Semiconductor device manufacturing: process – Radiation or energy treatment modifying properties of...
Reexamination Certificate
2002-04-11
2004-05-18
Kielin, Erik J. (Department: 2813)
Semiconductor device manufacturing: process
Radiation or energy treatment modifying properties of...
C438S796000
Reexamination Certificate
active
06737367
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method of thermally treating at least one layer, preferably comprising compound semiconductors, for activating foreign or impurity atoms passivated in the layer by hydrogen, according to which at least one layer is heated for a first time interval of less than 120 seconds to a temperature greater than a first temperature at which the specific layer or sheet resistance decreases.
The described method is used for the electrical activation of the p-doping of II-VI and III-V semiconductors that are produced by CVD (Chemical Vapor Deposition), especially by MOCVD (Metal Organic Chemical Vapor Deposition), processes. Such semiconductors are used, for example, for the manufacture of opto-electronic components (e.g. light emitting components such as blue light diodes or laser diodes). During the CVD processes, in addition to the acceptor hydrogen is also incorporated into the semiconductor layer during the p-doping (e.g. in III-V semiconductors Mg, C, Zn, Be, Cd, Ca, Ba, or in II-VI semiconductors N). Along with the acceptor atoms, the hydrogen form an electrically inactive complex, which leads to a passivation of the acceptor atoms (e.g. Mg) and hence to a high sheet resistance. A number of methods are known for activating the passivated acceptor atoms, according to which the electrically inactive hydrogen-acceptor complex (or in general hydrogen-foreign atom complex) are broken up and the hydrogen is removed from the p-doped or implanted layer by diffusion.
A method according to the initially described type for activating the hydrogen acceptor complexes is described in U.S. Pat. No. 5,786,233, whereby during the method the substrate is irradiated with short wave light, the photon energy of which is greater than the energy gap or band gap at the process temperature. The substrates are preferably heated to temperatures of approximately 650° C. to 800° C. for a duration of two to thirty minutes. In so doing, the complexes are broken up and the previously passivated acceptors (e.g. GaN:Mg) are activated, as a result of which the sheet resistance is reduced by up to several orders of magnitude, and the hole carrier concentration is correspondingly increased, respectively. As a result of the irradiation with short wavelength light, the activation of the acceptors and hence the hole carrier concentration were significantly increased. Since at still higher temperatures, however, the layer is thermally damaged and the p-diffusivity again decreases as the treatment duration increases, pursuant to U.S. Pat. No. 5,786,233 a longer annealing is preferably used at comparatively low temperatures.
Yoichi Kamiura et al.; Jpn.J.Appl.Phys. 37 (1998) L970-L971 describes the influence of UV irradiation upon the Mg activation of GaN films. In this connection, the GaN films are held in a furnace for about one hour at a temperature greater than an activation temperature of about 550° C. Upon irradiation of the Mg doped GaN layer with UV radiation, the activation temperature can be reduced approximately by 100° C., as a result of which the thermal stress of the substrates is similarly reduced.
In EP 0723303, there is described a light-emitting electronic component that is built up of a hetero structure, and a method for producing the same, according to which at approximately 600° C. with the aid of UV laser radiation, an annealing is carried out in order to increase the acceptor activation in the layers and to reduce the sheet resistance, respectively.
In Mamoru Miyachi et al.; Appl.Phys.Lett., Volume 72, No 9, 1101 (1998), there is described the thermal activation of Mg in GaN with the additional generation of charge carriers that are generated by applying a potential to the semiconductor structure. In addition, reference is made to the fact that a p-type or conducting characteristic of GaN that contains Mg is also achieved and can be influenced by an irradiation with low energy electrons.
All of the previously described methods serve for the activation of the hydrogen-passivated acceptors. The drawback of the above described methods is that relatively long process times are necessary for the activation, whereby in general the substrates (e.g. Sapphire, SiC, Si, AIN, ZnO or Al
2
O
3
), with the semiconductor films disposed thereon, are subjected to a high thermal stress, and in addition the throughput is very low.
SUMMARY OF THE INVENTION
It is an object of the present invention to eliminate these drawbacks.
Pursuant to the present invention, this object is realized in that with the initially described method, within the first time interval at least one layer is heated for a second time interval of up to 60 seconds to a second temperature that is greater than the first temperature, whereby during the method in at least one third time interval charge carriers are produced within the layer by electromagnetic radiation.
By means of the inventive method, the process duration is advantageously considerably shortened for the activation of the hydrogen-passivated foreign atoms (e.g. Mg) in one or more layers (e.g. GaN) that are comprised of compound semiconductors, whereby sheet resistance and hole carrier concentration are comparable with the aforementioned known methods.
The inventive method is preferably carried out in rapid heating or RTP (Rapid Thermal Processing) systems, since in RTP systems the semiconductor can be processed with very precise temperature-time processes and very high uniformity.
The first temperature of the inventive method is selected between 350° C. and 900° C., whereby for example with Mg-containing GaN (or in general with group III nitrides) a temperature between 350° C. and 600° C. is preferred. Depending upon the type of semiconductor, the first temperature can also be a function of the selection of the third time interval and of the intensity of the electromagnetic radiation and of the generation of minority charge carriers connected therewith. As the length of the third time interval increases, and with increasing Intensity of the electromagnetic radiation, then depending upon the type of semiconductor the first temperature can be decreased, which advantageously leads to a reduction of the thermal stress of the layer.
The second temperature during the second time interval is preferably selected between 700° C. and 1400° C. The selection of this temperature depends to a considerable extent upon the material of the compound semiconductor, whereby for example with Mg-containing GaN a second temperature between 850° C. and 1200° C. is preferably selected. By selecting a higher second temperature, the second time interval can preferably be considerably shortened, which similarly again leads to a reduction of the thermal stressing of the semiconductor layer or of the semiconductor layer system.
Heating the semiconductor to a second temperature that is greater than the decomposition temperature can be effected for a short period of time. If the surface of the semiconductor layer is provided with a coating (e.g. SiO
2
), or if the semiconductor layer is heated at an overpressure, for example in a hydrogen-free N
2
atmosphere, a decomposition of the compound semiconductor takes place only at higher temperatures, as a result of which the second temperature can be further increased. In this connection, time and temperature are selected in such a way that, for example in the case of Mg-doped GaN, the donor centers that result from nitrogen vacancies do not exceed the number of active Mg centers (in general active activator centers), so that in particular a p-type or conducting characteristic of the layer results. As a consequence, there is provided the possibility of setting or establishing the concentration and activation of donor and acceptor centers in wide ranges.
The duration of the third time interval, during which charge carriers are produced within the semiconductor layers by electromagnetic radiation, can be the same as the duration of the first time interval. In this connection, during the overall process portion of the
Drechsler Martin
Pelzmann Arthur
Becker R W
Kielin Erik J.
R W Becker & Associates
Smoot Stephen W.
Steag RTP Systems GmbH
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