KR100305124B1 - Impurity doping method with diffusion source of boron-silicide film - Google Patents

Abstract

PURPOSE: A solid phase diffusion process is provided to improve controllability of diffusion of boron impurity into a silicon substrate and to achieve a shallow junction by using a boron silicide film as diffusion source. CONSTITUTION: A process includes: cleaning the surface of a Si substrate(1) by removing a native oxide film thereof to expose an active surface; treating the active surface to form thereon a boron silicide film(2) as an impurity source; and introducing boron impurity from the boron silicide film into the Si substrate to form a boron diffusion layer(3). The boron diffusion layer(3) having a high surface concentration and a shallow junction is formed because the boron silicide film(2) is formed directly on the surface of the Si substrate(1). Because the boron silicide film(2) is chemically and physically stable, an improved diffusion controllability is obtained.

Description

Impurity doping method having boron silicide film diffusion source

1 (a) to 1 (c) are process step diagrams of a first embodiment according to the semiconductor device manufacturing method of the present invention.

2 (a)-(c) are conventional process steps for impurity diffusion.

3 is a graph showing the variation of the planar sheet resistance in the wafer with respect to the basic vacuum (background vacuum).

4 is a graph showing the relationship between film deposition temperature and boron silicide composition.

5 is a graph showing the relationship between the film thickness of the boron silicide film and the sheet resistance of the boron diffusion layer.

6 shows the relationship between the film thickness of the native oxide film and the sheet resistance of the boron diffusion layer.

7 is a schematic view showing a method for measuring boron silicide film thickness.

8 is a graph showing the concentration profile of impurities in the boron diffusion layer.

9 is a graph showing the chemical resistance of boron silicide films.

10 is a graph showing the chemical resistance of the boron film.

11 (a) to 11 (d) are process step diagrams of a second embodiment according to the semiconductor device manufacturing method of the present invention.

12 (a) to 12 (d) are process step diagrams of a third embodiment according to the semiconductor device manufacturing method of the present invention.

13 (a) to 13 (e) are process step diagrams of a fourth embodiment according to the semiconductor device manufacturing method of the present invention.

14 (a) and 14 (b) are process step diagrams of a fifth embodiment according to the semiconductor device manufacturing method of the present invention.

FIG. 15 is a graph showing the sheet resistance of the boron diffusion layer and its variation in the wafer for the period of the high temperature treatment before the diffusion treatment.

FIG. 16 is a graph showing the sheet resistance of the boron diffusion layer and its variation in the wafer for the period of the high temperature treatment after the diffusion treatment.

17 is a schematic view of the surface after annealing the boron silicide film.

18 (a) to 18 (d) are schematic diagrams showing a removal treatment of a boron silicide film.

Fig. 19 is a graph showing the sheet resistance of the diffusion layer after the diffusion treatment with respect to the film thickness of the boron silicide film and the oxidation conditions of the boron silicide film.

20 (a) to 20 (b) are process step diagrams of a sixth embodiment according to the semiconductor device manufacturing method of the present invention.

FIG. 21 is a graph showing the diffusivity of boron to silicon nitride film.

FIG. 22 is a graph showing the diffusivity of boron to silicon oxide film. FIG.

23 (a) to 23 (g) are schematic diagrams showing the degree of variation in sheet resistance in the boron diffusion layer with or without an overcoat.

24 (a) to 24 (c) are process step diagrams of a seventh embodiment according to the semiconductor device manufacturing method of the present invention.

25 (a) to 25 (e) are process step diagrams of an eighth embodiment of the semiconductor device manufacturing method of the present invention.

26 (a) to 26 (e) are process step diagrams of a ninth embodiment according to the method of manufacturing a semiconductor device of the present invention.

27 is a block diagram showing a method for evaluating the film thickness of an impurity film according to the method for evaluating a semiconductor device of the present invention.

Fig. 28 is a sectional view of a sample for explaining a method for evaluating the film thickness of an impurity film of the present invention.

FIG. 29 is a graph showing the relationship between the gas introduction period and the film thickness measured by the film thickness evaluation method as shown in FIG. 28. FIG.

30 is a graph showing the relationship between the film thickness measured by mechanical means and the film thickness achieved by the optical film thickness evaluation method according to the present invention.

31 is a block diagram of a semiconductor manufacturing apparatus according to the present invention.

FIG. 32 (a) is a graph depicting boron film thickness measured over a B ₂ H ₆ introduction period.

FIG. 32 (b) is a graph showing boron film thickness measured for pressure change of B ₂ H ₆ gas.

33 is a flowchart showing an impurity doping process according to the present invention.

34 is a cross-sectional view of a MISFET structure in accordance with the semiconductor device of the present invention having a boron silicide film on the surface of the source / drain regions.

35 is a cross-sectional view of another MISFET structure in accordance with the semiconductor device of the present invention having a boron silicide film on the surface of the source / drain regions and the gate electrode.

36 is a cross sectional view of an NPN bipolar transistor structure according to the semiconductor device of the present invention having a boron silicide film on a portion of the base region.

37 is a cross-sectional view of a PNP bipolar transistor structure in accordance with a semiconductor device of the present invention having a boron silicide film on the emitter region.

38 is a cross-sectional view showing a contact structure in which tungsten silicide is connected to a semiconductor region with a boron silicide film interposed therebetween.

Fig. 39 is a sectional view showing a contact structure in which tungsten is connected to a semiconductor region with a boron silicide film interposed therebetween.

40 is a cross-sectional view showing a contact structure in which a metal connecting portion having a barrier metal is connected to a semiconductor region with a boron silicide film interposed therebetween.

* Explanation of symbols for main parts of the drawings

1, 101, 111, 191, 201, 301, 501: silicon substrate

2, 103, 114, 192, 207, 302: boron silicide film

3, 104, 115, 193, 303: boron diffusion layer

102, 112, 206, 503: boron film

202: gate insulating film 213: gate oxide film

214: gate electrode 511: laser

512, 513: optical system 514: optical detector

515: computer

[Background of invention]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a semiconductor device such as a bipolar transistor and an insulated gate field effect transistor used in an electronic system such as a computer. A method of forming a conductive type and conductive region. More specifically, the present invention relates to a method for diffusing boron that functions as an acceptor inside a semiconductor layer, and a method for producing a boron silicide film that functions as an impurity film.

The present invention also relates to a method for evaluating an impurity diffusion film used in an impurity diffusion step in the manufacture of a semiconductor device, and an apparatus used in the production of a semiconductor capable of performing the evaluation method.

The present invention also relates to a structure of a semiconductor device such as a bipolar transistor or an insulated gate field effect transistor used in a computer or the like. More specifically, the present invention relates to the structure of the contact region, control electrode and active region of the semiconductor device.

As a conventional technique for introducing impurity elements into a semiconductor device, there is an ion implantation method. In the ion implantation method, the accelerated ions are directly impinged on the surface of the silicon substrate, and then, the silicon substrate is heat treated to diffuse the implanted ions. However, the ion implantation method has a limitation in reducing the thickness of the diffusion layer, because it is difficult to obtain a shallow diffusion layer due to the channel effect even when the acceleration voltage is lowered. In boron, more channel effects occur than in phosphorus and arsenic, and therefore, become a negligible difficulty in forming a P-type impurity layer. As the need for smaller semiconductor devices increases, there is a need to form shallower impurity layers in forming silicon substrates. However, currently widely used ion implantation methods do not satisfy this requirement.

Another known technique for introducing impurities into silicon substrates is the solid phase diffusion process. Since the solid phase diffusion method is closely related to the method of the present invention, it will be briefly described with reference to FIGS. 2 (a) to 2 (c) below. 2A is a step of preparing a silicon substrate 21 whose surface is substantially covered with an oxide film 22. In the subsequent step of FIG. 2 (b), a glass film containing boron as an impurity, that is, a BSG film 23, is formed on the substrate surface. This step, referred to as preliminary deposition of the BSG film 23, is performed by thermally oxidizing the surface of the substrate 21, for example, in a processing atmosphere containing boron.

Step (c) of the final step is to form the boron diffusion layer 26 by heat treatment. However, the solid phase diffusion method using impurity-containing glass such as BSG film as a diffusion source has the following drawbacks. Generally, the diffusion coefficient of P-type impurity boron used is 2 digits or more lower than that of a silicon substrate. Therefore, the impurity diffusion into the glass has a speed control step in the solid phase diffusion method. It must be heat treated at a high temperature of 1000 ° C. or higher to ensure sufficient hybridization of impurities into the silicon substrate. As a result, the impurity layer extends into the silicon layer, making it difficult to form a shallow junction.

In view of the above-mentioned cases, the ion implantation method using impurity glass and the solid phase diffusion method have disadvantages, respectively, and thus, other solid phase diffusion methods have been developed in recent years using impurity films themselves as diffusion sources.

For example, US Pat. No. 4,791,074 (1988) discloses a method comprising exposing a surface of a silicon substrate, depositing a boron film thereon, and heat treating the structure such that boron diffuses into the silicon substrate. Is disclosed. In the above method, the boron film is formed by, for example, vapor deposition.

The boron film typically deposits a boron film using a partially patterned oxide film as a mask on a silicon substrate surface for specific use for monitoring film thickness, and then selectively removes the mask and scans the deposited film surface. It has been evaluated by measuring the height difference of the membrane.

In addition, a conventional semiconductor device manufacturing apparatus uses an ion implantation method to form an active region, that is, a region doped with impurities. An impurity region is then formed in the Gaussian distribution, wherein the impurity concentration on the surface exhibits a distribution below the solid solubility limit of boron to silicon.

As described above, the conventional ion implantation method has a limitation in controlling the depth of the impurity layer. Another impurity doping method, i.e., a solid-phase diffusion method using the impurity film itself as a diffusion source, has essentially no limitation on the depth of the impurity layer.

However, the above-described solid phase diffusion method using the impurity film itself as a diffusion source has the following drawbacks. Impurity films such as boron films deposited on the exposed active surface of the silicon substrate do not always have chemical and physically stable structures. This structure is affected by the thermal chemical treatment used in the semiconductor manufacturing method, the film deposition amount, etc. will be significantly changed. The impurity concentration profile along the depth direction is not established with high precision as long as there are problems with stability and controllability of the impurity film.

However, in the impurity doping method using a boron or boron silicide film as the diffusion layer, the method of evaluating the impurity film is complicated. In the conventional boron film thickness evaluation method based on mechanical means, it is impossible to measure thickness of 100 GPa or less with sufficient high accuracy. In addition, the boron film is damaged because the evaluation is performed by contacting the probe with the surface. Thus, the wafer will be used only for monitoring film thickness, not for actual production. In addition, the monitoring wafers used for this particular application are not simply manufactured, but need to be prepared in a complex structure before evaluation. Therefore, the impurity diffusion method using the boron film cannot be easily introduced into a practical production line.

