Method of forming contact drawing from nickel on silicon wafers

FIELD: physics.

SUBSTANCE: method of forming contact drawing from nickel on silicon wafers involves formation of a dielectric film with windows, chemical deposition of nickel in said windows and formation of a nickel silicide interlayer from the gas phase during thermal decomposition of nickel tetracarbonyl vapour at temperature 200-300°C, pressure in the system of (1-10)-10-1 mm Hg and rate of supplying nickel tetracarbonyl vapour equal to 0.5-2 ml/min per dm2 of the covering surface. The nickel layer is then removed up to the nickel silicide layer through chemical etching and nickel is deposited via chemical deposition onto the nickel silicide interlayer in the window of the dielectric film.

EFFECT: invention enables formation of a transparent contact for an electroconductive layer based on nickel with low ohmic resistance, independent of the type of conductivity and degree of doping of the silicon surface.

1 ex, 1 tbl

 

The invention relates to the manufacture of semiconductor devices from silicon, in particular to the manufacture of solar cells.

The manufacturing process of most semiconductor devices of silicon is accompanied by the formation of a specific configuration of electrical contacts. When creating a contact, drawing the most widespread combination of the method of vacuum deposition of a continuous metal layer by photolithography chemical-resistant mask and the etching of the contact pattern (Ethmozine, Fpprec. "Planar technology silicon devices", Moscow, Energy, 1974).

The disadvantages of the known method of applying a contact pattern on the silicon are the necessity of using high vacuum and greater complexity of the process of photolithography.

There is a method of creating contact with the silicon film of Nickel by chemical deposition from solutions containing Nickel salt and a reducing agent type NaH2PO2instead of vacuum deposition (international application WO 2004/004928, IPC B05D 3/10, 2004).

The disadvantage of this method is the need for pre-activation of the silicon surface by deposition of gold. In addition to the consumption of the precious metal, the presence of gold on the silicon surface followed by diffusion of gold in about the eating of silicon at a temperature above 200°C, what causes the decrease of the lifetime of minority carriers in silicon and the deterioration of the operating characteristics of semiconductor devices. In addition, the precipitated Nickel contains from 5 to 10% of an impurity of phosphorus or boron, which creates the problem of obtaining low-resistance contact to silicon with a p-conductivity.

The closest in technical essence and the achieved effect of the present invention and taken as the prototype is known a method of creating a contact pattern of Nickel on silicon solar cells by forming on the surface of the wafer of the silicon nitride film of silicon of a thickness of about 0.1 μm, created by using a laser beam of Windows in this film, selective chemical vapor deposition from a solution of Nickel in Windows and heating to a temperature of 250-450°C, accompanied by the formation between Nickel and silicon layer of the silicide of Nickel (Ni2Si or NiSi) ("Front-side metallization of silicon solar cells by nickel plating and light induced silver plating", By M.Alemán, N.Bay, D.Barucha, S.W.Glunz and R.Preu, Galvanotechnik, 2, 2009, p.412-417).

The disadvantages of this method of creating a contact pattern on silicon solar cells are the suitability of this method only for silicon heavily doped with phosphorus (greater than 1018cm-3) and low adhesion of the Nickel to the surface of the silicon heavily doped with boron or aluminum, which prevents the to boost contact Nickel-based on both the area of the diode structures of silicon solar cells, in particular, in the manufacture of contact figure photoconverters with bilateral working surface.

Task to be solved by the present invention is directed is the provision of a robust contact conductive layer based on Nickel with low ohmic resistance regardless of the type of conductivity and the degree of doping of the silicon surface.

This task is solved in that a method of creating on the surface of silicon wafers durable electrically conductive layer of Nickel silicide, does not contain harmful impurities of phosphorus and boron.

The technical result is achieved by the fact that in the known method of applying a contact pattern of Nickel on silicon wafer, including the creation on the surface of the silicon dielectric films with Windows deposition of Nickel in the window, the formation of a layer of Nickel silicide, according to the invention the deposition of Nickel and the formation of a silicide layer of Nickel is produced in the gas phase by thermal decomposition vapor tetracarbonyl Nickel in the temperature range of 200-300°C, when the pressure in the system (1-10)·10-1mm Hg for 1 DM2cover the surface, then chemical etching to remove the layer of Nickel to the layer of Nickel silicide and chemical deposition put a Nickel on the layer of Nickel silicide in the window of the dielectric film.

