JP4849863B2 - Oxide film formation method - Google Patents

Description

  The present invention creates a high-quality insulating film that is the heart of a thin film transistor (TFT) or silicon device on an organic substrate, such as a silicon device on an organic substrate, where the process temperature is limited by the heat resistance of the substrate temperature. Related to technology.

  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 flexible information terminals (flexible PCs, mobile phones), silicon device fabrication techniques on organic (flexible) substrates such as plastic (polyimide) have become important. In this case, the process temperature is 250 ° C. or lower from the heat resistant temperature of polyimide or the like.

As these insulating films, silicon oxide films (SiO ₂ films) are mainly used. As a film forming method, a method of depositing a silicon oxide film by a thermal CVD (chemical vapor deposition) method or a plasma CVD method on polysilicon (for example, a film thickness of 50 nm) formed on glass (or an organic material) is mainly used. . In the case of the thermal CVD method, SiH ₄ + O ₂ is mainly used. However, an insulating film formed at 300 ° C. or lower has a problem that it contains a large amount of impurities and moisture, has low film density, has many pinholes and particles, has a low withstand voltage, and has a large leakage current.

In order to solve these problems, a plasma CVD method is used. For example, according to Non-Patent Document 1 (J. Vac. Sci. Technol. A21, 728 (2003)), a substrate temperature is measured by a CVD method using SiH ₄ + O ₂ gas in an ECR (Electron Cyclotron Resonance) plasma reactor. A high-quality insulating film having a withstand voltage of 4 MV / cm at 100 ° C., an interface state density of 10 ¹² [eV ⁻¹ cm ⁻² ], and a fixed charge density of 10 ¹¹ [cm ⁻² ] has been successfully produced.

However, when the plasma CVD method is used, the following problems occur. Since it is a plasma reaction in the gas phase, there are many particles, low step coverage, plasma stress is introduced into the film, ideal film density (2.2 g / cm ³ ), composition (Si: O = 1) : The process window (deposition temperature, gas pressure, gas flow rate, counter electrode distance, etc.) for realizing 2) is narrow and there are many particles, so it is necessary to frequently clean the film formation chamber, etc. is there.

In order to alleviate the above problems, an organic silicon material having a Si—O bond and a Si—H bond can be used as a film forming method in which a highly safe reaction gas is used, film forming conditions can be easily set, and generation of particles is suppressed. A thermal CVD process in a mixed gas containing ozone (which is easier to handle than SiH ₄ ) and ozone has been proposed. It utilizes the high reactive decomposability of ozone gas to organic matter.

According to Patent Document 1 (Japanese Patent Laid-Open No. 8-31815), good step coverage at 400 ° C. is achieved by thermal CVD using TMS (Trimethoxysilane), TES (Triethoxysilane), TEOS (Tetraethylorthosilicate) and ozone gas under normal pressure. It has succeeded in depositing the SiO ₂ film. However, since ozone is a pyrolytic gas and the concentration of the ozone gas used greatly affects the film quality, nitrogen as the carrier gas is used, and the ozone gas is diluted to a concentration that is sufficiently low and stable. As a result, effective supply of ozone gas, generation of a uniform CVD reaction near the substrate surface, and deposition of a uniform film are realized.

  On the other hand, according to Patent Document 2 (Japanese Patent Laid-Open No. 5-259155), the higher the concentration of ozone gas used, the lower the concentration of impurities such as hydrocarbons present in the film, the better the hygroscopic resistance, and the insulation characteristics. It is known that the leakage current is improved. In other words, when ozone gas is used, there is a trade-off relationship between the uniformity of the CVD film (film thickness and film quality) and the improvement of the film quality. Although we want to use the high organic substance decomposition power of ozone gas, it can be said that a process in which reactivity is controlled using high concentration ozone gas has not been established yet.

Furthermore, in a low temperature process of 300 ° C. or lower, even when CVD using an ozone-containing gas, mixing of C-based organic substances and water (and hydrogen and OH) into the film due to decomposition by-products in the vapor phase of the organic source gas is performed. For example, as reported in Non-Patent Document 2 (J. Vac. Sci. Technol. B8, 533 (1990)), the deposited film can be removed in a buffered hydrofluoric acid solution. As suggested by the fact that the etching rate is 4 times faster than that of the thermal oxide film, it is porous. When RTA (Rapid Thermal Annealing) is performed after deposition, the film density can be increased (appears as a decrease in the film etching rate). However, in order to obtain a film having a high density close to a thermal oxide film, heating above 400 ° C. is necessary, and it cannot be used during the film forming process on the glass or organic substrate as described above.
J. Vac. Sci. Technol. A 21, 728 (2003) JP-A-8-31815 JP-A-5-259155 J. et al. Vac. Sci. Technol. B8, 533 (1990)

  The present invention has been made in view of such circumstances. Due to the high reactivity of high-concentration (for example, a concentration of about 100%) ozone gas, the present invention is particularly uniform and high only in low-temperature processes (for example, 400 ° C. or less, further 200 ° C. or less). An object of the present invention is to provide an oxide film forming method capable of producing a quality insulating film.

