JPH04267517A - Formation method of semiconductor thin film - Google Patents

Abstract

PURPOSE:To arrange easily silicon atoms at the position of a prescribed crystal lattice and to improve a crystal growth rate by a method wherein a compressive stress is exerted on an amorphous silicon film. CONSTITUTION:A silicon oxide film 22 is selectively formed on a silicon substrate 21 and thereafter, an amorphous silicon film (a first film) 23 is formed on the whole surface and moreover, a silicon oxide film (a second film) 24 is formed thereon at a temperature lower than the temperature of crystallization of the film 23. Then, a heat treatment is performed for crystallizing the film 23 from a seed part 21a. At this time, a compression is made to cause in the film 24 to contrive to exert a compressive stress on the film 23.

Description

[Detailed description of the invention]

[Purpose of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a semiconductor device, and more particularly to a method of forming a semiconductor thin film.

0002

2. Description of the Related Art Recently, semiconductor device manufacturing technology has made remarkable progress, and integrated circuits have been miniaturized to the submicron order. However, even with such miniaturization, the limit of integration is being reached by simply reducing the size of each semiconductor element. Therefore, there is a need for a method of increasing the degree of integration by vertically overlapping some elements.

Therefore, in order to stack elements, a technology was developed in which an element is formed on a base, an insulating film is formed on this, a silicon film is then formed on this insulating film, and an element is formed on this silicon film. It has been done.

[0004] In such technology, there is a solid phase growth method as a method for forming the silicon film. This method is
This is a method in which an amorphous silicon film is deposited on an insulating film, and this amorphous silicon film is grown in a solid phase into a single crystal film or a polycrystalline film with large crystal grains by heat treatment. In this solid phase growth method, the temperature of the heat treatment is generally 5.
Since the temperature is as low as 00 to 800°C, there is no adverse effect such as damage to elements already formed on the underlying base.

However, the solid phase growth method described above has the following problems. That is, when crystallization progresses by solid phase growth, crystal nuclei are first generated in the amorphous silicon film, which then grow, and crystal growth progresses. However, at this time, another crystal nucleus is newly generated, and crystal growth proceeds separately from this nucleus, so each crystal collides with another newly formed crystal during the growth process, making it impossible for each crystal to grow sufficiently large. Can not.

The above-mentioned problems become more and more noticeable due to the effects of stress generated at the interface between the silicon film and the underlying insulating film, such as a silicon oxide film, when the amorphous silicon film is crystallized. FIG. 10 is an explanatory diagram illustrating this problem. As shown in this figure, a silicon oxide film 102 and an amorphous silicon film 103 are formed in this order on a silicon substrate 101, but at the interface between the amorphous silicon film 103 and the silicon oxide film 102, When the crystalline silicon film 103 is crystallized, a tensile stress 104 is applied to the amorphous silicon film 103 and the underlying silicon oxide film 102 is
A compressive stress 105 is applied to . In this case, the silicon atoms in the amorphous silicon film 103 are exposed to the tensile stress 1
04 prevents them from being arranged at predetermined positions in the crystal lattice. Therefore, the growth rate of the crystallized portion 103a of the amorphous silicon film 103 is extremely reduced, and as a result, many new crystal nuclei are generated during the crystal growth process, and crystallization from these nuclei also progresses. Put it away. As a result, there was a problem in that the size of the crystal grains became extremely small.

[0007]

[Problems to be Solved by the Invention] As described above, in the conventional method for forming semiconductor thin films, crystal growth from crystal nuclei does not extend long in an amorphous silicon film formed on an insulating film, resulting in crystal growth. The problem was that the grains did not grow large. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for forming a semiconductor thin film that can significantly increase the size of crystal grains. [Structure of the invention]

[0008]

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention provides a step of forming a first film made of an amorphous semiconductor on a substrate, and a step of forming a first film on the first film. Provided is a method for forming a semiconductor thin film, comprising the steps of: forming a second film at a temperature lower than the crystallization temperature of the first film; and crystallizing the first film by solid phase growth.

[0009]

[Function] The method for forming a semiconductor thin film according to the present invention,
Since the second film is formed on the first film made of an amorphous semiconductor formed on the substrate at a temperature lower than the crystallization temperature of the first film, the first film does not undergo crystallization. First, after this, the first film is crystallized while shrinking the second film, so that the first film is subjected to compressive stress by the second film. The atoms in the first film are quickly arranged at predetermined crystal lattice positions due to this compressive stress,
Therefore, the crystallization speed of the first film is significantly improved. Therefore, crystallization progresses significantly before new nuclei are formed in the film, making it possible to form a polycrystalline semiconductor film with large crystal grains and greatly improving the characteristics of elements formed in this film. can.

