CN113707546A - Method for forming ohmic contact of semiconductor device by selective laser annealing - Google Patents
Method for forming ohmic contact of semiconductor device by selective laser annealing Download PDFInfo
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Abstract
本发明公开了所述一种选择性激光退火形成半导体器件欧姆接触的方法，包括：激光器发射激光，形成所述激光退火需要的光源；光学系统将所述激光器发射的激光整形聚焦成以下三种光束类型中的任意一种后，发射到晶圆表面。所述三种光束类型：圆形平顶光束、正方形平顶光束以及线形平顶光束；位移电动平台控制晶圆实现XY方向的交叉移动，发射到晶圆表面的激光光束能量被暴露在表面的金属区域吸收，使得金属区域温度升高，超过合金反应产生所需的阈值温度，合金反应产生并形成欧姆接触。与此同时，该能量密度对器件的其它区域没有损伤或其它不利影响。
The invention discloses a method for forming an ohmic contact of a semiconductor device by selective laser annealing. The method includes: a laser emits laser light to form a light source required for the laser annealing; an optical system shapes and focuses the laser light emitted by the laser into the following three types After any one of the beam types, it is emitted to the wafer surface. The three types of beams are: circular flat top beam, square flat top beam and linear flat top beam; the displacement motorized platform controls the wafer to achieve cross movement in the XY direction, and the laser beam energy emitted to the surface of the wafer is exposed on the surface of the wafer. The metal region absorbs, so that the temperature of the metal region rises above the threshold temperature required for the alloying reaction to generate and form an ohmic contact. At the same time, the energy density does not damage or otherwise adversely affect other areas of the device.
Description
Technical Field
The invention relates to the field of semiconductor integrated circuits, in particular to a method for forming ohmic contact of a semiconductor device by selective laser annealing.
Background
Currently, the feature size of integrated circuits is continuously reduced, the types of materials involved are more and more, and the structures of devices used are more and more complex. The traditional heat treatment methods such as furnace tube annealing and rapid heat treatment are all 'integral annealing methods', that is, the sample wafer is entirely positioned in a heating environment, so that the temperature of all regions of the sample wafer is the same as the temperature of the annealing environment. The bulk annealing method currently faces a plurality of problems, mainly including:
the whole annealing is easy to cause thermal damage to the low-melting-point material;
(II) the whole annealing is easy to cause the in-layer diffusion of the material;
(III) interlayer diffusion of materials is easily caused by integral annealing;
and (IV) the integral annealing is easy to introduce attraction, so that the phenomena of peeling, warping, even substrate crushing and the like of the material occur.
Particularly, an ohmic contact technology, which is a key technology in integrated circuits, is also the technical field related to the invention, and the traditional heat treatment method also faces limitations; the main points are as follows:
the purpose of (I) the annealing of the ohmic contact alloy is to heat treat the metal-semiconductor contact area on the substrate, but when the integral annealing mode is used, the wafer is in a high-temperature state completely, and other areas which do not need to be heat treated can be damaged;
secondly, the integral annealing is easy to cause the undesired material in-layer diffusion and interlayer diffusion, and the device characteristics and reliability are influenced;
(III) bulk annealing for thin wafers (typically samples < 100um thick) can cause warping and even chipping of the wafer;
in (IV) high melting point semiconductor materials such as silicon carbide for ohmic contacts, the required annealing temperature needs to be as high as 1000 degrees Celsius. Such high temperatures pose challenges to the reliability and stability of the device;
(V) the maximum annealing temperature of the bulk annealing mode is limited, so that the relevant key physical parameters of the ohmic contact alloy are as follows: the condition ranges of the in-layer diffusion coefficient, the interlayer diffusion coefficient, the solid solubility, the interface reaction rate and the like are limited;
(sixth) the regions where ohmic contact formation is required during bulk annealing may "fully" form ohmic contacts, which may be undesirable in some applications and may even severely impact device reliability.
For example, in the application of ohmic contact of a GaN HEMT source and drain region, the source and drain region is densely covered with low-melting-point AlAu alloy through integral thermal annealing, and Au can be diffused to cause device failure in high-temperature application occasions.
