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WO1990003560A2 - Fabrication de microstructures a face frontale en oxynitrure - Google Patents

Fabrication de microstructures a face frontale en oxynitrure Download PDF

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Publication number
WO1990003560A2
WO1990003560A2 PCT/EP1989/001082 EP8901082W WO9003560A2 WO 1990003560 A2 WO1990003560 A2 WO 1990003560A2 EP 8901082 W EP8901082 W EP 8901082W WO 9003560 A2 WO9003560 A2 WO 9003560A2
Authority
WO
WIPO (PCT)
Prior art keywords
oxynitride
microstructure
forming
silicon
layer
Prior art date
Application number
PCT/EP1989/001082
Other languages
English (en)
Other versions
WO1990003560A3 (fr
Inventor
Georg Edward Gimpelson
Original Assignee
Siemens Aktiengesellschaft
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Siemens Aktiengesellschaft filed Critical Siemens Aktiengesellschaft
Publication of WO1990003560A2 publication Critical patent/WO1990003560A2/fr
Publication of WO1990003560A3 publication Critical patent/WO1990003560A3/fr

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L9/00—Measuring steady of quasi-steady pressure of fluid or fluent solid material by electric or magnetic pressure-sensitive elements; Transmitting or indicating the displacement of mechanical pressure-sensitive elements, used to measure the steady or quasi-steady pressure of a fluid or fluent solid material, by electric or magnetic means
    • G01L9/0041—Transmitting or indicating the displacement of flexible diaphragms
    • G01L9/0042—Constructional details associated with semiconductive diaphragm sensors, e.g. etching, or constructional details of non-semiconductive diaphragms