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1 to 6 are process cross-sectional views showing an embodiment of a method for forming a semiconductor thin film according to the present invention.

First, as shown in FIG. 1, an insulating film, for example a silicon oxide film 2, is formed to a thickness of 5000 angstroms on a silicon substrate 1, and then a polycrystalline silicon film 3 is further formed on this oxide film 2 to a thickness of 1000 angstroms. Formed in angstroms. This polycrystalline silicon film 3 is made of SiH4, He
The deposition was carried out by a conventional LPCVD method using a mixed gas of 1 to 100 mL at a substrate temperature of 610° C. and a pressure of 0.5 Torr.

Next, as shown in FIG.
By implanting ions into the polycrystalline silicon film 3, this film is made amorphous and an amorphous silicon film (first film) is formed.
It was set as 3. The conditions at this time were an acceleration voltage of 50 KeV and a dose of 1 x 1015 cm-2. Note that when the thickness of the polycrystalline silicon film 3 is 2000 angstroms, the film thickness is large, so in order to make the entire film amorphous, ions are implanted twice into the deep and shallow parts of the film. There is a need to. In this case, the ion implantation conditions are 50Ke
V, 2.5 x 1015 cm-2 and 120 KeV,5.
It was set to 4 x 1015 cm-2.

Next, as shown in FIG. 3, SiH4 and O
2, a silicon oxide film 5 was formed as the second film with a thickness of 3000 angstroms using an amorphous silicon film 3 at a substrate temperature of 400°C, a SiH4 flow rate of 200SCCM, an O2 flow rate of 200SCCM, and a pressure of 1 Torr. deposited on top. This deposited amorphous silicon film 3 was extremely porous and had poor electrical resistance. Further, at this time, the amorphous silicon film 3 remained in an amorphous state and did not undergo crystallization.

Furthermore, as shown in FIG.
℃, treatment time 20 hours in a non-oxidizing atmosphere, e.g. N2
Alternatively, heat treatment was performed in an atmosphere such as Ar. At this time, the amorphous silicon film 3 undergoes volumetric contraction due to crystallization.
In addition, the silicon oxide film 5 also undergoes volumetric contraction due to a change in the bonding state between SiO4 regular tetrahedrons and a decrease in interatomic distance. The volume contraction of the amorphous silicon film 3 is caused by the fact that a certain amount of time is required for the formation of crystal nuclei, while the bonding state of SiO4 regular tetrahedrons in the silicon oxide film 5 changes easily. causes early deposition and shrinkage. Also, the volume shrinkage rate of amorphous silicon is 2 to 3.
%, whereas the silicon oxide formed in this example is significantly larger at just under 10%. Therefore, the amorphous silicon film 3 is subjected to compressive stress by the silicon oxide film 5, and this stress significantly increases the speed of crystallization. That is, the silicon atoms in the amorphous silicon film 3 are quickly aligned at predetermined crystal lattice positions due to this stress, so that the crystallization rate of the amorphous silicon film 3 is significantly improved. In this example, the value of this compressive stress is 108 to 109 dym.
/cm2, and the crystallization rate was almost twice that of the case where the oxide film 5 was not used. If the crystallization rate is improved in this way, the crystal can grow to a large size before new nuclei are formed in the amorphous film. In fact, in this example, it was confirmed that crystal grains approximately twice the size were formed compared to the case without the oxide film 5. In this case, the formation rate (activation energy) of crystal nuclei remains unchanged.

Next, as shown in FIG. 5, the silicon oxide film 5 was removed using hydrofluoric acid or ammonium fluoride solution. Note that here, the removal of this oxide film may not be performed if desired. However, in the case of a thin element such as a thin film transistor, it is preferable to remove it in order to facilitate post-processing.

Finally, as shown in FIG. 6, after forming a source 6a and a drain 6b by ion implantation and forming an element isolation insulating film 7 by LOCOS method, a gate insulating film (thickness 350 to 450 angstroms) 8, Gate electrode (thickness 4000 angstroms)
9, interlayer insulating film 10, contact wiring 11a, 11b,
A passivation film 12 was formed to complete a thin film MOS transistor.

