KR800000439B1 - Method of selectively depositing glass on semiconductor devices - Google Patents

Abstract

The method comprises depositing charges of a selected polarity on the areas coated with isulating material of a semiconductor device having areas of "bare" semiconductor and areas coated with insulating material, immersing the charged device in a liquid composition comprising an insulating liquid and dispersed glass particles carrying a charge of particular polarity so that the glass particles may deposite selectively either onthe bare areas of semiconductor or on the areas coated with insulator, and removing the glass-coated device from the liquid compositon, drying and firing the coated device at a temp. enough to fuse th glass.

Description

A method for selectively forming a vitreous layer on a semiconductor device

1 is a partial cross-sectional view of a semiconductor thin film having a plurality of transistors, each separated by a recess,

2, 3 and 4 are cross-sectional views of a series of process steps in which one embodiment of the method of the present invention is applied to a thin plate of the semiconductor device illustrated in FIG.

5-8 are sectional views showing a process in which the method of another embodiment is applied to the thin plate of the semiconductor device illustrated in FIG.

9-12 are cross-sectional views of a process of coating a vitreous coating on another device by an embodiment according to the present invention;

13 is a side view of a suitable charging device used in the method of the present invention,

FIG. 14 is a partial front view of the apparatus illustrated in FIG.

The present invention relates to a method for selectively depositing a glass film on both portions of a semiconductor device having a "bare" portion and a portion coated with an insulating material.

In general, silicon dioxide has been used to inactivate the exposed surface of the silicon semiconductor device, particularly the exposed surface of the PN junction, but in most cases, additional protection has to be provided. Because such additional protection is necessary to protect the device for a long time, for example against water vapor or other contamination, and also to minimize the junction surface leakage current between other conductive regions, such as between the base and collector region of a bipolar transistor. Do.

Additional protection against contamination and reduction of leakage currents may be achieved by covering or sealing the device with a variety of synthetic resins or sheaths, but when covering or sealing with a sheath (which is often necessary before covering with synthetic resin) It is most preferable to form a continuous coating by depositing the superfine powder on the surface of the device by using a suspension in which fine particulate powder is dispersed in a liquid medium, and then heating to a temperature at which the superfine powder is appropriately melted.

The vitreous used to deactivate the semiconductor device is a harmless melting point to the semiconductor device, good adhesion to the surface of the device, a thermal expansion coefficient that matches at least approximately with the thermal expansion coefficient of the semiconductor device, impurities that adversely affect the electrical properties of the low porous device It must have many properties such as not being polluted.

Although there are many methods of deposition of the ultrafine powder, the work is a method of vaporizing a liquid after applying a slurry of the ultrafine powder to a surface of a semiconductor thin film containing a plurality of devices composed of known diffusion methods by applying a doctor blade. Another method is to precipitate attach the superfine powder to the surface of the device in suspension.

The method of applying the skid has several advantages as follows. That is, this usually requires a great deal of manual work, and because only one side of the thin plate can be applied in one process and mechanical grinding operation is involved, many damages to the thin plate and other defects occur. The selectivity obtained by this method also takes advantage of the topographical properties of the surface, ie the covering is limited to the recess.

In addition, the aforementioned sedimentation deposition method is a waste of time and ultrafine powder, and is non-selective.

Another method that has been used conventionally is the electrophoresis method. This method immerses a device with a positive or negative polarity in a suspension of a vitreous powder charged to the opposite polarity and flows a current through the suspension. In this case, the vitreous is selectively deposited only on the conductive portion of the surface of the device. In addition to not selectively attaching the chord to the insulating part, another drawback of this method is that it is not suitable for thickening the coating as a matter of adhesion. Conductive liquids are used to provide selectivity thereon, but they are more likely to be contaminants of the device because they have the property of dissolving more contaminants than non-conductive liquids.

The method according to the invention relates to an improved electrostatic method of selectively depositing a glass coating on both portions of a semiconductor device having a "b" portion and a portion coated with an insulating material. In this method, a specific polarity charge is given to a portion covered with an insulating material, and the charged device is immersed in a suspension of a vitreous powder charged at the same or opposite polarity as that of the insulating material. The vitreous powder is then attached to either the part or the sheath of the device, depending on the choice of polarity. The apparatus is lifted out of the suspension, dried and heated to melt the vitreous powder. According to this, a super thick film having a relatively thick adhesive property is obtained with selectivity.

