JP3183883B2 - Pattern formation method - Google Patents

Description

The present invention relates to a pattern forming method for forming a desired pattern by selectively etching a silicon oxide film, a nitride film, or the like.

(Prior Art) In pattern formation of a semiconductor device, lithography is an indispensable technology, and lithography that is simple and has good controllability is required. When considering the high integration and high functionality of semiconductor devices, electron beams that can be patterned finer than lithography using ordinary UV light,
A method using an ion beam or the like is effective. For example,
(A. Milgram et al .; J. Vac. Sci. Technol. B3 (1985) 87
9) describes an example of fine patterning using FIB (focus ion beam). For this example,
This will be briefly described below.

First, as shown in FIG.
The photoresist 2 is spin-coated to a thickness of about 2 μm, and then, as shown in FIG.
Bake at ℃ for 30 minutes. Next, as shown in FIG. 3 (c), an SOG solution is spin-coated on the photoresist 2, and then, as shown in FIG. 3 (d), curing is performed at 200 ° C. to form an SOG film having a thickness of about 125 nm. The film 3 is formed.

Next, as shown in FIG. 3E, Ga ions 4 having an acceleration voltage of 16 kV and a beam diameter of 0.4 μm are implanted into the SOG film 3 using an FIB apparatus. Thereafter, as shown in FIG.
Dry etching is performed on the entire surface of the SOG film 3 by RIE using F ₃ / O ₂ gas. As a result, due to the action of the F-based plasma ions 5, the region into which Ga ions are implanted remains without being etched, and a mask pattern is formed.

Finally, as shown in FIG. 3 (g), O ₂ gas was used.
When the photoresist 2 is etched by RIE, a two-layer resist mask including the photoresist 2 and the SOG film 3 is completed. Then, the base substrate 1 is selectively etched using the two-layer resist.

With this method, a resist mask can be formed on a semiconductor substrate, but the SOG film and the organic photoresist film are formed by processes that are difficult to use in a vacuum such as spin coating and baking. Therefore, it was incompatible with the integrated vacuum process.

Further, the formation of the above-described resist mask is required not only for the mask for substrate etching but also for patterning an oxide film or the like on the substrate. In this case, as in the above, it was not compatible with the integrated vacuum process.

In addition, productivity is reduced due to incompatibility with the integrated vacuum process, and furthermore, dust adheres and a natural oxide film is generated during patterning, and this is a factor that lowers the reliability of a finally manufactured device. Was.

(Problems to be Solved by the Invention) As described above, conventionally, when forming a mask pattern,
A method using a photoresist and SOG cannot perform a process in a vacuum, and cannot cope with a complex vacuum process. For this reason, there is a problem in terms of productivity, and further, there is a problem that the reliability of the element is reduced.

The present invention has been made in view of the above circumstances, and an object of the present invention is to form various patterns on a semiconductor substrate as an integrated vacuum process, thereby improving productivity and improving device reliability. It is another object of the present invention to provide a pattern forming method that can contribute to the above-mentioned factors.

[Structure of the Invention] (Means for Solving the Problems) The gist of the present invention is to inject a focused ion beam into a thin film such as a silicon oxide film or a silicon nitride film that can be formed in a vacuum apparatus, An object of the present invention is to pattern the thin film by suppressing the dry etching by a reaction product of ions and an etching gas.

That is, the present invention forms a thin film composed of a silicon nitride film or a silicon oxide film on a substrate, and then focuses Ga or In on the substrate.
Is selectively implanted into the thin film, and then the etching stop is performed by dry etching of an etching gas containing F to form an etching stop layer made of a fluoride of Ga or In at the ion-implanted portion. This is a method in which a thin film is selectively etched using a layer as a mask.

(Operation) According to the present invention, all of the formation of the thin film, the implantation of the focused ion beam, and the selective etching of the thin film can be performed in a vacuum or an atmosphere close to the vacuum. Therefore, patterning of various sizes can be formed at an arbitrary position on the semiconductor substrate by a vacuum integrated process, and productivity can be improved. Further, it is possible to prevent the adhesion of impurities and the formation of a natural oxide film due to exposing the substrate to the atmosphere, which can contribute to the improvement of the reliability of a finally manufactured device.

Here, when Ga (or In ion) is implanted into a thin film of SiN _X or SiO _X, a reaction product in dry etching including fluorine (F) is GaF _X (or InF _X ),
The rest is SiF _X. GaF _X (or InF _X ) remains non-volatile and FSi is volatile and is removed. As a result, the portion other than the ion-implanted portion is removed by the dry etching including F.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a sectional view showing a mask pattern forming step according to a method of an embodiment of the present invention. First, FIG. 1 (a)
As shown in FIG. 1, a SiN _X film 12 as a mask material is formed on a Si substrate 11 by a plasma excitation CVD apparatus using SiH ₄ , NH ₃ and N ₂ as reaction gases. In the figure, reference numeral 13 denotes plasma.

