CN106025000A - Handling method for epitaxy defect - Google Patents

Abstract

The invention discloses a method for treating epitaxial defects, which comprises the following steps: preparing at least one corrosion stop layer on the surface of the epitaxial wafer; destroying the corrosion stop layer of the convex part of the epitaxial defect by physical means to expose the corrosion stop layer the lower epitaxial layer; etch the exposed epitaxial layer by wet etching; remove the etch stop layer and prepare a passivation layer on the surface of the epitaxial wafer.

Description

A processing method for epitaxial defects

technical field

The invention relates to a method for processing epitaxial defects, belonging to the technical field of semiconductor devices and processes.

Background technique

Chemical vapor deposition methods such as metal-organic chemical vapor deposition (MOCVD) are widely used in LEDs and multi-junction solar cells. The epitaxial layers of both LEDs and multi-junction solar cells consist of multiple thin layers. Taking the most mature Ge/In _0.01 GaAs/GaInP triple-junction cell as an example, the epitaxial process is to grow the In _0.01 GaAs middle cell and the GaInP top cell on the Ge substrate by MOCVD, and each junction cell has a window layer and an emission region. , base region, and back field layer multilayer epitaxial structure, and there is a tunnel junction layer between the sub-cells.

In the process of chemical vapor deposition, it is difficult to ensure absolute cleanliness on the surface of the epitaxial wafer, and foreign objects such as particles and impurities often fall on the surface of the epitaxial wafer, which we call the phenomenon of epitaxial drop point. The epitaxial drop point will generally be covered layer by layer by subsequent epitaxial growth during the subsequent epitaxial growth process, and finally form a protrusion on the surface of the epitaxial wafer. The raised height is determined by the size of the dropped foreign object. Since the drop points cover the original epitaxial surface, the crystal quality of the epitaxial layer grown at the drop points will become poorer, and the arrangement of atoms will become disordered, closer to an amorphous state.

For optoelectronic devices such as LED devices and photovoltaic devices, the crystal quality of the epitaxial layer is very important. Poor crystal quality leads to a high probability of non-radiative recombination in the epitaxially grown semiconductor material. For photovoltaic devices, it will lead to smaller parallel resistance, increased leakage, and deterioration of fill factor or open circuit voltage performance. For LED devices, the internal leakage of the device will increase, the internal quantum efficiency will decrease, and the luminous brightness will decrease.

Contents of the invention

In order to solve the above technical problems, the present invention discloses a method for treating epitaxial defects, which includes the following steps: 1) preparing at least one corrosion stop layer on the surface of an epitaxial wafer with raised epitaxial defects; The corroded cut-off layer is physically destroyed to expose the epitaxial layer under the corroded cut-off layer; 3) The above-mentioned exposed epitaxial layer is etched by wet etching; 4) The corroded cut-off layer is removed and a passivation layer is prepared on the surface of the epitaxial wafer .

Further, the surface of the epitaxial wafer has multiple epitaxial layers of different semiconductor materials, the total thickness of which ranges from 1 μm to 50 μm.

Further, the raised portion of the epitaxial defect is formed during the epitaxial process due to foreign matters falling on the epitaxial surface, and the height of the raised portion ranges from 1 micron to hundreds of microns.

Further, the material of the etching stop layer includes but not limited to photoresist, dielectric material, and semiconductor, and its thickness ranges from 10 nm to 20 μm, which cannot be etched by the chemical solution used to etch the above epitaxial layer.

Further, the physical method for destroying the etch stop layer of the raised part of the epitaxial defect described in step 2) includes but not limited to scraping with a blade, scraping with a special tool, grinding, etc., after the etch stop layer is The underlying epitaxial layer is exposed after destruction. During the process of destroying the etch stop layer of the raised portion of the epitaxial defect, the epitaxial layer of the raised portion of the epitaxial defect may also be damaged, forming a pit.

Further, in step 3), the conditions of the wet etching are controlled so that the etching stop layer and its protected epitaxial layer are not destroyed, but only the epitaxial layer exposed at the epitaxial defect position is etched, and the wet etching can It is one-step etching or multi-step etching, and the multi-layer epitaxial layer at the position of the epitaxial defect is etched to form an etching pit. The conditions of wet etching can be controlled as needed to control the size of the corrosion pit.