Disclosure of Invention
The invention aims to: aiming at the problems, the method for forming the ohmic contact of the semiconductor device by selective laser annealing is provided, and the problem that other areas are damaged by adopting an integral annealing mode when the ohmic contact alloy is annealed in the prior art is solved; meanwhile, the problems that the material layer internal diffusion and the interlayer diffusion which are not expected to be generated easily due to the integral annealing influence the device characteristics and reliability are solved; meanwhile, the problem that the whole annealing process can cause the warping and even the fragmentation of the slice (usually referring to a sample slice with the thickness less than 100 um) is solved; meanwhile, the problems that when a high-melting-point semiconductor material such as silicon carbide forms ohmic contact, the required annealing temperature is high, and the reliability and the stability of equipment are easily damaged are solved; and simultaneously, the problem that the maximum annealing temperature is limited during integral annealing is solved.
The core point of the invention is based on the following principles:
1. semiconductor devices generally include semiconductor materials, dielectric materials, and metal materials, and different materials have different characteristics of reflection, absorption, and transmission of light, so that when irradiated under the same laser condition, the temperature changes of different materials are different.
2. The absorption of the metal material to light does not change much with the wavelength because the reflectivity of the metal material to light does not change much with the wavelength; however, the metal material still has some absorption of the laser light and can cause the metal temperature to rise due to the absorption of the laser energy.
3. The semiconductor material has a large variation in absorption of light, and generally, the semiconductor material has a weak absorption of laser light having photon energy smaller than its forbidden bandwidth and a strong absorption of laser light having photon energy larger than its forbidden bandwidth. In other words, the absorption of light by the semiconductor material can be controlled by wavelength changes.
4. The dielectric material generally has a large forbidden band width, so that the absorption of light in the visible band is weak, in other words, the laser irradiation does not have a significant influence on the dielectric material itself.
5. Interfaces in semiconductor devices also absorb light, and the absorption characteristics are related to the difference in refractive index between the two materials that make up the interface. If the interface is strongly absorbing to the laser, it will often cause delamination of the material above the interface.
Based on the principle that different materials and different interfaces in the semiconductor device have different absorption to laser, the difference exists; in other words, the laser processing can only work on a certain material or interface by selecting proper laser parameters including wavelength, energy density and the like, and in the invention, the laser annealing can only contribute to forming ohmic contact without damaging or acting other regions of the device by selecting proper laser wavelength and energy density.
The scheme particularly discloses a method for forming ohmic contact of a semiconductor device by selective laser annealing, which comprises the following steps:
the ohmic contact area of the semiconductor device is the area covered by the metal electrode, and when laser irradiates the area, the temperature of the metal absorbs the photon energy of the laser is increased; since metal is usually a good thermal conductor, the heat generated by the absorption of laser photons by the metal surface diffuses horizontally and depthwise, raising the temperature of the diffusion region. When the metal/semiconductor interface temperature exceeds the alloying temperature, an alloying reaction occurs and an ohmic contact is formed.
Selecting suitable laser parameters includes: (1) wavelength. The wavelength laser does not have strong absorption in semiconductor materials, dielectric materials and other interfaces without metal, which form a device, so that the metal ohmic contact is formed and the regions except the ohmic contact are not damaged. (2) Energy density. When the laser with the proper wavelength stated in the step (1) cannot be selected due to other factors, the ohmic contact can be realized while avoiding damage to the region except the ohmic contact due to different energy density thresholds of the interaction between different materials and the laser. For example, when the laser with the wavelength is applied to a semiconductor material, the threshold energy density of mutual reaction, material modification, melting and gasification, is ED 1; the threshold energy density of the interaction between the laser with the wavelength and the dielectric material, namely the modification, melting and gasification of the material is ED 2; the laser with the wavelength acts on the interface to ensure that the threshold energy density of the interface characteristics, such as change, peeling, stripping and modification, is ED 3; the laser light of this wavelength is applied to the metal/semiconductor interface such that the threshold energy density at which the alloy reacts to produce and form an ohmic contact is ED 4. If the appropriate ED5 is selected such that ED1, ED2, ED3 < ED5 < ED4, ohmic contact can be achieved while avoiding impact or damage to other regions of the device.