Although the present invention can be applied to the manufacture of several different kinds of semiconductor devices, a case of forming a plurality of bipolar transistors on a single sheet of single crystal semiconductor will be described in detail with reference to the accompanying drawings. .

As shown in FIG. 1, the unitary thin plate 2 of a semiconductor material such as silicon includes a plurality of transistors 4 formed by a known diffusion method or a combination of an epitaxial growth method and a diffusion method. Each transistor 4 has, for example, an N-type emitter region 6, a P-type base region 8 and an N-type collector region 10. The top face 14 of each transistor is covered with a foil 12 of insulating material. The lower surface 15 of the sheet is covered with another insulating film 13. Emitter region 6 and base region 8 are divided into PN junctions 16. Base region 8 and collector region 10 are isolated by PN junction 18. On the top surface 14 where the devices are arranged, lattice-shaped grooves are formed, which extend to the bottom of the PN junction 18 to form all four layer surfaces of each transistor 4. The exposed portion of the PN junction is preferably covered with a dielectric material to reduce leakage current through the junction and to protect it from ambient or in-process contamination. It is much more economical to perform this treatment while the device is part of the original thin plate 2 than to separate each device 4 from the thin plate and deposit the protective film required for each PN junction.

When a groove is formed by etching to form a mesa-type silicon thin plate, first, SiO ₂ (which is the backing material) covering the thin plate is formed into the shape of the groove using a conventional photolithography method, and the SiO ₂ is masked. Silicon is etched. In order to prevent the substrate from being etched and cut off, when forming a projection plate of Si0 ₂ or depositing porcelain by the method of the present invention, a space may be formed under the projection end, which may cause deterioration of electrical characteristics during subsequent processing. This protruding SiO ₂ is preferably removed before charge is applied and superficial deposition.

Any of at least two methods may be used for this removal. The thin plate may be sufficiently immersed in the oxide etching solution until there is no protrusion. In this case, the thickness of the oxide on the mesa surface is slightly reduced, but there is no problem. For example, after etching for 3 minutes with Transene Corporation's buffered hydrofluoric acid solution, about 25μ of protrusions were completely removed, resulting in a reduction in the SiO ₂ film on the mesa surface by only about 3000Å in the first 12000Å. Another method is to remove the protrusion using ultrasonic energy, 30 seconds in water using a Branson Model 41-4000 Ultrasonic cleaner, and 10 seconds in Freon TF. The protrusions were removed by treatment.

According to one embodiment of the present invention, the portion of the thin plate constituting the " I " silicon exposed in the grooves 20 is covered with a superfine protective film as follows. First, thin plate 2 is placed in a corona discharge device, for example, of two sets of thin vertical parallel metal wires supported by an insulating frame. In this case, care should be taken so that the main surface of the thin plate is parallel to the arrangement of the metal wires. The metal wire is, for example, a tungsten wire having a diameter of about 38 mu and a spacing of about 12.7 mm.

The distance of the parallel array tube is such that when the semiconductor thin plate 2 is placed therebetween, the metal wire is about 5.6 mm from the opposite surface of the thin plate. The distance between the surface to be charged and the metal wire is usually preferable to charge the insulating portion to saturation, but it can be changed to control the charge amount of the thin plate.

In order to obtain satisfactory charging results, it is preferable to use a charging device capable of positioning the top end of the thin plate at precisely equidistant distances to two sets of metal wires of the charging device. This satisfactory charging device is illustrated in FIGS. 13 and 14.

As illustrated in FIG. 13, the charging device 58 has a substrate 60 and a substrate 60 on which two frames 62 and 64 made of an insulating material such as methyl methacrylate resin are placed. Two days are spaced precisely against each other on the substrate 60. Each frame 62,64 has a top plate 74,76 horizontally mounted so that the expectation 66,68, the expectation 66,68 are parallel to the expectation 66,68 at the top of the side plates 70,72 and the side plates 70,72 which are erected at one end. Have Frames 62 and 64 are equipped with arrays of metal wires 78 and 80, respectively.

