DE1906203A1 - Process for the realization of diffusion processes using a laser beam as a heat source, in particular for the production of semiconductor components and device for carrying out the process - Google Patents

Description

IBM Germany International ßnro-Maschinen Gesellschaft mbH

Boeblingen, February 5, 1969 si-no

Applicant: International Business Machines

Corporation, Armonkj N.y. 105O ² I-

Official file number: New registration '

· .- I file number d. Applicant: Docket FI 9-67-II5

S method for the realization of diffusion processes using a laser beam as a heat source, in particular for the preparation of semiconductor device, un d r Before ichtung for performing the method

The one used in semiconductor technology for the manufacture of semiconductor component structures usual, on the use of alloy '" Processes based on or diffusion processes cannot be regarded as fully satisfactory. This is especially true when components with a complicated structure are to be manufactured, which include a large number of Has diffused zones, the geometry of the respective structure with high tolerance for a high number of Individual copies should be adhered to. Selective diffusion of doping materials in

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The semiconductor base material silicon is normally realized by first allowing a silicon dioxide or silicon dioxide layer to grow thermally on the semiconductor body at those points where diffusion regions are to be realized, making openings in the covering oxide layer and then making the openings in the above-mentioned manner masked semiconductor body at elevated temperatures a W steam exposing containing the desired dopants. The most common dopants are boron, phosphorus and arsenic, for which silicon oxide is a useful masking material, so that selective diffusion processes of the aforementioned type do not cause any particular difficulties.

However, the aforementioned method generally has the disadvantage> that the semiconductor wafer in the implementation of the respective Diffusion processes in their entirety increased temperatures £ must be exposed. During the various diffusion steps, this sometimes results in undesirable changes in the doping concentrations, as well as distortions the diffusion fronts. Furthermore, there can be difficulties result as a result of undesirable oxygen and moisture content and as a result of non-uniform flow rates of the Carrier gas within the tubular diffusion furnace. The above procedure also requires a division of the Total production in individual batches. The means of diffusion semiconductor wafers to be provided with a dopant are either in a closed reactor

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Tube in which the source of the materials to be diffused is also located, this arrangement being heated to elevated temperatures for a relatively long period of time. On the other hand, it is also customary to allow gas containing substances to be doped to flow over the platelets fitted in the reaction tube. The procedures mentioned are time-consuming, cumbersome and largely require manual work. Attempts to make the process continuous λ or to automate it for the purpose of reducing costs have so far been unsuccessful. As a modification of the known method, it has also already been known to carry out the diffusion processes in the semiconductor bodies by means of an electron beam as a heat source. Here, a thin layer of the doping material to be diffused is applied to the surface of the semiconductor body to be doped, after which local heating is generated in the desired areas of the semiconductor body by means of an electron beam. As a result of the selective heating by the electron beam, the dopants present in the covering layer diffuse selectively into the semiconductor body. However, such a procedure is very troublesome, since the entire process must be carried out within an evacuated vessel.

Furthermore, it has already been proposed to use a continuous laser beam as a heat source in order to achieve local heating of the semiconductor body sum for the purpose of carrying out

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To cause diffusion processes. Although such a continuous laser beam is a much improved source of heat represents for diffusion purposes, it was found that the diffusion. sion process not fast enough even in the manner mentioned can be set in motion. The selectively heated areas cannot be localized with sufficient sharpness so that a significant heat transfer in the vicinity of the selec- tiv areas to be heated takes place.

The diffusion processes known up to now can be attributed to them Effect according to the classical diffusion theory predetermine.

The present invention is based on the object. To specify a method for the diffusion of doping materials into a base body, in which the diffusion mechanism does not follow the laws of classical diffusion theory and due to which the heat supplied to the base conductor body to be doped is very much concentrated within the areas to be selectively doped, which allows the production of complex semiconductor structures with a high precision of the transitions and the overall geometry.

The method should be suitable for automation and the Do not necessarily require the use of diffusion masks., In addition, there should be no need for the entire semiconductor body having to heat up to higher temperatures.

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The mentioned method uses a laser beam for selective heating of predetermined areas of the body to be provided with diffused areas and is thereby characterized in that the irradiation or the selective heating of the body is carried out intermittently.

The method of the present invention is thus useful a pulsed laser beam and triggers a series of '

Difficulties in semiconductor diffusion technology. Due to the very narrow localization of the heat generation ensures that areas generated by previous diffusion processes within the semiconductor wafer remain unaffected by subsequent diffusion steps. As a result, e.g. sub-collectors and other areas created by diffusion do not expand or distort further during later diffusion steps what with the previously known diffusion processes | is inevitable.

