JPH07183570A - Multichip module - Google Patents

Abstract

PURPOSE:To make the speed of a system fast by a method wherein the optical waveguide of a multichip module which uses an optical signal in a part is made fine. CONSTITUTION:Parts 8 which are optical waveguides 2 composed of a silicon compound and in which light incident on and radiated from a multichip module substrate 1 composed of silicon is bent so as to be parallel to the face of the substrate at their terminal parts and parts 9 in which light is branched to a plurality of courses parallel to the face of the substrate in half parts of the optical waveguides are formed on the surface of the multichip module substrate. An optical signal which is incident perpendicularly on the face of the substrate is supplied to photodetectors 6 at the inside of semiconductor chips 3 which have been connected facedown to the substrate by means of the optical waveguides.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multichip module which uses an optical signal as a part thereof for high speed operation of a system.

[0002]

2. Description of the Related Art Conventionally, in a multi-chip module in which a system is composed of a plurality of semiconductor chips, it has been proposed to use an optical signal as a part of the signal, such as a clock signal, in order to improve the operation speed of the system. Has been done.
For example, in Japanese Patent Laid-Open No. 4-313269, a light emitting element and a light receiving element are provided in a module, and an optical signal from the light emitting element issued in synchronization with a clock signal is received by the light receiving element and converted into an electric signal. Supplying to a plurality of semiconductor chips is described. The propagation path of the optical signal here uses the space in the IC storage box (it is considered that a gas such as air exists), or as shown in FIG. 9 (FIG. 4 (b) of the present application). An optical fiber embedded in a printed circuit board on which a plurality of chips are mounted is used. In another conventional example, an optical signal produced outside the multi-chip module is supplied to the module by an optical fiber, and inside the module, the space provided therein is used to perform the optical signal. As shown in FIG. 7 (FIG. 4- (a) of the present application), a structure for supplying a signal to a light receiving element is used. Although the optical signal propagates in the space inside the module, in order to prevent the waveform from being distorted due to the synthesis of light coming from different propagation paths, the part that easily reflects the light in the multichip module and the light is absorbed and the reflection is reduced. An optical signal propagation path having a structure including a portion and a portion has been proposed.

[0003]

Among the conventional multi-chip modules described above, in which a box-shaped internal space such as a package is used for the optical signal propagation path, the light energy obtained by the light receiving element is the light emitting element. It becomes a very small part of the noise generated and is extremely inefficient. Furthermore, the possibility of cost reduction is reduced by specializing the package, such that the light reflection path extends to both the package inner wall and the module substrate, and in particular, it is necessary to improve the reflection on the package inner wall. There is.

Further, the method of using the optical fiber embedded in the module substrate requires a manufacturing technique for obtaining such a structure, which is different from the conventional substrate producing method. That is, the angle of the optical fiber is adjusted to receive the light that is vertically incident on the substrate, it is bent in the substrate parallel to the surface of the substrate, and the optical fiber is bent again in the substrate in the vertical direction to position the light receiving element in the chip. It is necessary to illuminate the structure well, especially if this structure is less than 1 mm, preferably 100 μm.
Realization with dimensions less than m is very difficult or even expensive.

[0005]