The present invention relates to a source gas containing organic silicon having a Si (silicon) -O (oxygen) bond or Si (silicon) -C (carbon) bond, or an organic metal having a metal element-oxygen bond or a metal element-carbon bond. Then, a high-concentration (for example, concentration of about 100%) ozone gas is used to cause a CVD reaction, and a high-quality SiO ₂ film is formed.

  The method for forming an oxide film according to the present invention includes organic silicon having a Si (silicon) -O (oxygen) bond or Si (silicon) -C (carbon) bond, or an organic metal having a metal element-oxygen bond or a metal element-carbon bond. An oxide film forming method for supplying an oxide film on the surface of the substrate by a CVD method (chemical vapor deposition method), supplying a source gas containing a high-concentration ozone gas to a substrate installed in a reaction furnace, The temperature of the substrate is adjusted to 400 ° C. or lower, and a mixed gas in which the raw material gas and high-concentration ozone gas are mixed in advance is supplied into the reaction furnace.

  The concentration of the high-concentration ozone gas is preferably about 100%, but is not limited to this. For example, ozone gas having a concentration of 80% or more can be used as necessary.

  Furthermore, in the oxide film forming method of the present invention, the mixed gas is continuously supplied and exhausted to allow the mixed gas to permeate into the reaction furnace.

  As the source gas, TEOS gas can be used.

  The substrate temperature is adjusted by irradiation from an outside of a reaction furnace of an infrared lamp or a heating unit having a heating element and holding the substrate.

  The reaction furnace is characterized by a reduced pressure cold wall system.

  The mixing ratio of the source gas and the high-concentration ozone gas can be set as appropriate. In particular, it is preferable to set the high-concentration ozone gas to a ratio of 4 to the source gas 1.

  In another oxide film forming method of the present invention, organic silicon, metal element-oxygen bond, or metal element-carbon bond having Si (silicon) -O (oxygen) bond or Si (silicon) -C (carbon) bond is used. An oxide film that alternately supplies a source gas containing an organic metal having high concentration and a high-concentration ozone gas to a substrate installed in a reaction furnace, and forms an oxide film on the surface of the substrate by a CVD method (chemical vapor deposition method) A method for forcibly evacuating gas in the reaction furnace, and forcibly evacuating one gas after supplying one gas and before supplying the other gas. Features.

  The temperature of the substrate is adjusted to 400 ° C. or lower, and further to 200 ° C. or lower.

  The forced gas exhaust is performed by supplying an inert gas such as nitrogen gas.

  Further, the substrate is irradiated with ultraviolet rays.

  As described above, according to the oxide film forming method of the present invention, due to the high reactivity of high-concentration (for example, concentration of about 100%) ozone gas, the process is particularly performed only at low temperature (for example, 400 ° C. or lower, further 200 ° C. or lower). A uniform and high-quality insulating film can be manufactured.

  Further, according to the first to sixth aspects of the invention, the temperature change by incorporating the local heating can be performed in a short time, the throughput can be increased, all the processes can be completed in one chamber, and the decompression process. It is effective for uniform film formation on a large substrate with a high gas flow rate, and it can simplify the process because it does not contain a diluent gas (carrier gas), extending the life of ozone, and by-products generated in the film. It is possible to promote the removal of the odor.

  According to the seventh to tenth aspects of the invention, in addition to the production of a uniform and high-quality insulating film in a low temperature process (for example, 400 ° C., further 200 ° C. or less), the controllability of the film formation amount can be improved. In addition, a modification effect can be obtained by incorporating ultraviolet irradiation into the CVD process.

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

The present embodiment contains organosilicon having a Si (silicon) -O (oxygen) bond or Si (silicon) -C (carbon) bond, or an organometallic having a metal element-oxygen bond or a metal element-carbon bond. A CVD reaction is caused by using a source gas and a high-concentration (concentration of about 100%) ozone gas, and a high-energy light source with good absorption is used therefor, thereby forming a high-quality SiO ₂ film.

