JP5493402B2 - Thin film, photomask blank, method for forming them, and film forming apparatus - Google Patents

Description

  The present invention relates to a thin film, a photomask blank, a method for forming the film, and a film forming apparatus, and more particularly to a thin film capable of reducing film formation defects and a photo film in a thin film used for a semiconductor device, a display device, a photomask, and the like. The present invention relates to a mask blank, a method for forming a film, and a film forming apparatus.

  In general, photolithography using visible light (g-line, h-line) or ultraviolet light (i-line, KrF, ArF) is widely used for patterning wiring and semiconductors used in semiconductor integrated circuits and display devices. ing. In recent years, along with the miniaturization of semiconductor integrated circuits, research and development relating to immersion ArF, EUVL (extreme ultralithography), nanoimprint lithography, and the like have been actively conducted as a manufacturing technique thereof.

  If there is a defect in the thin film that constitutes the mask for forming these devices or patterns, various problems such as malfunction and deterioration in durability are caused. Defects on the mask are particularly serious and are directly transferred to the wafer surface together with the mask pattern, which directly affects the device yield. Here, the defect means any abnormality on the mask which is transferred upon exposure or gives a dimensional change of 10% or more. The size is shown in the International Semiconductor Technology Roadmap (ITRS) as the square root of the area of the smallest size light defect or dark defect that is expected to be transferred in the corresponding generation. It is said that it is necessary to suppress it to 46 nm in 2010 and 36 nm or less in 2010. It is required that defects of these sizes do not exist on the mask. In addition, defects in semiconductor devices and display devices themselves lead to malfunction of the elements and cause a decrease in yield. Therefore, handling technology that does not cause defects, film formation processing technology, and cleaning technology become important.

  In addition to CVD (chemical vapor deposition), sputtering and vacuum deposition methods are used for mass production, and PLD (pulsed laser deposition) is also used at the research level. It has been. Each of these film forming methods is selectively used depending on the required thin film performance. CVD provides a high-quality film, but it is necessary to supply the material as a gas. In addition to the limited types of materials, gas containing a metal in its molecular structure is generally harmful to the human body or the environment, and it is abatement. There is a cost for equipment and facilities for preventing danger. In the vapor deposition, the application is limited because the adhesion is generally weak and a dense film cannot be obtained except for a special method such as activated vapor deposition. PLD has an advantage that a very good quality thin film can be obtained. However, since it is difficult to form a film on a large area, it is only used for material development at the laboratory level. In the sputtering method, it is only necessary to prepare a target, and large area uniform film formation is possible. In the past, the slow deposition rate has become a problem, but the magnetron sputtering method has been developed to solve the problem of deposition rate, and it is now widely used in the production of various thin films at the mass production site.

  However, especially in the sputtering method, a defect due to film formation occurs, causing a decrease in product yield. With the miniaturization of semiconductor circuits and the high definition of display devices, even defects of a size that have not been regarded as a problem have been affecting products. In order to cope with this, the structure of the vacuum chamber is changed so that the film attached to the sidewall does not peel off and adheres to the substrate, or dust in the chamber is lifted when moving from vacuum to atmospheric pressure or from atmospheric pressure to vacuum. Various methods have been adopted, such as a non-chamber structure, a pulsed DC power supply for preventing arcing, which is one of the causes of defects, and a change in cathode shape in the sputtering method. (For example, refer to Patent Document 1).

  A phenomenon called arcing during discharge, which is one of the causes of film formation defects in the sputtering method, is that the glow discharge used in normal film formation temporarily or permanently shifts to arc discharge for some reason. It refers to the phenomenon.

  Several mechanisms that cause arcing have been elucidated (see, for example, Non-Patent Document 1), and the arcing generation mechanism due to dielectric breakdown that can be a major source of particles that contribute to film formation defects is explained as follows. The

  During discharge by DC sputtering using a DC power supply, some of the sputtered particles and their reaction products are deposited on the target surface, resulting in a high non-conductive region on the cathode or a higher specific resistance than the target material. When microregions are formed, they form microcapacitors. This capacitor is charged to the plasma potential, but dielectric breakdown occurs due to the high electric field applied to its small shape. Once dielectric breakdown occurs, that part is filled with charge carriers, the current density increases locally, and the plasma runs to the arc state. When arcing occurs, the plasma impedance decreases rapidly, and all of the effective energy is injected into the arc discharge, generating an extremely high energy density locally. This causes the target surface to rupture, and the fragments also fly to the substrate side, causing them to be embedded as particles in the growing film or to damage the film.

