DE1772016A1 - Arrangement for mask adjustment with the light microscope when manufacturing integrated semiconductor circuits, in particular integrated transistors - Google Patents

Description

Arrangement for mask adjustment with the light microscope i when producing integrated semiconductor circuits, in particular integrated transistors. In solid-state circuit technology , it is known that all components of a circuit, such as transistors, diode, resistors and capacitors, are produced in a silicon wafer by several successive diffusion processes. The essential advantages of integrating these circuit elements in a common body arise from the fact that individual steps in the manufacturing process can be carried out simultaneously for a large number of components.

To produce the known integrated semiconductor circuit, the same methods can be used with only a few more process steps as in transistor production, and the number of interconnections is greatly reduced, and large parts of the connections, soldering points and housing parts required according to the old technology are saved.

Today, for the manufacture of solid-state circuits, the planar technology, which is also widely used in the manufacture of transistors, is used. Here, pn transitions are generated in the silicon by diffusion of dopants from the surface . The special feature here is that with the aid of an oryd layer on the surface of the semiconductor body, the diffusion of doping elements can be restricted to the places where this ozyd layer has been removed . This manufacturing method is known as masking the surface with 8i02. By defined to the Si02-free sites are geometric shapes that can be pn structures with just such forms generate. See, inter alia, H. Dorendorf and H. Ullrich "Integrated Semiconductor Circuits" Umschau 1965, Issue 23, B. 41-748, see also J. Wüstehube "Integrated Semiconductor Circuits", April 1966, Valvo GmbH Hamburg 1, especially B. 72-78. The known production of semiconductor integrated circuits is generally done using the Störstellendiftusion and epitaxy in connection with the photolithography. All circuit elements are created in the crystal at the same time , step by step in several work steps. Each operation is carried out on several hundred to several thousand circuits at the same time. The number of operations required is not much higher than when manufacturing individual transistors.

According to a known manufacturing process of fairly integrated semiconductor circuits, the semiconductor crystal is first covered with a layer of silicon dioxide (SiO2). This ozone layer can then be used as a mask for the substances used for doping.

At the points where the semiconductor crystal is to be doped, window-like openings are etched into the bilicium dioxide with the help of a photolithographic process. The dopant can only penetrate into the semiconductor crystal through this window during the subsequent diffusion process, while it is kept away from the underlying silicon at the other locations as a result of the "mask effect" of the oxide layer .

By re-covering with bilicium dioxide (SiO2) and repeating During the process, P and N zones lying one above the other can be identified in the silicon crystal of the desired shape, doping, timing and sequence.

The silicon dioxide film is particularly suitable for masking of the silicon crystal against almost all dopants.

In order to produce P and N zones as well as interconnects with the desired structure on the semiconductor crystal, the photolithographic process is used, which is also known as photo etching or photo masking, because the photoresist used to etch the oxide window serves as a mask. In this known production method, the crystal plate is adjusted in a special device with respect to the firmly clamped photomask. When the first mask is used, the crystal disc is still unprocessed.

In the case of the following masks, the alignment masks on the crystal, which originate from previous etching and diffusion processes, must be brought into line with the corresponding alignment masks on the photomask under the microscope. Then it is exposed and developed, whereby the exposed lacquer surfaces, which have become hard through polymerization, remain, and the unexposed lacquer surfaces are removed.

During the photoresist process, a photographic plate must be precisely aligned with the silicon wafer. It is already known to perform this adjustment under microscopic observation with the aid of micromanipulators, which allow defined small movements to be carried out by reducing the movement of the hand using levers and screws. Shifts of a few duns are thus possible in a defined and controlled manner. Vg1. Umschau 1965, issue 239, page 745, left column and see also AE Brennemann et al. "Two Interconnection Techniques for Large-Scale Circuit Integration", IBM Journal, Sept. 1967, pages 520-526.