The semiconductor device manufacturing method by ion implantation does not satisfy the need for shallow junction formation for realizing fine semiconductor devices due to known problems such as damage and channeling in silicon substrates. As long as the ion implantation method is used, the structural shape of the semiconductor device reflects the above problems.

The present invention is to overcome the above problems.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a semiconductor device having an extremely shallow impurity region and a method of manufacturing the same.

It is another object of the present invention to provide a semiconductor device comprising an impurity film which is less susceptible to thermal chemical treatment, and a manufacturing method thereof.

Another object of the present invention is to provide a semiconductor device having a low resistance between a connecting metal and a shallow impurity region and a method of manufacturing the same.

It is another object of the present invention to provide a high density integrated semiconductor device capable of operating at high speed and a method of manufacturing the same.

Another object of the present invention is to provide a semiconductor device having a high concentration impurity region and a manufacturing method thereof.

It is another object of the present invention to provide a method for evaluating the film thickness of an impurity film of a semiconductor device having an impurity film with rapid and high precision.

It is another object of the present invention to provide an apparatus for manufacturing a semiconductor used as an impurity film capable of producing a very thin impurity film with good controllability.

In connection with the above-mentioned problems of the prior art, it is an object of the present invention to provide a method for performing impurity diffusion with good controllability and stability using a membrane structure having high resistance to chemical physical processing. The object of the present invention is achieved by the following means. That is, the impurity diffusion method according to the present invention comprises a cleaning step of exposing the active surface of the silicon layer, and a boron silicide layer (chemical compound layer with silicon and impurity elements) as a reaction product from boron and silicon on the surface of the active surface. A processing step of forming a). Additionally, after the steps, a diffusion step of introducing boron impurities from the boron silicide layer into the silicon layer may be performed.

According to an embodiment of the present invention, the treating step further includes a film deposition step of forming a boron-containing deposition layer on an active surface, and thermally reacting the deposition layer with a silicon layer to form a boron silicide layer therefrom. It includes. In carrying out the heat treatment step, an additional step of selectively removing or etching the deposited layer containing boron may be performed before the heat treatment. In another embodiment of the present invention, a coating step of forming an overcoat on the boron silicide layer before the diffusion step may be included.

Another embodiment of the present invention includes a surface treatment step of selectively or completely removing the boron silicide layer by etching before or after the diffusion step.

The present invention provides a method for evaluating a film thickness of an impurity film, comprising irradiating light onto a boron film and analyzing reflected light. The present invention also provides an impurity film production apparatus that simultaneously performs film thickness evaluation in accordance with the evaluation method of the present invention. Therefore, the impurity diffusion method of the present invention includes controlling the film thickness once more when the measured value deviates from the predetermined value and then moving to the diffusion step.

The semiconductor device according to the present invention provides a stacked structure of an impurity doped semiconductor region and a boron silicide region. The depth of the impurity doped semiconductor region formed by performing the solid phase diffusion method may be shallower than the thickness of the boron silicide layer.

The semiconductor manufacturing method according to the present invention includes forming the boron silicide layer in direct contact with the surface of the silicon layer, and sometimes performing solid phase diffusion using the boron silicide layer as a diffusion source. Through the composition of the boron silicide layer, layer thickness and diffusion treatment temperature and duration control, a boron diffusion layer having a desired concentration profile along the thickness direction is achieved. In particular, by using the above-described method, an extremely thin impurity diffusion layer necessary for producing a microsemiconductor device is formed. Since the boron silicide film is more stable than the boron film conventionally used as a diffusion source, the manufacturing method can be controlled more easily, and provides greater freedom in the design of the processing step.

For example, after depositing a layer containing boron on the active surface of the silicon layer, the boron silicide layer may be formed by thermally reacting the deposition layer and the silicon layer. Unlike the boron silicide layer, the boron containing deposition layer is chemically or physically unstable and can be easily etched. Therefore, the necessary impurity diffusion region can be obtained by selectively removing the boron-containing deposition layer before performing the thermal reaction step.

Solid phase diffusion using a boron silicide layer as the diffusion source sometimes requires control of out-diffusion. This is done by forming an overcoat of the desired composition on the boron silicide before the diffusion step. The boron silicide layer used as the diffusion source can remain in the final device. However, it may be selectively removed for the purpose of further reducing the resistance of the electrical connection. In this case, an etching method including a specific surface treatment can be applied.

The method for evaluating a semiconductor device according to the present invention includes the step of evaluating the film thickness of the boron-silicon compound film or the boron film using optical means up to 100 GPa or less. Since this method is a non-contact method, the wafer on which the measurement is performed can be used in actual production. In addition, evaluation is performed in real time during impurity film deposition. The resistance of the diffusion layer formed after the diffusion step is controlled with high precision because diffusion is performed on the thickness controlled boron film.

The semiconductor device according to the present invention also includes a laminated structure of a boron silicide layer and a semiconductor region. By taking this structure, the semiconductor device of the present invention provides the following characteristics.

First, a semiconductor region doped with a high concentration of impurities without using an ion implantation method is manufactured. This enables a semiconductor device that is not affected by channeling and shadowing effects. Thus, a bipolar transistor having an extremely thin base region and an impurity profile with no emitter pushing effect, as well as a MISFET with good symmetry including shallow source / drain region junctions, are obtained.

Second, the boron silicide film itself acts as a barrier layer that suppresses spike phosphoric acid of the metal in the contact region. In addition, the semiconductor device having the above-described structure according to the present invention has an advantage in terms of the manufacturing method.

Above all, since the boron silicide film is more stable than the boron film conventionally used as a diffusion source, the use of the boron silicide film not only facilitates process control but also enables various process designs. In addition, since the boron silicide film itself contains a large amount of boron, the problem of impurity migration from the semiconductor region to the connection region is solved by compensating for the lost boron. More specifically, at the junction of the tungsten silicide film and the P + semiconductor region, for example, boron is lost from the junction due to an absorption phenomenon in which boron atoms migrate from the junction to the tungsten silicide layer.

The boron silicide film of the present invention effectively compensates for lost boron.

Referring to the accompanying drawings, preferred embodiments of the present invention will be described in detail below. 1 (a) to 1 (c) show process steps of an impurity diffusion process according to an embodiment of the present invention. In the step (a) of Fig. 1, the active layer of the silicon layer, ie, the silicon substrate 1, is exposed by cleaning. When the silicon substrate 1 includes an oxide film or the like, a process commonly used for removing the oxide film using hydrofluoric acid or the like is performed, followed by removal of the native oxide film. In particular, the natural oxide film covering the surface of the silicon substrate 1 is removed. This step is essential because a simple treatment with hydrofluoric acid only results in the formation of an immediate natural oxide film when exposed to air. The step of removing the native oxide film is set inside, for example, a vacuum chamber having a background pressure of 1 × 10 ⁻⁴ Pa or lower, for example, introducing hydrogen gas for a predetermined duration to a silicon substrate that is heated above 850 ° C. It includes a step. In this process, hydrogen gas is introduced until the internal pressure of the chamber is 1.3 × 10 ⁻² Pa. This process removes the native oxide film from the surface of the silicon layer to expose a chemically active silicon surface that can remain active for a long time. Alternatively, the native oxide film can be removed by etching with dilute hydrofluoric acid or by argon sputtering in vacuo, but the following steps must be taken immediately when using these methods.

3 is a graph of the flow of the sheet resistance of the diffusion layer after the device is completed and diffused to the initial vacuum of the chamber (here 1 Torr = 133 pa) in FIG. 1 (a). 3 shows that the sheet resistance flows significantly at 5% or more for a vacuum degree of 5 × 10 ⁻⁷ Torr. If a sufficiently high vacuum is not achieved, a clean silicon substrate cannot be obtained or its activity cannot be maintained.

The step of FIG. 1 (b) comprises forming the boron silicide layer 2 on the active surface inside the same vacuum chamber. In this embodiment, the boron silicide layer 2 is formed through a vapor phase thermal reaction between boron and silicon. In particular, a processing gas containing boron, for example diborene (B ₂ H ₆ ) is introduced into the vacuum chamber at a predetermined pressure in a state in which the silicon substrate 1 is heated to a temperature higher than 600 ° C. In this method, the processing gas is pyrolyzed such that boron atoms or molecules containing boron react directly with silicon atoms contained in the substrate to form silicon compounds, ie boron silicides. In the present invention, the boron silicide is a compound containing 80% or more atoms of impurity boron and 5-20% of silicon atoms. This reaction proceeds both up and down at the initial silicon surface 119. If the heat treatment lasts for several minutes or longer at a temperature of 850 ° C. or higher, the boron atoms are introduced from the boron silicide layer 2 into the silicon substrate 1 and simultaneously form a boron diffusion layer. Therefore, the temperature of the heat treatment forming the chemical mixture charge is preferably lower than 850 ° C. to prevent more boron atoms from diffusing into the silicon substrate.

The resulting compound of the boron silicide film is shown in FIG. The ordinate plots the silicon content (atomic%) and the abscissa plots the temperature of the heated substrate or the film deposition temperature. As a result of the experiments of the inventors, it was found that the oxygen content is at the level of 1% or less, and thus boron occupies almost all of the compound except the silicon. Since the silicon content increases with increasing temperature, resulting in a saturated silicon content of 20% or less at a temperature of 900 ° C. or higher, the graph clearly shows the dependence of the silicon content on the film deposition temperature. Thus, it can be seen from this that the boron content does not decrease to levels below 80%. This boron content is greater than the solubility limit for boron atoms in the form of silicon substrates and solid solutions. Since boron silicides require 5% or more of silicon to form a chemically and physically safe diffusion source, it can be seen from the graph of FIG. 4 that the film deposition should take place at temperatures higher than 600 ° C.

In the step (c) of FIG. 1, boron atoms are diffused from the boron silicide layer 2 to the silicon substrate 1 to form a predetermined diffusion layer 3. The temperature required for diffusion should be set higher than the temperature used in the first (b) degree step.

