JPH04221817A - Method for forming semiconductor film - Google Patents

Abstract

PURPOSE:To form a semiconductor film having a high specific conductance and one conductivity type by setting the substrate temperature at <=200 deg.C, preferably <=150 deg.C, at the time of sputtering. CONSTITUTION:Film formation is carried out by sputtering in an atmosphere containing hydrogen by using a single-crystal or polycrystalline silicon target 24 added with a tervalent or quiquevalent element which is used as an impurity for giving one conductivity type to the target 24 so that the specific conductance of the target 24 can become 100<-1>-0.1<-1> OMEGA-cm at a film forming temperature (substance temperature) of <=300 deg.C. In addition, it is possible to form a one conductivity type P type or N type semiconductor film with high specific conductance and crystallinity by setting the substrate temperature to be <=200 deg.C, preferably <=150 deg.C, at the time of sputtering.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for obtaining a P-type or N-type semiconductor, that is, a semiconductor film having one conductivity type, by a low-temperature process.

0002

2. Description of the Related Art As methods for obtaining semiconductors having one conductivity type through low-temperature processes, methods such as ion implantation and sputtering are known.

However, the method using ion implantation has a problem in productivity, and the method using sputtering can be performed at a low temperature of 200° C. or less and has the characteristics of excellent productivity, but The electrical properties of the film were poor (for example, the electrical properties of a device made using a semiconductor film obtained by sputtering were poor), making it impractical.

Conventional methods for obtaining P-type or N-type semiconductor films by sputtering include, for example, if a silicon film of one conductivity type is to be obtained, a target doped with an impurity to impart one conductivity type to single crystal silicon is used. sputtering in an atmosphere using only argon, or
It is known that sputtering is carried out using a single crystal silicon target to which no impurity imparting P-type or N-type conductivity is added in an argon atmosphere doped with a reactive gas containing an element imparting one conductivity type (for example, phosphine). It is considered to be a method. However, in the conventional method, 1
It was not possible to obtain a P-type or N-type semiconductor film having a conductivity of 0-5 (Ωcm)-1 or more. This is because impurities imparting P-type or N-type conductivity do not substitute in the semiconductor and become donors or acceptors.

[0005]

[Problems to be Solved by the Invention] An object of the present invention is to fabricate a semiconductor film having one conductivity type with high conductivity using a sputtering method that can be formed at low temperatures and has excellent productivity. do.

[0006]

[Means for Solving the Problems] The present invention provides an inert atmosphere containing hydrogen, such as argon, in which the partial pressure ratio of hydrogen is preferably 30% or more. A film is formed by sputtering using a single-crystal or polycrystalline semiconductor target to which a III- or V-valent element, which is an element that provides This method of manufacturing a semiconductor film is characterized in that a semiconductor film having one conductivity type, P type or N type, with low conductivity and high crystallinity is manufactured by setting the temperature of the substrate to 200° C. or lower.

The feature of the present invention is that at a film forming temperature (substrate temperature) of 300° C. or lower, a single crystal or polycrystalline silicon target has a conductivity of 100 (Ωcm) −1 to 0.1 (
A film is formed by sputtering in an atmosphere containing hydrogen using a target to which a III-valent or V-valent element, which is an impurity that imparts one conductivity type, is added so that Ωcm)-1, and further during this sputtering. The substrate temperature is set to 200°C or less, preferably 150°C or less. This is based on the experimental results shown in FIG. Figure 2 uses single crystal silicon as a target to which antimony (Sb) has been added so that the resistivity is 2 to 3 kΩ, and the pressure of a mixed atmosphere of hydrogen and argon is set to PH=
0.5pa, input RF power 400W, hydrogen pressure PT
Sputter film formation was performed using a magnetron-type RF sputtering apparatus shown in Figure 1 under film formation conditions such that hydrogen partial pressure (PH/PT) was 30%, and then sputter film formation was performed at 600°C in an inert gas for 72 hours. N was thermally annealed.
This figure shows the relationship between film-forming temperature and XRD intensity in a type silicon semiconductor film. Looking at this figure, the film formation temperature is 200℃.
It can be seen that the N-type silicon semiconductor film after thermal annealing has almost no crystallinity.