  Therefore, in the sputtering method, it is important to eliminate arcing in order to obtain a high quality film.

  However, although these measures including the anti-arcing technique have a certain effect, minute film formation defects still occur. In addition, in the film formation of the metal film using the metal target, particles are observed even though arcing does not occur. Therefore, the particle generation source by the mechanism different from the past was suggested.

  Therefore, we focused on particles growing in plasma, and in the film formation method in which the target material is irradiated with ions in the vacuum chamber and the target constituent materials are deposited on the substrate to form a thin film, ion irradiation is further turned on ( In a film forming method in which irradiation (irradiation) and OFF (non-irradiation) are repeated, the film forming method is characterized in that an OFF time included in a minimum unit of repetition, that is, one cycle is provided for at least 1 second. In other words, rather than continuous film formation, film formation is stopped once after a certain period of film formation, and after at least 1 second or more has elapsed, film formation is performed again for a certain period of time, and this is repeated to form a minute film. Defects have been greatly reduced (see Japanese Patent Application No. 2007-240608).

  However, even if this technology was introduced, it was not possible to eliminate all defects.

JP 2003-231965 A

I. Safi: Surf. Coat. Technol. 127 (2000) 203.

  An object of the present invention is to provide a film forming method and a film forming apparatus capable of reducing film forming defects in thin films used for semiconductor devices, display devices, photomasks and the like.

  The invention according to claim 1 of the present invention is a magnetron sputtering film forming method for forming a thin film, wherein a film is formed by masking a part of a target. The film forming method is characterized in that it includes a region where the amount of re-adhesion (deposition) on the surface is large, and also includes a region where the amount of sputtering of the target and the amount of re-adhesion (deposition) on the target antagonize. is there.

  The invention according to claim 2 of the present invention is characterized in that the mask further includes a part of a region where the sputtering amount of the target is larger than the amount of redeposition (deposition) on the target. This is a film forming method.

  According to a third aspect of the present invention, there is provided a magnetron sputtering film forming apparatus for forming a thin film, wherein a film is formed by masking a part of the target. The film forming apparatus includes a region where the amount of reattachment (deposition) to the substrate is large, and a region where the amount of sputtering of the target and the amount of reattachment (deposition) on the target compete with each other. is there.

  The invention according to claim 4 of the present invention is characterized in that the mask further includes a part of a region where the amount of sputtering of the target is larger than the amount of redeposition (deposition) on the target. This is a film forming apparatus.

  The invention according to claim 5 of the present invention is the film forming apparatus according to claim 3 or 4, wherein the mask is electrically grounded.

  The invention according to claim 6 of the present invention is the film forming apparatus according to claim 3 or 4, wherein the mask is electrically insulated from the cathode, the anode, or the earth. .

  The invention according to claim 7 of the present invention is a thin film produced by the film forming method according to claim 1 or 2.

  The invention according to claim 8 of the present invention is a photomask blank produced using the thin film according to claim 7.

  ADVANTAGE OF THE INVENTION According to this invention, the film-forming method and film-forming apparatus which can reduce film-forming defect in the thin film used for a semiconductor device, a display device, a photomask etc. can be provided.

A mask (shielding plate) installed in a form including an auxiliary line and a boundary representing a boundary between a target sputtering amount and an area where the amount of reattachment (deposition) on the target antagonizes according to the embodiment of the present invention. It is a target cross-sectional schematic diagram of the film-forming apparatus shown. It is a figure which shows a mode that a target structure or a deposit is sputtered on the target surface. It is a schematic diagram of the cross section of the target showing the shape change of the target that occurs in the conventional film formation.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  It is preferable to use a sputtering method as the basic film forming method according to the embodiment of the present invention. The sputtering method is a film-forming method in which Ar ions generated by glow discharge strike a target by bombarding the target (sputtering) and deposit it on a substrate to form a film. Any of DC, MF (medium wave), and RF can be used as a power source. However, using a pulsed DC power source is preferable because it can reduce film formation defects and increase productivity. Since the effect according to the embodiment of the present invention cannot be sufficiently confirmed when arcing occurs, it is desirable to introduce various mechanisms for suppressing arcing. Among the sputtering methods, the magnetron sputtering method is suitable for obtaining the maximum effect according to the embodiment of the present invention. In the magnetron sputtering method, ionization of the sputtering gas is efficiently caused by the magnetron on the back surface of the target, and as a result, the deposition rate can be increased to increase the throughput, but defects due to particles are likely to occur.

