Reactive sputter deposition of dielectric films

Abstract

Reactive sputter deposition method and system are disclosed, in which a catalyst gas, such as water vapor, is used to increase the overall deposition rate substantially without compromising formation of a dielectric compound layer and its optical transmission. Addition to the sputtering or reactive gas of the catalyst gas can result in an increase of a deposition rate of the dielectric oxide film substantially without increasing an optical absorption of the film.

Claims

1. A method, comprising: supplying a reactive gas to a reactive gas source that is inside a chamber, wherein the reactive gas source is a plasma-activated reactive gas source that is inside the chamber; forming a silicon dioxide layer on a substrate by releasing, from the plasma-activated reactive gas source, the reactive gas into the chamber in a manner that causes the reactive gas to react with silicon atoms; and adding a catalyst to the chamber in a manner that increases a deposition rate of the silicon dioxide layer without impacting optical absorption spectra of deposited silicon dioxide film.

2. The method of claim 1, further comprising: loading the substrate into a substrate holder before the silicon dioxide layer is formed on the substrate.

3. The method of claim 1, further comprising: activating a vacuum pump that that pumps out air from the chamber.

4. The method of claim 1, further comprising: injecting a sputtering gas, via a sputtering gas inlet, to a pre-defined pressure within the chamber.

5. The method of claim 1, further comprising: applying a voltage to one or more cathode targets in a manner that causes the silicon atoms to move from the one or more cathode targets towards the substrate and adhere to the substrate.

6. The method of claim 1, wherein the reactive gas comprises oxygen.

7. The method of claim 1, wherein the reactive gas reacts with the silicon atoms when the silicon atoms are adhered to the substrate.

8. The method of claim 1, wherein the reactive gas reacts with the silicon atoms in a gas phase between one or more cathode targets and the substrate.

9. The method of claim 1, wherein the catalyst is water vapor.

10. The method of claim 1, wherein the catalyst is added via a water vapor inlet.

11. The method of claim 1, wherein the catalyst is added via a needle valve.

12. The method of claim 1, wherein the catalyst is added at partial pressure levels of between 5*10.sup.−6 Torr and 5*10.sup.−4 Torr.

13. The method of claim 1, wherein the catalyst is added at partial pressure levels of between 1*10.sup.−5 Torr and 5*10.sup.−5 Torr.

14. A method, comprising: releasing, from a reactive gas source, a reactive gas into a chamber, wherein the reactive gas source is a plasma-activated reactive gas source that is inside the chamber; adding a catalyst to the chamber; and applying a voltage at a cathode target in a manner that forms a silicon dioxide film on a substrate by causing silicon atoms of the cathode target to react with the reactive gas and the catalyst.

15. The method of claim 14, further comprising: pumping air out from the chamber.

16. The method of claim 14, further comprising: providing a sputtering gas into the chamber, wherein the voltage ionizes the sputtering gas and causes argon ions to hit the cathode target.

17. The method of claim 14, wherein the catalyst comprises water vapor, and wherein the water vapor is added by feeding oxygen gas through a water bubbler.

18. A method, comprising: providing, from a plasma-activated reactive gas source that is inside a chamber, oxygen into the chamber; and adding water vapor to the chamber in a manner that increases a deposition rate of a silicon dioxide layer without affecting ultraviolet optical transmission of the silicon dioxide layer.

19. The method of claim 18, wherein the water vapor is added using a partial pressure range of between 1*10.sup.−5 Torr and 5*10.sup.−5 Torr.

20. The method of claim 1, wherein the reactive gas is supplied from outside the chamber to the reactive gas source.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Exemplary embodiments will now be described in conjunction with the drawings, in which:

(2) FIG. 1 is a schematic view of a reactive sputter deposition system of the invention;

(3) FIG. 2 is a flow chart of a method for the reactive sputter deposition according to the invention, using the reactive sputter deposition system of FIG. 1;

(4) FIG. 3 is an optical transmission plot of SiO.sub.2 layers grown using the system of FIG. 1, with addition of water vapor at a normal and an increased deposition rate;

(5) FIG. 4 is an optical transmission plot of SiO.sub.2 layers grown using the reactive sputter deposition system of FIG. 1, without addition of water vapor at a normal and an increased deposition rate; and

(6) FIG. 5 is a three-dimensional partially cut-out view of an embodiment of the reactive sputter deposition system of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

(7) While the present teachings are described in conjunction with various embodiments and examples, it is not intended that the present teachings be limited to such embodiments. On the contrary, the present teachings encompass various alternatives, modifications and equivalents, as will be appreciated by those of skill in the art.