Further, FIG. 3 shows a graph showing the relationship between the film formation temperature and the conductivity of the N-type silicon semiconductor film after the thermal annealing. Looking at this figure, it can be seen that the lower the film formation temperature, the higher the conductivity. Figure 3 shows that the conductivity of the target is 0.6 (Ω
Using a single-crystal silicon target to which antimony was added so that cm)-1, in a mixed atmosphere of hydrogen and argon at a pressure of 0.5 pa, hydrogen partial pressure ratio of 50%, RF
It is a graph showing the relationship between substrate temperature and conductivity when a film is formed under the condition of a power of 400W.

The trend shown in FIG. 2 can be explained by the following model. The silicon film obtained by sputtering in this example is sputtered in an atmosphere containing a large amount of hydrogen during sputtering, so the elements constituting the target form clusters of tens to hundreds of thousands of atoms. While the cluster flies out of the target and flies through the hydrogen plasma, the dangling bonds of the cluster are neutralized by hydrogen, and the cluster reaches the substrate. At this time, in the target,
Since the impurity imparting P-type or N-type conductivity acts as an acceptor or donor, it also serves as an acceptor or donor in the cluster flying toward the substrate. Therefore, when these clusters reach the substrate and form a silicon film, the impurity imparting P-type or N-type conductivity has the characteristic that it acts as an acceptor or donor in the film formed by sputtering.

When the clusters whose dangling bonds have been neutralized by hydrogen reach the substrate from the target, if the temperature during film formation is high, the hydrogen which has neutralized the dangling bonds of the silicon clusters is separated. On the final substrate, the clusters cannot combine with each other and form no order. Therefore, when a silicon film formed in an atmosphere of 200 degrees Celsius or higher is thermally annealed, it is unable to achieve a more highly ordered state, resulting in a lack of XRD intensity. On the other hand, when the temperature during film formation is low, the sputtered silicon clusters are bonded via hydrogen on the substrate. As a result, a relatively highly ordered state is achieved. This film is heated from 450 degrees to 7
By thermally annealing at a temperature of 1,000 degrees Celsius, the silicon clusters bonded through hydrogen become bonds between silicon atoms, transitioning to a higher ordered state, and bonding to each other due to the silicon present. Comrades of silicon are attracted to each other. When measured by laser Raman spectroscopy as a crystal, the peak of single crystal silicon is 521 cm as shown in Figure 5.
-1], a peak shifted to the lower frequency side is observed. This peak shifted to the lower frequency side than 521 cm-1 indicates a crystalline state with weak lattice distortion. In addition, the apparent particle size is calculated from the half-width of 50~
Although it is 500 Å and resembles a microcrystal,
In reality, there are a large number of highly crystalline regions having a cluster structure, and each cluster is bonded (anchored) with silicon to form a film having a semi-amorphous structure. Therefore, the orderliness of silicon films obtained by sputtering at low film-forming temperatures (in an atmosphere below 150°C) is further promoted by thermal annealing, whereas the orderliness of silicon films formed at high substrate temperatures is As mentioned above, it does not have order from the beginning, so even if it is thermally annealed, it is not possible to form a film with a semi-amorphous structure in which the clusters are bonded (anchored) with each other by silicon, and there are almost no XRD peaks. It is not.

From the above, when producing a semiconductor film having one conductivity type by sputtering using a target doped with an impurity imparting one conductivity type in an atmosphere of an inert gas containing hydrogen, sputtering It can be concluded that it is better to keep the substrate temperature at 200° C. or lower, preferably 150° C. or lower.

It goes without saying that the structure of the present invention can be applied not only to silicon semiconductors but also to other semiconductors. For example, impurities that impart one conductivity type (for example, boron, phosphorus, etc.
By simultaneously using silicon and germanium targets doped with I-valent and V-valent elements,
A semiconductor film of SixGe1-x having one conductivity type can be obtained. In this case, another feature is that by changing the area of each target, the composition ratio of the semiconductor film can be changed. According to this idea, a semiconductor film having a more complicated composition ratio can be obtained by using a plurality of targets simultaneously.

[0013]

[Example 1] This example is a magnetron type R shown in Fig. 1.
An N-type silicon semiconductor film is formed using an F sputtering device on a silicon oxide film with a thickness of 1000 Å on a glass substrate. The magnetron type RF sputtering apparatus shown in FIG. 1 will be explained below. The outline of the magnetron type RF sputtering apparatus shown in FIG. 1 will be explained below.

