JPH0812286B2 - Method for manufacturing diffraction grating of SiC substrate - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a diffraction grating in which a grating groove is directly formed on a SiC substrate. Diffraction gratings used for synchrotron radiation, high-power laser light, etc. need to be made of a material that has excellent thermal stability, no thermal strain, and good cooling properties, and SiC is suitable as such a material. There is.

[0002]

2. Description of the Related Art A conventional method for manufacturing a diffraction grating using SiC as a substrate is as follows. In the case of the blazed diffraction grating, a SiC substrate was coated with a gold (Au) layer, and the gold layer was cut with a grating groove by a Rulink engine or the like. SiC has excellent heat resistance and cooling properties, but since the gold layer is provided on the SiC to cut the grating groove in the gold layer, the diffraction grating itself is gold, and there was concern about the heat resistance. However, it is difficult in terms of hardness to directly mechanically engrave SiC, and even if an ion beam etching method used for forming a fine pattern is applied, a photoresist is used as a mask to expose a diffraction grating pattern. When it is created by S, the photoresist for the ion beam etching is S
Since the etching rate of iC was small, the photoresist was removed first, making it difficult to form a diffraction grating.

Since it is difficult to use the photoresist directly as a mask as described above, for example, when forming a pattern of SiC, a photoresist layer is provided on a SiC substrate and a mask of a lattice pattern is formed by an exposure method. The mask is lifted off with Al to form a mask having an Al lattice pattern on the substrate, and reactive ion etching with a mixed gas of CF ₄ + O _{2 is used} to form lattice grooves on the SiC surface, or to form a laminar diffraction grating. , P on SiC
MMA is applied and a PMMA lattice pattern is formed by electron beam lithography. This pattern is lifted off with Cr and CF ₄ + O is used as a lattice pattern mask on SiC.
_A method of performing reactive ion beam etching of ₂ has been proposed. In these methods, the mask with the first resist layer is once transferred to Al or Cr, and ion beam etching is performed using Al or Cr as a mask, so that the number of steps is increased, and the reactive ion etching causes a rough surface to be etched. Further, in the latter method, since the mask is manufactured by electron beam lithography, there is a problem that a periodic error appears in a grating pitch which is important as a diffraction grating, and it takes a long time to write a large area.

[0004]

SUMMARY OF THE INVENTION The present invention is an ion beam etching method using a photoresist mask.
It is intended to be applied to an iC substrate and enable to directly engrave the diffraction grating groove on the SiC substrate.

[0005]

A photoresist layer is provided on a SiC substrate, a mask of a grating pattern of a diffraction grating is formed by the photoresist layer, and a hydrocarbon fluoride and A
50 parts of hydrocarbon fluoride with the mixed gas of r
Ion beam etching is performed using a mixed gas of not more than%.

[0006]

The relative etching rate of SiC with respect to the photoresist when the mixing ratio of Ar to CF ₄ is changed by ion beam etching using a mixed gas of CF ₄ which is one kind of hydrocarbon fluoride and Ar as an etching gas As shown in FIG. 3, it has a maximum at a mixing ratio of CF ₄ to the mixed gas of around 50%, and the relative rate gradually decreases at 50% or less. The same trend is more pronounced with CHF ₃ . Near this maximum, the etching rate of SiC is about the same as that of photoresist. That is, the SiC can be etched to a depth approximately equal to the photoresist layer thickness. Since the relative etching rate changes linearly with the concentration at a location where the hydrocarbon fluoride concentration is lower than the maximum relative etching rate, the relative etching rate can be adjusted by this concentration.

