JP2002544667A - Method of cleaning silicon substrate surface and use for producing integrated electronic components - Google Patents

Abstract

(57) [Problem] To provide a planarized silicon surface which is completely free from contamination and has no unevenness. SOLUTION: After polishing, a low-energy, moderately charged positive ion stream of a predetermined density is generated, and this ion stream is directed to the surface of a silicon substrate, and the kinetic energy of the ions is reduced. By controlling the speed to be substantially zero at a predetermined distance from the surface, the cleaning is performed under vacuum to create a sufficiently large repulsion within the contamination and defects to be present at the substrate surface. A method for cleaning a surface of a single-crystal silicon substrate having 100 orientations for integrated electronic components, comprising obtaining a precisely flat surface by releasing only contamination and eliminating spot crystal defects.

Description

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a method for cleaning a silicon substrate surface, and the method can be applied to the manufacture of integrated electronic components. The present invention relates to the field of microelectronics on silicon substrates, and more particularly to the manufacture of integrated circuits and memories at very high integration densities. It applies to integrated electronic components in such circuits, such as diodes or transistors, or to very high integration density memories.

[0002] Single crystal silicon is widely used in the field of microelectronics.
It is available in the form of wafers cut from silicon bars. Typically, the cut is made on a crystallographic plane with 100 orientations, ie, perpendicular to the vector with coordinates 1; 0; 1, and the wafer is said to be in 100 orientations. After being cut, the substrate is polished and then cleaned. The cleaning step is to remove contaminants present on the substrate surface prior to performing various processes for manufacturing the integrated circuit.

[0003] In general, such contamination is caused by dielectric materials such as silicon oxide, silicon monoxide, organic residues from cleaning solutions or various silicon-based SiX compounds (X is a group such as nitrogen, carbon, etc.). Become. The silicon surface also has a flatness in its structure,
There may also be spot defects, such as two dimers, that impair "planarity", that is, "dimers", i.e., two silicon atoms that are strongly bonded to each other but not so strongly bonded to the crystal lattice. Conventionally, the cleaning method used is an RCA type chemical etching method (where RCA is the name of the company that developed this method). It consists of immersion in a hydrofluoric acid bath and washing with deionized water.

[0004] These methods are relatively selective, but also have some disadvantages:-etching of the silicon surface considerably increases the roughness;-strong acids such as hydrofluoric acid, ie The use of highly toxic acids requires cumbersome and expensive measures:-organic residues may be present due to the washing solution used; and-the reaction in aqueous media is precisely reproducible Cannot always be guaranteed, and drying is always difficult.

It is an object of the present invention to obtain a silicon surface that is completely free of contamination. Another object is to form a planarized silicon surface without any irregularities. To achieve these objectives, the present invention is directed to a specific remote interaction between moderately charged ions and a 100-oriented silicon surface to be cleaned, wherein the ions enter the surface without penetrating the surface. It is proposed to remove any existing contamination, such as dielectric material, and to remove dimer-type crystal defects. Remote selective interaction with the dielectric material allows the surface quality to remain intact, since the ions do not act or penetrate the single crystal surface.

A method utilizing remote argon ion interaction is described in French patent application FR 9
No. 6/16288. This method is fundamentally different from the above problem because it is intended to open hydrogen bonds on the surface of the substrate in order to form a saturated SiO ₂ layer on a previously hydrogenated silicon substrate. It is intended to solve the problem. It utilizes highly charged argon ions (Ar ¹⁷⁺ or Ar ¹⁸⁺ ) and a silicon surface with 111 orientation. When applied to the cleaning of a 100 silicon substrate, such a method would damage the silicon surface. Such highly charged ions create an electrostatic image around the silicon agglomerates, weakening such interaggregate bonds and removing them, as the Si-H bonds in the 100 plane are less likely to be cleaved than the 111 plane. And thereby form a crater by the "Coulomb" burst effect.

[0007] In contrast, the present invention aims to provide a completely cleaned and planarized surface. More specifically, the present invention provides, after polishing, a low-energy, moderately-charged, moderately-charged positive ion stream of predetermined density, and directing this ion stream to the surface of the silicon substrate, and By controlling the kinetic energy such that the velocity of the ions is substantially zero at a given distance from the surface, the cleaning is performed under vacuum to create a sufficient repulsion within the contamination and defects. Cleaning the surface of a single-crystal silicon substrate with 100 orientations for integrated electronic components, consisting of releasing only the contamination present on the substrate surface and eliminating spot crystal defects to obtain a precisely flat surface. Provide a method of conversion.

