JP2565291B2 - Fine pattern formation method - 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 for forming a fine pattern by doping with a minute electric field.

[0002]

2. Description of the Related Art Conventionally, when doping a substrate, it has been carried out using an ion implantation apparatus, and the process is shown in FIG. Ion implantation mask 3 on the substrate 31 to be doped
2 is patterned, and a desired doping material 33 is doped into the substrate 31 to be doped by using an ion implantation device to form a doping region 34. Finally, the ion implantation mask 32 is removed.

[0003]

However, in the above method, the steps are extremely long, and the energy of the ions used is very large, and the substrate surface is charged up, causing various problems.

An object of the present invention is to provide a microfabrication method which does not require a mask for ion implantation, and which can carry out processing with low energy and which can easily form highly precise microdoping. It is in.

[0005]

According to the present invention, a tapered conductive needle is brought close to a desired portion of a substrate to a distance where a tunnel current flows, and a voltage is applied between the needle and the substrate in this state. A method for forming a fine pattern, characterized in that an electric field spreading in a minute range is formed, a gas containing a dopant as a constituent element is caused to flow therethrough, and the gas is decomposed by the electric field previously formed to dope the substrate with the dopant. Is.

After the needle is brought close to the substrate, gas may be caused to flow, and then an electric field may be formed to dope. Alternatively, the needle may be moved closer after flowing the gas, and then an electric field may be formed to dope.

The present invention also includes a method of adsorbing gas molecules on the surface of the substrate only once when the gas is flown onto the substrate and removing the floating gas by evacuation.

For the doping gas, if the substrate is Si,
BCl ₃ , BBr ₃ , BF ₃ , B for B doping
H ₃ , B ₂ H _6, etc., or PC for P doping
AsH ₃ is used for As doping such as l ₃ and PH ₃ . Further, Si is used as a doping material for the GaAs substrate.
And Zn, and SiH ₄ and SiH ₂ C as gases, respectively
l ₂ , SiCl _4, etc., and Zn (CH ₃ ) ₂ etc. are present.

A conventional scanning tunneling microscope (STM: Scanning Tunneling) is used for the conductive needle.
Mechanical polishing or electropolishing of tungsten (W) or platinum (Pt) used in Microscope is used.

When a voltage (several volts) is applied between the needle and the substrate, the needle is brought closer to the surface of the substrate, and when the distance between the needle and the substrate becomes several angstroms, a current of several nanoamperes flows. Generally, this current is called a tunnel current or a field emission current depending on the current / voltage characteristics, and it is easy to measure the magnitude of the current.

Precise control of the distance between the needle and the substrate can be easily performed by using a piezoelectric element (PZT). Since this piezoelectric element has a piezoelectric ratio of about 5 angstrom / V and is made of ceramics, it can be easily processed and a precise positioning mechanism can be formed.

[0012]

The invention of claim 1 will be described with reference to FIG. After cleaning the substrate 13 placed in an ultrahigh vacuum, a gas containing a material to be doped as a constituent element is flown on the substrate 13. At this time, as shown in FIG. 1A, a part of the gas forms the adsorption layer 12 on the substrate surface 13, and the rest becomes the floating gas 11 in the container. In this state, the needle 14 is attached to the substrate surface 13
When a voltage 15 is applied between the substrate 13 and the needle 14 while approaching to, a minimum electric field 16 is formed. The adsorption layer 12 and the floating gas 11 under the electric field 16 are volatile gas 17 and doping atoms 18 at a low voltage of several V depending on the energy in the electric field.
And the volatile gas is dissociated from the substrate surface, and the doping atoms diffuse into the substrate (FIG. 1 (b)). If gas is kept flowing, decomposition and diffusion will occur continuously.

According to the fourth aspect of the present invention, the gas supply is stopped before the needle 14 is brought close to it, and the residual gas is exhausted leaving only one layer of the adsorption layer to dope only the doping atoms contained in one layer of the adsorption layer. It enables doping in extremely small planes and extremely shallow regions.