  Here, a method for obtaining a high-concentration (concentration of about 100%) ozone gas used in the present invention will be briefly described.

  As a method of generating ozone gas having a high concentration (concentration of about 100%), it has been introduced in Japanese Patent Publication No. 5-17164 that ozone gas generated can be once liquefied and then vaporized.

  The principle of liquefaction of ozone gas is to liquefy only ozone gas by the difference in vapor pressure between ozone and oxygen. For example, at 1 atmosphere, the boiling point of ozone is 161K, but the boiling point of oxygen is 90K. Therefore, if it is cooled to a temperature of 90K or more and less than 161K, most of ozone is in a liquid state and most of oxygen is in a gaseous state, so that only ozone can be separated as a liquid. Actually, since it is handled under reduced pressure conditions for safety against explosive properties of high-concentration ozone, the separation conditions are determined by the difference between the vapor pressures of ozone and oxygen under the temperature and pressure conditions. For example, considering a case where the temperature is 90 K and the pressure is 10 mmHg (= 13.3 hPa), the vapor pressure of ozone is almost 0 mmHg (= 0 Pa) at 90 K, but oxygen is about 690 mmHg (= 918 hPa), and only ozone is under this condition. Liquefied.

  When liquefied liquid ozone is used for the purpose of oxidation or the like in an oxidation treatment container, the temperature of the ozone chamber is raised to vaporize the liquid ozone and oxidize it as ozone gas through an ozone discharge pipe and a valve. Introduce into container. Since liquid ozone or high-concentration ozone gas has explosive properties, safety measures such as a safety valve for destroying and discharging the gas are taken in the unlikely event.

  Further, methods for continuously supplying high concentration (concentration of about 100%) ozone gas are introduced in JP 2001-133141 A, JP 2001-304756 A, and JP 2003-20209 A. This method has a multi-vessel structure with a plurality of ozone chambers, and each ozone chamber can be individually temperature controlled so that ozone can be liquefied (accumulated), supplied and discarded in sequence, and the concentration (concentration) can be increased by switching valves. (About 100%) Realizing continuous supply of ozone gas.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In each embodiment, organosilicon having a Si (silicon) -O (oxygen) bond or Si (silicon) -C (carbon) bond, or an organometallic having a metal element-oxygen bond or a metal element-carbon bond. TEOS was used as the raw material gas containing the.

[Embodiment 1]
In the present embodiment example 1, high-concentration ozone and TEOS are premixed and continuously supplied into a reaction furnace (CVD furnace). As a feature of this method, no carrier gas is used, reduced pressure (100 to 1000 Pa). ) CVD, cold wall, and the like, and these characteristics make it possible to promote the lifetime extension of ozone and the removal of by-products generated in the film. Note that ozone gas can be handled safely by performing flow rate control by pressure control.

First, a configuration example of the oxide film forming apparatus according to the first embodiment will be described based on the schematic diagram of FIG. As shown in FIG. 1, the oxide film forming apparatus 1 includes, for example, an infrared lamp irradiation from outside the reaction furnace, or a reaction furnace (CVD furnace) in which a heating unit 10b having a heating element and holding a substrate 10a is stored. 10, a pipe 2 having an ozone gas introduction valve V ₂ for introducing ozone gas into the reaction furnace 10, and a raw material gas introduction valve V ₃ for introducing a raw material gas into the reaction furnace 10. A pipe 3 connected outside the furnace 10, a pipe 4 provided with an exhaust valve V ₄ for discharging the gas in the reaction furnace 10, and a nitrogen gas introduction valve V ₅ for introducing nitrogen gas into the reaction furnace 10. And a pipe 5. Then, the ozone gas introduction valve V ₂ , the raw material gas introduction valve V ₃ , the exhaust valve V ₄ , and the nitrogen gas introduction valve V ₅ are appropriately opened and closed so that the ozone gas and the raw material gas are respectively placed in the reaction furnace 10. By supplying a constant amount, a silicon oxide film is formed on the surface of the substrate 10a.

As shown in FIG. 1, in the configuration in which the pipes 2 and 3 are connected to each other on the outer peripheral side of the reaction furnace 10 (in FIG. 1, they are connected by the connecting portion 23), the ozone gas introduction valve V ₂ and the raw material gas introduction valve V ₃ are When both are open, after the ozone gas and the raw material gas are mixed at the connecting portion 23, the mixed gas is introduced into the reaction furnace 10. The mixed gas can be obtained, for example, by introducing ozone gas and raw material gas separately into the reaction furnace 10 (for example, through each supply port) and mixing them in the reaction furnace 10, In this case, the concentration distribution of each gas in the reaction furnace 10 becomes complicated.