SiN _X is, for example, Si ₃ N ₄ or SiN. As the film forming conditions at this time, assuming that the substrate temperature is 250 ° C., the RF output is 200 W, and the reaction gas flow rate ratio is SiH ₄ : NH ₃ : N ₂ = 1: 2: 10, SiN _X having a deposition time of 40 minutes and a thickness of about 800 nm is used. A film 12 is formed.

Next, as shown in FIG. 1 (b), FIB to SiN _X film 12
Ga ions 14 focused at an acceleration voltage of 40 kV are selectively implanted by the apparatus. At this time, the area to be left as a mask
Implant Ga ions. In the figure, reference numeral 15 denotes an ion implantation region.

Next, as shown in FIG. 1 (c), the SiN _x film 12 is dry-etched by radicals 16 of CF ₄ gas using a microwave-excited chemical dry etching apparatus. At this time, the ion-implanted region 15 serves as a mask and the SiN _x film 12 is selectively etched for a reason to be described later.

Thereafter, the substrate 11 can be selectively etched by dry etching using the ion-implanted region 15 remaining without being etched and the SiN _X film 12 thereunder as a mask.

Here, the reason why the ion implantation region 15 functions as a mask will be described. In SiN _X , F radicals cause Si
Although F _X is the reaction product, this FSi is volatile and is easily removed. On the other hand, GaF _X by a radical of the ion-implanted region 15 in the F system is the reaction product, this GaF _X is non-volatile, it will remain unremoved. Therefore,
In the case of F-based radicals, the ion implantation region 15 serves as a mask,
The SiN _X other than the implantation region is removed.

FIG. 2 shows the change in the etching rate with respect to the dose of Ga ions. If the dose of ions implanted into SiN _X is larger than a certain value, the etching rate becomes a very small value. That is, a region in which ions are implanted beyond a certain threshold value becomes an etching stop layer (mask). This threshold ion dose is determined by the film quality of SiN _X , G
aDepending on the ion implantation conditions and CDE conditions,
injecting Ga at 40kV to iN _X, when performing CDE only CF ₄ gas, a very small etching rate in the region subjected to injection of 10 ¹⁶ cm ^-2 or more dose. Therefore, the region where the ion implantation above the threshold value is performed is not removed by etching and remains, and functions as a negative resist mask.

As described above, according to the present embodiment, the photoresist and the SOG
A mask of SiN _X can be formed on the substrate 11 without using any other means. In this case, since all the processes can be performed in a vacuum or a state close to the vacuum, a vacuum integrated process can be realized, and productivity can be improved. Further, since the substrate 11 is not exposed to the air, it is possible to prevent the adhesion of dust and the formation of a natural oxide film beforehand, and to improve the reliability of an element finally manufactured.

Further, as shown in FIG.
Since ions have a concentration peak at the upper portion of the SiN _X film 12, only the surface layer functions as an etching stop layer during dry etching as shown in FIG. 1 (c). That is, because of the surface patterning, it is possible to easily form a fine pattern by using a fine beam of the FIB.
At that time, submicron patterning becomes possible by replacing dry etching with RIE or ECR plasma type RIBE effective for fine patterning.

The present invention is not limited to the embodiments described above. In the embodiment, SiN _X is used as the thin film, but SiO _X can be used instead. When SiO _X is used as a mask material, thermal CV using SiH ₄ and O ₂ as a reaction gas
By forming a film with D and performing other processes under substantially the same conditions as in the above-described embodiment, patterning of SiO _X can be performed.

In the embodiment, the case where the thin film is formed as a mask for etching the substrate has been described. However, the present invention can be applied to the turning of the thin film itself such as SiN _X or SiO _X as the insulating film. In addition, In can be used instead of Ga as the ion to be implanted. In addition, various modifications can be made without departing from the scope of the present invention.

[Effects of the Invention] As described above, according to the present invention, it is possible to pattern a thin film by an integrated vacuum process, and to realize a pattern forming method that can contribute to an improvement in productivity and an improvement in device reliability. it can.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a mask pattern forming step according to a method of an embodiment of the present invention, FIG. 2 is a characteristic diagram showing a change in etching rate with respect to an ion dose in an ion-implanted region, and FIG. It is sectional drawing which shows a pattern formation process. 11 ... Si substrate, 12 ... SiN _X film, 13 ... Plasma, 14 ... Ga ion, 15 ... Ion implantation area, 16 ... Radical,

Claims (1)

(57) [Claims] A step of forming a thin film of a silicon nitride film or a silicon oxide film on a substrate; a step of selectively injecting a focused ion beam of Ga or In into the thin film; and an etching gas containing F Selectively etching the thin film using the etching stop layer as a mask while generating an etching stop layer made of Ga or In fluoride in the ion-implanted portion by dry etching. Pattern formation method.