Definitions

  • the present invention relates to oxynitride frontside microstructures, and to their fabrication.
  • the silicon-based electronics are used to store control algorithms, process information, and to direct actuators to perform various functions,
  • micromachined cantilivered beam produces a minute resistance change when flexed by the force of acceleration.
  • the output signal from this micromachined sensor is very small (millivolts), so that additional electronic circuitry is necessary for signal conditioning and amplification.
  • These electronic circuits are usually integrated circuit chips which are interconnected to the micromachined element. Different aspects of micromachining are reviewed in Lee et al, "Silicon Micromachining Technology For Automotive Applications", SAE Publication No. SP 655, February 1986, and the entire content of that publication is hereby incorporated by reference.
  • a disadvantage associated with polycrystalline silicon is that it possesses an inherent high compressive stress.
  • undoped polycrystalline silicon has a stress of the order of -5x10 9 dyne/cm2. This high compressive stress is a disadvantage especially when polysilicon is used for the fabrication of free-standing microstructures, such as cantilivers or bridges, which must be mechanically stable and must not buckle or break.
  • Such structures must have a low level of stress in order to produce free-standing stable structures of sufficient dimension to be useful as a sensing element.
  • silane gas is injected into a process tube at low pressure and a temperature of approximately 625°C. These processing conditions produce a very uniform layer of deposited polysilicon material on a substrate.
  • the polysilicon layer and the underlying substrate will produce a net compressive stress force in the polysilicon and this gives rise to the disadvantages noted earlier.
  • a method of producing a microstructure comprising forming an oxynitride microstructure on the surface of a silicon substrate.
  • a method of forming an integrated silicon sensor comprising forming an oxynitride microstructure on a major surface of a substrate having at least one integrated circuit provided on that major surface, under conditions which do not adversely affect the integrated circuit.
  • a device comprising a semiconductor substrate and an oxynitride microstructure disposed on a major surface of the substrate.
  • the oxynitride microstructure at relatively low temperatures, typically not higher than 500°C, and preferably within the range of about 80 to 450°C, it is possible to fabricate sensors and other components on a prefabricated integrated circuit without destroying or otherwise harming the electronics.
  • the method of the present invention thus facilitates exploitation of the so-called "foundry" concept in which integrated circuit processing is first carried out on a silicon wafer and this is followed, at a later stage, by fabrication of integrated sensor microstructures on vacant real estate of the wafer.
  • the sensor microstructures at temperatures less than 500°C, and preferably less than 400°C, it is possible to introduce a large number of sensors having different architecture without damaging the electronic circuitry already present on the wafer.
  • a further advantage realized according to the present invention is that the fabrication of the microstructures can be controlled so as to produce a low stress oxynitride.
  • the stress of the oxynitride of the microstructures of the present invention is less than about 5x10 8 dynes/cm2, and
  • 6 8 may be in the range of 5x10 to 5x10
  • the material ordinarily used for fabrication of microstructures is polysilicon but, as indicated earlier, polysilicon suffers from an inherent compressive stress, and requires deposition temperatures in excess of 550°C, usually in the region of 625 to 650°C. This inherent compressive stress associated with polysilicon makes that material somewhat unsuitable for the fabrication of sensors which rely on a bridge or cantiliver-type configuration.
  • the stress of the oxynitride microstructure can be carefully controlled by adjusting the ingredients used to form the oxynitride, typically silane, nitrous oxide and nitrogen.
  • FIGS 1 through 6 show schematically the principal method steps of the present invention
  • Figure 7 shows a side view of an integrated silicon sensor comprising an integrated circuit and a cantilever oxynitride microstructure
  • Figure 8 shows an enlarged cross-sectional view of embodiments of the cantilever of Figure 7.
  • oxynitride is an insulator
  • the sensor comprising oxynitride is adapted for measurement of the sensed phenomenon, such as fluid flow rate, pressure or acceleration, utilizing capacitive, piezo electric or piezo resistive techniques. This is discussed below in connection with Figures 7 and 8.
  • a silicon substrate 2 typically in the form of a wafer, on which there is formed a spacer layer 4.
  • the spacer layer may be a metal layer such as an aluminum layer formed by sputtering aluminum at elevated temperatures, typically . about 200°C, using conventional sputtering technology.
  • the spacer layer 4 may be an oxide layer, for example a layer of silicon dioxide formed by oxidizing the silicon substrate 2 at an elevated temperature, for example 950 to 1100°C, typically 1000 to 1050°C, for a period of about 3 to 6 hours, usually about 4 hours, in the presence of steam.
  • the process in which the silicon dioxide layer is formed is conventional, and well known to a person of ordinary skill in this art.
  • the resulting spacer layer 4 is generally about 1 to 2 microns thick.
  • the spacer layer 4 is then etched using conventional photolithography techniques to produce an etched spacer layer.
  • the spacer layer is coated with an emulsion 6 of a standard photoresist material, and subjected to ultraviolet light through a mask 8 to define a desired pattern in the photoresist material, as shown in Figure 2.
  • the exposed photoresist material is then developed and etched using conventional techniques to produce an etched spacer layer as shown in Figure 3. It can be clearly seen in Figure 3 that the etched layer 4 has windows 10 extending through to the silicon substrate 2.
  • An oxynitride layer 12 is then deposited on the etched spacer layer 4 to produce the structure shown in Figure 4.
  • the oxynitride is deposited utilizing plasma-enhanced chemical vapor deposition (PECVD) to produce an oxynitride layer having a thickness of, for example, between 1000 and 25000 Angstroms, such as 7000 to 8000 Angstroms.
  • PECVD plasma-enhanced chemical vapor deposition
  • the oxynitride layer is formed from a mixture of silane (silicon tetrahydride), nitrous oxide and nitrogen.