FIG. 5 shows the observed resistance of the boron diffusion layer 3 upon completion of the first (c) degree step as shown in the continuous steps of FIGS. 1 (a) to 1 (c). The ordinate of the graph is the sheet resistance (Ω / sq), and the abscissa is the thickness (A) of the boron silicide (SiB) film. The boron silicide used in this case was obtained by evaporation at 900 ° C. and went through a diffusion step at 900 ° C. It can be seen from the graph that a stable sheet resistance is obtained in a SiB film deposited at a thickness of 100 GPa or more. Thereafter, a constant sheet resistance is obtained regardless of the film thickness, and the fact that the sheet resistance remains the same as the thickness of the SiB film is increased indicates that the diffusion concentration of boron is independent of the thickness of the SiB film. Thus, doping can work uniformly for SiB films 100 kPa or thicker, even with some flow of thickness.

The boron silicide film contains a higher amount of boron atoms than the solubility limit for boron, since the solubility limit is overdiffused from the boron silicide film to the silicon substrate as the atoms diffuse. In addition, the diffusion constant for boron inside the boron silicide film should be higher than the diffusion constant inside the silicon substrate. Therefore, the silicon content of the boron silicide film is not excessively increased.

A cleaning step prior to forming the boron silicide layer is necessary in the present invention to expose the active surface by removing the native oxide film from the silicon substrate. 6 clearly shows the effect of the cleaning step. The ordinate of the graph represents the sheet resistance (ρ _s ) of the boron diffusion layer, and the abscissa represents the thickness of the SiO ₂ natural oxide film before the substrate undergoes the cleaning step. In this case, a sample subjected to heat diffusion treatment at 900 ° C. was used for the measurement. It can be seen from the graph that a sheet resistance of 100 Ω / sq or less can be obtained by reducing the native oxide film to a thickness of about 10 GPa or less. This demonstrates that silicon from the substrate more easily interacts with boron atoms from the gas phase, creating a boron silicide film. Moreover, since solid phase diffusion occurs directly from the diffusion source, i.e., the boron silicide layer, without a natural oxide film, solid phase diffusion can be sufficiently performed. If the amount of residual natural oxide film is 10 Pa or more, and the sheet resistance of the boron diffusion layer is increased, impurity diffusion hardly occurs. That is, the presence of the native oxide film prevents the formation of a stable boron silicide film. In other words, the boron silicide film may be selectively formed only on a region having a native oxide film having a thickness of 10 kPa or less. The etching method comprises partially masking the boron silicide film on the SiO ₂ film by sputtering, thereafter etching the boron silicide film by an iterative process using nitric acid and hydrofluoric acid, and then with a step meter Measuring the height difference. In the above measurement, a sample prepared by heat treating the boron silicide film at 800 ° C. was used. On the other hand, the lift-off (lift off) method includes the steps of forming a film of boron silicide on a Si substrate having a pre-mask portion as a SiO ₂ film, and thereafter, the SiO film thickness to the step meter after removing the _second film masking (b) Measuring. However, in actual mass production, a simpler method for determining film thickness is required. A determination method in this regard will be described later.

The observed results are summarized in Table 1. This measurement was made on two samples with boron silicide films obtained under different conditions 1 and 2. Condition 1 includes introducing a processing gas for 600 seconds to form a boron silicide film, and Condition 2 includes introducing a gas for 1,000 seconds. Table 1 shows that the height difference b measured by the lift-off method under condition 1 is 37 kV, which is clearly different from 84 kV obtained by the etching method. With respect to the measurement result for the film obtained under the condition 2, the height difference b of 65 kV obtained by the lift-off method is clearly different from 140 kV obtained by the etching method. The etching method tends to have a larger film thickness. From this, it can be seen that the silicon inside the boron silicide film is formed by reaction of a processing gas such as diborene with the silicon substrate, and that the borgo silicide film is formed by thermal reaction between silicon and boron rather than being deposited.

Thus, the boron silicide film is effectively and selectively formed on the exposed surface of the silicon substrate in accordance with the present formation mechanism. The boron silicide film is not effectively obtained on the oxide film, and a film in which oxygen, boron, and silicon are distributed away from the surface, respectively, is formed. This film is an oxide film containing boron diffused from its surface, and therefore, differs from that of the present invention.

TABLE 1

Condition 1: gas introduction period 600 seconds

Condition 2: gas introduction period 1,000 seconds

The depth profile of atomic boron concentration inside the boron diffusion layer is shown in FIG. In the graph, atomic boron concentration (atoms / cm ³ ) and depth (nm) are shown in ordinate and abscissa, respectively. Concentration profiles were obtained on samples subjected to thermal diffusion treatment at 900 ° C. with different treatment periods using Secondary ion mass spectroscopy (SIMS). The boron diffusion layer deepens with increasing heat treatment time, while the boron concentration in the surface of the diffusion layer maintains a constant value of about 8 × 10 ¹⁹ stoms / cm ³ for a duration of 10 to 60 minutes. This particular concentration is considered to be the high solubility limit of boron in silicon.

FIG. 9 shows the results obtained on boron silicide films through experiments for testing resistance to chemicals. Boron silicide films formed on the exposed silicon surface prior to diffusion treatment were chemically treated using a number of chemical products. Thereafter, the sheet resistance ρ _s of the boron diffusion layer was measured. The sheet resistance obtained on the untreated sample is shown in dashed lines for comparison. Compared to the untreated sample, it can be seen that the sheet resistance is slightly increased in chemically treated samples using nitric acid and hot nitric acid, but this increase is small and almost negligible. Furthermore, it can be seen that chemical treatment using sulfuric acid, aqueous hydrogen peroxide and sulfuric acid, and hydrofluoric acid and phosphoric acid, respectively, did not affect sheet resistance. Therefore, it can be said that the boron silicide film is very safe for chemical products.

In FIG. 10, the chemical resistance of the boron film is shown to be compared with the results shown in FIG. The data plotted on the graph was obtained by measuring the sheet resistance of the boron diffusion layer obtained by the diffusion treatment using a boron film as the diffusion source. The boron film thus obtained was subjected to chemical treatment using a plurality of chemical products before the diffusion treatment. The level of sheet resistance obtained on an untreated chemical sample is shown in dashed lines in the graph. It can be seen that the sheet resistance is slightly increased in the samples treated with nitric acid, a mixture of sulfuric acid and aqueous hydrogen peroxide, and hydrofluoric acid, respectively. In particular, in samples treated with high temperature nitric acid, the sheet resistance is observed to rise to 3 kΩ / sq. Very high resistance occurs due to decomposition of the boron film when treated with high temperature nitric acid, which makes it impossible to sufficiently diffuse the boron atoms. In conclusion, the boron film is inferior to the boron silicide film with respect to chemical resistance.

A second embodiment according to the impurity diffusion process of the present invention will be described with reference to FIGS. 11 (a) to 11 (d). Step 11 (a) includes cleaning the Si substrate 101 for removing the native oxide film from the surface. This step is similar to the step shown in FIG. 1 (a). Subsequently, in step 11 (b), the boron film 102 is deposited on the exposed active surface of the Si substrate 101. This step differs from that shown in FIG. 1 (b) of the first embodiment in that the boron film 102 is deposited once on the surface of the substrate in the boron silicide rod of the first embodiment. Thereafter, in step 11 (c), the boron film 102 is replaced with the boron silicide film 103. Since the boron film is chemically unstable compared with the boron silicide film, it is preferable that the boron film 102 be immediately placed in an N ₂ gas atmosphere or react to form a silicide. Otherwise, the boron film is exposed to air and easily oxidized. When the boron film reacts with the boron silicide film 103, a very thin boron diffusion layer is simultaneously formed between the Si substrate 101 and the boron silicide film 103. In the final step of FIG. 11 (d), atomic boron in the boron silicide film 103 diffuses into the Si substrate 101. This eleventh step (d) is performed in the same manner as the one shown in FIG. Moreover, the boron diffusion layer 104 can be freely controlled by further diffusion treatment at higher temperatures than those used when reacting boron and silicon to obtain boron silicides. Further diffusion treatment at higher temperatures, for example, increases the concentration of diffused boron on the surface since the concentration depends on the solubility limit as a function of temperature.

The eleventh step (b), which is the feature step in this embodiment, is also described in more detail below. After completion of the substrate cleaning in step 11 (a), introduction of hydrogen gas used for removal of the native oxide film is stopped, and the temperature of the substrate is set at a level lower than 700 ° C., in which boron does not break the silicide reaction. After maintaining a stable temperature and a target temperature, a process gas containing boron or a boron compound, ie, a gas of diborene (B ₂ H ₆ ), for example, has an internal pressure of 1.3 × 10 ⁻² Pa The boron film 102 is formed by introducing it to the surface of the Si substrate 101 for a predetermined duration of time under the conditions maintained. In this case the substrate temperature is set at a level lower than 700 ° C. needed to pyrolyze diborene and deposit boron. Suitably, the substrate temperature is selected within the range of 500 to 700 ° C. in view of accelerating the deposition rate. However, in the case of a CVD film, the film deposition at a substrate temperature of 400 ° C. leads to the formation of the boron film 102 containing a large amount of hydrogen. Alternatively, the boron film may be subjected to a deposition process at a temperature of 700 ° C or higher. In this case, as can be seen from the graph of FIG. 4, it is considered that the formation of the boron silicide film 103 proceeds partially at the same time as the formation of the boron film. The amount of boron absorbed, ie, the film thickness of the boron film 102, can be set to a desired level by controlling the substrate temperature and the duration and pressure of the diborene gas introduced into the chamber. The boron film is selectively formed on the exposed surface of the Si substrate while the thin film is formed. Thereafter, the boron film 102 thus obtained reacts to form the boron silicide film 103. In particular, the boron atoms inside the boron film 102 react with the silicon atoms inside the silicon substrate 101 to form the boron silicide film 103. Therefore, it can be seen that the boron silicon film 103 is selectively formed in the portion forming the boron film 102 on the exposed surface of the silicon substrate. When the boron film is formed on the oxide film, the boron atoms only diffuse into the oxide film. In the eleventh step (d), the boron diffusion layer 104 is formed using the boron silicide film 103 as a solid diffusion source.

In this embodiment, the boron film 102 is formed by pyrolysing diborene gas, and then allowing boron atoms obtained therefrom to be absorbed on the active surface of the Si substrate. However, the process according to the present invention is not limited thereto, and physical vapor deposition (PVD) including molecular beam epitaxy (CVD) chemical vapor deposition (CVD), vacuum deposition, sputtering and the like; Other processes such as may be well applied to the deposition of the boron film 102. Moreover, methods such as spin coating can be used. Thereafter, a low temperature process that can be performed at a level of room temperature can also be applied to form the boron film 102.