Next, we will compare the mobility when a MOS device is manufactured using a polycrystalline silicon film formed by the method according to the present invention using an oxide film compared to that of polycrystalline silicon film formed by a conventional method that does not use an oxide film. A comparison was made with the case of membrane.

FIG. 7 is a characteristic diagram showing the mobility of a film formed by the method according to the present invention, and FIG. 8 is a characteristic diagram showing the mobility of a film formed by the conventional method. As can be seen from these figures, the MOS when using the present invention
The device has higher mobility and smaller variations than conventional MOS devices. That is,
It can be seen that the device characteristics were improved.

Note that the MOS device formed by the method of the present invention was manufactured in the following manner. That is, in order to form a channel in the amorphous silicon film formed by the method of the above embodiment, phosphorus was applied at an acceleration voltage of 15 KeV and a dose of 1×1.
Ions were implanted to a thickness of 0.13 cm@-2, and a silicon oxide film was deposited to a thickness of 2000 .ANG. by the same method as in the above embodiment. The amorphous silicon film was further crystallized by heat treatment at 700° C. for 5 hours, and a MOS element having a width of 1 μm and a length of 0.5 μm was fabricated on this film. Here, by performing heat treatment at a high temperature of 700° C. for 5 hours for a short time, the size of crystal grains was reduced and variation in mobility between elements was suppressed as much as possible.

On the other hand, a MOS element formed by the conventional method was crystallized without a silicon oxide film as before, and a MOS element of the same size as the one according to the present invention was fabricated using this film.

Furthermore, the size of the crystal grains of the above-mentioned MOS device was measured by observation using a transmission electron microscope. As a result, the MOS device using the present invention has a maximum crystal grain size of approximately 0.5 μm, which is 2.
It was more than twice as large, and the variation in grain size was also small. The reason for this is that by using the method of the present invention, the size of the crystal grains can be made sufficiently large due to the compressive stress received from the silicon oxide film, and the sizes can be made uniform while being appropriately smaller than the channel region. It is from. Therefore, the channel region of any device can stably contain approximately the same number of small grain boundaries, and device characteristics can be improved. Next, another embodiment in which the present invention is applied to a method of crystallizing an amorphous silicon film using a part of the surface of a silicon substrate as a seed will be described.

FIG. 9 is a sectional view showing this embodiment. As shown in this figure, there is a LOCOS on the silicon substrate 21.
A silicon oxide film 22 is selectively formed by a method, and an amorphous silicon film (first film) 23 is formed on the entire surface thereof. This amorphous silicon film 23 is made by depositing a polycrystalline silicon film with a thickness of 2000 angstroms and implanting silicon ions (acceleration voltage/dose amount: 50 KeV/2.5×
1015cm-2,120Kev /5.4×1015
cm-2) to become amorphous. Here, the surface of the silicon substrate 21 on which the silicon oxide film 22 is not formed is connected to the amorphous silicon film 23 as a seed portion 21a, and amorphous silicon is crystallized from this seed portion 21a. 23a is its crystallized portion. Furthermore, a silicon oxide film 24 is formed as a second film on the amorphous silicon film 23. This film 24 is made of S by the CVD method.
iO2 was deposited under the same conditions as in the process of FIG. 5 described above.

The amorphous silicon film 23 was crystallized by subjecting the above sample to heat treatment under the same conditions as in the process shown in FIG. 4 described above. As a result, the seed part 2 is
The distance from 1a that could be made into a single crystal was 15 μm, which was a dramatic improvement compared to the distance of 5 μm according to the conventional method.

The reason for this is that during the heat treatment for crystallizing the amorphous silicon film 23, the silicon oxide film 24 contracts in the direction of arrow A, and due to this contraction, the amorphous silicon film 2
This is because compressive stress acts in the direction of the arrow B in 3, so crystal growth is promoted by the same effect as in the above-mentioned embodiment.

Note that the present invention is not limited to the above embodiments. For example, the conditions for forming a silicon oxide film on an amorphous silicon film include a substrate temperature of 350 to 50°C.
It is preferable that the temperature is within the range of 00°C, the flow rates of both SiH4 and O2 are within the range of 50 to 500 SCCM, and the pressure is 1 Torr or less, and can be changed as appropriate based on this range.

Furthermore, a silicon nitride film may be used as the second film instead of the silicon oxide film described above, and can be formed using a gas such as SiH4 or NH3. In this case, the forming conditions include a substrate temperature of 350 to 500.
℃, the flow rates of SiH4 and NH3 are both 50℃.
It is preferably within the range of ~500 SCCM.

