SU1010997A1 - Method of detecting defects with increased leakage currents in semiconductor structures - Google Patents

Abstract

THE METHOD OF DETECTING DEFECTS WITH UNDERLATING CURRENTS LEAKAGE IN SEMICONDUCTORS. STRUCTURE, based on the electrochemical decoration of defects by bringing the surfaces of the semiconductor structure of the SP and p-layers into contact with the electrolyte, the inclusion of a voltage source between the semiconductor structure and the electrolyte and visual detection of defects so that, in order to ensure non-destructive detection of defects with increased leakage currents in semiconductor structures having a pn-junction parallel to the plane of the semiconductor structure, the p-layer of the semiconductor structure The tours are brought into contact with the electrolyte for anodic oxidation, the lusse pole of the voltage source is connected to the g-layer, the voltage is set to a lower voltage across the p-j junction, but a higher cut-off voltage from the p-junction, d anodic oxidation until the current through the semiconductor structure ceases, then the p-layer of the semiconductor structure is brought into contact with the electrolyte for electrochemical metal deposition, a voltage is applied between the electrolyte and the h-layer of the semiconductor structure, ime The value of the nat-жен cutoff of the p – n junction, but lower voltage during anodic oxidation, the minus pole of the voltage source is connected to the n-layer of the semiconductor – sulfur structure. "Sl

Description

The invention relates to semiconductor technology and can be used to control semiconductor structures in the manufacturing process of semiconductor devices.

The known method of detecting defects with increased leakage currents in semiconductor structures is based on the effect on the surface of the structure by an electron probe in an electron microscope.

 The disadvantage of this method is its unsuitability for inspecting defects of structures with flat pn-junctions located at a depth of more than 10 microns from the surface.

The closest technical solution is the method of detecting defects with increased leakage currents in semiconductor structures based on electrochemical. decorating defects by contacting the surface of a semiconductor structure with n and p-layers in contact with the electrolyte, switching between a semiconductor structure and an electrolyte of a voltage source, and visual detection of defects.

The disadvantage of this method is its destructive nature, due to the difficulty of removing the metal deposited on the defects, and also because the deposited metal increases the leakage currents through the defects,

The purpose of the invention is to provide non-destructive detection of defects with increased leakage currents in semiconductor structures having a p-n junction parallel to the plane of the semiconductor structure.

The goal is achieved by the fact that in the method of detecting defects with increased leakage currents in semiconductor structures, the p-layer of the semiconductor structure is brought into contact with the anodic oxidation electrolyte, the positive pole of the voltage source is connected to the P-layer the breakdown of a pnn jump, but a higher cutoff voltage of the pn junction, produces anodic oxidation until the current through the semiconductor structure stops, then the p layer of the semiconductor structure is brought into contact with a cell for electrochemical metal deposition, a voltage is applied between the electrolyte and the p-layer of the semiconductor structure, having a magnitude greater voltage cutoff p-n-cross-over, but lower voltage during anodic oxidation, and the negative pole of the voltage source is connected to C - a layer of semiconductor structure ,,

Figures 1-3 show the steps of the method.

The scheme contains p-layer 1 semiconductor structure, p-layer 2 semiconductor structure, p-n junction 3, defect 4 with increased current leakage, protective coating 5 ends, electrolyte 6 for oxidation, negative electrode 7, positive electrode 8, film 9 anode oxide, electrolyte 10 for metal deposition, deposited metal layer II.

The method is carried out as follows.

First, all end surfaces of the semiconductor structure are protected by an insulating coating 5 (protection is shown only for two ends of the semiconductor structure). An insulating coating is applied to protect the exit points of the p – n junction at the ends of the semiconductor structure.

