FR2571538A1 - METHOD OF MAKING THIN FILM RESISTOR, AND RESISTANCE OBTAINED THEREBY - Google Patents

Abstract

THE INVENTION CONCERNS THIN-LAYER RESISTORS OF HIGH VALUES DEPOSITED ON SUBSTRATES OF INTEGRATED CIRCUITS OR HYBRID HYPERFREQUENCY CIRCUITS. THE PROCESS ACCORDING TO THE INVENTION USES AS STARTING MATERIAL A METAL SILICIDE, OF GENERAL FORM M SI OR M M, M ,, SI. THE METAL SILICIDE IS NITRIDE, IN THE SPRAYING APPARATUS BY A NITROGEN PLASMA IN THE ARGON. THE DEPOSIT OBTAINED INCLUDES A MIXTURE OF METAL, RESISTIVE, AND OF SILICON NITRIDE SI N, INSULATING. THE CONCENTRATION OF NITROGEN IN ARGON, THE PROPORTIONS OF METAL X AND SILICON Y IN SILICIDE AND THE POWER DENSITY OF THE EVAPORATION SOURCE, BY ADJUSTING THE ACTIVITY OF THE PLASMA, ALLOWS TO ADJUST THE RESISTIVITY OF THE THIN LAYER . APPLICATION TO SI, GA AS INTEGRATED CIRCUITS AND HYPERFREQUENCY HYBRID CIRCUITS, ON AL O OR BE O.

Description

J

  METHOD FOR MAKING RESISTANCE IN A THIN LAYER,

  AND RESISTANCE OBTAINED BY THIS PROCESS

  The present invention relates to a method for producing resistances of high values, in a thin layer, obtained by spraying. These resistors are intended more particularly for the manufacture of integrated circuits, on a substrate such as silicon or the materials of group 111-V such as GaAs, or for the fabrication of hybrid circuits, in particular at microwave frequencies, on substrates such as alumina or beryllium oxide. The production method according to the invention makes it possible to deposit on these substrates resistances

  whose value is high in a wide range of values.

  The thin film resistors are generally obtained by depositing a metal or a mixture of metals, under vacuum, the one or more

  deposited constituents which in themselves have high resistivities: the resistance

  The effectiveness of the thin layer obtained is close to the resistivity of the metal or mixture of metals, alloy or eutectic, since there is no chemical modification of the starting material during the

  deposit of the thin layer. The resistivity range is therefore

  limited by the physical conditions of the deposit, and by the

of the layer produced.

  According to the invention a very broad range of resistivity is obtained, for the same material, using as starting material a metal silicide which is more or less nitrided during the deposition operation of the thin layer, in the presence of a plasma, a part of nitrogen in argon. The deposit obtained contains a metal mixed with a silicon nitride of general formula SiaNb, which is a dielectric, that is to say an insulator, whose proportion in the mixture and the composition-the indices a and b- are in direct relationship with the proportion of nitrogen in the plasma. Therefore, modify a single parameter of the deposition conditions, i.e. the partial pressure of nitrogen during the spraying of simple elements such as Ta, Ti, Al, etc. This nitrogen partial pressure also corresponds to a residual pressure of air and the amount of nitrogen present in the metallization chamber is not sufficient to create a nitriding of the deposited metals under vacuum. - the speed of deposition, the power of the source which

  evaporates the metals to deposit them under vacuum.

  the composition of the deposited mixtures.

  In all cases, until now, the resistivity of the metal layer obtained is still slightly greater than that of the bulk material, because of oxygen pollution, for example, which oxidizes the metals during the depot. Thus -the range of resistivity

  possible according to this deposit method is quite weak.

  If it is necessary to produce layers of higher controlled resistivity, such as for example p7 100 // .lcm, then most often materials such as

  "CERMETS" which are NiCr / SiO mixtures. The range of resistance

  The desired efficiency is then a function of the choice of the ratio of the respective quantities of NiCr, which is the conductor of electricity, although

  resistive, and SiO which is an insulator.

  But there are cases of specific applications that

  resistance of very high values and to dissipate a certain power, all things being equal

  since it is an integrated circuit or a hybrid circuit

  frequency. To obtain such resistances of very high values, it is not permissible to reduce by too much the thickness of the layer, this

  which increases the resistivity of the resistive band, because it is neces-

  to adhere to the upper limits of current density.

  In these cases, it is necessary to use layers having a resistance

  very high level, for example by depositing metal mixtures

  polluted with oxygen that forms oxides.

  It can therefore be seen that in the known art it is difficult to have for the same starting material a range of resistivity that is extended. Thus, if it is necessary to deposit different nitrogen pressure resistances in the plasma, it makes it possible to adjust the resistivity of the

  deposited resistive layer: the SiaNb alloy dilutes the metal.

  More specifically, the invention relates to a method for producing thin-film resistors, deposited on an integrated circuit or hybrid circuit substrate, in a sputtering apparatus, characterized in that the starting material is a metal silicide, and what a nitrogen plasma in argon is introduced

  in the spraying apparatus, the nitriding nitrogen, the metal silicide

  to give a depot comprising at least one metal mixed with

  a silicon nitride alloy of general formula (SiaNb) M.

  The invention will be better understood by the description more

  follow-up, supported by a comparison with the recall

  of a known method for producing thin film resistors.