This arrangement consists of nine metal wires each strained on a vertical plane equidistantly. One end of each metal wire is fixed near one outer edge of the base 66,68, and the bottom end is fixed to one end of the tension spring 86. The other end of the tension spring 86 is attached to the adjustment screw 88. The adjusting screw 88 is attached to the rods 92,94 respectively provided on the members 82,84 of the synthetic resin agent disposed in the longitudinal direction along each outer edge of the plate 74,76.

The metal wires in the array 78,80 bypass the outer edges of the plate 74,76, respectively.

92 and 94 are connected to a high voltage power supply (not shown) on the rod.

When the thin plate 2 is charged, it is held vertically between the metal wire arrays 78 and 80 by the suspending means 96. Suspension means are provided with a pair of horizontal metal tracks 100,102 and a sheet holder 108 (FIG. 14), which are arranged parallel to the upper side of the four pillars 98, the top plate 74, 76, and each inclined inwardly. It is provided.

The thin plate holder 108 serves as a pedestal 110 having a V-shaped cross section and a pair of supporting jaw members 112 and 114 disposed below it. The jaw member 112 has a grooved finger 116 at the bottom, and the jaw member 1l4 has two identical ground protrusions (118, 120). These ground protrusions 116, 118 and 120 are arranged to vertically support the thin plate 2.

The bracket 110 of the cross section has a smooth side which is inclined at an angle formed by the inclined planes 104 and 106 of the manufacture 110 and 102, and is designed to be mounted on the tracks 100 and 102 so as to be in electrical contact therewith. It is preferable that the sheet holder is moved at a speed of about 8 cm per second before and after the charging process so that the sheet is uniformly charged on its surface.

A negative voltage of about 6,200V is applied to the metal wire.

The inside of the charging device is air or nitrogen, but when silicon dioxide is made of an insulating material, the relative humidity is adjusted to about 30% at 25 ° C. It is preferable to increase the charging voltage as much as possible because the cross section of the charge on the thin plate 2 becomes clearer and the charging becomes more uniform. The upper limit of relative humidity is a function of the time from charging to the thin plate surface before immersion in the vitreous suspension. This time is most suitable for 1 second, but if it is very short, the relative humidity is also good because the time for the charge to escape is small. If the insulating material to be charged is made hydrophobic, the relative humidity can be further increased. Indeed, when using Wacocoat SC 180 Photorisist (Philip A. Hunt Chemical Corp.) as the insulating material, the relative humidity can be 65% or higher.

The held thin plate of the thin plate holder is grounded in contact with its edge and is exposed to corona discharge for about 5-15 seconds. As a result, as shown in FIG. 2, the gas ion layer 22 is negatively charged on the insulating film 12 on the top 14 of the apparatus, and the same ion layer 24 is formed on the insulating film 13 on the 15th surface of the thin plate 2.

The sign of the charge depends on whether or not the deposited superparticles are negatively charged or positively charged in the liquid, or whether or not the superfine particles are deposited on the insulating films 12 and 13, or deposited on the "I" silicon. Let's go. In this embodiment, charging by corona discharge is negative.

The gas ions 22 and 24 by corona discharge reach the surface of the thin plate 2 and precipitate and deposit on the insulating films 12 and 13 (FIG. 2). The ions attached to the semiconductor surface are effectively neutralized and do not form surface charges. In the “me” silicon plane of 20, an extremely thin oxide film 26 of about 20 kV is formed soon when exposed to air, but this film 26 is very thin, and thus does not act as an insulating material on gas ions. Therefore, the charging layer is not formed at the bottom. In order to maintain the charge and to prevent the formation of pinholes, the thickness of the oxide should be at least about 1,000 mm 3.

It is preferable that the vitreous powder make a suitable suspension about 1 day before the electrification treatment. Chojaja suitable for inactivating semiconductor devices is No. 1 manufactured by Corning Glass Co., Ltd. 7723 Innotecb Co. (IP 760) and IP 820 (IP 820). Noja No. The approximate composition of 7723 is as follows.

The approximate composition of IP 760 seconds is as follows.

The approximate composition of IP 820 is as follows.

여기서 백분율은 모두 중량백분율이다.

The percentages here are all percentages by weight.

At the time of purchase, Ipizo contains about 75% by weight of particles having a particle size of 12μ or less and about 25% by weight of 3μ or less. The vitreous powder is dispersed in an insulating medium containing a charge agent.