In FIG. 1, (12) is a substrate, (13)
is a holder that can be rotated as required (14
) is a heater for heating the substrate, (15) is a gas introduction system, (
17) is a valve for a gas introduction system, and (18) is a gas supply system, such as a cylinder filled with hydrogen. Although only one type of gas supply system is shown in FIG. 1, other gas supply systems such as argon, phosphin, diborane, nitrogen, etc. may be provided as necessary; in this case, multiple gas introduction systems may be provided. At the same time, a gas may be introduced into the reaction chamber. In addition, (19) is a high frequency power source (13.56MHz
), (20) is a high frequency matching device, and (
21) is a magnetron portion provided with a circular permanent magnet (22) that rotates as required.

Further, (23) is a shutter for preventing sputtered particles (sputtered atoms, clusters, ions, etc.) from reaching the substrate. This shutter (
23) prevents impurities from reaching the substrate as sputtered particles immediately after sputtering starts, but can be used to prevent sputtered particles from reaching the surface on which sputtered particles are formed, if necessary. (24) is the target. The target may contain impurity elements such as phosphorus, boron,
By mixing fluorine or other halogen elements, a thin film doped with impurities can be formed. (
25) is a gas exhaust system, (26) is a turbo molecular pump, and (27) is an oil rotary pump. Also (28), (
29) is an exhaust system valve. Furthermore, (34) is equipped with an evacuation system (34) equipped with a cryopump (31) and a rotary pump (33) in order to evacuate a higher vacuum state and specific impurities. Note that (30) and (33) are valves of this exhaust system (34).

Among these, the exhaust system (34) equipped with a cryopump is mainly used for high vacuum evacuation before film formation, and is capable of exhausting the reaction paper bath to a temperature of about 10-10 Torr, and removes gases adsorbed in the reaction chamber. and molecules can be exhausted. In particular, high vacuum evacuation before film formation is effective in reducing the amount of impurities such as oxygen, carbon, and nitrogen contained in the film.

In this embodiment, the substrate (12) was heated by the heater (14), but it may also be heated by an infrared lamp.

In this example, a molten silicon target with a resistivity ρ = 0.60 Ωcm to which antimony, which is an impurity imparting one conductivity type, was added was used, but other impurities imparting one conductivity type were used. For example, it goes without saying that As and Sb can be used for N type, and B can be used for P type. Furthermore, it is effective to increase the conductivity of the target as high as possible by a method such as thermal annealing. The film forming conditions were a hydrogen partial pressure as a parameter in a mixed atmosphere of hydrogen and argon, a film forming temperature of 150°C, a pressure of 0.5 pa, and an RF power of 400 W. A film was formed to a thickness of 2000 Å on a glass substrate. did.

FIG. 4 shows the relationship between the electrical conductivity σ (Ωcm) −1 of the N-type semiconductor film obtained in this example and the volume % of hydrogen in the atmosphere during film formation. Looking at Figure 2, when the hydrogen partial pressure during sputtering is 30% or more, σ = 1.
It can be seen that a value of 0-2 (Ωcm)-1 or more is obtained.

FIG. 5 shows a Raman spectrum obtained in this example. As shown in the figure, it can be seen that when the hydrogen partial pressure PH is increased with respect to the total pressure PT, a sharp peak occurs at a location lower than the peak of single crystal silicon, 521 cm-1.

In general, if a value of σ = 10-1 (Ωcm)-1 or more can be obtained, it is sufficiently practical as a source and drain region of an insulated gate field effect transistor. Considering this, a silicon film of one conductivity type (in this case, an N-type silicon film) obtained by sputtering in an inert atmosphere doped with hydrogen can be deposited over a large area, It can be said that it is a semiconducting non-conducting film having one conductivity type, which is more economical and has excellent electrical characteristics compared to impurity ion doping.

[0022] The conductivity of the film obtained by this sputtering is 1/100 to 1/3 of the conductivity of the target, that is, a P-type or N-type film having a conductivity of 0.1 (Ωcm) −1 or more. It is useful to be able to obtain semiconductors.