Then the semiconductor structure from the side of the p-layer is immersed in the electrolyte 6 to a depth less than the thickness of the structure. Due to this, only the p-layer 2 is in contact with the electrolyte and the P-layer 1 is not in contact with the electrolyte. The electrolyte is chosen such that when a current passes between the structure and the electrolyte a layer of anodic oxide forms on the surface of the structure. Since the anodic oxide lesions are realized when a voltage is applied to the structure, so that this voltage simultaneously displaces the pn junction in the opposite direction, the semiconductor structure is immersed in the electrolyte by the p layer, on which local films of anodic oxide are grown. Voltage Uq is applied between electrolyte 6c using electrode 7 and h / layer 1 using an 8 ' electrode plus it is applied to n-layer 1, and minus to electrolyte 6. This provides a p-p junction in the opposite direction, at which the current through ". {(- the transition flows only in places of defects 4 with increased leakage of current. Power lines are shown by dashed lines. Let us indicate the values of the voltages used in the description: Up - voltage during anodic oxidation, UM voltage at electrochemical metal deposition , and „p-pitch voltage p-p-trans stroke, UQ-cutoff voltage of the p-h-junction. The voltage U applied to the electrodes 7 and 8, falls mainly in the drug-G) junction in places free from leaks. In order to avoid a breakdown of the p-r transition in the course of local anodic oxidation, the magnitude of the voltage I0 at the electrodes 7 and 8 is set to be less than the voltage of the breakdown and the p-P transition. The magnitude of the voltage And at anodic oxidation determines the thickness of the layer of anodic oxide. In order for the anodic oxide film to not break down during the following electrochemical metal deposition operation, the minimum voltage must be greater than the voltage. Uvi used in the deposition of metal. Od, is set greater than the cut-off voltage U o. Therefore, Up is also set greater than Ug. As a result of the operation described above, a local film of anodic oxide 9 grows in the places of current leakage through the pn junction. Moreover, due to current spreading, over the p layer, the area of the anodic oxide film is slightly larger than the area of current leakage sites, which is a positive factor ensuring the healing of the joints. current check film anodic oxide. Anodic oxidation is carried out until the current is completely stopped, which ensures complete insulation of the current leakage sites and eliminates the effect of current leakage on the characteristic-n-interceptor (a. The next operation is electrochemical deposition of the metal in places free from anodic oxide. For this structure C; local anodic oxide films on the p-layer are immersed from the p-layer to a depth h less than the thickness of the semiconductor structure in the electrolyte 7 for electrochemical deposition of metals, such as electrolyte for electrochemical deposition Cycle deposition. Metal deposition is carried out by applying a minus to the p-layer of structures), and the value of U m of this voltage is set higher than the voltage of the electric torch.ioP p-junction, but me1 11. 1 of magnitude. voltage and g used for anodic acidification of this structure. The limitation of U "(J a is determined by the need to ensure a low resistance of the p-fr junction in order to obtain the current required for the rapid deposition of a metal layer of a given thickness. The resistance of the P j transition decreases by several orders of magnitude as the voltage increases from the value of a lower cutoff voltage to the value of a higher cutoff voltage. Limiting l) f, Ua ensures the stability of the anodic oxide film in the process of electrochemical metal deposition, since the anodic oxide film withstands the voltage only less than the voltage at which this film was obtained. in the process of anode sislenia. As a result of this operation, the metal is deposited only in places free from anodic oxide, which ensures a reliable decoration of current leakage sites, since the free from surface areas indicate the points of current leakage. In this case, since the metal is deposited only in the places of the semiconductor structure, in which there is no leakage current, the influence of current leakage on the characteristics of the p –T junction is excluded. Example 1. The method is implemented in the study of the structure of a photocell based on a heterojunction p-gallium arsenide - p -a solid solution in the aluminum-gallium-mouse-K system. The total thickness of the gallium arsenide substrate and p-gallium arsenide layer is 300 μm, the p-layer thickness -. 0.5 MKMi Breakdown voltage in a given structure {jj, p 5.5–6 V. Cutoff voltage of a p – t junction in the forward direction 1) 1.4 V. The ends of the structure are protected with a CLE lacquer. The local anodic oxidation of the p-layer is carried out in an electrolyte;

Mixed with an aqueous solution of ammonia and ethylene glycol, taken in a ratio that provides a pH of 5.8 and 2.5 parts of tartaric acid. The temperature of the solution is 20-25 ° C. The structure is immersed in the electrolyte, p-layer down (figure 2, to a depth of 100 - 200 microns.

