JP4563918B2 - Method for producing single crystal SiC substrate - Google Patents

Description

  The present invention relates to a method for manufacturing a single crystal SiC substrate using, for example, an insulating layer embedded semiconductor substrate.

  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.

The above-described insulating layer embedded type semiconductor SiC substrate is, for example, 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. ). 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 above circumstances, and an object of the present invention is to provide a method for producing a single crystal SiC substrate that can improve the crystallinity of the SiC layer to be epitaxially grown and improve the surface flatness.

In order to achieve the above object, a method for producing a single crystal SiC substrate according to the present invention comprises epitaxially growing a single crystal SiC film, which is a thin film having a thickness of 1 nm to 15 nm on the surface, using the single crystal SiC film as a seed layer. A method of forming a single crystal SiC layer by:
The gist is that the single crystal SiC film is used as a seed layer , and epitaxial growth is performed by rapid heating at a temperature rising rate of 25 ° C. or more per second.

That is, the method for producing a single crystal SiC substrate according to the present invention requires rapid heating at a heating rate of 25 ° C. or more per second using a single crystal SiC film, which is a thin film having a thickness of 1 nm to 15 nm, as a seed layer. The time can be shortened to the limit, the disappearance of the partial seed layer due to sublimation can be almost completely prevented, the crystallinity of the single crystal SiC layer produced by epitaxial growth is improved, and the flatness of the surface is greatly improved. improves. Further, 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. At this time, when the single crystal SiC film serving as a seed layer is a thin film of 1 nm to 15 nm, the deterioration of crystallinity due to sublimation becomes remarkable. The effect of improving the flatness of the surface by improving the crystallinity of the SiC layer is remarkable and effective.

In the present invention, in the temperature range to reach the epitaxial growth temperature, in a temperature range up to at least 1100 ° C. or more epitaxial growth temperature, in the case of performing the rapid heating, SiC is at easy 1100 ° C. or more epitaxial growth temperature Doma sublimation in the temperature region, since carrying out the rapid heating at a heating rate of more per 25 ° C., is possible to shorten the residence time of the temperature range to the limit, almost completely disappears partial seed layer by sublimation The crystallinity of the single crystal SiC layer produced by epitaxial growth can be improved, and the surface flatness can be greatly improved.

  In the present invention, when the rapid heating is RTP heating, rapid heating can be performed relatively easily at a temperature rising rate of 25 ° C. or more per second. The disappearance of the layer can be prevented, the crystallinity of the single crystal SiC layer to be grown can be improved, and the flatness of the surface can be improved.

In the present invention, an SOI substrate having a surface Si layer and a buried insulating layer having a predetermined thickness is prepared, and the SOI substrate is heated in a hydrocarbon gas atmosphere to transform the surface Si layer into a single crystal SiC film. When a substrate having a single crystal SiC film formed on the surface is formed, the single crystal SiC film disappears by sublimation even in the SiO ₂ layer constituting the SOI substrate or epitaxial growth in a temperature range where Si does not soften or melt. Therefore, the effect of preventing the disappearance of the seed layer by rapid heating, improving the crystallinity of the single crystal SiC layer to be grown, and improving the flatness of the surface is remarkable.

  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 producing a single crystal SiC 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 3 into a single crystal SiC thin film 5. Then, the single crystal SiC thin film 5 is epitaxially grown as a seed layer 5. At this time the epitaxial growth, the temperature range to reach the epitaxial growth temperature, in a temperature range up to at least 1100 ° C. or more epitaxial growth temperature is epitaxially grown by performing rapid heating at a heating rate of more per 25 ° C..

  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 has 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 layer 6 is formed by epitaxial growth thereafter, the crystallinity of SiC is improved, so that a single crystal SiC layer 6 having a clean single crystal and a uniform film thickness can be obtained. 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. The SiC layer 6 is grown.

At this time, in the temperature range to reach the epitaxial growth temperature, in a temperature range up to at least 1100 ° C. or more epitaxial growth temperature is epitaxially grown by performing rapid heating at a heating rate of more per 25 ° C..

  The rate of temperature increase during the rapid heating needs to be 25 ° C. or more per second, more preferably 30 ° C. or more per second, and more preferably 40 ° C. or more per second. If the rate of temperature rise does not reach 25 ° C per second, the time during which the substrate is exposed to a temperature range of 1100 ° C or higher where SiC is likely to sublime is increased until the epitaxial growth temperature is reached, during which time SiC sublimates and partially disappears. This is because the crystallinity of the single crystal SiC layer 6 produced by epitaxial growth is deteriorated or the smoothness of the surface is deteriorated.

  The temperature range for the rapid heating needs to be at least a temperature range of 1100 ° C. or higher until the epitaxial growth temperature is reached, but may be 1000 ° C. or higher, or an epitaxial growth temperature of 900 ° C. or higher, or 800 ° C. or higher. It can be up to temperature. The rapid heating from room temperature to the epitaxial growth temperature can also be performed.