When adjusting a photomask with a semiconductor plate coated with photoresist on the known mask adjustment and exposure device, however , there are often difficulties because the microscope images are out of focus and the magnifications that can be achieved are too low. The 3i @ roskop data, lens size, depth of field and total magnification are determined by the adjustment device, due to the necessary minimum distance between the photomask and the semiconductor wafer during adjustment (greater than or equal to 40u). As a result, only those lenses can be considered whose depth of field corresponds approximately to this distance.

The adjustment of a contact hole photo mask is particularly critical with an emitter-diffused semiconductor die. The actual adjustment points are insufficient for proper alignment, and therefore the emitter contact holes Be adjusted via the emitter diffusion zones.

Figure 1 is used with the entered dimensions for illustration of aligning an emitter contact hole mask 2 over an emitter diffused one Semiconductor wafer 1 at approximately 100 times overall magnification.

The contrast-weakening ones make the adjustment more difficult Circumstances such as the photoresist layer on the semiconductor die and the microscope viewing through an upstream yellow filter.

With the elimination and limitation of the difficulties presented The problem underlying the invention is concerned with Disadvantages.

For an arrangement for mask alignment with the optical microscope in the manufacture of semiconductor integrated circuits in particular in the manufacture of integrated transistors preferably by impurity diffusion and epitaxial deposition, in combination with photolithography, the invention consists then in that a Fernsehnikroskop serves as Lichtnikroskop whose lichtnikroskopischer part in two having parallel beam paths in the lower part of a respective objectively, whose mutual axial spacing to the spacing of two Justiergarken in the mask plane or in a Par allelic to the mask plane, and in that the images generated simultaneously with the two lenses only by lichtopti- specific components to a image are to unite, which then passes on the photosensitive layer of the image pickup tube of the television camera for imaging, so that finally the markings of the lower part of the microscopic and also above the markings t ragen- the semiconductor die insertable mask on the screen of the connected directly to the television camera combined television receiver are displayed on.

The television microscope, a connection between a microscope and a television camera, is already known per se, see Prof. Dr. Paul Görlich "The development of scientific devices since Ernst Abbe-operation" in the journal fine device technology Issue 5/1965, page 193-211 with the Figure 5 on page 194 (VEB, Yerlag technology, Berlin) and see. Furthermore, Prof. Dr. Werner gleen "From the work of the research laboratory of Siemens & Halske" Siemens magazine November issue 1962, pages 757 to 771 with the figure 14 on the page 17680 These known television microscopes, however, set up for metallographic structural examinations, but not for the mask alignment applicable in the manufacture of integrated semiconductor circuits. They also do not contain bin lens tubes as in the invention. They are not set up for the simultaneous viewing of two images, which are produced by two separate lenses and which are close to one another. The invention is explained in more detail below with reference to the schematic drawing in FIG. 2 for a particularly favorable, for example, embodiment. In the bar representations beams are represented by individual emit light for simplicity.

In FIG. 2, 3 denotes the microscope object table which carries the semiconductor crystal plate 5 and which can be adjusted or rotated in two transverse directions by the device 4. The object table 3 also contains devices, not specifically shown in the drawing, for fastening the object 5. The markings on the semiconductor wafer 5 are shown in FIG. 2 by 6 and ? designated. The photomask 8 which can be pushed in above it also contains alignment marks, which are identified by 9 and 10 . Die_genannten alignment marks are suitably circular rings in pairs in the cover case (top and bottom) are superimposed concentrically.

The light microscopic part of the arrangement according to the invention contains in the lower part the two parallel-axis objective tubes 11 and 12 with objectives a and b. The two Tubusse 11 and 12 are provided with their axes vertically above the stage 3 at a mutual distance s. This axis distance between the two Tubusse 11 and 12 is equal to the pitch of the two alignment marks 9 and 10 and equal to the pitch of the two alignment marks 6 and? . The bundle of light rays incident into the tube 11 via the objective a is denoted by 13, and the second bundle of light rays incident into the barrel 12 via the other objective b is denoted by 14 in FIG. These two light beams 13 and 14 are with the mirrors 15 and 16 in the optical component 1? deflected and united there to form a common beam of light 18.