Furthermore, in the configuration of the present invention, the substrate is grounded (
However, in order to reduce the effect of ion sputtering on the substrate, the substrate (generally a glass substrate, silicon substrate, etc. is used) may be electrically floating, that is, insulated from the surroundings. It is better to make it .

In this example, an N-type silicon semiconductor film was fabricated on a substrate using a target doped with antimony, but the target used for sputtering film formation contained impurities that imparted N-type conductivity. If so, phosphorus (P
), arsenic (As), antimony (Sb), etc., and boron (B) as an impurity that imparts a P-type conductor.
), a single crystal or polycrystalline silicon target to which a III-valent element such as aluminum (Al) is added can be used. Furthermore, as a single crystal or polycrystalline semiconductor target, not only silicon, but also Ge, Se, and compound semiconductors such as gallium arsenide, gallium antimony, etc. may be used depending on the semiconductor film to be formed.

In the structure of the present invention, the semiconductor film having one conductivity type after film formation may be thermally annealed at a temperature of 700° C. or lower.

Conventionally, a conductivity of 10-2 (Ωcm)-1 or higher, which was obtained by thermally annealing a semiconductor film having one conductivity type obtained by sputtering or CVD, can be obtained by sputtering at a low temperature (below 150°C). This is a major feature of the present invention. This is clear from the Raman spectrum of the N-type semiconductor film obtained by the method of the present invention immediately after film formation and without annealing, as shown in FIG. Looking at Figure 5, we see that the partial pressure of hydrogen is 5
N obtained by sputtering in a 0% atmosphere
The Raman spectrum of a single-crystal silicon (c-S) type semiconductor film is
It can be seen that a peak indicating crystallinity appears at a wave number lower than the peak i) at 521 cm-1.

In this embodiment, the exhaust system (34) shown in the magnetron type RF sputtering apparatus shown in FIG.
Selectively exhausting specific impurities, such as oxygen, carbon, and nitrogen, by using a cryopump provided in the device has a great effect on improving the quality of the semiconductor film formed by sputtering. For example, if impurities such as oxygen, carbon, and nitrogen are present in a P-type or N-type semiconductor film to which impurities that impart one conductivity type are added, in addition to impurities that contribute as acceptors or donors, it is possible to use that semiconductor film. This adversely affects the performance of the device when it is fabricated. For example, if oxygen elements are present in a semiconductor layer constituting a solar cell, conversion efficiency and durability may deteriorate. Therefore, by efficiently exhausting these impurities such as oxygen, carbon, and nitrogen, it is possible to prevent adverse effects on the semiconductor film.

By using a cryopump, which is an adsorption pump provided in the sputtering apparatus shown in FIG. 1 used in this example, molecules consisting of impurities such as oxygen, carbon, and nitrogen can be efficiently exhausted. . For example, in this example, when film formation was performed using only the exhaust system (25) equipped with a turbo molecular pump, the oxygen concentration contained in the formed film was measured using SIMS (secondary ion mass spectrometry). According to the method, the oxygen concentration was about 3 x 1019 cm-3, but even at the same film forming pressure, the oxygen concentration in the film formed by using the exhaust system (34) equipped with a cryopump was 6 x 1018 cm-3. I was able to make it 3. The carbon concentration in the formed film was 3×10
16 cm-3 can be obtained, hydrogen is 4 x 1020c
m-3, and when compared with 4 x 1022 cm-3 of silicon, it was 1 atomic %.

In the configuration of the present invention, since data has been obtained that a relatively high film forming pressure of about 2.5 pa is good, it is inappropriate to perform film forming in an ultra-high vacuum state. Therefore, as described above, the use of a cryopump that can exhaust oxygen, carbon, and nitrogen as adsorbed molecules has a significant effect. Furthermore, in the present invention, in a mixed atmosphere of an inert gas such as argon and hydrogen,
Since the film is formed by sputtering, oxygen, which is the most problematic impurity, combines with hydrogen to become molecules and exists in the reaction space. Therefore, as mentioned above, by using a cryopump, these molecules consisting of oxygen and hydrogen can be efficiently pumped out. Furthermore, when forming a semiconductor film that must contain impurities that contribute to P-type or N-type conductivity (e.g., phosphorus, antimony) as in the structure of the present invention, vapor phase processing such as CVD using a reactive gas is performed. In the growth method, since it is necessary to add impurities that contribute to the conductivity type into the gas phase, there is a problem that unnecessary impurities are inevitably mixed in. As a method to solve such problems, there is a method of using a special reactor using extremely high purity reaction gas, but this method poses problems of cost and poor productivity.

