Method of making indium microcontacts by ion etching

FIELD: physics.

SUBSTANCE: in the method of making indium microcontacts, a wafer with arrays of large integrated circuits or photodiode arrays is protected by a photoresist film which is perforated at contact points, a layer of indium having a thickness which corresponds to the height of the microcontacts is sprayed, and a photoresist mask is deposited by photolithography. Microcontacts are formed by etching with ions of an inert gas until indium is fully sprays in spaces between the contacts; remains of the photoresist mask on tops of the microcontacts and the bottom protective film are removed in organic solvents or by etching in oxygen plasma.

EFFECT: technique for forming microcontacts by a separating interval at the base.

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The invention relates to the technology of indium point contacts for the connection of large-scale integrated circuits (LSI) and photodiode arrays.

One of the problems in the technology photodetector module is to obtain a system of indium pier point contacts as a matrix of photodiodes, and a matrix of silicon VLSI, joined by the method of the inverted crystal.

It is known that the formation of point contacts in the following ways:

1. Spraying a layer of indium thickness of 10-15 μm and chemical etching through a mask of photoresist [C.O bolter, I.D. Burlakov, M.V. Sednev Way to build photodetecting devices. Patent of the Russian Federation. No. 2308788 from 20.01.06].

2. Spraying a layer of indium over the free mask [Klimenko A.G., etc. Especially plastic indium microscopy for matrix FPU on CdHgTe //avtometriya p.4. - 1998. - C.105].

3. Spraying a layer of indium 10-15 μm through a mask of photoresist thickness greater than the thickness of India, and negative profile, followed by "explosion" [Jutao Jiang, Stanley Tsao et.al.. Fabrication of indium bumps for hybrid FPA applications. Infrared Physics and Technology. 45 (2004) 143-151].

4. Electrochemical deposition of indium in the openings of the photoresist [3, Jutao Jiang, Stanley Tsao et.al.. Fabrication of indium bumps for hybrid FPA applications. Infrared Physics and Technology. 45(2004) 143-151].

5. Spraying a layer of indium thickness of 5 μm through a mask of photoresist of a thickness exceeding 15 μm, followed by "Bang" and reflow in polyp the market [Young-Ho Kirn, Jong-Hwa Choi, Kang-Sik Choi, Her Chul Lee, and Choonh-Ki Kim, New Reflow Process for Indium Bump // Proc. of SPIE. 1996 - Vol.3061. - PP.60-67,,. Johann Ziegler, Markus Finck, Rolf Kruger Thomas Simon, Joachim Wendler, "Long Linear HqCdTe arrays with superior temperature-cycling-reliabyti", Proceedings of SPIE Vci. 4028, 2001, Tissot I.L. etc. Collective flip - chip technology for CdHgTe I.R.F.R.A. // Proc. SPIE, 1996. - Vol.2894. - P.115].

These methods have certain limitations when applied to technologies of formation of point contacts in industrial output photodetector matrix with a pitch between elements 15÷30 µm.

In the case of a direct etching the deposited layer of indium through a mask of photoresist dissolution process India is isotropic. Therefore, the minimum distance between the point contacts may not be less than the thickness of India. Thus, when the required height of the point contacts 10÷12 μm and the minimum width of the separating contacts grooves 5 μm, photoresistive mask will Podravina before the end of the etching layer. In addition, due to nonuniform etching area is difficult to make point contacts with the same dimensions on top of the plates more than 4÷5 cm2.

When forming point contacts plating over the free mask is almost impossible to avoid galvanic coupling between the elements of the matrix due to warping of the mask a large area and is associated with podpisaniem.

Deposition of thick layers of India through a mask of photoresist is accompanied by sarestoniemi masks and reduced bore holes. Therefore, the application of this method with step matrix 15÷17 μm and the height of the point contacts 10÷12 mm is very problematic.

Spraying a layer of indium thickness of 5 μm through a thick (15 ám) mask of photoresist followed by an 'explosion' and melt in the hemisphere does not provide the desired height of the point contacts 10÷12 μm due to the insufficient amount of indium in the deposited layer with a small step in the matrix. In addition, remelting is carried out at a temperature of 170°C. heating of the photodiode array to a temperature unacceptable due to the potential for degradation of p-n junctions in some cases.

To form point contacts by the method of electrochemical deposition, widely and successfully used in the manufacture of printed circuit boards, the creation of a continuous electrically conductive layer and then etching the purpose of the galvanic separation of point contacts. Certain difficulties in the implementation of the forming point contacts electrochemical deposition creates a non-uniform thickness of the growing layer and the need to remove residual salt solutions [3, Jutao Jiang, Stanley Tsao et.al.. Fabrication of indium bumps for hybrid FPA applications. Infrared Physics and Technology. 45 (2004) 143-151].