[0007]

EXAMPLE FIG. 2 shows the concentration ratio of CF ₄ and CF ₄ + Ar on the horizontal axis and the etching rate of ion beam etching on the vertical axis, with SiC and the photoresist OFPR50.
An etching rate of 00 was shown. The etching rate is the etching depth per minute in nm when etching is performed at 1 mA per cm ² , and the white circles are photoresist and the black circles are SiC. CF ₄ concentration 50
%, The photoresist etching rate is minimum. For SiC, the etching rate changes sharply at around 50%. FIG. 3 is a rewrite of FIG. 2 showing the relative etching rate of SiC with respect to the photoresist. There is a maximum at a CF ₄ concentration of around 50%, and the relative etching rate is C at a lower CF ₄ concentration.
It is a region where the relative etching rate can be adjusted monotonically with the concentration of F ₄ and can be adjusted by the concentration of CF ₄ , and this region is the designated region in the present invention.

When performing ion beam etching of SiC with CF ₄ , the reactivity of F is greater with respect to Si than with C, and is exhausted by the reaction with Si, so that it does not exist sufficiently to react with C. C also remains on the etching surface, and in addition, since C in CF ₄ does not have an object that contributes to the reaction, precipitation of C also occurs. These Cs have a very large effect of being removed by the ordinary ion beam etching action due to collision of irradiation ions, so SiC
On the other hand, even if CF ₄ is used, the etching rate is not so high. When Ar is added to this, C that remains and precipitates due to the ion beam etching action of Ar is removed.
_{When the} CF ₄ concentration is increased with a mixed gas of ₄ + Ar, the etching rate gradually increases because the cleaning effect of Ar and A
Etching effect on C in SiC by r and CF ₄
It is shown that all of the etching effects on Si in SiC by reactive ion beam etching are working effectively. When CF exceeds 50%, the effect of cleaning the residual and precipitated C by Ar catches up with the residual precipitation of C. And the etching rate of CF ₄ alone is lost. This is considered to be the reason why the characteristic of the relative etching rate as shown in FIG. 3 is expressed. That is, the term "ion beam etching" in the present invention means ion beam etching in which a complex action is performed such that neither reactive ion beam etching nor simple ion beam etching is the main action.

In FIGS. 4 and 5, the etching gas is CHF ₃ +.
In the graphs corresponding to FIGS. 2 and 3 when the mixed gas of Ar is used, in this case, there is a region where the relative etching rate is higher than 1 (the region where the etching rate of SiC is higher than that of photoresist). , Even in this case C
The gradient characteristic region on the low concentration side of HF ₃ is the designated region of the present invention.

FIG. 1 shows each step of one embodiment of the present invention.
In FIG. 1, A shows a substrate 1 in which a SiC layer is grown on sintered SiC by a CVD method and the surface is optically polished. On this substrate, 300 layers 2 of OFPR5000 are used as photoresist.
Spin coat to a thickness of nm and bake in a fresh air oven at 90 ° C. for 30 minutes (FIG. 1B). Next He
-The grating pattern is printed and developed by the holographic exposure method by the two-beam interference of the light of the wavelength of 441.6 nm of the Cd laser, and the photoresist 2 is left in a sinusoidal cross section, and this is used as a mask of the grating pattern (FIG. 1C) . Ion beam etching is performed from the direction of 5 ° from the substrate surface, at a CF ₄ / (CF ₄ + Ar) = 45% orthogonal to the stripes of the photoresist lattice mask, until the photoresist is absent (FIG. 1D). Thus, a SiC blazed diffraction grating having a lattice constant of 1200 / mm was completed. The blaze angle (θ in FIG. 1D) of this diffraction grating is 2 °. The diffraction grating thus obtained can be sufficiently used in this state in the region where the reaction rate of SiC is sufficiently obtained, and in other wavelength regions, a layer of Au or Pt may be coated as required. Good. Alternatively, an X-ray multilayer film may be coated.