From the above, as in this example, a turbo molecular pump and a cryopump are used in combination to provide a semiconductor film, particularly one conductivity type, by sputtering in an inert atmosphere containing hydrogen without using a reactive gas. II
The method for producing a semiconductor film containing I-valent and V-valent elements is as follows:
This method can efficiently exhaust oxygen, carbon, and nitrogen, which are unnecessary impurities in the semiconductor film being formed, and can be said to be an extremely low-cost method with excellent productivity.

In the structure of the present invention, the N-type semiconductor film after deposition may be thermally annealed at a temperature of 700° C. or lower.

In the present invention, a single-crystal or polycrystalline semiconductor target is used as a target, and I, which is an impurity that imparts P-type or N-type conductivity, is used in the target.
Since the valent II or V-valent impurities are 100% ionized, that is, the III-valent or V-valent impurities are completely substituted as acceptors or donors, the impurities can be removed by sputtering this target in an atmosphere containing hydrogen. The cluster in which is substituted as an acceptor or donor flies toward the substrate and reaches the substrate while neutralizing the dangling bonds by hydrogen plasma, so that the above III in the semiconductor film formed by sputtering The valent or V-valent impurities had a high ionization rate, and these impurities could be substituted as acceptors or donors to increase the ionization rate.

It goes without saying that the structure of the present invention is applicable not only to silicon semiconductors but also to other semiconductors. For example, silicon to which an impurity is added that gives it one conductivity type.
By using a target of and germanium at the same time, a semiconductor film of SixGe1-x having one conductivity type can be obtained. In this case, by changing the area of each target, the composition ratio of the semiconductor film can be changed. According to this idea, a semiconductor film having a more complicated composition ratio can be obtained by using a plurality of targets simultaneously.

Furthermore, during sputtering, a halogen element is added to the atmosphere, and 0.1 to 10% of NF3 or the like is added to neutralize the dangling bonds of clusters of sputtered atoms, similar to hydrogen. Good too.

[0035]

[Embodiment 2] In this embodiment, the magnetron type R shown in FIG.
A P-type SixGe1-x semiconductor film doped with boron (B) was obtained using an F sputtering device. In this example, a magnetron type RF sputtering device was used at a pressure of 2.5 pa, an RF power of 200 W, and a substrate temperature of 1
Sputtering was performed at 00°C in a mixed atmosphere of hydrogen and argon with a hydrogen partial pressure ratio of 80%, and then at 600°C.
, N-type SixGe1- which was thermally annealed for 72 hours.
x semiconductor film. Single crystal targets of silicon and germanium are formed on a substrate by distributing and arranging a plurality of molten substrates containing 1×1017 cm-3 or more of phosphorus in the same area, and then rotating the substrate side by planetary rotation. The uniformity of the N-type SixGe1-x semiconductor film was improved.

In this example as well, since boron in the silicon and germanium single crystal targets is substituted as an acceptor, the target has a conductivity that is 1/100 to 1/3 of that of the target, which is a feature of the present invention. A P-type semiconductor can be manufactured.

The reaction pressure was set as high as 2.5 pa based on the experimental results shown in FIG. 6 conducted by the present inventor. Figure 6 shows the pressure and XRD intensity (
ITENSITY). Figure 6
The film formation conditions under which this data was obtained were phosphorus in a single crystal or polycrystalline silicon target with a target resistivity of 2.
The film-forming temperature was 150° C., the RF power was 400 W, and the atmosphere was a mixed atmosphere of hydrogen and argon with a hydrogen partial pressure ratio (PT/PT) of 30%. After film formation, 6
Thermal annealing was performed at 00°C for 72 hours. From FIG. 5, it can be seen that higher crystallinity is exhibited when the reaction pressure is about 2.5 pa.

The RF power was set to 200 W based on the experimental results shown in FIG. The data shown in FIG. 7 is the input power and XRD intensity (ITENSITY) during film formation when the film formation pressure is 0.5 pa under the same manufacturing conditions as shown in FIG.
This shows the relationship between It can be seen from FIG. 7 that the crystallinity of the semiconductor film is higher when the input power during sputtering is relatively low, about 200 W.

