DE3104024A1 - REACTIVE SPRAY SETTING OF SILICON - Google Patents

Description

description

The present invention relates to a method for producing a microminiature component according to the preamble of claim 1.

Such components are, for example, integrated circuits. The invention relates in particular to the formation of fine-line patterns in such components by means of dry etching processes.

There is great interest in the training of Apply dry processing methods to patterns in workpieces such as semiconductor wafers. That Interest in such methods is justified by their generally better resolution and easier controllability of Dimensions and shapes compared to conventional wet etching. As a result, dry etching is being used more and more in the formation of patterns in the processing of, for example, semiconductor wafers for the production of integrated ones Large circuits (LSI components).

Various dry etching methods are known in which

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gaseous plasma is used. This is described, for example, in "Plasma-Assisted Etching for Pattern Transfer" by CJ Mogab and WR Harshbarger, J. Vac. May be. & Tech., 16 (2), March / April 1979, p. 408. As indicated in this article, recent efforts have been directed specifically to the development of methods in which reactive gas plasma is used to carry out chemical reactions Bombardment with charged particles can be intensified. One such advantageous process, referred to as reactive sputter (or ion) etching, is described in the above-mentioned article by Mogab-Harshbarger and in Proc. 6th Int ¹ I Vacuum Congr. 1974, Japan. J. Appl. Phys., Suppl. 2, pt. 1, pp. 435-438, 1974.

Significant efforts have recently been made to provide reliable reactive sputter etching techniques Try forming fine-line patterns on silicon surfaces. Activities in connection with the etching of polysilicon were of particular interest. Polysilicon layers, both doped and undoped, form the starting layers for economically significant ones LSI components, such as dynamic 64K write / MOS-type read-only memories (RAMs). It has been recognized that improved methods of forming patterns in silicon reactive sputter etching, if available, could contribute to a noticeable reduction in costs and

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to improve the performance of such devices or other structures, the silicon substrates or layers contain.

The invention is therefore based on the object of an improved Indicate dry etching process. Specifically, a reactive sputter etching process for silicon is provided will.

This task is carried out by the characterizing part of the claim 1 specified features solved. In a special embodiment of the invention, the reactive atomization is used of monocrystalline silicon and doped or undoped polycrystalline silicon achieved in one Chlorine plasma at relatively low power and pressure. With monocrystalline silicon and undoped polycrystalline! Silicon is the edge profile of the etched layer anisotropic. With doped polycrystalline silicon this can Edge profile can be controlled so that it is somewhere in the range between complete isotropy and complete Anirostropia lies.

In the following, the invention is explained in more detail with the aid of exemplary embodiments. Show it

Fig. 1 is a schematic representation of a special, parallel

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Plates having reactor, in which the process according to the invention carried out v, ⁷ can be grounded,

FIG. 2 is a cross-sectional view of a masked monocrystalline silicon member made in accordance with the teaching of FIG present invention can be etched, and

3 is a cross-sectional view of a masked polycrystalline silicon layer made in accordance with the teachings of the present invention Invention is etched.

According to the invention, reactive sputter etching is carried out, for example, in a reactor having parallel plates, as shown in Fig. 1, or in another reactor of known type.

The reactor shown in Fig. 1 as a specific example with parallel plates contains an etching chamber 10, which by a non-conductive cylinder 12 and two conductive face plates 14 and 16 is formed. The cylinder 12 can, for example consist of glass, the plates 14 and 16 can each consist of aluminum. Furthermore, the one shown contains Reactor a conductive workpiece holder 18, which also consists, for example, of aluminum. In a descriptive Example consists of the bottom of the holder 18 from a

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25.4 cm large circular area, which can accommodate seven, each 7.6 cm large wafers is designed.

The wafers 20 whose lower (i.e., front) faces are to be etched are on the underside as shown in Figure 1 a plate 22 attached. The plate 22 is designed such that it can be attached to the holder 18 by suitable fastening devices (not shown) such as brackets or screws can be attached. According to one feature of the invention the plate 22 is made of conductive material such as aluminum, and the top or back surfaces of the Wafers 20 are held in electrical contact with the plate.

