JP2834243B2 - Antistatic method in electron beam lithography - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention relates to electron beam lithography, and more particularly to an antistatic method for performing electron lithography on a semiconductor wafer surface.

[Conventional technology]

When a large-scale integrated circuit or the like is formed on the surface of a semiconductor wafer (hereinafter abbreviated as “wafer”) using an electron beam lithography apparatus, if an insulating film such as an oxide film is coated on the surface of the wafer, a ground or the like may be formed. If care is not taken, charges that have passed through the insulating film during the electron beam drawing process are accumulated in the wafer. Such a charging phenomenon causes a change in the potential of the wafer, adversely affects electron beam drawing, and causes a position shift in a drawn pattern.

Therefore, various techniques have been conventionally proposed as antistatic measures.

For example, as disclosed in Japanese Patent Laying-Open No. 57-13741, only the insulating film on the side surface (peripheral edge) of the wafer is removed by a rotary grinder or the like, and the portion of the insulating film removed on the side surface of the wafer is grounded via wiring. As disclosed in JP-A-58-103135, plasma ions are emitted to a stage control system of an electron beam lithography apparatus to neutralize negative charges charged on a substrate. As disclosed in JP 61-46019,
A charged conductive piece implanted with ions is pressed against a side surface of the wafer to remove charges accumulated on the substrate, or as disclosed in JP-A-63-90130, an electrode pin and a ground pin are connected to the wafer. By pressing against the surface insulating film with the force of an elastic member, before performing electron beam drawing, discharge is performed between these pins to locally destroy the insulating film and simultaneously stab the pins into the wafer surface. By grounding the wafer, charge accumulation during electron beam writing is eliminated or reduced.

[Problems to be solved by the invention]

By the way, the above-mentioned prior art requires special instruments and devices such as a rotary grinder, a plasma ion generator, a charged conductive piece for ion implantation, and pins for discharging and grounding. Furthermore, in the prior art, when a conductive piece, a pin, or the like is pressed or stabbed, the wafer surface is damaged, dust or the like adheres to the damaged portion, and when the insulating film is thick, the wafer may be damaged. Causes poor contact with conductive pieces, pins, etc.
Poor grounding sometimes occurred.

The present invention has been made in view of the above points, and its purpose is to eliminate the need for a special device for removing an insulating film, a charge neutralizing device, and the like, and without damaging the wafer surface. Another object of the present invention is to reliably eliminate the charging phenomenon during electron beam drawing and to assure high-accuracy electron beam drawing.

[Means for solving the problem]

The above object is to provide an electron beam lithography system for irradiating an electron beam on a surface of a semiconductor wafer coated with an insulating film to perform drawing, wherein the first step of irradiating an arbitrary portion on the conductor wafer with the electron beam, This is achieved by including a second step of bringing a member for grounding into contact with a dielectric breakdown point on the semiconductor wafer generated in the first step.

[Action]

When performing electron beam lithography, if an insulating film is previously irradiated with an electron beam at an arbitrary position on a wafer surface, a local charging phenomenon occurs. Among the insulating films coated on the wafer, the insulating film on the peripheral edge (side surface) of the wafer has a relatively incomplete coating structure and is thinner than other portions.

Therefore, when local electrification and development are generated in advance on the insulating film of the wafer at the time of electron beam writing, a discharge occurs between the peripheral edge of the wafer and the wafer holder adjacent thereto, and dielectric breakdown occurs on the peripheral edge of the wafer.

Then, the wafer is grounded by the contact between the wafer and the wafer holder (earth member) via the dielectric breakdown portion, and thereafter, when electron beam drawing is performed, the wafer surface is always kept at the same potential. It is possible to perform good electron beam writing.

〔Example〕

 An embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is an explanatory view showing an example of antistatic of the present invention, FIG. 2 is a longitudinal sectional view of FIG. 1, and FIG. 3 is a system configuration diagram of an electron beam drawing apparatus to which the present invention is applied. , FIG.
The flowchart is shown.

First, the overall configuration of the electron beam drawing apparatus will be described with reference to FIG.

In FIG. 3, 1 is an electron gun, 2 is an aperture, 3 is an electron lens for focusing (first lens), 4 is a blanking electrode,
5 is an aperture, 6 is a convergence electron lens (second lens), 7
Is a deflector, 8 is a backscattered electron detector for detecting a mark, 9 is a wafer, and 10 is a stage.

The electron beam output from the electron gun 1 is controlled to a desired shape by the first and second lenses 3 and 6 and the apertures 2 and 5, and is deflected by the deflector 7 based on a predetermined drawing pattern signal. 9 Irradiated on the surface. Reference numeral 16 denotes a deflection control system.

The area where the electron beam is deflected by the deflector 7 is about 3 mm, which is limited by accuracy. In order to form a predetermined drawing pattern on the entire surface of the wafer 9, for each drawing area,
The stage 10 is moved by using the laser length measuring device 11, the laser control system 13, and the servo control system 12, and the mark disposed on the wafer is detected by using the reflected electron detector 8 and the mark detection system 15, Performs highly accurate wafer positioning.