Another advantage of the invention is in the fact too see that extremely short times are required for the actual diffusion processes, with no vacuum apparatus whatsoever is required. As is the case, for example, in a special method mentioned above, in which as V / arm source an electron beam is used. As a result of the properties mentioned, the method is suitable according to the Invention for automation and for continuous

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previously known diffusion processes only more or less strong batches could be subjected to the same process sequence. Although the process basically works without additional masking steps, In addition, coverings by masking layers can also be used for this purpose. ,, certain areas of-.-to doping semiconductor wafer with respect to the laser Shield £ supplied radiant energy.

Details of the invention emerge from the following; Description in conjunction with the drawings.

In these mean:

Figure 1 is a schematic representation of a preferred

Embodiment of an apparatus for performing the method according to the present invention;

Figure 2 is a partial perspective view of one after

Methods of the present invention integrated circuit without metallic connecting lines and

Figure 3 is a cross-sectional view corresponding to Figure 2, in which the metallic connecting lines are also shown.

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FIG. 1 shows schematically an apparatus for carrying out the method according to the present invention. A light beam 19 generated by the pulsed laser 18 is directed onto the surface of a semiconductor substrate 10, on which a thin layer 11 of a material containing the desired dopants is applied. The substrate 10 made of semiconductor material is located on a support 12. This allows a defined position in a precise manner change of the substrate with the help of the spindles 14, 15 and make, the latter two spindles one. Allow change of position within the XY plane. A pulse-shaped light beam 19 generated by the plague laser 18 falls on the surface of the semiconductor wafer 10 after passing through a lens system. As can be seen from FIG. 1, part of the beam passes through the beam splitter 20 and through the objective lens 21 onto the semiconductor substrate. A second component of the beam 19 arrives after reflection at the beam splitter 20 and after passing through a second beam splitter 24 as well as after focusing through the lens 25 on a comparator 26 'This serves to _: readiness of the radiation impulses and / or as a monitor for the diffusion process, which will be explained in detail later . The light source 28 can be arranged in such a way that its light beam is focused by the lens 20 and reflected at the beam splitter 24 and 25 and reaches the surface of the semiconductor wafer 10. This light beam from the source serves as an indicator of the position

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of the laser relative to the semiconductor wafer.

The apparatus shown in FIG. 1 can be automated in a conventional manner by combining it with a Data processing device which is programmed to create a desired diffusion pattern.

Suitable systems for driving the in Χ, Υ, Ζ-direction acting spindles 15, 16 and 17 are provided signals from the programmed data processing machine for controlling these systems to be delivered. The data processing machine that simultaneously ignites the laser source at the appropriate moment and then the movement of the Halblexterplate in a caused a new situation, is not shown in the drawing,

In operation, a single from the laser source is Io after Beam pulse directed down onto the surface of the semiconductor wafer 10 in the cover 11 of the semiconductor wafer 10 cause dopants contained to diffuse into the semiconductor body 10. Because this diffusion occurs almost instantaneously, and the heat generation is localized to a very limited area, results no noticeable heating of the total semiconductor body 10 during the diffusion process, which is in complete contrast to other, so far common diffusion processes.

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Any suitable material, which contains the desired dopant can be used.

This can be either of the P or N conductivity type.

As is known, SiOp layers which have grown in pyrolysis are preferably used as cover layers for silicon, which in turn are used are doped with phosphorus, boron, arsenic or any other element imparting P or N conductivity type.

On the other hand, applied layers of PGO ^ glass or boron glass is used as a dopant-containing covering layer on the surface of the semiconductor base body also at relatively low temperatures temperature-I ⁽⁰ C 6OO ° C 70o).

Such a layer acting as a dopant source can be made, for example, by introducing the semiconductor wafer into a vapor from a compound of the dopant can be used, which decomposes in a suitable manner, for example in a vapor from boron trichloride (BCl,) or from arsenic trichloride.

The layer 11 may cover or as contiguous be ä applied as a layer with a specific geometry using conventional photolithographic techniques can be applied. The composition and the thickness of the layer can be used as parameters in order to reduce or exclude possible damage to the semiconductor surface.

A laser beam source operated in a suitable manner in pulse mode is used to carry out the method of the present invention. Solid state lasers are preferred executed as ruby laser, neodymium laser and the like.