  Thin film resistors, on an integrated circuit or hybrid microwave circuit, are currently and generally obtained by depositing a metal or a mixture of metals deposited by sputtering, reactive or non-reactive. The metals chosen to make resistors are themselves metals that are bad electrical conductors: for example nickel does not have good conductivity, as is chromium, and the nickel-chromium alloy is commonly used to make resistances. The resistivity of the layers thus produced is close to the resistivity of the bulk material because there is no chemical modification of the starting material. Under these conditions, the resistivity of the thin layers essentially depends on the conditions of realization of the

  deposit, these conditions may slightly vary the resistivity.

  It depends for example on: - the residual pressure of oxygen or water vapor in the metallization chamber during the deposition of reactive metals with oxygen and water vapor, such as Ti, Cr, Al ... etc. This residual pressure is not controlled and corresponds to the pressure

  partial air in a chamber at 10-2 torr.

  on a hybrid circuit, with rather different values between them, then it becomes obligatory to have recourse to different

  technologies, imposed according to the value of the resistances.

  The method according to the invention makes it possible to produce resistors in thin layers in a wide range of resistivity,

  modifying a single parameter of the conditions of dep8t. According to the invention

  tion, a metal compound is used which is chemically modified

  In the course of deposition, by varying the nitrogen pressure in an argon plasma during the deposition of the resistive layer, this metal compound is more or less nitrided. The deposit is then made of a metal, which is conductive, and a silicon nitride SiaNb, which is a dielectric. The mixture in varying proportions of metal and silicon nitride makes it possible to vary the resistivity of the layer. Nitrogen is the most convenient compound to use, but other reactive molecules such as oxygen can be used to chemically modify the

the thin layer deposited.

  The compounds that can be used in the context of this invention are metal silicides. They sometimes form well-defined mixtures having a general formula MSi 2, that is to say they consist of two silicon atoms bonded to a metal atom M. The most well-known and common defined compounds are TaSi 2, MoSi 2 , WSi2, TiSi2, which are stable on silicon, and therefore do not react with the substrate of an integrated circuit if it is silicon. These compounds are considered as conductors,

  but they become resistive by nitriding.

  The invention can also use any silicide compound, without restriction on the composition, such as Mx Siy, in which the ratio

  x / y defines the resistivity range chosen.

  Finally and more generally, the invention can use

  poly-metal silicides, of the formula Mx M'x, M "x, Siy.

  The value of the resistivity is obtained by choosing the concentration of nitrogen in the argon nitrogen mixture during the silicide deposition by reactive cathodic sputtering. Indeed the

2 5 7 1 5 3 8

  more or less amount of nitrogen in the gaseous nitride plus or minus the silicide during deposition. An amorphous deposit is thus obtained comprising a metal mixed with a certain amount of silicon nitride. The larger the amount of silicon nitride, the greater the resistivity of the deposit. Thus, by adjusting the x / y ratio, in a mixture of Mx Siy formulas, it is possible, according to the method of the invention, to produce thin layers having a low or greater resistivity, up to high values. In the example M Si if y-O, to k x Y 12 p Z 10-4-r.cm and on the contrary if x - 0, fP = 10 -.L.cm, since

  in this case we tend to a limit SiN which is a dielectric.

  The process was carried out with a compound that is given

  by way of example: Wx Tiz Siy in which x = 0.3, z = 0.7, y = 0.8.

  The layers deposited by reactive sputtering on a target in the presence of a nitrogen and argon plasma, have a resistivity which varies from 2.10-4.4 cm at 3.5 × 10 -2 cm -1 for a nitrogen concentration. which varies from 0 to 50% in argon The variation of the resistivity with the nitrogen content in argon is given in the table below:

N2% - 2.5 5 10) 20 30 40 1 50

  The range of resistivity can be further expanded for the same starting compound, by increasing the power density, in the vacuum metallization apparatus: the increase of the power density increases plasma ionization which

  increases the nitriding of the metal silicide.

  The invention, which is simple to implement, is essentially used in the production of integrated circuits or hybrid circuits, especially in the microwave domain, on GaAs or alumina and beryllium oxide type substrates. It also concerns resistances in discrete components, on

ceramic substrates.

Claims (7)

  A method for producing thin film resistors, deposited on an integrated circuit or hybrid circuit substrate, in a sputtering apparatus, characterized in that the starting material is a metal silicide, and in that a plasma of nitrogen in the argon is introduced into the sputtering apparatus, the nitrogen nitriding the metal silicide to give a depot comprising at least one metal mixed with a silicon nitride alloy of general formula (SiaNb) M. -   2. Process for the production of resistors according to claim 1, characterized in that the metal silicide is a defined compound   of form M Si2, such as Ta Si2, Si2 Si, W Si2, Ti Si2.   3. Process for producing resistors according to claim 1, characterized in that the metal silicide is a mixture of Mx Siy monometallic form.   4. Process for the production of resistors according to claim 1, characterized in that the metal silicide is a mixture of   Mx M'x form, M "x ,, Siy, polymetallic.   5. Process for producing resistors, according to any one of   Claims 2 to 4, characterized in that the ratio of metal (x) /   silicon (y) defines the resistivity range of the deposited thin film. 6. A method of producing resistors according to claim 1, characterized in that the nitrogen concentration in the argon, in the spraying apparatus, adjusts the resistivity of the deposited thin film, the resistivity being in direct relationship with the nitridation of metal silicide, which is directly related to   nitrogen concentration in the plasma.   7. Resistance in thin layer, of high value (p> 100 / cm), deposited on a semiconductor substrate such as Si or GaAs, or insulator such as Al 2 O 3 or BeO, characterized in that it comprises a mixture of at least one metal M and silicon nitride alloy SiaNby obtained by nitriding a silicide   metal, according to the method of any one of the claims 1 to 6.