  As the reaction furnace 10, it is preferable to use a reduced pressure reaction furnace employing a cold wall type CVD reduced pressure furnace capable of heating only the substrate 10a. In this case, an exhaust pump (not shown) is connected to the pipe 4. Moreover, the installation form of the board | substrate 10a in the reaction furnace 10 may employ | adopt any known vertical type or horizontal type. The material of the reaction furnace 10 may be a material that is not reactive with ozone. For example, quartz, stainless steel, aluminum, titanium, etc. are mentioned.

  The introduction of ozone gas into the reaction furnace 10 can be performed while adjusting the flow rate by pressure control, for example, and according to this method, the ozone gas (for example, high-concentration liquid ozone is vaporized). The obtained ozone gas) can be handled more safely.

  The source gas may be an organic substance having a Si—C bond or a Si—O bond. For example, TEOS (Tetraethylorthosilicate), HMDS (Hexamethyldisilazane), etc. are mentioned. In addition, the introduction of the raw material gas into the reaction furnace 10 can be performed, for example, by adjusting the flow rate with a heating-integrated flow meter, and according to this method, the preceding stage of the heating-integrated flow meter (that is, The source gas exists as a liquid on the upstream side of the introduction path of the source gas, and exists as a gas on the subsequent stage (that is, downstream of the introduction path of the source gas). In addition, in the flow path of the source gas in the oxide film forming apparatus 1, in order to measure re-liquefaction prevention of the source gas, for example, it is desirable to heat the flow path and keep it at a predetermined temperature (for example, 70 ° C. or higher).

The required partial pressure of ozone introduced in the reaction furnace 10 varies depending on the raw material gas used. In general, the source gas is completely oxidized to CO ₂ and H ₂ O, and more than the amount necessary for transforming silicon into a completely oxidized state (SiO ₂ ) by surplus oxygen atoms is filled. For example, when TEOS gas is used as the source gas, as is apparent from the following chemical formula, a film in which silicon is completely oxidized can be formed at a pressure (number of moles) eight times that of TEOS, and at the same time, an organic substance can be converted into CO ₂ and H ₂ O can be discharged from the substrate surface deposited film.

Si (OC ₂ H ₅ ) ₄ + 8O ₃ → SiO ₂ + 8CO ₂ + 10H ₂ O
For heating the substrate 10a by the heating unit 10b, a method using a known heating means that has been conventionally used can be adopted. For example, a means (or a heating element) for irradiating infrared lamp light from the outside of the reactor is provided. In addition, a method of holding the substrate, a method of irradiating a halogen lamp light to an infrared absorption stage for holding the substrate (for example, made of sintered SiC), or a substrate 10a on a heater stage using a heating element. A holding method can be adopted.

  For exhausting the gas in the reaction furnace 10, a system used in a conventional low pressure CVD furnace may be used as it is. In this case, for example, the pipe 4 requires a detoxifying device such as a particle trap and a dry pump having an ultimate vacuum of about 1 Pa or less, for example, a mechanical booster pump (for example, exhaust speed 1000 l / min).

  Next, an example of an oxide film forming procedure using the oxide film forming apparatus 1 as described above will be described.

First, a silicon substrate (or polysilicon or the like) 10a that has been subjected to hydrogen termination in advance is placed in the heater unit 10b, and then the reaction furnace 10 is evacuated through the pipe 4 so that the inside of the reaction furnace 10 is exhausted. The pressure is reduced (for example, the pressure is reduced to 1 Pa or less). In this decompression step, N ₂ purge is repeatedly performed through the pipes 4 and 5 as necessary.

  Thereafter, the temperature is raised to a desired process temperature (substrate temperature) in the heating unit 10b (for example, 100 ° C. to 400 ° C.). Since the water adhering to the inside of the reaction furnace 10 or the silicon substrate 10a may evaporate along with this temperature raising process, the temperature raising process is performed while exhausting the inside of the reaction furnace 10 through the pipe 4.

  Then, predetermined amounts of ozone gas and source gas are continuously supplied into the reactor 10 via the pipes 2 and 3 (for example, a mixed gas of ozone gas and source gas is continuously supplied), and the surface of the substrate 10a is supplied. Oxide film formation by CVD is started. As described above, when supplying each gas, for example, it is desirable to watch (for example, monitor the pipe 3) so that the amount of the raw material gas in the reaction furnace 10 does not become excessive.

