JP4511378B2 - Method for forming single crystal SiC layer using SOI substrate - Google Patents

Description

The present invention relates to a method of forming a single crystal SiC layer using an SOI substrate which is a semiconductor substrate embedded with an insulating layer.

  Single crystal SiC (silicon carbide) is attracting attention as a next-generation semiconductor device material because of its excellent thermal and chemical stability, strong mechanical strength, and resistance to radiation. In addition, an SOI substrate having a buried insulating layer is excellent in achieving high-speed circuit and low power consumption, and is promising as a next-generation LSI substrate. Therefore, an insulating layer embedded semiconductor SiC substrate that fuses these two features is very promising as a semiconductor device material.

An insulating layer embedded type semiconductor SiC substrate as described above includes an insulating layer embedded type Si substrate (SOI substrate) having a surface Si layer and an embedded insulating layer (SiO ₂ layer) existing below the surface Si layer. Use to make. That is, the surface Si layer of the SOI substrate is thinned to about 10 nm, carbonized at a high temperature to be transformed into a single crystal SiC thin film, and SiC is grown by an epitaxial method using the single crystal SiC thin film as a seed layer (for example, below) Patent Document 1).
JP 2003-224248 A

However, in the manufacturing method described above, the single crystal SiC thin film formed by carbonization is an extremely thin film. Therefore, when epitaxial growth is performed at a high temperature after that, the single crystal SiC thin film disappears locally due to sublimation, There was a problem that the SiO ₂ layer was partially exposed. As described above, when the single crystal SiC thin film as the seed layer partially disappears, the crystallinity of the single crystal SiC layer produced by epitaxial growth is deteriorated, and the surface flatness is also poor.

The present invention has been made in view of the circumstances as described above, and relates to a method for forming a single crystal SiC layer using an SOI substrate that can improve the crystallinity of an epitaxially grown SiC layer and improve surface flatness. For the purpose of provision.

In order to achieve the above object, a method for forming a single crystal SiC layer using an SOI substrate of the present invention comprises preparing an SOI substrate having a surface Si layer and a buried insulating layer having a predetermined thickness, and carbonizing the SOI substrate. A method of forming a single crystal SiC layer by heating in a hydrogen-based gas atmosphere to transform the surface Si layer into a single crystal SiC film and epitaxially growing the single crystal SiC film as a seed layer,
Forming a single crystal SiC film as a seed layer as a thin film of 1 nm to 15 nm;
Single seed SiC is deposited on the seed layer by first-stage epitaxial growth set at a relatively lower growth temperature than the second-stage epitaxial growth described later within a temperature range of 700 to 1050 ° C. Further depositing single crystal SiC on the seed layer while preventing disappearance due to sublimation,
The gist is to grow single-crystal SiC by second-stage epitaxial growth set at a growth temperature relatively higher than that of the first-stage epitaxial growth within a temperature range of 1100 to 1405 ° C.

That is, the method for forming a single crystal SiC layer using the SOI substrate of the present invention is a growth at a lower temperature than the second stage epitaxial growth described later in the temperature range of 700 to 1050 ° C. with respect to the seed layer. depositing a single-crystal SiC by the first stage epitaxial growth is set to a temperature more depositing a single-crystal SiC on the seed layer while preventing the loss due to sublimation of the seed layer, above the temperature range of 1100-1405 ° C. Single-crystal SiC is grown by second-stage epitaxial growth set to a relatively higher growth temperature than the first-stage epitaxial growth . In this way, first, the epitaxial growth is performed at the first stage set at a relatively low growth temperature, thereby preventing the seed layer of the single crystal SiC thin film formed by carbonization from disappearing by sublimation. Single crystal SiC is deposited on the seed layer to increase the thickness. Next, since the seed layer is increased in thickness in the first stage by performing epitaxial growth in a full-scale high temperature region in the second stage set at a relatively high growth temperature, a partial seed by sublimation is obtained. The disappearance of the layer can be completely prevented, the crystallinity of the single crystal SiC layer formed by epitaxial growth is improved, and the flatness of the surface is greatly improved. Furthermore, when another semiconductor film such as an epitaxial GaN film is formed thereafter, the crystallinity and film thickness uniformity of the semiconductor film are excellent.

