DD224153A1 - PROCESS FOR PRODUCING CHEMICALLY SENSITIVE MEMBRANES - Google Patents

Abstract

The invention relates to a method for the production of chemically sensitive membranes, in particular for chemical sensors based on field effect semiconductor devices for the detection of ions, atoms and molecules in gases or solutions. The object of the invention is to have available a process for the preparation of chemically sensitive membranes with an adjustable broad spectrum of use and high chemical stability. The invention has for its object to develop a process for the preparation of chemically sensitive membranes, which should be fully compatible with microelectronics technology. According to the invention, this object is achieved in that the uppermost layer of the gate insulator material is modified by bombardment with ions, atoms or molecules, that chemically sensitizing substances are subsequently introduced into this layer by diffusion in the electric field and finally aftertreated thermally or by particle bombardment.

Description

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Field of application of, invention,

The invention relates to a method for the production of chemically sensitive membranes, in particular for chemical sensors based on field effect semiconductor devices for the detection of ions, atoms and. Molecules in gases or solutions.

Characteristic of the known technical solutions

Chemical sensors are known whose principle of action is based on the field effect on the semiconductor. Examples of this are the ISJJET / P. Berveld: IEEE Trans. Browedical Engineering, BME 19 (1972) 342 /, the ion-sensitive diode / CC. Wen, TC Chen, JH Zemal: IEEE Trans. ED, ED-26 (1979) 1945 / and the gas sensitive SET / I. Lundström, MS Shiwaraman, C. Swenson: Technical Digest Int. Electron, Devices Meeting Washington (1975) 631 /. These sensors contain, above the active, controllable region, for example the gate region of an ISJ ¹ ET, a membrane which, when interacting with the surrounding medium, generates a phase boundary potential serving as an electronic input signal, ie the electrical component exhibits chemical sensitivity. A desired chemical selectivity of this sensor also requires specific interactions of the membrane with the different particle types in the measuring medium. These interactions depend on the chemical composition and structure of the membrane so that their composition determines the degree of sensitivity and selectivity of the chemical sensor.

Targeted influencing of sensitivity and selectivity is necessary for the production of multifunctional

Sensors. High stability of the sensors for their long-term use requires both high chemical resistance and high mechanical strength of the membrane. Membrane fabrication seeks compatibility with microelectronics technology. Known membranes are insulator membranes, inorganic, ionic conductor membranes and homogeneous and heterogeneous polymer membranes,.

As insulator membranes known gate insulator substances themselves, such as SiO ₂ * ^ 3 ^ 4 V * Al ₂ CU but also Ta ₂ Oc- used. The preparation of such membranes is carried out according to the microelectronic technology common methods of thermal oxidation, sputtering and chemical vapor deposition. The isolator diaphragms are mechanically very resistant, 'have in the case of Si ^ l., Of the Al ₀ O-, and Ta ₂ Oc also high chemical resistance. But they are only useful for pH measurements. /H. Abe, M. Esashi, T. Matsuo: "IESE Trans, on Electron DeK, ED-26 (1979) 1-939 7.

The preparation of inorganic ionic conductor membranes for pH and pK measurements is carried out by deposition of SiIikatgläsern from organic solutions and subsequent annealing. Lifting the microelectronic technology-foreign · production, these layers have the disadvantage of low stability. / T. Matsuo, M. Esashi: Sensors and Actuators Ί (1981) 77 Λ The same applies to vapor-deposited silver halide membranes for pAg, pCl and. pBr measurements only low stability expected. / R.P. Buck, D.E. Hackleman: Analytical Chemistry 49 (1977) 2315 /. Another known method for Hefstellung of. chemically sensitive membranes is the coating of the gate insulator region with a polymer film in which

chemically sensitive substances are embedded. / BRD-OS 2 610 530 /. Here, chemically sensitive substances (e.g., valinomycin for K-sensor) are added to a solution which is recovered by admixing a plasticizer by dissolving a polymer in a suitable solvent. The application in the gate area is done either by pouring or by immersion. After evaporation of the solvent, a polymer film with chemically sensitive properties remains adhered to the gate insulator. But they have lower stability compared to inorganic plague membranes.