  • the relative proportions of silane, nitrous oxide and nitrogen are carefully chosen so as to ensure that the resulting oxynitride layer is of low stress, i.e. less than 5x10 8dyne/cm2. It has been found that this can be achieved by adjusting the relative amounts of silane, nitrous oxide and nitrogen so that the volume ratio between those constituents is 0.5 to
  • nitrogen preferably about 1 (silane) :6 (nitrous oxide) :10 (nitrogen) .
  • the stress of the microstructures of the present invention is measured by techniques known to persons of ordinary skill in this art.
  • the method described by Guckel et al, "A Simple Technique for the Determination of Mechanical ' Strain in Thin Films with Application to Polysilicon", J. App. Phys., 1671, 1985 may be used to measure the strain in the silicidated microstrucure.
  • the stress is then calculated from a knowledge of Young's modulus using known mathematical techniques.
  • An alternative method for measuring the stress is to use a stress guage, such as the one manufactured by Ionic Systems Inc. under the model number 30122. Such a guage measures the average stress across the wafer.
  • the deposition of the oxynitride layer is carried out at a temperature of not more than 500°C 7 and is preferably in the region of 150 to 300°C.
  • the deposition is effected under reduced pressure, typically in the region of about 200 to 400 microtorr (mtorr), preferably about 300 mtorr.
  • the deposition is carried for a period of about 20 to 40 minutes, depending on the desired thickness of oxynitride layer, and at a power level of about 40 to 60 watts.
  • an oxynitride layer having a thickness of about 7200 Angstroms can be obtained by depositing oxynitride under conditions of plasma-enhanced chemical vapor deposition using silane, nitrous oxide and nitrogen in a volume ratio of about 1:6:10 at a pressure of about 300 mtorr, a temperature of about 300 ⁇ C, over a time period of about 20 minutes at a power level of 45 watts.
  • the oxynitride layer 12 is then subjected to etching using conventional photoresist techniques. This produces an etched oxynitride layer 12 as shown in Figure 5.
  • Figure 6 shows the result of etching the spacer layer (or sacrificial layer) 4 to give a low stress free-standing microstructure 14.
  • the microstructure 14 can possess cantiliver portions 16 or bridge portions 18 which are stable and do not buckle or break in view of the absence of tensile or compressive stress in the oxynitride material.
  • the stress of the oxynitride layer is less than 5x10 8dyne/cm2 , and preferably less than 1x10 8 dyne/cm2.
  • FIG. 7 A particularly preferred aspect of the present invention is illustrated in Figure 7.
  • an oxynitride microstructure 20 formed on the frontside 22 of the silicon substrate 2 in close proximity to the integrated circuit 24.
  • the fabrication of such frontside microstructures is made possible by the fact that the present invention is carried out at temperatures not higher than 500°C, and preferably less than 400 C, so that adjacent integrated circuit electronics are not subjected to heat damage.
  • a further important advantage associated with this approach is that all of the processing and manipulation of the wafer is effected on one side of the silicon substrate (i.e. the frontside), thereby obviating the need to effect processing manipulation on both sides of the wafer, such as is required when using conventional back-etch techniques. The overall strength of the integrated sensor is thereby increased, and the overall cost of production is reduced.
  • Figure 8 shows a cantilever of the invention adapted for measuring acceleration as reflected by flexing of the cantilever terminal portion 26.
  • the cantilever 20 has a metal layer 30 sandwiched between two layers of oxynitride 32, 34.
  • Such a structure may be fabricated using conventional deposition techniques, e.g. sputtering or evaporation, discussed earlier.
  • the metal may be selected from aluminum, platinum, nickel, titanium, tungsten, gold, chromium, silver, palladium, titanium-tungsten, titanium-platinum, aluminum-silicon, aluminum-silicon-copper.
  • the preferred metal layer is aluminum.
  • the layer can be present as a thin layer, for example not more than 1000 Angstroms thick. While the preferred structure shown in Figure 8 contains three layers, it is possible to use two layers or more than three layers. Whichever arrangement is employed, it is important to encapsulate the metal layer (as shown in Figure 8), especially when the layer is aluminum, to minimise corrosion and wear.
  • the capacitive change is being measured as a result of flexing of the cantilever 20 with respect to the substrate 2.
  • a piezoelectric or piezoresistive element such as that shown at 36.
  • the element is disposed on a highly stressed part of the cantilever structure 20 and detects movement of the free end of the cantilever.
  • Any suitable piezoelectric material for example zinc oxide, or piezoresistive material, for example silicon, may be used.
  • Three silicon wafers having an aluminum film formed on the surface thereof were prepared using conventional electron (E)-beam techniques at 200°C.
  • the thickness of the aluminum film in each instance was about 2 microns.
  • An emulsion of standard photoresist material was then applied to the aluminum film of each of the three wafers, and each were exposed to ultraviolet light through a standard contact mask.
  • Each wafer was then developed and subjected to etching using standard procedures to etch the aluminum film down to the silicon in accordance with the pattern of the mask.
  • a nitride film was deposited on the wafer using plasma-enhanced chemical vapor deposition under the following conditions:
  • a nitride layer was deposited on the wafer using PECVD under the following conditions: SiH 4 -17% (8.5 seem) NH 3 -55% (41.25 seem) N 2 -10% (100 seem)
  • the PECVD was carried out at 350°C for 34 minutes at a power level of 57 watts and a pressure of 350 mtorr. This resulted in a nitride layer having a thickness of about 7300 Angstroms.
  • An oxynitride layer was deposited on the wafer under the following conditions: SiH 4 -20% (10 seem) NH 2 0 -80% (60.0 seem) N 2 -10% (100 seem)
  • the PECVD was carried out at a temperature of 300°C for 23 minutes at a power level of 45 watts and a pressure of 300 mtorr. This resulted in a oxynitride layer having a thickness of about 7200 Angstroms.
  • etching reactive ion etching
  • a sacrificial layer etch was carried out using potassium hydroxide or "pirahana” (a hydrogen peroxide/sulphuric acid mixture) to remove remaining aluminum and produce a free-standing microstructure.
  • potassium hydroxide or "pirahana” a hydrogen peroxide/sulphuric acid mixture
  • Samples 1 and 2 collapsed due to high stress present in the nitride layer.
  • Sample 3 resulted in a stable, low stress oxynitride free-standing structure which did not collapse or buckle, as evidenced by scanning electron microscope (SEM) photography.

