JPS62188342A - Direct printing of fire-resistant wire for integrated circuit device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for writing micron-sized refractory metal lines directly onto a silicon surface at speeds of several centimeters per second. More specifically, the present invention relates to laser-induced chemical vapor deposition (laser-induced chemical vapor deposition).
The present invention relates to a method for depositing tungsten on silicon surfaces by CVD. The method of the present invention is particularly useful for forming conductive interconnect lines in integrated circuits after a fabrication process.

In the manufacture of large-scale integrated circuits and very large-scale integrated circuits, it may be desirable to be able to make arbitrary electrical connections between various portions of a substrate.

There are several reasons why such operation is desirable. For example, in the case of gate arrays, customization (i.e., creating products to individual specifications) is commonly achieved by cutting interconnect lines. This cutting can be done using a focused laser beam or by passing a sufficiently large current through the fusing wire. However, it would also be desirable to be able to perform customization such as gate arrays by forming conductive lines rather than making such cuts. In addition, yield problems may arise in the manufacture of liquid crystal displays, particularly large-sized and/or matrix φ addressing type liquid crystal displays. A defect that often occurs in such devices is an open circuit (disconnection) in a gate line or data line. In such cases, all lines of the display may cease to function. More generally, disconnections are particularly likely to occur when there is a step, such as when a conductive line crosses over another line.

Therefore, it would be highly desirable to optionally form conductive interconnect lines that bridge broken or degraded sections. Furthermore, very large scale integrated circuits (VL
SI) In the manufacture of chips = 4 - it cannot be said that the yield is always as high as desired.

Some of the defects that occur during such processing can be eliminated by optionally adding connecting wires of micron dimensions to correct the defects found (particularly break defects). In summary, the desire to install optional interconnect lines in very large scale integrated circuit and packaging applications has led to increased interest in directly writing metal structures using means such as laser beams. Other uses of such technology include correction of wafer and mask defects, yield enhancement, localized masking and coating, and custom circuit fabrication.

It has been reported that polycrystalline silicon structures of submicron dimensions are formed by pyrolysis using 5iC1a vapor and hydrogen gas in conjunction with an argon laser.

Regarding this, please refer to “Applied Physics Letters”.
), Vol. 44, p. 267 (1984). In another line of research, a thermal chemical vapor deposition method has been used to form tungsten films by using hydrogen based on the following reduction reaction.

wp6+3112 →W+611P
(1) Tungsten hexafluoride (W) in the presence of hydrogen
The reduction mechanism of F2) has been extensively studied. In this regard, see the Journal of the Electrochemical Society.
hcmteal 5ociety) 'J, 114th
Volume 701 (1967), J.F. Berkeley, A. Brenner, and W. E.
er & W. E. Reed). In addition, [Journal of' Electrochemical Society
chemical 5ociety) J, No. 125
See also the article by W.A. Bryant, Vol. 1534 (1978). In these studies, hydrogen is used as the gas for reducing tungsten hexafluoride.

However, when writing lines of refractory metal directly onto silicon surfaces by the use of lasers, the use of hydrogen as a reducing atmosphere has several disadvantages. For example, resolution may be limited at high writing speeds because the reaction mechanism involves gas phase reactions. Although the exact basis for all the reaction phenomena that occur during this type of hydrogen reduction reaction is not well understood, it is generally believed that the limiting factor in resolution is the involvement of hydrogen in the reaction. Moreover, the surface topography of metal lines formed when hydrogen reduction reactions are used in conjunction with lasers is typically not as smooth as that obtained when surface reduction reactions alone are used.