(8) Referring to FIG. 1, a reactive sputter deposition system 100 for coating a substrate 102 with a dielectric coating 104 includes a sputtering chamber 106, an optional anode 108, and a cathode target 110, disposed within the chamber 106. A substrate holder 112 for holding the substrate 102 is disposed within the chamber 106 opposite the cathode target 110. A sputtering gas inlet 114 and a water vapor inlet 116 are disposed in a bottom wall 118 of the chamber 106. A plasma-activated reactive gas source 120 is placed next to the substrate 102. A vacuum pump 122 is connected to the vacuum chamber 106.

(9) In operation, the substrate 102 is loaded into the substrate holder 112, and the vacuum pump 122 is activated to pump out the air as indicated by an arrow 124. A sputtering gas, in this example argon, is injected via the sputtering gas inlet 114, to a pre-defined pressure within the chamber 106. A reactive gas, in this example oxygen, is supplied to the plasma-activated reactive gas source 120. The cathode target 110 is, in this example, a silicon target. A DC, pulsed DC, AC, or RF voltage is applied to the silicon cathode target 110, causing ionization of the argon. In case of the AC applied voltage, two cathode targets 110 are typically used, and the anode 108 is not required. Positively charged argon ions (Ar.sup.+) hit the cathode target 110 as shown with dotted lines 125, causing silicon atoms of the cathode target 110 to fly towards the substrate 102, as shown with dashed lines 126, and adhere to the substrate 102. The plasma-activated reactive gas source 120 releases the oxygen at a pre-defined pressure level. The oxygen reacts with the silicon atoms 126 adhered to the substrate 102, forming the silicon dioxide layer 104 on the substrate 102. The oxidation can also occur in the gas phase between the cathode target 110 and the substrate 102.

(10) The inventors have discovered that adding a catalyst, such as water vapor, to the chamber 106 allows one to increase the deposition rate of the silicon dioxide film 104 substantially without impacting optical absorption spectra of the deposited silicon dioxide film 104. The water vapor was added to the chamber 106 through water vapor inlet 116 at partial pressure levels of between 5*10.sup.−6 Torr and 5*10.sup.−4 Torr.

(11) Referring to FIG. 2, a method 200 for reactive sputter deposition of a dielectric compound layer, in this example the silicon dioxide film 104, onto the substrate 102, includes a step 202 of providing the reactive sputtering chamber 106. In a step 204, air is pumped out from the chamber 106. In a step 206, the sputtering gas (e.g. argon) and the reactive gas (e.g. oxygen) are provided in the chamber 106. In a step 208, the oxidation catalyst, such as water vapor, is added in the chamber 106, preferably at a partial pressure of between 5*10.sup.−6 Torr and 5*10.sup.−4 Torr, and more preferably at 1*10.sup.−5 Torr and 5*10.sup.−5 Torr. In a step 210, a voltage is applied at the cathode target 110, to ionize the argon gas and cause argon ions to hit the cathode target 110, causing silicon atoms of the cathode target 110 to fly towards the substrate 102, adhere to the substrate 102, and react with the oxygen and the water vapor, thereby forming the silicon dioxide film 104 on the substrate 102. In the step 208, the water vapor can be added by feeding the oxygen gas through a water bubbler.

(12) Adding the water vapor in the step 208 has been found to increase the deposition rate of the silicon dioxide layer 104, substantially without affecting ultraviolet optical transmission of the silicon dioxide layer 104. Referring to FIG. 3, a measured optical spectrum 301 corresponds to a silicon dioxide sample obtained after 30 minutes of deposition at a rate of 0.84 nm/s at the total pressure of 3.5*10.sup.−7 Torr, and no water vapor added. An optical spectrum 302 corresponds to a silicon dioxide sample obtained after 30 minutes of deposition at a deposition rate increased by 10%, to 0.92 nm/s, at the partial water vapor pressure of 3*10.sup.−5 Torr. One can clearly see that the optical transmission spectrum is substantially unaffected at the wavelength of between 270 nm and 800 nm. The optical transmission between 250 nm and 270 nm is actually improved. The smaller wavelength ripple period of the spectrum 302 obtained with water vapor indicates that in 30 minutes of deposition at the increased deposition rate, a thicker silicon dioxide layer 104 was indeed formed. This result indicates that adding water vapor to the reactive sputtering chamber 106 improves the deposition rate by at least 10% without increasing a percentage of unoxidized silicon atoms in the silicon dioxide film 104.

(13) To verify that the increased deposition rate is indeed due to the presence of the water vapor, a control experiment was performed, in which the sputtering rate was increased in absence of water vapor. Turning now to FIG. 4, the optical spectrum 301 is reproduced from FIG. 3 for comparison. A control optical spectrum 402 corresponds to a silicon dioxide sample obtained after 30 minutes of deposition at the increased deposition rate of 0.92 nm/s, however without addition of water vapor. One can see that the optical transmission in the control experiment was considerably worse, especially in the ultraviolet wavelength range of 250 nm to 450 nm. In contrast, the UV wavelength range of the second transmission spectrum 302 of FIG. 3 is essentially unaffected. Thus, adding water vapor at a partial pressure of between 5*10.sup.−6 Torr and 5*10.sup.−4 Torr enables an increase of a deposition rate of the silicon dioxide layer 104 substantially without affecting ultraviolet optical transmission of the silicon dioxide layer 104.

