33, 37, 39 set to open and the valve 36 set to open, the annealing furnace is irradiated with ultraviolet light in the oxidation furnace 31, and the sample is annealed. Is done.

(Embodiment 4)
Further, the laser light source for activating polysilicon may be shared with the light source for ultraviolet light irradiation annealing. In the process of making a polysilicon TFT, there are a number of techniques for activating the polysilicon at a low temperature by local irradiation with laser irradiation near the ultraviolet light wavelength (P. Baeri et. At., Thin Film and Epitaxy A 314-363). 1994)). When an excimer light source having a wavelength of 254 nm or 308 nm is used, a light annealing process can be performed using this light source.

  In this embodiment, the light irradiation annealing process is performed in a polysilicon activation chamber. Accordingly, a pipe for supplying an atmosphere gas for light irradiation annealing to the polysilicon activation chamber and an irradiation window for introducing ultraviolet light are provided, and annealing is performed while the substrate in the chamber is irradiated with ultraviolet light. Gas is supplied and exhausted.

  Also in a system for activating polysilicon using a YAG laser of 532 nm (for example, JP-A-2002-92358), light irradiation annealing may be performed using this wavelength. This is because there is absorption on the silicon surface even in the wavelength region of 532 nm, and a modification effect by surface heating can be expected.

In each of the above embodiments, a method for modifying a thin film made of polysilicon, which is an example of a thin film, has been described. However, the modification method according to the invention is a metal oxide formed on a silicon substrate or a glass substrate. It is also effective as a method for modifying a thin film comprising The metal oxide thin film has a wide range of applications such as gate insulating films for LSI (capacitors), ferroelectric films, gate insulating films for TFTs (thin film transistors), and transparent conductive films. Al ₂ O ₃ films (aluminum oxides) Film), Zr ₂ O ₅ film (zirconium oxide film), HfO ₂ film (hafnium oxide film), Ta ₂ O ₃ film (tantalum oxide film), TiO ₂ film (titanium oxide film), ZnO film (zinc oxide film) Etc. are exemplified.

BRIEF DESCRIPTION OF THE DRAWINGS The schematic block diagram of the optical annealing processing apparatus which concerns on 1st embodiment of invention. Structural defect absorption curve. Explanatory drawing of the temperature dependence of the film compressibility and etching rate of an oxide film. FTIR (Fourier transform infrared) analysis results. Change in etching rate with respect to annealing gas pressure and annealing time. The JE characteristic figure in the MIS structure before and behind optical annealing. The CV characteristic figure in a MIS structure. The time chart which demonstrated the continuous flow type process which concerns on 2nd embodiment of invention by the time-dependent change of process gas pressure. The time chart which demonstrated the alternate supply type process which concerns on 2nd embodiment of invention by the time-dependent change of process gas pressure. The schematic block diagram of the processing apparatus which concerns on 3rd embodiment of invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Optical annealing apparatus 2 ... Annealing furnace 20 ... Susceptor 21, 22 ... Irradiation window 3, 4, 5 ... Cylinder 6, 7 ... Light source 8 ... Exhaust pump 9 ... Exclusion cylinder 10 ... Substrate 11,12 ... Optical path V1, V2, V3, V4 ... valve 30 ... film forming apparatus 31 ... oxidation furnace, 311 ... irradiation window 32 ... CVD furnace, 321 ... irradiation window 33, 36, 37, 39 ... bulb 34 ... light source 38 ... annealing gas cylinder 41, 42. Beam splitter

Claims (12)

  A method for modifying a thin film, comprising: irradiating a thin film of a substrate that has undergone a CVD process with ultraviolet light and modifying the thin film using surface heating by absorption of ultraviolet light. 2. The method of modifying a thin film according to claim 1, wherein local heating by absorption of ultraviolet light at a defect site of the thin film is used. The thin film modification method according to claim 1, wherein the light source for irradiating the ultraviolet light is a pulse laser or a continuous wave laser. 4. The method for modifying a thin film according to claim 3, wherein irradiation of a light source that emits light in a visible light region other than an ultraviolet wavelength region is provided to the thin film during the modification of the thin film. 4. The method for modifying a thin film according to claim 3, wherein the light source for irradiating the ultraviolet light irradiates light having a wavelength longer than 210 nm. The reforming is performed using surface heating by absorbing ultraviolet light of the thin film in an atmosphere in which an oxidizing gas, a reducing gas, and an inert gas are separately provided. 2. A method for modifying a thin film according to item 1. The thin film modification method according to claim 6, wherein ozone gas is provided as the oxidizing gas. The method for reforming a thin film according to claim 6, wherein diluted hydrogen gas is provided as the reducing gas. The thin film modification method according to claim 1, wherein the thin film is modified in a chamber in which the thin film is manufactured. The method for reforming a thin film according to any one of claims 1 to 9, wherein the method is performed alternately with the CVD step. The method for modifying a thin film according to claim 1, wherein the thin film is a thin film made of polysilicon or a metal oxide.   12. The method of modifying a thin film according to claim 11, wherein a light source used for activating the thin film made of polysilicon is also used as a light source used for modifying the thin film made of the metal oxide.

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