DE102004022402A1 - Dry etching of layer sequence, for anisotropic etching of aluminum-containing substrates, by etching fourth layer in plasma comprising halogen-containing gas, and third layer in plasma comprising halogen- and nitrogen-containing gases - Google Patents

Abstract

The method involves applying a mask to a fourth layer, and etching the non-masked regions of the fourth layer in a first plasma (P1), mainly comprising halogen-containing gas. The third layer is etched in a second plasma (P2), mainly comprising halogen-containing and nitrogen-containing gases. The second layer is etched in a third plasm (P1), which is preferably the same as the first plasma.

Description

The The present invention relates to a method of anisotropic etching of aluminum-containing substrates.

Even though in principle applicable to any structures, the present Invention and the underlying problem below with regard to the production of metal interconnects in DRAM memory modules explained.

It There is a need in memory modules as large amounts of data as possible save a short time. A memory module consists of a Variety of memory cells. Each of the memory cells is over internal Tracks of the memory module with the external contacts of the memory module connectable. about These tracks are transported data, which in the memory chip should be stored. The data to be stored are electrical Signals on the external contacts. The transport speed the data depends thus of the propagation speed of electrical signals in the tracks. The propagation velocity electrical Signals are highest in metallic conductors. Therefore, there is an interest to make the tracks within a memory block made of metal.

One preferred metal for Lines in memory modules is aluminum. the reason for that is Aluminum is relatively simple let process.

pure Aluminum tends to electromigration. That means that while a Electricity flows Aluminum atoms are transported. The transported aluminum atoms Among other things, they are then deposited in the areas of printed circuit boards contacted by Semiconductor substrates from. this leads to among other undesirable ones Conductor bridges. This is a cause for Aging defects of components. By adding silicon or copper to aluminum becomes the electromigration of aluminum reduced.

During heat treatment steps The semiconductor manufacturing process diffuses aluminum into adjacent ones Semiconductor layers. this leads to too unwanted galvanic connections. The diffusion is through a thin barrier layer of titanium and / or a titanium-tungsten alloy between the semiconductor layer and the aluminum layer prevented.

Around To structure the aluminum, a mask is created. A step to generate the mask is to expose a photoresist on a surface of the aluminum is applied. This will be a pattern of a mask template transferred to the photoresist. The surface of epitaxially deposited aluminum is very highly reflective. During exposure, the reflected light rays interfere with the incident light rays. This forms an interference pattern which, inter alia, depends on the surface condition of the aluminum, the thickness of the photoresist layer and the mask template depends. The Interference pattern changed undesirably the pattern which is transferred to the photoresist. Therefore, the Avoid generation of interference patterns. This is on the surface of the aluminum deposited an antireflection layer of titanium nitride.

A typical sequence of layers for structuring aluminum and creating metallic lines is shown in FIG 3 shown. The layer sequence contains a thin barrier layer S2 made of titanium, a thick aluminum layer S3 and finally a thin antireflection layer S4 made of titanium and titanium nitride. The layer sequence is applied to an insulating substrate S1. The substrate S1 insulates the conductive aluminum-containing layer S3 of structures (not shown) that attaches to the bottom surface 10 the substrate layer S1 adjacent. Preferably, the substrate S1 contains silicon dioxide or undoped semiconductor material. In 3 is an already etched trench with a trench bottom 8th and moat walls 7 shown. On a top surface 6 the anti-reflection layer S4 is applied a mask S5. Typically, the mask S5 consists of exposed photoresist.

An exemplary method etches the three layers in one stage with a plasma P2 in a reaction chamber. The plasma P2 is typically composed of the gases Cl ₂ , BCl ₃ and N ₂ . The volume fractions of the gases are kept constant during the etching process. The reaction product AlCl ₃ of aluminum and the chlorine-containing gases is gaseous and is pumped out of the reaction chamber. The addition of N ₂ leads to the formation of polymer deposits S6 on the trench walls 7 , These polymer deposits S6 passivate the trench walls and prevent the trench walls 7 be etched by the chlorine-containing gases. The polymer deposits S6 in the area of the trench bottom 8th are physically, mainly removed by the BCl ₃ molecules. Therefore, the aluminum is in the area of the trench bottom 8th etched through the chlorine-containing gases. The passivation of the trench walls and the non-passivated soil allow an anisotropic etching of the aluminum.