The process of this embodiment includes the step of forming the boron film 102 once and then heat treating it to obtain the boron silicide film 103. As described above, the boron film 102 can be easily etched, particularly using chemicals. Therefore, when selectively forming the boron diffusion layer 104 or the boron diffusion region, it is preferable to pattern the boron film 102 using the process of this embodiment. It can be seen from the graph of FIG. 10 that high temperature nitric acid can be used well as an etching solution, for example. Alternatively, ion milling or dry etching may be used instead of wet etching.

Differences in the chemical properties between the boron silicide film and the boron film can be used for accurate control of the dopant concentration. Generally, when B ₂ H ₆ is applied at 600 ° C. or higher, an unreacted boron film remains on the boron silicide film that has already reacted with silicon. In other words, the absorbed boron layer consists of a boron silicide layer and a boron layer in the case of such treatment conditions. The presence of the boron film in the diffusion step is an undesirable result such as instability to the chemical treatment of the boron film in the treatment step between the formation of the absorbed boron layer and the solid phase diffusion and non-uniform distribution of sheet resistance depending on the distribution of the film thickness. Generates. Thus, the removal of the boron film prior to solid phase diffusion is very effective in obtaining accurate control of the carrier concentration in the boron doped layer. Similarly, in the case of B ₂ H ₆ implantation at a temperature lower than 600 ° C., the boron film is partially converted to a boron silicide film by a heat treatment of 600 ° C. or higher and the unreacted boron film is selectively removed before solid phase diffusion. Therefore, if the silicide formation is limited only by temperature, the thickness of the boron silicide film is necessarily made uniform.

12 (a) to 12 (c), a third embodiment of impurity diffusion according to the present invention will be described below. In contrast to the first and second embodiments described above, wherein silicon atoms for the boron silicide film are applied to the silicon substrate, the third embodiment includes supplying both boron atoms and silicon atoms by gas supply. In step 12 (a), the native oxide film is removed from the surface of the Si substrate 301. This step is similar to the first and second embodiments described above. FIG. 12B illustrates supplying diborene (B ₂ H ₆ ) and dicrosilane (SiH ₂ Cl ₂ ) as a gas for forming a boron silicide film on the exposed active surface of the Si substrate 301. Include. The vacuum chamber and wafer were both heated to 800 ° C. during this step. Be selectively deposited on the surface of the boron silicide film, for example 1 × 10 ^-3 Torr of pressure diborane alkylene with 1 × 10 ^-6 Torr Si substrate 301 at about a rate of 10Å / min by the silane as thickeners of Can be. In this embodiment, the boron silicide film 302 is formed on top of the surface of the Si substrate 301. Since both boron atoms and silicon atoms are supplied externally through pyrolysis of gas, the boron silicide film becomes one of the deposition forms. The use of silane (SiH ₄ ) as the gas for supplying silicon atoms can form boron silicide films at temperatures lower than about 500 ° C.

In the case of manufacturing the deep diffusion layer, in the sequential twelfth step (c), the boron atoms inside the boron silicide film are thermally diffused to the silicon substrate 301 to form the boron diffusion layer 303. The characteristic of this embodiment compared to the conventional process based on epitaxial growth of silicon containing impurity atoms is that the boron silicide film according to the present invention contains boron as a main component. In particular, boron is used in membranes in amounts much higher than the solubility limit in silicon and in amounts of 50% or more of the entire membrane. Membranes obtained by conventional epitaxial growth contain less boron than the solubility limit, and their structure is also based on silicon.

An impurity diffusion process according to a fourth embodiment of the present invention will be described below with reference to FIGS. 13 (a) to 13 (e). The process according to the present embodiment is an improvement of the second embodiment, and prevents the diffusion (external diffusion) of boron atoms from the silicide film to the outside during the reaction or diffusion of silicon and boron to form boron silicide, An overcoat is formed for the purpose of preventing oxidation. Step 13 (a) includes cleaning the surface of the Si substrate 111. In the next FIG. 13 (b) step, the boron film 112 is deposited on the surface of the Si substrate 111, and this step is performed in the same manner as the step referred to in FIG. 1 (b). Then, the boron film 112 is covered with the overcoat 113 in the next step 13 (c).

Thereafter, in the step 13d, the boron film 112 is heat-treated at a substrate temperature of 700 ° C. or higher to convert the boron film into the boron silicide film 114. In the final step 13 (e), boron is diffused into the substrate 111 using the boron silicide film 114 as a diffusion source. As a result, the boron diffusion layer 115 is formed at the boundary between the Si substrate 111 and the boron silicide film 114 at the same time and external diffusion is prevented by the overcoat 113. That is, the overcoat 113 prevents boron diffusion from the boron silicide film 114 into the film formed (not shown) on the upper side thereof. The overcoat may be made of, for example, a silicon nitrate film and may also be formed by CVD or the like. The overcoat is formed at a temperature lower than 700 ° C. to avoid formation of a silicide film from the boron film.

A fifth embodiment according to the impurity diffusion process of the present invention is described below with reference to FIG. In a first step A, the surface of the Si substrate 121 is cleaned. In a next step (B), a boron silicide film 122 is formed directly on the Si substrate 121. In this case, the substrate is heated to 700 ° C. or higher to simultaneously form the boron diffusion layer 123 between the boron silicide film 122 and the Si substrate 121. That is, the step (B) includes a thermal diffusion process to introduce boron as an impurity from the boron silicide film 122 to the silicon substrate 121.

As described above, the process according to the present embodiment is the first shown in FIGS. 1 (a) to 1 (c) in that the processing step for forming the boron silicide layer and the diffusion step are performed in a single step. It differs from an Example. Boron diffusion layer 123 having a desired depth profile of impurity concentration may be obtained by controlling the processing steps for forming the boron silicide film and controlling the temperature and duration of heating of the substrate. With regard to the duration of various heat treatments, reference may be made to the graph shown in FIG. In this case, the substrate is heated and annealed at a temperature setting within the range of about 1,100 ° C.

However, the step of forming the boron silicide layer and the diffusion step are generally distinguished, and conditions such as temperature and air pressure are different from each other. In separating and treating the steps, the diffusion step or annealing step is carried out in a vacuum or inert gas environment. By performing the above steps, a boron diffusion layer 123 using the boron silicide film 122 as a diffusion source is formed while simultaneously activating impurities such as boron atoms. The boron impurity diffusion layer 123 having a desired impurity concentration and connection depth can be obtained by adjusting annealing conditions such as substrate temperature and heating duration. The boron silicide film 122 formed by the process of this embodiment is annealed in the same vacuum chamber, but the process need not be limited to the form as described above, and another apparatus using the lamp annealing process by removing the substrate from the vacuum chamber. Modifications such as annealing within are also possible.

Once the boron silicide film is formed, special care must be taken to set the conditions for the heat treatment. FIG. 15 shows the film resistance of the diffusion layer obtained by thermally annealing in an N ₂ gas environment at 900 ° C. using a boron silicide film formed at 800 ° C. as the diffusion source. The abscissa represents the time interval in which the diffusion layer stays at 800 ° C. before performing annealing at 900 ° C., and the ordinate indicates the sheet resistance of the diffusion layer and the sheet resistance in the plane of the layer obtained after annealing the diffusion layer at 900 ° C. Indicates agitation. The diffusion layer is left in the N ₂ gas environment and the 0 ₂ gas environment at 800 ° C. It is shown in FIG. 15 that the sheet resistance causes a very large change by oxygen contained in small amounts in the atmosphere even at low temperatures below the annealing temperature of 900 ° C. When the exposure time to oxygen is short, for example, at 800 ° C. for 30 minutes, diffusion is accelerated. When the exposure time is longer than 30 minutes or more at 800 ° C., the boron silicide film is oxidized to form a high sheet resistance. Therefore, the exposure time as well as the temperature and / or atmosphere must be adjusted during the conversion step from the diffusion step to the annealing treatment step. Preferably, the annealing treatment is performed under an environment where oxidation does not occur. If the environment contains unavoidable oxygen, the time and process during the conversion step must be controlled.

FIG. 16 shows the sheet resistance in the wafer and its fluctuations in the plane in the case of the diffusion layer obtained by maintaining at 800 ° C after diffusion and annealing at 900 ° C in an N ₂ gas environment using a boron silicide film formed at 800 ° C as a diffusion source. Indicates. The abscissa of the figure shows the exposure time of the diffusion layer at 800 ° C. It is evident from the figure that the sheet resistance is also increased by oxidation occurring on the diffusion layer after annealing.

It is concluded from the above that the heat treatment after the formation of the boron silicide film, ie the annealing as well as the annealing before or after the annealing, must be carried out both in a high vacuum or in an inert gas environment free of oxygen.

The annealing step is preferably carried out in an inert gas environment such as N ₂ gas or in a vacuum. If the annealing is performed in an active atmosphere containing oxygen gas, moisture, or the like, the surface of the boron silicide film is oxidized to generate non-uniform sheet resistance in the boron diffusion layer. FIG. 17 is a micrograph of the boron silicide film surface annealed and changed in an active atmosphere. It can be seen that the annealing process produces fine grains that exhibit a partially milky white appearance on the surface of the wafer. By observing the milky white part at 1000 times magnification, it can be found that it contains fine grains of boron oxide and boron silicon oxide. The sheet resistance of this part is very high. This is due to oxygen incorporated into the boron silicide film by oxidation.

The shape of the micro grains annealed under different environmental conditions are summarized in Table 2. The shapes of the fine grains obtained at different annealing temperatures and environments are given in the table above. The 0 table indicates that no fine grains were observed and the X table indicates the occurrence of fine grains. Table 2 shows that no fine grains were formed by annealing at any temperature in a vacuum or nitrogen gas environment. In contrast, annealing in an oxygen gas environment generates fine grains in the temperature range of 500 ° C. to 800 ° C. by surface oxidation of the boron silicide film. Similarly, fine grains are also formed by annealing in an environment containing moisture.

In order to prevent the formation of the fine grains, diffusion must be carried out at a temperature of 800 ° C. or higher. Moreover, the heating rate or cooling rate from high temperature to achieve the height temperature for the diffusion step should be set at 10 ° C / min or higher. By increasing the temperature rise and fall rates, the treatment time in the temperature range from 500 ° C. to 800 ° C. can be reduced to prevent the formation of fine grains. The initial heating temperature for the boron silicide layer from room temperature should be lower than 500 ° C. If the initial temperature is higher than 500 ° C., the generation of fine grains cannot be prevented.