  The rapid heating is preferably RTP (Rapid Thermal Processing) heating. As the RTP heating apparatus, for example, a lamp heating type heating apparatus in which an infrared lamp by heat radiation is added as a heating means to a reaction tube into which a process gas is introduced can be used.

  FIG. 4 shows an example of a rapid heating / rapid cooling device (RTP device) suitably used in the present invention.

  In the figure, reference numeral 10 denotes a heat treatment apparatus (RTP apparatus). The heat treatment apparatus 10 includes a chamber 11 made of quartz, and heats a wafer 18 as a substrate in the chamber 11. Heating is performed by a heating lamp 12 arranged so as to surround the chamber 11 from above, below, left and right. The heating lamps 12 can control power supplied independently.

  A gas introduction port 19 is provided on the gas introduction side of the chamber 11, and an auto shutter 13 is provided on the gas exhaust side to block outside air. The auto shutter 13 is provided with a wafer insertion opening (not shown) that can be opened and closed by a gate valve. In addition, the auto shutter 13 is provided with a gas exhaust port 20 so that the furnace atmosphere can be adjusted.

  The wafer 18 is placed on a support jig, for example, a three-point support 15 formed on the quartz tray 14. A quartz buffer 16 is provided on the quartz tray 14 on the gas inlet 19 side, so that the gas introduced from the gas inlet 19 can be prevented from directly hitting the wafer 18.

  The chamber 11 is provided with a temperature measurement special window (not shown), and the pyrometer 17 installed outside the chamber 11 can measure the temperature of the wafer 18 through the special window.

  By the heat treatment apparatus 10 as described above, the process of rapidly heating / rapidly cooling the wafer 18 is performed as follows.

  First, a wafer 18 is placed in the chamber 11 from a wafer insertion port (not shown) by a wafer handling device (not shown) arranged adjacent to the heat treatment apparatus 10 and placed on the quartz tray 14, and then the auto shutter 13 is closed. Then, electric power is supplied to the heating lamp 12 to raise the temperature of the wafer 18 to a predetermined epitaxial growth temperature. At this time, the temperature is increased at a temperature increase rate of 25 ° C. or more per second, and the time required from the room temperature to the target temperature is about 5 to 20 seconds, for example.

  Next, high temperature heat treatment can be applied to the wafer 18 by holding at that temperature for a predetermined time. When the high temperature heat treatment is completed after a predetermined time, the output of the heating lamp 12 is lowered and the temperature of the wafer 18 is lowered. At this time, the temperature can be lowered in about 20 seconds, for example. Finally, the heat treatment is completed by taking out the wafer with the wafer handling apparatus.

  Specifically, in the epitaxial growth, for example, the single crystal SiC layer 6 is 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 propane is supplied into the processing chamber at a gas flow rate of about 1 sccm. By processing at this growth temperature, the single crystal SiC layer 6 can be grown by epitaxial growth using the single crystal SiC thin film 5 as the seed layer 5.

  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 6 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 a single crystal SiC layer 6 is 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, while a temperature of 800 to By processing at 1405 ° C., the GaN layer 8 can be formed on the secondary single crystal SiC layer 6.

By this method, the time of epitaxial growth, the temperature region in SiC sublimation tends 1100 ° C. or more epitaxial growth temperature Doma, from doing a rapid heating at a heating rate of more per 25 ° C., the temperature range The residence time can be shortened to the limit, the disappearance of the partial seed layer 5 due to sublimation can be almost completely prevented, the crystallinity of the single crystal SiC layer 6 produced by epitaxial growth is improved, and the flatness of the surface is improved. Is also 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 film to be the seed layer 5 is a thin film having a thickness of 1 nm to 15 nm, when the single crystal SiC film to be the seed layer 5 is a thin film having a thickness of 1 nm to 15 nm, the deterioration of crystallinity due to sublimation is remarkable. Therefore, the effect of preventing the disappearance of the seed layer 5 by rapid heating, improving the crystallinity of the single crystal SiC layer 6 to be grown, and improving the flatness of the surface is remarkable.

  In addition, the rapid heating is RTP heating, so that the rapid heating can be performed relatively easily at a temperature rising rate of 25 ° C. or more per second. It is possible to prevent disappearance, improve the crystallinity of the single crystal SiC layer 6 to be grown, and improve the surface flatness.

Also, an SOI substrate 1 having a surface Si layer 3 and a buried insulating layer 4 having a predetermined thickness is prepared, and the SOI substrate 1 is heated in a hydrocarbon gas atmosphere to form the surface Si layer 3 as a single crystal SiC thin film. 5 to form a substrate having a single-crystal SiC thin film 5 formed on the surface, and even in the epitaxial growth in the temperature range where the SiO ₂ layer constituting the SOI substrate 1 and Si are not softened or melted, the single crystal is obtained by sublimation. Since the SiC thin film 5 tends to disappear, the effect of preventing the disappearance of the seed layer 5 by rapid heating and improving the flatness of the surface by improving the crystallinity of the single crystal SiC layer 6 to be grown appears significantly. It is effective.