According to preferred features: the ion generation controls the density (number of ions per unit area and unit time) by applying an extraction voltage and the direction by magnetic sorting as a function of the mass / charge ratio The ions are selected in terms of velocity and direction by filtering, i.e. by band or high-pass field filtering and collimation, for example, by a series of diaphragms; The applied ions are slowed down by application; the ions produced are rare gas ions with a uniform charge, such as argon ions, in particular Ar ^{8+ to} Ar ¹²⁺ , neon or krypton ions; 1 square centimeter, 10 ⁸ ions per second (ion
s / cm ² . s) to 10 ¹⁵ ions / cm ² . s.

[0009] The method of the present invention has the advantage of being "planarized" insofar as contamination can be selectively removed without damaging the silicon. Once the contamination is removed, the subsequent continuous supply of ions will extract free electrons from the silicon bulk. Thus, the cleaned surface area, i.e., the area having no contamination, does not accumulate any charge that is commensurate with the ions, and the process of extracting material never begins. Similarly, this method planarizes in terms of eliminating crystal defects. Moreover, for the reasons mentioned in the above paragraph, the method is self-stopping as soon as all contamination or all surface defects are eliminated, the ion-matter interaction ceases. In a specific application, the method of the present invention allows for the formation of SiO ₂ thin film layers that can be used as diffusion barriers for integrated electronic components such as transistors and diodes.

As an example, a metal-oxide-semiconductor (MOS) transistor takes the form of a single crystal silicon substrate. Silicon has two electrodes, two heavily n ⁺ doped regions that make up the source and drain. The thickness of these regions is about 1 micrometer (μm) to 3 μm. Between these electrodes,
On the substrate is a grid formed on a 100-oriented silicon wafer.
The bottom of the grid in contact with the substrate is formed of a layer of a high melting point metal oxide such as titanium or tantalum which forms the grid oxide. Grid oxides are typically made by cathode sputtering or ion beam deposition (IBD). Because the oxide has a high dielectric constant, it is possible to increase the thickness of the insulator to avoid the formation of "pinholes" that cause short circuits that can destroy the transistor.

In such components, a major problem appears when using an oxide of a high melting point metal. Once deposited on the substrate, these oxides form alloys with the monocrystalline silicon over time, forming the corresponding refractory metal silicide. This silicide formed directly under the grid is very detrimental to component performance. By forming a precisely flat SiO ₂ thin film layer directly below the refractory metal oxide, there is no path for leakage of a substance that easily forms harmful silicide due to oxide / silicon interaction. An effective barrier against diffusion is provided.

In order to form such a silicon oxide layer, the present invention provides a method as described above, followed by a remote interaction step under vacuum between the oxide ion stream and the silicon substrate surface (the kinetic energy of the ions is The speed is a predetermined distance from the surface, for example 1
(Controlled to be substantially zero at a distance of 0 Angstroms (Å) to 20Å), it is proposed to prepare a silicon substrate containing the refractory metal oxide. In specific embodiment conditions, the oxidizing ions are selected, directed, moderated O ⁺ ions, and the silicon substrate is below 500 ° C., preferably 200 ° C.
It is maintained at a temperature in the range of from 500C to 500C. In another embodiment, the cleaning step using the method described above is followed by a step of passivating the surface by hydrogenation using a hydrofluoric acid and ammonium ion bath. The resulting passivation is of the type developed by Bell Telephone Inc. using known methods.

[0013] Following the hydrogenation step, a remote interaction with moderately charged ions under vacuum is performed to cleave the Si-H bond, followed by an oxidation step of filling the cleaved bond with oxygen gas. Ion selected under vacuum, preferably, a medium charged argon ions, for example, in the range of Ar ⁴⁺ to Ar ⁸⁺ showed a uniform charge, oxidation, a controlled oxygen gas under pressure It is done by introducing. According to another preferred feature, the temperature of the silicon substrate is maintained in the range of 200 ° C. to 500 ° C. and other moderately charged noble gases (neon, krypton, xenon, etc.) can be used. The silicon substrate is kept under vacuum to deposit the high melting point oxide. Other features and advantages of the present invention will become apparent from the following detailed description of non-limiting embodiments, taken in conjunction with the accompanying drawings.

