RU2405071C1 - METHOD OF PRODUCING MONOCRYSTALLINE SiC - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: method of producing monocrystalline SiC involves sublimation of a source of SiC 9 placed in a crucible onto a substrate made from a seed crystal of SiC 8 when the vapour phase passes from the source of SiC 9 through a barrier carbon catcher (BCC). The BCC used is less than two overlapping plates 10, 11 made from heat-resistant material (graphite, tantalum or niobium) and which lie in parallel to the base of the crucible such that h=(0.2-0.6)·d·(I-γ), where h is the distance between the overlapping plates, mm; d is the diametre of the crucible, mm; γ is the overlap ratio (the ratio of the area covered by neighbouring plates to the area of the crucible), equal to 0.5-0.8.

EFFECT: higher rate of growth of SiC with high quality of the desired product.

4 cl, 1 tbl, 3 dwg

Description

The invention relates to microelectronics and relates to a technology for producing single-crystal SiC, a widely used material used in the manufacture of integrated circuits.

A known method for producing single-crystal SiC by sublimation of a source of SiC placed in a crucible onto a substrate of a seed SiC single crystal (see, for example: JP 2008074662, C30B 29/36, C30B 29/10, 2008; EP 1164211, C30B 23/00, C30B 29/36, 2001; JP 2006069851, C30B 29/36, C30B 29/10, 2006).

However, the target product obtained by this method has low structural perfection due to the micropores contained in it, resulting from the capture of carbon particles from the gas phase by a growing SiC crystal. This leads to low reliability of microelectronic circuits made from it.

To suppress microdefects and stresses developing from the outer edge of the seed crystal, the outer surfaces of single-crystal SiC obtained by sublimation of the source on a substrate are subjected to sublimation etching in the early stages of crystal growth (JP 2007176718, C30B 29/36, C30B 29/10, 2007).

Another way to improve the quality of the target product is to grow single-crystal SiC in thermal contact with polycrystalline SiC, which provides equalization of the surface temperature of the target product to prevent microcracks (JP 2001114598, C30B 29/36, C30B 29/10, 2001). As a means for equalizing thermal fields, it is known to use a heat shield installed in a SiC vapor phase transfer space (JP 2000264795, C30B 23/00, C30B 29/36, C30B 29/10, 2000).

One of the ways of developing modern methods for producing single-crystal SiC by sublimation of a SiC source placed in a crucible onto a substrate from a SiC seed single crystal is to implement the local quality principle. To this end, longitudinal graphite baffles are installed on the vapor phase path, dividing the transferred SiC flow into sections for subsequent condensation on the corresponding seed crystals according to the number of formed sections (WO 2006124103, C30B 23/00, C20B 29/36, C30B 35/00, C30B 29 / 10, 2006).

Another way is the diffusion separation of the vapor phase components with the subsequent redirection of the separated ballast components into the space formed outside the growth zone of the target product (JP 2007320794, C30B 29/36, C30B 23/06, C30B 29/10, C30B 23/02, 2007; JP 2008115033, C30B 29/36, C30B 29/10, 2008).

However, the target product obtained by these methods continues to contain defects due to the ingress of carbon particles into its structure.

The closest to the claimed technical essence and the achieved quality of the target product is a method for producing single-crystal SiC, which provides for the sublimation of a SiC source placed in a crucible onto a substrate from a SiC seed single crystal when the vapor phase of a SiC source passes through a carbon trap, which is a partition made of porous carbon (US 4866005, H01L 21/205, H01L 21/36, 1989).

The disadvantage of the prototype method is the low growth rate of the target product due to a significant obstacle to the passage of the vapor phase of SiC through a partition made of porous carbon. In addition, the quality of the target product, characterized by the density of micropores, is also low.

The technical problem of the proposed method is to improve the quality of the target product and its growth rate.

The solution to this technical problem lies in the fact that in the method for producing single-crystal SiC, which involves the sublimation of a SiC source placed in a crucible onto a substrate from a SiC seed single crystal when the vapor phase of a SiC source passes through a carbon barrier, the following change is made: as a carbon barrier use at least two overlapping plates made of heat-resistant material and installed parallel to the base of the crucible from the calculation

where h is the distance between the overlapping plates, mm;

d is the diameter of the crucible, mm;

γ is the overlap coefficient (the ratio of the area covered by adjacent plates to the area of the crucible), equal to 0.5 ÷ 0.8.