A disadvantage of the mentioned method is that during the etching of the thin titanhalti layers S2, S4 reinforced to form polymer deposit S6 in the etched trenches. The polymer deposits S6 must be removed for subsequent processing steps of the memory modules.

However, these strong polymer deposits S6 are difficult to remove. Furthermore, during the etching, the strong polymer deposit S6 partially peels off the trench walls 7 , Thus, the exposed trench walls 7 are exposed to the etching gas Cl ₂ , resulting in that there the trench walls 7 be etched. The result is an uneven etching of the trench walls 7 , The reinforced etched areas of the trench walls lead to locally thinned tracks. This leads to increased defect formation in structures of small dimensions.

The Object of the method according to the invention This is an improved method for anisotropic etching of to create aluminum-containing layers, the formation being excessively strong Polymer deposits during etching the titanium-containing layers should be prevented.

According to the invention this Problem solved by the method specified in claim 1.

With the method according to the invention let yourself reduce the defect rate for components with metallic interconnects.

The The method according to the invention etches the layer sequence not with an etching step with a plasma, with a predominantly constant composition of Gases, but in three etching steps with corresponding plasmas, which have different compositions have the gases. The aluminum-containing layer is according to the well-known Process etched with chlorine-containing and nitrogen-containing gas. there becomes by the proportion of the nitrogen-containing gas passivation the trench walls achieved by polymer deposits, which for anisotropic etching of aluminum-containing layer are necessary. The titanium-containing layers become Etched without nitrogen-containing gas. This will produce polymer deposition during the etching of the titanium-containing layers advantageously reduced.

In the dependent claims find advantageous developments and refinements of specified in claim 1 method.

According to one preferred development, the three etching steps in a reaction chamber carried out, the gas quantity of nitrogen-containing gases in the reaction chamber is controlled and adjusted so that for the etching steps for the titanium-containing Layers the gas amount of nitrogen-containing gases in the reaction chamber is reduced and for the etching step the gas quantity of nitrogen-containing gases in the reaction chamber is increased.

According to one preferred development is the amount of nitrogen-containing gas Gas for the etching steps reduces the titanium-containing layers to zero.

According to a preferred development, the nitrogen-containing gas contains predominantly N ₂ .

According to a preferred development, the halogen-containing gas contains predominantly a gas mixture of BCl ₃ and Cl ₂ .

According to one preferred embodiment, a respective duration of the etching is corresponding to at least one of the etching steps given, with the respective duration determines how long the sequence of layers is etched with the plasma of the corresponding etching step.

According to one preferred development is in each case an endpoint corresponding to at least one of the etching steps signaled by an endpoint check, with the respective endpoint when the etching the layer sequence with the plasma of the respective etching step is ended.

According to one preferred development signals the endpoint control the Endpoint for a respective step of the steps when one or more etch products the plasma of the respective step with one or more materials the etched Layer below the layer to be etched be detected by the respective step, the below the too corrosive Layer of the respective step, which is layer on which the layer to be etched of the respective step was applied directly.

According to one contains preferred training the aluminum-containing material predominantly aluminum, which to advantageous reduction of electromigration copper and / or Silicon is mixed.

According to one preferred training put the fourth shift and / or the second layer is composed of several sub-layers. The part layers contain predominantly titanium and / or titanium-containing materials. One typical titanium-containing material is titanium nitride.

According to a preferred development, at least one of the plasmas used contains a methane-containing gas. The methane-containing gas typically provides hydrocarbon monomers to form the polymer layer needed to passivate the trench walls.

According to one contains preferred training at least one of the plasmas used a noble gas-containing gas. Noble gas-containing gases are typically used for physical removal the polymer deposits in the trench bottom and allow advantageously an increase the anisotropic nature of the etching process.

embodiments of the invention are described using the drawings in the following description explained in more detail.

It demonstrate:

1 a schematic representation of a partial section of a masked layer sequence for etching according to an embodiment of the present invention;

2a C is a schematic representation of partial sections of the layer sequence during processing according to an embodiment of the present invention; and

3 a schematic representation of a partial section of a layer sequences, which were etched by an exemplary method.

In the same reference numerals designate the same or functionally identical Ingredients.