Object of the invention '''

The object of the invention is to provide a method for. Preparation of Chemical Sensitive Membranes with Adjustable Wide Range of Use and High Chemical Stability Available.

Explanation of the essence of the invention

The invention has for its object to develop a process for the preparation of chemically sensitive membranes, which should be fully compatible with microelectronics technology. According to the invention, this object is achieved in that the uppermost layer of the gate insulator material is modified by bombardment with ions, atoms or molecules, that subsequently chemically sensitizing substances are introduced into this layer by diffusion in the electric field and finally aftertreated thermally or by particle bombardment.

Advantageously, the diffusion takes place in the electric field in a liquid medium in which the chemically sensitizing substances (dopants) are present in homogeneous form. With the help of an electrode also located in this medium, a voltage is applied so that the polarity of the gate insulator bearing

Semiconductor substrate opposite to your sign dea dopant. With the help of the field energy, the dopant ions migrate to the gate insulator and are incorporated in its surface.

The uppermost layer of the gate insulator can be pretreated by particle bombardment. By specifying the dose and the energy as well as by selecting the type of bombardment particles, a defined region of the gate insulator surface can be created in which the incorporation of the dopants by diffusion preferably takes place. The projectile particles used are inert particles or particles of chemically sensitizing substances, so that a chemical surface modification can also be associated with the structural surface modification. ^. ,

Since the particle whisker first causes radiation damage in the insulator which disturbs the electronic sensor function, aftertreatment is required. This aftertreatment is carried out using the usual in microtechnology annealing (for example, thermal or non-conventional annealing by means of high-energy radiation, such as laser, light, Elektrorien- or ion radiation). ^x

In the process design according to the invention, as a result of the low field energy in the diffusion in the electric field, penetration of the dopants into the fissure or through the gate-to-gate phase boundary can occur.

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insulator semiconductor substrate also for dot-anden

be avoided with small masses and high diffusibility, so that the effectiveness of the gate insulator is fully maintained. Due to the possibility of choosing the dopants by type and amount, both the sensitivity and the selectivity of the membrane and thus

of the sensor can be varied within wide limits. The system isolator / membrane can be kept very thin, so that very short response times of the sensor can be realized. A very high stability of the membrane is achieved by the matrix effect of the chemically stable insulator material.

embodiment

The invention will be explained in more detail below with reference to exemplary embodiments.

The starting point is a 100 nm thick gate insulator layer of Si, 1f, which is produced on a silicon semiconductor substrate by means of a 50 nm-thick SiO 2 semiconductor substrate by the usual methods of semiconductor technology. The vacuum is then applied to the Si-JL layer by vacuum evaporation applied a 50 nm thick PiIm of Al, which is then annealed at 450 ⁰ G. for 20 min in a dry atmosphere of nitrogen and then removed in hot phosphoric acid. To produce a sodium-sensitive membrane, Ar ions are injected through this membrane into the Si ₇ N. surface at a dose of 10 ions / cm ² and at an energy of 20 keV. The thus modified gate surface is now exposed to a treatment in an electric impulse using the semiconductor material as a cathode and an auxiliary anode made of Pt. This treatment is carried out in a 1 M KCl solution at a voltage of 5 V between the cathode and the anode for 5 hours.

In a variant of this exemplary embodiment for producing a Ua-sensitive membrane, in a first method step Al ions are mixed with one dose

of 10 ions / cm and with an energy of 15 IceV injected into the Si ^ N surface, then in the thus modified surface K-ions are diffused under the conditions already described · the aftertreatment consists in a tempering in air atmosphere ·

Claims (2)

invention claim 1. A process for the preparation of chemically sensitive membranes, in particular for chemical sensors based on field effect semiconductor devices for the detection of ions, atoms and molecules in gases and solutions, characterized in that the uppermost layer of the gate insulator material modified by bombardment with ions, atoms or molecules is that subsequently in this layer chemically sensitizing substances are introduced by diffusion in the electric field and finally aftertreated thermally or by particle bombardment « 2. The method according to item 1, characterized in that the diffusion takes place in the electric field in a liquid medium.