The most optimal method for forming point contacts on the matrix of PSEs and silicon BIS increments of 15÷30 µm is reactive ion etching. Ionized HF gas development is de chemically active ions, accelerated field autopolarity, bombarding the exposed areas of India turns it into gaseous products, pumped by a vacuum pump. Unfortunately connections India have high melting and boiling points. The lowest melting point 207°C at the connection InJ [NS Akhmetov, General and inorganic chemistry. M High school, 1981, S. 679]. Therefore, to obtain a significant increase in the rate of etching of India by the method of reactive plasma etching at a temperature not exceeding 100°C, it is not possible.

A known method of making point contacts of indium ion etching [Baltar C.O, Korneev PPM, among them US, Sednev MV, Applied physics. No. 1, 2011], taken as the closest analogue. Method of etching ions of the inert gas allows to reproduce with precision the dimensions of the mask deposited on the surface of any material. While the etching process is anisotropic in the direction of the ions of the working gas. Speed ion etching India three times greater than the etching rate of the photoresist and the thickness of the photoresist 3-4 μm, the depth of etching India will be 9÷12 μm. The etching rate of the molybdenum is much smaller and equal to 0.2 μm/hour, so for etching indium thickness of 10 μm, a sufficient mask of the Mo thickness of 0.6 μm.

The disadvantage of this method is vozmozhnosti selective spraying of a layer of India. This is a fundamental limitation of the method since all the materials are sprayed, but with different speeds. Therefore, as soon as a layer of indium treated, starts spraying base (photosensitive elements of the matrix or BIS reading)

The objective of the invention is to provide a technology of forming of the system of indium column of point contacts with the height of 4-12 μm in increments of less than 30 μm and a width of the separating their area 3-5 μm as a matrix of photodiodes, and a matrix of silicon BIS, joined by the method of the inverted crystal. The technical result of the invention is industrial technology of formation of point contacts in increments of up to 15 μm., height 4÷12 microns separating gap at the base of 3÷5 μm on the wafer size from units to tens of cm2.

The technical result is achieved by the fact that in the proposed method of fabrication of indium point contacts the plate with matrices BIS or photodiode matrix protects perforated at points of contact with a film of photoresist, sprayed on it a layer of India, the thickness of which is equal to the height of the point contacts, methods of photolithography put a mask of photoresist to form point contacts by etching with ions of inert gas until complete dispersion India in the intervals between contacts and debris removal photoresistive mask on top of point contacts the bottom of the protective film in the organic solvent or etching in oxygen plasma.

The process sequence of the proposed method is illustrated in Fig.1-6.

Figure 1 shows a surface plate with crystals of BIS readout or IR photodiode matrices with metal contacts.

Figure 2 shows the application of a protective layer of photoresist and opening Windows to the metal contacts of the matrix.

Figure 3 shows the deposition of a layer of India.

Figure 4 shows the fabrication of the mask of photoresist on the surface of India for the etching of point contacts.

Figure 5 shows ion etching of indium between the point contacts.

Figure 6 shows the removal of remnants of the photoresistive mask on top of the point contacts and the lower protective film in the organic solvent or etching in oxygen plasma.

On the figures presents the following elements:

1 - plate crystals IR photodiode array or silicon BIS reading;

2 - metal contacts (e.g., vanadium or Nickel);

3 - a protective layer of photoresist;

4 - layer, India;

5 - photoresistive mask;

6 - point contact from India.

Example: production of matrix indium point contacts is carried out in the following sequence:

on Si wafer with matrices BIS reading or matrix of photodiodes with metal contacts (Fig 1) put a protective layer of positive fo is resist thickness of 1-2 μm (figure 2);

- a protective layer of photoresist is dried on a hotplate at a temperature of 100-110°C for 5 min and hold a standard photolithography to open "Windows" to the metal contacts (figure 2);

- on a protective layer of photoresist sprayed sing India, whose thickness corresponds to the height of point contacts (figure 3);

- put the second layer of positive photoresist PPG-4 thickness of 3-4 μm and conduct standard photolithography for the manufacture of the mask (figure 4);

- etching by argon ions with an energy of 500-1000 eV to full atomization of India in places free from the photoresist to form point contacts (figure 5);

- remove the remnants of the photoresistive mask on top of the point contacts and the lower protective film in the organic solvent or etching in an oxygen plasma (6);

Next is cutting plate in a matrix BIS reading or matrix of photodiodes.

The method of manufacture of indium point contacts on semiconductor wafers with matrices BIS reading or photodiode matrices, including the deposition of a layer of India, the protection of places where there should be indium point contacts, a mask of photoresist to a thickness of 3-4 μm, ion etching layer, India, removal of residual photoresist in organic solvents and/or plasma of oxygen, characterized in that before the deposition of India put the protective mask of photoresist with a thickness of 1-2 μm vmesto, where there should be contact.



 

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