The present invention, since a single crystal SiC film serving as the seed layer is a thin film of 1 nm to 15 nm, in the epitaxial growth in the temperature range of the SiO ₂ layer and Si is not to soften or melt that constitutes the SOI substrate, a single crystal by sublimation Since the SiC film tends to disappear, the effect of improving the surface flatness by improving the crystallinity of the single crystal SiC layer to be grown by preventing the disappearance of the seed layer in two steps is effective. is there.

The present invention, the growth temperature of the epitaxial growth of the first stage are the temperature range of 700 to 1050 ° C., while preventing the seed layer of the single crystal SiC thin film formed by the carbonization process to disappear sublimation Single crystal SiC is deposited on the seed layer, and the disappearance of the seed layer in the subsequent second stage is effectively and reliably prevented.

The growth temperature of the present invention is the two-step epitaxial growth are the temperature range of 1100 ~1405 ℃, in a temperature range where the SiO ₂ layer and Si is not to soften or melt that constitutes the SOI substrate, the crystallinity and surface A single crystal SiC layer with good flatness can be epitaxially grown.

  Next, the best mode for carrying out the present invention will be described.

FIG. 1 is a process diagram showing an embodiment of a method for forming a single crystal SiC layer using an SOI substrate of the present invention.

  The method of the present invention prepares an SOI substrate 1 having a surface Si layer 3 and a buried insulating layer 4 having a predetermined thickness. Next, the thickness of the surface Si layer 3 of the SOI substrate 1 is reduced to 1 nm to 15 nm. Next, the SOI substrate 1 is heated in a hydrocarbon gas atmosphere to transform the surface Si layer 4 into a single crystal SiC thin film 5.

  Then, when the single crystal SiC thin film 5 is epitaxially grown as the seed layer 5, the first stage in which the epitaxial growth is set to a relatively low growth temperature and the second stage in which the growth is set to a relatively high temperature. The epitaxial growth is performed in stages by at least two stages of processing.

  Hereinafter, each step will be described in detail.

As shown in FIG. 2A, in the SOI substrate 1, a SiO ₂ layer having a predetermined thickness is formed as a buried insulating layer 4 in the vicinity of the surface of the Si base material 2, and a surface Si layer 3 having a predetermined thickness is formed on the surface. Is formed. The buried insulating layer 4 is set to have a thickness of about 1 to 200 nm.

  As shown in FIG. 2B, the prepared SOI substrate 1 is subjected to a process of reducing the thickness of the surface Si layer 3 of the SOI substrate 1 to make it thinner. This thinning is performed, for example, by heating the SOI substrate 1 in an oxidizing atmosphere so that a predetermined depth from the surface of the surface Si layer 3 is left so that a Si layer having a desired thickness remains in the vicinity of the interface with the buried insulating layer 4. After the oxidation, the oxide layer formed on the surface is removed by etching with hydrofluoric acid or the like to form a thin film.

  At this time, the thickness of the thinned surface Si layer 3 is preferably set to about 1 nm to 15 nm, more preferably about 1 nm to 10 nm, and further preferably about 3 nm to 7 nm. If the thickness of the thinned surface Si layer 3 is less than 1 nm, the primary single-crystal SiC layer 6 is not sufficiently formed by the subsequent transformation step, which also hinders the production of the primary single-crystal SiC layer 6 in the subsequent transformation step. Because it brings

  Further, if the thickness of the thinned surface Si layer 3 exceeds 15 nm, the single crystal SiC thin film 5 is difficult to disappear by sublimation in the subsequent epitaxial growth after carbonization treatment, so that it is difficult to obtain the effects of the present invention. It is.

  Further, when a nitrogen-containing Si layer is formed in the vicinity of the interface between the buried insulating layer 4 and the surface Si layer 3 by ion implantation thereafter, it is necessary to form the nitrogen-containing Si layer at a deep position from the surface. Therefore, it is necessary to increase the energy level of the surface Si layer 3 and the crystallinity of the surface Si layer 3 may be lowered. Further, since nitrogen needs to be ion-implanted from the surface to a deep place, the nitrogen distribution region in the depth direction is also widened. For this reason, when a predetermined nitrogen-containing Si layer is formed in a region near the interface between the surface Si layer 3 and the buried insulating layer 4, the abundance ratio of the surface layer that does not contain nitrogen in the surface Si layer 3 is reduced. This is because there is a risk of hindering the generation of the primary single crystal SiC layer 6 in the subsequent modification step.