FIG. 6 shows the progress of etching in the above example.
It will be explained by. When a striped photoresist 2 substrate is irradiated with an ion beam from an oblique direction, the shadow of the photoresist 2 initially covers the exposed surface of the substrate and only the photoresist is etched. On the other hand, the generality is not lost even if the photoresist mask is started from the place where the hatching is shown in the figure. Assuming that the relative etching rate between the photoresist and the substrate SiC is 1, the etching in the ion beam irradiation direction proceeds at the same speed in the photoresist and the substrate until the ion beam in the range ab runs out of the photoresist. The area of the triangle Iroha is etched and the angle Iroha becomes a right angle. In the meantime, the ion beam in the range of bc that irradiates the exposed surface of the substrate by grazing the photoresist on the right side etches the range of triangular Rohany. The steep slope side inclination angle of the groove having a triangular cross section formed in this way is determined by the relative etching rate between the substrate and the photoresist, and can be set variously by selecting this value.

In another embodiment, CHF ₃ + Ar is used as an etching gas in the same operation as described above, and CH
Ion beam etching was performed with F ₃ / (CHF ₃ + Ar) = 33% to obtain a diffraction grating similar to the above example.

The application of the invention is not limited to the fabrication of blazed diffraction gratings. It can also be applied to the production of a laminar diffraction grating as shown in FIG. In this case, the emission direction of the ion beam is perpendicular to the substrate surface. Since the grating groove is shallow in the laminar type grating, the photoresist mask remains even if the grating groove is etched to a predetermined depth. The remaining photoresist may be removed by ashing with O ₂ plasma. A photoresist layer is formed to a thickness of 300 nm, and etching is performed until the groove depth reaches 110 nm. At this time, the photoresist remains at a height of about 200 nm at the highest position, and assuming that the photoresist had a half-sine wave shape at the beginning, the width of the photoresist when the groove depth reaches a predetermined value is also large. Is about 0.8 times, and the cross section becomes a trapezoidal groove. The inclination of both sides of the groove is determined by the relative etching rate of the substrate with respect to the photoresist.

[0014]

INDUSTRIAL APPLICABILITY The present invention uses a mixed gas of a hydrocarbon fluoride such as CF ₄ or CHF ₃ or a mixture of a hydrocarbon fluoride and Ar as an etching gas in the ion beam etching of SiC. By performing etching in a concentration range of 50% or less with respect to the above mixed gas, etching using a photoresist as a mask becomes possible, a mask of a lattice pattern can be formed by an exposure method, and the accuracy of the mask is improved and the process is simplified. Thus, the roughness of the etching surface of the substrate due to residual precipitation of C is prevented, the etching rate by the hydrocarbon fluoride or hydrocarbon fluoride is increased, and the precipitation of C etc. on the inner surface of the ion beam etching apparatus is also performed by Ar.
Since it is purified by the etching action of 1, the frequency of maintenance of the etching device can be reduced.

[Brief description of drawings]

FIG. 1 is a diagram showing each step of the process of one embodiment of the present invention.

FIG. 2 is a graph showing the ion beam etching characteristics of a CF ₄ + Ar mixed gas photoresist and SiC.

FIG. 3 is a graph showing relative characteristics of the above gas with respect to photoresist and SiC.

FIG. 4 is a graph similar to FIG. 2 for a CHF ₃ + Ar mixed gas.

5 is a graph similar to FIG. 3 for the above gas.

FIG. 6 is a diagram for explaining the progress of etching in oblique irradiation with an ion beam.

FIG. 7 is a sectional view of a laminar diffraction grating.

[Explanation of symbols]

 1 substrate 2 photoresist layer

Claims (1)

[Claims] 1. A photoresist layer is provided on a SiC substrate, and a lattice pattern is baked and developed on the photoresist by an exposure method to be used as a mask of the lattice pattern, which is carbonized with a mixed gas of a fluoride or a hydrocarbon fluoride and Ar. 50% concentration of fluoride or hydrocarbon fluoride in the above mixed gas
A method for producing a diffraction grating on a SiC substrate, which comprises performing ion beam etching using the following gas as an etching gas to directly engrave the SiC substrate.