DD256390A1 - METHOD FOR ACHIEVING PRESENT, ESPECIALLY EQUIVALENT DOSE DISTRIBUTIONS IN IRRADIATION WITH A CORPUSCULAR RAY AND MASK FOR CARRYING OUT THE PROCESS - Google Patents

Abstract

The invention relates to a method for achieving predetermined, in particular uniform dose distributions during irradiation with a corpuscular beam whose intensity preferably satisfies the normal distribution. By hiding a part of the corpuscular beam within a radius outside which the intensity is equal to zero, an equal distribution of the intensity is achieved. The mask required for this purpose has permeable and impermeable areas, the ratio of which, in the case of normal distribution, is approximately one circumference. The image of the mask rotates on the irradiated workpiece either by the fact that the mask rotates itself, or that with electrically charged corpuscles of the corpuscular beam, a time-varying magnetic field causes the rotation of the image. Fig. 1

Description

b = 2πΓ (1 - exp (-

2r ₀ '"

is sufficient and that the radius of the active mask region (5a) is a little smaller than V2 times the radius (r ₀ ) of the scattering of the particle beam (2).

For this 1 page drawings

Field of application of the invention

The invention relates to a method for achieving predetermined, in particular uniform dose distributions during the irradiation of workpieces with a corpuscular beam.

The workpiece is therefore, in particular, a semiconductor wafer which is subjected to full-area scarfing in the course of processing, without scanning the beam of the ion implantation or of the particle beam lithography.

The invention includes the provision of a suitable mask.

Characteristic of the known state of the art

When machining workpieces with corpuscular beams, it is often necessary to irradiate larger areas of the workpiece surface in a time interval with a predetermined number of particles of the particle beam. Especially with semiconductor wafers, there is the technological requirement of a uniform irradiation of the workpiece. For example, in ion implantation and ion lithography, maximum dose inhomogeneity of 2% is considered acceptable.

The intensity distribution of the particle beam generated by a corresponding source in a plane perpendicular to the direction of propagation corresponds, in a first approximation, to the Gaussian normal distribution along a radius of the beam with the maximum intensity mentioned by the center beam.

in order to meet the requirement that the dose inhomogeneity be at most 0.02, the beam must be suppressed circularly at 0.201 r ₀ , where r _{0 is} the Räclius where the intensity curve has the inflection points. The intensity satisfies the following formula.

I = I _o exp (--- j-)

The dose as integral over the radius satisfies the formula D = 2jrr _o ² l _o (1 - exp (- ^ -)) = D ₀ (I -ι

and with η = D / D _o results

η (0.201 T ₀ ) = 0.02, ie 0.98D ₀ .

hidden.

To increase the efficiency, in EP 0027628 the corpuscular beam is moved periodically in one or more directions perpendicular to the propagation direction of the particle beam. However, movement of the corpuscular beam is not always possible because of the size of the workpieces or other processing steps to be performed simultaneously.

Object of the invention

The object of the invention is to develop a method for achieving predetermined, in particular uniform dose distributions during irradiation with a corpuscular beam, in the case of full-surface irradiation, a high efficiency with respect to the total radiation of the source is achieved with low inhomogeneity of the intensity of the corpuscular beam. The corpuscular beam or the workpiece is not moved during the irradiation. The invention includes the development of the associated mask.

Explanation of the essence of the invention

The object of the invention is to develop a method for a uniform dose distribution of a corpuscular beam by within such a range by appropriate measures such a proportion of the intensity is hidden, that after the irradiation period, the dose distribution within this area is constant. The associated mask should be easy to produce.

The method is used to achieve predetermined, in particular uniform dose distributions in a corpuscular beam whose intensity profile perpendicular to the propagation direction of a particular distribution, preferably satisfies the normal distribution.

According to the invention, an additional mask is introduced into the corpuscular beam whose image rotates η times on the workpiece to be machined.

The mask has permeable and impermeable regions in the active mask region for the corpuscular beam. Due to the rotation of the image of the mask, the impermeable and the permeable regions cause, to a certain extent, such a weakening of the corpuscular beam in accordance with their circumferential proportions.

In an embodiment of the invention, the mask is rotatably mounted and by rotating the mask about a pivot point which lies on the center beam, rotates the image on the workpiece.