  At this time, a nitrogen-containing Si layer is formed in a region near the interface between the surface Si layer 3 and the buried oxide layer 4 by performing ion implantation of N ions after the surface Si layer 3 is thinned. The surface Si layer 3 can be transformed into the single crystal SiC thin film 5 by heating the SOI substrate 1 in a hydrocarbon gas atmosphere.

  As shown in FIG. 2C, the SOI substrate 1 having the thinned surface Si layer 3 is heated in a hydrocarbon gas atmosphere to transform the surface Si layer 3 into a single crystal SiC thin film 5. .

  For example, in the heating furnace capable of controlling the atmosphere, the transformation step can be performed by adjusting the temperature while switching the atmosphere gas (hydrogen gas and hydrocarbon gas) introduced into the heating furnace.

  With the apparatus as described above, the SOI substrate 1 is installed in a heating furnace, and while the mixed gas of hydrogen gas and hydrocarbon gas is supplied into the heating furnace, the ambient temperature in the heating furnace is raised. The surface Si layer 3 of the SOI substrate 1 is transformed into a single crystal SiC thin film 5.

  At this time, the SOI substrate 1 is installed in a heating furnace, and a mixed gas in which a hydrocarbon gas is mixed at a ratio of 1% by volume with respect to the hydrogen gas is supplied into the heating furnace. Moreover, the atmospheric temperature in a heating furnace is heated to 1200-1405 degreeC similarly to supply of this mixed gas. By this heating, the surface Si layer 3 of the SOI substrate 1 can be transformed into the single crystal SiC thin film 5.

  Here, the hydrogen gas is a carrier gas, and propane gas, for example, is used as the hydrocarbon gas. For example, if the supply amount of hydrogen gas from the cylinder is 1000 cc / min, the supply amount of hydrocarbon gas from the cylinder is set to 10 cc / min.

  At this time, as described above, after forming the nitrogen-containing Si layer in the surface Si layer 3 in the vicinity of the interface between the surface Si layer 3 and the buried insulating layer 4, the SOI substrate 1 is heated in a hydrocarbon gas atmosphere. Then, when the surface Si layer 3 is transformed into the primary single crystal SiC layer 6, the crystallinity of SiC in the subsequent epitaxial growth is improved.

  That is, the nitrogen-containing Si layer is Si containing nitrogen and has a low reactivity and is inactive compared to pure Si. For this reason, by forming a stable nitrogen-containing Si layer at a high temperature in a region near the interface between the surface Si layer 3 and the buried insulating layer 4 in the surface Si layer 3, the generated SiC is buried. It is prevented from entering the insulating layer 4 and destabilizing the interface, and the SiC / insulating layer interface becomes uniform. Therefore, even when the single crystal SiC layers 6 and 7 are subsequently formed by epitaxial growth, the crystallinity of SiC is improved, so that the single crystal SiC layers 6 and 7 having a uniform single crystal thickness can be obtained. Become. Further, when another semiconductor film such as the epitaxial GaN layer 8 is formed thereafter, the crystallinity and film thickness uniformity of the semiconductor film are excellent.

  Since the single crystal SiC thin film 5 is obtained by modifying the surface Si layer 3, the film thickness thereof is substantially equal to the film thickness of the surface Si layer 3. That is, the film thickness of the single crystal SiC thin film 5 can be arbitrarily controlled by controlling the film thickness of the surface Si layer 3 of the SOI substrate 1.

  If necessary, the above process may be performed excessively to deposit single crystal SiC on the single crystal SiC thin film 5. By performing the above process excessively (for example, continuing for several minutes to several hours), a carbon thin film is deposited on the single crystal SiC thin film 5.

  As shown in FIGS. 3D and 3E, the single crystal SiC thin film 5 is epitaxially grown as the seed layer 5 on the SOI substrate 1 subjected to the carbonization treatment, so that a single crystal is formed on the seed layer 5. SiC layers 6 and 7 are grown.

