JPH0883768A - Method and device for forming thin film - Google Patents

Abstract

PURPOSE: To safely and easily clean a semiconductor substrate on which an oxide film is formed at a low temperature by heating the substrate in a high- vacuum, hydrogen gas, argon gas, or nitrogen gas atmosphere in which the coming off of oxides from the surface of the semiconductor is substantially faster than the oxidation of the surface. CONSTITUTION: An oxide film having 1nm thick is formed on the surface of a semiconductor (Si) substrate 2 for forming thin film by treating the substrate 2 with sulfuric acid and hydrogen peroxide solution. The substrate 2 is introduced to a thin film forming device and set in a pretreatment chamber 3 and Si ions are implanted into the oxide film with energy of 20-1,000eV by operating an ion implanting device 6. Then the substrate 2 carrying the oxide film implanted with Si ions is introduced to a thin film growing chamber 4 and heated in a vacuum. As a result of the heating, the oxide film is evaporated and the clean surface of the Si substrate is exposed. After the surface of the Si substrate 2 is cleaned and a disilane gas is introduced to the chamber 4, and then, an Si thin film is grown on the cleaned surface of the substrate 2, the substrate 2 is taken out from the chamber 4 through an unloading chamber 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a semiconductor device.

[0002]

2. Description of the Related Art In a semiconductor device manufacturing process, a thin film growth technique has been attracting attention as a pn junction forming means instead of an ion implantation method. That is, in the case of the ion implantation method, the fluctuation of the distribution of the impurities in the depth direction due to the ion implantation essentially occurs, whereas in the thin film growth method, the semiconductor layers containing different impurities are laminated to make it extremely steep. It may be possible to form an excellent bonding interface. However, in a semiconductor device manufacturing process to which a thin film forming (growth) technique is applied, residual impurities on the surface of a semiconductor (crystal) substrate have an extremely large effect on the quality of the manufactured semiconductor device. For example, in the case of a Si crystal surface, residual impurities such as a natural oxide film, organic contaminants, and heavy metals on the surface make it difficult to control the thin gate oxide film with high accuracy and deteriorate the electrical characteristics such as withstand voltage. Invite. Alternatively, in the production of a metal ohmic contact, it acts as a process impeding factor or a device performance deteriorating factor such as an increase in series resistance or deterioration of rectification characteristics. Therefore, it can be said that the formation of a clean semiconductor crystal surface free from the above-mentioned residual impurities is indispensable in the semiconductor manufacturing apparatus manufacturing process.

However, in the conventional method for cleaning the surface of a semiconductor (crystal) substrate, it is difficult to say that the residual impurities on the crystal surface are not necessarily sufficiently reduced, and it is considered that this is due to contamination of the semiconductor crystal surface. Degradation of semiconductor device performance is often observed as process dependence. As a solution to this problem, a method of covering the Si surface with an oxide film by RCA cleaning (W. Kern RCA Review Vol.31 (1970)) may be applied.

Generally, when an oxide film is formed on a Si substrate, residual impurities on the Si substrate before the oxide film is formed, that is, carbon,
Oxygen and the like are taken into the oxide film. Therefore, if the adhesion of residual impurities to the surface of the Si substrate can be suppressed in the next step of removing the oxide film after forming the oxide film, a clean Si surface can be obtained. In the case of the above-mentioned RCA cleaning, after forming an oxide film of 1 nm or more on the Si substrate, it is introduced into a vacuum device that can heat the Si substrate, and it is possible to contaminate the Si substrate, for example, about 10 ^-8 Pa. 900 ~ in low vacuum
By heating at a temperature of 1000 ° C, the oxide film can be desorbed and a clean surface can be obtained.

Further, as another means for the low temperature process, for example, an aqueous solution of chemicals such as hydrogen peroxide, sulfuric acid-hydrogen peroxide, nitric acid, ammonia hydroxide-hydrogen peroxide, hydrochloric acid-hydrogen peroxide, or oxygen gas. , Hydrochloric acid-oxygen gas,
Means for forming (generating) an oxide film by treating in a gas atmosphere such as hydrogen-oxygen gas, and then performing heat treatment at 900 ° C. in a vacuum to volatilize the generated oxide film to expose a clean surface. Is also known.

[0006]

In the RCA cleaning means, the oxide film forming process is relatively simple, and the interface is protected by the oxide film even when left in the atmosphere.
Easy to handle. However, not only is an evacuation device capable of heating the Si substrate under high vacuum indispensable, but, for example, when processing large-diameter wafers of 6 inches or more, an increase in device size and an increase in device price become issues. . Furthermore, the biggest problem is that the miniaturization of devices created on a semiconductor substrate is remarkable, and in recent ICs and the like, complicated semiconductor manufacturing processes for forming different semiconductor devices on the same substrate are beginning to be required. It is in. That is,
A process of forming a semiconductor device at a lower temperature has become indispensable without applying the conventional high vacuum heating process in all steps. For example, in the case where a thin film having different electrical conductivity is grown (formed) on the patterning surface by performing patterning processing or the like on the surface of the semiconductor substrate on which the doping layer is formed by the ion implantation method or the like, the doping of the semiconductor substrate is performed. In order not to destroy the profile, it is important to perform the surface cleaning treatment at a low temperature prior to thin film growth (formation). More specifically, for example, combine bipolar transistors and MOS transistors
In a Bi-CMOS LSI or the like, the bipolar part is created after the CMOS part is created. If the substrate surface is cleaned at high temperature before the base layer of the bipolar part is formed by the thin film growth technique, the CM
There is concern that the impurity distribution in the OS part will change significantly and the device characteristics will deteriorate. That is, for example, a semiconductor manufacturing process is performed at a substrate temperature of 800 ° C. or lower, that is, a process capable of obtaining a clean Si substrate surface at a lower temperature is beginning to be required in substrate cleaning. More specifically, the impurities in the thin film growth raw material and the thin film growth atmosphere are reduced as much as possible, while the temperature during film formation is reduced by using a clean surface Si substrate and setting the substrate temperature to about 750 ° C or lower. Impurity diffusion due to is reduced to a negligible level, and a steep interface can be formed.