Therefore, the scheme provides a method for forming ohmic contact of a semiconductor device by selective laser annealing, and the specific selection method is as follows:
selecting laser with proper wavelength and/or energy density to irradiate the interface of the metal and the semiconductor to form ohmic contact without influencing other areas;
the selection method of the proper wavelength comprises the following steps: selecting laser wavelengths according to different absorption degrees of the metal material to be annealed, the semiconductor material to be annealed and the dielectric material on laser photons, so that the laser with the wavelength only acts on the metal material to be annealed and the semiconductor material to be annealed and does not influence the dielectric material;
the selection method of the proper energy density comprises the following steps: such that the selected energy density ED5 satisfies the following inequality
ED1，ED2，ED3＜ED5＜ED4
Wherein ED1 is threshold energy density of mutual reaction-material modification, melting and gasification-when laser acts on semiconductor material;
in the formula, ED2 is threshold energy density of mutual reaction of the laser acting on the dielectric material, namely the material is modified, melted and gasified;
the ED3 is threshold energy density of the interface characteristic changed-peeling, stripping and modification-caused by the action of laser on the interface;
wherein ED4 is the threshold energy density at which a laser acts on the metal/semiconductor interface such that the alloy reacts to produce and form an ohmic contact;
the energy densities are all selected under the same wavelength.
The invention also provides a method for forming the ohmic contact of the semiconductor device by selective laser annealing, which comprises a set of system for forming the ohmic contact of the semiconductor, wherein the system comprises a laser, an optical system and a displacement system; the laser emitted by the laser meets the selection of the semiconductor annealing laser in the method;
the laser emits laser into the optical system, and then the laser is emitted into the displacement system by the optical system to process the wafer in the displacement system;
the laser is used for emitting laser and forming a light source required by the laser annealing device, and comprises one or more combinations of a solid laser, a fiber laser, a disc laser and a semiconductor laser;
the laser has a wavelength of from 200nm to 2000nm and a pulse width ranging from picoseconds to milliseconds.
The optical system is used for shaping the laser emitted by the laser into round flat-top, square flat-top or linear flat-top light spots and then emitting the light spots to the surface of a sample;
the optical system comprises an optical shaping element and a focusing system, wherein the optical shaping element comprises but is not limited to a beam shaping mirror; the optical shaping element and the focusing mirror are used for shaping the laser emitted by the laser into flat-top light spots and emitting the flat-top light spots to the surface of the sample.
The optical shaping element or the focusing system can move in the longitudinal axis direction; for adjusting the distance of the sample to the focal plane of the cylindrical focusing system;
the displacement system is used for placing a sample and adjusting the position of the sample, and comprises a vacuum suction table 131 for placing the sample and a displacement platform 132; the vacuum suction table 131 can carry out vacuum adsorption and fixation on a sample with the size of 4-12 inches, and the displacement platform 132 can carry out three-axis movement of a transverse axis, a vertical axis and a longitudinal axis;
the movement of the horizontal axis and the vertical axis of the displacement platform enables the laser to scan the surface of the sample or select a fixed position on the surface of the sample for scanning; the longitudinal axis of the displacement platform functions to adjust the distance of the sample to the focal plane of the cylindrical focusing system.
The displacement system is arranged in a vacuum and/or inert gas environment;
furthermore, the displacement system is arranged in a vacuum chamber, the vacuum chamber comprises a low vacuum pump set and a high vacuum pump set, and a high vacuum environment is generated in the vacuum chamber through the low vacuum pump set and the high vacuum pump set, so that the alloy reaction is not influenced by oxygen.
Furthermore, the vacuum chamber can be provided with gases such as nitrogen, argon, oxygen and the like so as to meet the requirements of different processes;
further, the displacement system is arranged in a coaxial inert gas purging device, and the coaxial inert gas purging device provides a local inert gas environment for the laser irradiation area to prevent oxygen pollution in the annealing process.
Further, the optical system comprises a flat top shaping element and a focusing system, and is responsible for shaping the laser emitted by the laser into one of a circular flat top beam, a square flat top beam and a linear flat top beam.
Further, the lens used in the beam focusing system for realizing the circular flat-top beam or the square flat-top beam comprises: plano-convex lenses, biconvex lenses, and other optical elements or combinations of elements that perform a focusing function.