TABLE 2

In manufacturing a semiconductor device according to the impurity diffusion process of the present invention, there may be a case where the boron silicide layer used as the solid phase diffusion source has to be removed. However, the boron silicide layer is chemically and physically very stable so that the etching is useless. In this case, oxidation can be used in reverse to facilitate removal of the boron silicide film. Examples of the removal process are shown in FIGS. 18 (a) to 18 (d). In this process, the boron silicide film 2 formed directly on the surface of the Si substrate 1 is once oxidized, for example, by wet oxidation for about 5 minutes at a substrate temperature of 400 ° to 800 ° C. Dry oxidation processes may be used instead of wet oxidation. In this manner, an oxide film 401 is obtained from the boron silicide film. Therefore, the boron silicide film is oxidized and can no longer be resistant to chemicals, and is easily removed by, for example, etching with hydrofluoric acid. 18 (b) and 18 (d) are referred to by reference to the concentration profile of the boron silicide film after and before the oxidation treatment. Simple comparisons of concentration profiles indicate that large amounts of oxygen are introduced into the boron silicide film after oxidation treatment.

19 shows the oxidation characteristics of the boron silicide film. In the graph, the film thickness of the boron silicide film before and after oxidation treatment and the sheet resistance of the diffusion layer after annealing are shown on the ordinate. The boron silicide film is easy to oxidize, and the film whose thickness before the oxidation treatment is about 130 mm 3 is easily reduced in thickness by oxidation. The oxidation rate of the boron silicide film is much lower than that of the boron film, but sufficiently higher than that of the silicon substrate. This means that the boron film is oxidized at a low temperature below 400 ° C., but the boron silicide film is difficult to oxidize in the same temperature range. At elevated temperatures not higher than 800 ° C., the boron silicide film can be easily acidified but the Si substrate is not oxidized at all. Thus, the boron silicide film can be selectively removed without affecting the structure under the substrate surface by first oxidizing the boron silicide film well only in the temperature range of 400 ° C to 800 ° C and then removing the oxide film with hydrofluoric acid. . It is not good to oxidize above the temperature because the Si substrate is also oxidized at a high temperature of 800 ° C or higher.

A sixth embodiment according to the impurity diffusion process of the present invention is shown in FIGS. 20 (a) to 20 (d). First, the surface of the Si substrate 151 is cleaned or activated in step 20 (a) in the same manner as in the above-described embodiment. In the next step 20 (b), a boron silicide film 152 is formed on the surface of the Si substrate 151. The step of FIG. 20 (b) may be executed in the same manner as the step of the first embodiment shown in FIG. 1 (b). In the next step 20 (c), the overcoat 153 is formed on the boron silicide film 152. The overcoat 153 prevents the occurrence of external diffusion.

In the step shown in FIG. 13 (c) of the fourth embodiment, the overcoat 113 is formed on the boron film 112. However, in the present embodiment, it is different from that described above, and the overcoat 153 is formed on the boron silicide film 152. In the last step of FIG. 20 (d), a thermal diffusion process is performed to form the boron diffusion layer 154 between the boron silicide film 152 and the Si substrate 151. The step (d) of FIG. 20 may be executed in the same manner as the step of the first embodiment shown in the drawing of (c). The overcoat 153 prevents the occurrence of external diffusion and improves the homogeneity of the sheet resistance of the boron diffusion layer 154.

The silicon nitride film or silicon nitrogen oxide film is good as an overcoat, and most preferably, a Si ₃ N ₄ film and a SiON film terminated by a CVD process are preferred. The overcoat is well formed at a low temperature not higher than 850 ° C. to prevent boron atoms from diffusing into the Si substrate 151 in large quantities. Silicon nitride and silicon nitrogen oxide films are suitable as overcoats because the diffusion rate of boron atoms therein is very low.

21 shows the depth profile of boron atoms in the boron film using the silicon nitride film as a barrier. The depth profile can be obtained by depositing a boron film on the surface of a Si substrate including a nitride film and then annealing the composite layer structure to analyze the sample obtained by AES (acoustic emission spectroscopy). As clearly observed from the profile of FIG. 21, the silicon nitride film blocks boron atoms and prevents them from reaching the Si substrate. Therefore, diffusion of boron atoms into the external environment can be prevented by forming a silicon nitride film as an overcoat on the boron silicide film.

FIG. 22 provided as a comparison means is a depth profile of boron concentration inside the boron diffusion layer when the silicon oxide film is used as a barrier instead of the silicon nitride film. Since the boron atoms diffuse into the silicon oxide film at a high rate, the boron atoms easily penetrate into the silicon oxide film. 22 shows that the boron atoms have not yet migrated to the Si substrate through the silicon oxide film thickness, but the boron atoms easily reach the Si substrate and diffuse into it by increasing the annealing temperature or lengthening the annealing time.

The diffusion treatment was carried out with or without an overcoat, and the dispersion of sheet resistance ρ _s in the diffusion layer was measured. The results are shown in FIGS. 23 (a) to 23 (f). The process comprising steps 23 (a) to 23 (d) is a process in which a silicon nitride overcoat is used, and another process comprising steps 23 (e) to 23 (g) as well. Is a step of not using the overcoat 411. The diffusion layer obtained through the former process has an average sheet resistance of 72.9 Ω / sq with a change of σ _s of 4.2% relative to the average sheet resistance (ρ _s ), and the diffusion layer obtained through the latter process has an average sheet. It has an average sheet resistance of 80.1 Ω / sq with a change σ _s of 9 7% with respect to the resistance. Finally, the use of the overcoat 411 prevents the oxidation of the boron silicide film and the occurrence of external diffusion during the diffusion treatment so that the fluctuation of the sheet resistance in the impurity diffusion layer 3 is less than ½ of that of the diffusion layer obtained without using the overcoat. do.

With reference to FIGS. 24 (a) to 24 (c), a seventh embodiment of the impurity diffusion method according to the present invention is described below. First, in FIG. 24 (a), the boron silicide film 192 is formed on the surface of the Si substrate 191. A boron silicide film is used as the diffusion layer to effect solid phase diffusion to establish the boron diffusion layer 193. This step is the same as that described in the fifth and sixth embodiments. This embodiment is characterized by the next step, FIG. 24 (b), and includes removing the residual boron silicide film 192 remaining after the diffusion step. The boron silicide film is removed to lower the electrical contact resistance for the boron diffusion layer 193, which process includes selectively or wholly etching the boron silicide film 192. Since the silicide film 192 has a relatively high resistance, removal is required in this case to achieve a low resistance contact. Thus, Figure 24 (b) includes wet etching the boron silicide film 192 using a mixed melt of hydrofluoric acid and HNO ₃ . In FIG. 24C, a metal film is formed on the surface of the boron diffusion layer of the boron diffusion layer 193 used as a direct connection portion. In particular, as described above, the metals used for the metal film 194 are Ti, Co, Mo, and W. In addition, polysilicon or amorphous silicon doped with impurities may be used in place of the above-described metals.

In a modified method, the removing step of FIG. 24 (b) is subdivided into FIGS. 24 (ba) and 24 (bb) degrees. FIG. 24 (ba) includes converting the boron silicide film to a film 195 having boron oxide and silicon oxide. This step proceeds in the same order as described with reference to FIG. As described above, the final film having boron oxide and silicon oxide can be easily removed because the chemical and physical stability is lower than that of the boron silicide film. In particular, the film containing the oxide is removed by wet etching with hydrofluoric acid in FIG. 24 (bb). Optionally, dry etching may be performed by applying acceleration characteristics based on F or C1 instead of performing the 24th (ba) and 24th (bb) degrees.

With reference to FIGS. 25 (a) to 25 (e), an eighth embodiment according to a method for manufacturing a semiconductor device of the present invention is described below. In this embodiment, an impurity diffusion method is used to form the source / drain regions of the MOS transistors. Step 25 (a) includes forming a device isolation region 202 having a field oxide film by LOCOS that oxidizes the surface of the N-type Si substrate 201. Thereafter, by integrating the gate insulating film 202, the gate electrode 204 is formed on the active region surrounded by the device isolation region 202. The surface of the gate electrode is covered with an oxide film 205. After etching and treating the oxide film 205 provided on the surface of the substrate for doping with hydrofluoric acid, the wafer is placed inside the high vacuum chamber, and the residual natural oxide film having a thickness of about 20 kPa from the surface of the N-type Si substrate 201 is formed. The cleaning process is performed to remove the and to obtain the area having the active surface.

In the same chamber described above, the step 25 (b) of depositing the boron film 206 on the entire surface of the substrate is performed immediately after removal of the natural oxide film of step 25 (a). In this embodiment a partial pressure of diborene (B ₂ H ₆ ) gas of 5 × 10 ⁻⁵ Torr is introduced onto the surface of the substrate heated to 600 ° C. for 2,000 seconds to deposit a boron film. Therefore, the boron film 206 of 500 m thickness is absorbed on the surface of the substrate. Generally this absorption treatment is performed well at a substrate temperature of 300 to 700 캜.

Step 25 (c) has a step of converting the boron film 206 into the boron silicide film 207. This step is performed to anneal the boron film for 60 minutes in an inert gas atmosphere such as nitrogen or in vacuo, and maintains the substrate temperature at 800 ° C. In this method, the boron film absorbed on the active surface of the Si substrate 201 is selectively converted to the boron silicide film 207. In this step, the boron atoms thinly absorbed on the device isolation region 202 and the oxide film 205 diffuse into the oxide film because they are not in direct contact with the Si substrate 201. However, when they are absorbed thick they retain the same absorbency. The treatment for carrying out the thermal reaction is performed well in the temperature range of 700 to 1,000 ° C. and in an inert gas atmosphere without water and oxygen to prevent the occurrence of oxidation.

The residual boron film 206 is selectively removed in the step 25 (d). This step is performed by applying nitric acid to the surface of the substrate. Since the boron silicide does not dissolve with nitric acid, the boron silicide film 207 remains intact. Annealing is performed to form the source region 208 and the drain region 209 using the boron silicide film 207 as a diffusion source. The temperature or annealing temperature for the thermal diffusion treatment is set higher than the temperature used to form the boron silicide film in step 25 (c). In this embodiment, it is selectively removed from regions other than the source region 208 and the drain region 209 which are converted to boron silicide. In fact, the boron atoms diffuse into the silicon substrate in the twenty-fifth (c) degree step of converting the boron film 206 into a boron silicide film, and thus, the twenty-five (e) step is not always necessary. In the case where the diffusion depth is limited only by the step 25 (c), it is possible to make the depth of the diffusion region thin as compared with the thickness of the boron silicide film.