In this example, the substrate temperature was set at 100° C., as shown in FIG.
This is based on the experimental results shown in . The data shown in FIG. 2 was obtained under the same manufacturing conditions as shown in FIG.
This figure shows the relationship between the substrate temperature and the XRD intensity of the obtained film. Looking at this Figure 4, it can be seen that when the film formation temperature (substrate temperature in this case) is 100°C or higher, the crystallinity of the film after thermal annealing becomes low, whereas when the film is formed at 100°C or lower, the It can be seen that the film after annealing has high crystallinity. As mentioned above, when a film is formed at a low temperature, the sputtered silicon clusters are bonded by hydrogen in the atmosphere, and thermal annealing forms bonds between silicon clusters, so even if thermal annealing is performed, the crystallinity remains This is to preserve and promote.

In this embodiment as well, the conductivity of the sputtered film can be increased by increasing the conductivity of the target. This is because, as mentioned above, impurities that have become acceptors or donors in the target are present at a high ionization rate in the film formed by sputtering in an atmosphere containing hydrogen, and are replaced as acceptors or donors. , 1 of the target conductivity
This is because a P-type or N-type semiconductor film having a high conductivity of /100 to 1/3 can be obtained.

[0041]

Example 3 In this example, an N-type semiconductor film mixed with phosphorus of SixC1-x (0≦X≦1) was obtained under the same conditions as in Example 2. In this example,
The stoichiometric ratio can be changed by finely dispersing silicon and carbon targets and changing their amounts. In this case, the target or substrate was rotated to increase the uniformity of the produced film.

In the examples in this specification, targets doped with antimony, phosphorus, boron, etc., which are elements that impart one conductivity type to a semiconductor, were used; however, targets to which these impurities were not added ( Si, Ge, Si
Using targets such as x, Ge1-x, SixC1-x (0≦X≦1), Si, Ge, SixGe1-x, S
It goes without saying that a semiconductor film such as ixC1-x (0≦X≦1) may also be fabricated.

[0043]

Effects of the Invention: Using a semiconductor target doped with impurities having one conductivity type, which is the structure of the present invention, in an inert atmosphere containing hydrogen where the partial pressure of hydrogen is 30% or more, the temperature is below 200°C. By performing sputtering at a substrate temperature of , it was possible to obtain a semiconductor film having one conductivity type with high conductivity.

[Brief explanation of the drawing]

FIG. 1 shows a sputtering apparatus used to implement the method of the present invention.

FIG. 2 shows the relationship between the deposition temperature and XRD intensity of an N-type silicon semiconductor film obtained by the method of the present invention.

FIG. 3 shows the relationship between the conductivity of an N-type silicon semiconductor film obtained by the method of the present invention and the substrate temperature during film formation.

FIG. 4 shows the relationship between the conductivity of an N-type silicon semiconductor film obtained by the method of the present invention and the hydrogen partial pressure during film formation.

FIG. 5 shows a Raman spectrum of an N-type silicon semiconductor film obtained by the method of the present invention.

FIG. 6 shows the relationship between the deposition pressure and XRD intensity of an N-type silicon semiconductor film obtained by the method of the present invention.

FIG. 7 shows the relationship between input RF power and XRD intensity during deposition of an N-type silicon semiconductor film obtained by the method of the present invention.

Claims (3)

[Claims] 1. A method for producing a semiconductor film, in which a semiconductor film having one conductivity type is produced on a substrate by sputtering using a semiconductor target to which an element imparting one conductivity type is added in an atmosphere containing hydrogen. A method for manufacturing a semiconductor film, characterized in that the temperature of the substrate is kept at 200° C. or less during the sputtering. 2. In claim 1, the atmosphere containing hydrogen is a semiconductor film characterized in that the partial pressure of hydrogen is 30% or more of the total pressure of the atmosphere consisting of hydrogen and an inert gas such as argon. Fabrication method. 3. In claim 1, the semiconductor target to which an element imparting one conductivity type is added is Si, Ge, or SixG to which a III-valent or V-valent impurity is added.
A semiconductor film manufacturing method characterized by using a single crystal or polycrystalline semiconductor of e1-x, Six, C1-x, (0≦X≦1).