As shown in FIG. 4, in the epitaxial growth step, the first single crystal SiC layer 6 is formed on the seed layer 5 by performing epitaxial growth at a growth temperature T ₁ that is relatively lower than the second stage described later. In step (FIG. 3D), epitaxial growth is performed at a growth temperature T ₂ that is relatively higher than that in the first step to form a secondary single crystal SiC layer 7 on the primary single crystal SiC layer 6. Epitaxial growth is performed stepwise by at least two steps of treatment with the second step (FIG. 3E).

  Specifically, in the epitaxial growth, for example, the single crystal SiC layers 6 and 7 are grown under the following conditions. For example, the SOI substrate 1 on which the single-crystal SiC thin film 5 is formed is placed in a processing chamber, and a raw material gas such as monomethylsilane or silane and poropan is supplied into the processing chamber at a gas flow rate of about 1 sccm. By processing at the growth temperature, single crystal SiC layers 6 and 7 can be grown by epitaxial growth using the single crystal SiC thin film 5 as a seed layer 5.

  Of the two growth temperatures, the first growth temperature is 700 to 1200 ° C. A more preferable growth temperature for the first stage is 800 to 1100 ° C., and a most preferable temperature is 900 to 1050 ° C. If the growth temperature in the first stage is too high, the single crystal SiC thin film 5 obtained by the carbonization process sublimates and partially disappears, and the effect of the present invention cannot be obtained. This is because if the growth temperature is too low, single-crystal SiC having a higher crystallinity cannot be grown on the seed layer 5 of the single-crystal SiC thin film 5.

  In addition, the growth temperature of the second and subsequent stages among the two stages of growth temperatures is performed within a temperature range of 1000 to 1405 ° C. More preferably, the growth temperature in the second stage is 1000 to 1200 ° C, and the most preferable temperature is 1050 to 1150 ° C. If the growth temperature in the second stage is too high, the buried oxide layer 4 is softened, the Si base material 2 is softened or melted, and the crystallinity and flatness of the formed secondary single crystal SiC layer 7 are deteriorated. On the contrary, if the growth temperature in the second stage is too low, the secondary single crystal SiC layer 7 with good crystallinity cannot be obtained.

  As shown in FIG. 3F, after that, another semiconductor film such as a GaN layer 8 is formed on the secondary single crystal SiC layer 7 by epitaxial growth as necessary.

  In the epitaxial growth, for example, the GaN layer 8 is grown under the following conditions. For example, an SOI substrate 1 on which single-crystal SiC layers 6 and 7 are epitaxially grown is placed in a processing chamber, and a raw material gas such as trimethylgallium and ammonia is supplied into the processing chamber at a gas flow rate of about 1 sccm. By performing the treatment at 800 to 1405 ° C., the GaN layer 8 can be formed on the secondary single crystal SiC layer 7.

  In such a method, first, the seed layer 5 of the single crystal SiC thin film 5 formed by carbonization is prevented from disappearing by sublimation by performing epitaxial growth at the first stage set at a relatively low growth temperature. However, the primary single crystal SiC 6 is deposited on the seed layer 5 to increase the thickness. Next, since the seed layer 5 has increased in thickness in the first stage by performing epitaxial growth in a full-scale high temperature region in the second stage set at a relatively high growth temperature, partial growth by sublimation is possible. The disappearance of the seed layer 5 can be completely prevented, the crystallinity of the secondary single crystal SiC layer 7 produced by epitaxial growth is improved, and the flatness of the surface is greatly improved. Furthermore, when another semiconductor film such as the epitaxial GaN film 8 is formed thereafter, the crystallinity and film thickness uniformity of the semiconductor film are excellent.

Further, since the single crystal SiC thin film 5 serving as the seed layer 5 is a thin film having a thickness of 1 nm to 15 nm, even in the epitaxial growth in the temperature range in which the SiO ₂ layer and Si that constitute the SOI substrate 1 are not softened or melted, the single crystal SiC thin film 5 is formed by sublimation. Since the crystalline SiC thin film 5 tends to disappear, the effect of improving the flatness of the surface by preventing the disappearance of the seed layer 5 in two steps and improving the crystallinity of the single crystal SiC layers 6 and 7 to be grown is remarkable. Appears effectively.