A ninth embodiment according to the present invention is described below with reference to FIGS. 26 (a) to 26 (e). Similar to the embodiment described above, the source region and the drain region for the MOS transistor are formed using the impurity diffusion method according to the present invention. Step 26 (a) also includes forming a device isolation region 212 having a field oxide film formed on the surface of the N-type Si substrate 211. Thereafter, a gate electrode 214 is formed at the center of the active region surrounded by the isolation region 212, and a gate insulating film 213 is formed between the isolation region and the gate electrode 214. Thereafter, after covering the gate electrode 214 with an oxide film, the oxide film is removed only from the top of the gate electrode 214 to form the sidewall 215. Sidewalls are utilized to realize the LDD structure. Thereafter, the gate oxide film 213 on the surface of the Si substrate is etched to provide source and drain regions. Finally, the wafer is positioned inside the vacuum chamber to remove the native oxide film from the surface of the source and drain regions to expose the active surface on the Si substrate 211.

Next, in step 26 (b), the boron film 216 is formed on the entire surface of the substrate 211. This step must be processed immediately after step 26 (a) so that the exposed active surface obtained in step 26 (a) can be utilized in step 26 (b). Deposition of the boron film is accomplished in the same manner as in step 25 as already described with reference to FIGS. 25 (a) to 25 (e). The boron film 216 thus obtained is directly thermally treated to obtain a boron silicide film 217. Also, the step 26 (c) is similar to the step 25 (c) shown in FIGS. 25 (a) to 25 (e).

However, in this embodiment, not only the boron film of the active region but also the boron film of the gate electrode 214 is reacted to obtain a boron silicide film. This occurs in this embodiment because the boron film 216 is deposited on the gate electrode 214 in direct contact with the gate electrode constituent material containing silicon, such as polysilicon, for example. Thus, silicon atoms react directly with the boron atoms to form a boron silicide film. However, since the sidewall is not made of silicon, the boron film formed on the sidewall 215 does not react to form the boron silicide film. This means that only the surface of the gate electrode 214 and the surface of the source-drain region 217 selectively react to form a boron silicide film.

In step 26 (d), an unnecessary boron film 216 such as boron in the sidewall is removed. If the boron film deposited in step 26 (b) is thin enough to leave no residual boron film, step 26 (d) may be omitted. Step 26 (d) may be performed in the same manner as step 25 (d) as described above with reference to FIGS. 25 (a) to 25 (e). It can be seen from the figure that the gate electrode 214 having a reduced thickness is positioned between the gate insulating film 213 and the boron silicide film 217. In the final step 26 (e), the source region 218 and the drain region 219 are formed by annealing the structure obtained in the step so that the boron atoms diffuse from the boron silicide film. At the same time as the source and drain regions are formed, the gate electrode made of polysilicon is heavily doped with boron impurities to form the P + gate electrode 220. Use of a silicon nitrogen oxide film having a oxide film or a composite film composed of a silicon nitrogen film as the gate insulating film 213 effectively prevents boron from penetrating into the substrate from the gate electrode 220 through the gate insulating film 213.

In this example, boron was used as a P-type impurity. Since boron enables formation of a uniform boron silicide film on the surface of the silicon substrate, the use of boron is preferable. Thus, any P-type impurity may be used as well, provided a uniform silicide film is provided on the surface of the silicon substrate. Furthermore, not only P-type impurities but also N-type impurities such as phosphorus can be used to enable an N-type impurity diffusion layer using a silicide as a solid diffusion source. In addition, modifications of the above-described embodiments may be made without departing from the scope of the present invention.

Referring to the accompanying drawings, a process for evaluating a semiconductor device, in particular, a process for evaluating the film thickness of an impurity film according to the present invention will be described below.

27 is a block diagram showing a process for evaluating the film thickness of an impurity diffusion source.

In this step, the thickness of the boron film 503 formed on the surface of the silicon substrate 501 as the impurity diffusion source is evaluated. The process comprises irradiating a light source, that is, a projection beam from a helium neon (He-Ne) laser 511 to the surface of the boron film 503 at an entrance time θ, and detecting the reflected light with the optical detector 514. Consists of steps. The incident light beam path and the reflected light path include optical systems 512 and 513 that adjust the polarization plane, respectively. This configuration can be seen in FIG. The thickness of the boron film 503 can be evaluated by observing the density change of the polarization component of the reflected light with respect to the density of the polarization component of the incident light, and the change of the density comes from the change of the refractive index. Film thickness evaluation devices based on polarization analysis are commercially available as ellipsometers. In a special ellipsometer, a square wave plate is used as the optical system 512 to convert incident light into elliptical polarization, and then the reflected light is passed through an analyzer, that is, the optical system 513 to form linearly polarized light along the polarization plane. The rotation angle of the analyzer resulting in the minimum light density is automatically obtained, and the refractive index of the thin film and thus the thin film thickness is calculated by the computer 515. This method is commonly employed in semiconductor manufacturing lines to evaluate the thickness of silicon oxide and silicon nitride films.

However, the method using the ellipsometer is not suitable for thin films having a thickness of 200 GPa or less, since it is theoretically impossible to obtain two parameters, namely refractive index and film thickness, in such thin films. As a result, the refractive index is normally input to the computer at a predetermined value, thereby accurately obtaining only the film thickness. However, the film thickness of the boron film or the boron silicon mixed film cannot be obtained because its refractive index is not known, unlike in the case of the silicon dioxide film.

Therefore, the refractive index input to the ellipsometer is obtained as follows. First, the thickness of the boron film is measured by conventional mechanical means, and then a refractive index corresponding to the same thickness is obtained by a calculator. 28 shows a boron film sample in cross section, the thickness of which is measured by mechanical means. The boron film 503 deposited on the surface of the silicon substrate 501 was partially removed using the silicon oxide film sputtering film 521 as a mask, and the silicon oxide film 521 was then selectively removed to thereby remove the height difference d. A boron film having was obtained. This height difference was measured by mechanical means of the contact probe type to obtain the film thickness. The boron film 503 may be selectively removed from the surface of the silicon substrate 501 because it is completely chemically different from the silicon substrate 501. Moreover, the boron film can be easily oxidized at room temperature. That is, the boron film can be removed by oxidizing with nitric acid at about 80 ° C., and the oxide film can be removed again using hydrofluoric acid. When the boron film 503 is thick, the steps of nitric acid treatment and hydrofluoric acid treatment may be repeatedly performed to selectively remove the entire boron film from the silicon substrate. Since a part of the masking film, that is, the silicon oxide film 521 is also lost by an acid treatment process, first, a film having a thickness of 1 μm or more must be formed. After the boron film 503 is patterned, the masking film 521 is selectively removed using hydrofluoric acid. The boron film 503 remains unreacted because it is etched with hydrofluoric acid, and the silicon substrate is hardly lost in the above process. The film thickness lost by the said process is 10 kPa or less.

The thickness of the boron film 503 was evaluated with the structure shown in FIG. 28, and the result is given in FIG. The film thickness was obtained by a linear relationship between the film thickness and the duration of introduction of the diborene gas for depositing the boron film 503. The correlation between the film thickness obtained by the optical measuring method using an ellipsometer and the film thickness obtained by the mechanical means as shown in FIG. 29 is given in FIG. The refractive index for the same sample used in the measurement obtained with the results of FIG. 29 was selected and the refractive index thus obtained was used to evaluate other samples with different thicknesses. The results are shown in the graph of FIG. It was found that the correlation between the thickness obtained by the ellipsometer and the thickness obtained by the mechanical means had a 100% relationship, and the boron film would have a uniform structure regardless of the film thickness. The fact that a uniform structure is formed and the fact that the boron film can be clearly distinguished from the silicon substrate with a clear boundary enable the evaluation using optical means. In an actual manufacturing line, the refractive index input to the ellipsometer need not be exactly the same as shown in FIG. 30, but the estimated film thickness can be obtained using the refractive index 1.45 of the oxide film as an input value.

The actual film thickness can be derived from the estimated film thickness by verifying the correlation between the estimated film thickness and the mechanically obtained film thickness. That is, the thickness of the boron film can be evaluated using an ellipsometer without obtaining its refractive index. First, the estimated film thickness is obtained from the estimated refractive index to calculate the actual film thickness. That is, the film thickness of the boron film can be evaluated using an ellipsometer without obtaining its refractive index. The estimated film thickness can be obtained with the estimated refractive index, and a correlation coefficient between the estimated film thickness and the film thickness measured by mechanical means must be established in advance so that the following film thickness evaluation can be performed using only the ellipsometer.

FIG. 31 shows a boron film deposition apparatus equipped with an optical means for evaluating the film thickness, that is, an ellipsometer. The silicon wafer 533 in which the boron film 534 is to be formed on the surface of the silicon wafer is mounted on the support 532 which is located inside the apparatus 531 for depositing the boron film. The boron film deposition apparatus 531 includes transparent windows 538 and 539. Light rays are irradiated from the light source and the optical system 535 to the surface of the silicon wafer 533 through the transparent window 538, and light rays reflected from the surface are passed through the transparent window 539, similar to the transparent window on the incident side, through the optical system and the optical detector. It is introduced into 536. The film thickness of the boron film is automatically calculated using a computer from the output of the optical detector 536 and the observed rotation angle of the optical system. The boron film deposition apparatus 531 includes a chamber capable of obtaining a high vacuum of 10 ⁻⁶ Torr or more. The boron film 534 is formed directly on the silicon substrate 533 without interposing a natural oxide film therebetween. Therefore, the apparatus should be composed of a high vacuum chamber in which no natural oxide film can be deposited in the chamber. The film thickness of the boron film 534 on the sample is evaluated by a non-contact method using a light beam at high vacuum. The use of probes to cause contact with the sample requires space within the chamber for the probe to operate mechanically. However, chambers of high vacuum are not desirable for devices of this type because the pressure inside the chamber is affected by external air pressure through the space for actuating the probe. It can be seen that the above-mentioned non-contact measuring method enables evaluation of the film thickness of the boron film inside the high vacuum chamber for the first time. The method also allows simultaneous evaluation of the film thickness of the boron film deposited inside the high vacuum chamber.

FIG. 32 (a) is a graph showing the growth of the boron film with the passage of time for introducing diborene (B ₂ H ₆ ) into the chamber. From this graph, the film thickness with the increase of the time for introducing the gas can be evaluated. Typically, the film deposition process is controlled to obtain a uniform thickness without deviating from the predetermined film thickness.