However, at present, in particular, a complete solution for cleaning the surface of a Si substrate, which can be expected to have an effect of a low temperature process, has not been shown, and Si at a lower temperature cannot be obtained.
Realization of a surface cleaning process has been desired. And after removing the natural oxide film in hydrogen fluoride (HF) solution,
It has recently been shown that hydrogen-terminated surfaces are relatively stable in air. However, the residual impurities on the surface cannot be a decisive surface holding method because residual impurities such as carbon and oxygen increase with the surface density on the order of%, as time passes after the treatment. Further, there is also an attempt to omit the cleaning step with pure water after the natural oxide film is removed by the hydrogen fluoride aqueous solution, in order to prevent the oxide film from being generated again during the cleaning value of pure water.
However, this method takes out the substrate and jig immediately after they are immersed in the hydrofluoric acid aqueous solution, which is extremely corrosive (with a small amount of hydrogen fluoride aqueous solution droplets attached), and proceeds to the next step.
There is an industrial problem.

As described above, semiconductors (crystals), for example,
In the thin film formation process on the si substrate, the surface control technology that can be realized at low temperature is indispensable to ensure the cleanliness of the semiconductor (crystal) substrate surface at a lower temperature and control the interface with the thin film to be formed. However, the conventionally known method is safe and simple, and it is difficult to form an oxide film, crystal, amorphous, poly, etc. on the semiconductor surface while ensuring cleanliness. There was a problem that was.

The present invention has been made in view of the above circumstances, and realizes cleaning of a semiconductor surface at a lower temperature, safely and simply, and a high quality thin film is formed on the surface of a semiconductor substrate. An object of the present invention is to provide a thin film forming method and a thin film forming apparatus capable of realizing a high-performance semiconductor device.

[0010]

A first thin film forming method according to the present invention comprises a step of forming an oxide film having a film thickness of 1 nm or less on a surface of a semiconductor substrate, and a high vacuum of the semiconductor substrate having the oxide film formed thereon. , A step of heating in an atmosphere in which the desorption of oxides from the surface is substantially faster than the oxidation of the semiconductor surface, such as hydrogen gas, argon gas, or nitrogen gas, and the surface oxide film is desorbed by the heating. And a step of forming a thin film on the cleaned semiconductor surface.

In this thin film forming method, prior to the step of forming an oxide film having a thickness of 1 nm or less on the surface of the semiconductor substrate, the surface of the semiconductor substrate is washed with a liquid having a faster etching rate than an oxidizing rate. It is desirable that the heating step be performed, and that heating in an atmosphere in which oxide desorption is faster is performed at 800 ° C. or lower.

A second method of forming a thin film according to the present invention comprises a step of forming an oxide film on a surface of a semiconductor substrate and a step of implanting silicon ions into the oxide film of the formed semiconductor substrate with energy of 20 to 1000 eV. And the semiconductor substrate that has been subjected to the ion implantation process under high vacuum, hydrogen gas, argon gas,
A step of performing a heat treatment in an atmosphere of nitrogen gas or a mixed gas of two or more of these gases to volatilize and remove the oxide film to obtain a clean semiconductor surface; and a step of forming a thin film on the cleaned semiconductor surface. It is characterized by comprising and.

A third method of forming a thin film according to the present invention comprises the steps of immersing a semiconductor substrate in a hydrogen fluoride solution to remove an oxide film on the substrate surface, and terminating the semiconductor substrate surface from which the oxide film has been removed with hydrogen. And the semiconductor substrate whose surface is terminated with hydrogen has a residual oxygen partial pressure and residual water vapor partial pressure of 1 ×.
The process of accommodating and mounting in a vacuum of 10 ^-8 Pa or less, and controlling the oxygen partial pressure of the vacuum system to 1 × 10 ^-6 Pa to 1 × 10 ^-3 Pa, while the semiconductor substrate temperature is 500 to 800 ° C. And removing impurities on the surface by controlling the temperature to 2) and introducing a source gas to grow a thin film on the surface of the semiconductor substrate.

In this thin film forming method, when the semiconductor substrate has a pn junction at at least one place, it is desirable to set the substrate temperature during film formation to 750 ° C. or lower.

A thin film forming apparatus according to the present invention comprises a vacuum container for growth, and an exhaust mechanism for exhausting the inside of the vacuum container to a vacuum system having a residual oxygen partial pressure and a residual water vapor partial pressure of 1 × 10 ⁻⁸ Pa or less. A substrate supporting mechanism that is installed in the vacuum container and supports a semiconductor substrate for growth; a substrate heater that can control the temperature of the semiconductor substrate supported by the substrate supporting mechanism to 500 to 800 ° C .; and the vacuum container A raw material gas introduction part for introducing a raw material gas containing a group IV element inside, and the oxygen partial pressure of the vacuum system
It is characterized by comprising an oxygen partial pressure control unit for controlling the pressure from × 10 ^-6 Pa to 1 × 10 ^-3 Pa.