Further, the lens used by the beam focusing system for realizing the one-dimensional flat-topped beam comprises: plano-convex lenses, biconvex lenses, cylindrical lenses, and other optical elements or combinations of elements that perform a focusing function.
Further, before the optical system shapes the laser emitted by the laser into a circular flat-top beam, a square flat-top spot or a linear flat-top spot, the method further includes: the device comprises a beam expanding and collimating system, an aperture diaphragm and a reflector, wherein the beam expanding and collimating system expands, collimates and amplifies laser emitted by a laser to form a parallel light source; the reflector changes the direction of the parallel light source so that the parallel light source is emitted into the optical system.
In summary, due to the adoption of the technical scheme, the invention has the beneficial effects that:
1. the invention can select a wavelength or energy density of laser with different light absorption for different materials to act on the interface between the metal and the semiconductor to form ohmic contact without influencing other areas.
Drawings
FIG. 1 is a schematic diagram of the overall system of the present invention;
FIG. 2 is a schematic diagram of a semiconductor device structure according to the present invention;
FIG. 3 is a schematic view of an interface in a semiconductor device of the present invention;
FIG. 4 is a view showing the structure of a PN junction device on a GaAs substrate in embodiment 4 of the present invention;
FIG. 5 is an interface in a PN junction device on a GaAs substrate in embodiment 4 of the present invention;
FIG. 6 is an absorption coefficient versus wavelength curve for different semiconductor materials in example 4 of the present invention;
FIG. 7 is a graph of the absorption characteristics of the laser light by the different materials, interfaces, and threshold energy density values in response to the laser light in example 4 of the present invention;
the labels in the figure are: 11. a laser; 12. an optical system; 13. a displacement system; 14. a beam expanding collimation system; 15. an aperture diaphragm; 16. a mirror; 121. an optical shaping element; 122. a focusing system; 131. a vacuum sheet suction table; 132. a displacement platform.
Detailed Description
All of the features disclosed in this specification, or all of the steps in any method or process so disclosed, may be combined in any combination, except combinations of features and/or steps that are mutually exclusive.
Any feature disclosed in this specification (including any accompanying claims, abstract) may be replaced by alternative features serving equivalent or similar purposes, unless expressly stated otherwise. That is, unless expressly stated otherwise, each feature is only an example of a generic series of equivalent or similar features.
In the description of the present invention, it is to be understood that the terms "upper", "lower", "left", "right", and the like, indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, and are only for convenience in describing the present invention and simplifying the description, but do not indicate or imply that the referred devices or elements must have a specific orientation, be constructed in a specific orientation, and be operated, and thus, should not be construed as limiting the present invention.
Furthermore, the terms "first," "second," and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first," "second," etc. may explicitly or implicitly include one or more of that feature.
Example 1
The scheme provides a method for forming ohmic contact of a semiconductor device by selective laser annealing, which comprises a selection method of semiconductor annealing laser, and the specific selection method comprises the following steps:
selecting laser with proper wavelength and/or energy density to irradiate the interface of the metal and the semiconductor to form ohmic contact without influencing other areas;
the selection method of the proper wavelength comprises the following steps: selecting laser wavelengths according to different absorption degrees of the metal material to be annealed, the semiconductor material to be annealed and the dielectric material on laser photons, so that the laser with the wavelength only acts on the metal material to be annealed and the semiconductor material to be annealed and does not influence the dielectric material;
the selection method of the proper energy density comprises the following steps: such that the selected energy density ED5 satisfies the following inequality
ED1，ED2，ED3＜ED5＜ED4
Wherein ED1 is threshold energy density of mutual reaction-material modification, melting and gasification-when laser acts on semiconductor material;
in the formula, ED2 is threshold energy density of mutual reaction of the laser acting on the dielectric material, namely the material is modified, melted and gasified;
the ED3 is threshold energy density of the interface characteristic changed-peeling, stripping and modification-caused by the action of laser on the interface;
wherein ED4 is the threshold energy density at which a laser acts on the metal/semiconductor interface such that the alloy reacts to produce and form an ohmic contact;
the energy densities are all selected under the same wavelength.