SUMMARY OF THE INVENTION The method of the present invention for depositing a refractory metal on a silicon surface is described in accordance with a preferred embodiment in which the silicon surface is placed in an atmosphere containing a gaseous refractory metal compound, such as tungsten hexafluoride. Ru. In such an atmosphere, the silicon surface is heated by a focused beam of electromagnetic radiation, such as a laser beam. Such heating is performed along a defined path to heat the silicon surface to a temperature sufficient to initiate a surface reduction reaction of the refractory metal compound. As a result, the refractory metal is reduced and deposited replacing a portion of the silicon surface. In accordance with a preferred embodiment of the invention, the use of an argon laser with a power of about 50 milliwatts and a focused spot size of about 20 microns (full width at a value equal to 1/2 of the maximum) allows Smooth tungsten lines having a length of approximately 2 to 15 microns in width are deposited on the silicon surface. It should be noted that the method of the invention can be carried out on surfaces consisting of crystalline silicon, polycrystalline silicon or amorphous silicon. The process according to the invention is preferably carried out in a reaction chamber containing tungsten hexafluoride having a partial pressure of 1 to 100 Torr and an argon buffer gas having a partial pressure of about 1 atmosphere. The refractory metal layer formed typically has a thickness of about 100 to 1000
It has a thickness of angstroms. In the method of the invention, the silicon surface itself acts as a reducing agent for the metal-containing gas. For example, when using tungsten hexafluoride, the following chemical reaction occurs.

2WFa + 881 → 2W + 3SiP4 (2
) In laser beam-induced chemical vapor deposition, the reaction typically occurs over a short period of time, from a few seconds to a few milliseconds, which is controlled by the scanning speed of the beam in the laser and the spot size. Additionally, deposition conditions can be adjusted by varying laser power, scanning speed, and gas pressure.

One of the objects of the invention is to provide a method for writing refractory metal lines directly onto a silicon surface.

It is also an object of the present invention to provide a method for optionally and custom forming metal interconnect lines on electrical circuit chips.

It is a further object of the present invention to provide a method for improving yield in various semiconductor manufacturing processes, including the manufacture of very large scale integrated circuit chips and liquid crystal displays.

It is also an object of the present invention to provide a method of forming interconnects useful in electronic circuit packaging applications.

Furthermore, it is an object of the present invention to provide a method for correcting a semiconductor chip mask.

Furthermore, it is another object of the present invention to provide a means for correcting defects in wafers and chip masks, thereby improving the yield of semiconductor manufacturing processes.

Although the gist of the present invention is specifically set forth in the claims, the structure and method of carrying out the present invention as well as additional objects and advantages can be best understood by reading the following description with reference to the accompanying drawings. It will be well understood.

DETAILED DESCRIPTION OF THE INVENTION There are two basic approaches to fabricating electronic materials and devices using laser-induced microchemical reactions: One is a deposition method based on directly induced pyrolytic or photolytic reactions, and the second is a deposition method based on changing the surface conditions by means of laser radiation. methods of promoting or suppressing film formation by altering the catalytic reaction or nucleation barrier. In a preferred embodiment of the present invention, a reduction reaction of tungsten hexafluoride by a silicon surface is used; - Induced by localized heating using a laser beam, the spot size of such a laser beam typically having a width of about 10 to 20 microns, since such pyrolysis reactions are strongly dependent on local temperature. , the reaction rate is strongly influenced by nonlinear temperature conditions such as those caused by a focused laser beam. For example, if the temperature distribution induced by the incident beam is Gaussian, the width of the line actually formed is It can be seen that the width is significantly smaller than the width itself.For example, the temperature distribution induced by a beam exhibiting a Gaussian distribution can be expressed by:

1 (r) −1(, exp(−0,5r2/ro 2
) (3) where r□ is the characteristic width of the beam. This highly nonlinear distribution of temperature and temperature dependence of reaction rate results in linewidths significantly less than 10 microns.

Another interesting property found in microchemical processes, such as those induced by micron-sized heat sources, is the increased reactant flux obtained. The reaction rate of a heterogeneous reaction at a gas-solid interface is generally limited by the diffusion of reactants and/or products or the reaction rate at the solid surface. The flux of reactants flowing into the reaction zone under high pressure increases as the dimensions of the reaction zone are reduced to small values compared to the gas diffusion length. In contrast, for extensively heated surfaces, the flux of reactants under high pressure is typically limited by gas phase diffusion.