  Here, the magnetron sputtering method according to the embodiment of the present invention will be described. In the magnetron sputtering method, a semicircular magnetic field line is generated on the target by the magnet on the back surface of the target. Due to the magnetic field and the electric field applied to the target (cathode), electrons move (drift) along the magnetic field lines while spirally rotating (cycloid motion). Since the magnetic field strength decreases as the magnetic field lines move away from the target surface, electrons drifting away from the target receive a force in the traveling direction. On the other hand, the electrons traveling toward the target surface receive a force so as to be pushed back for the same reason (magnetic mirror). In this way, the electrons reciprocate along one curved line of magnetic force that intersects the target surface at two points. During this time, the electrons collide with the sputtering gas, lose energy, and are eventually trapped by the anode. Since electron impact ionization with the sputtering gas is effectively performed where a magnetic field component parallel to the target surface is obtained, the ion current distribution on the target is the density distribution of the sputter gas ions that have been electron impact ionized. It is almost equal to the density distribution of fast electrons with sufficient energy. Depending on the shape of the magnetic field, this distribution is assumed to follow a normal distribution. The target is sputtered by sputter gas ions ionized at this time. Accordingly, a sputter-etched trace is engraved on the target along the shape of this density distribution.

  The target composition (sputtered particles) sputtered out adheres to the inner wall of the chamber, various shields around the target, or the target in addition to the substrate. In addition, when a reactive gas such as oxygen is present in the chamber, reaction products generated between the sputtered particles and the reactive gas may adhere. Here, these are collectively referred to as deposits.

If the deposition rate of the deposit on the target at a certain position is v _depo and the sputter etching rate of the target at that position is v _sp , the amount depends on the position (location) on the target from the distribution of ion density. I know that there is. Thriving part sputter etching, i.e. in the region 302 satisfies the v _depo «v _sp shown in FIG. 3, the deposit is not a big problem with film forming defects to be sputter etched immediately. Area deposition rate and targeting the outer peripheral portion is very large in the opposite, i.e. in the region 301 satisfies the v _depo >> V _sp shown in FIG. 3, the arcing if the deposit is performed and DC sputtering when the insulating It causes inducing and hence causes film formation defects. The arcing prevention technique / mechanism in this area is a known technique. In the middle region, that is, in the middle of the regions 301 and 302 where the deposition rate and the sputtering rate almost antagonize as shown in FIG. 3, the thickness of the target does not seem to be changed, but it is not not sputtered. We have found that this region is a source of film formation defects due to particles.

  The particle generation mechanism we have found is as follows.

  In the sputtering method, as shown in FIG. 2A, in the sputtering, the target constituent material 201 is knocked out by ion bombardment of the target. In addition, as shown in FIG. 2B, sputtered particles may reattach (deposit) 202 on the target surface on the target, but in the region where the sputter amount is larger than the deposition amount, The deposited particles are sputtered and scattered immediately. In a region where the amount of deposition and the amount of sputtering are antagonized, there is a possibility that the deposit cluster 203 deposited to some extent scatters as it is and reaches the substrate as particles, resulting in film formation defects (FIG. 2C). In a region where the amount of deposition is larger than the amount of spatter, it is no longer a target sputter but rather a sputter of deposit (FIG. 2 (d)).

  The conventional method of masking only a region with a large amount of deposition was intended to prevent an insulator from being deposited on the target surface to which the cathode voltage is applied in order to prevent arcing. Moreover, in the region where the deposition amount and the sputtering amount antagonize, it was not recognized that the region was not deposited or not sputtered. Semiconductor devices and display devices are becoming more and more miniaturized, especially in the photomask that is the original plate when manufacturing them, and even fine particles are not allowed, and this area is important for preventing the generation of fine particles that can be attributed to clusters. Therefore, it is necessary to deal with this part.

