JP2646369B2 - Method for manufacturing SOI substrate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] The present invention relates to an improvement in a method for manufacturing a so-called SOI substrate in which a silicon layer is formed on an insulator layer, and a polycrystalline silicon layer is formed on a silicon dioxide layer as an underlayer. In a so-called SOI substrate manufacturing method in which a polycrystalline silicon layer is once melted and then recrystallized by irradiating a laser through an antireflection cap layer formed thereon, at least the recrystallized silicon layer No twinning defects and grain boundaries occur near the surface,
For the purpose of improving the surface of the recrystallized silicon layer so that no irregularities occur, a polycrystalline silicon layer is formed on the silicon dioxide layer, and an anti-reflection cap layer is formed on the polycrystalline silicon layer. Forming, irradiating the polycrystalline silicon layer with laser through the antireflection cap layer, and melting and recrystallizing the polycrystalline silicon layer to improve the crystallinity. In the method for manufacturing an SOI substrate formed by forming a layer, after the step, the antireflection cap layer is removed, and laser irradiation is performed with lower energy than the laser irradiation performed in the step. Only the surface layer of the recrystallized polycrystalline silicon layer is melted again and recrystallized again to produce a polycrystalline silicon layer with further improved crystallinity.

[Industrial applications]

The present invention relates to an improvement in a so-called SOI substrate manufacturing method in which a silicon layer is formed on an insulator layer. In particular, the present invention relates to an improvement in a method for manufacturing a so-called SOI substrate in which a polycrystalline silicon layer is formed on a silicon dioxide layer, and the polycrystalline silicon layer is once melted and then recrystallized by laser irradiation.

[Conventional technology]

A method of manufacturing a so-called SOI substrate according to the related art will be briefly described.

Referring to FIG. 4, the surface of a silicon substrate 1 is oxidized to form an underlying silicon dioxide layer 2 having a thickness of about 1 μm, and a polycrystalline silicon layer 3 having a thickness of about 8,000 mm is formed by CVD or the like. A laminated body of the silicon dioxide layer 41 and the silicon nitride layer 42 as the antireflection cap layer 4 (the thickness of both the silicon dioxide layer 41 and the silicon nitride layer 42 is about 300 mm, the former being the lower layer). Laser irradiation is performed via the anti-reflection cap layer 4. The reason for using this antireflection cap layer 4 is to measure the effective use of laser energy. The laser used is, for example, a continuous wave of an argon laser having a wavelength of 5,145 °, and its power is usually about 3 W. When using the continuous wave of this argon laser, the substrate temperature is set to 450 ° C., and the laser beam is scanned at about 10 cm / sec.

[Problems to be solved by the invention]

The cross section of the SOI substrate manufactured by performing the method of manufacturing a so-called SOI substrate according to the prior art described above is observed using an electron microscope for observing the cross section, as shown in FIG. Twinning type defects A and grain boundaries B extending from the silicon layer 2 into the recrystallized silicon layer 31 and twinning extending from the antireflection cap layer 4 into the recrystallized silicon layer 31. Type defects C and grain boundaries D are recognized. In addition, since the antireflection cap layer 4 functions as a “template” in the recrystallization step, in the recrystallized silicon layer 31, near the interface with the antireflection cap layer 4, The occurrence of the distortion field E is inevitable. Therefore, the surface of the recrystallized silicon layer 31 is inevitable to have irregularities.

Among the above disadvantages, it is desirable to remove the twinning type defects C and grain boundaries D near the surface of the recrystallized silicon layer 31 and the irregularities and the strain field E on the surface of the recrystallized silicon layer 31 by all means. . This is because the element is formed in this region.

An object of the present invention is to meet this demand, and to form a polycrystalline silicon layer on an underlying silicon dioxide layer and irradiate the layer with a laser through an antireflection cap layer formed thereon. In a method for manufacturing a so-called SOI substrate, which is formed by melting and recrystallizing a crystalline silicon layer once,
It is an object of the present invention to improve twining defects and grain boundaries at least in the vicinity of the surface of the recrystallized silicon layer so that no irregularities occur on the surface of the recrystallized silicon layer.

[Means for solving the problem]

The above object is achieved by forming a polycrystalline silicon layer (3) on a silicon dioxide layer (2), forming an antireflection cap layer (4) on the polycrystalline silicon layer (3), The polycrystalline silicon layer (3) is irradiated with laser through the cap layer (4), and the polycrystalline silicon layer (3) is irradiated.
Is once melted and then recrystallized to form a polycrystalline silicon layer (31) having improved crystallinity. In the method for manufacturing an SOI substrate, after the step, the antireflection cap layer (4) is formed. Removed, laser irradiation with energy weaker than the laser irradiation performed in the above step,
Only the surface layer of the recrystallized polycrystalline silicon layer (31) is again melted and recrystallized to form a polycrystalline silicon layer (32) with further improved crystallinity. Achieved.

[Action]

The function of the antireflection cap layer 4 is as described above.
It is to utilize the energy of a laser effectively. Since the above-mentioned drawbacks are based on the presence of the anti-reflection cap layer 4, in the present invention, after the original effect of the anti-reflection cap layer 4 is fully utilized, it is removed. The defect generated based on the above-mentioned side effect is repaired by lightly irradiating the laser.

〔Example〕

Hereinafter, a method for manufacturing an SOI substrate according to an embodiment of the present invention will be further described with reference to the drawings.