The wafers 20 according to FIG. 1 are grounded on the plate 22 by a with openings equipped cover plate 24 held in place. The openings are positioned and aligned with respect to the wafer 20 in such a way that each opening is slightly different has a smaller diameter than the correspondingly aligned wafer. In this way, the main part is the front surface each wafer exposed for the etching process. The cover plate 24 is attached to plate 22 by any conventional arrangement.

Advantageously, in the etching device according to 3/4

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Fig. 1 contained cover plate 24 made of difficult to atomize material, which does not chemically react with the etching gas to form a non-volatile material. Come as such material anodized aluminum and quartz glass in question.

The workpiece holder 18 according to FIG. 1 is via an RF tuning network 26 capacitively coupled to an HF generator 28, which is designed, for example, in such a way that it holds the holder 18 operates at a frequency of 13.56 megahertz. Furthermore is the holder 18 via a filter network comprising a coil 30 and a capacitor 32, to a measuring device 34, which the Indicates peak value of the RF voltage applied to the holder 18, connected.

In Fig. 1, the end plate 14 is at a reference potential, for example open! "and forms the Anorde of the reactor. The workpiece holder 18 forms the operated cathode of the reactor. In the in Fig. 1 as Example shown special reactor, the distance between anode and cathode is about 25.4 cm, the diameter of the Anode plate is approximately 43.2 cm.

The face plate 16 shown in Fig. 1 is also grounded. Furthermore, the plate 16 has an open end having a cylindrical shield 36 that holds the holder 18 surrounds, connected and is therefore on ground. The one

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Portion of holder 18 that extends through plate 16, is electrically isolated from the plate by a non-conductive socket 38.

According to the invention, a chlorine gas atmosphere is created in the chamber 10 testifies. The chlorine gas flows into the chamber in a controlled manner from a conventional source 40. Furthermore, by a conventional Pump 42 to maintain a predetermined low pressure in the chamber.

By introducing chlorine gas into the chamber 10 and creating an electric field between the anode 14 and the cathode 18, a reactive plasma is generated in the chamber 10. The resulting plasma is identified in the drawing by a uniformly dark area in the immediate vicinity Proximity of the material surface to be etched. On the material surfaces Volatile substances formed during the etching process are evacuated from the chamber by the pump 42.

FIG. 2 shows in cross section a section of one of the wafers 20 to be etched in the chamber 10. According to FIG a substrate 48 of monocrystalline silicon one in conventional Mask layer 46 patterned in a manner is formed. It is the monocrystalline silicon is either p- or η-doped silicon, which has a resistivity of about 1 to 10 ohm-cm. He-

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according to the invention, the unmasked portions of the silicon substrate 48 are removed in a reactive sputter support process to form vertical walled formations in to form the substrate, which have practically no undercuts of the overlying masking layer 46. As in 2 is indicated by dashed lines 47, such an anisotropic etching of the substrate 48 forms a precise one defined channel.

The possibility of anisotropic etching in monocrystalline silicon is of practical importance in the manufacture of electronic micro-miniature components. For example, the above-mentioned channel in the substrate 48 according to FIG. 2 forms one Intermediate stage in the process of manufacturing a microminiature MOS capacitor. Other component structures, required anisotropic etching of a substrate or a layer of monocrystalline silicon during the manufacturing process make are known to the person skilled in the art.

The anisotropic etching of both doped and non-doped polysilicon layers is of particular importance in production of LSI components. For example, in the manufacture of MOS-RAMs it is typically in different Process steps necessary to provide thin layers of doped or undoped polysilicon with an exact pattern.

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3 shows a section of an MQS RAM component in cross section, which has a polysilicon layer to be etched. Fig. 3 shows a thin (for example 50 nanometer thick) Layer 50 of silicon dioxide on a monocrystalline silicon part 52. On top of layer 50 is a layer 54 of polycrystalline silicon. Layer 54 is for example 500 nanometers thick. On top of the layer 54 to be etched is one in a conventional manner with a Patterned masking layer 56.