The present invention was made based on the following experiments and trials. That is, a silicon (Si) substrate on which a native oxide remains is immersed in an aqueous solution of hydrogen fluoride, and the relationship between the immersion time (seconds) and the remaining film thickness of the native oxide (nm) is examined. As shown in FIG. 1, it was possible to control the oxide film thickness on the order of sub-nm. Next, an oxide film with a film thickness of 1 nm or less, for example 0.5 nm, is formed on the treated surface on the Si substrate surface, and then introduced into a high vacuum (for example, 2 × 10 ^-7 Pa) and 800 ° C or less (for example, 790 ° C Fig. 2 shows the amount of impurities remaining on the substrate surface after heating with) by Auger-Electron-Spectroscopy (AES). Detachment of the oxide film on the surface was confirmed. Here, the substrate surface from which the oxide film has been removed by heating at a low temperature of 800 ° C. or lower is subjected to hydrogen termination treatment on the Si substrate surface by, for example, cleaning with a hydrofluoric acid solution and pure water, and then,
It is shown that the amount of carbon and oxygen as residual impurities on the surface of the substrate are reduced to several times each, as compared with the cleaning surface after being introduced into a vacuum through the atmosphere. That is, it has been found that the oxide film is easily detached even by heat treatment at a lower temperature depending on the thickness of the oxide film.

The oxide film formed (formed) on the surface of the Si substrate is, for example, SiO ₂ to SiO ₂ by the implantation of Si ions.
It was found that the composition of the oxide film changes, and volatilizes easily at lower temperatures to expose a clean Si substrate surface.

Further, before the required thin film such as a Si layer is grown on the surface of the semiconductor substrate whose surface is terminated with hydrogen, the oxygen partial pressure of the atmosphere in the container easily ensures the cleanliness of the substrate growth surface. -It was confirmed that a good quality semiconductor layer (film) can be formed after being maintained. The present invention has been achieved by focusing on these points.

[0019]

According to the first thin film forming method, the oxide film is desorbed (or desorbed) at a substrate heating temperature lower than the conventional one by forming the oxide film thinner than the conventional one on the semiconductor substrate. It is possible to obtain a clean surface at a lower temperature by suppressing the amount of surface residual impurities as compared with the conventional method. Therefore, it becomes possible to prevent the oxidation of the surface of the semiconductor substrate and the re-adsorption of organic substances, and it is easy to improve the electrical characteristics of the element that forms the interface between this surface and the thin film formed on the surface, and it is possible to further improve the electrical characteristics. It is possible to obtain a high-performance semiconductor device.

According to the second thin film forming method, by injecting silicon (Si) ions into the oxide film, the composition of the oxide film changes from SiO ₂ to SiO which is more easily volatilized or evaporated, so that at a lower temperature. Not only is it possible to expose a clean substrate surface, but it is also possible to avoid or significantly reduce the adverse effects on the doping files and the like previously formed on the substrate. Therefore, when it is used as a manufacturing method of a semiconductor device having a steep junction interface, the fluctuation of the impurity distribution in each impurity-implanted region where the pn junction is already formed is suppressed, so that the characteristics are not deteriorated. A desired semiconductor device can be formed.

According to the third thin film forming method, oxygen is cleaned at a substrate temperature of, for example, about 700 ° C. by utilizing its high vapor pressure at the initial bonding of the element constituting the substrate, for example, silicon. The exposed surface can be exposed and oxygen can be supplied to the cleaned surface to desorb the surface atoms.
That is, prior to forming the required film, the substrate is heated in an atmosphere in which the oxygen partial pressure is selected within a predetermined range, so that the rate of oxidation is slower than the rate of SiO release and the substrate surface is covered with carbon impurities. Etch with to clean the surface,
After that, a thin film forming a sharp interface junction is grown.

Further, according to the thin film forming apparatus, the third
The method of forming a thin film can be easily and reliably performed with good reproducibility.

[0023]

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

Example 1 First, a doping pattern was provided and a film thickness of 5 nm was formed on the surface.
Prepare a Si substrate on which some natural oxide remains, and attach it to the vacuum container of the vapor phase film deposition device prepared in advance,
For example, after evacuating to a high vacuum of 2 × 10 ^-7 Pa, 790 ℃
The Si substrate was heat treated at. In this heat treatment, Si
The release of the oxide film was substantially faster than the formation of the oxide film by the oxidation of the substrate surface, and the clean substrate surface was exposed.
Then, oxygen gas and silane gas were introduced into the vacuum container to grow a silicon oxide film having a film thickness of about 8 nm on the cleaned substrate surface. Next, the Si substrate on which the silicon oxide film was formed was set in a sputtering apparatus, and a metal electrode layer was provided on the surface of the silicon oxide film to prepare a semiconductor device with a gate electrode of a MOS capacitor.

When the breakdown electric field strength of the gate oxide film of the semiconductor device prepared above was measured, FIG.
As shown in Fig. 3, the average breakdown voltage was about 11 MV / cm, which was higher than that of the comparative example (Fig. 3 (b)). In the comparative example, the breakdown electric field strength of the gate oxide film of the semiconductor device prepared under the same conditions except that the natural oxide film was removed with an aqueous solution of hydrofluoric acid and then washed with pure water to form a cleaned surface. Is.

