JP2553926B2 - Method of forming selective metal thin film - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a technique for manufacturing a semiconductor device or the like. In particular, the present invention relates to a method for doping impurities in a desired fine pattern on a substrate surface and then plating the substrate surface with a plating method. The present invention also relates to a method for forming a metal thin film selectively by depositing a metal thin film in a pattern.

(Prior Art) A resist process is used for forming a fine pattern in a semiconductor. Hereinafter, the resist process of a general light exposure resist will be described with reference to the flow chart of the resist process shown in FIGS. 2A to 2F.

(A) First, a metal film such as Al is adhered onto a substrate by vapor deposition or the like, and the metal surface is cleaned to improve the adhesion of the resist (FIG. 2A).

(B) The resist is applied by spin coating or the like.
After application, the resist is dried (prebaked) to remove the solvent of the resist (FIG. 2B).

(C) Next, exposure is performed through a photomask having a desired pattern (FIG. 2C).

(D) Development is performed to remove the resist at the exposed or unexposed locations to form a resist pattern. Thereafter, heat drying (post baking) is performed (FIG. 2D).

(E) Next, an etching process is performed on the exposed metal film from which the resist has been removed. Etching includes wet etching with a liquid and dry etching with a gas. The metal film is removed by this etching process, and a metal film having a desired fine pattern is formed on the substrate (2E
Figure).

(F) Finally, the resist that is solidified by exposure and post-baking is peeled off by a heated organic solvent or strong acid (FIG. 2F).

Through the above steps, a fine metal pattern such as a semiconductor device is generated.

Note that there is also a method of forming a fine metal pattern by first patterning a resist and thereafter depositing a metal film.

(Problems to be Solved by the Invention) In the above-described method of forming a fine pattern by light exposure, although the automation of the process is progressing, the number of processes is large and it is desired to omit the process. In addition, any method that is actually used uses a resist, but the resist is such that resolution and adhesion are affected by use conditions, a uniform film thickness is formed, and a final peeling process is performed. The use of strong acids and the like makes it difficult to treat the waste liquid, and furthermore, in order to maintain the quality of the resist, it is necessary to pay sufficient attention to its storage. Further, in order to form a fine pattern, many know-how elements are required, for example, exposure conditions, etching conditions, and temperature conditions must be accurately maintained.

Formation of high-precision fine patterns is indispensable for high speed and high integration of semiconductor devices, and simplification of a resist process is required for improvement of throughput.

An object of the present invention is to provide a technique for selectively forming a metal thin film on the surface of a semiconductor substrate without using a conventional resist process.

(Means for Solving the Problems) Laser light is irradiated on the surface of the semiconductor substrate in an impurity gas atmosphere, thereby decomposing the impurity gas, and doping the decomposed impurity into a molten region of the substrate. Forming a pattern-shaped region having a higher electron density or a lower electron density than the other portion on the surface, and exposing both the region having the higher electron density or the lower electron density and the other portion to the semiconductor substrate; The above object is achieved by a method of forming a selective metal thin film, characterized by immersing in a solution containing metal atoms, and selectively depositing the metal thin film only in a region having a higher electron density on the surface of the semiconductor substrate. be able to.

(Function) By doping the semiconductor substrate surface with laser light, portions having different electron densities are formed on the substrate surface. When the substrate is plated in a metal solution, a metal thin film is selectively formed on the substrate surface by using a difference in electron density on the substrate surface without using a resist mask.

The conductivity type of the substrate and the conductivity type of the doping can be arbitrarily selected. When the conductivity type of the substrate and the doping is the same, the difference in the electron density on the substrate surface is formed by the difference in the impurity concentration.

Since an excimer laser has a short wavelength and a short pulse, it can heat and melt an extremely shallow region near the surface. Therefore, by irradiating an excimer laser beam in an impurity gas atmosphere, the impurity gas can be decomposed, and the decomposed impurities can be doped into the molten region at a high concentration. Further, when irradiation is performed through a mask having a desired pattern, local heating can be performed, and impurity doping can be performed in a fine pattern. In addition, if an excimer laser is used, if the aperture of the mask and the performance of the reduction projection lens are manufactured with high precision, the linearity of the laser can form a high-precision difference in electrical resistivity, and the plating follows there. This allows a thin film to be deposited on the substrate surface at the atomic level.