A voltage of 4.5-5 V is applied between the platinum electrode immersed in the electrolyte and the P region of the structure (plus the structure), which leads to the formation of anodic oxide films 90-100 A thick in the places of current leaks p -n-junction. Anodic oxidation is carried out until the current ceases. The sizes of the oxidized sites vary from several microns to several tens of microns. With thicknesses of the order of 100 A, local areas of the anodic oxide film of such small size are practically indistinguishable. Visualization of leaks is accomplished by decorating them with a nickel layer. For this, the structure is immersed in the electrolyte with the p-layer down, as shown in FIG. The electrolyte consists of a mixture, g / l: nickel sulphate NiS0 70-75; sodium sulfate 40-50} boric acid HjBO. 20-25; sodium chloride NaCl 5-10, pH of pH 5.5-5.8. A voltage of 4 V (minus to the structure) is applied between the nickel electrode immersed in the electrolyte and the structure, which, while maintaining the structure in the electrolyte for 2-3 minutes, leads to the deposition of a nickel layer 0.5–1 µm thick in places not covered with a film of anodic oxide.

As a result of the anodic oxidation and deposition of nickel, a reliable decoration of current leakage sites is ensured.

When making contact contacts to the p-ip region of the structure, the contact to the p-region provides a nickel layer deposited in places free from the anode film. The current-voltage characteristic of the pn-junction does not show the effect of current leaks.

PRI mme R 2. This method is implemented in the study of a heterostructure with a p-P-transition in a solid aluminum-gallium solution. The differences from Example 1 are in terms of the voltages used in anodic oxidation and electrochemical deposition of metal. Cutoff voltage is about 2.0 V.

With a voltage value of liq 2.5, the thickness of the anodic oxide band is 40-60 A, which also, as in Example 1, provides isolation of current leakage points during subsequent electrochemical deposition of metal, which is carried out at a voltage of 2.2 V.

Thus, the method ensures the decoration of leaks and completely eliminates the effect of these leaks on the characteristics of the p-h-transition.

The method can be used in the manufacture of contacts to semiconductor structures, especially to thin layers, where the probability of a pn junction going to the front surface and shorting it during metal deposition is high. current leaks in pp junctions and isolation of the pp junction emergence to the surface with the help of anodic oxide prior to deposition of the metal ensure the elimination of the effect of these defects on the pn junction characteristics.

Thus, the proposed method makes it possible not only to study the p-C-junction leakages by decorating them, but also to heal these leaks in order to eliminate their influence on the operation of the instruments created and to increase the percentage of usable structures.

So, when creating a contact grid to the layers with a thickness of 0.5 µm in photocells based on gallium arsenide by ordinary electrochemical deposition, the percentage of yield of structures with their area of 1 cm was 2030%. When using the same method, this figure increased to 80-90%.

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Claims (1)

METHOD FOR IDENTIFYING DEFECTS WITH HIGH LEAKAGE CURRENTS IN SEMICONDUCTOR. STRUCTURES based on the electrochemical decoration of defects by bringing the surfaces of the semiconductor structure with η and p layers into contact with the electrolyte, turning on the voltage source between the semiconductor structure and the electrolyte and the visual Figure 1 of defect detection, which consists in that, in order to provide non-destructive detection of defects with increased leakage currents in semiconductor structures having a p-η junction parallel to the plane of the semiconductor structure, the p-layer of the semiconductor structure is brought into contact with an electrolyte for anodic oxidation, the dusse pole of the voltage source is connected to the η-layer, the voltage value is set lower than the breakdown voltage of the p-b junction, but higher than the cut-off voltage of the p – P junction, anodic oxidation is performed termination of the current through the semiconductor structure, then the p-layer of the semiconductor structure is brought into contact with the electrolyte for electrochemical deposition of the metal, a voltage is applied between the electrolyte and the h-layer of the semiconductor structure, having a cut-off voltage of the p-P junction, but lower voltage during anodic oxidation, moreover, the negative pole of the voltage source is connected to A — a layer of the semiconductor structure. 1 .1010997