The relationship between the amount of residual impurities after cleaning the surface of the Si substrate and the stacking fault density (cm ⁻² ) was evaluated by Auger-Electron-Spectroscopy (AES). It was as shown in FIG. That is,
The amount of residual impurities on the cleaned surface was measured by AES, then the stacking fault density of the vapor-deposited silicon film on the cleaned surface was measured, and the relationship between the two was examined and evaluated. The amount of residual impurities was 2% or less, and the stacking fault density was 2 / cm ² or less. On the other hand, as a comparative example, the amount of residual impurities when the silicon film was grown under the same conditions, except that the natural oxide film was removed with an aqueous solution of hydrogen fluoride and then washed with pure water to form a cleaned surface. FIG. 4 also shows the relationship between and the stacking fault density. In the case of the comparative example, the amount of surface residual impurities was 4 to 8% and the stacking fault density was 20 defects / cm ² or more.

Here, the high breakdown electric field strength of the oxide film greatly contributes to the improvement of the electrical characteristics of the memory device such as DRAM and the ultra-high speed device or the improvement of the product yield. In addition, the reduction of stacking fault density can be solved by reducing the occurrence of electrical leakage through the growth film when operating as a device.
Since it is avoided, the reliability of the semiconductor device is improved.

In the above description, the case of forming a clean surface by using a thinly controlled natural oxide film was explained, but in reality, the natural oxide film formed on the surface of a commercially available substrate should not be used as it is. There is also. Specifically, the following cleaning liquids for the purpose of removing organic substances and metal contamination, that is, oxidizing action such as hydrogen peroxide, sulfuric acid-hydrogen peroxide, nitric acid, ammonia hydroxide-hydrogen peroxide, hydrochloric acid-hydrogen peroxide, etc. It is also possible to form (generate) an oxide film by processing in an aqueous chemical solution containing a certain amount of chemicals or in a gas atmosphere of oxygen gas, hydrochloric acid-oxygen gas, hydrogen-oxygen gas or the like. Alternatively, the oxide film can be formed from the gas phase by a dry oxidation method, a thermal oxidation method, or the like, but in any case, the thickness of the oxide film needs to be 1 nm or less.

Further, as another method for forming an oxide film on a Si substrate, there is a means for forming a desired oxide film directly on the surface of a silicon substrate which has been cleaned in advance while controlling the film thickness. That is, after removing the natural oxide film on the Si substrate surface with a hydrofluoric acid solution or the like, rinsing with pure water with a dissolved oxygen concentration of 300 ppb facilitates the interaction between the Si substrate surface and pure water, and The substrate (crystal) surface is etched. With this etching action, the Si substrate (crystal) surface is flattened while preventing the Si substrate surface from being oxidized and preventing surface contamination. Then, a step of forming a new oxide film may be performed subsequent to this cleaning step. Here, "continuously" means forming an oxide film while being held in the liquid used in the cleaning step or by replacing the liquid without taking it out from the liquid.

The cleaning liquid that can be used in this step is an oxidation of silicon such as pure water containing only oxygen, sulfuric acid + hydrogen peroxide solution, hydrogen fluoride + hydrogen peroxide solution, hydrochloric acid + hydrogen peroxide solution. It is an agent. The concentration of oxygen added here should be high enough to form an oxide film, and specifically, it is preferably about 300 ppb to 9 ppm. In any case, after the cleaning step, the oxide film is formed on the surface of the Si substrate without removing the semiconductor substrate from the liquid. For example,
If pure water is used in the cleaning step and pure water is used also in the step of forming the oxide film, the liquid used in the cleaning step and the step of forming the oxide film are the same, so there is no need to replace the liquid. I'm sorry. On the other hand, when pure water is used in the washing step and sulfuric acid + hydrogen peroxide solution is used in the step of forming an oxide film, if the liquid is replaced without removing the semiconductor substrate, the crystal surface of the semiconductor is cleaned. The oxide film can be formed as it is. That is, as in the conventional case, by removing the Si substrate from the liquid for oxidation after the cleaning step, it is possible to prevent the surface of the crystal cleaned in the cleaning step from being contaminated.

Even when the Si substrate is taken out from the gas, if the surface density of the Si substrate is 1% or more, after the Si substrate is temporarily put in an atmosphere of an inert gas that does not cause oxygen / carbon contamination, By performing the step of forming the oxide film, the same effect as in the case of forming the oxide film continuously can be obtained. Here, examples of the inert gas include vacuum in which the partial pressure of organic components or oxygen is controlled, hydrogen gas, nitrogen gas, argon gas, helium gas, and the like.

Although the example of forming the Si thin film and the oxide film on the surface of the Si substrate has been described above, the same action and effect can be obtained in forming a thin film such as an amorphous silicon layer or a polysilicon layer.

Example 2 First, a thin film forming apparatus having a schematic structure shown in FIG. 5 was prepared. In FIG. 5, 1 is a load lock chamber for transferring a semiconductor substrate (for example, Si substrate) 2 for thin film formation, 3 is a pretreatment chamber for pretreating the Si substrate 2 for thin film formation, 4 is a thin film growth chamber, and 5 is a thin film growth chamber. An unloading chamber for receiving the Si substrate 2 on which a required thin film is grown, and 6 is an ion implantation apparatus for implanting silicon (Si) ions into the Si substrate 2 in the pretreatment chamber 3 at an energy of 20 to 1000 eV. .