After performing the oxide film forming step for a predetermined time, the supply of the ozone gas and the source gas is stopped (at the same time or the source gas is stopped first), and the heating by the heating unit 10b is stopped. ₂ Repeat the purge. Then, the silicon substrate 10a is taken out from the reaction furnace 10.

In the oxide film forming procedure described above, it is desired that the source gas is not adsorbed (adsorbed by liquefaction or the like) in the reaction furnace 10. For example, if the source gas is excessively present in the reaction furnace 10, the source gas is liable to be liquefied, so that N ₂ purge needs to be repeated. In particular, when the raw material gas is used without being diluted (for example, in the case of an example described later), the raw material gas is easily adsorbed excessively on the surface of the silicon substrate 10a, and the oxide film forming step is started in that state. There is a possibility that the quality of the oxide film will be greatly deteriorated, or each part (for example, pumps) of the oxide film forming apparatus 1 may be overloaded and cause a failure (conventionally, the material gas is reduced to about 1/100, for example. Use diluted).

  Next, a sample S of an oxide film is formed based on the first embodiment described above. In the sample S, film formation rate and etching rate characteristics with respect to the process temperature (FIG. 2), FTIR infrared spectroscopy for each process temperature. Spectral characteristics (FIG. 3), relative dielectric constant and fixed charge density characteristics with respect to process temperature (FIG. 4), and leakage current characteristics with respect to applied voltage at the process temperature of 300 ° C. (FIG. 5) were examined.

  The silicon substrate 10a is a 1.2 mm square chip-shaped Si (110) substrate that is hydrogen-terminated with a 0.5 wt% hydrofluoric acid solution (in the hydrofluoric acid solution until immediately before film formation). Soaked) was used.

  Further, in the heating unit 10b, a sintered SiC susceptor is used, and a heating infrared lamp is irradiated from outside the reaction furnace 10 toward the susceptor to raise the temperature (temperature scan range 150 ° C. to 400 ° C. at atmospheric pressure). Temperature calibration). Here, in order to deliver the heating infrared lamp light into the reaction furnace 10, a part of the reaction furnace 10 (above the susceptor in the reaction furnace 10) was made of transmissive glass. That is, by irradiating the heating infrared lamp light from above the susceptor, the heating light passes through the silicon substrate 10a and is absorbed by the susceptor under the silicon substrate 10a.

Further, in the oxide film forming process, 24 ccm of high-concentration ozone gas is supplied via the pipe 2 (the amount determined by the pressure difference after being calibrated with the calibration gas (oxygen) is supplied), and 3 sccm of TEOS gas is supplied via the pipe 3. Alternatively, by supplying 6 sccm (supplying a digitally controlled amount through a heating integrated flow meter), a mixed gas of these high-concentration ozone gas and TEOS gas (that is, mixing at a mixing ratio of O ₃ / TEOS = 8 or 4) Gas) was continuously fed into the reactor 10.

  Furthermore, in the oxide film forming step, the pressure in the reaction furnace 10 was fixed at 800 Pa, the process time was 3 minutes or 6 minutes, and the process temperature was 100 ° C. to 400 ° C.

  First, from the results shown in FIG. 2, the film formation rate of the sample S (the horizontal axis on the left side in FIG. 2) increases the process temperature in the low temperature region (about 270 ° C. or less) of the process temperature of 100 ° C. to 400 ° C. Although it rises monotonously, it can be read that after reaching the maximum value in the intermediate temperature range (about 300 ° C.), it decreases as the process temperature rises in the high temperature range (above about 330 ° C.).

  In the case of an oxide film obtained by a general CVD method (CVD method caused by reaction promotion by thermal energy), the film formation rate changes monotonously (exponentially increases) with respect to the process temperature. As shown, the reason why the change in the deposition rate of the sample S becomes non-monotonous is thought to be because the reaction between the high-concentration ozone gas and the TEOS gas differs with respect to the silicon substrate surface. That is, in the case of the high temperature region, the reaction between the high-concentration ozone gas and the TEOS gas becomes active before the respective gases reach the silicon substrate (regions separated by a predetermined distance) (react before reaching the silicon substrate). On the other hand, in the low temperature region, the reaction rate is relatively slow, so even if each gas reaches the silicon substrate surface, the proportion of the reacted component is small until it can contribute to film formation. it is conceivable that.