Example 2
Referring to fig. 1, based on the above embodiment 1, the present invention further provides a method for forming an ohmic contact of a semiconductor device by selective laser annealing, the method comprising a system for forming the ohmic contact of the semiconductor device,
the system comprises a laser 11, an optical system 12 and a displacement system 13; the laser emitted by the laser 11 meets the selection of the semiconductor annealing laser in the method;
the laser 11 emits laser light into the optical system 12, and then the laser light is incident into the displacement system 13 through the optical system 12 to process the wafer in the displacement system 13; the displacement system 13 controls the wafer to realize the cross movement in the XY direction, and the energy of the laser beam emitted to the surface of the wafer is absorbed by the metal area exposed on the surface, so that the temperature of the metal area is increased to exceed the threshold temperature required by the alloy reaction, and the alloy reaction generates and forms ohmic contact. At the same time, the energy density does not damage or otherwise adversely affect other regions of the device
The laser 11 is used for emitting laser to form a light source required by the laser annealing device, and the laser 11 comprises one or more combinations of a solid laser 11, a fiber laser 11, a disc laser 11 and a semiconductor laser 11;
the laser 11 has a wavelength from 200nm to 2000nm and a pulse width ranging from picoseconds to milliseconds. Because semiconductor devices comprise various materials, and different materials have different light absorption, the invention is mainly focused on providing a thought and a method, and particularly different materials and device structures need to select different laser wavelengths according to requirements, so that specific wavelength values do not need to be given at present.
The optical system 12 is used for shaping the laser emitted by the laser 11 into round flat-top, square flat-top or linear flat-top light spots and then emitting the light spots onto the surface of a sample;
the optical system 12 includes an optical shaping element 121 and a focusing system 122, the optical shaping element 121 includes, but is not limited to, a beam shaping mirror; the optical shaping element 121 and the focusing mirror are used for shaping the laser emitted by the laser 11 into a flat-top spot and emitting the flat-top spot onto the surface of the sample.
The optical shaping element 121 or the focusing system 122 can move in the longitudinal axis direction; for adjusting the distance of the sample to the focal plane of the cylindrical focusing system 122;
the displacement system 13 is used for placing a sample and adjusting the position of the sample, and the displacement system 13 comprises a vacuum suction table 131131 for placing the sample and a displacement platform 132132; the vacuum suction table 131131 can carry out vacuum adsorption and fixation on a sample with the size of 4 inches to 12 inches, and the displacement platform 132132 can carry out three-axis movement of a transverse axis, a vertical axis and a longitudinal axis;
the movement of the horizontal and vertical axes of the displacement platform 132 enables the laser to scan the sample surface or select a fixed position on the sample surface for scanning; the longitudinal axis of the translation stage 132 functions to adjust the distance of the sample from the focal plane of the cylindrical focusing system 122.
The displacement system 13 is arranged in a vacuum and/or inert gas environment;
in other embodiments, displacement system 13 is disposed in a vacuum chamber that includes a rough pump set and a fine pump set, and a fine vacuum environment is created in the vacuum chamber by the rough pump set and the fine pump set to ensure that the alloy reaction is not affected by oxygen.
In other embodiments, the vacuum chamber may be further configured with gases such as nitrogen, argon, oxygen, etc. to meet the requirements of different processes;
in other embodiments, the displacement system 13 is provided in a coaxial inert gas purging device that provides a local inert gas environment for the laser irradiation area to prevent oxygen contamination of the annealing process.
The optical system 12 includes a flat-top shaping element and a focusing system 122, and is responsible for shaping the laser light emitted by the laser 11 into one of a circular flat-top beam, a square flat-top beam, and a linear flat-top beam.
The lens used by the beam focusing system 122 to achieve a circular flat-top beam or a square flat-top beam includes: plano-convex lenses, biconvex lenses, and other optical elements or combinations of elements that perform a focusing function.
The lens used by the beam focusing system 122 to implement a one-dimensional flat-topped beam includes: plano-convex lenses, biconvex lenses, cylindrical lenses, and other optical elements or combinations of elements that perform a focusing function.