On the other hand, a Si substrate having an oxide film with a thickness of 1 nm formed on the surface by treatment with sulfuric acid + hydrogen peroxide solution is prepared, and this Si substrate is introduced into the thin film forming apparatus and pretreatment chamber 3 Then, the ion implanter 6 was operated to implant Si ions into the oxide film at a doping amount of 1.5 × 10 ¹⁵ cm ^-2 and 200 eV. In addition, FIG. 6 shows Si ion implantation energy and
It shows the relationship of the projective range (Rp) of Si ions. For example, when Rp = 5 nm, Si ions penetrate into the oxide film. Therefore, the thickness of the oxide film, Si ion implantation amount, ion implantation energy, etc. can be selected as appropriate. Good. Here, it is desirable that the thickness of the oxide film is 1 nm or less, but up to about 2 nm is acceptable. That is, if the film thickness is 2 nm or less, the Si ion implantation causes the oxide film to become a low-order oxide film and easily volatilize, and vaporization is possible even at a low temperature.

Next, Si ions were implanted into the oxide film.
The Si substrate 2 is introduced into the thin film growth chamber 4 and heat-treated in vacuum. FIG. 7 is a spectrum diagram showing a state where the oxide film is separated by this heat treatment. That is, regarding the Si substrate 2 in which Si ions are implanted into the oxide film, the relationship with the detachment of the oxide film at the heating temperature under vacuum is shown by TDS (Thermal Desor).
Ption Spectroscopy) evaluated and examined the curve A
As shown in, the oxide film was found to detach from the center temperature around 700 ° C, and the oxide film was easily evaporated to expose a clean Si substrate surface. In addition, as a comparative example in FIG.
A curve a shows the relationship between the heating temperature and the removal of the oxide film when Si ions were not implanted. As can be seen from the curve a, in the case of the comparative example, the central temperature at which the oxide film desorbs is 900 ° C.
It is in the vicinity, and is 200 ° C. higher than that of the example.

After the surface of the Si substrate 2 is cleaned, disilane gas is introduced into the thin film growth chamber 4 so that the cleaned surface has a thickness of 1
After stacking and growing 00nm Si thin film, unload chamber 5
Taken out through. The impurity SIMS profiles of the Si substrate and the Si thin film were measured for the Si substrate on which the Si thin films were laminated and grown in this way. As shown in Fig. 8 (a), the Si thin film / Si substrate interface had carbon 2 × There were only 10 ¹² cm ^-2 and oxygen 2 × 10 ¹² cm ^-2 . In addition, the laminated
The stacking fault concentration of the grown Si thin film was 10 ² / cm ² or less.

In the above, after the Si ions were implanted into the oxide film on the surface of the Si substrate 2 and left in the atmosphere for a month, the surface was cleaned by heating at 700 ° C. in vacuum. Then, a Si thin film having a thickness of nm was laminated and grown, and then taken out through the unload chamber 5. In this way, stack Si thin films
Impurity SIMS profiles of the Si substrate and the Si thin film were measured for the grown Si substrate, and the results are as shown in FIG. 9. The Si thin film / Si substrate interface had carbon 2 × 10 ¹² c.
There were only m ^-2 and oxygen 2 x 10 ¹² cm ^-2 . The stacking fault density of the stacked and grown Si thin film is 10 ² / cm.
It was less than ² . From this example, Si ion implantation oxide film / Si
It can be seen that the substrate interface remains clean even if left in the atmosphere.

For comparison, the impurity SIMS when Si thin films are laminated and grown under the same conditions except that the hydrogen fluoride aqueous solution is used for cleaning without implanting Si ions into the oxide film. As shown in Fig. 8 (b), the oxygen impurity concentration was 2 × 10 ¹² cm ^-2 , but the carbon impurity concentration was
High as 6 × 10 ¹² cm ^-2 and stacking fault concentration of Si thin film is 10 ⁴ /
It was cm ² .

Further, in the above embodiment, as the Si substrate 2,
Using the Si substrate with the source region 2a and the drain region 2b pre-formed, the oxide film formed on the surface under the same conditions as above
After implanting Si ions and heating to evaporate the oxide film to expose the clean surface, vapor phase growth of the oxide film and vapor phase growth of the Si thin film are performed, and then patterning is performed to perform the Si thin film bipolar. I made a transistor. The result of measuring and evaluating the impurity profile of the CMOS part of this Si thin film bipolar transistor is schematically shown in Fig. 10 (a). In FIG. 10 (a), the solid line shows the impurity profile before the cleaning treatment, and the dotted line shows the impurity profile after the cleaning treatment.

For comparison, the impurities in the CMOS portion of the Si thin film bipolar transistor prepared under the same conditions were used except that the cleaning treatment was performed by vacuum heating at 900 ° C. without implanting Si ions into the oxide film. The profile is shown schematically in Fig. 10 (b). Here, the solid line is the impurity profile before the cleaning process, and the dotted line is the impurity profile after the cleaning process. As can be seen from these comparisons, in the case of the embodiment, since the diffusion of the doping impurities does not occur, the channel length hardly changes.
It is suitable for forming SI semiconductor devices and is expected to improve yield. On the other hand, in the case of the comparative example, the diffusion of the doping impurities occurs and the change of the channel length is recognized.

Example 3 First, a thin film forming apparatus having a schematic sectional view of the structure shown in FIG. 11 was prepared. In FIG. 11, reference numeral 7 denotes a vacuum container type film forming chamber in which a raw material gas is introduced to grow a semiconductor film or the like, which is made of, for example, stainless steel and is formed so that the container wall can be cooled with cooling water. 8 is a semiconductor substrate for growth (eg, Si substrate)
The growth temperature is held in the film forming chamber 7 with the growth surface facing downward, while the heating heater 9 mounted on the back surface can heat the substrate to a temperature of about 850 ° C. Further, 10 is a load lock chamber connected to the film forming chamber 7 via a gate valve 11, and the growth Si substrate 8 can be formed without reducing the vacuum (for example, 10 ⁻⁷ Pa or more) in the film forming chamber 7. A vacuum degree of 5 × 10 ⁻⁶ Pa or higher can be maintained because it can be carried in or out of the film forming chamber 7. Here, when the growth Si substrate 8 is carried into the film forming chamber 7, the degree of vacuum in the film forming chamber 7 is 5 × 10 5.
Even when the pressure reaches ^-6 Pa, the degree of vacuum in the film forming chamber 7 can be restored to 10 ^-7 Pa after about 30 minutes.