3 shows a basic representation of various sections of the same memory device. In some sections The layer of the component to be produced consists of doped polysilicon, which is the usual name for this Poly-1 level. In other portions of the same device, the layer 54 consists of undoped polysilicon. These undoped layer is usually referred to as poly-2 plane.

In accordance with the present invention, anisotropic etching of layers of either doped or undoped polysilicon is used achieved. The anisotropic etching of the layer 54 according to FIG. 3 is shown there by the dashed lines 58. According to the invention, however, it is also possible to achieve isotropic etching of doped polysilicon layers. A full

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permanent isotropic profile is shown in Fig. 3 by the curved dashed lines 60 indicated. Furthermore, according to a feature of the present invention, it is possible to use the Etching of a doped polysilicon layer to selectively control in order to create an edge profile in the layer between those shown in FIG. 3 shown to achieve fully anisotropic and fully isotropic cases.

The term "doped" polysilicon is used herein to refer to Connection to a polysilbium layer, which is a p-type dopant, such as phosphorus, was added. The dopant concentration of such a layer is controlled in such a way that that there is a specific resistance in the range between 20 and 100 ohm-cm.

Various materials are suitable for forming in accordance with the invention of the patterned masking layers 46 and 56 of Figures 2 and 3, respectively. These materials comprise organic and inorganic covering material, silicon dioxide, magnesium oxide, aluminum oxide, titanium, tantalum, tungsten oxide, cobalt oxide and the refractory silicon compounds of titanium, tantalum and tungsten. Those made from these materials Masking layers are patterned using conventional lithography and etching techniques.

According to the invention reactive atomization is monocrystalline

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silicon and doped or undoped polycrystalline Silicon carried out in a chlorine gas atmosphere. In a preferred embodiment, it contains in the etching chamber produced atmosphere essentially pure chlorine. Typically this means in a practical example, that the chlorine gas, which has a purity of about 95 to 99.5% is the only component that is targeted, i. H. is expediently entered into the chamber. Among those here specified special process conditions is used such a pure chlorine gas atmosphere to achieve a relatively high etching rate for silicon. In addition, the Selectivity between the silicon to be etched and other layers (such as the masking layer and other layers, for example in the component structure z. B. made of silicon dioxide> stand) relatively high. In addition, only chlorine gas is used as the medium introduced into the chamber generally preferred due to the relatively simple handling and controllability of only one gas supplying source.

According to the invention, however, constituents other than Chlorine can be introduced into the reaction chamber to achieve a controlled etching of silicon, provided that the process conditions specified here are observed. In general, however, the addition of other ingredients continues to the chlorine the differential etching rate between

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the silicon and other materials such as. B. silicon dioxide, in the structure to be machined. For example can be added to the chlorine for carrying out reactive sputter etching of silicon, such as B. argon or other noble gases, up to about 20 to 25 vol .-%, nitrogen up to about 20 to 25 vol .-% or Helium up to about 50% by volume.

According to the invention, the etching z. B. be carried out in a parallel plate reactor, as shown in Fig. 1, or in a multi-facet reactor of known design. For anisotropic etching with such a system , a chlorine partial pressure of about 20/3 microbar is generated in the etching karamer according to a specific example of the present invention. For the specially illustrated reactor with parallel plates, chlorine gas is introduced into the etching chamber, advantageously at a volume rate of about 10 cm per minute. In the case of a multi-facet reactor, a

Generates chlorine gas flow of about 30 cm per minute.

According to the present invention, a power density becomes

of, for example, about 0.20 watts per cm on the surfaces of the workpiece to be etched in a multi-facet reactor. For a reactor with parallel plates this is

2 Power density, for example 0.25 watt per cm '.

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Under the special conditions specified above, each became monocrystalline silicon and undoped polycrystalline Silicon etched anisotropically in the specified facilities at a rate of about 60 nanometers per minute. at For each reactor, the corresponding anisotropic etch rate for doped polysilicon was about 120 nanometers per minute.