  Further, it can be seen that the process temperature at which the film formation speed is maximized depends on the ratio of the high-concentration ozone gas in the mixed gas, which is considered to be due to the difference in the collision ratio between the high-concentration ozone gas and the TEOS gas. . That is, when using low-concentration ozone gas (for example, 2% ozone gas) as in the prior art, for example, obtained from high-concentration oxygen gas (about 100% oxygen gas) (for example, several percent in oxygen by an ozone generator) 2), and the oxygen gas is inert and acts as a carrier gas in the intermediate temperature region as shown in FIG. 2, so that the low-concentration ozone gas and the source gas react relatively. It is considered difficult. On the other hand, when high-concentration ozone gas is used, the carrier gas is not used, and the high-concentration ozone gas and the raw material gas are relatively easy to react with each other. It is considered to exist in the area.

  On the other hand, it can be seen that the etching rate of sample S (right horizontal axis in FIG. 2) is smaller in the temperature region where the film formation rate is smaller (the intermediate temperature region in FIG. 2). That is, in the case of an oxide film obtained by a general CVD method, as the deposition rate value increases, the density of the oxide film is deteriorated and the etching rate increases. From the results, it can be considered that the film quality of the sample S becomes denser as the film formation rate increases. However, when the etching rate in a general thermal oxide film was also examined in the same manner, it was about 5 nm / mm, and the etching rate shown in FIG. 2 exceeded 20 nm / min. Can be read that it is not dense (there is a difference of about 4 times).

Next, from the results shown in FIG. 3, the peak of the corresponding frequency (1250 cm ⁻¹ ) is hardly detected at each process temperature in CH ₃ , and the peak of the corresponding frequency (950 cm ⁻¹ ) is slightly detected in OH. Although detected, it can be seen that the magnitude of the peak decreases with increasing process temperature. On the other hand, in Si—O—Si, since the peak of the corresponding frequency (1070 cm ⁻¹ ) is clearly detected at each process temperature, a Si—O network is formed at each process temperature. Can be read. Such a phenomenon becomes more prominent as the peak shoulder (1100 cm ⁻¹ ) becomes lower in temperature. Note that this peak is the amount of Si—O determined by the degree of cage. Therefore, it can be seen that the sample S can generate Si—O even at a low temperature, but the impurities decrease as the temperature increases.

Next, from the results shown in FIG. 4, the relative dielectric constant of SiO _{2 in} the sample S is generally an ideal oxide film (relative dielectric constant 3.9) and an oxide film containing a large amount of hydroxyl groups (relative dielectric constant). 98) is known to take values between. This dielectric constant is mainly determined by the amount of water contained in the oxide film.

  For example, when the process temperature is in the high temperature region, the dielectric constant approaching 3.9 corresponds to the OH peak becoming smaller as the temperature becomes higher as shown in FIG. That is, it can be seen that the hydroxyl group, which is an impurity that causes dielectric breakdown, easily separates from the oxide film as the temperature rises.

On the other hand, in the fixed electrification density (Qfix; the density of electric charge existing in the sample S obtained from the flat band shift voltage in CV measurement), the lower the fixed electrification density, the better the result. For example, in the case of a thermal oxide film, it is about 10 ¹⁰ level, but it can be read that the fixed electrification density of the sample S is one to two orders of magnitude higher than that of the thermal oxide film. Among the results shown in FIG. 4, the process temperature (270 ° C.) when the fixed charge density is the lowest matches the process temperature when the film formation rate is the highest in FIG. However, in FIG. 2, a film formation rate substantially equal to the process temperature of 270 ° C. is obtained even at the process temperature of 330 ° C., whereas in FIG. 4, the fixed charge density decreases at the process temperature of 330 ° C. I can read. This is presumably because the deposition temperature affects not only the reaction rate on the surface of the silicon substrate but also the reaction rate in the gas phase.

  Next, it can be seen from the results shown in FIG. 5 that the breakdown of the sample S occurs near an applied voltage of 8 MV / cm, which is equivalent to the breakdown in the case of an oxide film obtained by general plasma CVD. This result shows that the sample S has almost the same insulation characteristics as the oxide film obtained by plasma CVD, and the leakage current at a constant applied voltage (about 3 MV / cm or less) is lower than that of the oxide film obtained by plasma CVD. It shows that the sample S has better insulation characteristics.