In an embodiment of the invention, a direction parallel to the propagation direction of the corpuscular beam and uniform in its intensity variable magnetic field, is passed by the beam. Due to the equations of motion for charged particles in the magnetic field, when the magnetic field changes uniformly from an initial value to a final value, rotation of the corpuscular beam from an initial to an end angle is achieved. If the difference between the two angles is equal to 2π, this means a complete rotation of the image on the workpiece.

The mask for carrying out the method has an optionally rotatable frame. In this frame, a reinforced mask edge is clamped, followed by a compensation zone, which encloses an active mask area.

According to the invention are within the active mask area permeable and impermeable areas. On a partial circumference, the ratio of the width of the impermeable to the partial circumference of normal distribution in the particle beam of the formula is sufficient

b = 2i7-r (1-exp (-)) ^ r _o ·

with r = V2 r ₀ , ie the radius at which the highest uniform intensity distribution can be achieved theoretically, the width b of the impermeable area is just zero, so is the largest Radius of the active mask area slightly smaller than V2 r _o chosen so that the mechanical stability for the inner impermeable areas is given. In the case of a distribution other than the normal distribution, the boundary of the impermeable area must be determined separately.

embodiment

The invention is explained in more detail in an embodiment and with reference to a drawing. Show

Fig. 1: a basic arrangement for carrying out the method according to the invention Fig.2: the mask for carrying out the method according to the invention

In Fig. 1, an arrangement is shown in a basic form, which is suitable for carrying out the method according to the invention. It contains a corpuscular beam source 1 from which a corpuscular beam 2 exits.

The beam with the maximum intensity is referred to as the center beam 2 a. In its course, the corpuscular beam 2 passes through a corpuscular optical arrangement 3 consisting of different elements and leaves it as a corpuscular beam 2 suitable for machining a workpiece 4, which, however, still has the corpuscular beam 2 with respect to the center beam 2a

r ²

Normal distribution I = l _o exp (j-) is sufficient.

2 r _o

The still normally distributed corpuscular beam 2 now passes through a mask 5, in which such an area is hidden, that the remaining corpuscular beam 2 along the radius of the normal distribution is sufficient, but a sum of the intensities is constant on a circumference. By rotation of this mask 5 to the center beam 2 a, this spatial distribution is averaged over time, so that in an integer rotation of the mask 5, the dose distribution behind the mask 5 is constant.

For targeted processing of the workpiece 4 while still another template 6 is arranged in front of the workpiece 4.

FIG. 2 shows the mask 5 for carrying out the method with the section of the active mask region 5a.

Within a ring 7 is a propeller-like aperture as impermeable area 8, which with the ring. 7

connected is. Since with a maximum yield and uniform distribution the ring 7 has a radius of \ [2 r ₀ at I = I ₀ exp (j-)

For reasons of mechanical stability, the radius of the ring 7 is slightly smaller than λβ. r ₀ .

The ring 7 and the impermeable area 8 limit the permeable area 9.

The ratio of impermeable area 8 on a perimeter to the sum of impermeable area 8 and permeable area 9 satisfies the formula

= 2ir (1 -exp (-

2r ₀ ² ''

2r ² - r ²

• η - pvn ι - '

such that a side boundary of the opaque region gives b '= - (1-exp (^ -5-)).

r

Claims (4)

1. A method for achieving predetermined, in particular uniform dose distributions during irradiation with a corpuscular beam whose intensity profile perpendicular to the propagation direction of a certain, preferably the Normalverteilurrg sufficient, characterized in that in the corpuscular beam (2) an additional mask (5) is introduced, wherein the Mask (5) in the active mask area (5a) has permeable and impermeable areas (9; 8), and in that the image of the mask (5) rotates η times during a processing period. 2. The method according to claim 1, characterized in that a rotatable mask (5) rotates about an axis which coincides with the center beam (2a). 3. The method according to claim 1, characterized in that the corpuscular beam (2) of electrically charged particles passes a direction parallel to the propagation direction of the beam and in its intensity uniformly variable magnetic field. 4. A mask for carrying out the method according to claim 1 to 3 with an optionally rotatable frame in which a reinforced mask edge is clamped, a compensation zone and an active mask area, characterized in that the ratio permeable area (9) to the sum of permeable area ( 9) and impermeable area (8) along a circumference determined by the radius (r) is determined by the distribution and in normal distribution of the formula