A multi-chip module of the present invention comprises a multi-chip module substrate made of single crystal silicon, and a silicon-based compound formed by embedding at least a part thereof in a series of substrate surfaces. And a means for bending light in a direction substantially perpendicular to the substrate surface, which is provided at the end of the waveguide, and provided on the way of the waveguide to split the light into a plurality of paths at the substrate surface. Means, a metal wiring provided on the substrate, and a plurality of semiconductor pellets connected to a part of the metal wiring via bumps so that an electronic circuit is formed on the surface and the surface faces the optical waveguide. And a light-receiving element formed on the surface of the semiconductor pellet, and by adopting such a structure, the light propagation path has a silicon surface microfabrication technology with a wealth of accumulated know-how over the years. And by the bump can be formed only by connection technology of the silicon pellet and the silicon substrate.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a first embodiment of the present invention. A compound semiconductor pellet 2 including a light emitting element 5 and a silicon semiconductor pellet 3 including a light receiving element 6 are mechanically and electrically connected via a bump 4 made of gold on a multi-chip module substrate 1 made of single crystal silicon. In particular, the light emitted from the light emitting element enters the optical waveguide 7 made of a silicon compound, changes its direction by the reflecting surface 8, and enters the light receiving element.
(In order to clarify transmission and reception of the optical system signal, the wiring of the electric signal system is not drawn at all except the bump in the same sectional view.)
(b) is a plan view, in which a semiconductor pellet 2 including a light emitting element 5 (dotted circle) irradiates an optical waveguide 7 with an optical signal in a direction perpendicular to the same plane, and the reflection plane 8 shown in FIG. In the meantime, the light is reflected in the direction, and finally reaches the light receiving element 6 after passing through an optical branch point 9 provided on the way of the optical waveguide several times. The electric system signal reaches the semiconductor pellet through the bump 4 by the metal wiring 10 provided on the module substrate. The metal wiring and the optical waveguide do not interfere with each other and can be crossed. In the present embodiment, there are far more electric system signal lines than optical system signals, but they are omitted altogether except for one place for the sake of clarity. In this embodiment, a clock signal is supplied as an optical signal to the light receiving element in each chip. By doing so, the timing deviation (clock skew) at each clock signal receiving end is greatly improved as compared with the case where electric signals are supplied to a plurality of pellets. The light emitting element is given a clock signal by an electric system signal, and the light receiving element gives the electric system signal output to the electric system element on the same pellet.

FIG. 2 shows an example of a method of forming an optical waveguide.
First, the multi-chip module substrate 1 made of single crystal silicon is subjected to 45 ° taper etching at a position where light enters and exits in the vertical direction by using an anisotropic etching technique (FIG. 2A). Similarly, anisotropic etching is performed at a position to be a passage of the next light in a direction parallel to the module substrate so that the wall surface becomes vertical this time. At this time, etching is performed so that the bottom surface of the hole previously formed remains a little and to the same depth as the bottom surface (FIG. 2B). In the figure, it is drawn in a slightly deeply etched state due to variations. At the time of this etching, an optical branching structure along the optical waveguide is also formed. Next, in order to reduce the energy loss due to diffused reflection in the waveguide and the sag of the waveform, the silicon is thinly oxidized to form a smooth SiO ₂ surface and SiO ₂ is formed on the surface (FIG. 2 (c)).
Next, the nitride film 22 is formed to have a thickness that fills at least the etched depth. Then, the surface is made flat by, for example, a chemical mechanical polishing technique or the like to form an optical waveguide on the silicon substrate. The structure of the stereoscopic image is shown in FIG. The surface 23 in the figure is the vertical reflection surface, and the surface 2
Reference numeral 4 is a horizontal reflecting surface at the light branching portion.

According to the forming method described above, the width of the optical waveguide can be realized on the order of several microns from the current silicon surface processing technology. In the case of the clock signal according to the embodiment shown in FIG. 1, the fineness of the optical waveguide on the multi-chip module substrate is designed to be about 50 μm intervals even if the density of terminals requiring the clock signal on the semiconductor chip is high. Because it can be adjusted, as a result, the above 50μ
It is very easy to supply light to the light receiving elements arranged at m intervals by the optical waveguide having a width of several microns. The depth of the optical waveguide is about 1 μm.

In FIG. 2, the surface is flattened by the CMP technique in order to facilitate the formation of the electric metal wiring on the module substrate. However, if the surface is slightly uneven, the effect is small. The optical waveguide portion may be raised to the same extent as the conventional semiconductor chip surface (about 0.5 μm) by a completely different optical waveguide forming method shown in FIG. Further, in order to prevent light from leaking out of the waveguide and reducing the amount of light energy due to diffused reflection from the side and bottom of the optical waveguide, the waveguide may be covered by the same method as the wiring metal formation.