Before performing the cleaning according to the present invention, a silicon substrate having a 100-plane orientation is first etched to roughly remove a natural oxide formed on the surface. The substrate is then placed in a reaction chamber under a high vacuum of about 10 ⁻¹¹ mbar (mbar) to 10 ⁻¹³ mbar generated by conventional pumping means such as ultra-vacuum pumping means. The reaction chamber is housed in a generator that produces a stream of ^{Ar12 +} argon ions from an ion source, such as an electron cyclotron resonance (ECR) type ion source. The ion source has a low kinetic energy of several kiloelectron volts per charge (keV / q, q is the number of charges per ion), typically in the range of 1 keV / q to 20 keV / q, in this embodiment 10 keV / q. To produce an ion having The ion source is tuned in this case by applying an extraction voltage equal to 10 kilovolts (kV). The direction of the ions is controlled by a sorting magnet except for ions having a lateral velocity component larger than a predetermined value.

Means for selecting both speed and direction are also provided in the ion path between the ion source and the silicon substrate for processing. These means are filter means and consist of a combination of the following: a band or high-pass field filter known to those skilled in the art for selecting ions as a function of the kinetic energy of the ions, about 10 keV / q. Ions with equal kinetic energy are selected in this embodiment; and-Flow collimator means in the form of a series of diaphragms having a diameter of about millimeters.

Another function of the selection means is to direct ions towards the silicon substrate. The deceleration field slows the ions as they approach the silicon substrate so that their velocities approach or equal zero. This electric field is applied by a plain capacitor combined with a potentiometer. This application is controlled by a deceleration voltage that helps provide each ion energy ranging from a few electron volts (eV) to zero. The magnitude of the deceleration voltage is equal to 10 kV in this embodiment, but determines the approach distance of the ions and the size of the interaction area between the argon ions and the contamination present on the silicon substrate surface.

In FIG. 1, this contamination is shown in the form of small pieces of organic substance 11 composed of SiO ₂ layer 10 and SiC, partially covering surface 21 of single crystal silicon substrate 20. As the ^{Ar12 +} ions 30 approach the layer 10, the valence bonds in the region 12 of this layer facing the ions 30 are weakened. At the same time, the ions induce an electrostatic image in this area. The induced charge is negative, creating a repulsion greater than the cohesive force of the material: the positive cohesive material 13 is thus released, but the dielectric material remains on the surface. The magnitude of the repulsive force depends on the characteristics of the ion flow, and in particular, 10 ⁸ ions / cm ² . s ~
10 ¹⁵ ions / cm ² . It depends on the charge density, which can be in the range of s.

In embodiments: the ion beam exhibits a current of 120 microamps (μA) and 1 cm ²
The density of the incident ions is 6 × 10 ¹³ ions / cm ² . -set temperature equal to 300 ° C. Similarly, agglomerated material 14 is released from organic material 11 when argon ions 30 approach this type of contamination.

On the other hand, when the ions 30 approach a non-contaminated area of the silicon surface 21 such as the area 21 a, the ions extract electrons 31 that have been extracted from deep in the silicon substrate 20, otherwise. Avoid the presence of charges that might pull aggregated silicon from the substrate surface. Thus, as long as contamination is present on the silicon substrate surface, the charged ions will release the contamination, but the elimination of the substance will end as soon as the contamination is eliminated, so this process is in fact self-terminating.

The positively charged and released agglomerates are attracted to the electrostatic screen. By measuring the charge on the screen, it is possible to detect when the effect of the ions has stopped because the charge has become constant, that is, when the cleaning has been completed. The method also planarizes both in that contamination is eliminated from the surface and in that it makes it possible to eliminate dimer-type defects in the crystal lattice surface as shown in FIG. . In this figure, the dimer 40 is in the form of two bonded silicon atoms 41 and 42.