1 shows a representation of a partial section of a masked layer sequence for etching according to an embodiment of the present invention. An aluminum-containing layer S3 is shown. The layer S3 preferably consists of an aluminum-copper alloy or aluminum with added silicon. A layer S1 is made of a non-conductive substrate, preferably silicon dioxide or undoped semiconductor material. Between the substrate layer S1 and the aluminum-containing layer S3 is a thin barrier layer S2. The barrier layer S2 is made of titanium.

The Barrier layer S2 prevents during heat treatment steps the Semiconductor technology Aluminum from the layer S3 into the substrate S1 diffused. A mask S5 is applied to the layer sequence. The mask S5 consists of exposed photoresist. Between the mask S5 and the aluminum-containing layer S3 is an antireflection layer S4. The antireflection layer S4 consists of a thin layer of titanium and titanium nitride. The antireflection layer S4 prevents the exposure of the Photoresists form interferences. The otherwise resulting interference pattern would the exposure of the photoresist influence and thus would a Mask S5 is generated which does not correspond to a desired template.

2a shows a representation of a partial section of the layer sequence 1 , The layer sequence is introduced into a reaction chamber. A plasma P1 contains Cl ₂ -containing and BCl ₃ -containing gases. The gases of the plasma move vertically on the uppermost surface 6 the sequence of layers. In the unmasked areas, the gases react with the antireflective layer S4. The duration of the etching with the plasma P1 is adjusted so that the unmasked areas of the antireflection layer S4 are etched away over the entire area of the substrate. The present embodiment of the method according to the invention provides for the duration of the etching with the plasma P1 vorzugegeben. In a further advantageous embodiment, the etching with the plasma P1 is terminated when the reaction products of the plasma P1 with the aluminum-containing layer S3 are detected in a suitable manner.

A another embodiment finish the etching with the plasma P2, if much of it the antireflective layer S4 etched is. This is of particular interest when the uniformity of the etching process over the entire layer sequence is low. When etching the aluminum-containing Layer S3 with the nitrogen-poor or nitrogen-free plasma P2 store no passivating polymer deposits on the grave walls from. This would to an undercurrent to lead. It may be more advantageous, remaining proportions of the titanium-containing Etch antireflective layer S4 with a nitrogen-containing plasma and increased Tolerate polymer deposits.

The next step for etching the aluminum copper alloy is in 2 B shown. After the suitably selected duration for the first etching step, the composition of the gases of the plasma is changed. A plasma P2 contains a nitrogen-containing gas in addition to the gases of the plasma P1.

The addition of nitrogen results in polymer deposits on the trench walls of the etched trench. These polymer deposits are a key property of the anisotropic etch process of aluminum-containing substrates. The polymer deposits passivate the trench walls 7 , At the bottom of the ditch 8th no polymers are deposited, since these are physically removed by the plasma P2, especially by BCl ₃ . Thus, the substrate becomes selective in the region of the trench bottom 8th etched.

The strength of the polymer deposit on the trench walls 7 The trench can be increased by increasing the nitrogen content in the gas mixture. The polymer deposits are removed in a further processing step of the semiconductor technology. It is advantageous if the polymer deposits can be easily removed. Among other things, an excessive strength of the polymer deposits has a negative effect. Therefore, it is necessary to adjust the nitrogen concentration so that not too many polymers attach to the trench walls, on the other hand, a sufficiently thick polymer layer must be ensured in order to achieve a passivation of the trench walls.

The Layer sequence is etched with the plasma P2 until At one point of the layer sequence, the titanium-containing barrier layer S2 is exposed. This is timed by changing the duration the etching step with the plasma P2 determines appropriate. Another embodiment provides an endpoint control. At an endpoint check will be Reaction products of the etching gases analyzed with the layer sequence using suitable methods. If Reaction products with the etching gases be detected with the barrier layer S2, it is shown that the aluminum-containing layer S3 is etched away at least in one region. If the proof of the etched products with the barrier layer S2, the etching with the plasma P2 either terminated immediately or the layer S3 still over-etched for a predetermined duration. The over-etching is partly necessary, because the uniformity of the etching over the entire layer sequence is limited.