Further, 12 and 13 are ultimate vacuums at which the film forming chamber 7 and the load lock chamber 10 are evacuated to required vacuum levels, respectively.
It is a turbo molecular pump with a pressure of 10 ^-8 Pa and an ultimate vacuum of 10 ^-7 Pa.
Reference numeral 14 is a source gas introducing nozzle for introducing a film forming source gas into the film forming chamber 7, and 15 is an oxidizing / desorbing gas introducing nozzle for introducing an oxidizing / desorbing gas into the film forming chamber 7. Further, each of the gas introduction nozzles 14 and 15 has an exhaust system 1 for each system.
It is connected to the gas cylinders 18a, 18b, 18c, 18d through 6a, 16b and spare chambers 17a, 17b that can be exhausted.

Here, the high pressure gas cylinder 18a is, for example, disilane gas (100%), and 18b is, for example, diborane gas 1%.
Nitrogen gas is a diluent gas type dopant source, and a pressure reducing valve 19
After depressurizing with a and 19b, mass flow controller 20
The flow rates are controlled by a and 20b, and if necessary, they are mixed in the preliminary chamber 17a and supplied to the film forming chamber 7. On the other hand, the high pressure gas cylinder 18c is, for example, a hydrogen gas source for terminating the surface with hydrogen after heating the substrate 8 at a high temperature, and 18d is, for example, a mixed gas source in which oxygen gas for oxidizing the surface of the substrate 8 is diluted with hydrogen gas. After the pressure is reduced by the pressure reducing valves 19c and 19d, the flow rate is controlled by the mass flow controllers 20c and 20d, and if necessary, they are mixed in the preliminary chamber 17b and supplied to the film forming chamber 7. The reason why the introduction paths of the raw material gas and the oxygen gas are separated is to prevent the raw material gas mainly consisting of a hydrogen compound from reacting with oxygen and decomposing,
It is also possible to avoid mixing oxygen into the raw material gas introduction path and always keep the residual oxygen partial pressure low. Furthermore, in this configuration, since the surface of the substrate is terminated with hydrogen,
Contamination after surface cleaning is avoided.

Next, thin film formation using the thin film forming apparatus having the above-mentioned structure will be described.

First, after degreasing with sulfuric acid, 0.5
% Hydrogen fluoride aqueous solution to remove the natural oxide film on the surface, wash with ultrapure water without passing through the air, and then dry in high-purity nitrogen gas. Prepare a Si wafer with a hydrogen termination formed as the growth substrate 8. did. The growth substrate 8 is inserted into the load lock chamber 10, the inside of the load lock chamber 10 is evacuated, and the degree of vacuum is
When the pressure reached 10 ⁻⁵ Pa, the gate valve 11 was opened, and the growth substrate 8 was loaded into the vacuum-deposited film forming chamber 7,
While the valve 11 was closed, the growth substrate 8 was set at a predetermined position.

Next, when 80 SCCM of hydrogen gas was introduced from the hydrogen gas source 18c into the film forming chamber 7, the degree of vacuum in the film forming chamber 7 became 0.2 Pa. In this state, the growth Si substrate 8 was heated to 750 ° C. by the heater 9 for heating, and 0.4 SCCM of oxygen-hydrogen mixed gas was introduced into the film forming chamber 7 from the mixed gas source 18d. It became 10 ^-6 Pa.
After maintaining this state for 30 minutes, the introduction of the mixed gas was stopped, and the temperature of the growth substrate 8 was further lowered to 650 ° C.

After that, when the temperature of the growth Si substrate 8 becomes stable, the introduction of the hydrogen gas is stopped and the source gas source
Disilane gas 1.0 SCCM from 18a, and dopant source
Introducing 0.1% diborane gas 0.1 SCCM from 18b into the film forming chamber 7 and growing a p-type Si thin film for about 30 minutes to form a 100 nm thick Si film.
A thin film crystal was obtained.