A second embodiment of the present invention is shown in FIG. This embodiment is different from the first embodiment in that there is no light emitting element for emitting an optical signal, but an optical signal is given from outside the module by an optical fiber. That is, an optical signal sent from the outside through the optical fiber 31 travels along the optical waveguide 7 formed on the surface of the silicon module substrate 8 at the reflecting surface 8 and is provided on the semiconductor chip 3 at the reflecting surface 8. It is incident on the light receiving element 6. In the figure, reference numeral 32 denotes an optical fiber guide which is fixed on the substrate 1, and the deviation from the position of the hole on the upper surface of the package 33 is absorbed by the guide.

[0011]

As described above, according to the present invention, an optical waveguide in a multi-chip module is formed by a silicon compound embedded in the surface of a module substrate using silicon, and the same substrate is faced down via bumps. By adopting a structure that transmits and receives light to and from the semiconductor chip connected to, it has become possible to realize the same structure based on the conventional microfabrication technology for the silicon surface. Moreover, it becomes possible to form an optical waveguide with good optical energy transfer efficiency, and more optical signal systems can be introduced into the multi-chip module.
This has the effect of improving performance.

[Brief description of drawings]

FIG. 1 is a sectional view and a plan view showing a first embodiment of the present invention.

FIG. 2 is a diagram showing an example of a procedure for forming an optical waveguide forming the basis of the present invention.

FIG. 3 is a diagram showing a second embodiment of the present invention.

FIG. 4 is a diagram showing a conventional example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Multi-chip module substrate 2 Semiconductor chip 3 having a light emitting element 3 Semiconductor chip 4 having a light receiving element 4 Connection chip 5 Light emitting element 6 Light receiving element 7 Optical waveguide 8 Light reflecting surface 9 therein Optical path branching portion 10 Metal wiring 21 SiO ₂ film 22 Si ₃ N ₄ film 23, 24 Light reflecting surface 31 Optical fiber 32 Optical fiber guide 33, 43 Module package

[Procedure amendment]

[Submission date] May 12, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0002

[Correction method] Change

[Correction content]

[0002]

2. Description of the Related Art Conventionally, in a multi-chip module in which a system is composed of a plurality of semiconductor chips, it has been proposed to use an optical signal as a part of the signal, such as a clock signal, in order to improve the operation speed of the system. Has been done.
For example, in Japanese Patent Laid-Open No. 4-313269, a light emitting element and a light receiving element are provided in a module, and an optical signal from an issuing element which is issued in synchronization with a clock signal is received by the light receiving element and converted into an electric signal. Supplying to a plurality of semiconductor chips is described. The propagation path of the optical signal here uses the space inside the IC storage box (it is considered that a gas such as air exists), or as shown in FIG. 9 (FIG. 4 (b) of the present application). An optical fiber embedded in a printed circuit board on which a plurality of chips are mounted is used. Another conventional example (Japanese Patent Application No. 5-2 of the same applicant as the present application)
73338) , an optical signal produced outside the multi-chip module is supplied to the module by an optical fiber, and the optical signal is received in the module by utilizing the space provided therein as in the conventional example. And the structure for supplying the light to the light source in the multi-chip module as in the conventional example as shown in FIG. Although the optical signal propagates through the multi-chip module, a portion that easily reflects light and a portion that absorbs light and reduces reflection are provided in order to prevent the waveform from being distorted due to the synthesis of light coming from different propagation paths. Optical signal propagation paths with different structures have been proposed.

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Claims (3)

[Claims] 1. A multi-chip module substrate made of single crystal silicon, an optical waveguide made of a silicon compound formed by embedding at least a part of the substrate in the substrate, and an optical waveguide provided at an end of the optical waveguide. A means for bending light in a direction substantially perpendicular to the substrate surface, a means provided on the way of the optical waveguide for branching light into a plurality of paths parallel to the substrate surface, and a metal wiring provided on the substrate, A plurality of semiconductor pellets having an electronic circuit formed on a surface thereof and connected to a part of the metal wiring via bumps so that the surface faces the optical waveguide, and a light receiving element formed on the surface of the semiconductor pellet. A multi-chip module characterized in that 2. The multi-chip module according to claim 1, wherein the light incident on the optical waveguide is generated from a light emitting element provided on the substrate. 3. The multichip module according to claim 1, wherein the light incident on the optical waveguide is introduced from outside the substrate by an optical waveguide means.