The next etching step is in 2c shown. The titanium barrier layer S2 is etched with the plasma P1 like the antireflection layer S4. For this purpose, the nitrogen content in the gas mixture of the plasma is to be reduced. This etching step takes place until the barrier layer S2 has been etched over the entire layer sequence. Now, the right and left regions of layer S3 are as in FIG 2c represented, galvanically isolated from each other. It should be noted that for this purpose, the barrier layer S2 must be completely etched, as this is also conductive.

Of the Advantage the layer sequence S4, S3, S3 in three instead of in one step to etch is that while the etching the layers S2 and S4 no or only to a small extent polymer deposits arise.

Even though the present invention described above with reference to preferred embodiments it is not limited to that, but in many ways and modifiable.

In addition to the gases mentioned, it is additionally possible to use gases containing noble gas. The noble gas-containing gases increase the anisotropic etching behavior, preferably by polymer deposits in the region of the trench bottom 7 physically remove.

In addition to the mentioned Gases can be additionally or instead of the chlorine-containing gases, a fluorine-containing gas for etching the Use barrier layer S2 and / or the antireflective layer S4.

S1

layer made of insulating substrate

S2

barrier layer

S3

aluminous layer

S4

Anti-reflective coating

S5

mask

S6

Polymer deposits

6

top area

7

grave soil

8th

grave wall

10

lowest area

P1

nitrogen-poor or nitrogen-free plasma

P2

plasma with nitrogenous gas

Claims (13)

Method for dry etching a layer sequence, which comprises: a first layer (S1) which is an insulating layer Contains substrate, a second layer (S2), which predominantly contains titanium-containing materials contains which is applied to the first layer (S1), a third layer (S3), which contains predominantly aluminum and / or an aluminum alloy, the is applied to the second layer (S2), and a fourth layer (S4), which contains predominantly titanium-containing materials, the on the third layer (S3), with the following steps: a) Applying a mask (S5) to the fourth layer (S4); b) etching the non-masked areas of the fourth layer (S4) in a first Plasma (P1), whereby the plasma first (P1) predominantly from halogenhaltigen Composed of gases; c) etching the third layer (S3) in a second plasma (P2), wherein the second plasma (P2) of halogen-containing and nitrogen-containing Composed of gases; and d) etching the second layer (S2) in a third plasma (P1). The method of claim 1, wherein the third plasma (P1) is equal to the first plasma (P3). The method of claim 1 or 2, wherein steps b), c) and d) are carried out in a reaction chamber, wherein the gas amount of nitrogen-containing gases in the reaction chamber is controlled and adjusted so that for steps b) and d) the amount of nitrogen containing nitrogen Gases is reduced in the reaction chamber and for the step c) the Gas amount of nitrogen-containing gases is increased in the reaction chamber. The method of claim 3, wherein the amount of gas nitrogen-containing gas in the reaction chamber for steps b) and / or d) is reduced to zero. A process according to any one of the preceding claims, wherein the nitrogen-containing gas is predominantly N ₂ . Method according to one of the preceding claims, wherein the halogen-containing gas is predominantly a gas mixture of BCl ₃ and Cl ₂ . Method according to one of the preceding claims, wherein one duration corresponding to at least one of the steps b), c) or d), whereby the respective duration determines how long the sequence of layers with the plasma of each step etched becomes. Method according to one of the preceding claims, wherein one endpoint corresponding to at least one of the steps b), c) or d) is signaled by an end point control, wherein the respective end point determines when the etching of the layer sequence with the plasma of the respective step is terminated. The method of claim 6, wherein the endpoint control the endpoint for signals a respective step of steps b), c) or d), if one or more etching products the plasma of the respective step with one or more materials of the etched Layer below the layer to be etched the respective step are detected, the below the one to be etched Layer of the respective step, which is layer on which the layer to be etched of the respective step was applied directly. A method according to any one of the preceding claims, wherein the aluminum-containing material consists predominantly of aluminum, which copper and / or silicon are mixed. Method according to one of the preceding claims, wherein the fourth layer and / or the second layer consists of several Partial layers composed, these sub-layers predominantly titanium and / or containing titanium-containing materials. Method according to one of the preceding claims, wherein in at least one of steps b) to d) a methane-containing gas contained in the plasma. Method according to one of the preceding claims, wherein in at least one of steps b) to d) one or more noble gas-containing Gases are contained in the plasma.