Suitable insulating insulating agents are halogenated hydrocarbons such as Genesolve D (Allied Chemical Co.) or Freon TF (du Pont). These are either 1,1,2-trichloro-1,2,2-tripleethane. Another suitable is Isopar G (Exxon Corp.), which is a mixture of isoparaffinic hydrocarbons, which can be said to be a narrow range of very high purity isoparaffinic hydrocarbons. Genesolve D and Freon Thief are the most suitable media because they are denser, faster in vaporization and nonflammable than isopar. Freon Thi F evaporates very quickly, so it needs to be dried for a few minutes before the sheet is put into the furnace.

The charge agent is a surfactant as shown in the following table.

[table]

Where R is a polybutyl group

In the table, OEL 1200 has the following structural formula and has a weight of 2.10% nitrogen and an alkylation degree of 43.

here

It was found that the ultrasonic stirrer of input 100W for 5 minutes was used to disperse the supernatant when using the IP 820 superparagraph, which is suitable for destroying the coagulation of fine particles.

If this is not done, the adherent grass may become lumpy due to the clot, and in some cases, the grass may be attached where it should not be attached.

The stock solution used in the following example is 1) 100 ml of Freon tea OLOA 1200 in l00g. It melt | dissolves in F. 2) 8 ml of this solution is added to 392 ml of Freon f.

Example 1

In order to deposit 760 seconds of the P.P.I. on the thin plate of the mesa-type power transistor, photoresist is deposited on the surface of the mesa in duplicate to make the frontal body 5 mu.

As described above, it is assumed that the porcelain is deposited in the groove.

7 ml of the stock solution is added to 450 ml of Freon, and 4 g of the vitreous powder is added again and shaken for 2 minutes to form an initial powder suspension. Leave for at least 1 day for stabilization of this.

In performing deposition, the thin plate is negatively charged by corona discharge and then immersed in a Pyrex beaker containing the suspension for 6 seconds. During the vitreous deposition, the contents of the beaker are stirred at moderate speed.

As shown in Fig. 3, the supercapsule 28 is deposited in the defect 20, but is not attached to the insulation coatings 12 and 13. After the vitreous coating, the volatile material (including the photosensitive material) was incinerated at about 525 ° C, and the vitreous was melted again, and the thickness of the coating 28 was about 40 mu.

Example 2

In this embodiment, an IP 820 element is deposited on a thin plate (not illustrated) of a thyristor having a mesa structure. In the thin plate, grooves are formed on both sides thereof to give mesa structures at both ends. About 1.2 micron SiO ₂ is deposited on the mesa.

10 ml of the undiluted solution is added to 400 ml of freon, and 8 g of the vitreous powder is further added, followed by shaking for 2 minutes. After leaving the supernatant suspension for one day, the supernatant deposition was carried out in the same manner as in Example 1 except that the suspension immersion time was 10 seconds. After deposition, the volatiles are evaporated and the porcelain is fused.

The sample produced in this example had an excellent bonding coating with a molten glass layer of about 30 mu. As a result of the electrical test of the collector base junction, a breakdown voltage of 1000 V or more, a leakage current of about 4 μA at room temperature, and about 38 μA at 100 ° C. were obtained.

Example 3

When inactivating a semiconductor device with a vibrator, it is often necessary to select the coefficient of thermal expansion of the vibrator to match that of the semiconductor device. This type of choja contains boron, and the melting temperature may be higher as it affects the doping state of silicon. In such a case, in order to protect the silicon from the doping effect of the vibrator, it is preferable to perform the vitreous coating on the SiO ₂ film without directly applying the silicon on the silicon.

In this embodiment, an SiO ₂ film 30 having a thickness of 8000 kPa is applied only to the grooves 20 of the thin plate 2 (FIG. 5). This can be done using ordinary mask techniques. The thin plate also has an extremely thin oxide film 31 on the upper surface of the mesa (by exposure to air at this time) and an identical oxide film 33 on the lower surface. The coated thin plate is then transferred to dry air (relative humidity 27%). As a result, a positive gas ion layer is formed on the SiO ₂ film 30 in the groove 20 (FIG. 6). There is no charge on the very thin oxide films 31,33.

A mixture of 4.5 ml of the stock solution and 300 ml of freon prepared as the charged agent and the solvent was added thereto, and 9 g of Corning No.7723 supercapital powder was added thereto, followed by shaking for 2 minutes. If the thin plate was immersed in this suspension for 10 seconds, 34 of the superfine powder was produced only at the 30th position of the SiO ₂ film (Fig. 7).