Before the optical system 12 shapes the laser light emitted by the laser 11 into a circular flat-top beam, a square flat-top spot or a linear flat-top spot, the method further includes: the device comprises a beam expanding and collimating system 14, an aperture diaphragm 15 and a reflector 16, wherein the beam expanding and collimating system 14 expands, collimates and amplifies laser emitted by a laser 11 to form a parallel light source; the reflector 16 changes the direction of the parallel light source to make the parallel light source emit into the optical system 12; the aperture diaphragm 15 is used for filtering stray light at the edge of the light spot after beam expansion and collimation.
The size of the square flat-top light spot can be adjusted according to the sizes of different samples, and the size of the square flat-top light spot is determined by the diameter of a light spot emitted by the laser light source after passing through the beam expanding and collimating system 14 and the focal length of the lens.
The size of the laser beam waist is in the range of 3mm-20 mm; the reflector 16 is also used to change the direction of the middle portion of the collimated light source intercepted by the aperture stop 15, so that the collimated light source is perpendicularly incident to the optical shaping element 121.
Example 3
Based on the above embodiment 2, the present solution is described in conjunction with the typical structure of an example semiconductor device, please refer to fig. 2,
fig. 2 is a typical two-terminal semiconductor device, which includes a metal material 1, a metal material 2, a semiconductor material 1, a semiconductor material 2, and a substrate material 3, wherein the semiconductor material 1 and the semiconductor material 2 may form a semiconductor device having electrical characteristics, such as a PN junction; '
The interface in the semiconductor device of fig. 2 is shown in fig. 3; the semiconductor device comprises an interface 1 consisting of a metal material 1 and air, an interface 2 (ohmic contact area) consisting of the metal material 1 and a semiconductor material 1, an interface 3 (realizing device electrical characteristics) consisting of the semiconductor material 1 and the semiconductor material 2, an interface 4 consisting of the semiconductor material 2 and a substrate material, an interface 5 consisting of the metal material 2 and air, and an interface 6 (ohmic contact area) consisting of the metal material 2 and the semiconductor material 2.
The laser annealing points for forming the ohmic contact are as follows: (1) the laser wavelength is chosen such that it is not strongly absorbing at the interface of the semiconductor material except the metal and the semiconductor material as a whole.
For example, for GaAs devices, the bandgap is 1.42eV, which corresponds to a wavelength of about 900 nm. Therefore, laser with the wavelength of more than 900nm does not absorb obviously in the GaAs material, and does not cause obvious damage to the semiconductor material. But the wavelength still has a certain absorption in the metallic material 1 and the metallic material 2.
(2) Selecting a proper energy density; the metal material 1 and the metal material 2 can absorb heat and reach the temperature required for forming ohmic contact under the energy density, and meanwhile, the semiconductor material and other interfaces irrelevant to the ohmic contact are not damaged under the energy density.
Example 4
Based on the above embodiment 2, the present solution is described in conjunction with the typical structure of the example semiconductor device and the specific materials involved, please refer to fig. 4,
in the specific embodiment, the device type is a PN junction device on a GaAs substrate, and the structural schematic diagram is shown in FIG. 4; the materials involved in the device mainly comprise: the GaAs substrate, P type GaAs layer, N type GaAs layer, 100nm thick gold electrode;
a device interface; the interface included in the GaAs PN junction device is shown in FIG. 5; mainly comprises the following steps: an interface between the GaAs substrate and the P-type GaAs, an interface between the P-type GaAs and the N-type GaAs, an interface between the P-type GaAs and the 100nm thick gold, and an interface between the N-type GaAs and the 100nm thick gold;
selecting laser wavelength; according to the absorption curves of different semiconductor materials for the wavelength, as shown in FIG. 6, for the GaAs material, when the laser wavelength is more than 900nm, the material has no absorption for the laser light; while gold with a thickness of 100nm still absorbs laser light with a wavelength of more than 900 nm. Based on this, the laser wavelength can be selected to be 980 nm;
the absorption characteristics of the different materials, the interface to the laser and the threshold energy density in reaction with the laser are shown in table 7 below:
based on the description shown in FIG. 7, irradiation with a laser having a wavelength of 980nm and an energy density of 1J/cm2 was selected, but the temperature at the metal/GaAs interface was increased by the absorption of laser energy by the metal and heat was diffused beyond the alloy temperature, so that no reaction occurred at the other materials and interfaces.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.