The overlap coefficient of adjacent plates of the barrier trap is

where S ₁ , S ₂ - the area of the respective adjacent plates, cm ² ;

S is the area of the base of the crucible, cm ² .

A causal relationship between the changes made and the achieved increase in the SiC growth rate is that passing the vapor phase through a new barrier trap allows it to be cleaned of carbon particles at low aerodynamic resistance to flow passage, whereas when passing the vapor phase through porous carbon, the aerodynamic resistance was great. The causal relationship of the changes with the achieved improvement in the quality of the target product is not theoretically known. It was established experimentally and, apparently, consists in improving the filtering ability of the new barrier trap (it is possible that it captures not only carbon, but also other ballast components).

The rationale for the operating parameters is given in the above example.

To pass the SiC vapor phase, a barrier trap can be used, the plates of which are made of graphite, tantalum or niobium. Of these, graphite is the best material since it is the cheapest and most durable.

In the technical implementation of the method, the plates of the carbon trap can be in the form of a segment of the base of the crucible. In another embodiment, one of the plates of the carbon barrier trap has a ring shape, while through holes are made in the adjacent plate for passage of the vapor phase between these plates.

Figure 1 shows a diagram of a crucible for implementing the proposed method; figure 2 and 3 depict options for carbon barrier traps. The table shows the technical characteristics of the method for various values of the operating parameters for the given example.

As a technical means for implementing the proposed method can be used a crucible (figure 1), containing a cylindrical body, side wall 1, bottom 2 and cover 3 of which are made of dense MPG-6 graphite. On the side wall 1 of the crucible, a spiral 4 of a resistive electric heater and a heat-insulating layer 5 made of graphite felt are sequentially located outside from the outside. Elements 1 to 5 are placed in a cylindrical vacuum chamber 6 of a sublimation unit. Inside the crucible body, a holder 7 is mounted on its lid 3 to place a seed silicon carbide single crystal 8. At the bottom 2 of the crucible are located the feedstock 9 - polycrystals of silicon carbide, which serve as a source of the resulting target product. Between the feedstock 9 and the seed single crystal 8, a carbon trap is installed in the crucible formed from two overlapping plates 10 and 11 (a variant with a large number of overlapping plates is possible) made of HFA graphite foil 2 mm thick.

In the described example, overlapping plates 10 and 11 are used, the shape of which is shown in FIGS. 2 and 3.

In the embodiment of FIG. 2, the plates 10 and 11 of the carbon barrier trap are in the form of a crucible base segment limited by an arc of more than 180 ° of the circumference of its inner diameter.

In the embodiment of FIG. 3, one of the plates of the carbon barrier trap has a ring shape, the outer diameter of which is equal to the inner diameter of the crucible, and through holes are made in the adjacent plate for passage of the SiC vapor phase between these plates. The last condition is met if the orthogonal projections of these through holes fall into the area of the ring of the adjacent plate.

For experimental verification of the method, a seed crystal 8 of SiC polytype 4H of a nominal orientation (0001) and a deviation of 9 ° in the azimuth direction [11-20] with an average surface micropore density of 10-30 cm ^{-2 was used} . This material was subjected to sequential double-sided grinding and polishing on diamond pastes with a decrease in the grain size of the abrasive to 0.25 μm, followed by etching in molten KOH for 10 min at 600 ° C and ultrasonic washing in deionized water.

A high-purity powdery silicon carbide manufactured by Saint-Gobain (Norge), with a grain size of ≈l00 μm, was used as a SiC source. SiC powder is placed in a crucible (Fig. 1) with an inner diameter of d = 80 mm and preliminary sintering is carried out in vacuum for 2 hours at 2000 ° C to remove the oxide layer on the grain surfaces and reduce the specific surface of the powder.

Then, after cooling the crucible, the seed crystal 8 is fixed in its holder 7. The vacuum chamber 6 is pumped out to a pressure of 8 · 10 ^-6 mm Hg, and the crucible is heated to 1000 ° C using an electric coil 4 and kept at this temperature for 1 h to remove residual contaminants. After that, the vacuum chamber 8 is filled with argon to a pressure of 100 mm Hg. and heated to a source temperature of SiC equal to 2220 ° C. The temperature of the seed crystal is 2030 ° C. It is held at the indicated temperature and pressure for 1 h, after which the vacuum chamber 6 is pumped out to an argon pressure of 3 mm Hg, at which the SiC ingot grows on the seed crystal 8 for 12-18 hours. After growing the ingot of the target product, the vacuum chamber is cooled to room temperature and depressurized. A single-crystal ingot of silicon carbide polytype 4H is extracted from the crucible.