With the aid of the mirror 19 in the beam path 18, part (22, 23) of the light beam can be branched off into the binocular 8 stem 20, 21, while the other part 25 is fed from the single tube 24 to the projection eyepiece 26. However, the deflection device is advantageously designed in such a way that the entire light bundle can be passed either into the two eyepiece tubes 20 and 21 or onto the projection eyepiece 26 by manually switching over from 19.

The two eyepiece tubes or eyepiece sockets set up for two-eye viewing are one below the other in the drawing, so that only the front (20) is visible in the drawing. The same applies accordingly to the two beam paths 22 and 23.

The eyepiece distance of the binocular optical system '(20, 21,' 221 23) should coincide as precisely as possible with the eye distance, because otherwise the congruence with the eye pupil and. so that the optical imaging deteriorates and light is lost.

The light beam emerging from the lens system 26 then arrives the light-sensitive layer of the image pick-up tube of the television camera 2? the electrical line 28 is connected to the television playback device 29.

The light pipe of 29 is shown folded 90o in FIG. It is expediently in a rigid structural unit with the light microscopic part to be viewed from the same side as the insight for binocular vision on the double tube 20, 21.

As a result of the inner photo effect of the photosensitive layer of the Image pick-up tube of the camera 2'7 call lighting changes conductivity changes in this layer, so that on its rear side an image equivalent to the optical image Charge image is created. This charge image is scanned line by line and delivers thus a time-variable, in the amplitude of the charge and thus of the brightness of the respectively scanned pixel dependent signal.

In the case of the invention, the signal pulse program differs with regard to the synchronization pulse sequence by the standard public television from: The number of lines is expedient 875 for a device according to Fig 2 and a screen with 36em diagonal length in television receiver 29..

The viewing device 29 is a television receiver to which, in contrast to the home television set, the video signal is fed via cable (28) and without a carrier. In the viewing device 29 is this in the camera 2? resulting "electronic image" is converted back into an optical image.

In the case of an automatic setting of the crystal plate 5 in the adjusted position, a photoelectric tracking system is also provided which contains the photoelectric receiver 31, which is set up in front of the viewing device 29 in the beam path 30. A comparator 32 is connected to this scanner or receiver 31, possibly in connection with an electronic computing system. The output of the device 32 is connected to the motorized adjusting element 4 via the electrical line 33.

The light microscopic part of the arrangement of FIG. 2 corresponds finally still holds the illumination apparatus 34, 35 for a uniform illumination of the two microscopic objects for a Auflichtjustierung wherein zweckaUig the illuminated tend radiation from 34, 35 from the objektiveeitigen and for imaging unused space by means of a non-loading Sonders Glaskondensors illustrated is supplied.

The device according to the invention can advantageously also provided with a means for selectively obtaining a transit and Auflichtbelichtung of the objects (9, 10 and 6, 4) be tet ausgestat-. In the embodiment shown in FIG. 2, an observation device is provided in the incident light mode. The irradiation occurs from 34 and 35 via the yellow filters 36 and 37.

In the arrangement shown in FIG. 2, the objective and the projection plane can be adjusted independently of one another, even if the television camera 27 with the light microscopic part and preferably also with the viewing device 29 and the ring lighting 34 or 35 form a compact structural unit .

The high number of lines of 875 lines of the built-in television camera 27 selected in the invention results in a particularly fine resolution for viewing the microscope image on a screen .

In order to obtain sharp images, it is advantageous in the present case to use objectives (a, b) with low magnification but large depths of focus (approx. 5z) .

By changing the distance between the television camera 27 and the light microscope, almost any magnification can be achieved and transmitted to the screen 29 , preferably with the interposition of an additional lens . In one embodiment of the invention , a gain of 1200 was achieved.