Here, paying attention to the results shown in FIG. 2 to FIG. 3, in FIG. 2, the film formation rate when O ₃ / TEOS = 4 is larger than the film formation rate when O ₃ / TEOS = 8. Even in the etching rate, better characteristics than in the case of O ₃ / TEOS = 8 are obtained. That is, focusing attention only on the result of FIG. 2, the film forming speed in the case of O ₃ / TEOS = 4 is superior to that in the case of O ₃ / TEOS = 8.

However, when paying attention to the results shown in FIG. 4, both the dielectric constant and the fixed charge density are superior when O ₃ / TEOS = 4 than when O ₃ / TEOS = 8. This is presumably because the TEOS component is taken into the oxide film in an unreacted state due to a decrease in the relative amount of the ozone component in the mixed gas. Note that it is known that even if the CVD method using TEOS gas and ozone gas is used in the conventional method, the oxide film is further modified when ozone is supplied excessively.

[Embodiment 2]
Next, an oxide film forming apparatus according to Embodiment 2 will be described. In the first embodiment, the mixed gas obtained by mixing the raw material gas and the high-concentration ozone gas in advance is supplied into the reactor. In the second embodiment, the raw material gas and the high-concentration ozone gas are supplied. Each is introduced separately into the reaction furnace (for example, switching through a valve or the like, introduction through each supply port) to form a target oxide film. In the oxide film forming apparatus, for example, substantially the same one as in the first embodiment can be applied.

Next, an example of an oxide film forming procedure using the oxide film forming apparatus 1 of the second embodiment will be described. First, as in the first embodiment, a silicon substrate 10a that has been previously hydrogen-terminated is placed in the heating unit 10b, and after undergoing a depressurization step and a temperature raising step (repeated N ₂ purge as necessary). From the above, a raw material gas is supplied into the reaction furnace 10 through the pipe 3, and a predetermined amount of the raw material gas is attached to the surface of the substrate 10a.

After the deposition step, the supply of the source gas is stopped, and the source gas remaining in the reaction furnace 1 is exhausted (only the source gas that has not adhered to the silicon substrate 1 is exhausted). It should be noted that the adjustment of the amount of source gas attached to the silicon substrate 1 may be performed by repeating N ₂ purge as necessary.

  Then, a predetermined amount of ozone gas is supplied to the inside of the reaction furnace 10 through the pipe 2 and reacted with the raw material gas adhering to the surface of the substrate 10a, thereby starting the formation of an oxide film by CVD. Note that the supply amount of ozone gas is desirably large so as to sufficiently react with the attached raw material gas. In addition, when the reaction rate is slow, in order to expose the ozone gas to the surface of the attached raw material gas for a certain period of time, for example, the reaction furnace 10 is sealed (for example, all the introduction valves are closed and sealed). , Hold for a predetermined time.

After performing the oxide film forming step for a predetermined time, similarly to the first embodiment, the supply of ozone gas is stopped and the heating by the heating unit 10b is stopped, and then N ₂ purge is repeated as necessary. Do.

  The above-described oxide film formation procedure is performed a plurality of times, for example, according to the target thickness of the oxide film, and then the silicon substrate 10a is taken out from the reaction furnace 10.

In the present embodiment example 2 described above, an insulating oxide film is formed according to the amount of source gas adhering to the silicon substrate surface, and although the film formation rate is inferior to that of the embodiment example 1, the gas phase reaction is performed. Therefore, the complete surface reaction CVD without any defects can be performed, so that the quality of the oxide film can be remarkably improved. Further, not only the CVD method but also the ALD method can be applied in forming the oxide film [Example 3 of this embodiment].
Next, an oxide film forming apparatus according to Embodiment 3 will be described. In the present embodiment example, a target oxide film is formed by applying a specific ultraviolet lamp in the oxide film forming process using the oxide film forming apparatus substantially the same as in the second embodiment.

Next, an example of an oxide film forming procedure using the oxide film forming apparatus 1 of the third embodiment will be described. First, similarly to the second embodiment, the silicon substrate 10a that has been previously hydrogen-terminated is placed in the heating unit 10b, and is subjected to a depressurization step, a temperature raising step, and an adhesion step (repeating N ₂ purge as necessary). Do).

  Thereafter, a predetermined amount of ozone gas is supplied into the reaction furnace 10 through the pipe 2 and reacted with the raw material gas adhering to the surface of the substrate 10a, thereby starting oxide film formation by CVD. At this time, the reaction region is irradiated with specific ultraviolet lamp light. Thereby, ozone in the ozone gas is decomposed, and active oxygen having a stronger oxidizing power than the ozone reaches the substrate surface. This active oxygen is capable of easily decomposing TEOS bonds, and it can be expected to remove impurities in the oxide film and increase the deposition rate.