16 is a computer for program-controlling the whole system of the electron beam lithography system, and 17 is a blanker control system.

Next, specific examples of the antistatic method according to the present invention will be described with reference to the first example.
This will be described with reference to FIG.

Reference numeral 20 denotes a cassette (wafer holder) for holding the wafer 9, which is mounted on the stage 10.

The wafer 9 is made of, for example, silicon, and its surface is coated with a silicon oxide film (hereinafter, referred to as an insulating film) 9A as a masked film. The insulating film 9A has a thickness of several μm.

As described in the section of the prior art, the insulating film 9A causes the electron beam during electron beam writing to accumulate (charge) electric charges on the wafer surface, causing a pattern shift and other adverse effects on electron beam writing accuracy. Therefore, in this embodiment, an antistatic measure is taken as follows.

In other words, the stage is controlled to move at the time of electron beam lithography, and positioning is performed so that a portion of the wafer surface that is not needed as a product of the wafer comes to the irradiation position of the electron beam. Here, the unnecessary portion is a portion that becomes unnecessary when the wafer 9 is cut out, and corresponds to a portion of the wafer surface near the wafer periphery.

Next, the unnecessary portion of the wafer is irradiated with the electron beam B1. In FIG. 1, B1 is shown as an electron beam used for dielectric breakdown, and B2 is shown as an electron beam used for electron beam drawing.

The insulating film around the wafer edge tends to be thinner than the other portions, and when the insulating film 9A is locally charged by the irradiation of the electron beam B1, a discharge is generated between the insulating film around the wafer edge and the cassette. Then, a part of the insulating film on the periphery of the wafer is broken down.

If the wafer 9 and the cassette 20 are brought into contact with each other at this breakdown point, grounding becomes possible. If electron beam drawing is performed in the ground state, the wafer surface can always be kept at the same potential.
High-precision electron beam writing without pattern shift can be executed.

The electron beam B2 used for electron beam drawing is usually
At 30 kv, the current density is about 1 μA. However, if the current density of the electron beam B1 for the dielectric breakdown performed before that is set higher than this (for example, about 10 times), the dielectric breakdown is quickly performed. be able to. According to the experimental result, when there is an oxide film 9A of several μm, dielectric breakdown occurs within 1 second or less.

In addition, as for the control of the electron beam irradiation in the dielectric breakdown, time control is performed, or if an ammeter is connected between the cassette 20 and the ground, the dielectric breakdown is detected by the current measurement, and the beam irradiation is terminated. , Is reasonable.

FIG. 4 is a flowchart showing an operation process of electron beam drawing, wherein steps S1 to S5 show the dielectric breakdown process,
Steps S6 to S9 show the electron beam drawing process.

〔The invention's effect〕

According to the present invention, the wafer is grounded by using an electron beam used for electron beam lithography and a method of causing dielectric breakdown at an unnecessary portion of the wafer before the drawing process, so that a special tool or device is used. Without this, it is possible to prevent electrification in electron beam lithography. Further, the time required for such dielectric breakdown can be ensured in an extremely short time, and can be performed without damaging the wafer surface.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing an example of antistatic of the present invention, FIG.
1 is a longitudinal sectional view of FIG. 1, FIG. 3 is a system configuration diagram of an electron beam drawing apparatus to which the present invention is applied, and FIG. 4 is a flowchart thereof. B1 ... Electron beam for dielectric breakdown, B2 ... Electron beam for electron beam drawing, 9 ... Semiconductor wafer, 9A ... Insulating film, 20 ... Wafer holder (cassette).

Continuation of the front page (56) References JP-A-57-193030 (JP, A) JP-A-58-31527 (JP, A) JP-A-57-13741 (JP, A) JP-A-2-143430 (JP) JP-A-60-74521 (JP, A) JP-A-54-64477 (JP, A) JP-A-3-166714 (JP, A) JP-A-3-30416 (JP, A) 58-103135 (JP, A) JP-A-58-86727 (JP, A) JP-A-2-237132 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01L 21/027

Claims (3)

(57) [Claims] 1. An electron beam lithography system for irradiating an electron beam onto a surface of a semiconductor wafer coated with an insulating film to perform drawing, wherein a first step of irradiating an arbitrary portion on the semiconductor wafer with an electron beam; 2. A method for preventing electrification in electron beam lithography, comprising a second step of bringing a member for grounding into contact with a dielectric breakdown location on the semiconductor wafer generated in the first step. 2. A method according to claim 1, wherein said electron beam for dielectric breakdown has a higher current density than an electron beam used for electron beam drawing. 3. The method according to claim 1, wherein the irradiation of the electron beam for the dielectric breakdown is performed by time management or by connecting an ammeter between the semiconductor wafer holder and the ground. An antistatic method in electron beam lithography that terminates beam irradiation when dielectric breakdown is detected by current measurement.