In order to achieve the anisotropic etching of a doped polysilicon layer in the manner described, it is essential that that the back of the workpiece to be etched is in good electrical contact with the operated one during the etching process Cathode electrode is held. Otherwise isotropic etching of the doped polysilicon layer results. At niphtdo ~ oriented polysilicon and monocrystalline silicon, however, anisotropic etching is achieved regardless of whether the back of the workpiece makes electrical contact with the operated Has cathode electrode.

Anisotropic etching processes of the type described above are marked by a relatively high differential etch rate with respect to, for example, silicon dioxide and conventional ones Covering materials such as B. HPR-204 (obtained from Philip A. Hunt Chemical Corp. Palisades Park, New Jersey can be). The exemplary methods discussed above for monocrystalline silicon and undoped polysilicon etch silicon about 30 times faster than silicon

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dioxide and about three times faster than masking material. The one explained above Doped polysilician process etches the polysilicon layer approximately fifty times faster than silica and about six times faster than masking material.

The anisotropic reactive sputter etching specifically explained above is merely exemplary in nature. In general According to the teaching of the present invention, such etching can be carried out by selecting chlorine partial pressures, Chlorine gas flows and power densities in the ranges from 8/3 to 200/3 microbar, 2 to 150 cm per minute (with the exception that for etching in the aforementioned multi-facet reactor the gas flow is at least 10 cm per minute

2
must) or 0.03 to 2 watts per cm.

As mentioned above, isotropic etching of doped polysilicon results if the back of the workpiece to be etched is not kept in electrical contact with the operated cathode electrode of the etching device. According to one feature of the present invention, isotropic etching of doped polysilicon is achieved while the back side of the workpiece is kept in electrical contact with the operated cathode electrode. This is achieved through Create special conditions in the etching chamber, as outlined below. In particular, by changing these conditions the etching process can be controlled in such a way that there is a possibility of variation between complete isotropy

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and complete anisotropy.

According to a specific example, it becomes completely isotropic reactive sputter etching of doped polysilicon in a chlorine gas atmosphere within a parallel plate reactor achieved in that a chlorine partial pressure in the reactor of, for example, about 80/3 microbar, a gas flow of about 10 cm per minute and a power density of 0.125 watts

per cm is created. The corresponding numbers in a multi-facet reactor are 80/3, 30 and 0.10, respectively. By varying this parameter between the values specified in this section and the values specified above for anisotropic Etching doped polysilicon, the edge profile of the etched layer can be controlled so that it is anywhere in is the range between complete isotropy and complete anisotropy.

So if these parameters are, for example, 20 microbar, 10

3 2

cm per minute and 0.20 watt per cm are selected, one obtains etching conditions for doped polysilicon which are exactly f ^ ast lie between complete isotropy and complete anisotropy. Under these conditions the strength is on Undercuts (maximum lateral etching) about half the vertical thickness of the etched layer.

The above-mentioned specific examples of the isotropic 1300 51 / OSSi

reactive sputter etching doped polysilicon serve just the intuition. According to the invention, such a thing can be achieved Etching are generally carried out in that chlorine partial pressures, Chlorine gas flows and power densities in the

Ranges 8/3 to 200/3 microbar, 2 to 150 cm ³ per minute,

2
or 0.06 to 2 watts per cm can be selected. By selecting specific values from these ranges to obtain isotropic etching of doped polysilicon instead of anisotropic etching, the peculiarity of each set of selected values is that for a given power density there is a corresponding minimum or threshold pressure above which isotropic etching occurs. With increasing power density, the corresponding threshold pressure for isotropic etching increases linearly. On the other hand, for a given pressure there is a maximum power density below which isotropic etching takes place.