Each atom of the dimer also binds to two other silicon atoms, respectively, 51 and 53 and 52 and 54, with these four atoms located at successive vertices of the rectangle. The bond between each atom of the dimer and the rectangular atom forms a triangle toward the center of the rectangle, and the dimers 41-42 overlap the plane P where the four atoms 51-54 are located. This constitutes a detachment of the crystal lattice from the 100 plane, indicating an irregular surface. This means that it is not as flat as it could be. Since each atom of such a dimer bonds only to three atoms, the dimer exhibits structural instability. Thus, atoms 41 and 42 are open bond bonds extending away from the set of bonds between the dimer and the atoms 51 and 54 of the crystal lattice.
) To form hanging bonds 61 and 62. As the argon ions 30 approach the dimer, the bond with the crystal lattice weakens and cleaves: dimers 41-42 are then released from the 100 crystal face of the silicon substrate.

[0022] Any crystal defects of this type, trimer, or other irregular conformation that may include atoms other than silicon (eg, O and X) necessarily result in weaker bonds than the rest of the crystal plane. Cause and thus constitute spot crystal defects, which are also eliminated by remote ionic interactions. A specific application of the method of the invention is to obtain a precisely flat SiO ₂ thin film layer on a silicon substrate for integrated electronic components. This SiO ₂ layer can be used in particular as a barrier against the diffusion of the refractory metal oxide. To make such a silicon oxide layer, the surface of the silicon substrate must first be EC
It is carefully prepared in a cleaning step using the method described above in a reaction chamber housed in an R generator.

In one oxidation example, the surface is then subjected to a remote interaction between an oxidizing ion stream, specifically an O ⁺ ion stream, and the silicon substrate surface under vacuum. The argon gas is thus replaced by oxygen gas in the reaction chamber and the parameters of the reaction chamber configuration are reset to appropriate values by a person skilled in the art:-the argon valve is closed and the oxygen valve is opened; Adjusting the magnetic field of the ion selection magnet, which selects the ions as a function of their mass / charge ratio,
Adjust by setting the applied voltage;-Adjust the diaphragm opening;-Do not change the draw voltage and deceleration voltage.

O ⁺ ions are sorted at a rate by magnetic filtering using a reflection filter and directed towards the silicon substrate. After that, the ions are about 10Å to 20２０.
Decelerate by applying a deceleration voltage such that its velocity is equal to or near zero at a predetermined distance from the surface equal to Å. The silicon substrate is kept at a temperature lower than 500 ° C. In this embodiment, it is equal to 300 ° C. The rate at which SiO ₂ grows tends to asymptotically go to zero. This makes the control of the oxide thickness easier. In another example of oxidation, the cleaning step is followed by a step of passivating the surface by hydrogenation using a hydrofluoric acid and ammonium ion bath. The resulting passivation is of the type developed by Bell Telephone Inc. using known methods.

The silicon surface is covered with a single layer of hydrogen atoms forming a Si—H bond with the silicon surface. In a reaction chamber under a high vacuum of 10 ⁻⁹ Pa to ^{10 −10} Pa, these bonds form a mutual interaction with moderately charged argon ions Ar ^{4+ to} Ar ⁸⁺ , in this example specifically Ar ^8+. It is cleaved by action and filled by the supply of oxygen gas. Remote interaction with argon ions is performed in a manner similar to that described above for the cleaning process. Oxidation is performed in this embodiment by introducing oxygen gas at a controlled pressure of about 10 ^-6 Torr. However, in order to promote cleavage of the Si—H bond and promote oxidation, the silicon substrate is heated to a temperature in the range of 200 ° C. to 500 ° C., specifically, 300 ° C. in this embodiment.
To maintain.

During the previous step, the thickness of the oxide layer is predetermined and uniform since the oxide layer is formed on the dangling bonds of a monolayer of hydrogen formed on a very flat surface. Then, this embodiment self-stops. The substrate is transported to another reaction chamber, while still under vacuum, to deposit an overlying layer of refractory oxide on a silicon substrate while providing the oxide in accordance with one or the other embodiments described above. It is. In this chamber the substrate is subjected to such deposition.

The invention is not limited to the embodiments described and illustrated. For example, the first
In one embodiment, other types of oxide ions, such as water vapor-derived ions, may be used in the second embodiment, and other moderately charged ions, such as oxidation temperatures (up to 500 ° C. for the least charged ions). ), Ions of a rare gas (neon, krypton, etc.) can be used. Further, oxygen gas may be present in the reaction chamber from the beginning of ion generation or as soon as the first ions approach the surface of the silicon.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing how unnecessary substances are extracted from a single crystal silicon substrate by applying a method of the present invention.