The above principle is the same when the reaction gas is made to flow after the needle is brought close to it, and then the electric field is applied, or when the reaction gas is made to flow and then the needle is brought near and then the electric field is applied. In this way, the minimum electric field 16 is applied to the substrate surface 13.
Thus, a fine pattern is formed. Generally a minimum electric field 1
Since the intensity of 6 is low, the doping rate is low and the controllability of doping is good.

[0015]

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 2 is a schematic diagram showing the structure of an apparatus used in one embodiment of the present invention. In this device, the piezoelectric element 202 for moving the needle 207, the gas storage chamber 203, and the substrate holder 2
01. First, an embodiment of the invention of claim 1 will be described. In this embodiment, the substrate 208 is S
i and BCl ₃ is used as the doping gas 204. The vacuum chamber 205 10 ^- was evacuated to ⁶ Torr, flow doping gas 204 through vacuum valve 206.

As the needle 207, platinum Pt 210 mechanically polished is used. This needle is moved using the piezoelectric element 202, and the bias voltage and current between the needle 207 and the substrate 208 are controlled through the electric control system 209. Bias voltage is 1
When the voltage is set to V and the needle 207 is brought closer to a desired position of the sample 208 and the distance between the needle 207 and the substrate 208 becomes about 2 nm, a current starts to flow rapidly. Adsorbed molecules by being formed electric field is decomposed into B and Cl _2, Cl ₂ is suspended in the vacuum vessel 205. After stopping the flow of gas, the gas in the vacuum container 205 is exhausted. In this embodiment, a desired position of 50 nm
B was locally doped in the x50 nm region.

Further, in the embodiment of the invention of claim 4, in order to improve the accuracy of doping, the inside of the vacuum container 205 is set to 10
^- was evacuated to ^{1 0} Torr, a BCl ₃ doping gas 204 only slightly (vacuum of 10 ^- at ⁹ Torr about 10 seconds) passed after the gas molecules adsorbed on the substrate 213, a vacuum container 10 ^{- 1} Evacuate to ⁰ Torr and exhaust floating gas. The electric field is applied to the substrate 2 in the same manner as described above.
When it is formed in 08, only one layer of the adsorbed gas molecule is decomposed and doped, so that the impurity concentration can be controlled extremely precisely. If necessary, the steps from adsorption to dope can be repeated several times to reach the target concentration.

[0019]

As described above, according to the present invention,
It is possible to dope fine regions on a substrate without requiring a large-scale device and high energy as in the case of an ion implantation device.

[Brief description of drawings]

FIG. 1 is an explanatory view schematically showing formation of a fine pattern according to the present invention.

FIG. 2 is a schematic diagram showing an example of an apparatus for carrying out the method of the present invention.

FIG. 3 is a schematic diagram showing a conventional technique.

[Explanation of symbols]

 11 Floating Gas 12 Adsorption Layer 13 Surface Element 14 Needle 15 Voltage 16 Minimal Electric Field 17 Volatile Gas Molecule 18 Doping Atom 31 Doped Substrate 32 Mask 33 Doping Material 34 Doping Area 202 Piezoelectric Element 204 Reactive Gas 207 Needle

Claims (4)

(57) [Claims] 1. A tapered conductive needle is brought close to a desired portion of a substrate to a distance where a tunnel current flows, and in this state, a voltage is applied between the needle and the substrate to form an electric field spreading in a minute range. Then, a gas containing a dopant as a constituent element is caused to flow therethrough, and the gas is decomposed by the electric field previously formed to dope the substrate with the dopant. 2. The fine pattern forming method according to claim 1, wherein a gas is caused to flow after the needle is brought close to the substrate, and then an electric field is formed to dope. 3. The method for forming a fine pattern according to claim 1, wherein after the gas is passed, the needle is brought close to the needle, and then an electric field is formed to dope. 4. The method for forming a fine pattern according to claim 1, 2 or 3, wherein when the gas is flown on the substrate, gas molecules are adsorbed on the surface of the substrate only once and the floating gas is removed by evacuation. .