After the oxide film forming step is performed for a predetermined time, the supply of ozone gas is stopped and the heating by the heating unit 10b is stopped as in the second embodiment while continuing the irradiation with the ultraviolet lamp light. After that, the N ₂ purge is repeated as necessary. As described above, by continuously irradiating the ultraviolet lamp light after the oxide film forming step (that is, by irradiating the ultraviolet lamp light after being formed in one cycle of the oxide film forming procedure described above), the surface of the oxide film Modification of the quality of the oxide film can be expected by local heating.

  And after performing the oxide film formation procedure shown above several times, for example according to the thickness of the target oxide film, the silicon substrate 10a is taken out from the reaction furnace 10.

  In the present embodiment example 3 described above, the oxide film insulation is configured according to the amount of the source gas adhering to the silicon substrate surface, and although the film formation rate is inferior to that of the embodiment example 1, the gas phase reaction is performed. In addition to being able to carry out complete surface reaction CVD without any impurities, it is possible to remove impurities in the oxide film by irradiating with ultraviolet lamp light, increasing the film formation speed and improving the film quality of the oxide film as compared with the second embodiment. Can be planned.

Schematic which shows the structural example of the oxide film forming apparatus of Embodiment 1 of this invention. FIG. 6 is a characteristic diagram of film formation rate and etching rate with respect to process temperature according to Embodiment 1; The FTIR infrared spectroscopy spectrum characteristic figure according to process temperature concerning Example 1 of an embodiment. FIG. 5 is a graph showing a relative dielectric constant and a fixed charge density characteristic with respect to a process temperature according to Embodiment 1. 6 shows leakage current characteristics with respect to applied voltage when the process temperature is 300 ° C. according to the first embodiment.

Explanation of symbols

1 ... oxide film forming apparatus 2, 3, 4, 5 ... pipe _{V 2, V 3, V 4} , V 5 ... Valve 10 ... reactor 10a ... substrate 10b ... heating units 23 ... connecting portion

Claims (10)

80 vol obtained by vaporizing raw material gas containing organosilicon having Si-O bond or Si-C bond, or organic metal having metal element-oxygen bond or metal element-carbon bond, and liquid ozone whose vapor pressure is controlled % or more and high-concentration ozone gas is supplied without using a carrier gas against the installation the substrate depressurized reactor, a oxide film forming method for forming an oxide film on the surface of the substrate by a CVD method ,
The temperature of the substrate is adjusted to 400 ° C. or lower, and a mixed gas in which the raw material gas and high-concentration ozone gas are mixed in advance is supplied into the reaction furnace,
A method for forming an oxide film, comprising: reacting a raw material gas in the mixed gas with a high-concentration ozone gas to form an oxide film.   The method of forming an oxide film according to claim 1, wherein the mixed gas is continuously supplied and exhausted to allow the mixed gas to permeate into the reaction furnace.   The method for forming an oxide film according to claim 1, wherein the source gas is TEOS.   The said substrate temperature is adjusted with the heating unit which has the heating from the irradiation from the outside of the reaction furnace of an infrared lamp, or a heat generating body, and holding the said board | substrate. Oxide film forming method.   5. The oxide film forming method according to claim 1, wherein the reaction furnace is a reduced pressure cold wall system.   6. The mixing ratio of the source gas and the high-concentration ozone gas is set to a ratio of 4 for the high-concentration ozone gas with respect to the source gas 1. 6. Oxide film formation method. 80 vol obtained by vaporizing raw material gas containing organosilicon having Si-O bond or Si-C bond, or organic metal having metal element-oxygen bond or metal element-carbon bond, and liquid ozone whose vapor pressure is controlled % or more and high-concentration ozone gas, an oxide film forming method alternately supplying without using a carrier gas against the installation the substrate depressurized reactor, to form an oxide film on the surface of the substrate by a CVD method There,
The reactor is provided with a means for forcibly exhausting gas, and after supplying one gas, before supplying the other gas, forcibly exhausting one gas,
A method of forming an oxide film, comprising: reacting a source gas attached to the substrate with a high-concentration ozone gas to form an oxide film.   The method for forming an oxide film according to claim 7, wherein the temperature of the substrate is adjusted to 400 ° C. or lower.   9. The method for forming an oxide film according to claim 7, wherein the forcible gas is exhausted by supplying an inert gas.   The method for forming an oxide film according to claim 7, wherein the substrate is irradiated with ultraviolet rays.

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