Geometrical considerations indicate that the net reaction rate in microchemistry induced by a focused laser beam is several orders of magnitude higher than that observed when diffusion is limited, such as in furnace heating. It can be early. For example, for a focused beam of 10 microns in diameter exhibiting a Gaussian distribution, I x 10'' under a pressure of 100 Torr.
A reactant flux of cm' 9 sec-' is obtained. However, for a 1 mm diameter beam exhibiting a Gaussian distribution, the reactant flux is 1 x 1019 cITl-2 5e
It decreases to C-1D. It can therefore be seen that the method of the present invention can achieve rapid line writing speeds on the order of a few centimeters per second. These parameters are important when considering the throughput of the production line.

Hereinafter, one embodiment of the present invention will be described with reference to FIGS. 1A to 1E. First, FIG. 1A shows conductive elements 11 and 12, such as metal islands or strips, to be connected by refractory metal conductors or wires. Such electrically conductive elements 11 and 12 typically
0 as part of a metal pattern formed on an integrated circuit chip or similar device.

Although conductive elements 11 and 12 are illustrated as being in the same plane, for purposes of the present invention, the methods described herein are not limited to such a situation. It is important to understand that. According to one embodiment of the invention, a silicon layer 15 is placed over the structure shown in FIG. 1A. Such a silicon layer 1
5 can be made of crystalline silicon, polycrystalline silicon or amorphous silicon. However, silicon layer 15 typically comprises amorphous or polycrystalline silicon rather than crystalline silicon because lower processing temperatures are generally desirable. This is because crystalline silicon typically requires processing at higher temperatures.

Referring now to FIG. 1C, one embodiment of the method of the present invention will be described in which a focused laser beam 18 is moved between points A and B as shown.

As a result, silicon layer 15 is subjected to localized heating induced by the laser beam.

As a result of the heating in an atmosphere of a reactive gaseous refractory metal compound, the heated silicon in silicon layer 15 reacts according to equation (2) above. laser·
A portion of the silicon layer along the path of the beam is converted to tungsten, and at the same time gaseous silicon tetrafluoride is produced.

It should also be understood that molybdenum hexafluoride can be similarly used to deposit molybdenum.

FIG. 1C also shows material 1 to the left of laser beam 18.
It is also shown that material to the right of laser beam 18 (and to the left of point B) has not yet been processed, although 6 has already been converted according to the invention.

The following Figure 1D shows the state of the substrate at the end of the laser writing process. The unconverted amorphous silicon can then be removed, for example, by etching in a KOH solution.

The resulting structure is shown in Figure 1E.

In one embodiment of the present invention, approximately 5 Watts of tungsten hexafluoride is applied in a reaction chamber containing tungsten hexafluoride having a partial pressure of 50 Torr and an inert argon buffer gas having a partial pressure of approximately 1 atmosphere. By scanning a crystalline silicon surface with a focused argon laser beam with a power output and a spot size of about 20 microns, fine tungsten lines with a minimum linewidth of 1 micron are formed at a speed of several centimeters per second. Ta. The resistivity of the tungsten wire formed was less than 1 milliohm-cm.

In another embodiment of the method of the present invention, a nonwoven fabric is placed on a silicon dioxide substrate in a reaction chamber containing tungsten hexafluoride having a partial pressure of 50 Torr and argon gas having a partial pressure of 1 atmosphere. Approximately 1 on the crystalline silicon layer
A tungsten film with a thickness of 0.00 nanometers or more was formed. Note that any of a CW laser, a YAG laser, and a pulsed frequency-multiplied YAG laser can be used.

-16 In the present invention, the silicon surface is approximately 350 to 550
It should be noted that heating to a temperature of 0.degree. C. is generally desirable. It should also be noted that excessively high temperatures should be avoided as they tend to form tungsten silicide. Furthermore, while it is preferred to use a laser beam to provide localized heating, it should be understood that other sources of focusable radiant energy may also be used. Furthermore, it should be understood that even faster scanning speeds are possible in accordance with the method of the present invention.