In the boron film forming apparatus provided with the optical measuring means as shown in FIG. 31, the film thickness is evaluated to stop the introduction of the diborene gas by a signal when the achievement of the predetermined thickness is detected. The detected film thickness can be obtained from the output of the optical detector or by computer calculation based on the output. Therefore, the impurity film of uniform thickness can be obtained by the apparatus which controls the formation of a film by feeding back the measurement signal about a film thickness to a gas pressure control part. If the film thickness is calculated from the output of the optical detector, the apparatus must be equipped with a computer.

Figure 32 (b) is a graph showing the signal for the film thickness obtained during the film deposition. In this graph, the horizontal axis represents the signal for the film thickness, and the vertical axis represents the gas pressure of the diborene gas. The boron film grows in the direction indicated by the arrow in the drawing with the introduction of the gas. For example, in forming a film having a thickness of 100 kPa, the gas pressure of the diborene gas can be controlled to zero when it is confirmed that the desired thickness is achieved by the output signal of the film thickness meter. Thus, by feeding back the observation of an optical thickness meter such as an ellipsometer to the means for controlling the growth of the impurity film, an impurity film forming apparatus capable of producing a film having good replicability and small thickness variation can be achieved. Since the light source of the optical thickness meter is in principle a point light source, the thickness distribution in the wafer can be evaluated by taking a plurality of points for evaluation. In addition, the output of the optical thickness meter, which is an electrical signal, can be easily fed back into the gas pressure or temperature for controlling film growth. In the case of ellipsometers, the optical detector is a photo-electric conversion element that easily generates an electrical signal corresponding to the film thickness. Thus, it can be seen that an automatic film deposition apparatus can be easily obtained.

33 shows a film thickness control process for film deposition without an optical means for evaluating the film thickness. In this step, the wafer on which the boron film is formed is taken out of the chamber and the thickness of the boron thin film is evaluated using an ellipsometer. Next, the film thickness obtained in the above manner is compared with the standard desired film thickness. If the thickness is thinner than the target thickness, the film may be reinserted into the chamber to continue film deposition, or may be etched to reduce the film thickness to a predetermined value. The film of the desired thickness thus obtained is then subjected to a diffusion process to diffuse boron into the silicon substrate. It can be seen that the process requires withdrawing the membrane from the high vacuum chamber each time the thickness is evaluated. As described above, the boron film is unstable enough to easily oxidize even at low temperatures such as room temperature. As a result, the process has poor accuracy in evaluating the film thickness. On the contrary, by using the impurity film forming apparatus provided with the optical means for film thickness evaluation, it is possible to evaluate the film thickness with high precision under high vacuum.

The above description was made using the boron film as a specific sample of a thin film for impurity diffusion. It was found from the experimental results of the present inventors that the optical film thickness evaluation is applicable to the thin film of the boron silicon composite. A thin film of boron silicon composite (boron silicide) is obtained by reacting boron in a gas with silicon on a silicon substrate at a temperature of 600 ° C. or higher, and cannot be obtained by simple deposition of boron on a silicon substrate as in the case of a boron film. The interface between the boron silicide film and the silicon substrate proceeds deeper into the silicon substrate as compared to the silicon substrate surface before the boron silicide film is formed. This phenomenon is similar to the case of forming a silicon oxide film on a silicon substrate by thermal oxidation. According to the analysis performed by the inventors, it was found that a boron silicon film having a uniform structure was formed along the thickness direction of the film. It was also seen that a distinct bonding surface was formed between the silicon substrate and the boron silicide film. Thus, it shows that evaluation using optical means such as ellipsometer is effective in this case as well. The boron silicide film is chemically more stable than the boron film. Therefore, additional measures are required to form the sample into the structure shown in FIG. After measuring the thickness by mechanical means, calculating the correction factor to obtain the actual optical film thickness, and then forming the structure shown in FIG. 28 is the same as in the evaluation of the boron film. However, in the case of a chemically more stable boron silicide film, the oxide may be oxidized with nitric acid and the etching with hydrofluoric acid may be repeatedly performed on the film to selectively remove only the boron silicide film from the silicon substrate to form a height difference. In fact, it was found that the silicon substrate was etched only 10 ms after about 10 iterations.

The boron film or boron silicide film mentioned in the above description of the present invention is formed by supplying diborene gas to the surface of the active silicon substrate from which the natural oxide film is removed. The chemically active surface of a silicon substrate that does not have a native oxide film cannot be obtained by conventional simple treatment with hydrofluoric acid, which means that the boron film or boron silicide film is pyrolyzed of diborene gas at a high temperature of 400 ° C. or higher in this process. Because it is formed by. In this case, before the film of the desired tissue is formed, an oxide film is easily formed at a high temperature of 400 ° C or higher. Even when the tissue is not subjected to high temperature treatment at 400 ° C. or higher, the surface of the silicon substrate is easily coated with an oxide film of about 10 mm thick when the surface is exposed to air containing air. The growth rate of the boron film or the boron silicide film is considerably lower when only about 10 GPa oxide film is present. Therefore, removing the natural oxide film or maintaining the active surface of the silicon substrate in the high vacuum chamber becomes a necessary condition. In order to form the impurity diffusion region, a boron film or a boron silicide film having a thickness of about 200 mm 3 is sufficient. Typically, the film is formed to a thickness of about 100 mm 3. For example, in order to obtain a diffusion layer having a concentration of 10 ²⁰ atoms / cm ³ and a depth of 0.1 mu m, an impurity diffusion layer having a thickness of about 10 mW is theoretically sufficient. Since the boron film is made of only 100% boron, that is, impurity atoms, and the boron silicon film (containing 5 to 20% of silicon atoms) contains about 80% or more of boron atoms, the thin film serves as an impurity diffusion source. Therefore, a diffusion layer having a small variation in thickness can be obtained by evaluating a film thickness of about 100 GPa using optical means.

In introducing impurities directly into the silicon substrate from a film containing 80% or more of impurities by diffusion, a thin impurity film of about 100 kV is used. Thus, not only accurate evaluation of the film thickness but also precise control of the film thickness can form a shallow diffusion layer having a thickness of 1 m or less.

In order to realize the optical evaluation of the present invention for the boron film or the boron silicide film, the silicon substrate should be free of surface oxide film. This is not only due to the above-mentioned reason that the growth of the boron film or the boron silicide film is delayed. For example, an accurate evaluation of the film thickness of a sample composed of a silicon substrate having a natural oxide film having a thickness of about 20 GPa and a boron film or a boron silicide film having a thickness of about 100 GPa formed thereon could not be performed. This failure is due to the existence of too many unknowns. Since the sample has a multilayer structure composed of a silicon layer, a silicon oxide layer, and a boron (or boron silicide) layer, three unknowns must be obtained. As a result, the thickness of the boron film cannot be obtained with an ellipsometer. Therefore, forming a boron film or a boron silicide film directly on the silicon substrate is an essential condition for enabling optical measurement. Although the optical constant, i.e., the refractive index of the silicon oxide film, is certainly known, the thickness of the boron film in the multilayer structure is very difficult to measure because the film thickness is unknown.

The above description of the present invention has been made in relation to a method based on polarization analysis using an ellipsometer as an optical means for evaluation. However, the present invention is not limited only to the polarization analysis method. In addition, the above embodiments have been described using a boron film or a boron silicide film as an impurity diffusion source. However, other impurity films may also be employed except for a film containing a high concentration of oxygen, such as a boron silicate glass (BSG) film in which the isolation of impurities occurs between the silicon substrate and the boron silicate glass film. In this case, the method according to the present invention cannot be applied because the arrangement of tissues along the film thickness direction becomes nonuniform. Further, it is proved that the method for evaluating the film thickness of the impurity diffusion source according to the present invention is applicable to the residual film obtained after thermal diffusion. That is, the thickness of the impurity film can be obtained before and after diffusion. As already explained, the boron film or boron silicide film cannot be formed in the oxide film but can be formed in both the silicon substrate and the silicon nitride film. Therefore, the present invention is not limited only to the use including the silicon substrate. An evaluation may be performed on a sample containing a boron film on a silicon substrate on which a silicon nitride film thicker than 10 times or more than the boron film is formed.

The semiconductor device according to the present invention will be described below with reference to the drawings and preferred embodiments.

First, the process of manufacturing the boron silicide film used for the semiconductor device of this invention is demonstrated again with reference to drawings.

1 (a) to 1 (c) show the manufacturing method and structure of the simplest form of the semiconductor device of the present invention. In the step shown in FIG. 1 (a), the active surface of the N-type silicon region 1 is exposed. In particular, the native oxide film covering the surface of the silicon region 1 is removed, for example, by heating the region in vacuum, etching with dilute hydrofluoric acid, and argon sputtering in vacuum. In a continuous step corresponding to FIG. 1 (b), boron silicide regions are formed on the active surface using diborene (B ₂ H ₆ ) such as boron containing gas. The silicon atoms in the silicon region 1 react directly with the boron containing molecule or boron atoms to form the boron silicide film 2. In this step, the reaction is simultaneously processed on both the upper and lower surfaces of the initial face. In the next step of forming the boron silicide film 2, the heat treatment temperature is set at a relatively high temperature so that boron atoms can be diffused from the boron silicide film into the silicon region 1 to form the boron diffusion region 3. Lasts a long time. In this method, the boron diffusion region 3 is formed simultaneously with the installation of the boron silicide film 2.

The composition of the boron silicide film is shown in FIG. In the graph of FIG. 4, the Si content by atoms is taken in the ordinate, and the processing temperature or film deposition temperature of the substrate is taken in the abscissa. As clearly shown in FIG. 4, the Si content depends on the film deposition temperature. Chemically and physically suitable diffusion sources are obtained only when a predetermined level or more Si content is achieved. Thus, the film is deposited at a temperature of 700 ° C. or higher.

Figure 9 summarizes the results of experiments testing the chemical stability of boron silicide films. The deposited boron silicide film undergoes various chemical treatments using a number of chemicals before the diffusion treatment of the film. In FIG. 9, the chemical treatment form applied to the sample is given in abscissa, and the observed sheet resistance ρ _s of the diffusion layer after diffusion treatment is given in ordinate. The sheet resistance of the chemically untreated sample is indicated by the dashed line. Sheet resistance is somewhat increased by samples following chemical treatment with nitric acid or hot nitric acid compared to untreated samples. However, this increase is small and the effects of chemical treatment of the sample are negligible and safe. Boron silicide films are very safe for chemical products.