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  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Pressure Sensors (AREA)
  • Formation Of Insulating Films (AREA)

Abstract

Le procédé décrit sert à produire une microstructure en oxynitrure à faible contrainte sur un substrat semiconducteur à des températures ne dépassant pas 500°C. Ledit procédé est particulièrement adapté pour fabriquer des capteurs en silicium intégrés, dans lesquels la microstrucutre en oxynitrure est formée sur un substrat dans des conditions n'affectant pas les éléments électroniques du circuit intégré.
PCT/EP1989/001082 1988-09-30 1989-09-18 Fabrication de microstructures a face frontale en oxynitrure WO1990003560A2 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US25280188A 1988-09-30 1988-09-30
US252,801 1988-09-30

Publications (2)

Publication Number Publication Date
WO1990003560A2 true WO1990003560A2 (fr) 1990-04-05
WO1990003560A3 WO1990003560A3 (fr) 1990-05-17

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Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0604405A1 (fr) * 1990-04-18 1994-06-29 Terumo Kabushiki Kaisha Détecteur aux rayonnements infrarouges et procédé de sa fabrication
US5397720A (en) * 1994-01-07 1995-03-14 The Regents Of The University Of Texas System Method of making MOS transistor having improved oxynitride dielectric
US5478765A (en) * 1994-05-04 1995-12-26 Regents Of The University Of Texas System Method of making an ultra thin dielectric for electronic devices
FR2783530A1 (fr) * 1998-09-21 2000-03-24 Commissariat Energie Atomique Procede de preparation, par nitruration, d'un substrat de silicium pour la formation d'une couche isolante mince
US6294787B1 (en) 1997-08-14 2001-09-25 Heimann Optoelectronics Gmbh Sensor system and manufacturing process as well as self-testing process
DE19758939B4 (de) * 1997-08-14 2014-07-03 Excelitas Technologies Singapore Pte Ltd Verfahren zur Herstellung eines Substrats, Sensorsystem

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3679663D1 (de) * 1986-01-07 1991-07-11 Emi Plc Thorn Druckempfindlicher durchflusssensor.

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0604405A1 (fr) * 1990-04-18 1994-06-29 Terumo Kabushiki Kaisha Détecteur aux rayonnements infrarouges et procédé de sa fabrication
US5397720A (en) * 1994-01-07 1995-03-14 The Regents Of The University Of Texas System Method of making MOS transistor having improved oxynitride dielectric
US5541436A (en) * 1994-01-07 1996-07-30 The Regents Of The University Of Texas System MOS transistor having improved oxynitride dielectric
US5478765A (en) * 1994-05-04 1995-12-26 Regents Of The University Of Texas System Method of making an ultra thin dielectric for electronic devices
US6294787B1 (en) 1997-08-14 2001-09-25 Heimann Optoelectronics Gmbh Sensor system and manufacturing process as well as self-testing process
DE19758939B4 (de) * 1997-08-14 2014-07-03 Excelitas Technologies Singapore Pte Ltd Verfahren zur Herstellung eines Substrats, Sensorsystem
FR2783530A1 (fr) * 1998-09-21 2000-03-24 Commissariat Energie Atomique Procede de preparation, par nitruration, d'un substrat de silicium pour la formation d'une couche isolante mince
WO2000017412A1 (fr) * 1998-09-21 2000-03-30 Commissariat A L'energie Atomique Procede de traitement, par nitruration, d'un substrat de silicium pour la formation d'une couche isolante mince
US6551698B1 (en) 1998-09-21 2003-04-22 Commissariat A L'energie Atomique Method for treating a silicon substrate, by nitriding, to form a thin insulating layer

Also Published As

Publication number Publication date
CA1317034C (fr) 1993-04-27
WO1990003560A3 (fr) 1990-05-17

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