As can be seen from the above description, according to the method of the present invention, micron-sized lines of refractory metal can be written directly onto a silicon surface at relatively high speeds. It will also be appreciated that the present invention provides high resolution and creates narrow lines by exploiting the non-linear temperature dependence of chemical reaction rates. Furthermore, it will be appreciated that the method of the present invention provides a means for writing thin lines of moderate electrical resistivity without contamination by various impurities. According to the present invention, conductive lines □ can also be formed even when it is necessary to traverse locations with different heights in an integrated circuit.

In summary, the method of the invention achieves all of the above objectives.

Although the present invention has been described in detail in connection with specific preferred embodiments, it will be obvious to those skilled in the art that various modifications and changes may be made thereto. Therefore, the scope of the claims is:
It is to be understood that the invention is intended to cover all such variations and modifications as do not depart from the spirit and scope of the invention.

[Brief explanation of drawings]

FIG. 1A is a cross-sectional view of a substrate with a pair of metal structures to be electrically connected by a conductive material according to the method of the present invention, and FIG. 1B is a cross-sectional view of a substrate with a polycrystalline silicon layer or an amorphous silicon layer added. FIG. 1C is a cross-sectional view of the substrate of FIG. 1A, FIG. 1D is a cross-sectional view of the substrate of FIG. 1C after the focused beam has traveled the desired writing distance, and FIG. 1E is a cross-sectional view of the substrate of FIG. 1D is a cross-sectional view of the substrate of FIG. 1D showing the resulting structure; FIG. In the figure, 10 is a substrate, 11 and 12 are metal conductive elements, 15 is a silicon layer, 16 is a refractory metal wire, and 18
represents a focused beam of electromagnetic radiation.

Claims (1)

Claims: 1. A method for depositing a refractory metal on a silicon surface, comprising: (a) placing the silicon surface in an atmosphere of at least one gaseous refractory metal compound that can be reduced by silicon, and then (b) ) heating the silicon surface in the atmosphere along a defined path with a focused beam of electromagnetic radiation to a temperature sufficient to initiate surface reduction of the refractory metal compound, thereby reducing the refractory metal; A method comprising the step of depositing silicon to replace at least a portion of silicon in the silicon surface. 2. The method of claim 1, wherein the silicon surface is made of a material selected from crystalline silicon, polycrystalline silicon and amorphous silicon. 3. The method of claim 1, wherein said heating step is carried out by a focused laser beam. 4. The method of claim 3, wherein the laser beam is generated by a YAG laser. 5. The method of claim 3, wherein the laser beam is focused to a spot about 20 microns in diameter. 6. The method of claim 1, wherein said gaseous refractory metal compound is selected from the group consisting of tungsten hexafluoride and molybdenum hexafluoride. 7. The method of claim 1, wherein said gaseous refractory metal compound is present at a partial pressure of about 1 to 100 torr. 8. The method of claim 7, wherein said gaseous refractory metal compound is present at a partial pressure of about 100 Torr. 9. The method of claim 1, wherein the silicon surface is heated to a temperature of about 350-550°C. 10. The method of claim 1, wherein said temperature is insufficient to initiate refractory metal silicide formation. 11. The method of claim 1, wherein the atmosphere surrounding the silicon surface contains an inert buffer gas. 12. The method of claim 11, wherein said buffer gas comprises argon. 13. The method of claim 12, wherein said argon is present at a partial pressure of about 1 atmosphere. 14. In a method for electrically connecting electrical conductors arranged on a substrate, (a) a silicon layer is arranged to cover the substrate and the conductor to form a silicon surface; (b) already covered. (c) disposing the silicon surface in the atmosphere by a focused beam of electromagnetic radiation along a defined path between the conductors; A method comprising the step of heating the refractory metal compound to a temperature sufficient to initiate surface reduction, thereby forming a conductive path of the refractory metal between the conductors. 15. The method according to claim 14, further comprising the step of removing unreacted silicon from the silicon layer.