Further, the removal of the corrosion stop layer and the preparation of the passivation layer in step 4) are a two-step process, the corrosion stop layer can be removed first, and then the passivation layer can be prepared; the passivation layer can also be prepared first, and then the corrosion stop layer can be used as The mask strips off the passivation layer in areas other than the aforementioned etch pits. The passivation layer is a dielectric material, and has the function of passivating the sidewall of the corrosion pit and reducing the sidewall leakage.

Furthermore, the processing method can be combined with the chip process, and the procedures in the chip process are inserted into the process of the processing method according to actual needs.

The present invention also provides a method for manufacturing a semiconductor device, including steps: 1) using epitaxial growth technology to form an epitaxial layer, which has epitaxial defect protrusions formed due to foreign matter falling on the epitaxial surface during the epitaxial process; 2) in At least one corrosion stop layer is prepared on the surface of the epitaxial layer; 3) The corrosion stop layer of the raised part of the epitaxial defect is physically destroyed to expose the epitaxial layer under the corrosion stop layer; 4) The method of wet etching Etching the exposed epitaxial layer; 5) removing the etch stop layer.

The innovations and advantages of the present invention are: combining physical and chemical methods, using physical methods to destroy the corrosion stop layer of the raised part of the epitaxial defect, so that the corrosion stop layer only protects the epitaxial layer outside the raised part during the chemical wet etching process , to achieve selective etching and passivation of the epitaxial layer at the raised defect site. After etching and passivation, the epitaxial layer with poor crystal quality around the epitaxial drop point is removed, reducing the non-radiative recombination due to poor crystal quality, and at the same time, the sidewall of the etch pit is passivated by chemical etching and preparing a dielectric layer , reducing leakage.

The invention can be used in LED or photovoltaic fields. For multi-junction solar cells, adopting the present invention can eliminate the impact of raised epitaxial defects on the performance of the battery chip, reduce non-radiative recombination caused by dropped points, and ensure normal open circuit voltage and fill factor, while epitaxial defects The diameter is generally between a few microns and tens of microns, and its area accounts for a very small proportion of the area of the epitaxial wafer, less than one-thousandth, so the treatment method described above will not have a significant impact on the short-circuit current. For LED devices, the use of the present invention can partially eliminate the internal leakage caused by epitaxial defects and avoid the influence of internal quantum efficiency. At the same time, when the chip size is large, the epitaxial area damaged by this treatment method is relatively small, so its The influence of the luminous brightness is also small, thereby improving the yield rate of the chip.

Description of drawings

Fig. 1 shows a flow chart of a processing method for epitaxial defects implemented according to the present invention.

2 to 5 show schematic diagrams of the process of fabricating multi-junction solar cells implemented according to the present invention.

Marked in the figure:

001: Ge substrate;

002: In _0.01 GaAs sub-cell;

003: extension drop point;

004: GaInP sub-cell;

005: GaAs ohmic contact layer;

006: SiO ₂ corrosion stop layer;

007: knife;

008: front electrode;

009: anti-reflection film;

010: Back electrode.

detailed description

The present invention will be further described below in conjunction with the examples, but the protection scope of the present invention should not be limited thereby.

The following embodiment discloses a treatment method for epitaxial defects caused by epitaxial dropout phenomenon, please refer to FIG. Chemical method, using physical methods to destroy the corrosion stop layer of the raised part of the epitaxial defect, in the process of chemical wet etching, the corrosion stop layer only protects the epitaxial layer other than the raised position, and realizes the protection of the epitaxial layer of the raised defect position Selective corrosion and passivation.

Taking a multi-junction solar cell as an example, the method for manufacturing a semiconductor device using the above processing method will be described in detail below.

As shown in Figure 2, the substrate used in this example is a Ge substrate 001, and an InGaAs subcell 002, a GaInP subcell 004, and a GaAs ohmic contact layer 005 are sequentially grown on the Ge buffer layer by MOCVD. In this example, impurity particles drop off the surface of the epitaxial wafer after the growth of the InGaAs sub-cell, forming the epitaxial drop point 003, which is covered by GaInP and GaAs epitaxial layers during the subsequent growth process.

As shown in FIG. 2 , a SiO ₂ etch stop layer 006 with a thickness of 500 nm was prepared on the front surface of the epitaxial wafer by PECVD. Use a cutter 007 to scrape the surface of the epitaxial wafer, so that the corrosion stop layer and part of the epitaxial layer at the protrusion of the epitaxial drop point are scraped off, exposing the lower epitaxial layer, as shown in FIG. 3 .