(Effects of the Invention) According to the present invention, a metal thin film can be formed on a pattern thereof without a resist, so that the semiconductor manufacturing process can be considerably simplified as compared with the conventional method. Further, the present invention is particularly effective for forming electrodes such as ohmic contacts in semiconductor device fabrication. Furthermore, the present invention enables metal plating on substances other than semiconductors that are difficult to be plated by performing surface treatment using the laser disclosed in the present invention, and is applicable not only to semiconductor production but also to various fields. Is opened. Furthermore, the present invention not only eliminates the need for a resist process, but also eliminates the concern that the resist adheres to a mask in the conventional method, and simplifies the process, making device fabrication easier and economical ripple effect. Great effect. Also, regarding the waste liquid treatment method,
Since a known plating solution is used, there is no need to worry as much as in the conventional method.

(Examples) Hereinafter, the present invention will be described in detail based on examples.

(Example 1) FIG. 1A is a schematic diagram showing an example of an impurity doping process, and FIG. 1B is a schematic diagram showing a metal thin film forming process by a plating method of the present invention after doping with impurities. FIG. 1C is a cross-sectional view in which a metal thin film is selectively formed on a substrate surface.

Based on FIG. 1A, first, formation of a pattern-shaped region having a different resistivity from other portions will be described. Si-doped n-type (100) HB GaAs substrate with carrier concentration of 2.5 × 10 ^-17 cm ^-3
12, Dopandogasu of 10% SiH ₄ and He diluent (pressure 100Tor
r) It is kept in the atmosphere of 11. An excimer laser beam 15 emitted by a KrF excimer laser device (wavelength 248 nm, pulse width 23 nS) with a laser fluence of 380 mJ / cm ² and a pulse of 10 pulses is applied to a reticulum 13 having a fine pattern of 20 μm Cr on a synthetic quartz substrate 13. And lens performance is 0.
25, substrate 1 through reduction projection optical lens 14 with reduction ratio of 1/5
Irradiated on 2. Due to this irradiation, the surface of the substrate is doped with Si impurities, and the substrate is highly concentrated and very shallow.
The fine pattern 16 of the n ⁺ active region is selectively formed. At this time, the irradiation line width of the laser beam on the substrate
It is 4 μm because it is reduced to 1/5.

The sample formed with the different resistivity patterns was
The sample was immersed in a 0.8% copper sulfide (CuSO ₄ ) solution 17 shown in the figure, a circuit was formed between the sample 18 and the anode 19 with the sample 18 serving as the cathode 18. As a result, it was possible to form a fine pattern of a metal thin film by selectively depositing a Cu metal thin film only on the above-mentioned doped region.
Note that the cathode 18 may be configured so that a needle-shaped electrode is directly applied to the fine pattern 16.

FIG. 1C is a cross-sectional view of a substrate having a fine pattern of deposited Cu metal 20 obtained under the above conditions. When the Cu metal deposited substrate was observed with a scanning electron microscope, the width of the fine line formed on the substrate was 3.4 μm, and the thickness was about 0.18 μm. The line width at this time was smaller than the laser beam irradiation line width. It can be controlled by changing the energy of the laser beam and the plating time. Also,
The film thickness can be controlled by the plating time.

In order to further reduce the line width as compared with the present embodiment, it is possible to improve the resolution of the reduction projection device.

Example 2 Next, an example in which a metal thin film is selectively deposited without applying an electric field to the sample from the outside will be described with reference to FIGS. 3A and 3B.

(A) First, as in the case of selective metal thin film formation by electrolytic plating (FIG. 1A), n-type GaAs was doped with Si in a pattern.