  Therefore, not only the region where the amount of reattachment (deposition) on the target is larger than the amount of sputtering of the target, but also the region where the amount of sputtering of the target and the amount of reattachment (deposition) on the target antagonize is shielded. Defects generated during film formation can be reduced.

  FIG. 1 shows a mask placed in a form including an auxiliary line and a boundary representing a boundary between a region where a sputtering amount of the target 101 and a redeposition (deposition) amount on the target compete with each other according to the embodiment of the present invention. It is a target cross-sectional schematic diagram which shows (shielding plate) 102. As shown in FIG. 1, in the embodiment of the present invention, the shielding plate 102 for forming a film by masking a part of the target 101 has a sputtering amount of the target and a reattachment (deposition) amount on the target. It installs so that the area | region 100 which antagonizes may be included.

  In order to further reduce defects, there is a region where the spatter amount of the target and the reattachment (deposition) amount on the target antagonize, and the target spatter amount is larger than the reattachment (deposition) amount on the target. It is good to install to include a part. However, if a region where the amount of sputtering of the target is larger than the amount of redeposition (deposition) on the target is shielded widely, the film forming speed is reduced, that is, the manufacturing throughput is reduced. Therefore, when shielding the area where the target sputtering amount is larger than the amount of redeposition (deposition) on the target, the range depends on the size and shape of the target, but the number and size of allowable particles Therefore, it is comprehensively judged for the cost increase due to the decrease in the film forming speed.

  The material of the shielding plate 102 is not limited, but the same material and surface shape as those of the deposition preventing plate installed in the vacuum chamber are preferable. For example, stainless steel subjected to surface treatment such as aluminum spraying is effective, but is not limited thereto. The shielding plate 102 is preferably grounded. When installing in a place where grounding is not possible, the shielding plate 102 is insulated from the cathode by mediating an insulator having a high withstand voltage.

  In glow discharge plasma often used in sputtering, an electric field gives energy to ions and electrons in the plasma. The magnitude of the energy is a function of the particle mass. Since the mass of the electron is much smaller than the mass of the ion, the action of the electric field mainly gives energy to the electron. Since electrons have a very small mass, the average velocity is very high compared to other particles such as ions and neutral particles in the plasma. From elementary physics, the number of particles incident on the wall is expressed as nc / 4 per unit area. Here, n represents the density of the particles, and c represents the average velocity of the particles. If there is a substrate that is electrically insulated in the plasma, electrons, ions, and neutral particles are incident on the substrate according to the above formula, but the average velocity of electrons in the plasma is as follows. The amount of incident light on the substrate is larger than that of the electron and the substrate starts to be negatively charged with respect to the plasma. Eventually, the inflow of electrons will be somewhat limited due to repulsion due to the negative potential of the substrate, and ions will be attracted because the substrate is at a negative potential, eventually becoming a negative potential where the electron inflow and ion inflow reach equilibrium. Calm down. The potential of the substrate at this time is called a floating potential (Vf), and similarly, the potential of the plasma is called a plasma potential (Vp).

  In film formation using the sputtering method, ions are accelerated by the potential difference between Vp and the cathode voltage (Vc), and this causes a target that also serves as the cathode to bombard and cause sputtering. Under general film formation conditions, Vc reaches several hundred volts, whereas the potential difference between Vp and Vf is about several tens of volts. Therefore, the threshold voltage required to cause sputtering is not reached or reached. Since the potential difference is small, the probability that the mask deposition mechanism is sputtered is very low. By using such a configuration, a mechanism for masking and forming a film can be installed directly on the target.

  That is, by doing so, the shielding plate 102 is only charged to a floating potential (Vf) having a voltage much lower than the cathode voltage (Vc) in the plasma, and the sputtering of the shielding plate 102 itself can be suppressed. In addition, defects due to mixing of different metals into the film being formed can be prevented.

  The target material does not matter. However, in order to maximize the effects of the present invention, it is necessary to suppress the influence of other particles as much as possible. Therefore, it is preferable to use a material that does not easily cause arcing, for example, a metal target. Is not to be done.