The thin plate is lifted out of the suspension to dissipate the remaining volatiles and fusion is carried out to form a coating 34 (Fig. 8). The thickness of this fusion film is about 35 mu.

Example 4

In this embodiment, in order to reduce the breakdown voltage of the diode, a supercapsule is formed in the groove of the mesa type thin plate. As shown in FIG. 9, the silicon diode thin plate 36 has a P-type lower layer 38 and an N-type upper layer 40 isolated by a PN junction 41. The thin plate 36 is provided with a grid-shaped groove 43, but the groove 43 reaches the P-type layer 38.

As in Example 3, the silicon in the grooves is coated with a SiO ₂ relatively thick film 42, and the thin plate is formed on the surface of SiO ₂ with respect to the positive corona discharge. An extremely thin oxide film 48 is formed on the upper surface of the mesa 46, and an extremely thin oxide film 52 is formed on the lower surface of the thin plate 50, but these thin plates do not act as a charge storage layer. 10 ml of the solvent and the charged solution are added to 400 ml of Freon, and 6 g of 760 S. powder is shaken for 2 minutes and shaken for 2 minutes to prepare the suspension.

After stirring the suspension and immersing the charging thin plate therein for 6 seconds, the supernatant powder layer 44 is attached only to the surface of the thick film 42 of SiO ₂ .

The volatiles are evaporated and the vitreous melts to form layer 44 (FIG. 10). By repeating the charging process and the supercapsulation process, a second supercapsulation film 54 was formed on the first supercapsulation film 44 (FIG. 1L), and when the second film was melted, the second layer was a composite superlayer 56 (FIG. 12). ). In the vitreous suspension used for the deposition of the second vitreous coating, the vitreous powder exerts a charge opposite to the charge on the first coating.

In this diode, a breakdown voltage of 1700 V was observed at room temperature.

Dry nitrogen and dry air are used as the ambient air for corona discharge. However, nitrogen is more preferable because ozone generation by corona discharge is much less and higher voltage can be used without causing arc discharge. The amount of charge applied to the liquid solution needs to be sufficient for any of the particles of the same charge to carry the same sign even when the thickest supercapsule is needed. If this optimum amount is exceeded, excess ions are generated, which neutralizes the charge on the insulating region of the thin plate, thereby reducing the amount of supernatant that can be deposited. However, the amount of charge agent can be used to change the thickness of the supercapsule.

When deciding how much charge should be used, make a suitable vitreous suspension, add a small amount of charge, and soak the plate with the charged pattern in the suspension. If the amount of the charge agent is too small, the vitreous is attached to both the charged and non-charged regions. There, a separate vitreous suspension is taken, and a little amount of charge is added to it, and the thin plate having the charging pattern is immersed again to see the result.

In this way, the charging agent is gradually added to the new suspension and added until the supernatant is allowed to adhere only to the charged or non-charged region by the charge code.

Once a suitable amount of chargeant is found for adding a predetermined amount of choza in Freon, the amount of the whole charge when the amount of choza is changed is determined by proportional irradiation.

In the above example, silicon dioxide and a photosensitive material are mentioned as materials suitable for the insulating coating, but other insulating materials usually used for semiconductor devices such as silicon nitride can also be used. If the insulating material is organic (as in Example 1), it must be removed before fusion of the vitreous powder.

This method can also be used in the case of performing ultra-fine deposition on both sides of the insulating material covering region (the insulating material is an inorganic material) on the one side of the thin plate of conductor and the "I" semiconductor region on the other side. This can be done by applying an opposite polarity charge to the covering region with the insulating material on the other side and immersing the thin plate in the supernatant suspension.

Claims (1)

As described in the text and illustrated in the drawings, in a semiconductor device having a "b" portion and a portion coated with an insulating material, a charge of a characteristic polarity is given on the insulating material, and the charged device is specified in an insulating medium. Submerged in the liquid composition by dispersing the polarized charged powder, the powder is selectively deposited on either the exposed surface of the semiconductor or the coated surface of the insulating material, and the device is removed from the liquid composition and dried. And selectively forming a vitreous layer on both portions of the semiconductor device having both portions, wherein the vitreous is heated to a temperature sufficient to melt.

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