The exposed GaAs ohmic contact layer 005 and In ₀ are etched using a mixed solution of H ₂ O ₂ and H ₃ PO _{4 . 01} For the GaAs sub-cell epitaxial layer 002, the GaInP sub-cell epitaxial layer 004 is etched with a mixed solution of HCl and H ₃ PO ₄ to form corrosion pits, and the epitaxial drop point 003 also falls off. During the etching process, the size of the etching pit is controlled by controlling the time, so that the diameter of the etching pit is slightly larger than the diameter of the raised epitaxial defect before epitaxial wafer processing, so as to ensure that the epitaxial layer with poor crystal quality around the epitaxial drop point is removed. Afterwards, the etch stop layer 006 is etched away with HF, as shown in FIG. 4 .

The AuGeNi/Ag/Au front electrode 008 was prepared by the lift-off method, and the GaAs ohmic contact layer 005 other than the electrode was etched away with a mixed solution of citric acid and H ₂ O ₂ using the front electrode as a mask. The TiO _x /Al ₂ O ₃ anti-reflection film 009 is prepared on the surface of the chip by means of electron beam evaporation, and the anti-reflection film on the side wall of the etching pit will also play a passivation role. Using the photoresist as a mask, use HF to etch away the anti-reflection film on the front electrode. Evaporate Ti/Pd/Ag on the back of the substrate as the back electrode 010, as shown in FIG. 5 . Finally, a single battery chip is formed by dicing and dicing line corrosion passivation.

Obtained through the above aspects, it can eliminate the impact of raised epitaxial defects on the performance of battery chips, reduce the non-radiative recombination caused by drop points, and ensure the normal open circuit voltage and fill factor, while the diameter of epitaxial defects is generally several microns Between tens of microns, its area accounts for a very small proportion of the area of the epitaxial wafer, less than one-thousandth, so the treatment method will not have a significant impact on the short-circuit current.

Claims (10)

1. A processing method for epitaxial defects, the steps comprising: preparing at least one corrosion stop layer on the surface of an epitaxial wafer having epitaxial defect protrusions; Destroying the corrosion stop layer of the raised part of the epitaxial defect by physical means, exposing the epitaxial layer under the corrosion stop layer; Etching the above-mentioned exposed epitaxial layer by a wet etching method; Remove etch stop layer. 2 . The method for treating epitaxial defects according to claim 1 , wherein the surface of the epitaxial wafer has multiple epitaxial layers of different semiconductor materials, the total thickness of which ranges from 1 μm to 50 μm. 3. The processing method of a kind of epitaxial defect according to claim 1, characterized in that: the material of the etching stop layer is photoresist, dielectric material or semiconductor material, which is not affected by the chemical solution used to etch the above-mentioned epitaxial layer corrosion. 4 . The method for processing epitaxial defects according to claim 1 , wherein the thickness of the etch stop layer is between 10 nm and 20 nm. 5. A method for processing epitaxial defects according to claim 1, characterized in that: the raised portion of the epitaxial defect is formed during the epitaxial process due to foreign matter falling on the epitaxial surface, and the height of the raised portion is The range is between 1~1000μm. 6. A processing method for epitaxial defects according to claim 1, characterized in that: the physical method for destroying the etching stop layer of the raised part of the epitaxial defects in step 2) includes blade scraping, special The scraping or grinding of the tooling exposes the underlying epitaxial layer after the etch stop layer is destroyed. 7. A processing method for epitaxial defects according to claim 1, characterized in that: in step 2), in the process of destroying the etching stop layer of the raised part of the epitaxial defect, the raised part of the epitaxial defect is also destroyed at the same time epitaxial layer, forming pits. 8. A method for treating epitaxial defects according to claim 1, characterized in that: in the step 3), the conditions of the wet etching are controlled so that only the epitaxial layer at the position of the epitaxial defect is etched to form corrosion pits. 9. A method for processing epitaxial defects according to claim 1, characterized in that: the processing method is combined with the continued chip process, and the procedures in the chip process are inserted into the process of the processing method according to actual needs. 10. A method for manufacturing a semiconductor device, comprising the steps of: 1) The epitaxial layer is formed by epitaxial growth technology, which has epitaxial defect protrusions formed by foreign matter falling on the epitaxial surface during the epitaxial process; 2) preparing at least one corrosion stop layer on the surface of the epitaxial layer; 3) Destroying the corrosion cut-off layer of the raised part of the epitaxial defect by physical means, exposing the epitaxial layer under the corrosion cut-off layer; 4) Etching the above-mentioned exposed epitaxial layer by wet etching; 5) Remove the corrosion stop layer.