In addition to the expediently selected magnification , a very useful image with maximum contrast can be set in the invention by regulating the brightness and contrast. A prerequisite for perfect image reproduction is, in particular, that the objectives used are of good quality and that the microscope lighting is adequate.

Objectives particularly suitable for the present purposes are: 1.) 5x objective with an aperture of 0.1 and the usual total magnification of 50z, the maximum total magnification of 100z, a depth of 40 to 50 / u at the usual magnification and a Depth of field of less than 30 / ü at maximum magnification. 2.) 8z lens with an aperture of 0.8 and a standard total magnification of 160z, a depth of focus of 30 / u at normal magnification, and a depth of focus less than 20 / u painter at maximum magnification.

Claims (1)

Claims 1.) arrangement derschlagen to mask adjustment with dem.Lichtmikroskop the manufacture integzierter semiconductor circuits, particularly in the manufacture of integrated transistors, preferably by impurity diffusion and epitaxial NIE, in conjunction with the photolithography, characterized in that a television microscope serving as the light microscope, The light microscopic part of which has two parallel beam paths (13, 14) in the lower part each with an objective (a, b), the mutual axial distance (s) of which corresponds to the distance between two alignment marks (9, 10) in the mask plane or in a parallel to Mask level corresponds, and that the images generated simultaneously with the two lenses (a, b). By light-optical components (1?) Are to be combined into a single image, which is then placed on the light-sensitive layer of the image pick-up tube of the television camera (2?) For imaging arrives, so that finally the markings (10, 9) below the light micro scopic part and above the also markings (?, 6) supporting semiconductor wafer (5) retractable mask (8) on the screen of the television camera ( 27) immediately connected television receiver (29) are further mapped united . 2.) Maakenjustier assembly according to claim 1, characterized in that the DAB image merging of the parted by the two overall objectives (a, b) images the in two different planes marks (9, 10 and 6, 7) generated via Binocular tubes (20, 21) are observable. 3.) mask adjustment arrangement according to claims 1 and 2, characterized in that by manually switching an optical component (19) which is arranged in the beam path (18) of the combined images , either a visual observation with the eyepiece, especially with binoculars Angled viewing (20, 21), or via the projection eyepiece (26) with the screen of the television receiver (29) can be produced . 4.) Maskenjustier arrangement according to claims 1 to 3, characterized in that the DAB structurally combined with the light microscopic part engebaute to a compact unit zusa "television equipment .is operated (27, 28, 29) with a number of lines from the 875th 5.) Maskenjustier arrangement according to claims 1 to 4, characterized in that the DAB lens and the projection plane are independently adjustable sindp 6) Maskenjustier arrangement according to claims 1 to 59 characterized in that the television receiver 29 to the television camera (27) is connected without a carrier via cable (28) . 7.) Maskenjustier arrangement according to claims 1 to 69 characterized in that each of the two lens barrels (11, 12) in the light-optical microscope part of a ring light (34, is arranged for the incident light mode conces- 36 and 35, 37). 8.) Maskenjustier assembly according to claims 1-79 characterized in that a device for achieving a wahlwei- sen Durc- incident illumination and the Obwalden is provided projects. 9.) Mask adjustment arrangement according to claims 1 to 8, characterized in that the two objectives (a, b) of the light microscopic part have a low magnification, about 5z, but a relatively large depth of focus about 40 to 501u at usual magnifications . 10.) Haskenjustier arrangement according to claims 1 to characterized in that the light-microscopic part with the Helligkeite- and contrast adjustment in televisions part of an image nasal contrast can be adjusted by combination of the light optical magnification. 11.) Mask adjustment arrangement according to Claims 1 to 10, characterized in that a follow-up control with a photoelectric scanning device (31), which is placed in front of the screen (29), and with a comparison device (32), which is based on the adjustment mechanism ( 4) of the stage (3) acts, the adjustment of the markings takes place automatically.