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The intensity of the on the surface of the semiconductor die

■■: '■' Il--: directed laser beam pulse can be varied between 2 to 2 χ 10 joules / mm. The intensity at a given point on the substrate can be controlled by defocusing the beam component, extending it over a larger area. Furthermore, different types of beam splitters can be used for this purpose, which render a variable portion of the total beam ineffective through reflection. The pulse duration of the beam can be changed between 0.001 and 100 msec. The energy density and the pulse duration can be changed in order to adapt the method to the most diverse requirements. The diffusion depth can be controlled both by changing the energy density and the pulse width and with the aid of the material selected for the cover on the surface of the semiconductor body to be doped. "The doping concentration in the diffused region produced can also be controlled

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can be controlled by the choice of cover material Proportion of dopant within the cover that Pulse intensity as well as the pulse duration. In practice, the thickness of the cover layer is within a Range from 250 S to 4 ^.

The method of the present invention can be used for the manufacture. Position of different types of semiconductor components b * e-. can be used for both discrete transistors and diodes as well as for integrated circuit devices with a

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Variety of different active and passive elements, which are isolated from one another, but one common belong to monocrystalline semiconductor bodies. To further explain the inventive concept, the following is the Manufacture of a special semiconductor component described, which insulation junctions, sub-collectors and various has further diffused zones and, overall, represents a relatively complex integrated circuit, I. as shown in FIGS. 2 and 3.

FIG. 3 shows the cross section of a typical structure as it can be produced as a sequence of diffused regions using the present inventive concept. The semiconductor component 50 has a substrate 52 * on which an NPN transistor 54 is arranged, specifically insulated from the substrate 52 and from further transistors and passive elements, the zones 56 representing insulation diffusions. d Transistor 54 has the Kolle]: goal area 58, the base region 60 and emitter region 62. Transistor 54 .is from the substrate by a PN junction on both the bottom and on the lateral boundary surfaces insulated.

In the production of the configuration 50 is used as the initial process step uses a semiconductor die of the P conductivity type, which preferably has a resistivity from 10 to 2Ό-Χ2.Χ cm. The platelet is preferably made from nonocrystalline silicon, which in conventional ^

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Can be obtained by drawing from the melt, which has a desired doping co-nitration. Of the Semiconductor bodies obtained by such a drawing process are then mechanically converted into a multitude of .Tile cut up. After cutting the platelets lapped and chemically polished. Then on the surface of the plate 52 applied a cover layer, which a

W has doping material of the N conductivity type. The plate is now, as shown in FIG. 1, attached to the support 12. The laser beam is now switched on in order to diffuse the dopant into the semiconductor wafer, as a result of which the zone labeled 53, which represents the subcollector of the transistor 54, is created. The plate 52 can be in a defined manner at high speed relative to the. Laser beam are moved, whereby the possibility of producing different mutually separate diffusion

£ areas results. On the other hand, the semiconductor wafer to be doped can also be shielded by means of a mask, whereby the pulsed laser beam which hits the wafer is directed, can only be effective when it is on exposed areas of the semiconductor wafer to be doped hits. Containing dopants of the N conductivity type Cover layer is then removed. Then an epitaxial N conductivity type layer on the surface of the platelet, v / as can be realized using a conventional method. This layer

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forms the area in which the transistor 54 is located within the completed overall configuration. This is produced by means of a subsequent diffusion step. A layer containing dopant of the P conductivity type is then applied to the surface of the epitaxially grown layer and the structure thus obtained is attached to the support 12. Now diffusion steps for forming the insulating zones 56% ■ carried out, which in turn either by use of a suitable masking device on the surface of the wafer, or by a suitably controlled relative movement between. Laser beam and support · or semiconductor wafers can be accomplished. A lattice-shaped pattern produced in this manner is shown in detail in FIG. It must be ensured that the Isolierdiffusion down extending down to the surface of the substrate 52, thus arranged in a lattice form areas like

are completely isolated from each other by at least one PN junction. Then the base zones 60 are generated, by the laser beam in a to generate the diffusion areas is controlled in a suitable manner. Here, the doped substances come from the same cover layer, It is pointed out that the base zone oO is not that deep extends, as is the case for the isolation zone 56. As mentioned above, the required depth is given by Variation of the energy density of the laser beam adjusted. This can be done in a known way by changing the output

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energy of the laser source or by changing the pulse duration or caused by defocusing the laser beam will. The cover is then removed and replaced by a other N * conductivity-imparting dopant-containing material layer replaced. The emitter diffusions 62 and the diffusion are now used to generate the zones high conductivity 64 for the collector 65 carried out. The cover is then removed again and through

™ replaces an insulating cover to be applied which preferably consists of silicon dioxide. In this layer of silicon dioxide 66 holes are then etched in above the collector, base and emitter zones 58, 60 and 62. Subsequently- a metallic layer is applied to the cover 66 applied to a metallic connection with the zones 58, 60, 62. Metal vapor deposition and etching processes known in the art are used for this purpose. the various desired switching connections between active

φ and passive elements of the integrated circuit can depending according to the requirements of the present overall circuit to be created.