Furthermore, as an amorphous silicon film,
Even if it is not made by ion implantation as mentioned above, S
Films directly formed by the CVD method using iH4, Si2 H6, etc. showed similar behavior, and similar results could be obtained in both cases by heat treatment using the method according to the present invention. The CVD conditions mentioned here are that the temperature for depositing amorphous silicon is in the range of 450 to 600°C, and when silane gas is used as the raw material gas, the partial pressure is 0.1
~5.0 Torr, and when disilane gas is used, its partial pressure is in the range of 0.1 to 5.0 Torr.

Furthermore, the heat treatment temperature for solid phase growth is preferably 550 to 700° C., and the amorphous semiconductor film to be grown in solid phase may be made of a material other than amorphous silicon.

In addition, the crystal growth rate is generally increased by adding impurities, but in the method for forming a semiconductor thin film according to the present invention, in the solid phase growth method, the amount of impurities is extremely small.
For example, even an amount equivalent to channel ion implantation has the effect of sufficiently enlarging crystal grains. According to experiments, similar effects were found with group III or group V impurities such as boron and arsenic in addition to phosphorus.

Furthermore, by changing the thickness of the silicon oxide film formed on the amorphous silicon film, the crystal growth rate can be changed, and the size of the crystal grains can be controlled to match the size of the channel of the device. was completed. That is, in this case, when the thickness of the silicon oxide film is increased, the compressive stress applied to the amorphous silicon film increases, and therefore the size of the crystal grains increases. Conversely, when the film thickness is reduced, the size of the crystal grains becomes smaller.

Furthermore, according to the method according to the invention,
By increasing the crystal growth rate, the total time required for crystallization could be shortened, and the process time could be shortened.

[0032]

[Effects of the Invention] According to the method for forming a semiconductor thin film according to the present invention, a polycrystalline semiconductor film with large crystal grains can be formed, and the characteristics of elements formed in this film can be significantly improved. .

[Brief explanation of the drawing]

FIG. 1 is a process sectional view showing an embodiment of a method for forming a semiconductor thin film according to the present invention.

FIG. 2 is a process cross-sectional view showing an embodiment of the method for forming a semiconductor thin film according to the present invention.

FIG. 3 is a process cross-sectional view showing an embodiment of the method for forming a semiconductor thin film according to the present invention.

FIG. 4 is a process cross-sectional view showing an embodiment of the method for forming a semiconductor thin film according to the present invention.

FIG. 5 is a process cross-sectional view showing an embodiment of the method for forming a semiconductor thin film according to the present invention.

FIG. 6 is a process sectional view showing an embodiment of the method for forming a semiconductor thin film according to the present invention.

FIG. 7 is a characteristic diagram showing the mobility when a MOS device is manufactured using a semiconductor thin film formed by the method according to the present invention.

FIG. 8 is a characteristic diagram showing the mobility when a MOS device is manufactured using a semiconductor thin film formed by a conventional method.

FIG. 9 is a sectional view showing another embodiment using the present invention.

FIG. 10 is an explanatory diagram illustrating problems with the conventional method.

[Explanation of symbols]

1,21,101...Silicon substrate, 2,22,102...Silicon oxide film, 3,23,103...Amorphous silicon film, 4...Silicon ion, 5,24...Silicon oxide film (second film), 6a... Source, 6b... Drain, 7... Element isolation insulating film, 8... Gate insulating film, 9... Gate electrode, 10... Interlayer insulating film, 11a, 11b... Contact wiring, 12... Passivation film, 21a... Seed part, 23a , 103a...Crystallized portion of the amorphous silicon film, A
... direction of contraction of silicon oxide film 24, B... direction of compressive stress acting on amorphous silicon film 23, 103... amorphous silicon film, 104... tensile stress, 105... compressive stress.

Claims (4)

[Claims] 1. A step of forming a first film made of an amorphous semiconductor on a substrate, and forming a second film on the first film at a temperature lower than the crystallization temperature of the first film. A method for forming a semiconductor thin film, comprising the steps of: and crystallizing the first film by solid phase growth. 2. The method of forming a semiconductor thin film according to claim 1, wherein a step of removing the second film is performed after the step of crystallizing the first film. 3. The method of forming a semiconductor thin film according to claim 1, wherein the first film is an amorphous silicon film, and the second film is a silicon oxide film or a silicon nitride film. 4. Claim 3, wherein the silicon oxide film or the silicon nitride film is formed by a CVD method.
The method for forming the semiconductor thin film described above.