  In this way, a film is formed by masking a region including a region where the amount of sputtering of the target and the amount of redeposition (deposition) on the target antagonizes, and by using such an apparatus, Deposition defects caused by particles can be reduced.

  Since the thin film produced according to the embodiment of the present invention has very few film formation defects, it can be used in any application that dislikes defects. In particular, since defects in photomask blanks and thin film transistors are directly linked to a decrease in yield, it is effective to improve the yield by applying a low-defect thin film manufactured according to the embodiment of the present invention to this.

  When a substrate for a photomask blank is used as the substrate and a light shielding material is used as the target, a photomask blank having a low defect density can be obtained by this film formation method. By patterning this, a low defect density photomask can be obtained.

  Similarly, a thin film transistor can be obtained with a high yield by selecting appropriate targets for the electrode material, semiconductor material, and dielectric material, and forming and patterning each layer by applying this film formation method.

  Hereinafter, an example of a film forming method of the present invention and an example of a photomask manufactured by applying the film forming method will be described.

  A magnetron sputtering method was used as the film forming method. The power source was a pulsed DC power source, and the pulse parameters were 20 kHz and the duty ratio was 90%. This corresponds to an ON time of 45 microseconds and an OFF time of 5 microseconds. A pulse obtained by multiplying this pulse by a long-period pulse with an ON time of 30 seconds and an OFF time of 5 minutes was used as a DC output used for film formation according to this example.

  A 6025 standard quartz glass substrate for a photomask was used as the substrate, and Ta was used as the target 101. The region that shields the surface of the target 101 includes, as a reference, a region in which the amount of sputtering on the surface of the target 101 and the amount of deposition on the surface of the target 101 are in conflict and the thickness of the target 101 does not change. Further, a region where the sputtering amount of the target 101 is larger than the amount of redeposition (deposition) on the target 101 was shielded by 5 mm.

  Ar was introduced as a sputtering gas, and an electric power of 800 W was applied to start film formation. Film formation was completed when 12 cycles had elapsed in the long-cycle pulse.

By using such a method or using an apparatus incorporating such a method, only ^two film formation defects having a size of 0.35 μm or more were observed in the range of 144 cm ^{2 in} the produced thin film. there were.

(Comparative example)
On the other hand, when a film is formed as a comparative example, that is, the film forming conditions are as described above, and only the above-described shielding plate 102 is not installed in the apparatus configuration, there is a variation depending on the number of executions, but 0.35 μm. 21 to 105 film-forming defects having the above size were observed in the range of 144 cm ² .

  Even in the case of the example and the comparative example, the arc counter indicates the numerical value 0, and it is confirmed that no arcing has occurred.

  Moreover, since the thin film obtained by the Example has few film formation defects, as a result of processing the thin film as a photomask using a general photolithography method, a very good photomask having a low defect density was obtained.

100 ... Boundary 101 of the area where the sputtering amount of the target and the amount of redeposition (deposition) on the target compete with each other ... the target 102 ... the mask (shielding plate)
201... Sputtered particles 202... Sputtered particles 203 reattached (deposited) on the target surface... Sputtered particle clusters (cluster) reattached (deposited) on the target surface.
204... Particles 301 that are sputtered out from a lump of sputtered particles that have been reattached (deposited) on the target surface. ..Area 303 in which the amount of target spatter is larger than the amount of redeposition (deposition) on the target 303..

Claims (3)

In a film forming method for forming a film by masking a part of a target by a magnetron sputtering film forming method for forming a thin film,
The mask has a first region in which a deposition rate of reattachment (deposition) on the target is larger than a sputter etching rate of the target, and the sputter etching rate of the target is reattached on the target ( A deposition method comprising a part of a second region larger than the deposition rate of the deposit) and a region between the first region and the second region . In a magnetron sputtering film forming apparatus that performs thin film production, a film forming apparatus that forms a film while masking a part of a target.
The mask includes a first region in which a deposition rate of a reattachment (deposition) on the target is larger than a sputter etching rate of the target, and the sputter etching rate of the target is on the target. A film forming comprising: a part of a second region larger than the deposition rate of the reattachment (deposition) to the surface; and a region between the first region and the second region. apparatus. The film forming apparatus according to claim 2 , wherein the mask is electrically grounded.

Images