In FIG. 10, the resistance of the boron film to chemicals is given in comparison with the results given in FIG. The lateral and longitudinal coordinates of the graph are the same as those in FIG. Sheet resistance is somewhat increased by samples treated with nitric acid, a mixture of aqueous hydrogen peroxide and sulfuric acid, and hydrofluoric acid, respectively. In particular, the sheet resistance can be seen to rise to 3 kΩ / sq in the sample treated with hot nitric acid. Very high resistance is due to the dissolution of the silicon film treated with hot nitric acid which is unsuitable for sufficiently diffusing boron atoms. The boron film is lower than the boron silicide film with respect to chemical resistance.

Preferred embodiments of the present invention are described in detail below with reference to FIGS. 34 to 40. An AP channel insulated gate field effect transistor (Metal Insulator Semiconductor Field Effect Transistor, hereinafter referred to as MISFET) as shown in FIG. 34 in its structural cross section is implemented according to the semiconductor device of the present invention. An example is described below. In the structure shown in FIG. 34, the P-type semiconductor region 612 formed on the surface of a portion of the N-type semiconductor region 611 includes a source and a drain of the MISFET. This embodiment is characterized in that the boron silicide region 613 is formed on the P-type semiconductor region 612. The boron silicide region 613 and the P-type semiconductor region 612 are formed in the order as shown in FIG. Moreover, the process step is designed such that boron silicide does not finally remain on the N-type polysilicon gate 614. The design of the process step is omitted from this description because it is not a major part of the present invention.

Referring to FIG. 34, the boron silicide region 63 effectively acts as a barrier to metal spikes that achieve electrical contact between the metal contact 616 and the P-type diffusion region 612 through the interlayer insulating film 615. . In a preferred embodiment, the gate electrode is made of polysilicon. However, this is within the spirit of the present invention if a bilayer electrode material comprising polysilicon and tungsten silicon is used as the electrode material. The structure as shown in FIG. 34 is obtained by the process as shown in FIGS. 25 (a) to 25 (e). The depth of the P-type semiconductor region 612 is shallow compared to the width of the deflection layer of the region 612 because the boron silicide region 613 effectively acts as a barrier to metal spikes. The width of the diffusion region 612 is thinner than the thickness of the boron silicide region 613. The impurity concentration in the diffusion region is less than the solid solubility of boron for silicon. The impurity concentration of the boron silicide region 613 is higher than the high solubility of boron with respect to silicon.

Referring to FIG. 35, a cross-sectional schematic diagram of a P-type channel MISFET having a P-type polysilicon gate 624 in accordance with another embodiment of the present invention is shown. This is similar to the structure shown in FIG. 34 and the MISFET of the present invention includes a boron silicide region 623 and a P-type semiconductor region 622 on the surface of the N-type semiconductor region 621. However, the MISFET of this embodiment is characterized in that it additionally includes a boron silicide region 623 on the P-type polysilicon gate 624. In this embodiment, all boron silicide regions 623 are formed simultaneously. 34 and 35, a BSG film, generally not boron silicide, is formed on the insulating film spacers 610 and 620. The semiconductor device as shown in FIG. 35 can be easily obtained by the manufacturing process shown in FIGS. 26 (a) to 26 (e).

An NPN bipolar transistor having a structure shown in cross-sectional view of FIG. 36 is described as a third embodiment of the present invention. Referring to FIG. 36, the N-type region is provided on the N-type collector region 632, and the P-type base region 633 and the boron silicide region 634 are the first (a) to the first (c). Are formed by the order described in relation to However, as a result of the CVD insulating film 636 patterning when forming the N-type emitter region 635, the boron silicide region 634 obtained as described above is partially provided to provide an arrangement as shown in FIG. Is removed. The P-type base region 633 and the insulating film 636 in addition to having the insulating film 636 at the outer periphery of the electrical junction of the P-type base region 633 and the N-type emitter region 635 according to the prior art. By providing a new boron silicide region 634 in between, a stable interface is obtained between the base face and the insulating film 636. As a result of this new structure, transistor characteristics with reduced noise are realized.

Referring to FIG. 1, the P-type base region 633 may be shallow to 0.1 μm or less in depth. Similarly, a cross-sectional view of the PNP bipolar transistor as in the fourth embodiment is shown in FIG. The PNP bipolar transistor includes a P-type collector region 641 and a P-type epitaxial region 642 on the N-type base region. Moreover, the P-type emitter region 644 and the boron silicide region 645 are provided with the insulating film 646 therebetween at the outer periphery of the above-described structure. Again in this case, the P-type emitter region 644 and the boron silicide region 645 are achieved by implementing the order described with respect to FIG.

As described above, the emitter with boron silicide region 645 exhibits improved resistance to metal spikes in electrical contact with the metal connections.

A fifth embodiment of the semiconductor device according to the present invention is shown in FIG. Referring to FIG. 38, a boron silicide region is provided between an impurity doped semiconductor region and a connection portion of a high melting point metal compound that provides an electrical contact therebetween. In the process of providing a tungsten silicide film such as a connection for a high melting point metal that does not melt under 1000 ° C. on the impurity doped semiconductor region 651 via the interlayer insulating film 652, the semiconductor film 654 generally includes a base, In particular, it is formed under the tungsten silicide film 653 to improve the adhesion of the tungsten silicide film 655 to the interlayer insulating film 652. To realize this structure, dopant atoms are often absorbed into the P-type semiconductor by the semiconductor film 654 during its fabrication step. As a result, the device experiences the problem of increased contact resistance because dopants are absorbed into the semiconductor film 654.

In order to overcome the problem of the above embodiment, the above-described impurity doping method forms and uses the P-type semiconductor region 651 in addition to the conventional structure, thereby forming a boron silicide region formed simultaneously with the formation of the P-type semiconductor region 651. A structure having 653 is realized. In this method, the compensation of the dopant atoms lost due to the above phenomenon is done by the above structure including a boron silicide region 653 containing a large amount of boron. Thus, the above-described problems occurring during the manufacturing process are reduced and a suitable and sufficiently low contact resistance is realized.

A sixth embodiment according to the present invention similar to the method described above is shown in FIG. Referring to FIG. 39, which is a cross-sectional view of the structure, a boron silicide region is provided between a connection of a high melting point metal and an impurity doped semiconductor region that is not melted at 1000 DEG C or lower to achieve electrical connection therebetween. FIG. 39 shows a structure including a tungsten region 664 and a P-type semiconductor region 661 that are electrically connected, and an imitation interlayer insulating film 662 is mixed therebetween. The boron silicide region 663 in this structure has the function of stabilizing the interface between tungsten 664 and the semiconductor region 661. A structural cross section including a contact having a barrier metal in the seventh embodiment according to the semiconductor device of the present invention is shown in FIG. In this case, the connection part may include, for example, a structure including titanium film 634 and titanium nitride as a barrier metal, or the connection part may be a metal connection part including aluminum, silicon, copper, or the like. It can be incorporated with the barrier metal described above to provide a antagonistic structure of the barrier metal with -Si-Cu.

In the structure shown in FIG. 40, a metal connection including a barrier metal is electrically connected to a P-type semiconductor region 671 having a boron silicide region 673 with a patterned interlayer insulating film 672 interposed therebetween. Is connected. This type of contact structure yields improved resistance and electron atom transport for metal spikes even if a thin impurity diffusion layer is provided in the semiconductor region 671.

As described above, the method for manufacturing a semiconductor according to the present invention is a diffusion method comprising utilizing a boron silicide film as a solid phase diffusion source for directly introducing impurity boron inside a silicon layer. Thus, the method is effective for forming an impurity diffusion layer having a high surface concentration and a thin junction. Therefore, the method is effective for realizing high density and large directization of the semiconductor device. Moreover, boron silicide films used as solid phase diffusion sources are chemically and physically suitable to allow for variations in semiconductor fabrication methods and improved degrees of freedom for the method design.

A method for evaluating an impurity film according to the evaluation method of the present invention comprises the steps of radiating a light beam to the surface of an impurity film, measuring the change in intensity of the reflected light and evaluating the film thickness from the measured values and the effective refractive index. Steps. Thus, the method is advantageous in that it is a fast method of automatically providing a film thickness by non-contact measurement. Moreover, using an apparatus for producing an impurity film having a vacuum chamber to directly form an impurity film therein, means for radiating a light beam inside the vacuum chamber, and optical means for evaluating the film thickness from the reflected light beam. It is effective to control the impurity film more accurately. In particular, the feedback of the film thickness output signal optically obtained to control the gas pressure or the temperature of forming the impurity film is more effective for obtaining the impurity film with a more precisely controlled film thickness.

Furthermore, an impurity diffusion layer having a lower scattering is obtained by the impurity doping method according to the present invention in which an impurity film is formed directly on a silicon substrate, the impurity film is optically measured, and the film is diffused after obtaining a predetermined film thickness.

Moreover, the Yal according to the present invention is a semiconductor device having a layer structure of boron silicide together with a semiconductor region having an impurity doped junction, which is firstly effective for achieving a high speed operating fine MISFET and bipolar transistor by a thin diffusion layer. Second, the device has a great effect on the reliability of semiconductor devices such as improved resistance to electronic principle movement at the contact portion and prevention of metal spikes.

Claims (2)

Placing a silicon substrate in a vacuum chamber of 850 ° C. or higher, removing the native oxide film formed on the surface of the silicon substrate, exposing the silicon substrate surface, and subsequently introducing B ₂ H ₆ into the vacuum chamber in the same vacuum chamber; And heating the silicon substrate temperature between 600 and 850 ° C., forming a boron silicide film comprising at least 80 atomic% boron and at least 5 atomic% silicon on the exposed silicon surface, subsequently, forming the boron silicide film And thermally diffusing boron of the boron silicide film on the silicon substrate at a temperature higher than the temperature of the forming step. Placing the silicon substrate in a vacuum chamber of 850 ° C. or higher, removing the native oxide film formed on the surface of the silicon substrate to expose the silicon substrate surface, and subsequently introducing B ₂ H ₆ into the vacuum chamber in the same vacuum chamber; Heating the silicon substrate temperature between 600 and 850 ° C. to form a boron silicide film comprising at least 80 atomic% boron and at least 5 atomic% silicon on the exposed silicon surface, and subsequently, a laser having a first polarization characteristic Irradiating incident light obliquely to the surface of the boron silicide film via a first polarizer, detecting a reflected light having a second polarization characteristic which is a reflected light of the incident light with a photo detector through a second polarizer, and Light is measured by measuring the thickness of the boron silicide film from the first polarization property, the second polarization property, and the refractive index of the boron silicide film. Measuring the thickness of the boron silicide film by using an appropriate means; and subsequently, thermally diffusing the boron of the boron silicide film on the silicon substrate at a temperature higher than the temperature of the process of forming the boron silicide film. Semiconductor device manufacturing method.