The growth rate of the ingot is determined by direct measurement of the thickness of the ingot, as well as gravimetrically (by changing the weight of the holder 7 with the seed 8 and the target product built up on it). The density of micropores and dislocation in the ingot is determined under a microscope after alkaline etching of the surface of the target product. Inclusions of carbon in the grown ingot are identified visually under a microscope, as well as using x-ray diffraction analysis.

The results of 6-fold tests of the process options in an argon medium at the indicated temperatures of the SiC source and the seed single crystal, equal to 2220 ° C and 2030 ° C, respectively, the pressure in the vacuum chamber 6, equal to 3 mm Hg, and various values of the coefficient of overlap of the plates 10 and 11 and the distances h between the plates are shown in the table.

As can be seen from the table, with the optimal value of the parameters of the carbon barrier trap γ = 0.6 and h = 0.4d (l-γ), the growth rate of the target product is 1.5 mm / h, and the micropore density in it is 25 cm ^-2 . With an increase in the overlap coefficient of plates 10 and 11 in the carbon trap to γ = 0.8, the micropore density slightly decreases (up to 19 cm ^-2 ), however, the growth rate of the target product sharply decreases (up to 0.7 mm / h). A further (transcendental) increase in the coefficient γ leads to a halt in the growth of the target product due to overgrowth of the barrier trap with a SiC film. A decrease in the coefficient γ leads to an increase in the growth rate of the target product to 2.4 mm / h, however, its quality sharply worsens (micropore density 62 cm ^-2 or more). The quality of the target product obtained by the prototype method is characterized by a micropore density of not less than 100 cm ^-2 at a growth rate of single-crystal SiC not more than 1 mm / h.

Thus, the use of the proposed method allows to increase the growth rate of single-crystal SiC by 1.5 times while improving the quality of the target product by 4 times in relation to micropore density. The technical result, a derivative of the achieved, is to increase labor productivity and yield of the target product, as well as reducing the material consumption and the complexity of the method.

Table Technical characteristics of the target product and the method of its production, depending on the value of the operational parameters of the sublimation process VALUES OF MODE PARAMETERS SPECIFICATIONS γ h, mm [rel. units] SiC growth rate, mm / h The density of micropores, cm ^-2 0.4 34 [0.7 <1-γ)] 2.4 ± 0.4 > 100 0.5 24 [0.6d (1-γ)] 1.8 ± 0.3 62 ± 8 0.6 13 [0.4d (1-γ)] 1.5 ± 0.2 25 ± 4 0.8 3 [0,2d (1-γ)] 0.7 ± 0.2 19 ± 4 0.9 1 [0,1d (1-γ)] The process stops due to overgrowth of the barrier trap with a SiC film - US 4866005 (prototype) no more than 1.0 * no less than 100 ** * prototype data; ** data of authors.

Claims (4)

1. A method of producing single-crystal SiC, comprising sublimating a SiC source placed in a crucible onto a substrate of a SiC seed single crystal when the vapor phase of the SiC source passes through a carbon barrier trap, characterized in that at least two overlapping plates are used as the carbon barrier trap from heat-resistant material and installed parallel to the base of the crucible from the calculation
h = (0.2 ÷ 0.6) · d · (1-γ),
where h is the distance between the overlapping plates, mm;
d is the diameter of the crucible, mm;
γ is the overlap coefficient (the ratio of the area covered by adjacent plates to the area of the crucible), equal to 0.5-0.8. 2. The method according to claim 1, characterized in that the vapor phase of the SiC source is passed through a barrier trap, the plates of which are made of graphite, tantalum or niobium. 3. The method according to claim 1, characterized in that the vapor phase of the SiC source is passed through a barrier trap, the plates of which are in the form of a segment of the base of the crucible. 4. The method according to claim 1, characterized in that the vapor phase of the SiC source is passed through a barrier trap, one of the plates of which has a ring shape, and through holes are made in the adjacent plate for passage of the vapor phase between these plates.

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