(B) As shown in FIG. 3A, the thus-doped sample was placed in a commercially available electroless plating solution Au-24s (manufactured by Kojundo Chemical Co., Ltd.) 22 at 70 ° C. for 5 minutes. The plating was performed by dipping.

(C) As a result, as shown in FIG. 3B, the doping region
Metal thin film (Au) 24 was selectively deposited only on 23.

FIG. 4 is a scanning electron micrograph of a sample on which a selective metal thin film was formed by the above procedure. At this time, n-type
Si doping of GaAs is performed by using He diluted 10% SiH _{4 at} 100 Torr pressure.
In, KrF with laser fluence 365mJ / cm ² and pulse number 10
It is performed by irradiating excimer laser light, immersion in plating solution Au-24s (manufactured by Kojundo Chemical Co., Ltd.) at 70 ° C,
Performed for 5 minutes. From FIG. 4, the Au thin film is deposited only on the doped region (light portion), and no deposition on the undoped region is observed (dark portion). The line width of the deposited film at this time is 1.57 μm
And the film thickness was about 60 nm. The line width and the film thickness can be controlled by changing the laser fluence for doping and the plating time.

The method of the present invention is particularly effective for forming ohmic contacts in semiconductor device fabrication. That is, since the metal thin film can be selectively deposited only in the high-concentration electron region doped with Si, a non-alloyed ohmic electrode having low contact resistance can be formed in a self-aligned manner. FIG. 5 shows the result of evaluating the contact resistance of the manufactured ohmic electrode. According to the procedure shown in FIGS. 3A and 3B, an Au thin film was deposited in the form of dots, and the resistance between the dots was measured while changing the distance between the dots. At this time, the Si doping to the n-type GaAs is performed by irradiating a KrF excimer laser beam with a laser fluence of 355 mJ / cm ² and a pulse number of 10 in He-diluted 10% SiH ₄ at a pressure of 100 Torr, and a plating solution Au. Immersion in −24 s (manufactured by Kojundo Chemical Co., Ltd.) was performed at 70 ° C. for 10 minutes. Extrapolating the distance between dots to 0 makes the contact resistance 6.8 × 1
The value was estimated to be 0 ^-5 Ωcm ^2, which was two orders of magnitude smaller than that of an alloyed electrode using ordinary Au-Ge-Ni.

[Brief description of the drawings]

1A is a schematic diagram showing an example of a doping process of a fine pattern, FIG. 1B is a schematic diagram of a selective metal thin film forming process by electroplating according to the present invention, and FIG. 1C is a sample formed by the present invention. 2A to 2F are flow charts of a fine processing process by a conventional resist process. FIG. 3A is a schematic diagram of a selective metal thin film forming process according to the present invention when no external electric field is applied, FIG. 3B is a cross-sectional view of a sample formed by the process shown in FIG. 3A, FIG. Is a scanning electron micrograph showing the metal structure of the sample formed by the process shown in FIG. 3A, and FIG. 5 is a graph showing the results of evaluating the contact resistance of the manufactured ohmic electrode. (Explanation of Signs) 11: Reactive gas, 12: GaAs substrate, 13: Retilk, 14: Reduction projection optical device, 15: Excimer laser, 16: Fine pattern, 17: Hardened copper solution, 18 …… Cathode, 19 …… Anode, 20 …… Cu metal deposition layer.

Claims (2)

(57) [Claims] 1. A method for irradiating a surface of a semiconductor substrate with a laser beam in an impurity gas atmosphere, thereby decomposing an impurity gas, doping the decomposed impurities into a molten region of the substrate, and applying another impurity to the surface. Forming a patterned region having a higher electron density or a lower electron density than a portion, exposing both the region having the higher electron density or the lower electron density and the other portion to the semiconductor substrate with metal atoms. A method of forming a metal thin film selectively on a surface of the semiconductor substrate, the metal thin film being selectively deposited only in a region having a higher electron density on the surface of the semiconductor substrate. 2. The method according to claim 1, wherein said laser beam is an excimer laser beam.