Claims (10)
1. A method for forming ohmic contact of a semiconductor device by selective laser annealing is characterized in that: the method comprises a selection method of semiconductor annealing laser, which comprises the following specific selection method:
laser light with proper wavelength and/or energy density is selected to irradiate the interface of the metal and the semiconductor, so that ohmic contact is formed without influencing other areas.
2. The method of forming an ohmic contact to a semiconductor device by selective laser annealing of claim 1, wherein: the selection method of the proper wavelength comprises the following steps: the laser wavelength is selected according to different absorption degrees of the metal material to be annealed, the semiconductor material to be annealed and the dielectric material on laser photons, so that the laser with the wavelength only acts on the metal material to be annealed and the semiconductor material to be annealed and does not influence the dielectric material.
3. A method of forming a semiconductor device ohmic contact by selective laser annealing as claimed in claim 2 wherein: the selection method of the proper energy density comprises the following steps: such that the selected energy density ED5 satisfies the following inequality
ED1，ED2，ED3＜ED5＜ED4
Wherein ED1 is threshold energy density of mutual reaction-material modification, melting and gasification-when laser acts on semiconductor material;
in the formula, ED2 is threshold energy density of mutual reaction of the laser acting on the dielectric material, namely the material is modified, melted and gasified;
the ED3 is threshold energy density of the interface characteristic changed-peeling, stripping and modification-caused by the action of laser on the interface;
where ED4 is the threshold energy density at which a laser acts on the metal/semiconductor interface so that the alloy reaction produces and forms an ohmic contact.
4. A method of forming a semiconductor device ohmic contact by selective laser annealing as claimed in claim 3 wherein: comprises forming an ohmic contact system of the semiconductor device by selective laser annealing;
the system comprises a laser, an optical system and a displacement system; the laser emitted by the laser meets the semiconductor annealing laser selected by the selection method of claim 1;
the laser emits laser into the optical system, and then the laser is incident into the displacement system through the optical system, and the wafer in the displacement system is processed.
5. The method of forming an ohmic contact to a semiconductor device by selective laser annealing of claim 4, wherein: the laser is one or a combination of a solid laser, a fiber laser, a disc laser and a semiconductor laser.
6. The method of forming an ohmic contact to a semiconductor device by selective laser annealing of claim 4, wherein: the optical system is used for shaping laser emitted by the laser into round flat-top, square flat-top or linear flat-top light spots and then emitting the light spots to the surface of a sample; the optical system comprises an optical shaping element and a focusing system, wherein the optical shaping element comprises but is not limited to a beam shaping mirror; the optical shaping element and the focusing mirror are used for shaping the laser emitted by the laser into flat-top light spots and emitting the flat-top light spots to the surface of the sample.
7. The method of forming an ohmic contact to a semiconductor device by selective laser annealing of claim 6, wherein: the optical shaping element or the focusing system may be movable in the direction of the longitudinal axis.
8. The method of forming ohmic contacts to a semiconductor device by selective laser annealing as claimed in any one of claims 4 to 6, wherein: the displacement system is used for placing a sample and adjusting the position of the sample, and comprises a vacuum suction table for placing the sample and a displacement platform; the vacuum suction table can be used for carrying out vacuum adsorption and fixing on a sample, and the displacement platform can be used for carrying out triaxial movement of a transverse axis, a vertical axis and a longitudinal axis.
9. The method of forming ohmic contacts to a semiconductor device by selective laser annealing as claimed in any one of claims 4 to 6, wherein: the displacement system is disposed in a vacuum and/or inert gas environment.
10. The method of forming an ohmic contact to a semiconductor device by selective laser annealing of claim 9, wherein: the system for forming the semiconductor ohmic contact comprises a beam expanding and collimating system, an aperture diaphragm and a reflector; the beam expanding and collimating system expands, collimates and amplifies laser emitted by the laser to form a parallel light source; the reflector changes the direction of the parallel light source to enable the parallel light source to be emitted into the optical system; the aperture diaphragm is used for filtering stray light at the edge of the light spot after beam expanding and collimating.
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