See FIG. 2. As in the prior art, the surface of a silicon substrate 1 is oxidized to form an underlying silicon dioxide layer 2 having a thickness of about 1 .mu.m.
After forming a polycrystalline silicon layer 3 having a thickness of about 8,000 mm using a method or the like, a laminate of a silicon dioxide layer 41 and a silicon nitride layer 42 as an antireflection cap layer 4 (the silicon dioxide layer 41 is also nitrided). The thickness of the silicon layer 42 is also about 300 mm,
The former is the lower class. ) Is formed, and laser irradiation is performed via the antireflection cap layer 4. The laser used in this step is, for example, a continuous wave of an argon laser having a wavelength of 5,145 °, and its power is usually about 3 W. When using the continuous wave of this argon laser, the substrate temperature is 45
The temperature is set to 0 ° C., and the laser beam is scanned at about 10 cm / sec.

Referring to FIG. 3, as a result of the above laser irradiation, twinning type defects A and grain boundaries B extend into the silicon layer 31 recrystallized from the underlying silicon dioxide layer 2 and, as shown in FIG. In the silicon layer 31 recrystallized from the layer 4, a twinning type defect C or a grain boundary D
Extends, and a strain field E exists near the interface with the antireflection cap layer 4.

1a and 1b. Here, after removing the antireflection cap layer 4 and exposing the recrystallized polycrystalline silicon layer 31, laser irradiation is performed using, for example, a continuous wave argon laser (5,145 °). Is shown. At this time, since the substrate temperature is 450 ° C. and the anti-reflection cap layer 4 is not present, the absorbed energy is small, and only the surface layer of the recrystallized polycrystalline silicon layer 31 is melted. Recrystallized. At this time, the twinning defects C and the grain boundaries D extending from the surface layer of the recrystallized polycrystalline silicon layer 31 toward the inside disappear, and further, the recrystallized polycrystalline silicon layer 31 is further reduced. The surface layer 32 is flattened as shown in FIG.
The distortion field E disappears.

See FIGS. 1c and 1d. FIG. 1c is a cross-sectional observation electron micrograph showing the crystal structure of the cross section of the SOI substrate after the above steps, and FIG. 1d is a schematic view thereof. In the schematic diagram of FIG. 1d, 2 is an underlying silicon dioxide layer, and 31 is a recrystallized polycrystalline silicon layer.
Reference numeral 31 denotes a region where the crystallinity and flatness are improved by the present invention (only the surface layer of the polycrystalline silicon layer 31 which has been recrystallized and has improved crystallinity is again melted and recrystallized, and Twinning defects C and grain boundaries D extending from the surface layer of the crystalline silicon layer 31 toward the inside thereof disappear, the surface layer is flattened, the strain field E disappears, and the crystallinity is further improved. Silicon layer 32), 5
Is a polycrystalline silicon layer formed for cross-sectional observation.
No defect other than one stacking fault indicated by F is recognized at all, and it is recognized that the effect of the present invention is extremely remarkable.

〔The invention's effect〕

As described above, in the method for manufacturing an SOI substrate according to the present invention, after completing the normal steps of the method for manufacturing an SOI substrate according to the related art, the anti-reflection cap layer is removed,
Since laser irradiation is performed with lower energy than the laser irradiation performed in the above step, and only the surface layer of the recrystallized polycrystalline silicon layer is melted again and recrystallized again, Only the surface layer of the crystallized polycrystalline silicon layer is melted again, and when it is recrystallized again, it is recrystallized as a free surface, and defects are completely removed from at least the surface layer of the recrystallized polycrystalline silicon layer. The surface layer of the polycrystalline silicon layer which has been eliminated and recrystallized again becomes flat.

[Brief description of the drawings]

1a and 1b are explanatory views showing a remelting step according to the gist of the method for manufacturing an SOI substrate according to one embodiment of the present invention. FIG. 1c is a micrograph showing a crystal structure of an SOI substrate manufactured by performing the method for manufacturing an SOI substrate according to one embodiment of the present invention. FIG. 1d is a simulated view of the micrograph shown in FIG. 1c. 2 and 3 are process diagrams of a method for manufacturing an SOI substrate according to one embodiment of the present invention. FIG. 4 and FIG. 5 are process diagrams of a method for manufacturing an SOI substrate according to a conventional technique. DESCRIPTION OF SYMBOLS 1 ... Silicon substrate, 2 ... Silicon dioxide layer, 3 ... Polycrystalline silicon layer, 31 ... Recrystallized polycrystalline silicon layer, 32 ... Recrystallized again to make defect-free and flattened 4... Anti-reflective cap layer, 41... Silicon dioxide layer, 42... Silicon nitride layer, A... Twining type defect, B... Grain boundary, C. D: grain boundary, E: strain field, F: one stacking fault.

Claims (1)

(57) [Claims] 1. A polycrystalline silicon layer (3) is formed on a silicon dioxide layer (2), and an antireflection cap layer (4) is formed on the polycrystalline silicon layer (3). The polycrystalline silicon layer (3) is irradiated with a laser through the cap layer (4), and the polycrystalline silicon layer (3) is once melted and then recrystallized to form a recrystallized polycrystalline silicon layer. (31) In the method for manufacturing an SOI substrate, the antireflection cap layer (4) is removed after the step, and laser irradiation is performed with lower energy than the laser irradiation performed in the step. Manufacturing only the surface layer of the recrystallized polycrystalline silicon layer (31) again and recrystallizing it to form a recrystallized polycrystalline silicon layer (32). Method.