The impurity distribution in the depth (thickness) direction of the formed Si thin film was measured by a secondary ion mass spectrometer (SIMS), and it was as shown in FIG. 12 (a). That is, the substrate 8
Carbon and oxygen as impurities are slightly detected at the depth of 100 nm corresponding to the / growth film interface, but it is assumed that all of these impurities are (flat) at the interface, and the concentration per surface is estimated. And carbon is 3 × 10 ¹² / cm ^-2 , oxygen is
It becomes 4 × 10 ¹² / cm ^-2 . For comparison, the heat treatment under the partial pressure of oxygen prior to the growth of the Si film was omitted, and the film was heated to 650 ° C. immediately after being introduced into the film forming chamber 7 and kept under the same conditions as described above to form a p-type film having a thickness of 100 nm. A Si thin film was grown. The results of measuring the impurity distribution in the depth direction of this p-type Si thin film with a secondary ion mass spectrometer are shown in FIG. 12 (b). In the case of this comparative example, the carbon concentration as an impurity at the substrate 8 / growth film interface is 6
The impurity concentration was × 10 ¹³ / cm ^-2 and the oxygen concentration was 5 × 10 ¹³ / cm ^-2 , and 1020 times more impurities remained than in the case of the example. Further, as another comparative example, after the substrate was heat-treated in a hydrogen gas atmosphere without introducing oxygen gas, p
FIG. 12 (c) shows the result of measuring the impurity distribution in the depth direction of this p-type Si film after growing the p-type Si film. in this case,
The oxygen concentration was reduced to 3 × 10 ¹² / cm ^-2 , but the carbon concentration was 5.5 × 10 ¹³ / cm ^-2, which was hardly reduced.
As can be seen from this Example and Comparative Example, the initial oxide film on the surface of the Si substrate was easily separated (removed) by heating at 750 ° C.
However, heat treatment under partial pressure of oxygen is effective for removing carbon-based impurities. Example 4 First, a quartz reaction tube capable of accommodating / mounting 24 6-inch Si substrates was used as a film forming apparatus main body, and after accommodating / mounting Si substrates, the ultimate vacuum in the quartz reaction tube was 10 ⁻⁸ Pa. In order to obtain the above, a vapor phase film deposition apparatus comprising two turbo molecular pumps having an exhaust capacity of 1500 L / min and a main exhaust apparatus was prepared. This vapor phase film forming apparatus is provided with a load lock chamber for preventing a decrease in vacuum when inserting and mounting a Si substrate in a quartz reaction tube, and further, a raw material gas such as disilane gas or diborane gas, and A gas introduction line for introducing oxygen gas is also attached.

On the other hand, as the Si substrate, one having a CMOS transistor and bipolar transistor mixed device configuration was prepared. That is, the source for the MOS transistor
Impurity diffusion in the drain portion is completed, an oxide film including a gate oxide film is further formed on the entire surface, and a Poly-Si layer is accumulated on the oxide film surface in the gate region. In addition, the bipolar transistor portion is doped with n-type having a higher concentration than the substrate to form a collector, and the n-type controls the region where the base layer is formed on the doping layer.
A Si substrate having an oxide film with an opening partly prepared was prepared. That is, the region where the active transistor is formed on the surface of the Si substrate is the Si substrate covered with the oxide film except for the portion where the base layer is to be formed.

Next, the plurality of Si substrates were placed in a quartz beaker containing a 3% aqueous solution of hydrogen fluoride in a state of being shielded from the atmosphere and subjected to etching treatment for 2 minutes to spontaneously oxidize the surface on which the base layer was to be formed. The film was removed. After that, while keeping the atmosphere shielded from the atmosphere, a 3% aqueous solution of hydrogen fluoride was replaced with pure water whose dissolved oxygen was reduced to 10 ppb or less,
After washing with water for a minute, the pure water was replaced with nitrogen gas and dried, and then taken out into the air and carried into the load lock chamber of the thin film forming apparatus. At this point, load lock chamber 10 ^-4
After evacuating to about Pa, the Si substrate carried into the load lock chamber was inserted through a gate valve into a quartz reaction tube into which hydrogen gas was introduced so that the temperature was 500 ° C and the oxygen partial pressure was 1 Pa. Transported. Even after the Si substrate was inserted and transported, while continuing to introduce hydrogen gas into the quartz reaction tube,
Exhausted for about 30 minutes.

After that, the temperature in the quartz reaction tube was raised to 700
While raising the temperature to 0 ° C., oxygen gas is introduced together with the hydrogen gas for 20 minutes so that the oxygen partial pressure becomes 3 × 10 ⁻⁵ Pa,
After that, introduction of only hydrogen gas was continued. When the temperature inside the quartz reaction tube was lowered to 550 ° C, the introduction of hydrogen gas was stopped, and at the same time, disilane (partial pressure
0.3 Pa) and diborane (partial pressure 10 ⁻³ Pa) were introduced for 40 minutes to form a p-type Si layer having a thickness of 50 nm on the Si substrate surface. After forming this p-type Si layer, stop the introduction of raw material gas, switch to the introduction of hydrogen gas again, fill the inside of the quartz reaction tube with hydrogen gas atmosphere, then lower the temperature to 500 ° C and load the Si substrate. I took it out to the lock room. Next, of the p-type Si layer grown on the entire surface of the Si substrate, the base layer and the extraction electrode portion were left, and the other portions were removed by etching to form a base portion.

In the production of Bi-CMOS bipolar transistor, if the base layer is formed by the above means,
Since it is not necessary to raise the substrate temperature to 750 ° C or higher, there is no fear that the doping profile of the already formed CMOS part will change. This means that in Bi-CMOS,
This means that there is no need to design for the extra heat load on the CMOS part, which makes it possible to form a finer CMOS part (capable of high-speed operation) in Bi-CMOS. Further, since fluctuations and variations in channel length due to re-diffusion of the doping layers of the source / drain portions in the CMOS portion are prevented / suppressed, reliability and yield can be improved.

The present invention is not limited to the above embodiments, and various modifications can be made without departing from the spirit of the invention. For example, as the semiconductor substrate for thin film growth, the Si substrate and the Si substrate for Bi-CMOS have been exemplified above.
And so on.

[0054]

As can be seen from the above description, according to the thin film forming means of the present invention, the thin film growth surface of the semiconductor substrate can be easily cleaned, and a required thin film can be grown while maintaining the clean surface. To be done. Therefore, it is possible to form a high-quality thin film in which contamination of the substrate / growth film interface is suppressed, and as a result, a high-performance semiconductor device can be provided. Moreover, at the time of cleaning the substrate surface, at most 750
Since the heat treatment at about ℃ is sufficient, there is no fear of causing deformation of the already formed doving pattern or change of the channel length, so that not only the yield can be improved but also the cost can be reduced.