Should the tmetal, that gas-phase method thermal deposition of Nickel from tetracarbonyl Nickel allows to obtain a Nickel film without impurities of phosphorus and boron, which are electrically active impurities in silicon and prevent the creation of a low resistance contact, respectively, with p - and n-type conductivity silicon. In addition, the deposited Nickel has a high chemical activity, contributing to a low-temperature formation of a layer of Nickel silicide.

The invention is illustrated in the following example, the manufacture of the contact pattern for double-sided panels.

Example

Used silicon wafer diode structure of p+-R-p+or R+-p-p+created by diffusion doping one side of the plates phosphorus, and other boron to a concentration of about 1020cm-3. Both sides of the plate are covered by the antireflection film of silicon nitride with a thickness of about 80 nm, for example, by the method of plasma-chemical deposition from a mixture of monosilane and ammonia. Instead of silicon nitride can be applied film of SiO2Ta2O5, Al2O3, ZnO, SnO2, In2O3. Using a pulsed picosecond laser scanning in the film of silicon nitride or other specified dielectric films on both sides of the plates creates a window of pure silicon, with the appropriate form of the desired contact pattern.

Then the plate was placed in a vacuum chamber and the system is pumped to a residual pressure of ~1·10-1mm Hg After that, the plate is heated to a temperature of 200°C and in the camera serves a couple of tetracarbonyl Nickel (TKN) at the rate of 2 ml/min per 1 DM2the surface of a silicon wafer for 1 minute, Then the speed of the feed vapor TKN reduce to 6.5 ml/min and the process is conducted at a temperature of 300°C for 1 min After cessation vapor TKN plate maintained at a temperature of 400°C for another 5 minutes. In the process of deposition of Nickel on the heated surface of the wafer in the Windows of pure silicon is the formation of a silicide layer of Nickel of a thickness exceeding 10 nm.

At temperatures above 200°C To form the compound Ni2Si, and at temperatures above 400°C connection NiSi. On the surface of silicon, closed film of silicon nitride, Nickel does not enter into chemical reaction with silicon nitride. Then not reacted with silicon Nickel is removed by acid etching without damaging the film of silicon nitride. In the Windows of silicon nitride on both sides of the silicon wafers remains a film of Nickel silicide with a thickness of 10 nm, and selectively precipitate the Nickel film thickness of about 0.2 μm from a solution by a known chemical vapor deposition. If necessary, the Nickel film can be further applied galvanically copper with a thickness of several microns.

Other examples of the application of Nickel films using gas-phase method presented in the table.

As follows from the table, the deviation from the stated technological parameters of deposition of Nickel on silicon wafers in cases reduce the temperature of the heating plate (example 3) or reduce the feed rate of the vapor tetracarbonyl Nickel (example 5) leads to a decrease in the rate of their deposition and to obtain thin films of uneven thickness. In cases raise the temperature of the heating plates (example 2), increase the speed of the feed vapor tetracarbonyl Nickel (example 4) or exceeding the working pressure (example 6) are formed Nickel film is dark grey or brushed with inclusions of carbon.

Forming a film of Nickel silicide helps to obtain a mechanically stable and low resistance contact at the finishing stage chemical precipitation of Nickel on parts of the silicon-coated Nickel silicide. Thus, the task of applying inexpensive contacts on both sides of double-sided solar cells from silicon.

A method of creating a contact pattern of Nickel on silicon wafer, including the establishment of the dielectric film with the Windows, the deposition of Nickel in the window and the formation of a layer of silicide of Nickel, characterized in that the deposition of Nickel and education p is Aslani silicide of Nickel is produced in the gas phase by thermal decomposition vapor tetracarbonyl Nickel in the temperature range of 200-300°C, when the pressure in the system (1÷10)·10-1mm Hg at a feed rate of vapor tetracarbonyl Nickel 0,5÷2 ml/min per 1 DM2cover the surface, then chemical etching to remove the layer of Nickel to the layer of Nickel silicide and chemical deposition put a Nickel on the layer of Nickel silicide in the window of the dielectric film.



 

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1 tbl

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