In accordance with the present invention, the combination of a relatively low power density is a relatively low one Partial pressure of the chlorine and an adequate flow of chlorine gas into the etching chamber are effective to create the basis for efficient To create an etching reaction. On the part of the applicant it is assumed that in the etching process described on the to be etched Ions striking the workpiece activate chlorine particles on the surface of the workpiece. The chlorine activated in this way, in turn reacts with the material to be etched (silicon), so that

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volatile substances arise from the etching chamber durgh the connected pump must be removed. In practice, the flow of chlorine into the chamber is advantageously over one Threshold held. In this way you get an adequate supply of the material (chlorine), creating a special Etching rate is achieved and maintained during the etching process.

The reactive sputter etching processes discussed above, ver ~ apply relatively low pressures and low conduction densities. Due to the specified low power densities arise When carrying out the method, no "noteworthy thermally induced disturbances such as, for example Workpiece deflection or changes in size in the system itself. Furthermore, the availability and design of the HF generators for operating the etching system are made easier by the successful performance requirements.

In addition, the methods described are characterized by a relatively high uniformity of the etching rate on each individual workpiece and from one workpiece to another. It has been found that such fluctuations in the etching rate do not in practice exceed t 2%.

In addition, the methods according to the invention have no impact on pollution, (As you know, the burden is the

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Dependence of the etching time on the total area to be etched. It was also determined that the edge profile, the etching rate and the selectivity of each of these processing operations are practically independent of the special pattern _{geometry f} shape size and the mask material used in the etching.

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Claims (6)

BLUMBACH WESER BERGEN KRAMER - PATENTANWÄLTE JN MUNICH AND WIESBADEN Palenlconsuli Radeckestrasse 43 8000 Munich 60 Telephone (089) 883603 / SS3604 Telex 05-212313 Telegrams Patentconsult Patenlconsult Sonnenberger Straße 43 6200 Wiesbaden Telephone (06121) 5629-! 3/561998 Telex 04-186237 Telegrams Patentconsult Western Electric Company, Incorporated New York, N.Y., USA Maydan 17 Reactive sputter etching of silicon Claims / Method for producing a microminiature component, in which, in the course of the process, a silicon part is placed at least once in a device for reactive sputter etching is to be etched anisotropically, the device being positioned between an anode electrode and a cathode electrode Contains existing plasma, brought by the application of an electric field on a between the electrodes gaseous medium is generated, characterized in that the gaseous medium is active reactive element contains chlorine, which is activated on the part by impinging ions from the plasma in order to deal with .130051 / 0661 Munich: R. Kramer Dipl.-Ing. · V /. Weser Dipl.-Phys. Dr. rer. nat. · E. Hoffmann Dipl.-Ing. Wiesbaden: P.G. Blumbach Dipl.-Ing. . P. Bergen Prof. Dr. jur. Dipl.-Ing., Pat.-Ass., Pat.-Anw. until 1979 G. Zwirner Dipl.-Ing. Dipl.-W.-Ing. to combine the silicon and become a volatile substance that is removed from the device that the portion to be etched of the part (z. B. 20) of doped polycrystalline Silicon, with a mask having a pattern on the surface to be etched, and that the part is kept in electrical contact with one of the electrodes during the etching. 2. The method according to claim 1, characterized in that that the chlorine has a partial pressure of 8/3 to 200/3 microbar (2 to 50 χ 10 Torr), and that the power density 0.03 to 2 watts on the surface to be etched per cm. 3. The method according to claim 2, characterized in that that the silicon part is kept in electrical contact with the cathode electrode. 4. The method according to claim 3, characterized in that that in the device chlorine gas with a volume 3 entered a speed of about 2 to 150 cm per minute will. 5. The method according to claim 3, characterized in that that the device has a reactor with parallel 13ÖQ51 / 05S1 Has plates in which a chlorine partial pressure of about 20/3 microbar is generated that entered chlorine gas at a volume rate of about 10 cm per minute into the reactor is, and that in the reactor the power density at the surface of the part to be etched to about 0.25 watts per 2
cm is set. 6. The method according to claim 3, characterized in that that the gas introduced into the chamber consists essentially of pure chlorine. 130ÖS1 / 0561