JPS62145819A - Laser etching method - Google Patents

Abstract

PURPOSE:To etch a silicon to be etched with charged particles without loss of a silicon layer by laser emitting the silicon in an atmosphere containing NH3. CONSTITUTION:This is a method for patterning a silicon while making it react to the etching of the silicon by a low laser output. NH3 has a property to absorb a light of short wavelength such as 3,100Angstrom or shorter and decompose. When a laser is emitted to the silicon surface (400 deg.C of substrate temperature) in the NHd3, nitride film is formed on the silicon surface. Since the silicon nitride film preferably absorbs the light of 2,500Angstrom or shorter in wavelength, it can be excited by a far ultraviolet laser, the light-excited nitride film is heated to decompose etching gas containing fluorine compound to generate fluorine atoms having large reactivity, thereby etching the silicon nitride film.

Description

[Detailed Description of the Invention] 3. Name (Industrial Application Field) The present invention relates to a laser etching method that is expected to be used as a submicron processing technology for VLSI.

<Prior Art> As integrated circuits become more densely packed, submicron processing technology becomes necessary.

As a technique to enable submicron processing, methods using charged particles (reactive ion etching, reactive ion beam etching, focused ion beam etching, etc.) have been developed.

<Problems to be Solved by the Invention> In the above-mentioned conventional submicron processing technology using charged particles, the semiconductor, which is the workpiece, is exposed to the charged particles, so the device characteristics of the finished semiconductor may be affected. Not only is there a risk that the characteristics will deviate from the intended characteristics, but it is also inevitable that the number of steps will increase as it becomes necessary to form and remove a resist pattern as a mask for pattern formation in etching processing. .

The conventionally widely used wet etching method using an etching solution can avoid changes in device characteristics due to the use of charged particles as described above, but etching progresses isotropically, making it difficult to process the pattern. This method has the drawback of reduced accuracy, making it difficult to apply it to submicron processes.

Means to solve problems〉 The present invention uses a laser etching method to produce a single crystal.

A method for patterning polycrystalline or amorphous silicon provides an etching process that allows etching reactions to occur under low laser power.

However, NH3 has the property of absorbing and decomposing short wavelength light such as 3100A or less, and when a laser is irradiated on the silicon surface (substrate temperature 400°C) in NH3, nitridation occurs on the silicon surface. A film is formed. This silicon nitride film absorbs light with a wavelength of 250 OA or less, so it can be excited by a deep ultraviolet laser.The photoexcited nitride film is heated and decomposes the etching gas containing fluorine compounds, making it highly reactive. The silicon nitride film is etched by generating fluorine atoms. Therefore, prior to etching the silicon to be processed, an atmosphere in which a film can be formed is provided in advance, and the silicon is etched by irradiating it with a laser that oscillates at far ultraviolet wavelengths.

<Function>' Figure 1 shows the experimental results showing the relationship between laser peak output and etch rate when polycrystalline silicon and silicon nitride films are irradiated with deep ultraviolet laser (wavelength 1930A), respectively.
This shows that the etch rate of the silicon nitride film is 10 times or more higher than that of silicon.

Therefore, at the same laser output, the etching rate of a silicon nitride film is about 10 times higher than that of a silicon substrate or silicon film. If the laser output is the same, the etching will be faster, and if the etching speed is the same, the etching can be done with a lower laser output.

<Example 1> In this example, a silicon substrate to be processed is first placed in an NH3 atmosphere and irradiated with a far ultraviolet laser to nitride the area to be etched, and then irradiated with a far ultraviolet laser in a fluorine compound gas. Then, the silicon nitride film is selectively removed.

As a far-ultraviolet laser, a source with a wavelength (3100 A or less) having a large optical absorption coefficient in silicon and silicon nitride films is used, and an etching apparatus as shown in FIG. 2 is used.

