DE3032461A1 - Alloyed metal contact prodn. on oriented semiconductor crystal - by rastering surface with intense pulsed laser light before applying metal assists alloying - Google Patents

Abstract

In the prodn. of alloyed metal contact layers on crystal-oriented semiconductor surfaces by energy pulse radiation, the intended area of the semiconductor surface is first rastered with a close sequence of intensive laser light pulses. Then the metal layer is applied and alloyed with the semiconductor surface in conventional manner. The process is used on (100) oriented Si crystals used for the prodn. of transistors, esp. thyristors contg. controllable short circuits produced by integrated FETs. Pretreatment favours alloying and the formation of alloy layers of uniform thickness.

Description

Process for producing alloyed metal contacts

layers - on crystal-oriented semiconductor surfaces by means of Energy pulse irradiation.

The present patent application relates to a method of manufacture of alloyed metal contact layers on crystal-oriented semiconductor surfaces by means of energy pulse radiation.

Such a method is from German patent specification 28 25 212 known. In this process extremely aunne metal layers, which through Vapor deposition, sputtering, electrodeposition or ion implantation on one Semiconductor substrate have been applied, with an intense short laser light pulse irradiated and thereby alloyed to the semiconductor surface.

The irradiation conditions must be chosen so that in No significant diffusion takes place on the substrate. The pulse duration of the laser light pulses is therefore in the nanosecond range. The known process is based on the manufacture extremely thin metal structures, such as those used in VLSI technology, for example find limited.

In semiconductor technology, one generally chooses the surfaces e.g. for silicon material from which components are to be manufactured, in which Plane of a certain preferred crystal orientation.

For example, the thyristors of the future will be more integrated with the help of Contain controllable short circuits generated by field effect transistors. Hence will it may be necessary to use power semiconductor and MOS technology together to combine. While in the power semiconductor technology because of the good alloyability 11-oriented silicon is used, is preferably 9100> -oriented in MOS technology Silicon processed as the starting material because it has different crystal properties are considerably more significant.

Another important consideration is that # 100 # silicon base material Can be drawn more easily and doped more homogeneously than # 111 # silicon. 9100> silicon can therefore be produced much more economically. Using the # 100 # silicon would therefore also be more advantageous for the production of power semiconductor components.

The use of <1 00 -oriented silicon for the production of Thyristors, however, interfere with the alloy between metal layers and silicon on difficulties. The aluminum-silicon alloy is made in (100> -oriented Silicon surfaces very uneven, so the negative blocking ability is very is deficient.

The object on which the invention is based is therefore to the ability to alloy a thin surface layer of the <1 00 -oriented To increase silicon crystal wafer compared to the contact metal, thus the entire The surface is alloyed right at the beginning of the alloying process and thus a uniform thick alloy layer is achieved.

According to the invention, this object is achieved in that prior to application of the metal contact layer is the area of the semiconductor surface provided for the metal contact is scanned with a dense sequence of intense laser light pulses, then the metal layer is applied and in a known manner in the semiconductor surface area is alloyed.

Dabeili-egt within the scope of the invention that as a semiconductor surface a silicon crystal surface oriented in the # 100 # direction and as a contact metal z. B.

Aluminum, which is preferably pressed on in the form of a foil, is used.

According to a particularly favorable embodiment according to the teaching of the invention is a Nd: YG pulse laser with a wavelength of 1.06 / µm, a Pulse duration of 0.5 µs and a power in the range of 50 watts used - that Light beam of the laser focused on a diameter of 50 e and the semiconductor surface to be treated with a pulse frequency of 4 kHz through dense Placing the individual beam cross-sections scanned next to one another. The whole Irradiation time for an approximately 7.5 cm large # 100 # -oriented silicon crystal wafer for this example is approx.

1 minute.

The method according to the teaching of the invention can be as follows Explain: Will a silicon surface with a short laser light pulse outside a critical intensity Ikr irradiated, so evaporated from the irradiated surface area- e; as silicon. This creates a small crater the diameter of the laser beam. When this point cools down, one with many forms, especially at the crater edges Dislocation lines through-grown polycrystalline surface layer. Will be the critical one If intensity 1kr is not exceeded too much, the dislocation line network remains limited to this surface layer.

The dense network of dislocation lines and the different orientations the crystallites of the polycrystalline Favor surface layer the dissolving of the silicon by the aluminum and that also with (100> -oriented Silicon wafers, so that there is a uniformly thin surface aluminum-silicon alloy layer trains.