  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 is placed in a processing chamber, heated to 1250 ° C. while flowing 1 slm of H ₂ gas and 10 sccm of C ₃ H ₈ in the processing chamber, carbonized for 15 minutes, SiC is transformed, and the thickness is increased. A single-crystal SiC thin film 5 of 5 nm was formed and once cooled, a sample was prepared.

  Then, using the heat treatment apparatus 10 of FIG. 4, RTP heating was performed to an epitaxial growth temperature of 1200 ° C. while flowing 0.1 sccm of monomethylsilane. The temperature rise state at that time is shown in FIG. The average rate of temperature increase in this example was 230 ° C. per second.

  In the example of FIG. 5, it is the influence of the feedback control that the temperature rise is slightly delayed around 620 ° C. and 1050 ° C., respectively. Thus, even if the temperature increase rate is slightly slowed during the temperature increase process, the object of the present invention is achieved if the average temperature increase rate at least in a predetermined temperature range until reaching the epitaxial growth temperature is 25 ° C. or more per second. Such an aspect is also included in the present invention.

  Then, the epitaxial growth was performed by maintaining the above epitaxial growth temperature for 10 minutes to form a single crystal SiC layer 6 having a thickness of 500 nm.

  On the other hand, as a comparative example, a temperature was raised by a resistance heating heat treatment apparatus and epitaxial growth was performed by holding at 1200 ° C. for 10 minutes was prepared. The temperature rise state at that time is shown in FIG. In the example of FIG. 6, the temperature is kept several times in order to stabilize the temperature. In this example, the rate of temperature increase excluding the time of holding at a constant temperature is about 2 ° C. per second.

  Next, the extent to which the heating rate affects the crystallinity of the SiC film was investigated.

  The sample of Example 1 was subjected to RTP heating to an epitaxial growth temperature of 1200 ° C. while flowing 0.1 sccm of monomethylsilane using the heat treatment apparatus 10 of FIG. Epitaxial growth was performed by setting the rate of temperature rise at this time to 13 ° C., 24 ° C., 40 ° C., 100 ° C., and 200 ° C. per second.

  Evaluation of crystallinity after epitaxial growth was performed as follows. That is, first, every sample is epitaxially grown on the crystal orientation (100) plane of the substrate, the crystal after the epitaxial growth is subjected to X-ray diffraction, and the diffraction chart is output.

  For example, FIG. 7A illustrates an example of a diffraction chart with good crystallinity, and FIG. 7B illustrates an example of a diffraction chart with poor crystallinity. Since epitaxial growth is performed on the crystal orientation (100) plane, when the crystallinity is good, the peak of the (100) plane appears large and the peak of the (111) plane appears small as shown in FIG. However, as the crystallinity deteriorates, the peak of the (111) plane appears larger as shown in FIG. 7B, and the peak of the (100) plane appears smaller.

  Then, the ratio h1 / h2 between the peak height h1 of the (100) plane excluding the background and the peak height h2 of the (111) plane is the peak intensity ratio (100) / (111). The larger the crystallinity, the larger the value.

  FIG. 8 is a plot of the peak intensity ratio (100) / (111) for each sample. As can be seen from the figure, when the heating rate is slower than 24 ° C. per second, the crystallinity is extremely deteriorated.

  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 manufacturing method of the single crystal SiC substrate of one Example of this invention. It is a figure which shows the manufacturing method of the said single crystal SiC substrate. It is a figure which shows the manufacturing method of the said single crystal SiC substrate. It is a figure which shows an example of an RTP apparatus. It is a figure which shows the temperature rising state of an Example. It is a figure which shows the temperature rising state of a comparative example. It is a figure explaining the evaluation method of crystallinity. It is a figure which shows the evaluation result of crystallinity.

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 Single crystal SiC layer 8 GaN layer 10 Heat treatment device 11 Chamber 12 Heating lamp 13 Auto shutter 14 Quartz tray 15 Three-point support 16 Buffer 17 Pyrometer 18 Wafer 19 Gas inlet 20 Gas exhaust

Claims (4)

A method of forming a single crystal SiC layer by epitaxially growing the single crystal SiC film as a seed layer on a substrate having a single crystal SiC film that is a thin film having a thickness of 1 nm to 15 nm on the surface,
A method for producing a single crystal SiC substrate, wherein the single crystal SiC film is used as a seed layer and epitaxial growth is performed by rapid heating at a temperature rising rate of 25 ° C. or more per second. The method for producing a single-crystal SiC substrate according to claim 1 , wherein the rapid heating is performed in a temperature range up to an epitaxial growth temperature of at least 1100 ° C in a temperature range until reaching the epitaxial growth temperature . 3. The method for producing a single crystal SiC substrate according to claim 1, wherein the rapid heating is RTP heating. 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. The method for producing a single crystal SiC substrate according to any one of claims 1 to 3 , wherein a substrate on which a crystalline SiC film is formed is formed.