That is, in the figure, a silicon substrate 8 is placed on a substrate holder 2 installed in an etching chamber I. The substrate holding table 2 has a built-in substrate temperature control device for maintaining the mounted silicon substrate 3 at a predetermined temperature. A light introduction window 4 for introducing the laser is provided in a part of the wall surface of the etching chamber, and the far ultraviolet laser (ArF excimer laser wavelength 19 BOA) generated by the far ultraviolet laser oscillator 5 is used to etching the silicon substrate in the etching chamber I. 3. Irradiate on. A reaction gas is sucked into the etching chamber 1.

Pipes 6, 6 for evacuation are attached to supply atmospheric gas such as etching gas at a controlled pressure and flow rate.

In the above etching apparatus, first, N is added to the etching chamber.
While flowing H3 gas, the silicon substrate 3 is irradiated with a laser. The NH3 molecules absorb the laser beam and decompose, forming a silicon nitride film on the surface of the silicon substrate. The silicon substrate surface is irradiated with the laser again to a desired thickness. The nitride film, which has been irradiated with the laser again, is optically excited and heated to excite SF6 and decompose near the nitride film, generating highly reactive fluorine atoms and etching the silicon nitride film.

It should be noted that what is removed in the above etching process is the area irradiated with the laser, and in order to selectively proceed with etching to finish the desired pattern, K is used to remove the patterned mask before etching with the laser irradiation. It is formed in advance on the surface of the silicon substrate. H8i, A4° high melting point metals can be used as the mask material. This type of mask material has a higher surface reflectance for ultraviolet light (less UV absorption) than a silicon nitride film, and also has greater thermal conductivity, so the laser power required for etching is higher than that for a silicon nitride film. It's advantageous. Note that the mask material may be applied before or after nitriding the silicon substrate.

After etching the silicon substrate as described above,
The silicon in the region to be etched is temporarily changed to silicon nitride, and this silicon nitride is etched using SF6 gas, thereby etching the silicon substrate.

<Example 2> In this example, a case will be described in which NH3 gas for nitriding silicon is mixed into the etching gas.

Using the same etching apparatus as in Example I above, a silicon substrate with a mask formed thereon is placed inside the chamber of the same etching apparatus. Next, SF6 gas mixed with NH3 gas is introduced into the room, and deep ultraviolet laser is irradiated in this atmosphere.

In this embodiment, the nitridation of silicon and the etching of silicon nitride proceed almost simultaneously, and a pattern corresponding to the mask is formed on the surface of the silicon substrate.

The above-mentioned silicon substrate can be applied to any of single crystal, polycrystal, and amorphous, and by preheating the silicon substrate, the efficiency of nitriding can be increased, and the overall etching speed can be further improved. It is possible.

<Effects of the Invention> According to the present invention, etching can be performed without damaging the silicon layer due to charged particles, etc., and there is no risk of adversely affecting the characteristics of semiconductor elements fabricated using a silicon substrate. , it is possible to perform an etching process that can produce semiconductor elements of stable commercial quality.

Additionally, compared to when silicon is immediately laser etched, it can be etched with a lower laser power, reducing the burden on the equipment, and increasing the laser beam diameter increases the processing speed for the same area. be able to.

[Brief explanation of drawings]

FIG. 1 is a diagram of etching characteristics of polycrystalline silicon and silicon nitride films, and FIG. 2 is a schematic diagram of a laser etching apparatus to which the present invention is applied. 1. Etching chamber, 3: Silicon substrate, 4: Laser introduction window, 5: Far-UV laser oscillator, 6.

Claims (1)

[Claims] 1) In a method of etching silicon exposed to an etching gas atmosphere by irradiating it with a laser that oscillates at a wavelength in the deep ultraviolet region, the silicon to be etched is etched using NH_3
A laser etching method characterized by performing laser irradiation treatment in an atmosphere containing. 2) The laser etching method according to claim 1, wherein the NH_3 is added to an etching gas. 3) The laser etching method according to claim 1, wherein the laser irradiation in the atmosphere containing NH_3 is performed in advance before exposing the silicon to an etching gas atmosphere and irradiating the silicon with the laser. . 4) The laser etching method according to claim 1, wherein the etching gas contains a fluorine compound. 5) The laser etching method according to claim 4, wherein the fluorine compound is SF_6 or NF_3.