Electron beam diffraction diagrams in reflection show from the unirradiated, lapped disk back the Kikuchi diagram of a perfect single crystal Surface layer. After laser irradiation in air, diffuse Debye-Scherrer rings become visible on a thin, not necessarily stoichiometric oxide layer Clues. This oxide layer is approx. 30 nm thick. After etching with hydrofluoric acid appear individual Bragg references superimposed with a Debve-Scherrer ring system, that originates from polycrystalline surface areas. The crater floors are likely to be monocrystalline while the crater rims have a polycrystalline structure. So that is The more finely focused the laser light beam, the more effective the method and the closer the individual radiation spots are. In contrast to that in the German patent 28 25 212 described method for alloying The method according to the invention is particularly useful for producing extremely thin structures thicker alloy layers are suitable.

In the following, using an exemplary embodiment and the figures 1 to 4 the individual process steps are shown schematically and briefly explained will.

The same reference numerals apply to the same parts in the figures.

A silicon crystal wafer 1 with one oriented in the <i00 direction Surface is, as shown in Figure 1, with sharply focused, intense Laser light pulses 2 irradiated scanning, so that evaporation craters with a thin Surface layer 3 of extensive dislocation line networks and Polycrystals are formed which no longer offer any resistance to the subsequent alloy oppose.

As can be seen from FIG. 2, this disrupted surface layer 3 is applied is an aluminum layer 4 by vapor deposition, sputtering, electrodeposition or applied by pressing a film on and alloyed into the semiconductor body 1. In the process, an aluminum-silicon melt is initially formed on the silicon crystal disk 1 14 (see Figure 3), which during the cooling phase into an aluminum-silicon eutectic 24 and a p-conductive silicon layer 5 passes over (see Figure 4).

After performing the method according to the teaching of the invention the following results were obtained with regard to the electrical parameters: Thyristors, which are generated controllable by means of integrated field effect transistors Contains short circuits, made from <10C5 silicon. Part of the 00> -. Oriented Before alloying, silicon wafers were subjected to the laser treatment according to the invention subjected. The frequency of the measured blocking ability URIV in the negative direction can be seen from FIGS. 5 and 6. The blocking ability is with the untreated Discs (see Figure 5), as was also found in earlier experiments, bad. In the case of the laser-treated disks (see FIG. 6), however, the negative one Blocking ability fundamentally improved and reaches the blocking ability of thyristors made of <111> -oriented silicon. This shows that <i 00> -oriented silicon can be alloyed with aluminum if the surface to be alloyed a corresponding laser treatment has been given beforehand. Be at the laser itself there are no special quality requirements.

By the method according to the teaching of the invention is the opportunity given to better integrate the MOS technology and the bipolar technology.

7 claims 6 figures Blank page

Claims (7)

Claims. Process for the production of alloyed metal contact layers crystal-oriented semiconductor surfaces by means of energy pulse radiation, d a d u r c h g e -k e n n z e i c h n et - that before the application of the metal contact layer the area of the semiconductor surface intended for metal contact with a dense sequence of intense laser light pulses is scanned, then the metal layer is applied and alloyed into the semiconductor surface in a known manner. 2. The method according to claim 1, d a d u r c h g e -k e n n z e i c -h n e t that the semiconductor surface is a silicon crystal surface oriented in the # 100 # direction and aluminum contact metal is used. 3. The method according to claim 2, d a d u r c h g e -k e nn z e i c h Not that the aluminum is pressed on in the form of a foil. 4. The method according to claim 1 to 3, d a d u r c h g e -k e n n z e i c h n e t- that a Nd: YAG pulse laser with a wavelength # of 1, O & / um, a pulse duration of 0.5 µs and a power in the range of 50 W is used. 5. The method according to claim 4, d a d u r c h g e -k e n n ze i c h n e t that the light beam of the laser focuses on a diameter of 50 microns and the semiconductor surface to be treated with a pulse frequency of 4 kHz scanned by placing the individual beam cross-sections close together will. 6. The method according to claim 1 to 5, since d u r c h g e k e n n z -e i c h n e t that the entire irradiation time for about 7.5 cm large <100 [beta] -oriented silicon crystal disk set to approx. 1 minute will. 7. Application of the method according to claim 1 to 6 for the production of semiconductor components, in particular for the production of thyristors, which Contain controllable short circuits generated by means of integrated field effect transistors.