GB2133618A

GB2133618A - Fabricating semiconductor circuits

Info

Publication number: GB2133618A
Application number: GB08332939A
Authority: GB
Inventors: Anthony Ernest Adams
Original assignee: General Electric Co PLC
Current assignee: General Electric Co PLC
Priority date: 1983-01-05
Filing date: 1983-12-09
Publication date: 1984-07-25
Also published as: GB8332939D0; GB2133618B

Abstract

A method of annealing (eg. driving in and activating impurities in) selected regions of a semi-conductor substrate 3 during fabrication of a circuit in the substrate. A laser beam is directed onto the substrate 3 through a mask 13 which shields the non-selected regions of the substrate from the laser beam, the masked beam being focussed onto the substrate 3 by an optical system 11. <IMAGE>

Description

SPECIFICATION Fabricating semiconductor circuits This invention relates to methods of fabricating semiconductor circuits.

A basic feature of conventional methods of fabricating semiconductor circuits is the formation, on the surface of a substrate of semiconductor material, of a layer of material in which are formed windows which define selected regions of the substrate into which dopant material is required to be introduced. A series of diffusions or ion-implantations is then used to introduce dopant material through the windows into the regions of the substrate defined by the windows followed by controlled furnace anneals to drive the dopant material into the substrate and cause the doped regions of the substrate to become electrically active.

It has been demonstrated that a beam of laser radiation, either in the form of a pulsed beam illuminating the whole substrate or a scanned cw beam, may be used as an alternative to furnace annealing. However, extreme care must then be taken to avoid damage to the masking layer defining the windows. One proposed method of overcoming this difficulty is to deposit additional layers to reflect radiation away from the substrate except from the doped regions it is desired to anneal. However, this technique requires several preparation steps and is difficult to carry out satisfactorily.

It is an object of the present invention to provide an alternative laser annealing technique which avoids the above mentioned difficulties.

According to the present invention, a method of annealing selected regions of a substrate of semiconductor material during fabrication of a circuit in the substrate comprises directing a beam of radiation onto said substrate through a mask such that nonselected regions are shielded from said radiation by the mask.

The radiation is suitably laser radiation.

The invention also provides an apparatus for carrying out a method according to the invention comprising: a source of radiation; an optical system arranged to direct radiation from said source onto a surface ofa semiconductor body; and means for mounting a mask between the source and the optical system; the optical system being adapted to provide an image of the mask on the surface of the semiconductor body.

One method and apparatus in accordance with the invention will now be described, by way of example, with reference to the accompanying drawing which is a schematic diagram of the apparatus.

Referring to the drawing, the apparatus comprises a chamber 1 in which a silicon substrate 3 to be pro cessed is contained, the substrate containing a pre defined pattern of doped regions which it is desired to anneal. The atmosphere within the chamber 1 is controllable by means of a vacuum and gas handling system (not shown) connected with the chamber via a suitable duct 5.

Radiation derived from a laser 7, for example a Q-switched ruby laser, is directed onto a main face of the substrate 3 by way of a beam profiling optical system 9 and a further optical system 11. The optical system 11 is disposed in the chamber 1 and a mask 13 is disposed in the wall of the chamber 1 in the path of the radiation between the two optical systems 9 and 11.

The beam profiling system 9 is used to process the spatial intensity of the laser beam so as to produce a beam which is uniform over its cross-section to within a few per cent. The system 9 suitably comprises a lens arrangement or a laser amplifier running in saturation.

The system 11 comprises a high quality beam splitter 15 which deflects the beam received through the mask 13 through a lens system 17 onto a phase con- jugate mirror 19, the lens system 17 serving to reduce the size of the projected mask to match the aperture of the mirror 19. After reflection at the mirror 19 the radiation passes through the beam splitter 15 to impinge on the substrate 3 which is positioned at an optically equivalent position to the mask 13.

The mask 13 comprises a metal pattern on a thin quartz plate, the pattern corresponding to areas ofthe substrate 3 which it is not desired to anneal, i.e. to those areas ofthe substrate 3 which are required to be shielded from the radiation.

In use of the apparatus the substrate 3 is first accurately positioned with respect to the projected image of the mask 13, and the laser 7 then pulsed at high power to effect the required annealing as rapidly as possible. Alignment of mask image and substrate 3 may be facilitated by incorporating a few alignment holes (not shown) in the mask 13 and aligning the images of the holes with corresponding holes etched in the substrate 3. A low power helium-neon or other suitable laser may be used for this purpose.

To reduce the risk of laser induced damage to the mask 13 and optical systems 9 and 11, the peak power passing through these components may be limited to a suitably low level, and the laser energy raised to the required level for annealing by a laser amplifier (not shown positioned at the optically equivalent position to the mask 13.

Claims

1. A method of annealing selected regions of a substrate of semiconductor material during fabrication of a circuit in the substrate comprising directing a beam of radiation onto said substrate through a mask such that non-selected regions are shielded from said radiation by the mask.

2. A method according to Claim 1 in which said radiation is laser radiation.

3. An apparatus for carrying out a method accord- ingtoeitheroneofthepreceding claims, comprising: a source of radiation; an optical system arranged to direct radiation from said source onto a surface of a semiconductor body; and means for mounting a mask between the source and the optical system, the optical system being adapted to provide an image of the mask on the surface of the semiconductor body.

4. An apparatus according to Claim 3 in which said optical system comprises: a beam splitter arranged to direct radiation after it has passed through said mask onto a phase conjugate mirror arranged to reflect said radiation through said beam splitter onto said surface.

5. An apparatus according to Claim 4 in which a lens system is interposed in the radiation path between said beam splitter and said mirror, said lens system being effective to substantially match area of said radiation beam to the aperture of said mirror.

6. An apparatus according to Ciaim 3 or Claim 4 in which a laser amplifier in interposed in the radiation path between said beam splitter and said surface.

7. A method of annealing selected regions of a substrate of semiconductor material during fabrication of a circuit in the substrate, substantially as herinbefore described, with reference to the accompanying drawing.

8. An apparatus for carrying out the method of Claim 7, substantially as hereinbefore described with reference to the accompanying drawings.