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing the immersion time dependence of the natural oxide film thickness of a Si substrate surface in a hydrofluoric acid aqueous solution.

FIG. 2 is a characteristic diagram showing the relationship between the amount of impurities before and after vacuum heating after forming a thin oxide film on the surface of a Si substrate.

3A is a characteristic diagram showing an example of breakdown electric field strength of an oxide film formed by the thin film forming method according to the present invention, and FIG. 3B is an example of breakdown electric field strength of an oxide film formed by a conventional thin film forming method. FIG.

FIG. 4 is a characteristic diagram showing a comparison between the stacking fault density and the amount of surface impurities in the Si film formed by the thin film forming method according to the present invention and the Si film formed by the conventional method.

FIG. 5 is a sectional view showing a schematic configuration example of a thin film forming apparatus used in the thin film forming method according to the present invention.

FIG. 6 is a characteristic diagram showing the relationship between the projected range of Si ions and the acceleration energy.

FIG. 7 is a characteristic diagram showing a comparison between the heating temperature and the oxide film desorption (desorption) in the thin film forming method according to the present invention and the conventional forming method.

FIG. 8 (a) is Si formed by the thin film forming method according to the present invention.
A characteristic diagram showing an example of the impurity profile at the interface between the grown film and the Si substrate, (b) is the Si grown film and Si formed by the conventional thin film forming method.
The characteristic view which shows the example of the impurity profile of a board | substrate interface.

FIG. 9 is a characteristic diagram showing an example of an impurity profile at the Si substrate interface with another Si growth film formed by the thin film forming method according to the present invention.

FIG. 10 (a) is a schematic view showing a change state of a channel length before and after heating for cleaning in a Bi-CMOS manufactured by applying the thin film forming method according to the present invention, and (b) is a conventional thin film formation. The schematic diagram which shows the change state of the channel length before and after heating of the cleaning in Bi-CMOS manufactured by applying the method.

FIG. 11 is a sectional view showing a schematic configuration example of a thin film forming apparatus according to the present invention.

FIG. 12 (a) is a characteristic diagram showing an example of an impurity profile at the interface between a Si growth film formed by another thin film formation method according to the present invention and a Si substrate, and (b) and (c) are conventional thin film formations different from each other. The characteristic view which shows the example of the impurity profile of the Si growth film formed by the method, and the Si substrate interface.

[Explanation of symbols]

1,10 …… Load lock chamber 2,8 …… Si substrate for growth
2a …… source 2b …… drain 3 …… pretreatment chamber 4,7 …… thin film growth chamber 5 …… unload chamber 6 …… ion implantation equipment 9 …… heating heater 11 …… gate valve
12, 13 …… Turbo molecular pump 14 …… Raw material gas introduction nozzle 15 …… Oxide film detachment (desorption) nozzle

Claims (4)

[Claims] 1. A step of forming an oxide film having a film thickness of 1 nm or less on the surface of a semiconductor substrate, and a step of forming the oxide film on the semiconductor substrate by high vacuum, hydrogen gas, argon gas, nitrogen gas, etc. A step of heating in an atmosphere in which the oxide is substantially desorbed from the surface faster, and a step of desorbing the surface oxide film by the heating to obtain a clean semiconductor surface,
And a step of forming a thin film on the cleaned semiconductor surface. 2. A step of forming an oxide film on the surface of a semiconductor substrate, a step of implanting silicon ions into the oxide film of the formed semiconductor substrate with energy of 20 to 1000 eV, and a semiconductor subjected to the ion implantation treatment. A step of subjecting the substrate to a heat treatment in an atmosphere of high vacuum, hydrogen gas, argon gas, nitrogen gas or a mixed gas thereof to volatilize and remove the oxide film to obtain a clean semiconductor surface; and the cleaned semiconductor. And a step of forming a thin film on the surface. 3. A step of immersing a semiconductor substrate in a hydrogen fluoride-based solution to remove an oxide film on the surface of the substrate, a step of terminating the surface of the semiconductor substrate from which the oxide film has been removed with hydrogen, and a step of terminating the surface with hydrogen. Accommodating and mounting the converted semiconductor substrate in a vacuum with residual oxygen partial pressure and residual water vapor partial pressure of 1 × 10 ^-8 Pa or less, and the oxygen partial pressure of the vacuum system from 1 × 10 ^-6 Pa to 1 × Ten
^-3 Pa, while controlling the semiconductor substrate temperature to 500 to 800 ° C to remove surface impurities, and then introducing a source gas to grow a thin film on the semiconductor substrate surface. And a method for forming a thin film. 4. A vacuum container for growth, an exhaust mechanism for exhausting the inside of the vacuum container to a vacuum system having a residual oxygen partial pressure and a residual water vapor partial pressure of 1 × 10 ⁻⁸ Pa or less, and the interior of the vacuum container. A substrate support mechanism that supports the semiconductor substrate for growth, a temperature controllable substrate heater that heats the semiconductor substrate supported by the substrate support mechanism to 500 to 800 ° C.
A source gas introduction part for introducing a source gas containing a group IV element,
An apparatus for forming a thin film, comprising: an oxygen partial pressure controller for controlling the oxygen partial pressure of the vacuum system to 1 × 10 ⁻⁶ Pa to 1 × 10 ⁻³ Pa.