FIG. 2 is a perspective view of a dimer-type surface defect in a crystal lattice.

──────────────────────────────────────────────────続 き Continuation of front page (81) Designated country EP (AT, BE, CH, CY, DE, DK, ES, FI, FR, GB, GR, IE, IT, LU, MC, NL, PT, SE ), OA (BF, BJ, CF, CG, CI, CM, GA, GN, GW, ML, MR, NE, SN, TD, TG), AP (GH, GM, KE, LS, MW, SD, SL, SZ, TZ, UG, ZW), EA (AM, AZ, BY, KG, KZ, MD, RU, TJ, TM), AE, AG, AL, AM, AT, AU, AZ, BA, BB, BG, BR, BY, CA, CH, CN, CR, CU, CZ, DE, DK, DM, DZ, EE, ES, FI, GB, GD, GE, GH, GM, HR , HU, ID, IL, IN, IS, JP, KE, KG, KP, KR, KZ, LC, LK, LR, LS, LT, LU, LV, MA, MD, MG, MK, MN, MW, MX, NO, NZ, PL, PT, RO, RU, SD, SE, SG, SI, SK, SL, TJ, TM, TR, TT, TZ, UA, UG, US, UZ, VN, YU, ZA Lazari, Jean-Pierre France, F.-38700 Corin, Shmand Marano, 45 (72) Inventor Bolson, Jill France, F.-91190 Gif-sur-Yvette, Rue des Genet, 25 (72) Inventor Fromman, Michelle France, F-91290 La Norville, Santier du Parc, 5bis F-term (reference) 5F058 BC01 BC02 BE10 BF14 BF73

Claims (10)

[Claims] After polishing, a stream of low energy, moderately charged positive ions (30) of predetermined density is generated and directed to the surface (21) of the silicon substrate (20). And by controlling the kinetic energy of the ions (30) such that the velocities of the ions are substantially zero at a predetermined distance from the surface, the cleaning is performed under vacuum to provide sufficient contamination and contamination. A magnitude repulsion is generated to release only the contamination (10, 11) present on the substrate surface and to eliminate spot crystal defects (40),
A method for cleaning a surface of a single-crystal silicon substrate having 100 orientations for an integrated electronic component, comprising obtaining a precisely flat surface. 2. Ion generation is achieved by applying an extraction voltage to increase density.
2. The method of claim 1 wherein the direction is controlled by magnetic sorting and as the ions approach the surface, they are decelerated by applying an appropriate voltage. 3. The method of claim 2, wherein the ions are selected by filtering in direction by collimation for the velocity towards the silicon substrate by a band or high field electric field. 4. The method according to claim 1, wherein the generated ions are rare gas ions having a uniform charge. 5. The method of claim 4, wherein the ions produced are argon ions having a charge in the range of Ar ^{8+ to} Ar ¹²⁺ . 6. A method for preparing a silicon substrate according to claim 1, comprising: interacting a stream of oxide ions with a surface of the silicon substrate under vacuum, wherein the velocity of the ions is substantially at a predetermined distance from the surface. Kinetic energy of ions is controlled so as to be zero, and in particular, a SiO ₂ layer is formed on a surface of a silicon substrate cut out in 100 planes for use as a barrier against diffusion to integrated electronic components. Use of the cleaning method of 1. 7. The oxide ions are selected, directed, decelerated O ⁺ ions and the silicon substrate is maintained at a temperature below 500 ° C., preferably in the range of 200 ° C. to 500 ° C. Use of 6. 8. The cleaning step is followed by a step of passivating the surface by hydrogenation using a hydrofluoric acid and ammonium ion bath, followed by moderately charged inert gas ions and vacuum. Below, a silicon substrate cut out in 100 planes to perform an oxidizing step of remotely interacting, cleaving Si-H bonds and filling the cleaved bonds with oxygen gas, especially as a barrier against diffusion into integrated electronic components Use of the cleaning method according to claim 1 for forming a SiO ₂ layer on the surface of a substrate. 9. Use according to claim 8, wherein the moderately charged ions are argon ions of uniform charge ranging from Ar ^{4+ to} Ar ⁸⁺ and the oxygen gas is pressure controlled. 10. The pressure of oxygen gas is controlled, and the temperature of the silicon substrate is set to 200.
9. Use according to claim 8, maintained at a value in the range of <RTIgt;