(14) The water vapor partial pressure range of between 1*10.sup.−5 Torr and 5*10.sup.−5 Torr is preferred. In all cases, the pumping speed was approximately 10,800 Us, resulting in a gas flow of between 20 sccm and 30 sccm; the gas flow of 25 sccm+−2 sccm was found to be optimal for SiO.sub.2.

(15) The water vapor can be introduced into the chamber 106 via a needle valve, to supply small controllable amounts of liquid water. The needle, not shown, can protrude inside the chamber and be hidden behind a shield, for example protective foil, not shown. The water vapor can also be obtained outside the chamber 106 by evaporating a small amount of water and adding the vapor to the oxygen supplied to the plasma activated oxygen source 120. The pre-formed water vapor can also be fed through the anode 108. For process control purposes, it is advantageous to introduce the water vapor with the other processes gasses, especially with the reactive gas, feeding the mixture of the reactive gas and water vapor into the plasma activated gas source 120.

(16) The cathode target 110 can include silicon, aluminum, titanium, and other metals or semiconductors. The sputtering gas can include not only argon but another, preferably inert, gas such as neon, krypton, or xenon. The sputtering gas is selected to match the atomic mass of the target material as closely as possible for better transfer of mechanical impulse upon collision of the sputtering ions with the atoms of the target 110.

(17) Various atomic groups of the water molecules may act as a catalyst to improve the oxidation efficiency of the reactive sputtering process. Applying a high negative voltage at the cathode target 110 creates a plasma in front of the cathode target 110, where positively charged argon ions are accelerated towards the negatively charged cathode target 110. A second function of the plasma, additional to the plasma created at the plasma activated oxygen source 120, is to create activated atomic oxygen and oxygen ions. These excited oxygen species can oxidize metals much more efficiently than O.sub.2 molecules. Water now dissociates in the plasma and can form H.sup.+, H.sub.2, O*, O.sup.−, or HO.sup.− species. All of the oxygen containing ones improve the oxidation efficiency.

(18) One probable mechanism is that H.sub.2O molecules dissociate into H.sub.2 and O, and that the atomic oxygen O combines more easily with the metal atoms in the sputtering bloom than molecular oxygen O.sub.2. Adding ozone (O.sub.3) may also increase the deposition efficiency without impacting the optical absorption spectra in the wavelength ranges specified. Another possibility is that OH— is formed in the plasma which will be accelerated away from the negatively charged cathode target 110, and will recombine not at the target surface but either in the sputter bloom, or on the substrate 102, or a wall of the chamber 106, increasing the probability of oxidizing the growing film 104. Another possible mechanism is that the hydrogen forming upon H.sub.2O molecules dissociation may assist oxidization of the film 104. Thus, hydrogen may be used in place of water vapor in the system 100 of FIG. 1 operated according to the method 200 of FIG. 2. To deposit the dielectric oxide film 104 on the substrate 102, water vapor, ozone gas, or hydrogen gas are added to the reactive gas, to increase the deposition rate of the dielectric oxide film 104 substantially without increasing an optical absorption of the film 104 in the wavelength range of between 250 and 750 nm, or at least between 420 nm and 750 nm, depending on the oxide film material.

(19) Turning now to FIG. 5 with further reference to FIG. 1, a preferred embodiment 500 of the reactive sputtering deposition system 100 is presented. A multi-substrate holder 512 of the reactive magnetron sputtering deposition system 500 rotates about a vertical axis within a chamber 506 for simultaneous deposition of the coating, not shown, onto a plurality of the substrates 102. A pair of ring cathode targets 510 are used in place of the single cathode target 110. The mixture of the reactive gas and the water vapor is fed through a pair of inlets 520 disposed at the centers of the corresponding ring cathode targets 510. The inlets 520 are connected to a reservoir 530 having therein the reactive gas pre-mixed with the water vapor provided by an optional water vapor source 536, which can include a water vaporizer. An optional loading dock 532 contains a cassette 102A of extra substrates for subsequent loading into the chamber 506 through the gate valve 550 by means of a substrate handler 534. The turbo pumps 522 pump the air out of the chamber 506. The mixture of the reactive gas and the water vapor can also be added through the anode 108.

(20) The foregoing description of one or more embodiments of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. It is intended that the scope of the invention be limited not by this detailed description, but rather by the claims appended hereto.