  Furthermore, since the growth temperature of the first stage of the two stages of growth temperature is in the temperature range of 700 to 1200 ° C., the seed layer 5 of the single crystal SiC thin film 5 formed by the carbonization process disappears by sublimation. The primary single crystal SiC 6 is deposited on the seed layer 5 while preventing the seed layer 5 from disappearing effectively and reliably in the second stage.

In the present invention, the growth temperature of the second and subsequent stages among the two stages of growth temperatures is within the temperature range of 1000 to 1405 ° C., so that the SiO ₂ layer and Si constituting the SOI substrate 1 are softened or melted. The secondary single crystal SiC layer 7 having good crystallinity and surface flatness can be epitaxially grown in a temperature range where no crystallization occurs.

  Next, examples of the method for producing a single crystal SiC substrate of the present invention will be described.

  A 30 mm square SOI substrate 1 having a surface Si layer 3 having a thickness of 100 nm was prepared as a sample. The SOI substrate 1 of the above sample was heated at 1100 ° C. for 90 minutes while flowing oxygen gas at 1 slm to form an oxide film on the surface, and then etched with hydrofluoric acid or the like to form a surface Si layer 3 having a thickness of 5 nm. It was thinned.

The SOI substrate 1 was placed in a processing chamber, heated at 1250 ° C. while flowing 1 slm of H ₂ gas and 10 sccm of C ₃ H ₈ in the processing chamber, and subjected to carbonization for 15 minutes to perform SiC conversion.

  Then, by holding 0.1 sccm monomethylsilane in the processing chamber at 1000 ° C. for 20 minutes, the first stage SiC is epitaxially grown to form a primary single crystal SiC layer 6 having a thickness of 15 nm and a total thickness of 20 nm. Single crystal SiC.

  Next, the processing temperature was raised to 1100 ° C. and held for 90 minutes, whereby second-stage SiC epitaxial growth was performed to form a secondary single crystal SiC layer 7 having a thickness of 80 nm to obtain a single crystal SiC having a total thickness of 100 nm.

  On the other hand, a comparative example was prepared in which the first stage at 1000 ° C. was not performed and only one stage of epitaxial growth was held at 1100 ° C. for 90 minutes.

  The surface RMS roughness roughness of the single crystal SiC substrate of the above example was 5.95 nm, whereas the surface RMS roughness roughness of the single crystal SiC substrate of the comparative example was 38.90 nm, compared with the comparative example. It can be seen that the surface flatness is greatly improved in the example.

  The present invention can be applied to the manufacture of semiconductor substrates used for large scale integrated circuits and the like.

It is process drawing which shows the method of forming the single crystal SiC layer using the SOI substrate of one Example of this invention. It is a figure which shows the method of forming the single crystal SiC layer using the said SOI substrate . It is a figure which shows the method of forming the single crystal SiC layer using the said SOI substrate . It is a figure which shows the temperature conditions of epitaxial growth.

Explanation of symbols

1 SOI substrate 2 Si base material 3 Surface Si layer 4 Buried insulating layer (oxide layer)
5 Seed layer (single crystal SiC thin film)
6 Primary single crystal SiC layer 7 Secondary single crystal SiC layer 8 GaN layer

Claims (1)

An SOI substrate having a surface Si layer having a predetermined thickness and a buried insulating layer is prepared, and the SOI substrate is heated in a hydrocarbon-based gas atmosphere to transform the surface Si layer into a single crystal SiC film. A method of forming a single crystal SiC layer by epitaxial growth using a SiC film as a seed layer,
Forming a single crystal SiC film as a seed layer as a thin film of 1 nm to 15 nm;
Single seed SiC is deposited on the seed layer by first-stage epitaxial growth set at a relatively lower growth temperature than the second-stage epitaxial growth described later within a temperature range of 700 to 1050 ° C. Further depositing single crystal SiC on the seed layer while preventing disappearance due to sublimation,
Single crystal SiC using a SOI substrate is characterized in that single crystal SiC is grown by a second stage epitaxial growth set at a growth temperature relatively higher than the first stage epitaxial growth within a temperature range of 1100 to 1405 ° C. A method of forming a crystalline SiC layer .

Images