The following example is intended to use the apparatus shown in FIG. 1 to carry out the method according to the present invention ", with particular reference to the Differences between the Diffus' ionsme chanisme η accordingly the known diffusion method and the method according to the present invention is pointed out.

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Example: .

A cover layer of PgOc was applied to a polished, defect-free, single-crystalline silicon wafer made of P-conductive material with a surface oriented in a (111) plane. This was done by painting on a solution of P ₂ Oc in acetone, the resulting cover being about 2000 8 thick. The cover layer was dried and then placed in the beam path of a laser beam diffusion apparatus according to FIG. The beam was focused on the surface of the semiconductor wafer and exposed to a single pulse with a duration of one msec and an energy density of 2.10 joules / mm. To measure this value, a thermocouple was used as a. Sensor used. The surface selectively struck by the light beam was about 4 in diameter. 10 mm. The remaining cover layer of P ₂ Oc was removed by rinsing in a hydrogen fluoride solution. The existence of a PN junction was verified by means of a point-shaped probe. In addition, the diffused transition was measured with a curve recorder, whereby the characteristics of a Zener breakdown were clearly recorded, which can also be regarded as conclusive evidence of the existence of a diode. The area diffused into the semiconductor wafer was also detected by means of a conventional beveling and coloring process, the depth of the diffusion areas being measured and recorded .vrufede.

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Using the relationship j — §— exp - (X. ² / 4Dt) = N _K between the transition depth X. and the diffusion cons, D and the time t divided under the assumption of the boundary condition that the diffusion is in an infinite half-range of the semiconductor takes place on the basis of a limited source, the diffusion constant, which represents a value for the diffusivity, is a value of about 10 ^y cm / sec.

In the above expression, Q means the total proportion of the diffusion substance and N. means the general doping concentration (background concentration). '

For comparison purposes, the diffusion constant of

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Phosphorus at 1000 ° C in a standard diffusion process

Determined value of the order of 10 ~ ^ cm / see lies. ·

A comparison of these values for the diffusion constants shows that the diffusion constant, which when using a Pulse-driven lasers are considered to be three to four orders of magnitude is larger than when using a conventional one Heat source is the case. A certain vagueness in These measurements come about because the temperature, of the semiconductor wafer at the point of the laser beam caused diffusion of a measurement is not accessible. However, the large difference in the calculated diffusion constants given above shows that the diffusion mechanism,

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which is the basis of the classic diffusion process, itself must be markedly different from the one who has to differ from one pulsed laser beam is triggered. Here is to note that, apparently, even in the application of a continuous laser beam, essentially only one is not very strong significant modification of the previously common heat sources can be seen. The extraordinarily large

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differed for the diffusion constants for the ^ described above different diffusion processes represents a completely unexpected result.

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Claims (1)

1906201 Claims Process for the realization of diffusion processes using a laser beam as a heat source, in particular for the production of semiconductor components, characterized in that a pulsed laser beam is used. Method according to claim 1, characterized in that the structure of the diffused zones to be created by a precisely controlled relative movement between Radiation source and semiconductor base body is generated without the use of masking processes. Method according to claims 1 and 2, characterized in that the depth of the diffused zones through the choice of the pulse duration and / or the radiation energy of the laser beam is controlled. Process according to claims 1 to 3, characterized in that that the energy density of a single impulse on the surface of the diffused zones P Jl P seeing body between 2 joules / mm and 2.10 joules / mm is chosen. 9 0 96-477 FI 9-67-115 Process according to Claims 1 to 4, characterized in that that masking method known per se is used for the selective shielding of the radiant energy will. Device for performing the method according to the Claims 1 to 5, characterized in that a supplied by a natural light source (28), j | partially parallel to the laser beam (19) Light beam in connection with the comparator (26) for Intensity display of the laser beam pulses and / or is provided as a monitor for the diffusion process. PI 9-67-115 909847/0996 ~ D Void β i fe s ι